Pilot-Scale Anaerobic Co-Digestion of Palm Oil Mill Effluent with Moringa Oleifera Filtrate in an Integrated Anaerobic-Aerobic Bioreactor

Inconsistent digestion of palm oil mill effluent (POME) causes difficulties for regulatory compliance plus inadequate biogas generation. In this study, Moringa Oleifera filtrate was co-digested with POME in a pilot-scale integrated anaerobic-aerobic bioreactor (IAAB) having three processes/compartments: anaerobic, aerobic and sedimentation. A 35-day monitoring was carried out for the mono- and co-digestion processes at an organic loading rate (OLR) of 30.0 g COD/L.day. Addition of M. oleifera filtrate at 500 mg/L was capable of removing 95-96%, 99-100% and 93-96% chemical oxygen demand, biochemical oxygen demand (BOD) and total suspended solid, respectively with overall improvement up to 6% in final POME quality and 72% for methane yield. The final discharge remained stable consistently and complied with the set limit (BOD & LE; 20 mg/L) despite high OLR was employed. The ability of the IAAB to hold high concentration of mixed liquor volatile suspended solids (56,000-67,000 mg/L), coupled with high carbon (C) and nitrogen (N) sources as food to microorganisms (F/M), and the ability of the dimeric cationic protein in the shelled M. oleifera to coagulate POME solids had successfully provided appropriate F/M and C/N ratios for co-digestion. The formation of large and dense flocs aided by M. oleifera extract allowed sludge to settle down easily as reflected by the average sludge volume index (SVI) of 34 (i.e., less than the preferred SVI of 100). The IAAB system exhibited good stability and pH adjustment was unnecessary. Long-term IAAB performance data is required to demonstrate its doable implementation on a large scale.