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Anaerobic Digestion: Greenhouse Gas
Emission Reduction and Energy Generation
Kelsi Bracmort
Analyst in Agricultural Conservation and Natural Resources Policy
January 4, 2010
Congressional Research Service
7-5700
www.crs.gov
R40667
CRS Report for Congress
P
repared for Members and Committees of Congress
c11173008
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Anaerobic Digestion: Greenhouse Gas Emission Reduction and Energy Generation
Summary
Anaerobic digestion technology may help to address two congressional concerns that have some
measure of interdependence: development of clean energy sources and reduction of greenhouse
gas emissions. Anaerobic digestion technology breaks down a feedstock—usually manure from
livestock operations—to produce a variety of outputs including methane. An anaerobic digestion
system may reduce greenhouse gas emissions because it captures the methane from manure that
might otherwise be released into the atmosphere as a potent greenhouse gas. The technology may
contribute to the development of clean energy because the captured methane can be used as an
energy source to produce heat or generate electricity.
Anaerobic digestion technology has been implemented sparingly, with 125 anaerobic digestion
systems operating nationwide. Some barriers to adoption include high capital costs, questions
about reliability, and varying payment rates for the electricity generated by anaerobic digestion
systems. Two sources of federal financial assistance that may make the technology more
attractive are the Section 9007 Rural Energy for America Program of the Food, Conservation, and
Energy Act of 2008 (2008 farm bill, P.L. 110-246), and the Renewable Electricity Production Tax
Credit (26 U.S.C. §45).
Congress could decide to encourage development and use of the technology by (1) identifying the
primary technology benefit, so as to determine whether it should be pursued in the framework of
greenhouse gas emission reduction or clean energy development; (2) determining if the captured
methane will count as a carbon offset; and (3) considering additional financing options for the
technology.
This report provides information on anaerobic digestion systems, technology adoption, challenges
to widespread implementation, and policy interventions that could affect adoption of the
technology.
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Contents
Introduction ................................................................................................................................ 1
What Is an Anaerobic Digestion System? .................................................................................... 2
Characteristics of Anaerobic Digestion Systems .......................................................................... 5
Methane Capture................................................................................................................... 5
Biogas Quality and Use.........................................................................................................7
U.S. Adoption of Anaerobic Digestion Technology...................................................................... 9
Startup Financing ........................................................................................................................ 9
Anaerobic Digestion Obstacles.................................................................................................. 10
Issues for Congress ................................................................................................................... 12
Figures
Figure 1. Anaerobic Digestion System Schematic........................................................................ 2
Figure 2. Manure Characteristics and Handling Systems for Specific Types of Anaerobic
Digestion Systems.................................................................................................................... 3
Figure 3. Plug Flow AD System .................................................................................................. 3
Figure 4. Complete Mix AD System Schematic ........................................................................... 4
Figure 5. Greenhouse Gas Emissions (Methane and Nitrous Oxide) from Managed Waste
in 2005..................................................................................................................................... 7
Tables
Table 1. Methane Emissions from Animal Agriculture (Tg CO2e) ................................................ 6
Table 2. Methane Emissions from Manure Management (Tg CO2e) ............................................. 6
Table 3. Energy Content for Select Fuels ..................................................................................... 8
Contacts
Author Contact Information ...................................................................................................... 12
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Introduction
An anaerobic digestion system (AD system) captures the methane that may otherwise be released
from conventional manure handling methods, and has the potential to reduce greenhouse gas
emissions and produce clean energy. Absent such technology, confined animal feeding operations
typically collect and store manure (e.g., in a waste storage facility) under anaerobic conditions,
which produces the potent greenhouse gas methane. The methane is released into the atmosphere
as the manure decomposes while being stored. Livestock producers handle large quantities of
manure on a daily basis that emit methane.1 Some estimate that livestock operations produce
more than a billion tons of manure yearly2 and that 0.7% of total U.S. methane emissions are
from managed manure.3 Through methane capture, anaerobic digestion has the potential to reduce
these emissions.
