Researchers have created a microbial fuel cell that can convert methane directly to electricity.
The fuel cell could help to solve the problem of moving methane from place to place. Transporting methane from gas wellheads to market provides multiple opportunities for this greenhouse gas to leak into the atmosphere.
“Currently, we have to ship methane via pipelines,” says Thomas K. Wood, professor of chemical engineering at Penn State. “When you ship methane, you release a greenhouse gas. We can’t eliminate all the leakage, but we could cut it in half if we didn’t ship it via pipe long distances.”
The researchers’ goal is to use microbial fuel cells to convert methane into electricity near the wellheads, eliminating long-distance transport. That goal is still far in the future, but they now have created a bacteria-powered fuel cell that can convert the methane into small amounts of electricity.
“People have tried for decades to directly convert methane,” says Wood. “But they haven’t been able to do it with microbial fuel cells. We’ve engineered a strain of bacteria that can.”
Bottom of the sea
Microbial fuel cells convert chemical energy to electrical energy using microorganisms. They can run on most organic material, including wastewater, acetate, and brewing waste. Methane, however, causes some problems for microbial fuel cells because, while there are bacteria that consume methane, they live in the depths of the ocean and are not currently culturable in the laboratory.
“We know of a bacterium that can produce an energy enzyme that grabs methane,” says Wood. “We can’t grow them in captivity, but we looked at the DNA and found something from the bottom of the Black Sea and synthesized it.”
The researchers actually created a consortium of bacteria that produces electricity because each bacterium does its portion of the job. Using synthetic biological approaches, including DNA cloning, the researchers created a bacterium like those in the depths of the Black Sea, but one they can grow in the laboratory. This bacterium uses methane and produces acetate, electrons, and the energy enzyme that grabs electrons.
Shuttles from sludge
The researchers, who report the results in the journal Nature Communications, also added a mixture of bacteria found in sludge from an anaerobic digester—the last step in waste treatment. This sludge contains bacteria that produce compounds that can transport electrons to an electrode, but these bacteria needed to be acclimated to methane to survive in the fuel cell.
“We need electron shuttles in this process,” says Wood. “Bacteria in sludge act as those shuttles.”
Once electrons reach an electrode, the flow of electrons produces electricity. To increase the amount of electricity produced, the researchers used a naturally occurring bacterial genus—Geobacter—which consumes the acetate created by the synthetic bacteria that captures methane to produce electrons.
To show that an electron shuttle was necessary, the researchers ran the fuel cell with only the synthetic bacteria and Geobacter. The fuel cell produced no electricity. They added humic acids—a non-living electron shuttle—and the fuel cells worked. Bacteria from the sludge are better shuttles than humic acids because they are self-sustaining. The researchers have filed provisional patents on this process.
“This process makes a lot of electricity for a microbial fuel cell,” says Wood. “However, at this point that amount is 1,000 times less than the electricity produced by a methanol fuel cell.”
Additional researchers are from Penn State and the National Institute of Cardiology, Mexico City. The US Department of Energy’s Advanced Research Projects Agency—Energy supported this work.
Source: Penn State