Garbage and manure combine to create powerful assets for Maine dairy farm

Tom Bell
March 15, 2015
Press Herald
Adam Wintle sees too much of a good thing when he reads the electronic panel attached to the side of his $6 million anaerobic digestion system. An engine generates electricity by consuming 340 cubic feet of methane-rich biogas gas per minute. But another 200 cubic feet of gas is shooting up a pipe and burning off in a flare.
“We’ve got a lot of excess gas,” Wintle says. “That gas could be running another engine.”
The digester is essentially two enormous crockpots that cook a stew of cow manure and food waste at 100 degrees. Built just over three years ago, it is the largest anaerobic digester in Maine and among the largest in the United States. It produces enough electricity to power all the homes in a town the size of Boothbay Harbor.
The 1,000 milking cows at the adjacent Stonyvale Farm supply the manure. Hospitals, restaurants and grocery stores provide the discarded food.
Wintle, 34, his brother, John, 37, and sister, Sarah, 35, are ambitious, and they enjoy the support of their major investor, Stonyvale Farm, the second-largest dairy farm in the state.
The Wintles plans to add two more engines and build two more 25-foot-tall, 400,000-gallon digester vessels – the concrete containers in which the slurry of manure and food waste is cooked. If construction of the $10 million project goes ahead, the expanded facility would operate more efficiently and generate 3 megawatts of electricity – three times as much as it produces today.
When completed, it will produce the same amount of electricity as produced by the 17 digesters in Vermont. Because the Vermont digesters use only manure, they can’t produce as much electricity as the Exeter facility. Manure keeps the digesters running smoothly, Wintle says, but it’s the food waste that makes them a powerful producer of biogas.
The major obstacle to the siblings’ expansion plans is getting enough food to mix with the manure.
About 20,000 tons of food waste get dumped into the digester annually, but a stream of 50,000 tons is needed to make the expansion project work.
“The choke hold on expansion is food waste,” Adam Wintle says.