EPA 600/R-14/240 September 2014 www.epa.gov/ord
United States
Environmental Protection
Agency
Food Waste to Energy: How Six Water
Resource Recovery Facilities are Boosting
Biosas Production and the Bottom Line
Office of Research and Development
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EPA/600/R-14/240
September 2014
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EPA/600/R-14/240
September 2014
Food Waste to Energy:
How Six Water Resource Recovery Facilities are
Boosting Biogas Production and the Bottom Line
Region 9 San Francisco, CA and
National Risk Management Research Lab
Office of Research and Development
Cincinnati, OH
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EPA/600/R-14/240
September 2014
Foreword
The US Environmental Protection Agency (US EPA) is charged by Congress with
protecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions leading
to a compatible balance between human activities and the ability of natural systems
to support and nurture life. To meet this mandate, US EPA's research program is
providing data and technical support for solving environmental problems today and
building a science knowledge base necessary to manage our ecological resources
wisely, understand how pollutants affect our health, and prevent or reduce
environmental risks in the future.
The National Risk Management Research Laboratory (NRMRL) is the Agency's
center for investigation of technological and management approaches for
preventing and reducing risks from pollution that threaten human health and the
environment. The focus of the Laboratory's research program is on methods and
their cost-effectiveness for prevention and control of pollution to air, land, water,
and subsurface resources; protection of water quality in public water systems;
remediation of contaminated sites, sediments and ground water; prevention and
control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates
with both public and private sector partners to foster technologies that reduce the
cost of compliance and to anticipate emerging problems. NRMRL's research
provides solutions to environmental problems by: developing and promoting
technologies that protect and improve the environment; advancing scientific and
engineering information to support regulatory and policy decisions; and providing
the technical support and information transfer to ensure implementation of
environmental regulations and strategies at the national, state, and community
levels.
This publication has been produced as part of the Laboratory's strategic long-term
research plan. It is published and made available by US EPA's Office of Research
and Development to assist the user community and to link researchers with their
clients.
Cynthia Sonich-Mullin, Director
National Risk Management Research Laboratory
IV
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EPA/600/R-14/240
September 2014
Abstract
Water Resource Recovery Facilities (WRRFs) with anaerobic digestion have
been harnessing biogas for heat and power since at least the 1920's. A few are
approaching "energy neutrality" and some are becoming "energy positive"
through a combination of energy efficiency measures and the addition of
outside organic wastes. Enhancing biogas production by adding fats, oil and
grease (FOG) to digesters has become a familiar practice. Less widespread is
the addition of other types of food waste, ranging from municipally collected
food scraps to the byproducts of food processing facilities and agricultural
production. Co-digesting with food waste, however, is becoming more
common. As energy prices rise and as tighter regulations increase the cost of
compliance, WRRFs across the county are tapping excess capacity while
tempering rates. This report presents the co-digestion practices, performance,
and the experiences of six such WRRFs. The report describes the types of food
waste co-digested and the strategies—specifically, the tools, timing, and
partnerships—employed to manage the material. Additionally, the report
describes how the facilities manage wastewater solids, providing information
about power production, biosolids use, and program costs.
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EPA/600/R-14/240
September 2014
Acknowledgements and Notice
We are very thankful to the six interviewed Water Resource Recovery Facilities.
Staff generously contributed their time and expertise. Jason Dow, Sophia Skoda,
John Hake, Chuck Rogers, Joe Zakovec, Sharon Thieszen, and David S. Henderson
not only participated in the original interviews, but continued to work with EPA
over the last year. Thank you Jason, Sophia, John, Chuck, Joe, Sharon and David
for sharing your facility's story with EPA, and for allowing us to share it with
communities across the country.
Lauren Fillmore (Senior Program Director, Water Environment Research
Foundation, Alexandria, VA), Robert B. Williams (Development Engineer, UC
Davis California Biomass Collaborative, Davis, CA), Greg Kester (Director of
Renewable Resource Programs, California Association of Sanitation Agencies,
Sacramento, CA) and Jason Turgeon (Physical Scientist, EPA Region 1, Boston,
MA) peer-reviewed the report. Thank you, Lauren, Rob, Greg, and Jason for your
suggestions and corrections.
Charlotte Ely led the team to produce the report with Sarah Hardy, Andrea Sproul,
Suzanne Maher, and Steve Rock.
This report has been peer reviewed by the U.S. Environmental Protection Agency
Office of Research and Development and approved for publication. Mention of
trade names or commercial products does not constitute endorsement or
recommendation by EPA for use.
VI
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EPA/600/R-14/240
September 2014
Table of Contents
Table of Contents vii
List of Figures vii
List of Tables vii
List of Appendices viii
List of Abbreviations, Acronyms, and Initialisms ix
1 Introduction 1
1.1 Managing Waste More Sustainably 1
1.2 Generating Renewable Energy 2
1.3 Ensuring Affordable Rates 3
1.4 Celebrating Success: Six examples of WRRF co-digestion projects 4
2 What is co-digested? 6
3 How much is co-digested, and when? How is it delivered? 10
4 How much is stored? What processing is required? 12
5 How much biogas is produced? How is it used? 15
6 How much biosolids are produced? How are they managed? 20
7 How much did the facilities invest in co-digestion infrastructure? 22
8 Summary & Conclusions 26
9 Appendices 29
10 References 36
List of Figures
Figure 1: Total MSW waste by percentage after recycling and composting 1
Figure 2: Comparing the carbon footprint of several food waste disposal options 2
Figure 3: Description of a 1922 biogas to energy project 3
Figure 4: Wastewater treatment facility photos 6
Figure 5: EBMUD process schematic 12
Figure 6: Marin Sanitation Service process schematic 13
Figure 7: Central Marin Sanitation Agency process schematic 13
Figure 8: West Lafayette WRRF's partnership with Purdue University 14
Figure 9: Microturbines at the Sheboygan WRRF 17
List of Tables
Table 1: Basic facility descriptions 5
Table 2: Types of co-digested food waste 9
Table 3: Food waste (FW): Volume and delivery process 11
Table 4: Food waste storage and processing 15
Table 5: 2013 Renewable Volume Obligations (U.S. EPA 2013, U.S. EPA 2014e) 18
Table 6: Biogas production, storage, and use at interviewed facilities 19
Table 7: Biosolids management 21
Table 8: FY13-14 rates for EBMUD tipping fees 23
Table 9: Cost, savings, and revenue 25
vii
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EPA/600/R-14/240
September 2014
List of Appendices
Appendix A: Survey questions for WWRFs 29
Appendix B: Example Standard Operating Prodecures 31
Vlll
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EPA/600/R-14/240
September 2014
List of Abbreviations,
AD
ADC
ADM
ADWF
ARRA
BOD
GGE
CARB
CEC
CHP
CHPCE
CMSA
CNG
CPI
CPUC
CWSRF
EA
EBMUD
EPA
F2E
FIT
FOG
GGE
HCTP
ICE
kW, kWh/MGD
LCFS
MSS
MG
MOD
MSW
MW,MWh
NPDES
O&M
PG&E
PPA
RFS
RAM
RIN
RVO
SGIP
SRF
SWRCB
WDR
WERF
WRRF
WWTF
Acronyms, and Initial isms
Anaerobic digester
Alternative daily cover
Anaerobically digested materials
Average dry weather flow
American Reinvestment and Recovery Act
Biochemical oxygen demand
Gallons of gasoline equivalent
California Air Resources Board
California Energy Commission
Combined heat and power
CHP Clean Energy
Central Marin Sanitation Agency
Compressed Natural Gas
Consumer price index
California Public Utilities Commission
Clean Water State Revolving Fund
Enforcement Agency Notification
East Bay Municipal Utility District
Environmental Protection Agency
Food to energy
Feed-in Tariff
Fats, oil, and grease
Gallons of gasoline equivalent
The Hill Canyon Wastewater Treatment Plant
Internal combustion engine
Kilowatts, Kilowatt hours per million gallons a day
Low carbon fuel standard
Marin Sanitation Service
Million gallons
Million gallons per day
Municipal Solid Waste
Megawatts, Megawatt hour
National Pollution Discharge Elimination System
Operations and maintenance
Pacific Gas and Electric
Power purchase agreement
Renewable Fuel Standard
Renewable Auction Mechanism
Renewable Identification Number
Renewable Volume Obligations
Self generation incentive program
State Revolving Fund
State Water Resources Control Board
Waste Discharge Requirement
Water Environmental Research Foundation
Water Resource Recovery Facility (a.k.a WWTFs)
Wastewater Treatment Facilities
IX
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Food Waste to Energy
1 Introduction
To protect human health and the environment, communities must have adequate infrastructure to handle
waste, critically the waste we throw away (solid waste) and the waste we flush down toilets (wastewater).
Modern solid waste and wastewater management approaches have remedied many of the historically
associated aesthetic, ecological, and public health problems; but they have engendered systems that
contribute to current crises, notably climate change. By diverting energy-rich food waste from landfills to
existing anaerobic digesters at Water Resource Recovery Facilities (WRRFs), co-digestion can help
communities manage waste more sustainably, generate renewable energy, and continue to provide
essential services at affordable rates. To help communities evaluate solid waste and wastewater
management options, this report presents the co-digestion practices and performance of six WRRFs,
providing information about the food waste material, including receipt, storage and processing; biogas
and biosolids production and use; and program costs.
1.1 Managing Waste More Sustainably
Landfills are the third largest anthropogenic source of methane (CH4) emissions in the United States,
accounting for 18.1% of total emissions in 2012 (U.S. EPA 2014b). While emitted in smaller quantities
than carbon dioxide (CO2), CH4
currently contributes to more than
one-third of today's anthropogenic
warming because its global warming
potential is 25 times greater than
CO2 (Global Methane Initiative
Other 4.3%
Rubber,
leather &
textiles
11.2%
Paper &
paperboard
14.8%
Yard
Trimmings
8.7%
Plastics
17.6%
2014).
Figure 1: Total MSW waste by
percentage after recycling and
composting (U.S. EPA 2014a)
According to the U.S. Environmental
Protection Agency (EPA), food
waste represents 14.5% of the
municipal solid waste (MSW)
stream, and most of what's generated
is wasted. Of the more 251 million
tons of MSW Americans generated
in 2012, food waste comprised 36.43
million tons, only 1.74 million tons
(4.8%) of which was recovered (U.S.
EPA 2014a). Of the 163 million tons
of discarded MSW, food waste comprised 34.69 million tons, or 21% of total MSW discards (Figure 1).
By diverting food waste from landfills and into existing WRRF digesters, communities can reduce
greenhouse gas emissions and protect water quality.
Co-digestion at WRRFs can reduce the carbon footprint of waste management by diverting food waste
from landfills, where methane may be generated and released into the atmosphere; by capturing and
combusting CH41; by minimizing MSW hauling distances, reducing truck traffic and associated air
Metals
9.0%
Glass
Of the 2,400 or so currently operating or recently closed MSW landfills in the United States, only 636 have methane utilization projects (U.S.
