The combination effect of preozonation and CNTs layer modification on low-pressure membrane fouling control in treating NOM and EfOM

Abstract

In this study, the combination effect of preozonation and carbon nanotubes (CNTs) layer modification on low-pressure membrane (LPM) fouling control was systematically investigated. To understand the alleviation mechanism of the hybrid process, natural organic matter (NOM) from IHSS and effluent organic matter (EfOM) from actual sewage effluent were both selected as the typical organic foulants presented in actual surface water and wastewater. A dead-end continuous flow model combined with programmable logic control system was used to operate four membrane filtration units and their backwash processes. With a constant permeates flux, the fouling resistant of CNT modified LPM after preozonation could be evaluated according to the increase in transmembrane pressure (TMP). The results revealed that the hybrid approach of preozonation and CNTs modification could significantly improve the anti-fouling ability of LPM, reduce the backwash frequency, and improve the reversibility of membrane fouling. During the filtration of EfOM and NOM, preozonation improved the water treatment capacity of the CNTs modified membranes. The experiment of mass balance revealed that preozonation enhanced the recoverability of CNTs modified membrane and greatly increased its operation time in treating EfOM and NOM. The molecular weight distribution as well as EEM analysis demonstrated the dissimilar characteristics of EfOM and NOM, which caused the different treatment efficiency by preozonation and CNT modification. The mechanism of EfOM/NOM fouling on LPM was summarized as the primary blocking by medium-MW EfOM/NOM. CNTs modification had a better effect on the control of LPM fouling when treating EfOM, as it removed the medium-MW EfOM by adsorption and prevented the pores blockage of the original PVDF membrane. Preozonation had a better effect on the control of LPM fouling when treating NOM, as it greatly changed the MWD of NOM by removing medium-MW NOM. The combination effect of the hybrid preozonation and CNTs modification resulted in the most effective fouling control of LPM by both decreasing the medium-MW and large-MW EfOM/NOM. At the same time, it decreased irreversible fouling related with membrane pore blocking. The hybrid approach demonstrated its promising application for LPM fouling control in actual sewage water and surface water treatment process.