Effect of flow rate, draw solution concentration and temperature on the performance of TFC FO membrane, and the potential use of RO reject brine as a draw solution in FO-RO hybrid systems

The main objective of this research study was to investigate the effect of feed and draw solution flow rate, draw solution concentration (2.5-7.7 wt% NaCl) and draw solution temperature (23 degrees C-60 degrees C) on the performance of a commercial polyamide thin-film composite forward osmosis (FO) flat sheet membrane in the active-layer-facing-draw solution (AL-DS) membrane orientation. Increasing the feed and draw solution flow rate improved the membrane flux by mitigating concentration polarization effects on both sides of the membrane. The membrane flux also increased at higher draw solution concentration due to higher osmotic pressure. Additionally, it was found that increasing the draw solution temperature slightly improved the membrane flux but the temperature effect was negligible due to the severe effect of concentration polarization. It was observed from experimental results that the salt rejection was maintained above 98% at all operating conditions, and an optimal water flux of 11.4 L m(-2)h(-1) was reported at a flow rate of 48 mL min(-1) with deionized water as feed and 7.7 wt% NaCl as draw solution at 40 degrees C. The water flux across the membranes decreased when brine at 7.7 wt% NaCl was used as the draw solution and raw seawater as the feed solution in active-layer-facing-feed solution (AL-FS) membrane orientation because of concentration polarization effects and lower osmotic pressure. The results showed that the performance of FO membranes is influenced by the operating conditions. Therefore, optimizing these conditions is essential and can significantly improve the performance of FO membranes.