City trash plus farm leftovers may yield clean energy

For ethanol research, technician David Bozzi weighs pulp recovered from garbage (a sample of which is in the plastic bag, at left) while microbiologist Diana Franqui adds glucose-releasing enzymes to a blend of plant material and pulp suspended in water. On the table, the plastic tray at left contains pulp from garbage; the tray at right holds rice straw--a plant waste left after rice harvest. (ARS photo by Peggy Greb.)

Tomorrow's household garbage might be blended with after-harvest leftovers from fields, orchards, and vineyards to make ethanol and other kinds of bioenergy. Agricultural Research Service scientists are investigating this straightforward, eco-friendly strategy in their laboratories at the agency's Western Regional Research Center in Albany, Calif.

In most instances, agricultural wastes like rice straw, almond hulls, and the oversize outer leaves of iceberg lettuce will have to be pretreated before being used as a bioenergy resource. That's according to Kevin Holtman, an ARS research chemist who's working out the details of the garbage-to-gas approach.

The garbage, known as "municipal solid waste," or "MSW," would also be pretreated, Holtman noted.

The garbage would be processed in a jumbo-size autoclave, a device which acts something like a giant pressure cooker to convert the MSW into grey, lightweight clumps. The pretreated agricultural wastes and autoclaved MSW would then be transferred to a biofermenter. Yeasts and enzymes would be added, to make ethanol.

Holtman and colleagues David Bozzi, an engineering technician, and Diana Franqui, a microbiologist, are determining the best ways to use just water and heat, instead of hazardous chemicals, to pretreat the farm wastes, thus keeping the biorefining process environmentally friendly.

The team, part of the Bioproduct Chemistry and Engineering Research Unit at the Albany research center, is collaborating in the research and development venture with Comprehensive Resources, Recovery and Reuse, Inc., or "CR3," of Reno, Nev., and with the Salinas (Calif.) Valley Solid Waste Authority.

Besides producing biofuels, the biorefinery would also reduce the volume at landfills and minimize the need for new ones.

Read more about the research in the October 2008 issue of Agricultural Research magazine, available online at: http://www.ars.usda.gov/is/AR/archive/oct08/energy1008.htm

ARS is a scientific research agency of the U.S. Department of Agriculture.

11/10/08
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Date: 10/31/08

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