Waste not

Organic leftovers a renewable source of energy? Davis center demonstrates that it works.

Ruihong Zhang, professor of biological and agricultural engineering at UC Davis, discusses the anaerobic-digestion plant, which she developed over the past eight years, with Dave Konwinski, CEO of Onsite Power Systems, a partner in the project.

Ruihong Zhang, professor of biological and agricultural engineering at UC Davis, discusses the anaerobic-digestion plant, which she developed over the past eight years, with Dave Konwinski, CEO of Onsite Power Systems, a partner in the project.

Photo By Larry Dalton

A busboy at Oliveto, an upscale restaurant in Oakland, scrapes leftovers off plates and into a compost bin. The food scraps were once Italian dishes made from local, organic fruits and vegetables, sustainably raised meats and poultry, and conscientiously harvested fish. Soon, the ex-garb will flourish again.

“California sends so much organic waste to landfills. All that waste has energy,” said Dave Konwinski, CEO of Onsite Power Systems, Inc., which is collaborating with UC Davis on a project to transform food waste into a renewable source of energy for electricity generation and vehicle fuel. The Biogas Energy Project is one of many across the state seeking to develop clean technology and find solutions to global warming in unexpected places.

Every day, trucks collect about 300 tons of food scraps from 2,100 restaurants in San Francisco and 150 more in Oakland. They haul some of it 70 miles to a $1 million state-of-the-art anaerobic-digester plant, the first large-scale commercial demonstration system of its kind located at UC Davis’ wastewater-treatment plant south of the campus.

As soon as the anaerobic digester becomes fully operational the first week of February, it will begin transforming eight tons of food waste a day into energy. Each ton of leftovers is capable of producing enough electricity to power 10 homes for one day. The biogas generated from the digester also can be processed to become fuel in the form of compressed natural gas for cars, trucks and other commercial vehicles. Currently, Californians rely on petroleum-based fuels for 96 percent of our transportation needs, and transportation fuels account for 41 percent of the state’s annual greenhouse-gas emissions.

Here’s how the digester works: Digestion happens as bacteria decomposes organic matter, such as meat and vegetable scraps, animal waste and yard clippings. The digester mixes the waste with water in giant steel tanks (no chemicals are added). Naturally occurring anaerobic bacteria, which thrive in the oxygen-free environment, break waste into organic acids, producing hydrogen ready for use as fuel. Water containing organic acids mix with other bacteria to produce methane for use in compressed natural-gas vehicles. Methane also can be burned to power a generator that produces electricity.

The digester is the first to produce both methane and hydrogen in separate stages, said Ruihong Zhang, UC Davis professor of biological and agricultural engineering, who developed the technology over the past eight years. The California Energy Commission, interested in preventing the environmental pollution caused by waste disposal and converting biomass materials into useful byproducts, provided major funding to develop the digester.

The project also will help reduce landfill volume. More than 5 million tons of food scraps—not all of it organic—go into California landfills each year, releasing unchecked methane into the atmosphere.

While some waste for the project is generated locally on campus, most still travels 70 miles to the digester. Onsite Power Systems is working to resolve that problem of fuel inefficiency. Ultimately, clean-energy advocates want commercial and institutional food generators to compost food scraps on-site.

The Davis-based Onsite Power Systems, founded in 1996, is a privately held bioenergy company that focuses on the commercialization of advanced technologies and renewable energy. In 2004, UC Davis issued an agreement with the company to construct the anaerobic digester. Onsite Power Systems has an exclusive licensing agreement for the technology and hopes to sell similar power-production systems to businesses that generate waste, such as food processors, farms and dairies. Food-processing plants across the country and delegations from China, Taiwan, Scotland, Germany and more, have expressed interest in the technology. The company currently is working to develop larger digesters for cities that can process between 50 and 200 tons a day.

The Biogas Energy Project is one of many efforts to promote, and invest in, clean energy in the fight against global warming. SMUD launched its “Leftovers to Lights” program a year ago to explore opportunities for biogas production and to provide funding for demonstration projects. The program identified large sources of food waste, including hotels, hospitals and prisons, and reported that 45 Sacramento-area businesses that responded to a survey were found to produce enough food waste to power as many as 4,100 homes a year. The next step is determining what businesses can house anaerobic digesters.

Food waste makes up about 18 percent of the city’s commercial garbage. More than 200,000 tons of food waste is disposed of each year in Sacramento County, a potential energy resource that could go directly back into the city’s power grid. SMUD hopes to derive 23 percent of its electricity from renewable sources by 2011, said Ruth MacDougall, a SMUD manager. It currently obtains about 10 percent from these sources, which include the sun, winds and biogas.

Last month, Governor Arnold Schwarzenegger called for the development of a transportation fuel standard to reduce carbon emissions in California. The directive follows the Global Warming Solutions Act passed in 2006 that set statewide limits on heat-trapping pollution. The new standard aims to reduce the carbon intensity of passenger-vehicle fuels by at least 10 percent by 2020. Transportation experts at UC Davis and UC Berkeley will draft the air-quality standard, with funding from the San Francisco-based Energy Foundation. The standard will address methods for reducing the output of climate-changing carbon dioxide in a way that provides industry with the flexibility and incentive to introduce new fuels, said Dan Sperling, director of the UC Davis Institute of Transportation Studies and co-leader of the project.

And that’s where programs like the Biogas Energy Project come into play, as its anaerobic digester begins converting those leftover food scraps into clean energy and biofuels for cars and trucks. “Soon, we will literally be seeing the local impact of this technology on the street,” said Konwinski.