Study On Mathematical Modeling Of Desalination By Electrodialysis

Electrodialysis technology is one of membrane separation technologies with the characteristic that ions of solution transfer through ion-exchange membranes. Electrodialysis desalination is a technology which simultaneously uses electrodialysis and electrolysis process. The migration process of ions between solution and ion-exchange membrane is main desalination process. ion-exchange membrane is the most critical part of Electrodialysis cell. Now electrodialysis has been widely used in different fields for its high efficiency and low energy consumption. Under the directly electric field, electrodialysis technology utilizes the selectivity of ion-exchange membrane permeability to separate the electrolyte from the solution, with the potential difference as the driving force, in order to realize the purposes of dilution, concentration or purification of the solution.According to the property that ion electromigration happens on the external electric field, a mathematical modeling for desalination by electrodialysis (ED) was established using an ED channel mass balance and fundamental electrochemical equations. Experiments were conducted to investigate the effect of voltages, flow rates and feed concentrations on ED cell performance and the model parameter was calculated using the outlet concentration in the dilute compartment. Using experimental data, the equation was fitted forβas a function of voltage, flow rate and feed concentrations. Using multiple regression procedure, the model gives the values of the concentration in the dilute compartment for various voltages, flow rates and feed concentrations.The effect of voltages, flow rates and feed concentrations on ED cell performance was investigated. As can be seen, at higher flow rates the amount of separated salt falls and separation performance decreases. Because a greater flow rate means a lower residence time, this means ions that are between the membranes do not have enough time to transfer through the membranes. Obviously, at a constant concentration, the cell performance increases by increasing voltage and as a result the amount of salt in the product water decreases. There is good agreement between the experimental and calculated results, it was found that the mathematical modeling could be used to well predict the process. According to comparing the model and experimental results of different feed concentration, increasing concentration decreases ED cell performance due to the fact that the concentration polarization phenomenon is more important at high concentrations. The result confirms that ED is more useful for low feed concentrations.