Anaerobic Co-digestion of Fruit and Vegetable Waste and Sewage Sludge

Abstract

Fruit and vegetable wastes are generated in large quantities around the world. This kind of residue constitutes a source of nuisance in municipal landfills because of its high biodegradability. Another residue that is generated in large quantities around the world and also constitutes a source of nuisance is the sewage sludge. Both residues can be treated together by the anaerobic co-digestion process. In this sense, the aim of the present study was to evaluate the anaerobic co-digestion of fruit and vegetable waste and sewage sludge, in order to monitor the waste stabilization time and the biogas generation, among others. The study was conducted in a 70 litter stainless steel anaerobic reactor, with no mixing system, at room temperature (25±5ºC), during a period of 105 days. The fruit and vegetable wastes were collected in a central distribution market for food, and were shredded and blended before the experiment. The seed inoculum was collected in an anaerobic domestic sewage station of treatment. The parameters analyzed were: chemical oxygen demand, C/N and C/N/P ratios, pH, alkalinity, volatile fatty acids, and biogas generation. The results showed that the chemical oxygen demand was reduced around 20%. The parameters, pH, alkalinity and volatile fatty acids were stabilized, but the C/N wasn’t stabilized. The final value obtained for C/N ratio was around 20/1. The biogas generation was around 331 litters and most of the biogas production occurred during the first month of the experiment. The low chemical oxygen demand removal, the high C/N ratio and the biogas generation almost always in the first few days of the experiment probably indicate that this residue, although being organic, presents difficulties in its degradation, maybe because of the high organic load that was applied to the reactor. The fact of the reactor being disproved by a mixing system can also have contributed to the low residue degradation.