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Wasteshed
Analysis TM
CAAP – Methane Recovery Feasibility Study
Completed by HDR Engineering, Inc. on behalf
of the City of Iowa City, to support the Climate
Action and Adaptation Plan (CAAP) and the
associated Action Items 3.7 and 3.8.
Iowa City, Iowa
February 27, 2020
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Table of Contents
Wasteshed Analysis ................................................................................................................... 4
Iowa City WWTP Solids .......................................................................................................... 5
Landfill and Compost Wastes ................................................................................................. 5
Outside Wastes ...................................................................................................................... 6
Food Service Wastes .......................................................................................................... 7
Fats, Oils, and Grease (FOG) Waste .................................................................................. 7
Agricultural Residues .......................................................................................................... 7
Animal Feed Operations ..................................................................................................... 8
Biodiesel Facilities .............................................................................................................. 8
Municipal WWTP Solids ...................................................................................................... 8
Ethanol Facilities ................................................................................................................. 8
Food (and Beverage) Manufacturing Facilities .................................................................... 9
Paper Manufacturing Facilities ...........................................................................................10
Consumer Products ...........................................................................................................10
HDR Engineering, Inc.
Morgan Mays, PE
Project Manager
5815 Council St. NE, Suite B
Cedar Rapids, IA 52302
D 319.423.6318 M 319.400.2718
Morgan.Mays@hdrinc.com
hdrinc.com/follow-us
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Technical Memorandum
Date: Thursday, February 27, 2020
Project: City of Iowa City – Climate Action and Adaptation Plan Methane Feasibility Study
To: Joe Welter, IA City; Tim Wilkey, IA City; Jennifer Jordan, IA City
From: Morgan Mays, HDR; Eric Evans, HDR; Eric Sonsthagen, HDR
Subject: Wasteshed Analysis TM
This memorandum presents the next step in the methane feasibility study as part of the City of
Iowa City’s (City’s) Climate Action and Adaptation Plan (CAAP) Methane Feasibility Study. As
shown in Figure 1, the overall methane feasibility study is a holistic evaluation intended to
capture the interconnected facilities. This TM focuses on the inputs side of the overall feasibility
study including municipal solids waste (MSW), compostables, municipal wastewater solids
(residues), and industrial (manufacturing) wastes. The objective of this TM is to identify and
quantify waste sources that makeup the inputs. As a result, it focuses on wasteshed organics
that can be utilized at the wastewater treatment plant (WWTP) and the landfill.
The wasteshed evaluation evaluates solids currently digested at the WWTP and organics
disposed in the current landfill. The wasteshed also evaluates external organic wastes, not
currently received by these two facilities that could be directed to the facilities to enhance biogas
production potential. Source separated organics, or hauled wastes, may be brought in from
industries and commercial facilities, or diverted from composting. The outside wastes may
increase biogas production at the WWTP, in the landfill, or at both facilities.
Figure 1. Interconnected Methane Feasibility Study, Wasteshed or Inputs Analysis
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Wasteshed Analysis
This wasteshed analysis evaluates waste generation potential at the WWTP and landfill from
outside sources (such as composting). Wastes generated can be utilized in either the digestion
system at the WWTP or directed to the landfill to generate biogas. The economic and
greenhouse gas (GHG) impacts of waste diversion to the WWTP or landfill differ. This analysis
focuses on 1) identifying waste streams that makeup the wasteshed, and 2) conducting a
preliminary evaluation of the implications of directing waste streams to either the WWTP or the
landfill.
An overall summary of the wasteshed is presented in Table 1. The WWTP wasteshed consists
of WWTP solids (currently treated at WWTP), consumer product waste (generated by Proctor
and Gamble), and leachate waste (generated by the landfill. Landfill wastes include yard waste,
food service waste, paper waste, and other wastes. The compost facility receives yard waste
and food service waste primarily. A range of outside waste sources including fats, oils and
grease (FOG) waste, biodiesel waste, and food manufacturing waste.
