food scraps

Serving Up Energy and Compost from Organic Waste

food scrapsFood waste and yard debris thrown into North America’s municipal solid waste stream could provide enough energy to power more than 1.5 million homes and be turned into more than 30 million tons of compost every year, according to estimates made by Harvest Power, Inc. Communities can use these "wasted" resources to help solve sustainability challenges using the following recipe.

First Ingredient: SSO
Source separated organics (SSO) refers to organic waste (such as food scraps and yard debris) separated from the rest of the waste stream at the point of origin. For example, when homeowners collect plate scrapings, carrot peels, coffee grounds, and bread crusts in a separate collection container, they are participating in an SSO program. Typically they collect the scraps by placing a pail lined with newspaper on their kitchen counter or under the sink. Every couple of days, they bring the food scraps out to a larger organics bin also used to collect yard debris. If the household composts on its own, the food scraps stay on site and turn into rich, crumbly soil. Otherwise, the organic materials are collected by the city or trash hauler and transported to a commercial composting facility. Businesses, especially restaurants and grocery stores, do the same, only on a larger scale. By segregating organic materials from the waste stream, communities are able to:

  • keep nutrients within the region,
  • increase recycling rates,
  • produce valued soil products,
  • promote green jobs, and
  • produce clean energy.

In addition, SSO can reduce transportation costs associated with waste disposal if the heavy organic materials are brought to sites closer than landfills. SSO also can lower greenhouse gas emissions if enough organic materials are removed from landfills to minimize landfill gas.

Many communities already source separate their organic materials from the waste stream. In 2009, more than 90 towns and cities in the United States reported offering residential food waste collection. Regions and cities with SSO programs include: Metro Vancouver, British Columbia; Seattle and King County, Wash.; Portland Metro region; Ore.; the San Francisco Bay Area, Calif.; Alameda County, Calif.; and Dubuque, Iowa.

Second Ingredient: Community Buy-in
Implementing SSO programs requires some part of the community to be “switched on” or tuned in. This momentum may start at the policymaking level. For example, San Francisco and Seattle have mandated residential organics collection. Other times, the force comes from the bottom up as more grocers, businesses, restaurants, and households demand their cities and haulers provide organics collection services.

Organic waste diversion can come with challenges, but these can be managed through creative solutions. For example, some communities have addressed the “ick factor” associated with sorting by pointing out that organic waste is a part of household garbage; we are just putting it in a different bucket. Households and food service establishments generate food scraps no matter how careful they are at preparing meals. Peels, rinds, coffee grounds, and plate scrapings are a waste in the trash bin. In an organics bin, they get recycled into compost and cycled back into community agricultural sites such as yards, gardens and farms.

Third Ingredient: HSAD
The most efficient way to manage waste is to not generate it in the first place. Ideally, every home and business would compost their food scraps in their backyard, balcony, or parking lot. Because this is not yet feasible, organics processing solutions must be able to:

  • handle large-scale volumes of organic materials,
  • be located near urban cores,
  • operate with exceptional odor control, and
  • produce clean energy.

High solids anaerobic digestion (HSAD) is one technology that meets these requirements. Anaerobic digestion occurs when organic matter breaks down in the absence of oxygen. It happens in cows’ stomachs. It also happens in landfills, albeit on a much slower timeline, and without the benefits of a high-quality compost product packed with nutrients. Anaerobic digestion has been used for years to treat liquid slurries high in organic content such as wastewater, sludge, and manure.

Today, an industry is emerging in which organic waste processing facilities use anaerobic digestion to process SSO and create readily available renewable energy and usable compost. Essentially, HSAD facilities place organic feedstock into garage-like airtight containers that minimize odor. Naturally occurring microbes break down the waste, producing biogas (methane and carbon dioxide). The biogas is captured and used to produce renewable electricity. It also can be cleaned to meet pipeline natural gas standards or further processed into compressed natural gas (bioCNG) for transportation fuel. Finally, the organics processor can compost the remaining digestate (the product resulting from microbe activity on the food and yard waste) and add it to soil products for farms and gardens. Through successful organic waste management, communities can also see significant cost savings. For example, the City of Port Coquitlam, B.C. estimates that its SSO program, coupled with biweekly garbage pickup, increases recycling, reduces wastewater treatment costs and saves taxpayers as much as $45,500 per year.

Organic materials are nature’s version of batteries: in a sense, they are stored sunlight, or stored energy. Management of organic waste using these three key ingredients is a power play: HSAD technology unlocks the energy captured in food scraps and yard debris, and composting creates soil products that can be returned to the earth. Communities that start to put these programs and technologies in place can use resources they already have “at their disposal.”

About the Author

Meredith Sorensen is outreach manager at Harvest Power. The company provides technologies, project development, and product marketing capabilities to extract the maximum value from organic waste through the production of renewable energy in combination with high-quality compost-based soil and mulch products.