Turning food scraps into energy

Composters, waste districts study use of food waste for power

By Candace Page, Free Press Staff Writer • April 1, 2009

RANDOLPH CENTER — Vermonters dump 120,000 to 140,000 tons of food waste into landfills every year. Composters and solid waste districts have begun to ask whether all those carrot peels and chicken bones could be turned into energy instead.

“We’re at a time in the world with high energy costs when no waste should go underutilized, and that includes our food scraps, yard waste, wood waste,” said Tom Gilbert of Highfields Institute, a Hardwick research center, as he opened the discussion at the third annual Vermont Organics Recycling Summit on Tuesday.

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But food waste also contains calories — potential energy — that can be burned after the waste undergoes a process called anaerobic digestion.

When food is stored in the absence of oxygen (in a closed container, for example), microbes break down the matter, converting much of it into methane gas. The gas can be burned; the remaining solids can be composted for other uses.

Already, a dozen or more Vermont farms use anaerobic digestion to process manure to produce electricity.

“Anaerobic digestion is the future of organic waste management in the United States,” Leslie Hoffman of Earth Pledge told a conference session. Earth Pledge is a nonprofit group proposing to install a 500-ton-a-day anaerobic digester in the New York City area.

In Vermont, the most intriguing possibility is the mixing of manure and food waste to create energy. Food scraps typically have a higher energy value than manure, so adding a steady stream of food waste could make energy production more economically feasible for small and medium-sized farms, experts said Tuesday.

The Central Vermont Solid Waste Management District and Vermont Technical College recently won a $600,000 federal Department of Energy grant to study just such a pilot project.

The college has two 120-cow dairy farms — and an annual heating bill that tops $1 million. The solid waste district has a “zero waste” goal, and is looking for ways to dispose of food waste.

Together, they will study the feasibility of installing an anaerobic digester on the VTC campus, fueled by manure and some of the region’s food waste.

“We don’t have enough cows. Food scraps may be the answer for us,” Joan Richmond-Hall, a Vermont Tech associate professor, told the conference.

Anaerobic digesting of food waste faces a dozen hurdles, from technology challenges to permitting to concerns about possible pathogens in the residue. The VTC-waste district pilot is intended to tackle some of those issues.

There is also a deeper, unanswered policy question: Is energy production the best use of organic waste? Some at Tuesday’s conference argued that composting and soil regeneration remain the best answer for Vermont, which might be too small to achieve economies of scale in turning food waste into energy.

Richmond-Hall said there probably is no single answer. In very rural areas where collecting food waste is costly and energy-intensive, digesters might not be the most efficient answer.

But, “for a farm near a little urban center, it could be a great part of a zero-waste strategy,” she said.

Contact Candace Page at 660-1865 or This email address is being protected from spam bots, you need Javascript enabled to view it

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