Lettuce Power Up: Turning Food Waste into Energy

The next time you don’t finish your salad at a restaurant, it may end up powering your lights at home. A pioneering food waste-to-energy project at the East Bay Municipal Utility District (EBMUD) wastewater treatment plant in California shows how.

Food waste is America’s second most prevalent material reaching landfills, and only 2.5 percent of this waste material is recycled, composted, or reused. Anaerobic digestion is one way food waste can be turned into energy through a series of processes in which microorganisms break down biodegradable material in the absence of oxygen.

“It’s a really awesome substrate to be digesting,” says US Environmental Protection Agency (EPA) spokesperson Laura Moreno, “because it’s extremely energy-rich.”

But it’s not easy to prepare. A 2006 EPA grant helped EBMUD develop a patent for decontaminating and homogenizing food scraps into an applesauce-like slurry, optimizing it for digestion.

It’s a really awesome substrate to be digesting.

Thanks to the patent, in 2006 the wastewater treatment plant, nestled at the base of the Bay Bridge in Oakland, became America’s first plant to generate electricity with post-consumer food waste. And soon, with the addition of a new 4.5 MW turbine that will bump up the plant’s capacity to 10MW, it will send biomass-generated energy back to the green energy-hungry California power grid.

“There’s a lot of organic waste out there,” says EBMUD Wastewater Director Dave Williams, “and we just decided to tap into its energy.”

More energy, less food waste

Currently, the plant generates 90 percent of the 5MW it needs to operate from the biogas it produces by anaerobically digesting wastewater biosolids, 100 trucks a day of food-processing waste, and about 40 tons per day of food scraps from area restaurants and grocery stores.

The amount of post-consumer food waste will jump to 120 tons per day when the new turbine is brought online early in 2012. Other wastewater treatment plants and power-generating entities are following EBMUD’s blueprint.

So, the next meal you finish and toss, you might be seeing again.

Illustration by Jing Wei