From Onion Waste to Onion Power: An Industrial Solution to Harvesting Power from Food Waste

Gills Onions processes nearly 363 metric tons (tonnes) (400 tons) of raw onions each day, and produces up to 136 tonnes (150 tons) of residual onion waste. Previously, this onion waste was land-applied on Gills Onions' at an annual expense of $400,000 and caused odors and other problems. Gills Onions sought an innovative solution to help manage residual onion waste in a cost-effective, sustainable manner.Gills Onions, of Oxnard, California, hired HDR Engineering, Inc. (HDR), of Omaha, Nebraska, to help develop a waste-to-energy system, titled Advanced Energy Recovery System (AERS), to convert onion wastes to energy. The AERS process consists of juice extraction from waste onions, equalization, anaerobic treatment using an Upflow Anaerobic Sludge Blanket (UASB) reactor, biogas conditioning, and energy production using fuel cells. The project reduced the quantity of residual onion waste by 75 percent. The 0.6 megawatts (MW) of electricity generated from fuel cells supplies 100 percent of Gills Onions' base electrical load and 38 percent of its annual average load.The AERS annual operating cost is nearly $300,000. This project saves Gills Onions nearly $700,000 and $400,000 each year in energy and hauling costs, respectively. These operational savings from the AERS will pay back the project's capital cost in approximately 6 years.The Gills Onions' AERS is an example of innovation in organics management, exemplifying how a solid organic waste (onion peels in this case) can be processed and fed to a digester to boost biogas and energy production at a publicly-owned treatment works (POTW). The Gills Onions project also shows that other organic wastes, in addition to traditional high-strength wastes like fats, oils, and greases (FOG), should be considered for POTW co-digestion programs. Some of the same benefits realized by Gills Onions could also benefit municipalities. Accepting unconventional organic waste streams for co-digestion at a POTW would reduce a municipality's energy costs, generate additional tipping fees, produce renewable energy, reduce carbon footprint, and help meet a City's sustainability goals.