As part of the future steps in this evaluation, data from Table 1 will be revisited to determine if
the wastes are directed to the best final destination based on minimizing GHG generation. For
example, should compost and outside waste streams be considered for the WWTP or the
landfill. Further, should current WWTP or landfill wastes be redirected; e.g. landfilled instead of
digested at the WWTP or vice versa.
Table 1. Summary of Wasteshed for the WWTP, the Landfill, and wastes currently directed to composting
Waste Stream or Source
WWTP1
(ton/yr)
Landfill2
(ton/yr)
Composting
(ton/yr)
Outside
Wastes3
(ton/yr)
WWTP Solids (Residues) 2,535-2,580 300 N/A 2,500-3,000
Yard Waste4 N/A 2,492 8,263 0
Food Service Waste 0 32,534 728 300-400
FOG Waste 0 N/A N/A 2,000-2,500
Biodiesel Waste 0 N/A N/A 24,000-26,000
Ethanol Waste 0 N/A N/A
Food (and Beverage)
Waste
0 N/A N/A 3,000-3,500
Paper Mfr / Paper Waste5 0 9,576 N/A 0
Consumer Product
Waste6
850-900 N/A N/A 0
Leachate Waste6 15-20 N/A N/A 0
Other Landfilled Wastes --- 86,282 --- ---
TOTAL 3,400-3,500 131,184 8,991 31,800-35,400
1Ranges are estimated based on the projected total wastes in the wasteshed and a range of capture
efficiencies that would be typical for this waste source. WWTP Solids are currently process at the WWTP,
but all other waste streams represent new waste potential for the WWTP.
2 Landfill disposal rates assume the most recent five year average total disposal tonnage and mean
composition determined in the 2017 Iowa Statewide Waste Characterization Study for the Iowa City
Landfill Sort Data; as presented in Section, “Landfill and Compost Wastes” of this TM.
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3 Outside wastes - not currently received by the WWTP, the landfill, or the compost facility (possibly from
outside of Iowa City).
4 Includes leaves.
5 Paper waste quantity reflects only the compostable fraction of paper waste.
6 Received on liquid treatment side; i.e. not directly fed to digestion process. Mass represents the solids
potential from the organic content of the liquid stream. This is a current part of the WWTP solids mass.
Iowa City WWTP Solids
Solids residuals are generated by both primary and secondary treatment process at the WWTP
currently. These solids are captured or generated onsite due to the influent pollutant load. Table
2 shows that the average raw solids generated (primary plus secondary solids, based on the
digester feed rate, is 19,500 lb/d. Future solids production rates are expected to increase as
Iowa City grows as shown in Table 2. If Iowa City expands differently (more rapidly or slowly)
than in recent history, adjustments to this projection should be made. A more detailed analysis
of solids generation at the WWTP is included in the existing facilities evaluation TM.
Table 2. Raw Solids Generation (lb/d)
2017-2019
Raw Solids to Digesters
2030
Raw Solids to Digesters
2040
Raw Solids to Digesters
Average 19,500 21,200 22,900
50th Perc. 19,000 20,700 22,300
91.7th Perc. 24,800 26,300 28,400
99.7th Perc. 36,800 49,600 53,600
The yield factor is assumed to represent the typical yield for the WWTP. This solids generation
rate corresponds to an average overall (primary and secondary) solids yield of 0.9 lb-TSS/lb-
cBOD5. As flows and loads increase, it is assumed this yield factor is representative of future
potential solids capture and generation by the system. It may be possible to increase the yield, if
desired, to capture more solids and increase biogas production. Increased yield may be
achieved by enhancing primary clarifier capture using chemical coagulants.
Table 3. Overall Plant Yield
Plant Solids Yield
(lb-TSS/lb-cBOD5)
Average 0.90
Stand. Dev. 0.24
50th Perc. 0.88
Landfill and Compost Wastes
The Iowa City Sanitary Landfill has disposed of approximately 131,180 tons of waste annually
on average from 2015 through 2019 based on the historical waste disposal rates. Over this
same time period the population of Iowa City has grown an average of 1.2 percent per year and
the per capita waste disposal has averaged approximately 1.8 tons per person per year. The
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amount of material landfilled in 2019 decreased by approximately 9 percent from 2018 and was
approximately 2.7 percent lower than the recent 5-year average disposal rate. In discussions
with the City landfill staff, the recent trend of reduced waste disposed of at the landfill is
expected to continue in the near term future.