In addition, anaerobic digestion of manure produces biogas—a combination of methane, carbon
dioxide, and trace amounts of other gases that can be used for renewable energy purposes or
flared.4 Recent legislation pertaining to agricultural sources of renewable energy has focused
primarily on corn-based ethanol and cellulosic ethanol for liquid fuel purposes, and not biogas.5
The economic environment is not currently favorable to profit from the investment required to
compress biogas6 produced from an AD system into a liquid fuel. There are, however, several
successful cases where an engine-generator set has been used to generate electricity from the
biogas or the biogas is burned in a boiler to produce heat. Biogas from an AD system could be
used to assist livestock producers in an effort to have an energy self-sufficient operation as well
as, potentially, to sell electricity to the local utility.
There are 125 AD systems operating nationally. Some factors that may be responsible for the low
technology adoption rates are high capital costs, reliability concerns, and payment rates for the
electricity generated. Congress may consider encouraging increased adoption of the technology
by (1) identifying the primary technology benefit, so as to determine whether AD should be
pursued in the framework of greenhouse gas emission reduction or clean energy development; (2)
determining if the captured methane will count as a carbon offset; and (3) considering additional
financing options for the technology. Moreover, Congress may receive insight on collaborative
techniques by monitoring the first public-private partnership agreement between the U.S.
Department of Agriculture and the Innovation Center for U.S. Dairy to reduce greenhouse gas
1 For example, the amount of manure excreted from one lactating dairy cow is estimated at 150 pounds per day based
on the American Society of Agricultural and Biological Engineers (ASABE) Manure Production and Characteristics
Standard D384.2, March 2005.
2 Amanda D. Cuellar and Michael E. Webber, “Cow Power: The Energy and Emissions Benefits of Converting Manure
to Biogas,” Environmental Research Letters, vol. 3 (2008).
3 The agriculture sector was responsible for roughly 6% of all U.S. greenhouse gas emissions in 2007, approximately
11% of which is attributable to methane emissions from managed manure. U.S. Environmental Protection Agency,
2009 U.S. Greenhouse Gas Inventory Report, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2007,
2009.
4 Flaring is the combustion of gas without commercial purposes. Flaring emits fewer greenhouse gases than simply
releasing the biogas as is into the atmosphere. See the “Biogas Quality and Use” section for additional details.
5 For more information on agriculture-based renewable energy, see CRS Report RL34130, Renewable Energy
Programs in the 2008 Farm Bill, by Megan Stubbs, CRS Report RL34738, Cellulosic Biofuels: Analysis of Policy
Issues for Congress, by Kelsi Bracmort et al., and CRS Report RL32712, Agriculture-Based Renewable Energy
Production, by Randy Schnepf.
6 Biogas consists of 60%-70% methane, 30%-40% carbon dioxide, and trace amounts of other gases.
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emissions from dairy operations by 25% by 2020.7 One goal of the agreement is to “accelerate
and streamline the process for adopting anaerobic digesters by the United States dairy farm
operators through various USDA programs.”8
This report provides information on AD systems, technology adoption, and challenges to
widespread technology implementation, and explores the issues facing Congress concerning
adoption of the technology.
What Is an Anaerobic Digestion System?
Most manure management systems used on livestock operations store the manure in an open
facility, allowing the manure to decompose naturally, which releases the potent greenhouse gas
methane into the atmosphere. By contrast, an AD system feeds manure into a digester that breaks
it down in a closed facility in the absence of oxygen (see Figure 1). The digested feedstock9 is
contained for a period of time10 as anaerobic bacteria decompose the manure to produce several
outputs, including biogas, liquid effluent, and dry matter. The captured biogas is flared (see
footnote 4) or used for energy. The liquid effluent may be applied to the land as a fertilizer. The
digested dry matter may be sold as a soil amendment product or used for animal bedding. AD
systems have other benefits (e.g., odor reduction) that may curb negative impacts of livestock
operations, including environmental pollution.11
Figure 1. Anaerobic Digestion System Schematic
Source: U.S. EPA, The AgSTAR Program.
7 U.S. Department of Agriculture, “Agriculture Secretary Vilsack, Dairy Producers Sign Historic Agreement to Cut
Greenhouse Gas Emissions by 25% by 2020,” press release, December 15, 2009, http://www.usda.gov/wps/portal/
!ut/p/_s.7_0_A/7_0_1OB?contentidonly=true&contentid=2009/12/0613.xml.
