Removal of phenolic compounds from palm oil mill effluent by thermophilic Bacillus thermoleovorans strain A2 and their effect on anaerobic digestion

Abstract

Anaerobic digestion is commonly used for the treatment of palm oil mill effluent (POME) due to its efficiency in removing high organic content with the production of renewable energy in the form of methane. The presence of phenolic compounds in the POME has inhibitory effects on anaerobic bacterial growth. The major POME phenolic compounds were identified as gallic acid, protocatechuic acid, p-hydroxybenzoic acid, caffeic acid, syringic acid, vanillic acid, p-coumaric acid, ferulic acid and phenol. In this study, to reduce their toxicity, pretreatment of POME with the thermophilic phenol-degrading bacteria, Bacillus thermoleovorans strain A2, was performed. The A2 strain was able to aerobically degrade the phenolic compounds over a wide range of temperatures and pH values but the optimum conditions were found at 60 °C and pH 7. The maximum efficiency of the removal of phenolic compounds was 61.1% with a degradation rate of 4.03 mg L−1 h−1. This aerobic pretreatment was able to partially degrade all the individual phenolic compounds but to different extents. Some of the remaining phenolic compounds were further reduced by the anaerobic process. The anaerobic digestion of the aerobically pretreated POME was able to produce a methane yield 1.7–10.8 times higher than that of untreated POME. The results show that the inhibitory effects of phenolic compounds can be detoxified by pretreatment with thermophilic bacteria.