Production of Biogas from Palm Oil Mill Effluent at Pilot Scale: Effect of Recycle Sludge

An anaerobic digestion of palm oil mill effluent (POME) for production of biogas was carried out at pilot scale under thermophilic condition. The objective of this research is to maintain short hydraulic retention time (HRT) and high degradation of the POME to biogas by applying recycle sludge. Fresh POME from PTPN IV without further treatment was used as feed. The fermentation process occurred in a digester tank with the type of continuous stirred tank reactor has a volume of 3 m3 equipped with electrical heaters, mixer, insulators, and baffles in it. To create continuous operation, fresh POME was fed intermittently. A series of experiments with and without recycle sludge were conducted with 616 litres palm oil mill effluent/day feed rate, temperature of feed tank 70 oC, digester tank temperature of 55 oC, stirring rate of 37.5 rpm, six days of hydraulic retention time, and 34% of recycle sludge. The result showed that by extending solid retention time in return sludge process where 34% of digested slurry recycled to the digester, improvement of volatile solid (VS) degradation was obtained around 82.83% at HRT of 6 days. Then, chemical oxygen demand (COD) removal efficiency could be reached until 81% by performing recycle sludge.