First Mass. Food-Scrap Digester Under Construction

Crapo Hill Landfill in Dartmouth seen as a future site for a bioenergy facility

By JOYCE ROWLEY/ecoRI News contributor

DARTMOUTH, Mass. — The state’s first anaerobic digester designed specifically for food scrap is under construction at the Crapo Hill Landfill. It is scheduled to begin operating this June, just in time to meet the Massachusetts food-scrap ban that is set to begin in October.

The CommonWealth Resource Management Corporation (CRMC) received Massachusetts Department of Environmental Protection (DEP) approval last September for a 12-ton or 3,000-gallon-per-day pilot food scrap anaerobic digester as part of what CRMC is calling a “bioenergy facility” on leased land at the landfill. CRMC currently runs a 3.3-megawatt landfill-gas-to-energy (LFGTE) plant at the site.

“It’s unique now, but in the context of an emerging market created by New York, Massachusetts and other parts of New England banning food waste, you’ll be seeing a lot more of them,” said Tom Yeransian, a principal partner at CRMC.

Massachusetts joined Vermont and Connecticut in banning organic waste disposal last year, when it banned high-volume food waste generators. The ban only affects facilities that generate more than 2,000 pounds of food scrap a week. In real numbers, that’s a staggering 450,000 tons of food scrap that was being buried or burned annually, according to DEP.

Under the ban, food can be repurposed or donated if useable. Food scrap also can be composted or sent to an animal-feed operation. The remainder will go to private or state-run anaerobic digesters that take organic waste and reduce its volume through microbial degradation in a zero-oxygen chamber. The results are methane, carbon dioxide and heat.

CRMC’s $1 million pilot anaerobic facility will be a continuous feed, wet, 100,000-gallon digester. The slurried feedstock mixture will be comprised of 50 percent food scrap, 25 percent fats, oils and greases, and 25 percent high-grade wastewater treatment sludge. The biogas, comprised of at least 61 percent methane, will be connected to the existing LFGTE and burned for energy generation.

“We were interested in supplementing our existing landfill-gas-to-energy plant,” Yeransian said. “We had capacity for additional biogas.”

According to the DEP permit, the pilot anaerobic digester is expected to generate 25 cubic feet per minute of biogas during its initial phase. When in full swing, the amount of electricity produced will bump up the existing plant production to 4.1 megawatts.

“We want to run the pilot for a year to see how it performs through all four seasons,” Yeransian said. If successful, CRMC will expand the operation to 120 tons or 30,000 gallons per day and a 1.2 million-gallon digester. The tenfold increase in organic waste will yield an anticipated 25 percent increase in biogas.

Anaerobic digestion produces fewer greenhouse gas emissions compared to landfilling these materials, as it captures more methane in a more efficient method and releases less carbon dioxide, according to Gregory Cooper of the DEP. Food scrap also yields higher methane content than other organic wastes, he said.

Other benefits
Part of the bioenergy facility’s goal is to find beneficial uses of leftover digestate. It could be used as a low-nutrient fertilizer, or increase the value of yard composting material. Yeransian said the disposition of the digestate is a new market as well.

“The opportunity of being located at the landfill is that the digestate can be used in a closed and capped cell. The biological degradation slows down after capping,” Yeransian said. “By reintroducing moisture from the digestate water with low nutrients, it can rejuvenate those areas and make more biogas.”

Siting the bioenergy facility at an existing landfill with an existing landfill-gas power plant also means that no new infrastructure is needed to handle truck traffic. Also, the facility isn’t being built atop greenfields, and it will help extend the landfill’s capacity.

The project will help larger organic waste producers meet the state’s food-scrap ban. The University of Massachusetts at Dartmouth, SouthCoast Health Systems’ St. Luke’s Hospital in New Bedford and the Bristol County Correctional Facilities currently bring their solid waste to the landfill, according to Scott Alfonse, executive director for the Greater New Bedford Regional Refuse Management District.

So far, the project has received $400,000 in grant money from the Massachusetts Clean Energy Results Program, DEP and the Massachusetts Clean Energy Center. The balance of the cost is being provided by private investment.