HomeMy WebLinkAbout[2012] OM Manual - Consolidation Project
Iowa City
Process Operation Manual
Prepared for
Wastewater T reatment F acilities
C onsolidation P roject
Iowa City, Iowa
March , 2016
By Brown and Caldwell
30 East Seventh Street, Suite 2500
St. Paul, MN 55101
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Table of Contents
List of Figures ...................................................................................................................................................... x
List of Tables ....................................................................................................................................................... v
List of Abbreviations ........................................................................................................................................ viii
1.1 Purpose of Manual ....................................................................................................................... 1-1
1.2 Updating the Manual .................................................................................................................... 1-1
1.3 Plant Information .......................................................................................................................... 1-1
1.3.1 Plant Overview ................................................................................................................ 1-1
1.3.2 Plant Power Supply ......................................................................................................... 1-4
1.3.3 Historical Flows and Loads Data ................................................................................... 1-5
1.3.4 Design Flows and Loads ................................................................................................ 1-5
1.4 Related Documents ...................................................................................................................... 1-6
1.4.1 Manufacturer’s Operations and Maintenance Manuals .............................................. 1-6
1.4.2 References ...................................................................................................................... 1-6
2.1 Waste Load Allocation .................................................................................................................. 2-1
3.1 Liquid Stream Operations ............................................................................................................ 3-1
3.2 Primary Clarification ..................................................................................................................... 3-3
3.2.1 Primary Clarifier Design ................................................................................................. 3-3
3.2.2 Primary Clarifier Operation ............................................................................................ 3-3
3.2.3 Primary Sludge Withdrawal Operation .......................................................................... 3-4
3.3 Secondary Treatment ................................................................................................................... 3-6
3.3.1 Secondary Clarifier Operational Background ............................................................... 3-6
3.3.2 Aeration Basins Operational Background ..................................................................... 3-8
3.3.3 BAR Operational Background ...................................................................................... 3-11
3.3.4 Secondary Treatment Operating Strategy ................................................................... 3-12
3.4 Solids Handling ........................................................................................................................... 3-16
3.4.1 TPAD Operational Strategy ........................................................................................... 3-16
3.4.2 Sludge Thickening ........................................................................................................ 3-19
3.4.3 Dewatering and Storage .............................................................................................. 3-19
4.1 Influent Channel/Bar Screens ................................................................................................... 4-21
4.2 Influent Pumping ........................................................................................................................ 4-21
4.2.1 System Description ...................................................................................................... 4-21
4.2.2 Design Data .................................................................................................................. 4-21
4.2.3 Operation and Control .................................................................................................. 4-21
4.2.4 Equipment Data ............................................................................................................ 4-22
4.2.5 Maintenance ................................................................................................................. 4-23
4.3 Influent Flow Metering ................................................................................................................ 4-24
4.3.1 System Description ...................................................................................................... 4-24
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4.3.2 Design Criteria .............................................................................................................. 4-24
4.3.3 Operation and Control ................................................................................................. 4-24
4.3.4 Equipment Data ........................................................................................................... 4-25
4.3.5 Maintenance ................................................................................................................ 4-25
4.4 Grit Removal ............................................................................................................................... 4-26
4.4.1 System Description ...................................................................................................... 4-26
4.4.2 Design Data .................................................................................................................. 4-27
4.4.3 Operation and Control ................................................................................................. 4-27
4.4.4 Equipment Data ........................................................................................................... 4-28
4.4.5 Maintenance ................................................................................................................ 4-30
4.5 Grit Dewatering ........................................................................................................................... 4-31
4.6 Grit Washing ............................................................................................................................... 4-31
4.7 Influent Flow Equalization Basin ............................................................................................... 4-31
4.7.1 System Description ...................................................................................................... 4-32
4.7.2 Design Data .................................................................................................................. 4-32
4.7.3 Operation and Control ................................................................................................. 4-32
4.7.4 Equipment Data ........................................................................................................... 4-33
4.7.5 Maintenance ................................................................................................................ 4-34
5.1 Primary Clarification ......................................................................................................................5-2
5.1.1 System Description .........................................................................................................5-2
5.1.2 Design Data .....................................................................................................................5-2
5.1.3 Operation and Control ....................................................................................................5-2
5.1.4 Equipment Data ..............................................................................................................5-4
5.1.5 Maintenance ...................................................................................................................5-6
5.2 Primary Sludge/Scum Pumps & Grinders ...................................................................................5-6
5.2.1 System Description .........................................................................................................5-6
5.2.2 Design Data .....................................................................................................................5-7
5.2.3 Operation and Control ....................................................................................................5-7
5.2.4 Equipment Data ..............................................................................................................5-9
5.2.5 Maintenance ................................................................................................................ 5-11
6.1 Secondary Treatment Overview ....................................................................................................6-1
6.2 Aeration Basins .............................................................................................................................6-1
6.2.1 Aeration Basin Influent Channel ....................................................................................6-1
6.2.2 Aeration Basins ...............................................................................................................6-1
6.2.3 Aeration Basin Effluent Channel and Surface Film Classification ...............................6-4
6.3 Aeration System ............................................................................................................................6-6
6.3.1 System Description .........................................................................................................6-6
6.3.2 Design Data .....................................................................................................................6-6
6.3.3 Aeration Blowers .............................................................................................................6-6
6.3.4 Aeration Diffusers ........................................................................................................ 6-10
6.3.5 Aeration Airflow Control ............................................................................................... 6-12
6.4 Mixed Liquor Recycle Pumping ................................................................................................. 6-20
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6.4.1 System Description ...................................................................................................... 6-20
6.4.2 Design Data .................................................................................................................. 6-20
6.4.3 Operation and Control .................................................................................................. 6-20
6.4.4 Equipment Data ............................................................................................................ 6-20
6.4.5 Maintenance ................................................................................................................. 6-21
6.5 Mechanical Mixing ...................................................................................................................... 6-22
6.5.1 System Description ...................................................................................................... 6-22
6.5.2 Design Data .................................................................................................................. 6-22
6.5.3 Operation and Control .................................................................................................. 6-22
6.5.4 Equipment Data ............................................................................................................ 6-22
6.5.5 Maintenance ................................................................................................................. 6-23
6.6 RAS Box and Surface Film Classifier ......................................................................................... 6-24
6.6.1 System Description ...................................................................................................... 6-24
6.6.2 Design Data .................................................................................................................. 6-24
6.6.3 Operation and Control .................................................................................................. 6-25
6.6.4 Equipment Data ............................................................................................................ 6-25
6.6.5 Maintenance ................................................................................................................. 6-26
6.7 Secondary Clarification............................................................................................................... 6-26
6.7.1 System Description ...................................................................................................... 6-26
6.7.2 Design Data .................................................................................................................. 6-27
6.7.3 Operation and Control .................................................................................................. 6-27
6.7.4 Equipment Data ............................................................................................................ 6-28
6.7.5 Maintenance ................................................................................................................. 6-30
6.8 RAS Pumping............................................................................................................................... 6-31
6.8.1 System Description ...................................................................................................... 6-31
6.8.2 Design Data .................................................................................................................. 6-31
6.8.3 Operation and Control .................................................................................................. 6-31
6.8.4 Equipment Data ............................................................................................................ 6-31
6.8.5 Maintenance ................................................................................................................. 6-32
6.9 WAS Pumping .............................................................................................................................. 6-33
6.9.1 System Description ...................................................................................................... 6-33
6.9.2 Design Data .................................................................................................................. 6-33
6.9.3 Operation and Control .................................................................................................. 6-33
6.9.4 Equipment Data ............................................................................................................ 6-34
6.9.5 Maintenance ................................................................................................................. 6-34
6.10 BAR Reactor (Tanks) ................................................................................................................... 6-35
6.10.1 System Description ...................................................................................................... 6-36
6.10.2 Design Data .................................................................................................................. 6-37
6.10.3 Operation and Control .................................................................................................. 6-37
6.10.4 Equipment Data ............................................................................................................ 6-37
6.10.5 Maintenance ................................................................................................................. 6-39
6.11 High Strength Flow Equalization ................................................................................................ 6-40
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6.11.1 System Description ...................................................................................................... 6-40
6.11.2 Design Data .................................................................................................................. 6-40
6.11.3 Operation and Control ................................................................................................. 6-40
6.11.4 Equipment Data ........................................................................................................... 6-41
6.11.5 Maintenance ................................................................................................................ 6-41
7.1 Ultraviolet (UV) Disinfection ..........................................................................................................7-1
7.1.1 System Description .........................................................................................................7-2
7.1.2 Design Data .....................................................................................................................7-4
7.1.3 Operation and Control ....................................................................................................7-4
7.1.4 Equipment Data ..............................................................................................................7-7
7.1.5 Maintenance ...................................................................................................................7-9
7.2 Effluent Water System ............................................................................................................... 7-11
7.2.1 System Description ...................................................................................................... 7-11
7.2.2 Design Data .................................................................................................................. 7-12
7.2.3 Operation and Control ................................................................................................. 7-12
7.2.4 Equipment Data ........................................................................................................... 7-12
7.2.5 Maintenance ...................................................................................................................7-2
7.3 Service Water Chlorination ...........................................................................................................7-2
7.3.1 System Description .........................................................................................................7-3
7.3.2 Design Data .....................................................................................................................7-3
7.3.3 Operation and Control ....................................................................................................7-3
7.3.4 Equipment Data ..............................................................................................................7-4
7.3.5 Maintenance ...................................................................................................................7-4
8.1 Primary Sludge Thickening ...........................................................................................................8-1
8.2 WAS Thickening .............................................................................................................................8-1
8.2.1 System Description .........................................................................................................8-2
8.2.2 Design Data .....................................................................................................................8-2
8.2.3 Operation and Control ....................................................................................................8-3
8.2.4 Equipment Data ..............................................................................................................8-4
8.2.5 Maintenance ...................................................................................................................8-5
8.3 Anaerobic Digestion ......................................................................................................................8-5
8.3.1 System Description .........................................................................................................8-6
8.3.2 Design Data .....................................................................................................................8-7
8.3.3 Operation and Control ....................................................................................................8-8
8.3.4 Equipment Data ..............................................................................................................8-9
8.3.5 Maintenance ................................................................................................................ 8-12
8.4 Polymer Addition ........................................................................................................................ 8-14
8.4.1 System Description ...................................................................................................... 8-14
8.4.1 Design Data .................................................................................................................. 8-14
8.4.2 Operation and Control ................................................................................................. 8-15
8.4.3 Equipment Data ........................................................................................................... 8-15
8.4.4 Maintenance ................................................................................................................ 8-16
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8.5 Dewatering .................................................................................................................................. 8-17
8.6 Cake Conveyance ....................................................................................................................... 8-18
8.6.1 System Description ...................................................................................................... 8-18
8.6.2 Design Data .................................................................................................................. 8-18
8.6.3 Operation and Control .................................................................................................. 8-18
8.6.4 Equipment Data ............................................................................................................ 8-18
8.6.5 Maintenance ................................................................................................................. 8-19
8.7 Cake Storage ............................................................................................................................... 8-19
8.7.1 System Description ...................................................................................................... 8-20
8.7.2 Design Data .................................................................................................................. 8-20
8.7.3 Operation and Control .................................................................................................. 8-20
8.7.4 Equipment Data ............................................................................................................ 8-21
8.7.5 Maintenance ................................................................................................................. 8-21
Appendix A: IDNR WLA Water Quality Requirements .................................................................................... A-1
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List of Figures
Figure 1-1. Phase 1 Improvements Prior to Construction............................................................................1-3
Figure 1-1X. Phase 1 Improvements After Construction. .............................................................................1-4
Figure 2-1. South WWTP Effluent Water Quality Requirements (WLA) .......................................................2-1
Figure A1. Primary Sludge %TS Versus Sludge Blanket Depth (San Jose/Santa Clara, CA)......................3-5
Figure Y1. Secondary Clarifier Failure Criteria and Mitigating Steps. ..........................................................3-7
Figure Y2. Iowa City South Wastewater Treatment Plant Secondary Treatment Operational Flowsheet 3-13
Figure Y3. Example Graphic for Required Secondary Clarifier Area at Plant Influent of 30 mgd and RAS of
15 mgd .................................................................................................................................................. 3-15
Figure 3-Y1. Minimum Number of Digesters Required per Sludge Flow (peak 15-day rolling average) 3-18
Figure 4-1. Preliminary Treatment Flow Diagram. ..................................................................................... 4-20
Figure 4-2. SKB Influent Pumps P1304A, P1305A and P1306A (KSB Manufacturer’s Manual). ......... 4-22
Figure 4-3. Smith and Loveless – Pista Grit Chamber (smithandloveless.com). .................................... 4-26
Figure 5-1. Primary Treatment Flow Scheme. ..............................................................................................5-1
Figure 5-2. Primary Sludge Pump Diagram. ..................................................................................................5-9
Figure 6-1. Aeration Basin Schematic. ..........................................................................................................6-2
Figure 6-2. Turbo Blower Installed at South WWTP. .....................................................................................6-8
Figure 6-3. Blower Staging for Increasing Airflows – Both Turbo Blowers Available. .............................. 6-14
Figure 6-4. Blower Staging for Increasing Airflows – One Turbo Blower Available. ................................. 6-15
Figure 6-5. BAR Reactor Schematic. .......................................................................................................... 6-35
Figure 6-6. BAR Reactor 4320. .................................................................................................................. 6-36
Figure 7-1. Typical UV Disinfection System Layout. .....................................................................................7-2
Figure 7-2. South WWTP UV Disinfection System.........................................................................................7-2
Figure 7-3. Typical UV Module (Ozonia). .......................................................................................................7-3
Figure 7-4. Effluent Water Pumps (left) and Filters (right). ....................................................................... 7-12
Figure 8-1. RDT (left) and Flocculation Well (right). .....................................................................................8-2
Figure 8-2. Cake Storage Facility (Under Construction). ............................................................................ 8-20
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List of Tables
Table 1-1. Combined North and South WWTP Historical Flows ................................................................. 1-5
Table 1-2. Combined North and South WWTP Historical Loads ................................................................. 1-5
Table 1-3. South WWTP Design Flows and Loads Summary ...................................................................... 1-6
Table 3-1. Flow Driven Liquid Stream Operation Strategy1 ......................................................................... 3-2
Table 3-X1. Digester Tank Data ................................................................................................................. 3-16
Table 4-1. Phase 1 (2025) Influent Pump Design Data ........................................................................... 4-21
Table 4-2. Influent Pumping Equipment Data ............................................................................................ 4-23
Table 4-3. Influent Pumping Maintenance Data ....................................................................................... 4-24
Table 4-4. Influent Flow Meter Design Data ............................................................................................... 4-24
Table 4-5. Flow Measurement Equipment Data ........................................................................................ 4-25
Table 4-6. Grit Removal Design Data ......................................................................................................... 4-27
Table 4-7. Grit Equipment Data .................................................................................................................. 4-28
Table 4-8. Grit Removal Equipment Maintenance ..................................................................................... 4-30
Table 4-9. Influent Flow Equalization Basin Design................................................................................... 4-32
Table 4-10. Flow Equalization Basin Flow Measurement Equipment Data ............................................. 4-33
Table 4-11. Flow Equalization Basin Flow Measurement Maintenance .................................................. 4-34
Table 5-1. Primary Clarifier Design Data ...................................................................................................... 5-2
Table 5-2. Primary Clarifier Tankage Equipment Data ................................................................................ 5-4
Table 5-3. Primary Clarifier Maintenance ..................................................................................................... 5-6
Table 5-4. Primary Sludge Design Data ........................................................................................................ 5-7
Table 5-5. Clarifier 3300, 3400 and 3500 Primary Sludge/Scum Pumps ................................................ 5-9
Table 5-6. Primary Clarifier 3300,3400 and 3500 Sludge/Scum Pumps & Grinders Maintenance ..... 5-11
Table 6-1. Minimum/Maximum Air Flow Capacity Requirements per Aeration Train ............................... 6-2
Table 6-2. Aeration Basin Data ..................................................................................................................... 6-3
Table 6-3. Aeration Basin Effluent Channel Equipment .............................................................................. 6-5
Table 6-4. Aeration Effluent Channel Equipment Maintenance ................................................................. 6-5
Table 6-5. Airflow Requirements at the Iowa City South WWTP ................................................................. 6-6
Table 6-6. Turbo Blower Equipment ............................................................................................................. 6-9
Table 6-7. Aeration Turbo Blower Scheduled Maintenance ......................................................................... 6-9
Table 6-8. Diffuser Operating Conditions ................................................................................................... 6-11
Table 6-9. Installed Diffusers ...................................................................................................................... 6-11
Table 6-10. Aeration Piping and Diffuser Maintenance Schedule ............................................................. 6-12
Table 6-11. Airflow Control Valve Limits at the Iowa City South WWTP .................................................... 6-17
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Table 6-12. Airflow Control Equipment ...................................................................................................... 6-18
Table 6-13. Airflow Control Equipment Maintenance .............................................................................. 6-19
Table 6-14. IMLR Pumping Design Criteria ................................................................................................ 6-20
Table 6-15. IMLR System ............................................................................................................................ 6-20
Table 6-16. IMLR System Maintenance ...................................................................................................... 6-21
Table 6-17. Mechanical Mixing Design Data ............................................................................................. 6-22
Table 6-18. Mechanical Mixing Equipment Data ...................................................................................... 6-23
Table 6-19. Mechanical Mixing Equipment Maintenance ........................................................................ 6-24
Table 6-20. RAS Box and Surface Film Classifier Design Criteria ............................................................ 6-25
Table 6-21. RAS Box and Surface Film Classifier Equipment ................................................................... 6-25
Table 6-22. RAS Box and Surface Film Classifier Equipment Maintenance ............................................ 6-26
Table 6-23. Secondary Clarifier System Design Data ............................................................................... 6-27
Table 6-24. Secondary Clarifiers 5500 and 5600 Equipment .................................................................. 6-28
Table 6-25. Secondary Clarifiers 5500 and 5600 Maintenance ............................................................. 6-30
Table 6-26. RAS Pumping Design Criteria .................................................................................................. 6-31
Table 6-27. Clarifier 5500 and 5600 RAS Pumping Equipment .............................................................. 6-31
Table 6-28. RAS Pumping Maintenance .................................................................................................... 6-32
Table 6-29. WAS Pump Design Data .......................................................................................................... 6-33
Table 6-30. WAS Pumping ......................................................................................................................... 6-34
Table 6-31. WAS Pumping Maintenance ................................................................................................... 6-34
Table 6-32. BAR Reactor Equipment Data ................................................................................................ 6-37
Table 6-33. BAR Reactor Equipment Maintenance .................................................................................. 6-39
Table 6-34. HSW Tank Maintenance .......................................................................................................... 6-41
Table 7-1. UV System Design Requirements ................................................................................................7-4
Table 7-2. Operate Individual Modules from Module Screen ......................................................................7-5
Table 7-3. Operate all Modules per Channel from Channel Screen ...........................................................7-6
Table 7-4. UV Disinfection Equipment List ...................................................................................................7-7
Table 7-5. UV System Maintenance Schedule..............................................................................................7-9
Table 7-6. Effluent Water Design Criteria .................................................................................................. 7-12
Table 7-7. Effluent/Irrigation Water Equipment ...........................................................................................7-1
Table 7-8. Effluent Water Maintenance ........................................................................................................7-2
Table 7-9. Service Water Chlorination System Design Data ........................................................................7-3
Table 7-10. Service Water Chlorination Equipment .....................................................................................7-4
Table 7-11. Service Water Chlorination Equipment Maintenance ..............................................................7-4
Table 8-1. WAS Thickening Design Criteria ...................................................................................................8-2
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Table 8-2. WAS RDT Thickening Equipment Data ....................................................................................... 8-4
Table 8-3. RDT Maintenance Procedures.................................................................................................... 8-5
Table 8-4. Anaerobic Digestion Design Criteria ........................................................................................... 8-7
Table 8-5. Anaerobic Digestion Equipment .................................................................................................. 8-9
Table 8-6. Anaerobic Digestion Equipment ................................................................................................ 8-12
Table 8-6. Polymer Addition Design Criteria ............................................................................................... 8-14
Table 8-7. Polymer Addition Equipment Data ............................................................................................ 8-15
Table 8-7. Polymer Addition Equipment Maintenance .............................................................................. 8-16
Table 8-8. Cake Conveyance Design Data ................................................................................................. 8-18
Table 8-9. Cake Conveyance Equipment Data ........................................................................................... 8-18
Table 8-10. Cake Conveyance Equipment Maintenance .......................................................................... 8-19
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List of Abbreviations
AWW average wet weather
BAR bioaugmentation re-aeration
BC Brown and Caldwell
BFP Belt Filter Press
BOD biochemical oxygen demand
cBOD5 carbonaceous biochemical oxygen demand (five day)
CFD computational fluid dynamics
COD chemical oxygen demand
DNA deoxyribonucleic acid
FRP fiberglass reinforced polyester
gpd gallons per day
gph gallons per hour
gpm gallons per minute
GTE grit tank (chamber) effluent
HMI human machine interface
hp horsepower
HRT hydraulic retention time
HSW high strength waste
IDNR Iowa Department of Natural Resources
IMLR internal mixed liquor recycle
LPDC lamp power distribution center
mgd million gallons per day
MLE Modified Ludzack-Ettinger
MLSS mixed liquor suspended solids
MSC multi-stage centrifugal
nm nanometer
NPDES National Pollutant Discharge Elimination System
O&M operation and maintenance
PHWW peak hour wet weather
PLC programmable logic controller
PSU power supply unit
RAS return activated sludge
RDT rotary drum thickener
RNA ribonucleic acid
rpm revolutions per minute
SBD sludge blanket depth
Introduction Section 1
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scfm standard cubic feet per minute
SCADA supervisory control and data acquisition
sf square feet
SLR solids loading rate
SOP standard operating procedure
SOR surface overflow rate
SRT solids retention time
TDH total dynamic head
TKN total Kjeldahl nitrogen
TS total solids
TSS total suspended solids
TP total phosphorus
UV ultra violet
UMCP UV main control panel
UVT ultra violet transmittance
VFD variable frequency drive
WAS waste activated sludge
WLA waste load allocation
WWTP wastewater treatment plant
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Section 1 Introduction
This Operation and Maintenance (O&M) Manual for the City of Iowa City South Wastewater Treatment
Plant (WWTP) serves as a guide to those responsible for running and maintaining the South WWTP and
its associated systems and facilities.
The expansion of the South WWTP to meet the projected year 2040 flows and loads has been divided
into two phases. This approach efficiently constructs facilities in a stepwise manner to meet the flows
and loads as they increase over time. Phase 1 construction provided facilities to meet the projected
2025 demands. Phase 2 construction will prepare the South WWTP to meet the 2040 flows and loads
with the recommended facilities being constructed around 2025.
1.1 Purpose of Manual
This manual has been designed as a general guide for the operation and maintenance of the South
WWTP following the construction of the Phase 1 facilities. The manual provides an operating strategy,
overall system process descriptions, design data where applicable, operation and control strategies,
data for equipment installed in Phase 1, and maintenance recommendations. The information in this
manual is intended to orient Plant Staff about the wastewater facilities and to provide a resource for all
Plant Staff addressing equipment or process problems. This manual is not intended to provide detailed
information on servicing treatment equipment. Manufacturers’ O&M manuals should be consulted for
equipment specific information.
Unit Processes and pre-existing equipment not affected by the Phase 1 expansion are generally not
covered in this manual.
1.2 Updating the Manual
It is very important that all modifications, refinements, or changes to processes and operation be noted
in this manual. Plant Operators are encouraged to update spreadsheets, forms, checklists, and
procedures and add notes related to operator experience. New Plant Operators benefit from this
accumulated knowledge.
1.3 Plant Information
1.3.1 Plant Overview
The Iowa City Wastewater Division maintains and operates the South WWTP located in Johnson County,
Iowa, in east-central Iowa near the Iowa River at 4366 Napoleon St. SE Iowa City, Iowa 55240.
After the decommissioning of the North Wastewater Treatment Plant (ca. January 2014), and expansion
of the South WWTP the combined flow formerly managed by both facilities will be treated by the South
WWTP alone. The upgraded South WWTP is designed to meet the effluent requirements specified in the
Iowa Department of Natural Resources (IDNR) waste load allocation analysis for a shore discharge into
the Iowa River at the location of the existing South WWTP outfall.
The South WWTP is located approximately three miles southeast of the downtown area and is in a
predominately rural area, adjacent to the City’s soccer complex. The expanded Plant is rated at 30
million gallons per day (mgd), except the influent pumping station has a total capacity of 60 mgd.
Secondary treatment is provided by single nitrifying activated sludge. Treatment units include a 17.6
mgd flow equalization basin, a high strength equalization tank, influent screening, influent pumping
station, two vortex grit units, five primary clarifiers, four ten cell activated sludge aeration trains, high
Section 1 Introduction
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strength biological treatment tank (or the bioaugmentation re-aeration, BAR, tank), mixed liquor pumping
station, six secondary clarifiers, and sludge pumping stations. The treated wastewater effluent is
disinfected by ultra violet disinfection and released to the Iowa River approximately four miles
downstream of Iowa City.
Solids produced at the South WWTP are anaerobically digested via temperature phased digestion in six
digesters. Prior to digestion, the waste activated sludge (WAS) is thickened by three rotary drum
thickeners (RDTs). Digested solids are dewatered, stored, and land applied in the spring and the fall.
The filtrate from dewatering, termed high strength waste (HSW) is recycled to high strength biological
treatment tank via the high strength equalization tank and associated pumping station.
Figure 1-1 highlights the major facilities constructed as part of the Phase 1 expansion prior to
construction. Figure 1-1X is a similar aerial photograph after construction. Not shown are three new
influent pumps that replace three antiquated units. Overall, the major facility additions include:
• Three new influent pumps
• Expanded equalization basin
• Modified influent pump station discharge channel
• Two vortex grit tanks and associated pump vault
• Fifth primary clarifier, new splitter box, modified sludge pumping on two existing clarifiers
• Modified aeration basin influent channel and extended basins with new effluent channel
• Two turbo blowers for aeration
• Two additional secondary clarifiers and new splitter box
• UV disinfection system
• Modified service water and irrigation water system
• Sodium hypochlorite facility
• Additional RDT for WAS thickening
• Dewatered solids (cake) storage facility
• Expanded HSW equalization tank
• HSW biological treatment tank – BAR
• Maintenance warehouse
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Figure 1-1. Phase 1 Improvements Prior to Construction.
Section 1 Introduction
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Figure 2-1X. Phase 1 Improvements After Construction.
1.3.2 Plant Power Supply
Power supply to the South WWTP is provided by Eastern Iowa Light and Power. The South WWTP is
currently served by the Sand Road Substation that has two independent separate sources of power. If
one source of transmission power is lost the utility can switch to the alternate source using radio
controlled switching. In addition, the South WWTP currently has a 1,000 kW emergency generator which
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can be used to service critical loads in the rare event that both power sources are out of service. The
system is set up for plant staff to selectively place loads online in case of a power outage.
1.3.3 Historical Flows and Loads Data
Combined historical influent flows and loads for the North Plant and South WWTP are shown in Tables 1-
1 and 1-2. These flows and loads served as a basis for projecting the requirements in the Phases 1 and
2. They also illustrate the requirements when combining both plants.
Table 1-1. Combined North and South WWTP Historical Flows
Parameters Flow (mgd) Date
Average Daily Flow (ADF) 11.3 2005-2009
Minimum Flow 5.8 9/18/2002
Average Dry Weather (ADW) Flow 8.0 12/18/2005 – 1/16/2006
Average Wet Weather (AWW) Flow 18.6 4/8/2008 – 5/7/2008
Maximum Wet Weather (MWW) Flow 33.1 10/30/2009
Historic PHWW Flow 44.9 7/21/2008
Source: 2011 Facility Plan, Stanley Consultants and Brown and Caldwell
Table 1-2. Combined North and South WWTP Historical Loads
Parameter Period Value (lb/d) Date/Period
cBOD5
Annual Average 15,425 2006-2010
Maximum Month 21,643 10/1/2009
Maximum Week 25,193 9/24/2009
Maximum Day 31,381 8/12/2009
TSS
Annual Average 17,110 2006-2010
Maximum Month 22,075 6/28/2006
Maximum Week 28,541 5/11/2008
Maximum Day 33,796 5/8/2008
TKN
Annual Average 3,316 2006-2010
Maximum Month 4,665 10/3/2009
Maximum Week 5,232 9/27/2009
Maximum Day 6,754 2/24/2010
Source: 2011 Facility Plan, Stanley Consultants and Brown and Caldwell
1.3.4 Design Flows and Loads
Design flows and loads for the South WWTP have been estimated for 2025 (Phase 1) and 2040 (Phase
2). Design flows and loads have been estimated by using historical data and expected population and
industrial growth. Table 1-3 summarizes the South WWTP flows and loads for both phases.
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Table 1-3. South WWTP Design Flows and Loads Summary
Year 2025 (Phase 1) Year 2040 (Phase 2)
Max. Month Max. Day Max. Month Max. Day
Flow (mgd) 24.2 43.3 29.8 53.1
cBOD5 (lb/day)
Residential
Commercial/ Light Industrial
Industrial
Total
15,484
2,218
14,956
32,658
19,329
2,756
25,660
47,745
18,785
2,843
22,045
43,473
23,312
3,527
37,269
64,108
TSS (lb/day)
Residential
Commercial/ Light Industrial
Industrial
Total
17,022
2,639
14,725
34,385
23,764
3,693
28,196
55,653
19,891
3,303
23,500
46,694
28,480
4,729
44,300
77,509
TKN (lb/day)
Residential
Commercial/ Light Industrial
Industrial
Total
4,478
915
918
6,311
6,637
1,358
1,495
9,490
5,224
1,152
1,580
7,956
7,856
1,732
2,637
12,225
Source: 2011 Facility Plan, Stanley Consultants and Brown and Caldwell
The flows listed above represent the South WWTP influent. The expanded equalization basin is able to
reduce the peak flows. In doing so, the design flows for the unit processes starting at grit removal and
downstream are designed for a peak sustained flow of 30 mgd for Phase 1.
1.4 Related Documents
1.4.1 Manufacturer’s Operations and Maintenance Manuals
Manuals have been provided for this project, and previously for existing equipment. .
1.4.2 References
The following reference documents have been used to prepare this O&M manual
• Stanley Consultants, Brown and Caldwell, Facility Plan for Expansion of South Wastewater
Treatment Plant, Feb. 2011
• Stanley Consultants, Brown and Caldwell, Preliminary Engineering Report for Expansion of South
Wastewater Treatment Plant, May 2011
• Brown and Caldwell, Technical Memorandum No. 1 – Secondary Clarifier Capacity Modeling, April
6, 2011
• Brown and Caldwell, Technical Memorandum No. 2 – South Plant Wastewater Characterization
and BioWin Calibration, April 6, 2011
• Brown and Caldwell, Technical Memorandum No. 3 – Secondary Alternative Assessment, April 6,
2011
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• Brown and Caldwell, Technical Memorandum No. 8 – Plant Hydraulic Evaluation, December 16,
2011
• Brown and Caldwell, Technical Memorandum No. 9 – Secondary Treatment Process Alternative
Update, May 3, 2011
• Brown and Caldwell, Technical Memorandum No. 14 – Aeration Blower Design, July 27, 2011
• Stanley Consultants, Brown and Caldwell, Technical Memorandum No. 15 – Response to IDNR
Review Comments on Iowa City Facilities Planning Study and Preliminary Engineering Report, July
25, 2011
• Stanley Consultants, Brown and Caldwell, Response to IDNR Comments in August 22 E-mail,
September 12, 2011
• New and existing vendor Operations and Maintenance manuals
• Phase 1 construction record drawings have been provided, but are not included here
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Section 2 Regulatory Requirements
2.1 Waste Load Allocation
In February 2011, the IDNR provided the City of Iowa City waste load allocations (WLA). The South
WWTP expansion was designed to meet the effluent water quality criteria in the WLA. The critical design
parameter is meeting the ammonia limits during cold weather periods when nitrification is depressed.
The critical concentration and mass loading limits are shown in Figure 2-1. The WLA in its entirety can
be found in Appendix A.
Figure 2-1. South WWTP Effluent Water Quality Requirements (WLA)
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Section 3 Process Operational
Strategies
The South WWTP consists of liquid treatment processes and solids treatment processes. The liquid
treatment processes downstream of and including grit removal must be designed and operated to pass
the maximum design flow (30 mgd, Phase 1) while everything upstream is designed to handle 60 mgd.
In the liquid treatment process the most complex system is secondary treatment. Focused sections on
operating the primary clarifiers, secondary treatment system, and digestion system, plus operations of
supporting systems, have been included.
3.1 Liquid Stream Operations
Several unit processes at the South WWTP are operated on based on hydraulic capacity or according to
flow rate. Those facilities include the influent screens, influent pump station, influent equalization basin,
grit removal, primary clarifiers, and UV disinfection. Other unit processes such as secondary treatment,
sludge thickening, digestion, and dewatering have other capacity considerations and are discussed later.
Table 3-1 summarizes the hydraulic capacity considerations for operation of the flow driven unit
processes. For most of the unit processes, the plant flow dictates the number of units in service to
provide the necessary hydraulic capacity. The disinfection system is a little different where operations
are dictated by having an adequate number of units online to meet the plant flow rate and the
transmissivity of the effluent to achieve the proper dose. Also, the capacity of the influent pump station
can be increased for short periods of time by increasing the wet well level, as noted in the table
footnotes. Otherwise, operations adhere to the unit process hydraulic rating.
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Table 3-1. Flow Driven Liquid Stream Operation Strategy1
Unit Process
Flow Criteria
5 mgd 10 mgd 15 mgd 30 mgd 45 mgd 60 mgd
Influent Screens Confirm both units
are online
Begin utilizing
screen bypass
channel
Hydraulic capacity
Influent Pump
Station2
Operate one pump
at reduced speed
to achieve desired
output; vary speed
to stabilize WW
level. Pump 1
should shut off at
El. 619.7.
If Pump 1 at
maximum speed
and WW level
continues to rise,
start Pump 2;
operate both
pumps at same
speed until WW
level stabilizes.
Pump 2 starts at
El.621.5 and shuts
off at El. 621.0
Bring Pump 3
online when Pumps
1 and 2 reach
maximum speed
and WW continues
to rise; operate all
three pumps at
same speed; Pump
3 starts at El.
623.0 and shuts off
at El. 622.5.
Operate Pump 4
when Pumps 1, 2,
and 3 reach full
speed and WW
continues to rise;
Operate all four
pumps at same
speed. Pump 4
starts at El. 624.5
and shuts off at El.
624.0.
