System utilizes waste to reduce handling, electricity costs
By LISA LIEBERMAN
For the Capital Press
One of the biggest challenges any large agricultural operation faces is what to do with the leftovers.
Until about a year ago, Gills Onions, one of the largest onion processors in the world, had been processing 1 million pounds of onions and generating 200,000 to 300,000 pounds of waste a day. It spread the waste as compost on its 15,000-plus acres of farmland near Oxnard, Calif.
Disposing of the waste was expensive and time-consuming, costing the company about $450,000 in labor alone, said Nikki Rodoni, sustainability coordinator at Gills Onions.
"As the company has grown in the past years the amount of waste has grown, too, so we wanted to figure out something else to do with it," Rodoni said.
The company was also facing higher electricity costs -- 12 to 13 cents per kilowatt-hour plus a 15 percent rate increase. So the Gills family decided to pursue a long-held dream of converting onion waste into electricity.
Although dairy farms and breweries convert waste products into methane gas using an anaerobic digester, the potential for onions was unknown.
The company enlisted the help of researchers from the University of California-Davis and private engineers. The scientists discovered that the sugar content in onion waste would feed methane-producing microbes.
"This type of project had never been done before, and we didn't know how it was going to turn out. But it's worked out a lot better than we anticipated," Rodoni said.
The company's energy recovery project officially launched in 2008 and went fully online in 2009.
The liquid waste from the onions -- which comprises about 75 percent of the total waste -- is separated from the solid onion waste. The juice is then diluted and diverted to the energy recovery system's automated anaerobic digestion process. Microorganisms in the digester convert the juice's sugar content into methane and carbon dioxide. The methane is then fed into two 300-kilowatt fuel cells, which create energy.
"We're supplying 100 percent of our base load of energy, which is always at a minimum of 600 kilowatts because of our huge refrigeration system, and 60 percent of our overall electricity," Rodoni said.
The power generated each year would power 460 homes for a year.
The project cost about $9.5 million, but the savings in labor needed to haul the waste away plus an anticipated $750,000 savings a year in electricity costs should pay off quickly. The company also received $2.7 million in incentives for the project from Southern California Gas Co.
The next step is finding a use for the solid onion waste. Right now, most of the solids are being sold as cattle feed. Gills Onions wants to find a way to extract quercetin, a high-value flavanoid, from the fibrous parts of onion waste to use in the pharmaceutical industry.
"There's been research done that shows that quercetin is really good for mental alertness and the respiratory system," Rodoni said. "We found that most quercetin out there is synthetically made and that onions have one of the highest natural sources of it."
The company plans to work with the Department of Defense to explore incorporating quercetin additives into ready-to-eat meals and creating food supplements for energy drinks and other food additives, Rodoni said.
Eventually, Gills Onions wants to put 100 percent of its waste to use and eliminate its carbon footprint, Rodoni said.
"For some of the fibrous parts that we don't use for food supplements, we want to find a way to incorporate them into packing materials. Onions have really strong fibers, which we think will work well in these materials," Rodoni said.
Gills Onions is testing different varieties of onions in various growing regions in the state to see which varieties are optimal for creating energy and other valuable byproducts.
"We're just in the infancy stages of all this, but we're going to continue finding ways to utilize waste," Rodoni said.
At the moment, the energy recovery system at Gills Onions is one of the largest of its kind installed in California, Rodoni said. Utility companies in general are offering incentives and encouraging other industries to come up with similar energy-saving systems.
"Eventually, we could see other industries using this same type of technology to produce energy," Rodoni said.