Inside a family farm’s biogas system producing enough power for 200 homes

NOTE: See also accompanying main story, "B.C. is leading the way in growing Canada's biogas-renewable natural gas sector, say industry experts."

Gord Green and his son Dave were looking for a way to supplement their family farm’s income while helping the environment. They decided that biogas offered a solution.

Greenholm Farms, near Embro — about 40 kilometres northeast of London, Ont. — is now utilizing manure from about 250 dairy cattle to produce methane gas used to generate electricity on the 750-acre farm.

“This was an opportunity to make some money from our existing manure, plus it was a good thing for the environment,” Gord Green said in an interview. “It was a case of growing the business and adding value.”

Greenholm Farms now generates 500 kilowatts per hour of electricity — enough to supply more than 200 homes.

The Greens invested about $4 million to buy two above-ground anerobic digesters designed and constructed by PlanET Biogas Solutions, based in St. Catharines, Ont.

The digesters essentially are large sealed, insulated round tanks with dome roofs. Bladders at the top of the digesters collect the methane gas produced by bacteria biologically breaking down the methane in manure and other organic waste in an anaerobic environment — meaning an environment without oxygen.

Methane collected in the biogas system is used to fuel engines that run generators to produce the electricity. Heat from the system is reused and circulated by pipeline circuits to maintain the digesters’ constant 37 degrees C — or “hot tub temperature,” as Green put it.

The Greens signed a feed-in tariff-based power purchase agreement with the Ontario Power Authority to sell the electricity they produce to the provincial grid. The agreement provides a guaranteed price for the power over a 20-year period.

“We’re getting paid more for what we sell than what it costs to buy the power back for use on our farm,” Green said.

The family’s biogas system continuously produces power around the clock. However, the power purchase agreement limits the amount of electricity that the Greens are able to sell into the grid to 500 kilowatts per hour. So any excess methane is burned in a flare stack.

In addition to cattle manure, the farm’s two digesters use expired fruits and vegetables from grocery stores as well as potatoes that don’t make the grade for commercial scale. The Greens get paid tipping fees for receiving these off-farm organic materials rather than having them go to a landfill.

Along with keeping the methane — a potent greenhouse gas — out of the atmosphere, the Greens say their biogas systems provides other benefits. The solid material that comes out of the digesters is put through a press, which results in a peat moss-like material that’s essentially sterilized.

“Bacteria growing in it aren’t the problem you would have if just did this with raw manure,” Green said.

“We bed the cattle with this stuff,” he said. “So we get free bedding material. And then it gets recycled back through the digester with the manure.”

Liquids produced by the digesters are spread as fertilizer on the farm’s fields. This material not only retains the nutrients that crops need, going through the digesters enhances the availability of nitrogen for crops, Green said. The liquid fertilizer also has much less odour than regular manure, he added.

The Greens’ biogas system and associated new manure storage required them to develop a nutrient management strategy. Regulators had to approve the system, including inspections to ensure all the piping and other fittings were safe and up to code.

The Greens started producing gas from their first digester in 2013, and from the second unit in 2018. Green estimated it will take about 10 years for the two digesters to pay for themselves and the family farm to see a return on investment.

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