Biological Oxidation of Dissolved Methane in Palm Oil Mill Biogas Effluents Using an Anoxic Methane-Oxidizing Consortium

Abstract

This study investigated the potential of anoxic methane-oxidizing consortia This study investigated the potential of anoxic methane-oxidizing consortia for mitigating dissolved methane in palm oil mill biogas effluents. Microbial consortia from five soil sources were evaluated under various conditions. The cattle farm effluent-derived consortium demonstrated the highest methane reduction efficiency of 76.89% after a 3-week incubation period, with a methane consumption rate of 49.37 mg-CH₄/m²/d. The landfill soil consortium showed the second-highest performance with a 75.48% reduction efficiency under shaking conditions. Environmental factors significantly influenced methane oxidation performance. Optimal conditions were identified as 35°C, pH 7.0, 0.5 mg/L dissolved oxygen, 55 mg/L nitrate concentration, and 5 g/L NaCl. Plastic media enhanced methane reduction efficiency for most microbial sources, particularly for the cattle farm effluent consortium (67.07% efficiency). Characterization of the palm oil mill biogas effluent revealed a COD of 13.15 g/L, BOD of 7.11 g/L, and total Kjeldahl nitrogen of 0.73 g/L. Carbon mass balance analysis confirmed biological methane oxidation, with 45% converted to CO₂, 38% incorporated into biomass, and 12% as dissolved organic carbon. The developed system can potentially mitigate up to 23,067 t CO₂e/year for an average palm oil mill, with associated cost savings of approximately 115,335 USD/year through carbon credits, assuming a credit value of 5 USD/t CO₂e. These findings demonstrate the potential of anoxic methane-oxidizing consortia for greenhouse gas mitigation in the palm oil industry. The study provides insights into optimal conditions and microbial sources for efficient methane oxidation, paving the way for developing effective biological treatment systems for palm oil mill effluents.