Microbial fuel cells, which harness the power of bacteria, are not a new phenomenon. Researchers have studied them for years and have used a variety of liquid solutions, including glucose, acetate, and lactate, to produce electricity. Scientists have also sought to tap the power of baking yeasts and even ocean sediment microbes.
But Logan's group aims to generate power directly from an undesirable and ubiquitous materialuntreated wastewater. It's a matter of practical application.
"We needed to find a way to allow a reactor to operate using water with lots of particles, not pure lab solutions," Logan said. "As a first feasibility study, our reactor has proven that it can handle this kind of material."
While early results show promise, consumers shouldn't plan to end their electric utility service or fill their septic systems in anytime soon. The Penn State researchers say that while they've slowly increased their reactor's power output, it still falls far short of an average home's electric needs.
"Right now the power density is too low. We need more efficiency, meaning more electrons on electrodes in less area," Logan said.
The researchers say a second hurdle is cost. The average home would not be able to afford such a reactor even if they were availableat least for now.
"It's not cheap. It's currently not an economically feasible process," Logan said. "But it's like anything else in the early stages until you figure out how to make it cost effective. Computers that do less than a pocket calculator used to cost a million dollars."
Yet the potential is promising enough that the group can think big. "Our goal is to replace your local [wastewater] treatment plant with a power plant where you accomplish treatment but also generate electricity," Logan said.
The cost of treating 33 billion gallons (126 billion liters) of wastewater in the U.S. alone costs some 25 billion dollars (U.S.) a year. Significant funds are spent to power the process.
"We spend a lot of our national electricity expenditure on waste treatment. We could greatly reduce that number while generating additional electricity," Logan said.
One of the largest expenses incurred while treating wastewater is the process of adding oxygen to the wastewater, called "activated sludge." The aeration is necessary to promote biological action that breaks down waste. The Penn State microbial reactor could greatly reduce this expense because a key component, by design, receives oxygen directly from air.
It's unclear if the Penn State microbial reactor could be used to treat sewage in its entirety. But the system has proved comparable to other anaerobic treatment methods by removing about 80 percent of wastewater's chemical oxygen demand.
Logan believes the wastewater treatment benefits of his device could someday be significant.
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