Methane Digesters
In a Nutshell
Methane digesters take waste material (old-food, animal and human waste) and extracts methane. The methane can then be used to produce energy. Some methane digesters will turn the manure into animal bedding and other useable products. This tool can be very valuable to dairy farmers.
Practical Solution
The “How To”-
Methane digesters, also known as anaerobic digesters, "collect manure and convert the energy stored in its organic matter into methane, which is used to produce energy... 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." *
Methane digesters have numerous benefits including producing renewable energy. It also improves air quality by reducing greenhouse gas emissions and oders from the manure. Methane digester owners can sell the energy generated and qualify for carbon credit paymers. The left over manure is actually a better fertilizer for crops and the manure can even be further processed into bedding for farm animials.
A feasibility study must be completed in order to identify a source and likely quantity of inputs, the anticipated volume of outputs, electric buy back rates, as well as end users for liquid and solid materials, nutrients, and LP gas. The study will identify which components of the system are feasible, and which are not. A design phase would be the next step; followed by financing, construction and operation.
USDA Natural Resources Conservation Service would be the government authority on this subject matter; their Conservation Practice Standard can be found at: http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_026149.pdf
*Quote is from: http://www.mda.state.mn.us/protecting/conservation/practices/digester.aspx
Planning & Zoning-
As methane digesters are generally sited in rural, agricultural areas, and they reduce nutrient runoff and livestock odor, there are generally few planning and/or zoning. Any issues would be identified within the feasibility study phase.
Dollars & Cents-
There are far too many variables to provide a general economic summary. Electric buy-back rates in the mid-west are relatively low, and therefore other sources of income, such as tipping fees associated with co-substrates, or local use of the LP gas (vehicle fleets) is critical to making a methane digester feasible. While methane digesters are generally associated with animals, and specifically animal waste, it can also be successfully implemented in other industries where there is a large volume of waste.
Here are the names of a few companies that sell methane digesters, pleaes contact them for further information about purchasing a methane digester: Valley Air 2020, Cady Inc. and SEaB Energy.
For those of you who are the do-it-yourself type, The Urban Farm Guys have an instructional video on how to make our own methane digester. Their digester is designed to handle manure generated by an individual and not a farm animal.
Measuring Success-
Methane digesters will contribute to two of the OneSTL performance measures. The first is air quality, which we measure by number of days the EPA Air Quality Index exceeds 100 for ozone and pariculate matter. The desired trend is for the number of days to drop. The 2010 baseline is 19 days.
Another meaure is the greenhouse gas emissions for the region, measured by the total carbon dioxide equivalent emissions per capita. The 2010 baseline was mtC02e, and the desired trend is for this number to go down.
Case Studies
Discover More-
US EPA AgStar: Recovering Value from Waste; Anaerobic Digester System Basics http://www.epa.gov/agstar/documents/recovering_value_from_waste.pdf
Midwest Rural Energy Council, http://www.mrec.org/anerobicdigestion.html
Purdue University: Basics of Energy Production through Anaerobic Digestion of Livestock Manure http://www.extension.purdue.edu/extmedia/ID/ID-406-W.pdf
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