Full Scale Anaerobic Digester for Treating Palm Oil Mill Wastewater

Abstract

This study was conducted to evaluate and improve the performance of the existing full-scale anaerobic digester for treating palm oil mill wastewater at Asian Palm Oil Co., Ltd. Krabi, Thailand. Trials were conducted at hydraulic retention times (HRT) of 14, 10, 7 and 6.5 days which correspond to average organic loading rates (OLR) of 2.43, 5.09, 6.50 and 8.70 kg COD/m 3 d, respectively. Average BOD 5 and COD removal efficiency was found to be about 93% and 65%, respectively. Wide variations of influent flow and organic loading were carefully monitored to achieve suitable operation criteria. To ensure suitable and stable biological removal efficiency, pH in the digester should not be less than 7.0 at influent temperatures in the range of 35-45°C. At HRT of seven days, corresponding to OLR 6.50 kg COD/m 3 d, a specific methane gas generation of 0.35 m 3 CH4/kgCOD was achieved, with an average CH 4 content of 67%. The biogas produced from anaerobic digesters is a cheap source of energy which can be used as a gas engine fuel to produce electricity. Up till now, the biogas plant has generated and sold a total of 7.5 Million kWh of alternative electricity to the Provincial Electricity Authority of Thailand.