This is the anaerobic digester at the Oklahoma State University Swine Research and Education Center.
A new pathway to biogas from swine manure A digester specifically designed for hog farms could open doors to biogas production. by Doug Hamilton
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hen in Wisconsin a number of years ago, I had the opportunity to tour the Dane County Community Digester, which produces biogas (a mixture of high-energy methane and no-energy carbon dioxide) from manure collected from three dairy farms. The manure is mixed with fat and grease from restaurants in nearby Madison. The manure and grease contain enough energy to run a two-megawatt generator. On the bus ride back to the conference headquarters, I overheard a conversation between two fellow passengers.
“That was impressive. Too bad it’s not possible to produce methane from pig manure,” one of them said. My first impulse was to jump up and shout, “No! No! That’s not true!” But not wanting to prove I was rudely listening in on their conversation, I kept to myself.
It is possible My fellow passenger was wrong, of course. Pound for pound, swine manure produces just as much biogas as any other manure, and usually at a higher methane content. What the person should have said was, “Because we
10 | Journal of Nutrient Management | May 2022
F3 10-11 May 2022 Swine Biogas.indd 1
handle swine manure as a liquid, its low wet mass methane potential makes it difficult to digest economically.” Wet-mass methane potential is the volume of methane you can expect to produce from a given mass of manure as it is fed to a digester. Adding water to swine manure makes it easy to move, but it also dilutes the organic matter. It is the organic matter that gets converted to biogas. We pay for ease of handling with low wet mass methane potential. In the southern United States and in the tropics, liquid swine manure is flushed into anaerobic lagoons. A lagoon jofnm.com
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