September 2021
EMERGING ISSUES IN
FOOD WASTE MANAGEMENT
Commercial Pre-Processing
Technologies
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Disclaimer
This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved
for publication. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
Acknowledgements
EPA would like to thank the following stakeholders for their valuable input on the draft report:
Michelle Andrews, Washington State Department of Ecology
Angel Arroyo-Rodriguez, Ohio Environmental Protection Agency
Alyson Brunelli, Rhode Island Department of Environmental Management
Will Elder, Oregon Metro
Charlotte Ely, California State Water Resources Control Board
Gary Feinland, New York State Department of Environmental Conservation
John Fischer, Massachusetts Department of Environmental Protection
Justin Gast, Oregon Department of Environmental Quality
Josh Kelly, Vermont Agency of Natural Resources
Leslie Lipton, New York City Department of Environmental Protection
Amy McClure, Indiana Department of Environmental Management
Jennifer McDonnell, New York City Department of Environmental Protection
Kyle Pogue, CalRecycle
Ken Powell, Kansas Department of Health & Environment
Sally Rowland, New York State Department of Environmental Conservation
Chery Sullivan, Washington State Department of Agriculture
Nick Van Eyck, New York City Department of Sanitation
Kawsar Vazifdar, Los Angeles County Department of Public Works
EPA would like to thank the following people for their independent peer review of the report:
Jacqueline Ebner, Ph.D., Bard College
Nora Goldstein, BioCycle
Yuan You, Ph.D., Yale University
This paper was prepared by ICF Incorporated, L.L. C. for the U.S. Environmental Protection Agency, Office of
Research and Development, under USEPA Contract No. 68HERC19D0003. External peer review was
coordinated by Eastern Research Group, Inc., under USEPA Contract No. EP-C-17-017
Commercial Food Waste Pre-Processing Technologies
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Executive Summary
Food waste—defined as food that is produced for human consumption but not ultimately consumed by humans—
is a major global environmental, social, and economic challenge. Recognizing the critical importance of reducing
food loss and waste, in 2015 the U.S. Environmental Protection Agency (EPA) and U.S. Department of
Agriculture announced the U.S. Food Loss and Waste Reduction Goal to halve food loss and waste by 2030. One
of EPA's strategies to help meet this goal is to encourage diversion of food waste from landfills to reduce methane
emissions and recover value (i.e., nutrients or energy) from food waste. In addition, some states, like California,
Massachusetts, and Vermont, and municipalities, like Austin, Boulder, and New York City, are instituting bans on
landfilling food waste or implementing new recycling programs to reduce the amount of food waste sent to landfills
and incinerators. To meet these new regulations and/or to meet their own economic and environmental goals,
some commercial and institutional generators of food waste—including grocery stores, restaurants, hotels,
universities, and correctional facilities— are installing on-site food waste pre-processing technologies.
In this issue paper, EPA seeks to assess the environmental value of commercial food waste pre-processing
technologies to understand whether (and, if so, under what conditions) each class of these technologies can (a)
enable or increase the recycling of food waste; and/or (b) reduce the overall environmental impact of food waste,
and thus inform whether policymakers should encourage the use of each class of pre-processing technology. The
paper discusses each of following five general categories of these technologies:
¦ Grinders, which mechanically reduce the volume of food waste by macerating it into a slurry;
¦ Biodigesters, which biologically treat food waste under aerobic conditions with additives like microbes,
enzymes, and fresh water to digest the waste into a slurry;
¦ Pulpers, which mechanically reduce the volume of food waste by compressing it into a semi-dry pulp;
¦ Dehydrators, which thermally treat food waste to evaporate the liquid and create a dry pulp; and
¦ Aerobic in-vessel units, which use the natural aerobic decomposition process and bulking additives like
sawdust to create a semi-dry product that requires further curing.
Each pre-processing technology requires different inputs and creates different outputs, and technologies may be
used in combination with one another at a single facility. While almost no independent, peer-reviewed life cycle
assessments have been performed on these technologies, many helpful insights exist in the literature.
Food waste can be recycled to produce biogas and/or soil amendments with or without pre-processing at the
waste generation site, and the use of on-site pre-processing technologies does not guarantee recycling. However,
all these technologies require source separation of food waste from inorganic waste, which is an important first
step toward recycling. Once food waste is separated, food waste can be recycled on-site or hauled off-site to a
composting, anaerobic digestion (AD), or other recycling facility.
Pre-processing technologies that produce liquid outputs (grinders and biodigesters) typically send the output
down the drain. Whether biogas is recovered from the food waste is dependent upon whether the receiving
wastewater resource recovery facility (WRRF) has AD capabilities. After treatment (with or without AD) at a
WRRF, biosolids remain. These biosolids may be recycled (with or without further processing) and land applied
as a soil amendment - or they may be landfilled.
In general, pre-processing technologies that send liquefied food waste down the drain shift the burden of food
waste management from landfills to municipal sewage systems and WRRFs. The net environmental burden of
this shift has not been thoroughly explored in the literature. Sending additional organic waste, high in biological
oxygen demand (BOD), total suspended solids (TSS), and fats, oils, and grease (FOG), through the sewer can
result in fugitive methane emissions and may require additional energy for pumping systems and water treatment
processes. This waste can also cause operational problems for the water treatment systems, especially in low
flow, combined, or aging systems. The shift could also be financial: commercial food waste generators that send
Commerciai Food Waste Pre-Processing Technologies
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liquefied food waste down the drain avoid paying tipping fees to landfills, but unless fees are imposed on the
generators by the WRRF, municipal ratepayers may bear the added costs of sewer maintenance and additional
treatment. In addition, many of the concerns with these technologies could multiply in scale if grinders and/or
biodigesters become more broadly adopted among commercial food waste generators.
However, generators may also choose to collect liquid outputs from grinders or biodigesters and haul them off-site
for biogas recovery via AD at a stand-alone AD or an AD at a WRRF. Food waste may lose energy potential as it
travels through the sewer system and earlier parts of the WRRF. Available data indicates greater greenhouse gas
(GHG) emissions benefit for trucking effluent from the generator to an AD unit versus sending the same effluent
via sewer conveyance to a WRRF with AD. Biosolids will remain and, as above, may be recycled and land
applied, or landfilled.
For technologies that produce semi-dry or dry outputs (pulpers, dehydrators, aerobic in-vessel units), generators
must decide where to send the output. Generators may recycle the pre-processed food waste into a stable soil
amendment by hauling it off-site for centralized composting or, in the case of dehydrators and aerobic in-vessel
units, by further curing it on-site or off-site. The soil amendments created by dehydrators and aerobic in-vessel
units are not compost in the traditional sense, and much remains to be learned about their stability and suitability
for different uses. Facilities may also send the semi-dry or dry pre-processed food waste to a landfill or
incinerator. The dry outputs are lower in weight and volume than unprocessed food waste, so if it is sent off-site,
hauling-related fuel use and GHG emissions are reduced. Pulper and dehydrators remove water from the food
waste and typically send this water down the drain, which may raise similar concerns to those noted above for
grinders and biodigesters.
Based the current state of available research, EPA cannot conclude whether the environmental benefits of pre-
processing commercial food waste (and sending the pre-processed waste to a composting or AD facility, WRRF,
landfill, or incinerator) are greater than simply hauling unprocessed waste directly to the intended destination.
EPA encourages the diversion of food waste streams to composting or AD operations, rather than landfills and
incinerators, but cannot yet conclude whether or how the use of pre-processing technologies changes the
environmental benefits or impacts of these choices. Scientifically rigorous data are needed to complete a life cycle
assessment of the use of on-site pre-processing technologies in addition to, or in lieu of, traditional food waste
pathways. Priority research gaps include:
¦ Independently verified operating and performance data for pre-processing technologies.
¦ Measurement of fugitive methane emissions from sewer conveyance of food waste.
¦ Comparative analysis of biogas potential of food waste that has been unprocessed, pre-processed by
grinder, or pre-processed by aerobic digester, and then sent down the drain to a WRRF with AD or
hauled directly to the AD unit.
¦ Environmental and economic impacts on municipal sewer systems and WRRFs of additional liquefied
food waste (from grinders and biodigesters) and wastewater extracted from food waste (from pulpers
and dehydrators) being sent down the drain.
¦ Effect of pre-processing technology use on food waste generators' decision whether or not to recycle
(i.e., does pre-processing technology use encourage or discourage recycling).
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Table of Contents
1. Introduction 1
1.1. Scope and Methods 4
2. Grinders 5
2.1. Inputs 6
2.2. End Products 6
2.3. Environmental Benefits and Impacts 7
3. Biodigesters 12
3.1. Inputs 13
3.2. End Products 14
3.3. Environmental Benefits and Impacts 15
4. Pulpers 18
4.1. Inputs 19
4.2. End Products 19
4.3. Environmental Benefits and Impacts 19
5. Dehydrators 21
5.1. Inputs 22
5.2. End Products 23
5.3. Environmental Benefits and Impacts 24
6. Aerobic In-Vessel Units 26
6.1. Inputs 27
6.2. End Products 27
6.3. Environmental Benefits 27
7. Analysis of Environmental Considerations 30
8. Conclusions and Research Gaps 33
8.1. Conclusions 33
8.2. Research Gaps 35
9. References 37
Appendix A. Literature Search Methodology 41
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Tables
Table 1. Comparison of Various On-site Grinders 11
Table 2. Comparison of Various On-site Biodigesters 17
Table 3. Comparison of Various On-site Pulpers 20
Table 4. Comparison of Various On-site Dehydrators 25
Table 5. Comparison of Various On-site Aerobic In-vessel Units 29
Figures
Figure 1. Comparison of On-site Commercial Food Waste Pre-processing Technologies 3
Figure 2. Salvajor ScrapMaster Grinder 5
Figure 3. InSinkErator Grind2Energy 6
Figure 4. Comparison of the Carbon Footprint (as C02e) from Hauling vs. Sewer Transport 7
Figure 5. Power Knot LFC-70 Biodigester in the Fujitsu Campus Cafeteria in Sunnyvale, California 13
Figure 6. Liquefied Food Waste Output from a Biodigester Entering the Sewer System 14
Figure 7. Somat SPC-50S Pulping System (includes grinder) 18
Figure 8. Somat Dehydrators in St. Cloud Hospital in Minnesota 22
Figure 9. Increased Fungal Growth Over Time on Dehydrated Food Waste 23
Figure 10. DTE EnviroDrum Aerobic In-vessel Unit 27
Figure 11. Pulper Paired with a Dehydratorto Maximize the Water Removed from Food Waste 33
Text Boxes
Text Box 1. Potential Concerns with Sending Pre-processed Food Waste Down the Drain 9
Text Box 2. State and Local Policies Regarding Grinders and Biodigesters 16
Acronyms
AD anaerobic digestion
BOD biological oxygen demand
EPA U.S. Environmental Protection Agency
FOG fats, oils, and grease
GHG greenhouse gas
LCA life cycle analysis
MRF mixed materials recovery facility
MSW municipal solid waste
TSS total suspended solids
USDA U.S. Department of Agriculture
WERF Water Environment Research Foundation
WRRF wastewater resource recovery facility
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1. INTRODUCTION
The purpose of this issue paper is to assess the environmental value of food waste1 pre-processing technologies
(e.g., biodigesters, grinders, and pulpers) used on-site by businesses and institutions that generate food waste.
EPA seeks to understand whether (and, if so, under what conditions) pre-processing technologies can (a) enable
or increase the recycling of food waste; and/or (b) reduce the overall environmental impact of food waste. The
issue paper also identifies research gaps, where new research may help to inform whether U.S. federal, state,
and local policymakers should encourage the use of each class of pre-processing technology to meet
environmental objectives.
1.1. Background
Wasted food is a major global environmental, social, and economic challenge. Preventing food waste can save
natural resources and avoid a myriad of environmental impacts, and recycling unavoidable food waste, such as
inedible peels and bones, can reduce greenhouse gas (GHG) emissions and improve soil quality. In the United
States today, food waste is typically landfilled or incinerated. The U.S. Environmental Protection Agency (EPA)
estimates that more food reaches landfills and incinerators than any other single material in our everyday trash,
constituting 24 percent of landfilled municipal solid waste (MSW) and 22 percent of combusted MSW (U.S. EPA,
2020).
In 2015, the EPA and U.S. Department of Agriculture (USDA) announced the U.S. Food Loss and Waste
Reduction Goal to halve per capita food waste at the retail and consumer level (including consumer-facing
businesses and institutions) by the year 2030. To date, thirty three businesses and organizations have publicly
committed to halve FLW in their U.S. operations by 2030 as part of EPA's Food Loss and Waste 2030 Champions
group, and two-thirds of the world's 50 largest food companies have set a similar FLW reduction target (U.S. EPA,
2020; Flanagan et al., 2019). In addition, some states, like California, Massachusetts, and Vermont, and
municipalities, like Austin, Boulder, and New York City, are instituting bans on landfilling food waste or
implementing new recycling programs to reduce the amount of food waste sent to landfills and incinerators. For
example, Massachusetts banned the landfilling of commercial organic waste by businesses and institutions that
dispose of 1 ton or more of organics per week (MassDEP, 2020). California requires commercial and public
entities that generate over 4 cubic yards of organic waste per week to arrange for food waste recycling services to
pick up their waste (CalRecycle, 2020b).
Many commercial generators of food waste are seeking methods to reduce the amount of food waste they send to
landfills and incinerators. Large-volume generators of food waste—including grocery stores, restaurants, hotels,
universities, and correctional facilities—have several choices once they have separated food waste from inorganic
waste. A common strategy is to have a third-party hauler pick up and deliver the waste to a centralized
composting or anaerobic digestion (AD) facility or to a farm for use as animal feed (RecyclingWorksMA, 2018;
Goldstein and Dreizen, 2017; Gorrie, 2015).
