In addition to making milk, Vermont’s dairy cows create a lot of manure. And what to do with that waste can sometimes be a challenge.
Anaerobic digesters have existed for decades to capture methane gas from the waste which can be used to generate electricity. But the systems are expensive and complicated, meaning they've been limited to only the state’s largest dairy farms.
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Green Mountain Power is hoping to change that dynamic by building a community digester to serve three St. Albans farms. And the utility says new technology will be added to the system to help clean up Lake Champlain.
Paul Bourbeau has been thinking about anaerobic digesters for over 15 years, but hasn’t been able to make it a reality on his dairy farm. “To do it on our own, the dollars and cents don’t add up,” he said.
Green Mountain Power’s Josh Castonguay says in addition to the cost, some farmers just don’t want to operate electrical generation equipment, so a community digester is the next logical step. Manure from Bourbeau’s farm and the neighboring farm would be pumped to the digester. Waste from another nearby farm would be trucked in.
Castonguay says the plant would generate 800 kilowatts of baseload power, and could improve reliability in the area by feeding a micro-grid. But unlike other producers of cow power, this digester would include a system to treat the separated waste.
“You have the standard digester, then it will go through another process to extract more phosphorus from the manure stream. It gets physically separated out," he said. "It can have anywhere from 70 to 80 percent less phosphorus. Liquid goes back to the farms. They can apply it to their fields, but it has less phosphorus in it. So in an area like the bay that’s pretty overloaded with phosphorus, this will go almost a third of the way toward what the EPA is asking us to reduce here in the bay."
The digester will be built, owned and maintained by Green Mountain Power.
“What we worked on in this case is what we’ve called a manure supply agreement. It might be the first of its kind ever, where in exchange for providing the manure, they get back the bedding at no cost. So that offsets a cost to them for buying sawdust," Castonguay said. "They also get a royalty payment. We give them a percentage of revenue that the project makes back to the farmers that are taking part."
Bourbeau says the bedding is the measurable benefit to his farm, but he sees the environmental value from the project. “Being able to capture that excess phosphorus that is not needed in this area, being able to put that into a product that is more manageable and can be put on trucks and in packages and can be moved away from this area and be put to areas that really need phosphorus, that’s a really big deal too," he says.
Green Mountain Power presented the plans to the town this week. Some residents had raised concern about the potential for odor and pest issues associated with any food waste that the digester accepts. GMP’s David Dunn says pre-consumer food waste, like creamery byproducts, could come to the digester, but it would be a small amount. “About 64,000 tons per year of dairy manure. Roughly 2,000 to 2,700 tons of food waste per year, so a relatively small percentage.”
While the town select-board had made a motion against supporting the project, Select Board member Dave McWilliams said the presentation changed his mind.
“We’re going to revisit that motion and clarify that we want local control. But the presentation that they did today, I’m very supportive of it now,” McWilliams said. “Getting the phosphorus out of the bay is one of the biggest things that we need to do to save Lake Champlain.”
The Public Service Board will have the final say on the project. Green Mountain Power has filed an application for a certificate of public good. If it’s approved, the utility will build what it hopes is its first community digester next summer.
This story has been edited to correct the spelling Josh Castonguay's name.