Effects of surfactants and oil-in-water emulsions on reverse osmosis membrane performance

Abstract

Oily wastewater from various industries is a major source of pollution. Membrane-based separation is a promising technique for treating oil-in-water emulsions. However, membrane fouling remains a crucial drawback for wide application of membrane separation in oily wastewater treatment. This study was performed to gain a better understanding of the fouling of two commercial reverse osmosis membranes by oil-in-water emulsions. Cellulose acetate (CA) and polyamide (PA) reverse osmosis (RO) membranes were used in the separation of olive oil-in-water emulsions stabilized by nonionic, cationic, and anionic surfactants in a dead-end separation configuration. Both membranes exhibited high total organic carbon (TOC) rejection. Analysis of the results indicated that the permeate flux from the cellulose acetate membrane did not depend on the surfactant type or oil concentration present, whereas the permeate flux from the polyamide membrane was influenced by the type of surfactant used in the oil-in-water emulsion. It appears that the surfactant was adsorbed onto the polyamide membrane surface due to electrostatic and hydrophilic/hydrophobic interactions. The results of this study provide useful insights into membrane fouling during emulsion separation. The CA membrane exhibited less fouling than the PA membrane, making it a better candidate for oily wastewater treatment. The PA membrane was more effective at treating the emulsion stabilized by an anionic surfactant. Determining the feed composition and membrane properties before separation allows better fouling control, thus reducing treatment costs.