Commercial food waste generators can also utilize on-site pre-processing technologies that either reduce the
weight and volume of food waste (thus reducing the cost, difficulty, and GHG emissions associated with hauling
food waste) or break down and liquify the food waste to the point that it can sent directly down the drain into the
existing municipal sewage system or captured in a vessel that can be transported to an AD facility. Some pre-
processing technologies provide additional advantages for commercial food waste generators, including
minimizing odors and storage space needed for food waste.
The U.S. market for on-site commercial food waste pre-processing technologies is small, but has grown during
the past decade (Goldstein and Dreizen, 2017). A diverse range of mechanical, thermal, or biological options are
1 In this paper food waste is defined as food that is produced for human consumption but not ultimately consumed by humans.
Commercial Food Waste Pre-Processing Technologies
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available. The following five general categories of these technologies are each discussed in detail in this issue
paper:
¦ Grinders, which mechanically reduce the volume of food waste by macerating it into a slurry;
¦ Biodigesters, which biologically treat food waste under aerobic conditions with additives like microbes,
enzymes, and fresh water to digest the waste into a slurry;
¦ Pulpers, which mechanically reduce the volume of food waste by compressing it into a semi-dry pulp;
¦ Dehydrators, which thermally treat food waste to evaporate the liquid and create a dry pulp; and
¦ Aerobic in-vessel units, which use the natural aerobic decomposition process and bulking additives like
sawdust to create a semi-dry product that requires further curing.
Each pre-processing technology requires different inputs and creates different outputs, and technologies may be
used in combination with one another at a single facility. This issue paper describes each of the five pre-
processing technologies listed above, including the types and capacities of food waste that may be processed,
the resources (such as water and energy) required to operate the technologies, and the availability and use of the
technology in the United States. A discussion of environmental considerations related to each technology follows.
After using one or more pre-processing technologies, commercial food waste generators must also manage the
products or effluents. For example, a liquid product may be disposed of down the drain (if allowed), a dry pulp can
be processed into compost, or a reduced weight and volume of food waste may simply be hauled to a centralized
composting facility, AD facility, landfill or incinerator. The issue paper concludes with a summary of the
environmental considerations associated with food waste pre-processing technologies, information gaps, and
research needs.
Figure 1 provides an overall summary of the available information on pre-processing technologies.
Commercial Food Waste Pre-Processing Technologies
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On-site Commercial Food Waste Pre-Processing Technologies
Grinders Biodigesters Pulpers Dehydrators Aerobic
In-vessel Units
Mechanically macerate Aerobically digest food Typically use grinder Thermally process food Aerobically digest food
food waste into small waste into a liquid then mechanically waste and evaporate waste into semi-dry
particles and liquid press water out of food the liquid product
waste to create a pulp
Use in the United States
600+ units
600+ units
500+ units
120+ units
Food Waste Inputs
XL Food Waste^^^ Fats/Oils/Grease Bones/Shells/Pits Computable
. ' ' T ' ' Serviceware
X
X
X
X
*
X
X
X
4444
f
4
Liquid
4 Water } Energy
Other Inputs
Biological Additives
y Sawdust/
^ Woodchips
Liquid
End Product
Semi-dry
4144
44
f J!
Si
Semi-dry Semi-dry
Sewer to WRRF
OR
Truck to AD
Transportation & Destination
Sewer to WRRF
4h 4n
Truck to compost or
dehydrator
,80%
Truck to compost or
landfill
,80%
4,15-80%
Hauling Weight Reduction Hauling Weight Reduction Hauling Weight Reduction
OR
Soil Amendment Soil Amendment
%
%
FIGURE 1. COMPARISON OF ON-SITE COMMERCIAL FOOD WASTE
PRE PROCESSING TECHNOLOGIES
WRRF = wastewater resource recovery facility; AD = anaerobic digestion
Commercial Food Waste Pre-Processing Technologies
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1.2. Scope and Methods
Various brands and models of each type of commercial food waste pre-processing technology are discussed;
however, all models and brands are not necessarily included in this paper. In addition, several classes of
technology were considered outside the scope of this paper and thus excluded, such as:
¦ Smaller, decentralized versions of traditional food waste pathways, such as composting (e.g., the Susteca
AB Big Hanna, Wakan Environment Inc. CITYPOD, Jora Tumbler, and NATh Sustainable HotRot) and
anaerobic digestion (e.g., SEaB Energy, Impact Bioenergy, and Living Arts Systems);
¦ Technologies that separate organic waste from municipal solid waste (e.g., Anaergia Organics Extrusion
Press) to enable processing at an AD facility;
¦ Technologies typically used by composting and AD facilities, farms, or food processing facilities, rather
than consumer-facing businesses and institutions that generate food waste, including de-packagers2 and
technologies to process food waste prior to using it as animal feed.
This issue paper is based upon a review of available literature. Since very limited peer-reviewed research is
available on this topic, the issue paper relies heavily on gray (non-peer-reviewed) literature, including the
comprehensive overview of on-site systems published by RecyclingWorks Massachusetts (RecyclingWorksMA,
2018); the Composting Collaborative's Pretreatment Directory (The Composting Collaborative, 2020), which was
funded in part by EPA; and the California Department of Resources Recycling and Recovery (CalRecycle)
guidance documents (CalRecycle, 2020c, d). The issue paper also relies upon articles, case studies, and
interviews from the organics recycling e-magazine BioCycle3 (Coker, 2019; Goldstein and Dreizen, 2017; Coker,
2016; Goldstein, 2015; Neale, 2013; Sullivan, 2012) and shares information provided by the manufacturers or
vendors themselves that has not been independently confirmed by peer-reviewed research. More detailed
information on the literature search strategy can be found in Appendix A. Throughout the paper, metric tons are
used to measure greenhouse gases and standard tons are used to measure food waste, unless otherwise noted.
2 A discussion of de-packagers can be found in another EPA report in this series: "Emerging Issues in Food Waste Management: Plastic
Contamination" CERA 600-R-21-001. August 2021).
3 In 2020 BioCycle transitioned from a print magazine to a weekly e-newsletter, BioCycle CONNECT, and a newly relaunched website,
BioCycle.net.
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2. GRINDERS
One of the simplest ways to mechanically reduce the volume of food waste is to
grind it up into a slurry. Grinders are commercial-sized garbage disposal systems
that macerate food waste into a liquid effluent that is typically disposed of directly
down the drain into the municipal sewage system. It can also be captured and
hauled to an AD facility (Neale, 2013). Grinders can be purchased as stand-alone
units (Figure 2) or may be combined with other technologies (e.g., pulpers) into
larger pre-processing systems. Grinders are one of the more popular pre-
processing technologies chosen by commercial food waste generators, with tens of
thousands of commercial grinders currently in use across the United States
(RecyclingWorksMA, 2018; Wright and Jones, 2017).
Product information—including processing capacity, accepted inputs, water and
energy usage, cost, and trends of use in the United States—is summarized for
several types of grinders on the market in Table 1 (located at the end of Section 2).
Processing capacities of grinders range from 250 pounds of food waste per day to
5 tons of food waste per hour; however, these are all manufacturer claims and
none of this information has been independently verified through peer-reviewed
research. Manufacturers claim that grinder models that capture the slurry on-site
for transport to an AD facility produce "significant volume reduction" though it is
unclear what significant means in this case (InSinkErator, 2020).
Food Waste
Fats/Oils/Grease
Other Inputs
FIGURE 2. SALVAJOR SCRAPMASTER GRINDER
Photo Credit: Salvajor (2018c)
4444
Water
60-480 gallons/hr
Wf
Energy
2.74-6.5 UW
End Product
Liquid
Transportation &
Destination
Sewer to WRRF
*
OR
Truck to AD
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2.1. Inputs
Grinders usually require three inputs: food waste, electricity, and water. In general, the systems summarized in
Table 1 accept all solid or liquid organic waste (including fats, oils, and grease), but do not accept any inorganic
waste like metal, plastic (e.g., food service ware4 and packaging), or other trash. According to the manufacturers
of the grinder models listed in Table 1, the units use 1 to 8 gallons of water per minute (it is unclear how many
minutes the water typically runs). The energy usage was not reported by any of the manufacturers except
Salvajor, whose various models require 2.74 to 6.5 kW electricity (it is unclear to which processing time this
wattage applies). Estimates of resources required per ton of food waste processed are not available.
2.2. End Products
Grinders generally produce one end product, the slurry of ground-up food waste, and most grinder models send
the slurry directly down the drain into the municipal sewage system. The fact that grinder output can be sent
directly down the drain, without the need for storing, hauling, or other processing, makes grinders a popular
choice for commercial facilities that generate large quantities of food waste (Wright and Jones, 2017),
Some models, like the InSinkErator Grind2Energy (Figure 3) and Landia Biochop, do not send the slurry down the
drain but instead capture it in a large onsite holding tank (that can be stored outside) so a liquid waste hauler can
pick up the slurry and transport to an AD facility for conversion to bioenergy (InSinkErator, 2020). These hauling-
based grinders may present environmental advantages over their sewer-based counterparts. One study showed
that hauling food waste slurry to an AD facility reduces GHG emissions and generates more biogas during AD
compared to sending the slurry down the drain for AD at the wastewater resource recovery facility (WRRF) (Parry,
2012). This study is discussed more in Section 2.3.
FIGURE 3. INSINKERATOR GRIND2ENERGY GRINDER
Photo Credit: Emerson (2020)
4 Service ware includes plates, serving trays, cups, utensils, and associated items.
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2.3. Environmental Benefits and Impacts
Grinders raise multiple potential environmental concerns, most of which are associated with sending the pre-
processed food waste down the drain. These factors are discussed in detail in Text Box 1, as they apply to all
technologies that send food waste down the drain.
However, these technologies can also process food waste into a pumpable slurry that can be used by anaerobic
digesters. Grinder models designed to capture effluent (rather than send it down the drain) so it can be hauled to
an AD facility for conversion to bioenergy exhibit a different set of environmental impacts and benefits. A 2013
study published by Water Environment Research Foundation (WERF) (Parry, 2012)5 conducted a life-cycle
assessment (LCA) to compare the impacts of five different food waste management methods including two types
of grinders: ones where effluent is sent down the drain, into the sewer, and on to a wastewater resource recovery
facility6 (WRRF) operating with AD; and ones that collect effluent for hauling to AD facility. The former focused on
residential effluent, while the latter examined commercial effluent. The study also assessed collection and hauling
of commercial food waste to a landfill, composting facility, and mixed materials recovery facility (MRF), where it is
separated and then taken to either a landfill or AD facility. Vendor data was preferred source of information for the
study, followed by literature and professional experience of author. The study was peer-reviewed, but funded by
InSinkErator (Parry, 2013).
1,500
1,000
| 500
u
J 0
M
W
uj -500
rM
o
u -1,000
-1,500 -
WRRF/Sewers WRRF/Hauled
Noil-Biogenic C02e
FIGURE 4. COMPARISON OF THE CARBON FOOTPRINT (IN C02e)
FROM HAULING VS. SEWER TRANSPORT TO WRRF
Source: Parry (2012)
5 Parry is the author of the WERF study referenced, thus the citation (Parry, 2012) does not include WERF.
6 This report uses the term wastewater resource recovery facility (WRRF) in lieu of the term wastewater treatment plant (WWTP) used in some
source material to highlight the potential for recycling by the facilities.
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The WERF study found that hauling liquified food waste by truck and processing it via AD yields lower GHG
emissions (measured as carbon dioxide equivalent, CChe) than sending liquefied food waste down the drain,
through the sewer, and then processing it at a WRRF with AD (Figure 4). These lower emissions were primarily
due to electricity generation from the biogas produced from AD (credit was given for avoided electricity generation
by traditional means) and avoided fugitive emissions of methane in the sewer system.7 When comparing the
emissions of hauling food waste to a WRRF vs. sending it to a WRRF via the sewer, the author estimated that
hauling via truck contributed to 60 CChe, while conveying the same amount of food waste to the WRRF via sewer
contributed 1,100 C02e of fugitive methane emissions (Parry, 2012). The author noted that little is known about
the anaerobic decomposition rate of food waste in the sewer system and assumed a degradation rate of 15
percent in their study (Parry, 2012). The study found that conveying food waste via sewer and processing it at a
WRRF with AD yielded higher GHG emissions than composting, but lower GHG emissions than landfilling.
The WERF study also found that hauling and direct addition of food waste slurry to a WRRF's AD also yielded
more biogas production than sending the liquified food waste through the sewer system to the WRRF's AD due to
low efficiency in capturing food waste in the primary stages of wastewater treatment (Wright and Jones, 2017;
Parry, 2012).
The California State Water Resource Board found similar results in their co-digestion capacity analysis: they
estimated that co-digestion of food waste in a WRRF (transported there via hauling) leads to a net emissions
reduction factor of 0.65 to 0.70 metric tons C02 per wet ton of food waste, as compared to landfilling (SWRCB,
2019). Both studies indicate the emissions associated with hauling food waste by truck are not significant
compared to potential GHG benefits of producing bioenergy. A comparison of the net environmental value of
sending a commercial (not residential) food waste slurry through the sewer system to WRRF with AD with ending
unprocessed food waste directly to AD facility is not available in the literature. However, this research indicates
that hauling-based grinders may have environmental advantages over their sewer-based counterparts.
