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Manure has potential as source of biofuels
By Becky Beyers
The faint but unmistakable odor of pig manure wafts through Jun Zhu's lab as a sludgy-looking black liquid slowly percolates from five-gallon plastic bottles through plastic tubes and into smaller silver-covered fermentation units.
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Jun Zhu, an associate professor in the Department of Bioproducts and Biosystems Engineering, is working on turning swine manure into hydrogen. His graduate students, including Yecong Li, left, monitor the lab and record results twice a day. |
The lab at the Southern Research and Outreach Center in Waseca is testing whether fermenting swine manure to create the maximum amount of hydrogen gas—and
eventually turning the gas into cells that provide electricity—is viable.
It’s just one of several CFANS-related projects that involve using manure as a source of renewable energy. Zhu’s project is in the testing stage; a larger project has been up and running for several years on a Princeton-area farm; another is just getting started on the St. Paul campus.
Hydrogen from hogs
The Waseca project, begun in late 2005, uses two small anaerobic digester units, each built with a plastic input tank, a fermenting unit, pumps that transfer the liquid manure from the holding tank into the fermentation process, and gauges that measure the amounts of hydrogen, methane and other gases being produced. The system uses dark fermentation—the heated container where fermentation takes place is covered with reflective cloth so no light can get in—because bacteria are more active that way, Zhu says. The bacteria make the manure decompose, giving off a gas that’s a mixture of mostly methane and hydrogen.
Zhu chose swine manure for the project because pigs’ higher-protein diet creates a more biodegradable waste than what comes from mostly plant-eating cows, he says. Because of the differences in waste, existing systems that create energy from cow manure won’t work as well with swine manure.
Graduate students Yecong Li and Xiao Wu spent the summer working in the lab, checking gauges twice a day and adjusting pH levels and temperature to see which combinations yielded the best—i.e., highest percentage of hydrogen—readings from the resulting gases.
The system averages 10 percent to 11 percent hydrogen but has reached levels as high as 40 percent, Zhu says. Once the level consistently is at 30 percent to 40 percent hydrogen, he’ll begin developing a system that removes methane and other gases to produce nearly pure hydrogen, and ultimately will try to scale up the process to commercial size.
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