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Concentration of CO2 in the Atmosphere

The Largest Anaerobic Digester in the Northeast

A Vermont dairy farm, a Vermont utility, a Vermont college, and national energy innovators working together for the environment.

The largest anaerobic digester in the Northeast began full-scale production of renewable natural gas (RNG) this month at the Goodrich Farm in Salisbury, VT. (Glenn Russell/VTDigger)

George Harvey

The largest anaerobic digester in the Northeast started operations with a commissioning ceremony on July 21. Among the people attending were representatives from the Goodrich Family Farm, Middlebury College, Vanguard Renewables, Vermont Gas Systems (VGS), and the state of Vermont. We point out to anyone who might say that an anaerobic digester is not much to cheer about that the state of Vermont was represented by both Vermont Governor Phil Scott and Lieutenant Governor Molly Gray.

We might start by considering the business and educational organizations involved in this story:

The Goodrich Family Farm is a dairy farm in Salisbury, Vermont. It was founded in 1956, with a herd of ten cows. Today, it has expanded to have a herd of 900 cows, in addition to 2,400 of acres of land used to grow corn and hay. The owners of the farm have been working to have the lowest environmental impact possible, including dealing with the manure from all those cows. Left to itself, the manure would emit large amounts of methane into the atmosphere, along with phosphorous compounds that would eventually get to Lake Champlain.

The Goodrich Family Farm. (Vanguard Gas Systems)

Middlebury College is in Middlebury, Vermont, the next town over from Salisbury. The college is well-known for its efforts to end its use of fossil fuels, switching entirely to renewable resources. Historically, the college has been dependent on natural gas for heat. Over the years, it has actively sought a way to replace natural gas, a fossil fuel primarily made up of methane.

Vanguard Renewables is based in Wellesley, Massachusetts. It develops, owns, and operates anaerobic digesters sited on farms. Its anaerobic digesters convert organic waste materials, typically manure and food waste, into bio-methane and fertilizer. It has worked mainly in the Northeast, but it is expanding to work across the country.

VGS owns and operates natural gas infrastructure in Vermont. One of its pipelines was laid out in such a way that it could carry bio-methane from the Goodrich Family Farm to Middlebury College.

Every day, about 100 tons of manure is mixed with 180 tons of unavoidable food waste from Vermont businesses, such as Ben & Jerry’s and Cabot/Agri-Mark. This is mixed in a 250,000-gallon pre-treatment tank. After the material is treated, it is moved into one of the two 925,000-gallon anaerobic digesters at the farm. The digesters are maintained as environments where the particular microflora in the process could be happily doing their jobs.

The products of this work are a gas and a mix of solids and liquids. Both of these need to be treated before they can be used. The gas has to be treated to remove compounds that would negatively affect use in equipment designed for natural gas, after which, the bio-methane is a drop-in replacement for the fossil fuel. The solid and liquid materials need to be treated to remove phosphorus compounds that would pollute the waters leading to Lake Champlain and the lake itself.

We should note that the methane captured in this process would have been emitted anyway. This is a natural process and part of the way nature breaks down such organic materials as manure. However, since methane is a greenhouse gas twenty to eighty times as powerful as carbon dioxide, trapping and burning it reduces the load of greenhouse gases quite a lot.

Also, the phosphorous and other compounds that have been removed from the effluent would otherwise have gone into the soil and water of the area, supporting unwanted biological activity in Lake Champlain, included blooms of algae and cyanobacteria. The fact that these materials have been removed is very beneficial for aquatic life.

Once the bio-methane is created, it can be injected into the natural gas pipes VGS operates. The pipes move the gas to Middlebury College, which burns it for heat and cooking. The college has contracted to buy 55% of the gas produced by the digester at the Goodrich Family Farm.

Vermont already has a number of biodigesters, all working in a similar manner. All of them operate to the benefit of our environment. Addressing those attending the commissioning, Governor Scott said. “Think about it – we’ve got a Vermont farm, a Vermont utility, a Vermont college, and national energy innovators all coming together to build a model for our region. And it can be replicated in other parts of the state and country, as well. This is truly transformative work that Vermonters can be proud of.”

Lieutenant Governor Molly Gray added, “This includes continuing our efforts to weatherize homes, make solar and community solar available to Vermonters and supporting incentives for Vermonters to purchase electric vehicles.”

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