Membrane filtration of natural organic matter: Initial comparison of rejection and flux decline characteristics with ultrafiltration and nanofiltration membranes

Two source waters containing natural organic matter;(NOM) with different ph ysical and chemical characteristics were crossflow-filtered using four type s of membranes having different material and geometric properties. Transpor t measurements of NOM rejection and Aux decline were made. A resistances-in -series model was used to represent and quantitatively compare membrane flu x decline and recovery. As anticipated, the resistance due to specific adso rption depended on the concentration at the membrane interface. For the two membranes showing evidence of NOM adsorption, reducing the initial flux (w hich we infer to also reduce the interfacial NOM concentration) also lowere d the measured resistance assigned to adsorption in our protocol. Relative molecular mass (RMM) distribution measurements (by size exclusion chromatog raphy) were used to calculate the average RMM of the NOM and persuasively i llustrated that the nominal relative molecular mass cut-off(MWCO) of a memb rane is not the unique predictor of rejection characteristics for NOM compo unds. Size exclusion, electrostatic repulsion, and NOM aromaticity all infl uenced the NOM rejection. For a given wafer composition (including pH and i onic strength), membrane characteristics (such as the surface charge, hydro phobicity and nominal MWCO) can be combined with the NOM properties (such a s total dissolved organic carbon, specific UV absorbance at 254 nm and humi c content) to provide a consistent qualitative rationale for the transport results. Published by Elsevier Science Ltd.