Assessment of various membrane fouling indexes under seawater conditions

In this study, various foulants are tested with the conventional fouling indexes such as silt density index (SDI) and modifi ed fouling index (MFI) under high TDS conditions to evaluate the practical appliance of these indexes for RO desalination. A new approach for developing a more realistic fouling index is investigated based on fl ow fi eld-fl ow fraction (Fl-FFF) analysis. The results showed that the SDI and MFI for the feed waters containing the particulate foulants larger than the pore size of the membranes used in SDI and MFI measurements were not signifi cantly aff ected by the feed water salinity. This is due to the fact that the main fouling mechanism is the deposition of particles on the membrane surface and, hence, the cake fi ltration controls the permeate fl ux. In case of the particles as well as organics smaller than the pore size of the membranes, the SDI and MFI failed to accurately predict the fouling potential of feed waters with high salinity. In addition, the characteristics of membrane (i.e., hydrophobicity) also played an important role in determining membrane performance. Based on the results from Fl-FFF analyses, it was demonstrated that both qualitative and quantitative assessments of fouling potential of feed waters with diff erent foulants and TDS conditions were possible.

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