A study of poly (sodium 4-styrenesulfonate) as draw solute in forward osmosis

• Novel draw solutes based on PSS have been studied.
• The pH, conductivity and viscosity of PSS have also been investigated.
• 0.24 g·mL− 1 PSS (70,000) draw solute exhibits the best FO performance.
• The repeatability of FO performance improves with increasing the PSS Mw.
• The PSS was easily recycled by a low pressure-driven UF system under 2 bar.

Draw solution (DS) has a great influence on the forward osmosis (FO) technology. The study of novel draw solute is essential in the development of FO technology. In this paper, poly (sodium 4-styrenesulfonate) (PSS) polyelectrolytes with different molecular weights (Mws) and different concentrations were studied. The physical properties, such as pH, conductivity and viscosity, have also been investigated. The conductivity increases with the increase of PSS concentration, which may lead to higher osmotic pressure. Higher viscosity, lower diffusion coefficient and more severe concentration polarization, which is generated by the polyelectrolyte with higher Mw, result in a lower water flux. Among the PSS polyelectrolytes, 0.24 g·mL− 1 PSS (70,000) exhibits the best FO flux. Experiment results demonstrate the advantage of using PSS as draw solute to conventional ionic salt of 0.5 mol·L− 1 NaCl.The regeneration of PSS from diluted DSs and the repeatability of the FO performance after recovery have been evaluated. The PSS was easily recycled by a low pressure-driven ultrafiltration (UF) system under 2 bar with low energy consumption. In order to realize a satisfactory regeneration of PSS DS in the FO process, it is necessary to select or prepare an appropriate UF membrane with accurate MWCO.