Water purification by reducing the concentration of ionic impurities has been an area of considerable technical interest. Water treatment technologies have rapidly advanced in recent years to where a myriad of options have been developed for this purpose. The most well-known processes include electrodialysis, electrodeionization (EDI), liquid chromatography, membrane filtration, and ion exchange. Producing pure water without regeneration chemicals is now a practical reality. EDI is a separation process combining electrodialysis and conventional ion exchange (IX); the resulting hybrid process does not entail regenerant chemicals. EDI technology has been reported in the literature since 1950s (1, 2).
The first patent for EDI was granted to a Dutch company in 1957 (3). A patent for the purification of acetone with EDI was also granted to Kollsman (2) in 1957. For fundamentally the same reasons that reverse osmosis (RO) system are cost-effectively replacing cation and anion units, EDI systems can also supplant mixed-bed deionizers (4). The EDI process is preferred in many systems primarily because of the environmental benefit of no required hazardous regenerant chemicals and the inherent superiority of a continuous process over a batch process (5).