8 Memorandum of Understanding between the United States Department of Agriculture and The Innovation Center for
U.S. Dairy, December 15, 2009, http://www.usda.gov/documents/FINAL_USDA_DAIRY_GHG_AGREEMENT.pdf.
9 The feedstock is usually manure, but can also include other organic matter. The digestion of two or more types of
organic matter is referred to as co-digestion.
10 The time required for the manure to be treated is referred to as the hydraulic retention time (HRT). HRT is normally
expressed in days.
11 For more information on environmental issues facing the livestock community, see CRS Report RL32948, Air
Quality Issues and Animal Agriculture: A Primer, by Claudia Copeland, and CRS Report RL33691, Animal Waste and
Hazardous Substances: Current Laws and Legislative Issues, by Claudia Copeland.
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An AD system is designed and constructed to suit the needs of an individual livestock operation
and is typically selected based on the total solids (TS) content12 of the manure and the manure
handling system (see Figure 2). Other criteria taken into consideration when building an AD
system include the feedstock quantity, feedstock quality, feedstock availability, feedstock
handling, demand for effluent, use of captured biogas, and transportation logistics (e.g., feedstock
may be transported to an AD system if it is not available on-site, or effluent transported to a
receiving entity if not used on-site).
Figure 2. Manure Characteristics and Handling Systems for Specific Types of
Anaerobic Digestion Systems
Source: US EPA, The AgSTAR Program.
Figure 3. Plug Flow AD System
Source: EPA, The AgSTAR Program.
12 Total solids content for manure is the amount of solid material remaining after all moisture has been removed from a
sample.
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Three Common AD System Types Found in the United States
Covered lagoon AD system:
• Usual y an earthen structure containing manure affixed with a flexible geosynthetic cover
(e.g., high density polyethylene).
• Typically operated at ambient temperature.
• Biogas production may occur seasonal y when weather is warmer.
• Ideal for manure with 0.5%-2% TS content.
• Time required to treat manure ranges from approximately 30 to 60 days.
• Low capital costs.
Plug flow AD system (see Figure 3):
• Usually a rectangular concrete tank affixed with a flexible geosynthetic cover.
• Digestion occurs in a plug fashion where the digested manure exits the system as raw
manure enters the system.
• Heated structure.
• Ideal for manure with 11%-13% TS content.
• Time required to treat manure ranges from approximately 18 to 20 days.
Complete mix AD system (see Figure 4):
• Usually a round concrete or steel tank.
• Heated structure.
• Capable of digesting a range of feedstock with varying total solids content.
• Ideal for manure with 3%-10% TS content.
• Time required to treat manure ranges from approximately 5 to 20 days.
• High capital costs.
Figure 4. Complete Mix AD System Schematic
Source: Renewable Energy Association.
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AD systems in the United States are in use on dairy cow, swine, and poultry operations. More
than 75% of the operating AD systems are located on dairy cow operations. Some argue that less
complex AD systems could be constructed on dairy cow operations at a lower cost and that the
manure could be easily transported to the AD system, thus making them more economically
appealing. Others contend that fewer AD systems are installed on swine operations because many
swine operations currently store liquid manure in pits beneath the livestock; the producer would
need to redesign the swine operation to incorporate an AD system. Installation of an AD system
on a swine operation may also be more expensive if a storage facility must be constructed to
contain the digested feedstock. Some assert that AD systems are not a favorable addition to a
poultry operation partly because the litter is dry and may require more resources for transport to
an AD system and additional inputs to digest.
Characteristics of Anaerobic Digestion Systems
Methane Capture
Methane (CH4) is one of the primary greenhouse gases associated with the agricultural sector.13
The odorless, colorless, flammable gas is potent because it is 21 times more effective at trapping
heat in the atmosphere than carbon dioxide (CO2) over a 100-year timeframe.14 In other words, it
takes 21 tons of CO2 to equal the effect of 1 ton of CH4. Methane has a relatively short
atmospheric lifetime (approximately 12 years) when compared to the atmospheric lifetime for
carbon dioxide, which has a half-life of roughly 100 years; thus some argue that efforts to capture
methane from anthropogenic sources may provide near-term climate change abatement.
