Bacteria convert food processing waste to hydrogen

Penn State environmental engineers estimate, based on tests with wastewater from small Pennsylvania food processors, that typical large food manufacturers could use their starch-rich wastewater to produce hydrogen gas worth close to $5 million or more each year. They present their findings today at the 103rd General Meeting of the American Society for Microbiology.

Steven Van Ginkel, doctoral candidate, and Dr. Sang-Eun Oh, post-doctoral researcher in environmental engineering, conducted the tests.

“In addition to hydrogen, which can be used as a fuel and industrial feedstock, methane, the main component of natural gas, can be generated from the wastewaters,” says Van Ginkel. Both hydrogen and methane can be converted into electricity via fuel cells at close to 80% efficiency. “By extracting hydrogen and methane from their wastewaters, these plants can also reap significant savings by not needing to aerate. Aeration makes up 20 to 80 percent of wastewater treatment costs.”

Van Ginkel presented the Penn State team’s findings in a poster, Turning America’s Waste into Energy, today (May 20) at 9 a.m . His co-authors are Dr. Oh and Dr. Bruce Logan, director of the Penn State Hydrogen Energy Center and Kappe professor of environmental engineering.

In the tests, Van Ginkel and Oh added hydrogen-producing bacteria to samples of wastewater from the Pennsylvania food processors. The bacteria were obtained from ordinary soil collected at Penn State and then heat-treated to kill all bacteria except those that produce spores. Spores are a dormant, heat resistant, bacterial form adapted to survive in unfavorable environments but able to begin growing again in favorable conditions.

“The spores contain bacteria that can produce hydrogen and once they are introduced into the wastewater, they eat the food in the water and produce hydrogen in a normal fermentation process,” says Van Ginkel.

Keeping the wastewater slightly acidic in the hydrogen production step helps to prevent any methane-producing bacteria from growing and consuming hydrogen.

After only a day of fermentation in oxygen-free or anaerobic conditions, the hydrogen-producing bacteria fill the headspace in the fermentation flasks with biogas containing 60 percent hydrogen and 40 percent carbon dioxide.

In the second stage of the process, the acidity in the wastewater is changed and methane-producing bacteria added. The bacteria eat the leftovers, grow and generate methane.

The solid material or sludge left over from fermentation is only one-fourth to one-fifth the volume from typical aerobic treatment processes.

“Using this continuous fermentation process, we can strip nearly all of the energy out of the wastewater in forms that people can use now. While this approach has high capital costs at the outset, our calculations show that it could pay off well both environmentally and financially for some food processors in the long run. In many instances, existing treatment plants can easily be retrofitted to produce hydrogen and methane at a much lower capital cost,” says Van Ginkel.

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The research was supported by the National Science Foundation Biogeochemical Research Initiation Education grant.

This release is a summary of a presentation from the 103rd General Meeting of the American Society for Microbiology, May 18-22, 2003, in Washington, DC. Additional information on these and other presentations at the 103rd ASM General Meeting can be found online at http://www.asm.org/Media/index.asp?bid=17053 or by contacting Jim Sliwa (jsliwa@asmusa.org) in the ASM Office of Communications. The phone number for the General Meeting Press Room is (202) 249-4064 and will be active from 12:00 noon EDT, May 18 until 12:00 noon EDT, May 22.

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