Table 4. Historical Landfill Quantities
FY Year Total Disposal
(tons)
Yard Waste
@ 1.9%
(tons)
Food Waste
@ 24.8%
(tons)
Paper Waste
@ 7.3%
(tons)
2015 123,692 2,350 30,676 9,030
2016 126,875 2,411 31,465 9,262
2017 137,107 2,605 34,003 10,009
2018 140,657 2,672 34,883 10,268
2019 127,587 2,424 31,642 9,314
5-year Average 131,184 2,492 32,534 9,576
During 2015 through 2019, the amount of material processed by composting has averaged
approximately 8,990 tons per year. The amount of material processed by the composting facility
has been relatively steady over this timeframe as it is operating near capacity based on its
existing footprint constraints. Future quantities of material composted are expected to be near
the recent historical average as no changes to the composting operation method or area are
known at this time.
Table 5. Historical Compost Quantities
FY Year Total Disposal
(tons)
Leaves
(tons)
Yard Waste
(tons)
Food Waste
(tons)
2015 7,454 197 6,817 440
2016 8,850 1,588 6,713 549
2017 10,018 1,068 8,197 753
2018 8,109 488 6,590 1,032
2019 10,524 1,075 8,583 866
5-year Average 8,991 883 7,380 728
Outside Wastes
Additional outside organic waste streams not currently directed to the WWTP, the landfill, or the
compost facilities, such as from industries and commercial facilities, could be captured and used
to increase biogas (methane) production rates. This section describes several potential sources
of external or hauled wastes to be considered as part of the wasteshed analysis including food
service wastes; fats, oils, and grease (FOG); biodiesel waste; ethanol waste; and food
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manufacturing waste1. Potential waste sources have been evaluated based on the Iowa biogas
assessment model (IBAM).
Food Service Wastes
Food service wastes include organic, solids wastes from restaurants and schools. These wastes
may be directed to either the WWTP or the landfill; however, enhanced receiving facilities are
needed to utilize and process the material at the WWTP. Incorporation into WWTP anaerobic
digesters would be further limited by the capacity available within the digestion process.
For Iowa City, the highest potential for food service waste would be from the University of Iowa
including the hospitals. Currently, the University of Iowa has invested heavily into a composting
program and currently composts over 800,000 lb/yr (400 ton/yr) of food service wastes. The
biogas potential of food service waste at the WWTP is typically between 9 and 14 ft3/lb-volatile
solid removed (VSR).
Fats, Oils, and Grease (FOG) Waste
Fats, oils and grease (FOG) are the waste captured in grease traps from restaurants and
industrial pretreatment processes (e.g. dissolved air flotation [DAF] separation). Food service
establishments (FSE) are typically the largest FOG contributors, but some industries (e.g.
renderers) generate FOG as well. It is estimated that sewer discharges of grease from food
preparation are on the order of 50 to 100 lb/person/year with an additional 15 lb/person/year of
waste grease generated from other sources.
Direct addition of FOG into the anaerobic digestion process results in increased biogas
production at the WWTP. Similar to food service wastes, enhanced receiving facilities are
recommended for use at the WWTP. Depending on the source, a single FSE generates
between 800 and 17,000 lb/year of FOG. FOG quality varies, but in general, FOG digestion
results in biogas production yields at the WWTP between 18 and 25 ft3/lb-VSR. Biogas
production by FOG addition is connected to a FOG program by the city and maybe be
considered as part of an overall program. This waste stream is generally not applicable for
landfilling due to the high moisture content.
