Biomethanation of Palm Oil Mill Effluent (POME) with a thermophilic mixed culture cultivated using POME as a substrate

Anaerobic systems operated under thermophilic condition often encounter longer start-up period and operating problems pertaining to temperature shift when mesophilic seed sludge were utilized as thermophilic sludge. Bioaugmentation products for thermophilic conditions were not readily available in the market. Hence, a thermophilic mixed culture has been cultivated specifically for Palm Oil Mill Effluent (POME) treatment at thermophilic conditions using a batch Continuous Stirred Tank Reactor (CSTR) where POME was utilized as a substrate for the growth of microbes. The thermophilic mixed culture managed to reduce at least 90% of Chemical Oxygen Demand (COD) in POME with a hydraulic retention time (HRT) of 6 days with a MLSS concentration of 14,000 mg/L. The biogas produced from the batch CSTR contained at least 64% of methane. The kinetic parameters for batch thermophilic POME treatment were obtained by fitting the Chen and Hashimoto's model to the experimental data. The maximum substrate utilization rate for this system was found to be 0.476 day−1, which was higher than the systems operated under mesophilic range, and dimensionless kinetic parameters k and Q were −1.365 and 0.0007 respectively. The mixed culture had a methanogenic population which consisted of Methanosaeta thermophila, Methanosarcina thermophila, Methanobacterium thermoautotrophicum, Methanobacterium thermoformicicum and Methanobacterium wolfei.