Specific degradation of phenolic compounds from palm oil mill effluent using ozonation and its impact on methane fermentation

Abstract

In this study, the inhibition to anaerobic digestion of phenolic compounds present in palm oil mill effluent (POME) was quantified in batch and continuous operations to assess their effects on methane fermentation. Caffeic acid (CAF), at its concentration in POME, was found to be the most effective inhibitor of the microbial community in hydrolysis, acidogenesis, and methanogenesis phases. To mitigate the toxicity of anaerobic digestion (AD), the pretreatment of POME with various ozone dosages (0.1 to 0.4 gO3/Lwastewater) was performed to determine the effectiveness of specific phenolic compounds destruction. The ozone pretreatment was able to significantly degrade these phenolic molecules and alter their profile in POME over the wide ranges of ozone dosage. Ozone dosage of 0.2 gO3/Lwastewater was optimal to cause the individual concentration to drop below the strong inhibitory levels. When POME was ozonized, the overall total phenolic compounds in the effluent were reduced by 75 % from 613 to 155 mg/L. The overall volumetric biogas yields correspondingly increased by 67 % from 0.3 to 0.5 L/Lreactor.d with the improved specific methane yield from 6.3 ± 0.2 to 9.3 ± 0.1 LCH4/m3. The results demonstrated that the inhibitory effects of phenolic compounds could significantly be detoxified by pretreatment with ozone to enhance anaerobic digestion performance.