HomeMy WebLinkAbout[2011] Tech Memo - Consolidation Project - Condition Assessment1392627;)—StanleyConsultantsINC30EastSeventhStreetSuite1500St.Paul,MN55101Tel:651-298-0710Fax:651-298-1931Preparedfor:CityofIowaCityProjectTitle:IowaCitySouthPlantExpansionProjectNo:TechnicalMemorandumNo.17Subject:IowaCitySouthWastewaterTreatmentPlantExistingFacilitiesandConditionDate:December29,2011To:BenClark,CityofIowaCityDaveElias,CityofIowaCityFrom:MichaelMacaulay,BrownandCaldwellBennettReischauer,StanleyConsultants,Inc.Preparedby:Reviewedby:-Reviewedby:Limitations:ThisdocumentwaspreparedsolelyforCityofIowaCityinaccordancewithprofessionalstandardsatthetimetheserviceswereperformedandinaccordancewiththecontractbetweenCityofIowaCityandStanleyConsultantsdatedMay10,2010.ThisdocumentisgovernedbythespecificscopeofworkauthorizedbyCityofIowaCity;itisnotintendedtoberelieduponbyanyotherpartyexceptforregulatotyauthoritiescontemplatedbythescopeofwork.WehavereliedoninformationorinstructionsprovidedbyCityofIowaCityandotherpartiesand,unlessotherwiseexpresslyindicated,havemadenoindependentinvestigationastothevalidity,completeness,oraccuracyofsuchinformation.LloydWinchell,BrownandCaIdwelljj!)fiu17/,j1JcMichaelMacaulay,PE,Bro4L.aAdCaidwellBennettReischauer,PE,StanleyConsultantsBrownANDCaidwelL
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Table of Contents
List of Figures .................................................................................................................................................................. iii
List of Tables ..................................................................................................................................................................... v
1. Executive Summary.................................................................................................................................................... 1
1.1 Objective ........................................................................................................................................................... 1
1.2 Plant Description ............................................................................................................................................. 2
1.3 Condition Assessment .................................................................................................................................... 3
2. Introduction ................................................................................................................................................................. 4
3. Description of Existing Wastewater Facility ........................................................................................................... 4
3.1 Preliminary Treatment .................................................................................................................................... 8
3.1.1 Influent Junction Structure .............................................................................................................. 8
3.1.2 Septage Receiving Station .............................................................................................................. 8
3.1.3 Screening ........................................................................................................................................... 9
3.1.4 Influent Pumping ............................................................................................................................ 10
3.1.5 Plant Flow Control Gate ................................................................................................................. 11
3.1.6 Parshall Flumes .............................................................................................................................. 11
3.1.7 Vortex Grit Removal ....................................................................................................................... 11
3.1.8 Aerated Grit Removal .................................................................................................................... 13
3.1.9 Flow Equalization ............................................................................................................................ 13
3.1.10 High Strength Equalization ........................................................................................................... 14
3.2 Primary Treatment ........................................................................................................................................ 16
3.3 Secondary Treatment ................................................................................................................................... 19
3.3.1 Biological Reactors ........................................................................................................................ 19
3.3.2 Aeration Blowers ............................................................................................................................ 21
3.3.3 Secondary Clarifiers ....................................................................................................................... 22
3.3.4 RAS Pumping .................................................................................................................................. 23
3.3.5 WAS Pumping ................................................................................................................................. 23
3.4 Disinfection..................................................................................................................................................... 24
3.4.1 Chlorination ..................................................................................................................................... 24
3.4.2 Sulfur Dioxide System.................................................................................................................... 26
3.5 Outfall .............................................................................................................................................................. 27
3.6 Waste Activated Sludge Thickening ........................................................................................................... 27
3.6.1 Rotary Drum Thickeners ................................................................................................................ 27
3.6.2 Thickened Sludge Pumps .............................................................................................................. 28
3.6.3 Thickener Wash Water Pumps ..................................................................................................... 29
3.6.4 WAS Thickening Polymer Addition .............................................................................................. 29
3.7 Anaerobic Digestion ...................................................................................................................................... 30
3.7.1 Tanks ................................................................................................................................................ 30
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3.7.2 Sludge Pumping Systems ............................................................................................................. 33
3.7.3 Sludge Heating................................................................................................................................ 36
3.7.4 Digester Gas Handling ................................................................................................................... 41
3.8 Biosolids Dewatering .................................................................................................................................... 41
3.8.1 Belt Filter Press Feed Pumps ....................................................................................................... 42
3.8.2 Belt Filter Presses ........................................................................................................................... 42
3.8.3 BFP Polymer Addition .................................................................................................................... 43
3.8.4 Conveyance ..................................................................................................................................... 43
3.8.5 Dewatered Biosolids Storage Pad ............................................................................................... 43
3.9 Ancillary Systems .......................................................................................................................................... 44
3.9.1 Effluent Water ................................................................................................................................. 44
3.9.2 Dewatering Pump Station ............................................................................................................. 44
3.9.3 De-Foaming System ....................................................................................................................... 45
3.9.4 Sampling Systems .......................................................................................................................... 45
3.9.5 Influent Pump Station Sump Pumps .......................................................................................... 45
3.9.6 Soccer Field Irrigation .................................................................................................................... 46
3.9.7 Plant Security .................................................................................................................................. 46
3.9.8 Structural Overview ........................................................................................................................ 46
3.9.9 Electrical Overview ......................................................................................................................... 46
3.9.10 Instrumentation and Control Overview ....................................................................................... 49
3.9.11 HVAC and Plumbing Overview ...................................................................................................... 51
4. Facility Condition ...................................................................................................................................................... 54
List of Figures
Figure 1. Iowa City South Wastewater Treatment Plant Existing Liquid Stream Treatment Flow
Schematic ................................................................................................................................................................. 5
Figure 2. Iowa City South Wastewater Treatment Plant Exisiting Solid Stream Treatment Flow
Schematic ................................................................................................................................................................. 6
Figure 3. Interceptor Junction Structure ..................................................................................................................... 8
Figure 4. Septage Receiving Station ........................................................................................................................... 9
Figure 5. Mechanical Bar Screen and Power Unit .................................................................................................. 10
Figure 6. Influent Pumps (left pump installed in 1990, right pump in 2001) ................................................... 11
Figure 7. Grit Chamber and Pump Plan ................................................................................................................... 12
Figure 8. Grit Dewatering System ............................................................................................................................. 13
Figure 9. Equalization Facilities ................................................................................................................................. 14
Figure 10. High Strength Equalization Pump Station ............................................................................................ 15
Figure 11. High Strength Equalization Tank ............................................................................................................ 16
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Figure 12. Primary Clarifier Layout ........................................................................................................................... 17
Figure 13. Primary Clarifier Weirs (left 1990 installation, right 2001 installation) .......................................... 18
Figure 14. Primary Sludge Pump and Grinder ........................................................................................................ 19
Figure 15. Biological Reactors ................................................................................................................................... 20
Figure 16. Aeration System Blower .......................................................................................................................... 21
Figure 17. Secondary Clarifiers.................................................................................................................................. 22
Figure 18. RAS Pumps (1990 installation on left, 2001 installation spare on right) ....................................... 23
Figure 19. WAS Pumps ............................................................................................................................................... 24
Figure 20. Chlorine Mixing Tank Section .................................................................................................................. 25
Figure 21. Chlorine Contact Tanks ............................................................................................................................ 26
Figure 22. Sulfur Dioxide Mixing Tank Section ....................................................................................................... 27
Figure 23. Rotary Drum Thickeners ........................................................................................................................... 28
Figure 24. Thickened WAS Pumps ............................................................................................................................. 28
Figure 25. Dry Polymer Processing Unit .................................................................................................................... 29
Figure 26. Original Digesters – Installed 1990 ........................................................................................................ 31
Figure 27. Digester Gas Mixing Compressors .......................................................................................................... 31
Figure 28. Digestion Tanks (larger thermophilic/mesophilic on left and mesophilic on right) ........................ 32
Figure 29. Digested Sludge Storage Tank ................................................................................................................ 33
Figure 30. Raw Sludge Pumps ................................................................................................................................... 34
Figure 31. Sludge Transfer Pumps (1990 installation on left, 2001 on right).................................................... 35
Figure 32. Sludge Circulation Pumps (1990 installation on left, 2001 on right) ............................................... 36
Figure 33. Sludge/Sludge Heat Exchangers ............................................................................................................. 37
Figure 34. Hot Water to Sludge Heat Exchangers – Larger Units ......................................................................... 37
Figure 35. Water Plate and Frame Heat Exchangers (larger unit on left, smaller on right) ............................. 38
Figure 36. Primary Heating Loop Circulating Water Pumps (building heating pump in foreground) ............. 39
Figure 37. Secondary Heating Loop Circulating Water Pumps (north pump on left, south pump on
right) ......................................................................................................................................................................... 39
Figure 38. Sludge Heat Exchanging Boilers .............................................................................................................. 40
Figure 39. Digester Gas Boilers (left) and Booster Fan (right) ............................................................................... 41
Figure 40. Waste Digester Gas Flares (1990 installation on left, 2001 installation on right) ......................... 41
Figure 41. Belt Filter Press Feed Pumps ................................................................................................................... 42
Figure 42. Belt Filter Presses ...................................................................................................................................... 43
Figure 43. Effluent Water Pumps (5 of 6 pictured) ................................................................................................. 44
Figure 44. Influent Pump Station Dry Well Sump Pump Installation ................................................................... 46
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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List of Tables
Table ES-1. Iowa City SWWTP Unit Processes ............................................................................................................ 2
Table ES-2. Replacement Schedule for Key Areas at the SWWTP ......................................................................... 3
Table 2. Iowa City SWWTP Process Unit Capacities .................................................................................................. 7
Table 3. Condition Rating Scale Description ............................................................................................................ 55
Table 4. Asset Functional Rating Scale Description ................................................................................................ 55
Table 5. Replacement Schedule for Key Areas at the SWWTP ............................................................................. 56
Table 1. Iowa City SWWTP Facilities Data ................................................................................................................ 57
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1. Executive Summary
1.1 Objective
This technical memorandum describes the existing Iowa City South Wastewater Treatment Plant
(SWWTP) mechanical/process facilities, including the capacity and condition of equipment and process
units. Supporting control, HVAC, structural, and electrical systems are briefly discussed separately and
as they pertain to the equipment and process units if applicable. Furthermore, operational and
maintenance issues are described.
A field inspection was conducted on July 27-28, 2010 by plant, Stanley, and Brown and Caldwell staff
to inventory assets, note asset condition, and better understand operation and maintenance issues.
The field inspection was used to create the repair and replacement schedule of major assets included
near the end of this memorandum.
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1.2 Plant Description
Originally constructed in 1990 and then expanded in 2001, the SWWTP is located just south of Iowa
City and consists of both liquids and solids treatment processes. Table ES-1 lists the various unit
processes currently in use at the SWWTP.
Table ES-1. Iowa City SWWTP Unit Processes
Stream Unit Process
Liquid Stream
Influent Screening
Influent Pumping
Flow Equalization
Flow Metering
High Strength Waste Equalization
Grit Removal
Primary Treatment
Secondary Treatment
Activated Sludge Treat-
ment
Secondary Clarification
Disinfection
Outfall
Solid Stream
WAS Thickening
Thermophilic Digestion
Mesophilic Digestion
Dewatering
Dewatered Biosolids Storage
Miscellaneous
Effluent Water Reuse
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1.3 Condition Assessment
The equipment and structures associated with the unit processes listed in Table ES-1 were inspected
with input from plant staff to determine their remaining useful life. Table ES-2 lists the expected
replacement schedule for key assets.
Table ES-2. Replacement Schedule for Key Areas at the SWWTP
Time Frame Asset Installation Date
0-5 years Influent Pumps – Original 1990
Dry Polymer Handling 1990
Dewatered Biosolids Conveyors 1990
Effluent Water Pumps 1999
Aeration Diffusers 2001
Various Building HVAC Systems 1990/2001
SCADA System Panels 1990/2001
6-15 years High Strength Equalization Pumps and Mixers 2001
Grit Mechanical Systems 2001
Polymer Delivery Systems 1990/2001
Aeration Tank Mixers 2001
Primary Clarifier Collectors - Original 1990
Primary Sludge Pumps 2003/2009
RAS Pumps 1990/2001
WAS Pumps 1990
Thickened Sludge Pumps 1990
Digester and Sludge EQ Tank Mechanical Mixers 2001
Digestion Pumping Systems – Original 1990
Sludge Dewatering System 1990
Sludge Heat Exchanger Boilers – Original 1990
15-20 years Influent Pumps - Expansion 2001
Mechanical Bar Screens 1990
Primary/Secondary Clarifier Collectors – Expansion 2001
High Strength Equalization Tank
Rotary Drum Thickeners 2001
Digestion Pumping and Heat Exchange Systems -
Expansion 2001
Digester Gas Boilers 2001
21-30 years Aeration Blowers 2001
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Other ancillary and supporting systems were investigated and recommendations for replacement are
listed in the respective sections.
2. Introduction
Stanley Consultants and Brown and Caldwell were contracted by the City of Iowa City to conduct facility
planning and design activities related to combining the North and South Wastewater Treatment Plants
at the South Wastewater Treatment Plant (SWWTP). As part of the scope a review of the existing
assets at the SWWTP and their condition were to be conducted. This technical memorandum presents
the state of the SWWTP assets and estimates their remaining useful life.
On July 27-28 a focused asset field inspection was conducted by Stanley Consultants and Brown and
Caldwell staff. Plant staff participated in the field inspection and provided valuable first hand opera-
tion and maintenance information. This formal inspection was supplemented with multiple follow up
inspections and correspondence with plant staff to arrive at the information presented in this technical
memorandum.
3. Description of Existing Wastewater Facility
The SWWTP was originally constructed in 1990. The plant was then expanded in 2001, which included
increased capacity and improved treatment processes. The SWWTP is sited on approximately 50
acres, located about 3 miles due south of downtown Iowa City. The Iowa River is the receiving body for
the SWWTP discharge. The liquid stream process includes preliminary treatment, primary treatment,
nitrifying activated sludge using fine bubble diffusion, disinfection by chlorine, and dechlorination by
sulfur dioxide as depicted in Figure 1. The solids processing facilities include waste activated sludge
(WAS) thickening, combined primary sludge and thickened WAS thermophilic/mesophilic anaerobic
digestion, and belt filter press dewatering as depicted in Figure 2. The SWWTP also handles the sludge
generated at the Iowa City North Wastewater Treatment Plant (NWWTP). This sludge is sent to the
digestion system.