Operate all five duty
pumps at the same
speed; maximum
pump output is
required for 60 mgd
of influent flow
(without using
equalization). Pump
5 starts at El. 626.0
and shuts off at El.
625.5.
Hydraulic capacity
Influent
Equalization Anything over 30
mgd flows to EQ Main plant rated capacity
Grit Removal Confirm both units
are online Treatment capacity
Primary
Clarification3
Average flow – 2
clarifiers
Peak flow – 1
clarifiers
Average flow – 3
clarifiers
Peak flow – 2
clarifiers
Average flow – 4
clarifiers
Peak flow – 2
clarifiers
Average flow – NA
Peak flow – 4
clarifiers
Average SOR = 1,000
gal/sf-d
Peak Flow SOR = 2,000
gal/sf-d
Disinfection Confirm both units
are online
Anything over 30
mgd bypasses UV Hydraulic capacity
1Assumes everything is available at design capacity.
2 Additional output can be obtained by raising the liquid level in the wet well up to 631.0. For every 2 ft of wet well level, an additional 0.5 mgd output per pump can be obtained. Note,
however, that this constitutes a “run-out” condition for the pump and is not recommended for extended periods. The best efficiency point for the new influent p umps is approximately 8100
gpm and wet well liquid elevation of 621.0.
3Recommended operations are to maintain all available clarifiers in service to accommodate unexpected peak flows.
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3.2 Primary Clarification
Primary clarifiers remove settleable particulate solids in the influent wastewater using gravity separation.
Influent wastewater is fed to the primary clarifier through a center column/feed well where it flows
radially into the tank. Clarified effluent is collected using peripheral launders and captured solids are
moved to a central hopper using a scraper collector mechanism and pumped from the hopper to the
anaerobic digester complex. Primary clarifier total suspended solids (TSS) removal averaged 64% during
the July 15, 2010 through July 26, 2010 wastewater characterization testing - typical for a municipal
wastewater.
Removal of particulate material will also reduce influent particulate carbonaceous biochemical oxygen
demand (cBOD5), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) loadings. During the
wastewater characterization effort from July 15, 2010 through July 26, 2010 the median cBOD5, TKN,
and TP removals were 44%, 11% and 26%, respectively. TSS and cBOD5 removal in the primary clarifiers
are incredibly important to downstream aeration basin operations. TSS removal in the primary clarifiers
reduces the aeration basin mixed liquor suspended solids (MLSS) concentrations which in turn
decreases the secondary clarifier solids loading to minimize risk of high effluent TSS discharges and
maximize plant capacity. Primary clarifier cBOD5 removal is the most cost effective method to reduce
cBOD5 loadings and reduces the oxygen demand/aeration requirements in the downstream aeration
basins - an energy intensive process. Process modeling shows aeration airflow requirements increase by
roughly 74% on average if primary clarifiers are not included in the plant treatment scheme. Proper
operation of the primary clarifiers is paramount to maximize capacity and efficiency.
3.2.1 Primary Clarifier Design
Phase 1 Improvements adds one additional primary clarifier to the existing pod of four clarifiers. Each
primary clarifier has a nominal tank diameter of 70 feet with a 12-foot side water depth. At the Phase 1
maximum design flow of 30 million gallons per day (mgd), the primary clarifier surface overflow rate
(SOR) with all tanks in service is 1500 gal/sf-d (6 mgd/tank). Under Phase 1 average dry weather (ADW)
flows of 10.5 mgd the SOR will be 680 gal/sf-d with one unit out of service.
Each primary clarifier has a 300 gpm grinder and rotary lobe sludge pump for pumping primary sludge to
the sludge holding tank. The primary clarifiers are equipped with rake, or scraper, type sludge collectors
that direct sludge to a hopper at the center of the tank for withdrawal by the sludge pumping system.
The collector mechanism is driven by gear reducer assembly with a 5 hp motor.
3.2.2 Primary Clarifier Operation
Historically primary clarifier design is based on the SOR. To determine the SOR in real time, divide the
plant influent flow by the total surface area of the online primary clarifiers. For example, if the influent
flow is 30 mgd and 5 primary clarifiers are in service, the SOR is:
𝑂𝑂𝑂=𝑂𝑖𝑙𝑎𝑙𝑡𝑎𝑙𝑡
𝑂𝐴𝑙𝑙𝑙𝑖𝑙𝑎
=
(30𝑘𝑎𝑎)(106 𝑎𝑎𝑘
𝑘𝑎𝑎)
𝜋
4 (70𝑎𝑘)2 (5 𝑎𝑘𝑎𝑘�ℎ𝑎�ℎ𝑎𝑘𝑘)
=1,560 𝑎𝑎𝑘
𝑘𝑎−𝑎
It is recommended that the plant operate all its primary clarifiers to maximize influent TSS and cBOD5
removal and minimize impacts to downstream secondary treatment system.
Primary clarifier particulate removal performance can be monitored to determine the efficiency of the
system. Wastewater treatment plant investigations conducted by WERF indicate that primary clarifier
performance is a function of the influent solids characteristics and SOR (Determine the Effect of
Individual Wastewater Characteristics and Variances on Primary Clarifier Performance, WERF, 00-CTS-2,
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2006). WERF developed the following removal models (Equations A1 and A2) for TSS and cBOD5
removal.
𝐷𝑅𝑅𝑅=𝐷𝑅𝑅𝑅𝑙𝑎𝑤(1 −𝑎
−𝜆
𝑅𝑂𝑅) 𝐷𝑘𝑘𝑎𝑘�ℎ𝑘𝑘 𝐴1
where:
ETSS =TSS removal (decimal)
ETSSmax =1 −(𝑅𝑅𝑅𝑛𝑛𝑛
𝑅𝑅𝑅𝑃𝐼
)
TSS𝑙𝑙𝑙=nonsettleable TSS concentration (mg/L)
TSS𝑂𝐼=primary influent TSS concentration (mg/L)
𝜆=settling constant (gal/sf −d)
SOR =surface overflow rate (gal/sf −d)
and,
𝐷𝑎𝐴𝑂𝐷5 =𝐷𝑎𝐴𝑂𝐷5𝑙𝑎𝑤(1 −𝑎
−𝜆
𝑅𝑂𝑅) 𝐷𝑘𝑘𝑎𝑘�ℎ𝑘𝑘 𝐴2
where:
E𝑎𝐴𝑂𝐷5 =TSS removal (decimal)
E𝑎𝐴𝑂𝐷5max =1 −(𝑎𝐴𝑂𝐷5𝑛𝑛𝑛
𝑎𝐴𝑂𝐷5𝑃𝐼
)
𝑎𝐴𝑂𝐷5 𝑙𝑙𝑙=nonsettleable 𝑎𝐴𝑂𝐷5 concentration (mg/L)
𝑎𝐴𝑂𝐷5 𝑂𝐼=primary influent 𝑎𝐴𝑂𝐷5 concentration (mg/L)
𝜆=same as above
SOR =same as above
Based on the wastewater characterization data from July 15, 2010 through July 26, 2010 and all
clarifiers were online, primary clarifier TSS and cBOD5 removal performance can be estimated using the
following equations.
𝐷𝑅𝑅𝑅=(1 −58
𝑂𝑂𝑂𝑂𝐼
)(1 −𝑎
−35,167
𝑅𝑂𝑅)
𝐷𝑎𝐴𝑂𝐷5 =(1 −91
𝑎𝐴𝑂𝐷5 𝑂𝐼
)(1 −𝑎
−35,167
𝑅𝑂𝑅)
It is recommended the plant begin monitoring primary clarifier effluent TSS and cBOD5 a minimum of
three times per week to confirm the settling constant (λ) and the non-settleable fractions during both
warm and cold weather conditions.
3.2.3 Primary Sludge Withdrawal Operation
Primary sludge is currently thickened in the primary clarifiers to approximately 4% total solids (TS) prior
to being pumped to the sludge blending tank ahead of the anaerobic digestion system. To avoid
hydraulic bottlenecking in the primary sludge piping, the five sludge pumps are operated on a timer so
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that the number of pumps pumping at the same time is limited. The current timed sludge pump
operation was developed by plant staff, and consists of pumping from each clarifier for 5 minutes every
two hours. The pumping cycles between clarifiers are also staggered so that hydraulic capacity of the
sludge piping is not overwhelmed.
Thickening of the primary sludge is required to maintain the minimum 15 day hydraulic retention time
(HRT) in the anaerobic digestion system, see Section 3.4. The design basis is to thicken primary sludge
to 4% TS which avoids adding an additional anaerobic digester in Phase 1. The 4% TS concentration
was selected based on plant experience and can be monitored by the sludge density meter located on
the main primary sludge pipeline downstream of combined sludge pump discharge. Operations need to
coordinate the anaerobic digestion HRT and primary sludge solids concentration closely to provide
minimum 15 day HRT in the digestion system.
Primary sludge thickening is achieved by allowing the primary sludge to develop a sludge blanket which
compacts with time. Plant operating data from 2007 through 2009 shows primary sludge
concentrations of approximately 4.6% TS were achieved operating with a sludge blanket depth of less
than one foot.
Figure A1 represents data taken from the San Jose/Santa Clara plant in California (“Primary Clarification
Evaluation and Optimization Study”, San Jose/Santa Clara WWTP, Brown and Caldwell). Two noteworthy
observations from the San Jose/Santa Clara study are 1) the sludge blanket depth required to achieve
approximately 4% TS (~4.5 ft) is significantly deeper than Iowa City and 2) carrying sludge blankets
depths greater than five feet does not increase thickened solids concentrations. It is recommended to
establish a similar curve for the Iowa City South Plant primary sludge to optimize thickening performance
at the lowest possible blanket depth.
Figure A1. Primary Sludge %TS Versus Sludge Blanket Depth (San Jose/Santa Clara, CA).
The alternative to operating with a sludge blanket is to continuously, or more frequently, pump primary
sludge out of the clarifier to effectively operate with no sludge blanket. The additional volume of water
carried with the sludge would decrease the HRT in the anaerobic digestion system but may be
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acceptable until the HRT on that system approaches the 15 day minimum. Another advantage to
operating without a sludge blanket is reduced risk of losing solids during high flow events with
subsequent negative impacts to the downstream aeration tanks.
3.3 Secondary Treatment
This section presents a brief and succinct operating strategy for the Iowa City WWTP secondary
treatment system which includes the aeration basins, secondary clarifiers, BAR reactor. The operating
strategy identifies key operating parameters for each of the three secondary treatment system
components. The information contained herein is largely based on the findings reported in the technical
memorandums prepared by Brown and Caldwell.
This technical memorandum discusses operational strategies in the following order:
1. Secondary Clarifiers
2. Aeration Basins
3. BAR System
4. Overall Secondary Treatment Process
3.3.1 Secondary Clarifier Operational Background
The Iowa City South Plant secondary clarifiers are designed for a maximum allowable solids load rate
(SLR) of approximately 42 lb/sf-d, see Technical Memorandum Number 1 (TM1) – Secondary Clarifier
Capacity Modeling prepared by Brown and Caldwell (April 6, 2011). The 42 lb/sf-d was based on a
design SVI of 150 mL/g at the maximum return sludge pumping rate of 3.75 or 7.50 mgd/clarifier for
the 80-ft diameter and 115-ft diameter clarifiers, respectively. Under peak flow conditions (30 mgd for
Phase 1) this equates to a MLSS of 3,430 mg/L and assumes all clarifiers are in operation. The design
approved by the IDNR is on a slightly different basis of 37 lb/sf-d under peak conditions, and 30 lb/sf-d
at 120% RAS and AWW flow of 24.2 mgd. The South WWTP design relies on maintaining good sludge
quality (SVI of 150 mL/g) by proper operation of the classifying and anoxic selectors, stable operations
using solids retention time (SRT) control, and return activated sludge (RAS) chlorination if needed.
The SLR can easily be calculated for real time operational management per Equation 3-1:
𝑂𝐿𝑂=
(𝐿𝐿𝑂𝑂)(𝑂+𝑂𝑅)(8.34 𝑘𝑎−𝐿
𝑘𝑎−𝐿𝐷)
𝑂𝐴𝑎
𝐷𝑘𝑘𝑎𝑘�ℎ𝑘𝑘 3 −1
Where,
SLR = solids loading rate (lb/sf-d)
MLSS = mixed liquor TSS concentration (mg/L)
Q = anticipated peak wet weather plant equalized influent flow rate (mgd) to the
secondary treatment system
QR = anticipated peak RAS flow rate (mgd)
SAc = operational secondary clarifier surface area (sf)
Equation 3-1 uses the anticipated peak influent and RAS flow to maintain acceptable clarifier surface
area for periods when wet weather occurs and the plant is not able to place additional clarifiers in
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service in short order. The clarifier surface areas for various clarifier combinations is tabulated in Table
X4 located below.
For example, if all six secondary clarifiers are in operation (40,880 sf) at a MLSS concentration of 2,000
mg/L, plant influent flow of 30 mgd, and a RAS flow rate of 15 mgd; the SLR would be:
𝑂𝐿𝑂=
(2,000 𝑘𝑎
𝐿)(30 𝑘𝑎𝑎+15 𝑘𝑎𝑎)(8.34 𝑘𝑎−𝐿
𝑘𝑎−𝐿𝐷)
40,880 𝑘𝑎=18 𝑘𝑎
𝑘𝑎−𝑎
Wet Weather Operations. If the clarifiers are nearing failure due to high SLR during wet weather, as
determined by high effluent total suspended solids, or sludge blanket depths approaching the bottom of
the centerwell or ½ the clarifier side wall depth; the first corrective step is to increase the RAS flow rate.
If the increased RAS flow rate does not reduce the clarifier blankets, additional secondary clarifiers
should be placed in service. A secondary alternative would be to equalize influent flow. Operations
should also check the operating mainstream aerobic SRT. If the aerobic SRT is greater than the
minimum values (5 days with BAR and 7 days without BAR), the plant should commence reducing the
SRT to reduce the MLSS and associated SLR. Finally, chlorinating the RAS should improve sludge
settling. Figure Y1 below illustrates the failure criteria and mitigating steps to take.
Figure Y1. Secondary Clarifier Failure Criteria and Mitigating Steps.
As sludge quality varies (represented by SVI) the maximum allowable SLR also changes. Table X1 below
summarizes the maximum allowable SLR at various SVI levels for Iowa City. The same calculations apply
for the various SVI levels to determine whether the actual SLR is within the maximum allowable value.
Table X1. Maximum Allowable SLR at Various SVI Levels
SVI (mL/g) Maximum Allowable SLR (lb/sf-d)
100 50
125 47
150 42
175 39
200 37
Normal Operations. Under normal conditions the secondary clarifiers will be well within the SLR capacity
and control of the unit process is simply to maintain a sludge blanket depth (SBD) of 1-ft or less at the
peak diurnal flow period by varying the RAS rate. This SBD is based on the strategy of removing the
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sludge as soon as it settles, maintaining the solids in the aeration basins as much as possible and
avoiding the risk of denitrification occurring in the sludge blanket which causes the sludge to rise.
Denitrification may also be facilitated by low aeration basin effluent DO (<0.5 mg/L) if cell 10 is not
being aerated. Alternatively, excessive aeration in cell 10 may entrain bubbles with the sludge, inhibiting
settling. In either case, operation of cell 10 can play a role in sludge settling.
Until the projected flows and loads for the design are realized, the clarifiers will be under loaded at the
target SRTs. It is possible to operate with less than six clarifiers, but the risk is treating an unexpected
peak flow. Alternatively, all six clarifiers can be operated normally with the RAS pumps turned down as
low as possible to limit the amount pumping with at most a 1-ft deep sludge blanket but also take into
consideration the concentration of RAS/WAS sent to the rotary drum thickeners (RDTs) and the impact
on thickening. A starting point would be to set the RAS rate at 50% of the peak plant influent rate and
then allow it to be flow paced.
Important Note: Groundwater levels around the clarifiers must be measured prior to draining a clarifier
and must always be lower than the water surface elevation in the clarifiers to prevent uplift forces from
damaging the floor of the clarifiers.
3.3.2 Aeration Basins Operational Background
To achieve the desired level of BOD removal and nitrification, the secondary treatment system was
designed to operate at a mainstream aerobic SRT of 5 days, minimum (do not count the BAR biomass
inventory) with the BAR reactor in service. If the BAR reactor is not in service, similar effluent quality can
be achieved under cold weather operations by operating the mainstream aerobic SRT at 7 days,
minimum. When operating at these SRTs, the aeration basin MLSS concentration will vary in response
to changes in the primary effluent BOD loading and to a lesser extent primary effluent inert solids as
shown in Equation 3-2.
𝐿𝐿𝑂𝑂=𝑂𝑂𝑂∙𝑂
𝑉(𝐷𝑂𝑂𝑂𝐷+𝑌∙𝐴𝑂𝐷𝑂𝐷−𝐴𝑂𝐷𝑂𝐷
1 +𝑎∙𝑂𝑂𝑂) 𝐷𝑘𝑘𝑎𝑘�ℎ𝑘𝑘 3 −2
Where,
SRT = solids retention time (d)
Q = plant equalized influent flow rate to the secondary aeration basin (mgd)
V = aeration basin volume (ft3)
ISSPE = primary effluent inert suspended solids (mg/L)
Y = biomass yield (mg TSS/mg BOD)
BODPE = primary effluent biochemical oxygen demand (mg/L)
BODSE = secondary effluent biochemical oxygen demand (mg/L)
b = endogenous decay rate (d-1)
To maintain the MLSS concentration within an acceptable range that prevents overloading the
secondary clarifiers, the operator can primarily change the SRT and/or number of aeration basins in
service. The target MLSS range at the South WWTP is 2,000 to 4,000 mg/L. Equations 3-3 and 3-4
provide an approximate estimate of the change in SRT or number of aeration basins required to achieve
a target MLSS concentration.
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𝑂𝑂𝑂𝑡𝑎𝑟𝑎𝑎𝑡=𝐿𝐿𝑂𝑂𝑘𝑎𝑘𝑎𝑎𝑘
𝐿𝐿𝑂𝑂𝑘𝑘�ℎ𝑎�ℎ𝑘𝑎𝑘
𝑂𝑂𝑂𝑙𝑟𝑖𝑎𝑖𝑙𝑎𝑙 𝐷𝑘𝑘𝑎𝑘�ℎ𝑘𝑘 3 −3
𝐴𝑎𝑘�ℎ𝑘𝑘𝑡𝑎𝑟𝑎𝑎𝑡=𝐿𝐿𝑂𝑂𝑘𝑘�ℎ𝑎�ℎ𝑘𝑎𝑘
𝐿𝐿𝑂𝑂𝑘𝑎𝑘𝑎𝑎𝑘
𝐴𝑎𝑘�ℎ𝑘𝑘𝑙𝑟𝑖𝑎𝑖𝑙𝑎𝑙 𝐷𝑘𝑘𝑎𝑘�ℎ𝑘𝑘 3 −4
For example, assume that the plant is operating with an aerobic SRT of 10 days, MLSS concentration is
at 4,000 mg/L, three aeration basins in service, and the SLR on the secondary clarifiers is approaching
the allowable limit. To reduce the clarifier SLR, the MLSS concentration target is chosen to be 3,000
mg/L. Per Equations 3-3 and 3-4, either the SRT can be reduced to 7.5 days or the number of aeration
basins can be increased to four.
𝑂𝑂𝑂𝑡𝑎𝑟𝑎𝑎𝑡=
3,000 𝑘𝑎
𝐿
4,000 𝑘𝑎
𝐿
(10 𝑎𝑎𝑘𝑘)=7.5 𝑎𝑎𝑘𝑘
𝐴𝑎𝑘�ℎ𝑘𝑘𝑡𝑎𝑟𝑎𝑎𝑡=
4,000 𝑘𝑎
𝐿
3,000 𝑘𝑎
𝐿
(3 𝑎𝑎𝑘�ℎ𝑘𝑘)=4 𝑎𝑎𝑘�ℎ𝑘𝑘
Maintaining SRT (aerobic SRT in the case of Iowa City) on a day to day basis is achieved by constantly
wasting a portion of the solids in the secondary system (WAS). Conceptually, the aerobic SRT is
equivalent to the mass of solids in the aerated portion of the aeration basins divided by the wasting rate.
For example, the WAS mass rate is calculated below to maintain an aerobic SRT of 10 days with four
aeration basins online, cells 4-10 are aerated (1.25 MG), and the MLSS is 3,000 mg/L.
𝑉𝐴𝑂(𝑘𝑎
𝑎)=
𝑉𝑎𝑎𝑟𝑎𝑡𝑎𝑎𝐿𝐿𝑂𝑂(8.34 𝑘𝑎−𝐿
𝑘𝑎−𝐿𝐷)
𝑂𝑂𝑂𝑎𝑎𝑟𝑙𝑎𝑖𝑎
=
(4 𝑎𝑎𝑘�ℎ𝑘𝑘)(1.25 𝐿𝐷 𝑎𝑎𝑘𝑎𝑘𝑎𝑎
𝑎𝑎𝑘�ℎ𝑘)(3,000 𝑘𝑎
𝐿)(3.78𝑘106 𝐿
𝐿𝐷)
(10 𝑎𝑎𝑘𝑘)(453,592 𝑘𝑎
1 𝑘𝑎)
=12,500 𝑘𝑎
𝑎
In terms of a flow rate, assuming the WAS TSS concentration is 7,000 mg/L (equivalent to 0.7% TS or
0.007 lb solid/lb solution):
𝑉𝐴𝑂(𝑘𝑎𝑎)=
(12,500 𝑘𝑎
𝑎)
(0.007 𝑘𝑎 𝑘𝑘𝑘�ℎ𝑎
𝑘𝑎 𝑘𝑘𝑘𝑘𝑘�ℎ𝑘𝑘)(8.34 𝑘𝑎
𝑎𝑎𝑘)(106 𝑎𝑎𝑘
𝐿𝐷)
=0.21 𝑘𝑎𝑎
Table X2 provides a summary of the individual cell volumes for quick reference.
Table X2. Aeration Basin Cell Volume
Cell Volume of Each Cell (MG)
1-8 0.15
9-10 0.25
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It is recommended to waste solids continuously to provide a relatively constant TSS concentration to the
RDTs. This requires a flow paced RAS system as well. A relatively constant TSS concentration to the
RDTs will stabilize the polymer dose and capture efficiency in that process.
Internal Mixed Liquor Recycle. The aeration basins are also equipped with an internal mixed liquor
return (IMLR) system. The IMLR system provides nitrate recycle back to the head of the aeration basins
to drive an anoxic selector in the first two or three cells. The anoxic selector is provided to minimize
filamentous organism growth which can degrade sludge settleability. The anoxic selector operates by
providing a desirable environment for good settling, denitrifying organisms. These organisms use the
nitrate provided by the RAS or IMLR to degrade the incoming readily degradable organics that
filamentous organisms require. Operationally, the combined recycle from the RAS and IMLR systems
needs to be roughly equal to the plant influent flow rate. Whether this flow is RAS or IMLR does not
matter for operations of the anoxic selector. The optimal feed TSS concentration to the RDTs and
maintaining a 1-ft sludge blanket in the secondary clarifiers will determine how much RAS can be
delivered. Iowa City will need to trial what RAS flow rate works best and then use the IMLR system to
fulfill the 100% requirement based on plant influent flow. The 100% setpoint, or flow pacing of the
combined RAS and IMLR to plant influent, will mitigate excessive or insufficient recycle plus maintain
somewhat steady RAS concentrations for efficient RDT operation.
The ratio of (RAS+IMLR):plant influent can be fine tuned using two parameters, the soluble chemical
oxygen demand (sCOD) and nitrate levels through the aeration basins.
• An insufficient (RAS+IMLR):plant influent ratio is characterized by the sCOD leaving the selector cells
being greater than the sCOD in the aeration basin effluent (> 5 mg/L difference) and low nitrate
levels at the end of the selector cells (< 0.5 mg/L). Corrective action is to increase the IMLR flow
rate.
• Too high of a (RAS+IMLR):plant influent ratio is characterized by a high nitrate concentration at the
end of the selectors (> 1 mg/L) or high dissolved oxygen (DO) in the initial selector cell (>0.3 mg/L).
Corrective action is to decrease the IMLR flow rate.
• Also, if the selector effluent nitrate is greater than 1 mg/L and the selector effluent sCOD is greater
than the aeration basin effluent sCOD, then additional selector volume is required.
• Insufficient nitrification in the aerated cells and subsequent recycle by the IMLR of ammonia (>3
mg/L) will also impede the anoxic selector. In this case confirm the aerated cells DO and aerobic
SRT are adequate and increase either if necessary.
Table X3 summarizes the anoxic selector troubleshooting including IMLR flow rate impacts for Iowa City.
It should be noted that when analyzing the aeration basin/selector sCOD, nitrate and DO grab samples
should be used. The grab samples should separate the solids immediately through decanting and
collecting supernatant liquid as the analysis sample or employ direct filtration using a filter syringe.
Table X3. Anoxic Selector Troubleshooting
Scenario Characteristic Value Action
Normal Operation
● (RAS+IMLR):plant influent ratio ≈ 1.0
● Selector effluent sCOD ≈ secondary effluent (or final effluent ) sCOD
● Selector effluent nitrate is 0.5 to 1.0 mg/L
● Selector DO < 0.3 mg/L
None
Insufficient IMLR ● Selector effluent sCOD > secondary effluent sCOD by at least 5 mg/L
● Selector effluent nitrate < 0.5 mg/L Increase IMLR rate
Excessive IMLR ● Selector effluent nitrate > 1 mg/L Decrease IMLR rate
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Excessive Aeration or IMLR ● Selector DO > 0.3 mg/L Reduce operating DO at end of
aeration basins or reduce recycle flow
Insufficient Selector Volume ● Selector effluent sCOD > secondary effluent sCOD by at least 5 mg/L
● Selector effluent nitrate > 1 mg/L
Convert first aerated cell to selector
mode
Excessive NH3 ● Secondary effluent ammonia > 3mg/L Check SRT and DO
Delayed Treatment. Another operational consideration within the aeration basins is where oxygen is
required for treatment and where it is most efficiently provided. In the first aerated cell of the aeration
basins oxygen demand is high, but the oxygen transfer efficiency is low. In later aerated cells the
“cleaner” wastewater has a higher oxygen transfer efficiency, thus treatment occurring in these zones
requires less energy. Operationally speaking, the DO in the first aerated cells should be maintained at
1.5 to 2.0 mg/L (first 2 or 3 aerated cells) and then allowed to depress to as low as 0.8 mg/L in
remaining cells. This will delay nitrification to the end of the tank where oxygen transfer efficiency is
higher. The exact operation (i.e. number of cells with depressed DO) will need to be trialed by Iowa City
while ensuring permit treatment levels are met.
Surface Film Classification. Two surface film classifiers have been constructed at the South WWTP as
part of the Phase 1 expansion: 1) RAS box surface film classifier and, 2) aeration basin effluent channel
surface film classifier. The classifiers are used to selectively pressure the removal of poor settling
filamentous microorganisms. The classifiers impart the pressure by skimming the top of the flow stream
which is where the filamentous microorganisms tend to collect given their tendency to float. The
skimmings are sent directly to the solids handling process, so the continuous removal of any filamentous
growth helps maintain a good settling sludge. The RAS box surface film classifier operates as the WAS
removal point as well, so it is continuously in operation. The aeration basin effluent channel surface film
classifier is only needed if foam is collecting in the aeration basin effluent channel or to assist the RAS
box surface film classifier during periods of extraordinary foam issues.
3.3.3 BAR Operational Background
Iowa City is required to remove ammonia and does so by nitrifying the ammonia in the secondary
treatment process. As the load at Iowa City increases in the coming years the subsequent SLR will also
increase. Eventually the load/SLR increase will approach the design limit on the secondary clarifiers
(SLR = 42 lb/sf-d at SVI = 150 mL/g). To reduce the SLR while still meeting nitrification requirements
the BAR tank can be used to decrease the required SRT to nitrify.
The BAR system is a high rate process that nitrifies the ammonia laden filtrate from the belt filter
presses (BFPs) used to dewater the anaerobically digested sludge. This BFP filtrate contains a
significant amount of the ammonia load on the secondary treatment system. The advantages of the BAR
at Iowa City are less overall aeration basin volume is required and the nitrifying organisms grown in the
BAR are used to seed the main aeration basins.
Use of the BAR tank is dictated by the SLR limits on the secondary clarifiers and the aerobic SRT.
Modeling indicates that nitrification can become unstable during cold weather periods when operating at
an aerobic SRT of less than 7 days, see Technical Memorandum 9 (TM9) – Secondary Treatment
Process Alternative Update prepared by Brown and Caldwell (July 27, 2011). With the BAR tank online,
the aerobic SRT can be reduced to 5 days while maintaining nitrification. This lowers the MLSS
concentration by 5/7ths, which will reduce clarifier SLR to within the allowable limits. For example,
assume that the calculated SLR is 42 lb/sf-d and the mainstream aerobic SRT has already been dropped
to 7 days to reduce the MLSS load. The BAR tank can be brought online to further reduce the aerobic
SRT to 5 days which proportionately decreases the MLSS resulting in a new SLR of 30 lb/sf-d (5/7ths of
42 lb/sf-d).
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The BAR tank enhances nitrification stability when operating at aerobic SRTs between 5 and 7 days
under cold weather conditions. BAR operations will not improve nitrification stability if the mainstream
aerobic SRT is sufficient to achieve full nitrification (i.e.7 days or more during cold weather). Although,
the plant can operate the BAR tank when fully nitrifying in the mainstream as the oxygen transfer in the
BAR reactor may be better than in the aeration basin, possibly reducing the aeration air requirements.
On the other hand, the amount of residual alkalinity in the BAR tank must be closely monitored to
maintain at least 75 mg/L as CaCO3 to avoid a corrosive water. If alkalinity is being depressed beyond
this level, alkalinity addition in the form of caustic or additional plant recycle flows (RDT or plant effluent)
is required.
The effluent from the BAR can be sent back to the head of the aeration basins or into cell 5. The
treatment design for the Phase 1 expansion only requires BAR effluent to be sent to the head of the
aeration basins to help drive the anoxic selector. The alternative discharge location to cell 5 was
included in the event the South WWTP needs to pursue lower phosphorus limits. By diverting the BAR
effluent to cell 5 allows the upstream cells (1-3) to be operated in an anaerobic mode which will
biologically sequester phosphorus in the solids (TSS). At the time of the Phase 1 expansion design, there
was inadequate phosphorus in the wastewater to reliably drive an anaerobic selector and biologically
remove phosphorus. The wastewater characteristics may change over time, and the alternative BAR
effluent discharge location provides the South WWTP with operationally flexibility.
The high strength equalization tank is used to equalize the filtrate from the belt filter presses so as not to
overwhelm the receiving treatment process. The tank is designed to equalize the maximum month
filtrate flow for the projected year 2025 flows and loads. The operation of the tank is to discharge a
constant flow of HSW to the BAR system, or aeration basins by way of a discharge into the influent
channel just downstream of the RAS selector. Based on experience, plant staff will control the discharge
flow rate from the tank so as to maintain a constant as possible rate to the receiving location.
3.3.4 Secondary Treatment Operating Strategy
The secondary treatment system must be operated as an integrated system for successful treatment.
The following operational flowsheet (Figure Y2) identifies the steps to take for various scenarios. Key
aspects of the flowsheet are:
• The flowsheet assumes the plant is operating at a target mainstream aerobic SRT of 7 - 10 days.
• If the MLSS concentration is outside the desired operating range of 2,000 – 4,000 mg/L the SRT or
number of aeration basins online can be adjusted.
• Once the MLSS is within the desired operating MLSS range the number of secondary clarifiers
required for the specific conditions can be determined. If there is more secondary clarification than
required an optimization step can be taken to determine whether or not the number of clarifiers or
aeration basins can be reduced. Alternatively, if additional secondary clarifiers are required, either
additional clarifiers or aeration basins should be placed into service if possible to reduce the SLR to
within acceptable limits.
• If additional secondary clarifiers or aeration basins are not available, than either reducing the SRT or
bringing on the BAR system online are possible solutions.
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Figure Y2. Iowa City South Wastewater Treatment Plant Secondary Treatment Operatio nal Flowsheet
To illustrate the use of the flowsheet and referenced equations assume the following:
• Plant Influent Flow = 30 mgd
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• RAS Flow = 15 mgd
• MLSS = 4,500 mg/L
• Aerobic SRT = 9 days
• SVI = 150 mL/g
• Aeration Basins Online = 4
• Secondary Clarifiers Online = 4 at 80-ft diameter and 1 at 115-ft diameter
• BAR is offline
Step 1 - the MLSS concentration is greater than the desired 2,000 – 4,000 mg/L operating range. In
this case either the aerobic SRT can be decreased or aeration basin volume can be increased. Since
there are no additional aeration basins available, reduce the aerobic SRT. Rearranging Equation 3-3 and
targeting a new aerobic SRT of 8 days yields the new MLSS concentration:
𝐿𝐿𝑂𝑂𝑙𝑎𝑤=8 𝑎𝑎𝑘𝑘
9 𝑎𝑎𝑘𝑘(4,500 𝑘𝑎
𝐿)=4,000 𝑘𝑎
𝐿
Step 2 – based on the new MLSS concentration the required secondary clarifier square footage can be
calculated using the maximum allowable SLR of 42 lb/sf-d at the stated SVI of 150 mL/g. Gaphs can be
derived for different flow rates utilizing a rearranged Equation 3-1 for the various SVI conditions. Figure
Y3 was produced for this example. Under the stated conditions 36,000 sf of secondary clarifier surface
area is required.
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Figure Y3. Example Graphic for Required Secondary Clarifier Area at Plant Influent of 30 mgd and RAS of 15 mgd
Step 3 – the surface area required (36,000 sf) is greater than that provided by the secondary clarifiers
online per the Table X4 (30,493 sf).