EPA 2014c). Furthermore, landfill methane capture efficiency varies considerably—from as low as 35% to as high as 90% (Spokas et al 2006),
resulting in significant fugitive emissions. In comparison, WRRFs harness methane much more efficiently, typically capturing and combusting
99% of the biogas produced in their anaerobic digesters (WERF 2012a).
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Food Waste to Energy
emissions (DiStefano and Belenkey 2009); and by sequestering carbon into soil structure through the land
application of biosolids (Brown and Leonard 2004). In an evaluation of food waste disposal options, the
Water Environmental Research Foundation (WERF) identified co-digesting hauled-in food waste at
WRRFs as the only carbon negative, i.e. greenhouse gas reducing, waste management strategy (Figure 2)
(WERF2012a).
Non-Biogenic CO2e Emissions (tons/yr)
Figure 2: Comparing the carbon footprint of several food waste disposal options:
landfilling, composting, delivering food waste to WRRFs via sewers, hauling food waste to
WRRFs via trucks, and separating food waste at a mixed materials recovery facility (MRF)
(WERF 2012a)
Diverting food waste from landfills can also protect water quality. When waste decomposes in landfills, it
creates leachate, a liquid composed primarily of dissolved organic matter, inorganic ions such as
ammonia, phosphate, and sulfate, and heavy metals (Christensen et al. 2001). Diverting food waste from
landfills reduces the volume of organic matter, correspondingly reducing not only the amount of leachate
but also the concentration of dissolved organic matter in the leachate. Leachate leaks from landfills
without adequate liners, percolating into soils and groundwater, potentially increasing biological oxygen
demand and nutrient loads in adjacent water bodies (Camargo and Alonso 2006, Diaz 2001, Kronvang et
al. 2005). By diverting food waste, landfills are less likely to contribute eutrophic and hypoxic events and
hence can help protect water quality.
1.2 Generating Renewable Energy
Delivering water and wastewater services is an energy-intensive effort, as the water is treated, pumped,
and consumed, and then the resulting wastewater is pumped to and treated at WRRFs. WRRFs in the
United States use approximately 30.2 billion kWh per year, or about 0.8% of national electricity use
(Electric Power Research Institute 2013). Water and wastewater utilities are typically the largest energy
consumers in municipalities, often accounting for 30-40% of total energy consumed by municipal
governments (U.S. EPA 2012). For WRRFs, energy bills can be -30% of total operation and
maintenance (O&M) costs (Cams 2005), usually representing a facility's second or third biggest expense.
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Food Waste to Energy
While WRRFs consume a lot of energy, they also have the potential to harness energy. Municipal
wastewater contains five to ten times as much chemical and thermal energy as is currently required to
treat it (WERF 2011). WRRFs with anaerobic digesters can utilize existing infrastructure to become net
producers of energy (Frijns et al. 2013).When microorganisms break down organic materials in the
absence of oxygen, they produce biogas as a byproduct. Biogas, composed primarily of CH4 (60 to 70%)
and CO2, can be used as a fuel source, much like natural gas. Fueling engines with biogas generates
electricity and heat, providing many benefits to WRRFs, such as producing power at a cost below retail
rates, displacing purchased fuels for thermal needs, and enhancing power reliability for the plant.
"Sewage gas" has been powering some WRRFs since at least the 1920s (Figure 3).
Gas from Sewage Waste Runs City Power Plant
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rfn-u* num« each ytwr rae k« turn**! i»lo
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Food Waste to Energy
production. These strategies are increasingly common and increasingly necessary. To address population
change, climate change impacts, increased energy costs, deteriorating infrastructure, and stricter water
quality regulations, WRRFs must invest in repairs and upgrades.
Many cities spend more money than they take in on providing sewer services. Between 1991 and 2005,
local governments, on average, generated only 88% of the funds expended (U.S. Conference of Mayors
2007). Nationally, the wastewater "funding gap" amounts to billions of dollars. Over the next 20 years,
the country nationally faces a shortage of $298.1 billion for wastewater and stormwater needs (U.S. EPA
2008). Historically, the federal government provided about 70% of the funds needed to build and upgrade
treatment plants (U.S. EPA 2000). Today, about 25% of the public funding for water infrastructure
projects is provided by the federal government (Musick 2010).
Since the dissolution of the construction grants program, the federal government's largest contribution to
America's wastewater infrastructure has been through the EPA's Clean Water State Revolving Fund
(CWSRF). Over the last two and half decades, the CWSRF provided over $100 billion in low-interest
loans. But the country's projected wastewater infrastructure costs over the next 20 years are nearly three
times greater than what EPA has funded over the past 25. With less public funding available and
increased costs expected, creative financing is essential.
For many WRRFs, boosting biogas production by co-digesting with food waste may help bridge funding
gaps. For facilities that do not produce sufficient biogas to economically justify CHP, co-digestion can
improve project economics and, in many cases, be the tipping point for investing in CHP (WERF 2012b).
For facilities already invested in CHP, co-digestion can facilitate goals for energy independence.
Minimizing and, for an increasing number of WRRFs, eliminating energy costs conserves capital needed
for repairs and upgrades. Furthermore, FOG and food waste tipping fees can generate revenue. By saving
money on energy and earning money through tipping fees, many WRRFs can secure funding for capital
improvements that would otherwise be obtained by raising rates.
1.4 Celebrating Success: Six examples of WRRF co-digestion projects
An estimated 216 WRRFs located in the U.S. haul in food waste (primarily FOG) for co-digestion with
sewage sludge. This accounts for approximately 17% of WRRFs that process sewage sludge using
anaerobic digestion (Qi, Beecher, and Finn 2013). This report presents the experiences of six WRRFs that
are co-digesting with food waste to boost biogas production. These facilities were selected because they
were willing to share their stories. Based on published articles, webinars, and conference presentations,
numerous WRRFs were identified as potential candidates. Candidate plants were contacted and asked to
participate. Six responded. Those who responded were given a list of questions (Appendix A), the
answers of which provided a basic understanding of the operation and management of the plant. After the
plant operators compiled the requested data, interviews were conducted over the phone. While a limited
sample, they nonetheless reflect the diversity of their sector, varying in capacity and employing
management strategies suited to their unique infrastructural, geographic and economic circumstances. The
following plants were interviewed (also see Table 1, Figure 4):
The Central Marin Sanitation Agency (CMSA) is located in San Rafael, California. CMSA is a
regional wastewater agency serving about 120,000 customers. Up to six billion gallons of wastewater per
year are treated and released. The CMSA treats an average dry weather flow (ADWF) of seven million
gallons per day (MGD) with the capacity to treat 125 MGD. The WRRF has two anaerobic digesters,
with a combined capacity of approximately two million gallons (MG). The facility started their co-
digestion program in 2013 with FOG and began receiving food waste in late January 2014. Before co-
digestion, CMSA produced enough biogas to provide approximately eight hours of power. With co-
digestion, they are hoping to meet all the plant's power needs with the biogas produced on site.
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Food Waste to Energy
The East Bay Municipal Utility District (EBMUD) serves approximately 650,000 people in an 88-
square-mile area along the east shore of the San Francisco Bay, treating wastewater from Alameda,
Albany, Berkeley, El Cerrito, Emeryville, Kensington, Oakland, Piedmont, and a part of Richmond. The
facility treats an ADWF of 60 MOD with the capacity to treat 168 MOD. It has 11 anaerobic digesters
with the combined capacity of approximately 22 MG. EBMUD began co-digesting in 2002 and, in 2012,
EBMUD became the first wastewater treatment plant in North America to produce more renewable
energy onsite than is needed to run the facility.
The Hill Canyon Wastewater Treatment Plant (HCTP) provides wastewater treatment for 90% of the
128,000 residents of Thousand Oaks in California. HCTP currently treats an ADWF of 9.5 MOD and has
the capacity to treat 14 MOD. The digester design capacity is 2.8 million gallons. Biogas produced from
digested solids and food waste fuels a 295 kW and a 630 kW engine. Hill Canyon will soon become
energy positive.
The Sheboygan Regional Wastewater Treatment Facility in Wisconsin, serves the city of Sheboygan,
Sheboygan Falls, Village of Kohler, the Town of Lima, the Town of Sheboygan, and the Town of Wilson.
The WRRF treats an average dry weather flow of 18.4 MGD and has the capacity to treat 56.8 MGD.
The WRRF has three anaerobic digesters with a capacity of 4.8 MG. The resulting biogas fuels ten 30kW
and two 200 kW microturbines, producing 2,300 megawatt hours of electricity annually. This is used to
meet 90% of the facility's annual electrical needs and 85% of its annual heating requirements.
The West Lafayette Wastewater Treatment Utility in Indiana serves West Lafayette's 29,000 residents
and Purdue University. The plant treats an ADWF of 7.8 MGD, and has the capacity to treat 10.5 MGD.
West Lafayette has two anaerobic digesters with a combined capacity of 1.0 MG. On average, the facility
meets 20% of its power needs using the biogas generated on-site.
The Janesville Wastewater Treatment Facility in Wisconsin serves approximately 62,000 people. The
facility's ADWF is 12.5 MGD with a capacity of 17.75 MGD. The anaerobic digester capacity is 2.5
MG. In 2013, the facility co-digested approximately 300,000 gallons of food waste. 90% of Janesville's
biogas is used to generate electricity that is sold to the grid, enabling the facility to meet 27% of its
electricity needs and 65% of its digester heating needs. The remaining biogas (10%) is used to produce
clean natural gas for use in facility vehicles.
Table 1: Basic facility descriptions
Facility Name
CMSA
EBMUD
Hill Canyon
Sheboygan
West Lafayette
Janesville
Location
San Rafael, CA
Oakland, CA
Thousand Oaks, CA
Sheboygan, WI
West Lafayette, IN
Janesville, WI
Treatment
Plant Flow
ADWF
(MGD)
7.0
60.0
9
18.4
7.8
12.5
Treatment
Plant Flow
Capacity
(MGD)
125.0
168.0
14
56.8
10.5
25
Anaerobic
Digester Capacity
(MGD)
2.0
22
2.8
4.8
1.0
2.5
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Food Waste to Energy
Figure 4: Wastewater treatment facility photos
f
Photo provided courtesy of CMSA
.
Photo provided courtesy of EBMUD
Photo provided courtesy of Hill Canyon
Photo provided courtesy of Sheboygan
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Food Waste to Energy
Photo provided courtesy of West Lafayette
Photo provided courtesy of Janesville
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Food Waste to Energy
2 What is co-digested?
Increasingly, water resource recovery
facilities (WRRFs) with excess digester
capacity are co-digesting a variety of
organic waste materials, especially
energy-rich carbohydrate, protein, and
lipid wastes.
• Lipid wastes include fats, oils, and
greases (collectively referred to as
FOG).
• Simple carbohydrate wastes include
bakery waste, brewery waste, and
sugar-based solutions such as those
from confectionaries and soda pop
producers; more complex
carbohydrate wastes include fruits and
vegetables as well as mixed
organics—including the organic
fraction of municipal solid waste
stream.
