Minimization of short-term low-pressure membrane fouling using a magnetic ion exchange (MIEX®) resin

• PVDF membrane fouling reduction by MIEX varied significantly among different waters.
• Both terrestrial and microbial DOM fouled PVDF ultrafiltration membranes.
• Microbial DOM was more important to membrane fouling than terrestrial DOM.
• MIEX preferentially removed terrestrial DOM over microbial DOM.
• Fouling reduction correlated well with microbial DOM via an inverse linear function.

Two challenges to low-pressure membrane (LPM) filtration are limited rejection of dissolved organic matter (DOM) and membrane fouling by DOM. The magnetic ion exchange resin MIEX® (Ixom Watercare Inc.) has been demonstrated to remove substantial amounts of DOM from many source waters, suggesting that MIEX can both reduce DOM content in membrane feed waters and minimize LPM fouling. We tested the effect of MIEX pretreatment on the reduction of short-term LPM fouling potential using feed waters varying in DOM concentration and composition. Four natural and two synthetic waters were studied and a polyvinylidene fluoride (PVDF) hollow-fiber ultrafiltration membrane was used in membrane fouling tests. To evaluate whether MIEX removes the fractions of DOM that cause LPM fouling, the DOM in raw, MIEX-treated, and membrane feed and backwash waters was characterized in terms of DOM concentration and composition. Results showed that: (i) the efficacy of MIEX to reduce LPM fouling varies broadly with source water; (ii) MIEX preferentially removes terrestrial DOM over microbial DOM; (iii) microbial DOM is a more important contributor to LPM fouling than terrestrial DOM, relative to their respective concentrations in source waters; and (iv) the fluorescence intensity of microbial DOM in source waters can be used as a quantitative indicator of the ability of MIEX to reduce their membrane fouling potential. Thus, when ion exchange resin processes are used for DOM removal towards membrane fouling reduction, it is advisable to use a resin that has been designed to effectively remove microbial DOM.

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