Table X4. Possible Secondary Clarifier Combinations and Related Square Footage
1 small 2 small 1 large 3 small 4 small
1 small
1 large
2 small
1 large
Surface Area (sf) 5,027 10,053 10,387 15,080 20,106 15,413 20,440
2 large
3 small
1 large
1 small
2 large
4 small
1 large
2 small
2 large
3 small
2 large
4 small
2 large
Surface Area (sf) 20,774 25,467 25,800 30,493 30,827 35,853 40,880
Step 4 – in this case the most logical solution would be to place a secondary clarifier in service, but
assuming the second 115-ft diameter clarifier is not available and since all the aeration basins are in
service either the aerobic SRT has to be reduce or the BAR system can be brought online. If the aerobic
SRT is reduced to 7 days (lowest allowable to maintain adequate nitrification without BAR) the MLSS
concentration is calculated in the same manner as Step 1:
𝐿𝐿𝑂𝑂𝑙𝑎𝑤=7 𝑎𝑎𝑘𝑘
8 𝑎𝑎𝑘𝑘(4,000 𝑘𝑎
𝐿)=3,500 𝑘𝑎
𝐿
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Step 5 – using the new MLSS and Figure Y3 the required secondary clarifier surface area is about
31,000 sf, still higher than the online secondary clarifiers provide. The final option is to place the BAR
system online. By doing so the new MLSS concentration is:
𝐿𝐿𝑂𝑂𝑘𝑎𝑘𝐴𝐴𝑅=𝐴𝑎𝑘𝑘𝑎�ℎ𝑎 𝑂𝑂𝑂𝐴𝐴𝑅
𝐴𝑎𝑘𝑘𝑎�ℎ𝑎 𝑂𝑂𝑂𝐿𝐿𝐷
𝐿𝐿𝑂𝑂𝑘𝑘�ℎ𝑎�ℎ𝑘𝑎𝑘=5 𝑎𝑎𝑘𝑘
7 𝑎𝑎𝑘𝑘(3,500 𝑘𝑎
𝐿)=2,500 𝑘𝑎
𝐿
Bringing the BAR system online has dropped to the required secondary clarifier surface area to about
22,500 sf per Figure Y3, which is within the surface area provided by the online clarifiers.
3.4 Solids Handling
At the South WWTP the solids handling processes treat various sources of solids and achieve a reusable
product used for land application. The various sources of solids processed include primary sludge and
scum, WAS, secondary scum, scum from the aeration basin effluent channel surface film classifier,
primary sludge/scum and WAS are thickened separately. The thickened sludges and are sent to the
digestion process with the secondary scum and surface film classified scum. After digestion the solids
are dewatered and then stored until land application (seasonal) is carried out.
Solids treatment at the Iowa City South WWTP is centered on the temperature phased anaerobic
digestion (TPAD) system. Primary sludge and waste activated sludge (WAS) are collected in the primary
clarifiers and from the return activated sludge box, respectively. Both sludges are thickened prior to the
TPAD system to minimize the flow rate needing treatment. Primary sludge is thickened in the primary
clarifiers while WAS is thickened in rotary drum thickeners (RDTs). After TPAD treatment the resulting
sludge is dewatered using belt filter presses and then stored in an open side storage shed. The stored
high quality (Class A) biosolids product is land applied in the spring and fall.
The following provides a high level operational strategy for the TPAD system and supporting processes.
3.4.1 TPAD Operational Strategy
TPAD consists of two types of digesters, thermophilic and meso philic, differentiated by the operating
temperatures. Generally speaking the thermophilic process is operated at ~130 °F while the mesophilic
is cooler at ~98 °F. The two temperature regimes facilitate growth of different organisms and combines
the high rate solids destruction in the thermophilic stage with additional destruction of solids and odor
compounds in the mesophilic stage.
The TPAD system is designed based on hydraulic retention time (HRT) to achieve solids and pathogen
reduction. The critical operational criteria for the TPAD system is maintaining a minimum 15 day total
HRT (in the case of the digestion process where solids and liquid carrying them are not considered
separate the HRT is equivalent to the solids retention time, or SRT). The HRT criteria is further broken
down into a minimum of 5 days in the thermophilic stage and 10 days in the mesophilic stage. As long
as these two HRTs meet their individual minimums the TPAD process is operating as designed. In the
event that the digested sludge does not meet the Class A requirements under the design HRTs, increase
the HRTs until an acceptable product is consistently produced.
The Iowa City South Plant has a total of six digesters and two of those have the capability to operate at
thermophilic temperatures. Table 3-X1 identifies the digesters and their volumes.
Table 3-X1. Digester Tank Data
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Digester Temperature Phase
Diameter
(ft)
Sidewater
Depth (ft) Volume (gal)
T8101 thermophilic 55 27 520,000
T8201 thermophilic/mesophilic 55 27 520,000
T8301 mesophilic 45 27 340,000
T8401 mesophilic 45 27 340,000
T8601 mesophilic 45 27 340,000
T8701 mesophilic 45 27 340,000
Total 2,400,000
To calculate the HRT simply divide the working volume (i.e. any known permanently settled debris in the
digester reduces the volume available for treatment) of online digesters by the influent sludge flow rate
as illustrated below:
𝐷𝑂𝑂=(𝑘𝑘𝑘𝑘𝑘𝑎 𝑘𝑘𝑘�ℎ𝑘𝑎 𝑎�ℎ𝑎𝑎𝑘𝑘𝑎𝑘𝑘 (𝑎𝑎𝑘)
𝑘𝑘𝑘𝑎𝑎𝑎 𝑎𝑘𝑘𝑘 𝑘𝑎𝑘𝑎 (𝑎𝑘𝑎))(𝑘𝑘𝑘𝑘�ℎ𝑘𝑎 𝑘𝑘𝑘𝑘𝑘𝑎 %)
For example, assuming the sludge flow rate is 72,000 gpd and T8101 is the only thermophilic digester
and T8301 and T8401 are the only available mesophilic digesters and 10% of the digester volume is
cluttered with settled debris the thermophilic and mesophilic HRTs are as follows:
𝑂�𝑎𝑘𝑘𝑘𝑘𝑖ℎ𝑘�ℎ𝑎 𝐷𝑂𝑂=(520,000 𝑎𝑎𝑘)
(72,000 𝑎𝑘𝑎)(0.9 𝑎𝑘𝑎�ℎ𝑘𝑎𝑎𝑘𝑎)=6.5 𝑎𝑎𝑘𝑘
𝐿𝑎𝑘𝑘𝑘𝑖ℎ𝑘�ℎ𝑎 𝐷𝑂𝑂=(340,000 𝑎𝑎𝑘+340,000 𝑎𝑎𝑘)
(72,000 𝑎𝑘𝑎)(0.9 𝑎𝑘𝑎�ℎ𝑘𝑎𝑎𝑘𝑎)=8.5 𝑎𝑎𝑘𝑘
Even though the total HRT is 15 days (6.5 days + 8.5 days) in this example the mesophilic HRT is too low
(< 10 days) and either another mesophilic digester needs to be brought online or the sludge flow rate
reduced, discussed later.
Figure 3-Y1 below illustrates the number of digesters required at various thickened sludge flows into the
process. The two options illustrated below for mesophilic digestion are differentiated only by whether
T8201 is available for mesophilic operation. Figure 1 does not account for any debris. If a percentage
of the digester is fouled by debris simply increase the sludge flow in Figure 1 by the amount of digester
volume lost (e.g. if 10% of the digester is filled with settled debris than multiply the measured sludge
flow rate by 1.1).
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Figure 3-Y1. Minimum Number of Digesters Required per Sludge Flow (peak 15-day rolling average)
With the number of digesters available Iowa City may choose to save energy by idling those not needed,
though the risk is not having enough volume online during a peak event. Increasing Iowa City’s flexibility
is that fact that T8201 can be operated as either thermophilic or mesophilic so when T8101 provides
adequate thermophilic HRT, T8201 may be used in mesophilic mode. The benefit would be offsetting
two smaller mesophilic digesters in some instances, whereby one large digester is more efficient than
two small ones.
An operational strategy pioneered by Iowa City is supernating digested solids. Assuming there is
adequate HRT, the final two digesters (T8601 and T8701) can be operated in a supernating mode. In
this mode of operation digested sludge is stored in these digesters and cooled with a recently installed
heat exchanger. Cooler sludge separates better, yielding a distinct solids free layer and a thickened
sludge layer at the bottom. The upper solids free layer can be drawn off using recently u pgraded
motorized valves at four side water levels. This supernatant has high ammonia content and is therefore
drained to the high strength pumping station. Any liquid removed from the digested sludge prior to
dewatering results in less energy and polymer at the belt filter presses. Plant staff will be trialing specific
operating procedures, however previous trials indicated that once the sludge is cooled to 86 °F the
liquid has separated allowing decanting to proceed. The separating temperature can be investigated at
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bench scale by taking a beaker of digested sludge and monitoring the temperature and when separation
occurs.
3.4.2 Sludge Thickening
The sludge thickening processes are used to minimize the flow to the TPAD system and thereby
maximize the HRT and minimize the sludge heating demand. In the event that the TPAD HRT is less than
design begin investigating the quality of the thickened sludges.
Primary sludge is thickened in the primary clarifiers by maintaining a relatively deep sludge blanket.
Iowa City staff indicated that concentrations of 4% TS are achievable on average. In the event that the
TPAD HRT is too low and the primary sludge is less than 4% TS consider reducing the primary sludge
pumping rate to allow additional thickening in the clarifier. Continuously monitor the sludge blanket
depths to reduce the risk of losing solids to the secondary treatment system.
WAS is pumped to and thickened by the RDTs (3 total). Each unit is rated for 350 gpm. It is more energy
efficient to run one RDT at a higher capacity than two at lower capacity.
The RDTs have historically produced 5% TS on average and this concentration was used as a design
basis. In the event that the WAS is less than 5% TS investigate the RDT operation. In particular, review
the polymer dose and washwater flow. Coincidentally, operating the RDTs to produce thicker sludge
reduces the heating demand in the digesters as well.
After thickening, each sludge stream is pumped to the sludge equalization tank (T8001) where the
streams are mixed prior to thermophilic digestion. The following calculation illustrates the impact on
HRT that dilute sludges can have. For this example assume 4.5 %TS mixed sludge at 50 gpm (24 gpm of
4% TS primary sludge and 26 gpm of 5% TS WAS) compared to the resulting flow rate at 3.5% TS.
𝑂�𝑎𝑘𝑘𝑘𝑘𝑖ℎ𝑘�ℎ𝑎 𝐷𝑂𝑂 @ 4.5% 𝑂𝑂=(520,000 𝑎𝑎𝑘)
(50𝑎𝑘𝑘)(1 𝑎𝑎𝑘
1,440 𝑘�ℎ𝑘)(0.9 𝑎𝑘𝑎�ℎ𝑘𝑎𝑎𝑘𝑎)=6.5 𝑎𝑎𝑘𝑘
𝑂𝑘𝑘𝑎𝑎𝑎 𝐷𝑘𝑘𝑘 @ 3.5% 𝑂𝑂=(50 𝑎𝑘𝑘)(4.5% 𝑂𝑂)
(3.5% 𝑂𝑂)=64 𝑎𝑘𝑘
𝑂�𝑎𝑘𝑘𝑘𝑘𝑖ℎ𝑘�ℎ𝑎 𝐷𝑂𝑂 @ 3.5% 𝑂𝑂=(520,000 𝑎𝑎𝑘)
(64𝑎𝑘𝑘)(1 𝑎𝑎𝑘
1,440 𝑘�ℎ𝑘)(0.9 𝑎𝑘𝑎�ℎ𝑘𝑎𝑎𝑘𝑎)=5.1 𝑎𝑎𝑘𝑘
This example illustrates the importance of achieving the design thickened sludge concentrations,
especially when additional HRT is required.
3.4.3 Dewatering and Storage
After digestion the sludge is stored in the sludge storage tank (T8801) until it is dewatered on the belt
filter presses (BFPs). After dewatering, the sludge, now termed cake, is stored in the open sided storage
shed until it is land applied. The BFPs are currently operated during the work week and about 8 hours
per day. To meet the increased sludge production the operations may have to be extended on an hours
per day or days per week basis. Presently, plant staff are favoring extending the dewatering operation to
7 days a week which facilitates filtrate (high strength waste) equalization management.
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Section 4 Preliminary Treatment
Preliminary Treatment, also referred to as the headworks, encompasses the influent screening, influent
pumping, flow measurement, grit removal facilities and influent flow equalization. The primary purposes
are to remove debris and grit from the waste stream, provide lift (influent pumping) to allow flow by
gravity through the remainder of the treatment facility, and control the flow into the facility. Figure 4-1
depicts the preliminary treatment processes and flow scheme.
Figure 4-1. Preliminary Treatment Flow Diagram.
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4.1 Influent Channel/Bar Screens
Unit Processes and pre-existing equipment not affected by the Phase 1 expansion are generally not
covered in this manual. The Influent Channel/Bar Screen unit process was not affected by the Phase 1
expansion.
4.2 Influent Pumping
General influent pumping system operation and control, and new influent pumping equipment are
covered in this section.
The influent pump station pumps provide lift to allow influent to flow by gravity through the remainder of
the treatment facility.
4.2.1 System Description
Influent pumping pumps consist of three KSB non-clog centrifugal pumps installed during the Phase 1
expansion in addition to three older Fairbanks Morse non-clog centrifugal pumps. All six pumps are of
the close-coupled motor type where the motor is directly fitted to the pump via a flange or a drive
lantern.
The three existing Fairbanks Morse pumps are equipped with TEFC motors that are not rated for
submerged conditions and will not operate if the dry well is ever flooded. The three KSB pumps are
equipped with dry pit submersible motors to allow continued operation if the dry well of the pump station
were flooded. The influent pumping capacity will be limited to the capacity of the three KSB pumps if the
dry well becomes flooded.
Hinged access grating in the floor over each pump allow removal with the existing overhead monorail
hoist.
Two sump pumps (P1331A and P1332A) are installed in the dry well of the influent pump station to
remove nuisance water collecting on the floor.
4.2.2 Design Data
Table 4-1. Phase 1 (2025) Influent Pump Design Data
Number of Pumps In Service Flow @ 46 ft TDH
1 8,330 gpm (12 mgd)
2 16,660 gpm (24 mgd)
3 24,990 gpm (36 mgd)
4 33,320 gpm (48 mgd)
5 41,650 gpm (60 mgd)
6 49,980 gpm (72 mgd)
4.2.3 Operation and Control
The influent pumps operate on VFDs to maintain an operator selected level in the pump station wet well.
A single pump will operate at increasing speed until the wet well level stabilizes or the pump maximum
speed is reached. When the pump maximum speed is reached and the wet well level is still rising, a
second pump will be called to operate. Additional pumps will be brought into service as needed to
maintain the wet well level set point. The lead and lag pump order is automatically alternated between
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each of the installed pumps and run time is monitored on the Plant SCADA system. Section 3 provides a
more detailed control strategy.
Influent Pumps P1301A, P1302A and P1303A are the older Fairbanks Morse pumps.
Pumps P1304A, P1305A, and P1306A were installed in Phase 1 but modifications to existing
operational requirements were not required. Plant Staff may have altered the operational requirements
based on experience.
Sump pumps P1331A and P1332A are float controlled.
4.2.4 Equipment Data
Figure 4-2 depicts the major components of the KSB pumps. Table 4-2 summarizes the equipment data
for all six influent pumps plus the two sump pumps.
Figure 4-2. SKB Influent Pumps P1304A, P1305A and P1306A (K SB Manufacturer’s Manual).
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Table 4-2. Influent Pumping Equipment Data
Parameter Value
Fairbanks Morse Influent Pumps
Asset Tag
P1301A
P1302A
P1303A
Manufacturer Fairbanks
Type vertical dry pit
Model 16-E5741C
Quantity 3
Size 16 inch x 16 inch x 20 inch NSY
Unit Capacity 8,330 gpm (12 mgd) @ 46 ft
Motor 125 hp, TEFC, inverter duty
KSB Influent Pumps
Asset Tag
P1304A
P1305A
P1306A
Supplier Quality Flow Systems
Manufacturer KSB
Type dry-pit submersible
Model KRT K350-500/908UNG-D
Max. Operating Condition 8,330 gpm (12 mgd) @ 46 ft TDH
Min. Operating Condition 4,000 gpm (5.7 mgd) @ 40 ft TDH
Motor 121 hp
Motor Speed 900 rpm
Influent Sump Pumps
Asset Tag P1331A
P1332A
Quantity 2
Manufacturer Sta-Rite
Model EC650120T
Motor ½ hp 115 V, submersible PSC with thermal overload
4.2.5 Maintenance
Table 4-3 summarizes the manufacturer’s maintenance information for the influent pumps (P1304A,
P1305A and P1306A) and the influent pump station sump pumps (P1331A and P1332A) installed in
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Phase 1. Refer to the KSB Operations and Maintenance Manual for a more comprehensive listing of
troubleshooting and maintenance requirements.
Table 4-3. Influent Pumping Maintenance Data
Parameter Value
Influent Pumps P1304A, P1305A and P1306A
Measure the insulation resistance Every 4,000 operating hours or
at least once per year Check the power cables
Check sensors
Every 8,000 operating hours or
at least once every two years
Check for mechanical seal leakage
Change the lubricant and check the coolant
Lubricate the bearings
Perform a general overhaul (including
coolant change) Every 5 years
Sump Pumps P1331A and P1332A
Pump is permanently lubricated. No oiling or greasing is required in normal
service.
Do not allow pump to run in a dry sump. It will void the warranty and may
damage the pump.
4.3 Influent Flow Metering
An area/velocity flow meter, positioned in the influent pump discharge channel before the grit removal
tanks is used to alarm and monitor incoming flow to the treatment process.
4.3.1 System Description
Plant influent flow is measured by a flow meter downstream of the influent pump discharge channel and
before the grit removal tanks. The meter sits on the bottom of the channel and reads velocity of the flow
stream and depth. The meter is programmed with the geometry of the South WWTP channel to calculate
a flow rate.
4.3.2 Design Criteria
Table 4-4. Influent Flow Meter Design Data
Parameters Flow
Calibration Range 0-30 mgd
4.3.3 Operation and Control
Influent Flow Meter FE1501A is used to alarm and monitor incoming flow to the treatment process.
High flow conditions will be alarmed to alert Plant Operators of the need to divert flow to the
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equalization basin. The analog flow value is used by other processes throughout the Plant as a
pacing signal to control flow or chemical additions.
Flow is monitored by the Plant SCADA system and recorded.
4.3.4 Equipment Data
Table 4-5 below summarize the equipment data for the Influent Flow Meter. Also, four other flow meters
installed in Phase 1 are listed since the meters are identical. The specific sections discussing these
meters refer back to this table for specific equipment data.
Table 4-5. Flow Measurement Equipment Data
Parameter Value
Plant Flow Meters
Asset Tag
FE1501A (Plant Influent)
FE1502A (EQ Basin Flow)
FE1503A (EQ Basin Return Flow)
FE4230A (BAR HSW/RAS Flow)
FE6500A (UV Disinfection Influent Flow)
Manufacturer ADS Environmental Services
Sensor 5000-Pulse-SENS-W4
Transmitter FlowShark Pulse, 5000-PULSE-METER-10A1
Sensor Measurement
Principles:
1. Depth: Ultrasonic time transmit.
2. Redundant depth: Piezoresistive pressure.
3. Flow velocity: Correlation with digital pattern detection.
Frequency: 1 MHz.
Type: Combi-sensor with flow velocity sensor using cross-
correlation, depth measurement via water-ultrasonic (and
redundant pressure measurement), and temperature
measurement to compensate for effect of temperature on
velocity of sound.
Measurement Range
1. Ultrasonic depth: 0 to 6.56’ (0 to 1.99 m), lowest
absolutely measureable depth 0.13’ (0.03 m).
2. Pressure depth: 0 to 11.5’ (0 to 3.5 m).
3. Flow velocity: -3.28 to 19.7 fps (-0.99 to 6.00 mps).
4. Temperature: -4ºF to 140ºF.
Calibration Range
1. Influent pump discharge channel plant flow: 0 - 30 mgd.
2. Equalization basin bypass flow: 0 - 30 mgd.
3. Equalization basin return flow: 0 - 30 mgd.
4. BAR influent flow: 0 – 1,200 gpm.
5. UV disinfection system influent flow: 0 - 30 mgd
4.3.5 Maintenance
The manufacturer suggests cleaning the transmitter enclosure and removing silt/debris from the
sensors as needed. On a semi-annual basis the manufacturer recommends calibrating the pressure
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sensors. See http://www.adsenv.com/ADSCorp/menus/pdfs/product%20manuals/FlowSharkPulseManualA1.pdf for
more details.
4.4 Grit Removal
Grit entrained with the influent flow can cause premature wear of pumping and other mechanical
equipment and can collect in pipes and tanks, reducing hydraulic capacity if not removed. Grit typically
consists of inorganic sand, fine gravel, and matter which will not be degraded through the South WWTP
biological processes. Grit is removed from the influent, washed, dewatered, and taken to the City landfill
for disposal.
Vortex grit removal relies on a hydraulically and mechanically induced vortex to capture solids in the
center hopper of a circular tank, or chamber. Flow is introduced to the Chamber and a slow speed
paddle mixer adds mixing energy to maintain the vortex. Grit settles to the intermediate slab and is
forced to a center hopper where it collects for removal. Lighter organic material is suspended in the
liquid stream by the paddle mixers and passes through to the primary clarifiers. Figure 4-3 depicts the
type of system installed in Phase 1.
Figure 4-3. Smith and Loveless – Pista Grit Chamber (smithandloveless.com).
4.4.1 System Description
The grit removal system consists of two vortex grit chambers and associated grit pumps that pump the
grit slurry to the grit dewatering building. Each vortex grit chamber is equipped with one duty grit pump
installed; there is one uninstalled spare pump provided for redundancy. The grit slurry is pumped from
the hopper to the grit concentrators, washers and grit classifiers, to achieve a relatively clean product for
disposal.
Effluent from the vortex grit chambers is conveyed to the downstream primary clarifiers via two 36 inch
pipes. A cross connection in the grit system effluent well is provided to allow the flow to equally
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distribute between the pipes. The cross connection will become more important when the third grit tank
is installed in Phase 2 to meet future flows.
4.4.2 Design Data
The grit pumping equipment is located in a below grade vault. In this configuration the pump suction is
below the bottom of the grit hopper, enhancing grit removal. This arrangement also allows access to the
pumps through surface level hatches for routine pump maintenance without removing the pump from
service. Table 4-6 summarizes the design data used for the grit removal system.
Table 4-6. Grit Removal Design Data
Parameter Value
Grit Chamber
Total Design Flow 30 mgd
Treatment Capacity 15 mgd, per unit
Hydraulic Capacity 30 mgd per unit
Removal Efficiency
• 95% of material larger than 50 mesh
• 85% of material smaller than 50 mesh but larger than 70 mesh
• 65% of material smaller than 70 mesh but larger than 100
Grit Pumps
Unit Capacity 350 gpm @ 43 ft TDH
4.4.3 Operation and Control
Hydraulic Flow - The system is designed to provide effective grit removal at flow rates up to 30 mgd with
both units in service, although hydraulically, each unit can accommodate 30 mgd. When the velocities
become low, grit can settle in the influent flume. Velocity in the influent flume must exceed 2 feet per
second during part of the day to prevent grit accumulation. On the other hand, high flows can cause a
reduction in grit removal efficiency. During high flow events grit should be pumped out of the grit hopper
more frequently. Large volumes of grit in the hopper can cause compaction and bridging which can
hamper removal. For this reason, an effluent water nozzle is provided in the grit hopper bottom to help
fluidize grit prior to and during pumping.
Motorized grit chamber isolation gates (GT2501A and GT2601A) located in the influent channel ahead
of the grit chambers are normally open and used to control flow to the grit chambers. Although gate
actuators are provided with 4-20 mA positioning and feedback signals, their operational functions are for
full open and full close positioning. These gates are controlled manually from any SCADA terminal.
Manually operated grit chamber isolation gates (GT2502A and GT2602A) control grit chamber effluent
(GTE) flow out of the grit chambers and direct flow to the grit effluent well which combines flow prior to
the primary splitter box.
Grit chamber isolation gate GT2503A is manually operated and can be used to equalize the GTE flow
between the two 36 inch pipes leading to the primary splitter box. In low flow conditions all GTE flow can
be isolated to one grit chamber/pipe to maximize velocity and minimize grit settling in the pipe.
Grit Collectors and Pumps - Vortex grit removal equipment COL2501A and COL2601A replace existing
grit removal systems, but functionally operate the same. Likewise new grit pumps P2501A and P2601A
replace existing grit pumps, but functionally they operate the same. No programming modifications were
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required to these systems unless changes have been instituted by Plant Staff. The existing PLC
configured logic was replicated with following the exceptions. The original grit pumps were submersible
pumps and the new pumps installed in Phase 1 are not. Therefore, all control and monitoring
associated with the moisture and high motor temperature alarms in the original grit pumps has been
deleted.
Axial Flow Propeller – The manufacturer recommends the bottom of the blade to be set 3 inches from
the floor and the pitch at 45 degrees for the most efficient capture of grit and exclusion of the organics.
If more organics need to be excluded, the blades can be lowered. This may reduce the recovery of fine
grit. If more grit and organics need to be recovered, the propeller can be raised.
Grit Slurry Removal – The Vortex Grit Chamber Storage Hopper (the bottom of the grit chamber) is sized
to hold 24 hours of normal grit accumulation. This volume should be used for maintenance purposes
only. Grit needs to be removed every 8 hours as a normal maximum and more frequently if practical or
grit will compact in the grit storage hopper, causing it to bridge and hamper removal by the grit pumps. It
should typically take 10-15 minutes to discharge 8 hours of grit accumulation. (Smith & Loveless, Inc.)
Grit slurry is pumped to the grit cyclone and classifier by grit pumps P2501A and P2601A.
The classifier operates during the pumping cycle and continues to operate for an operator selected
period of time after grit pumping stops. The washed grit empties into a dumpster (or the slab within the
Grit Dewatering Building) and is removed as needed.
Effluent Water Flushing - Solenoid flow valves FV2501A and FV2601A are used periodically for the
flushing of grit from the bottom of the vortex grit chamber storage hopper and the associated pump
suction pipe. The flushing water solenoid valves are provided with a local Open-Close-Remote selector
switch for manual or automatic operation; manual ball valves downstream of the flow control solenoid
valve can isolate flow from the storage hopper and the pump suction pipe. When in Remote position,
automatic or manual control is selectable from any SCADA terminal through a software configured Open-
Close-Auto function. In Auto position the PLC controls the repeat cycle type operation of the flushing
solenoid valve. Off and On times can be set from any SCADA terminal for automatic operation. It is
recommended that the manual valve to the pump suction remain open to allow the pump suction pipe to
be backflushed into the grit hopper prior to pump operation. In this operation, the solenoid valve would
open for an operator defined period prior to pump operation (typically 15 -20 seconds) and continue for
approximately 1 minute while the pump operates. Likewise, it is recommended to fluidize the grit hopper
contents prior to pumping (10 – 15 seconds) and for a short duration after pumping is initiated (1-2
minutes).
4.4.4 Equipment Data
Table 4-7 summarizes the equipment data for the grit removal system.
Table 4-7. Grit Equipment Data
Parameter Value
Grit Chambers
Asset Tag COL2501A
COL2601A
Manufacturer Smith & Loveless/Pista
Quantity 2
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Style 360-B
Size 18 ft Diameter
Type vortex grit
Rotation (1) Clockwise, (1) Counter-Clockwise
Drive Motor
Frame Type TEFC
rpm 1,800
hp 2
Duty standard
Grit Pumps
Asset Tag P2501A
P2601A
Manufacturer Morris
Model 3x3-16 HC2
Type Series 6100, Type CT Recessed Impeller
Quantity 3 (including 1 uninstalled spare)
Rotation Left Hand
Design Point 350 gpm @ 43 ft TDH
Discharge vertical up discharge
Grit Pump Motors
Manufacturer Nidec
Enclosure TEFC
Frame 286T
hp 15
rpm 960
Solenoid Flow Valves
Asset Tag FV2501A
FV2601A
Manufacturer Asco
Model EF 8210G100, 120 VAC
Type Solenoid Valve
Motorized Grit Chamber Isolation Gates
Asset Tag
GT2501A
GT2502A
GT2601A
GT2602A
Manufacturer Whipps, Inc.
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Series 921 Slide Gate
Size 54” x 36”
Actuator AUMA SA," 1-16A, Electric
4.4.5 Maintenance
Maintenance information was provided by the manufacturers of the grit collector mechanism, grit
pumps, solenoid flushing valves, and flow control gates. Table 4-8 summarizes the information
provided. Refer to the manufacturer’s Operations and Maintenance Manual for a more comprehensive
listing of troubleshooting and maintenance requirements.
Table 4-8. Grit Removal Equipment Maintenance
Equipment Maintenance Frequency Lubricants Required
Paddle Drive
Motor Sealed Unit None
Gear Reducer ~10,000 operating hours, or after 3 years at
the latest
ISO 220 EP Type Oil
Turntable Bearing Check Oil Level: Monthly ISO No. 68, EP No. 2
Replace Oil: 6 Months (Spring & Fall) ISO No. 68, EP No. 2
Grit Pump
Grit Pump Inspect oil daily, change if dirty or excessively
cloudy, or after 6 months
SAE #30W Non
Detergent Motor Oil or
turbine oil such as
AGMA #4
Pump Seal Yearly Check for possible
replacement
Solenoid Valves
Keep the medium flowing through the solenoid operator or valve as free from dirt and foreign
material as possible.
Periodic exercise of the valve should be considered if ambient or fluid conditions are such
that corrosion, elastomer degradation, fluid contamination build up, or other conditions that
could impede solenoid valve shifting are possible. The actual frequency of exercise necessary
will depend on specific operating conditions. A successful operating history is the best
indication of a proper interval between exercise cycles.
Depending on the medium and service conditions, periodic inspection of internal valve parts
for damage or excessive wear is recommended. Thoroughly clean all parts. If parts are worn
or damaged, install a complete rebuild kit.
Gates
Equipment Activity Frequency Lubricants Required
Gate Visual Inspection At least every 6
months for signs of N/A
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misalignment, damage
or corrosion
Threaded portion of
operating Stems Clean and Grease
Every 6 months, or
whenever exposed to
severe dust.
Chevron Ultra Duty
EP-2 Sunoco – Ultra
Prestige 2EP Or Equal
Operating Stems in
High Temp areas Clean and Grease
Every 6 months, or
whenever exposed to
severe dust.
SI-123 or Equal
Manual Operators
(Type 101, 102, 104)
Lubricate all grease
fittings Annually
Chevron Ultra Duty
EP-2 Sunoco – Ultra
Prestige 2EP Or Equal
Modulating electric
operators
Remove and inspect
operating nut for
wear. Replace when
wear is evident.
After first 6 months of
operation, and then
annually
N/A
AUMA SA14 1-26
Electric Actuator
Check elastomer
seals Regularly N/A
Perform test run (if
used infrequently) Every 6 months N/A
Check bolts between
multi-turn actuator
and valve/gearbox
for tightness
Annually N/A
Change
grease/exchange
seals
4 – 6 years N/A
4.5 Grit Dewatering
Unit Processes and pre-existing equipment not affected by the Phase 1 expansion are generally not
covered in this manual. The grit dewatering process was not affected by the Phase 1 expansion, and is
not covered here.
4.6 Grit Washing
Unit Processes and pre-existing equipment not affected by the Phase 1 expansion are generally not
covered in this manual. The grit washing process was not affected by the Phase 1 expansion, and is not
covered here.
4.7 Influent Flow Equalization Basin
The rate of influent flow to the South WWTP is continually fluctuating. Flow rate fluctuations can have a
negative effect on treatment system performance and at high flows overwhelm the treatment capacity.
To minimize those effects, the influent flow equalization basin is used to equalize influent wastewater
flows before going through the treatment process, especially during high flow periods.
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4.7.1 System Description
The influent flow equalization basin is a bentonite lined asphalt paved earthen basin designed to provide
approximately 17.6 million gallons of equalization storage capacity. The basin is a single cell covering
approximately 11 acres. Excess flow is bypassed to the basin after influent screening and pumping.
During off-peak periods basin effluent flows back to the interceptor junction structure ahead of the
influent pump station by gravity. An emergency overflow to the South WWTP outfall pipe is provided for
use if the water level in the basin ever to exceeds the design elevation.
4.7.2 Design Data
The influent flow equalization basin design volume was determined through analysis of historic flow
records and computer dynamic hydraulic modeling of the collection system for the projected 2025 and
2040 peak flow conditions including the Peak Hour Wet Weather (PHWW) flow equivalent to the 10-year,
1-hour storm event. The basin size was selected to limit influent flows to the grit removal system to 30
mgd for the Phase 1 (2025) expansion and 45 mgd for Phase 2 (2040). Flows in excess of these rates
will be stored in the EQ basin. At design capacity, the average water depth will be approximately 9 feet.
The return flow system that conveys flow from the basin to the interceptor junction structure consists of
a 24 inch and a 12 inch pipe, both of which convey flow from the basin to the return flow manhole.
There is a gate on each of these pipes, located in the return flow manhole, for flow control. Flow is
returned from this manhole to a flow measurement structure, and then to the interceptor junction
structure, through 24 inch EBE piping.
The equalization basin emergency overflow consists of a vertical intake pipe with adequate capacity to
convey the year 2040 bypass flow (36 mgd) with approximately 2.6 feet of freeboard.
Table 4-9 summarizes the resulting design of the influent flow equalization basin.
Table 4-9. Influent Flow Equalization Basin Design
Parameter Value
Inside Basin Width 470 ft at bottom of berm
Inside Basin Length 540 ft at bottom of berm
Basin Depth 12.3 ft
Design Capacity Water Depth 9 ft
Top Berm Width 10 ft
Inner Side Slopes 3H:1V
Outer Side Slopes 4H:1V for West, South, and East Berms
3H:1V for North Berm
Basin Top Width 554 ft at the top center of the berms
Basin Top Length 624 ft at the top center of the berms
Basin Volume 17.6 million gallons
4.7.3 Operation and Control
Bypass flow control gate GT1502A is normally closed, and can be opened to divert plant influent flow
from the plant influent pump discharge channel to the influent flow equalization basin during high
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influent flow conditions or as required. The gate is manually positioned by Plant Operators from any
SCADA terminal. A high flow alarm extracted from the influent flow meter (FE1501A) alerts the Plant
Operators of a high flow condition and the need to position the bypass flow control gate.
Return flow control gate GT1701A is used to return raw sewage from the basin back to the head of
South WWTP. The gate is manually positioned by Plant Operators from any SCADA terminal. The return
flow rate is monitored from a signal received from the equalization basin return flow meter FE1503A. A
high flow alarm extracted from FE1501A alerts Plant Operators of a high flow condition and need to
reposition return flow control gate.
Equalization basin drain gate GT1702A is used to drain raw sewage from the basin at a lower elevation
than that of return flow control gate GT1701A back to head of South WWTP. The gate is manually
positioned by Plant Operators from any SCADA terminal.
4.7.4 Equipment Data
The influent flow equalization basin equipment is summarized in Table 4-10.
Table 4-10. Flow Equalization Basin Flow Measurement Equipment Data
Parameter Value
Equalization Basin Flow Meters
Asset Tag FE1502A
FE1503A
See Table 4-5, Influent Flow Metering for details
Equalization Basin Return Flow Control Gates
Asset Tag GT1701A
Manufacturer Whipps, Inc.