• Protein wastes include meat, poultry,
and dairy waste products such as
cheese whey.
• Other waste organic feedstocks
include glycerin from biodiesel fuel prod
In 2002, EBMUD partnered with San Francisco and its
waste hauler, Recology, to co-digest post-consumer food
waste. Recology collects an average of 600 tons of
source-separated organic material each day, 20-40 tons of
which has been preprocessed and delivered to EBMUD.
In 2014, CMS A partnered with the Marin Sanitation
Service (MSS) to launch the Central Marin Food-to-
Energy Program. MSS collects post-consumer food waste
from 41 commercial customers (including restaurants and
supermarkets), preprocesses the waste and then delivers it
to CSMA.
Both Recology and MSS work closely with local
governments to attain aggressive zero waste goals: San
Francisco aims to reach zero waste by 2020; Marin
Country by 2025.
Because food waste comprises such a large percentage of
the MSW stream, both communities have heavily
invested in residential and commercial organic collection
program (San Francisco Department of the Environment
2014, Zero Waste Marin 2014).
uction.
For more information, WERF (2014) provides an extensive literature review summarizing the
performance of these various materials.
The interviewed facilities co-digested with various types of carbohydrate, protein, and lipid wastes. The
wastes were selected for a number of different reasons, including proximity, availability, dependability,
associated tipping fees, and biogas yield. Some food waste materials (e.g. sugary wastes) appear to
produce biogas with a relatively low percentage of methane while other food waste materials (e.g.
glycerin) produce biogas with a relatively high percentage of methane. Some food waste materials came
from relatively far sources. For example, EBMUD receives chicken blood from as far away as
California's Central Valley. Others only accepted food waste from nearby sources. West Lafayette, for
example, receives cafeteria waste from Purdue University, which is located across the street from the
facility.
Some facilities accept a variety of wastes. The Hill Canyon operator explained that, as food waste sources
can be intermittent and inconsistent, co-digestion has required some experimentation. Other facilities co-
digest with one material. Janesville, for example, only co-digests with chocolate waste. In the past,
Janesville accepted soft drink and whey wastes, but stopped because the soft drink waste was often
contaminated with plastics, and the whey waste too high in chlorides, which can be corrosive. Other
facilities—notably EBMUD and CMSA— have forged partnerships with municipal waste haulers,
helping nearby communities to reach waste diversion goals.
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Food Waste to Energy
Almost all of the interviewed WRRFs co-digest with FOG. Most of the facilities obtain FOG from local
restaurants, groceries, and bakeries. West Lafayette also receives FOG directly from residents. Table 2
summarizes what food waste materials the facilities co-digest.
CMSA
FOG
Post-consumer
commercial
EBMUD
FOG
Winery waste
Industrial liquids
and solids
Animal
processing &
rendering
Post-consumer
commercial
Post-consumer
residential (pilot)
Hill
Canyon
FOG
Industrial,
including
from fruit
juice, frappe,
beer, and
cheese
producers.
Restaurant
Biodiesel
waste, e.g.
glycerin
Sheboygan
FOG
Industrial
including:
dairy, soda
processing,
and off-spec
beverage
Ethanol
production
waste:
including thin
stillage and
corn syrup
West
Lafayette
FOG
Purdue cafeteria
food scraps
Agricultural
waste from
Purdue's Ag.
Research
program
Spoiled produce
donations
Janesville
Chocolate
waste
Table 2 Types of co-digested food waste
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Food Waste to Energy
3 How much is co-digested, and when? How is it delivered?
The six interviewed facilities accept varying
amounts of food waste throughout the year. For
West Lafayette, its deliveries are seasonal. The
WRRF receives an annual average of 370 gallons
of food from Purdue University's cafeteria, but
that material is only delivered while school is in
session. Janesville accepts 350,000 gallons of
waste per year (i.e. 958 GPD), but greater volumes
of chocolate waste are delivered during holidays
(Christmas, Valentine's Day, etc.). CMSA started
co-digesting in February 2014, and the facility is
currently receiving about 10,000 gallons of FOG
per day and four tons (i.e. 1,100 gallons) of food
waste per day. As more commercial customers
(an anticipated 200) participate in MSS's organics
collection program, CMSA may receive as much
as 20 tons per day.
EBMUD accepts food waste seven days a week,
365 days a year. EBMUD has daily received 20-40
tons of post-consumer food waste from San
Francisco's waste hauler, Recology. Each day,
EBMUD additionally receives 100 truckloads
containing liquid- and solid wastes from 20-30
industrial food processors. While EBMUD would
not disclose the exact volume of co-digested food
waste, the interviewed representative did
acknowledge that the facility brings in a volume of
food waste equal to less than 1% of their average
flow (i.e. 0.6 MOD). Because so much waste
arrives from so many different sources, EBMUD
carefully monitors deliveries.
The EBMUD Materials Management program facilitates the addition of outside liquid and solids wastes,
providing customer service to the waste generators and haulers, and ensuring that the added material is
safe (EBMUD 2012a). In order to deliver outside waste, the waste must be permitted. In addition to a
permit, EBMUD also requires the customer be insured, that appropriate analytical data and "material
safety data sheets" be provided, and that a "material acceptance agreement" is signed. Once the waste
material is reviewed and approved, deliveries to EBMUD occur as they do at the other interviewed
facilities. Haulers approach the facility and are recognized either by a guard at a guard station or through
a mechanized identification system. The haulers enter the facility and deliver the waste to the designated
area. Table 3 shows the volumes of waste accepted throughout the year and summarizes how the facilities
manage deliveries.
EBMUD permits haulers to deliver food waste,
and is permitted to accept it. To receive, process
and co-digest solid and liquid food waste in
California, a WRRF may hold two permits from
two state agencies: A National Pollution
Discharge Elimination System (NPDES) permit
from the State Water Resources Control Board
(SWRCB), and a solid waste permit from the
California Department of Resources and
Recycling (CalRecycle).
CalRecycle has issued EBMUD and CMSA
"Enforcement Agency Notifications" (EAs), the
least burdensome of the permitting tiers
(CalRecycle 2014). EBMUD's EA classifies their
receipt of solid food waste as a "biosolids
composting" activity and limits their intake to
250 tons per day (CalRecycle 2009); CMSA's EA
classifies their receipt of solid food waste as
"solid waste disposal" activity and limits their
intake to 15 tons per day (County of Marin
Environmental Health Services 2012).
Both CMSA and EBMUD NPDES permits
additionally address the management of "food
processing waste" (SWRCB 2012) and "food
industry waste" (SWRCB 2010), respectively.
The NPDES permits do not limit the volume of
food waste the facilities can receive.
10
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Food Waste to Energy
Table 3 Food waste (FW): Volume and delivery process
Waste Type
Average
Quantity
Processed
(GPD)
Delivery
CMSA
FOG
10,000
FW
1,100
Monitored
entrance to
receiving
facility
Hauler must
fill out form
and show
permit
EBMUD
FOG
<600
,000*
FW
<600
,000*
Monitored
entrance
Hauler
must show
ID badge,
permit, and
tanker
decal
number
Hill Canyon
FOG
>25,
000
FW
>25,
000
Monitored
discharge
Random
sampling to
ensure
of co-
safety
digested
material
Sheboygan
FOG
500
FW
60,000
Permitted
haulers enter a
monitored
entrance when
open
After hours,
permitted
haulers enter
the facility via
Radio
Frequency
Identification
(RFID)
West
Lafayette
FOG
142
FW
1
Monitored
and limited
delivery
Janesville
FW
857
Monitored
delivery
and
discharge
"exact sums not provided
11
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Food Waste to Energy
4 How much is stored? What processing is required?
Generally, the interviewed facilities add FOG and food waste into the digesters as soon as possible.
Janesville, for example, pumps half of their weekly load (i.e. -3,000 gallons of chocolate waste) into the
digesters the day they receive it, and the rest the next day. Janesville does this because their holding tanks
do not mix the waste. As the material will settle over time, Janesville must feed the chocolate into the
digesters before it becomes too difficult to pump. Most of the interviewed facilities, however, possess the
capacity to store waste over longer periods, if needed. Table 4 summarizes the food waste storage
capacity of each facility
While FOG does not require much processing, other types of food waste do. As with wastewater entering
the headworks, the facilities remove large pieces of debris with bar screens. Food waste is then chopped
and ground before entering the digesters. Some facilities (e.g. Thousand Oaks) chop and grind food waste
on-site. EBMUD and CMSA chop and grind food waste that has also been chopped and ground
elsewhere. After receiving preprocessed source-separated commercial food waste, EBMUD further
processes the material, using a rock trap/grinder to remove larger debris and then a paddle finisher to
remove grit and fibrous material (Figure 5).
Figure 5: EBMUD process schematic
" Food Waste
Finisher
To Land
Application
To Landfill
or
Recycling
12
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Food Waste to Energy
CMSA follows a similar protocol to EBMUD: the MSS hauls food waste collected from commercial
customers to its transfer station, where the contaminants are manually removed and the food waste is
chopped into 1-inch solids. Then the MSS hauls the waste to CMSA (Figure 6).
Figure 6: Marin Sanitation Service process schematic
Food Waste bins &
Fork Lift containers
dumping
Sorting
Shredder
Sorted and
shredded food
wastes
To
Receiving/Processing
Facility at Wastewater
Treatment Plant
At CMSA, the food waste, at approximately 25% solids, is combined with FOG in a large, underground
storage tank. The FOG/food waste slurry is further diluted with treated effluent, and then further
processed with, as with EBMUD, a rock trap/grinder followed by a drum screen paddle finisher. The
resultant 10% solids slurry is then pumped into the digester (Figure 7).
Figure 7: Central Marin Sanitation Agency process schematic
Food waste
from Transfer
Facility
25% ± Solids
Dilution Water
(Treated effluent)
Food Waste 10% Solids
tofc»i',ti
Debris Box
Drum Screen Paddle
Finisher
d
Debris Box
(plastics-fibers I0%oftotal)
The food waste that the West Lafayette WRRF receives from the Purdue University cafeteria is
preprocessed on campus. The University had originally purchased equipment to collect, macerate, and
transport cafeteria food waste so that it could be composted (Kennedy/Jenks Consultants). However, the
composting program never materialized. When the West Lafayette operator read about the failed compost
program in the local paper, he called the University and asked to tour the cafeteria's new system. He
observed "baby food for the digesters" and promptly offered to take the University's waste. The images
below show the techniques used to preprocess Purdue's cafeteria food waste.
13
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Food Waste to Energy
Figure 8: West Lafayette's partnership with Purdue University
Food waste is scraped from
jlates at the kitchen cafeteria.
Water conveys food waste to an
industrial grinder.
A classifier deposits ground
food waste into a toter.
During the school year, Purdue delivers 15
20 toters to the WRRF each day.
At the West Lafayette WRRF, an operator stands by as
the cart tipper empties a toter into the hopper.
