Performance of forward osmosis processes under different operating conditions and draw solutes

In this research, a forward osmosis (FO) system with its draw solution chamber being a completely-mixed tank (CSTR) reactor was developed for dynamic studies on FO's self-limiting flux behavior. The performance of "fresh water" production and reverse diffusion in the FO process were evaluated under the influence of different mixing intensities and different draw solutes in the draw solution chamber. The experimental data indicated that a) increasing mixing intensity could decrease the dilutive external concentration polarization (ECP), but much stronger stirring is not necessary; b) under the same bulk osmotic pressure of 14 atm, Al ₂(SO ₄) ₃ could make higher flux of the fresh water compared with NaCl solution; c) the sharp flux decrease of the FO system during the first 30 minutes depends on the dilutive ECP, and after about 30 minutes, the flux is relatively stable; and d) reverse diffusion of NaCl solution increases exponentially with an increase in the bulk osmotic pressure, while that of Al ₂(SO ₄) ₃ is negligible due to the bigger diameter of the hydrated aluminum ion. Results of this study indicate that the CSTR FO reactors are suitable for evaluation of dynamic nature of the FO self-limiting flux behavior.