About a decade ago, a fifth generation dairy farm in Penobscot County installed a system for managing the vast piles of manure produced by its 1,000 cows. By loading the manure into large, heated tanks filled with microbes, they could generate electricity using a technique called anaerobic digestion. It was a decision made primarily for business reasons — to cut the farm’s energy costs and bring new income from the excess electricity it generates. But soon, the farm realized it could get even more bang for its buck by adding another organic material into the mix: leftover food.
“We realized that the economics were much more attractive,” said John Wintle, who manages the Exeter facility and is part of the family that owns Stonyvale Farm. “You can make a lot more gas per pound of food waste than you can from dairy manure, because the dairy manure has already been digested by the cow. So with the same footprint, if we took in food waste, we could make a lot more gas, a lot more electricity.”
Within a few years, Stonyvale Farm grew to include a set of companies, including its digestion business, Exeter Agri-Energy, and an offshoot, Agri-Cycle Energy, that trucks in many tons of food waste from Maine and beyond to mix with the manure. After investing heavily in upgrades over a seven-year period — subsidized by around $3 million in government grants — they now operate three digesters and a depackaging machine that, when operating at full scale, can power 2,500 homes. They send the packaging removed from food to ecomaine in Portland, where it’s burned in a waste-to-energy incinerator.
While many farms across the country have installed anaerobic digesters to handle their manure in recent decades, it’s less common for them to operate at that scale or to add food waste to them. No other farms in Maine do so, and the federal government is only aware of a few dozen similar operations — including several in Massachusetts and Vermont. However, another farm in Clinton, Maine is now working to install a digester to convert just its cow manure to natural gas.