Via Community News Service, a University of Vermont journalism internship
ST. ALBANS — Cherry Garcia, Chunky Monkey, Phish Food, and Half-Baked — just some of the 98 distinctive ice cream flavors from the popular Vermont-born company Ben and Jerry’s. In St. Albans, 100 million pints are made annually, but more than 5,000 gallons of ice cream waste are left behind each day.
So when PurposeEnergy, a New Hampshire-based enterprise owned by renewable energy investment managers, Quinbrook, opened its third Vermont-based waste facility in May, the company helped provide a solution for Ben and Jerry’s waste problem.
That facility is called an anaerobic digester, and it uses bacteria to decompose organic material like manure, wastewater, and food waste. The breakdown of the waste generates biogas and digestate. The biogas can be used to generate electricity. The digestate, or sludge, is a nutrient-rich material similar to manure, that can be used as fertilizer on farms. It can also be broken down even more into a pre-processed water then sent to wastewater treatment plants.
“It’s basically like a stomach,” said Jenna Evans, the sustainability manager for Ben and Jerry’s, one of the companies that partnered with the facility to process its waste. “The bacteria eats the solids, and all the food waste generates methane.”
Anaerobic digesters became popular in the 1970s during the U.S. energy crisis. Now there are about 2,500 digesters across the country producing biogas, commonly considered a source of renewable energy. Despite drawbacks such as risk of methane leaks or the high price of digesters, these systems help reduce road traffic, greenhouse gas emissions, and air pollution.
The Ben and Jerry’s factory produces two types of ice cream waste. The first one, high-strength dairy waste, is a concentration of water mixed with ice cream that is cleaned from factory pipes. The other form of waste is unsellable pints that have been returned to the facility.
The high-strength dairy waste is sent through an underground pipeline to the St. Albans digester only 1,000 feet away. The returned pints are processed at a Casella depackaging facility in Williston and trucked back to the St. Albans digester.
The biogas used to generate electricity is siphoned into the Green Mountain Power grid 24 hours a day. The one-megawatt generator can power roughly 1,000 homes.
Anaerobic digestion is a natural process that can happen in environments with a lack of oxygen, like wetlands. But the waste facilities act to seal the process and make it more efficient. And while organic waste is typically managed through an unchecked anaerobic environment like landfills, that process is inefficient and allows methane, a potent greenhouse gas, to escape, said Lauren Ray, an agricultural sustainability and energy engineer at Cornell University’s Pro-Dairy program.
But when anaerobic digestion produces biogas, a mix of methane and carbon dioxide, it can be captured to generate electricity or heat. It can also be upgraded to be used in a pipeline or for vehicle fuel by removing carbon dioxide through various techniques, Ray said.
While the official ribbon-cutting was this spring, the St. Albans facility, which focuses on food and beverage waste, has been operating since December, bringing in waste like beer and chocolate and turning it into energy and nutrient-rich material.
When PurposeEnergy approached Ben and Jerry’s, both companies saw this as an opportunity to give new life to its ice cream waste. Before the opening of the facility, which sits on land purchased from the Franklin County Industrial Development Corporation, some Vermont companies would have traveled long miles to get rid of their waste in a digester.
Ben and Jerry’s previously sent its ice cream waste to 19 different places with digesters, including some Caring Dairy farms — a network of farmers partnered with the company — who had individual on-farm digesters. Another outlet used was a community digester from the waste management company, Casella.
“It was a big network around New England,” Evans, the company’s sustainability manager, said. The challenge for the company was finding who was available to take the leftover ice cream waste that day, while also raising concern for adding carbon emissions when trucking the waste over to the outlets.
This didn’t sit well with the ice cream producers, who have worked to improve their overall carbon emissions rates and who encourage their customers to be environmentally conscious.
Evans called it a “big problem” that the company didn’t have a solution to.
“It had to be this partner [PurposeEnergy] that was looking to solve a problem for a variety of different businesses in the area,” Evans said.
Rather than trucking their waste, the Ben and Jerry’s St. Albans factory sends it through a high-density polyethylene pipe underground, thanks to the short distance between the two facilities. The pipe sends ice cream to a waste tank, which pumps it directly to the digester, according to Hasper Kuno, the director of partner success at PurposeEnergy.
