AWWA WQTC62389

Reverse osmosis (RO) and nanofiltration (NF) membrane technologies are becoming increasingly attractive alternatives to conventional treatment processes for drinking water treatment because of their ability to provide effective rejection barriers against a broad range of water contaminants, and for their adaptability to treat water from sources of lower quality in areas in which other water resources are becoming limited. Furthermore, membrane treatment plants tend to be more compact than conventional plants, thus making them more economical in highly populated areas in which minimizing plant layout area becomes critical (Wiesner et al., 1994). However, a broader implementation of RO/NF processes is somewhat inhibited by prevailing problems such as concentration polarization and associated fouling and scaling effects that are important factors affecting the cost of RO/NF membrane treatment systems (Braghetta et al., 1998). In order to minimize the risk of these detrimental effects taking place, RO/NF systems are currently operated at limited pressures so that the permeate flux does not exceed a critical maximum value. Although experimental evidence is available to support this practice, recent results have shown that the concentration polarization layer of Rhodamine-WT (MW=521), used as a surrogate compound for organic water contaminants, could be disrupted at permeate flux levels significantly higher than that currently considered as critical. Comprehensive investigation is needed to validate this new idea because several factors including solute diffusivity coefficient, permeate flux, and rejection efficiency affect concentration polarization. The effect that this disruption could have on fouling and the rejection of chemical contaminants also remains to be elucidated. Based on this background, the primary objective of this project is to systematically investigate the influence of operating pressure and shear conditions on concentration polarization and the associated rejection of selected contaminants by RO/NF membranes in the absence and presence of foulant surrogates. It is anticipated that information gained from this research will contribute to a better understanding of the concentration polarization phenomena and the development of recommendations for optimum treatment of natural waters with RO/NF membranes with special emphasis in achieving high removal of organic contaminants with minimal risk of the occurrence of fouling. Includes 5 references, figure.