Mechanisms of Membrane Fouling Control by Integrated Magnetic Ion Exchange and Coagulation

Colloidal natural organic matter (NOM) is an important foulant to low-pressure membranes (LPMs) employed in drinking water treatment. Removal of colloidal NOM by magnetic ion exchange (MIEX), coagulation, and integrated MIEX and coagulation was investigated in this study to determine the relationship between colloidal NOM removal and membrane fouling reduction. The results showed that coagulation did not selectively remove colloidal NOM and the optimal coagulant dose was primarily determined by the concentration of humic substances. Comparatively, MIEX pretreatment preferentially removed humic substances and reduced the coagulant dose needed for colloidal NOM removal as a result of coagulation stoichiometry. A matched-pair analysis showed that integrated MIEX and coagulation pretreatment at much lower coagulant doses was as effective as coagulation in reducing membrane fouling. It is concluded that integrated MIEX and coagulation is potentially a viable pretreatment approach to reduce membrane fouling and in general removal of colloidal NOM in feedwater is an effective approach for membrane fouling control and should be considered in the research, development, and application of novel LPM-based treatment processes.