Table 1 is located at the end of this document and provides a summary of existing equipment design
data. Table 2 provides date on existing process unit capacities.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 1. Iowa City South Wastewater Treatment Plant Existing Liquid Stream Treatment Flow Schematic
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 2. Iowa City South Wastewater Treatment Plant Existing Solid Stream Treatment Flow Schematic
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Table 2. Iowa City SWWTP Process Unit Capacities
Process Key Criteria Process Units Capacity/Unit Firm Capacity Total Capacity Comments
Liquid Stream
Influent Screening 2 30 mgd 30 mgd 60 mgd manufacturer’s rating
Influent Pumping flow at 46 ft TDH 6 8,330 gpm 41,650 gpm 49,980 gpm manufacturer’s rating
EQ Basins 2 Cell 1 - 2.1 MG
Cell 2 - 4.3 MG - 6.4 MG
Plant Influent Parshall Flume 70% submergence 1 55 mgd - 55 mgd calculated
Grit Tanks 2 12.5 mgd
6 mgd
12.5 mgd
6 mgd
25 mgd
12 mgd
manufacturer's rating
de-rated manufacturer’s rating
Primary Treatment 1,000/2,100 gpd/ft2 at annual
average/peak hour flow 4 4.4 mgd
9.3 mgd
13.2 mgd
27.9 mgd
17.6 mgd
37.2 mgd BC design criteria
Secondary Treatment SLR – 42 lb/d-ft2
SOR – 895 gpd/ft2 4 4.5 mgd 13.5 mgd 18 mgd
10-day aerobic SRT
SVI = 150 mL/g
3,000 mg/L MLSS
RAS = 3.75 mgd/clarifier
Disinfection 19 minutes detention time at max
wet weather flow 2 12.6 mgd 25.2 mgd 25.2 mgd 165,000 gallons in each tank
Outfall 100-year flood, SO2 weir not
flooded
1 21 mgd - 21 mgd hydraulically modeled
Solid Stream
WAS Thickening 2 350 gpm
31 lb/min
350 gpm
31 lb/min
700 gpm
62 lb/min
manufacturer’s rating
Thermophilic Digestion 5-day hydraulic retention time 1 – 55’ dia. 103,550 gpd
55,375 lb VSS/d 103,550 gpd 103,550 gpd
Mesophilic Digestion 15-day hydraulic retention time 1 – 55’ dia.
4 – 45’ dia.
34,520 gpd
22,800 gpd
34,520 gpd
91,210 gpd 125,720 gpd
Belt Filter Press 3 1,000 lb/hr 2,000 lb/hr 3,000 lb/hr manufacturer’s rating
Dewatered Biosolids Storage
Pad
120-180 days (10 States
Standards)
1 202,500 ft3 - 202,500 ft3 historically handles 365 days of
dewatered biosolids
Miscellaneous
Effluent Water Pumps flow at 231 ft TDH 6 250 gpm 1,250 gpm 1,500 gpm manufacturer’s rating
8
3.1 Preliminary Treatment
The preliminary treatment facilities include interceptor junction structure, influent screening, influent
pumping, vortex grit removal, high strength equalization, and flow equalization. A single Parshall flume
measures the flow entering plant downstream of the equalization and the influent pump station. Parshall
flumes also measure the flow into and out of the flow equalization basins. A bypass around the vortex grit
chambers can direct flow directly to the primary clarifiers.
3.1.1 Influent Junction Structure
The interceptor junction structure is located upstream of the screening/influent pump station building. The
structure combines flow from the 66 in Southeast Interceptor from the north, 48 in South River Corridor
Interceptor from the west, a 24 in equalization effluent pipe, 12 in line from the septage receiving station,
and 8 in and 18 in drain lines as shown in Figure 3. The flow is combined and discharged to the influent
channel for the mechanical bar screens. There are no immediate concerns regarding this structure.
Figure 3. Interceptor Junction Structure
3.1.2 Septage Receiving Station
Septage trucks discharge their tank contents into the septage receiving station, show in Figure 4 located
near the screening/influent pump station building. The station is composed of an electrically heated
concrete pad sloped to a drain and surrounded by three walls. Septage flows by gravity to the influent
junction structure via a 12 in pipe. This pipe is equipped with a 3 in effluent water flushing connection to
clear clogs. A branch of the effluent water line supplies a hose station for rinsing the station. Operational-
ly, the drain screen was noted as requiring periodic cleaning and there is no form of security entrance or
monitoring for trucks discharging after plant staff leaves for the evening.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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.
Figure 4. Septage Receiving Station
3.1.3 Screening
Plant influent flow is conveyed from the influent junction structure to two, 4 ft wide channels, each with a
climber style mechanically cleaned bar screen. The bar screens were installed in 1990. The screens are
constructed of stainless steel and appear to be in good condition. The hydraulic power units that replaced
electric drives also seem to be in good condition and are reportedly working well. Figure 5 shows a screen
and power unit. The bar screens have 5/8 in openings to capture rags and debris. The spacing does allow
some material to pass downstream for removal in the grit removal or primary treatment facilities.
The screenings are removed and automatically dumped into rolling totes. When full, plant staff manually
rolls totes over to the dewatered grit collection pad in the grit building for subsequent landfill disposal.
Based upon a peak hour bar screen operating velocity of 3 ft/s, each bar screen is rated for 30 million
gallons per day (mgd) or a total capacity of 60 mgd. Under normal operations, one of the bar screens is in
operation.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 5. Mechanical Bar Screen and Power Unit
3.1.4 Influent Pumping
Screened wastewater flows by gravity into the influent pump station wet well where it is lifted above grade
and is discharged into a channel feeding the rest of the plant. Under the original 1990 construction five
line shaft pumps were installed, three large and two small, relatively. In the 2001 expansion the two small
pumps were removed and replaced with three direct coupled pumps with nominal capacity equal to that of
the three existing large pumps.
Each pump has a manufacturer’s rating of 8,330 gallons per minute (gpm) at 46 ft of total dynamic head
(TDH). Under normal operation conditions, one pump is running at 95% of full speed. Together the pump-
ing station has a firm and total capacity of 60 mgd and 72 mgd, respectively. Although, during field testing
the older line shaft pumps exhibited reduced capacity. Generally the pumps are performing acceptably. It
was noted, however, that the older pumps have broken off impeller nuts and are therefore run less fre-
quently.
No significant operational problems were noted during the inspection other than one of the pump’s dis-
charge piping reportedly vibrates excessively when the pump speed exceeds 90%, however as can be seen
in Figure 6 the pumps are displaying surface corrosion, especially the older pumps. Also noted was that
removing all but the two centrally located pumps is difficult due limited crane access and interfering
discharge piping bracing. There may also be a feasible opportunity for energy savings by operating the wet
well at a higher level during normal flow conditions.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 6. Influent Pumps (left pump installed in 1990, right pump in 2001)
3.1.5 Plant Flow Control Gate
The plant flow control gate is located downstream of the influent pump discharge and equalization over-
flow and can isolate or choke flow to the rest of the plant. The gate is 36 in wide by 60 in high. The gate
was installed in 1990 and appears to be in good condition. No operational issues were noted during the
field inspection.
3.1.6 Parshall Flumes
Three Parshall flumes measure the plant flow, equalization overflow, and equalization return flow. The
plant flow flume was resized to a 36 in throat in 2001 with a capacity of 26 mgd at 2.2 ft of head. The
plant flow flume is located just upstream of the grit removal facilities. The equalization overflow flume
also has a 36 in throat width and 45 mgd capacity. The equalization overflow flume is located in the
bypass channel downstream of the influent pump discharge channel. The equalization return flume has an
18 in throat and 16 mgd capacity, located in a dedicated structure northeast of the influent pump station
building.
In general the flumes looked to be in good condition. During an influent pump trial a foam layer was
created and it was noted that measuring instrumentation did not provide reliable readings for the plant
flow flume.
3.1.7 Vortex Grit Removal
Grit Removal Chambers – An aerated grit tank was constructed and 1990 and replaced in 2001 with two
vortex grit chambers, see Figure 7. Each chamber is 13 ft in diameter with 12 ft sides and was designed
for a 1.6 minute detention time at 5 mgd. The installed units each have a manufacturer’s rating of 12.5
mgd, however, recent experience at other installations implies the real capacity of these units is roughly
half. The grit chamber mixers consist of a 5 ft propeller driven by a 1 hp motor with a variable speed drive.
The grit chambers can be bypassed and taken out of service for maintenance.
The chambers looked to be in good structural condition. The gear reducer housing for the mixer drive is
corroding. The mixer impeller and shaft were in service and could not be inspected.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Plant staff noted that the two 36 in grit effluent lines allow silt escaping the grit chambers to settle during
average flows. When a large flow event occurs the silt is washed downstream into the primary clarifier
splitter box and the primary clarifiers themselves. This causes the plant to increase the primary sludge
pumping rate to avoid clogging issues and vactor out the splitter box. Upgrades to the grit removal system
will be included to help mitigate grit carry over.
Figure 7. Grit Chamber and Pump Plan
Grit Pumps – After settling, grit flows by gravity into the grit pump wet well. Each chamber has a dedicated
pump, there is no redundancy. The pumps are submersible Wemco Model C slurry pumps with recessed
impellers rated at 250 gpm at 34 TDH. Grit is pumped intermittently to the grit separation and washing
equipment in the grit building. The grit pumps were in service and, therefore, not inspected. Given the age
and severe service plus the fact that several pipe fittings have been eroded and failed, these pumps have
likely undergone considerable wear as well. Furthermore, plant staff report the discharge lines are clog-
ging more frequently. A standby pump is stored on site if one should fail.
The motor control center (MCC) operating the grit system is located within the grit building. The atmos-
phere within the girt building is very aggressive and the MCC is in poor condition. A separate building or
disconnected room should be provided for the MCC in the planning period.
Grit Separators/Washers –The grit slurry is pumped to a Wemco Hydrogritters consisting of two cyclonic
separators, each feeding to a screw type grit classifier (washer) as shown in Figure 8. The cyclones are
rated for 350 gpm at 12.5 psig each, yielding an underflow of 17 gpm. The washer can handle 24 gpm
while maintaining a 95% capture of 150 mesh grit. The wasted grit appears to be relatively dry and is
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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discharged onto the floor of the grit building for loading and disposal in a landfill. This system appeared to
be in good condition and there were no issued reported by plant staff.
Figure 8. Grit Dewatering System
3.1.8 Aerated Grit Removal
An aerated grit system was installed in 1990. This system has been abandoned, but the assets were left in
place. Those assets include the two 2,100 ft3 grit tanks and clamshell bucket crane system located near
the newer vortex grit chambers and a set of compressors in a dedicated room of the influent pump station
building. These assets appear to be in reasonable condition yet and may be considered for reuse or
removal to free up space.
3.1.9 Flow Equalization
The plant is equipped with flow equalization for dampening peak flow events. Two 2.1 million gallon (MG)
flow equalization basins were constructed in 1990. During the 2001 expansion the east basin was ex-
panded to 4.4 MG, giving the plant a total equalization capacity of 6.4 MG. When flows increase such that
the level in the influent pump discharge channel exceeds elevation 656.50 it will begin to flow over the
bypass weir and begin filling the first equalization basin. The second basin starts to fill when the first
reaches elevation 648.30. The basins are drained via a 24 in pipe network leading back to influent
junction structure. Return flow is controlled by a gate installed on the 24 in pipe and just upstream of the
return flow measuring flume discussed above. Flow will start to bypass the plant untreated should the
level in the equalization basins reach 648.60 which equates to 6.2 million gallons in the equalization
basins. The system is depicted in Figure 9.
In the 2001 expansion the basins had concrete bottoms and asphalted slopes installed. The slopes are
displaying significant cracks and should be resurfaced within the planning period. Otherwise the basins
and associated structures appear to be in good condition. Plant staff did note that heavy machinery
cannot access the easternmost basin (Cell 2) to remove solids buildup.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 9. Equalization Facilities
3.1.10 High Strength Equalization
High strength waste, primarily belt filter press filtrate and sanitary waste, is flows by gravity through the
plant drain sewers to the high strength equalization pump station. Flow is pumped into and stored in the
high strength equalization tank before being bled back to the influent junction structure. The system is
generally utilized when the belt filter presses are in operation, or normally three days per week. Equalizing
the press filtrate avoids overwhelming the biological treatment process with ammonia.
High Strength Equalization Pumping Station – Two submersible centrifugal pumps transfer flow into the
equalization tank. The pumps are rated for 450 gpm at 40 TDH. The pumps are intermittently run based
on the level in the wet well. The pumps were in service and, therefore, not inspected. The pump station is,
however, working well as indicated by plant staff. The layout of the pump station is depicted in Figure 10.
As shown, space for a third pump was provided in the structure.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 10. High Strength Equalization Pump Station
High Strength Equalization Tank – The high strength equalization tank is 62 ft in diameter and 15 ft tall.
The maximum side water depth is 13 ft based on the elevation of the overflow pipe. At this level the tank
can hold approximately 311,000 gallons. The tank is constructed of a concrete bottom with steel plate
walls.
The tank contents are mixed with two submersible 4 hp mechanical mixers. The mixers were in service
during the field inspection and could not be examined; however plant staff did not report any issues with
them.
High strength flow is discharged from the tank through a metering structure and back to the head of the
plant just downstream of the mechanical bar screens. The flow is controlled by a control valve located in
the metering structure.
Structurally the tank looks to be in good condition as can be seen in Figure 11. No corrosion was evident
outside or inside the tank. Plant staff did report that level transducers in the tank have detached and
become stuck in the 10 in withdrawal pipe or in the isolation valves in the metering structure. Further
noted was that the tank cannot quite hold a full (8 hour) day of belt filter press filtrate. Increasing the
height of the tank to accommodate the current and future filtrate flow will be considered in the planning
period.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 11. High Strength Equalization Tank
3.2 Primary Treatment
Primary treatment is provided by primary clarifiers and associated sludge pumps and scum removal
system.
