Anaerobic co-digestion of palm oil mill effluent with rumen fluid as a co-substrate

►The semi-continuous stirred tank reactors (SCSTR) were applied under anaerobic mesophilic conditions at 37 ± 3 °C to treat the supernatant layer of the raw palm oil mill effluent (POME). ►The anaerobically digested sludge POME (ADS-POME) mixed with rumen fluid (RF) that taken from the first compartment of cow stomach (5% and 10% by volume) and used as a co-digestion then compared with (ADS-POME) as a mono-digestion. ►The treatment done at different hydraulic retention time (HRT) and organic loading rate (OLR). The results showed that the co-digestion of (10% RF + 90% ADS-POME) has high COD removal at maximum HRT with lowest OLR and the higher methane content was at minimum HRT with higher OLR. ►All digesters had a good stability in terms of pH. The concentration of MLVSS was decreased with long HRT and low OLR within all digesters. The co-digestion showed an efficient ability for COD removal efficiency and maintains methane content within acceptable level.