Exploring an innovative surfactant and phosphate-based draw solution for forward osmosis desalination

Abstract

The reverse salt flux phenomenon of forward osmosis affects the quality of the feed water, reduces water flux, and increases the cost for replenishing lost draw solute. In this study, a novel draw solution comprising a mixture of Triton X100 and Na3PO4 for minimizing the reverse salt flux during forward osmosis (FO) was explored. The results indicated that the reverse salt flux caused by coupling 0.5mM Triton X100 to 0.55M Na3PO4 draw solution was only 0.13g/m2h, and the specific reverse salt flux was 0.03g/L using DI water as the feed solution, which are the lowest recorded values among all forward osmosis studies. Hydrophobic attractive interactions between tail groups of Triton X100 with the FO membrane are believed to be the main mechanism for minimizing salt leakage. Results from desalination experiments demonstrated that using 0.55M Na3PO4 coupled with 0.5mM Triton X100 as the draw solution and brackish water and seawater as the feed solution with total dissolved solids of 4090 and 36,800ppm achieved water fluxes of 4.89L/m2h and 1.15L/m2h, respectively. Furthermore, using a two-stage ultrafiltration–nanofiltration system for the draw solution recovery enabled 98% recovery of solutes.