Effect of solution chemistry on the surface property of reverse osmosis membranes under seawater conditions

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-film composite (TFC) RO membranes were characterized for chemical and physical properties. Membrane characterization was performed under both the low (i.e., 10 mg/L) and high (i.e., 35,000 mg/L) TDS conditions to see how these surface characteristics are affected by seawater-level TDS. Results showed that both the chemical and physical surface properties were altered significantly under the high TDS condition with becoming more favorable to membrane fouling, namely, less negatively charged, more hydrophobic, and rougher. Mechanisms responsible 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 different with respect to the surface characteristics determined at the low TDS condition. It was confirmed that the chemical and physical properties were interrelated and, thus, variations in chemical properties with respect to the solution chemistry applied led to changes in physical properties and vice versa.