Treatment of surfactants with concentrations below critical micelle concentration by ultrafiltration: A mini-review

Surfactants are widely distributed in wastewater at concentrations below the critical micelle concentration (CMC). Generally, surfactant monomers are smaller than the pore sizes of ultrafiltration (UF) membranes, meaning that they can not be effectively rejected through sieving. However, it has been reported that surfactants with low concentrations play a non-negligible role during the UF process. UF performance is highly dependent on the interactions (e.g. electrostatic and hydrophobic) between surfactants and membrane and/or other pollutants. Given this, this review focuses on the treatment of surfactants with concentrations below the CMC values by UF processes. The effects of several variables including membrane properties, operation parameters, surfactant type, and feed concentration on the retention coefficient and membrane fouling are summarized. Finally, the potential fouling mechanisms and fouling control methods are discussed.