Boosting Biogas Yield from Palm Oil Residues through Microbial Immobilization and Kinetic Analysis

This study investigates the enhancement of biogas production from palm oil mill residues through microbial immobilization on zeolite during anaerobic co-digestion. SEM/EDX analysis showed that fresh sludge contained approximately 45.1 wt% organic carbon and 1.25 wt% calcium, while spent sludge demonstrated increased porosity and biofilm formation, indicating successful microbial colonization on zeolite surfaces. FTIR analysis revealed significant degradation of organic functional groups in substrates such as palm oil mill effluent (POME), palm kernel shell (PKS), fibrous biomass (FBK), mesocarp fiber (MF), and cow dung, confirming effective substrate breakdown. GC-MS characterization of biogas identified methane concentrations reaching 65%, along with minor volatile organic compounds, demonstrating efficient methanogenesis. Zeta potential measurements indicated values ranging from –15 mV to +5 mV, facilitating microbial adhesion and biofilm stability. Kinetic modelling using pseudo-first order, pseudo-second order, and Monod models showed that immobilization with 10% zeolite increased the biogas production rate constant (k) from 0.035 to 0.078 day⁻¹, reducing lag phase duration by 30%. Experimental results demonstrated a cumulative biogas yield increase from 210 mL/g volatile solids (VS) without zeolite to 455 mL/g VS with zeolite, more than doubling production. These findings suggest that zeolite-supported microbial immobilization enhances substrate biodegradability, stabilizes operational conditions, and mitigates inhibitory effects, offering a scalable and efficient strategy for renewable bioenergy generation from palm oil residues.