Recycling Food Waste

Organic Farmers Hope Anaerobic Digester Becomes Cash Cow

Farmer Joe Durando of Possum Hollow Farm in Florida, spreads effluent from a new machine that 'digests' cafeteria food waste for use as a soil amendment on nearby farms. Photo by Dave O'Keefe

Florida organic farmers seeking an alternative to expensive organic fertilizers are testing a new technology that converts food waste to liquid fertilizer. 'The digester works something like a cow's stomach - in fact, rumen microbiologists were some of the pioneers of this technology,' says Dave O'Keefe, of Full Circle Solutions, Inc., who designed the system for small farms with the aid of a SARE grant. The digester resides at Possum Hollow Farm, where grower Joe Durando recycles approximately two tons of cafeteria food waste weekly. Anaerobic bacteria in the digester convert the food waste to methane and carbon dioxide, while the nutrients remain in the water or in a small amount of solid residue that can be land applied or cured to a mature compost. Durando, one of three farmers testing the fertilizer, uses the methane to heat the digester and the nutrient-rich water to fertilize his fields. The fertilizer nitrogen value produced from two tons of food waste per week ranges from $800 to more than $10,000 annually if calculated on the basis of nitrogen values in poultry litter or fish emulsion, respectively. Additional farm income could be derived from tipping fees for accepting food waste; a $20-per-ton tipping fee would produce $2,000 extra annual income. For more information, go to www.sare.org/projects/ and search for LS98-090

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