“For [Ben and Jerry’s], they were able to show huge carbon savings,” Kuno said. This includes reducing emissions from trucking the waste as well as reducing landfilled waste, the third largest source of human-related methane emissions, according to the Environmental Protection Agency.
Evans estimated the digester would save 7,000 metric tons of carbon from being emitted, but said the company would reevaluate that metric after a full year of use. If successful, that would be equivalent to somewhere around the weight of 175 full-grown humpback whales.
To fund the company’s annual goal of producing 7,000 megawatt hours of energy, PurposeEnergy has a contract through the Standard Offer Program, a program with the state’s Public Utility Department established in 2009 to promote the increase of small renewable energy generation in Vermont.
“This type of project is what the program was designed to encourage,” said TJ Poor, the director of regulated utility planning at the Public Utility Commission. He called putting the end products of the digester into the city’s grids, farms, and water utilities, “a public good and use.”
An impact study done beforehand by the PUC made sure there were no adverse effects from putting the digester’s generated electricity into the power grid, according to Poor.
While Poor focuses primarily on energy, the digester could also benefit Vermont farms.
The solid waste at the St. Albans facility gets sent out to up to 10 regulated Vermont farms that PurposeEnergy is partnered with, who use the waste as animal bedding, in fertilizer, and as amendments to strengthen their soil and crops.
The digestate is a beneficial alternative to manure because of its lack of odor and lower solids, making it easy to pump and manage, Ray said.
PurposeEnergy’s plan is to make roughly ten tons of solid material a day, up to six days a week, according to Kuno.
Meanwhile, the biologically broken down liquids from the digestate is sent to the city of St. Albans wastewater treatment facility, where they can put the treated liquids back into the city.
Kuno said the digester also sequesters phosphorus as part of its process, which keeps it out of the effluent produced. The phosphorus is then relocated into solid waste, which can hold onto it for plants, and becomes less susceptible to surface runoff.
In spite of the sustainable management from these digesters, there are also many obstacles that these facilities have to face.
“Organic waste management requires tradeoffs,” said Matthew Scarborough, an associate professor at the University of Vermont in the Department of Civil and Environmental Engineering, in an email.
Ray said one of the drawbacks of the digester is the relatively high cost to build and operate the system. She said, like any other energy system, digesters are a long-term asset with a lifetime of 20-30 years.
“There needs to be appropriate value given for the renewable and reliable energy source it generates, to compete with fossil fuels,” Ray said. Plus, the greenhouse gas reduction from managing waste that digesters can provide, she said, can justify the cost.
Another drawback of anaerobic digesters is the risk of gas leakage — primarily methane — from the facility and into the atmosphere. Although a small contribution to overall emissions, it is still a factor that many companies are trying to find solutions to. Leaked gas means loss of revenue for these facilities that profit when they put the gas into an electrical grid.
PurposeEnergy’s facilities are 100% sealed off, according to Maddy Fitch, a PurposeEnergy intern. The company follows standards from the American National Standards Institute and uses 150-pound flanges, a ring-shaped tool that seals pipes, valves, pumps, and other industrial equipment in the facility.
All PurposeEnergy operators wear gas monitors that measure and detect methane, hydrogen sulfide, oxygen, and carbon dioxide. There are also ambient air monitors around the plants that check and detect leaks.
Other digester downsides are its dependence on transportation, as well as its reliance on waste that needs to be diluted; however, Ben and Jerry’s solves this with its proximity to the facility, and from sending ice cream waste that is already watered down.
“As with any digester, minimizing fugitive emissions, complying with air pollution permits, and active operations and maintenance are needed to ensure the digester is successful and potential negative impacts are minimized,” Scarborough said.
Scarbourgh said this digester is among the best he’s seen when it comes to digestate management. He also praises their work generating local electricity, supporting the St. Albans economy, and reducing high emissions from hauling.
“Nothing’s perfect,” Evans said. “It’s not without impact at all, but it’s certainly the best way we know how to manage our organic waste stream.”
“This is a really elegant solution for a big problem for a lot of food companies,” Evans said.