An electrodialysis model for determination of the optimal current density

In light of broad use of the electrodialysis (ED) processes, it has become crucial to minimize its operating costs. The total cost of the ED process consists of energy, investment and maintenance costs. Energy cost increases linearly with the current density while the investment cost decreases with current density, resulting from the membrane cost. This trend implies that current density is a design parameter that has considerable influence on the process cost. In this study, we performed an overall cost assessment of an ED process as a function of current density and determined an economically optimal current density for the batch electrodialysis of NaCl using a rigorous model. Salt concentration and energy consumption predicted by the model were in good agreement with the experimental results. Further, membrane area and power consumption were calculated as a function of current density using the proposed procedure. The overall cost assessment shows that the selection of an optimal current density enabled to significantly reduce the ED process cost.

A model that describes the relationship between the resistance of a cell pair and the salt concentration in the dilute solution was proposed. Membrane area and power consumption were calculated accordingly by the model equations and parameters determined experimentally. At various current densities, total costs were estimated and an optimal current density was determined. This study may provide a guideline for design of an electrodialysis system to be operated economically.