Tang M.; Chen Y.; Xie H.; Chen Q.; Yu X. and Ou R. 2023. ACS ES&T Water 3(8): 2797-804.

In this study, four poly(diallyl dimethylammonium chloride) (PDDA) with different molecular weights are applied for forward osmosis concentration of high-salinity wastewater; meanwhile, the quantified effect of osmotic pressure and viscosity on the FO water flux is studied systematically. The 35 wt % PDDA (<100 kDa) solution could provide a water flux of 8.8 LMH with DI water as feed, and a water flux of 8.0 LMH with 15,400 ppm synthetic high-salinity wastewater as feed. Osmotic pressure plays a major and positive role in the FO water flux, while viscosity plays a secondary and negative role. Specifically, the FO water flux exhibited a variation of 115% using four PDDA draw solutions with the same viscosity and different osmotic pressures, while it showed a variation of 11.5% with the same osmotic pressure and different viscosities. The relationship of solute diffusion resistivity K and viscosity η was formularized for detailed discussion. The data of 28 polyelectrolyte solutions are summarized and demonstrate similar inference.

Schematic illustration of the FO process and water flux of different membranes and running modes. (a) Schematic illustration of the FO process with polyelectrolyte solution as a draw agent. (b) FO water flux of CTA-ES and CTA-NW FO membrane with 20 wt % PDDA (MW < 100 kDa) as draw solution and DI water as feed solution. (c) Water flux of 20 wt % PDDA (MW < 100 kDa) solution under different running modes.