Citrus Peel Waste a Potential Source of Ethanol

Thanks to recent hikes in gasoline prices, there is a renewed interest in finding a cheaper way to fill up the gas tank. Researchers at the Agricultural Research Service (ARS) Citrus and Subtropical Products Laboratory in Winter Haven, Fla. have been working on a potential substitute: citrus peels.

In 1992, Karel Grohmann, then research leader of the Winter Haven lab, began researching the feasibility of converting citrus peel waste into fuel ethanol. Citrus waste materials are rich in pectin, cellulose and hemicellusic polysaccharides, which can be hydrolyzed into sugars and fermented into alcohol. Most of this dried peel residue—a total of 1.2 million tons annually in Florida alone—is currently marketed as low-value cattle feed, despite its relatively high processing cost.

In 2004, Bill Widmer, an ARS chemist at Winter Haven, picked up where Grohmann left off, with the help of a cooperative research and development agreement partner, Renewable Spirits LLC of Delray Beach, Fla. Widmer and his scientific team first modified the process to substantially reduce the amount of enzyme required to convert the citrus waste carbohydrates to sugars and ethanol. Now the process shows economic promise for large-volume production.

Beginning with the one-quart-to-one-gallon laboratory process developed by Grohmann, the process was modified to work at 10-gallon, 100-gallon and 1,000-gallon batch levels. A 10,000-gallon pilot facility is currently under construction, and should be finished by sometime this year. With further research, according to Widmer, Florida's citrus peel waste could yield up to 80 million gallons of ethanol per year.

Read more about the research in the April issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's principle scientific research agency.