Cows Show Promise As Powerplants
Sep 28, 2005 - 3:19:00 AM
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We've run some of these trials well over 30 days without a decrease in the voltage output. Both studies suggest that cow waste is a promising fuel source. It's cheap and plentiful, and it may someday be a useful source of sustainable energy in developing parts of the world.
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By Ohio State University,
[RxPG] 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 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, said 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 presented their findings on August 31 in Washington, D.C., at the national meeting of the American Chemical Society. Christy and Rismani-Yazdi conducted the work with Ohio State colleagues Olli Tuovinen, a professor of microbiology, and Burk Dehority, a professor of animal sciences.
The researchers extracted rumen fluid from a living cow. The researchers 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 a foot high and about 6 inches 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. Two small pieces of plain graphite served as the fuel cell's electrodes (an electrode draws and emits electrical charge.) The researchers used a meter to measure the output of the fuel cell.
That output reached a consistent maximum of 0.58 volts. Putting a couple of these fuel cells together should generate enough power to run a rechargeable double-A battery, Rismani-Yazdi said.
In related work done in Christy's lab, she and Rismani-Yazdi, along with a number of undergraduate students, used actual cow manure to power a microbial fuel cell. These individual cells produced between 300 and 400 millivolts.
In that work, the researchers didn't need to use cellulose to feed microbes, as some plant material passes undigested through a cow.
We've run some of these trials well over 30 days without a decrease in the voltage output, Christy said. Both studies suggest that cow waste is a promising fuel source. While the source of energy for the fuel cell used in these studies is somewhat unique, microbial fuel cells aren't a new idea; other scientists have produced electricity from a handful of specific microbes and also from effluent from municipal wastewater.
The hope is that one day livestock farmers could use their farm's livestock waste lagoon as a huge fuel cell and generate enough power for their operation, Rismani-Yazdi said.Using cow dung as an energy source isn't a new idea some farmers already use the methane released by livestock waste to power machinery and lights. But converting methane into electricity requires costly equipment one California farmer reportedly spent $280,000 to convert his operation to a methane digester system.
Methane still needs to undergo combustion, which creates issues with energy efficiency, said Hamid Rismani-Yazdi, the study's lead author and a graduate student in food, agricultural and biological engineering at Ohio State.
Publication:
The researchers presented their findings on August 31 in Washington, D.C., at the national meeting of the American Chemical Society.
On the web:
fabe.osu.edu 
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This work was supported in part by the Ohio Agricultural Research and Development Center in Wooster.
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