Forward osmosis desalination using ferric sulfate draw solute

Lack of suitable draw solutes is one of the major limiting factors hindering commercial realization of forward osmosis (FO) desalination process. This study investigates the feasibility of ferric sulfate as draw solute in FO desalination. A laboratory-scale, cross-flow FO apparatus utilizing commercial FO membrane (cellulose triacetate-based) was used to desalinate synthesized (5000 ppm NaCl) brackish water and (40,000 ppm NaCl) seawater using 280,000 ppm ferric sulfate draw solution at ambient conditions. The observed average water flux was 3.75 and 1.61 L/m2 h in case of brackish and seawater, respectively. Using deionized water as feed solution, reverse ferric sulfate flux of 1.88 g/m2 h was observed. Product water was recovered from the diluted draw solution by precipitation reaction using barium hydroxide. Pure water samples with salt contents of 60 and 80 ppm were obtained by desalinating brackish and seawater feed, respectively.