Major sources of methane emissions from animal agriculture are enteric fermentation15 and
manure management (see Table 1). While enteric fermentation emissions are much larger than
manure management emissions, they are also much more difficult (nearly impossible) to control.
Emission factors16 affiliated with methane released from enteric fermentation, and conversion
factors17 affiliated with methane released from a manure management system, are used to
estimate overall methane emissions from animal agriculture. Estimation incorporates a multi-step
process that takes into account livestock population data, waste characteristics, waste
management system data, and other variables.
13 For additional information concerning agricultural sources of methane, see CRS Report RL33898, Climate Change:
The Role of the U.S. Agriculture Sector, by Renée Johnson
14 The IPCC Second Assessment Report issued in 1996 assigned methane a Global Warming Potential of 21. Global
Warming Potential is an estimate of how much a greenhouse gas affects climate change over a quantity of time relative
to CO2, which has a GWP value of 1.
15 Enteric fermentation is the production and release of methane via eructation (burping) and flatulence as ruminant
animals digest their feed.
16 The amount of methane produced by an animal expressed per mass unit for one year (kg CH4/head/year).
17 The potential amount of methane produced from a manure management system for a given animal expressed in
percent. The factor for dry manure management systems may vary according to climate.
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Table 1. Methane Emissions from Animal Agriculture (Tg CO2e)
Source 2005 2006
2007
Enteric fermentation
136.0
138.2
139.0
Manure management
41.8
41.9
44.0
Source: US EPA, 2009 U.S. Greenhouse Gas Inventory Report
Notes: Select values obtained from EPA, 2009 U.S. Greenhouse Gas Inventory Report, Table 6-1. A teragram
(Tg) is equivalent to 1 trillion grams. A Tg CO2e (teragram of carbon dioxide equivalent) is a principal unit of
measurement across greenhouse gases. Agricultural activities and livestock emit an assortment of greenhouse
gases in various quantities given numerous factors. CO2e is used to compare greenhouse gases emitted from
different sources on the same basis.
Capturing methane with an AD system is beneficial because it reduces emissions of a harmful
greenhouse gas from an agricultural source of methane: managed manure (e.g., manure stored in
pit storage, an anaerobic lagoon, or a storage facility).18 Swine and dairy cattle are the two
dominant livestock emitters of methane for managed manure (see Table 2). Emissions from
managed manure vary on a statewide basis depending on the livestock population and the manure
handling systems in place (see Figure 5).
Table 2. Methane Emissions from Manure Management (Tg CO2e)
Animal Type
2005
2006
2007
Swine 18.6
18.3
19.7
Dairy cattle
17.2
17.5
18.1
Poultry 2.7
2.7
2.7
Beef cattle
2.4
2.5
2.4
Horses 0.8
0.8
0.8
Sheep 0.1
0.1
0.1
Goats +
+
+
Source: US EPA, 2009 U.S. Greenhouse Gas Inventory Report
Notes: Select values obtained from EPA, 2009 U.S. Greenhouse Gas Inventory Report, Table 6-6. The + symbol
denotes a value that does not exceed 0.05 Tg CO2e. A Tg CO2e (teragram of carbon dioxide equivalent) is a
principal unit of measurement across greenhouse gases. Agricultural activities and livestock emit an assortment
of greenhouse gases in various quantities given numerous factors. CO2e is used to compare greenhouse gases
emitted from different sources on the same basis.
18 Manure that is not managed (e.g., manure deposited in a pasture from livestock grazing) has low methane emissions,
but relatively high nitrous oxide emissions. The greenhouse gas nitrous oxide is 310 times more effective at trapping
heat in the atmosphere than carbon dioxide over a 100-year timeframe.
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Figure 5. Greenhouse Gas Emissions (Methane and Nitrous Oxide)
from Managed Waste in 2005
Source: USDA, U.S. Agriculture and Forestry Greenhouse Gas Inventory: 1990-2005.
Captured methane may qualify as a carbon offset because the methane would no longer be
released directly into the atmosphere. Carbon offsets19 are a facet of the climate change cap-and-
trade program debate currently underway in the 111th Congress. Accurate quantification and
verification of the methane captured from an AD system requires robust data, observed or
inferred, to ensure that actual reductions are occurring as projected.