To accommodate the food waste from the cafeteria, the West Lafayette WRRF constructed a receiving
station: a platform with a cart tipper that empties the University's toters into a hopper. From the hopper,
the food waste passes through a grinder and then into repurposed wet and dry wells (now one big tank
with 16,000 gallons of storage capacity). FOG passes through a "heavy object trap" before entering the
repurposed wet and dry wells. The food waste/FOG slurry is mixed with warm sludge before being
14
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Food Waste to Energy
pumped to the digester. Many of the facilities mix the slurry with warm sludge to decrease viscosity. The
facilities feed the slurry into the digesters at different rates, and different solids concentrations. Table 4
summarizes the processing techniques of each of the facilities.
Table 4 Food waste storage and processing
Digester
conditions
Storage
(gallons)
Pre-
processing
Feed
Rate (GPM)*
% total
solids**
CMSA
Mesophilic
20,000
Hauler
Sorts &
grinds into
1-inch
solids
On-site
Grinder
&
Paddle
finisher
30
10%
EBMUD
Thermophilic
40,000 for
solid wastes;
8 1,000 for
liquid wastes
Haulers
Remove large
objects &
metals
Grind into
~2-inch solids
On-site
Grinder &
Paddle
finisher
550
35%
Hill
Canyon
Mesophilic
20,000
(expanding
to 50,000)
On-site
Cleaned for
contaminants
then chopped
and mixed.
Fed through
manually
raked bar
screen before
entering
digester
10-20
5% (FOG)
Sheboygan
Mesophilic
500,000
On-site
Screen at
unloading
Grind
effluent
sometimes
added to
decrease
acidity or
chloride
content
35-55
3%
West
Lafayette
Mesophilic
16,000
Campus
Food waste
Separated
& ground
On-site
Food waste
Grinder
FOG
Heavy
object trap
30
-20%
Janesville
Mesophilic
7,000
On-site
Mechanical
bar screen
25
4.5%
* Gallons per Minute (GPM) ** Varies greatly with the material.
15
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Food Waste to Energy
5 How much biogas is produced? How is it used?
The interviewed facilities reported that co-digesting with food waste and FOG has greatly increased
biogas production. For at least three of the facilities, it has more than doubled biogas production. All of
the interviewed facilities would like to co-digest more. EBMUD, for example, actively seeks out new
sources of waste for their trucked waste program: a full-time business development representative
identifies and recruits potential customers.
As with the volume of food waste received (section 2), biogas production, correspondingly, varies
throughout the day and throughout the year. Table 6, row 2, shows average daily biogas production for
each of the six facilities.
Every one of the interviewed facilities uses a co-generation, or Combined Heat and Power (CHP), system
to manage their biogas. CMS A runs biogas through a 750 kW Internal Combustion Engine-generator
(ICE). Before CMSA started co-digesting, they produced enough biogas to meet 40% of the plant's
electricity needs. If the current amounts of FOG and food waste (10,000 gallons of FOG and 1,100
gallons of food waste per day) continue to be delivered, the Agency will generate at least 60% of its
energy needs. As additional food waste is delivered, which is desired and expected, the percentage will
continue to increase. Assuming the current amounts of FOG and food waste continue to be co-digested,
CMSA expects the system will produce 3,460 MWh per year and 150,612 therms/year.
EBMUD is already energy positive. The facility currently generates about 129% of its energy needs on
on-site, using 3 ICEs—capable of producing 2 to 2.5 MW each —and a new 4.5 MW gas turbine. With a
total energy capacity of 11 MW, the ICEs and turbine can meet 100 to 200% of the facility's demand. Of
the 52,561 MWh generated in 2013, the WRRF used 40,782 MWh. The surplus is exported and sold.
EBMUD established a Power Purchase Agreement2 (PPA) with the nearby Port of Oakland. The PPA is a
contract that guarantees EBMUD will provide the Port with a certain amount of energy at a fixed rate. If
EBMUD generates more than what the agreement stipulates and the Port declines it, that electricity can be
sold to others.
In 2013, Hill Canyon produced an average of 450,000 cubic feet of biogas per day; the biogas was
directed to two 250 kW and one 295 kW ICEs to generate 4,600 MWh of electricity and 3,000,000 therms
of heat. The electricity generated by the engines replaced what would have otherwise been drawn from
the grid. The waste heat was used to the warm the digesters and the administration building. Hill Canyon
flared about 275,000 cubic feet of biogas per day because it lacked the engine capacity to combust it.
Now, with an updated system comprised of two ICEs (the 295 kW and a new 630 kW engine), the facility
will soon meet or exceed its power needs.
At the Sheboygan WRRF, biogas is used in boilers to produce heat to warm the digesters. Biogas is also
used to power ten 30 kW microturbines and two 200 kW microturbines (Figure 9). In 2006, the facility
installed the ten 30 kW microturbines, which are capable of producing a combined 300 kW of electrical
power and recovering 10 therms of heat per hour. In 2008, the facility began co-digesting with high
strength organic wastes and biogas production jumped 150%, prompting the CHP system's expansion. In
2010, Sheboygan installed two 200 kW microturbines. The two 200 kW microturbines are capable of
producing 400 kW of electricity and 14 therms per hour. Most of the year, the Sheboygan WRRF is
energy positive.
PPAs are finance contracts between the signatory (e.g. the port) and a third-party renewable energy developer (e.g. EBMUD). The third party
owns, operates, and maintains the renewable energy system. In exchange for upfront costs and maintenance, the signatory commits to buying the
energy at a predetermined rate over a predetermined time period.
16
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Food Waste to Energy
Figure 9: Microturbines at the Sheboygan WRRF
Source: Sheboygan Regional Wastewater Treatment Facility 2011
WRRFs can sell excess electricity to the grid. To do so, the facilities must meet interconnection
standards, which can include complex and costly technical and contractual considerations. EBMUD,
for example, spent $1.3 million to upgrade their interconnection to Pacific Gas and Electric's (PG&E)
distribution lines. Whether a WRRF sells to a third party (e.g. EBMUD's PPA with the Port) or to the
local electric utility, the facility must interconnect. In most states (DSIRE 2013), WRRFs can sell
electricity back to the grid by establishing a net metering agreement with their electric utility. Net
metering credits renewable energy generators that deliver to the grid. The local utility tracks each kwh
consumed and received. When a WRRF generates more electricity than it consumes, the electric utility
credits the excess delivered to the grid. These credits can, in turn, be used to offset power purchased
from the utility when the WRRF consumes more than it generates.
Different states have different interconnection and net metering policies, some more supportive than
others (Freeing the Grid 2014). In California, for example, the major electric utilities must offer net
metering to all eligible facilities (one MW or less solar, wind, fuel cell or biogas systems) until they
reach a legislated limit (DSIRE 2014). Larger capacity systems are eligible for other renewable energy
procurement programs. Systems under three MW may participate in California's Feed-in Tariff (FIT)
program (CPUC 2014a); systems greater than three MW and less than 20 MW may participate in the
Renewable Auction Mechanism (RAM) program (CPUC 2014b). Unlike net-metering, the FIT and
RAM programs do not commit utilities to purchasing the electricity at full retail value; rather, as with
PPAs, the utilities commit to buying electricity at a predetermined rate over a predetermined time
period.
For some WRRFs, selling excess electricity back to the grid can be prohibitively burdensome — not
only because it requires familiarity with concepts heretofore peripheral to wastewater operations; but
also because interconnection costs can affect project economics. Interconnection costs can be as much
as 5-10% of the installation cost of new generation.
The West Lafayette WRRF also generates heat and electricity with microturbines and a boiler. The
facility relies on two 65 kW microturbines to produce an annual average of 679 MWh. When Purdue is in
session, the waste heat from the microturbines is used to warm the digesters; when not in session (i.e.
when the facility is not receiving cafeteria waste), biogas production drops and the digesters must also be
17
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Food Waste to Energy
heated with a natural-gas fired boiler. Overall, waste heat warms the digesters 90-95% of the time. The
West Lafayette CHP system meets less than 20% of the facility's electricity needs. The facility would like
to increase biogas production, but the plant operators face two challenges: 1) the facility possesses no
biogas storage capacity (and so all excess biogas is flared) and 2) the microturbines are fully utilized
(except when school's out). The facility is considering adding another microturbine.
The Janesville WRRF has been generating heat and power since 1985. They started with two 150 kW
ICEs, and have progressively invested in a larger, more efficient, and diverse system. Currently, biogas is
used to generate heat, power, and vehicle fuel, specifically, compressed natural gas (CNG). Using one
200 kW and four 65 kW microturbines, the facility produced 1,717 MWh in 2013, meeting 27% of its
electricity needs. Roughly 65,000 therms of waste heat were recovered from the microturbines and used
to warm the digesters. On average, Janesville produces 120,000 cubic feet per day of biogas with about
90% dedicated to the microturbines. The remaining goes to fuel (CNG) production. However, this
allocation fluctuates. As the operator explained, the relative amount of electricity and fuel produced
"...depends on demand. We adjust accordingly. During on-peak hours, we produce more electricity;
during off-peak, we produce more CNG."
Janesville can produce as much as 275 Gallons of Gasoline Equivalent (GGE) per day of BioCNG. In
2013, the facility produced 1,982 GGE. To produce the CNG, the biogas runs through a proprietary gas
conditioning system. The CNG is stored and dispensed on-site. At the time of the interview, the CNG was
used to fuel four facility vehicles: a dual-fuel Ford F-250 truck, two dual-fuel Ford F-150 trucks, and a
dual-fuel Ford Fusion Sedan and one lawn mower, a CNG Dixie Chopper. Within the next ten years,
Janesville hopes to produce enough CNG to fuel 40 vehicles.
Table 6 summarizes how the six interviewed facilities produce, store, and use biogas.
As a producer of BioCNG, Janesville could participate in the national Renewable Fuel Standard (RFS)
program. Managed by the U.S. EPA, the RFS program mandates that 36 billion gallons of renewable fuel
be blended into the nation's transportation fuel by 2022 (U.S. EPA 2014d). The RFS obligates producers
of gasoline (including refiners, importers, and blenders) to meet the mandate, and established a trading
program to ensure compliance (U.S. EPA 2007a). The trading program allows obligated parties to comply
by producing or purchasing Renewable Identification Numbers (RINs).
A RIN is a 38-digit number generated by the production or import of one gallon of renewable fuel; it
uniquely identifies the fuel, providing, among other details, information about the fuel category (U.S.
EPA 2007b). RFS fuel categories include cellulosic biofuel, biomass based diesel, advanced biofuels, and
renewable fuel. The obligated parties must produce or purchase a specified volume of fuel in each
category. These Renewable Volume Obligations (RVOs) change each year. Table 5 shows the 2013
RVOs associated with each fuel category (U.S. EPA 2013, U.S. EPA 2014e).
Table 5 2013 Renewable Volume Obligations (U.S. EPA 2013, U.S. EPA 2014e).
