Digester Makes Dairy Farm Super Sustainable; Manure and Food Waste Yield Heat, Electricity, Fertilizer, and Bedding
The Recorder, January 13, 2017, by Richie Davis
The 500 Holstein cows chewing in the Bar-Way Farms barn don’t seem to notice, but something exciting is happening with their manure.
And when spring arrives, farmer Peter Melnick says, he’ll be thrilled to be spreading a liquid fertilizer from the new $5 million electricity- and heat-producing waste digester that’s getting ready for operation. It still needs to be connected to the electric grid and needs to start receiving food waste shipments, but the “bugs” are already at work generating methane gas that will fuel a 1-megawatt electricity generator and heat the farm.
The 700,000-gallon oval-shaped concrete tank, only the top 11 feet of which is visible above ground behind the barn off Mill Village Road, is three-quarters full with manure that the farm has been saving up, awaiting the arrival of the first delivery of food waste by month’s end. The food waste fuel that will supplement the farm manure is the result of the state’s ban on large-scale commercial organic waste at landfills.
The racetrack-shaped “fuel” tank has two boat propellers on opposite ends to push the waste down the center.
The tank is topped by a pair of insulated rubber domes inflated by the gas that the material is giving off as the manure undergoes anaerobic digestion at 105 degrees. There’s a resemblance to twin nuclear reactor domes, but Melnick says he prefers to think of the expanding and contracting membrane as giant inner tubes. The system is kept under low pressure, he says, and the worst that could happen would be for the rubber membrane to puncture.
Once the organic waste begins arriving — at the rate of 50 tons on two to three trucks a day, much of it from “de-packaging plants” that remove out-of-date, discarded or spoiled produce, juice and other foods — the slurry will be pumped into a 100,000-gallon hydrolyzer tank together with 20 tons of manure daily, to be combined as “a big stew” for four or five days before going to the oval-shaped digester for 21 to 30 days.
Open House in the Spring
Melnick says he’s looking forward to an open-house celebration sometime this spring to acknowledge Bar-Way Gas LLC’s appreciation to “everyone who helped this become a reality: USDA’s Natural Resources Conservation Service, which provided a $335,000 grant, the state’s Clean Energy Center, which awarded another $400,000, as well as the state Department of Environmental Protection, Eversource and lenders for the project.
The open house will also be a chance for neighbors who have expressed interest in having 90 percent of odors eliminated from application of what had been manure to fields to visit.
The high-efficiency digester, which uses a Canadian CH Four Biogas design, will be operated by Vanguard Renewable of Wellesley, which will arrange with Casella Resource Solutions for procurement of food waste and its delivery.
From the digester, the 7 million gallons of material goes into a separator that yields about 3 percent solids, for use as cattle bedding material and liquid digestate, which can be spread on fields.
“We’re excited,” Melnick says. “We used to have to buy commercial fertilizer. The (digestate’s) nutrient content is the same as manure and the nitrogen content is more available, but the methane and sulphur are removed, so the odor’s reduced by 90 percent.
The system, which allows the manure to be plowed directly into a hydrolyzer pit along with wastewater from barn cleaning, also will feed the organic bedding right along with it, so everything gets recycled.
In addition to being paid for accepting the food waste, Bar-Way will also sell off 85 percent of the 1 megawatt of power the digester generates every day, with the rest siphoned off to run the system and the farm.
“I used to import my fertilizer and my oil for heat,” said Melnick, who’s already planning a greenhouse to use some 3 million BTUs of heat an hour to take advantage of what won’t be needed for farm buildings or to run the digester. “Now I’ll be able to make all my own. That’s what sustainability is all about. And we’re taking care of the waste locally and using it for a lot of good things.”
In fact, Melnick sees a dairy farm as the perfect place to put a methane digester, rather than as part of an industrial operation. Taking care of it is like feeding cows’ stomachs. You’ve got to watch out for bugs, and you’re trying for maximum production, but you have to be careful what you feed cows. A dairy farmer understands that. And you can use the materials for bedding, heat, electricity, and fertilizer. People are always amazed at how the pieces work together. I call it a balance of nature, with man’s technology also at work.”
You can reach Richie Davis at firstname.lastname@example.org
or 413-772-0261, ext. 269