Efect of solution chemistry on the surface property of reverse osmosis membranes under seawater conditions Juhee Yang, Sangyoup Lee, Eunsu Lee, Joohee Lee, Seungkwan Hong* Department of Civil, Environmental and Architectural Engineering, Korea University, 1, 5-ka, Anam-Dong, Sungbuk-Gu, Seoul 136-713, Korea Tel. +82-2-3290-3322; Fax: +82-2-928-7656; email: skhong21@korea.ac.kr Received 13 November 2008; revised 17 December 2008; accepted 24 December 2008 Abstract Recent studies have shown that the rougher, less negatively charged, and more hydrophobic membranes are prone to organic fouling. These surface characteristics of RO membranes, however, have been usually determined at very low TDS conditions, while seawater contains ten to thousand times more TDS than surface and even brackish waters. In this study, three aromatic polyamide thin-flm composite (TFC) RO membranes were characterized for chemical and physical properties. Membrane characterization was per- formed under both the low (i.e., 10 mg/L) and high (i.e., 35,000 mg/L) TDS conditions to see how these sur- face characteristics are afected by seawater-level TDS. Results showed that both the chemical and physical surface properties were altered signifcantly under the high TDS condition with becoming more favorable to membrane fouling, namely, less negatively charged, more hydrophobic, and rougher. Mechanisms responsi- ble for these changes such as charge screening and osmotic swelling are delineated. The way of changing in surface characteristics under the high TDS condition was substantially diferent with respect to the surface characteristics determined at the low TDS condition. It was confrmed that the chemical and physical prop- erties were interrelated and, thus, variations in chemical properties with respect to the solution chemistry applied led to changes in physical properties and vice versa. Keywords: Membrane surface characterization; Seawater TDS; RO membranes; Surface charge; Hydrophobicity; Surface roughness *Corresponding author. Presented at the 2nd joint workshop between the Center for Seawater Desalination Plant and the European Desalination Society, Gwangju Institute of Science and Technology, Korea, October 8–9, 2008. Desalination 247 (2009) 1 1 48– 61 0011-9164/09/$– See front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.desal.2008.12.020