Fuel category
Cellulosic biofuels
Biomass based diesel
Advanced biofuels
Renewable fuel
2013 RVO Volumes
(gallons)
810,185
1,280,000,000
2,750,000,000
16,550,000,000
2013 RVO Percentages
(of total U.S. fuel produced)
0.0005%
1.13%
1.62%
9.74%
18
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Food Waste to Energy
WRRF biogas had been classified as an advanced biofuel, but was reclassified to be a cellulosic feedstock
in the July 2014 Pathways II Final Rule (U.S. EPA 2014f). WRRF-derived fuels and electricity used in
the transportation sector (to, for example, power an electric car) can now generate cellulosic RINs. RINs
are traded in an open marketplace, and prices are controlled by supply and demand. Cellulosic RINs may
become more valuable for two reasons: 1) They have been relatively rare, and obligated parties must meet
RVOs; and 2) Cellulosic fuels are the "one-stop-shop" of the RIN marketplace, as they can be used to
meet the RVOs of any RFS fuel category. While Janesville has not yet registered under the RFS, the
WRRF is now considering generating RINs for their BioCNG.
Table 6 Biogas production, storage, and use at interviewed facilities
Facility
% increase
w/ co-
digestion
Biogas
production
(cubic feet/
day,
averaged)
Biogas Use
Electricity
(MWh/year)
Heat
(therms/year)
Fuel
(GGE/year)
Biogas
Storage
Storage
capacity
(cubic feet)
%of
electricity
demand
generated
on-site
(annual
average)
CMSA
60%
252,000
CHP
ICE
Boiler*
3,460
150,612
N/A
Flexible
membrane
covers
200,000
60%
EBMUD
Over
100%
2,400,000
CHP
ICE
Boiler
Turbine
52,000
2,300,000
N/A
Membrane
dome over
1 digester
200,000
128%
Hill
Canyon
250%
450,000
CHP
ICE
Boiler*
4,600
3,000,000
N/A
Excess
flared
None
80-85%
(soon to
be 100%)
Sheboygan
150-300%
560,000
CHP
Microturbines
Boilers
2,300
84,000
N/A
Minimal
storage in 1
digester
Negligible
90%
West
Lafayette
N/A**
92,160
CHP
Microturbines
679
Not measured
N/A
Excess flared
None
16-18%
Janesville
40%
120,000
CHP
Microturbin
esCNG
1,717
>65,000
1,982
Flexible
membrane
covers
102,000
27%
* Used to heat digesters if CHP system is offline
** The facility started co-digesting as soon as the CHP system went into place. There is no baseline
which to compare it.
19
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Food Waste to Energy
6 How much biosolids are produced? How are they managed?
Biosolids are the nutrient-rich organic materials resulting from the treatment of domestic sewage in a
WRRF. There are several beneficial uses for biosolids, including landfill alternative daily cover (ADC),
composting, land application (to manage forests, fertilize farmland, etc.), mine reclamation, or energy
generation (e.g. gasification). Biosolids may also be incinerated, disposed of in landfills, and/or stored for
future use.
The interviewed facilities produce varying amounts of biosolids, dedicating the biosolids to a mix of uses,
depending on quality, quantity, time of year, and affecting regulations. When used for land application,
biosolids are classified as class A or class B depending on the level of treatment. Class A biosolids are
treated to inactivate pathogens and are subject to fewer regulations, while class B biosolids are treated to
remove 99 percent of pathogens and are subject to greater regulation (Water Environment Federation
2010).
In California, the land application of biosolids is heavily regulated, and, in some counties, effectively
banned. Some counties only prohibit land application at certain times of the year. CMSA, for example,
transports its class B biosolids to Sonoma County, where farmers can land apply from June to October
(the dry season); the rest of the year, CMSA sends biosolids to a landfill for use as ADC. EBMUD, on the
other hand, sends biosolids to farms for use as fertilizer and to landfills for use as ADC year-round.
In 2013, EBMUD produced 14,716 dry metric tons of class B biosolids, dedicating approximately 40% of
that to agricultural land application, 59% to use as ADC, and 1% to two stand-alone food waste digesters.
As the immediately surrounding counties have prohibited year-round application, EBMUD transported
5,942 dry metric tons of biosolids over 100-miles to Merced County, where farmers can land apply
throughout the year. By sending 8,664 dry metric tons of biosolids to local landfills for use as ADC,
EBMUD substantially reduced hauling distances and the associated costs. The two stand-alone food waste
digestion projects (Hillmar Cheese and Zero Waste) used, respectively, 100 and 10 dry metric tons of
EBMUD biosolids as a "starter," co-digesting to develop the desired metabolic activity.
Hill Canyon is located in Ventura County, a jurisdiction which has effectively banned the land application
of biosolids. The WRRF currently sends 100% of its class B biosolids to the Toland landfill, where they
are heat dried (to meet class A standards). In the future, the landfill operators hope to sell the treated
biosolids as a soil amendment; currently, it's used as ADC. In order to reduce the amount sent to landfills,
Hill Canyon will soon enter into "biosolids transformation" arrangement that will generate energy and
reduce hauling volumes. The facility is considering a range of technologies, including pyrolysis,
gasification, supercritical water oxidation, and hydrothermal processing.
West Lafayette land applied 348 dry metric tons of biosolids in 2013, and was able to do so year-round
because the Indiana Department of Environmental Protection permitted the land application of the
WRRF's biosolids onto snow-covered or frozen ground. When West Lafayette cannot immediately land
apply (e.g. because farmers' schedules unexpectedly shift), the biosolids are either stored on-site or — if
the on-site storage capacity is exceeded — sent to a regional facility, where the biosolids are stored until
they can be land applied.
Janesville land applies 100% of its class B biosolids between spring and fall (the exact timing depends on
when the growing season begins and ends). During the winter, the facility stores biosolids on-site, and
begins land applying when the growing season starts again. Similarly, Sheboygan land applies 100% of
its biosolids from April to October; as with Janesville, the WRRF stores them on-site during the winter
months.
20
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Food Waste to Energy
Co-digesting at WRRFs that land-apply biosolids contributes to the creation of a valuable soil amendment
used to grow crops, manage forests, and restore land. Of the six interviewed facilities, half of these land-
applied all of the biosolids they produced. The Sheboygan (WI), Janesville (WI), and West Lafayette (IN)
WRRFs hauled biosolids to nearby farmland to fertilize fields and increase soil moisture. Both CMS A
and EMUD land applied a portion of their biosolids. Only Hill Canyon sent everything to a landfill. The
biosolids management strategies of the interviewed WRRFs reflects national trends. In the U.S., 55% of
biosolids are applied to soils for agronomic, silviculture, and/or land restoration purposes (NEBRA 2007).
Table 7 Biosolids management
Quantity
produced
(dry metric
tons per
year)
Biosolids
use
Percent to
each use
CMSA
1,302
Dry season:
Land
applied
ADC
Wet season:
ADC
Land
Applied:
31%
ADC:
69%
EBMUD
14,716
Dry
season:
Land
applied
ADC
Wet
season:
ADC
Disposal
Land
Applied:
40%
ADC: 59%
Other: 1%
Hill
Canyon
2,011
Year-round:
ADC
Disposal
Landfill
disposal or
ADC:
100%
Sheboygan
3,278
Spring-Fall:
Land
Applied
Winter:
Stored on-
site
Land
Applied:
100%
West
Lafayette
370
Year-round:
Land
Applied
Land
Applied:
100%
Janesville
1,277
Spring-Fall:
Land
Applied
Winter:
Stored on-
site
Land
Applied:
100%
Table 7 shows how the interviewed facilities manage their biosolids. The interviewed facilities did not
quantitatively describe how co-digestion has affected the volume of biosolids production. Instead,
EBMUD, West Lafayette, and Sheboygan indicated "commensurate" or "proportional" increases in
production of biosolids with co-digestion.
21
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Food Waste to Energy
1 How much did the facilities invest in co-digestion infrastructure?
All but one of the interviewed facilities received some amount of grant funding to help finance their co-
digestion efforts. However, the grants represented relatively small portions of overall project costs. For
the interviewed facilities, money saved by reducing energy use and the money earned from tipping fees
have made these projects economical.
In 2008, CMSA received $20,000 in seed funding from their local utility, PG&E, to complete a methane
capture feasibility study (Marshall 2014). The PG&E grant represented a very small portion of the total
project costs. Over the course of six years, CMSA will have spent $7.65 million on digester upgrades and
the co-digestion project, investing not only in the construction of the new solid and liquid waste receiving
station, but also in the installation of other critical project components, such as a more effective and
energy-efficient digester mixing system, new flexible membrane covers (to replace the digesters' 25 year-
old floating steel covers), and a new hydrogen sulfide removal system. Of the $7.65 million, $1.9 million
was used to construct the FOG and food waste receiving facility.
Having only started co-digesting in February 2014 CMSA has not realized major savings, but the agency
is optimistic. By reducing the consumption of—and, eventually, no longer purchasing—natural gas, they
expect to save as much as $396,900 per year. Once CMSA exports electricity back to the grid, the agency
will also realize electricity savings. At present, there are none. CMSA also generates revenue via tipping
fees. CMSA charges $.10/gallon, $.08/gallon, and $20/ton for FOG, septic, and food waste, respectively.
Based on the annual percentage change of the greater San Francisco Area All Urban Consumer Price
Index (CPI) index, CMSA's food waste tipping fee will very likely increase 1-3% annually (CMSA
2013).
If all of the area's food waste generators were to participate in the organics collection program, CMSA
could receive as much as 20 tons of food waste per day. With a tipping fee as low as $20/ton, CMSA
could make as much as $144,000/year from food waste tipping fees. While the program is in its infancy,
the agency will nonetheless earn a fair amount this year. Assuming CMSA continues to daily receive
10,000 gallons of FOG and four tons of food waste through 2014, the associated tipping fees should
generate roughly $400,000. If CMSA receives as much as 20 tons of food waste per day, the agency
estimates the project will be paid back in 2.89 years; if they never receive more organic material than
what is currently co-digested, the agency estimates the project will be paid back in 7.82 years.
EBMUD received funding from numerous sources, including a 2002 grant awarded through California
Senate Bill (SB) 5X, a one-time grant program funding peak-load reduction and supply augmentation
projects; a 2004 California Energy Commission (CEC) grant for $0.5 million; and a 2006 EPA grant for
$50,000 (EBMUD 2012b). While grant funding helped kick-start the project, the system is paying for
itself (EBMUD 2012b). EBMUD generates millions of dollars each year in revenue from tipping fees and
energy sales. Tipping fees range from $0.03/gallon for liquid organic material to as much as $65/ton for
solid organic material (See Table 8). In 2012, EBMUD brought in $8 million through tipping fees (Day
2012). Energy savings and sales yield, on average, an additional $3 million a year.