Primary Clarifiers – Primary treatment is provided by four circular primary clarifiers as depicted in Figure
12. Each clarifier is 70 ft in diameter with a side water depth of 12 ft. The southern primary clarifiers were
installed in 1990 and have the original collection mechanisms. The northern primary clarifiers were
installed in 2001. Both sets are constructed with outboard weirs and rake sludge collection mechanisms.
The collector mechanisms are driven by 0.75 hp motors.
Flow is conveyed from the plant headworks via two 36 in pipes to the primary splitter box which utilizes
weirs to distribute the flow. Flow is conveyed through 24 in pipes to each clarifier center well.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 12. Primary Clarifier Layout
Each primary clarifier can treat peak hour flows of 9.3 mgd at overflow rates of 2,100 gpd/ft2. With one
unit out of service, the peak hour flow capacity is roughly 27.9 mgd.
The new clarifiers and collectors appear to be in good condition. The influent piping to the northeast
clarifier was not installed level, resulting in reduced capacity from air pockets and uneven flow distribution
in the splitter box.
The older clarifiers have carbon steel weirs installed as opposed to stainless steel in the new clarifiers.
Even though they have been re-painted they are severely corroded as seen in Figure 13. The collector
mechanism drive housings are showing signs of corrosion as well.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 13. Primary Clarifier Weirs (left 1990 installation, right 2001 installation)
The increased flux of silt from the two influent 36 in pipes during high flows and related operational issues
on primary treatment was discussed in the grit removal section above.
Plant staff noted that there is not a good sampling point for the primary effluent since return activated
sludge (RAS) is returned to the biological process via the southern two primary clarifier effluent launders.
The plant discharges the RAS in this location instead of in the aeration tanks distribution channel, but has
recently reverted back to the channel as originally designed.
Care must also be taken when dewatering a clarifier to confirm the groundwater table is low enough so not
to float the structure. Several dewatering wells have been installed around the secondary clarifiers and
plant staff has submersible pumps on hand to install in case the water table needs to be lowered.
Primary Sludge Pumps – Primary sludge is raked into a hopper near the center of each clarifier. Sludge is
withdrawn by a 6 in pipe to sludge pumping building by the primary sludge pumps. There are two pumps
rated at 300 gpm and 115.5 ft TDH, each. The original pumps installed in 1990 were replaced and those
replaced were also recently replaced in 2006 due to poor performance. The current pumps are Vogelsang
rotary lobe type as shown in Figure 14. The sludge is pumped to the sludge digesting system. Prior to
pumping the sludge is sent through a 5 hp grinder. Each pump has a dedicated grinder.
The primary pumps are also used to pump primary and secondary scum. The primary scum consists of the
scum captured off the primary clarifiers as well as the grit chambers. Secondary scum is fed by the scum
collectors on the secondary clarifiers and from the aeration tanks influent and discharge channels. Each
stream has a dedicated collection manhole near the sludge pumping building that is fitted with a 1 hp
mechanical mixer to keep the contents homogenized.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 14. Primary Sludge Pump and Grinder
The primary sludge pumps appear to be in good condition and are reportedly working well. The primary
sludge and scum grinders were rebuilt ca. 2006 and appear to be working well also. It was noted that
some of the valves are leaking and should be replaced. The piping also needs to be re-painted. The scum
mixers are seldom used and appear to be in working order.
3.3 Secondary Treatment
Secondary treatment is currently achieved using a single-stage nitrifying activated sludge system. The
secondary system consists of aeration tanks, mechanical mixers, aeration blowers, aeration distribution
equipment, secondary clarifiers, mixed liquor return pumps, RAS pumps, waste activated sludge (WAS)
pumps, and scum pumping.
3.3.1 Biological Reactors
The plant currently has four biological reactors. The reactors were designed with many features to provide
process flexibility, as discussed below. The general reactor layout is depicted in Figure 15.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 15. Biological Reactors
Aeration Tanks – There are four tanks available for biological secondary treatment. In 1990, four square
completely mixed activated sludge reactors with surface aerators were constructed. In the 2001 expan-
sion the original tanks were retrofitted and extended to serve as four rectangular pseudo-plug flow reac-
tors. Each tank is 428 ft long by 25.6 ft wide. At the maximum side water depth of 14.9 ft each tank is
approximately 1.2 million gallons (mg), for total volume of 4.8 mg. Each tank is divided into 8 cells by
masonry baffles for process flexibility. Mud valves are used for draining the tanks.
The tanks in general appear to be in good condition. The tank drain valves have been troublesome by not
sealing properly. It was discovered that the valves had brass trim and subsequently two of the four tanks
have had the brass replaced with stainless steel. The other two tanks are slated for the same improve-
ment.
Care must also be taken when dewatering a tank to confirm the groundwater table is low enough so not to
float the structure. Several dewatering wells have been installed around the secondary clarifiers and the
plant has submersible pumps on hand to install in case the water table needs to be lowered.
Air Diffuser System – The tanks are equipped with fine pore rubber membrane diffusers for transferring
oxygen. The diffusers are fed air through a polyvinyl chloride (PVC) (submersed) and stainless steel (ex-
posed) pipe network, including control valves. The fine pore diffusers have performed well with minimal
maintenance and have only been cleaned once since their installation, although they are relatively old for
industry standards. The PVC piping system has experienced several failures at joints, reportedly from thin
schedule material. The condition of the diffusers was not observed during inspection. The air flow control
valves regulating the flow off the main header at each drop are oversized and do not provide adequate
control.
Anoxic Mixers – As shown in Figure 15 the first four cells of each tank have a mechanical mixer, installed
in 2001. There used to be a mixer in Cell 8 of each tank as well, but were removed. Each mixer is 7.5 hp.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
21
Plant staff report the mixers are working well, however the condition of the mixers was not observed during
the field inspection. When the mixers do need maintenance, a crane company has to be called in to
remove them since the plant’s boom truck cannot reach the centrally located units.
Mixed Liquor Recycle – The biological reactor system was provided the capability of returning mixed liquor
to the head of the system to achieve certain process goals. Two submersible pumps were installed in
2001 within the tank effluent channel as noted on Figure 15. Each pump is rated for 8,680 gpm at 5.1 ft
TDH. The mixed liquor system has seen little use and the pumps were not visible during the field inspec-
tion.
3.3.2 Aeration Blowers
There are five six-stage centrifugal blowers installed in 2001 providing air to the biological reactors. Each
unit is rated for 6,250 scfm at 7.5 psig. The blowers have motorized inlet control valves to regulate the
flow. The drives are 300 hp constant speed. Typically, two blowers are in operation. Figure 16 shows a
typical blower as installed. The blowers are in good condition, requiring little maintenance.
Figure 16. Aeration System Blower
Currently the volume of air delivered to the aeration system is controlled by the number of blowers in
operation and by closing the inlet control valves. Typically, two blowers are run and throttled to a low
capacity in case one unit trips off. Recent operating data show these control valves are at about 30% open
on average. A lot of energy is lost across the control valve at this setting. In a 2009 energy audit, the hired
firm considered the installation of variable speed drives to limit the pressure drop across the control valves
at air demands less than the blower capacity. Another approach would be to install a smaller blower
capable of meeting the average demand without the need for throttling. This topic is discussed in more
depth in the energy technical memorandum.
One maintenance concern was raised during the field inspection regarding the blowers. The monorail
system used for removing the blower motors is rated at 4.5 tons. The blowers themselves weigh approx-
imately 5.9 tons. A contractor has to be hired if the blowers need to be removed.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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3.3.3 Secondary Clarifiers
Mixed liquor from the biological reactors is conveyed through a 48 in pipe to the secondary clarifier splitter
box. The splitter box uses weirs to evenly distribute the flow to each of the four clarifiers through 36 in
pipes. Each clarifier is 80 ft in diameter. The northern two clarifiers, constructed in 1990, have a side
water depth of 12 ft where the new southern clarifiers, constructed in 2001, have a side water depth of 16
ft. The newer clarifiers also have inboard weirs and collection launders compared to the outboard configu-
ration on the older clarifiers, see Figure 17. Another distinction between the old and new clarifiers is that
new version has a submersible RAS pumping station incorporated into the structure instead of in a sepa-
rate dry well configuration like the old installation.
Figure 17. Secondary Clarifiers
Each clarifier has a collector mechanism comprising of a 1.5 hp drive system, bottom scraper and sludge
suction piping, scum skimmer, flocculation well, and influent well. The mechanisms appear to be in good
condition, except there is some corrosion on the older systems. This is especially evident in the overflow
weirs, which are carbon steel on the older clarifiers and stainless steel on the new clarifiers, similar to the
primary treatment system. Both new and old clarifier drive housings are, however, displaying minor
corrosion.
While the older clarifiers are operating well, the center wells were attached using steel fasteners. The
fasteners in one clarifier failed, causing the center well to drop. As a result the steel fasteners on both
older clarifiers have been replaced with stainless steel.
Scum collected by a surface skimmer and pushed into a collection box. The scum is collected in a man-
hole near the sludge pumping building where a 0.5 hp mixer keeps the scum homogenous. From the
manhole the scum is pumped to the digestion process by the primary sludge pumps, as noted previously.
The scum collection and mixing system look to be in good condition, except the collection system on the
older clarifiers is showing corrosion.
Care must also be taken when dewatering a clarifier to confirm the groundwater table is low enough so not
to float the structure. Several dewatering wells have been installed around the secondary clarifiers and
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
23
plant staff has submersible pumps on hand to install in case the water table needs to be lowered. The
northwest clarifier (5100) was dewatered causing the tank to float which caused extensive damage to the
piping.
As a part of the planning work the secondary clarifiers were modeled hydrodynamically. The results of the
modeling are discussed in Technical Memorandum 1 – Secondary Clarifier Capacity Modeling. The sec-
ondary clarifiers can treat 4.5 mgd each.
3.3.4 RAS Pumping
Three non-clog centrifugal variable speed pumps, installed in 1990, are used to pump RAS from the old
clarifiers. These three pumps are rated for 2,600 gpm at 28 ft TDH. Recent records indicate two of these
pumps are operated continuously. These pumps have a day and night pumping regime. These pumps
appear to be in good condition, see Figure 18, and plant staff reports no issues with their operation.
Figure 18. RAS Pumps (1990 installation on left, 2001 installation spare on right)
As mentioned above, each of the new clarifiers, installed in 2001, has a dedicated submersible pump
station incorporated into its structure. These pumps are variable speed non-clog centrifugals and are rated
for 3,000 gpm at 22 ft TDH. Each of these pumps is in continuous operation. The pumps do have the
same pumping regime as the older pumps. There is an identical new pump in storage in case one of the
operating pumps should fail, Figure 18. Plant staff report these pumps have been working satisfactorily;
although, one of the pumps was shipped back to the manufacturer three times due to poor installation and
subsequent failure. The pumps were not available for visual inspection since they were in service.
The RAS discharge at the time of the field inspection was into the launders of the two older (southern)
primary clarifiers. Shortly thereafter the RAS was re-routed to the aeration tank influent distribution
channel.
The piping associated with these pumps should be re-painted.
3.3.5 WAS Pumping
Two non-clog centrifugal variable speed pumps are used for WAS pumping. Each pump is rated for 350
gpm at 15 ft TDH. One pump generally services the older clarifiers while the other services the newer
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
24
clarifiers. These pumps feed the rotary drum thickeners (RDTs) and operate only when the RDTs are in
operation. These pumps appear to be in good condition, see Figure 19, and plant staff is satisfied with
their performance.
The piping and appurtenances associated with these pumps should be re-painted.
Figure 19. WAS Pumps
3.4 Disinfection
The effluent disinfection system currently uses gaseous chlorine and sulfur dioxide. Both the chlorination
and dechlorination systems were installed in 1990 and upgraded in 2001. The plant has the ability to
deliver chlorine solution to the secondary scum collection manhole, secondary clarifiers, RAS system,
influent pump station, and the effluent water system. The doors on both the chlorine and sulfur dioxide
rooms are kept locked at all times.
During the field inspection it was noted that the chlorine rooms do not have a scrubber to remove chlorine
gas in the case of an emergency. The addition of a scrubber should be considered if chlorine gas will
continue to be the disinfection agent. In general, the ventilation system would shut down in the event of a
leak and the scrubber fan would start, reducing the amount of chlorine that might escape from the build-
ing.
3.4.1 Chlorination
Gas Chlorine System – The plant has a conventional chlorine gas feed system, with two banks of cylinders
connected at a time. When low pressure is observed on the bank that is in service, the system automati-
cally switches to the bank that is on standby. The lead bank of four cylinders is on a load cell, to provide an
indication of the amount of chlorine remaining. There were originally two load cells, but to increase
overhead room for switching cylinders one load cell was removed. Chlorine gas is withdrawn under pres-
sure from one bank of cylinders to the automatic switchover/vacuum regulator valve (VRV). Upstream of
the VRV, the piping is under pressure. Downstream of the VRV, the entire system is under vacuum. The
system is flow paced to control the chlorine feed rate. The chlorinators are rated at 1,000 lb/day each.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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The metered chlorine gas is mixed with effluent water by injectors rated at 1,500 lb/day each. The chlo-
rine solution is then distributed to the points mentioned above as needed.
Liquid System – The liquid system draws liquid off the bottom of the chlorine cylinders and is evaporated
by two evaporation units at 6,000 lb/day. The evaporated chlorine is then sent through the same gas
system as described above, starting at the chlorinators.
Chlorine Mixing Tank – Chlorine solution is piped to diffusers in either of the chlorine mixing tanks. The
mixing tanks hold approximately 10,600 gallons at 10 mgd for a residence time of 1.5 minutes. Mixing is
provided by a 7.5 hp Lightnin mixer. Additional mixing is provided by an overhanging wall midway through
tank forcing the flow under, see Figure 20. The tank and mixer appear to be in good condition. Plant staff
noted that the mixer is not used.
Figure 20. Chlorine Mixing Tank Section
Chlorine Contact Tank – There are two parallel chlorine contact tanks as depicted in Figure 21. Each tank
is divided into two cells with three passes each. Each tank has a volume of approximately 165,000 gallons
at a side water depth of 9.3 feet. The actual depth, and volume, varies with flow. The tanks were con-
structed with a serpentine flow pattern. The chlorine contact tanks provide 19 minutes of detention time
at a maximum wet weather flow rate of 25.2 mgd (design flow for the 2001 expansion). Presently one cell
of the east contact tank is serving as a well for the soccer field irrigation system. The tanks appear to be in
good condition.
