Effect of torrefaction of palm frond on methane yield through anaerobic co-digestion with palm oil mill effluent

Palm frond (PF) is an abundant biomass from oil palm plantations, which can be effectively utilized as a co-feedstock for the anaerobic digestion of palm oil mill effluent (POME). In this study torrefaction (mild pyrolysis) was utilized as a pre-treatment for palm frond (PF) biomass before its co-digestion with POME. This investigation seeks to unlock the untapped potential of these waste streams, particularly focusing on the enhancement of methane yield and biogas generation. The study encompasses a range of torrefaction temperatures spanning from 240 °C to 350 °C, each applied at a residence time of 30 min. The raw and torrefied PF underwent 28-day anaerobic digestion process under mesophilic conditions, maintained at 37 °C. As torrefaction temperature increased, the mass yield decreased from 80 to 50 wt%. Moreover, FTIR analysis demonstrated a notable reduction in major peaks representing hydroxy, carbonyl, and ether functional groups as torrefaction temperature increased, which confirmed the chemical composition changes in biomass. The findings of this study revealed a methane yield of 1.36 L CH₄ / g VS, which represented a remarkable 209 % increase in methane production compared to the digestion of raw PF with POME. The high removal efficiencies for POME characteristics were noticed after co-digestion.