Anaerobic Digesters Slow to Come On-Line in R.I.

The Johnston, R.I., facility will feature two 2.5-million gallon digestion tanks, which will break down food scrap anaerobically. (Kevin Proft/ecoRI News photos)

The Johnston, R.I., facility will feature two 2.5-million gallon digestion tanks, which will break down food scrap anaerobically. (Kevin Proft/ecoRI News photos)

By KEVIN PROFT/ecoRI News staff

JOHNSTON, R.I. — Rhode Island’s first two anaerobic digesters were expected to be up and running by now, based on timelines provided by the owners of each project.

In Johnston, the Blue Sphere Corp., an Israeli-based company, stated in November 2015 that it expected its facility to be operational by the beginning of this year. In the Quonset Business Park in North Kingstown, NEO Energy, a New-Hampshire based company, initially expected its facility to be operational by the end of 2014. In May 2015, NEO modified its timeline, saying that it hoped to have the facility built by the end of 2016.

Currently, Blue Sphere’s project remains under construction; the Quonset project has yet to break ground.

Anaerobic digesters process food scrap in such a way that it produces methane, which is burned on-site to create electricity, and a soil amendment that can be sold to farmers for certain applications. This disposal method for food scrap is generally considered more responsible than sending it to the landfill, where it occupies valuable space and accelerates climate change via methane emissions.

Opponents of anaerobic digesters say food scrap would be better used to rehabilitate soil.

Generators will turn the methane into electricity, and excess heat from the generators will be used to maintain the proper temperature of the digesters. The black tanks in the background are the wastewater treatment tanks.

Generators will turn the methane into electricity, and excess heat from the generators will be used to maintain the proper temperature of the digesters. The black tanks in the background are the wastewater treatment tanks.

Johnston project
Blue Sphere broke ground on its Johnston facility in May of last year. When completed, it will accept 250 tons of food scrap daily and generate 3.2 megawatts of electricity. Hansel Tineo, a project manager for Austep, the Italian-based builder and future operator of the facility, said it will begin accepting food scrap come springtime and be fully operational by this summer.

The facility will include at least 11 structures. Waste haulers will deliver food scrap to a reception building, where automated equipment sorts out contaminants such as plastic, and pulps the food scrap. Once pulped, the food scrap moves through a holding tank and into one of two 2.5-million gallon digestion tanks, where it breaks down anaerobically — without oxygen.

The food scrap will then enter a second, smaller digestion tank, where it further decomposes. Anaerobic digestion takes between three and four months, according to Chris Duhamel, vice president at DiPrete Engineering, the local engineering firm that helped usher the project through its complicated permitting process.

The methane created during anaerobic digestion will be piped to on-site generators that burn the gas to create electricity, which gets distributed to the power grid. Upon leaving the smaller digestion tank, the solid and liquid byproducts of the digestion process are separated. The liquids get treated in a four-tank wastewater treatment system until they are about as clean or cleaner than residential wastewater. The liquid will then be introduced into the Narragansett Bay Authority’s collection system, which will further treat the wastewater at a downstream treatment plant, according to Duhamel.

The solid byproducts of the digestion process are dried, then sold as a fertilizer.

The facility will receive revenue from three sources: a tip fee charged to waste haulers delivering food scrap; the sale of energy to National Grid; and the sale of fertilizer. National Grid has agreed to buy electricity for a price not to exceed 10 cents per kilowatt-hour for the first year, followed by annual 2 percent price increases, according to David Graves, a spokesman for National Grid. The contract lasts for 15 years, with the possibility of an extension that must be approved by the state Public Utilities Commission.

North Kingstown project
While Blue Sphere’s facility in Johnston nears completion, NEO Energy’s facility planned for the Quonset Business Park has yet to break ground, despite the company's initial expectation to have the facility completed by the end of 2014.

The project remains in the environmental permitting process, according to Tony Callendrello, chief operating officer for NEO Energy. He couldn't provide a timeline for how the project will proceed.

The Rhode Island Department of Environmental Management's Office of Air Resources issued a draft permit to Neo Energy on Feb. 24 for its review and comment, according to an agency spokeswoman. To date, the department hasn’t received a response to the draft permit, she said. The Office of Waste Management issued a putrescible waste composting registration to Neo Energy in January.

The proposed project would accept about 68 tons of food scrap daily and generate 500 kilowatts of energy. NEO signed a power-purchase agreement with National Grid in September 2014. The utility company agreed to buy energy from the anaerobic digestion facility for 19.55 cents per kilowatt-hour. In accordance with state law, the contract will terminate 36 months after its signing — Sept. 5, 2017 — if the facility isn't complete by then.

Tiverton idea
Blue Sphere, in conjunction with DiPrete Engineering and Austep, is considering building an anaerobic digester on an 8-acre town-owned parcel in the industrial park off Progress Road in Tiverton. The plant would be 1-2 megawatts, according to Mark Rousseau, Tiverton's town planner.

Blue Sphere has provided a letter of intent to the town to buy the land if it's able to secure the required permits and a power-purchase agreement with National Grid, according to Rousseau. A public presentation about the proposed facility was held at a Town Council meeting last spring and included representatives from Blue Sphere, DiPrete Engineering and Austep. Rousseau expects to have more information on the status of the project by June.

The industrial park is already the site of a 265-megawatt natural gas-fired power plant operated by Tiverton Power.

"I support renewable energy, but I think its going to take a long time to get ourselves off natural gas," said Rousseau, regarding the discrepancy in electrical output between the existing fossil-fuel power plant and the proposed anaerobic digester. "We just have to keep chipping away."