Electrodeionization (EDI) Ion-exchange Membranes Reverse Osmosis

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Abstract

Editor’s note: Welcome to a technical article from our library of more than 2,100 technical and water business articles published since 1984. This article by Anil Jha and Joseph Gifford was published in the July/August 2004 issue of Ultrapure Water Journal. This article examines the use of EDI as an alternative to traditional mix-bed ion exchange.

Continuous electrodeionization (CEDI) technology is now commonly used as a post reverse osmosis (RO), makeup deionization (DI) process in a variety of applications, such as microelectronics, steam generation, biotechnology, pharmaceutical, and food and beverage. Some efforts have been made in the past to develop this technology as a final polishing step and as a replacement to mixed beds for microelectronics applications.  These efforts have met limited success and have not been cost effective.

The latest innovations in the CEDI process combined with low-cost CEDI module and system designs have resulted in a cost effective alternative to mixed-bed DI. Operating data from multiple tests at a variety of sites and under various feedwater conditions consistently show that the product water quality of these CEDI devices is continuously maintained above 18 megohm-cm with over 99.9% silica and boron removal.  A cost comparison between mixed-bed DI and the latest CEDI systems indicate that CEDI can become the technology of choice for all future microelectronics pure water applications. 

CEDI devices are comprised of cation- and anion-permeable membranes alternating in a module with spaces in between configured to create liquid flow compartments with inlets and outlets.  The diluting compartments are bound by an anion-exchange membrane (AEM) facing the positively charged anode, and a cation-exchange membrane (CEM) facing the negatively charged cathode.  The concentrating compartments are bound by an AEM facing the cathode and a CEM facing the anode. 

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