Series 925
Size 24” x 24”
Operator AUMA SA14 1-26 Electric Actuator
Equalization Basin Drain Flow Control Gate
Asset Tag GT1702A
Manufacturer Whipps, Inc.
Series 925
Size 12” x 12”
Operator AUMA SA14 1-26 Electric Actuator
Equalization Basin Flow Control Gate
Asset Tag GT1502A
Manufacturer Whipps, Inc.
Series 924
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Size 64” x 53”
Operator AUMA SA14 1-26A Electric
4.7.5 Maintenance
Table 4-11 identifies the maintenance required for the equalization basin and that recommended for
supporting equipment.
Table 4-11. Flow Equalization Basin Flow Measurement Maintenance
Parameter Value
Equalization Basin
After each use the equalization basin should be inspected for settled debris and
subsequently removed if present.
Equalization Basin Flow Meters
None recommended by manufacturer
Gates
Gate and actuator maintenance data identical to that listed for Grit Removal,
Table 4-8
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Section 5 Primary Treatment
Primary treatment at the South WWTP consists of clarification that separates the settleable sludge and
floating scum from the flow stream prior to secondary treatment. Figure 5-1 depicts the flow scheme at
the South WWTP.
Figure 5-1. Primary Treatment Flow Scheme.
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5.1 Primary Clarification
Primary clarification is the physical process that separates settleable and floatable solids from
wastewater. In the primary clarifiers the velocity of the water is reduced to allow sedimentation to take
place. Heavier solids "settle” to the bottom of the tank where they are collected by a rotating
mechanism. Lighter solids stay in suspension and are treated later, and still-lighter floating materials
are skimmed off the surface. Performing its primary function of removing settleable solids minimizes the
secondary treatment system loading.
After primary clarification, effluent from the five clarifiers is directed to the aeration influent channel.
Sludge and scum are sent to the digesters for further processing.
5.1.1 System Description
The primary clarification system includes a flow splitting box, the clarifiers themselves, and the related
sludge/scum pumping systems. The flow splitter passively and evenly distributes flow to the five
clarifiers. The flow splitter was designed to accommodate a future sixth primary clarifier. As solids float
or settle in the clarifiers a rotating collection arm collects and directs the sludge/scum to pumps that
pump to the digestion system while the main liquid flow continues by gravity from the clarifiers to the
aeration basins.
5.1.2 Design Data
Table 5-1. Primary Clarifier Design Data
Parameter Value
Size 70 ft diameter, 12 ft sidewater depth
Inlet flow rate per clarifier, maximum 6.0 mgd
5.1.3 Operation and Control
Influent Splitter Box - The splitter box is a concrete vault housing primary flow splitter gates GT3101A,
GT3102A, GT3103A, GT3104A and GT3105A. The gates are manually operated and direct grit tank
effluent flow to Primary Clarifiers 3100, 3200, 3300, 3400 and 3500. Flow is evenly distributed due to
the relatively high headloss through the isolation gate opening. The only control function is to open or
close a gate to take a clarifier out of service.
Primary Clarifier Collectors - Solids collection is constantly occurring when the clarifiers are operating. A
scraper-style collection mechanism rotates along the floor of each clarifier, driven by a centrally located
drive unit. The scrapers move the settled solids on the floor of the clarifier to a sludge withdrawal well at
the center of the clarifier. The drive mechanism is equipped with overload protection and alarming at
several different levels of torque with the last torque overload setting configured to shut the unit off to
prevent damage to the equipment. The drive mechanism is also equipped with a backup mechanical
overload protection device. Each clarifier will report alarms to SCADA and will enable remote shutoff.
Clarifiers can be put into service remotely, however local start up is recommended in order to verify
actual field conditions prior to putting the system into operation.
When Primary Clarifier Collectors COL3101A and COL3201A , COL3301A, COL3401A and COL3501A are
in the AUTO mode locally, they are operated by the Plant Operator from the South Sludge Pumping
Station (SSPUS) PC-base HMI or the corresponding SCADA screen by selection of software configured
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START and STOP push buttons. High-high torque shutdown logic is hardwired into the motor control
center circuitry. PLC inputs for torque alarms are for alarming only.
The following operations for the collector are taken from the manufacturer’s O&M manual (Walker
Process Equipment. IOM-6090-20-1). Important Note: Groundwater levels around the clarifiers must be
measured prior to draining a clarifier and must always be lower than the water surface elevation in the
clarifiers to prevent uplift forces from damaging the floor of the clarifiers.
Collector Shutdown
If the collector must be shut down or is used in intermittent or peak flow service, the following
procedure should be followed with any necessary modifications to suit the specific conditions at
the time of shutdown.
1. The influent to the clarifier should be shut off. If available and desired, plant effluent
may be recycled through the basin to maintain flow and circulation in the tank. This is
desirable if the tank is not drained during winter shutdowns as it will reduce surface icing
in most cases. If the influent is shut off during periods of cold temperatures and the
clarifier is not drained, provision must be made to preclude damage to the clarifier and
mechanism due to icing of the tank contents. Icing can cause serious problems due to
both expansion and the formation of ice sheets which could interfere with mechanism
rotation.
2. The collector mechanism should be operated after the influent has been shut off until
the clarifier bottom has been cleared of sludge. Once the sludge has been removed from
the clarifier, the mechanism may be shut down. If plant effluent is recycled through the
clarifier, the mechanism may continue to rotate.
3. If desirable, the clarifier may be drained and taken out of service. If clarifier is to be
drained confirm groundwater is low, or pump down accordingly prior to tank draining.
This decision must be made after considering the affects of weather on the empty
clarifier and the duration of the idle period. If the mechanism is to be shut down, the
drive must be prepared for short or long term storage.
Collector Emergency Shutdown Procedures
In the event of an emergency:
1. Turn off the power to the collector at the control panel.
2. Lock out the unit electrically.
3. Stop flow to clarifier as soon as possible.
4. Correct reason for shutdown before resuming operation.
Procedure after Collector Failure
1. In the event of a failure, turn off the power to the collector at the control panel if not
already off.
2. Lock out the unit electrically until the problem is diagnosed and corrected.
3. If it is anticipated that the clarifier will be out of service for an extended period of time,
stop flow to clarifier.
4. Consult the Troubleshooting Instructions included in manufacturer’s O&M manual and
correct reason for the failure.
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5. If the unit has been out of service for an extended period of time consult the Start-Up
Procedures included in the manufacturer’s O&M manual.
Collector Seasonal Operation
The equipment is designed for continuous operation under all normal weather conditions.
Humidity, snow, rain and ambient temperature ranges are not a factor in the operation of this
equipment.
There is no operational change required between summer and winter operation. During periods
of freezing temperatures, the clarifier should be drained if the flow to the clarifier is bypassed. If
flow to the clarifier is not bypassed and icing becomes a problem, then the scum deflector(s)
should be dismantled and removed from the tank and the skimmer(s) re-adjusted to travel above
the liquid level.
Primary Scum Mixer - Primary scum mixer MX3001A is located in primary scum collection manhole was
existing prior to the Phase 1 construction and is not discussed herein.
Primary Effluent Sample Pump - Primary effluent sample pump P3042A draws samples from the
combined effluent flow from Primary Clarifiers 3100, 3200, 3300, and 3400. This pump was existing
prior to the Phase 1 construction and is not discussed herein.
5.1.4 Equipment Data
Table 5-2 summarizes the primary treatment equipment data for the facilities installed in Phase 1. This
includes primary clarifier 3500 and associated equipment, the primary splitter box, and new
scum/sludge equipment for primary clarifiers 3300 and 3400. The equipment not installed as a part of
the Phase 1 expansion is not covered.
Table 5-2. Primary Clarifier Tankage Equipment Data
Parameter Value
Primary Clarifier 3500
Asset Tag COL3501A
Manufacturer Walker Process Equipment
Size 70 ft diameter, 12 ft sidewater depth
Mechanism Model Type RSP
Mechanism Rotation Clockwise
Maximum Inlet Flow 6.0 mgd
Mechanism Rotation Speed/Arm Trip
Velocity
0.055 rpm / 12.0 FPM
Torque Indicator & Overload Protection
System
The overload protection system consists of a
Belleville spring stack assembly housed between the
worm shaft and the torque indicator. The torque
indicator enclosure houses a pointer mechanism and
a graduated dial for torque indication, factory set trip
collars and microswitches which are to be used for
activating an alarm, shutdown and back-up
shutdown. The enclosure includes an acrylic window
for viewing the indicator dial.
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Torque Limiter
Boston Gear Centric Clutch Series H1906, Model
WOR06NBHP28 with a 48 tooth ANSI 60 driven
sprocket. Release setting corresponds to 150% of
the continuous operating torque.
Gear Torque/Overload Protection Set
Points
Continuous: 20,000 ft-lb
Alarm: 20,000 ft-lb
Shutdown: 24,000 ft-lb
Back-Up Shutdown: 28,000 ft-lb
Centric Clutch: 30,000 ft-lb
Scraper-style sludge collection
mechanism drive motor
½ hp, 1,800 rpm, 3/60/460v
Weir length 201 (64’ diameter single weir)
Primary Scum Boxes
Number 3 (one each for 3300, 3400, and 3500)
Design flow rate 1.1 gpm
Design storage interval 2 hour
Volume 140 gallons
Primary Sludge/Scum Pumping Vaults
Number 3 (one each for 3300, 3400, and 3500)
Dimensions 10 ft by 15 ft and 23 ft deep
Access ladder
Primary Flow Splitter Isolation Gates
Asset Tag
GT3101A
GT3102A
GT3103A
GT3104A
GT3105A
Manufacturer Whipps. Inc.
Series 921 Slide Gate
Size 18” x 60”
Operator Manual Type 102
Primary Flow Splitter Box Balancing Gate
Asset Tag GT3107A
Manufacturer Whipps. Inc.
Series 921 Slide Gate
Size 42” x 42”
Operator Manual Type 102
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5.1.5 Maintenance
Maintenance information from the manufacturer for the equipment installed in the Phase 1 expansion is
noted in Table 5-3. Refer to the manufacturer’s Operations and Maintenance Manual for a more
comprehensive listing of troubleshooting and maintenance requirements
Table 5-3. Primary Clarifier Maintenance
Primary Clarifier 3500 Skimmer
1. Observe the operation of the skimmer once each day as it passes over the scum box. Correct
any cause of hesitation, binding or misalignment.
2. All bolts and nuts should be kept tight and original alignments and adjustments maintained.
Inspections should be made at regular intervals.
3. Wherever possible, examine gears and all wearing parts periodically to determine whether
excessive wear is taking place.
4. Test the overload alarm at least once per week to make sure that the mechanism is protected.
5. If the power is shut off, or if the mechanism is stopped for any reason for longer than an hour,
by-pass the flow until the machine is again started.
6. Keep the machine and surroundings clean and touch up all rust spots with paint frequently.
7. The entire mechanism above and below the waterline should be painted at least once every
two years.
(Walker Process Equipment. 9/25/2012. Contract Q20801)
Gates
Gate and actuator maintenance data identical to that listed for Grit Removal, Table 4-8
5.2 Primary Sludge/Scum Pumps & Grinders
Unit Processes and pre-existing equipment not affected by the Phase 1 expansion are generally not
covered in this manual. The primary sludge/scum pumping system operation and control and new
equipment specifications is included. Specifics of existing equipment are not included.
The goal of the primary sludge pumping operation is to remove settled sludge in the primary clarifiers
and to do so intermittently so as to allow the sludge to thicken. The target thickening point is an average
concentration of 4% TS.
The sludge grinders operate in an inline fashion ahead of the pumps and reduce oversized solids that
could cause jamming and damage to pumps and process equipment.
5.2.1 System Description
After primary clarification, i.e. the removal of settleable and floatable solids, effluent flow from the five
clarifiers is directed to the aeration influent channel. Primary sludge and scum are sent to the sludge
equalization tank before being pumped to the digesters for further processing.
Primary sludge is drawn from the primary clarifiers by five rotary lobe type pumps and macerated by
sludge grinders. Sludge pumps and grinders for primary clarifiers 3100 and 3200 are located in the
adjacent Sludge Pumping Building. Sludge/scum pumps and grinders for primary clarifiers 3300, 3400,
and 3500 are located in vaults adjacent to each clarifier.
Primary Clarifiers 3100 and 3200 - Two rotary lobe type primary sludge pumps (P7101A and P7102A),
and associated primary sludge grinders (GRD7101A and GRD7102A) are located in the Sludge Pumping
Building. They service Primary Clarifiers 3100 and 3200, transferring sludge to the digestion process via
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the sludge equalization tank. There are 4 inch water connections installed on the pump suction piping in
order to facilitate backflushing. Scum from primary clarifiers 3100 and 3200 flows by gravity from the
clarifiers to a scum collection manhole that is periodically pumped down by primary sludge pump
P7102A.
Clarifiers 3300, 3400 and 3500 - These clarifiers are fitted with adjacent sludge pumping vaults on their
sludge withdrawal pipes shortening the sludge suction piping to limit the possibility of plugging. One
rotary lobe type primary sludge pump (P3301A, P3401A, and P3501A) and associated sludge grinder
(GRD3301A, GRD3401A and GRD3501A) are installed inside each of the three vaults. The primary
sludge pumps convey sludge and scum from their respective clarifiers to the sludge equalization tank.
Similarly, 4 inch water connections are installed on the pump suction piping for each of the three pumps
in order to facilitate backflushing. The sludge pumping vaults also house a scum well where scum
skimmed from the surface of the clarifiers is stored. The sludge pumps are operated intermittently to
empty the sludge vault and scum well, consolidating the scum with the primary sludge as it is pumped to
the sludge equalization tank.
Primary Clarifier Scum Collection - Scum is removed from the surface of the clarifiers by rotating scum
collection mechanisms. The scum flows by gravity to a scum well within the sludge pumping vaults for
3300, 3400, and 3500. Scum flows by gravity to the primary scum collection manhole for clarifiers
3100 and 3200. The manhole is fitted with a mixer (MX3001A) to homogenize the scum and facilitate
pumping. Scum is pumped intermittently from these locations to the sludge equalization tank along with
primary sludge by the primary sludge pumps.
Sludge Metering - Primary sludge density meter DE3001A and flow meter FE3001A located in sludge
metering vault monitor the sludge and scum pumped from the primary clarifiers 3300, 3400, and 3500
to the sludge equalization tank. Sludge density meter DE7101A and flow meter FE7101A are located in
the Sludge Pumping Building where they meter primary sludge from primary clarifiers 3100 and 3200.
The density meter was installed in the Phase 1 expansion while the flow meter was already installed.
5.2.2 Design Data
Table 5-4. Primary Sludge Design Data
Parameter Value
Unit Capacity 300 gpm @ 115 ft TDH
Primary Sludge Concentration 4% TS
5.2.3 Operation and Control
5.2.3.1 Clarifiers 3100 and 3200
Control and operations of the primary clarifiers 3100 and 3200, including sludge/scum systems, was
not changed as a part of the Phase 1 expansion.
5.2.3.2 Clarifiers 3300, 3400 and 3500
Primary pumps operate on a timed cycle, with operator-selected timer settings. Normally, one primary
sludge pump operates. Pumps are monitored and controlled from SCADA.
Primary clarifier sludge suction valves FV3301A, FV3401A, and FV3501A must be open to draw sludge
from their associated primary clarifiers 3300, 3400 and 3500. Primary sludge pumps P3301A, P3401A,
and P3501A and primary sludge grinders GDR3301A, GDR3401A and GDR3501A are interlocked to
operate when their corresponding primary clarifier sludge discharge valve is proven open by monitoring
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the fully open valve actuator limit switch. The operating cycle of each sludge discharge valve can be set
from any SCADA terminal on a repeat cycle timer basis. Both open time and close time can be set
independently for all three clarifier valves. Request for operation of sludge discharge valve is interlocked
with all three primary sludge pumps such that a valve open request signal, based on repeat cycle timer
setting, shall be delayed if any primary sludge pump is operating. Once all primary sludge pumps have
been proven off by monitoring running PLC input, the valve having been in queue the longest will open
for a preset duration of time. The open time period will be temporarily interrupted if the associated
clarifier scum valve is requested to open as defined below.
Primary sludge pumps P3301A, P3401A, P3501A are only allowed to operate in automatic mode when
associated primary sludge grinder is running. Each primary sludge pump is provided with a local Hand-
Off-Remote selector switch for manual or automatic operation. When in remote position, automatic or
manual control is selectable from any SCADA terminal through a software configured Hand-Off-Auto
function. The hand position is interlocked such that the corresponding primary sludge grinder must be
running.
If the primary sludge is not prone to hardening upon standing still based on plant experience, leave the
sludge in the pump during normal downtimes. Before long downtime periods flush the pump with the
plant effluent system.
Shut down the pump and all upstream and downstream system components immediately in the event of
malfunctions until the cause has been found and rectified. Otherwise, permanent damage to the
components cannot be ruled out.
5.2.3.3 Primary Sludge Grinders
Primary sludge grinders GDR3301A, GDR3401A and GDR3501A are provided with a package control
panel. A Hand-Off-Remote selector switch is provided on each control panel. When in remote position,
automatic or manual control is selectable from any SCADA terminal through a software configured Hand-
Off-Auto function. When SCADA function is in auto, grinder will run from a PLC run command. The
primary sludge grinder will start first when either corresponding primary clarifier sludge suction valve or a
primary clarifier scum suction valve is proven open.
5.2.3.4 Scum Pumping
For primary clarifiers 3300, 3400 and 3500, primary clarifier scum suction valves FV3302A, FV3402A,
and FV3502A open to draw scum from their associated primary clarifier scum well. When the scum level
in the associated scum well reaches a high level the valve will be requested to open. If the
corresponding primary clarifier sludge suction valve is open, the sludge discharge valve will immediately
close, stopping the corresponding primary sludge pump and primary sludge grinder. Once the primary
clarifier sludge suction valve is proven closed by monitoring the fully closed valve actuator limit switch,
the scum suction valve will open and corresponding sludge pump and grinder will start. The scum
suction valve will remain open until the scum well is empty. Once the scum well is empty, pressure in
the discharge piping will be near zero. When this pressure is detected by the associated discharge pipe
pressure switch PSP3302A, PSP3402A, and PSP3502A, respectively, the valve will close, again proven
by valve actuator closed limit switch. If the scum removal process interrupted a clarifier sludge
drawdown cycle, the corresponding primary clarifier sludge suction valve will again open. If high level is
reached in a primary clarifier scum well while another scum well level drawdown is in progress, the new
request will wait until normal drawdown cycle is completed. Scum well drawdown takes preference over
any sludge drawdown cycle.
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5.2.4 Equipment Data
Börger rotary lobe pumps are self-priming, valveless positive displacement pumps. The rotors are turned
in opposite directions via an external drive using two parallel shafts as illustrated in Figure 5-2. The
geometry of the rotors results in a complete separation of the suction chamber (1) and pressure
chamber (3). The synchronous rotation of the rotor pairs creates a vacuum on the priming side of the
pump, which can be defined by the direction of rotation of the drive. This vacuum draws the liquid into
the pump chamber. The dynamic transfer from the suction chamber to the pressure chamber (2) allows
low-pulsation pumping (when screw rotors are used, pumping is almost pulsation-free). The pumped
medium is forced into the pressure lines on the pressure side (3) through the rotating, intermeshing
rotors. The symmetrical construction of the rotary lobe pump means that the flow direction can be
changed by reversing the direction of rotation, provided this is allowed by the piping system. When the
rotor pair is at a standstill, the pump seals off almost completely. (Börger, LLC Operating and
Maintenance Manual Nov. 2012)
Figure 5-2. Primary Sludge Pump Diagram.
Table 5-5 summarizes the equipment data for the primary sludge and scum pumping systems that were
installed in the Phase 1 expansion.
Table 5-5. Clarifier 3300, 3400 and 3500 Primary Sludge/Scum Pumps
Parameter Value
Sludge Pumps
Asset Tag
P3301A
P3401A
P3501A
Manufacturer Börger
Type Rotary Lobe
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Model CL520
Quantity 4 (including 1 uninstalled spare)
Direction of Flow (Facing Front
Cover)
Reversible
Capacity 300 gpm @ 50 psi
Pump Speed 270 rpm
Solid Size 2” diameter
Sludge Pump Motor
Manufacturer Toshiba
Model EQP Global SD 0204SDSR42A-P
hp 20
rpm 1,770
Sludge Pump Gear Reducer
Manufacturer Nord Gear Corporation
Type Helical In-line
Model Nord SK42-250TC
Gear Ratio, Output Speed 6.19:1 / 286 rpm
Sludge Grinders
Asset Tag
GDR3301A
GDR3401A
GDR3501A
Manufacturer Franklin Miller. Inc.
Machine Taskmaster Inline
Model TM851206
Rotor Speed 60 rpm
hp 3
Average Flow 600 gpm
Pressure Drop 0.9 psi
Primary Sludge Density Meter
Asset Tag DE3001A
Manufacturer Metso Automation
Type Sludge Density Analyzer
Model DE/DIT 6” Flow Thru Wafer Body
Measuring Range 0-35% TS
Primary Sludge Flow Meter
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Asset Tag FE3001A
Manufacturer ABB Watermaster
Model FEV125.150.V.1.S.4.A1.B.1.A.1.A.2.P.2.B.3.A.1
.M5.V3.CWC, 614C220U01
Calibration Range 0-400 gpm
Meter Size 6”
Primary Clarifier Sludge Valves
Asset Tag
FV3301A
FV3401A
FV3501A
FV3302A
FV3402A
FV3502A
Manufacturer DeZurick
Style 100% Area Rectangular Port Eccentric Plug Valve
Size 6 inch
Actuator AUMA SARExC 07.5/GS63.3 ELECTRIC MOTOR
OPERATOR
Pressure Switches
Asset Tag
PSP3302A
PSP3402A
PSP3502A
Manufacturer Ashcroft
Model B724-B-X06-FS-NH/50-201SS-04T-CK
5.2.5 Maintenance
Table 5-6 summarizes the maintenance information provided by the manufacturers for the primary
sludge and scum systems installed in the Phase 1 expansion. Refer to the manufacturer’s Operations
and Maintenance Manual for a more comprehensive listing of troubleshooting and maintenance
requirements.
Table 5-6. Primary Clarifier 3300,3400 and 3500 Sludge/Scum Pumps & Grinders Maintenance
Inspection/Maintenance
Frequency
(Approx.)
Operating
Hours Measures
Sludge Pumps
Cleaning the outer surfaces When
Necessary
See chapter 6.1 of
manufacturer manual
“Machine Care”
Visual check for leaks Daily 24 Replace the seals, when
necessary
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Audible check for smooth
running Daily 24
Check the suction line, rectify
the cavitation, check the rotors
and replace when necessary
Check of functions and rated
capacity Weekly 168 Replace wear parts, when
necessary
Check the oil level of the gear
unit in the oil sight glass Monthly 720 Refill, when necessary
Check pump and components
for tight fit and possible
damages
Quarterly 2,160
Fasten loosened parts tightly,
replace damaged parts
Check the level of the quench
fluid in the intermediate
chamber
6 Months 4,320
Refill, when necessary
Replace the lubricants 2 Years 10,000 See manufacturer manual
chapter 6.2.2
Sludge Pump Motors
Inspect motor at regular intervals. Keep motor clean and vent openings clear.
Frame 256T is furnished with double sealed or shielded bearings, pre-lubricated prior to
installation. Grease fittings are not supplied and bearings are designed for average 100,000
hours operation under standard conditions.
Sludge Pump Gear Reducer
Lubrication
(Mineral/Synthetic) 2/4 years 10,000/20,000
Acceptable oil level is ½ inch
below the bottom of the fill
plug threads.
OIL SPECIFICATIONS - Consult the sticker adjacent to the fill plug to determine the type of
lubricant installed at the factory.
Sludge Grinders
Maintenance Item Frequency Measures
Visual Inspection Weekly Inspect
Cutter Cartridges Semi-Annually Inspect
Speed Reducer Quarterly Inspect
Gear Lubrication Annually Lubricate
Seal Inspection Annually Inspect
Fasteners Annually Inspect
Motor Quarterly/Semi-Annually Inspect/Lubricate
Pressure Switches
No maintenance procedures are required by manufacturer’s manual
Plug Valve
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No maintenance procedures are required by manufacturer’s manual
Flow Meter
No maintenance procedures are required by manufacturer’s manual
Primary Sludge Density Meter
No maintenance procedures are required by manufacturer’s manual
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Section 6 Secondary Treatment
6.1 Secondary Treatment Overview
Secondary treatment consists of the following components: aeration basins with internal mixed liquor
recycle, aeration blowers, diffusers, secondary clarifiers, return activated sludge (RAS) pumps, waste
activated sludge (WAS) pumps, and classifying selectors. Associated with secondary treatment is the
BAR and HSW equalization systems that treat the ammonia laden filtrate for the belt filter presses
dewatering the anaerobically digested sludge.
The objective of the secondary treatment processes is to remove biodegradable organic compounds and
ammonia (NH3) in accordance with the WLA. See Section 2 for further discussion on the WLA.
6.2 Aeration Basins
6.2.1 Aeration Basin Influent Channel
Primary effluent, high strength waste (or BAR effluent), and RAS enters the aeration basin influent
channel which provides flow and load equalization prior to distribution to the four aeration trains by a
series of isolation gates. The aeration basin influent channel is rated for 30 mgd.
6.2.2 Aeration Basins
6.2.2.1 System Description
Four aeration basins, each equipped with an anoxic selector, provide residence time for the activated
sludge to remove the target pollutants and grow additional biomass. This is called the Modified Ludzack-
Ettinger (MLE) process. Each basin is equipped with fine bubble diffusers, internal mixed liquor recycle,
mixers for keeping the biomass (suspended solids) in suspension, and instrumentation used for
monitoring and control. Figure 6-1 depicts the aeration basins and the associated systems.
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Figure 6-1. Aeration Basin Schematic.
6.2.2.2 Design Data
The aeration basins are configured in a single-pass arrangement. There are four aeration trains. The
aeration basins are designed to achieve nitrification at an aerobic solids retention time (SRT) of 7 days
or 5 days with the BAR system in operation at year 2025 projected flows and loads. To achieve the
desired levels of treatment, each cell requires a certain amount of air. Table 6-1 defines the maximum
and minimum airflow requirements for each cell.
Table 6-1. Minimum/Maximum Air Flow Capacity
Requirements per Aeration Train
Cell Number Each Cell, scfm
1 0/960
2 0/880
3 0/1954
4 680/1050
5 538/870
6 480/756
7 400/730
8 340/650
9 420/860
10 300/750
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6.2.2.3 Operation and Control
Operation and control of the aeration basins themselves is limited to how many trains are required and
what cells require aeration. Section 3 provides a discussion on operation of the aeration basins. In
general, the first two or three cells will serve as the anoxic selector and the remaining cells will be
aerated (MLE configuration).
The ammonia sensors installed in Aeration Basin 4 are for monitoring purposes only. Section 3
discusses operation of the aeration basins to meet permitted ammonia levels.
Operation and control of the airflow and mechanical mixers are discussed in Sections 6.5 and 6.7,
respectively.
6.2.2.4 Equipment Data
There are four aeration trains; each 600 ft L x 25.5ft W x 15ft water depth, and each of the four basins
has a volume of approximately 1.71 million gallons. Baffle walls divide the first 420 ft of tanks into 8
equal cells; each nominally 52 ft L x 25.5 ft W x 15 ft water depth. The final 174 ft of each tank is not
physically divided into separate cells, however they are considered to be 2 separate cells (9 and 10) and
as such have separate diffuser grids. Aeration Basin 4 is equipped with DO and ammonia sensor in cells
3, 5, and 8. The DO meters are discussed in Section 6.3.5. Table 6-2 summarizes the aeration basin
dimensions and volumes and the ammonia meters.
Table 6-2. Aeration Basin Data
Parameter Value
Aeration Basins
Total Reactor Volume 6.8 MG
Volume per Train 1.7 MG
Minimum aeration basin aerobic SRT (with BAR) 5 days
Minimum aeration basin aerobic SRT 7 days
Aerobic hydraulic retention time (HRT) at AWW flow 6.7 hr
Aerobic HRT at peak flow 4.1 hr
Anoxic/Anaerobic selector total volume 1.8 MG
Anoxic/Anaerobic selector volume per train 0.45 MG
Aerobic total volume 5.0 MG
Aerobic volume per train 1.25 MG
Sidewater depth 15 ft
Ammonia Meters
Asset Tag AEZ4143A2
AEZ4145A2
AEZ4148A2
Manufacturer Hach
Model NH4D sc
Calibration Range 0-100 mg/L
Other systems supporting the aeration basins are summarized in later sections.
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6.2.2.5 Maintenance
The aeration basins themselves do not require regular maintenance. When basins are taken out of
service and drained, any solids that settled should be removed.
The ammonia analyzer should be cleaned, checked for damage, and verified with lab analysis every 30
days. Every 6 months the sensor cartridge needs to be replaced.
Maintenance for other equipment located in the aeration basins is discussed later.
6.2.3 Aeration Basin Effluent Channel and Surface Film Classification
The aeration basin effluent channel collects the mixed liquor from the aeration basins. A surface film
classifier is located near the end of the channel and is used to mitigate the development of nuisance
foam causing organisms. This is achieved by selective removal of the organisms on the surface of the
flow, where foaming organisms would reside.
6.2.3.1 System Description
The mixed liquor is split in the aeration basin effluent channel into three possible streams:
1. The bulk of the mixed liquor flows by gravity to the secondary flow splitter box which
distributes flow to the secondary clarifiers.
2. A portion of the mixed liquor flows into the internal mixed liquor recycle sump where pumps
P4460A and P4470A pump mixed liquor back to the head of the aeration basins.
3. A small portion of the mixed liquor is captured by the surface film classifier and is pumped by
P4440A and P4450A to the secondary scum system.
The surface film classifier consists of a stainless steel baffle, sump located adjacent to the aeration
basin effluent channel, and pumps (P4440A and P4450A) with associated discharge piping. The baffle
skims the top of the aeration basin effluent channel over a downward-opening weir gate (GT4430A) and
into the surface film classifier sump. The contents of the sump are pumped to the secondary scum
collection manhole near secondary clarifiers 5100 and 5200. From there the combined scum is
pumped to the sludge equalization tank by secondary scum pump P5001A.
This classifier is redundant to the one located in the RAS Box, which is discussed later.
Effluent spray water is also provided to knock down foam in the surface film classifier sump.
6.2.3.2 Design Data
Since the aeration basin effluent channel was new construction in the Phase 1 expansion it was
designed to pass up to 45 mgd (year 2040 design flow).
The surface film classifier is designed to remove 170 gpm.
The internal mixed liquor recycle system is discussed in Section 6.4.
6.2.3.3 Operation and Control
Aeration Basin Effluent Channel Surface Film Classifier Baffle – This baffle is fixed and is not adjustable.
Weir Gate GT4430A – This gate can be manually adjusted to achieve the desired foam removal rate. It
is anticipated that this gate will be normally closed since RAS wasting at the RAS location is preferable to
aeration basin effluent channel where mixed liquor is wasted, and since the RAS surface film classifier is
expected to control filamentous organisms in the system. Use of this installation is intended only during
foaming events that are unsuccessfully controlled by the RAS location or if foam is trapped in the
aeration basin effluent channel.
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Aeration Basin Effluent Channel Surface Film Classifier Pumps - Pumps P4440A and P4450A are
constant speed pumps operating based on water level in the sump. Four level switches: 1) low-low, 2)
low, 3) high, and 4) high-high determine the pump operation. The low-low and high-high switches
indicate alarm conditions. The high switch calls a pump into service while the low switch turns the pump
off. The two pumps are identical with one serving as duty and the other as standby. Floating materials
can accumulate in the sump. During periodic cleaning cycles the pump level is drawn down until the
pump breaks suction in order to remove any floating material. High pump amp draw is used to indicate
that the pump has broken suction and the cleaning cycle is complete.
6.2.3.4 Equipment Data
Table 6-3 summarizes the equipment installed in the aeration basin effluent channel.
Table 6-3. Aeration Basin Effluent Channel Equipment
Parameter Value
Surface Film Classifier Pumps
Asset Tag P4440A
P4450A
Manufacturer KSB
Model KRT F-80-200/14U2G
Type Submersible Solids Handling
Unit Capacity 170 gpm @ 6.5’ TDH
Motor 1.1 hp, 1,750 rpm
Surface Film Classifier Weir Gate
Asset Tag GT4430A
Manufacturer Whipps, Inc.
Model 923
Size 36” x 36”
Actuator Type 102 Manual
Mixed Liquor Recycle Pumps
Pumps are covered in Section 6.4 of this manual
6.2.3.5 Maintenance
Maintenance information for the aeration basin effluent channel systems are summarized below in Table
6-4 or reference to other sections of this manual. Refer to the manufacturer’s Operations and
Maintenance Manual for a more comprehensive listing of troubleshooting and maintenance
requirements
Table 6-4. Aeration Effluent Channel Equipment Maintenance
Parameter Value
Surface Film Classifier Pumps
Insulation resistance test Every 4,000 operating hours;
at least once a year Checking the electric cables
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Visual inspection of lifting chain /
rope
Check of monitoring equipment Every 10,000 operating hours;
at least every three years Oil change
General overhaul Every five years
Surface Film Classifier Weir Gate
Find gate and actuator maintenance data in Grit Removal, Table 4-8
Mixed Liquor Recycle Pumps
Pumps are covered in Section 6.4 of this manual
6.3 Aeration System
Oxygen needed in the aeration basins is transferred to the mixed liquor by the aeration system. The fine
bubble aeration system takes compressed atmospheric air, provided by aeration blowers, and passes it
through the diffuser elements forming millions of fine bubbles that pass through the mixed liquor. The
millions of very small bubbles have a much greater cumulative surface area than larger bubbles formed
by coarse diffusers. This allows the oxygen in the air filled bubbles to diffuse into the mixed liquor more
efficiently. Microorganisms can then absorb the oxygen through their cell walls and use it for respiration.
6.3.1 System Description
A total of seven aeration blowers; five multi-stage centrifugal (MSC) blowers and two high speed turbo
blowers, discharging into a common header are staged to provide airflow to the aeration basins, BAR
tanks, the RAS Box, and UV disinfection and bypass channels. Air is diffused via submerged piping and
9 inch diameter fine bubble membrane disc diffusers.
6.3.2 Design Data
Under normal conditions the MSC blowers are operated at a constant amp draw condition in order to
maximize their output while controlling surge. At the same time the high speed turbo blower speed is
modulated to maintain pressure on the blower discharge header. Table 6-5 summarizes the air
requirements at the South WWTP.
