Membrane filtration of natural organic matter: comparison of flux decline,NOM rejection, and foulants during filtration with three UF membranes

Three ultrafiltration membranes [thin-film composite, polyethersulfone (PES ), and sulfonated PES] which have different chemistries and nominal relativ e molecular mass cut-offs (MWCO), were compared in terms of their character istics of flux; decline, rejection of natural organic matter (NOM), and the adsorbed foulants, with two very different (relatively hydrophilic and hyd rophobic) NOM-contaifiing source waters. To facilitate comparison, the rati o (J(o)/k) of the initial pure water flux J(o) to the estimated boundary la yer mass transfer coefficient k was used to define similar initial hydrodyn amic operating conditions for the three different membranes, The membranes showed differences in NOM rejection when filtering hydrophilic NOM-source w ater, and also exhibited differences in flux decline with the hydrophobic N OM-source water. Flux decline and NOM-rejection were quantified using a res istances-in-series model-and effective molecular mass cut-off, respectively . Non-charged NOM fractions (hydrophilic and hydrophobic neutrals/bases) we re found to be significant foulants for these negatively charged membranes.