Agricultural Residues
Agricultural or ag residues are not being considered as a waste or feedstock for generating
biogas by Iowa City at this time. While there is substantial carbon available from agricultural
residues, the WWTP digestion system is not configured to support digestion of ag residues,
which could compromise the treatment process. This waste stream could be landfilled and
decompose to generate landfill gas, however, existing gate fees for disposal may not support
acceptance on a large scale. Separate consideration could be given to a future program and
partnership with the power plant to collect, dry, and utilize these ag residues as a fuel source.
1 Feeding of hauled waste into an anaerobic digestion system is best achieved with a dedicated receiving
system designed with rock removal, screenings removal, heating, and storage for controlled addition of
digestible materials.
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Animal Feed Operations
Wastes from animal feed operations are not being considered as a waste or feedstock for
generating biogas by Iowa City at this time. As with ag residues, the WWTP digestion system is
not configured to support digestion of wastes from animal feed operations, which could
compromise the treatment process. This waste stream is generally not applicable for landfilling
due to the high moisture content.
Biodiesel Facilities
Biodiesel facilities convert agricultural products (soy, algae, etc.) and residues into diesel fuel.
Waste from biodiesel facilities include waste glycerin (containing a high cBOD5 content) and
wastewater (containing high concentrations of highly biodegradable methanol). Both of these
streams offer a high biogas potential due to the high organic carbon content. Biodiesel wastes
generate between 5 and 10 ft3/lb-VSR. Despite the potential biogas from biodiesel wastes,
biodiesel production within a 25 mile radius of Iowa City is limited. Iowa biogas assessment
model shows a biodiesel plant near Washington (Iowa Renewable Energy) and another plant
near Crawfordsville (W2 Fuel). The Washington plant generates approximately 100,000 to
110,000 lb/d of waste potential, and the biogas plant near Crawfordsville generates between
34,000 and 35,000 lb/d of waste. These waste streams are typically liquid in nature but highly
concentrated and could be hauled to the WWTP. This waste stream is generally not applicable
for landfilling due to the high moisture content.
Municipal WWTP Solids
In addition to digesting solids generated at Iowa City’s WWTP, solids from other nearby WWTPs
could be hauled into either the Iowa City WWTP or landfill and converted to biogas. Regional
treatment of WWTP solids is often evaluated as an option to gain cost efficiency. Nearby
facilities that generate WWTP solids include Coralville, West Liberty, Muscatine, and Cedar
Rapids. The total estimate WWTP solids is between 13,000 and 16,000 lb/d (2,500 and 3,000
ton/yr) excluding Cedar Rapids2. In general, solids from wastewater plants generate between 12
and 18 ft3/lb-VSR in a WWTP anaerobic digestion process. Hauling of solids from outside
WWTPs results in GHG emission and costs due to transport depending on hauling distance and
the water content of the solids. Additional drying of solids may be required prior to landfilling to
reduce the moisture content prior to disposal within the landfill.
Ethanol Facilities
Ethanol or bio-ethanol facilities convert agricultural products (wheat, corn, etc.) and residues
(cellulosic) into ethanol for use as fuel. Ethanol production results in a wastewater stream with a
high organic content (as much as 100 mg-chemical oxygen demand [COD]/L) that can yield
biogas on the order of 18 ft3/lb-VSR. Despite the potential biogas from ethanol wastes, ethanol
production within a 25 mile radius of Iowa City is limited. Iowa biogas assessment model shows
an ethanol plant in Cedar Rapids (ADM) and Blairstown (Fiberight LLC). The waste potential of
the Cedar Rapids Plant provided by the model and may be limited since the Cedar Rapids
2 Cedar Rapids owns and operates a large WWTP with its own solids treatment process managing 100
dry ton per day (DTPD) of solids residues.
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facility is a dry corn milling plant (high utilization efficiency). The waste potential of the
Blairstown Plant is 73,000-74,000 lb/d, but the plant is indicated to be idle currently.
