Thermophilic anaerobic co-digestion of oil palm empty fruit bunches with palm oil mill effluent for efficient biogas production

The effect of pretreatment methods for improved biodegradability and biogas production of oil palm empty fruit bunches (EFB) and its co-digestion with palm oil mill effluent (POME) was investigated. The maximum methane potential of POME was 502 mL CH4/g VS-added corresponding to 33.2 m3 CH4/ton POME and 98% biodegradability. Meanwhile, the maximum methane potential of EFB was 202 mL CH4/g VS-added corresponding to 79.1 m3 CH4/ton EFB with 38% biodegradability. Co-digestion of EFB with POME enhanced microbial biodegradability and resulted in 25–32% higher methane production at mixing ratios of 0.4:1, 0.8:1 and 2.3:1 on VS basis than digesting EFB alone. The methane yield was 276–340 mL CH4/g VS-added for co-digestion of EFB with POME at mixing ratios of 0.4:1–2.3:1, while minor improvement was observed at mixing ratios of 6.8:1 and 11:1 (175–197 mL CH4/g VS-added). The best improved was achieved from co-digestion of treated EFB by NaOH presoaking and hydrothermal treatment with POME, which resulted in 98% improvement in methane yield comparing with co-digesting untreated EFB. The maximum methane production of co-digestion treated EFB with POME was 82.7 m3 CH4/ton of mixed treated EFB and POME (6.8:1), corresponding to methane yield of 392 mL CH4/g VS-added. The electricity production of 1 ton mixture of treated EFB and POME would be 1190 MJ or 330 kW h of electricity. The study shows that there is a great potential to co-digestion treated EFB with POME for bioenergy production.