The effect of surface characteristics on RO membrane performance

The characteristics of membrane surface have a significant effect on membrane performance. In this study two commercial reverse osmosis membranes both made from polyvinyl alcohol named TFC-ULP and TFC-SR2 were challenged with tap water. The performances of the membranes were completely different. For the first type of membrane, i.e. TFC-ULP, a high ion rejection (around 72%) with a low flux (around 7 l/m².h) was obtained. However the second membrane (TFC-SR2) showed much higher flux (88 l/m².h) and much lower rejection (around 15%). This behavior may be attributed to the roughness of the membrane surface. The electron microscopy of the membranes showed that the first type of membrane has a rough surface while the second type has smooth surface. The effect may be due to the adsorption and trapping of the ions on the rough surface of TFC-ULP membrane. This leads to higher rejection which causes higher resistance against the flow and hence lower flux. The smooth surface of the TFC-SR2 membrane has less ability to adsorb the ions providing lower rejection, lower membrane resistance and higher flux.