On the Massachusetts dairy farm, there is a 550,000-gallon underground tank capable of processing about 9,000 tons of cow manure per year. This oxygen-free tank mixes sewage waste at temperatures of 95 and 105 degrees Fahrenheit, and further encourages bacteria to feed on carbon, nitrogen, and other organic matter.
This process is known as anaerobic digestion, where methane is finally produced. Next, through a network of pipes, the gas is then directed to a special engine that burns methane to produce heat and electricity. The remaining organic matter that cannot be digested after the anaerobic process can still be used for agricultural purposes.
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Smithsonianmag