Energy from Cull Fruit
ABSTRACT A12-month investigation was conducted to study energy extraction from fruit residue. Cull fruits were fermented to produce ethanol, the ethanol was distilled off from the resulting beer, and the stillage was anaerobically digested to produce methane. During the first eight months, laboratory scale studies were conducted on cull fruit samples (apple, cantaloupe, grape, honeydew, orange, peach, pear, and plum). Samples were fermented in 4-L batch fermentors; the ethanol was subsequently removed from the solutions using a laboratory still; finally, the stillages were digested using 4-L batch anaerobic digesters. During the latter four months of the investigation peach culls were processed in a pilot size, batch mode, ethanol plant. The resulting stillages were fed to a 100-L, continuous mode, anaerobic digester. Sufficient methane gas was produced from the majority of the stillage tested to meet distillation energy requirements.