Watts from Wastewater?
A new technology is being developed that can turn raw sewage into raw power. The device, called a microbial fuel cell, not only treats wastewater, but also provides a clean energy source with the potential for enormous financial savings, according to scientists at Pennsylvania State University.
Although power output is still relatively low, they say the technology is improving rapidly and eventually could be used to run a small wastewater treatment plant, which would be especially attractive in developing countries. It also could be used to treat waste from animal farms, food processing plants and even manned space missions.
The report appears in the Nov. 1 edition of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world’s largest scientific society.
Similar in design to a hydrogen fuel cell, the microbial fuel cell captures electrons that are naturally released by bacteria as they digest organic matter and then it converts the electrons into electrical current.
"We generated up to 72 watts per square meter, which is 2.8 times that generated in a larger device reported earlier this year in ES&T," said Bruce Logan, Ph.D., an environmental engineer at Pennsylvania State University and co-author of the paper. While still a relatively small amount of power, the researchers have used these types of devices to run a small fan.
The technology is developing rapidly. Since submitting the current paper, Logan and his colleagues have tweaked microbial fuel cell devices to produce up to 350 watts per square meter. "Two years ago we had 0.1 . . . and now we’re in the 100s," he said. "We’d like to get in the range of 500-1000. We’re looking for another order of magnitude increase."
Logan doesn’t envision using his microbial fuel cell for the same type of applications as hydrogen fuel cells, such as in automobiles or houses. "We see using this any place where there’s a high concentration of organic matter," he said.
The most obvious application would be in wastewater treatment plants, which essentially could power themselves as they treat water. Such a technology would be particularly useful in developing countries, Logan suggests, because it would produce a net amount of electricity, offering a reason to keep a treatment plant running besides just treating wastewater. "Even if it’s only powering a cell phone tower, that would be a reason enough to keep it going," he said.
David Bagley, a scientist at the University of Toronto, has calculated that the energy potential in wastewater is almost 10 times the cost to treat it. "If we could achieve just one-twentieth of that power, we could break even," Logan said. "We’re confident we’re going to be able to do more than that."
"In our system, the two electrodes are separated by a proton exchange membrane (PEM), just like in a conventional hydrogen fuel cell," said Logan. "It opens the door to using existing hydrogen-gas based stack technologies with bacteria in water."
At the moment, scientists can’t exactly pull a hydrogen fuel cell off the shelf and use it to treat wastewater, but the design principles are very similar. Wastewater flows on one side of the cell and air flows on the other, continuously generating electricity while also removing organic matter from the water.
The device also could be used to treat waste from the food processing industry and farms — especially hog farms, which have tremendous problems with costs and odors, Logan said. NASA scientists are even developing a similar technology to be used in manned space missions, turning the astronauts’ waste into extra power.
Logan plans to build a larger version of his microbial fuel cell for demonstrations; he hopes to have the design completed in about six months.