Waste has become a lot more valuable to the largest processor of fresh-cut onions in the United States. California-based onion processor Gills Onions used to discard roughly 300,000 pounds of onion waste—inedible skins, tops, and tails—each day, but now this waste is being converted into a biogas that helps power the plant. The owners of Gills Onions are hoping their new Advanced Energy Recovery System, unveiled in July 2009, will be both eco-friendly and cost effective.
The system works by compressing waste to separate onion juice from solid onion pieces. The solid component is sold as cattle feed, and the juice is put into an anaerobic digester where it is converted into methane and carbon dioxide, or in other words, biogas. In a fuel cell, the newly formed biogas is combined with oxygen, producing water and electricity. Onion juice is now meeting about 40% of the energy requirements for Gills Onions, following a $9.5 million investment.