Effects of feed and draw solution temperature on the performance of Aquaporin HFFO.6 membrane in forward osmosis

Abstract

Recently, forward osmosis (FO) has attracted attention in many potential applications including food processing, fertilizers and manufacturing industries. This study investigates the effects of feed solution (FS) and draw solution (DS) temperature on the water flux, reverse salt flux, and specific reverse salt flux. The temperature of both the DS and FS were varied at the same time. Four typical temperatures such as 20 °C, 25 °C, 30 °C and 35 °C were selected to maintain at FS and DS sides, respectively, for each iteration. Except for the temperature, the other operating conditions like concentration, flow rates, and the type of membrane used were not varied in this experiment. The experiments were performed with tap water as FS and 1.5 M of NaCl as DS. The flow rates of the DS and FS were maintained at 15 L min−1 and 25 L min−1, respectively. The membrane used was the hollow fiber forward osmosis (HFFO.6) membrane procured from Aquaporin A/S, Denmark. The results showed that as temperature increased from 20 °C to 35 °C, the water flux, reserve salt flux (RSF), and specific reverse salt flux were enhanced. This was due to the enhanced diffusion coefficient of both DS and FS on increasing the temperature. This further reduces the concentration polarization and in turn augments the water flux. However, consequently, reverse and specific reverse solute flux also increased on temperature, which is not desirable for an efficient FO system. Hence, it is recommended to operate the FO at a minimum required temperature considering the other influencing other operational parameters such as specific reverse solute flux, recovery and rejection percentage.