Ohio State University ecological engineers will be demonstrating a newly developed, small-scale biodigester at the upcoming Farm Science Review, Sept. 21-23, at the Molly Caren Agricultural Center in London, OH. Jay Martin, a researcher with the Ohio Agricultural Research and Development Center, recently developed a modified, fixed-dome digester that can make methane from manure. The methane can be burned as an alternative to natural gas or propane, or converted to electricity using a generator.

The 300-gal. biodigester, installed at Waterman Agriculture and Natural Resources Laboratory in Columbus, is designed for average-sized and smaller livestock farms (150 dairy cows, on average). "There are less than 200 digesters working on livestock farms in the United States and those digesters are designed for large-scale industrial dairy operations in the range of 10,000 or 15,000 head,” Martin explains. “And they are expensive – costing around $1 million to implement. Right now, only farms with around 1,000 cows or larger can use digesters.”

Recognizing the need for smaller-scale, affordable biodigesters, Martin and his colleagues turned to technologies widely used in China, India and South American nations, such as Costa Rica, and adapted a biodigester for Ohio's climate. The result is a biodigester that can generate 500 liters of biogas a day – 60% methane and 40% carbon dioxide. Currently, 10 gal. of manure is added per day and the renewable energy generated is enough to cook a few meals.

The biodigester technology being demonstrated at Farm Science Review is a mini version of the Waterman model. Martin says the technology represents the first step in determining how successful biodigesters can be on Ohio farms. "One of the challenges of a biodigester is the air temperature. The microbes that turn the organic matter into biogas are sensitive to colder temperatures," he explains. "How the biodigester performs in winter will help determine if such technology can be successful in Ohio."

The Waterman biodigester was installed last October. Researchers began monitoring biogas generation this spring. If successful, Martin envisions scaling up the biodigester to 5,000 or 10,000 gal. "A 1,000-gallon biodigester is probably the minimum right now that a farmer would need to get up and running. The smaller-scale version is much more affordable – costing about $100/cow," Martin says. "The key to the design is based on optimum amount of manure that can be collected per day for the greatest amount of biogas produced."

Researchers are still exploring minimum and maximum manure loads that the 300-gal. biodigester can handle. Too little manure means not enough biogas is created. Too much manure, and the pH drops, killing off the microbes that create the biogas. For more information, log on to fsr.osu.edu.