Mini-biodigester offers big output for Ontario dairy farm

Ontario’s only mini-biodigester has been operating for more than a year and has changed how Harcolm Farms manages manure

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After about 18 months of operation, Ontario’s one and only mini-digester is going strong. It’s situated at Harcolm Farms near Beachville, Ont., and owned by dairy farmers Rob and Rachel McKinlay.

Minis are a fraction of the cost of a full-sized digester (there are more than 40 here in Ontario) and require much simpler permitting. Full-sized digesters also require an engineering team, a full impact assessment and months of construction, explains John Hawkes, a project development manager at Martin Energy Group, which installed the mini for the McKinlays, imported as a ‘kit’ from the Belgium-based manufacturer ‘Bioelectric.’

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The components are assembled in a matter of days on a concrete pad, but a crane is needed to lift the stainless steel reactor panels, liner and roof.

Bioelectric has installed more than 220 of these systems on small dairy farms (milking herds of at least 50 cows) in several countries in Europe over the last few years. Working with Martin Energy Group, the firm has also installed two in North America so far, for the McKinlays here in Ontario last year and one in Pennsylvania this year.

The McKinlay mini produces 20 kW of electricity, well into the typical range of 10 to 50 kW.

Like its big cousins however, minis also produce lots of heat from their generator engines — more heat energy in fact, says Hawkes, than the electrical energy they produce. Still, with the fierce Canadian winter bearing down on Ontario again last fall, Rob McKinlay says it was “definitely a question for us” if their mini was going to produce any excess heat.

“But even with this past winter, which was pretty harsh, we found there was definitely enough waste heat that it would be worth putting in a heat-exchange system,” he says. “So, we’re looking at that for the future. We’d have to purchase and install the exchanger and then a heating loop to take the heat from the liquid in the digester to the farm shop and other buildings with underground insulated pipes and so on.”

Heat, power production, simple permitting, quick assembly and low cost aside, mini-digesters (like all digesters) also help farmers reduce their environmental impact.

Using a digester means that the release of methane into the atmosphere from manure when it’s stored in a lagoon is avoided as the methane from digested manure is converted to carbon dioxide, a much less intense greenhouse gas. Minis are in fact designed to run on manure alone, and they therefore have no requirement for off-farm feedstock, Hawkes explains, which avoids truck traffic.

In McKinlay’s case, because he currently milks about 65 cows, he adds stale grain (about half a skid steer bucket a day) to his mini to optimize gas production. However, he believes 20kW of electricity production can be achieved with a mini that uses only manure from about 100 milking cows. He and Rachel plan to go that route, increasing their milking herd as quota becomes available.

Like other dairy farmer digester owners, the McKinlays gain other benefits from their small digester. The digestate is put through a screw press, the solids are used for bedding and the remaining liquid is spread on the fields.

“I think of the digester as a manure processing plant, a way to get some energy out of it before it goes on the field anyway,” McKinlay says. “There’s a small pump that moves the digestate into our existing manure tank, and it’s actually runnier coming out than it is going in. And in terms of odour, there was a noticeable reduction compared to last year, when we applied the liquid manure after we did fourth cut in the last week of August this year.”

McKinlay is happy to talk about how much he likes his mini — and he’s done so at three packed ‘open houses’ he and Rachel held over the past year.

With that strong level of interest, some farmers may want to quickly apply for funding that’s currently available. Farm businesses and other small-and medium-sized businesses in Ontario and several other provinces can now apply for federal financial assistance with ‘energy-saving projects,’ with a deadline of Oct. 14 or until the funding is exhausted. There’s an online guide for preparing proposals and an online application portal as well, but Hawkes says Martin Energy Group is available to help farmers to put together applications for minis.

“With more than 3,000 dairy farms in Ontario and 4,000 in Quebec, there’s a lot of room for a major effect on greenhouse gases if dairy farms embrace the small-scale digester.”

There is no funding available for mini-digesters under the Ontario Environmental Farm Plan right now.

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