Enhancement of Electrochemical–Anaerobic Digested Palm Oil Mill Effluent Waste Activated Sludge in Solids Minimization and Biogas Production: Bench–Scale Verification

The development of the palm oil industry has induced the generation of palm oil mill effluent (POME) together with its waste activated sludge (WAS) in recent years. This study aims to discover new opportunities in treating POME WAS that has high organic content with low degradability but having potential in converting waste into energy. The optimized electrochemical oxidation (EO) of pre-treated WAS was applied prior to anaerobic digestion (AD) to improve the POME WAS digestibility (by assessing its solids minimization and biogas production) under mesophilic conditions at 30 ± 0.5 °C and solids retention time of 15 days. The enhancement in sludge minimization was verified, with 1.6-fold over the control at steady-state. Promising results were obtained with a total chemical oxygen demand (COD) removal of 68.8% with 11.47 mL CH4/g CODadded in pre-treat digester, compared with 37.1% and 3.9 mL CH4/g CODadded in control digester. It is also worth noting that the specific energy (SE) obtained for this EO pre-treated AD system is 2505 kJ/kg TS with about 94% increment in methane production. It is evident that this system was applicable on POME WAS in ameliorating solids minimization as well as enhancing biogas production.