COLUMBUS , Ohio – A new study suggests that some of themicroorganisms found in cow waste may provide a reliable source ofelectricity.
Results showed that the microbes in about a half aliter of rumen fluid – fermented, liquefied feed extracted from therumen, the largest chamber of a cow's stomach – produced about 600millivolts of electricity. That's about half the voltage needed to runone rechargeable AA-sized battery, said Ann Christy, a study co-authorand an associate professor of food, agricultural and biologicalengineering at Ohio State University.
While rumen fluid itselfwon't be used as an energy source, some of the microorganisms found inthe fluid are also found in cow dung, which may prove to be a goodsource for generating electricity. In fact, in a related experiment,the researchers used cow manure directly to create energy for a fuelcell.
Using cow dung as an energy source isn't a new idea – somefarmers already use the methane released by livestock waste to powermachinery and lights. But converting methane into electricity requirescostly equipment – one California farmer reportedly spent $280,000 toconvert his operation to a methane digester system.
“Methanestill needs to undergo combustion, which creates issues with energyefficiency,” said Hamid Rismani-Yazdi, the study's lead author and agraduate student in food, agricultural and biological engineering atOhio State.
The research showed how electricity can be created asthe microorganisms in rumen fluid break down cellulose – a complexcarbohydrate that is the primary component of the roughage that cowseat. That breakdown releases electrons.
This study represents the first time that scientists have used cellulose to help charge a fuel cell.
Theresearchers presented their findings on August 31 in Washington, D.C.,at the national meeting of the American Chemical Society. Christy andRismani-Yazdi conducted the work with Ohio State colleagues OlliTuovinen, a professor of microbiology, and Burk Dehority, a professorof animal sciences.
The researchers extracted rumen fluid from aliving cow. The rumen is essentially a fermentation vat crawling withmicroorganisms where much of the food that a cow eats is temporarilyheld and is continuously churned until it can be completely digested.This liquid mass is what scientists call rumen fluid.
Theresearchers collected the fluid through a cannula, a surgicallyimplanted tube that leads directly from the cow's hide into its rumen.The cow used in the study ate a normal diet.
The researchersfilled each of two sterilized glass chambers with strained rumen fluidto create the microbial fuel cell. Each chamber was about a foot highand about 6 inches in diameter.
The chambers were separated by aspecial 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 thatconnects the two electrodes, creates electrical current.
Theanode chamber was filled with rumen fluid and cellulose, which servedas a food source for the microorganisms. Cellulose is plentiful on mostfarms, as harvesting usually leaves behind plenty of it in the form ofcrop residue in the fields.
The other chamber, the cathode, wasfilled with potassium ferricyanide, a chemical that acts as anoxidizing agent to round out the electrical circuit.
Two smallpieces of plain graphite served as the fuel cell's electrodes (anelectrode draws and emits electrical charge.) A piece of graphite wasplaced in each chamber. The researchers used a meter to measure theoutput of the fuel cell.
That output reached a consistent maximumof 0.58 volts. After about four days, the voltage fell to around 0.2volts, at which time the researchers added fresh cellulose to bring thevoltage back up to a higher level.
“While that's a very smallamount of voltage, the results show that it is possible to createelectricity from cow waste,” Christy said.
“Putting a couple ofthese fuel cells together should generate enough power to run arechargeable double-A battery,” Rismani-Yazdi said.
In relatedwork done in Christy's lab, she and Rismani-Yazdi, along with a numberof undergraduate students, used actual cow manure to power a microbialfuel cell. These individual cells produced between 300 and 400millivolts.
“The students put a few of these cells together andwere able to fuel their rechargeable batteries over and over again,”Christy said.
In that work, the researchers didn't need to usecellulose to feed microbes, as some plant material passes undigestedthrough a cow.
“We've run some of these trials well over 30 dayswithout a decrease in the voltage output,” Christy said. “Both studiessuggest that cow waste is a promising fuel source. It's cheap andplentiful, and it may someday be a useful source of sustainable energyin developing parts of the world.”
While the source of energy forthe fuel cell used in these studies is somewhat unique, microbial fuelcells aren't a new idea; other scientists have produced electricityfrom a handful of specific microbes and also from effluent frommunicipal wastewater.
“Although it's too early to tell if thiskind of fuel cell can produce significantly more electricity, the factthat the rumen fluid worked in our study means that there areadditional electricity-producing microbes that we have yet toidentify,” Christy said.
“The hope is that one day livestockfarmers could use their farm's livestock waste lagoon as a huge fuelcell and generate enough power for their operation,” Rismani-Yazdi said.
This work was supported in part by the Ohio Agricultural Research and Development Center in Wooster.
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