Care must also be taken when dewatering a tank to confirm the groundwater table is low enough so not to
float the structure. Several dewatering wells have been installed around the secondary clarifiers and plant
staff has submersible pumps on hand to install in case the water table needs to be lowered.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 21. Chlorine Contact Tanks
3.4.2 Sulfur Dioxide System
Sulfur Dioxide Gas System – The sulfur dioxide feed system is virtually identical to the gas chlorination
system, except that there are fewer cylinders in each bank. Instead of a mixer, the sulfur dioxide solution
is routed to a diffuser located in the sulfur dioxide mixing tank at the end of the chlorine contact tank.
Sulfur Dioxide Mixing Tank – Sulfur dioxide solution is piped to diffusers in either of the sulfur dioxide
mixing tanks. The mixing tanks hold approximately 12,700 gallons at 10 mgd for a residence time of 1.8
minutes. There is no mechanical mixing, although the tank has one rising wall and an overhanging wall to
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
27
provide an up and down flow path, see Figure 22. The tank and mixer appear to be in good condition.
Plant staff noted that the mixer is not used.
Figure 22. Sulfur Dioxide Mixing Tank Section
3.5 Outfall
The SWWTP currently discharges treated flow from the disinfection system to the plant outfall via a 42 in
pipe. This pipe combines with the plant bypass from the equalization basins and continues to the Iowa
River in a 60 in pipe. The hydraulic capacity of the outfall without flooding the sulfur dioxide (SO2) is 21
mgd when the river is at the 100 year flood event. The pipe was installed in 1989. The outfall was not
observed during the inspection.
3.6 Waste Activated Sludge Thickening
Wasted sludge is pumped off the RAS piping to the WAS thickening system located in the solids
processing building. The thickening system was installed in 2001. WAS was previously sent directly to the
digestion system.
3.6.1 Rotary Drum Thickeners
WAS is thickened using rotary drum thickeners, displayed in Figure 23. Thickened sludge falls into a
hopper and is then pumped to the digestion process. Thickening filtrate is routed to the high strength
equalization tank through the plant drain system.
Each RDT is rated to process 350 gpm of 0.6% percent solids or roughly 12.6 DT/d. Based on the last
three years of operation WAS is thickened to 5.0 percent solids and uses 16 pounds of polymer per dry ton
of solids. Generally only one unit is run at a time for roughly 6-8 hours per day, five days per week. The
RDTs are reported to be very reliable.
These units have limited capacity due to sharing a common discharge pipe with the primary sludge pumps.
When operating simultaneously the head is too high for the discharge pumps.
Plant staff noted that it would be helpful to have a mechanical adjustment on the rotary drive belt. Also, a
direct drop into the thickened sludge pump suction would improve the pump performance.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 23. Rotary Drum Thickeners
3.6.2 Thickened Sludge Pumps
Two progressive cavity variable speed pumps are used to transfer thickened WAS to the digestion process,
Figure 24. Each pump is rated for 36 gpm at 80 ft TDH. Each RDT has a dedicated thickened sludge
pump. The thickened sludge line ties into the primary sludge line at a buried connection. This results in
the thickened sludge pumps and primary sludge pumps competing against one another. Plant staff
indicates that primary sludge pumps become overloaded when this occurs.
These pumps appear to be in reasonable condition, see Figure 24, and plant staff are satisfied with their
performance. The base plates and housings are corroding. The rotors and stator were replaced in 2005.
Figure 24. Thickened WAS Pumps
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3.6.3 Thickener Wash Water Pumps
Two pumps boost effluent water into the RDTs for washing solids. Each pump is rated for 20 gpm at 104 ft
TDH. Each RDT has a dedicated wash water pump. The pumps are located under the RDT framing and are
hard to access. Furthermore, the pumps have required their motors to be replaced five times each since
installation. Relocating these pumps should be considered.
3.6.4 WAS Thickening Polymer Addition
Polymer is currently added to the WAS to enhance thickening in the RDTs. The plant is currently using
Pennwalt brand polymer. The system comprises of a dry processing unit, mixing/aging tanks, and meter-
ing pumps.
Dry Processing Unit – Bags, 50lb, of dry polymer are loaded into the processing unit by hand. The unit
slurries the polymer with effluent water and transfers it to the mixing/aging tanks. The unit is used for
both RDT thickening and belt filter press dewatering (BFP) polymers. The unit was installed in 1990 and is
displaying wear, see Figure 25. This equipment should be replaced for the upcoming planning effort. Plant
staff noted that they would prefer super sack bulk polymer to limit manual handling. Plus two make-up
units, one dedicated for a type of polymer, would help operations staff.
Figure 25. Dry Polymer Processing Unit
Mixing/Aging Tanks – Slurried polymer is transferred to two fiberglass mixing/aging tanks prior to being
metered to the RDTs. The tanks containing polymer used in the RDTs are located on the south side of the
polymer room and are labeled T9335 and T9336. Each tank can hold 1,600 gallons. Each tank has a 1.5
hp mixer. The tanks are not showing any signs of cracking or fatigue and the mixers look to be in good
condition.
Metering Pumps – Polymer solution is metered to the RDTs by two variable speed progressive cavity
pumps. The pumps are rated for 4 gpm at 185 psig with a 1.5 hp motor. During a follow up visit the
southern pump (P9312) had been taken out for service. The rotors and stators were reportedly replaced in
2005 as well. The pumps are showing some wear, but are working satisfactorily.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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3.7 Anaerobic Digestion
Sludge produced at the SWWTP and the Iowa City North Wastewater Treatment Plant (NWWTP) is
processed by temperature-phased anaerobic digestion (TPAD). In 1990 two mesophilic single-stage
digesters were constructed in conjunction with an identically sized digested sludge storage tank. In 2001
four additional tanks were constructed with two larger tanks sized to accommodate thermophilic digestion,
only one actually operates at thermophilic temperatures while the other is mesophilic, and two smaller
tanks for strictly mesophilic digestion. The entire system is currently operating as a three stage process
with a thermophilic stage followed by two mesophilic stages. The SWWTP is currently producing a Class 1
biosolid that is land applied. Aside from the tanks, particular components of the digestion system are the
sludge heating system, circulating and transfer sludge pumping, and gas handling. The general flow
diagram for the digestion process is as noted in Figure 2.
The system was designed for a 50% volatile solids reduction and a hydraulic retention time of 15.3 days.
3.7.1 Tanks
A total of eight tanks are utilized in the digestion process. Before digestion the scum/primary sludge and
thickened WAS are blended in the sludge equalization tank. There is one thermophilic digestion tank
followed by five mesophilic digestion tanks and then the digested sludge storage tank.
Equalization Tank – The sludge equalization tank was part of the 2001 expansion and receives
scum/primary sludge and thickened WAS from the SWWTP processes and primary sludge from the
NWWTP. The NWWTP sludge flow ties into the 8 in SWWTP sludge line. The cast-in-place concrete tank is
located on the eastern end of the new solids complex. The tank has dimensions of 25 ft by 23.5 ft and
14.5 ft high at the walls. The tank holds a nominal volume of 64,000 gallons, not including the volume of
the sloped bottom and sump. According to plant staff 60,000-70,000 gallons of sludge is pumped from
the tank on an average day. The tank is mixed with a 5 hp mechanical mixer.
The exterior of the tank and mixer looked to be in good condition. Plant staff did not note any issues with
the tank.
Ferric chloride is added to the equalization tank at average rate of 7.5 gpd to control hydrogen sulfide
formation. Plant staff did not note any issues with this system.
Original Digestion Tanks – The two original digesters installed in 1990 are currently operated as a second
mesophilic stage for the digestion process. Blended sludge is first digested by the thermophilic digester,
then three mesophilic digesters, and finally the two original digesters. Each of the original digestion tanks
is 45 ft in diameter with a side water depth of 27 ft. The volume at full is approximately 340,000 gallons.
The tanks are cast-in-place concrete with brick veneer. Each digester is fitted with a floating cover with gas
collection appurtenances, shown in Figure 26.
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Figure 26. Original Digesters – Installed 1990
The contents of the tanks are mixed with a digester gas mixing system. The system consists of the gas
withdrawal piping as seen in Figure 26, a gas compression system, and gas mixing guns within the tanks.
The gas compressors, a total of three, appear to be recent replacements and are rated for 196 cfm at 11
psig at constant speed. One compressor was taken out at the time of the field inspection. A typical
compressor is shown in Figure 27. Compressed digester gas is sent back to the original digesters and
released via a mixing gun. Each tank has three guns that bubble the gas within a vertical tube, drawing
sludge with it and consequently mixing the tanks. The mixing guns were not available for field inspection.
Figure 27. Digester Gas Mixing Compressors
The digestion tanks appear to be in good condition. The mixing system also looks serviceable given the
recent replacement of the compressors. The associated motors, drives, piping, etc., however, are showing
wear and corrosion. Overall the mixing system has required significant maintenance in its life.
New Digestion Tanks – Four digestion tanks were constructed in the 2001 expansion. Two of the tanks are
relatively larger since they can operate at the higher rate thermophilic process. The two larger tanks are
55 ft in diameter and have a side water depth of 27 ft with a full volume of 520,000 gallons. Currently,
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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only one of the larger tanks (T8101, northeast tank) is under thermophilic control while the other is meso-
philic. The tanks are show in Figure 28.
The two smaller tanks are 45 ft in diameter with a side water depth of 27 ft. The volume at full is approx-
imately 340,000 gallons. These tanks are strictly designed for mesophilic control. The tanks can be seen
in Figure 28.
Figure 28. Digestion Tanks (larger thermophilic/mesophilic on left and mesophilic on right)
Each tank is equipped with two external draft tube mixing systems. The two larger tanks have 10 hp mixers
while the smaller tanks have 7.5 hp mixers. All tanks are cast-in-place concrete construction with brick
veneer. The covers are fixed.
The new digestion tanks appear to be in good condition and operate well also. Some minor deterioration
of the roof edges were noted by plant staff. One of the mixers had been shipped with a bad bearing, but
otherwise they have operated well. The draft tubes have not needed to be cleaned to date.
Digested Sludge Storage Tank – Digested sludge is transferred into the digested sludge storage tank for
holding prior to dewatering. The tank was constructed in 1990 and is similar in size to the other mesophil-
ic tanks at 45 ft in diameter with a side water depth of 27 ft with an approximate volume of 340,000
gallons. The tank is also constructed similarly with brick veneer over cast-in-place concrete. The cover is a
fixed dome as shown in Figure 29.
The tank has operated well, but as can be seen by the white stains in Figure 29, leaks are depositing
struvite on the exterior of the tank. The roof edging is also deteriorated.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 29. Digested Sludge Storage Tank
The tank is mixed with two 20 hp submersible mechanical mixers. Plant staff noted these work well, but
the mixers were not available for inspection. The mixers cannot, however, be operated when the tank is
drawn down since the reduced load allows the drive to run faster and consequently wear out the gear
boxes.
Ferric chloride is added to the digested sludge tank at average rate of 4.5 gpd to control hydrogen sulfide
formation. Plant staff did not note any issues with this system.
3.7.2 Sludge Pumping Systems
The anaerobic digesters require several pumping systems to operate. These systems include raw sludge
feed, sludge transferring, sludge circulation, and dewatering sludge feed. These systems are described
below.
Raw Sludge Pumps – Two disc pumps, pictured in Figure 30, transfer raw sludge (i.e. blended primary
sludge, scum, and thickened WAS) to the thermophilic digester. Each pump is rated for 300 gpm at 148 ft
TDH at 6% solids. The pumps are equipped with 50 hp variable speed drives. Each pump runs about 4.7
to 5.1 hours per day, based on recent data. The pumps look to be in good condition and plant staff did not
report any problems.
The feed pumps are protected by an upstream grinder. The grinder is driven by a 3 hp motor and rated for
600 gpm. The grinder appeared to be in good condition.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 30. Raw Sludge Pumps
Transfer Pumps – Six pumps transfer sludge between the new digesters and then onto the older digesters.
An additional three pumps transfer sludge from the old digesters into the digested sludge storage tank.
The pumps are non-clog solids handling centrifugal pumps.
Three pumps transfer sludge from the larger thermophilic and mesophilic digesters to the smaller meso-
philic digesters installed in 2001. In addition, three pumps transfer sludge from the new mesophilic
digesters to the older pair, as depicted in Figure 31. These pumps were installed in 2001 with the new
digestion complex. These pumps are also protected by two 3 hp grinders rated for 600 gpm each.
Three pumps transfer sludge from the older mesophilic digesters into the digested sludge storage tank, as
photographed in Figure 31. Each pump is rated for 250 gpm at 55 ft TDH. The pumps are belt driven by
7.5 hp motors.
Generally speaking, the pumps appear to be in good condition. The older pumps are showing some
handling wear on the housings, presumably from disassembly for maintenance. The plant staff did not
raise any issues with these pumping systems.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
35
Figure 31. Sludge Transfer Pumps (1990 installation on left, 2001 on right)
Circulating Pumps – Nine pumps circulate sludge within digesters. Three are dedicated to each pair of
digesters; that is the two larger digesters constructed in 2001, two smaller mesophilic digesters con-
structed in 2001, and the two digesters constructed in 1990. The pumps are non-clog solids handling
centrifugal pumps.
Three horizontal pumps circulate sludge within the larger thermophilic and mesophilic digesters. These
pumps were installed in 2001 with the new digestion complex. Each pump is rated for 600 gpm at 52 ft
TDH. They are belt driven by 25 hp constant speed motors. The pumps are protected by two 3 hp grinders
rated for 600 gpm each.
Three horizontal pumps circulate sludge within the smaller mesophilic digesters constructed in 2001,
shown in Figure 32. These pumps were installed in 2001 with the new digestion complex. Each pump is
rated for 200 gpm at 39 ft TDH. They are belt driven by 10 hp constant speed motors. The pumps are
protected by two 3 hp grinders rated for 600 gpm each.
