Pioneering Energy Resource Recovery on Food Waste at Gills Onions

Gills Onions, the nation's largest fresh-cut onion processor, pioneered an engineering marvel that takes their previously discarded onion waste and converts into energy by way of anaerobic digestion and fuel cell technology. This landmark project won Gills the American Consulting Engineers Council (ACEC) 2010 National Grand Conceptor Award.Gills Onions processes nearly 363 metric tons of onions per day and generates one third of it as wastes: peels, tops and tails. Historically, the waste was land applied at Gills Onions farming fields and resulted in multiple issues: offensive odors from fields, soil acidification, growth impairment, pests, potential ground water contamination, expensive and labor intensive waste hauling, air pollution from diesel engines, traffic control, muddy soil and waste piling up at processing facility during raining season. Gills Onions expended nearly 400,000 a year on this inconvenient, unsustainable, expensive and labor-intensive waste disposal method and realized the need for reducing the amount of waste going out of their processing facility.Research conducted in 2005 confirmed that the sugar content in onion waste lends itself to fermentation and anaerobic digestion. Gills Onion teamed up with HDR (Omaha, Nebraska) to engineer the system titled the Advanced Energy Recovery System (AERS). The AERS process contains onion juice extraction, flow equalization, an Upflow Anaerobic Sludge Blanket (UASB) anaerobic digester, a heating system, biogas cleanup, fuel cells and flare. The preliminary treatment step in the AERS process reduces their onion waste by 75% on a mass basis. The separated biomass (25% of their feed on a mass basis) is sold as cattle feed. The 75% of their feed on a mass basis is processed through the UASB energy recovery process to produce biogas out of onion juice. The AERS process yields 0.6 MW of clean electricity using two fuel cells. The 0.6 MW of electricity generated from fuel cells supplies 100% of Gills base load.The AERS project ultimately cost Gills Onion 10.8 million. Gills Onions received assistance: 3.2 million from American Recovery and Reinvestment Act (ARRA) of 2009 and 2.7 million from Sempra Energy as part of the utility's renewable energy Self Generation Incentive Program. Operational cost of AERS is around 300,000 a year. However, the project saves Gills 400,000 a year on waste hauling/disposal and 700,000 a year on electricity purchase (800,000 net savings). Additionally, the revenue from onion cake sold as cattle feed covers the major fraction of onion juice extraction facility operational cost and 750 annual waste hauling trips to the central valley.