Engineers at Oregon State University–Corvallis have discovered how to produce electricity directly from wastewater, using microbial fuel cells. As a result, in the future, waste treatment plants may not only generate 100 percent of their own power—but also may sell excess electricity.

The new technology developed at OSU effectively cleans wastewater while producing from 10 times to 50 times more electricity, per volume, than most other approaches using microbial fuel cells (and100 times more electricity than some).

The researchers believe that their breakthrough could change the way that wastewater is treated worldwide, replacing the widely used “activated sludge” process that has been in use for nearly a century. Their findings, funded by the National Science Foundation, have just been published in the professional journal Energy and Environmental Science.

“If this technology works on a commercial scale the way we believe it will, the treatment of wastewater could be a huge energy producer, not a huge energy cost,” said Hong Liu, an associate professor in the OSU Department of Biological and Ecological Engineering. “This could have an impact around the world, save a great deal of money, provide better water treatment and promote energy sustainability.”

Experts estimate that about 3 percent of the electrical energy consumed in the United States and other developed nations is used to treat wastewater, and a majority of that electricity is produced by fossil fuels that contribute to global warming.

But if the biodegradable characteristics of wastewater can be tapped to realize their full potential, they could theoretically provide many times the energy that is now being in the activated sludge process, with no additional greenhouse emissions.

OSU researchers reported several years ago on the promise of this technology, but at that time the systems in use produced far less electrical power. With new concepts —reduced anode-cathode spacing, evolved microbes and new separator materials— the technology can now produce more than two kilowatts per cubic meter of liquid reactor volume. This amount of power density far exceeds anything else accomplished to date with microbial fuel cells.

The system also works better than an alternative approach to creating electricity from wastewater, based on anaerobic digestion that produces methane. The new process treats the wastewater more effectively and doesn’t present any of the environmental drawbacks of the other—such as production of unwanted hydrogen sulfide or possible release of methane, a potent greenhouse gas.

The OSU system now has been proven at a substantial scale in the laboratory, Liu said, and the next step would be a pilot study. Funding is now being sought for such a test. A good candidate, she said, might be a food processing plant, where a contained system produces a steady supply of certain types of wastewater that would provide significant amounts of electricity.

Continued research also should find even more optimal use of necessary microbes, reduced material costs and improved function of the technology at commercial scales, OSU scientists said. Once advances are made to reduce high initial costs, researchers estimate that the capital construction costs of this new technology should be comparable to that of the activated sludge systems now in widespread use today— and even less expensive when future sales of excess electricity are factored in.

This technology cleans sewage by a very different approach than the aerobic bacteria used in the past. Bacteria oxidize the organic matter and, in the process, produce electrons that run from the anode to the cathode within the fuel cell, creating an electrical current. Almost any type of organic waste material can be used to produce electricity – not only wastewater, but also grass straw, animal waste, and byproducts from such operations as the wine, beer or dairy industries.

The approach may also have special value in developing nations, where access to electricity is limited.

The ability of microbes to produce electricity has been known for decades, but only recently have technological advances made this type of energy generation substantial enough to be of commercial use.

The OSU College of Engineering is among the nation’s largest and most productive engineering programs. In the past six years, the college has more than doubled its research expenditures to $27.5 million by emphasizing highly collaborative research that solves global problems, spins out new companies, and produces opportunities for students through hands-on learning.

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