Cellulose is not digestible by humans, that's why it's considered dietary fiber. Plants produce it to use as their cell walls and to provide rigidity to their structure. Along with lignin and hemicellulose, cellulose makes up a large amount of the biomass produced by plants.
Some animals, ruminants and termites for example, can break down cellulose with the aid of bacteria that live in their digestive tract but most vertebrates derive little nutrition from it.
Penn State researchers now say careful pairing of bacteria can create a fuel cell that consumes cellulose and produces electricity.
"We have gotten microbial fuel cells to work with all kinds of biodegradable substances including glucose, wastewater and other organic wastes," says John M. Regan, assistant professor of environmental engineering. "But, cellulose is tricky. There is no known microbe that can degrade cellulose and reduce the anode.
"We overcame this by putting together a microbe that can degrade and ferment cellulose and an anode-reducing bacterium that can live off the fermentation products," he says.
Microbial fuel cells work through the action of bacteria that can pass electrons to an anode. The electrons flow from the anode through a wire to the cathode, producing an electric current. In the process, the bacteria consume organic matter in the water or sediment.
The researchers, who include Regan; Thomas E. Ward, research associate; and Zhiyong Ren, graduate student, looked at Clostridium cellulolyticum, a bacterium that ferments cellulose, and Geobacter sulfurreducens, an electroactive bacterium. Both are anaerobic, living in places where no free oxygen exists. This fermenter produces acetate, ethanol and hydrogen. The electroactive bacteria consumed some of the acetate and ethanol. They report the results of their study in a recent online issue of Environmental Science and Technology.
"We thought that maybe we did not need a binary setup, maybe uncharacterized bacterial consortia would work" says Regan. "It worked, but not as well as the two specifically paired bacteria."
One problem with anaerobic bacteria – and the reason the researchers looked into an uncharacterized mixture of bacteria – is that currently the most efficient microbial fuel cells use an air cathode. Unfortunately, it is impossible to have an air cathode without some oxygen leaking into the reaction chamber, killing strictly anaerobic bacteria and reducing output.
"We tried an aerobic cathode with the binary culture and it will not work," says Regan.
The researchers settled on a two-chamber fuel cell that produced a maximum of 150 milliwatts per square meter.
"We achieved a low power density because of the two chamber system," says Regan. "Current fuel cell designs produce about ten times that."
Currently the researchers are using pure, processed cellulose without any hemicellulose or lignin. They are just beginning to look at other cellulose products so the fuel cells can operate on less manufactured feedstock. As a proof of concept, the researchers are happy with their results, but they would like to see the power density increase. One approach would be to find a community of bacteria that could tolerate small amounts of oxygen because some of the bacteria use up the oxygen before it reached the anaerobic bacteria. Another approach would be to improve the design of the oxygenless fuel cell.
The U.S. Department of Agriculture supported this work.
Source: Penn State
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Ghost Light From Dead Galaxies - A Hubble Halloween
- Greenpeace Says Its GMOs Are Better Than Science's GMOs, Still Hates Golden Rice
- Reduce Prostate Cancer Risk By Sleeping With Lots Of Women - But Not Men
- Homo Floresiensis: Hobbit Species Continues To Provoke Questions About Human Evolution
- Everyone Hates Daylight Savings Time - But It Might Improve Public Health
- Okay With Disgusting Images? You Vote This Way 95 Percent Of The Time
- Supersonic Laser-Propelled Aircraft Get A Step Closer
- "Twelve years in a major urban public school system, and I couldn't once bring myself to eat a school..."
- "Hardly a day goes by without some creative new take on the eternal Evil White Man meme. Without..."
- "There would be no controversy if it were all balloons and ponies stories like that. But I hope..."
- "Let's talk about this disaster: I lost a course at the university where I work and became ineligible..."
- "Partisan nastiness doesn't advance dialogue. We are all in this together. You asked for solutions..."
- Battle of Britain: NGOs and scientists clash over proposal to loosen EU GMO restrictions
- Genetically modified clean energy from bacteria
- Designer babies: You can screen for cystic fibrosis but intelligence is a ways off
- Science as profane: What superstition of 1752 and 2014 share in common
- What’s so “natural” about “natural crop breeding”?
- Worried you have cancer? Take a Google pill!