Anaerobic Digesters Continue Growth
in U.S. Livestock Market
November 2007
Construction of anaerobic digestion
systems for livestock manure stabilization
and energy production has accelerated
substantially in the past several years. EPA
estimates that there are currently about
111 digesters operating at commercial
livestock facilities in the United States.
In 2007, farm digester systems produced
an estimated 215 million kilowatt-hours
equivalent of useable energy (Figure 1).
Besides generating electricity (170 million
kWh), some operations use the gas as a
boiler fuel, some upgrade the gas for
injection into the natural gas pipeline, and
m11 ii ii
2003 2004
Year
Figure 1. Trends in Energy Production by Anaerobic Digesters - 2000 through
2007
some flare gas for odor control. Many of the projects
that generate electricity also capture waste heat for
various on-farm thermal uses.
Digester Profiles
The majority of commercially operating systems (Figure
2) are plug flow and complete mix reactors (both tanks
and covered lagoons) operating at mesophilic
temperatures (95° - 105°F). The remainder of the
Miscellaneous/
Unknown —
7
Covered Lagoon
19
systems include covered lagoons operating at ambient
temperature, and attached growth and induced blanket
reactors. European-style complete mix systems are also
emerging in the U.S. market.
Although the majority of systems are still farm owned
and operated, using only livestock manure, other
approaches are emerging. These include the
commingling of high strength organic wastes (e.g., food
waste, ag waste, cheese whey) to increase gas
production per unit volume of reactor; third party
owned/operated systems; centralized systems handling
manure from multiple farms; and direct gas sales to
customers or gas utilities. Most digester systems (80
percent) currently are found in the dairy industry in the
Midwest, West, and Northeast (Figure 3).
Figure 2. Number of Operating Anaerobic Digesters by Technology
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[ Number Operating / Total Energy Producltar
Energy production in MWhequivalent
Figure 3. 2007 Operating Manure Digesters
Some of the factors that are influencing the growth in
interest in anaerobic digester systems include:
1) improved digester designs and demonstrated biogas
production and engine-generator set reliability,
2) concern about odors and other environmental
impacts of manure management practices, 3) an
increase in governmental cost share programs, 4) an
increase in interest by utilities in purchasing electricity
and biogas to meet renewable portfolio standards and
green energy programs, and 5) the potential for sale of
carbon credits to generate income.
Financial Incentives
Financial incentives have increased the deployment rate
of manure digester systems. For example, grants
awarded under Section 9006, Renewable Energy and
Energy Efficiency, of the 2002 Farm Bill have been one
of the primary methods for farms to
partially fund installation of
commercially proven livestock waste
digestion technologies. Since 2003,
USDA has awarded a total of about $31
million for anaerobic digestion systems
(Figure 4).
A number of State programs have
provided significant funding for the
installation of anaerobic digester
systems historically, with many more
dedicating resources to this activity.
Some of the state programs providing
funding include the California Energy
Commission, Iowa Department of Natural Resources,
New York State Energy Research and Development
Authority, Pennsylvania Energy Harvest Grant Program,
Wisconsin Focus on Energy, and the emerging North
Carolina Lagoon Replacement Program. While some of
these programs have shifted to evaluating energy,
economic, and environmental performance of
operational systems, many still provide significant
financial and technical resources to assist livestock
producers in developing anaerobic digester systems.
2006
$2.9 million
2007
$1.8 million
2003
$12.9 million
2005
$4.4 million
2004
$9.3 million
Figure 4. Annual USDA Funding for Anaerobic Digesters at
Livestock Operations
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