Two bacteria better than one in cellulose-fed fuel cell

July 27, 2007

No currently known bacteria that allow termites and cows to digest cellulose, can power a microbial fuel cell and those bacteria that can produce electrical current cannot eat cellulose. But careful pairing of bacteria can create a fuel cell that consumes cellulose and produces electricity, according to a team of Penn State researchers.

"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.

Plants produce cellulose to use as their cell walls and to provide rigidity to their structure. Along with lignin and hemicellulose, they make up huge amounts 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. Humans and most vertebrates derive little nutrition from cellulose.

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.
-end-
The U.S. Department of Agriculture supported this work.

Penn State

Related Bacteria Articles from Brightsurf:

Siblings can also differ from one another in bacteria
A research team from the University of Tübingen and the German Center for Infection Research (DZIF) is investigating how pathogens influence the immune response of their host with genetic variation.

How bacteria fertilize soya
Soya and clover have their very own fertiliser factories in their roots, where bacteria manufacture ammonium, which is crucial for plant growth.

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.

Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.

Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.

Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.

Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.

How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.

The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?

Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.

Read More: Bacteria News and Bacteria Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.