EBMUD heavily invested in the infrastructure needed to support this system: $5 million to construct the
food waste receiving station, $1.3 million in interconnection fees, and another $30 million for the new gas
turbine. Additional costs include operating and maintaining the system, managing a greater volume of
biosolids (and hence purchasing more polymer, hauling more biosolids, etc.), and staffing the Materials
Management program, which consists of five full-time employees. EBMUD considers co-digestion a very
beneficial investment, for the agency and for their customers. As the interviewed representative
explained, EBMUD pursued co-digestion ".. .to create a net benefit for our ratepayers." By finding a
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Food Waste to Energy
creative way to use their excess digester capacity, EBMUD has increased the agency's revenue, securing
funding for capital improvements that otherwise would have been obtained by raising rates.
Table 8 FY13-14 rates for EBMUD tipping fees
Septage
FOG
Liquid Organic Material
Protein Material
Solid Organic Material
$0.07/gal
$0.11/gal non-concentrated
$0.15/gal concentrated
$0.03/gal
$0.06/gal up to 10% Total Solids
$0.08/gal over 10% Total Solids
$30/ton - $65/ton
Source: EBMUD 2014
Partially funded by the California Public Utilities Commission's Self Generation Incentive Program
(SGIP), Hill Canyon's engines will soon provide at least 100% of the facility's energy needs. The
remaining funding was contributed by a third party. Hill Canyon forged a PPA with CHP Clean Energy
(CHPCE). Hill Canyon pays $.07/kWh to CHPCE, rather than 0.16/kWh to Southern California Edison.
The WRRF estimates they save roughly $300,000 a year on avoided energy costs. While very little of the
utility's funds were used to finance the CHP system, Hill Canyon invested $400,000 to construct a FOG
and liquid waste receiving station. In total, the receiving station cost $800,000; the American
Reinvestment and Recovery Act (ARRA) funded the difference. The WRRF's renewable energy
initiatives, along with energy efficiency and process optimization projects, have kept the monthly sewer
service charge for a single-family residence stable for nearly a decade. They have also advanced their
local Energy Action Plan.
In 2012, the City of Thousand Oaks adopted an Energy Action Plan. The plan identified "energy
standards and policies to guide the City in achieving its long-term objectives in energy efficiency,
renewable energy, and carbon emission reductions" (City of Thousand Oaks 2012). The Hill Canyon
WRRF has been a driving force in helping City attain its 2017 goals to reduce energy use by an
additional ten percent. In 2011, City facilities consumed over 11 million kWh. By committing to reduce
energy use by 10% from the 2011 baseline, the City of Thousand Oaks committed to reducing
1,344,938 kWh (City of Thousand Oaks 2014).
Between 2011 and 2013 the Hill Canyon WRRF reduced energy by 715,483 kWh. Between 2011 and
2013, the Hill Canyon WRRF increased onsite renewable energy generation by 1,890,101 kWh.
Through energy efficiency, process optimization, and on-site renewable energy generation, Hill Canyon
had, by 2013, exceeded the City's 2017 goal.
Communities across the country are setting targets to reduce energy use. Typically the largest energy
consumers in municipalities and often possessing the existing infrastructure to generate renewable
energy onsite, WRRFs are critical partners in helping cities advance energy reduction and renewable
energy generation efforts.
Both Sheboygan and Janesville received grant funding ($225,960 and $138,421 respectively) from
Wisconsin's Focus on Energy, a statewide energy efficiency and renewable resource program funded by
the state's electric utilities.
Initially, Sheboygan entered into a PPA, and the third party absorbed the remaining installation and
maintenance costs for the first phase of the CHP system (i.e. the ten 30 kW microturbines). Eventually,
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Food Waste to Energy
the facility purchased the microturbines and installed the two 200 kW microturbines (phase two). In total,
Sheboygan invested $301,000 for the first phase and $1,295,000 for the second phase. Additionally, the
city invested $75,000 in infrastructure to blend and mix the food waste (i.e. an in-line strainer, a mixing
pump, and a feed pump) and another $350,000 to upgrade the boiler. In total $2,021,000 in city funds
were invested in the CHP and co-digestion system. In 2012, Sheboygan earned $366,000 through
reduced electricity costs, $75,000 in reduced natural gas costs, and $290,800 through tipping fees.
Increased competition for high strength food waste, however, is affecting earnings. In 2013, Sheboygan
received more waste and earned less in tipping fees. The WRRF is now accepting the majority of food
waste for free.
There were also two distinct phases to Janesville's (most recent) biogas initiatives (Botts and Zacovek).
During the first phase, Janesville upgraded its biogas-to-energy system (i.e. installed the dual membrane
gas storage system, the conditioning and compressor system, the four 65 kW microturbines, etc.). These
upgrades cost $1,196,752, and were partially funded by the Focus on Energy grant. Once Janesville
installed the microturbines, the facility entered into a net metering agreement with the local energy
provider, Alliant Energy. During the second phase, Janesville added the 200 kW microturbine and the
BioCNG system. These upgrades cost $880,000, and were partially funded with a $125,000 grant from
the WI State Energy Office. The biogas-to-energy system improvements were part of a broader
$30,000,000 expansion project, which Janesville helped fund by increasing rates (by 7.5%). With
$9,000/year earned in tipping fees and an estimated $257,80I/year saved in heat, electricity, and fuel
costs, Janesville estimates the projects will be paid back in 7 years.
The West Lafayette "digester renovation and alternative power source" project cost $10.4 million. The
facility drew from the general fund to pay for the foodwaste receiving station. The FOG collection and
CHP systems were financed with a low-interest loan from the Indiana Finance Authority's State
Revolving Fund (SRF) program. By saving $80,000/year in reduced energy costs and generating an
average of $10,0007 year in tipping fees (from FOG only; Purdue is not charged), the WRRF estimates the
investment will be paid back in 12 years. While West Lafayette moderately increased wastewater rates to
pay back the SRF loan, the money saved on energy and earned in tipping fees will ultimately help
minimize future rate increases.
Table 9 summarizes sources of funding, project earnings, and estimated payback periods.
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Food Waste to Energy
Table 9: Cost, savings, and revenue
Funding
Assistance
Capital
Investment
(million $)
Tipping
Fees
($/year)
Energy-
derived
savings
($/year)
Estimated
Pay-Back
(years)*
CMSA
PG&E
$1.9
< $400,000
Gas:
$396,900
Electric:
n/a
2.9-7.8
EBMUD
U.S. EPA
CEC
SB5X
$35
$8,000,000
Gas&
Electric:
$3,000,000
3.2
Hill
Canyon
SGIP
ARRA
$.4
$307,000
Gas&
Electric:
$3,000,000
0
Sheboygan
Focus On
Energy
$2.02
$296,800
Gas:
$296,800
Electric:
$366,000
2.7
West
Lafayette
None
$10.4
$10,000
Gas:
$30,000
Electric:
$50,000
12
Janesville
Focus On
Energy
State Energy
Office
$2.07
$9,000
Gas:
$28,000
Electric:
$224,801
Fuel:
$5,000
7
* These estimates were provided by the interviewed WRRFs and incorporate factors not discussed in this
report.
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Food Waste to Energy
8 Summary & Conclusions
This report has described the co-digestion practices and performance of six WRRFs: the Central Marin
Sanitation Agency (CMSA), the East Bay Municipal Utility District (EBMUD), and the Hill Canyon
Treatment Plant in California; the Sheboygan and Janesville facilities in Wisconsin; and the West
Lafayette Wastewater Treatment Utility in Indiana. They have shared information about the food waste
material, receipt, storage and processing; biogas and biosolids production and use; and program costs.
The interviewed facilities relied on different materials, technologies, management strategies, and funding
mechanisms, yet their responses to the question "Would you recommend that other facilities pursue co-
digestion?" were unanimously affirmative. Each of the six organizations agreed that, although co-
digestion presents challenges, the benefits outweigh the difficulties.
Even the Sheboygan (WI) WRRF— which is not only making less money in tipping fees than it has in
previous years, but must also repair and coat the concrete walls and floors of their receiving tank and
install new stainless steel piping throughout so that the system can tolerate the acidity of trucked in FOG
and food waste— is determined to realize "complete energy self-sufficiency..." and so is ".. .planning to
diversify (their) high strength waste loading to include more sources..." (City of Sheboygan Regional
Wastewater Treatment Facility 2014). For WRRFs with excess capacity, co-digestion can be a
fundamental feature in plans for energy independence. Revenue earned through tipping fees and costs
reduced through energy savings (electricity, heat, and fuel) can be used to help finance repairs and
upgrades, tempering rate increases and adapting municipal budgets to shortfalls in public infrastructure
funding.
Although traditional sources of federal funding for public infrastructure have declined, federal incentives
for renewable fuels are increasing. In July 2014, EPA's Renewable Fuel Standard (RFS) recognized
biogas as a transportation fuel feedstock, designating the resulting fuel as "cellulosic," likely conferring
greater value to the associated RINs. Some states are also incentivizing renewable fuels production. In
May 2014, the California Air Resources Board (CARB) announced a Low Carbon Fuel Standard (LCFS)
pathway for WRRF-derived biogas (CARB 2014). Both the RFS and the LCFS have set renewable fuel
targets. Obligated to meet the mandates, refiners can generate RINs and LCFS credits to comply; they can
also trade them. While the renewable fuels market has been volatile, experts expect that generating credits
will prove lucrative. In conjunction with co-digestion, state and federal renewable fuel incentives may
enable many WRRFs to initiate or expand biogas to energy projects.
With the ability to not only offset their own large energy requirements but to generate surplus heat,
electricity, and/or fuel, WRRFs are uniquely equipped to advance local climate change mitigation efforts.
For example, the City of Thousand Oaks' (CA) 2011 Energy Action Plan identified renewable energy and
energy efficiency efforts at the Hill Canyon Treatment Plant—which, of all its municipal facilities, had
the biggest electricity bill and second biggest emissions load—as central to attaining the City's
greenhouse gas reduction goals (City of Thousand Oaks 2012). As Hill Canyon co-digests more food
waste and generates more renewable energy, the City of Thousand Oaks will likely revise their targets.
Co-digestion can also facilitate waste diversion goals. For example, San Francisco is committed to
diverting 75% of its discards from landfills by 2010, and 100% by 2020. Diverting organics (food and
yard material) is a major component of the City's "zero waste" strategy. San Francisco currently collects
an average of 600 tons of source-separated organic material each day. While the majority is composted,
the EBMUD has— as part of an eight-year pilot program— received 20 to 40 tons per day. San Francisco
has pursued co-digestion as a way to reduce the volume of hauled organic waste, improve handling, and
control emissions3 (Sullivan 2011). To reach its diversion goals, San Francisco plans to increase the
3 Anaerobically digesting food waste stabilizes it, mitigating the volatile organic compounds (VOCs) that would otherwise be emitted at
composting operations (California Integrated Waste Management Board 2008, Mata-Alvarez, Mace, and Llabres 2000).
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Food Waste to Energy
volume of anaerobically digested food and yard material—although source-separated organics will no
longer be co-digested.