Table 6-5. Airflow Requirements at the Iowa City South WWTP
Design Criteria Airflow (scfm)
Firm Capacity1 33,000
Total Capacity 39,250
1Assumes largest unit out of service and maintaining a 2.0 mg/L DO level in
aeration basins.
6.3.3 Aeration Blowers
There are two types of aeration blowers at the South WWTP, MSC and high speed turbos. The MSC
blowers were installed prior to the Phase 1 expansion and are not discussed in this manual except for
the revised control strategy required to accommodate the high speed turbo blowers.
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6.3.3.1 Multi-Stage Centrifugal Blowers
The five MSC blowers (B4502A, B4503A, B4504A, B4505A and B4506A) are constant speed machines
with the airflow controlled by inlet control valves (PCV4502A, PCV4503A, PCV4504A, PCV4505A, and
PCV4506A). Each of these blowers can produce 6,250 scfm at 7.5 psig. Each blower also has a local
control panel. Normally these blowers are controlled by the plant PLC, which is discussed in more detail
in Section 6.3.5.
6.3.3.2 High-Speed Turbo Blowers
The turbo blowers are single-stage centrifugal high speed air bearing type. Compared to the MSC
blowers, the turbo blowers are much more efficient at turndown conditions.
6.3.3.2.1 System Description
The turbo blowers consist of a blower core, a VFD and a controller. The blower core consists of an
efficient high speed motor, impeller and semi-permanent air foil bearings.
The air foil bearing works by creating a pressure on the surface of the bearing foil using the viscosity of
the air flowing through the annulus formed by the bearing housing and the motor rotor. This pressure
supports the rotor and does not allow metal to metal contact between the rotor and bearing at
operational speeds. The lack of contact allows the high speeds and efficiency of the turbo blowers.
Each blower is equipped with an equipment protective package to provide shutdown and alarming for
surge, vibration, and temperature.
Figure 6-2 depicts one of the installed turbo blowers (B4501A).
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Figure 6-2. Turbo Blower Installed at South WWTP.
6.3.3.2.2 Design Data
The two turbo blowers are designed to produce 2,000 - 4,000 scfm per blower at 7.5 psig. The turbo
blowers are meant to modulate over this range to increase overall system efficiency.
6.3.3.2.3 Operation and Control
Each high speed blower has a PLC provided with the blower package that is connected to the plant PLC.
Generally, the turbo blowers are operated to handle the normal modulations in airflow demand since
they remain highly efficient when turned down. The turbo blowers will modulate their airflow based on
the pressure in the common discharge header shared with the MSC blowers. Normally these blowers
are controlled by the plant PLC, which is discussed in more detail in Section 6.3.5.
Emergency Operation and Control - The turbo blowers are fitted with an emergency stop button. Pressing
it disables the VFD from operating. Before operation or maintenance work, verify the position of the
emergency stop button and verify the power is disconnected if working within the energized
compartments of the units.
In case of an emergency stop, the breaker inside the system will not shut off. The power within the unit
will remain energized unless the power source feeding the unit is turned off. Therefore, do not touch the
terminals and follow all prescribed lock-out-tag-out procedures before proceeding with any maintenance
work.
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Verify the emergency stop button functions regularly by depressing the button while the unit is not
operating. To reset the emergency stop button turn the button clockwise. Once the button is released,
the emergency stop button is reset.
6.3.3.2.4 Equipment Data
Table 6-6 summarizes the equipment data for the two turbo blowers installed in the Phase 1 expansion.
Table 6-6. Turbo Blower Equipment
Parameter Value
High Speed Turbo Blowers
Asset Tag B4501A
B4507A
Quantity 2
Manufacturer Neuros
Model NX200-C070
Bearing Bump Type Air Foil
Coupling Direct
Noise 80 db
Rate Motor Output Power 200 hp
6.3.3.2.5 Maintenance
Maintenance to the turbo blowers should be performed only by personnel trained by the manufacturer in
the specific maintenance activity. Table 6-7 summarizes the maintenance activities provided by the
manufacturer. Refer to the manufacturer’s Operations and Maintenance Manual for a more
comprehensive listing of troubleshooting and maintenance requirements
Table 6-7. Aeration Turbo Blower Scheduled Maintenance
Frequency Maintenance Activity
Daily or at
least twice a
week
Check for unusual noise and vibration.
Ensure area around the blower is free from debris, flammable or explosive
materials.
Check the inlet pressure drop (DPI) value on the touch screen.
• It should remain 0 to 0.0306 kgf/cm2 (0.435 PSI).
• When it reaches 0.0176 kgf/cm2 (0.25 PSIG), or once a month, stop the blower
and verify the conditions of the front and rear filters as they may need to be
cleaned.
• A warning pops up on the touch screen when the inlet pressure drop reaches
0.0290 kgf/cm2 (0.413 PSIG).
• A shutdown alarm is triggered when the inlet pressure drop sensor reaches
0.0306 kgf/cm2 (0.435 PSIG).
Check the coolant level.
• A level gauge and a pressure gauge are installed on the side door near the
tank.
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• The coolant level should remain between 50% and 75%. Filling over 75% leaves
no room for the liquid to expand due to heat.
• The coolant pressure gauge should read between 2.0 and 2.2 bar
(approximately 30 psi).
• Refer to the coolant supplement manual in the manufacturer’s manual for more
information.
Check the discharge pipe system. Its discharge pressure should vary within a
range of +/-10%.
Record the following running values:
• Motor speed (rpm) and temperature (°F)
• Suction flow rate (scfm) and temperature (°F)
• Discharge pressure (PSIG) and temperature (°F)
• Filter pressure drop (PSIG)
• Bearing temperature (°F)
• Power consumption (kW)
• Rotor vibration (mil)
• VFD temperature (°F)
• Ambient temperature (°F) and ambient relative humidity (%)
Monthly • Clean filters after stopping the blower. Exchange the dirty filter with a clean
filter.
• Clean the dirty filter with water (no soap) and avoid using a pressure washer.
• If the area is very dusty, clean filter more than once a month. Filters should be
washed and changed no more than three times before they are replaced.
Quarterly After powering off the blower:
• Check the inside of the blower for normal wear and tear such as accumulated
dust and leakage.
• Check for overheating in the power cable and terminal blocks.
Annually Perform annual check-up. It is recommended that the blower be checked annually
by an APG-Neuros field service engineer.
Every Two
Years
Replace antifreeze. Refer to the coolant supplement manual in the manufacturer’s
manual for more information.
6.3.4 Aeration Diffusers
Nine inch fine bubble membrane disc diffusers are utilized for air distribution in the aeration basins, RAS
Box, BAR tanks, and UV channels. Those employed in the aeration basins are discussed here.
6.3.4.1 System Description
Each cell in the aeration basins has a prescribed number of diffusers installed. These diffusers are
supplied air by a network of piping at the bottom of the basins which is connected to the piping running
along the basins above the water level and ultimately connecting back to the blowers.
6.3.4.2 Design Data
The diffuser system is designed to deliver the airflows listed in Table 6-1. The number of diffusers is
determined by allowable operating conditions in Table 6-8.
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Table 6-8. Diffuser Operating Conditions
Min./diffuser Max./diffuser Avg./diffuser
Airflow Range 0.05 scfm Short Term: 7 scfm
Long Term: 4 scfm 1 to 2 scfm
6.3.4.3 Operation and Control
The overall aeration control system dictates the flow of air through the diffusers and is discussed in
Section 6.3.5. In case of emergency, to shut down the fine bubble aeration system, turn off the manual
air supply valve that connects the diffuser grid to the air header running along the surface of the basin.
Flow Control Valve FCV4310A can be closed to stop airflow to the BAR Tanks and RAS Selector Basin.
6.3.4.4 Equipment Data
The diffusers are 9 inch diameter and SSII type manufactured by Sanitaire/Xylem. In order to meet the
design airflows summarized above each cell requires a certain number of diffusers. Table 6-9
summarizes the number of diffusers installed per cell.
Table 6-9. Installed Diffusers
Cell Number Diffusers per Cell
1 480
2 440
3 680
4 680
5 538
6 480
7 400
8 340
9 420
10 300
6.3.4.5 Maintenance
Over time, fine bubble aeration diffusers may foul and require cleaning. The rate of fouling, type of
fouling, and physical nature of the fouling depends primarily on the constituents in the wastewater. The
results of diffuser fouling include loss of oxygen transfer efficiency, higher system backpressure requiring
higher blower output, increased air demand, and increased operating costs. Several maintenance
procedures can be performed to maintain system performance. The diffuser manufacturer recommends
the following maintenance practices.
Visual Inspection – Visually inspect the aeration basin surface pattern. The flow should be, for the most
part, a nice quiescent pattern. Excessive course bubbling throughout the basin indicates the diffusers
may be fouling. Large boiling in an isolated area indicates a failure in the submerged pipe system. Pipe
system leaks are typically caused by loose joints or degraded gaskets and should be repaired quickly to
avoid loss of system efficiency.
Moisture Purging – Moisture may enter the aeration system through condensate buildup and minor
leaks in the pipe system resulting in increased air velocity, headloss and poor air distribution. For
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maximum purge results, lower the air flow in the grid. The system uses a sump with an eductor line that
extends from the grid to above the water surface and ends with a manual ball valve.
Air Bumping – Air bumping is the process of increasing the air flow rate per diffuser for 20-30 minutes
once per week. Air bumping helps to reduce back pressure in aeration systems and blowers. The
practice will aid in sloughing off settled debris and may extend the period between diffuser cleanings.
Table 6-10 summarizes the manufacturer’s recommended maintenance practices. Refer to the
manufacturer’s Operations and Maintenance Manual for a more comprehensive listing of
troubleshooting and maintenance requirements
Table 6-10. Aeration Piping and Diffuser Maintenance Schedule
Frequency Action
Daily 1. Visual inspection
2. Operating pressure and airflow monitoring
Weekly
1. Purge condensation from aeration grids (see Section V, Page 23 of manufacturer
O&M manual)
2. Air bump diffusers to blow off any settled debris
Monthly None
Yearly
1. Drain aeration basin (air should remain on at 1 scfm (1.7 m3/hr) per diffuser as
basin is drained)
2. Remove excess settled solids if any have accumulated
3. Clean diffusers
4. Inspect system piping and support hardware to ensure all components are intact
and tight
5. Inspect diffuser retainer rings to be sure all rings are in place and tight (see
Section V, Page 15, Figure 36 of manufacturer O&M Manual)
6.3.5 Aeration Airflow Control
Aeration airflow control is provided by DO sensors in the basins, flow control valves installed on the air
headers, and the blowers themselves. Each aeration train has three air control zones along the length of
the train and ten distinct cells. Each zone has an airflow control valve and a flow meter. Train 4 has
dissolved oxygen (DO) probes in cells three, five and eight. The signal from the DO interface is used to
evaluate basin performance and control operations. A signal is sent to the airflow control valve to adjust
the valve position as required to maintain consistent DO concentration in the contents of each train. The
trains without DO probes will be controlled by signals from DO probes in train 4.
6.3.5.1 System Description
The primary function of the aeration control system is to minimize blower energy use by maintaining the
DO setpoint in each aeration zone, while also providing a sufficient minimum airflow to maintain the
solids in suspension. Under high load conditions and near the front of the basin (cells 3 or 4) airflow
rates are generally governed by the DO setpoint. Under low load conditions and near the end of the
basin the minimum airflow rates required for mixing determines the appropriate flow to the zone. Each
control zone is assigned minimum and maximum airflow settings to prevent diffuser clogging or damage.
It is important to control the first aeration zone downstream of the cells operated as anoxic selectors
(Zone 1) to a DO setpoint of 1.5-2.0. Lower DO setpoints in zones 2 and 3 can provide additional energy
savings if effluent ammonia levels remain low.
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Cells 3, 5, and 8 in Aeration Train 4 are equipped with DO probes. Valves in parallel Aeration Trains 1, 2,
and 3 use an emulation strategy to set valve positions matching valve positions in Train 4. However, if
field DO measurements show that the Train 1, 2, or 3 levels are too high or too low, each valve’s bias
signal can be adjusted to make it open slightly more or slightly less as needed.
As the control valves adjust the aeration basin airflows, the pressure in the blower discharge header
changes. A higher header pressure indicates that the aeration demands have reduced. The blower
output is automatically turned down to maintain the pressure setpoint and match the aeration airflow
requirements. Conversely, a lower header pressure indicates that the aeration demands have increased
and the blower output is automatically increased. The two high speed turbo blowers use VFDs to
minimize energy use over the range of airflow conditions. One or more of the five MSC blowers can be
operated at a constant output in conjunction with a modulating turbo-blower.
6.3.5.2 Operation and Control
The operation of the blowers is regulated by the air demands in the aeration basins. The air demand is
controlled by the DO levels in the basins in relation to the DO setpoints, which are usually around 1.5 to
2.0 mg/L. The following details the operation of the blowers and flow control valves in response to
changes in DO (i.e. airflow demand). The following operational detail starts with the blowers and works
downstream to the flow control valves and DO meters.
6.3.5.2.1 Aeration Blower Sequencing
1. The selection of which blower is to be first on line, second on line, etc. is manually selected by
plant operator from any SCADA terminal. There are independent groupings set for two turbo and
five MSC blowers.
2. Changing sequence order of an operating blower requires the blower control system to be placed
in manual to prevent blowers from being placed on line automatically. The operating blower to
be replaced can be manually stopped from any SCADA terminal. Once blower output air flow has
been detected as being zero, the replacement blower of same type is manually started. All
parameters of the replaced blower are maintained for the replacement blower. This includes
inlet air valve positioning for an MSC blower and speed reference signal input for a turbo blower.
Once the replacement blower is online and operating in a stable manner, the blower control
system returns to automatic mode.
6.3.5.2.2 Aeration Blower Staging – Increasing Airflows
The following outline explains the blower staging procedure in response to an airflow demand increase.
In general, blowers are staged to maximize the number of turbo blowers in service, while using MSC
blowers to provide base-load capacity. Refer to Figure 6-3 and Figure 6-4 below for expected blower
combinations to be used over various flow ranges.
1. Blowers are started and stopped as required to meet the pressure setpoint determined by the
plant staff.
2. The need to bring a blower online is determined by the inability of online blowers to meet the
pressure setpoint.
3. When a turbo blower is at full speed and is unable to maintain the pressure setpoint due to
increasing air demand, the second turbo blower will start if not already running.
4. When two turbo blowers are operating at full speed and are unable to maintain the pressure
setpoint due to increasing air demand, one turbo blower will shutdown and one MSC blower shall
be started to replace it. The same occurs if only one turbo blower is available. If, however,
demand continues to increase beyond maximum loading of the MSC blower(s), the turbo blower
shall be started to supplement air demand requirements.
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5. When blower discharge pressure increases, blower performance shifts to left on its curve and
approaches its surge point. During automatic blower starting, operating turbo blowers shall be
controlled to avoid possible surge conditions. Prior to placing additional MSC or turbo blowers
online, any operating turbo blowers will temporarily slow down to 85% of maximum speed. After
the new blower is successfully started, the turbo blowers will ramp up over a 15 minute period at
a controlled rate and will then resume modulation in response to the pressure setpoint.
6. Time delays for start/stop stabilization, high pressure, low pressure, and valve limits have been
integrated into the programming to reduce premature re-staging of blowers.
7. Airflow rates for all blowers are monitored by the plant PLC. Low airflow will alarm at all SCADA
locations prior to blowers being within 10% of the surge point.
Figure 6-3. Blower Staging for Increasing Airflows – Both Turbo Blowers Available.
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Figure 6-4. Blower Staging for Increasing Airflows – One Turbo Blower Available.
6.3.5.2.3 Aeration Blower Staging – Decreasing Airflows:
The following outline explains the blower staging procedure in response to an airflow demand decrease.
Again, the blowers are staged to maximize the number of turbo blowers in service with the MSC blowers
providing base-load capacity. Figure 6-3 and Figure 6-4 illustrate the blower combinations at varying
airflows.
1. The need to take a blower offline is determined by the ability of fewer blowers to meet the
pressure setpoint.
2. When two turbo blowers are operating at their minimum speed and the pressure setpoint is
exceeded, one turbo blower sill shutdown.
3. When one turbo blower and one or more MSC blower(s) are in service and the turbo blower is
operating at its minimum speed and the pressure setpoint is exceeded, one MSC blower will
shutdown and the second turbo blower will start (reference Figure 6-3).
4. When one turbo blower is operating at minimum speed with one or more MSC blower(s) in
service and the second turbo blower is out of service, if the pressure setpoint is exceeded, the
turbo blower will shutdown and the system will operate with only the MSC blower(s) as shown in
Figure 6-4. If air demand continues to decrease and the MSC blower(s) are at their minimum
loading condition, one MSC blower will shutdown and the available turbo blower will start.
6.3.5.2.4 Blower Pressure and Inlet Valve Control
The following outline describes the control of the various blowers to maintain the pressure setpoint.
1. The plant PLC modulates the output of all running turbo blowers together as required to meet the
pressure setpoint. This creates a percent loading setpoint to be applied to all running turbo
blowers. The modulation control is dampened to limit continuous variations in blower speed.
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2. Each turbo blower’s motor is loaded based on the percent loading setpoint for the system. The
plant PLC controls each turbo blower identically to achieve the correct loading. Each blower’s
PLC controls the load range between surge conditions and motor full load amps to maximize
capacity and turndown capability.
3. Each turbo blower has a modulating blow-off valve that prevents operating near surge conditions
and provides additional capacity adjustment. The turbo blower controls are configured to
minimize use of blow-off valve because during periods of blow-off discharge header pressure is
unstable resulting in unstable control.
4. When MSC blowers are operated in parallel with the turbo blowers each MSC blower’s motor is
loaded based on an operator-selected amp loading setpoint. The plant PLC controls each
blower’s inlet valve individually to achieve the correct loading. Each MSC blower’s load range
shall be manually set between surge conditions and motor full load amps to maximize capacity.
5. If only MSC blowers are in service each blower’s motor shall be manually loaded to achieve
percent loading setpoint for system.
6. MSC blower inlet valves are closed when blower is not running.
6.3.5.2.5 Blower Header Pressure Setpoint Alarming:
1. Alarms alert the plant operator to manually adjust the blower discharge pressure setpoint to
maintain aeration valves within their controllable range, and keep the blower system at its
optimum efficiency.
2. If one or more airflow control valves are at maximum position, then blower head discharge
pressure is too low. In this scenario, control of the aeration basin will be difficult and DO levels
may drop. The maximum position is percentage open value beyond which flow control with the
valve becomes difficult, typically around 60% open. The maximum allowable valve position shall
be at the limit of this stable operating range. Detection of one or more control valves at
maximum position creates an alarm at each SCADA terminal.
3. If one or more airflow control valves are at minimum position, then blower head discharge
pressure is too high. Producing the same quantity of air at a lower pressure shall result in more
efficient operation of blowers, and keeps valves in their effective control range. The minimum
position is the percentage open value beyond which flow control with valve becomes difficult,
typically 15% open. Detection of one or more control valves at minimum position creates an
alarm at each SCADA terminal.
4. If it is determined that maximum and minimum valve positioning alarms are occurring
simultaneously, aeration basin airflow piping headers need to be balanced to manually limit
airflow as required.
6.3.5.2.6 Airflow Control Valves
1. Aeration basin zone airflow control valves FCV 4111A, FCV 4112A, FCV 4121A, FCV 4122, FCV
4131, FCV 4132, FCV 4141 and FCV 4142A were installed prior to the Phase 1 expansion.
These valves control airflow two the first two cells of each aeration basin. These cells will be
operated as selectors and do not require airflow unless the mechanical mixers fail and mixing is
required.
2. The aeration basins are divided into three airflow control zones, see Table 6-11. Each control
zone has minimum and maximum airflow settings to prevent diffuser clogging or damage.
Airflows outside of this range initiate an alarm condition.
3. Airflow control valves FCV 4113A, FCV 4115A, FCV 4118A, FCV 4123A, FCV 4125A, FCV 4128A,
FCV 4138A, FCV 4133A, FCV 4135A, FCV 4138A, FCV 4143A, FCV 4145A and FCV 4148A were
installed in the Phase 1 expansion. When the valve actuator is in remote mode the plant PLC
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automatically position the valves to maintain a DO or airflow setpoint. Cells 3, 5, and 8 in
Aeration Basin 4 are equipped with DO probes (AEZ4143A, AEZ4145A and AEZ4148A,
respectively). Valves in parallel basins (1, 2, and 3) are positioned using the same control signal
coming from the plant PLC generated by the DO probes in Aeration Basin 4. Each valve has a
bias adjustment that allows the plant operator to manually bias the position of each valve to
achieve the proper DO in each basin.
4. Three control modes are possible at the South WWTP: 1) DO control, 2) airflow control, and 3)
manual control.
a. DO Control:
i. The plant PLC modulates the airflow control valves to maintain DO setpoints in the
aeration basins. The PLC is configured with Master (DO) and Slave (airflow) loops. The
Master loop calculates required airflow needed to maintain the DO setpoint and passes
(cascades) the airflow setpoint to Slave loop. The Slave loop modulates the airflow
control valve position to maintain required airflow. This is known as a ‘Cascade’ loop
controller.
ii. The DO control system maintains DO in a settable minimum range from 0.5 to 8.0 mg/L,
settable from any SCADA terminal. Minimum DO values may be set for each control
zone or a uniform setpoint for all zones can be selected.
iii. DO control is accomplished by use of the DO probes in Aeration Basin 4. The setting
resulting from the operation of Aeration Basin 4 is applied to the other three basins.
The other three basins can be biased, as discussed earlier, to adjust the basins for
slight differences from that of Aeration Basin 4.
iv. This is normal mode of operation for Aeration Basins.
b. Airflow Control:
i. The Slave loop shall modulate airflow control valve position to maintain airflow. This
mode utilizes the Slave portion of ‘Cascade’ loop controller.
ii. Each control zone is equipped with a thermal mass flow meter (FE4113A, FE4115A,
FE4118A, FE4123A, FE4125A, FE4128A, FE4138A, FE4133A, FE4135A, FE4138A,
FE4143A, FE4145A and FE4148A).
iii. Each control zone has minimum and maximum airflow settings per Table 6-11. The
minimum and maximum airflow settings are not changeable from SCADA terminals.
Table 6-11. Airflow Control Valve Limits at the Iowa City South WWTP
Control Zone
Aeration
Basin Cells
Minimum Airflow per
Zone (scfm)
Maximum Airflow
per Zone (scfm)
1 3,4 1,100 2,200
2 5,6,7 850 2,900
3 8,9,10 570 2,650
iv. Airflow control mode is normally used to keep a basin in service when its DO probe is
out of service for a short period of time. An example of this would be cleaning of a DO
probe. When switching from DO to airflow mode and back, the plant PLC shall
automatically remember the latest airflow value to provide a “bumpless” transition.
Once the probe has been cleaned and placed back in service, the mode may be set
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back to DO control. This can also be accomplished by placing instrument in “hold” from
any SCADA terminal while cleaning.
c. Manual Control:
i. Valve positioning is possible from any SCADA terminal in manual mode as long as local
valve actuator controls are in the remote position.
ii. Manual mode is normally utilized for manual control of a basin during special
circumstances only.
6.3.5.3 Equipment Data
Table 6-12 summarizes the equipment data for the airflow control system described.
Table 6-12. Airflow Control Equipment
Parameter Value
Blower Inlet Air Control Valve
Asset Tag PCV4506A
Manufacturer (existing)
Size 16 inch
Operator Electric
Aeration Air Flow Control Valves
Asset Tag FCV4113A
FCV4115A
FCV4118A
FCV4123A
FCV4125A
FCV4128A
FCV4131A
FCV4133A
FCV4134A
FCV4135A
FCV4138A
FCV4143A
FCV4145A
FCV4148A
Manufacturer Bray Valve and Controls
Description
Resilient seated butterfly valve
with electric motor operator
31-14-118/SAR/GS
Style Series 31 Lugged Style
Size 10”
Pressure Rating 175 psi
Operator AUMA SAR07.5/GS63.3
Mass Thermal Flow Meters
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Asset Tag FE4113A
FE4115A
FE4118A
FE4123A
FE4125A
FE4128A
FE4131A
FE4135A
FE4138A
FE4143A
FE4145A
FE4148A
FE4310A
FE4320A
Manufacturer Thermal Instrument Co.
Model 62-9/9500 Remote Electronics
Calibration Range FE4113A to FE4148A = 0-4,000 scfm
FE4310A = 0-5,000 scfm
FE4320A = 0-2,000 scfm
DO Meters
Asset Tag AEZ4143A1
AEZ4145A1
AEZ4148A1
Manufacturer Hach
Model LDO
Calibration Range 0-20 mg/L
6.3.5.4 Maintenance
Maintenance information provided by the manufacturers is summarized in Table 6-13. Refer to the
manufacturer’s Operations and Maintenance Manual for a more comprehensive listing of
troubleshooting and maintenance requirements
Table 6-13. Airflow Control Equipment Maintenance
Parameter Value
Airflow Control Valves
No routine maintenance is recommended by the valve manufacturer
Actuator maintenance data identical to that listed for Grit Removal, Table 4-8
Mass Thermal Flow Meters
No maintenance recommendations in manufacturer’s O&M manual
DO Meters
Clean and inspect meter every 90 days.
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6.4 Mixed Liquor Recycle Pumping
Mixed liquor is recycled from the aeration basin effluent channel back to cell 1. This internal mixed
liquor recycle (IMLR) drives the anoxic selector that is required to promote conditions that grow good
settling microorganisms (i.e. secondary sludge). A good settling sludge improves secondary clarifier
performance.
6.4.1 System Description
The mixed liquor recycle pumps recirculate mixed liquor from the aeration basin effluent channel to the
cell 1 of each aeration basin. Mixed liquor recycle pumps P4460A and P4470A are located in the mixed
liquor recycle pump vault at the south end of and adjacent to the aeration basins. Mixed liquor is drawn
from a sump in the aeration basin effluent channel through the wall by 20 inch pipes dedicated to each
pump. The two pumps pump into a common discharge pipe where a flow meter (FE4465A) measures
the IMLR flow rate. Flow is evenly split between the four aeration basins by valves located on each
branch of the main pipe. The IMLR piping system re-purposes a step feed RAS system and thus has the
capability of being fed into cells 1 – 4. The Phase 1 design, however, only requires the IMLR to be fed
into cell 1.
Controls are interfaced with the PLC in the Disinfection Storage Building. The mixed Liquor recycle
pumps have VFDs, also located in Disinfection Storage Building.
6.4.2 Design Data
The design of the IMLR system is based on flow alone. The IMLR flow requirement is based on achieving
a flow rate equal to the aeration basin influent flow (primary clarifier effluent) when adding the IMLR and
RAS flow rates together. Table 6-14 summarizes the design criteria for the IMLR pumps.
Table 6-14. IMLR Pumping Design Criteria
Parameter Value
Minimum Unit Operating Condition 3,000 gpm @ 8 ft TDH
Unit Capacity 7,500 gpm @ 27 ft TDH
6.4.3 Operation and Control
IMLR pumps P4460A and P4470A were installed in the Phase 1 expansion, but their operation is the
same as the previously installed pumps serving the same purpose. The flow rate is manually set by the
plant operator from any SCADA terminal as a percentage of plant influent flow as measured by the flow
meter FE1501A. The PLC configured PID controller adjusts pump speed to maintain set flow compared
to flow measured by recycle magnetic flow meter FE4465A. The IMLR pumps operate in a lead-lag
manner.
6.4.4 Equipment Data
The main equipment making up the IMLR system is the pumps and flow meter. Table 6-15 summarizes
attributes of each.
Table 6-15. IMLR System
Parameter Value
IMLR Pumps
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Asset Tag P4460A
P4470A
Manufacturer KSB
Model KRTK350-500/R758UNG-D
Pump Type Dry-Pit Submersible
Motor Type 758UNG
Motor Horsepower 75
Motor Speed 900 rpm
Unit Design Flow 7,500 gpm
Design Head 27 ft
Maximum Unit Flow 9,500 gpm
IMLR Magnetic Flow Meter
Asset Tag FE4465A
Manufacturer ABB WaterMaster
Model FEF121.500.K.1.S.4.A1.B.1.A.1.A.2.A.2.B.3.A.1.
M5.V3.CWC,614C220U0
Calibration Range 0-15,000 gpm
Meter Size 20 inch
6.4.5 Maintenance
Table 6-16 summarizes the manufacturer recommended maintenance for the IMLR components. Refer
to the manufacturer’s Operations and Maintenance Manual for a more comprehensive listing of
troubleshooting and maintenance requirements
Table 6-16. IMLR System Maintenance
Parameter Value
IMLR Pumps
Measure the insulation resistance
Every 4,000 hours; or at least once a year Check the power cables
Visually inspect the lifting
chain/rope
Check the sensors
Every 8,000 hours; or at least every 2 years
Check the mechanical seal
leakage
Change the lubricant and check
the coolant
Lubricate the bearings
Perform a general overhaul Every 5 years
IMLR Magnetic Flow Meter
No maintenance procedures are recommended by the manufacturer.
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6.5 Mechanical Mixing
Mechanical mixers are installed in certain locations to keep solids from settling where it is undesired. In
the Phase 1 expansion mixers were installed in the aeration basins and BAR tank. There are additional
mixers in the aeration basins installed prior to the Phase 1 expansion and are not covered in this
manual.
6.5.1 System Description
Aeration Influent Channel Mixing - Influent channel mixers MX4100A, MX4101A, MX4102A, MX4103A,
and MX4104A are staged along the length of the channel prior to where the channel constricts. The
mixers are evenly spaced along the influent channel and each has a dedicated zone of mixing.
Aeration Basin Mechanical Mixing - Submersible mechanical mixers are in place in cells 1-5, and 8-10 of
the four aeration basins. The mixers are provided in case these cells are operated with aeration air.
Mixers in cells 1 and 2 are normally on. Mixers in cell 5 (MX4115A, MX4125A, MX4135A and MX4145A)
and cell 10 (mixers MX4110A1, MX4110A2, MX4120A1, MX4120A2, MX4130A1, MX4130A2,
MX4140A1, and MX4140A2) were installed as part of the Phase 1 expansion.
BAR Tank Mechanical Mixing – The mixers in the BAR tank (MX4311A, MX4312A, MX4321A and
MX4322A) were installed as part of the Phase 1 expansion. Two mixers are installed in each BAR Tank
(4310 and 4320)
6.5.2 Design Data
Table 6-17 summarizes design criteria for the mechanical mixing systems.
Table 6-17. Mechanical Mixing Design Data
Aeration Basin
(cell 5)
Aeration Basin
(cell 10)
BAR
(1 tank)
Influent
Channel (each
zone)
Mixing Volume (gal) 149,000 249,000 315,000 67,000
Velocity Gradient (sec-1-) 75 75 75 75
Mean Velocity (ft/sec) 1.0 1.0 1.0 0.25
Quantity per area 1 2 2 1
VFD No No Yes Yes
6.5.3 Operation and Control
The BAR tank and aeration basin influent channel mixers are adjustable speed units. Selection of which
mixer should operate and at what speed is manually selected by the plant operators from any SCADA
terminal. The required mixer speed to maintain solids in suspension in these locations will be
determined by plant operating experience.
The mixers installed in the aeration basin during the Phase 1 expansion are constant speed and should
be turned on whenever the aeration air is turned off or is less than 0.12 scfm/sf.
6.5.4 Equipment Data
The equipment data for the mechanical mixers is summarized in Table 6-18.
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Table 6-18. Mechanical Mixing Equipment Data
Parameter Value
Influent Channel Mixers
Asset Tag MX4100A
MX4101A
MX4102A
MX4103A
MX4104A
Supplier Electric Pump
Manufacturer Flygt
Model No. SR4650.490-SR125805SJ
Propeller diameter 8.27 inch
Propeller speed 1,675 rpm
Motor Horsepower 2.3
Aeration Basin and BAR Mixers
Asset Tag Cell 5 MX4115A
MX4125A
MX4135A
MX4145A
Asset Tag Cell 10 MX4110A1
MX4110A2
MX4120A1
MX4120A2
MX4130A1
MX4130A2
MX4140A1
MX4140A2
Asset Tag BAR Tank MX4311A
MX4312A
MX4321A
MX4322A
Supplier Electric Pump
Manufacturer Flygt
Model No. SR4620.410-SR042113SJ
Propeller diameter 22.8 inch
Propeller speed 580 rpm
Motor Horsepower 8.3
6.5.5 Maintenance
Maintenance data provided by the manufacturer is summarized in Table 6-19. Refer to the
manufacturer’s Operations and Maintenance Manual for a more comprehensive listing of
troubleshooting and maintenance requirements
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Table 6-19. Mechanical Mixing Equipment Maintenance
Model SR4650.490-SR125805SJ
Parameter Interval
Periodical Inspection
(see manufacturer manual for details)
Up to 12,000 hours or 3 years,
whichever comes first.
Major Overhaul
(see manufacturer manual for details)
Up to 24,000 hours or 6 years,
whichever comes first.
Model SR4620.410-SR042113SJ
Periodical Inspection
(see manufacturer manual for details)
Up to 4,000 hours or 1 year, whichever
comes first.
Major Overhaul
(see manufacturer manual for details)
Up to 12,000 hours or 3 years,
whichever comes first.
6.6 RAS Box and Surface Film Classifier
The RAS box and surface film classifier are used to collect and precondition the RAS before it is returned
to the aeration basins or wasted. The system is configured to selectively waste foam causing organisms
from the surface of the RAS box. As the RAS flow leaves the RAS box as much as possible is directed to
the BAR tank when that process is operating, while the remainder of the flow enters the aeration basin
influent channel.
6.6.1 System Description
The RAS box and surface film classifier is a concrete tank adjacent to the BAR tanks. After being
collected in the secondary clarifiers RAS is pumped to the RAS box and surface film classifier by up to
nine RAS pumps. Air is bubbled into the RAS box to induce flotation of the foam causing organisms,
where they collect on or near the surface. As RAS progresses through the RAS box in plug flow fashion
the surface is skimmed and wasted via the WAS pumping system. This system serves as both a solids
wasting facility but also as a foam control measure.
Flow out of the RAS box is controlled by one weir plate and two gates;
• The fixed weir plate at the end of the tank controls the water level in the RAS box prior to
discharging into the aeration basin influent channel.
• The BAR RAS gate diverts RAS flow into the BAR HSW/RAS channel after skimming.
• The downward-opening WAS/Classifier weir gate skims RAS into the WAS sump, from which it is
pumped to the rotary drum thickeners.
