Application of Poly(diallyl dimethylammonium chloride) as a Forward Osmosis Draw Agent: The Quantified Effect of Osmotic Pressure and Viscosity

In this study, four poly(diallyldimethylammonium chloride)(PDDA)with different molecular weights are applied for forward osmosis concentrationof high-salinity wastewater; meanwhile, the quantified effect of osmoticpressure and viscosity on the FO water flux is studied systematically.The 35 wt % PDDA (<100 kDa) solution could provide a water fluxof 8.8 LMH with DI water as feed, and a water flux of 8.0 LMH with15,400 ppm synthetic high-salinity wastewater as feed. Osmotic pressureplays a major and positive role in the FO water flux, while viscosityplays a secondary and negative role. Specifically, the FO water fluxexhibited a variation of 115% using four PDDA draw solutions withthe same viscosity and different osmotic pressures, while it showeda variation of 11.5% with the same osmotic pressure and differentviscosities. The relationship of solute diffusion resistivity K and viscosity & eta; was formularized for detailed discussion.The data of 28 polyelectrolyte solutions are summarized and demonstratesimilar inference. The quantifiedeffect of osmotic pressure and viscosityof polyelectrolyte draw solutions on FO water flux is studied to providedraw selection recommendations.