Promoting Circular Economy in the Palm Oil Industry through Biogas Codigestion of Palm Oil Mill Effluent and Empty Fruit Bunch Pressed Wastewater

Abstract

This research aimed to investigate the biogas production and circular economy perspective in the palm oil industry through codigestion of oil palm empty fruit bunch (EFB) pressing wastewater and palm oil mill effluent (POME). The EFB pressing method constitutes an alternative new technology used to extract the remaining oil, increasing palm oil product; however, it produces highly polluted wastewater. Batch experiments were carried out at 35 °C to investigate the optimal ratios of EFB wastewater, inoculums, and POME. The optimal condition was 45% POME + 50% seed + 5% EFB wastewater. This condition was then used in semicontinuous fermentation where the optimal hydraulic retention time (HRT) totaled 25 days. The accumulated biogas was 18,679 mL/L while the accumulated methane totaled 6778 mL/L. The methane content was 62%, and the COD removal efficiency was 67%. The sludge produced from the HRT 25-days digester complied with the organic compost standard which could be further used to nourish the soil. An economic analysis of the EFB pressing project revealed a higher internal rate ratio with shorter payback compared with the conventional process. These results provide information on the circular economic approach to promote sustainable palm oil processing.