Biogas Quality and Use
Another AD system benefit is the production of biogas, which can be used as a renewable energy
source. Biogas consists of 60%-70% methane, 30%-40% carbon dioxide, and trace amounts of
other gases (e.g., hydrogen sulfide, ammonia, hydrogen, nitrogen gas, carbon monoxide). Biogas
can be explosive if exposed to air, depending on the concentration of methane in a confined
space. The quality (i.e., heat value) and amount of biogas produced varies based on the hydraulic
retention time of the AD system, the manure total solids content, and temperature.
Biogas can be used to produce heat or generate electricity. The biogas may be burned in a boiler
for space heating or water heating on-site. Another option is to use an engine-generator set to
create electricity from the biogas. Biogas that is upgraded to pipeline quality20 may be sold to a
natural gas utility. Typically a producer will decide on only one use for the biogas—either
19 A carbon offset is a measurable reduction, avoidance, or sequestration of GHG emissions from a source not covered
by an emission reduction program. For more information on carbon offsets, see CRS Report RL34705, Potential Offset
Supply in a Cap-and-Trade Program, by Jonathan L. Ramseur, and CRS Report RL34436, The Role of Offsets in a
Greenhouse Gas Emissions Cap-and-Trade Program: Potential Benefits and Concerns, by Jonathan L. Ramseur.
20 Pipeline quality is achieved by the removal of carbon dioxide and other contaminants so that only the methane is sold
to the natural gas utility.
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generating electricity or producing heat—due to the expense associated with energy generation
and boiler equipment. Few choose to sell the biogas to a natural gas utility.21
If electricity is generated from the captured biogas, it may be sold to a utility in addition to its on-
site use.22 A rule of thumb is that 7-10 cows supply fuel for 1 kilowatt capacity.23 Sales to a utility
require a contractual agreement between the producer and the local utility provider that typically
outlines safety, reliability, and performance standards. Additionally, any federal and state
environmental requirements must be met (e.g., AD system generators may have to meet Best
Available Control Technology24 requirements). Net metering,25 a preferred form of billing for
many renewable electricity generators, is an option for producers selling the electricity generated
to electric utilities in 40 states.26
Biogas may be used as a fuel if it contains at a minimum a 50% concentration of methane
(CH4).27 The biogas must be cleaned, upgraded, and compressed if it is to be used in a mobile
engine. Cleaning biogas removes hydrogen sulfide. Removing any moisture and carbon dioxide
upgrades the biogas and increases the British thermal unit (Btu) value.28 With an energy content
of 600 Btu/ft3 for biogas with approximately a 60% methane concentration, biogas is a low-Btu
fuel compared to other fuels (see Table 3). A high-Btu fuel is necessary for energy applications
requiring greater amounts of power.
Table 3. Energy Content for Select Fuels
Fuel Energy
Content
Biogasa 600
Btu/ft3
Natural gas
1,000 Btu/ft3
Propane 92,000
Btu/gal on
Diesel fuel
138,000 Btu/gal on
Coal 25,000,000
Btu/ton
Source: James C. Barker. Methane Fuel Gas from Livestock Wastes: A Summary. North Carolina State University
Cooperative Extension Service, EBAE 071-80, 2001.
a. Assumes a 60% methane concentration.
21 Elizabeth R. Leuer, Jeffrey Hyde, and Tom L. Richard, “Investing in Methane Digesters on Pennsylvania Dairy
Farms: Implications of Scale Economics and Environmental Programs,” Agricultural and Resources Economics
Review, vol. 37, no. 2 (October 2008), pp. 188-203.
22 The quality of the biogas, measured by its Btu value, necessary to generate electricity varies depending on the
engine.
23 Wisconsin Focus on energy, Farm Energy from Manure, REN2003-0602, 2002, http://focusonenergy.com/files/
Document_Management_System/Renewables/farmenergyfrommanure_factsheet.pdf.
24 Best Available Control Technology (BACT) is a pollution control standard mandated by the Clean Air Act.
25 Net metering is an energy metering method that uses a bidirectional meter, thus allowing the meter to run backwards
if a customer generates more electricity than being consumed.
