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Concentration of CO2 in the Atmosphere

Vermont Technical College’s Anaerobic Digester

VTC's Anaerobic Digester. Photo courtesy of VTC.

VTC’s Anaerobic Digester. Photo courtesy of VTC.

By George Harvey

Can you imagine anything more exciting than an anaerobic digester, filled with waste food scraps from a school cafeteria, agricultural spoilage, chopped hay, and lots and lots of manure, pumping out methane (aka swamp gas)? If you can answer “yes” to this question, I suggest a chat with Mary O’Leary, an Assistant Professor at Vermont Technical College In Randolph. She may not change your answer, but she will, at the very least, make you understand the question in a new light.

Mary is the project manager of VTC’s new Anaerobic Digester Project. The project is under way, and is expected to produce heat and power from the beginning of March. It is expected to produce 375 kW of power, and the waste heat from the generator will be captured to heat four buildings, which will be connected in time.

Anaerobic digestion is a natural process, which can be understood from the workings of a cow’s stomach. Bacteria break down cellulose and other nutrients, using some of the energy in them as food. If there is no oxygen available, the bacteria ferment the food in a way that releases methane gas.

Methane from the process is the most important constituent of natural gas, and can be used just about anywhere natural gas is used. In the case of VTC, the gas is used to run a generator, supplying power to the grid as a net-metered project. When waste heat is captured, the whole process is highly efficient.

Best of all, the VTC anaerobic digester provides a set of very important benefits to the environment. One is that it is a renewable source of both electricity and heat.

Another environmental benefit is that the system prevents methane from manure from getting into the atmosphere. Methane is estimated as having twenty to forty times the power of carbon dioxide as a greenhouse gas, burning it to carbon dioxide is a benefit, for global warming.

Additionally, by intercepting waste from various sources, the system reduces the load on conventional waste-handling facilities. The feedstock is 51% manure, spoilage, and hay. The rest will be food waste and by-products, including whey and waste from dining facilities. Various organizations are partnering with VTC for this, including local farms. Grow Compost will be supplying waste from food sources, and Highfields Center for Composting is working with VTC on training and research (links at the end of the article). Other waste may come from dairies, breweries, restaurants, and other sources.

The digester needs 450,000 gallons of feedstock just to get started. Once it is going, 15,000 gallons has to be added each day. Clearly, some of this would have been used as fertilizer in the past. There is no reason to feel bad about that, however, because the by-product of the process can also be used as fertilizer, and since non-agricultural waste is used, there is more of it. We might note that human waste will not be used, and permits to process food scraps have requirements for specific monitoring to make sure operations are within parameters for good health.

That the system is handling food waste is especially important because we are currently phasing out sending such waste to landfills. It will no longer be legal to send food waste to landfills as of 2017.

Funding for VTC’s anaerobic digester included a $1.5 million grant from the Vermont Sustainable Jobs Fund capital funding comes from grants from the U.S. Department of Energy, obtained with the help of U.S. Senator Patrick Leahy, and bond funding from the Vermont State Colleges. And invaluable help and funding have been provided by many other generous organizations and individuals including Vermont’s Clean Energy Development Fund, the Vermont Agency of Agriculture, Food and Markets, the Vermont’s Agency of Natural Resources, Vermont’s Department of Public Service, the SPEED program, the Natural Resource Conservation Service, the Kresge Foundation, the Town of Randolph, and the Tri-Town Alliance.

Stone environmental (stone-env.com) did a map showing amounts of waste. Bio-Metatech of Quebec (bio-methatech.com) designed the Lipp AD system and is overseeing construction. J. Hutchins of Richmond, Vermont did the site work. R.G. Gosselin of Derby Line, Vermont (rggosselininc.com) did the concrete work.

Highfields Center for Composting (highfieldscomposting.org), Grow Compost (growcompost.com) accepts home food scraps, and these can be used.

VTC’s digester has its own site at digester.vtc.edu.

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