Three vertical pumps circulate sludge within the two mesophilic digesters constructed in 1990, pictured in
Figure 32. These pumps have been in operation since 1990. Each pump is rated for 350 gpm at 22 ft
TDH. They are driven by 5 hp constant speed motors.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 32. Sludge Circulation Pumps (1990 installation on left, 2001 on right)
The new pumps look to be in good condition. The older pumps are showing exterior signs of wear. It
appears that at least one motor has been replaced for the 1990 installation, gray motor in background of
Figure 32. Plant staff did not raise any issues with either the 1990 or 2001 installations.
3.7.3 Sludge Heating
Sludge is heated prior to entering the digester tanks by sludge/sludge heat exchangers. The temperature
of the sludge once in the digesters is maintained by sludge/hot water heat exchangers. In the 2001
system hot water is supplied to the heat exchangers by two gas fired boilers that are also used to heat the
newer digester complex. In the 1990 system sludge is circulated directly through two gas fired boiler that
are also used to heat the older digester complex and sludge processing building.
Sludge/Sludge Heat Exchangers – Two spiral sludge to sludge heat exchangers preheat incoming raw
sludge prior to entering the thermophilic digester. The units are located in the basement of the new
digestion complex and were installed in 2001. Each unit has the capacity to transfer 4,501 kBtu/hr. The
heat exchangers are fed heated sludge from the thermophilic digester, by the relative sludge transfer
pumps, to heat the incoming raw sludge. The equipment is picture in Figure 33, and appears to be in good
condition. Plant staff did not raise any issues with this equipment and rarely need maintenance. The inlet
and outlet temperatures recorded during the field inspection indicate the heat exchangers are working as
designed.
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37
Figure 33. Sludge/Sludge Heat Exchangers
Circulating Sludge/Water Heat Exchangers – Four spiral hot water to sludge heat exchangers were in-
stalled in 2001 to maintain the temperature in the four new digester tanks. They are located in the above
grade space of the new digester building. The two larger units rated for 3,000 kBtu/hr service the two
larger thermophilic and mesophilic tanks. Two smaller units rated for 750/1,180 kBtu/hr (sum-
mer/winter) service the two smaller mesophilic tanks. Digester sludge is fed to the heat exchangers by the
respective circulating pumps while hot water is supplied by the new boiler system. Once heated, the
sludge is returned to the digester. The units seem to be in good condition, as seen in Figure 34 and the
plant staff did not note any issues.
Figure 34. Hot Water to Sludge Heat Exchangers – Larger Units
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Water Plate and Frame Heat Exchangers – Three plate and frame heat exchangers are used to transfer
heat from the secondary heating loops to effluent water in order to cool the circulating sludge if needed.
These are located in the above grade space of the new digester building next to the circulating sludge hot
water heat exchangers and were installed in 2001. The largest heat exchanger serves the thermophil-
ic/mesophilic digester tank couple. Two smaller, but identical, heat exchangers serve the two smaller
mesophilic digester tanks.
Some of the fasteners and piping related to the smaller heat exchangers is corroding, but the units look to
be in good condition as pictured in Figure 35. Plant staff did not note any issues.
Figure 35. Water Plate and Frame Heat Exchangers (larger unit on left, smaller on right)
Primary Heating Loop Circulating Water Pumps – Four centrifugal pumps circulate hot water from the gas
fired boilers in the new digestion complex. Three pumps circulate the hot water in a primary loop that can
feed as needed hot water to the sludge heating secondary loop. Two of these pumps are rated for 315
gpm at 65 ft TDH, while the third is rated for 270 gpm at 60 ft TDH. A fourth pump supplies hot water off
the primary loop to the building heating system. This pump is rated for 150 gpm at 20 ft TDH. The three
larger pumps are driven by constant speed 10 hp motors and the smaller a 1.5 hp motor. The pumps were
installed in 2001 and appear to be in good condition, as seen in Figure 36. Plant staff did not report any
issues.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 36. Primary Heating Loop Circulating Water Pumps (building heating pump in foreground)
Secondary Heating Loop Circulating Water Pumps – Four centrifugal pumps circulate hot water in the
secondary loop that controls the circulating sludge temperature. Each pump supplies hot water to the
water plate and frame heat exchangers and then downstream through the circulating sludge hot water
heat exchangers. The pumps are located in the new digestion complex and are divided, two on the north
side to service the larger thermophilic and mesophilic digesters and two on the south side to service the
smaller mesophilic digesters. The north pumps are larger and rated for 346 gpm at 45 ft TDH with a 7.5
hp constant speed motor. The south pumps are smaller and rated for 50 gpm at 46 ft TDH with a 1.5 hp
constant speed motor. The pumps were installed in 2001 and appear to be in good condition except some
minimal surface corrosion, as seen in Figure 37. Plant staff did not report any issues.
Figure 37. Secondary Heating Loop Circulating Water Pumps (north pump on left, south pump on right)
Sludge Heat Exchanging Boilers – Sludge circulated in the older mesophilic digesters is heated using two
direct heating boilers located in the old digestion complex. The boilers were also piped to provide building
heat. The units were installed in 1990. The units are piped to fire either natural gas or digester gas,
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
40
although they are currently run on natural gas. Each unit is rated for 1.5 MMBH and a sludge flow of 350
gpm. These boilers are reportedly used exclusively for heating the older digester complex and sludge
processing building. The boilers appear to be in decent condition although the east unit is leaking at one of
the sludge loop penetrations, as shown in Figure 38. Plant staff did not report any significant issues with
these boilers.
Figure 38. Sludge Heat Exchanging Boilers
Digester Gas Boilers – Two triple pass boilers were installed in 2001 in the new digestion complex to
provide heat for the sludge and to the building. Each boiler is rated for 9,683 MBH and 7,746 BHP. The
boilers were originally piped to run on digester gas with supplemental natural gas. The high siloxane
fraction of the digester gas has caused significant scaling issues in the boiler tubes and the gas inlet
valves. If running on digester gas, the boiler would need to be cleaned once per week requiring about 1
hour of labor. As such, one boiler is dedicated to natural gas (BLR8532, west) and one to digester gas
(BLR8531, east). Other than the maintenance issues described plant staff did not report other issues. The
boilers appear to be in good condition and are shown in Figure 39.
The dedicated digester gas boiler fires on a call for heat when the volume of digester gas stored reaches
5,500 ft3 and stops when it is pulled down to 4,500 ft3. Opportunities may exist for optimizing digester gas
usage versus natural gas since there appears to be some natural gas usage reported for digester heating,
even during the summer months. Plus, modulation between low to high fire should be investigated to
prolong digester gas firing and minimize on off cycling, which also contributes to waste gas flaring.
Currently the dedicated digester gas boiler cycles on and off approximately every half hour with the boiler
ramping up to high fire after ignition and start up.
Each boiler can be supplied digester gas by a booster fan that increases the gas pressure up to the re-
quired inlet pressure. The fans are multistage centrifugals rated for 71 icfm at 2.5 psig and are driven by 3
hp constant speed motors. Plant staff report that the motors have to be replaced each year. No other
issues were reported. A representative fan is pictured in Figure 39.
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Figure 39. Digester Gas Boilers (left) and Booster Fan (right)
3.7.4 Digester Gas Handling
Digester gas is collected and burned in boilers for heating, used for mixing digester contents, or flared
when the supply is in excess of the heating or mixing demand. Equipment associated with boilers and
mixing have been discussed previously.
Flares – Excess digester gas is flared. A flare system was installed in 1990 with the original digester
system and a new system with the 2001 expansion. Plant staff report the original flare is not used, but did
not report any issues with the new system. The flare starts when 9000 ft3 of gas is stored and stops at
7,000 ft3. The flares are pictured in Figure 40.
Figure 40. Waste Digester Gas Flares (1990 installation on left, 2001 installation on right)
3.8 Biosolids Dewatering
Once sludge has been digested, termed “biosolids" by the EPA, it is dewatered by belt filter presses and
stored on site until it can be land applied. The dewatering system was installed in 1990 and did not
require any major upgrades, other than to the polymer system, during the 2001 expansion.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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3.8.1 Belt Filter Press Feed Pumps
Biosolids are fed from the digested sludge storage tank to the belt filter presses via three positive dis-
placement double disc pumps. These pumps are located in the basement of the old digestion complex. All
three of the current pumps have various installation dates, specifically 1990, 1999, and 2001. The pumps
are pictured in Figure 41. The pumps are protected by two 3 hp grinders, which were reportedly re-built ca.
2005.
The pumps appear to be in good condition and plant staff did not note any specific issues. The grinders
also appear to be in good condition.
Figure 41. Belt Filter Press Feed Pumps
3.8.2 Belt Filter Presses
Biosolids are dewatered using three belt filter presses (BFPs) installed in 1990, pictured in Figure 42.
Dewatered Biosolids are conveyed to a hopper for discharge into a dump truck. Filtrate is routed to the
high strength equalization tank through the plant drain system.
Each BFP is rated to process roughly 1,000 lb/hr. Based on the last three years of operation digested
sludge at 1.5 percent is dewatered to 20.4 percent solids and uses 14.7 pounds of polymer per dry ton of
solids. Each unit has a mixing chamber with a 0.5 hp mixer to blend polymer and digested sludge. The
units are also provided a wash water pump that is rated to provide 50 gpm at 116 ft TDH. Generally all
three units run for 6 hours, three days per week. The BFPs are reportedly the most maintenance intensive
equipment at the SWWTP. They are showing some wear and plant staff replaces parts as needed. The
hydraulic and electrical/instrumentation systems have not been replaced, but are still working.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
43
Figure 42. Belt Filter Presses
3.8.3 BFP Polymer Addition
Polymer is currently added to the digested sludge to enhance thickening in the BFPs. The system compris-
es of a dry processing unit, mixing/aging tanks, and metering pumps.
Dry Processing Unit – This unit was previously described in the WAS thickening section. To summarize, 50
lb bags of dry polymer, specific for the digested sludge, are loaded into the processing unit to be slurried
and transferred to the mixing/aging tanks. The unit is nearing the end of its useful life and does not
provide dedicated polymer processing.
Mixing/Aging Tanks – Slurried polymer is transferred to two fiberglass mixing/aging tanks prior to being
metered to the BFPs. The tanks containing polymer used in the BFPs are located on the east side of the
polymer room and are labeled T9326 and T9327. Each tank can hold 1,600 gallons. Each tank has a 1.5
hp mixer. The tanks are not showing any signs of cracking or fatigue and the mixers look to be in good
condition.
Metering Pumps – Polymer solution is metered to the BFPs by four variable speed progressive cavity
pumps. The pumps are rated for 5 gpm at 42 psig with a 0.5 hp motor. The pumps are showing minimal
corrosion, but are working satisfactorily.
3.8.4 Conveyance
Dewatered Biosolids are conveyed up to the second story of the sludge processing facility. The biosolids
are discharged into a hopper which directs them into dump trucks. The hopper discharge gate is manual.
Plant staff noted that the conveyors are wearing out and some replacement parts had to be fabricated
since the manufacturer no longer supports these models. The system was installed in 1990 and will be
replaced during the planning period if budget allows.
3.8.5 Dewatered Biosolids Storage Pad
Dewatered biosolids are stored outdoors on an asphalt pad surrounded by a 4 ft concrete wall. The pad is
225 ft by 225 ft and is located just north of the solids processing facility. The pad has historically had the
capacity to hold one years worth of dewatered biosolids. Currently the pad is emptied in March to avoid
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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clogging the 18” drain line. Since it is not covered precipitation increases the moisture content of the
biosolids and thereby the difficulty of handling. Plant staff would like covering the pad to be considered.
3.9 Ancillary Systems
3.9.1 Effluent Water
Effluent water is used for BFP wash water, RDT wash water, polymer make-up water, chlorine and sulfur
dioxide solution water, grit washing, foam dispersant carrier water, digester cooling water, pump seal
water, flushing, and hydrants. There is an extensive network of piping through the plant that carries water
from the effluent water pumping station located in the chlorine building.
The original (1990) vertical turbine pumps were replaced with six horizontal end-suction centrifugal pumps
in 1999. Due to insufficient capacity the pump motors and impellers were upsized in 2002. Each pump is
rated for 250 gpm at 231 ft TDH. Typically three pumps are running at all times supplying background
demand such as digester cooling water, seal water, and foam spray. When the BFPs are running all six
pumps will run, which is three days a week for six to seven hours each day. There is no standby pump
available during the high flows.
Plant staff report that the two influent pipes supplying the effluent water pump wet well, 10 in and 14 in,
from the chlorine mixing tanks cannot provide enough flow during peak demand. Another issue is that the
motors, reportedly, are prone to burn out. During the field inspection it was noted that the pumping room
was extremely warm and the existing HVAC system could not provide adequate cooling. The pumps are
also situated at grade level, causing them to pull against a negative suction head, reducing the pump
efficiency. Also, as shown in Figure 43 the pumps, motors, and piping are all corroding. This system
should be considered for replacement with a more efficient and adequately sized system.
Figure 43. Effluent Water Pumps (5 of 6 pictured)
3.9.2 Dewatering Pump Station
The primary and secondary clarifiers, aeration tanks, and chlorine contact tanks can be dewatered, when
needed, by the dewatering pump station. Drain lines are piped to the dewatering pump station located just
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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west of the sludge pumping building. The drainage is pumped back to the primary flow splitter box by two
submersible solids handling pumps. Each pump is rated for 450 gpm at 40 ft TDH, with a 4 hp drive. The
pump station was originally constructed in 1990, but the pumps were upgraded in 2005. The system
reportedly works well.
3.9.3 De-Foaming System
A de-foaming system was installed in 2001 to control the foaming events the plant occasionally expe-
riences in the headworks. The system consists of a storage tank, pump, and distribution piping. The pump
and tank are located in the influent pump station building. The system is able to feed de-foaming solution
to the screening channel, influent pump station wet well, influent pump discharge channel, and plant flow
measuring channel. Plant staff mentioned the feed piping freezes on occasion.
3.9.4 Sampling Systems
The SWWTP has several sampling points with associated equipment. There are 15 total sampling pumps
at the point designated in Table 1. During the field inspection plant staff noted issues with the raw waste-
water and aeration tank sampling systems.
The raw wastewater sampling point is located directly downstream of the influent mechanically cleaned
bar screens in each of the screening channels. Plant staff reported that the sample pumps lose their
prime if the level in the screening channel gets too low. It was also reported that the discharge lines clog
with grit as well.