7 These two factors account for the negative total emissions of food waste hauled to WRRF with AD in the study.
Commercial Food Waste Pre-Processing Technologies wmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
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TEXT BOX 1. POTENTIAL CONCERNS WITH SENDING PRE-PROCESSED FOOD WASTE DOWN
THE DRAIN
Most grinders and biodigesters produce a liquid end product meant to simply be sent down the drain,
into the sewer system, and to the WRRF. By doing so, businesses and institutions can save money
by avoiding hauling and landfill tipping fees. Also, storage space is not required, as with methods that
require hauling. Businesses may also choose these technologies to be more environmentally
sustainable by avoiding the GHG emissions associated with hauling and landfilling food waste, or, in
some states and localities, to help them comply with organic waste laws. However, numerous
concerns arise when additional organic waste is added to the sewer and wastewater treatment
systems, especially if commercial food waste generators in a particular area more broadly adopt
grinders and/or biodigesters. Many of these concerns have not yet been quantified in the scientific
literature, and additional research in these areas is warranted. Here two kinds of concerns are
discussed - environmental and operational.
Potential environmental concerns:
¦ Fugitive methane emissions. As food waste travels through the sewer system and continues to
break down, it may generate methane emissions. A 2012 study by the Water Environment
Research Foundation (WERF) noted that little is known about the anaerobic decomposition rate
of food waste in the sewer system, and assumed a degradation rate of 15 percent in the sewer
system in their research (Parry, 2012).
¦ Loss ofbiogas potential. Food waste may also lose some of its energy potential (i.e., the
potential to create biogas through anaerobic digestion) as it moves through the sewer system
and continues to break down through the various stages of wastewater treatment before it
reaches the anaerobic digester in the WRRF. This may be exacerbated by digesting the food
waste in a biodigester before releasing it into the sewer system.
¦ Energy use in pumping systems. Transporting the slurry through sewer systems that use
pumping stations (versus gravity-based systems) may require increased energy use.
¦ WRRFs without anaerobic digestion. The liquid output of grinders and biodigesters can only
be recycled to produce biogas and biosolids if the receiving WRRF has AD capabilities.
However, currently only one out of three WRRFs, representing approximately 3.4 million tons per
year of available food waste processing capacity, have AD (U.S. EPA, 2021; Wright and Jones,
2017).
¦ Final destination for end products. While businesses may intend these technologies to divert
food waste from landfills (and thus avoid the associated GHG emissions), that diversion is
dependent on subsequent constraints and decisions by the receiving WRRF. The food waste
may still ultimately reach a landfill or incinerator after pre-processing. Once the waste is
processed via anaerobic digestion at the WRRF, the resulting biosolids may be landfilled rather
than recycled, due to characteristics of sewage sludge, with which it is co-digested at the WRRF.
(This issue arises regardless of whether food waste is sent down the drain or hauled to WRRF
AD.) EPA survey data from 2017 and 2018 found that 18 percent of WRRFs landfilled biosolids,
while 13 percent land applied biosolids (U.S. EPA, 2021, 2019, 2018). Biosolids can be applied
as alternative daily cover at landfills, and it is unclear whether survey responders classified this
activity as "landfilled" or "land applied." Biosolids may be landfilled for several reasons, including
cost (landfill tipping fees may be the cheapest option), odor, public opposition, or high
concentrations of metals or other toxins (from non-food materials).
continued on next page
Commercial Food Waste Pre-Processing Technologies
9
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Potential operational difficulties and costs:
¦ Additional treatment requirements. Liquified food waste often contains high levels of total
suspended solids (TSS), biological oxygen demand (BOD), and fats, oils, and grease (FOG)
(Dorsey and Rasmussen, 2012). One case study (Loyola Marymount University's dining hall)
measured pollutants in biodigester effluent and found higher BOD, TSS, and FOG levels than
are typically found in domestic raw sewage (Dorsey and Rasmussen, 2012). The study also
found high levels of nitrates, phosphates, and pathogen indicators in the effluent (Wright and
Jones, 2017). This additional pollution load could strain WRRFs, increasing the cost and energy
required to process and treat wastewater. In addition, smaller WRRFs or WRRFs with small pipe
sizes may not have sufficient capacity to accommodate significant increases in organic load
(Wright and Jones, 2017).
¦ Pipe corrosion. Effluent with high BOD content may interact with sulfates that are normally
produced in the human digestive tract (that subsequently enter the sewage system through toilet
flushing) and produce hydrogen sulfide. Hydrogen sulfide can convert to sulfuric acid which
corrodes pipes (CalRecycle, 2020d). Municipalities with small or aging pipes are particularly
vulnerable to the risks of corrosion (Neale, 2013).
¦ Clogs and slugs. A portion of the effluent from pre-processing technologies that accept FOG
may create clogs in the sewage system called "slugs" (CalRecycle, 2020d; Neale, 2013). Some
WRRF operators hypothesize that food waste simply re-congeals further downstream in the
sewage system to create slugs (Neale, 2013). Slugs can be challenging for municipal
wastewater managers to detect until they are very large and difficult to remove (CalRecycle,
2020d). In a 2004 Report to Congress, EPA identified that 74 percent of sanitary sewer
overflows were caused by blockages and 47 percent of the blockages were due to grease (U.S.
EPA, 2004). Several studies show that removing FOG from the sewer systems and hauling it
directly to a WRRF's anaerobic digester reduced sewer blockages and operating costs (Parry,
2014).
¦ Combined or "low flow" systems. There may be complications with sending additional food
down the drain in "low flow" water systems or combined systems that could discharge during
heavy rains. Where combined sewer outfall (i.e., one pipe transports rainwater runoff, domestic
sewage, and industrial wastewater) exists, increased food waste being discharged into the
sewer could increase the organic pollutant load of direct discharge into surface waters (Neale,
2013).
¦ Contamination. If small pieces of inorganic waste items from the food waste stream, like
particles of plastic, glass, or metal packaging or service ware, pass through the grinder, this
inorganic waste could be ground up along with the food waste and sent into the municipal
sewage system. "Chips" or other inputs provided by vendors are also entering the sewer
system, likely in disintegrated form. Persistent chemicals, such as per- and polyfluoroalkyl
substances (PFAS), in food waste are also an emerging concern. However, no information was
found in the literature about potential contaminants in grinder slurry or how well users separate
inorganic materials from food waste before using the grinding systems.
Commercial Food Waste Pre-Processing Technologies
10
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TABLE 1. COMPARISON OF VARIOUS ON-SITE GRINDERS
Brand of
Grinder
Description
Use in
the U.S.3
Accepted Inputs
from the Food
Waste Stream
Other Inputs
Transportation
and
Destination
Unit
Costsb
References (Non-
Peer Reviewed
and Manufacturer
Data)
InSinkErator
Grind2Energy
The InSinkErator grinds food
waste into a slurry that is
captured by an on-site holding
tank.
NR
All food waste
(including FOG);
does not accept any
nonorganic waste.
Water: 1-2 aallons/minute
Enerav: NR
Processina caDacitv:
1 ton/hour
Hauled by truck
to AD facility
NR
InSinkErator
(2020);
RecyclingWorksMA
(2018); Rulseh
(2016)
Landia
Biochop
The BioChop is a complete
processing unit (tank, grinder,
and automation) that
mechanically macerates and
liquefies the food wastes and
by-products.
NR
All food waste
(including FOG);
can handle small
amounts of
nonorganic waste
Water: Depends on
feedstock,
but generally not required
Enerav: Depends on
feedstock and volumes
Processina caDacitv:
Up to 5 tons/hour
Hauled by truck
to AD facility
$30,000-
200,000
Landia (2020);
Voell (2020)
Salvajor Food
Waste
Disposer
The Food Waste Disposer is
commercial garbage disposal
system that grinds food waste
into a slurry that is pumped
down the drain.
60,000
All organic waste;
does not accept
trash, metal, and
plastic.
Water: 5-8 aallons/minute
Enerav: 2.74-5 kWc
Processina caDacitv:
250-500 lbs/day
Sewer to
WRRF
$4,000-
6,000
RecyclingWorksMA
(2018); Salvajor
(2018a, 2018b)
Salvajor
ScrapMaster
The ScrapMaster is a dish
scraping station for large-scale
kitchens. It includes a pre-
flushing plume to rinse food
waste off dishes, trays, and
cookware, and a grinder that
macerates the food waste into
a slurry before it is sent down
the drain.
2,500
All organic waste;
does not accept
trash, metal, and
plastic.
Water: 7 aallons/minute
Enerav: 6.5 kWc
Processina caDacitv:
750 lbs/day
Sewer to
WRRF
$17,000
RecyclingWorksMA
(2018); Salvajor
(2018d)
FOG = fats, oils, and grease; NR = information was not reported.
a This column includes the number of systems installed in the U.S. This information was current as of 2018 (RecyclingWorksMA, 2018).
b The unit costs in this column are only the cost of purchasing the equipment noted. There are additional costs for installation, maintenance, and any additional material required. The dollar year
of the costs were not provided in the literature, but the date of the source's publication is noted in the references column.
°The time period or volume of food waste this energy use applies to was not reported
Commercial Food Waste Pre-Processing Technologies
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3. BIODIGESTERS
Biodigesters, also referred to as digesters, kitchen digesters, aerobic digesters,
liquefiers, or "wet systems" (CalRecycle, 2020d), use aerobic digestion to break down
food waste into a liquid within 24 hours. The resulting liquid is then disposed of down
the drain directly into the existing municipal sewage system.8 This method contrasts
with that used by grinders that simply macerate food waste into a slurry of smaller
particles before going down the drain into the sewer system (or being hauled to an AD
unit). In the aerobic digestion process, biological additives (typically microorganisms)
fueled by the presence of oxygen produce enzymes that subsequently break down and
decompose the organic material at an accelerated rate.
Biodigester systems provide an optimal environment for this natural digestion process
to occur and typically use a mechanized aeration technology, like a turner, agitator, or
paddle arms, to ensure an oxygen-rich environment is maintained. Some include a
built-in grinder or shredder (USCC, 2018). Incremental amounts of fresh water are also
added to the system, and within 24 hours, the food waste is converted to liquid. This
liquid output then typically passes through a screen and is disposed of directly into the
municipal sewage system. Biodigesters are continuous feed systems so food waste
can be added at any point if there is still room (Neale, 2013). Other benefits of
biodigesters are the reduction of odors, reduction of pests (like rodents and insects),
and increased sanitation due to the enclosed processing vessels that are normally
associated with storing food waste until it can be hauled away (USCC, 2018). An ideal
place to install a biodigester in a commercial kitchen is near the food preparation or
dishwashing station (Figure 5) (Goldstein and Dreizen, 2017).
There are multiple biodigesters on the market in the United States. Their product
information is summarized in Table 2 (located at the end of Section 3). The biodigester
brands described in Table 2 all work very similarly; the main differences are the type of
biological additives required and the volume of food waste they can process (Neale,
2013). The processing capacities of the biodigesters in Table 2 range from 45 to 2,400
pounds of food waste per day; however, none of these values have been
independently verified through peer-reviewed research. The biodigesters all come
equipped with analytics technology and scales to help food waste generators
understand the quantities and types of food waste they generate (BioHiTech, 2020;
ORCA, 2020a). While fewer biodigesters than grinders are in use in the United States
currently, the adoption of biodigesters grew in the last decade across the country.
Biodigesters
Use in U.S.
600+ units
Food Waste
Inputs
5^
Food Waste
*
Fats/Oils/Grease
Bones/Shells/Pits
X
Compostable Serviceware
Other Inputs
4
Water
0.6-13 gallons/hr
Energy
2.3-28.8 kWh/day
Biological Additives
Sawdust/Woodchips
End Product
Liquid
Transportation &
Destination
Sewer to WRRF
*
8 While hauling the biodigester output via truck to an AD facility may be feasible, there was no mention of this option in practice in the
literature.
Commercial Food Waste Pre-Processing Technologies
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FIGURE 5. POWER KNOT LFC-70 BIODIGESTER,
FUJITSU CAMPUS CAFETERIA, SUNNYVALE, CALIFORNIA
Photo Credit: Power Knot LLC (2019)
A few case studies ori biodigesters are available in the gray literature. In Sunnyvale, California, the Fujitsu
company's campus uses a Power Knot Liquid Food Composter5 system in the preparation area of their cafeteria
kitchen, which typically generates approximately 100 pounds/day of pre-consumerfood waste (Neale, 2014).
Fujitsu said its biodigester reduced its trash pick-up from daily to only 3 days a week, leading to a payback period
of 18 to 20 months on the $18,000 system (Neale, 2014). The Boston Marriott hotel in Quincy, Massachusetts,
installed a BioHiTech biodigester in its kitchen, near the dishwashing area, to help process the approximately 800
pounds of food waste it was generating daily. Originally, the hotel had a hauler collect unprocessed food waste
and transport it to a local composting facility six times a week, and using the biodigester instead led to both
"financial savings and logistical simplicity" (Neale, 2014).
3.1. Inputs
Biodigesters require four inputs: food waste, biological additives, water, and electricity. The biodigester systems
summarized in Table 2 generally accept all food waste except large bones, hard shells (like clam or mussel
shells), and grease or fat. They do not accept any nonorganic waste like plastics and metal. While the BioHiTech
systems accept liquid food waste, the ORCA systems do not.10 Biological additives are also required to accelerate
the aerobic digestion process in each system. All brands of biodigesters use their own proprietary mix of
microorganisms and/or enzymes. Vendors charge for the biological additives, which are added at intervals
ranging from continuously to once every 3 to 4 months (Neale, 2013). At least two vendors (ORCA and Power
Knot) require the addition of media called "chips" that house their blend of microorganisms. It is unclear from the
literature what these chips are made of and their fate.
Biodigesters require a continuous supply of fresh water pumped into the system to clean out the digestion vessel
and replenish the water lost when the liquid is discharged into the sewer system (CalRecycle, 2020d). The water
usage for the various brands of biodigesters (see Table 2) ranges from 30 to 500 gallons per day depending on
9 Though the Power Knot Liquid Food Composter contains "composter" in its name, it is a biodigester, not a composter.
10 A reason was not provided in the available literature.
Commercial Food Waste Pre-Processing Technologies
13
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the processing capacity of the unit. Estimates suggest that approximately 1 gallon of water is used for every 1 to 4
pounds of food waste processed (Neale, 2013). Electricity is also required to power each biodigester unit; the
energy usage across brands ranges from 2.3 to 28.8 kWh of electricity per day. Estimates of resources required
per ton of food waste processed are not available.
