Utility Turns Food Waste Into Green Energy

OAKLAND (Nov. 11, 2009)—While many see restaurant leftovers as trash, a San Francisco-area utility sees them as a source of energy.

The East Bay Municipal Utility District, which provides water and wastewater treatment in the eastern San Francisco Bay Area, is turning food scraps from 2,300 Bay Area restaurants and grocery stores into electricity to help it power its wastewater facility.

Every day, one or two 20-ton trucks pull up to the plant here and dump food waste into giant tanks. At the end of the process, the food scraps create methane gas. It helps power the plant's electricity-making generators.

The project is the first of its kind in the nation for a wastewater treatment plant, the Environmental Protection Agency says, and it's at the forefront of an almost untapped renewable energy resource.

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While a handful of utilities, companies and universities nationwide have attempted to recycle food scraps into energy, less than 3% of those scraps are diverted from landfills, the EPA says. Most often, food waste that doesn't go to landfills is composted for use in fertilizers. Every year, more than 30 million tons of food waste goes to landfills, the EPA says, accounting for about 20% of landfill waste.

The San Francisco-area utility district powers its wastewater plant, which serves about 650,000 Bay Area homes, by capturing methane gas by processing many kinds of waste, starting with wastewater. To take up excess capacity, the utility started collecting other waste in 2001, including that from wineries, dairies and chicken processors, says David Williams, director of wastewater for the utility.

Food scraps from restaurants and hotels were added in 2004. The plant now processes 100 to 200 tons of food scraps a week. The goal is to do 100 to 200 tons a day – enough to power the equivalent of 1,300 to 2,600 homes – and rapid expansion is now expected. By the end of next year, the district expects to create so much power from non-traditional waste that it'll be able to sell excess power to Pacific Gas & Electric, a local electricity supplier, Williams says.

If 50% of the USA's food waste went through a similar process as the one here, there'd be enough power for 2.5 million homes a year, the EPA says.

Dinner plates to electricity

The food-scrap project "hasn't been a cakewalk," Williams says.

Waste haulers, who pay the utility district to take the waste, collect the food scraps from restaurants and hotels as part of their normal garbage pickups.

Some of the haulers weed out big items, such as cardboard boxes used for produce. Other haulers have restaurants and grocers do more of the separation so that the waste is cleaner.

Upon arrival via truck at the plant, the food scraps look like mounds of wet dirt. They're dumped into 20,000-gallon underground tanks. There, grinders turn the scraps into a mud-like substance. Bigger items, such as rocks and utensils, fall out.

On a recent morning, it took just minutes for a 20-ton truck to unload. Pressure pulls most of the odors into the tank. Still, the smell of cheese was present.

"That all comes from last night's dinner plates," Williams said as he watched.

From the underground tanks, the waste is run through sieves that reject plastics, bottle caps and other small items.

Then, the waste goes into anaerobic "digesters," 2 million-gallon tanks filled with bacteria.

The bacteria break down the solids in the waste to 10% of their original volume. Methane gas is released in the process, which takes several weeks. Instead of being released into the atmosphere as a greenhouse gas – as can happen at landfills – the gas is sent via overhead pipe to the plant's power room.

The gas is consumed to make electricity; the leftover waste is composted for use as fertilizer.

"It's a very green program and pretty cutting edge," says Paul Morsen, executive director of the Central Contra Costa Solid Waste Authority. The district, formed to handle garbage contracts for six Bay Area communities, works with a garbage hauler to send food scraps to the East Bay utility for recycling. Forty-five restaurants in its service area signed up for the program, Morsen says. That'll double by early next year.

Response has been favorable to the year-old program, Morsen says. Some restaurants have had to wait to be added.

"We ask restaurants to do their part to clean the environment," he says. Since the program is still in its pilot phase, Morsen says it's unclear whether costs for participating restaurants will go up, down or stay the same.

If they go up, "We have confidence it won't be a huge increase," he says.

Educating busy busboys

The biggest challenge for the East Bay utility district is keeping plastics and other contaminants out of the food scraps and preventing them from clogging pipes should they get to the plant.

To help with that, haulers educate restaurant and grocery store workers on the need to separate food scraps from other trash. "You're trying to educate a busy busboy who may only be on the job a couple of months and perhaps making minimum wage. It's difficult," Williams says.

Waste separation is about to become more the norm, at least in San Francisco.

A city ordinance that took effect Oct. 21 requires almost every residence and business to have three color-coded bins for waste: blue for recycling, green for compost and black for trash. The composting bins are supplied to residents at no extra cost.

On a voluntary basis, city businesses and residents have been able to have curbside collection for food scraps in a separate bin since 2001. By separating food scraps – most of which are then composted – the businesses may end up paying less than if they'd sent the scraps to a landfill, says Robert Reed, a spokesman for Recology, San Francisco's waste collection company.

Even if the East Bay utility district fulfills its plans to process 200 tons of food waste a day, it'll tap less than 10% of the available supply, Williams says. If it got it all – 1,800 tons generated by commercial enterprises daily in the region – it could provide enough power for more than 25,000 homes.

"That's a small city," Williams says.

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