Enhancing Methane Production from Palm Oil Industry Waste through Thermotolerant Bacterial Bio-augmentation: Optimization and Kinetic Analysis

Abstract

This study investigated bio-augmentation strategies to enhance biogas production from palm oil industry residues through thermotolerant anaerobic digestion. Two bacterial strains, Cellulomonas sp. (HD19AZ1) and Themoanaerobacterium thermosaccarolyticum (PSU-2), were evaluated at various inoculum to microorganism (I:S) ratios for both single digestion of empty fruit bunches (EFB) and co-digestion with palm oil mill effluent (POME). Results demonstrated that bio-augmentation significantly improved substrate biodegradability and methane yields. With HD19AZ1, the optimal I:S ratio of 70:10% for single digestion achieved methane yields of 146.38 mL-CH₄/gVS (a 24.94 mL-CH₄/gVS substrate improvement), while the 65:15% ratio for co-digestion yielded 166.55 mL-CH₄/gVS (33.38 m³/tonne substrate improvement). These represented increases of 33.59% and 39.65% in biodegradability for single and co-digestion, respectively. Volatile solids removal reached 41.82% in single digestion and 47.59% in co-digestion under optimal conditions. Kinetic analysis revealed that bio-augmentation with HD19AZ1 achieved methane production rates of 3.90 mL-CH₄/d for single digestion and 6.70 mL-CH₄/d for co-digestion, while PSU-2 augmentation increased rates by 2.14 times compared to control samples. The hydrolysis constant (Kh) ranged from 0.0214-0.0375 d⁻¹ for single digestion and 0.0095-0.0232 d⁻¹ for co-digestion, with lag phases of 5.15-16.11 days and 18.29-43.14 days, respectively. Modified Gompertz modeling confirmed these parameters with R² values exceeding 0.97. This study demonstrates that strategic bio-augmentation with thermotolerant bacteria significantly enhances methane production from palm oil industry waste by improving substrate accessibility and accelerating the hydrolysis of recalcitrant lignocellulosic components, offering promising applications for industrial-scale biogas production.