GRANVILLE — Rockwood Farm has 600 cows and one 800,000-gallon stomach.
The “stomach,” an 18-foot-deep tank of cow manure and food waste slurry, is really an anaerobic digester.
Inside, natural microorganisms from the cow’s digestive tract grow in waste heated to 100 degrees, or about the same temperature as the inside of a cow.
The microbes make carbon dioxide and methane, gases that can be heard bubbling away beneath the crusty surface of the constantly churning slurry. The methane fuels a motor capable of generating 450 kilowatts at full power. That’s 3.5 million kilowatt-hours a year, or enough for 336 average American homes.
That’s also enough power to keep the family farm in business at a time when milk prices are not keeping up with the cost of production and other dairy farms across the northeast are selling their herds and closing down.
The digester occupies a corner of the Woodger family’s farmstead on a hillside in Granville, about 20 miles from Springfield. In addition to generating power, the digested waste is spread on their fields as fertilizer.
“We wouldn’t be doing it for any other reason than to keep the farm going,” said Richard C. Woodger, who started Rockwood Farm with his wife, Mary, in 1969.
The project meets a number of goals for the state, said John Lebeaux, commissioner of the Department of Agricultural Resources. It gives income for the farm. It cuts down on greenhouse gas emissions, because the methane would otherwise escape into the atmosphere. And it gives the state’s food waste a place to go.
“Dairy farms really are the linchpin of the agriculture in the state,” Lebeaux said. “Because they occupy so much land and they help to keep that land agricultural. So we need to do everything we can.”
Today the Woodgers’ sons Doug and Dan run the farm, where 415 cows get milked three times a day. The rest are young stock not ready to breed or not giving milk.
The Woodger family and Ag-Grid Energy, which helped develop the power plant, hosted an open house Wednesday. Among the guests were representatives of towns and government entities that buy net metering energy credits from the digester operation.
The generator started running about three months ago. It’s fed not only by liquefied cow manure from the farm but also liquid food waste from area factories including the Coca-Cola plant in Northampton, Agri-Mark’s butter and dried milk powder plant in West Springfield and area H.P. Hood dairy plants. The farm also takes grease from restaurants that would otherwise go to area sewage treatment facilities, where it doesn’t break down like it does in the digester, Dan Woodger said.
The farm gets two or three tanker truckloads of this waste every day, Woodger said.
Soon, the digester will start eating sold food waste, delivered to the farm from school cafeterias, hospitals, supermarkets and other cooking and eating establishments. First it will be fed through a machine that removes packaging and other contaminants.
“Like forks,” Dan Woodger said. “Or the bag from a bag of chips.”
The depackaging equipment will be one of only two such operations on farms in the state, said Greg Cooper, a director at the Massachusetts Department of Environmental Protection. All told there are eight digesters on Massachusetts farms.
“I keep hearing win, win, win, win,” Cooper said.
Massachusetts banned most commercial food waste from landfills back in 2014, Cooper said. But still more than 1 million tons of food waste ends up in landfills each year, mostly for lack of places to decompose and reuse it.
Sam Fox of American Mussel Harvesters in North Kingstown, Rhode Island, said the composting industry has had trouble growing due to the smell and other difficulties. The digester captures smells and might be a good disposal method for the tons of waste American Mussel Harvesters generates from growing, cleaning and processing mussels, oysters and clams.
He even brought along a plastic tub of the waste, picking through it to show the chunks of rotting meat and shards of shell.
The digester, engine, generator and depackaging equipment cost $5 million, said Rashi Akki, founder and CEO of Ag-Grid Energy. The project got some outside funding in grants: $500,000 from the Massachusetts Clean Energy Center, $250,00 from MassDEP and $150,00 from electrical utility Eversource.
The towns that bought energy credits from the project include Granville, Sherburne, Worthington, Dalton and Northfield, as well as the Hilltown Charter School in Easthampton and the Franklin Regional and Pioneer Valley transit authorities.
The farm itself consumes about 20 kilowatts of power at any given time, Richard Woodger said. Before generating his own power with the digester, it cost him $500 to $800 a month for power to run the fans that keep the cows comfortable, the milking equipment, the milk refrigeration equipment and other electrical appliances.
“That’s another savings,” he said.
And soon the farm will use the digester and its engine for hot water. Richard Woodger said it takes 180 gallons of boiling water to sanitize the farm’s milking equipment, and it’s a job that needs doing three times a day.