A new generation of reverse osmosis membranes, low-pressure reverse osmosis (LPRO) membranes, have been developed for operation under very low pressure (below 0.5 MPa). LPRO membranes have received attention especially for their application in the field of water and wastewater treatment, to provide a high water flux at low operating pressure while maintaining very good rejection levels of salts and organics. Our previous work on LPRO has shown that the rejection of some inorganic salts and organic compounds depends appreciably on the pH of the bulk solution, probably because LPRO membranes can have an electric charge. In this study we investigated experimentally the effectiveness of different LPRO membranes in separating inorganic salts and organic compounds from a bulk solution with different pH conditions. We also tried to measure membrane ξ-potential by using a streaming potential method. The results indicated that the membrane ξ-potential as well as the ion size or molecular weight of organics can be considered key factors in the rejection of ionic salts and dissociated organic compounds including pesticides and endocrine disruptors.

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