Polyelectrolytes-promoted Forward Osmosis Processes

The development of the forward osmosis (FO) process has been constrained by the slow development of appropriate draw solutions. Two significant concerns related to draw solutions are the draw solute leakage and intensive-energy requirement in recycling draw solutes after the FO process. FO would be much attractive if there is no draw solute leakage and the recycle of draw solutes is easy and economic.In this study, polyelectrolytes of a series of polyacrylic acid sodium salts (PAA-Na), were explored as draw solutes in the FO process. The characteristics of high solubility in water and flexibility in structural configuration ensure the suitability of PAA-Na as draw solutes and their relative ease in recycle through pressure-driven ultrafiltration (UF) membrane processes. The high water flux with insignificant salt leakage in the FO process and the high salt rejection in UF recycle processes reveal the superiority of PAA-Na to conventional ionic salts, such as NaCl, when comparing their FO performance via the same membranes. The repeatable performance of PAA-Na after recycle indicates the absence of any aggregation problems. The overall performance demonstrates that polyelectrolytes of PAA-Na series are promising as draw solutes, and the new concept of using polyelectrolytes as draw solutes in FO processes is applicable. The magnetic nanoparticle draw solutes can generate reasonably high osmotic pressure in FO system due to the functional groups on the nanoparticles surface and they can be regenerated through magnetic field and reused as draw solutes. Thermo-responsive magnetic nanoparticles are able to be regenerated with high efficiency as the thermo-responsive property can assist the regeneration in a low-strength magnetic field.