Co-digestion of used oils and urban landfill leachates with sewage sludge and the effect on the biogas production.

Abstract: This paper evaluates the potential of mesophilic anaerobic digestion (AD) in the treatment of used oils and landfill leachates through co-digestion of the sludge produced in a wastewater treatment plant (WWTP). Biomethane potential (BMP) tests were performed on two different co-substrates and on WWTP sludge. The biogas production per kg of fresh matter of the sludge generated in a WWTP was only 6.1Nl/kg due to its low volatile solids concentration. Biogas production of landfill leachates per kg of fresh matter was found to be low (12.4Nl/kg). The biogas production per kg of fresh matter for the used oil over a period of 47days (not completely degraded) was 970.6Nl/kg. Used oil was selected as co-substrate according to these results. Anaerobic co-digestion of sludge and used oil was conducted in a pilot plant fed in semi-continuous regime in the mesophilic range (38°C) to obtain their adequate mixture in order to ensure the correct function of the process. The optimum oil percentage in the mixture was 19% (volatile solids basis). Once the appropriate mixture was obtained the co-digestion process was carried out in the digester of the Pobla de Farnals WWTP. The co-digestion process improved the performance of volatile matter removal (showing an 11% increase over the period without co-digestion) as well as the biogas production (a 23.5% increase over the period without co-digestion) without disturbing the anaerobic digestion process. The total production of biogas per day in the WWTP increased over the period without co-digestion. [Copyright &y& Elsevier]