Effect of Iron Oxide Nanoparticles and Combined Pretreatment on Biogas Yield from Oil Palm Fruit Bunch under Mesophilic Conditions

Abstract

Aim of the Study: This study aimed to evaluate the effect of nanoparticle addition and substrate pretreatment on the biogas yield and quality of Oil Palm Empty Fruit Bunch (OPEFB) under mesophilic temperature conditions (30–40°C). Study Design: A laboratory-scale, multi-treatment batch experimental design was adopted using five 2.5-liter anaerobic digesters labeled A–E. The design allowed direct comparison of inoculum, substrate, pretreatment, and nanoparticle combinations under identical mesophilic conditions. Place and Duration of the Study: The study was conducted at the Power and Machinery Laboratory, Department of Agricultural Engineering, Ladoke Akintola University of Technology (LAUTECH), Ogbomoso, Nigeria, over a four-weeks digestion period between June and August 2025. Methodology: OPEFB was collected, air-dried, and subjected to thermal (boiling at 100°C for 30 minutes) and chemical (1% NaOH for 24 hours) pretreatments. Five digesters were prepared: A (inoculum only), B (inoculum + untreated OPEFB), C (inoculum + pretreated OPEFB), D (inoculum + untreated OPEFB + Fe₂O₃ nanoparticles), and E (inoculum + pretreated OPEFB + Fe₂O₃ nanoparticles). Iron oxide nanoparticles (1 g/L) were introduced to enhance microbial activity. Biogas volume was determined by water displacement, while CH₄, CO₂, H₂, and H₂S contents were analyzed using a gas analyzer. Results: Pretreatment and nanoparticle addition significantly improved biogas yield and methane concentration. Methane content increased from 55–60% (untreated) to 75–78% (pretreated + nanoparticles), while CO₂ decreased to about 25%. The integrated treatment enhanced cumulative biogas yield by 40% over the control, and the Modified Gompertz model (R² = 0.94) best described the kinetics. Conclusion: The study concludes that combining Fe₂O₃ nanoparticles with thermal–chemical pretreatment enhances OPEFB biodegradability, accelerates digestion, and improves methane quality. This integrated approach provides an efficient, eco-friendly pathway for converting oil palm waste into renewable energy, supporting sustainable waste management and energy security.