3.2. End Products
Biodigesters produce one end product: a filtered and liquified food waste.11 Biodigesters are connected directly to
a drain so the liquid output can be sent into the municipal sewage system from which it will ultimately end up in a
WRRF; the environmental impacts of this process are discussed in Text Box 1 and Section 3.3. Many biodigester
companies describe their technologies as "waste to water," however the iiquid produced by biodigesters is
categorically wastewater and not clean water (Neale, 2013). Other companies describe the organic liquid output
as graywater, a term normally used to describe the drainage water from on-site systems like bathtubs, showers,
sinks, and washing machines (CalRecycle, 2020d; Neale, 2013). However, graywater is typically clear in
appearance and has a low turbidity, whereas the output from the biodigester systems is not (CalRecycle, 2020d).
FIGURE 6. LIQUEFIED FOOD WASTE OUTPUT FROM A BIODIGESTER
ENTERING THE SEWER SYSTEM
Source: Rasmussen (2012)
11 Technically biodigesters convert 99 percent (not 100 percent) food waste into the liquefied stream. The available literature does not provide
an explanation; however, the Author supposes the 1 percent is likely solids captured by the filtering screen before waste enters the sewage
system and that the 1 percent may be ultimately landfilled or incinerated.
Commercial Food Waste Pre-Processing Technologies
14
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mental Benefits and Impacts
Biodigesters have both environmental benefits and impacts that are not quantitatively characterized in the
literature. Many of these factors are associated with sending the effluent down the drain. Those factors are
discussed in detail in Text Box 1. While biodigester companies describe their outputs as "a complete diversion
from landfill" (BioHiTech, 2020) and an "100% recycling solution" (ORCA, 2020b), these claims are improbable.
Independent research is needed to quantify biodigester output that is ultimately being recycled compared with
output that is being landfilled when it reaches a WRRF.
Unlike grinders, biodigesters may lower the BOD of food waste prior to release into the sewer thus reducing extra
strain on the WRRF, according to manufacturers (BioHiTech, 2020; ORCA, 2020a). However, the liquid output
from biodigesters reportedly still has relatively high levels of BOD in comparison to raw sewage (CalRecycle,
2020a) - and biodigestion may lower the effluent's biogas potential if receiving WRRF has AD. Furthermore, the
effluent quality varies by what type of food is being processed and what biological supplements have been added
to the system to aid the digestion process. For example, digested dough and dairy have higher BOD levels than
digested vegetables (CalRecycle, 2020d). No peer-reviewed research currently clarifies which biological additives
and which food types input into biodigesters produce a higher quality liquid effluent than others.
In addition to BOD, TSS, and FOG, liquified biodigester output also contains unbeneficial12 bacteria. A case study
of Loyola Marymount's dining hall found that the total coliform and enterococci concentrations in the ORCA output
were similar to what is typically found in low-strength domestic sewage (Dorsey and Rasmussen, 2012). While the
gray literature indicates that biodigester output has high levels of unbeneficial bacteria, this contention has yet to
be confirmed via peer-reviewed research.
Another environmental quality consideration is the amount of electricity and fresh water required to operate the
biodigester units. Biodigester units use approximately 20 to 500 gallons of water per day (though these data are
unverified by independent research), which should be considered when weighing the environmental pros and
cons of these systems (Neale, 2013). The amount of energy needed to power the system, treat the clean water
added to the system, and ultimately treat the effluent in the WRRF are all associated with increased GHG
emissions, not reductions (CalRecycle, 2020d). An independent, peer-reviewed LCA would be needed to
compare the environmental impacts of sending pre-processed liquified food waste down the drain versus not pre-
processing the food waste and hauling it straight to a landfill or centralized composting or AD facility.
An environmental benefit of biodigester systems is that many come equipped with scales and an integrated
analytics tool to quantify the amount and type of food waste entering the unit. The data provide commercial and
industrial food waste generators with a better understanding of which types of food are most often being wasted in
their facilities and enable more informed decisions about which types of food to purchase, cook, or manufacture
less of in the future to prevent food waste. Ultimately, this information can help businesses and institutions reduce
food waste and costs.
12 Meaning bacteria not intentionally added into the biodigester.
Commercial Food Waste Pre-Processing Technologies ¦¦¦¦¦¦¦
15
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TEXT BOX 2. STATE AND LOCAL POLICIES REGARDING GRINDERS AND BIODIGESTERS
EPA's National Pretreatment Program provides the necessary regulatory tools and authority to
states and localities to control pollutants that interfere with WRRF treatment processes, like FOG
entering the sewer system from food service establishments (U.S. EPA, 2012). However, state and
local governments vary in how they address liquefied food waste discharges into the sewer. The
regulations and fees charged may be higher than for some other types of discharges, and some
states, like California, recommend checking with local sewer districts and WRRFs to ensure
liquefied food waste is suitable to enter the sewer system (CalRecycle, 2020d). However, due to the
limited number of biodigesters in the U.S. and the fact that wastewater authorities have limited or
generalized knowledge of these systems, few revised wastewater or plumbing guidelines and
regulations apply specifically to biodigesters (Neale, 2013). Vendors may receive little oversight from
state and local wastewater permitting authorities in the U.S. when they install these systems and
may categorize the installation of a biodigester as a "replacement" of an existing plumbing fixture
(e.g., a slop sink) that does not require state or local permitting (Neale, 2013). Unless specifically
requested by a customer, vendors generally do not proactively contact local wastewater authorities
to determine the acceptable discharge levels of BOD, TSS, and FOG (Neale, 2013). However, the
pre-processing technology vendors and commercial food waste generators are both responsible for
complying with existing regulations, like the National Pretreatment Program standards (U.S. EPA,
2012).
State and local governments with landfill food waste disposal bans or mandatory food waste
recycling programs may encourage, actively or incidentally, the use of food waste pre-processing
technologies. In some states, compliance can be achieved (e.g., lowering the amount of food waste
sent to a landfill below a threshold) through the use of these technologies, while in other areas, such
as Massachusetts, compliance can only be achieved with grinders or biodigesters if the wastewater
utility receiving the waste approves it (Wright and Jones, 2017). In New York City, commercial
grinders are banned. In California, biodigester effluent is not considered compliant with the state
commercial organics law unless the entities in charge of the receiving sewage line and WRRF are
notified and agree that the WRRF will actually recycle the liquified food (CalRecycle, 2020d).
Commercial Food Waste Pre-Processing Technologies
16
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TABLE 2. COMPARISON OF VARIOUS ON-SITE BIODIGESTERS
Brand of
Biodigester
Description
Use in
the U.S.a
Accepted Inputs
from the Food
Waste Stream
Other Inputs
Transportation
and Destination
Unit
Costsb
References (Non-
Peer Reviewed
and Manufacturer
Data)
BioHiTech
America
Digesters
BioHiTech digesters use aerobic digestion and a
blend of microorganisms to break down food
waste into a liquid form within 24 hours. They can
process most food items without grinding or other
pre-processing required. The manufacturer claims
that once the food waste is completely broken
down, it is discharged as wastewater through any
standard sewer line.
400+
Meat, seafood,
poultry, produce,
dairy, liquids,
prepared foods,
grains, breads, and
pastries; do not
accept large bones,
fat trimmings, clam
or mussel shells,
bread dough,
packaging, paper,
or chemicals.
Water: 15-150 aallons/dav
Enerav: 2.5-13.3 kWh/davc
Bioloaical additives
Processina caDacitv: 500-
2,400 lbs/day
Sewer to WRRF
~$10,000-
50,000d
BioHiTech (2020);
The Composting
Collaborative
(2020);
RecyclingWorksMA
(2018)
ORCA
EcoWaste
Digester
The ORCA digesters use aerobic digestion, a
proprietary blend of microorganisms, and "ORCA
Biochips" (to serve as a substrate for the
microorganisms) to decompose food waste into a
liquid for discharge into the municipal wastewater
system within 24 hours.
79
Food waste
including chicken
bones, egg shells,
meat, fish, and
bread; do not
accept large bones,
liquids, grease,
coffee grinds, and
inorganic waste like
paper, plastics, and
metal
Water: 30-150 aallons/dav
Enerav:
10.32-28.8 kWh/day
Bioloaical additives
Processina caDacitv:
250-2,500 lbs/day
Sewer to WRRF
$10,000-
$50,000
ORCA (2020a);
The Composting
Collaborative
(2020);
RecyclingWorksMA
(2018)
Power Knot
Liquid Food
Composter
(LFC)
Biodigesters
The LFC biodigesters use aerobic digestion, a
proprietary blend of microorganisms and enzymes
(Powerzymes), a proprietary medium called
Powerchips that houses the Powerzymes, and a
rotating arm to liquify food waste within 24 hours.
The digestion is a continuous process so food
waste can be added at any time and all units
connect to the cloud to provide users with
statistics on the weight of the input waste and
usage. Power Knot has a range of eight sizes of
varying processing capacities to meet the differing
needs of users.
Hundreds
"Anything you can
eat," including
fruits, vegetables,
meat, fish, cheese,
bread, eggshells,
and lobster and
shrimp shells; do
not accept large
meat bones, fruit
pits, and oyster
shells.
Water: 14-320 aallons/dave
Enerav: 2.3-25.3 kWh/dav
Bioloaical additives
Processina caDacitv:
45-2,200 Ibs/hr
Sewer to WRRF
$10,000-
$250,000
Power Knot (2020);
The Composting
Collaborative
(2020);
RecyclingWorksMA
(2018)
FOG = fats, oils, and grease; NR = information was not reported.
aThis column includes the number of systems installed in the U.S. This information was current as of 2018 (RecyclingWorksMA, 2018).
b The unit costs in this column are only the cost of purchasing the equipment noted. There are additional costs for installation, maintenance, and any additional material required. The dollar year
of the costs were not provided in the literature, but the date of the source's publication is noted in the references column.
0 Converted from 75-400 kWh/month to 2.5-13.3 kWh/day (conversion factor = 1 month/30 days).
d Pricing information for the largest model (the Sequoia) was not found; a previous version of the BioHiTech biodigester with similar processing capacity (2,400 lbs/day) cost $25,000-50,000.
e Water usage information was not found for the largest model, the Power Knot LCF-1000.
Commercial Food Waste Pre-Processing Technologies
17
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Use in U.S.
Food Waste
Inputs
Other Inputs
4. PULPERS
FIGURE 7. SOMAT SPC-50S PULPING SYSTEM WITH GRINDER
Photo Credit: Somat (2018a)
One of the simplest ways to reduce the volume of food waste is to mechanically press
the liquid component out of food waste using a pulper, also referred to as a press or
dewaterer. A pulper creates a semi-dry end product. Pulpers usually include (or are
paired with) grinders (Figure 7) so that the incoming food waste is first mixed with water
and macerated before the pulper squeezes out excess water. Table 3 provides product
information for two available brands of pulpers. As of 2018, over 600 Somat pulping
systems were in use in the United States (no data was available for other pulper
brands).
Food Waste
Fats/Oils/Grease
Bones/Shells/Pits
X
Compostable Serviceware
44
Water
60-180 gallons/hr
Energy
402 kWh/day
Pulpers
600+ units
Metro Vancouver13 (2014) reviewed dewatering technologies and found that the main
benefits of these systems are that they can rapidly reduce the volume of food waste,
and materials can be continuously processed instead of processed in batches.
Additionally, the labor requirements of running the machine are minimal and the units
are compact and can be installed in small kitchen areas (if electrical and drainage
connections are available).
End Product
Semi-dry
Transportation &
Destination
Truck to compost or
dehydrator
Hauling Weight Reduction
13 Metro Vancouver is a federation of 21 municipalities, one Electoral Area and one Treaty First Nation that collaboratively plans for and
delivers regional-scale services. They are governed by a Board of Directors of elected officials from each local authority. Core services include
drinking water, wastewater treatment and solid waste management.
Commercial Food Waste Pre-Processing Technologies
18
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4.1. Inputs
Pulpers require three inputs: food waste, electricity, and water. While pulpers dewater food waste, the systems
also need additional water to help mix the food waste input in the unit prior to dewatering. They accept all solid or
liquid organic waste (including FOG) in addition to compostable service ware and napkins but do not accept
inorganic waste like glass, metal, wood, and fabric. The water and energy usages for pulpers are claimed to be 60
to 180 gallons of water per hour and 16.75 kWh per hour (energy data for Somat models only) though no
independent research has confirmed these values. Estimates of resources required per ton of food waste
processed are not available. Metro Vancouver (2014) found the biggest negatives of the dewatering systems are
the water and energy usage required to run the machines.
4.2. End Products
Pulpers produce two end products: a semi-dry food waste pulp and excess water removed during the pulping
process. The semi-dry pulp is typically sent to a composting facility or for further processing in a dehydrator
system (see Section 5) to remove additional water (Somat, 2018a, b). The excess water that is extracted from the
system is either sent down the drain or, in some brands like the Somat, first reused to help flush the feeding tray
or trough (RecyclingWorksMA, 2018).
mental Benefits and Impacts
Pulpers require natural resources, namely water and energy, to operate. One of the most significant
environmental benefits of pulpers is that they produce a pulp that can be processed into compost at a centralized
facility. Because pulpers purportedly reduce the volume and weight of commercial food waste by approximately
85 to 87.5 percent, pulpers help reduce the GHG emissions and fuel use associated with hauling food waste via
truck to composting facilities or landfills. No data were found on the magnitude of emissions reduced by pulpers
that divert food waste from landfill and decrease fuel use associated with transporting the waste. Whether
composters may need to add water back to the pulped waste to achieve optimal conditions for composting is not
discussed in the literature, and this could be cause for concern in areas where water is scarce. An LCA would be
needed to compare the environmental impacts of pulping versus not pulping food waste before sending it to a
composting facility or a landfill.
