Synergistic integration of hydrothermal pretreatment and co-digestion for enhanced biogas production from empty fruit bunches in high solids anaerobic digestion.

This study investigates the co-digestion of hydrothermally pretreated empty fruit bunches (EFB) at 190 °C for 5 min (HTP190-EFB) with decanter cake (DC) to improve biogas production in high solid anaerobic digestion (HSAD). The HTP190-EFB exhibited a 67.98 % reduction in total solids, along with the production of 0.89 g/L of sugar, 2.39 g/L of VFA, and 0.56 g/L of furfural in the liquid fraction. Co-digestion of HTP190-EFB with DC at mixing ratios of 5, 10, and 15 %w/v demonstrated improved methane yields and process stability compared to mono-digestion of HTP190-EFB. The highest methane yield of 372.69 mL CH/g-VS was achieved in the co-digestion with 5 %w/v DC, representing a 15 % increase compared to digestion of HTP190-EFB (324.30 mL CH/g-VS) alone. Synergistic effects were quantified, with the highest synergistic methane yield of 77.65 mL CH/g-VS observed in the co-digestion with 5 %w/v DC. Microbial community analysis revealed that co-digestion of hydrothermally pretreated EFB with decanter cake promoted the growth of sp., sp., sp., sp., and sp., contributing to enhanced biogas production compared to mono-digestion of pretreated EFB. Energy balance analysis revealed that co-digestion of HTP190-EFB with DC resulted in a total net energy of 599.95 kW, 52 % higher than mono-digestion of HTP190-EFB (394.62 kW). Economic analysis showed a shorter return on investment for the co-digestion system (0.86 years) compared to the mono-digestion of HTP190-EFB (1.02 years) and raw EFB (2.69 years). The co-digestion of HTP190-EFB with 5 %w/v DC offers a promising approach to optimize methane yield, process stability, and economic feasibility, supporting the palm oil industry for producing renewable energy and sustainable waste management.