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Accomplishments

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AgSTAR is one of EPA’s climate-protection partnership programs, which promotes investments in alternative energy technologies by encouraging the development and adoption of anaerobic digestion (AD) technology in the livestock sector. Since 2000, the use of biogas recovery systems with AD in the livestock sector has continued to increase, which has led to meaningful reductions in greenhouse gas emissions.

2014 Use and Benefits of AD in the Livestock Sector

AgSTAR estimates that approximately 247 AD systems were operating at commercial livestock farms in the United States in 2014. Learn more about AD Projects.

Anaerobic digestion of livestock waste reduces greenhouse gas (GHG) emissions in two ways:

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Environmental and Energy Benefits

Greenhouse Gas Emission Reductions (2000-2014)
Column chart showing the annual increase in greenhouse gas emissions reductions from 2000 through 2014. In 2014, AD systems directly reduced emissions by an estimated 3.44 million metric tons of carbon dioxide equivalent and approximately 0.54 million metric tons of carbon dioxide equivalent was avoided, producing a total emission reduction of 3.97 million metric tons of carbon dioxide equivalent.

2014 Total = Estimated 3.97 MMTCO2e

The chart above distinguishes the portion of the total emissions that were directly reduced and the emissions avoided from the reduction in fossil fuel use.

To be consistent with the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4)Exit EPA Disclaimer methodology, AgSTAR’s emission reduction calculations have been updated to reflect a global warming potential (GWP) of 25 for methane for 2014 and prior years.

Energy Generation (2000-2014)
Column chart showing the annual increase in the amount of energy produced by AD projects from 2000 through 20143. Approximately 890 million kilowatt hours equivalent of energy was generated by AD systems on livestock farms during 2014.

2014 Total = Approximately 940 million kilowatt hours (kWh) equivalent

AD systems generate usable energy each year by using biogas to generate electricity, as a boiler fuel for space or water heating, or for a variety of other uses.


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Visit the GHG Calculator

Greenhouse Gas Equivalencies

Understanding greenhouse gas emission reductions is challenging, so it helps to think of the environmental benefits in terms that are more relatable. Using EPA’s Greenhouse Gas Equivalencies Calculator, equivalencies are presented below for the total estimated emissions reductions from AD systems on livestock farms in 2014 (3.97 MMTCO2e).

CO2 emissions from one of the following:

More information 446,719,928 gallons of gasoline consumed
More information 4,264,232,009 pounds of coal burned
More information 52,555 tanker trucks’ worth of gasoline
More information 362,226 homes’ energy use for one year
More information 546,080 homes’ electricity use for one year
More information 21,287 railcars worth of coal burned
More information 165,416,667 propane cylinders used for home barbeques

Annual GHG emissions from one of the following:

More information 1,422,939 tons of waste sent to a landfill
More information 203,485 garbage trucks of waste recycled instead of landfilled



Carbon sequestered by one of the following:

More information 101,794,872 tree seedlings grown for 10 years
More information 3,254,098 acres of U.S. forests in one year
More information 30,654 acres of forests preserved from conversion to cropland in one year

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Anaerobic Digester System Designs and End Uses of Biogas

Operating AD System Designs in 2014 (Total = 247)

System Type Count Percentage
Plug Flow 102 42%
Complete Mix 91 38%
Covered Lagoon 36 15%
Induced Blanket Reactor 5 2%
Fixed Film 3 1%
Anaerobic Sequencing Batch Reactor 3 1%
Constant Volume 2 1%
Unknown 5 2%

Operational AD systems use several types of technologies to generate power. Complete mix and mixed plug flow designs accounted for 42 percent of all operational AD systems in 2014.


Trends in AD System Designs (2000-2014)
Line chart showing trend of AD system designs from 2000 through 2014. In 2014, 102 were plug flow, 91 projects were complete mix, 36 were covered lagoon. All other known designs accounted for 13 projects and the design was unknown for 5 projects.

The number of projects operating in 2014 is shown in parentheses.

Plug flow and complete mix systems continue to be the most common designs. AgSTAR anticipates that the use of complete mix designs will continue to expand as farms take advantage of opportunities offered through codigestion, which refers to the simultaneous anaerobic digestion of multiple organic wastes in one digester.

End Uses of Biogas in 2014 (Total = 247)

End Use Count Percentage
Combined Heat and Power (CHP) 124 50%
Electricity 89 36%
Boiler/Furnace Fuel 15 6%
Flared Full Time 12 5%
Unknown 7 3%

Captured biogas is used to generate electricity, as a fuel for boilers or furnaces, treated to create compressed natural gas, or for a combination of uses.


Trends in End Uses of Biogas (2000-2014)
Line chart showing the trend of biogas uses from 2000 through 2014. In 2014, 124 projects used biogas for combined heat and power, 89 generated electricity, 15 used biogas as fuel for boilers or furnaces, 12 flared the biogas full time, and the uf the biogas at 7 projects was unknown.

The number of projects operating in 2014 is shown in parentheses.

Combined heat and power continues to be the most common use for biogas followed by electricity generation. Visit the projects page to access details about AD projects across the United States.

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