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Cows as powerplants?

A new study suggests that some of the microorganisms found in cow waste may provide a reliable source of electricity.

Results showed that the microbes in about a half a liter (17 oz.) of rumen fluid--fermented, liquefied feed extracted from the rumen, the largest chamber of a cow's stomach--produced about 600 millivolts of electricity. That's about half the voltage needed to run one rechargeable AA-sized battery, says ASABE member Ann Christy, a study co-author and an associate professor of food, agricultural, and biological engineering at Ohio State University.

The research showed how electricity can be created as the microorganisms in rumen fluid break down cellulose--a complex carbohydrate that is the primary component of the roughage that cows eat. That breakdown releases electrons. This study represents the first time that scientists have used cellulose to help charge a fuel cell.

The researchers extracted rumen fluid from a living cow and collected the fluid through a cannula, a surgically implanted tube that leads directly from the cow's hide into its rumen. The cow used in the study ate a normal diet.

The researchers filled each of two sterilized glass chambers with strained rumen fluid to create the microbial fuel cell. Each chamber was about 30 cm (1 ft) high and about 15 cm (6 in.) in diameter.

The chambers were separated by a special material that allowed protons to move from the negative (anode) chamber into the positive (cathode) chamber. This movement of protons, along with the movement of electrons across the resistor and wire that connects the two electrodes, creates electrical current.

The anode chamber was filled with rumen fluid and cellulose, which served as a food source for the microorganisms. The other chamber, the cathode, was filled with potassium ferricyanide, a chemical that acts as an oxidizing agent to round out the electrical circuit.

Two small pieces of plain graphite served as the fuel cell's electrodes. A piece of graphite was placed in each chamber. The researchers used a meter to measure the output of the fuel cell.

That output reached a consistent maximum of 0.58 V. After about four days, the voltage fell to around 0.2 V, at which time the researchers added fresh cellulose to bring the voltage back up to a higher level.

"While that's a very small amount of voltage, the results show that it is possible to create electricity from cow waste," Christy says.

For more information, contact Christy, 614-292-3171,
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Title Annotation:Update
Publication:Resource: Engineering & Technology for a Sustainable World
Date:Nov 1, 2005
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