Synthesis, characterization and performance studies of mixed-matrix poly(vinyl chloride)-bentonite ultrafiltration membrane for the treatment of saline oily wastewater

The present study deals with the improvement of surface morphology, hydrophilicity and antifouling behavior of polyvinyl chloride (PVC) membrane by adding bentonite for ultrafiltration of oil-in-water emulsion under wide range of salinity (0–35000 ppm). Flat-sheet UF membranes were prepared by phase inversion technique using N, N-dimethylacetamide (DMAc) and water. Viscoelastic properties of the membrane casting solution were measured to fix sonication frequency, membrane casting speed and casting solution composition. Field-emission-scanning-electron-microscope and atomic-force-microscope were used to measure surface-porosity, pore-size distribution, pore density and roughness parameters of the membranes. Hydrophilicity of the membranes was determined by measuring equilibrium water content, contact angle and work of adhesion, whereas antifouling character was quantified by flux recovery ratio using saline oily-wastewater. Casting solution with PVC:DMAc:bentonite = 12.0:87.23:0.77 (i.e., PVC/bentonite-6) exhibited the maximum loss tangent and in-phase dynamic viscosity and resulted enhanced surface porosity (56.42–58.62%), root mean square surface roughness (127.6 nm), surface pore density (42.29–32.05 pores μm⁻²), hydrophilicity (work-of-adhesion:111.08 mN m⁻¹) and antifouling character (flux-recovery-ratio:81.97%). PVC/bentonite-6 also delivered improved performance to separate oily-wastewater with zero salinity (oil rejection: 97.0% and permeate flux: 186 L m⁻² h⁻¹) and 35000 ppm salinity (oil rejection: 92.5% and permeate flux: 94nL m⁻² h⁻¹) at 0.2 MPa trans-membrane pressure.