The aeration tank sampling system froze, causing the pipes to burst, and has yet to be repaired and
according to plant staff the system never worked properly. Plant staff are concerned the sampling lines
are too long for the system to purge the lines and collect representative samples. Also, the analytical
systems are in disrepair and the plant staff have yet to locate an individual who is qualified to repair them
or find the needed parts. This system should be replaced or removed.
3.9.5 Influent Pump Station Sump Pumps
Sump pump stations were not generally considered during the field inspection or in this plan. Neverthe-
less, plant staff pointed out the arrangement of the influent pump station dry well sump pumps as seen in
Figure 44. The arrangement is too tight and plant staff would like larger sump to make maintenance
easier. The sump should also be covered with grating to eliminate the falling hazard.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
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Figure 44. Influent Pump Station Dry Well Sump Pump Installation
3.9.6 Soccer Field Irrigation
The soccer field irrigation system filters chlorinated secondary clarifier effluent prior to irrigating the
adjacent soccer complex. The easternmost cell of the easternmost chlorine contact tank (6110) is used
as a storage tank for filtered product. The system provides 10-20 million gallons per year for irrigation.
3.9.7 Plant Security
The entire plant site is enclosed with a chain link security fence. The entrance gate is located immediately
in front of the administration building. During the night and other hours when the plant is not staffed the
entrance gate is closed and entrance can only be accessed with use of a security code typed into a keypad
at the entrance gate. In addition, the administration building is equipped with an alarm system with door
sensors and motion detectors in the hallways. If the alarm is tripped it sends a message to a call service
which then alerts plant personal so they can determine the reason for the alarm. The plant is equipped
with area lighting which can be used for illumination at night.
3.9.8 Structural Overview
The original plant was constructed in 1990 with a design capacity of 5 mgd. The plant was upgraded and
expanded to a design capacity of 10 mgd in 2001. The oldest portion of the plant is just over 20 years old.
The existing concrete structures are in good condition and can continue in service for many years. There is
some deterioration of steel in the clarifier mechanisms which needs to be addressed during the project
upgrade.
3.9.9 Electrical Overview
Electrical Service– Existing electrical service is primarily metered and originates from the Sand Road
Substation. The plant can be fed by three independent power feeds for reliability. In addition to Sand
Road power can be fed from the Sharon Road and Lone Tree substations.
On-site Generation – High reliability of electrical power is provided through the use of an on-site electrical
generator. The existing generator is rated at 1000kW. Automatic transfer of the loads between on-site
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
47
and off-site sources is provided by an automatic transfer switch at the generator location. Emergency
lighting is provided by battery where routine human habitation is required.
During the field inspection the electrical assets at the SWWTP were inspected and issues noted. Those
issues with additional observations are listed below. Detailed inventories or comprehensive descriptions of
the existing assets were not necessarily covered in this investigation.
General Electrical Design – The following considerations will be considered in the upcoming design and
should be reviewed for other projects at the SWWTP.
• Future designs should locate VFDs outside of MCCs. There are heating issues when enclosing
VFDs in MCCs.
• PVC covered rigid galvanized steel conduits should be used above grade when located in
process areas and PVC conduit in underground duct banks. Liquid tight conduits should be
used for final connection to equipment.
• Plant staff prefers local standby power and automatic transfer switches for each location.
• Lighting interior spaces should incorporate fluorescent bulbs instead of high pressure sodium
bulbs with fixtures matching the classification listing of space.
• Outdoor stainless steel unistrut installations in close proximity to the sludge processing areas
used clamps that are not stainless steel. The clamps are rusting and have failed in some
cases. The conduit clamps should be stainless steel with stainless steel fasteners.
• Confirm rigid galvanized steel conduit building stub outs are still intact (e.g. blower building).
In the future, for underground stub outs, PVC should be used unless analog signals are being
run through conduit.
Screening Building – The following issues and observations were noted regarding the electrical systems
associated with the mechanical bar screens.
• The original electric motor drives have been replaced with hydraulic drives.
Influent Pump Station Building – The following issues and observations were noted regarding the electrical
systems in the influent pump station building.
• The VFDs for the influent pumps should be better ventilated or replaced with dipped circuit
boards to provide better reliability.
• An electrical pullbox is located near the ceiling of the lower level under the ground level mo-
tor control center. The pullbox is not accessible without a scaffold system. Consider adding
permanent access without hindering pump removal.
Grit Removal Chambers – The following issues and observations were noted regarding the electrical
systems supporting the grit removal chambers.
• The grit mixer drives are inundated occasionally when chemical foaming occurs and need to
be replaced.
• Plant staff have had problems with mixing drives and would prefer a different manufacturer
if replaced.
Grit Building – The following issues and observations were noted regarding the electrical systems within
the grit building.
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• The atmosphere in the building is highly corrosive. The metal equipment is showing signs of
corrosion. MCC-5 should be replaced and relocated with the SCADA enclosure in a separate
room with ventilation. All electrical equipment in building should be replaced.
Primary Clarifiers – The following issues and observations were noted regarding the electrical systems
supporting the primary clarifiers.
• Plant staff noted that the existing drives used for the collectors in new primary clarifiers
(northern) should be replaced.
• The lights on each primary clarifier are not used. Plant staff would prefer to have the existing
photocells replaced with local switched contactors which require rewiring at most locations.
• Exposed conduits on the older clarifiers (southern) should be replaced with PVC coated rigid
galvanize steel conduit and new stainless steel unistrut supports with stainless steel clamps
and fasteners.
Aeration Tanks – The following issues and observations were noted regarding the electrical systems
supporting the aeration tanks.
• Heat trace circuits used to heat the sampling piping need to be reattached to piping. This
system should also be insulated.
Secondary Clarifiers – The following issues and observations were noted regarding the electrical systems
supporting the secondary clarifiers.
• Plant staff noted that the existing drives used for the collectors in new secondary clarifiers
(southern) should be replaced.
• The lights on each primary clarifier are not used. Plant staff would prefer to have the existing
photocells replaced with local switched contactors which require rewiring at most locations.
• Exposed conduits on the older clarifiers (northern) should be replaced with PVC coated rigid
galvanize steel conduit and new stainless steel unistrut supports with stainless steel clamps
and fasteners.
• RAS Pumps P5301 and P5401 have a junction box at top of their sumps that need to be re-
placed due to corrosion.
Chlorine Building and Contact Tanks – Replace all conduits exposed to chlorination process.
Digester Complexes – Everything appears to be in good condition.
Sludge Processing and Thickening Buildings – The following issues and observations were noted regarding
the electrical systems within the sludge processing and thickening buildings.
• Motors on RDTs need to be replaced. The original equipment control panels are corroding.
• All of the electrical equipment located in the belt filter press mechanical room is corroding.
• Control stations should have switches replaced with Allen Bradley 800H plastic switches that
will not corrode
• Polymer metering pumps are using two different types of VFDs.
• MCC – SP is in well ventilated space and is in good condition.
Administration Building – The electrical systems are in good condition. Electrical system will have to be
renovated if HVAC systems are changed.
Maintenance Building – The electrical systems are in good condition. Electrical system will have to be
renovated if HVAC systems are changed.
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3.9.10 Instrumentation and Control Overview
During the field inspection the instrumentation and control assets at the SWWTP were inspected and
issues noted. Those issues with additional observations are listed below. Detailed inventories or compre-
hensive descriptions of the existing assets were not necessarily covered in this investigation.
PLC/SCADA System – The following items were noted regarding the PLC/SCADA system during the field
inspection.
• Existing Allen Bradley (A-B) PLC-5 system processors were upgraded to PLC-5/40E CPUs dur-
ing the 2001 expansion.
• The existing A-B PLC-5 system should be upgraded to the newer A-B ControlLogix Programm-
able Automation Controller (PAC) platform. Allen Bradley offers a migration solution which
allows the reuse of the existing A-B PLC-5 I/O module swing arms, thus eliminating the need
to rewire field terminated wires. The use of this migration solution is preferred by plant staff.
• The existing SCADA system is running on a 32-bit Windows platform. It was discussed and
agreed that an upgrade to a 64-bit operating system would be advantageous. This would al-
so require the probable replacement of the SCADA computers and the local Windows-based
PLC panel HMIs.
• WIN911 remote alarm notification software installed on the SCADA computers is used for
off-hours alarming. According to plant staff the system gives false alarms. Plant staff feel
that most of the false alarms are generated because the associated field devices creating
the alarm inputs have been previously disconnected and the alarm inputs have not been
deactivated. All inputs should be re-evaluated if the SCADA system is upgraded.
Gas Monitoring – The following items were noted regarding the SWWTP gas monitoring systems during the
field inspection.
• Some of the original MSA Ultima gas detectors used to detect Hydrogen Sulfide (H2S), Com-
bustibles (LEL), Oxygen (O2), and Carbon Monoxide (CO) have been replaced with the newer
MSA Ultima XE version.
• Remaining Ultima model gas detectors should be replaced.
HVAC Controls – The following items were noted regarding the HVAC control systems during the field
inspection.
• Current building HVAC controls are interfaced with a Johnson Metasys DDC system. The orig-
inal plant design interfaced some ventilation fan controls with light switches through the PLC
System.
• Plant staff are interested in being able to adjust HVAC setpoint through the SCADA system
which is currently not possible.
• Optional interface can be performed by digital communication between the HVAC control and
SCADA systems. Plant staff recommend that HVAC controls be entirely embedded in the Al-
len Bradley PLC System.
Electrical Issues – The following electrical control issues were noted during the field inspection.
• Power Quality Monitoring
− Many of the existing MCCs are equipped with Westinghouse IQ Data Plus power quality
monitors. Presently the electrical parameters are only displaced locally.
− Plant staff prefer that this data be interfaced with the Allen Bradley PLC system for moni-
toring through the SCADA system.
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50
− During the field inspection it could not be determined whether the existing PQM units are
equipped with digital communication modules, such as RS-485, RS-232, or Ethernet
communication. If the appropriate hardware is not installed, they may be able to be field
modified to add the necessary digital communication cards.
• Variable Frequency Drives
− It appears that most of the VFDs interface with the Allen Bradley PLCs are hardwired I/O.
− Any new VFDs should be interfaced with the new PAC system utilizing Allen Bradley
EtherNet/IP communication protocol.
− Conversion of existing VFDs from hardwired to digital communication should be consi-
dered.
Primary Clarifiers – The following items were noted regarding the primary clarifier instrumentation and
control systems during the field inspection.
• Sludge blanket level sensors were removed from the new primary clarifiers (northern). The
Royce Model 2511 analyzer was also abandoned in place.
• Sludge level monitoring in the older primary clarifiers (southern) has also been abandoned.
• Replacing the sludge level monitoring should be considered in the upcoming design.
Aeration System – The following items were noted regarding the aeration instrumentation and control
systems during the field inspection.
• Aeration Blowers
− Each blower is provided with a local monitoring panel that displays blower amps and vi-
bration readouts. Plant staff would prefer that these values be made available for display
on the SCADA system.
− It is not known whether the existing lC Larson SmartMeter units are equipped with digital
communication modules, such as RS-485, RS-232, or Ethernet communication. If not,
they may be able to be field modified to add the necessary digital communication cards
or potentially replaced with newer units that do provide the digital communication option.
• Air Flow Switches
− Air flow at into each cell (8) for each train (4) is monitored using thermal flow switches.
Plant staff reported that the flow switches, probably the first in line, have short circuited
and taken the down the entire line. The aeration system PLC was provided by US Filter,
so no wiring drawings are available to evaluate the field wiring.
• Alka-Pro Sampling and Analyzer
− The aeration tank mixed liquor sampling system is in-operational as discussed above.
The system should be removed or replaced.
• Dissolved Oxygen Probes
− Dissolved oxygen (DO) was to be monitored in Cells 1, 6, and 8 in each of the four aera-
tion trains. According to plant staff, the DO probes have been disconnected and were re-
moved more than three years ago because they were not working. The probes have not
been replaced; however, the plant has new DO probes, suspended solids, and electronic
units manufactured by MJK Automation, model SuSix/Oxix ready to be installed.
• Plug Boxes
− Military-type plugs were originally installed along the length of all four (4) aeration tanks,
one at each of the eight cells. Each plug supplied 120VAC 3-phase power, and 24VDC
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
51
power to a field mounted device from the aeration system PLC panel. Pre-wire twisted
shielded cable was also installed for the custom application wiring.
− According to plant staff, the wire cable for the direct current applications is too small
creating an excessive voltage drop at the load end. The functionality of these boxes is still
desired, but the wiring must be modified to reduce voltage drop.
Secondary Clarifiers – The following items were noted regarding the secondary clarifier instrumentation
and control systems during the field inspection.
• Sludge blanket level sensors were removed from the new secondary clarifiers (southern).
The Royce Model 2511 analyzer was also abandoned in place.
• Sludge level monitoring in the older secondary clarifiers (northern) has also been abandoned.
• Replacing the sludge level monitoring should be considered in the upcoming design.
3.9.11 HVAC and Plumbing Overview
During the field inspection HVAC and plumbing assets in each building was examined. Presented below
are the issues that were identified during the inspection. Detailed inventories or comprehensive descrip-
tions of the existing assets were not necessarily covered in this investigation.
Screening Building – The following issues and observations were noted in the screening building during the
field inspection.
• Exhaust fan openings on north side below ground level are source of leaks into the building.
• The natural gas line entering the building needs to be painted.
• Natural gas is run to unit heaters in lower level of screen room and stair well. The unit hea-
ters are in need of replacement and the gas line is severely corroded.
• The natural gas line in ground level of the screen room needs to be replaced.
Influent Pump Station Building – The following issues and observations were noted in the influent pump
station building during the field inspection.
• The southerly located unit heater in the dry well needs to be replaced. The northerly located
unit heater in good condition. Flues for both unit heaters should be replaced.
• A direct fired unit heater was added to the east side of the dry well for additional heating.
• The blower room located at ground level has the original unit heater and it is in good condi-
tion.
• Air ducts in wet well are showing signs of severe corrosion and should be replaced.
• The cast iron drain in wet well is displaying severe corrosion and should be replaced.
• The original roof mounted makeup air units need to be replaced. The burners in these units
are severely corroded.
• The original fans on located on the roof are in serviceable condition. Many of the fans are lo-
cated at the edge of the roof making it difficult to service them safely.
