Application of BiVO4/TiO2/CNT Composite Photocatalysts for Membrane Fouling Control and Photocatalytic Membrane Regeneration during Dairy Wastewater Treatment

This study aimed to investigate the performance of composite photocatalytic membranes fabricated by incorporating multiple nanoparticles (TiO2, carbon nanotubes, BiVO4) into polyvinylidene fluoride membrane material for real dairy wastewater treatment. The composite photocatalytic membranes exhibited superior antifouling behavior, lower filtration resistance, better flux, and higher flux recovery ratio than the pristine membrane. Salinity, pH, and lactose concentration are determinant factors that affect filtration resistance and rejection performance during the ultrafiltration of dairy wastewater. Generally, higher irreversible and total resistances and slightly lower chemical oxygen demand (COD) rejections were found at higher salinity (expressed by electric conductivity values of >4 mS/cm) than lower salinity (<4 mS/cm) levels. The presence of lactose in dairy wastewater increased irreversible resistance and severely reduced COD rejection during ultrafiltration due to the ability of lactose to pass through the membranes. It was ascertained that membranes require further treatment after filtrating such wastewater. Lower resistances and slightly better COD rejections were observed at pH 7.5 and pH 9.5 compared to those observed at pH 4. Photocatalytic membranes fouled during the ultrafiltration of real dairy wastewater were regenerated by visible light irradiation. The membrane containing all constituents (i.e., TiO2, carbon nanotubes, and BiVO4) showed the best regeneration performance, exceeding that of the pristine membrane by 30%.

Automated summary

This study explored the performance of composite photocatalytic membranes made from multiple nanoparticles (TiO2, carbon nanotubes, BiVO4) and polyvinylidene fluoride. These membranes exhibited excellent resistance to fouling, low filtration resistance, high flux, and good flux recovery ratio compared to the pristine membrane. Salinity, pH, and lactose concentration were found to be key factors affecting filtration resistance and rejection performance during the ultrafiltration of dairy wastewater. Lactose in the wastewater increased irreversible resistance and significantly reduced COD rejection during ultrafiltration. Regeneration of fouled photocatalytic membranes was achieved through visible light irradiation, with the membrane containing all constituents showing the best regeneration performance, surpassing the pristine membrane by 30%.