Commercial Food Waste Pre-Processing Technologies
19
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TABLE 3. COMPARISON OF VARIOUS ON-SITE PULPERS
Brand of
Pulper
Description
Use in
the U.S.3
Accepted Inputs from
the Food Waste
Stream
Other Inputs
Transportation
and Destination
Unit Costs
References (Non-
Peer Reviewed
and Manufacturer
Data)
InSinkErator
WasteXpress
The WasteXpress grinds food
waste into a slurry that is fed
into a dewatering press. The
dewatered pulp is discharged
into a ten-gallon bin and the
captured water is sent down the
drain.
NR
Liquid and solid food
waste, napkins
Water: 120-180
gallons/hour0
Energy: NR
Processing
capacity:
700 Ibs/hr
Truck to
compost facility
(hauling weight
reduced 85%), or
Dehydrator
NR
Emerson (2016)
Somat pulpers, which come in
two unit sizes, mix commercial
Somat Close food waste with water and grind
Coupled it into a slurry that is fed into a
Pulpers dewatering press (called the
Hydra-Extractor) to produce a
semi-dry pulp.
All liquid and solid food
waste and compostable
trays, cups, and
600+ plasticware; does not
accept glass, china,
metal, stoneware, wood,
and towels.
Water: 60-120
gallons/hour
Energy: 16.75
kWh/hour
Processing
capacity:
900-1,250 Ibs/hr
Truck to
compost facility
(hauling weight
reduced 87.5%),
or
Dehydrator
$53,000-
$59,000
RecyclingWorksMA
(2018); Somat
(2018a, 2018b)
FOG = fats, oils, and grease; NR = information was not reported.
aThis column includes the number of systems installed in the U.S. This information was current as of 2018 (RecyclingWorksMA, 2018).
b The unit costs in this column are only the cost of purchasing the equipment noted. There are additional costs for installation, maintenance, and any additional material required. The dollar year
of the costs were not provided in the literature, but the date of the source's publication is noted in the references column.
0 Converted from 2-3 gallons/minute to 120-180 gallons/hour (conversion factor = 60 minutes/1 hour).
Commercial Food Waste Pre-Processing Technologies
20
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5. DEHYDRATORS
Dehydrators
Use in U.S.
500+ units
Food Waste
Inputs
Food Waste
Dehydrators transform commercial food waste into a dry end product. Instead of
mechanically dewatering food waste like pulpers, dehydrators, also called "dry
systems," use heat to process food waste and evaporate the liquid component to
create a dry biomass that, after further processing and/or curing, can be used as a soil
amendment, plant fertilizer, or animal feed (CalRecycle, 2020c; Goldstein and Dreizen,
2017; Neale, 2013). The evaporate captured by the system is typically condensed and
then sent down the drain into a municipal sewage system.
Dehydrators often include paddles, agitators, or grinders to stir and macerate the food
waste; they either include a pulper in the unit itself or are preceded by a stand-alone
pulperthat pre-processes the dehydrator input (USCC, 2018; Neale, 2013).
Dehydrators are typically placed near the food preparation area in kitchens
(CalRecycle, 2020c). Manufacturers recommend that locations with higher volumes of
food waste, like college cafeterias, separately pulp their food waste first and then put it
into the dehydrator unit to achieve the greatest volume and weight reduction possible
(Neale, 2013). Because dehydrators are batch systems, not continuous feed systems
(except for the GAIA models discussed below), users may need to temporarily store a
large amount of food waste while the cycle finishes for each batch, which might be
unfeasible for some potential users.
Product information is summarized in Table 4 for four of the most established
dehydrator brands on the market. Overall, the different brands have similar operations:
they heat food waste to evaporate the moisture and agitate it until the cycle is
complete, leaving a pulpy mass of dried food waste (CalRecycle, 2020c). Another type
of dehydrator system briefly mentioned in the literature is the BioGreen Hybrid system.
It combines operating elements of biodigesters with dehydrators to produce dried
organic pellets (Neale, 2013); however, no further information on this hybrid unit could
be found. The processing capacities of the dehydrators on the market range from 66 to
3,300 pounds of food waste per cycle (cycles range from 8 to 22 hours) and reduce the
volume and weight of food waste by 80 to 93 percent, though these specifications
remain unverified through independent research. Several hundred food waste
dehydrators are operating in the United States (Table 4). No information was found on
expected trends in the adoption of these systems in the future.
Metro Vancouver (2014) reviewed dehydrator technologies and found the main benefit
of these systems are that they provide a relatively inexpensive way to greatly reduce
the volume of food waste, with the downside that the end product requires further
processing before it can be used as a soil amendment. The systems are relatively
small and require little labor (i.e., users can "set and forget" until the cycle finishes
running), but interim storage is needed to store newly-generated food waste while a
batch is running (Metro Vancouver, 2014). A potential solution to avoid interim storage
is the use of two dehydrator units, though this may not be a viable option for some
commercial food waste generators (e.g., due to additional expenses and space
requirements). Another disadvantage of these systems is the high energy use required
to evaporate moisture (Metro Vancouver, 2014).
There are a few case studies on dehydrators in the literature highlighting volume
reduction and end uses. A 2-month pilot test of an EcoVim 250 dehydrator at a small
Virginia prison demonstrated that the dehydrator converted 131 pounds of raw food waste into 30 pounds of
dehydrated output, used 3 kw per hour (a cost of $4.50/day), and reduced the prison's solid waste disposal from
Fats/Oils/Grease
X
Compostable Serviceware
Other Inputs
Energy
1.8-700 kWh/cycle
End Product
Semi-dry
Transportation &
Destination
Truck to compost or
landfill
[>80%
Hauling Weight Reduction
OR
Soil Amendment
%
Commercial Food Waste Pre-Processing Technologies
21
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five bags per day to one bag per day (USCC, 2018). A large Hilton Head, South Carolina, resort uses three GAIA
dehydrators to process 20 to 35 percent of its food waste and cures its dehydrator output in an aerobic in-vessel
unit, and the end product is used as a soil amendment for the resort's landscaping (Kachook, 2018; USCC, 2018).
In Montville, Connecticut, Rand Whitney Recycling uses a GAIA 100 dehydrator at its large 7,500-person facility
to reduce the large amount of food waste stored on their loading dock (which was leading to pest issues, including
a mice and fruit fly infestation) (Neale, 2014). These systems were able to eliminate organics hauling costs and
use the dehydrated waste as a small component (~1 percent) of the mulch and composting mix they use for the
substantial landscaping at the facility (Neale, 2014). St. Cloud Hospital in St. Cloud, Minnesota, installed a pulper
and two Somat dehydrators (Figure 8) that reduced the facility's approximately 1,800 pounds of food waste per
day to one 30-gallon receptacle per week (Neale, 2014). In Figure 8, The dehydrator on the right has finished its
cycle and is unloading the dehydrated food waste while the dehydrator on the left is being loaded from food waste
that has been processed with a pulper first.
FIGURE 8. SOMAT DEHYDRATORS, ST. CLOUD HOSPITAL, MINNESOTA
Photo Credit: Somat (2014)
5.1. Inputs
Dehydrators require two inputs: food waste and energy. The dehydrator systems described in the previous
section generally can process a mix of food waste (though the systems vary on their ability to process FOG). The
exceptions are very hard food scraps, such as large bones, coconut shells, avocado pits, and clam/oyster shells.
One case study found that husks and sugar/oil should also not be combined in a batch or molasses will be
created, risking damage to the equipment (Kachook, 2018). The dehydrators can also process compostable
service ware and small amounts of paper and uncoated cardboard. Inorganic waste, like glass, metal, plastic,
cloth, and china, should not be included in the waste.
The energy required for the dehydrators to operate varies by model, ranging from 1.8 to 700 kWh of electricity per
cycle (cycles range from 8 to 22 hours). GAIA also manufactures gas-powered dehydrators that claim to use
approximately 8 to 55 Nm3 of gas14 per cycle. None of these energy use claims has been validated through
independent peer-reviewed research. Estimates of resources required per ton of food waste processed are not
available.
14 Nm3 is a normal cubic meter. It represents the quantity of dry natural gas that occupies one cubic meter under 0°C and an absolute pressure
of 1.01325 bar.
Commercial Food Waste Pre-Processing Technologies
22
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5.2. End Products
Dehydrators produce two end products: dehydrated food waste arid the reconstituted steam (i.e., condensate)
removed by the dehydration process. The dehydrated food waste is intended for use as a soil amendment
(typically after further processing) or composting feedstock, or it may ultimately be landfilled (CalRecycle, 2020c;
Neale, 2013). Data was not available in the literature on prevalence of on-sire curing or of end use. The
condensate produced by dehydrators is typically filtered and sent directly down the drain into a municipal sewage
system.
Some dehydrator manufacturers claim their systems are "Food Waste in, Compost Out," or "Food Waste in,
Potable Water Out" (Neale, 2013), but the dry output is not stable enough to be used directly as a soil
amendment. It requires a curing period or further processing in a composting facility before it is suitable for use as
compost (CalRecycle, 2020c). Curing is the process of allowing the dehydrator output to continue to mature and
fully decompose and stabilize over time (often a few weeks) to prevent odors, growth of large fungal colonies, and
attraction of disease vectors (e.g., flies) (Neale, 2013; Rasmussen and Bergstrom, 2011).
Local and state regulations and policies should be consulted prior to land application to determine permissibility or
compliance with applicable requirements. For example, California specifies that "dried food waste is not compost
or a compost product" as dehydrators do not biologically decompose food waste into a stable substance
(CalRecycle, 2020c). If the dried food waste becomes wet again, it can reabsorb water and regain similar
characteristics to unprocessed food waste like odor and attracting vectors (CalRecycle, 2020c).
In one case study, Loyola Marymount University evaluated the suitability of its dining hall's Somat dehydrator
output for use as a landscaping soil amendment (Rasmussen and Bergstrom, 2011). The dehydrated food waste
did not break down like normal compost and contained increased fungal growth (Figure 9) and attracted flies.
Interviews performed by BioCycle indicate that fungal growth is influenced by the amount of moisture remaining in
the dehydrated food waste after complete processing; the remaining moisture seems to vary from system to
system (Neale, 2013). Overall, composters interviewed by BioCycle expressed they were satisfied with receiving
dehydrated food waste as a composting feedstock due to the levels of valuable nutrients, like nitrogen and
carbon, it contained (Neale, 2013).
FIGURE 9. INCREASED FUNGAL GROWTH OVER TIME ON DEHYDRATED FOOD WASTE
Photo Credit: Rasmussen (2012)
Commercial Food Waste Pre-Processing Technologies
23
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A recent peer-reviewed study assessed the potential end uses of dehydrated food waste. Schroeder et al. (2020)
processed food waste streams from a variety of sources (including a restaurant, cafeteria, grocery store, hospital,
and juice manufacturer) in an EcoVim-66 dehydrator. They analyzed the dehydrated food waste output and
characterized it against several potential end uses, including use as fertilizer, composting feedstock, incineration
feedstock, fish feed, cattle feed, and pelletized fuel15 (Schroeder et al., 2020). Their results indicated that
dehydrated food waste was not suitable for use directly as fertilizer due to low nutrient levels (across all food
waste streams input into the system). However, they found that the dehydrated food waste was particularly suited
for use as fish feed (due to a high protein content), as well as composting or pyrolysis16 feedstock, pelletized fuel,
and cattle feed. Ultimately, their analysis showed that the composition of the food waste stream should be
matched to an end-use application for dehydration to be a worthwhile pre-processing strategy (Schroeder et al.,
2020).
Regarding the dehydrator condensate, no studies confirm that it is potable as some manufacturers claim (Neale,
2013). For example, dehydrator condensate may contain BODs (Neale, 2013).
mental Benefits and Impacts
A significant environmental benefit of dehydration is that it converts food waste into a compostable pulp that can
be cured and used as soil amendment or composting feedstock. Transportation of the pulp may still be needed if
it is not cured or added to a composter on-site, but as dehydrators reduce the volume and weight of food waste by
approximately 80 to 93 percent, emissions and fuel use associated with hauling are greatly reduced. No estimates
were found on the magnitude of emissions saved by dehydrators that divert food waste from landfill and reduce
fuel use associated with hauling.
Some environmental concerns regarding dehydrators require further research. BOD levels in the dehydrator
condensate may be a concern, and the effects of the dehydrator wastewater streams on municipal sewage pipes
and WRRFs are unknown. Additionally, dehydrators require a much larger amount of energy to operate compared
with other types of pre-processing technologies. An LCA would be needed to compare the environmental impacts
of dehydrating food waste and subsequently sending it to a centralized composting facility (or another destination,
such as an AD facility or landfill) versus not dehydrating the food waste and hauling it straight to the intended
destination.
15 Pelletized fuel is a type of biofuel created from compressed organic matter or biomass, including food waste. The pellets are commonly
burned as fuel for uses like commercial or residential heating, cooking, or power generation.
16 Pyrolysis is a thermochemical process in which biomass material, like food waste, is heated to a high temperature in the absence of oxygen.
One of the main products of pyrolysis is biochar, which is similar to charcoal and typically used as a soil amendment (Schroeder et al., 2020).
Commercial Food Waste Pre-Processing Technologies
24
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TABLE 4. COMPARISON OF VARIOUS ON-SITE DEHYDRATORS
Brand of
Description
Use in
the
U.S.a
Accepted Inputs from the
Other Inputs
Transportation and
Unit
References (Non-
Peer Reviewed
Dehydrator
Food Waste Stream
Destination
Costsb
and Manufacturer
Data)
The EcoVim dehydrators use an internal
decomposition chamber that is heated to
180°F to sterilize and evaporate the liquid
EcoVim in the batch of food waste placed into the
Dehydrators system. The drying cycle is complete when
a sensor detects a 0.01 % moisture level.
