Onions to the Rescue!

Gills Onions, the largest onion processor in the US was the focus article of the October 2010 issue of Civil Engineering Magazine. They are the only facility in the world who use anarobic digestion to convert onion water into methane, which is then used to power fuel cells.

The company processes, cuts, and peels roughly one million pounds of onions per day, thus leaving mountains of waste material. The company decided to use the waste to fuel their new $9.5 million Advanced Energy Recovery System (AERS) to convert that waste into useable energy. They have determined that disposing of 200,000 lbs of waste a day was costing the company $400,000 per year and now they are being used to pay off the system in only six years.

The process starts by collecting the onion peels and waste and placing them in a tank to be juiced. Lime is added to increase juice yield and the waste material is ground into pulp and then run through strainers to extract the juice. The juicing process generates roughly 20,000 galons of onion juice per day that is then poured into large equilazation tanks which serves as a preliminary fermenter or acidifier to increase the bolatile fatty acids and decrease the pH of the juice.

 When the juice is acified, it yields a higher methane production. The juice is then allowed to ferment in a reactor which collects the escaping gas and transports it to bio-fuel cells that are used to provide power to the facility and reduce power costs.

All in all this is a prime example of how ingenuity can produce monetary results in a green, energy effiecent way.