Anaerobic digestion is a biological process in which bacteria digest biomass
in an oxygen-free environment and produce a gas principally composed of methane
(CH4) and carbon dioxide (CO2), otherwise known as
biogas. This process is often used for sewage treatment or for managing animal waste. However, almost any
organic material can be processed in this manner. This includes biodegradable waste materials such as waste paper,
grass clippings, leftover food, sewage and animal waste.
The process of anaerobic digestion consists of
three basic steps. The first step is the decomposition or hydrolysis of plant
or animal matter. This step breaks down the organic material to usable-sized
molecules such as sugar. The second step is the conversion of decomposed matter
to organic acids. And finally, the acids are converted to biogas.
The biogas can be used to co-generate heat and
electricity, or it can be scrubbed (separated into purified streams of gases) and
compressed into a liquid fuel or used as an industrial chemical base for
creating other products. In addition to
biogas, anaerobic digesters can produce
raw material by-product streams that can be further refined into higher value
products such as fertilizer.
digestion of dairy wastes is receiving a lot of attention. Currently there are
approximately 600 operating dairy farms in the state, that manage nearly
250,000 dairy cows. These dairies are often identified as sources of odor,
water and air pollution, including greenhouse gas emissions. The use of
anaerobic digesters to help manage dairy wastes can alleviate many of these
environmental problems, while providing farmers with a new source of
Washington State University’s Center for Sustaining Agriculture and
Natural Resources has taken the lead in developing anaerobic digestion technologies
for dairy operations in Washington.
Through the Climate Friendly Farming initiative, WSU is investing in research,
technology development, demonstration and educational activities to advance the
use of this technology throughout the state. For more information on anaerobic
digestion and WSU activities related to this technology, please visit the Climate Friendly Farming
State support for anaerobic digestion applications
also extends beyond WSU activities. The Department of Ecology’s Beyond Waste program is looking
at a variety of sustainable, waste management technologies including anaerobic
digestion. In addition, the Energy
Freedom Fund, passed by the 2006 Washington
State legislature, has awarded funding
to two anaerobic digestion projects located near the cities of Sunnyside and Monroe, Washington.
State University Climate Friendly Farming
State Department of Ecology Beyond Waste Program
Northwest CHP Application Center
For dairy farmers and others interested in exploring the idea of using anaerobic digestion as a waste control measure, the Northwest CHP Application Center has developed a factsheet to help identify key questions prior to implementing an anaerobic digestion program. This factsheet can be found at the CHP Application Center website.