Good digestions

South Sacramento facility converts leftover food into natural gas; could power hundreds of homes and cars

This methane digester, located in south Sacramento, will turn food waste into natural gas.

This methane digester, located in south Sacramento, will turn food waste into natural gas.

Sacramento’s culinary big shots recently launched an ambitious marketing campaign to promote the region’s farm-to-fork dining scene. They’re hoping more tourists will visit the capital’s urban eateries and farmers markets.

But what happens between fork and landfill? Four newly whitewashed tanks in south Sacramento may be the answer.

Last week, a local company called Clean World Partners unveiled a new methane digester designed to convert organic waste into renewable natural gas. Starting this month, the facility will process 25 tons of food scraps per day and other garbage from Sacramento’s restaurants, supermarkets and schools. By next year, the digester’s capacity will quadruple, allowing Clean World to begin selling thousands of gallons of natural gas to local government and private vehicles.

The project, located at the long-vacant South Area Transfer Station off of Fruitridge Road, took only six months to finish after the California Energy Commission awarded Clean World a $6 million grant in June, nearly half of the $13 million needed for construction. The digester’s speedy launch “validates the state’s investment and the use of this money,” said Randy Roesser, deputy director of the CEC’s Fuels and Transportation Division.

Officials say the digester will help cut organic waste produced in the city while also reducing fossil-fuel consumption. According to the National Resources Defense Council, food waste makes up 20 percent of landfill waste in the United States. All of that decomposing garbage turns into methane, which is 23 times more potent than carbon dioxide in causing global warming.

Sacramento’s digester will also produce methane from food waste, but the gas won’t be released into the atmosphere. Natural-gas vehicles will convert the methane into carbon dioxide as they burn off the fuel.

Wait, carbon dioxide is bad, right?

Not in this case, said Ruihong Zhang, a UC Davis professor and the project’s chief technical adviser. Plants and agricultural crops remove carbon dioxide from the atmosphere through photosynthesis, and when those plants die and decompose, they release carbon dioxide back into the ecosystem. That’s where the digester comes in, Zhang explained.

“If we only burn gasoline or fossil fuel that we take out of the ground and burn it into CO2, that goes into the atmosphere, so there’s a net emission,” she said. “Through our process, because we take in the biomass created from CO2—the trees, food—there’s a closed loop.”

Officials estimate the digester will need about six weeks for gas to accumulate in the facility’s four large tanks. Eventually, the digester will produce 1 million gallons of natural gas per year, enough to power 1,000 vehicles or 500 homes. For now, the only company using the natural gas is Atlas Disposal, a Sacramento-based waste-management company that will also haul food waste to the digester.

Dave Sikich, the garbage company’s president and CEO, said he has upgraded 15 trucks with clean-burning natural-gas engines. They weren’t cheap—the natural-gas engines cost an additional $50,000—but Sikich thinks the investment was worth it.

“It’s probably going to be financially neutral for us in the short term,” he said. “When we can offer our customers that, we can take their waste and we can produce renewable natural gas not only for our fleet, but maybe for their fleet, then it’s just got this huge environmental benefit.”

The city of Sacramento may also use the digester next year for residential composting, according to Sacramento City Councilman Kevin McCarty, who represents District 6 where the Clean World facility is located. Instead of tossing food in garbage cans, under the composting program residents would place organic waste in their green refuse bins.

McCarty said officials will select one neighborhood in 2013 to test the idea before possibly expanding to the rest of Sacramento.

“If we can divert food waste that our residents currently put in their trash can, then one, we’re reducing it, and two, we’re reusing it for creating a renewable fueling source,” McCarty said.