How Kroger turned food waste into warehouse-powering energy

Every day, some 300 Ralphs and Food 4 Less grocery stores produce 150 tons of food waste. Until recently, all that food would get trucked to a distribution center in Compton, Calif., where it was combined and sent to a composter 100 miles away.

But now that food waste, which used to represent a cost in terms of both money and emissions, is providing cheap, clean energy for the distribution center.

Ralphs and Food 4 Less, a division of Kroger, installed an anaerobic digestion system at the center, which takes in food and puts out biogas, providing power for the campus where the center is located.

“Anything that can't be sold or donated comes into the system,” said Kendra Doyel, a spokesperson for Ralphs and Food 4 Less.

The system, designed by Feed Resource Recovery, has been in the works during the last four years. It allows Kroger to turn a waste stream into an energy resource for the 49-acre campus, which includes a creamery and corporate offices for Ralphs and Food 4 Less, along with the 650,000-square-foot distribution center.

From waste to resource

The process starts when food is brought to the center and put through a blending system that removes any inorganic material -- namely packaging, such as plastic, metal and glass -- and liquefies the food. What's left is just organic material that's mixed with wastewater from the creamery.

That mixture goes into an anaerobic digester, an oxygen-free piece of equipment full of microbes that break the food down, producing biogas and a mix of nutrients and minerals. The biogas is then compressed and purified on its way to the campus' microturbines and boilers, where it takes the place of nearly all of the natural gas that the center previously used. That biogas now provides 20 percent of the campus' power and has delivered an 18 percent return on investment for the project so far.

All the water that's left gets purified and released. The remaining physical material -- the minerals and nutrients -- is concentrated into a form that can be used as a fertilizer. Kroger and Feed Resource Recovery sell the feed to some local partners that refine it and sell it as compost, but they're also working on turning it into an actual product to put on the market, according to Nick Whitman, Feed Resource Recovery's president.

In addition to pulling energy out of waste, the system eliminates a large chunk of truck traffic. In the last 10 years, the center was sending food waste to a Bakersfield composter in multiple truckloads every day. Kroger estimates that the system will help avoid about 500,000 miles of diesel truck trips a year, saving money that used to pay contractors to move the waste around.

Kroger is Feed Resource Recovery's first client to take on a system such as the one at the Compton distribution center, but now the company has been in touch with other supermarkets and non-grocery companies interested in the system.

“The model we're talking about is very similar to how (some companies) treat cardboard and other recyclable materials,” Whitman said. “They use their infrastructure to bring that material back to distribution center and aggregate it.”

Making systems work

While the main aspects of the technology are fixed, the surrounding details can be tweaked, Whitman said.

“Depending on how much material (a company is) generating and what they are generating, we can alter the process,” Whitman said.

Some companies may need to use different containers, bring in waste more or less frequently and may have different energy needs, such as a higher demand for natural gas.

Whitman said that because Ralphs and Food 4 Less stores already were sending food waste to the Compton distribution center and aggregating it, there wasn't a huge difference in how employees had to handle the material. “It was obviously a slight difference,” Doyel said, “Just taking it through a different system.”

It required more effort to find a place on the campus to locate the system and work through various government regulations, Doyel said. Because of the scope of the system, she said, it involved waste, air quality, environmental impact and other regulations on city, county and state levels. “It took a lot of hands on deck,” she said.

The system first started about a year ago, but with various components added over time, it's only been completely operational since around May. While the company doesn't have full figures on the exact cost savings from the system, it does anticipate that at its current pace, it will process more than 55,000 tons of food waste a year.

“It's still a very new project,” Doyel said. “We'll continue to watch it, and because it's been so successful, Kroger is looking to expand it into other markets as well.”

Apple image by Luke via Flickr, all other images courtesy Feed Resource Recovery and Kroger