26 Interstate Renewable Energy Council , Map of state net metering rules, 2009, http://www.dsireusa.org.
27 Jenifer Beddoes, Kelsi Bracmort, and Robert Burns et al., An analysis of energy production costs from anaerobic
digestion systems on U.S. livestock production facilities, USDA Natural Resources Conservation Service, October
2007.
28 A Btu (British thermal unit) is a unit of energy used to express the heating value of fuels.
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Biogas is flared if not used for energy purposes. Flaring the biogas destroys the methane and
yields the greenhouse gas carbon dioxide (CO2) and water.29 Carbon dioxide has a longer
atmospheric lifetime (~100 years) and is less effective at trapping heat in the atmosphere when
compared to methane, which has an approximate atmospheric lifetime of 12 years. Some view the
release of the carbon dioxide due to biogas flaring as more environmentally acceptable than
releasing unused biogas into the atmosphere.30 Environmental impacts of flaring methane require
further investigation to determine flare efficiency under varying wind speeds and various biogas
compositions.
U.S. Adoption of Anaerobic Digestion Technology
Federal funding (discussed in the following section) has supported the installation of 125 AD
systems nationwide operating with a total annual energy production of approximately 244,000
megawatt-hours (MWh).31 Approximately 90% of the AD systems are currently generating
electricity. These AD systems restrict roughly 36,000 metric tons of methane, or 756,000 metric
tons of carbon dioxide equivalent (CO2e), from entering the atmosphere, which is comparable to
the annual greenhouse gas emissions from approximately 138,000 passenger vehicles.32
Startup Financing
Congress as well as states have enacted legislation that provides financial assistance for AD
system installation. Loans, grants, tax credits, tax exemptions, and production incentives are
common financial assistance tools available at the federal and state levels.33 One principal source
of federal funding is the Section 9007 Rural Energy for America Program (REAP) of the Food,
Conservation, and Energy Act of 2008 (2008 farm bill, P.L. 110-246).34 Section 9007 authorizes
$255 million in mandatory funding for 2009-2012, with an additional $25 million per year in
discretionary funding. For FY2009, $55 million is available, part of which is to be distributed to
eligible applicants for AD system projects. Grants dispensed to applicants are not to exceed 25%
29 Stoichiometric equation for biogas combustion: CH4 + 2O2 → CO2 + 2H2O.
30 According to the California Climate Action Registry, Livestock Project Reporting Protocol Version 2.1, August
2008, the CO2 released from flaring the biogas is considered biogenic and therefore more environmentally acceptable.
See http://www.climateregistry.org/resources/docs/protocols/project/livestock/
CCARLivestockProjectReportingProtocol2.1.pdf.
31 U.S. Environmental Protection Agency, The AgSTAR Program. Online AgSTAR Digest: Spring 2009. The
AgSTAR Program is a voluntary effort jointly sponsored by the U.S. Environmental Protection Agency, the U.S.
Department of Agriculture, and the U.S. Department of Energy. The program encourages biogas capture and utilization
at animal feeding operations that manage manures as liquids and slurries. One megawatt-hour (MWh) is equivalent to
1,000 kWh. The energy generated could provide approximately 21,724 average homes with electricity for one year
assuming the average residential home uses 936 kWh on a monthly basis (DOE).
32 Passenger vehicle estimate computed using the EPA Greenhouse Gas Equivalencies Calculator available at
http://www.epa.gov/solar/energy-resources/calculator.html. Calculation based on 2005 average fuel economy
assumptions and average vehicle miles traveled at 19.7 mpg and 11,856 miles per year, respectively. Additional
information on passenger vehicle calculation available at website provided.
33 For a comprehensive list of AD system financing tools, visit the EPA AgSTAR Funding Database website at
http://www.epa.gov/agstar/resources/funding.html and consult the EPA AgSTAR document Funding On-Farm Biogas
Recovery Systems: A Guide to Federal and State Resources, at http://www.epa.gov/agstar/pdf/ag_fund_doc.pdf.
34 REAP is an extension of the Farm Security and Rural Investment Act of 2002 (2002 farm bill, P.L. 107-171).
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of the cost of the activity. Loan guarantees dispensed to applicants are not to exceed $25 million.
