Field-Induced Redistribution of Surfactants at the Oil/Water Interface Reduces Membrane Fouling on Electrically Conducting UF Membranes

Membrane-based treatment of oily wastewater remains a large challenge, particularly under high salinity conditions. The main difficulty associated with this separation process is membrane fouling, which can be caused by oil wetting the membrane surface and/or by the coalescence of emulsified oil droplets on the membrane surface. In this study, we used electrically conducting carbon nanotube-based ultrafiltration membranes to treat an emulsified oil suspension at salinities as high as 100 mM. By modifying the electrical potential applied to the membrane surface, we demonstrate how fouling can be dramatically reduced, even under high salinity conditions. In addition, permeate water quality is shown to improve upon application of a negative potential. Using optical microscopy, we observe dramatic changes in the shape of oil droplets at the membrane/water interface upon the application of an electric potential to the surface. This change is associated with a re-distribution of charged surfactant molecules in response to the external electric field. This change in surfactant distribution is responsible for a change in the surface tension of the oil drops at the interface, which results in a decrease in oil coalescence and subsequent fouling. These membranes offer an attractive treatment option when separating emulsified oil from water under high salinity conditions.