Six sizes of EcoVim dehydrators are
available.
Food waste and up to 15%
paper and untreated
cardboard per cycle; does not
400+ accept large bones, avocado
pits, grease, and inorganic
waste like metal, plastic,
glass, or petrochemicals.
Water: Not required
Energy: 1.8-10 kWh/cycle
Processing capacity:
66-3,300 lbs/cycle
(cycles last 8-22 hours)
Truck to compost facility
(hauling weight reduced
80-90%), or
Direct soil amendment0,
or
Landfill
$10,000-
$100,000+
The Composting
Collaborative
(2020);
RecyclingWorksMA
(2018); EcoVim
(2015a, 2015b)
GAIA
Dehydrators
GAIA dehydrators heat each batch of food
waste to over 300°F, shred it with a built-in
blade, and churn the food waste during a
10-hour cycle. The GAIA systems also
include a blower chamber that allow
additional food waste to be added while a
cycle is running. The units are available in
a variety of sizes and include both electric
and gas models.
NR
Food waste and up to 10-
15% compostable packaging
per cycle; does not accept
large bones, clam/oyster
shells, avocado pits, FOG,
and inorganic waste like
silverware, cloth napkins,
plastic, glass, or cans.
Water: Not required
Energy: ~13-700 kWh/cycle
(electric system)
8-55 Nm3/cycle (gas system)
Processing capacity:
250-2,500+ lbs/day
(cycles last 10 hours)
Truck to compost facility
(hauling weight reduced
85-93%), or
Direct soil amendment0,
or
Landfill
$10,000-
$100,000+
(electric
system)
$50,000-
$100,000+
(gas
system)
The Composting
Collaborative
(2020)
Hungry
Giant Food
Waste Dry
Dehydration
System
The Hungry Giant system heats food
waste to produce a semi-dry end product
in 7-24 hours. The drying cycle is
complete once the moisture sensor detects
the food waste has reached a ~4-6%
moisture level. The the captured steam is
condensed and discharged down the
drain.
NR
Food waste, paper, and
paper napkins; does not
accept plastics, metals,
medicine, large bones,
seafood shells, and
crustaceans.
Water: Not required
Energy: NR
Processing capacity: NR
(cycles last 8-22 hours)
Truck to compost facility
(hauling weight reduced
80-93%), or
Direct soil amendment0,
or
Landfill
$19,500-
$153,000d
LA County Public
Works (2020);
Hungry Giant
Waste
Technologies
(2019)
The Somat DH-100w dehydrates
Somat DH- commercial food waste by heating it to
10Ow 180°F and mechanically agitating it with
Waste paddles until the dryness sensor stops the
Dehydrator cycle. The captured steam condensate is
discharged down the drain.
All food waste and
compostable service ware;
does not accept any
inorganic waste like glass,
100+ china, metal, stoneware,
fabric, and plastic. Cardboard
or leafy greens can be added
to greasy batches to aid FOG
absorption.
Water: Not required
Energy: 3.0 kWh/cycle
Processing capacity:
220 lbs/cycle
(cycles last 14-16 hours)
Truck to compost facility
(hauling weight reduced
83-93% alone, and 95%
when paired with a pulper),
or
Direct soil amendment0,
or
Landfill
RecyclingWorksMA
-$35,000 (2018); Somat
(2017)
FOG = fats, oils, and grease; NR = information was not reported.
aThis column includes the number of systems installed in the U.S. This information was current as of 2018 unless otherwise noted (RecyclingWorksMA, 2018).
b The unit costs in this column are only the cost of purchasing the equipment noted. There are additional costs for installation, maintenance, and any additional material required. The dollar year
of the costs were not provided in the literature, but the date of the source's publication is noted in the reference column.
0 Further curing or processing may be required before land application. dThis price was current as of 2020 (LA County Public Works, 2020).
Commercial Food Waste Pre-Processing Technologies
25
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6. AEROBIC IN-VESSEL UNITS
Aerobic in-vessel units are a type of on-site food waste pre-processing technology that
produce a semi-dry end product. Vendors also commonly refer to these units as in-
vessel accelerated "composters," however they should not be confused with traditional
composting systems, which have distinct composting and curing periods and produce
stable, mature compost (USCC, 2018). Though the systems are often named
"composters," the end product is not compost and requires further curing and
maturation prior to use as a soil amendment. There are on-site in-vessel composting
systems that do produce a stable compost (e.g., the Susteco AB Big Hanna, HotRot
1206, and Wakan Environmental Inc. CITYPOD) available to commercial food waste
generators, but these processing technologies are outside of the scope of this paper
and are not discussed (see Section 1.2 for a discussion of scope).
Aerobic in-vessel units typically comprise a rotating drum in which food waste (and
other compostable material) is mixed with carbonaceous bulking amendments like
woodchips or sawdust and aerobically decompose into a semi-dry end product using
naturally occurring microorganisms. The systems control the moisture, oxygen level,
and temperature inside the drum. Many of these units are very large, around the size
of a shipping container (Figure 10), so are used by institutions with abundant space
like universities and correctional facilities (Mendrey, 2013).
Product information for several aerobic in-vessel units is summarized in Table 5.
Vendors of the rotary drum systems (e.g., the DT-Environmental EnviroDrum, FOR
Solutions Composting Systems, and XACT Systems Bioreactor) claim that a semi-dry
product is produced within 3 to 7 days, but that the product requires additional curing
prior to use as a soil amendment. Other brands, like the Tidy Planet Rocket, take
longer to process the food waste (~14 days) and require at least 2 to 3 weeks of
curing prior to use. The in-vessel unit capacities range from 114 pounds to over 5
metric tons of food waste per day with a volume/weight reduction of 15 to 80 percent,
depending on the type of food waste input. It is unclear if this volume/weight reduction
excludes the weight of the bulking agent added. The units range in cost from $23,000
to $1,100,000. This higher end includes supplementary equipment options, for
example, a pre-shredder or loading hopper. A little over a hundred systems appear to
be in use across the United States.
A case study on Cedar Creek Correctional Facility near Olympia, Washington, was
reported in BioCycle (Mendrey, 2013). The facility uses the DT-Environmental
EnviroDrum (Figure 10) to process food waste along with wood chips and biosolids.
The materials require approximately 3 to 5 days to pass through the rotating drum.
The material is then unloaded, taken to a curing area, and cured for two to three
weeks prior to use as a soil amendment. The facility noted that it took six to nine
months to perfect the process due to difficulties maintaining a high enough
temperature to reduce moisture content adequately (Mendrey, 2013). No problems
were reported with the cured end product.
Aerobic
In-vessel Units
Use in U.S.
120+ units
Food Waste
Inputs
5^
Food Waste
Bones/Shells/Pits
X
Compostable Serviceware
Other Inputs
4444
Water
None Required
Energy
0.4-400 kWh/day
Biological Additives
Sawdust/Woodchips
End Product
P:
Semi-dry
Transportation &
Destination
s|, 15-80%
Hauling Weight Reduction
Soil Amendment
%
Commercial Food Waste Pre-Processing Technologies
26
-------
FIGURE 10. DT-ENVIRONMENTAL ENVIRODRUM AEROBIC IN-VESSEL UNIT
Photo Credit: DT-Environmental (n.d.)
6.1. Inputs
Aerobic in-vessel units require two inputs: food waste and a bulking amendment, like sawdust or woodchips
(USCC, 2018; Goldstein and Dreizen, 2017). The amount of bulking amendment added depends on the amount
and type of food waste being processed. The energy usage of the aerobic in-vessel units summarized in Table 5
varies greatly depending on the brand and unit size, using 0.4 to 400 kWh of electricity per day. No water is
needed to operate the units. Estimates of resources required per ton of food waste processed are not available.
6.2. End Products
Aerobic in-vessel units produce a semi-dry end product that many vendors and manufacturers refer to as
"compost" or "ready to use" (Goldstein and Dreizen, 2017). However, according to BioCycle's research, only a few
vendors of commercial aerobic in-vessel units produce finished compost that meets scientific standards for
compost stability within 7 days (Goldstein and Dreizen, 2017). The end product of many of these machines is not
mature or stable and has not fully gone through the natural aerobic decomposition process and the mesophilic
and thermophilic stages of composting. Most vendors state they meet pathogen and vector reduction targets in
the vessel but that additional curing is needed prior to use as soii amendment (Goldstein and Dreizen, 2017).
Since curing is necessary, the user needs to have space, either on-site or off-site, to store the maturing
material.17
6.3. Environmental Benefits and Impacts
Due to the very limited information in the literature about aerobic in-vessel units, the full span of environmental
benefits and impacts that these systems have is unknown. The most significant environmental benefit appears to
be that commercial food waste may be recycled (e.g., as a soil amendment) instead of landfiiled. Because this
technology reduces waste volume by as little as 15 percent, there may not be significant reductions in hauling
emissions and fuel use if the output needs to be transported elsewhere. Additionally, the units require bulking
amendments, like woodchips or sawdust, that must either be delivered or produced on-site. More research is
17 While hauling the biodigester output via truck to an AD facility may be feasible, there was no mention of this option in practice in the
literature.
Commercial Food Waste Pre-Processing Technologies
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needed to document these issues.
Commercial Food Waste Pre-Processing Technologies
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TABLE 5. COMPARISON OF VARIOUS ON-SITE AEROBIC IN-VESSEL UNITS
Brand of
Aerobic In-
vessel Unit
Description
Use in
the
U.S.a
Accepted Inputs from
the Food Waste Stream
Other Inputs
Transportation
and Destination
Unit Costsb
References (Non-
Peer Reviewed
and Manufacturer
Data)
DT-
Environmental
EnviroDrum
The EnviroDrum mixes and aerates
food waste and bulking agents (e.g.,
wood chips) with an auger within a
rotating drum. A semi-dry end
product is produced after 72 hours at
55°C. Four models are available that
have various processing capacities.
100+
Food waste, manure,
biosolids, green waste,
paper, bioplastics; does
not accept non-
compostable materials in
high concentrations
Water: Not reauired
Enerav: 25-400 kWh/dav
Sawdust or woodchiDS
Processina caDacitv:
3-25 cubic yards/day
(hauling weight
reduced 20-80%),
or
Direct soil
amendment0
~$90,000-
$350,000
RecyclingWorksMA
(2018)
FOR Solutions
Composting
Systems
FOR Solutions Composting Systems
are in-vessel rotary drum systems
that produce a semi-dry end product
in five days. Five models are
available that have different
processing capacities.
NR
Compostable materials
(excluding FOG) and
small amounts of paper
packaging; does not
accept non-
compostables, glass,
and metals
Water: Not reauired
Enerav:
23.85-65.33 kWh/day
Sawdust or woodchiDS
Processina caDacitv:
250-2,500 lbs/day
(hauling weight
reduced 25%), or
Direct soil
amendment0
$100,000+
The Composting
Collaborative
(2020)
Tidy Planet
Rocket
Composter
The Rocket Composters are
designed to process food wastes
from food service or catering. The
Rockets are continuous feed
systems that produce uncured
compost in 14 days, with an
additional 2-3 weeks of curing
required. There are six available unit
sizes with different processing
capacities.
20+
Cooked and uncooked
meat, fish, fruit, and
vegetables, garden
waste, and animal
waste; does not accept
liquids or large bones
Water: Not reauired
Enerav:
~1.7-45 kWh/day
Sawdust or woodchiDS
Processina caDacitv:
~114 lbs/day-5 metric
tons
(hauling weight
reduced 50%), or
Direct soil
amendment0
$23,000-
$1,100,000
(upper range
includes
supplemental
equipment)
LA County Public
Works (2020); Tidy
Planet (2020);
RecyclingWorksMA
(2018)
XACT Systems
BioReactor
The XACT BioReactor uses a slowly
rotating drum and naturally occurring
aerobic bacteria to decompose large
volumes of food waste into a semi-
dry end product in 4-7 days. The
seven available unit sizes come with
different processing capacities.
NR
Compostable materials,
including paper
packaging; does not
accept metals, large
bones, pits, waxed
cardboard, non-
compostable plastics
Water: Not reauired
Enerav: 0.4-4.5 kWh/dav
Sawdust or woodchiDS
Processina caDacitv:
1,500-2,500+ lbs/day
(hauling weight
reduced 15%), or
Direct soil
amendment0
$50,000-
$100,000+
The Composting
Collaborative
(2020)
FOG = fats, oils, and grease; NR = information was not reported.
aThis column includes the number of systems installed in the U.S. This information was current as of 2018 (RecyclingWorksMA, 2018).
b The unit costs in this column are only the cost of purchasing the equipment noted. There are additional costs for installation, maintenance, and any additional material required. The dollar year
of the costs were not provided in the literature, but the date of the source's publication is noted in the references column.
c Further curing or processing may be required before land application
Commercial Food Waste Pre-Processing Technologies
29
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7. ANALYSIS OF ENVIRONMENTAL
CONSIDERATIONS
This section synthesizes information from across the issue paper to address whether (and, if so, under what
conditions) commercial food waste pre-processing technologies (a) enable or increase the recycling of food
waste; and/or (b) reduce the overall environmental impact of food waste, and thus answer the paper's initial
research questions. While almost no independent, peer-reviewed life cycle assessments have been performed on
these technologies, many helpful insights exist in the literature. This section synthesizes the available data and
presents relevant findings.
Do pre-processing technologies enable or increase the recycling of food waste?
