1 September 2005
Forget Horsepower, Think Cow-Power
by Kate Melville
Findings presented at the national meeting of the American Chemical Society suggest that some of the micro-organisms found in cow waste could provide a reliable source of electricity.
Using cow poo for energy generation isn't a new idea. Some farmers already use the methane released by livestock waste to generate electrical power. But it requires costly equipment like methane digester systems, which are beyond the budget of many farmers. And besides that, the process is quite wasteful. "Methane still needs to undergo combustion, which creates issues with energy efficiency," said Hamid Rismani-Yazdi, the study's lead author from Ohio State.
The new research uses rumen fluid, found in the digestive system of cows. The results showed that the microbes in about a half a liter of rumen fluid - fermented, liquefied feed extracted from the cow's stomach - produced about 600 millivolts of electricity. The electricity is generated as the microorganisms in the rumen fluid break down cellulose - a complex carbohydrate that is the primary component of the roughage that cows eat. That breakdown releases electrons.
The researchers say that rumen fluid itself won't be used as an energy source but some of the microorganisms found in the fluid are also found in cow dung, which may prove to be equally good at generating electricity. And in a related experiment, that's just what the researchers found.
Co-researcher Ann Christy used actual cow manure to power a microbial fuel cell, the first time this has been demonstrated. The individual cells produced between 300 and 400 millivolts. "The students put a few of these cells together and were able to fuel their rechargeable batteries over and over again," Christy said. Importantly, the researchers didn't need to use cellulose to feed the microbes. The fuel is already in the dung in the form of plant material that passes undigested through the 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. It's cheap and plentiful, and it may someday be a useful source of sustainable energy in developing parts of the world." But for that to happen, the cow poo fuel cell will need to outperform other types of microbial fuel cell, such as those that have produced electricity from municipal wastewater. The researchers are optimistic. "Although it's too early to tell if this kind of fuel cell can produce significantly more electricity, the fact that the rumen fluid worked in our study means that there are additional electricity-producing microbes that we have yet to identify," Christy said.