Water flux behavior of blended solutions of ammonium bicarbonate mixed with eight salts respectively as draw solutions in forward osmosis

• Water fluxes of different NH4HCO3 mixed solutions in forward osmosis were studied.
• Blended solutions formed by NH4HCO3 and eight inorganic salts were draw solutions.
• After mixed single salt with NH4HCO3, the water flux increased notably.
• NH4Cl + NH4HCO3 mixture gained the highest water flux.

Forward osmosis (FO) is a novel membrane technology which has huge potential in the field of desalination and wastewater reclamation. Recoverable draw solutions (DS) with high osmotic pressure are crucial to FO process. This study investigated the water flux behavior of draw solutions formed by ammonium bicarbonate and eight soluble inorganic salts (K2SO4, NaCl, KCl, KNO3, NH4Cl, NH4NO3, urea and (NH4)2HPO4), respectively. A laboratory-scaled plate-and-frame FO setup with TFC FO membrane was used. The result indicated that the properties and water flux behavior of the aforementioned eight salt solutions were all enhanced after blended with NH4HCO3. Mixture of NH4Cl and NH4HCO3 exhibited the highest water flux when deionized water or simulated brackish water was used as feed solution (FS). Meanwhile, water flux of blended solution formed by urea and NH4HCO3 was the lowest. However, urea gained the highest water flux increase after blending with NH4HCO3. The osmotic driving force generated by draw solution in each FO process has not been utilized effectively no matter which kind of feed water was used. Moreover, the performance ratio (PR, experimental water flux divided by theoretical water flux) of most salt solutions decreased slightly after blending with NH4HCO3.