Microfiltration of oil emulsions stabilized by different surfactants

Abstract

Membrane-based filtration is a promising technique to treat the enormous amounts of oily wastewater, specifically those with micron-sized oil droplets. However, the understanding on the effect of the surfactants, that are inevitably present to stabilize the oil emulsion, on the filtration performance remains poor. This study aimed to investigate the effect of surfactant type (namely, non-ionic Tween 20, positively charged CTAB, and negatively charged SDS) on filtration flux and membrane fouling during the microfiltration of the surfactant-stabilized oil emulsion with mean droplet sizes of approximately 20 μm. The Optical Coherence Tomography (OCT) was employed to quantify the evolution of fouling, and both the DLVO and XDLVO models were used to quantify the oil droplet-membrane and oil droplet-deposited layer interaction energies. Two key understanding on the correlation between the DLVO and XDLVO predictions with flux and fouling were obtained. Firstly, the steep flux enhancement vis-à-vis a DI water feed by the feed containing CTAB-stabilized oil emulsion was tied to the attractive interaction of the surfactant with the membrane, as evident from the DLVO model. This attraction was not related to the extent of membrane fouling, which was relatively lesser for the CTAB-stabilized oil emulsion. Secondly, the extent of membrane fouling was tied to the repulsive energy magnitudes rather than attractive ones, specifically in that the least repulsive energy values of the Tween 20 – stabilized oil emulsion was linked to the most extensive fouling.