The maximum amount of a combined loan and grant can be no more than 75% of the cost of the
activity. Approximately $40 million in loans and grants from Section 9006 of the 2002 farm bill
was allocated for the construction of 121 AD system projects. A minimal share of the 121 AD
systems are operational, while most are still under development.35
Another source of financial assistance offered for anaerobic digestion projects is the Renewable
Electricity Production Tax Credit (REPTC; 26 U.S.C. §45).36 The REPTC grants a one cent per
kilowatt-hour tax credit for electricity generated from open-loop biomass (e.g., agricultural
livestock waste nutrients).37 The tax credit period is five years for an open-loop biomass facility
using agricultural livestock waste placed in service after October 22, 2004, and before August 9,
2005. The tax credit period is 10 years for a facility placed in service after August 8, 2005.
Anaerobic Digestion Obstacles
Some technology deployment and adoption barriers exist because of the complexity involved in
designing and operating an AD system. Thus far, a significant number of successful AD systems
are operated by producers who have sophisticated anaerobic digestion technology knowledge.
Some assert that the technology will reach its full potential when an array of concerns are
addressed. Some challenges include:38
• Lack of economic return. AD systems are capital-intensive. The cost fluctuates
depending upon the system type, system size, livestock operation type, and
factors specific to the site. Capital costs generally include the AD system cost,
the engine-generator set, the engineering design process, and installation. Extra
costs are incurred for additional elements (e.g., a post-digestion solids separator,
utility and interconnection fees). System costs range from a few hundred
thousand dollars to a few million dollars.39 A covered lagoon AD system could
cost at a minimum a few hundred thousand dollars.40 A complete mix AD system
or plug flow AD system can cost a few million dollars. An analysis of 38 AD
systems indicates that approximately one-third of the total system cost is
estimated to be spent on the electrical generation equipment.41 A producer may
find it feasible to forgo producing electricity to save money and to use the biogas
35 William F. Lazarus, Farm-Based Anaerobic Digesters as an Energy and Odor Control Technology: Background and
Policy Issues, USDA Office of the Chief Economist Office of Energy Policy and New Uses, Agricultural Economic
Report Number 843, February 2008, http://www.usda.gov/oce/reports/energy/AnerobicDigesters0308.pdf.
36 For more information on renewable energy policy, see CRS Report RL33578, Energy Tax Policy: History and
Current Issues, by Salvatore Lazzari, and CRS Report R40412, Energy Provisions in the American Recovery and
Reinvestment Act of 2009 (P.L. 111-5), coordinated by Fred Sissine.
37 For more information about the Renewable Electricity, Refined Coal, and Indian Coal production credit visit
http://www.irs.gov/pub/irs-pdf/f8835.pdf
38 No relative importance is intended by the order in which challenges are listed.
39 AgSTAR Program, Estimating Anaerobic Digestion Capital Costs for Dairy Farms, February 2009,
http://www.epa.gov/agstar/pdf/conf09/crenshaw_digester_cost.pdf.q
40 Assuming the producer is only purchasing the cover and the biogas recovery equipment to add to an existing lagoon.
41 Jenifer Beddoes, Kelsi Bracmort, and Robert Burns et al., An analysis of energy production costs from anaerobic
digestion systems on U.S. livestock production facilities, USDA Natural Resources Conservation Service, October
2007.
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produced on-site for heating purposes, which still requires a boiler. A general
approximation is that 300-500 head for a dairy cow operation and 2,000 head for
a swine operation is the minimum number of head necessary to produce
electricity with an AD system at a possible profit.42
• Reliability. Some argue that producers hesitate to adopt anaerobic digestion
technology due to the poor performance rate observed in the 1970s. AD system
performance has improved over time due to better engineering, construction
materials, and management. Communicating current performance rates may
provide producers with the information needed to gain more confidence in the
improved technology. AD system performance data may be expanded with
mandatory reporting on a periodic basis by an independent third party, which
might bolster performance claims made by some AD system construction
companies. Information (e.g., demonstration projects, long-term performance
records) that communicates recent performance may mitigate producers’ doubts
about technology reliability and may verify energy generation and greenhouse
gas emission reduction data reported.43 Some producers and construction
companies are opposed to a national reporting program because of the release of
potentially proprietary information.
