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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