Mathematical modeling of desalination by electrodialysis

Desalination of brackish water by electrodialysis (ED) was modeled based on separation experimental data of sodium ions. At steady-state operation of ED, the outlet concentration of dilute stream was measured at different voltages, flow rates and feed concentrations. The model started from a differential equation of steady-state mass balance. Neglecting resistances of ion-exchange membranes compared with resistances of bulk solutions in dilute and concentrate compartments and substituting a relation for solution resistance as a function of concentration, the final one-parameter model was obtained. The concentration gradient was also assumed to be constant along the membrane surface due to the very short residence time in dilute compartment and constancy of current density. The model parameter was determined by the experimental data. The approached model gives concentration of dilute compartment or separation percent for various voltages, flow rates and feed concentrations. In order to assess the reliability of the model, the predicted data were compared with measured experimental. It was found that the model could be used to well predict the process.