Application of a hybrid gravity-driven membrane filtration and dissolved ozone flotation (MDOF) process for wastewater reclamation and membrane fouling mitigation

Abstract

This study proposed a novel membrane filtration and dissolved ozone flotation integrated (MDOF) process and tested it at pilot scale. Membrane filtration in the MDOF process was operated in gravity-driven mode, and required no backwashing, flushing, or chemical cleaning. Because ozone was added in the MDOF process, ozonation, coagulation, and membrane filtration could occur in a single reactor. Moreover, in situ ozonation occurred in the MDOF process, which differs from the conventional pre-ozonation membrane filtration process. Significant enhancement of turbidity removal was further achieved through the addition of membrane filtration. Membrane fouling was mitigated in the MDOF process compared to the MDAF process. In situ ozonation in the MDOF process decreased the fluorescence intensity and transformed the high MW dissolved organics into small MW compounds. For the fouling layer, the extracellular polymeric substance (EPS) contents and cake layer morphology were analyzed. The results indicated that the contents of EPS decreased. Furthermore, a thinner and more loosely structured cake layer formed in the MDOF process. Because coagulation and ozonation occurred simultaneously in a single reactor, the generation of hydroxyl radicals was enhanced through the catalytic effect of Al-based coagulants on ozone decomposition, which further alleviated membrane fouling in the MDOF process.

Keywords: Dissolved ozone flotation; Gravity-driven membrane filtration; In situ ozonation; Membrane fouling.