Enhancing biogas production from empty fruit bunch through acetic acid pretreatment: process optimization and synergistic effects

Abstract

Empty fruit bunch (EFB), a lignocellulosic waste generated from the palm oil industry, has emerged as a promising feedstock for biogas production. The recalcitrant nature of EFB hinders its efficient biodegradation, necessitating effective pretreatment methods to enhance biogas yield. This study investigated the effect of weak acid pretreatment using acetic acid on the composition and structure of EFB and its subsequent anaerobic digestion performance. EFB was subjected to pretreatment with varying concentrations of acetic acid (0-10%) at room temperature for 7 days. The pretreated EFB was characterized using compositional analysis. Anaerobic digestion experiments were conducted in batch mode for 45 days at 35°C. Pretreatment with 4% acetic acid resulted in the highest methane yield of 265.77 mL-CH4/g-VS, representing a 55.21% improvement compared to untreated EFB. The synergistic effect of co-fermentation of acetic acid and EFB was observed at 4% acetic acid, with a synergistic CH4 value of 60.26. Compositional analysis revealed that acetic acid pretreatment led to a 12.5% reduction in lignin content and a 9.3% increase in cellulose content, enhancing the accessibility of cellulose for microbial degradation. The energy balance analysis indicated a positive net energy gain of 879.62 kWh per ton of EFB, while the economic analysis suggested a net profit of 60.00 USD per ton of EFB. Comparative analysis showed that acetic acid pretreatment outperformed other pretreatment methods, such as alkaline (28.77% improvement), steam explosion (10.96% improvement), and enzymatic (40.18% improvement) pretreatments, in terms of methane yield enhancement. The findings of this study demonstrate the effectiveness of weak aacid pretreatment in enhancing biogas production from EFB and its potential for large-scale application in the palm oil industry.