PRETREATED PALM OIL MILL EFFLUENT (POME) DIGESTION IN AN UP-FLOW ANAEROBIC SLUDGE FIXED FILM BIOREACTOR: A COMPARATIVE STUDY

An up-flow anaerobic sludge fixed film (UASFF) bioreactor was used to treat the pretreated palm oil mill effluent (POME). In physical pretreatment, POME was pre-settled for 2 h and the supernatant was fed into the reactor. In chemical pretreatment, optimum dosages of cationic and anionic polymers were used. Experiments of pretreated POME digestion were conducted based on a central composite face-centered design (CCFD) with two independent operating variables, feed flow rate (Q(F)) and up-flow velocity (V-up). The operating variables were varied to cover a wide range of organic loading rate (OLR) from 3.8 to 29 g COD/l.d. A stable TCOD removal efficiency of 83.5 % was achieved at the highest Q(F) (3.31 l/d, corresponding to OLR of 26 g COD/l.d) for pre-settled POME whereas only 62.2 % TCOD removal was achieved with chemically pretreated POME at Q(F) of 7.63l/d (corresponding to OLR of 29 g COD/l.d) and that too was coupled with process instability. At comparable OLRs i.e. 16.95 g COD/l.d (Q(F) = 2.16 l/d) for pre-settled POME and 16.42 g COD/l.d (Q(F) = 4.32 l/d) for chemically pretreated POME, the VFA concentrations for the two cases were also similar.