Anaerobic treatment of palm oil mill effluent by tank digesters

Abstract

Abstract Palm oil mill effluent was treated anaerobically in 210 dm −3 tank digesters in which inoculation with anaerobic seeding coupled with careful addition of lime could shorten the natural stabilisation process to about 30 days. The system was subsequently scaled up to 500 tonnes capacity. The characteristics of the anaerobically digested liquors were studied at 10 and 20 days hydraulic retention time (HRT) respectively, and close to 90% treatment efficiency could be achieved at 20 days HRT with complete microbial conversion of plant cell debris. However, the digested liquor still contained 0.325% (by wt) suspended solids. The kinetics of the anaerobic process show close resemblance to those treating other high strength organic wastes. Optimum gas production occurred only over a narrow pH range of 6.8–7.2 units. A methane content of 62–67% on gas production was noted about equivalent to 0.34 to 0.39 dm −3 CH 4 g −1 of BOD destroyed.