Enhancing the biogas production and the treated effluent quality via an alternative Palm Oil Mill Effluent (POME) treatment process: Integration of thermal pretreatment and dewatering

Abstract

To address the limitations associated with the disposal management and the treatment process of POME, an alternative process that consists of eliminating the cooling ponds and integrating a pretreatment technology combined with a dewatering device was proposed. Since the proposed treatment process has not been tested previously, the objective of this study is to investigate the effect of thermal pretreatment and solid loading alteration via dewatering on a thermophilic continuous set up consisting of an upflow anaerobic sludge blanket – hollow centered packed bed (UASB-HCPB) bioreactor. It was established that the best performing solid loading was the 40S:60L, which is made up of 40% by volume of POME settled solids and 60% of clarified liquid. Thermally pretreated 40S:60L solid loading had a significantly enhanced biogas production, methane purity, chemical oxygen demand (COD), biological oxygen demand (BOD), and total suspended solids (TSS) removal efficiencies. The reactor exhibited stability owing to the low volatile fatty acid/alkalinity ratio obtained throughout the run. With a reactor capacity of 5L, thermally pretreated 40S:60L achieved a daily biogas production volume of 48L and a methane purity of 77.2%. The COD, BOD, and TSS removal efficiencies of the thermally pretreated 40S:60L solid loading were evaluated to be 97.5, 95.1, and 94.5%. The enhanced process performance is due to the consistent solids concentration, which allowed a more effective mass transfer and transport in the medium. Meanwhile, thermal pretreatment promoted cell lysis, making the intercellular organic matter readily available for the bacteria consortium.