Pretreatments to control low-pressure membrane fouling: a review on the coagulant/adsorbent applied and contact modes with the feed

摘要

The application of low-pressure membranes (LPMs) to drinking water treatment has undergone tremendous developments in the past decades. Integration of pretreatment approaches has been devoted in conjunction with LPMs in mitigating membrane fouling, among which coagulation/adsorption pre-treatments are most frequently employed. However, the impact of coagulation/adsorption on fouling reduction is sometimes less pronounced and even adverse. The ability in mitigating membrane fouling varies significantly among various types of coagulants/adsorbents. The literature suggests that the contact modes between coagulants/adsorbents and the feed remarkably affect natural organic matter (NOM) removal and membrane behaviors. Compared with conventional approaches, for example, coagulation, coagulation + sedimentation, inline coagulation, adsorption + direct filtration, preadsorption or integrated adsorption treatments, which has limited effects to fouling control and occasionally even accelerate fouling, a novel approach named microgranular adsorptive filtration performs superior in NOM removal and fouling reduction. This article provides a critical review of the coagulation/adsorption pretreatments for LPMs using conventional coagulants/adsorbents and some novel solids. The difference and mechanism in the contact modes between adsorbents with the feed in NOM removal and fouling control are comprehensively discussed. Finally, it summarizes the results gathered here and emphasizes the need for further research.