Extracellular polymeric substances removal of dual-layer (PES/PVDF) hollow fiber UF membrane comprising multi-walled carbon nanotubes for preventing RO biofouling

The reverse osmosis (RO) pretreatment of the petrochemical refinery wastewater has been investigated using the dual-layer (PES/PVDF) hollow fiber nanocomposite membranes, which were fabricated comprising MWCNTs in both layers via the two-step TIPS/NIPS process. The dual-layer hollow fiber nanocomposite membrane had the reduced fouling propensity, the improved compaction resistance and the higher filtration performance than the dual-layer hollow fiber (PES/PVDF) membrane. The low concentration of bacteria in the permeate caused RO membrane biofouling due to the rapid growth in the environment of extracellular polymeric substances (EPS). In order to inhibit the RO membrane biofouling, EPSs were removed by using the hollow fiber nanocomposite UF membrane, including polysaccharides, biopolymers and proteins. The rejection of biopolymers (MWCO = 33 kDa) was higher than that of polysaccharides (MWCO = 40 kDa). With respect to protein removal, it was found that the bovine serum albumin and rejection of 90% could be achieved, which was strongly dependent on pH. The EPS removal achieved up to 98.2% with the optimized carboxylated MWCNTs loading in the (NcPES-0.2%)/(NcPVDF-0.5%) hollow fiber nanocomposite membrane. The permeate treated by the hollow fiber nanocomposite membrane had effectively inhibited the RO membrane biofouling by Escherichia coli, as a result of the lower concentration of turbidity and EPS. The resultant hollow fiber nanocomposite ultrafiltration membrane shows the feasibility of removing EPS coupled with a low rejection of total dissolved salts, which yields a superior pretreatment method to reduce biofouling of the subsequent purification by reverse osmosis.