The US state of Vermont is producing electricity from its dairy cow herdsEnvironmental News Network discusses a recent case study in Vermont which suggests that generating electricity from cow manure may be economically feasible. The seven-year study was conducted by six dairy farms, and produced 12 million kW hours of electricity per year.

The farms operate generators that run on methane from cow manure, a renewable energy source. One cow’s waste per day is sufficient to power two 100-watt light bulbs per day.

The process of producing power from manure is relatively simple and straight forward. The average cow is capable of producing over 30 gallons of manure every day. For a large farm with say 1,000 cows, that means 30,000 gallons of manure per day, quite a hefty load! The manure is fed into an anaerobic digester where it stays for 21 days at 100 degrees F. Bacteria convert the waste into methane gas. As the gas builds within the digester, the pressure rises, and the gas is exhausted through piping to the modified natural gas engine. The engine powers the generator, producing electricity. Excess heat from the engine is used to keep the digester warm.

Leftover manure that comes out of the digester is processed through a mechanical separator. The resulting odorless solid waste can be sold to the public as fertilizer.

The study concludes that the program’s success will depend on a number of factors. Economic feasibility will depend upon the base price of electricity in the state.  Financial support from the government may be necessary for the initial investments, and additional revenue from the sale of manure byproducts may be necessary.

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