Anaerobic digestion is not your grandma's compost heap.

March 1, 2011

4 Min Read
Composting Facilities Turning Food Waste and Yard Waste Into Energy

Meredith Sorensen

Banana peels. Grass clippings. Pizza crusts. The leftover meatloaf that never quite got finished off. This is organic waste, and Americans make A LOT of it. Exactly how much? According to Jonathan Bloom, author of “American Wasteland,” Americans waste at least 160 billion pounds of food per year, enough to fill the Rose Bowl up to the rim once a day, every day. And that doesn’t include leaves, branches and other yard waste.

On average, organic matter takes up about 30 percent of the weight in residential garbage cans, which means it has a massive environmental and economic impact. As those of us in the waste management industry know, it is expensive to truck food and yard waste to distant landfills where its valuable nutrients are lost forever. Once tipped, organic material sitting in that oxygen-poor environment creates methane, a greenhouse gas 25 times more potent than carbon dioxide. While many landfills have taken measures to capture that methane for power generation, organic materials can be put to much more efficient use if they are diverted before they reach the landfill.

A Rind Is a Terrible Thing to Waste

America’s organics recycling industry has grown precipitously over the last several decades, from several hundred composting facilities in the late 80s to nearly 3,800 in 2000, according to the U.S. Environmental Protection Agency. With composting well established, communities are increasingly taking their organics management system to the next level with anaerobic digestion.

Anaerobic digesters can be described as massive, highly efficient cow stomachs. In a warm, moist environment devoid of oxygen, trillions of microbes — the same kind that help cows digest food — break down the organic materials and produce biogas, a mixture of methane and carbon dioxide. Instead of allowing these gases to escape into the atmosphere, anaerobic digesters capture the biogas and convert it to electricity, pipeline-grade natural gas, or compressed natural gas that can be used for transportation fuel. Anaerobic digesters essentially capture the energy potential of organic waste and put it back into the energy grid.

Anaerobic digestion offers distinct advantages to communities wanting to harness the full potential of their discarded materials. Unlike landfills, digestion facilities can tailor the types of materials they process. This maximizes biogas yield and generation efficiency because, just like humans, anaerobic bacteria love consuming starches and fats but don’t care for the plastics found in landfills. Digesters, which can be sited relatively close to the sources of organic waste, are also used repeatedly, while distant landfills have a finite lifetime.

In addition to providing a source of renewable energy, organic waste that has been processed by an anaerobic digester can be composted into nutrient-rich soils and organic fertilizers. Used together, anaerobic digestion and composting are powerful tools for delivering energy and nutrients back into the community, all sourced from the community’s own discarded banana peels and pizza crusts.

It’s Real, and It’s Coming

Anaerobic digestion has become ubiquitous in Europe, especially in Germany. As of 2007, Germany was home to more than 3,700 biogas plants, which can produce a total of 1.3 gigawatts of energy. Andrea Horbelt of the German Biogas Association has said that 20 percent of Germany’s natural gas could be made from biogas by 2020.

Canada has undertaken bold initiatives to develop its renewable energy portfolio while finding solutions to cut back on waste. For example, when the metro Vancouver region launched its “Zero Waste Challenge,” aiming to recycle 70 percent of its waste by 2015, organic waste was a major focus. It found a local organics management facility — Fraser Richmond Soil & Fibre Ltd. — to turn the organic waste into compost and soil blends. Seven of the 23 member municipalities in the metro Vancouver region have already launched some version of a kitchen scrap diversion program to help meet their waste elimination goals.

In addition to helping the region meet its recycling goals, Fraser Richmond Soil & Fibre is building a high solids anaerobic digestion facility within the footprint of its existing composting site. The project has garnered support at the local and national levels, including a resounding endorsement by Natural Resources Canada, which invested $4 million (Canadian). The facility, owned and operated by Harvest Power, harnesses the full energy, nutrient and carbon potential from discarded organic materials.

Anaerobic digestion and composting are increasingly recognized as responsible ways to manage organic waste. As more American communities realize they can simultaneously create renewable energy, reduce waste, and return nutrients to the soil, all those banana peels, leaves and pizza crusts start to look a lot like gravy.

Meredith Sorensen is outreach manager at Harvest Power, based in Waltham, Mass. The company manages organic waste by capturing the energy, carbon and nutrient value from discarded organic materials.

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