for National Geographic News
Scientists say they have produced clean, renewable energy from the contents of a cow's stomach.
Researchers found they could generate electricity using the bacteria that occur naturally inside a cow's rumenthe first of four stomachs that breaks down grass and other fodder into a digestible mush.
The bovine stomach bacteria add to a growing list of cheap, plentiful, and non-polluting substances that run devices known as microbial fuel cells (MFCs).
MFCs are powered by electrons (the source of electricity) released by bacteria feeding on organic material. The microbes aren't fussy eaters, either. In tests, the bacteria have also fed on dead flies, fruit, even domestic wastewater and produced electricity.
Researchers at Ohio State University found that a pint (half a litre) of a cow's bacteria-infested rumen juice produced about 600 millivolts of electricity. The output is about half the voltage of a rechargeable AA-size battery.
Ann D. Christy, professor of food, agricultural, and biological engineering, said the team tapped into the electron transport system of rumen bacteria.
"The normal metabolism of electro-chemically active micro-organisms allows them to generate a small electrical current when placed in contact with the anode [negative electrode] of the microbial fuel cell," she said.
The cathode, the positive electrode of the experimental battery, was filled with a chemical oxidizing (electron-removing) agent to round out the electrical circuit.
Undergraduate students working in Christy's lab also managed to generate a similar voltage from microbial fuel cells using cow dung.
"The students put a few of these cells together and were able to fuel their rechargeable batteries over and over again," Christy added.
Farmers in California have already cottoned on to the energy potential of cow dung. Dairy operations are installing so-called methane digester systems, which harness methane, a greenhouse gas released in cattle waste, to generate electricity.
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