In the most simple terms, biodigestion is an anaerobic (meaning without oxygen) process that turns emissions from organic matter into a gas. The gas produced by biodigestion is mainly methane and carbon dioxide. (It also contains small amounts of nitrogen, hydrogen, and hydrogen sulphide.) In other words, you put manure in an enclosed container, add a little water to make what is called a slurry, keep most of the air from getting to it, and in a few days you get methane and carbon dioxide – a flammable fuel.
According to the Environmental Protection Agency (EPA) over 60% of methane emissions come from “human activities.” The production, storage, transmission, and distribution of natural gas and petroleum accounts for 30% of this number, landfills account for 17%, and “Enteric Fermentation” (a polite way of saying cow farts) accounts for 23%.
An additional 10% of “human activities” methane comes from manure as it decomposes in the fields. If you do the math, cows actually account for the largest percentage – 33% – of the methane production! (Please note a recent study completed in November of 2013 by MIT shows that methane released by cows and their manure may actually be 50-100% higher than the EPA’s previous estimates.)
You may know that methane is a greenhouse gas. Among the worst results of high methane quantities in the atmosphere are is its adverse affects on health (by contributing to poor air quality) and methane produces ozone.
The result of the biodigestion process is biogas. A viable fuel that can be used to cook or heat or run an engine. Once methane is burned it results in far less greenhouse gases than just letting the methane go directly into the atmosphere.
Of course, more than cow manure can be used in biodigesters. You can use horse and pig manure, dog poo, and, yes, even human manure. Decent results can also be had with food scraps.
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What can you do to help reduce methane levels? You can buy or build your own biodigester.