(371b) The Role of Ion Exchange Membranes and Operating Parameters in Selective Removal of Monovalent or Divalent Ions in Electrodialysis Process

Electrodialysis and electrodialysis reversal (ED/EDR) are two closely-related water purification processes which use an electrical field to propel ions through ion exchange membranes. The most effective use for these technologies has proven to be the production of potable water from brackish water resources; however, the ED/EDR process could also have several benefits in industrial applications, where the process can remove various charged elements. In brackish water resources and industrial water streams, water compositions differ, and the removal of particular monovalent or divalent ions may be more important than the removal of others. For this reason, the ability to selectively remove monovalent or divalent ions would be valuable. This experimental study, which investigates the nature of ion removal and the effects of type ion exchange membrane and operating parameters on the process, was conducted to explore the dominant empirical model on the selective removal of monovalent ions and divalent ions in the laboratory-scale ED process. The ED cell unit used in this set-up was the PCCell ED 64 0 02, a lab-scale electrodialyzer, which has the nominal capacity of 4-8 l/h for dilute and concentrate streams. A complete data acquisition system was used in order to continuously and accurately monitor and record the operating conditions in the experiment.  Complete lab-scale experiments, which tested the effects of ion exchange membrane types and different parameters on ion removal, were designed and conducted. The obtained results were used to develop an empirical model for the removal of monovalent and divalent ions in electrodialysis desalination processes using different ion exchange membranes. The developed model can be widely used for full-scale electrodialysis operations as soon as it is verified through pilot-scale experiments, which will be conducted in the next phase of the study at the Brackish Groundwater National Desalination Research Facility (BGNDRF) in Alamogordo, NM, on a pilot-scale EDR system with an influent flow rate capacity of 12 gallons per minute. Brackish feedwaters with different ion compositions and a wide range of initial conductivities, 1700-6500 μS/cm, can be acquired for the experiments from the nearby aquifer in Tularosa Basin.