Enhancing sludge stabilization and methane production in the anaerobic digestion of palm oil mill effluent using carbon conductive materials

Palm oil mill effluent (POME) sludge is lipid rich and requires effective treatment. Anaerobic digestion is an economically viable solution for reducing environmental impacts while supporting energy recovery. However, its performance is often constrained by the accumulation of volatile fatty acids. This study evaluated the dosage effect of carbon and carbon–graphite felts (3, 6, 9, and 12 g L⁻¹) on sludge stabilization and biogas production in lab-scale semi-continuous reactors under mesophilic conditions (37 ± 1 °C) at an organic loading rate of 1.5 g volatile solids (VS) L⁻¹ day⁻¹. The results showed that 3 g L⁻¹ of carbon felt increased methane production rate by 20% compared to the blank (0.257 NL-CH₄ gVS_added⁻¹ day⁻¹). The chemical oxygen demand and VS removal improved by 82% and 78%, respectively, compared to the blank, indicating significant organic matter degradation (p < 0.05). Total utilization of fatty acids reached 77%, demonstrating stable operational conditions and effective inhibition alleviation. Microbial community analysis revealed interactions involving Clostridium, Syntrophomonas, Methanosaeta, and Methanobacteria, suggesting improved direct interspecies electron transfer through conductive pathways. These findings demonstrate the effectiveness of conductive materials for stabilizing sludge and enhancing methane production, providing a practical solution for POME treatment.