The surface film classifier is simply the FRP baffle mounted towards the end of the RAS Box that skims
the surface of the RAS box. The purpose of the RAS box aeration system is to float foam causing
organisms and not transfer oxygen.
6.6.2 Design Data
The RAS box and surface film classifier was designed for Phase 2 flows because the construction is more
economical to build the built out structure during the Phase 1 expansion. The airflow rate to the RAS box
is designed to be constant to maintain mixing. Table 6-20 summarizes the design criteria for the RAS
box and surface film classifier.
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Table 6-20. RAS Box and Surface Film Classifier Design Criteria
Parameter Value
10 minute hydraulic retention time at Phase 2 (2040) average RAS flow rate
2040 average RAS flow rate 10 mgd
Tank Volume 70,000 gallons
Sidewater Depth 15.0 ft
Freeboard Depth 2.0 ft
Min/Max Airflow Requirement 0/152 scfm
6.6.3 Operation and Control
RAS Box - Air is provided to the RAS box and surface film classifier via the BAR tank aeration. The airflow
rate to the RAS box and surface film classifier should be constant. A manual valve is used to adjust the
airflow as needed for adequate mixing of the RAS flow. RAS normally overflows a fixed weir at the north
end of the tank and enters the aeration basin influent channel. In cases where it is desired to re-aerate,
de-aerate, or direct the RAS to the BAR tanks, as much of the RAS as possible may be redirected into the
BAR tanks.
RAS Surface Film Classifier and Weir Gate - The FRP baffle skimming the surface is fixed. The baffle
skims flow through a downward opening weir gate (GT4240A) into the WAS sump. The weir gate is
installed with an electrical operator and can be adjusted to achieve the desired wasting rate.
RAS Box Level Control Fixed Weir Plate - The weir plate controls the liquid level in the RAS Box. It is fixed
at elevation 648.5.
BAR RAS Gate - A downward opening gate (GT4230A) with a yolk mounted manual operator is in place
and used to control the flow of RAS into the BAR influent channel. The gate can be manually positioned
for a desired flow rate.
6.6.4 Equipment Data
The equipment making up the RAS box and surface film classifier is summarized in Table 6-21.
Table 6-21. RAS Box and Surface Film Classifier Equipment
Parameter Value
RAS Box
Length 140 ft
Width 9 ft
RAS Box Level Control Weir Plate
Asset Tag GT4200A
BAR RAS Gate
Asset Tag GT4230A
Manufacturer Whipps, Inc.
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Series 923
Size 18 inches x 30 inches
WAS/Classifier Weir Gate
Asset Tag GT4240A
Manufacturer Whipps, Inc.
Series 923
Size 18 inches x 30 inches
Actuator AUMA SA14.1-26A Electric Actuator
Air Diffusers
Number of Diffusers 152
6.6.5 Maintenance
The manufacturer’s maintenance recommendations for the RAS box and surface film classifier are
summarized in Table 6-22. Refer to the manufacturer’s Operations and Maintenance Manual for a more
comprehensive listing of troubleshooting and maintenance requirements
Table 6-22. RAS Box and Surface Film Classifier Equipment Maintenance
Gates
Equipment Maintenance Frequency Lubricants Required
Gate Visual inspection: at least every 6
months
N/A
Operating Stem Clean and grease: every 6 months,
or whenever exposed to severe
dust.
Chevron Ultra Duty
EP-2 Sunoco – Ultra Prestige 2EP
or equal
Diffuser System
See Section 6.3.4.5 for manufacturer’s recommended maintenance.
6.7 Secondary Clarification
The final step in the secondary treatment process, secondary clarification, serves to settle out the
biological floc (solids) in secondary clarifiers which produces high quality effluent that is low in BOD and
TSS.
6.7.1 System Description
The secondary clarification system includes the secondary splitter box, secondary clarifiers, RAS
collection and pumps, and scum collection and pumps. The two main purposes of this system are to:
1. Provide settling of activated sludge that yields a treated effluent meeting applicable regulatory
limits, and:
2. Control MLSS inventory in the aeration basins via control of clarifier underflow to the RAS and
WAS systems. Waste solids (WAS and scum) are routed to solids handling.
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Six clarifiers and associated RAS and scum removal systems are designed to manage projected flows
through year 2025 (Phase 1). Mixed liquor from the aeration basin effluent channel flows to the
secondary splitter box where it is distributed to the six clarifiers. Equal distribution is achieved by the
headloss induced through six individual slots that lead to pipes feeding each clarifier.
Space for a future clarifier is included in the clarifier layout. The splitter box includes a slot for a future
seventh clarifier.
Mixed liquor flow is introduced into each clarifier’s stilling well. The stilling well dissipates energy and
thereby reduces the turbulence in the mixed liquor enhancing settling. Clarifier performance is further
enhanced by a flocculation center-well (installed in Clarifiers 5300, 5400, 5500 and 5600) which
facilitates flocculation of the sludge particles, further enhancing settling. Clarified flow is discharged
over the peripheral effluent weirs.
Solids collection is constantly occurring when the clarifier is operating. A suction-style collection
mechanism rotates along the floor of the clarifiers, driven by a centrally located drive unit.
Scum is collected on the surface of the clarifier by a rotating arm that directs the scum into a hopper
that drains to collection manholes before being pumped to the digestion system.
6.7.2 Design Data
Clarifiers 5500 and 5600 and associated equipment were installed in the Phase 1 expansion. The
remaining clarifiers were constructed during prior expansions and are generally not covered in this
manual. Table 6-23 summarizes the design criteria of the secondary clarifiers and support systems
installed in the Phase 1 expansion.
Table 6-23. Secondary Clarifier System Design Data
Parameter Value
Secondary Clarifiers (5500 and 5600)
Diameter 115 ft
Maximum Allowable SLR 42 lb/d-sf at 150 mL/g SVI
Sidewater Depth 16 ft
Sludge Collection suction style rotating header
Secondary Clarifier Flow Splitter Box
Type cutthroat slotted weir flume
Number 6 flumes, 1 per secondary clarifier
Hydraulic Capacity 30 mgd
Secondary Scum Pumps
Unit Capacity 200 gpm @ 19 ft TDH
RAS Pumping
See Section 6.8.
6.7.3 Operation and Control
Secondary Clarifier Flow Splitter Box – A secondary clarifier flow Splitter box passively and evenly
distributes mixed liquor flow coming from the aeration basin effluent channel to each of the secondary
clarifiers. One cutthroat slotted weir flume is dedicated to each of the secondary clarifiers for flow
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distribution. Each flume weir also has a dedicated inlet gate, secondary flow splitter gates (GT5101A
through GT5106A), to isolate a secondary clarifier if out of service.
Secondary Clarifiers – The process control of the secondary clarifiers is discussed in Section 3. Settled
sludge is collected by each clarifier’s collector mechanism (COL 5501A and COL 5601A installed in
Phase 1 expansion). The collectors are spun by a constant speed drive equipped with a gear reducer to
achieve the desired rotational speed. Each collector drive mechanism is equipped with an overload
protection device and alarm system. The overload protection system alarms at increasing torque levels
and shuts off the drive at the high torque setpoint. A backup mechanical torque overload system is also
included.
Secondary clarifiers 5500 and 5600 are fitted with effluent isolation gates (GT5501A and GT5601A).
Similarly the RAS withdrawal pipe discharges into a pumping well and is fitted with isolation gates
(GT5502A and GT5602A).
Secondary clarifiers 5500 and 5600 are also fitted with a drainage pumping system. Secondary clarifier
drain pumps P5003A and P5004A pump into the plant’s drainage sewer.
Scum Handling - Scum is removed from the surface of each tank by a rotating scum collection
mechanism. The scum is scraped into a box where it flows by gravity to a secondary scum collection
manhole, one manhole is dedicated to secondary clarifiers 5500 and 5600 and separate one for the
other four clarifiers. Scum is pumped intermittently from these manholes to the digestion process by
secondary scum pumps P5001A and P5002A. P5001A serves clarifiers 5100, 5200, 5300 and 5400.
P5002A serves clarifiers 5500 and 5600.
The secondary clarifier scum pumps are controlled by level in the secondary scum collection manholes.
6.7.4 Equipment Data
Secondary clarifiers 5500 and 5600 were installed in the Phase 1 expansion and the details of the
related equipment are summarized in Table 6-24. The other clarifiers were constructed prior to the
Phase 1 expansion and are not covered in this manual except for the scum pumps that were replaced.
Table 6-24. Secondary Clarifiers 5500 and 5600 Equipment
Parameter Value
Clarifier Tanks and Mechanism
Size 115 ft diameter
Sidewater Depth 16 ft
Number 2
Sludge Collection Mechanism Suction-Style
Drive Motor 0.75 hp, 3 phase/60 Hz/460 V
RAS Pumps
RAS Pumping is covered in Section 6.8 of this manual.
Secondary Clarifier Scum Pumps
Asset Tag P5001A
P5002A
Quantity 3 (including 1 uninstalled spare)
Manufacturer KSB
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Model KRT F80-200/34UG
Type Submersible non-clog solids-handling
Unit Capacity 200 gpm
Total Dynamic Head 19 ft
Motor 5 hp
Motor Speed 1,750 rpm
Secondary Clarifier Drain Pumps
Asset Tag P5003A
P5004A
Quantity 3 (including 1 uninstalled spare)
Manufacturer KSB
Model KRT F80-200/34UG
Type Submersible non-clog solids-handling
Unit Capacity 350 gpm
Total Dynamic Head 15 ft
Motor 5 hp
Motor Speed 1,750 rpm
Influent Flow Splitter Gate
Asset Tag
GT5101A
GT5102A
GT5103A
GT5104A
Manufacturer Whipps, Inc.
Series 921
Size 24 inches x 42 inches
Actuator Type 102 Manual
Influent Flow Splitter Gates
Asset Tag GT5105A
GT5106A
Manufacturer Whipps, Inc.
Series 921
Size 48 inches x 42 inches
Actuator Type 102 Manual
Secondary Effluent Isolation Gates
Asset Tag GT5501A
GT5601A
Manufacturer Whipps, Inc.
Series 921
Size 72 inches x 30 inches
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Actuator Type 102 Manual
Secondary Sludge Isolation Gates
Asset Tag GT5502A
GT5602A
Manufacturer Whipps. Inc.
Series 925
Size 30 inches x 30 inches
Actuator Type 102 Manual
6.7.5 Maintenance
The manufacturer’s maintenance information for the equipment installed in the Phase 1 expansion is
summarized in Table 6-25. Refer to the manufacturer’s Operations and Maintenance Manual for a more
comprehensive listing of troubleshooting and maintenance requirements
Table 6-25. Secondary Clarifiers 5500 and 5600 Maintenance
Activity Interval
Collector Mechanisms
1. Observe the operation of the skimmer once each day as it passes over the scum box.
Correct any cause of hesitation, binding or misalignment.
2. All bolts and nuts should be kept tight and original alignments and adjustments
maintained. Inspections should be made at regular intervals.
3. Wherever possible, examine gears and all wearing parts periodically to determine
whether excessive wear is taking place.
4. Test the overload alarm at least once per week to make sure that the mechanism is
protected.
5. If the power is shut off, or if the mechanism is stopped for any reason for longer than
an hour, bypass the flow until the machine is again started.
6. Keep the machine and surroundings clean and touch up all rust spots with paint
frequently.
7. The entire mechanism above and below the waterline should be painted at least
once every two years.
Secondary Scum and Drain Pumps P5001A, P5002A, P5003A and P5004A
Insulation resistance test Every 4,000 operating hours;
at least once a year Checking the electric cables
Visual inspection of lifting equipment
Check of monitoring equipment Every 10,000 operating hours;
at least every three years Oil change
General overhaul Every five years
Gates
See Table 4-8 for gate maintenance information.
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6.8 RAS Pumping
RAS pumps are designed to return solids settled in the clarifier back to the aeration basin. These pumps
are designed to operate at variable flows in order to maintain a desirable sludge blanket in the clarifier.
Clarifier blankets (settled mixed liquor) contain microorganisms that “recycle” back to the aeration
basins maintaining the inventory of organisms in the aeration basins and treatment integrity. A portion
of the RAS is diverted as WAS in order to maintain the proper inventory of microorganisms in the
secondary system.
6.8.1 System Description
Secondary clarifiers utilize RAS pumps to recycle return sludge back to the aeration basins via the RAS
box and classifying selector process. Three dry pit RAS pumps P7121A, P7122A and P7123A located in
the Sludge Pumping Building convey RAS from secondary clarifiers 5100 and 5200. Clarifiers 5300 and
5400 are each serviced by local submersible pumps P5301A and P5401A respectively, delivering RAS to
the RAS box and classifying selector. Clarifiers 5500 and 5600 each have a pair of submersible RAS
pumps located in adjacent vaults. Pumps P5501A and P5502A service clarifier 5500, while pumps
P5601A and P5602A service clarifier 5600.
6.8.2 Design Data
The RAS pumps for clarifiers 5500 and 5600 were installed in the Phase 1 expansion and the design
criteria are summarized in Table 6-26.
Table 6-26. RAS Pumping Design Criteria
Parameter Value
Minimum Unit Operating Condition 1,500 gpm @ 22 ft TDH
Unit Capacity 3,000 gpm @ 26 ft TDH
6.8.3 Operation and Control
The RAS system operates continuously. RAS pump flow will automatically modulate based on the plant
influent flow rate, measured by Influent flow meter FE1501A. The RAS flow rate will be maintained at a
plant operator selected target flow based on a fixed percentage of the plant influent flow.
In the clarifiers with two dedicated RAS pumps (5500 and 5600), one RAS pump will normally operate.
During periods of high flow, if the pumped RAS flow rate falls below the target flow rate for more than 30
minutes the second pump will be started. The speed of the pumps is varied automatically utilizing the
variable frequency drives.
RAS Pumps P7121A, P7122A, P7123A, P5301A, and P5401A were installed prior to the Phase 1
expansion and the control of these pumps is unchanged.
See Section 3 for additional process control discussion on the RAS system.
6.8.4 Equipment Data
The RAS equipment installed during the Phase 1 expansion is summarized in Table 6-27.
Table 6-27. Clarifier 5500 and 5600 RAS Pumping Equipment
Parameter Value
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RAS Pumps
Asset Tag P5501A
P5502A
P5601A
P5602A
Quantity 5 (1 uninstalled spare)
Manufacturer KSB
Pump Type submersible solids handling
Model KRTK200-315/206UG
Unit Rated Flow 3,000 gpm
Rated Head 27 ft TDH
Motor Type 206UG
Motor Rating 24 hp
Motor Speed 1,160 rpm
Magnetic Flow Meter
Asset Tag FE5501A
FE5601A
Manufacturer ABB Watermaster
Model FEF121.450.K.1.S.4.A1.B.1.A.1.A.2.A.2.B.3.A.1.
M5.V3.CWC,614C220U01
Calibration Range 0-5,500 gpm
Meter Size 18 inch
6.8.5 Maintenance
The manufacturer’s maintenance data for the RAS pumps installed in the Phase 1 expansion is
summarized in Table 6-28. Refer to the manufacturer’s Operations and Maintenance Manual for a more
comprehensive listing of troubleshooting and maintenance requirements
Table 6-28. RAS Pumping Maintenance
Activity Interval
RAS Pumps
Measure the insulation resistance
Every 4,000 operating hours Check the power cables
Visually inspect the lifting chain/rope
Check the sensors
Every 10,000 operating hours Check the mechanical seal leakage
Change the lubricant
Lubricate the bearings
Perform a general overhaul Every 5 years
Flow Meters
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No maintenance practices are referenced in the manufacturer’s manual.
6.9 WAS Pumping
WAS is taken from the RAS box classifying selector to manage the amount of solids in the secondary
treatment process. This process maintains the SRT which in turn maintains stable secondary treatment.
The WAS system at South WWTP is designed to control foam causing organisms by preferentially wasting
them by skimming the surface of RAS box classifying selector. This innovation manages the design SVI
to a lower level, thus requiring fewer secondary clarifiers.
6.9.1 System Description
The WAS pumping system consists of submersible pumps P4410A, P4420A, P4430A that are installed
in a sump adjacent to the RAS box classifying selector. Flow is skimmed in the RAS box classifying
selector over a downward opening weir gate (GT4240A) into the WAS sump. The WAS pumps convey
flow to the rotary drum thickeners and is measured by flow meters FE4410A, FE4420A, and FE4430A.
6.9.2 Design Data
The design of the WAS pumping system revolves around the capacity of the pumps. Table 6-29 lists the
design criteria for the system.
Table 6-29. WAS Pump Design Data
Parameter Value
Minimum Unit Operating Condition 200 gpm @ 28 ft TDH
Unit Capacity 350 gpm @ 30 ft TDH
6.9.3 Operation and Control
Weir gate GT4240A is provided with a modulating electric actuator to control the flow rate and level in
the WAS sump. Level in the WAS sump is measured by a submersible pressure transducer. A level set
point can be input at any SCADA terminal to automatically control gate position.
Each WAS pump (P4410A, P4420A and P4430A) is associated with a specific rotary drum thickener
(THK9103A, THK9102A, and THK9101A, respectively).
The WAS Pumps have adjustable speed drives. A flow meter is located downstream of each pump to
monitor the flow to the respective rotary drum thickener. The maximum flow rate to each rotary drum
thickener can be set from any SCADA terminal. WAS pump speed is automatically controlled to achieve
the desired flow rate. The upper limit is set to 350 gpm, which is the maximum capacity of the rotary
drum thickeners.
A software interlock is established within the PLC to disable manual starting of WAS Pumps from SCADA
system unless the corresponding rotary drum thickener is operating and its WAS isolation valve is proven
open.
Low-low level float LSLL-L4400A provides a software interlock to stop operation of WAS Pumps P4410A
and P44420A on detection of low-low level. Low-low level float LSLL-L4401A provides a software
interlock to stop operation of WAS Pumps P4430A and is installed at a lower elevation compared to the
other switch. Pump P4430A is installed at a lower elevation than the other two pumps such that it can
be used to periodically empty the sump and remove any foam trapped at the surface. The automatic
cleaning pump down mode interval is set by the plant operators. This interval can be set from any
SCADA terminal in hours to be initialized after any WAS pumps have been operating. The cleaning pump
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down mode is disabled if pump P4430A is not operating. It is essential that pump P4430A be available
to pump down the lower portion of the wet well pumping station. At start of pump down cleaning cycle
the weir gate GT4240A will automatically close and WAS pump station PLC level controller is disabled.
Pumps P4410A and P4420A stop at their low-low level switch control. If previously running, P4430A will
continue to operate down to its corresponding low-low level elevation. The spray water will continue to
operate throughout pump down cycle. Once the cleaning pump down cycle has been completed weir
gate GT4240A will reopen, and the previously operating WAS pump(s) will start at the set level.
6.9.4 Equipment Data
Table 6-30 summarizes the equipment data of the WAS pumps and flow meters.
Table 6-30. WAS Pumping
Parameter Value
Asset Tag P4410A
P4420A
P4430A
Manufacturer KSB
Model Model KRT E80-200/34UG
Motor hp 5.0
Speed rpm 1,750
Magnetic Flow Meters
Asset Tag FE4410A
FE4420A
FE4430A
Manufacturer ABB WaterMaster
Model FEV125.150.V.1.S.4.A1.B.1.A.1.A.2.P.2.B.3.A.1.
M5.V3.CWC,614C220U01
Range of Flow 0-400 gpm
Meter Size 6 inches
6.9.5 Maintenance
Table 6-31 summarizes the manufacturer’s maintenance data for the WAS system. . Refer to the
manufacturer’s Operations and Maintenance Manual for a more comprehensive listing of
troubleshooting and maintenance requirements
Table 6-31. WAS Pumping Maintenance
Activity Interval
WAS Pumps
Measure the insulation resistance Every 4,000 operating hours;
at least once per year Check the electrical cables
Visually inspect the lifting chain/rope
Check the monitoring equipment
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Check the mechanical seal leakage Every 10,000 operating hours; at least
every three years Change the lubricant
Lubricate the bearings
Perform a general overhaul Every 5 years
The pump/motor shaft is supplied with grease-lubricated for life ball bearings. They
require no maintenance.
Flow Meters
No maintenance practices are referenced in the manufacturer’s manual.
6.10 BAR Reactor (Tanks)
The BAR process is used to treat the HSW with its high ammonia concentration, prior to its introduction
into the aeration basins. The BAR process is designed to remove the ammonia at a high rate. This
process also provides a source of nitrifying bacteria for the mainstream MLE process, preventing loss of
nitrification during cold weather periods. The BAR process tanks can also be operated as a RAS aeration
or de-aeration tanks to optimize the performance of the selector at the head of the aeration basins.
The nitrification process in the BAR tanks consumes alkalinity, and can require supplemental alkalinity
addition to prevent pH suppression which can limit nitrification. Suppressed nitrification may be
acceptable during warm weather conditions when main liquid stream (MLE) nitrification rates are high,
but during cold weather conditions alkalinity addition may be required.
Aeration is used in the BAR tanks to control DO at 2.0 mg/L to drive nitrification. When operations do
not require aeration, mechanical mixers are used to keep the solids in suspension.
Figure 6-5 depicts the BAR system.
Figure 6-5. BAR Reactor Schematic.
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6.10.1 System Description
The BAR system consists of two 300,000 gallon tanks (BAR tank 4320 is pictured in Figure 6-6). The
two BAR tanks are separated by a wall with gates that allow independent operation. Each tank is
capable of operating independently providing 100% redundancy.
Figure 6-6. BAR Reactor 4320.
HSW and RAS flow into the BAR RAS channel and on into the BAR tanks through a series of gates. HSW
flow is controlled by a motorized throttling valve FCV1801A. RAS flow is controlled by BAR RAS gate
GT4230A. The HSW can be fed to the head of either BAR tank. Isolation gates are installed at the head
of each tank (GT4310A and GT4320A). The HSW step feed weir gate GT4331A allows flow from the BAR
RAS channel about midway into BAR tank 4310.
The BAR tanks can function independently or together as one tank. Manual isolation gates GT4311A
and GT4312A can be used to separate tanks 1 and 2, respectively.
Both tanks are aerated with 9 inch membrane diffusers. Each BAR tank has one air control point. Flow
control valve FCV4310A controls aeration of tank 4310 and FCV4320A controls aeration of tank 4320.
BAR Effluent Flow can be directed to the aeration basins in multiple ways. Isolation gates GT4321A and
GT4322A at the south end of BAR Tank 4320 can be opened allowing effluent flow into the BAR effluent
channel. Once in the BAR effluent channel flow can: 1) gravity feed to the head of the aeration basin
influent channel, or 2) be directed to the telescoping valve sump by opening manual Gate GT4323A. In
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this sump four telescoping valves (TV4303A, TV4304A, TV4305A, and TV4306A) that allow feed to cell 5
of each aeration basin.
The BAR tanks are equipped to run in parallel or with one out of service. BAR Tank 4310 is fitted with
telescoping valve TV4301A which when opened allows BAR effluent from 4310 to flow directly to the
telescoping valve sump where it can either be distributed to cell 5 of the aeration basins or flow into the
BAR effluent channel through gate GT4323A and on to the head of the aeration basins. Similarly, BAR
tank 4320 has telescoping valve TV4302A which when opened directs BAR effluent from 4320 to the
telescoping valve sump. This flexibility may be important if nutrient removal strategies are employed in
the future, however the Phase 1 design is to direct all BAR effluent to the head of the aeration basins.
A permanent caustic addition system was not installed as a part of the Phase 1 expansion since it will
not likely be required for some time. In the meantime, alkalinity can be supplied by the RAS.
Four mechanical mixers, two in each BAR tank, are equipped with adjustable speed drives so that the
mixing can be optimized.
6.10.2 Design Data
The BAR system is designed to treat the projected 2040 (Phase 2) ammonia laden HSW stream. The
system was designed for Phase 2 since the construction was more economical in the Phase 1
expansion, 100% redundancy is provided during Phase 1, and the tankage is constructed for conversion
to a fifth aeration train if the treatment objectives are different in the future.
Overall, the general design of the BAR system allows the mainstream MLE SRT to be reduced to 5 days
from 7 days and still maintain nitrification.
6.10.3 Operation and Control
A more detailed process control strategy is discussed in Section 3.
BAR Aeration Control - The BAR reactor can be operated in two modes:
1. BAR or RAS Re-aeration Mode: One control valve, airflow meter, and DO probe will be used to
maintain an operator-adjustable DO set-point in the BAR tank. The BAR mixers will not operate in
this mode.
2. RAS De-aeration Mode: In RAS de-aeration mode the aeration control valves will be fully closed and
the BAR mixers will operate continuously.
Air flow into the BAR Tanks is controlled by airflow control valves FCV4310A and FCV4320A with
modulating electric actuators. The valve can be manually positioned from any SCADA terminal to control
airflow measured by mass thermal flow meters FE4310A and FE4320A. Aeration is used in the BAR
tanks to control DO at 2.0 mg/L (or other setpoint).
Mechanical Mixing - Mixers MX4311A, MX4312A, MX4321 and MX4322A are equipped with adjustable
speed drives. Mixers are off when the BAR tanks are in nitrification or RAS re-aeration mode and on
when in de-aeration mode. Selection of which mixer shall operate and at what speed can be manually
selected by plant operators from any SCADA terminal.
6.10.4 Equipment Data
Table 6-32 summarizes the equipment data for the BAR system or references where it can be found.
Table 6-32. BAR Reactor Equipment Data
Parameter Value
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Bar Tanks
Volume, each tank 300,000 gal
Telescoping Valves
Manufacturer Latanick Equipment, Inc.
Type WATT Telescoping Manually Operated
Ring Stem Design
Quantity 2 each, 24 inch 4 each, 4 inch
Asset Tag
TV4301A
TV4302A
TV4303A
TV4304A
TV4305A
TV4306A
BAR RAS Channel Flow Meter
Asset Tag FE4230A
See Table 4-5 Flow Measurement Equipment Data for details.
Flow Control Valves
Asset Tag FCV4310A
FCV4320A
Manufacturer Bray Valve and Controls
Description
Resilient Seated Butterfly Valve
with Electric Motor Operator
31-14-118/SAR/GS
Style Series 31 Lugged Style
Size 14 inch
Pressure Rating 175 psi
Operator AUMA SAR07.5/GS80.3 (FCV4310A)
AUMA SAR07.5/GS63.3 (FCV4320A)
Airflow Meters
Asset Tag FE4310A
FE4320A
See Table 6-12 Airflow Control Equipment for details.
BAR RAS Gate
Asset Tag GT4230A
Manufacturer Whipps, Inc.
Size 18 inch x 30 inch
Actuator Type 102 Manual
BAR Tank 4310 Isolation Gates
Asset Tag GT4311A
GT4312A
Manufacturer Whipps, Inc.
Model Series 923
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Size 48 inch x 30 inch
Actuator Type 102 Manual
BAR Tank 4320 Isolation Gates
Asset Tag GT4321A
GT4322A
Manufacturer Whipps, Inc.
Model Series 923
Size 48 inch x 30 inch
Actuator Type 102 Manual
HSW Step Feed Weir Gate
Asset Tag GT4331A
Manufacturer Whipps, Inc.
Model Series 921
Size 18 inch x 24 inch
Actuator Type 102 Manual
Telescoping Sump Stop Gate
Asset Tag GT4323A
Manufacturer Whipps, Inc.
Model Series 523
Size 24 inch x 48 inch
Actuator hand operated
Mechanical Mixers
Asset Tag
MX4311A
MX4312A
MX4321A
MX4322A
See Table 6-18 Mechanical Mixing Equipment Data for details.
Aeration Diffusers
Airflow 2,400 scfm each tank
Number 1,455 each tank
Type flexible membrane
Size 9 inch diameter
6.10.5 Maintenance
Table 6-33 summarizes the manufacturer’s maintenance data for the WAS system. Refer to the
manufacturer’s Operations and Maintenance Manual for a more comprehensive listing of
troubleshooting and maintenance requirements.
Table 6-33. BAR Reactor Equipment Maintenance
Parameter Value
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Telescoping Valves
No maintenance practices listed in manufacturer’s manual
Airflow Control Valves
See Table 6-12 details.
Airflow Meters
See Table 6-12 details.
Gates
Grease operator Every 6 months Clean and grease operating stem
Mechanical Mixers
See Table 6-19 details.
Aeration Diffusers
See Table 6-10 details.
6.11 High Strength Flow Equalization
The filtrate from dewatering and/or decant from the digestion process has a very high ammonia
concentration and is referred to as “high strength waste” (HSW). The ammonia in the HSW is high
enough that could result in ammonia breakthrough if it is discharged to the main liquid process stream
as it is produced. Equalization of the HSW controls the rate at which it is introduced to the main liquid
process.
6.11.1 System Description
The high strength flow equalization tank is a glass lined, bolted steel tank. Flow is pumped into the tank
from the adjacent high strength flow pumping station. Flow out of the tank is by gravity and is controlled
by a throttling valve and measured by a flow meter.
Equalized HSW is routed to the BAR Reactor for treatment prior to introduction into the aeration basins
or into the aeration basin influent channel.
The tank was constructed prior to the Phase 1 expansion, however it required expansion to meet the
projected flows.
6.11.2 Design Data
The HSW equalization tank is required to equalize 253,000 gpd (5 days per week, maximum month
basis) for the Phase 1 design. The existing tank was only 310,000 gallons, so as to equalize the flow to
a constant discharge rate an additional 90,000 gallons was required. The tank was designed to
accommodate two additional rings accounting for approximately 100,000 gallons per ring. Both rings
were installed in the Phase 1 expansion to provide the most operational flexibility.
6.11.3 Operation and Control
The HSW equalization tank outlet control valve FCV1801A modulates to maintain a constant flow rate to
the BAR process or aeration basin influent channel. HSW will be accumulated throughout the week so
that a constant flow can be maintained through the week and weekend. The discharge flow rate will be
increased or decreased to target a desired level in the tank, depending on the day of the week. Due to
hydraulics, three to four feet of HSW will remain at the bottom of the equalization tank unless plant staff
choose to empty the residual volume to the head of the plant.
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The formation of ice in the tank can result in damage to the tank. The mixers are kept on to reduce ice
formation.
If the HSW equalization tank is offline, HSW pumping station discharge isolation valve FV1811A can be
closed and HSW Pumping Station discharge isolation valve FV1812A can be opened to divert flow to the
Influent Flow Equalization Basin.
The HSW pumping station has an overflow pipe that diverts flow to the drain system and back to the
head of the plant if the level reaches an elevation of roughly 633.8.
6.11.4 Equipment Data
The only changes to the HSW equalization system in the Phase 1 expansion were expanding the
equalization tank. Two additional rings were installed bringing the total volume to 500,000 gallons. The
tank stands just over 24 ft tall and is 62 ft in diameter.
6.11.5 Maintenance
Periodic maintenance is required to keep the tank in proper operating condition, summarized in Table 6-
34. Refer to the manufacturer’s Operations and Maintenance Manual for a more comprehensive listing
of troubleshooting and maintenance requirements
Table 6-34. HSW Tank Maintenance
HSW Tank
Component Activity Frequency
Tank Exterior Inspect Annually
Tank Interior
Inspect 5 Years
Drain and Clean (hot water, cleaning
additives, and high pressure water
are not recommended)
Annually
Interior Glass Coating Visual Inspection Annually
Ladder and Platform Visual Inspection Each Use
Tank Roof Vent Screen Clean Annually
Overflow Pipe Inspect & Clean Regularly
Cathodic Protection
System
Contact Authorized Aquastore Tank
Dealer
Contact Authorized
Aquastore Tank Dealer
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Section 7 Effluent Treatment
Effluent treatment at the South WWTP includes UV disinfection, effluent water reuse (plant uses and
irrigation water for nearby soccer fields), and plant water chlorination facilities. Each of those areas is
discussed in this section.
7.1 Ultraviolet (UV) Disinfection
UV disinfection is a physical process that transfers electromagnetic energy from a mercury arc lamp to
an organism’s genetic material resulting in the destruction of the organism or preventing it from
reproducing. UV disinfection is commonly employed in the wastewater industry due to economics, ease
of operation and maintenance and lack of residual by-products that chemical disinfection systems
create.
In the UV-C light spectrum the wavelength 254 nm has been proven to be the most efficient to inactivate
microorganisms by damaging the nucleic acids (DNA and RNA), which disrupts the organism’s ability to
reproduce.
In normal applications, UV has the advantage that no chemicals are added to the water being treated
and that no disinfection by-products are formed. Due to the small foot print, the UV equipment can be
easily integrated into most existing water treatment plants.
UV light at a wavelength of 253.7 nm can severely damage eyes and skin if proper safety precautions
are not taken. Even very brief exposure to the eyes will cause arc eye, which is extremely uncomfortable
and upon repeated exposure may cause permanent damage. More information concerning UV hazards
and effective protective safety procedures are in the manufacturer’s O&M manual. Figure 7-1 shows a
typical configuration and components of a UV installation.
Eye
Shield
Crane
UV Main
Control Panel
Power
Supply Unit
Aquaray 3X
Module
Cleaning
Tank
Cable
Tray
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Figure 7-1. Typical UV Disinfection System Layout.
7.1.1 System Description
The UV disinfection system consists of two channels of UV equipment, a chemical cleaning tank, bypass
channel for additional hydraulic capacity, and aeration diffuser grids. Figure 7-2 pictures the installment
at the South WWTP.
Figure 7-2. South WWTP UV Disinfection System.
The UV system at the South WWTP consists of four UV modules per channel, each containing 36 lamps.
The modules are arranged with two side by side and then another pair just downstream. Each pair of
modules is considered a bank. Figure 7-3 is a schematic of a typical module.
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Figure 7-3. Typical UV Module (Ozonia).
The system incorporates a dose pacing scheme, where automatic control of the UV lamps will respond to
changes in plant flow. This feature can be disabled allowing manual control of the number of half-banks
activated along with their power (dim) level.
The low pressure high output (LP-HO) amalgam lamps are powered by electronic ballasts to generate
germicidal wavelengths of the UV spectrum (254 nm). The lamps are inserted in quartz sleeves and
isolated from the wastewater while delivering the required effluent inactivation energy. UV sensors are
installed to monitor the UV intensity from the lamps and guarantee that the proper intensity is delivered.
The effectiveness of the UV system depends on the intensity of the light and the time in contact with the
organism. Any condition that reduces either the intensity of the light or the contact time will decrease
system performance. Factors that can affect disinfection performance include flow rate, UV
transmission (measured as percent of UV light not absorbed after passing through 1 cm of water), the
amount of suspended solids in the flow, fouling (coating) of the quartz sleeves, and reduced output from
the UV lamps due to aging.
