Plug-flow manure digester. Photo MDA.
This on-farm methane-powered engine and generator produces energy from the manure in a digester. Photo MDA.
Anaerobic manure digesters (also called methane digesters) collect manure and convert the energy stored in its organic matter into methane, which is used to produce energy (gas or electricity) for on-farm or off-farm use. The conversion to methane is the result of anaerobic digestion—a biochemical process in which organic matter is decomposed by bacteria in the absence of oxygen. Digesters must be airtight (no oxygen) for anaerobic digestion to occur.
Methane is often called biogas; technically, biogas is methane plus other anaerobic digestion byproducts. At any rate, the gas is flared or combusted to generate energy—a process with multiple other benefits including (among others) significantly reduced feedlot odors and greenhouse gas emissions.
Generally, manure used in digesters should have a total solids concentration of 14% or less and be mostly free of soil, sand, stones or fibrous bedding material (it can be processed to remove these materials). Supplemental feedstocks such as food processing wastes and wastewater can often be added to manure digesters.
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Guidance from USDA's Natural Resources Conservation Service
MN Dept of Agriculture
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See contacts for specific programs that fund this practice in the side-by-side payment comparison or contact your local Soil and Water Conservation District