The role of membrane ξ-potential in solute rejection by low-pressure reverse osmosis membrane

Abstract

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.

Effect of Coexisting Natural Organic Matters (NOM) on the Rejection of Endocrine Disrupting Chemicals (EDCs) by A Low Pressure Reverse Osmosis (LPRO) Membrane

“…However, the rejections of ail the three EDCs increased with increasing solution pH in the pH range 7 to 10 and reached about 90% at pH 10. The increase in EDCs rejections with solution pH in these experiments is consistent with the results of earlier investigations [1,5,12]. Childress and Elimelch [13] mentioned the influence of solution pH on membrane surface charge characteristics due to functional groups that protonate and deprotonate over wide pH range.…”

“…HA and FA concentrations were measured with total organic carbon (TOC) analyzer (TOC-500A, Shimadzu). Membrane zeta potential was measured with Zeta-CAD (CAD Instruments Ltd., France) using streaming potential method with 10-3 rnol/z NaCl electrolyte [5]. The zeta potential values were calculated using the well-known Helmholz-Smoluchowski formula:~= 1.06 x 10 5 x (l/p) x (E/P), where p: specific resistance of solution and E/P: potential difference in operating pressure condition.…”

“…Ranatamskul et al [4] introduced a concept of ion partitioning at membrane-solution interface for rejection of chlorides and nitrates in nanofiltration. Ozaki et al, [5] discussed the role of membrane zeta potential on rejection of ionic and dissociated organics by LPRO membranes.…”

Distribution and Diffusion Behaviors of Perfluorinated Compounds with Low Pressure Reverse Osmosis Membranes

“…Although RO membrane filtration is the most efficient method in separating all kinds of solutes in water, it has been a costly method until now owing to a very high pressure involved with it. Low pressure reverse osmosis (LPRO) membranes have emerged as the promising alternative to RO membranes during the past decade (Koyuncu et al, 2001;Ozaki et al, 2002Ozaki et al, , 2005Ozaki et al, and 2008. The LPRO membranes can be used under very low pressures (< 1.0 MPa) while their pollutant removal efficiencies are comparable to those of RO membranes.…”

“…Molecular sieving, electrostatic repulsion, adsorption and diffusion have been pointed out as important solute retention mechanisms for RO membranes (Nghiem et al, 2002;Kimura et al, 2003b), NF membranes (Bruggen et al, 2002;Kimura et al, 2003a;Braeken et al, 2006) and LPRO membranes (Ozaki et al, 2002(Ozaki et al, , 2005(Ozaki et al, and 2008. Furthermore, only inorganic anions, pharmaceuticals and personal care products (PPCPs) and endocrine disrupting chemicals (EDCs) have been tested as solutes in almost all the investigations carried out to date.…”