Effects of crosslinking and thermal annealing modifications on the performance of nanohybrid PSf-ZnO membranes for the treatment of raw and ozonated petroleum refinery wastewater

Abstract

Petroleum refinery plant generates large quantity of organic contaminants rich petroleum refinery wastewater (PRW). Although membrane-based process can be a promising alternative of PRW treatments, it suffers from serious fouling phenomenon. In this study, nanohybrid membrane was fabricated by phase inversion technique through blending of polysulfone (PSf) and zinc oxide (ZnO) nanoparticles. The membrane was then modified by polyvinyl alcohol (PVA) coating and thermal annealing treatments to improve its physical characteristics, permeability-selectivity performance, and antifouling property. Furthermore, the ozonation of PRW prior to membrane filtration was also studied to mitigate the fouling formation. The results showed that 0.5% PVA coating reduced the ZnO agglomeration problem, while thermal annealing treatment induced the improvement of polymer packing density. The modifications also improved membrane’s physical strength (6.89–9.81 MPa) and surface hydrophilicity thus leading for antifouling property ehancement. The results proved that the addition of ZnO increased the permeation flux up to 38.10% and 176%, respectively. The rejection of NH3, chemical oxygen demand (COD) and total dissolved solid (TDS) during PRW treatment using modified nanohybrid PSf-ZnO membrane reached up to 96.01%, 96.97%, and 55.88%, respectively. The modifications of the membrane also resulted in significant reduction of irreversible fouling (RIR) from 29.96% to 8.95%, and with pre-ozonation the RIR was further reduced to 5.45%. As expected, the ozonation of PRW prior to membrane filtration significantly enhanced the flux recovery ratio (FRR) up to 94.55%. This antifouling behavior offers potential applications in the filtration process for wastewater with high organic contaminants.