The PLC located in the UV main control panel (UMCP), utilizes the flow meter (FE6500A) and UV
transmission (UVT) instrument outputs to determine the number of lamp modules and lamps in service
and then calculate the proper lamp brightness needed to effectively deactivate the microorganisms. An
ultrasonic level sensor is used to position the downstream motorized weir gates (GT6505A in the east
channel and GT6504A in the west) to maintain the proper level (between 63 and 69 inches from the
channel floor) in the channel; enough to submerge the lamps but not high enough to overflow the
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modules or channel. If the lamps are not submerged properly the lamp life is significantly reduced due
to corrosion and baked on deposits. If the water level in the channel is too high, untreated effluent could
pass through the channel.
The UV system is powered through the manufacturer supplied power supply unit (PSU). The voltage to
the PSU is reduced by stepdown transformers. From the PSU the power is distributed to individual lamps
by the lamp power distribution centers (LPDCs). Each LPDC power half of the lamps in a module (18).
Each UV channel is provided with influent and discharge isolation gates for taking a channel out of
service (GT6503A and GT6508A for the east channel and GT6501A and GT6506A for the west channel).
Similarly, the UV bypass channel has influent and discharge isolation gates (GT6502A and GT6507A).
The two UV channels are also provided with perforated gates (GT6511A in the east channel and
GT6510A in the west) at the influent to provide adequate headloss for good distribution between the two
channels. In the channel conveying the combined flow from the UV and UV bypass channels there is a
sluice gate (GT6509A) that connects to the effluent water storage tank.
Each UV channel and bypass channel have an aeration diffuser grid located downstream of UV modules
that can provide additional oxygen to the final effluent in the event that DO levels have fallen below
permissible level (5.0 mg/L from April through November and 2.8 mg/L the rest of the year).
7.1.2 Design Data
Table 7-1. UV System Design Requirements
Parameter Value
System Hydraulic Capacity 30 mgd
Head Loss 3.5 inches
Influent Source unfiltered secondary effluent
Average monthly BOD 20 mg/L
Average monthly TSS 30 mg/L
Average weekly TSS 45 mg/L
Design peak hourly flow 30 mgd
Wastewater temperature Min=7 0C, Max=25 0C
UV Transmittance
at 253.7 nm
>60 %
Performance 126 col/100 mL (E-coli, 30 day average)
7.1.3 Operation and Control
Disinfection is required between March 15 and November 15. The disinfection system must be
operating whenever wastewater is flowing through the channel during this time period. Any interruption
of operation will result in loss of disinfection performance.
The UV disinfection system is a packaged system provided with a PLC and HMI display. The system is
stand alone and used to control intensity of UV lamps. PLC I/O points are transferred to the plant SCADA
system for remote monitoring. Control is limited to the UV system HMI.
Flow meter FE6500A is used to regulate UV lamp intensity.
Discharge weir gates GT6502A and GT6505A are automatically positioned by the UV PLC to maintain a
fixed water level above the UV lamps.
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7.1.3.1 Auto Pace (Normal)
Normally, the UV system should be operated with all channels set to auto pace, which will maintain the
appropriate number of lamps and dim levels necessary to fully disinfect on fluctuating flow rates and
water UV transmittances.
The system can also be operated in manual or non-auto pace mode at the channel or module level. For
instance, a channel can be set in auto pace mode while a bank of modules is set to operate in manual.
If a part of the system is set to manual it may be necessary to manually increase the number of lamps on
in the other portions of the system to achieve the required UV dose.
7.1.3.2 Manual Operation
During periodic maintenance and troubleshooting it may be necessary to remove operating modules
from service. Before disconnecting and removing the modules ensure that their operation has been
switched to manual off for the system to automatically compensate and maintain proper disinfection.
Each time a module or a bank is switched to manual off for servicing the system automatically turns on
additional rows of lamps to compensate for the loss of UV energy. To restore dose pacing the only switch
the modules back to auto if the channel is already set to auto pace.
Do not exceed four on/off cycles per 24 hour period for the same lamps or equipment damage could
occur.
Tables 7-2 and 7-3 summarize the manual operation of the system.
Table 7-2. Operate Individual Modules from Module Screen
Selection Function
Select Manual
On
• LPDCs in the corresponding modules energize and all lamps go
to full output.
• A module set to MANUAL ON within a channel that is set to AUTO
PACE will not contribute to the dose pacing calculation.
• For channels having multiple modules across, all modules of a
bank should be set to AUTO for the bank to contribute to the
dose pacing.
• If a channel is set to AUTO PACE and one module of a bank is set
to MANUAL ON all the other modules within the bank switch
from AUTO to MANUAL ON automatically.
Select Manual
Off
• Corresponding module lamps turn off and the LPDCs de-energize.
• If a channel is set to AUTO PACE and one module of a bank is set
to MANUAL OFF all the other modules within the bank switch to
MANUAL OFF automatically.
Select Manual
Dim
• Works only when the module is in MANUAL ON mode.
• The selection opens a sub-screen where the user can type
individual lamp current setpoints between 2.8 and 4.5 amps for
each row. Typing in 0.0 amps will result in the corresponding row
to turn off.
Select Auto • Links the module operation to that of the channel.
• A module set to AUTO will not dose pace unless the channel is
set to AUTO PACE.
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Table 7-3. Operate all Modules per Channel from Channel Screen
Selection Function
All Manual
On
• LPDCs in the corresponding modules energize and all lamps go
to full output.
• A module set to MANUAL ON within a channel that is set to
AUTO PACE will not contribute to the dose pacing calculation.
All Manual
Off
• Corresponding module lamps turn off and the LPDCs de-
energize.
All Auto • Links the module operation to that of the channel.
• A module set to AUTO will not dose pace unless the channel is
set to AUTO PACE.
7.1.3.3 Cold Weather Operation
When the disinfection system is operated in sub-freezing ambient temperatures, care must be taken to
prevent damage to the quartz sleeves and UV lamps from snow and ice accumulation in the channels.
With effluent is flowing, the system is capable of operating at ambient temperatures well below the
freezing point. See Manufacturer O&M manual for more details about cold weather operation.
7.1.3.4 System Shutdown Procedures
Normal Shutdown– Before shutting down the UV disinfection equipment, stop the flow of wastewater
through the channel to prevent untreated release. At the HMI, switch each channel to non-auto pace
and select “all manual off”. At this point, all lamps in the channel should switch off and the LPDC
contactors should audibly disengage inside the PSU panels. Keep the PSU and UMCP panels powered.
Ensure that there are no broken quartz sleeves that could damage modules by allowing water to enter
the top enclosure.
Short Duration Shutdown – For shutdown periods lasting one day to one week, stop the flow, switch
each channel to non-auto pace and select “all manual off”. Wait for all LPDC contactors to audibly
disengage inside the PSU panels and turn off the main disconnect. Open the PSU panel door and switch
off all internal breakers with the exception of the breaker that supplies the panel heater. Close the PSU
door and switch on the main disconnect to keep the panel heater operating. This will help to prevent
condensation from forming inside the panel. Also, keep the UMCP panel powered. During normal
operation the temperature setpoint for the PSU panel heater should be 50 °F. However, for shutdown
periods the temperature setpoint should be raised to 70 °F.
To restore power to the PSU switch off the main disconnect, open the panel door and switch on all the
breakers inside. Drop the temperature setpoint of the internal heater to 50 °F. Close the panel door and
switch on the main disconnect. Once power to the PSU panels is restored the UV system will remain off
with all LPDCs de-energized. All channels will be in non-auto pace and all modules in manual off waiting
for further action at the HMI.
It is important to switch all modules to manual off before de-energizing power to the PSU panels;
otherwise the system auto-restore function may interfere during system restart operations.
Long Duration Shutdown - For shutdown periods lasting more than one week, turn off the system as
described above for short duration shutdowns. The panel heaters should remain operational at a
temperature set point of 70 °F to prevent condensation. Power should be de-energized to all panels
including the UMCP. Note that the battery life of the PLC inside the UMCP is only six months without
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power. Additionally, silica gel-based desiccant should be placed inside the control panels and in each
module top enclosure. Desiccant must be replaced at minimum every three months. Drain the channel
to prevent possible septic conditions and freezing during winter conditions. Verify that all ancillary
equipment is adequately lubricated and preserved during the extended shutdown condition. When
placing equipment back into service, inspect the modules for damage (especially broken sleeves) and
ensure that all cable connections are securely mated.
It is important to switch all modules to manual off before de-energizing power to the PSU panels
otherwise the system auto-restore function may interfere during the system restart operations. Once
power is restored the UV system will remain off with all LPDCs de-energized. All channels will be in non-
auto pace and all modules in manual off waiting for further action at the HMI.
Emergency Shutdown - Turn off the main disconnect of all PSU panels to completely shut down the
Disinfection System. Note that this will cause all modules to be turned off, therefore the effluent
wastewater stream will not be disinfected. If the shutdown lasts more than one week, refer to the long
duration shutdown procedure.
7.1.3.5 Loss of Electrical Power
Total Loss - If “restart last state” was enabled and the UMCP PLC battery is charged, the UV system will
automatically recover previous operating conditions once power is restored. This auto-restore feature
works whether the channels were set in auto pace or non-auto pace or whether individual modules were
set in manual on or dim. If “restart last state” was disabled the UV system will remain off with all LPDCs
de-energized. All channels will be in non-auto pace and all modules in manual off waiting for further
action at the HMI.
Partial Loss - If one or several PSUs lose power but the UMCP remains energized and if “restart last
state” is enabled with the UMCP SLC 5/05 PLC battery charged the UMCP will automatically restore the
disabled modules back to their previous operating conditions as soon as power to the PSU is restored. If
the “restart last state” is disabled or the PLC battery discharged the disabled modules will remain off
with all LPDCs de-energized. The corresponding channels will be in non-auto pace and modules in
manual off waiting for further action at the HMI. If the UMCP loses power while the PSU panels remain
energized, the operating status of all active modules in the process will remain un-changed for the
duration of the UMCP power loss. Essentially, the dose pacing function is disabled. If the “restart last
state” is enabled and the PLC battery charged, the system will recover previous operation without any
disturbance once power to the UMCP is restored. Conversely, if the “restart last state” is disabled or the
PLC battery discharged all lamps and all LPDCs will switch off once power to the UMCP is restored. All
channels will be in non-auto pace and all modules in manual off waiting for further action at the HMI.
7.1.3.6 Full On
Ensure that all PSU panel main disconnects are turned on. Set all modules to manual on from the
channel screens at the HMI. At this point all lamps of the UV system will turn on to full output.
7.1.4 Equipment Data
Table 7-4 summarizes the equipment provided with the UV packaged system and the ancillary
components required for the system operation.
Table 7-4. UV Disinfection Equipment List
Parameter Value
UV Equipment
Asset Tag UVM6501A
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UVM6502A
UVM6503A
UVM6504A
Manufacturer Ozonia North America
Model AQUARAY® 3X VLS
Quantity 8 with 36 lamps each
Level Switch 4 total (1 high and 1 low per channel), float type, Cornery
2900
Level Sensor 2 total (1 per channel) ultrasonic, transducer Siemens XRS-5
Echomax and transmitter Siemens HydroRanger 200
UV Intensity Sensor 4 total (1 per bank)
UV Transmittance Analyzer 1 HACH UVAS sc Probe, 5 mm with SC200 digital controller
PSU 2 (1 per channel)
UMCP 1
Transformers 2 (1 per channel), 460Delta-
230Y/133VAC/3Phase/60Hz/118KVA
Cleaning Tank 1 stainless steel (316), 785 gallon
UV Channel Influent Isolation Slide Gates
Asset Tag GT6501A
GT6503A
Manufacturer Whipps, Inc.
Series 921
Size 60 inch x 78 inch
Actuator Type 102 Manual (non-rising)
Perforated Flow Distribution Slide Gates
Asset Tag GT6510A
GT6511A
Manufacturer Whipps, Inc.
Series 501
Size 60 inch x 102inch
Actuator lifting holes
Level Control Weir Gates
Asset Tag GT6504A
GT6505A
Manufacturer Whipps, Inc.
Series 923
Size 60 inch x 70 inch
Actuator AUMA SA14.1-26 Electric
UV Channel Discharge Isolation Slide Gates
Asset Tag GT6506A
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GT6508A
Manufacturer Whipps, Inc.
Series 921
Size 60 inch x 32 inch
Actuator Type 102 Manual (non-rising)
Bypass Channel Influent Isolation Slide Gate
Asset Tag GT6502A
Manufacturer Whipps, Inc.
Series 921
Size 60 inch x 132 inch
Actuator EXEECO 185 Manual Gear Box (non-rising)
Bypass Channel Discharge Isolation Slide Gates
Asset Tag GT6507A
Manufacturer Whipps, Inc.
Series 921
Size 60 inch x 110 inch
Actuator Type 102 Manual (non-rising)
Effluent Water Sluice Gate
Asset Tag GT6509A
Manufacturer Whipps, Inc.
Series 925
Size 36 inch x 36 inch
Actuator Type 102 Manual
7.1.5 Maintenance
During periodic maintenance and troubleshooting it may be necessary to remove operating modules
from service. Reference the previously described shutdown instructions in Section 7.1.3.4.
Table 7-5 summarizes the manufacturer’s recommended maintenance. For more details on the UV
system maintenance refer to the manufacturer’s O&M manual.
Table 7-5. UV System Maintenance Schedule
Frequency Description
Daily
Check HMI for operating conditions and alarms. Address any alarm
conditions, ensure that any factors contributing to alarm conditions are
addressed (for instance, a broken quartz sleeve can cause a lamp to fail).
Check that the channel effluent water height is between 63 and 69
inches from the channel floor.
Visually inspect the modules for any abnormal conditions.
Run in channel air scour at least once per day for 30 minutes.
Check for proper operation of the PSU air conditioning units.
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Weekly
Check channel for build up of solids or algae, clean as required.
Cleaning of upstream equipment (such as clarifiers) can send large
clumps of algae to the UV channels. Take care to keep such debris out
of the UV channels. Large mats of algae can affect head loss through
the channel by blocking the flow of water, and can lead to broken
sleeves if the mat is large enough.
Monthly
Chemically clean the UV modules in the cleaning station (if necessary).
While removing the modules from the channel, inspect the sleeves for
breakage.
Open module lids and inspect the interior for abnormal conditions. Pay
attention to the lamp connectors. Ensure that the gasket on the
underneath of the lid is in good condition and that all latches are pulled
tight. Inspect condition of the cable connections to the module.
Verify lamp operating hours. Lamps will continue to operate after their
disinfection effectiveness has decreased to below the design level.
Lamps which have been in operation for more than 12,000 hours
(approximately 1.5 years) should be replaced. It is a good practice to
change all lamps in a UV module at the same time.
Gates – Manual Operator
Grease operator
Every 6 months Clean and grease
operating stem
Gates – Electric Operator
Clean and grease
operating stem Every 6 months
Test Run Every 6 months
Fastener Tightness 6 months after commissioning, every year thereafter
Grease Gear
Housing Every 6-8 years
7.1.5.1 Module Removal and Installation
The UV modules should be moved only with the lifting equipment supplied with the UV system. Two
people are required to move modules, one to operate the hoist and one to steady and position the
module. Before removing a module or bank from operation, ensure that additional rows of lamps are
turned on to compensate for the module or bank being serviced.
Refer to the manufacturer’s O&M manual for more detailed module removal and installations
procedures.
7.1.5.2 Lamp Maintenance
A UV lamp can be out as a result of a failed lamp and failed or overheated ballast card. If a lamp is out
refer to the troubleshooting procedures detailed in Module System Operating Instructions, Section 10.0
of the manufacturer’s O&M manual.
The replacement of the UV lamps can be done without removal of the submerged UV modules from the
channel. To replace a lamp refer to the instructions in Module System Operating Instructions Section
11.0, System Parts Replacement, in the manufacturer’s O&M manual.
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Other periodic maintenance activities such as replacement of quartz sleeves and wiper ring assemblies
require removing the module from the channel.
7.1.5.3 System Cleaning
Cleaning of quartz sleeves is essential for the efficient and effective operation of the disinfection system.
There are three methods commonly used to clean quartz sleeves as follows.
1. Repetitive mechanical wiping/cleaning of the sleeves with or without the use of an in-channel air
scour.
2. Manual hand scrub using SCOTCH-BRITETM pads and an ammonia based detergent.
3. Soaking of the module or bank inside the chemical cleaning station.
Each of these cleaning methods involves various equipment; such as a module integral mechanical
wiping/cleaning system, an in-channel air scour and a chemical cleaning station. Details on each
cleaning procedure can be found in the manufacturer’s O&M manual.
7.1.5.4 Lamp Disposal
New lamps will be delivered in boxes suitable for shipping of the spent lamps to the disposal facility,
contact manufacturer for address of disposal facility. The plant staff will be responsible for replacing
spent lamps with new lamps, packaging them in the appropriate boxes for shipping, and shipping the
lamps to the disposal facility. The manufacturer will pay all shipping costs for the shipping lamps to the
disposal facility for 10 years.
7.2 Effluent Water System
Filtered plant secondary effluent water is used within the plant for a variety of uses including irrigation,
chlorine solution makeup, scum and foam sprays at the various process units, hose bibs for cleaning,
belt filter press and rotary drum thickener wash water, grit flushing water, digester cooling, pump seal
water, and other miscellaneous small uses. The plant effluent water is filtered and occasionally
chlorinated to minimize algae (biofouling) growth in the effluent water system.
7.2.1 System Description
A portion of the east chlorine contact basin has been repurposed to function as an effluent water
storage basin. A portion of the effluent leaving the UV disinfection channels is passed through a sluice
gate (GT6509A) into the effluent water storage basin.
Three vertical turbine pumps equipped with VFDs pump to four effluent water filters and then to various
locations throughout the plant. One pump is used for redundancy. Space is allocated for a fourth pump
that may be required in Phase 2. Figure 7-4 is a photograph taken of the installed effluent water pumps
and filters.
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Figure 7-4. Effluent Water Pumps (left) and Filters (right).
The effluent water pumped from the Effluent water basin is dosed with liquid sodium hypochlorite
(NaOCI), prior to filtration. Liquid sodium hypochlorite reduces biological growth in the effluent water
system piping. For more detail see Section 7.3 “Service Water Chlorination” of this manual.
The irrigation system consists of two vertical turbine pumps and two automatic self cleaning filters.
Again, NaOCI is introduced to provide a disinfectant residual. After filtration, the water is sent to the
soccer complex irrigation system.
7.2.2 Design Data
Table 7-6. Effluent Water Design Criteria
Parameter Value
2025 Anticipated Flow Range 500 – 2,200 gpm
Effluent Water Pump Unit Capacity 1,000 gpm @ 231 ft TDH
Irrigation Water Pump Unit Capacity 500 gpm @ 231 ft TDH
7.2.3 Operation and Control
Effluent water pumps P6601A, P6602A, and P6603A have adjustable speed drives. The pumps are
selectable from any SCADA terminal as lead, lag1, and lag2. The speed of pumps can be automatically
adjusted to maintain a system pressure setpoint. The PLC configured PID controller will compare set
pressure to pressure measured by pressure transmitter PIT6601A. A single PID controller provides
output signal such that when multiple pumps are operating they operate at identical speeds.
Irrigation water pumps P6604A and P6605A also have adjustable speed drives. One pump operates at
a time. A PLC software configured PID controller is used to control pump speed to provide a set flow
rate. Flow meter FE6602A is used to provide process variable controller input.
Effluent water filters FLT6601A, FLT6602A, FLT6603A, and FLT6604A and irrigation water filters
FLT6605A and FLT6606A, have packaged control systems. Backwashing is automatically activated
through packaged controls, or manually initiated from any SCADA terminal.
7.2.4 Equipment Data
Table 7-7 summarizes the equipment for the effluent and irrigation water systems.
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Table 7-7. Effluent/Irrigation Water Equipment
Parameter Value
Effluent Water Pumps
Tag Number
P6601A
P6602A
P6603A
Manufacturer FlowServe
Type vertical turbine
Size 12EMM-4 Stg
Irrigation Water Pumps
Tag Number P6604A
P6605A
Manufacturer FlowServe
Type vertical turbine
Size 10EML-6 Stg
Effluent Filters
Tag Number
FLT6601A
FLT6602A
FLT6603A
FLT6604A
Manufacturer Amiad Water Systems
Size/Model 10 inch SAF-6000
Filtration Degree 100 micron
Maximum Unit Flow Rate 1,760 gpm
Motor 1/3 hp
Irrigation Filters
Tag Number FLT6605A
FLT6606A
Manufacturer Amiad Water Systems
Size/Model 6 inch SAF-4500
Filtration Degree 100 micron
Maximum Unit Flow Rate 1,100 gpm
Motor 1/4 hp
Effluent Flow Meter
Asset Tag FE6601A
Manufacturer ABB Watermaster
Model FEF121.250.K.1.S.4.A1.B.1.A.1.A.2.A.2.B.3.A.1.
M5.V3.CWC,614C220U01
Calibration Range 0-2,500 gpm
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Irrigation Flow Meter
Asset Tag FE6602A
Manufacturer ABB Watermaster
Model FEV125.100.V.1.S.4.A1.B.1.A.1.A.2.P.2.B.3.A.1...
M5.V3.CWC.614C220U01
Calibration Range 0-600 gpm
7.2.5 Maintenance
Table 7-8 summarizes the manufacturer’s maintenance information for the effluent and irrigation water
systems. Refer to the manufacturer’s Operations and Maintenance Manual for a more comprehensive
listing of troubleshooting and maintenance requirements
Table 7-8. Effluent Water Maintenance
Activity Interval
Effluent/Irrigation Water Vertical Turbine Pumps
• Check operating behavior. Ensure that noise, vibration and
bearing temperatures are within the allowable limits.
• Check that there is no abnormal fluid or lubricant leaks
(static and dynamic seals).
• Check shaft seal leaks and make sure that it is within the
acceptable limits.
Daily/Weekly
• Check foundation bolts for security of attachment and
corrosion.
• The coupling should be checked for correct alignment and
worn driving elements.
Semi-Annual
Effluent/Irrigation Filters
• Initiate a flushing cycle.
• Clean the 3/4" filter connected to the exhaust solenoid.
(Close the 3/4" valve and activate a flush cycle in order to
release pressure and then unscrew the filter bawl).
• Check that there is grease on the drive shaft, and drive
bushing. Add grease if necessary (SHELL, DARINA EP-2 OR
SIMILAR).
• Check for any leakage from the scanner shaft. If necessary,
replace the sealing nut internal o-ring.
Weekly
Flow Meters
No maintenance procedures referenced in manufacturer’s manual
7.3 Service Water Chlorination
After passing through the UV disinfection channels, a portion of the effluent water is passed through a
sluice gate into the effluent water storage basin. Effluent water from the basin is utilized by multiple
processes throughout the plant as well as for irrigation of the adjacent soccer fields. In order to ensure a
residual disinfectant, NaOCI is dosed into the effluent water pumped out of the basin. Even though it is
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treated with a disinfectant, effluent water is not potable water and should not be cross connected with a
potable water source.
7.3.1 System Description
The process chlorination system consists of storage tanks, metering pumps, and associated
appurtenances and piping to feed 15% NaOCl solution to the several areas in the plant. The chemical
storage tanks and feed pumps are located in the Sodium Hypochlorite Building at the south end of the
plant between the disinfections tanks and the Sludge Processing Facility. The NaOCl solution is fed into
the effluent water system, RAS box and classifying selector, and rotary drum thickener drain. The RAS
box and classifying selector and rotary drum thickener feed points are there to assist in reducing foam
events in the secondary treatment system.
7.3.2 Design Data
Table 7-9. Service Water Chlorination System Design Data
System Parameter Value
Effluent Water
Chlorination
Chlorine Dose 2-3 mg/L
Effluent Water Flow Rate 1,800 gpm
Chlorine Demand 43-65 lb Cl2/day
Irrigation Water
Chlorination
Chlorine Dose 2-3 mg/L
Irrigation Water Flow Rate 500 gpm
Chlorine Demand 12-18 lb Cl2/day
Secondary Clarifier
Chlorination
Chlorine Dose 2 mg/L
Secondary Clarifier Overflow
Rate 30 mgd
Chlorine Demand 500 lb Cl2/day
RAS Chlorination
Chlorine Dose 4 lb Cl2/day per 1,000 lb of MLVSS
MLVSS Concentration 2,500 mg/L
Chlorine Demand 750 lb Cl2/day
Sodium
Hypochlorite
Storage
- 10 days at peak demand
7.3.3 Operation and Control
Metering Pumps - Peristaltic metering pumps inject NaOCl into four process locations as defined below.
The plant operator sets the desired dosage based on the flow rate of the dosed stream.
• Metering pump P6721A injects NaOCl into the irrigation water discharge piping. Injection ratio of
NaOCl to irrigation water flow can be set from 0 to 0.30 gallons of NaOCl to every 10,000 gallons of
irrigation water.
• Metering pump P6722A injects NaOCl into the plant effluent water discharge piping. Injection ratio
of NaOCl to effluent water flow can be set from 0 to 0.30 gallons of NaOCl to every 10,000 gallons of
plant effluent water.
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• Metering pump P6723A injects NaOCl into the RAS box and classifying selector for filament control.
Injection ratio of NaOCl to RAS flow can be set from 0 to 0.20 gallons of NaOCl to every 10,000
gallons of RAS. This metering pump is also capable of being set at a steady feed rate.
• Metering pump P6724A injects NaOCl into the rotary drum thickener drain line. Injection ratio of
NaOCl to filtrate flow is settable from 0 to 0.85 gallons of NaOCl to every 10,000 gallons of filtrate.
This metering pump is capable of being set at a steady feed rate. This pump also is cross connected
with the other three pumps and serves as a standby pump, hence the turndown than the others.
Turndown is achieved by using different pump heads or tube sizes.
• The flow rates are also adjustable at the operator interface based on strength of hypochlorite and
dose delivered in mg/L.
• The hypochlorite inventory needs to be managed to keep the chemical fresh (30 days or less).
Storage Tanks - Filling the sodium hypochlorite storage tanks T6701A and T6702A is controlled through
hardwired relay logic in the fill station control panel associated with each tank. A high level is indicated
by a pilot light indication at the local control panel as measured by the tank level sensors LIT-T6701A
and LIT-T6702A, respectively. The high level alarm will automatically close the solenoid operated fill
valve (FV6701A and FV6702A).
7.3.4 Equipment Data
Table 7-10 summarizes the major equipment, tanks and pumps, of the service water chlorination
system.
Table 7-10. Service Water Chlorination Equipment
Parameter Value
Storage Tanks
Asset Tag T6701A (1,500 gal.)
T6702A (5,200 gal.)
Manufacturer Assmann Corp.
Peristaltic Metering Pumps
Asset Tag
P6721A
P6722A
P6723A
P6724A
Manufacturer FloMotion Systems
Unit Capacity 0.013-50.21 gph @ 100 psi
Model Series 2001HRI0XX9, variable speed
7.3.5 Maintenance
Table 7-11 summarizes the manufacturer’s maintenance information for the effluent and irrigation water
systems. Refer to the manufacturer’s Operations and Maintenance Manual for a more comprehensive
listing of troubleshooting and maintenance requirements
Table 7-11. Service Water Chlorination Equipment Maintenance
Activity Frequency
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Storage Tanks
Check each fitting and expansion joint for possible
seepage or leaks. Monthly
Flush the tank. Annually
Check the inside and outside surface of the tank for
crazing, cracking or unusual discoloration. Focus
around fitting areas.
After two years; every 6 months
thereafter
Peristaltic Metering Pumps
No maintenance practices listed in manufacturer’s manual.
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Section 8 Solids Handling
Solids handling at the South WWTP includes primary sludge and WAS thickening, anaerobic digestion,
dewatering, and cake storage. The Phase 1 expansion modified the primary sludge and WAS thickening,
mixing of the digested sludge in two digesters and the storage tank, digester heating and cooling,
polymer makeup systems for thickening and dewatering, cake conveyance, and cake storage systems.
These systems are discussed in this manual, below.
8.1 Primary Sludge Thickening
Primary sludge is thickened in the primary clarifiers. Management of the blanket depth in the clarifier
will significantly affect the total solids of the sludge pumped out of the unit. Typically, the deeper the
blanket depth, the thicker the sludge. Some exceptions exist, including stratification of the sludge
blanket if it is too old, usually caused by septicity and gassification. Depending on the nature of the
sludge, and perhaps the time of year, a low blanket depth can still produce very thick solids. Managing
the sludge blanket is necessary to protect the unit from excessive torque. If the sludge concentration is
allowed to get too thick, the clarifier mechanism will shut off on torque overload. Past experience with
the depth of blanket should be used as a guide when maintaining a blanket depth.
The target sludge concentration from the primary clarifiers is 4% TS. This is the level the plant has
historically been able to achieve. Achieving this target is critical in the digestion process where the
hydraulic retention time is the key criteria for treatment performance. If the primary clarifiers are not
able to thicken primary sludge to 4% TS and the Phase 1 projected flows and loads are realized there will
not be enough digestion capacity.
The process of thickening primary sludge in the primary clarifiers is covered in greater detail in the
Sections 3 and 5 of this manual.
8.2 WAS Thickening
The rotary drum thickeners (RDTs) thicken sludge by means of a rotating wedge-wire drum. WAS, dosed
with polymer is fed to the RDTs and then thickened, allowing filtrate to pass through the openings in the
drum. Angled flights on the inside of the drum direct the thickened sludge towards the discharge end of
the drum. The thickened sludge then exits the drum and is directed into a collection hopper of a
progressive cavity pump. Filtrate is returned to the head of the plant. Figure 8-1 depicts the RDTs
installed at the plant.
Proper dosage is critical in optimizing the performance of the thickener. Not only will the quality of the
thickened sludge be affected by dosing rates, but the quality of the filtrate will deteriorate in which
significant amounts of solids are returned to the head of the plant. Figure 8-1 pictures the flocculation
well of the RDTs where polymer and sludge are gently mixed to enhance thickening.
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Figure 8-1. RDT (left) and Flocculation Well (right).
8.2.1 System Description
WAS is a fraction of the RAS split off in the RAS box and classifying selector. Removal of the WAS from
the secondary system maintains an optimal amount of solids for secondary treatment. RDTs are used to
thicken the WAS to a target of 5% TS. The solids product resulting from the thickening process is termed
thickened waste activated sludge (TWAS).
Polymer is added to the WAS prior to entering the RDTs to enhance WAS liquid/solids separation.
Polymer addition is covered in more detail in Section 8.4.
After the TWAS exits the drum it is directed to a sludge hopper. Each RDT has a TWAS pump that
conveys TWAS from the sludge equalization tank where it is combined with primary sludge before being
pumped into the digesters.
The RDT filtrate is directed to the plant drain system back to the head of the plant. A chlorination feed is
provided in the event foaming occurs in the aeration basins and the filtrate would contain a portion of
the foam causing organisms that could potentially reseed the foam.
8.2.2 Design Data
Given that the RDT system does not have upstream storage, this system is susceptible to peak high
flows. As such the RDT system is designed to handle the maximum day WAS load with one RDT unit out
of service. Table 8-1 summarizes the design data of the RDT system.
Table 8-1. WAS Thickening Design Criteria
Parameter Value
Rotary Drum Thickeners
Total Units 3 (1 installed in Phase 1 expansion)
Unit Hydraulic Capacity 350 gpm
Phase 1 Maximum Day WAS Flow 660 gpm
Thickened Sludge (TWAS) Pump
Quantity 1 (installed in Phase 1 expansion)
Unit Capacity 36 gpm @ 80 ft TDH
Pump Speed 335 rpm
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8.2.3 Operation and Control
The new RDT is operated identically to the two existing units with one difference. The Phase 1 expansion
provides each RDT with a dedicated WAS pump and flow meter for reliable feed. Should the WAS flow
rate exceed the capacity of the on-line unit(s) the standby unit(s) will be called to start and WAS pump
speed will be adjusted to match the overall desired flow. The inlet control valve may also be modulated
to control flow. Connections are provided to temporarily redirect pumping from RDTs that are not in
service. WAS pumping is covered in the Section 6.9 of this manual.
Flocculation Mixer - The mixers (MX9101A, MX9102A and MX9103A) in the sludge flocculation well are
equipped with VFD drives. Based on experience, the plant staff manually sets the speed from the South
Drum Thickener Control Panel (SDTCP) or via any SCADA terminal to achieve the best results.
Initial operation of an RDT begins with proving the related WAS isolation valve (FV9111A, FV9112A, and
FV9113A) is open, WAS pump is operating, and polymer metering pump (discussed in Section 8.4) is
operating. Upon proof, the flocculation well will begin to fill with WAS that has already been dosed with
polymer. Once the level is above the mixing blades, the corresponding high level switch will initiate the
mixer. The mixer will be automatically started through the SDTCP PLC if the VFD local-remote selector
switch is in the remote position and auto is selected at either the SDTCP PC-based HMI or at a SCADA
terminal. Once the mixer is energized, the RDT motor will be energized if the local controls are in the
remote position and auto is selected at a SCADA terminal for the motor.
After an RDT has been shutdown, the mixer will continue to operate until manually stopped through a
momentary pushbutton located near the mixer. De-energization of the mixer should be performed
locally, in order to flush and clean the tank using the manual flush and drain valves. The local
momentary STOP contact closure is input into the SDTCP PLC for mixer motor shutdown.
RDT – The RDT drive motors are VFD driven. Based on plant experience the plant staff are able to
manually set the speed remotely from either the SDTCP or any SCADA terminal. RDTs can operate on a
timed schedule via the on time/off time settings of the system. This selection can be made from either
the SDTCP PC-based HMI or any SCADA terminal, with selection displayed on both, through SDTCP PLC
configured logic. If any one of the local selector switches for the RDT system components is not in
remote mode an alarm will be displayed at the SDTCP and SCADA terminals indicating this condition.
Initiation of a RDT begins by the opening of one WAS Isolation Valve, either automatically or manually
from the existing South Sludge Processing Station (SSPRS) or from the SDTCP. With a WAS isolation
valve proven open, the WAS pump associated with that valve will energize if all of the following
conditions exist:
1. Corresponding RDT WAS isolation valve has been proved open,
2. The flocculation well manual thickener washwater flow valve has been proven closed, and
3. The RDT drain valve has been proven closed.
A local warning horn near the RDTs will sound for 5 seconds as soon as a WAS valve is selected from any
location. Status of the WAS valves is displayed on the SDTCP. "System in Operation" status will be
provided on the SDTCP as long as any device within the RDT system is active.