Food waste can be recycled to produce biogas and/or soil amendments with or without pre-processing at the
waste generation site, and the use of on-site pre-processing technologies does not guarantee recycling. However,
all these technologies require source separation of food waste from inorganic waste, which is an important first
step toward recycling. Once food waste is separated, food waste can be recycled on-site or hauled off-site to a
composting, AD, or other recycling facility.
While businesses may use pre-processing technologies to divert food waste from landfills (and thus increase
recycling), that diversion is dependent on subsequent choices by the food waste generator and - if the waste is
being sent down the drain - details of the receiving WRRF and decisions by that WRRF. Food waste may still end
up in a landfill or incinerator after pre-processing.
For technologies that produce semi-dry or dry outputs (pulpers, dehydrators, aerobic in-vessel units), generators
must decide where to send the output, with a landfill or incinerator still an option. Generators may recycle the pre-
processed food waste into a stable soil amendment by hauling it off-site for centralized composting or, in the case
of dehydrators and aerobic in-vessel units, by further curing it on-site or off-site. Facilities may also send the semi-
dry or dry pre-processed food waste to a landfill or incinerator.
For technologies that produce liquid outputs (grinders and biodigesters), generators typically send the output
down the drain. Whether biogas is recovered from the food waste is dependent upon whether the receiving
WRRF has AD capabilities. After treatment (with or without AD) at a WRRF, biosolids remain. These biosolids
may be recycled (with or without further processing) and land applied as a soil amendment - or they may be
landfilled (e.g., because the landfill tipping fees are more economically viable for the WRRF than land application
or other beneficial use options). Generators may also collect liquid outputs and haul them off-site for biogas
recovery via AD at a stand-alone AD or an AD at a WRRF. Biosolids will remain and, as above, may be recycled
and land applied, or landfilled.
Whether the use of these pre-processing technologies increases the frequency of recycling is unknown - and is
impacted by a combination of commercial decisions (i.e., where they send output) and local infrastructure (i.e.,
what recycling options are available). For areas where the local WRRF has AD, the ease of sending food waste
down the drain after pre-processing (and through the sewer to the WRRF) may encourage recycling. In areas
where composting or AD facilities are not conveniently located, technologies like dehydrators and aerobic in-
vessel units may offer an opportunity for recycling; but in these same locations, sending food waste down the
drain will not result in recycling.
Do pre-processing technologies reduce the environmental impact of food waste?
The net environmental value of commercial food waste pre-processing technologies is not well understood and
likely depends upon whether they lead to increased recycling of food waste (i.e., the previous research question).
Based upon the information available, the core environmental benefits of pre-processing systems appear to be:
Commercial Food Waste Pre-Processing Technologies
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1) Reduced fuel use and GHG emissions from waste hauling. If the food waste is to be transported by
truck to its next destination, be it a composting or AD facility or a landfill or incinerator, many of these
technologies significantly reduce the volume and/or weight of food waste that must be transported,
thus reducing associated fuel use and GHG emissions. These technologies also may reduce the
frequency of hauling required.
2) Analytical tools to aid food waste prevention. Some types of pre-processing technologies, such as
biodigesters, come equipped with scales and analytical tools, providing users with useful information
about the types and amounts of food wasted, which can support waste prevention. Food waste
information and tracking tools, such as those from Leanpath or Winnow, can also be procured without
a biodigester (Leanpath, 2021; Winnow, 2021).
3) Enabling the creation of recycled products. Dehydrators and aerobic in-vessel units can transform
food waste into a useable product on-site, after additional processing and/or curing time, thus directly
enabling recycling. Technologies that produce a liquefied output (grinders and biodigesters) also
prepare food waste for AD; however, food waste can be hauled off-site for recycling without pre-
processing.
However, these benefits must be balanced against known and potential environmental impacts of the use of these
technologies, such as:
1) Energy and water use to operate the pre-processing technology. Some pre-processing technologies
use substantial amounts of energy and water during operation. A comparison of energy use by
technologies, and the fuel savings during transportation and energy recovery for pre-processed food
waste hauled to AD, for technologies that reduce hauling weight was not available in the literature.
2) Fugitive methane emissions. As food waste travels through the sewer system and continues to break
down, it may generate methane emissions. A comparison of food waste fugitive emissions from
sewer and from landfill was not available in the literature, nor was a comparison of landfill methane
emissions from unprocessed and pre-processed food waste.
3) Energy use for sewer transport and treatment at WRRF. Where sewer conveyance is assisted by
pumping systems, rather than gravity systems, transporting liquefied waste to WRRF increases the
system's energy use. Increased energy may also be needed to treat liquefied food waste, which is
typically has higher levels of BOD, TSS, and FOG than sewage. Liquefied food waste can also
contain nitrates, phosphates, unbeneficial bacteria, and other pathogens that must be treated. Similar
concerns may arise for treatment of excess water removed during the pulping process and
reconstituted steam removed by the dehydration process.
4) Increased pollution in direct discharges from combined sewer systems. Where combined sewer
outfall (i.e., one pipe transports rainwater runoff, domestic sewage, and industrial wastewater) exists,
increased food waste being discharged into the sewer could increase the organic pollutant load of
direct discharge into surface waters after heavy rains.
5) Reduced focus on the prevention of food waste. Many pre-processing technologies reduce the costs
associated with managing food waste (e.g., hauling costs and landfill tipping fees), thus may lower
the financial incentive for reducing the amount of food waste generated. While no literature exists on
commercial sector food waste decision-making, research on the residential sector demonstrates
decreased concern or guilt about food waste when recycling occurs that may lead to decreased
prevention of food waste (McDermott et al., 2019; Neff et al., 2015).
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The available literature does not quantify these potential benefits and impacts, thus the balance between them is
not yet fully understood. In general, pre-processing technologies that send wastewater down the drain partially or
wholly shift the burden of food waste management from landfills to WRRFs and municipal sewage systems. The
net environmental burden of this shift has not been thoroughly explored in the literature.
It is also unclear from the available literature how many of these technologies compare to one another as well.
The limited data available indicates hauling liquid outputs by truck from the commercial generator to an AD facility
may provide greater GHG benefits than sending the food waste down the drain to a WRRF with AD (California
State Water Resources Control Board (SWRCB), 2019; Parry, 2012) but other pathways have not yet been
compared.
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8. CONCLUSIONS AND RESEARCH GAPS
In this issue paper, EPA sought to understand the environmental benefits and impacts of commercial food waste
pre-processing technologies, identify any potential unintended environmental consequences, and inform whether
(and to what extent) policymakers should encourage the use of each class of pre-processing technology.
Because interest in food waste pre-processing, like food waste in general, has grown rapidly in recent years, it is
an emerging subject of scientific research. The state of the science and conclusions that can be drawn from the
current body of research are presented in Section 8.1. Section 8.2 identifies research gaps that could be help
inform policymakers and businesses about the environmental value of these technologies.
Food waste pre-processing technologies, such as grinders, biodigesters, pulpers, dehydrators, and aerobic in-
vessel units, are being employed by commercial food waste generators in the United States to meet economic or
environmental goals and/or comply with state and local organic waste laws. Many of these technologies are
marketed with strong messaging about their environmental benefits, but little peer-reviewed research has been
done to evaluate these claims. While only a limited number of food waste pre-processing technologies are being
used in the United States currently, this number may grow due to economic, environmental, or regulatory drivers.
Thus, it is important to understand the environmental value of these technologies, both in current use and if they
were used at scale (i.e., by many facilities) in a particular geographic area. All the pre-processing technologies
discussed in the report require energy and/or water to operate, and this must be considered in any analysis of the
environmental value of these technologies.
Currently, grinders and biodigesters appear to be the most popular pre-processing choices of commercial food
waste generators (Wright and Jones, 2017), but pre-processing technologies are often used in concert with one
another. For example, grinders are often paired with pulpers to remove excess water from the slurry created by
the grinder if the intended destination is not a WRRF, or a dehydrator may be paired with a pulper (with or without
a grinder) to further remove water (Figure 11).
Technologies like grinders and biodigesters, which typically discharge liquid effluent into the sewer system,18 shift,
the burden of managing food waste from landfills to WRRFs and municipal sewage systems, and the implications
of this shift are not weli understood. Sending additional organic waste, high in BOD, TSS, and FOG, through the
sewer can result in fugitive methane emissions and may require additional energy for pumping systems and water
18 At least one model offers the ability to collect effluent and haul it by truck to an AD facility.
Commercial Food Waste Pre-Processing Technologies 33
8.1. Conclusions
FIGURE 11. PULPER PAIRED WITH A DEHYDRATOR TO MAXIMIZE
THE WATER REMOVED FROM FOOD WASTE
Photo Credit: Somat (2012)
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treatment processes. This waste can also cause operational problems for the water treatment systems, especially
in low flow, combined, or aging systems. For example, effluent with high BOD may interact with sulfates from
sewage to create hydrogen sulfide, which corrodes pipes, and effluent with FOG may clog pipes resulting in
"slugs" that must be removed. There are also regulatory implications, including those under the National
Pretreatment Program, for pollutants like FOG that interfere with WRRF operations. If the receiving WRRF has
AD capabilities, bioenergy may be created from the energy potential of the food waste. However, not all WRRFs
have AD, and the food waste may lose energy potential as it travels through the sewer system and earlier parts of
the WRRF. In cities and states with landfill bans for commercial organics, utilizing these on-site systems may help
a generator stay under the 1 ton/week threshold, and thus continue to utilize disposal (rather than recycling) for
what remains.
Many of the potential environmental impacts of grinders and biodigesters are not quantified in the literature, so
they cannot yet be compared to the impacts of landfilling food waste (the most common alternative) or to hauling
unprocessed food waste to facilities for AD or composting (recommended over landfilling in EPA's Food Waste
Recovery Hierarchy). Available data indicates greater GHG emissions benefit for trucking effluent from the
generator to an AD unit versus sending the same effluent via sewer conveyance to a WRRF with AD for this
reason. Also, biodigesters typically include information and tracking tools which can enable the prevention of food
waste (the most preferable strategy in EPA's Food Waste Recovery Hierarchy). The realized benefits of these
tools have not yet been reported in the literature.
A shift in financial burden may also occur with the use of pre-processing technologies that send food waste down
the drain. Commercial food waste generators that grind and send food waste down the drain avoid paying tipping
fees to landfills for this waste, but unless fees are imposed on the generators by the WRRF, municipal ratepayers
may bear the added costs of sewer maintenance and additional treatment. In addition, many of the concerns with
these technologies could multiply in scale if grinders and/or biodigesters become more broadly adopted among
commercial food waste generators. For example, if many more generators within the service area of a municipal
WRRF begin to dispose liquified food waste down the drain, the treatment system may not be able to handle the
increased load.
Other technologies, such as pulpers, dehydrators and aerobic in-vessel units, produce dry outputs which can be
further processed or cured on-site into soil amendments, or sent to composting facilities, landfills, or incinerators.
The soil amendments created are not compost in the traditional sense, and much remains to be learned about
their stability and suitability for different uses. The dry outputs are lower in weight and volume than unprocessed
food waste, so if it is sent off-site, hauling-related fuel use and GHG emissions are reduced. Pulper and
dehydrators remove water from the food waste and typically send this water down the drain, which may raise
similar concerns to those noted above for grinders and biodigesters.
Based the current state of available research, EPA cannot conclude whether the environmental benefits of pre-
processing commercial food waste using these technologies (and sending the waste for further processing at a
composting or AD facility, WRRF, landfill, or incinerator) are greater than simply hauling unprocessed waste
directly to the intended destination, be it a composting or AD facility, WRRF, landfill, or incinerator. EPA
encourages the diversion of food waste streams to composting or AD operations, rather than landfills and
incinerators, but cannot yet conclude whether or how the use of pre-processing technologies changes the
environmental benefits or impacts of these choices.
A robust body of peer reviewed information is not available that documents and evaluates the overall benefits and
impacts to the environment of the pre-processing technologies discussed in this issue paper. In the absence of
this information, this issue paper summarized the limited information available in non-peer-reviewed sources,
including case studies, interviews, and manufacturer specifications and marketing materials. Given the
uncertainties and lack of independent data on these technologies, additional research is needed to better
understand the environmental benefits and costs of pre-processing technologies. The limited information that is
available should be substantiated through peer-reviewed research or an independent testing organization before
drawing actionable conclusions.
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8.2. Research Gaps
Based on the information reviewed for this issue paper, additional data collection and original research
(independent of equipment manufacturers) on the topics discussed below will increase understanding of the
overall environmental benefits and impacts associated with the use of food waste pre-processing technologies.
Addressing these research gaps can help decision makers and stakeholders evaluate the available technologies
relative to one another and relative to other food waste management options. Better information and more
informed decision making has the potential to reduce the overall environmental footprint of food waste in the
United States, to increases awareness about the environmental issues associated with food waste management,
and to encourage innovation in technology and practices. Priority research needs include:
¦ Life cycle assessment of the use of on-site pre-processing technologies in addition to, or in lieu
of, traditional food waste pathways. In-depth LCA studies are needed to determine the net
environmental value of using commercial food waste pre-processing technologies. Technologies should
be considered individually and in combinations seen in the field (i.e., a grinder, pulper, and dehydrator
paired together on-site). In order to perform this life cycle assessment, many of the knowledge gaps
listed below must be filled.
¦ Impact of pre-processing technologies on generators' choice among food waste pathways. Data
should be collected on the current destination (e.g., down the drain, composting, anaerobic digestion,
landfill, or combustion) of pre-processing end products to determine whether they may be enabling or
increasing recycling of food waste.
¦ Impacts of "wet" pre-processing outputs on municipal sewer systems and WRRFs. Research is
needed to determine whether technologies that send liquefied food waste down the drain (i.e., grinders
and biodigesters) and those that send wastewater extracted from food waste down the drain (i.e.,
pulpers and dehydrators) have adverse effects on the municipal sewer system and WRRFs. Potential
concerns include pipe corrosion, clogs, and the impacts of receiving large or inconsistent volumes of
additional organic matter with high levels of BOD, TSS, and FOG on WRRFs. In addition, issues of
scale should be studied, such as the potential change to the net environmental burden if growing
adoption of these technologies leads to more liquified food waste being sent down the drain.
