The performance of two-stage submerged anaerobic membrane bioreactor (2-sAnMBR) coupling with forward osmosis membrane (FO) for palm oil mill effluent (POME)

Abstract

Palm oil mill effluent (POME) contains abundant nutrients. The concept of POME treatment and nutrient recovery/removal applied as a sustainable development of wastewater treatment technologies. Two-stage submerged anaerobic membrane bioreactor (2-sAnMBR) combining with forward osmosis membrane (FO) was used to treatment POME. Two types of membranes including a commercial thin film composite (TFC) and cellulose triacetate (CTA), and different concentration of draw solutions which used NaCl as draw solution that including 2.0M, 3.0M and 4.0M were adopted to investigate the separated of nutrient in the permeate two-stage sAnMBR. In this work, the long-term operational control of the two-stage sAnMBR maintained organic loading rate (OLR) of 43, 57 and 99 kgCOD/m3/day in 9 months continuous operation of lab-scale. The formation and accumulation of extracellular polymeric substances (EPS) cause the adherence of biofilms to surfaces membrane. The phase II of two-stage sAnMBR shown polysaccharide and protein content in the cake layer; the ratio of polysaccharide/protein (C/P) was 0.26-0.28. The increasing of OLR led to high F/M ratio meanwhile the EPS concentrate and transmembrane pressure (TMP) was increased. The evolution of TMP indicated that attachment mechanisms, adsorption, and entrapment of protein EPS occurred in the pores of membrane (clogging). Nevertheless, the methanogenesis activity in sAnMBR was inhibited by acidogenesis bacteria due to the accumulated of volatile fatty acid (VFA) that acetic acid was highest about 30% however the calculation of hydrolysis ratio found up to 13.76% in phase III. A high concentration of VFA can inhibit methanogenesis occurred the rising of OLR causing to low methane yield. TFC membrane exhibited higher water permeability in FO process but more loss of water flux in comparison with CTA; the diffusion of Ca2+ ion in CTA, enhanced a cake layer formed on the membrane's active layer. Furthermore, the efficiency of nutrient removal by FO system reported phosphorus and ammonia up to 90-100% thus FO capability can recover nutrients and reduce chemical costs and it can decrease organic/inorganic substances. Moreover, the nutrients; nitrogen, phosphorus, and potassium were the most important of plant fertilizer so the best way to water fertilizer produce.