• The natural gas lines are generally in good condition. The roof gas line needs the surface rust
removed and painting.
• The building does not utilize energy recovery for the, code required, supply and exhaust for
the screen room and wet well. Potential heat recovery exists in these spaces.
Grit Building – The following issues and observations were noted in the grit building during the field inspec-
tion.
• Existing unit heaters installed in 2001 are showing signs of corrosion and should be replaced.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
52
• Exhaust fan on roof was not operating as indicated by the closed position of the back-draft
damper. The drive belt was broken.
Blower Building – The following issues and observations were noted in the blower building during the field
inspection.
• Westerly located exhaust fan in blower room was not operating during the field inspection.
• The potable water line in blower room is located directly above starters and needs to be relo-
cated to comply with code.
• The insect screens on louvers should be cleaned. Adding filters ahead of dampers should be
considered when insect screens are removed.
• Electrical room and control room were extremely warm. High temperatures in these spaces
may shorten the life of the electrical and control equipment. Consider adding cooling to keep
space at moderate temperatures.
• Existing unit heaters in all spaces are in good condition.
• No permanent roof access is provided. Access for maintenance of equipment on roof should
be provided.
Chlorine Building – The following issues and observations were noted in the chlorine building during the
field inspection.
• Potable water lines in effluent water pump room are severely corroded and should be re-
placed.
• No permanent roof access is provided. Access for maintenance of equipment on roof should
be provided.
• Original electrical equipment has been replaced and VFDs added. Space needs additional
ventilation.
• Insect screen on all louvers need to be cleaned. Adding filters ahead of dampers should be
considered when insect screens are removed.
• Switch for the exhaust fan in the sulfonator room is broken.
• Copper water lines, backflow preventer, and pressure reducing valve in chlorinator room are
severely corroded and may need to be replaced.
Sludge Pumping Building – The following issues and observations were noted in the sludge pumping
building during the field inspection.
• Electrical room has no ventilation and was extremely warm during field inspection. VFDs in
space may not be rated for the temperatures encountered.
• Electrical room unit heater needs to be replaced.
• Damper actuator on southwest corner of building is not connected to damper.
• Toilet does not appear to be operating properly.
• Entire building ventilation system does not appear to operate correctly.
• Backflow preventer and pressure reducing valve in the pump room need to be replaced due
to severe corrosion.
• No permanent roof access is provided. Access for maintenance of equipment on roof should
be provided.
New Digester Complex – The following issues and observations were noted in the new digester complex
during the field inspection.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
53
• Supply fans above digester gas boilers were not operating at time of visit. The starters for
the fans were set to the off position.
• The emergency eyewash and shower in basement does not have a tempered water system, a
cold water line is attached to unit.
• Air handling units serving spaces are showing signs of corrosion, but appear to be operable.
• The electrical room is extremely warm. May need to increase ventilation rate in this space to
maximize equipment life.
Old Digester Complex – The following issues and observations were noted in the old digester complex
during the field inspection.
• The roof drain covers are broken and need to be replaced.
• The air handling unit serving the boiler room is not operating. It appears controls are not op-
erating correctly. Unit shows signs of corrosion and should be replaced.
• Intake louver in compressor room needs to be cleaned, or insect screen removed and filters
installed.
• Effluent water pipe in compressor room is severely corroded.
• Air handling unit in compressor room should be replaced.
• There is no emergency eyewash in the basement of complex, only an emergency shower.
Solids Processing Building – The following issues and observations were noted in the solids processing
building during the field inspection.
• Belt filter Room
− Exhaust fan duct needs to be replaced.
− Potable water line, backflow preventer, and pressure reducing valve serving this room is
severely corroded.
− Roof drain piping is showing signs of corrosion.
− All HVAC controls are pneumatic. Consider replacing with new controls if equipment is
replaced.
− Hot water unit heaters need to be replaced.
− Emergency eyewash and shower needs a new eyewash assembly.
• Belt Filter Press Mechanical Room
− Air handling unit needs to be replaced.
− This space needs better cooling ventilation.
− Water heater appears to be recently replaced.
• Control room/Laboratory/Entrance
− Lots of condensation on windows viewing the belt filter press mechanical room was
noted.
− The spaces are generally well conditioned.
− Some form of leak above office at entrance to building, as noted by a damaged ceiling
tile, will need to be investigated during the design effort.
• Polymer Room
− There are no apparent issues.
− Exhaust fans were off during the field inspection, but space was not extremely warm.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
54
− Unit heaters should be replaced.
• Truck Bay
− Unit heaters need to be replaced.
• Roof
− Air handling unit serving the belt filter press mechanical room needs to be replaced.
− Existing fans for belt filter press mechanical room should be replaced.
Sludge Thickening Building – The following issues and observations were noted in the sludge thickening
building during the field inspection.
• Unit heaters in storage area are severely corroded and need to be replaced.
• Ducts from exhaust fan in storage area need to be replaced.
• Insect screen at louver is clogged with dirt. The insect screen should be cleaned screen or
replace with filters.
• Air handling unit serving weight area and sludge thickener room needs to be replaced.
• Ducts in sludge thickener room need to be replaced.
• A lot of corrosion was noted in the sludge thickener room. Consider increasing ventilation, or
different materials of construction.
Administration Building – The following issues and observations were noted in the administration building
during the field inspection.
• The existing chiller needs to be replaced. The chiller has had multiple compressor and fan
failures.
• The existing boiler needs to be replaced.
• Look at adding controls to laboratory to make it a variable air volume system.
• Consider adding heat recovery to laboratory system ventilation.
• Plant staff would like to change all HVAC controls to a PLC system. This will be investigated
during design.
Maintenance Building – There were no apparent issues in this building and the equipment appears to be in
good condition.
4. Facility Condition
A field condition assessment of the process assets and support systems at the SWWTP was conducted on
July 27-28, 2010 to garner an overall idea of the facility condition and areas that need improvement. The
assessment was performed by walking through the plant along the liquid and solids flow streams, starting
at the headworks. Participating in the walk through were members of Stanley, Brown and Caldwell, and
plant staff. The inspection team was represented by professionals specializing in the disciplines of
process, mechanical, HVAC, structural, instrumentation, control, and electrical. The accompanying plant
staff provided valuable operation and maintenance experience that would otherwise not be available.
Specific issues noted by plant staff are generally captured in the preceding descriptions. Plant staff
continued providing valuable assistance before and after the field work to supplement the collective pool
of information.
During the walk through the assessment team visually inspected and rated the assets based on condition
and functionality. The ratings were based on a numerical scale as described in Tables 3 and 4. Taking
these into consideration, along with plant staff input regarding operations and maintenance, and the
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
55
assets current length of service a remaining useful life was estimated. In addition to the ratings other
forms of information were collected, such as safety considerations, nameplate information, and materials
of construction if noteworthy.
Table 3. Condition Rating Scale Description
Rating Scale Description
1 Asset integrity severely compromised by corrosion, wear, weathering, settlement.
2 Moderate to high risk of failure.
3 Visible degradation of asset, but acceptable.
4 Well maintained, like new condition.
Table 4. Asset Functional Rating Scale Description
Rating Scale Description
0 Asset abandoned.
1 Asset is not currently functioning for its intended use.
2 Asset is in service but function is highly impaired.
3 Asset functions as intended, excessive maintenance required.
4 Asset functions as intended, minimal maintenance required.
In general, the SWWTP is in relatively good condition. A lot of the assets were installed during the 2001
upgrades and are well within their expected service life. If assets proved to be troublesome they have been
replaced, for the most part. Therefore, the assets critical to plant operation are running relatively well.
Table 5 summarizes the key areas requiring capital improvements, replacement, and the estimated
schedule. The information presented in Table 5 was not based on a comprehensive risk management
approach, only service life as it pertains to plant operation was generally considered. Table 5 was used
along with the alternative and capacity assessments to develop a capital improvement plan and cost
estimate that incorporates the facility needs.
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
56
Table 5. Replacement Schedule for Key Areas at the SWWTP
Time Frame Asset Installation Date
0-5 years Influent Pumps – Original 1990
Dry Polymer Handling 1990
Dewatered Biosolids Conveyors 1990
Effluent Water Pumps 1999
Aeration Diffusers 2001
Various Building HVAC Systems 1990/2001
SCADA System Panels 1990/2001
6-15 years High Strength Equalization Pumps and Mixers 2001
Grit Mechanical Systems 2001
Polymer Delivery Systems 1990/2001
Aeration Tank Mixers 2001
Primary Clarifier Collectors - Original 1990
Primary Sludge Pumps 2003/2009
RAS Pumps 1990/2001
WAS Pumps 1990
Thickened Sludge Pumps 1990
Digester and Sludge EQ Tank Mechanical Mixers 2001
Digestion Pumping Systems – Original 1990
Sludge Dewatering System 1990
Sludge Heat Exchanger Boilers – Original 1990
15-20 years Influent Pumps - Expansion 2001
Mechanical Bar Screens 1990
Primary/Secondary Clarifier Collectors – Expansion 2001
High Strength Equalization Tank
Rotary Drum Thickeners 2001
Digestion Pumping and Heat Exchange Systems - Expansion 2001
Digester Gas Boilers 2001
21-30 years Aeration Blowers 2001
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
57
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Preliminary Treatment
Flow Equalization Basins Cell 1, 2 1990 Cell 2 expanded in 2001
Number 2 All cells paved in 2001
Nominal Volume, MG
Cell 1 2.1
Cell 2 4.4
High Strength Equalization Tank T1810 2001
Number 1
Diameter, feet 62
Side Water, feet 13
Nominal Volume, gal 311,000
High Strength Equalization Pumps P1801, 1802 2001
Number 2
Type Submersible centrifugal
Manufacturer Flygt
Capacity, gpm, each 450
Head, feet 40
Horsepower 10
Drive Constant
High Strength Equalization Mixers MX1811, 1812 2001
Number 2
Type Submersible
Manufacturer Flygt
Horsepower 4
Drive Constant
Mechanical Bar Screens SCN1101, 1102 1990 Electrical drives changed to hydraulic in
2001
Number 2
Manufacturer Vulcan
Channel width, feet 4
Bar spacing, inches 5/8
Horsepower 10
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
58
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Influent Pumps - Expansion P1301-1303 2001
Number 3
Type Centrifugal
Manufacturer Fairbanks Morse
Capacity, gpm, each 8,330
Head, feet 46
Horsepower 125
Drive Variable
Influent Pumps - Original P1304-1306 1990
Number 3
Type Centrifugal
Manufacturer Allis Chalmers
Capacity, gpm, each 8,330
Head, feet 46
Horsepower 125
Drive Variable
Parshall Flumes FE1501-1503 1990 FE1501 enlarged in 2001
Number 3
Throat width, inches
FE1501 36 Plant Flow
FE 1502 36 Equalization Basin Influent
FE 1503 18 Equalization Basin Effluent
Plant Flow Control Gate GT1501 1990
Number 1
Size, inches 36 x 60
Grit Chambers 2300, 2400 2001
Number 2
Type Vortex
Diameter, feet 13
Side Water depth, feet 10.3
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
59
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Grit Tank Mixer COL2301, 2401 2001
Number 2
Manufacturer Jones and Attwood
Diameter, feet 5
Horsepower 1
Drive Variable
Grit Pumps P2301, 2401 2001
Number 2
Type Recessed impeller submersible
Manufacturer Wemco
Capacity, gpm, each 250
Head, feet 34
Horsepower 10
Drive Constant
Grit Cyclones SEP2703, 2704 2001
Number 2
Manufacturer Wemco
Size, inches 12
Capacity, gpm, each 350 At 12.5 psig
Grit Washers WHR2703, 2704 2001
Number 2
Manufacturer Wemco
Size, inches 12
Capacity, gpm, each 24 For 150 mesh particles
Horsepower 0.5
Drive Constant
Primary Treatment
Primary Clarifiers – Expansion 3300, 3400 2001
Number 2
Type Outboard weir
Diameter, feet 70
Side Water depth, feet 12
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
60
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Primary Clarifiers – Original 3100, 3200 1990
Number 2
