Formulating Novel Draw Solutions for Forward Osmosis

In recent years research has been done on the behavior and performance of membranes in different orientations (Forward Osmosis, Reverse Osmosis, Pressure Retarded Osmosis), although relatively few studies have been done analyzing the draw solutions for these systems.  This study evaluates draw solutions for an FO system operating in PRO mode, with emphasis on the effects of the concentration and composition of the draw solution.  Also, the system used was not a small bench scale, but rather a commercially available, full cartridge membrane system from Hydration Technology Innovations (HTI).  Three electrolytes were chosen for the study: Sodium Chloride, Potassium Chloride, and Calcium Chloride, and the effects of changing the concentrations, as well as mixing the electrolytes, were studied.  Since chloride is a common ion with all three electrolytes, the effects of the diffusivity coefficients and cation charge of the alkali metals could be studied.  Increasing the concentration of the draw solutions was found to increase the flux, but the relationship was not linear.  For example, doubling the concentration led to an approximately 35% increase in the output flux for all three electrolytes.  Also, when graphing the flux of individual electrolyte solutions against the diffusivity coefficients it was found that there was an inverse relationship, counter to all other studies and theories.  It should be noted that the velocity through the membranes was not held constant, as well as the temperature (since each test was conducted at room temperature).