What’s educational, gassy and green all over?

02 Jun 2014

Why, Vermont Tech’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 and faculty member Mary O’Leary. “We’re a sustainable college, and this will provide heat, energy and power in a renewable fashion. But even more important 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 business and computer science. Students can work from a shared computer drive on campus that includes building plans and information for homework, projects and labs.

The state is also hoping to benefit from the research students will conduct on the byproducts of the digester. Both nutrient-packed liquid effluent and low-moisture solids are produced, which can be spread on farm fields, like a traditional fertilizer. Students will do research to determine whether the product has any effect on 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 other organizations and individuals have been involved. The financial benefit to the college in the future will be lower fuel bills as well as income from the sale of electricity to the grid.


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

François Guay is the representative from the Quebec company Bio-Methatech that is overseeing construction. Bio-Methatech has the license to build the patented German LIPP GmbH biogas plants in the Northeastern U.S.  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 was to have the digester filled in January and operational by April, and sometime this summer, once the school has received the last permit it needs, food scraps will be added to the mechanical cow’s “meals.”

“By diverting organics like food waste from the cafeteria from the landfills, we’re already working toward compliance with Act 148,” 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 in 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, which are 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.

In early April, we generated enough biogas to power the generator and successfully passed power tests, thereby meeting our SPEED deadline (generating electricity and sending it back to the grid) two-and-a-half weeks ahead of schedule!  Unfortunately, we then had an electrical and mechanical failure that required us to shut the system down and drain the digester tank to repair the system.  All repairs have been completed, we have filled the digester tank back up, and we are heating. In early June we began daily feeding and electricity generation.   One alum and one current student are taking part in our first Digester Operator Certificate program this summer, and we have several research projects started and more proposed.  Look for news items and reports on the certificate program and  summer research work this fall.


We invite you to learn more about our digester, affectionately named Big Bertha (Big B) by the campus in an online poll, by following her on Twitter (@VTCBigB). If you have any questions about Big B, please contact Professor Mary O’Leary (Mo’leary2@vtc.edu).