• Lack of an engineering practice standard. A national practice standard that lists
performance criteria, safety precautions, technical components, and design
elements and has undergone review from a standards developing organization is
not available for anaerobic digestion technology. Some producers may be
reluctant to make a financial investment in a technology that may or may not
meet future environmental and technical requisites. The USDA Natural
Resources Conservation Service (NRCS) issued an anaerobic digester
conservation practice standard in 2003 that is currently undergoing public review
and comment.44
• Utility collaboration. Rates paid by utilities for the electricity generated from AD
systems vary by state and within each utility. It may not be economically
attractive for a producer to sell the renewable energy generated depending on the
cost per kilowatt-hour offered. Some net-metering agreements pay wholesale
rates instead of retail rates for the electricity generated, thus limiting potential
profitability. Some gas utility companies may be reluctant to accept a renewable
energy fuel originating from a technology with no official standard that may
contaminate an otherwise clean energy source.
• Unquantifiable co-benefits. Certain benefits (e.g., odor reduction) may not be
quantifiable in dollar terms but may add to the value of an AD system.
42 U.S. Environmental Protection Agency, Market Opportunities for Biogas Recovery Systems, EPA-430-8-06-004; The
Minnesota Project, Profits from Manure Power, http://www.mnproject.org/pdf/AD%20economics.pdf.; Wisconsin
Focus on Energy, Farm Energy from Manure, http://focusonenergy.com/files/Document_Management_System/
Renewables/farmenergyfrommanure_factsheet.pdf.
43 For an example of reporting criteria to communicate technology performance, see John H. Martin, A Protocol for
Quantifying and Reporting the Performance of Anaerobic Digestion Systems for Livestock Manures, January 2007.
44 The conservation practice standard must be adhered to for AD systems that will be constructed with financial or
technical support from USDA NRCS. Conservation practice standards are provided at http://www.nrcs.usda.gov/
technical/standards/nhcp.html.
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Anaerobic Digestion: Greenhouse Gas Emission Reduction and Energy Generation
• Operation and maintenance. AD systems perform optimally when they are well
maintained. Some estimate that daily AD system operation and maintenance may
require 30 minutes to an hour. The producer may have to acquire a level of
technical expertise not previously necessary.
Issues for Congress
The 111th Congress is faced with proposed legislation centered on clean energy and climate
change mitigation. There may be an opportunity for the agricultural community, particularly the
livestock industry, to participate in forthcoming efforts for energy generation and greenhouse gas
emission reduction with anaerobic digestion technology. Prior to incorporating anaerobic
digestion technology into legislation, Congress may choose to consider:
• Identifying the primary benefit offered by an AD system. Selecting a primary
benefit (renewable energy generation or greenhouse gas emission reduction) may
assist with determining which policy vehicle could support technology
deployment (e.g. energy legislation, climate change legislation, agricultural
legislation). A single message regarding the technology benefit may encourage
producers to adopt the technology to achieve the policy goal.
• Determining if the methane captured from the technology will be included as a
carbon offset. The climate change debate underway in the 111th Congress
includes carbon offsets as a potential greenhouse gas emission reduction strategy.
Producers may find it economically worthwhile to invest in AD technology if it
produces an additional revenue source in the form of carbon offsets. If the
methane captured and combusted is not treated as a carbon offset, will the 111th
Congress consider regulating the methane captured as a pollutant?
• Identifying whether alternate sources of financial support for technology
implementation are appropriate. Most of the federal financial assistance
available comes in loans and grants for AD system construction. A shorter
payback period for an AD system may occur if producers receive a more
substantial monetary sum for the energy generated and transferred to a utility
company via a federal electricity rate premium. Additional tax credits may also
improve the economic return for AD technology (e.g., raising the tax credit value
for agricultural livestock waste nutrients to that of closed-loop biomass for the
Renewable Electricity, Refined Coal, and Indian Coal Production Credit).
Author Contact Information
Kelsi Bracmort
Analyst in Agricultural Conservation and Natural
Resources Policy
kbracmort@crs.loc.gov, 7-7283
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