The majority of EBMUD biosolids are used for ADC. For San Francisco, co-digesting source-separated
organics at a WRRF that sends its biosolids to a landfill is not "the highest and best use." This has lead
EBMUD, San Francisco, and Recology to explore alternatives that will advance both the City's waste
diversion and the WRRF's renewable energy goals. Other West coast cities (e.g. Seattle and Portland) and
Northeast states (e.g. Massachusetts, Connecticut and Vermont) have banned food waste from landfills
(Henricks 2014). Concurrently, many communities, particularly in California, restrict the land application
of biosolids. As local and state ordinances simultaneously advocate for diverting organics and restricting
biosolids use, WRRFs with excess digester capacity present an attractive solution (i.e. co-digestion) with
an— in some places —unwelcome byproduct (i.e. biosolids).
Of the interviewed facilities that produce biosolids used as ADC, one, the Fiill Canyon (CA) WRRF,
sends 100% to landfill. Hill Canyon is located in and surrounded by counties with such restrictive permit
requirements that the land application of biosolids has effectively been banned. EBMUD (CA) and
CMS A (CA), respectively, land apply 40% and 31% of their biosolids, a result of nearby county
requirements which either prohibit land application or prohibit it during the rainy season. In areas with
very restrictive permit requirements, WRRFs such as Hill Canyon are evaluating "transformation"
options; these technologies would respect permit provisions while maximizing energy generation and
minimizing solids production.
While technologies such as pyrolysis and gasification may one day become standard, the interviewed
facilities, in the meantime, generate energy as wastewater treatment facilities have since the 1920's: with
sewage gas (Figure 3). Running biogas through internal combustion engines, microturbines, and/or
turbines, all of the interviewed facilities used CHP systems to keep their digesters warm and to power
their operations. Only one, the Janesville (WI) WRRF, additionally produces CNG to fuel vehicles.
Emerging national and state incentive programs such as the RFS and LCFS will likely prompt more
projects, as may prohibitively expensive interconnection fees and relevant air quality regulations4.
Streamlined waste management regulations may also facilitate more projects. To receive, process and co-
digest food waste in California, a WRRF is required to hold two permits from two state agencies: A
NPDES permit from the SWRCB, and a solid waste permit from CalRecycle. State agencies and the
California Association of Sanitation Agencies have been working to resolve this issue. CalRecycle is
proposing an exclusion for direct injection of "anaerobically digested materials" (ADM) into WRRF
digesters regulated under a NPDES or Waste Discharge Requirement (WDR) permit. The CalRecycle
exclusion would require that the WRRF develop proper Standard Operating Procedures to manage the
ADM (Appendix B).
While supportive regulations facilitate co-digestion, more significant to the interviewed facilities were
supportive partnerships. Whether an unplanned collaboration—such as repurposing Purdue's grinding
and pulping equipment to make "baby food" for the West Lafayette digesters— or more formal
partnerships—such as the arrangements between the WRRFs and the waste haulers—the interviewed
facilities indicated that leveraging the expertise and resources of other organizations can be very
beneficial. This was particularly true of the facilities that executed PPAs. Maximizing renewable energy
production requires focus and skills outside the traditional scope of wastewater treatment utilities (WERF
2012b). By partnering with an organization that specializes in renewable energy generation, WRRFs can
attain energy independence without developing exhaustive in-house expertise.
4 Biogas-to-fiiel may become an attractive option for WRRFs in extreme non-attainment areas (for criteria air pollutants such as ozone), where
local air districts have promulgated rules that complicate the permitting of stationary engines (e.g. California's South Coast Air Quality
Management District's rule 1110.2).
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Food Waste to Energy
Two of the interviewed facilities, the Hill Canyon (CA) and Sheboygan (WI) WRRFs, forged PPAs with
third-party renewable energy developers. PPAs ensure stable and often lower electricity rates, efface
maintenance costs, and provide the expertise WRRF operators may lack. Operators can, however, develop
the necessary expertise, and the facilities may eventually choose to purchase equipment they once leased.
Sheboygan, for example, originally partnered with Alliant Energy, but eventually purchased the 10
microturbines Alliant managed—and then installed 2 more. Now, Sheboygan carries the burden and the
benefit, assuming the maintenance costs and the savings.
WRRFs are accustomed to changing economic, regulatory, and biological conditions. Whether balancing
budgets, meeting more stringent discharge requirements, or responding to an unexpected peak in BOD,
WRRFs know how to adapt. Skills essential to operating a WRRF lend themselves to initiating and
maintaining co-digestion programs. As the Hill Canyon operator explains, it takes "... equal amounts of
FOG, frappo, determination, technology, joy, disappointment, teamwork and, an American trait we
should all appreciate, a belief in the power of self-reliance." In other words, excess digester capacity is
not the only existing asset a co-digestion program relies on.
Navigating unfamiliar regulations, investing in new equipment, and/or adjusting facility processes to
accommodate different waste streams can be challenging. But, for many WRRFs, increasing biogas
production will be a worthy incentive. Co-digestion has more than doubled biogas production at the
EBMUD, Hill Canyon, and Sheboygan; at CMSA and Janesville, it has increased biogas production by
60% and 40%, respectively; at West Lafayette, it propelled investment in the plant's first CHP system.
Because co-digestion markedly increases biogas production, it is and will continue to be a strategic
component of many WRRF renewable energy projects. Today, almost as many WRRFs co-digest (216) as
co-generate (270) (Qi, Beecher and Finn 2013). These numbers will likely rise concurrently as energy and
operating costs increase, waste diversion ordinances gain popularity, and climate change mitigation and
adaptation efforts advance.
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Food Waste to Energy Section 9 - Appendices
9 Appendices
Appendix A: Survey questions for WWRFs
Facility Information:
1. What is your facility design flow? What is your average dry weather flow?
2. What is your digester design capacity?
3. How have you estimated excess capacity? Do your estimates vary by season?
Foodwaste collection information:
4. Does the WRRF digest food waste? If so, what are they?
5. How far away are these sources?
6. Is there an issue with seasonality (especially from agricultural waste)?
7. What systems are in place to accept and store the various types of foodwaste?
Food waste processing information:
8. Does the WRRF pre-process the food waste before it enters the digester? If so, how does
it pre-process?
9. What volume of food waste is processed in a year?
10. At what rate does unprocessed food waste enter the facility?
• Average/min/max rate?
11. At what rate does processed food slurry enter the anaerobic digester?
• Average/min/max rate?
12. What is the percent total solids and ratio of volatile solids to total solids is the food waste
before it is mixed with the municipal sludge?
• What about for the combined food waste/municipal sludge feedstock?
13. How has co-digestion of foodwaste affected the biogas generated?
• What quantitative measures demonstrate this change? (Volume of biogas,
electricity generated, increased revenue, etc.)
• What other qualitative changes have been observed?
14. How sensitive are the digesters to feedstock variations?
• How have issues been remediated?
15. How has co-digestion affected biosolids production, and hauls?
16. Have there been odor problems from handling and digesting food waste?
Biogas Production
17. Are digesters operated under mesophilic or thermophilic conditions?
• At approximately what temperature?
18. Has the WRRF been able to determine the mean cell residence time or volatile solids
reduction since the 2008 report?
Biogas Storage and Utilization Information:
19. Does excess biogas need to be stored? How is excess managed?
20. What fraction of the WRRF's power needs are generated onsite?
21. How much power is produced on site annually?
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Food Waste to Energy Section 9 - Appendices
Cost, Savings, and Revenue Information:
22. What are the operation and management costs?
23. What were the equipment costs?
24. Were there any other revenue or cost savings as a result of co-digestion? Such as:
• electricity sold to the grid
• cost savings on biosolids disposal
• tipping fees
25. How have tipping fees affected the economics of the project?
26. What was the payback period? The return on investment?
Building Future Relationships
27. What were the most significant factors that led this WRRF to start co-digesting?
28. Overall, would this WRRF recommend that other facilities pursue co-digestion?
29. Are you willing to mentor other facilities considering foodwaste co-digestion projects?
30. Is the WRRF planning to sell the engineering designs?
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Food Waste to Energy Section 9 - Appendices
Appendix B: Example Standard Operating Procedures to Manage Anaerobically Digestible
Material (Curtsey of CSMA)
FOG/Food to Energy Receiving Facility Operations Document
Fats, Oils, and Grease, and Food Waste Receiving Station
April 2013
Purpose
This operating procedure (SOP) is intended to ensure that the delivery and processing of Fats,
Oils, and Grease (FOG) and Food Waste (FW) brought to the CMSA Treatment Plant are
conducted in a safe, efficient manner that protects the physical facilities, maintains adequate
treatment capacity, ensures proper overall operation, maximizes beneficial reuse, and maintains
acceptable effluent quality. This procedure is designed to comply with the requirements in
Special Provisions section C, subsection 5d. Fats, Oils, and Grease in CMSA's
NPDES permit.
Description
The FOG/FW Receiving Station (the Receiving Station) is located on the south western side of
the Agency's Solids Handling Building (1). The Receiving Station consists of a slurry tank, a
FOG receiving connection and FW receiving hatch opening into the slurry tank, and various
processing equipment. It is designed to receive and process FOG and FW, mix it with digested
sludge, and transport it to the Agency's Anaerobic Digesters (the Digesters). During normal
operation, methane gas (biogas) is produced (2) in the Digesters and used as a fuel source along
with natural gas to operate a cogeneration engine and generator that produces electricity and
waste heat. The electricity produced is used to power the Agency's facilities which offset's the
purchase of natural gas for engine fuel, and in the future electricity from Marin Clean Energy.
Captured waste heat is used to produce hot water for heating the Digesters and for other uses
throughout the Treatment Plant and Agency facilities.
Unlike typical wastewater treatment plant process equipment, the receiving station does not
receive raw wastewater from a collection system. The Receiving Station's slurry tank has a
working volume of 20,000 gallons and can accept up to 20 tons of FOG and/or FW per day, both
coming primarily from Food Service Establishments within the central Marin service area.
These wastes are delivered to the receiving station by FOG tanker and/or specialized food waste
hauling trucks. The received FOG and FW are processed by screening, grit/rock removal, mixing
with heated digested sludge, and holding for processing into the Digesters. Following the
anaerobic digestion process, the biosolids are dewatered by centrifuges and beneficially reused
as land applied soil amendments or utilized as alternative daily cover at a local landfill.
This facility includes integrated instrumentation and control systems for manipulating and
monitoring various aspects of the receiving station operation.
Definitions
Authorized Waste Haulers: Companies which have obtained access cards issued by CMSA and
are authorized to transport and dispose of FOG and Food wastes into the receiving station for
processing.
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Food Waste to Energy Section 9 - Appendices
Biosolids: Refers to treated municipal wastewater sludge that meets federal (EPA) pollutant and
pathogen requirements for land application and surface disposal.
Commercial Food Waste (FW): Food preparation wastes from commercial food service
establishments.
Fats, Oils and Grease (FOG): Oily organic compounds, derived from animal and/or plant
sources, that are generated during food preparation and cooking, and that are captured in grease
traps and interceptors at Food Service Establishments.
