• VTC has gut feeling about mechanical stomach
     | November 18,2013

    Vermont Technical College’s anaerobic digester is shown under construction in September.

    RANDOLPH — What’s educational, gassy and green all over? Why, Vermont Technical College’s mechanical cow, of course.

    When up and running, the anaerobic digester will process things like manure and crop waste from farms, as well as nonfarm organic material like yogurt whey, into biogas (primarily carbon dioxide and methane) that can then be converted into heat and electricity.

    Construction of the digester, the first of its kind in the United States, began in July, and immediately VTC had a hands-on learning forum for many of its programs.

    “It’s a fabulous educational opportunity,” said project manager Mary O’Leary.

    “We’re a sustainable college, and this will provide heat, energy and power in a renewable fashion, which is great. But the biggest piece is student-powered excellence. That’s what we’re all about.”

    The digester has already been introduced to students in curricula, from the agricultural and engineering aspects to even business and computer science, and they can work from a shared drive on campus with all the plans and information for homework, projects and labs.

    The state is also hoping to benefit from the research students will perform surrounding the byproducts of the digester. Both a nutrient-packed liquid effluent and low-moisture solids are produced, which can be spread on farm fields, and there is some concern about whether that will affect local water quality.

    O’Leary said soil and water quality is being managed by a regional community management plan, so the college and its partner farms are keeping track of the distribution of the digested materials and testing soils.

    Funding for the project, which totals just over $4 million, came from a combination of bond funding from the Vermont State Colleges and grants from the U.S. Department of Energy through the Vermont Sustainable Jobs Fund, though many organizations and individuals have been involved. The big financial benefits to the college will be lower fuel bills, as well as the sale of electricity to the grid.

    “This digester will help us fulfill our mission both educationally as a polytechnic institution and financially by lowering our energy costs,” said the president of the college, Phil Conroy Jr. “We’re really pleased to be able to put this together.”

    In addition to supplementing courses for students, the college will be offering a certificate program in digester operations and a continuing education course for those who may not need to be operators but need to know how it works. Several smaller-scale digesters are at work on farms throughout the country, and more cities are utilizing digesters for waste treatment.

    Francois Guay is the representative from the Quebec company Bio-Methatech overseeing construction. Bio-Methatech has the license to build the patented German LIPP GmbH biogas plants in the Northeastern U.S. and is constructing another in Franklin. The company has built one facility in Quebec, with plans for two more next year, but Guay said the price of electricity there is half what it is here.

    “Here it’s better economically for producing electricity than in Canada. There, the best place to use this technology is in the cities for processing the sewage sludge,” said Guay.

    The German-designed LIPP technology uses a patented metal folding technique for quick and lower-cost construction, but with high-quality stainless and galvanized steel for water tightness and high stability.

    “We built the tank with only four people in 20 days,” said Guay. “It’s a special technique. We bring the assembly equipment right to the site.”

    The goal is to have the digester operational in January, and by April, once the school has received the last permit it needs, food scraps will be added to the mechanical cow’s “meals.”

    “Which is great, because it ties with Act 148. We will be diverting those organics, like food waste from the cafeteria, from the landfills,” said O’Leary, referring to the Vermont legislation banning all organic materials from landfills by 2020.

    The digester will be “fed” almost 16,000 gallons of organic material a day. Starting in the preparation tank, the feedstock will be mixed and “chewed” before moving to the 135,000-gallon hydrolyzer tank, where microbes break down the material just as they do in a compost pile.

    Once the oxygen is used up by the microbial process (usually about three to six days), the hydrolyzed feedstock heads to the 410,000-gallon anaerobic digestion tank. Over the course of about 20 days microbes break down the material, releasing methane, carbon dioxide, hydrogen gas and water vapor collected in the 93,000-gallon gas bladder at the top of the tank.

    The biogas then travels to be burned in the generating engine to create heat and electricity. The leftover nutrient-rich slurry is separated into a liquid fertilizer, which travels to a 115,000-gallon tank to be spread on fields or moved to a holding pond, and solids, which can be used as animal bedding or composting fiber or also spread on fields.

    “It’s exciting, very exciting,” said O’Leary. “I’m looking forward to getting it up and running.”

    For more information, visit VTC’s website www.digester.vtc.edu.

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