Gills Onions, which both grows the eponymous crop and claims to operate the largest onion processing facility in the US, doesn't do things on a small scale. The cost of removing the onion waste left over after packaging was costing it over $400,000 a year, so the company looked for a way to reduce or eliminate that waste. Through a partnership with the Southern California Gas Company, Gills eventually found a way to turn this waste stream into 600kw of electricity. We talked with Hal Snyder, the VP of Customer Solutions for SoCalGas, to get the details on this project.

Snyder said that Gills had a history of working with SoCalGas on energy efficiency work, and the collaboration on this project was an extension of that relationship. The onion waste—the tops, bottoms, and skins left over after an onion is cut for packaging—provided a tempting target. "Any organic material has the potential for creating energy," as Snyder put it. The initial thought was that all of the onion could be processed for fuel, but cellulose bioreactors are still very much at the developmental stage.

But the onion waste contains a significant amount of material that's not cellulose, and squeezing it can release a liquid that Snyder called a complex mix of sugars and lipids; the remaining cellulose is being evaluated for its potential as fertilizer or cattle feed. The onion juice, however, has already found a use—in a 150,000 gallon (550,000l) anaerobic bioreactor, where it serves as food for a type of archaebacteria called a methanogen. These organisms thrive in the absence of oxygen, and the waste product of their metabolic use of carbohydrates and lipids is implied by their name: methane.

Given a constant flow of onion juice, the archaebacterial population is largely self-sustaining; Snyder said the original stock came from a similar Anheuser-Busch project. The organisms themselves provide some of the heat needed to keep the bioreactor running at an optimal temperature, and Gills uses waste heat from a natural gas burner to provide the rest. The bacteria produce some waste, but Gills is working with people at the University of California, San Diego to see if it has some value as fertilizer; it may ultimately be returned to the onion fields.

But the key byproduct of the archaebacteria is the methane, which constitutes about 75 percent of the gas coming off the bioreactor (which is a pretty high ratio, as these projects go). It gets fed to a pair of 300kw fuel cells, which convert it directly to energy. (Based on the size and manufacturer, these appear to be the hardware in question.) All told, the setup saves Gills about $700,000 of energy costs a year; combined with the reduced disposal costs, the setup is saving the company over a million dollars a year.

That said, the setup isn't cheap, since it includes a lot of customized equipment, and the up-front costs were in the neighborhood of $9 million. But SoCalGas participates in a state-mandated self-generation credit program that will contribute a total of $2.7 million to the project, cutting the payback time to only six years.

"Right now, it takes subsidies and support because this is emerging technology," Snyder said. "The technology exists, but it's about scale, size, and number of projects. It's just not at the scale where prices are declining yet, but it will be. Any organic waste, I think, will work with this process." He mentioned that SoCalGas is looking into other wastewater streams as potential power sources; he specifically mentioned a carrot processing facility that might have a profile very similar to Gills'.

We asked Snyder about the fact that many landfills are now being used to produce natural gas—the Gills project is essentially diverting some of that potential fuel source upstream. He suggested that figuring out what makes sense requires a careful analysis of the costs of transporting waste, the quality of the raw materials, etc. But the new focus on sustainability and domestic supplies of energy is ensuring that these sorts of analyses are actually getting done. "It's an exciting time to be in the energy business," he said.

Listing image by Kriss Szkurlatowski