Oily wastewater treatment by photocatalytic membranes: a review

Oily wastewaters are among the most challenging to treat in conventional treatment plants. They have been produced in increasing amounts in a wide range of compositions, which may lead to serious environmental and population health issues if not properly treated. Membrane separation processes have emerged as a promising alternative for efficient treatment of effluents. Nevertheless, membrane fouling is a critical drawback. This is especially true when used with oily wastewater due to the sticky nature of oil molecules. Photocatalytic membranes (PMs) with antifouling properties have been developed aiming the process intensification. When photocatalytic surfaces are irradiated by a suitable light source they generate oxidative radicals, which can react and degrade foulants and other compounds. Oily wastewaters possess unique properties compared to other types of effluents, and photocatalysis and membrane separation process performances depend on a complex range of parameters. Thus, this review presents and discusses research efforts to develop antifouling PMs for treating oily wastewater, including the parameters that influence membrane separation and photocatalytic processes. The main features sought for these membranes, including the degradation of foulants during filtration under irradiation, self-cleaning capability, hydrophilicity, and reduction of fouling layer density are comprehensively revised. Finally, although is not possible to compare directly the efficiency and performance of PMs to treat oily wastewater due to differences on the experimental protocol, different operating conditions, initial concentrations of target contaminants, light sources and configuration of PMs, the self-cleaning properties and antifouling effects achieved by this technology are highly promisor.