Food Service Establishment: Those establishments primarily engaged in preparing, serving or
otherwise making foodstuffs available for purchase and consumption.
FOG/FW Receiving Station: The facility at CMSA which receives, stores, and processes
FOG/FW from waste haulers with the purpose of introduction of the FOG/FW into the Digesters
and to increase biogas production.
FOG Delivery Sequence: The automated sequential steps required to receive and process FOG
deliveries.
Food waste Delivery Sequence: The automated sequential steps required to receive and process
food waste.
Hauled Waste: A non-hazardous liquid waste, as defined by the USEPA, which is prohibited
from discharge into:
(a) a sanitary sewer; or
(b) a storm sewer or watercourse.
Human Machine Interface (HMI/PLC): The user interfaces in a Treatment Plant's process
control system. They provide a graphics-based interface for controlling the process control and
monitoring system.
Interference: Discharges which, alone or in conjunction with a discharge from other sources
would:
1. Inhibit or disrupt the Treatment Plant, its treatment processes or operations, or the processing,
use, or disposal of its sludge processes; and
2. Therefore would a cause, or have the potential to cause, a violation of any permitted
requirement.
Liquid Waste Hauler: Any person, firm, corporation or other entity that collects, pumps,
transports and/or disposes of liquid wastes.
Odor Control System: A system to contain and remove odors from air in process environments.
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Food Waste to Energy Section 9 - Appendices
The Receiving Stations' odor control system includes air ducts, fans, and an activated carbon
media vessel. The carbon adsorbs volatile organic carbons (VOCs) and converts hydrogen
sulfide (H2S) to water soluble sulfur compounds by oxidation.
Treatment Plant: For the purpose of this SOP, these are any of the, facilities, structures, devices,
equipment or works owned by the CMS A for the purpose of the transmission, storage, treatment,
recycling and reclamation of municipal wastes.
Unacceptable Materials: Materials of a type, quality, or quantity that would adversely impact the
Food Waste receiving facility operations (e.g. clogging pipelines or damaging equipment).
Conditions of Acceptance of FOG/FW
CMS A has the right, but not the obligation, to inspect each load of hauled waste to confirm that
no unacceptable materials are contained therein. Lack of inspection of any load does not relieve
an authorized waste hauler from the obligation to not discharge any unacceptable materials into
the Receiving Station. The Receiving Station will receive FOG and/or FW from haulers six days
per week. The hours of operation are M-F 6:00 a.m. to 4:00 p.m., Saturdays 9:00 a.m. to 12:00
p.m., excluding Agency Holidays. Authorized waste haulers will fill out a Trucked Waste Record
(3) at CMSA's Administration Building prior to entering the Treatment Plant and proceeding to
the Receiving Station. The white line striped on the plant road provides visual direction to the
receiving station for first time users and emergency responders. CMSA reserves the right to
refuse or require scheduled delivery of any hauled waste, if doing so would be in the best interest
of the operation of the Treatment Plant to avoid process disruptions. Wastes that contain heavy
metals, toxic chemicals, and extreme pH, flammable or corrosive materials in concentrations
harmful to the treatment operation will not be accepted.
Unloading
The Receiving Station's equipment has been designed for receiving both FOG and FW waste
streams. Material is screened by a Rock Trap Grinder (FOG) and a Paddle Finisher (FW). These
machines are designed to prevent interference by screening the waste and removing materials
that could clog downstream equipment and/or cannot be anaerobically digested. The screenings
are directed to special debris bins for off-site disposal. FOG delivery is designed to be fully
automated after the delivery driver inserts an Agency issued access card into the card reader.
Prior to accepting FOG deliveries, the station's HMI will shut down all operating equipment and
valves feeding the Slurry Tank that could disturb or change the liquid level in the tank. The
Slurry Tank has a working volume of 20,000 gallons, based on a low operating level of 4.0 feet
and a high operating level of 11.0 feet. Food Waste Deliveries will be performed by Marin
Sanitary Service (MSS) with CMSA staff observing the deliveries. The Slurry Tank can accept a
single truck load of up to 20 tons of food waste every day. Guide posts and a concrete tire stop
are located to assist the MSS delivery drivers in properly positioning the truck so it will dump its
contents into the Slurry Tank without spilling onto the plant road. If a material spill needs to be
cleaned up, it can be rinsed to a nearby drain sump that is connected to the slurry tank,
identifiable by "Drains to Slurry Tank" marked drain sumps.
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Food Waste to Energy Section 9 - Appendices
Processing
After the Hauled Waste has been received and the slurry tank filled to the pre-established level,
an operator will initiate the slurry tank mixing sequence (4) from the FOG/FW FDVII. The station
PLC sets the amount of mixing time needed (based on source and amount) to create the slurry.
After appropriate slurry mixing, the receiving station goes into an automatic mixing mode using
the mix pumps, the paddle finisher, and/or the rock trap grinder.
Feeding
Feeding the slurry to the digesters is permitted only when the following conditions exist:
1. The FOG Delivery Sequence is not active
2. Food Waste Slurry Sequence is not active
3. Slurry Tank level is above the operator adjustable low level setting. (Initially set at 4.0 feet.)
4. Station recirculating pumps are operating.
5. Digester Gas Volume is less than 116,000 cubic feet
6. Digester liquid levels are less than 25 feet
Spill Prevention and Containment
The FOG and FW delivery areas are designed to drain rainwater directly into the Slurry Tank via
4-inch drain piping. There are no valves in this piping, so drainage will occur without operator
action. To prevent possible odor emissions from the Slurry Tank, each 4-inch tank connection
contains a P-trap. A 6-inch interconnected drain pipe with a buried plug valve is provided to
drain any FOG or FW spillage from either receiving pad directly into the slurry tank. The buried
plug valve should be closed at all other times to avoid the potential for odor emission through the
6-inch drain piping.
If the Slurry Tank needs to be drained (5) rapidly, two feed pumps and a recirculation pump can
be utilized. The pump discharges can be manually valved to the existing plant process waste
return sump in the Solids Handling Building and recycled to the plant Headworks. Pipe cleanouts
are located in the suction and discharge piping of the Receiving Station mixing pumps and the
feed pumps. CMSA's Emergency Response Plan (6) provides a detailed response in the event
that spilled waste makes its way into the Treatment Plant's storm drain system and cannot be
contained and pumped back to the treatment plant.
Vector and Odor Control
The Slurry Tank delivery hatch and Paddle Finisher sump hatch are two potentially significant
access points for vectors (rats, mice, insects, birds) into the receiving tank. These access points
shall be closed at all times except for during deliveries and maintenance activities. Fine mesh
screens have been attached to the tanks air intake and exhaust vents to exclude vectors from
those entry points.
The Odor Control System (OCS) has a gas detection meter that monitors for oxygen, hydrogen
sulfide, and flammable gases and vapors. The OCS draws air from the Slurry Tank and removes
the contaminants in the air stream before the air is released into the atmosphere. The fan for the
OCS can be started manually as needed to prevent emissions from the Slurry Tank. The media in
the OCS vessel is high quality activated carbon. When odor or hydrogen sulfide breakthrough
occurs, the media can be regenerated in place.
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Food Waste to Energy Section 9 - Appendices
Separate from the OCS, exhaust fans are included to minimize the potential for harmful gases to
accumulate in the lower equipment area. These fans are also designed to provide ventilation so
that the equipment area does not need to be designated as a hazardous area per the
National Electrical Code. Fans will be in operation at all times.
A chlorine solution can be sprayed into the Slurry Tank if needed to reduce odors that may be
present after FW is dumped into the slurry tank. This chlorine solution spray can be controlled
manually or by initiating the Chlorine Solution Spray Timer on the FOG/FW Screen at the FDVII.
Spray nozzles within the Slurry Tank direct the spray to the area below the food waste delivery
hatch where the FW is expected to mound.
Operations and Maintenance
It is expected that daily removal of rocks from the rock trap/grinder will be required. Operators
will be expected to perform daily general cleanup of the Receiving Facility. The bins with
rejected material from the rock trap/grinder and/or the paddle finisher will require periodic pick-
up and removal for disposal on an as yet to be determined frequency. Annually, grit removal
from the Slurry Tank will be required, the hose pump hoses will be inspected and replaced
depending on wear, and annual preventive maintenance will be performed on the rock trap
grinder, mixing pumps, and paddle finisher. O&M staff members will maintain appropriate
technical certification levels and possess the experience required for operating anaerobic
digesters and appurtenant equipment. Equipment-specific procedures are contained in the
Digester Improvements and FOG/Food to Energy Facility Operations Document dated
January 2013.
References
(1) CMS A Site-map with location reference
(2) "Methane Capture Feasibility Study, City of San Rafael and Central Marin Sanitation
Agency," Kennedy / Jenks Engineering Tech. Rep. KJ0868015 (2008). [no author]
(3) "Acceptance of Hauled Waste" CMSA Administrative Policy #11 (2012).
(4) "Digester Improvements and FOG/Food to Energy Facility Operations Document" (2013).
(5) Emergency Operating Procedure E21.01 "H:\Operations\Standard Operating
Procedures\eop21.01.
(6) CMSA Health and Safety Policy and Program "Emergency Response Plan" section 6, page 6-
2, Overflows from the Treatment Plant.
35
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Food Waste to Energy Section 10 - References
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Food Waste to Energy Section 10 - References
More WERF reports related to Energy Recovery
Water Environment Research Foundation. 2011 Evaluation of Processes to Reduce Activated
Sludge Solids Generation and Disposal (05-CTS3) February 2011
Water Environment Research Foundation. 2008. State of the Science Report on Energy and
Resource Recovery from Wastewater Solids (OWSO3R07) April 2008
WERF. 2010. Best Practices for Sustainable Wastewater Treatment (OWSO4R07a) January
2010
WERF. 2011. Site Demonstration of the Life-cycle Assessment Manager for Energy Recovery
Tool (OWSO4R07f) June 2011
WERF.2014. Co-Digestion of Organic Waste Products with Wastewater Solids and Economic
Model (OWSO5R07) January 2014
WERF. 2012. State of the Science on Biogas: Treatments, Co-Generation, and Utilization in
High Temperature Fuels Cells and as a Vehicle Fuel (OWSOlOClOa) February 2012
WERF.2014. Evaluation of the Efficiency of Biogas Treatment for the Removal of Siloxanes
(OWSO10C10) February 2014
WERF. 2012. Barriers to Biogas Utilization for Renewable Energy (OWSO11C10) June 2012
and factsheet October 2012
WERF. 2012. Reframing the Economics of Combined Heat and Power Projects: Creating a
Better Business Case through Holistic Benefit and Cost Analysis (OWSO1 IClOa) December
2012
Life Cycle Assessment Manager for Energy Recovery v. 2.0 2013
Combined Heat and Power System Evaluation Tool (U2R08B) August 2011
Flare Efficiency Estimator Tool (U2R08D) March 2013
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