Fouling mitigation and cleanability of TiO2 photocatalyst-modified PVDF membranes during ultrafiltration of model oily wastewater with different salt contents.

In the present study, TiO2-coated ultrafiltration membranes were prepared and used for oily water filtration (droplet size < 2 μm). The aim of this work was to investigate the effect of different salt contents on fouling and filtration properties of neat and TiO2-coated membranes during oil-in-water emulsion filtration. The effect of the TiO2 coating on the flux, surface free energy, and retention values was measured and compared with the neat membrane values. The cleanability of the fouled TiO2-coated membranes by UV irradiation was also investigated by measuring flux recovery and contact angles, and the chemical changes during cleaning were characterized by ATR-IR. It was found that increasing the salt content of the model wastewaters, oil-in-water emulsions, increased the zeta potential and the size of the droplets. The presence of the TiO2 coating decreases the membrane fouling during oily emulsion filtration compared to the neat membrane, due to the hydrophilicity of the coating regardless of the salt content of the emulsions. The neat and coated membrane oil retention was similar, 96 ± 2%. The coated membrane can be effectively cleaned with UV irradiation without additional chemicals and a significant flux recovery can be achieved. Monitoring of the cleaning process by following the membrane surface wettability and ATR-IR measurements showed that the recovery of flux does not mean the total elimination of the oil layer from the membrane surface.