Influence of biochar mass on solids removal efficiency and biochar transformation during anaerobic digestion of palm oil mill effluent

Abstract

Palm oil mill effluent (POME) is a high-strength organic wastewater that poses significant environmental challeng - es, yet holds substantial potential for biogas generation through anaerobic digestion (AD). This study investigated the influence of biochar mass loading (0, 1, 1.5, and 2 g/L) on solids removal efficiency, biochar physicochemical transformation, and biogas production kinetics during POME anaerobic digestion. Solids of total (TS) and solids of suspended of total ( TSS ) were monitored throughout the digestion period, while biochar characterization was performed using scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDX) and Brunau - er–Emmett–Teller (BET) analysis before and after the AD process. Results demonstrated that adding 2 g/L biochar yielded the highest TS and TSS degradation efficiencies of 76.2% and 72.22%, representing improvements of 24.92% and 35.42% over the control, respectively. SEM-EDX analysis revealed significant elemental transforma - tion of biochar during AD, including a decrease in carbon content from 53.8% to 49.8%, a substantial increase in silicon from 1.5% to 5.0%, and the emergence of new elements (Na and P), confirming the active role of biochar beyond that of a passive microbial support medium. BET analysis indicated a reduction in surface area from 9.368 to 4.815 m²/g, consistent with pore occupation by organic compounds and microbial colonization. These findings confirm that biochar mass loading significantly enhances POME treatment performance and provides mechanistic evidence of biochar transformation during anaerobic digestion.