In mid-May, The Kroger Co. drew back the curtain on a 150 tons/day anaerobic digestion system at its 59-acre Ralphs/Food4Less distribution center in Compton, California. The system started operating about a year earlier, but the parties involved wanted to be sure everything was running smoothly before its unveiling. The “Kroger Recovery System” is processing food waste from over 350 Ralphs and Food4Less grocery stores in all of southern California, and additional stores elsewhere in California and Nevada. “We began operating the digester about a year ago, and have increased throughput slowly and smartly and are now fully operational,” says Kendra Doyel, Vice-President of Public Relations at Ralphs.

Trucks delivering groceries to the stores back-haul the food waste — including some meats and bones — that is no longer edible and cannot be donated. The distribution center is adjacent to a Kroger creamery. Wastewater from the creamery is codigested with the food waste. Prior to starting the system, food waste from the grocery stores was hauled to Community Recycling & Resource Recovery’s source separated organics composting facility near Bakersfield, California. “The Kroger Recovery System is reducing area truck trips by more than 500,000 miles/year,” notes Doyel.

Digester System

The system was designed, installed and is currently operated by Feed Resource Recovery (FEED) based in Boston, Massachusetts. The company was founded in 2007 to manage food waste from the food retail and service sectors more efficiently. “Our initial focus was on smaller scale behind-the-store type systems,” explains Ryan Begin of FEED. “We built a pilot unit but soon recognized it would be more efficient to take advantage of economies of scale by building much larger systems. Essentially, in an application like Ralphs/Food4Less, we would have been installing units at over 350 individual stores, which would all have to be equipped and serviced. It became obvious that building larger plants to service a company like Kroger made much more sense, both financially, logistically and environmentally.”
FEED approached Kroger Co. about three years ago with the idea for the project, recalls Doyel. “They knew we were already diverting our food waste and brought their technology to us to consider. We went through the process of learning more, including the payback on our investment, and decided to move forward. The Kroger Recovery System is fully owned and staffed by Kroger.”
Neither Begin nor Doyel would provide many details about the actual system, which has a 2 million gallon reactor tank, and a 250,000-gallon staging tank for incoming material. A video prepared as part of the grand opening shows the basic components of the wet digestion system (see link on web version of this article). The grocery stores are not required to depackage any of the food waste. Therefore the first step is to load all food waste into a depackaging-type process, where nonorganic materials are removed and the feedstock is size reduced. Wastewater from the creamery is pumped into the staging tank.
Biogas is captured from the top of the reactor tank and fed to a gas conditioning unit to remove moisture and compress the gas. The facility has several Ingersoll Rand microturbines, which offset more than 20 percent of the energy demand of the distribution center. Heat is captured from the microturbines for the digester process. Conditioned biogas is also used in the boilers at the creamery. Digested solids are taken off site for composting.

A cornerstone of FEED’s system is the software that monitors and manages the entire system and process. “We pull data from every component of the facility, which is compiled and analyzed to gauge how well the system is operating,” explains Begin. “As part of our development process, we spent a lot of time on algorithms that enable us to look at trending, e.g., to determine when a pump may fail and to replace it before it does. The algorithms also adjust flow rates based on specific parameters being monitored, such as the chemical oxygen demand and volatile solids of incoming feedstocks. All of this information, including energy production, is fed into financial reports that enable Kroger to monitor if the system is meeting its expected return on investment.”
When the technology was being designed, Begin and his partner, Nick Whitman, conducted food waste audits at grocery stores to provide statistically representative data for the company’s software to model. The installation at the Ralphs/Food4Less distribution center is FEED’s first commercial scale project, and highlights the feasibility of integrating anaerobic digestion of food waste into an urban environment. Kroger is interested in installing similar systems at some of its other locations around the country. “We are still vetting it,” notes Doyel. “The Recovery System has only been operational at full-scale for a short period of time. We are very pleased with the performance to date.”