When the RDT operation is to be shutdown, either automatically by the selected of time, or manually via
a software configured "Close Waste Activated Sludge Valve" feature, the WAS isolation valve will be
closed. This feature is available at the SDTCP. This will cause the associated WAS pump to stop,
causing the polymer metering pump to stop. Once all of these pumps have been de-energized the RDT
WAS isolation valve will be automatically closed preventing any additional sludge/polymer mixture from
being fed to the flocculation well. With the RDT operating in the automatic mode, it will continue to
operate for a software pre-configured time in order to clean the unit of the sludge/polymer mixture.
TWAS Pumps - The TWAS pump motors are VFD driven. Plant staff set the RDT TWAS hopper level to be
maintained at the SDTCP or any SCADA terminal. The TWAS pumps can not run dry, so a low level switch
is provided to monitor low sludge level in the hopper. The contact from this level switch is input into the
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SDTCP PLC for pump control. Presence of this input will cause the TWAS pump to de-energize. If the
VFD is in remote and the auto is selected at either the SDTCP, the TWAS pump will re-energize when
sludge level in the hopper reaches the software level controller setpoint. In the hand mode, the level
switch function is bypassed completely.
Each TWAS pump discharge pressure is monitored. This high-high discharge pressure switch is
hardwired into the MCC motor control logic and will be active in either the hand or automatic mode of
operation. Each of the high-high discharge pressure switches are also input into the SDTCP PLC and
alarmed at the SDTCP. A high-high discharge pressure condition can be cleared by depressing the reset
pushbutton located on the SDTCP enclosure.
When the sludge/polymer mixture is no longer fed into the flocculation well, the level in the RDT
discharge hopper will fall. In the automatic mode, once low level is detected the TWAS pump will be de-
energized, as defined above.
When the TWAS pump is operating, the SDTCP PLC output for the associated seal water solenoid valves,
FV9111A1, FV9112A1 or FV9113A1, will be de-energized. These solenoid valves are fail open.
8.2.4 Equipment Data
Table 8-2 summarizes the equipment data for the RDT installed in the Phase 1 expansion. The other two
RDT systems were installed previously and are generally not covered in this manual.
Table 8-2. WAS RDT Thickening Equipment Data
Parameter Value
Rotary Drum Thickener THK9103A
Manufacturer Vulcan
Model LFST-608
T WAS % TS 5
Nominal Drum Length 8 ft
Drum Opening Size 0.020 inch (wedgewire slot opening)
Drum Motor 3 hp
Flocculation Well Mixer
(MX9103A) Motor
0.5 hp
Sludge Hopper Capacity 10 ft3
Rotary Drum Thickener WAS Isolation Valve FV9113A
Manufacturer DeZurik
Style PEF-DeZURIK 100% Area Rectangular Port
Eccentric Plug Valve
Size 6 inch
Actuator AUMA SA 07.5/GS63.3 electric motor operator
TWAS Pump
Asset Tag P9113A
Manufacturer Moyno
Type progressive cavity
Series/Model 2000 Series Model 1E012G1 CDQ 3AAA, One
Stage
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8.2.5 Maintenance
The manufacturer’s recommended maintenance for the RDT system installed in the Phase 1 expansion
is summarized in Table 8-3. Refer to the manufacturer’s Operations and Maintenance Manual for a
more comprehensive listing of troubleshooting and maintenance requirements
Table 8-3. RDT Maintenance Procedures
Parameter Value
RDT THK9103A
Daily
• Listen for any unusual operating noises.
• Verify that there are no leaks from the gearbox.
• Verify that the motor temperature is normal.
• Ensure that the feed and discharge pipes are not obstructed.
Weekly or every
30 operating hours
• Clean and inspect the outside of the equipment.
• Inspect the flocculation well, flow distribution tray, drum
screen, drain pan and outlet pipes for solids accumulation and
clean if necessary.
Monthly or every
100 operating hours
• Check all safety devices.
• Activate the emergency stop and verify it is functioning.
• Check the drum screen and trunnion wheels for smooth
operation.
• Grease trunnion wheels.
Semi-annually or every
600 operating hours
• Check all fasteners for tightness.
• Replace any missing fasteners.
• Check the oil level of the gearbox. Fill if required. Reference
the data sheets in the manufacturer’s manual for gearbox
lubricants and fill levels.
Annually or every
1,200 operating hours
• Check the motor and gearbox for damage.
• Check the motor and gearbox fasteners for tightness.
• Replace gearbox oil. Follow the gearbox manufacturer’s
instructions included in the manufacturer manual. Only use
gear oils approved by the gearbox manufacturer.
TWAS Pump P9113A
The Moyno 2000 pump has been designed for a minimum of maintenance, the
extent of which is routine adjustment and lubrication of packing. For further pump
maintenance and troubleshooting details see the manufacturer’s O&M manual.
RDT WAS Isolation Valve FV9113A
No maintenance recommendations are listed in manufacturer’s manual
8.3 Anaerobic Digestion
The bulk of the anaerobic digestion system was installed prior to the Phase 1 expansion is not generally
covered in this manual. Nevertheless a general operating strategy for the anaerobic digestion process is
provided in Section 3.
The anaerobic digestion improvements installed as a part of the Phase 1 expansion are discussed here
and include:
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1. Digester mixing systems for tanks T8601A, T8701A, and T8801A.
2. Decant system for tanks T8601A and T8701A.
3. Sludge heating and cooling improvements.
4. Digester gas conditioning and safety equipment.
8.3.1 System Description
Digester Mixing System - The digester mixing system consists of a circulating pump, inlet/outlet piping,
and mixing nozzles on the discharge piping. Each of the digester tanks (T8601A, T8701A, and T8801A)
has a dedicated system located in the basement of Digester Building 8600. The mixing system
circulates sludge in the digesters at an adequate velocity and trajectory so as to complete mix the tank.
A branch of the discharge piping is run above the operating surface in the digester to knock down foam
and entrain surface solids.
Digester Decanting – Plant staff have proven that after digestion if the sludge is allowed to sit the water
and solids began to separate once the temperature of the sludge has cooled to 86 °F. Draining the
water that has separated from the sludge is advantageous because this volume is not required to be
processed by the BFP dewatering equipment and reduces the polymer dose required. Since, the
digestion process does not always require tanks T8601A and T8701A to be actively digesting at elevated
temperatures, they can be used to cool and decant off the separated water. The equipment installed in
the Phase 1 expansion to enable the decanting includes four electrically actuated plug valves located at
varying elevations in each of tanks T8601A and T8701A. The water decanted is high in ammonia and is
drained to the HSW system.
The decant valving on the digested sludge storage tank (T8801A) is similar in nature, but was not
upgraded in the Phase 1 expansion.
The decant valves are located in both the basement and ground level room of Digester Building 8600.
Digester Heating and Cooling – The digester heating equipment has been upgraded in the Phase 1
expansion for tanks T8601A and T8701A. These tanks required a reliable heating system to provide
active digestion as sludge production increases. Each tank is supplied with its own sludge/water heat
exchanger (HEX9601A and HEX8701A, respectively). Sludge is circulated through the heat exchangers
by existing pumping systems. Hot water is supplied by the existing Burnham boilers in Digester Building
8500. The hot water is pumped to the HEX9601A and HEX8701A loops by two booster pumps (P8831A
and P8832A) and the each heat exchanger has it’s own hot water feed pump (P8611A and P8711A,
respectively). Each heat exchanger hot water loop has a three-way flow control valve to maintain
temperature setpoint (FCV8602A and FCV8702A, respectively). Hot water flow to the these heat
exchangers is monitored by flow meter FE8800A.
Until digester tanks T8601A and T8701A are required for active digestion they can be used as decant
tanks. In order to cool the digested sludge, that promotes the water/solid separation, in a timely manner
a cooling system has been provided in the Phase 1 expansion. Cool effluent water is supplied to heat
exchanger HX8802A by the effluent water system discussed in Section 7.2. Sludge is ciruclated for
either tank T8601A or T8701A by pumping systems installed prior to the Phase 1 expansion. A
temperature control valve (TCV8802A) regulates the flow of cool effluent water and thus the amount of
cooling.
The bulk of this equipment is located in the ground level space of the Digester Building 8600. The hot
water booster pumps are located in the basement of the same building.
Digester Gas – Digester gas from the dedicated thermophilic digester (T8101A) and swing
mesophilic/thermophilic digester (T8202A) were equipped with coolers ( in the Phase 1 expansion and
are located in the basement of the Digester Building 8500. Flame arrestors and sediment traps
(SEP8601A and SEP8701A, respectively) were also installed on the digester lines from tanks T8601A
and T8701A in the basement of the Digester Building 8600.
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8.3.2 Design Data
Table 8-4. Anaerobic Digestion Design Criteria
Parameter Value
Digester Mixing System
Number of Systems 3 (1 spare pump)
Pump Unit Capacity 1,310 gpm @ 40 ft TDH
Nozzles (Each Tank) • Two 2.5 inch diameter on floor
• One 1.5 inch diameter at surface
Decanting
Valve Size 3 inch
Digester Heat Exchangers (Heating)
Quantity 2
Heat Exchangeper Unit 575 kBtu/hr
Sludge Flow 350 gpm
Sludge Temperature 95 °F
Sludge Temperature Drop 3.3 °F
Hot Water Flow 50 gpm
Water Temperature 165 °F
Water Temperature Rise 23.6 °F
Digester Heat Exchangers (Cooling)
Quantity 1
Heat Exchange per Unit 1,800 kBtu/hr
Sludge Flow 350 gpm
Sludge Temperature 95 °F
Sludge Temperature Drop 10.3 °F
Cooling Water Flow 350 gpm
Water Temperature 62 °F
Water Temperature Rise 10.3 °F
Digester Gas Coolers
Quantity 2
Heat Exchange per Unit 15 kBtu/hr
Gas Flow 35 scfm
Gas Temperature 135 °F
Gas Temperature Drop 42.2 °F
Cooling Water Flow 9 gpm
Water Temperature 40 °F
Water Temperature Rise 3.3 °F
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8.3.3 Operation and Control
Digester Mixing System - The digester mixing systems are manually controlled from any SCADA terminal
as long as the local control is in remote mode. These systems are to operated on a timed basis based
on plant experience.
Digester Decanting – Control of the decanting valves is provided by the control panel located near the
sample sink in the basement of Digester Building 8600. The valves can be set to fully open or fully
close. Plant staff determine when to open the upper most decant valve by the temperature of the
sludge. Opening successively lower decant valves is determined by the quality of the decanted water as
measure by the TSS concentration. Section 3 provides more detail on the decanting process.
Digester Heating and Cooling – Revamped sludge heating and cooling systems were provided in the
Phase 1 expansion for digesters T8601A and T8701A. The following describes the operation and control
sequence of both the associated sludge and water systems. Heating and cooling is initiated by plant
operator entered setpoints.
Sludge Heating/Cooling
Sludge recirculated through digesters T8601A and T8701A may be heated or cooled depending on
which heat exchanger sludge is pumped. Heat exchangers HEX8601A and HEX8701A heat sludge and
heat exchanger HEX8802A cools sludge. Selection of heating or cooling of each digester is
independently selectable from any SCADA terminal. Both digesters may be selected for heating, but only
one Digester at a time is selectable for cooling.
For Digester T8601A, selection of sludge heat recirculation will automatically open heat exchanger
HEX8601A sludge isolation valves FV8611A and FV8612A and start circulating water pump P8611A.
Decant cooling heat exchanger sludge isolation valves FV8613A and FV8614A will be automatically
closed if open. Similarly, for Digester T8701A, selection of sludge heat recirculation will automatically
open heat exchanger HEX8701A sludge isolation valves FV8711A and FV8712A and start circulating
water pump P8711A. Decant cooling heat exchanger sludge isolation valves FV8713A and FV8714A will
be automatically closed if opened.
For digester T8601A, selection of sludge cooling recirculation will automatically close heat exchanger
HEX8601A sludge isolation valves FV8611A and FV8612A if open. And, automatically open decant
cooling heat exchanger sludge isolation valves FV8613A and FV8614A. Similarly, for digester T8701A,
selection of sludge cooling recirculation will automatically close heat exchanger HEX8701A sludge
isolation valves FV8711A and FV8712A if open. And, the decant cooling heat exchanger sludge isolation
valves will automatically open. In either case, when digesters T8601A and T8701A are selected for
cooling the cooling water flow control valve (TCV8802A) will open, allowing effluent water to flow through
heat exchanger HEX8802A.
Heat exchanger sludge isolation valves are provided with full open/full closed electric actuators for
automatic and remote operation.
Sludge recirculation pumps P8811A and P8812A are programmed to operate in conjunction with
circulating water pumps P8611A and P8711A, respectively when either heat exchangers HEX8601A or
HEX8701A are selected. Sludge recirculation pump P8813A is used as an on-line backup. Depending
on which of the sludge recirculation pump is replaced, it will operate in conjunction with the appropriate
circulating water pump. When recirculation mode for appropriate digester and heat exchanger
HEX8601A or HEX8701A combination is selected from any SCADA terminal both sludge recirculation
pump and circulating water pump will operate. The combination of operation for these two pumps will
only occur in heating mode. The appropriate sludge recirculation pump to be operated associated with
circulating water pump is determined by location of pump local Hand-Off-Auto selector switch. Manual
valve positioning is required to place Pump P 8813A in service.
Water Heating/Cooling
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Circulating water booster pumps P8831A and P8832A are provided with adjustable speed drives and
operate in a lead/lag arrangement. Selection of the lead and lag pump is settable form and SCADA
terminal and automatically alternates after a shutdown. Under normal operating conditions, one
circulating water pump operates at a time. Failure of either LEAD or LAG pump will automatically start
alternate pump and alarm condition. These pumps supply heating water to heat digesters T8601A and
T8701A, as well as building heating system equipment in Digester Building 8600 complex and Sludge
Processing Facility. Excess water not required through heating system and exchangers will pass back to
the boilers and is controlled by back pressure regulating valve PRV8600A. The circulating water booster
pumps are controlled by a flow setpoint, settable from any SCADA terminal. Flow meter FE8800A
provides the process variable feedback signal.
Hot water feed pumps P8611A and P8711A are provided with adjustable speed drives and are operated
in conjunction with sludge circulation pumps P8111A and P8812A, respectively, or the standby pump
P8813A. These pumps supply water through heat exchangers HEX8601A and HEX8701A to adjust the
temperature of sludge stored in digesters T8601A and T8701A. The temperature at inlet to heat
exchangers is measured by temperature sensors TEX8701A and TEX8701A, respectively. The
temperature setpoint modulates a three-way control valve (FCV8602A and FCV8702A, respectively) that
controls how much freshly heated water or cooler recirculated water is passed through the heat
exchangers. As the temperature decreases, the control system will cause more hot water to pass
through heat exchanger with less water recirculation bypassing high temperature water boilers. The
three-way valve is configured with Hand-Off-Auto functions. In auto mode the three-way valve is
positioned to maintain the desired set temperature. If off is selected the valve be forced to full
recirculation position, blocking additional hot water supply. The hand mode allows plant staff to
manually position three-way valve. The speed of each hot water feed pump is manually settable from
any SCADA terminal. Plant staff will determine the pump capacity required while viewing three-way valve
position for the most efficient operation.
Digester Gas – The equipment installed in the Phase 1 expansion does not have any specific control
strategy and is operates passively.
8.3.4 Equipment Data
Table 8-5 summarizes the equipment data for the equipment installed in the Phase 1 expansion.
Table 8-5. Anaerobic Digestion Equipment
Parameter Value
Digester Jet Mixing Pumps
Asset Tag
P8601A
P8701A
P8801A
Spare
Manufacturer Wemco
Type vertical chopper
Model 8 x 6, CFV4
Speed 1,165 rpm
Motor 25 hp
Digester T8601A and T8701A Decant Valves
Asset Tag FV8621A
FV8622A
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FV8623A
FV8624A
FV8721A
FV8722A
FV8723A
FV8724A
Manufacturer DeZurick
Style 100% area rectangular port eccentric plug valve
Description PEF,3,F1,CI,NBR,CR*X*CO1855
Size 3 inch
Actuator AUMA SAExC 07.5/GS63.3 Electric
Sludge Heating Heat Exchangers
Asset Tag HEX8601A
HEX8701A
Manufacturer Alfa Laval
Model 1H-SW-1W, 55 sf sludge spiral heat exchanger
Sludge Cooling Heat Exchanger
Asset Tag HEX8802A
Manufacturer Alfa Laval
Model 1H-STS-1W, 595 sf sludge spiral heat exchanger
Sludge Cooling Heat Exchanger Isolation Valves
Asset Tag
FV8613A
FV8614A
FV8713A
FV8714A
Manufacturer DeZurick
Style 100% area rectangular port eccentric plug valve
Description PEF,6,F1,CI,NBR,CR*x*CO1855
Size 6 inch
Actuator AUMA SAExC 07.5/GS63.3 Electric
Decant Cooling Temperature Control Valve
Asset Tag TCV-8802A
Manufacturer Nor’East Controls
Size 4 inch
Type globe temperature control valve, electrically operated
Model Series 9200, two-way double seated cage valve
Operator Jordan VA-1020 electric motor operator
Circulating Water Booster Pumps
Asset Tag P8831A
P8832A
Manufacturer Bell & Gosset
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Type in-line mounted centrifugal
Model Series 80 2.5x2.5x9.5B
Speed 1,800 rpm
Unit Capacity 225 gpm @ 48 ft TDH
Motor 7.5 hp
Boiler Return Pressure Regulating Valve
Asset Tag PRV8600A
Manufacturer CLA-VAL
Model 50-01BKB
Description flanged globe with viton diaphragm
Size 4 inch
Circulating Water Booster Pump Flow Meter
Asset Tag FE8880A (no maintenance)
Manufacturer ABB Watermaster
Model FEV125.080.V.1.S.4.A1.B.1.A.1.A.2.P.2.B.3.A.1...
M5.V3.CWC,614C220U01
Calibration Range 0-300 gpm
Hot Water Feed Pumps
Asset Tag P8611A
P8711A
Manufacturer Bell & Gosset
Type in-line mounted centrifugal
Model Series 80 1.5x1.5x7B
Speed 1,800 rpm
Unit Capacity 50 gpm @ 38 ft TDH
Motor 1.5 hp
Three-Way Control Valves
Asset Tag FCV8602A
FCV8702A
Manufacturer Trimeck
Model OpGL
Type three-way globe control with side port
Actuator Promation PL550
Digester Gas Coolers
Asset Tag -
Quantity 2
Manufacturer Xchanger
Model TV-050
Type fin/tube
Digester Gas Sediment Traps
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Asset Tag SEP8601A
SEP8701A
Manufacturer Varec
Model 233-06-FP
Size 6 inch
Material carbon steel
Digester Gas Flame Arrestors
Asset Tag -
Quantity 2
Manufacturer Varec
Model 520012
Size ¼ inch
Material aluminum housing, type 316 stainless steel element
Working Pressure 25 psig
8.3.5 Maintenance
Table 8-6 summarizes the maintenance activities of the digestion equipment supplied in the Phase 1
expansion. Refer to the manufacturer’s Operations and Maintenance Manual for a more comprehensive
listing of troubleshooting and maintenance requirements
Table 8-6. Anaerobic Digestion Equipment
Parameter Value
Digester Jet Mixing Pumps
Check pump operating conditions; pressure and
flow, seal leakage, vibration.
Daily
Check motor amperage; must be less than full load
amperage.
Monthly
Lubricate bearings; put one ounce of grease in
each grease fitting.
Quarterly or 1,500 hours:
whichever occurs first.
Check coupling; realign or replace as necessary.
Semi-annually or every
4,000 hours; whichever
comes first.
Disassemble, clean and adjust pump; replace parts
as necessary. Inspect and adjust clearance
between impeller and cutter bar and between
impeller and back cutter teeth.
Annually
Purge 3 ounces of grease through bearings. Annually
Check for loose fasteners. Semi-Annually
Check lubricant level; refill if necessary. Semi-Annually
Check lubricant quality; drain, flush and refill if
necessary.
Semi-Annually
Check alignment – check all couplings. Semi-Annually
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Digester Jet Mixing Pump Motor
General inspection: check for dirt, oil, grease,
water. Clean vents.
Quarterly or every 500
hours, whichever comes
first.
Dielectric insulation check.
Quarterly or every 500
hours, whichever comes
first.
Check electrical connections.
Quarterly or every 500
hours, whichever comes
first.
Relubrication with Polyrex EM (Exxon Mobil) Every 7,400 hours.
Digester Mixing Nozzles
When the tank has been drained, check the
nozzles for wear. Measure the inside diameter of
the nozzle and record the measurement.
Measurements taken over a few years will help to
develop an estimate of nozzle life under the plant’s
specific operating conditions.
Annually
When the tank has been drained, check the torque
on all fasteners - see installation sections of
manufacturer’s O&M manual for torque values.
Annually
Digester T8601A and T8701A Decant Valves
No maintenance practices are recommended, although if stem packing leaks
only tighten gland nuts until leak stops, replace packing if leak persists.
Sludge Heating and Cooling Heat Exchangers
No scheduled Maintenance required. If the digester shows indications of lower
than design temperatures, consider flushing the heat exchanger. See
manufacturer’s manual for procedure.
Sludge Cooling Heat Exchanger Isolation Valves
No maintenance practices are recommended, although if stem packing leaks
only tighten gland nuts until leak stops, replace packing if leak persists.
Decant Cooling Temperature Control Valve
Frequently check packing for leaks, replace if leaking.
Circulating Water Booster Pumps
No periodic maintenance is recommended.
Boiler Return Pressure Regulating Valve
No maintenance practices are recommended.
Circulating Water Booster Pump Flow Meter
No maintenance practices are recommended.
Circulating Water Pumps
No periodic maintenance is recommended.
Three-Way Control Valves
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Inspect end flanges and bonnet for signs of gasket
leakage. Tighten flange and bonnet bolting (if
required).
Periodically
Check the pressure-balance sleeve, metal bellows
seal, body drain plug, etc. (if included) for fluid
leakage to the atmosphere.
Keep valve clean and repaint areas affected by
severe oxidation.
Examine the valve for damage caused by corrosive
fumes or process drippings.
Check lubricant supply and add lubricant if
necessary.
Packing box bolting must be slightly over finger-
tight. Tighten only as necessary to prevent stem
leakage.
Digester Gas Coolers
Clean fins and tube passages periodically.
Digester Gas Sediment Traps
No maintenance information is recommended.
Digester Gas Flame Arrestors
No maintenance information is recommended.
8.4 Polymer Addition
Polymer is added to both the WAS before thickening and the digested sludge prior to dewatering to
enhance lquid/solids separation. Both of these processes use adifferent type of dry polymer. Both
polymers come as a dry powder and are slurried on site. The Phase 1 expansion included the
replacement of the slurrying equipment. One additional polymer metering pump was also added for WAS
thickening.
The other polymer addition equipment including metering pumps and mixing and aging takens were
installed prior to the Phase 1 expansion and are not covered in detail in this manual.
8.4.1 System Description
Polymer addition consists of packaged polymer feed systems, polymer mixing and aging tanks, and
polymer metering pumps that supply polymer solution to assist in the dewatering of digested sludge in
the belt filter presses or thickening WAS in the RDTs.
Polymer feed systems CFR9301A and CFR9302A automatically mix dry polymer with water to create a
homogeneous solution ready to be fed to the point of use.
Polymer Metering Pumps deliver polymer solution from the mixing and aging tanks to the belt filter
presses and RDTs. During delivery to the point of use the polymer solution is mixed through a static
mixer and the flow rate measured for control.
8.4.1 Design Data
Table 8-6. Polymer Addition Design Criteria
Parameter Value
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Polymer Metering Pump (RDTs)
Total Number of Units 3 (1 installed in Phase 1 expansion)
Unit Capacity 4 gpm @ 185 ft TDH
Pump Speed 345 rpm
Dry/Liquid Polymer Feed System
Unit Processing Rate 3.86 ft3/hr
8.4.2 Operation and Control
Dry polymer is purchased in 50 pound bags for both the WAS thickening and digested sludge
dewatering. The bags are loaded into of the hopper of respective polymer feed system where the dry
polymer is mixed with effluent water at a programmed rate. Each process has a dedicated polymer feed
system (CFR9301A and CFR9302A, digested sludge dewatering and WAS thickening respectively) and
mixing/aging tanks (T9326A and T9327A for the digested sludge dewatering and T9335A and T9336A
for the WAS thickening) where the liquefied polymer is gently stirred and stored prior to use. The
polymer feed system comes as a complete package with integral controls. Operation is limited to filling
the hopper with dry polymer and starting the unit. The dry/liquid polymer feed system cannot be control
remotely. Batches of liquid polymer can be made for extended unstaffed periods.
The only polymer metering pump added in the Phase 1 expansion was RDT polymer metering pump
P9313A which is dedicated to RDT THK9103A. Control of the pump is identical to the other two pumps
in that when the associated is called to start and the WAS pumping system is ready to deliver WAS the
polymer metering pump will start and run at a preset setpoint. The pump speed will vary to match any
flow variance in the WAS in order to maintain the setpoint mix ratio. Flow meter FE9313A monitors the
polymer solution flow rate and controls the polymer metering pump speed.
8.4.3 Equipment Data
Table 8-7 summarizes the polymer addition system equipment provided in the Phase 1 expansion.
Table 8-7. Polymer Addition Equipment Data
Parameter Value
Dry/Liquid Polymer Feed System
Asset Tag CFR9301A
CFR9302A
Manufacturer Siemens
Model DD4
Number of Units 2
Hopper 10 ft3
Water Supply 30 gpm
Minimum Operating Water Pressure 40 psi
Water Connection 1½ inch NPT
Emulsion Polymer Connection ½ inch NPT
Dust Collector
Donaldson Torit
Model 54
284 cfm
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½ hp motor
Feeder
AccuRate
Model 602
1.38 inch helix auger
¼ hp motor
50:1 turndown
Disperser Motor 1 hp
Compressor
Rietschle Thomas
Model 688FE44
1.60 cfm flow
100 psi maximum pressure
325 W motor
WAS Thickening Polymer Metering Pump
Asset Tag P9313A
Manufacturer Moyno 1000 Series
Model A2C CDQ 3APA, Two Stage
Motor Size 1.5 hp
WAS Thickening Polymer Flow Meter
Asset Tag FE9313A
Manufacturer ABB Watermaster
Model FEW121.025.A.1.D.4.A1.B.1.A.1.A.2.A.1.B.3.A.1.
M5.V3, 614C220U01
Calibration Range 0-35 gpm
8.4.4 Maintenance
Table 8-7 summarizes the manufacturer’s maintenance information for the effluent and irrigation water
systems. Refer to the manufacturer’s Operations and Maintenance Manual for a more comprehensive
listing of troubleshooting and maintenance requirements
Table 8-7. Polymer Addition Equipment Maintenance
Parameter Value
Dry/Liquid Polymer Feed System
Clean ancillary water and/or polymer strainers. Weekly
Flush mixing chamber by turning polymer feed off and allowing system
to batch with water only until all polymer residue disappears.
When shutdown, or
exceeds 1 week
Flush system. Monthly
Drain condensate from air compressor tank. Monthly
Check filter on air compressor and clean if necessary. Monthly
Annually inspect all water system safety and control valves for proper
function. Annually
AccuRate Feeder
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1. Adjust, lubricate and inspect chain on feeder. Use non-organic
based solutions or lubricants.
Monthly
2. Adjust and Inspect sprockets on feeder. Monthly
3. Inspect motor on feeder. Quarterly
4. Inspect gear reducer on feeder. Monthly
5. Inspect helix on feeder. Quarterly
6. Adjust and inspect nozzle on feeder. Quarterly
7. Inspect hopper on feeder. Quarterly
8. Inspect hopper extension filter on feeder. Weekly
9. Replace hopper extension filter on feeder. Semi-Annually
10. Inspect drive shaft on feeder. Quarterly
11. Inspect seals on feeder. Monthly
12. Replace seals on feeder. Semi-Annually
13. Inspect quill on feeder. Monthly
14. Inspect bearings and bushings on feeder. Monthly
15. Adjust and inspect fasteners on feeder. Monthly
16. Inspect keyways. Quarterly
17. Inspect eccentric shaft. Quarterly
Disperser Motor
1. Check that the motor is clean. Check that the interior and
exterior of the motor is free of dirt, oil, grease, water, etc. Oily
vapor, paper pulp, textile lint, etc. can accumulate and block
motor ventilation.
Quarterly or 500 hours 2. Use a “Megger” periodically to ensure that the integrity of the
winding insulation has been maintained. Record the Megger
readings. Immediately investigate any significant drop in
insulation resistance.
3. Check all electrical connectors to be sure that they are tight.
4. Replace ball bearings. Every 5 years
WAS Thickening Polymer Metering Pump
Periodic inspection and adjustment of the packing.
Flow Meter
No maintenance recommended in manufacturer’s manual.
8.5 Dewatering
There were no improvements made to the digested sludge dewatering system (belt filter presses) as part
of the Phase 1 expansion. An operation strategy is briefly discussed in Section 3, otherwise dewatering
is not specifically covered in this manual.
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8.6 Cake Conveyance
Once the digested sludge is dewatered (i.e. cake) the belt filter presses drop the cake onto a conveyor
system that transports the cake up high enough to fall into a dump truck. A horizontal belt and inclined
screw conveyor are required to accomplish the conveyance required.
8.6.1 System Description
The cake produced by the belt filter presses is dropped onto a horizontal belt conveyor (CON9401A) that
collects cake from all three presses. The horizontal conveyor moves the cake east just past the furthest
east belt filter press where it inclines slightly and offloads into an inclined and enclosed screw conveyor
(CON9402A). The screw conveyor moves the cake east still, but also about 15 ft vertically. The cake
then falls into a dump truck parked underneath.
8.6.2 Design Data
Table 8-8. Cake Conveyance Design Data
Parameter Value
Conveyor Capacity 3.4 wet tons/hour @ 20.3% TS
Cake Bulk Density 50 - 60 lb/ft3
Cake Solids 15 - 25% TS
8.6.3 Operation and Control
The conveyors installed in the Phase 1 expansion are provided with a local Hand-Off-Auto selector
switch. In auto the conveyors operate when any belt filter press system operates. The conveyors
continue to operate for a plant operator set period of time to clear conveyors of cake. Both conveyors
are equipped with safety switches for emergency shutdown that are connected to pull cords that run the
length of the conveyor.
8.6.4 Equipment Data
Table 8-9 summarizes the equipment data for the cake conveyance system.
Table 8-9. Cake Conveyance Equipment Data
Parameter Value
Horizontal Belt Conveyor
Asset Tag CON9401A
Manufacturer Custom Conveyor Corporation
Type horizontal sidewall
Width 24 inches
Nominal Length 52 ft
Maximum Belt Speed 75 ft/min
Motor Size 5 hp
Shaftless Screw Conveyor
Asset Tag CON9402A
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Manufacturer Custom Conveyor Corporation
Type shaftless screw conveyor
Incline 35° (from horizontal)
Shaft Size 12 inch diameter
Screw Rotation Speed 19 rpm
Motor Size 10 hp
Length 30.6 ft
8.6.5 Maintenance
The manufacturer’s recommended maintenance for the cake conveyance equipment is listed in Table 8-
10. Refer to the manufacturer’s Operations and Maintenance Manual for a more comprehensive listing
of troubleshooting and maintenance requirements
Table 8-10. Cake Conveyance Equipment Maintenance
Activity Lubricant Frequency
Horizontal Belt Conveyor
Clean-up around conveyor and
check belt tracking. - Daily
Observe belt wiper and adjust
accordingly. - Weekly
Check reducer oil level, lubricate
bearings, and lubricate idlers. NLGI #2 Monthly
Check drive belt tension. - Quarterly
Flush and fill gear reducer. SAE-80/90 Semi-Annually
Lubricate motor. Mobil Polyrex EM Annually (every 6,000 hours)
Shaftless Screw Conveyor
Clean-up around conveyor. - Daily
Check seal on drives. - Weekly
Check reducer oil level, check
trough liners for wear, and check
drive shaft seal.
- Monthly
Lubricate motor. Mobil Polyrex EM Annually (every 6,000 hours)
Flush and fill gear reducer. EP 220 Every 2 years (10,000 hours)
8.7 Cake Storage
Sludge digested by the temperature phase anaerobic digestion process has been demonstrated through
testing to meet Class 1 biosolids criteria. The dewatered biosolids are usually land applied during the
spring and fall when crop land is available. Some of the cake is used by the City of Iowa City during the
summer months for landscaping and soil amending. A covered storage facility is used to stockpile cake
between land application seasons.
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8.7.1 System Description
The covered cake storage facility consists of a covered concrete pad sloped to facilitate drainage, which
is collected in the HSW sewer system. The pad is constructed with perimeter concrete push walls to
contain the cake and facilitated loading. The push walls are 10 ft high corresponding to a maximum
desirable cake depth. A metal frame roof covers the pad. The roof is supported by metal columns
extending a minimum of 25 feet above the floor. The height provides clearance for cake handling
equipment. Under most conditions there will be adequate area for windrowing solids for further air
drying and stacking for extended storage. The space between the concrete push walls and metal roof is
left open to minimize costs and facilitate ventilation and continued drying. Figure 8-2 depicts the cake
storage facility under construction, note the roof decking has yet to be installed.
Figure 8-2. Cake Storage Facility (Under Construction).
8.7.2 Design Data
The storage facility can store 270 days of dewatered cake under projected Phase 1 cake production
conditions. Additional storage is available by an uncovered pad with similar construction minus the roof
as the covered facility.
8.7.3 Operation and Control
Cake is hauled from the belt filter presses to the storage facility. If the plant is actively windrowing, the
fresh cake would we windrowed and if storage space is limited the longest drying windrow would be
stacked.
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Any drainage seeping out of the cake drains to the east and is collected by a concrete swale at the
extreme west end of the facility. The swale directs the drainage to the HSW sewer since it will be high in
ammonia and may need special treatment by the BAR process, depending on how the plant is operating.
8.7.4 Equipment Data
The covered cake storage facility installed in the Phase 1 expansion spans 228 feet north to south and
265 feet east to west. The facility is divided into three bays with dividing push walls each 25.3 feet wide.
The outside and bay walls end approximately 60 feet from the west end of the facility to permit
equipment access.
8.7.5 Maintenance
The cake storage facility is virtually maintenance free. Care should be taken to ensure the drainage
system is clean and unclogged.
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Appendix A: IDNR WLA Water Quality Requirements
February 23, 2011
WLA Appendix A
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Appendix A WLA
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WLA Appendix A
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Appendix A WLA
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WLA Appendix A
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Appendix A WLA
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WLA Appendix A
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Appendix A WLA
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WLA Appendix A
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Appendix A WLA
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WLA Appendix A
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Appendix A WLA
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WLA Appendix A
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Appendix A WLA
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WLA Appendix A
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Appendix A WLA
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