Food (and Beverage) Manufacturing Facilities
Food (and beverage) manufacturing facilities vary from grain processing and cereal production
to corn syrup and soda bottling. Most of these manufacturing facilities produce waste streams
with a high organic content, but due to the wide range of facilities, the characteristics of the
waste stream vary considerably as well. Some waste streams are high in suspended solids
while others are very soluble. Some have a neutral pH while others are acid or alkaline. Waste
streams from food facilities act as good substrates for biogas generation generally, but it is
important to verify the impacts when fed to a WWTP digestion system; particularly when the
suspended solids content is high or pH is extreme; careful blending of food wastes with onsite
solids and other wastes can be used to maintain healthy digestion. Conversely, incorporation of
food wastes into a landfill maybe appropriate when the food wastes are high in solids but less
practical when highly soluble. The estimated waste production from food manufacturers within
25-30 miles of Iowa City is about 18,400-19,190 lb/d total (as listed below). Practical capture
and conversion of the organics is estimated to be less than 50% of the total, however.
Food Manufacturers List
Hubbard Feeds Inc. (Iowa City, IA) – 130-140 lb/d
Heyens Ice Cream (Iowa City, IA) – 30-40 lb/d
Brick Arch Winery (Iowa City, IA) – 5-10 lb/d
Backpocket Brewing (Coralville, IA) – 90-100 lb/d
Taste The World Inc. (Coralville, IA) – 20-30 lb/d
Cole’s Quality Foods, Inc. (North Liberty, IA) – 180-200 lb/d
West Liberty Foods (Processed Meats, West Liberty, IA) – 4,500-4,600 lb/d
West Liberty Locker & Processing (West Liberty, IA) – 20 – 30 lb/d
Tortilleria El Norte (West Liberty, IA) – 5-10 lb/d
Kalona Feed (Kalona, IA) – 10 – 20 lb/d
Dekalb Feed (Kalona, IA) – 90-100 lb/d
Farmer’s All Natural Creamery (Wellman, IA) – 290-300 lb/d
ADM Corn Processing (Cedar Rapids, IA) – 1,300-1,400 lb/d
Canadian Harvest (Cedar Rapids, IA) – 130 -140 lb/d
Cargill (Cedar Rapids, IA) – 1,000-1,100 lb/d
Diamond V (Cedar Rapids, IA) – 330-340 lb/d
General Mills (Cedar Rapids, IA) – 3,100-3,200 lb/d
Halal Food Processors (Cedar Rapids, IA) – 60-70 lb/d
Ingredion (Cedar Rapids, IA) – 1,000 – 1,100 lb/d
Kraft Heinz (Cedar Rapids, IA) – 900 – 910 lb/d
Midamar (Cedar Rapids, IA) – 90-100 lb/d
Quaker Oats (Cedar Rapids, IA) – 4,000-4,100 lb/d
Specialty Blending (Cedar Rapids, IA) – 290-300 lb/d
Third Base Sports & Brewery (Cedar Rapids, IA) – 130-140 lb/d
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TreeHouse Private Brands (Cedar Rapids, IA) – 670-680 lb/d
Roehrkasse Meat Co (Williamsburg, IA) – 20 – 30 lb/d
Paper Manufacturing Facilities
Paper manufacturing waste streams tend to be high in soluble organic wastes with a medium to
high biogas potential. In addition, paper production generates a consistent wastewater volume
and load typically, which results in process stability. Challenges with paper waste result from the
chemicals used in the process, which range from bleach to sulfuric acid. These chemicals can
inhibit the process or generate a high sulfide content. International Paper (Cedar Rapids) is the
closest paper manufacturer, but due to the high wastewater volume, it may not be practical as a
hauled in waste.
Consumer Products
Iowa City is home to one of Proctor and Gamble’s production plants. Proctor and Gamble is a
consumer products manufacturer. Their Iowa City plant produces body care products (shampoo,
soap, toothbrush) historically. Proctor and Gamble’s waste stream is a high volume waste
stream discharged to the WWTP’s liquid treatment process currently. Based on the waste
characteristics, Proctor and Gamble’s waste stream would be challenging to divert to the
anaerobic digesters directly. Additionally, Proctor and Gamble’s discharge contains siloxanes,
which become a component of the biogas when digested and require more intensive biogas
treatment.