An education in anaerobic digestion

By Graeme McNaughton/The Oshawa Express

Regional councillors and staff will be making their way to Europe this summer to learn more about using anaerobic digestion to generate power.

While there are many unknowns surrounding the trip and the future of such a project, such as budgets or the size of a future digester, what is known is how they work.

“Biogas is produced by bacteria that live in a tank…which is filled with a slurry of organic material,” says Chris Duke, a biogas program analyst with the Ministry of Agriculture, Food and Rural Affairs.

“The organic material can be manure, it can be food waste, it could be from energy crops. The gas that comes off is captured under a large rubber bubble or membrane, and it can be put directly into a boiler for heat or it can be used in an engine that turns a generator to generate electricity.”

Duke says that with digesters, there is a continuous flow of organic material going in and out in order to keep it operating.

“Almost all of them, they have a continuous flow in. So material flows in, and an equal amount flows out or is pumped out,” he says.

“The material goes in and gets fully mixed inside. They’re large enough that material would typically stay in there for from 10 to up to 50 days. Even in agricultural operations, it could be going up to 100 days.”

While anaerobic digesters have taken off in Europe as a means of greener energy production, Duke says there are several smaller scale digesters in Ontario.

“In Ontario, our smallest anaerobic digesters, they’re producing 100 kilowatts. So that would be enough for roughly 50 homes. The largest agriculture digester is 1.6 megawatts, so that would be enough for 800 houses,” he says.

Duke adds that there are two commercial digesters in Ontario – one in Elmira and another south of London.

“These are designed specifically to receive organics from waste generators and the only business these digesters have is the collection and processing of those organics, generating electricity,” he says.

While he wouldn’t rule it out, Duke says he doesn’t foresee larger scale anaerobic digesters coming to Ontario, such as the recently completed Heartland Biogas facility in Colorado, which can produce up to 50 megawatts of power according to the site’s operator, EDF Renewable Energy.

One thing holding such a large project back, Duke says, is that there may not be enough of the organic material needed to keep such a facility viable.

“One thing that we don’t have here in Ontario is very large feedlots or those very large dairy farms. We do have large dairy farms, but not to the size you’d see in the states. We don’t have very large pig farms either, which you’d see in the United States,” Duke says, speaking about manure, a key fuel source in many anaerobic digesters.

Duke adds that for a municipal digester, there would also have to be a focus on restricting the odour coming from both the trucks going into the facility, as well as from the facility itself.