Performance of Potassium Bicarbonate and Calcium Chloride Draw Solutions for Desalination of Saline Water Using Forward Osmosis

Forward osmosis (FO) has recently drawn attention as a promising membrane based method for seawater and brackish water desalination. In this study, we focus on the use of calciun chloride (CaCl2) and potassium bicarbonate (KHCO3) as inorganic salt draw solution candidates due to their appropriate performance in water flux and reverse salt diffusion as well as reasonable cost. The experiments were carried at 25 °C and cross-flow rate of 3 L min−1.  At the same osmotic pressure, the water flux of CaCl2 draw solution tested against deionized feed water, showed 20% higher permeation than KHCO3, which it was attributed to the lower internal concentration polarization (ICP). The reverse diffusion of CaCl2 was found higher than KHCO3 solution which it would be related to the smaller ionic size and the higher permeation of this salt through the membrane. The water flux for both draw solutions against 0.33 M NaCl feed solution was about 2.8 times lower than deionized feed water because of ICP. Higher concentrations of draw solution is required for increasing the water permeation from saline water feed towards the draw side.