Type Outboard weir
Diameter, feet 70
Side Water depth, feet 12
Primary Clarifier Collector Mechanisms – Expansion COL3301, 3401 2001
Number 2
Type Rake
Manufacturer Eimco
Horsepower 0.75
Drive Constant
Primary Clarifier Collector Mechanisms – Existing COL3101, 3201 1990
Number 2
Type Rake
Manufacturer Eimco
Horsepower 0.75
Drive Constant
Primary Scum Mixer MX 3001 1990 Rarely used
Number 1
Type Dual 3-bladed impellers
Manufacturer Siemens
Horsepower 1
Drive Constant
Primary Sludge/Scum Pump Grinders GDR7101, 7102 1990
Number 2
Type Twin shaft
Manufacturer JWC Environmental
Capacity, gpm, each 425
Horsepower 5
Drive Constant
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
61
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Primary Sludge/Scum Pumps P7101, 7102 2003/2009
Number 2
Type Rotary lobe
Manufacturer Vogelsang
Capacity, gpm, each 300
Head, feet 115.5
Horsepower 30 and 15 P7101 and P7102 respectively
Drive Variable
Secondary Treatment
Aeration Tanks 4110-4140 2001 Cells 7 and 8 of each tank retrofitted
from 1990 construction
Number 4
Number of cells, each 8
Length, feet 428
Width, feet 25.6
Side Water depth, feet 14.9
Nominal Volume, MG, each / total 1.2 / 4.8
Diffusers 2001
Type Rubber membrane
Aeration Tank Mixers
MX4111-4114
MX4121-4124
MX4131-4134
MX4141-4144
2001 Mixers in Cell 8 have been removed in
all tanks
Number 16
Type Submersible propeller
Manufacturer Flygt
Horsepower 7.5
Drive Constant
Blowers B4501-4505 2001
Number 5
Type Multi stage (6) centrifugal
Manufacturer Gardner Denver Lamson
Capacity, scfm, each 6,250
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
62
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Discharge pressure, psig 7.5
Horsepower 300
Drive Constant
Mixed Liquor Recycle Pumps P4101, 4102 2001 Rarely used
Number 2
Type Submersible centrifugal
Manufacturer Flygt
Capacity, gpm, each 8,680
Head, feet 5.1
Horsepower 30
Drive Variable
Secondary Clarifiers – Expansion 5300, 5400 2001
Number 2
Type Inboard weir
Diameter, feet 80
Side Water depth, feet 16
Secondary Clarifiers – Original 5100, 5200 1990
Number 2
Type Outboard weir
Diameter, feet 80
Side Water depth, feet 12
Secondary Clarifier Collector Mechanisms –
Expansion
COL5301, 5401 2001
Number 2
Type Suction header
Manufacturer Eimco
Horsepower 1.5
Drive Constant
Secondary Clarifier Collector Mechanisms – Existing COL5101, 5201 1990
Number 2
Type Suction header
Manufacturer Eimco
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
63
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Horsepower 1.5
Drive Constant
Secondary Scum Mixer MX5001 1990
Number 1
Type Dual 3-bladed impellers
Manufacturer Siemens
Horsepower 0.5
Drive Constant
RAS Pumps – Expansion P5301, 5401 2001
Number 2
Type Submersible centrifugal
Manufacturer Flygt
Capacity, gpm, each 3,000
Head, feet 22
Horsepower 25
Drive Variable
RAS Pumps – Original P7121-7123 1990 Upgraded in 2001
Number 3
Type Centrifugal
Manufacturer ITT – Allis Chalmers
Capacity, gpm, each 2,600
Head, feet 28
Horsepower 30
Drive Variable
WAS Pumps P7111, 7112 1990 Upgraded in 2001
Number 2
Type Centrifugal
Manufacturer Allis Chalmers
Capacity, gpm, each 350
Head, feet 15
Horsepower 3
Drive Variable
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
64
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Disinfection
Chlorine Contact Tanks 6110
6120
1990
2001
Number 2
Number of cells, each 2
Number of passes, each cell 3
Length, feet 79
Pass width, feet 5
Side Water depth, feet 9.3
Nominal Volume, gal, each / total 165,000 / 330,000
Chlorine Mixing Tanks -
Number 2
Dimensions, ft, length x width x height 14.3 x 8.5 x 11.8
Nominal Volume, gal, each 10,600 With discharge gate closed
Chlorine Mixing Tank Mixers MX6111
MX6121
1990
2001
Number 2
Type Propeller
Manufacturer J W Moore
Horsepower 7.5
Drive Constant
Chlorine Evaporators EPR6201
EPR6202
1990
2001
Not used
Number 2
Capacity, lb/day, each 6,000
Chlorinators CFR6201-6202
DFR6203, 6211
1990,
2001
Modified 2001
Number 4
Capacity, lb/day, each 2 @ 2,000 & 2 @ 3000
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
65
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Chlorine Injectors INJ6201,
INJ6202 & 6211
2001
1990
Modified 2001
Number 3
Capacity, lb/day, each 2 @ 1,500 & 1 @ 500
Sulfonators CFR6301, 6302 1990 Modified 2001
Number 2
Capacity, lb/day, each
Sulfur Dioxide Injectors INJ6301, 6302 1990, Modified 2001
Number 2
Capacity, lb/day, each 475
Sulfur Dioxide Mixing Tanks -
Number 2
Dimensions, ft, length x width x height 17 x11.2 x 9 Height is to top of discharge weir
Nominal Volume, gal, each 12,700
Solids Handling
Digested Sludge Storage Tank T8801 1990
Number 1
Diameter, feet 45
Side Water, feet 27
Volume, gal 340,000 Includes cone volume
Digested Sludge Storage Tank Mixers Mixer 1 and 2 1990
Number 2
Type Submersible propeller
Manufacturer Air-O-Lator
Horsepower 20
Drive Constant
Rotary Drum Thickeners THK9101, 9102 2001
Number 2
Capacity, gpm, each 350
Capacity, lb/min, each 31
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
66
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Manufacturer Vulcan
Rotary Drive Horsepower 3
Rotary Drive Variable
Mixer Drive Horsepower 0.75
Thickener Wash Water Pumps P9101, 9102 2001 Removed in 2011
Number 2
Type Centrifugal
Manufacturer Dayton
Capacity, gpm, each 20
Head, feet 104
Horsepower 5
Drive Constant
Thickened Sludge Pumps P9111, 9112 2001
Number 2
Type Progressive cavity
Manufacturer Moyno
Capacity, gpm, each 36
Head, feet 80
Horsepower 5
Drive Variable
Sludge Equalization Tank T8001 2001
Number 1
Width, feet 25
Length, feet 23.5
Height, feet 14.5
Nominal Volume, gal 64,000
Sludge Equalization Tank Mixer MX8001 2001
Number 1
Type Propeller
Manufacturer Eimco
Horsepower 5
Drive Constant
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
67
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Raw Sludge Feed Pumps P8501, 8502 2001
Number 2
Type Disc
Manufacturer Discflo
Capacity, gpm, each 200 / 300
Head, feet 86 / 148
Horsepower 50
Drive Variable
Raw Sludge Feed Pump Grinder GDR8501 2001
Number 1
Type In-line
Manufacturer JWC Environmental
Capacity, gpm, each 600
Horsepower 3
Drive Constant
Digesters – Expansion T8101-8401 2001 T 8101 serving as thermophilic stage
Number 4
Diameter, feet
T8101-8201
T8301-8401
55
45
Side Water, feet 27
Nominal Volume, gal
T8101-8201
T8301-8401
520,000
340,000
Includes cone volume
Digester Mixers
MX8101, 8102
MX8201, 8202
MX8301, 8302
MX8401, 8402
2001
Number 8
Type Draft tube
Manufacturer Eimco
Horsepower MX8101-8202
MX8301-8402
10
7.5
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
68
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Drive Variable
Digesters – Original Digester 1 and 2
T8601, 8701
1990 Includes cone volume
Number 2
Diameter, feet 45
Side Water, feet 27
Nominal Volume, gal 340,000
Sludge/Sludge Heat Exchangers HEX8501, 8502 2001
Number 2
Type Spiral
Manufacturer Alfa Laval
Capacity, kBtu/hr 4,501
Circulating Sludge/Water Heat Exchangers HEX8101, 8201
HEX8301, 8401
2001
Number 4
Type Spiral
Manufacturer Alfa Laval
Capacity, kBtu/hr, sum / win
HEX8101-8201
HEX8301, 8401
3,000
750 / 1,180
Water Plate and Frame Heat Exchangers HEX8202-8402 2001
Number 3
Type Plate
Manufacturer Alfa Laval
Capacity, kBtu/hr HEX8202
HEX8302, 8402
592
124
Circulating Sludge Pumps P8514-8516
P8524-8526
2001
Number 6
Type Centrifugal
Manufacturer Wemco
Capacity, gpm, each P8514-8516 600
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
69
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
P8524-8526 200
Head, feet P8514-8516
P8524-8526
52
39
Horsepower P8514-8516
P8524-8526
25
10
Drive Constant
Circulating Sludge Pump Grinders GDR8513, 8514
GDR8523, 8524
2001
Number 4
Type In-line
Manufacturer JWC Environmental
Capacity, gpm, each 600
Horsepower 3
Drive Constant
Transfer Sludge Pumps P8511-8513
P8521-8523
2001
Number 6
Type Centrifugal
Manufacturer Wemco
Capacity, gpm, each P8511-8513
P8521-8523
350 / 200
380 / 200
Head, feet P8511-8513
P8521-8523
55 / 68
27 / 41
Horsepower P8511-8513
P8521-8523
15
7.5
Drive P8511-8513
P8521-8523
Variable
Constant
Transfer Sludge Pump Grinders GDR8511, 8512
GDR8521, 8522
2001
Number 4
Type In-line
Manufacturer JWC Environmental
Capacity, gpm, each 600
Horsepower 3
Drive Constant
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
70
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Sludge Transfer Pumps STP-1 thru STP-3 2001-2004
Number 3
Type Centrifugal
Manufacturer Wemco
Capacity, gpm, each 250
Head, feet 55
Horsepower 7.5
Drive Constant
Sludge Recirculation Pumps SRP-1 thru SRP-3 1990 Original digester system
Number 3
Type Centrifugal
Manufacturer Allis Chalmers
Capacity, gpm, each 350
Head, feet 22
Horsepower 5
Drive Constant
Primary Heating Loop Circulating Water Pumps P8531-8534 2001
Number 4
Type Centrifugal
Manufacturer Bell & Gossett
Capacity, gpm, each P8531, 8533
P8532
P8534
315
270
150
Head, feet P8531, 8533
P8532
P8534
65
60
20
Horsepower P8531-8533
P8534
10
1.5
Drive Constant
Secondary Heating Loop Circulating Water Pumps P8101, 8201
P8301, 8401
2001
Number 4
Type Centrifugal
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
71
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Manufacturer Bell & Gossett
Capacity, gpm, each P8101, 8201
P8301, 8401
346
50
Head, feet P8101, 8201
P8301, 8401
45
46
Horsepower P8101, 8201
P8301, 8401
7.5
1.5
Drive Constant
Digester Gas Boilers BLR8531, 8532 2001
Number 2
Type Triple pass
Manufacturer Burnham
Rating, BHP 7,746
Output, MBH 9,683
Steam, lb/hr 9,256
Sludge Heat Exchanger Boilers BOILER-1, -2 1990 Original digester system
Number 2
Type Sludge/water
Manufacturer Carter
Rating, MMBH 1.5
Water flow, gpm 85
Sludge flow, gpm 350
Digester Gas Booster Fans DGBF8531, DGBF8532
Number 2
Type Multistage centrifugal
Manufacturer Spencer Turbine
Capacity, icfm, each 71
Discharge pressure, psig 2.5
Horsepower 3
Digester Gas Compressors GASCOMP-1 thru -3 Original digester gas mixing system
Number 2 GASCOMP-2 has been removed
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
72
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Type Rotary lobe
Manufacturer Sutorbilt
Capacity, scfm, each 196
Discharge pressure, psig 11.0
Horsepower 15
Drive Constant
Gas Flare - Expansion BNR8530 2001
Number 1
Manufacturer Varec
Capacity, scfm, each 370
Gas Flare - Original - 1990 Not used
Number 1
Manufacturer Not used
Capacity, scfm, each Not used
Package Dry/Liquid Polymer Processing Unit CFR9301 1990
Number 1
Manufacturer Wallace and Tiernan
Capacity, ft3 1.6
Horsepower 1/6
Drive Constant
Polymer Mixing/Aging Tanks T9326, 9327
T9335, 9336
1990
2002
BFP Polymer Tanks
RDT Polymer Tanks
Number 4
Volume, gal 1,600
Polymer Mixing/Aging Tank Mixers MX9326, 9327
MX9335, 9336
1990
2002
BFP Polymer Tank Mixers
RDT Polymer Tank Mixers
Number 4
Horsepower 1.5
Drive Constant
RDT Polymer Metering Pumps P9311, 9312 2001
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
73
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Number 2
Type Progressive cavity
Manufacturer Moyno
Capacity, gpm, each 4
Discharge pressure, psig 185
Horsepower 1.5
Drive Variable
BFP Polymer Metering Pumps P9321-9323,
P9326
1990
Number 4
Type Progressive cavity
Manufacturer Moyno
Capacity, gpm, each 5
Discharge pressure, psig 42
Horsepower 0.5
Drive Variable
Belt Filter Press Feed Pump Grinders SLUGRIN-1SD, -2SD 1990 Re-built ca. 2005
Number 2
Type Twin shaft
Manufacturer JWC Environmental
Capacity, gpm, each 100
Horsepower 3
Drive Constant
Belt Filter Press Feed Pumps BFPFEED-1 thru -3 1999, 1990, 2001
Number 3
Type Double disc
Manufacturer Penn Valley
Capacity, gpm, each 120
Head, feet 25
Horsepower 5
Drive Variable
Belt Filter Presses BFP-1 thru -3 1990
Number 3
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
74
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Type 2.2 meter
Manufacturer Enviroquip
Capacity, lb/hr, each 1,000
Horsepower 2
Drive Variable
Mixer horsepower 0.5
Wash water pump, number 3
Type Centrifugal
Manufacturer Peerless
Capacity, gpm, each 50
Head, feet 116
Horsepower 5
Dewatered Biosolids Conveyors CONVEY-1, -DRH, -DRV 1990
Number 3
Type CONVEY-1
CONVEY-DRH
CONVEY-DRV
Belt
Belt
Sandwich Belt
Manufacturer C-Tech Conveyor
Horsepower 5
Drive Constant
Dewatered Biosolids Hopper Discharge Gate - 1990
Number 1
Type Sliding gate
Capacity, cubic feet 14
Manufacturer XC-Tech Conveyor
Dewatered Biosolids Storage Pad 1990
Length, ft 225
Width, ft 225
Wall height, ft 4
Effluent Water
Effluent Water Pumps EFWP-1 thru -6 1999 Upsize motors and impellers in 2002
Number 6
Type Centrifugal
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
75
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Manufacturer Berkeley
Capacity, gpm, each 250
Head, feet 231
Horsepower 25
Drive Constant
Soccer Field Irrigation - 1996 Will be abandoned
Number 1
Type Filter
Filter Capacity, gpm 400
Pump Manufacturer Aurora New pumps in 2000 & 2001
Pump Capacity, gpm, each 150
Head, feet 250
Pump Horsepower 20
Backup Power
Standby Generator X 2002
Number 1
Type Diesel engine
Manufacturer Caterpillar
Generator rating, kW 1,000
Miscellaneous
Foam Control - 2001
Number 1
Type Solution spray
Pump Manufacturer LMI
Pump Horsepower 0.25
Ferric Chloride Addition
Number 2 Sludge Storage Tank (T8801)
Sludge Equalization Tank (T8001)
Type Storage vessel and metering
pump
Application Rate, gpd T8801
T8001
4.5
7.5
Iowa City South Wastewater Treatment Plant Existing Facilities and Condition
76
Table 1. Iowa City SWWTP Facilities Data
Parameter Value Year Installed Comments
Sample Pumps
Raw sewage, number 2
Primary effluent, number 1
Aeration basin influent, number 1
Aeration basin, number 7
Secondary effluent, number 1
Chlorinated effluent, number 2
Dechlorinated effluent, number 1
Tank Drain Dewatering Pumps 1990 New impellers in 2006
Number 2
Type Submersible centrifugal
Pump Manufacturer KSB
Pump Capacity, gpm 450
Head, feet 40
Pump Horsepower 4