¦ Energy potential of pre-processed food waste slurry sent "down the drain." Research is needed to
clarify how the potential for energy or biogas to be created from food waste is impacted when the waste
first travels through the sewer system and passes through various levels of wastewater treatment prior
to reaching the anaerobic digestion unit at the WRRF. Research is also needed to quantify the impact of
biodigester use on energy potential of food waste prior to sewer conveyance.
¦ Fugitive methane emissions from sewer conveyance. Research is needed to quantify fugitive
methane emissions from pre-processed food waste as it travels through the sewer.
¦ Independently verified operating and performance data. All the current data on the technologies'
processing capacities, volume/weight reduction, and energy and water usage included in this paper are
provided by technology manufacturers. Although the information may be accurate, independent, peer-
reviewed research is needed for it to be substantiated. In addition, consistent measurement methods
and metrics would support better comparisons among technologies. For example, the specifications
should be measured per ton of food waste (e.g., gallons of water used per ton of food waste, kWh of
energy used per ton of food waste).
¦ Land application of dehydrated food waste. A limited number of case studies on this topic provide
mixed and inconclusive findings. In some case studies, the land application of dehydrated food waste
results in fungal growth, odor, and vector attraction, like flies. Other case studies have found there are
Commercial Food Waste Pre-Processing Technologies
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no noticeable issues when the dehydrated food waste is land applied. Outcomes might depend on the
type of food waste feedstock, the moisture content, the local climate, curing time, destination (e.g., farm
or lawn), or other factors. More specific studies are needed to determine if land applying cured,
dehydrated food waste is recommended in certain instances or with certain type of food waste inputs.
¦ Contamination introduced by pre-processing technologies. Food waste streams, including pre-
processed food waste, may contain or be associated with undesirable contaminants19 such as plastic
(e.g., from packaging), chemicals of concern, or pathogens. Research is needed to characterize how
levels and types of contamination are affected by commercial food waste pre-processing.
19 A discussion of plastic and persistent chemical contaminants in food waste streams can be found in two other EPA reports in this series:
"Emerging Issues in Food Waste Management: Plastic Contamination" fEPA 600-R-21-001. August 2021) and "Emerging Issues in Food
Waste Management: Persistent Chemical Contaminants" fEPA 600-R-21-002. August 2021).
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APPENDIX A. LITERATURE SEARCH
METHODOLOGY
This appendix presents the literature search methodology used to identify, screen, and manage literature sources
for From Farm to Kitchen: The Environmental Impacts of U.S. Food Waste and associated issue papers like this
one on pre-processing technologies. The objective of the literature search was to identify the latest scientific
information about food waste and food waste reduction, including emerging technologies and approaches for
prevention, reuse, and recycling. In addition, analysis of the literature helped to identify knowledge gaps and the
most important areas for future scientific research.
Section A.1. Methodology for Peer-Reviewed Literature describes the literature search methodology for peer-
reviewed literature sources, and Section A.2 describes the identification of governmental and non-governmental
reports that are not published in the peer-reviewed scientific literature, referred to as "gray literature" in this
methodology.
This literature search identified and prioritized 3,219 peer-reviewed sources, 1,723 of which were screened as
relevant to the scope of the From Farm to Kitchen report and issue papers. These sources, as well as the key
gray literature (see Section A.2. Methodology for Gray Literature) and additional key sources identified in
supplemental, targeted literature searches, served as the primary corpus of literature from which literature
synthesis and report development were performed. The report and associated issue papers were developed by
primarily using the literature identified through this methodology but were not limited to this set of literature as
additional sources were identified subsequently (e.g., from peer-review recommendations).
A.1. Methodology for Peer-Reviewed Literature
Peer-reviewed literature was identified with a search of selected publication databases using keywords and
Boolean logic defined in this section. Titles and abstracts of the publications returned by the literature search were
processed to eliminate duplicates and then screened to identify a subset of "key" sources that meet criteria for
relevance and usefulness for the report or issue papers. Key sources were "tagged" to pre-defined topics to assist
authors in identifying the most relevant sources for particular topics covered in the report.
Peer Reviewed Literature Search Strategy
The search of peer-reviewed literature focused on references relevant to the scope of the food waste report and
issue papers from 2010-present, with special priority given to more recent papers, which were considered to be
2017-present. A targeted search to identify review papers from 2014-present was performed. During
development of the report and issue papers, additional targeted searches were performed as needed within the
2010-present corpus of literature, and subject matter experts also identified key sources, some of which were
dated in 2020 or 2021.
The following databases were searched for relevant peer-reviewed literature:
- AGRICOLA (AGRICultural OnLine Access): AGRICOLA records describe publications and resources
encompassing all aspects of agriculture and allied disciplines, including animal and veterinary sciences,
entomology, plant sciences, forestry, aquaculture and fisheries, farming and farming systems, agricultural
economics, extension and education, food and human nutrition, and earth and environmental sciences;
Produced by the National Agricultural Library (NAL), U.S. Department of Agriculture.
- AGRIS: AGRIS facilitates access to publications, journal articles, monographs, book chapters, and grey
literature - including unpublished science and technical reports, theses, dissertations and conference
papers in the area of agriculture and related sciences; Maintained by the Food and Agriculture
Organization of the United Nations (FAO).
- EBSCO: EBSCOhost Research Databases: Academic Search Complete; Energy & Power Source.
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- PubMed: US National Library of Medicine National Institutes of Health.
- Web of Science: Web of Science Core Collection, refined by Research Area. Clarivate Analytics.
Table A-1 outlines the searches performed and the combinations of keyword sets and Boolean operators used to
search each database. Four distinct sets of keywords were used to capture references with relevance to food
waste, pathways of food waste and food waste reduction, environmental impacts of food waste, and emerging
issues in the area of food waste. Sets were combined using Boolean logic to identify relevant references for
screening and evaluation. Search results were limited to publications written in English.
For each search, all references were downloaded into EndNote and then DeDuper was used to remove duplicate
references (i.e., references that appeared in more than one of the databases searched). DeDuper is a tool that
uses a two-phase approach to identify and resolve duplicates: (1) it locates duplicates using automated logic, and
(2) it employs machine learning to predict likely duplicates which are then verified manually.
TABLE A-1. SEARCH STRATEGY KEYWORDS
Set
Search Keywords and Boolean Logic
Food Waste
Food AND (waste OR loss OR "FLW') AND (prevention OR system OR consumed
OR Surplus OR Excess OR Uneaten OR reduction OR supply OR demand OR Per
capita OR Edible OR Inedible OR Safety OR recall OR packaging OR Preventable
OR Drivers OR Spoilage OR perishable OR Freshness OR harvest OR transportation
OR Processing OR manufacturing OR supermarket OR grocer* OR reuse OR
recycling OR seasonal OR projection OR future OR economic)
Pathways
("Source reduction" OR Awareness OR education OR campaign OR LeanPath OR
Photodiary OR storage OR Labeling OR (Refrigerator AND temperature) OR Cellar
OR Frozen OR "Meal kits" OR packaging OR Donation OR Upcycling OR "Animal
feed" OR "Anaerobic digestion" OR Co-digestion OR "Aerobic processes" OR
Composting OR "Controlled combustion" OR Incineration OR Landfill OR "Land
application" OR de-packaging OR "shelf life")
Environment
Environment* AND (use OR usage OR impacts) AND (climate OR "Air emissions" OR
"Water pollution" OR Pesticide OR Land OR Irrigation OR Energy OR fertilizer OR
water OR Herbicides))
Emerging Issues
((Compost* or compostable) AND (packaging OR serviceware OR utensil OR
tableware OR plate OR bowl))
To efficiently screen results, references were prioritized using topic extraction, also referred to as clustering, with
ICF's Document Classification and Topic Extraction Resource (DoCTER) software. The titles and abstracts from
all search results (i.e., AGRICOLA, AGRIS, EBSCO, PubMed, and Web of Science) were run through DoCTER's
topic extraction function. Each study was assigned to a single cluster based on text similarities in titles and
abstracts. Clusters were prioritized or eliminated for screening based on the relevance of the keywords identified.
Only prioritized studies published from 2014-present were screened for relevance.
Peer Reviewed Literature Screening and Tagging
The sources identified by the literature search were screened to identify those that are considered "key" sources
for the report and issue papers. To be considered a key source, a publication had to be relevant to the project
scope and exhibit at least most of the general attributes provided in EPA's Quality Assurance Instructions for
Contractors Citing Secondary Data, summarized below:
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¦ Focus: the work not only addresses the area of inquiry under consideration but also contributes to its
understanding.
¦ Verify: the work is consistent with accepted knowledge in the field or, if not, the new or varying
information is documented within the work; the work fits within the context of the literature and is
intellectually honest and authentic.
¦ Integrity: Is the work structurally sound? In a piece of research, is the design or research rationale logical
and appropriate?
¦ Rigor: the work is important, meaningful, and non-trivial relative to the field and exhibits enough depth of
intellect rather than superficial or simplistic reasoning.
¦ Utility: the work is useful and professionally relevant; it contributes to the field in terms of the
practitioners' understanding or decision-making on the topic.
¦ Clarity: Is it written clearly and appropriately for the nature of the study?
Relevance to the project scope was evaluated against the specific topics and criteria. In particular, relevant topics
included:
¦ Characterization of U.S. food waste, including but not limited to kinds of food, sources, amounts, and
reasons for loss or waste.
¦ Reduction strategies, including composting, anaerobic digestion, secondary industrial uses, animal
feed, donation, and source reduction.
¦ Lifecycle environmental costs and benefits of choices between and within levels of the EPA food
recovery hierarchy.
¦ Pre-processing technologies (e.g., grinding, heating, digestion) and their environmental implications
in use, including their potential to help reduce food waste.
¦ Food packaging and service ware and their relationships to food waste, including ways packaging
may impact prevention and recycling of food waste or use and value of products created by
recycling.
¦ Chemical contaminants (e.g., PFOS, PFAS, persistent herbicides) and the risk and problems posed
in food waste streams.
¦ Food system trends to identify well-recognized trends in the U.S. food system that may impact food
waste and summarize what has been written about their potential impacts.
¦ Unharvested or unutilized crops that do not reach the consumer market.
¦ Waste or loss during transportation, food processing/manufacturing/packaging facilities, or
wholesale food distributors.
¦ Waste or loss at supermarkets (e.g., unsold or spoiled products), restaurants, and households.
¦ Existing economic, social, and cultural drivers of food waste or barriers to food waste prevention,
reuse, and recycling efforts.
The following topics were not considered relevant:
¦ Unutilized livestock (e.g., due to market forces, routine mortality) or unharvested or unutilized feed
crops.
¦ Regulatory drivers of food waste or barriers to food waste prevention, reuse, and recycling efforts.
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¦ Broad economic impacts (e.g., on the agricultural sector) of food waste production, prevention,
reuse, and recycling efforts; economic costs and benefits for entities resulting from food waste
production and reduction strategies (e.g., as drivers).
The litstream™ tool was used to screen for key sources based on reference titles and abstracts, litstream™
facilitates screening by one or two independent reviewers, automatically compares categories, and identifies
discrepancies for resolution by another individual, litstream™ also allows users to design flexible data-extraction
forms, thus enabling the review team to perform the screening and tagging steps of the systematic review within
one software tool.
For publications identified as key sources, full text files were retrieved with EPA's Health & Environmental
Research Online (HERO) database as requested by authors. Then, authors used the full text of the key sources
to confirm topic area relevance and incorporate them into their literature synthesis.
A screening and tagging guidance document was developed to provide instructions and keywords associated with
the tags. To ensure internal consistency and accuracy of the litstream™ screening and tagging, a pilot screening
of 5-10 reference (per reviewer) was performed to provide feedback to the screening team. Additionally, 10% of
each reviewer's assigned citations were reviewed by a second reviewer. Discrepancies between the primary and
secondary reviews were resolved by lead authors.
A.2. Methodology for Gray Literature
Identifying key sources in the "grey literature" was essential to a comprehensive review and synthesis of the
report and issue papers. The review methodology for grey literature included a search strategy and approaches
for screening and tagging key sources.
Grey Literature Search Strategy
The peer-reviewed literature search was supplemented with relevant grey literature from the sources listed below:
¦ Grey literature publications cited by key sources identified by the EPA from prior related research.
These sources were screened as potential key sources.
¦ Grey literature publications identified by peer reviewers and subject matter experts who reviewed pre-
peer review drafts of the reports and issue papers (see the acknowledgments sections in the report
and each issue paper). These sources were considered key sources without screening.
¦ Targeted google and domain searches for selected governmental or non-governmental organizations.
The titles and URLs of potential sources identified by the searches were compiled in an Excel file used for
subsequent screening.
Grey Literature Screening and Tagging
Grey literature was screened in Excel using the key source criteria defined for peer-reviewed literature (see
Section A.1. Methodology for Peer-Reviewed Literature Screeners applied the criteria to each of the potential
sources in the database file described above (i.e., titles and URLs identified from searches). For each URL, the
screeners evaluated the sources by reviewing abstracts, executive summaries, forewords, keyword lists, or tables
of contents. When a screener identified a key source, they recorded additional information including publishing
organization, author names, and year for the source to proceed to tagging.
Tagging was only performed for the grey literature identified as key sources, and the same tags as used for peer-
reviewed literature (see Section A.1. Methodology for Peer-Reviewed Literature) were used for grey literature,
screeners applied the tags in columns within Excel.
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oEPA
U.S. Environmental Protection Agency
Office of Research and Development
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