Combined iron oxides and gypsum fouling of reverse osmosis membranes during desalination process

Abstract

Fouling is an inherent challenge in the Reverse Osmosis (RO) desalination process. Inorganic and colloidal compounds are frequently encountered on RO membrane surfaces. Although fouling is the topic of various studies, combined fouling notably by gypsum and iron oxides and their interaction is not yet studied. Therefore, the aim of this work is to study the combined fouling by gypsum and iron oxides and their interaction with the surface of the RO membrane. Gypsum and iron scaling were compared, and it was demonstrated that gypsum scaling caused severe water flux decline and induced membrane wetting. An important flux decline was also observed for iron scaling when the pH of feed solution is close to 6. Flux decline caused by combined fouling was compared with an individual fouling. A membrane fouling trials showed a synergistic effect between the dissolved calcium sulfate and iron oxide particles, which aggravated and accentuated RO the membrane fouling. The drop in normalized flux, caused by the combined fouling, was compared to the two-individual fouling (with gypsum and iron oxides), it appears that the combined one was 50% higher. The molecular interactions between iron oxides and gypsum as well as the properties of the formed crystals were determined by SEM/EDX and X-Ray Diffraction.