Waste Management

R.I.’s First Digester Expected to Take Food Scrap in June


Construction of the state's first anaerobic digester began in 2015. (ecoRI News)

JOHNSTON, R.I. — Rhode Island is on the verge of opening its first industrial anaerobic digester, offering another option in the long process to reduce waste and find a better use for the millions of pounds of food scrap wasted each year.

The $19 million facility, built near the Rhode Island Resource Recovery Corporation (RIRRC) on Shun Pike, is expected to begin taking deliveries of food scrap and other organic material next month. Through the process of fermenting this material in massive airtight tanks, the facility will produce two byproducts: electricity and a compost additive called biosolids.

Electricity is generated by burning methane that is released as the food scrap is transformed into a liquid, solid and gas. The liquid is treated and released into the sewage system. The residual solids are dried and sold as an amendment to fertilizer.

The facility is owned and developed by the Blue Sphere Corp., an Israeli-based company with its U.S. headquarters near its only other domestic anaerobic digester, in Charlotte, N.C.

The Rhode Island anaerobic digester represents the latest phase in the years-long effort to extend the life of the state’s primary landfill and create a sustainable solution to the mounting problem of wasted food. At the current rate, the Central Landfill is expected to reach capacity by 2038. About 18 percent of waste buried in the landfill is food scrap. Another 20 percent is organic material, such as paper and cardboard.

A Rhode Island law passed in 2014 and amended last year requires large restaurants, hotels, food manufactures and processors, universities, and grocery stores to donate their leftovers to food pantries, or send them to a farm for feed. Food scrap not fit to eat must be delivered to a compost facility or anaerobic digester as long as such a facility is within a 15-mile radius of the business or institution. There is no requirement for residential food-scrap collection. So far, Rhode Island only has two compost facilities: Earth Care Farm in Charlestown and The Compost Plant in Warren.

Blue Sphere is near major highways and food producers in Providence, Cranston and Warwick.

Rhode Island produces about 250 tons of food scrap daily. The Johnston digester is expected to accept between 250 and 300 tons of food scrap and organic material a day, including plant, grasses, leaves, and industrial sludges.

Beth Anne Clark, Blue Sphere’s project development manager and only U.S. employee, won’t yet name the organizations that will have their organic material, called feedstock, shipped to the facility. But she believes there is an adequate supply of unwanted food and organics in Rhode Island to feed the digester and supply local farms with animal feed and compost facilities with material.

“We’re an alternate destination to the landfill,” Clark said.

About a quarter-mile from the digester, RIRRC welcomes Blue Sphere to the neighborhood.

“Their anaerobic digestion operation will help to support Rhode Island’s organic waste statute and green economy,” said Brian Card, RIRRC’s director of operations and engineering. “The opening of their facility marks an important milestone for sustainable food management in Rhode Island.”

Greg Gerritt, founder of the annual Rhode Island Compost Conference & Trade Show, agrees that there will be plenty of organic material and food scrap to go around. He sees the opening of Blue Sphere as a major step forward for Rhode Island in terms of capacity to accept food scrap and the ability to divert a valuable resource from the Central Landfill.

“Hopefully, it will serve as a catalyst and get additional businesses thinking about better managing their food scrap,” Gerritt said.

How it works
Private haulers pay a tipping fee to deliver their organic material to the digester. The fee is less than that charged by RIRRC, which is about $65 a ton for commercial trash.

To avoid odors, the feedstock is emptied inside a warehouse that runs a negative air-pressure system to keep air from flowing outside. The feedstock first goes through a “depackaging” machine that removes plastic bags, bottles and most other food wrapping.

The remaining organic material is pureed and piped into one of the two 2.5-million-gallon digesters, where it sits for 30 days at about 165 degrees. With the help of special bacteria, the slurry digests like a giant stomach. The methane is captured and stored in tanks to provide fuel to run a 2-megawatt generator and a 1.2-megawatt generator. The electricity feeds into the electric grid.

Blue Sphere has a 15-year power-purchase agreement to sell the electricity to National Grid at a price of 9.5 cents per kilowatt-hour for the first year, followed by 2 percent annual price increases.

After 30 days, the slurry heads to a cold tank, where centrifuges separate the solid from the liquid. The solid is dried and sold as a soil amendment. The liquid is treated at an on-site wastewater treatment system, then discharged into the municipal sewage system.

The project broke ground in May 2015 and was originally expected to be running by late 2016.

It took a year and a half to receive all of the permits for the digester, about a year longer than needed for permitting a similar facility in Charlotte. The Rhode Island project required more stringent regulations to receive permits for air, water, and wastewater treatment, according to Cark. Blue Sphere spent $500,000 on a catalytic reduction system that wasn’t required in Charlotte.

“It’s good for citizens that regulators are looking out for your health and well-being,” Clark said. “But from a development standpoint, (the permitting process) might actually make the project un-bankable or unprofitable.”

Once running, the the facility is expected to employee up to seven employees.


Join the Discussion

View Comments

Leave a Reply

Your email address will not be published. Required fields are marked *

Your support keeps our reporters on the environmental beat.

Reader support is at the core of our nonprofit news model. Together, we can keep the environment in the headlines.


We use cookies to improve your experience and deliver personalized content. View Cookie Settings