Evaluating the performance of polystyrene sulfonate coupling with non ionic Triton-X114 surfactant as draw solution in forward osmosis and membrane distillation systems

Abstract

Herein, poly(sodium 4-styrenesulfonate) (PSS) with molecular weight of 70,000 (PSS-70,000) coupled with non-ionic surfactant Triton X-114 (TX-114) was exerted as draw solution (DS) in forward osmosis (FO) process for the first time to reduce salt reversal flux and enhance water recovery. In order to evaluate performances of this new type of draw solution, different concentrations of PSS-70,000 and TX-114 were prepared and implemented in FO process accordingly. When pure PSS-70,000 was used, high viscosity of 100% PS-70,000 inhibited the water flux as comparing with 50% PSS-70,000 since water passage was prevented from transferring through increasing thickness of draw solution. Interestingly, adding 1 mM TX-114 in 50% PSS-70,000 just slightly influenced on water flux but salt reversal flux was significantly reduced by 70% from 2.71 gMH to 0.92 gMH and reverse sodium was also reduced by 35.9%. Specifically, large molecular size of PSS-70,000 polyelectrolyte combining with a nucleophile ethylene oxide of TX-114 could effectively perform as a barrier to restrain electrophile sodium of PSS-70,000 reversing to the feed side. Moreover, the hydrophobic hydrocarbon tails of TX-114 retained on the hydrophobic surface of FO membrane was caused by the nonpolar–nonpolar interaction resulting in less reverse sodium. It can be concluded that the utilization of TX-114 with PSS-70,000 produced beneficial achievements since it did not only improve the performance of FO through reducing salt reversal flux but also effectively enhance the regeneration of diluted DS operated by membrane distillation (MD) process. Expressly, the repeatability of FO performance was revamped depending on the nonpolar interaction between the hydrophobic natures of 50% PSS-70,000/1 mM TX-114 based DS and hydrophobic surface of MD membrane.