10 Electroactive Media used in CEDI Devices

Figure 5
Removal mechanism in thick­cell, separate­bed EDI cell
Instead of splitting water at a resin/membrane or resin/resin interface, this process obtains the
hydrogen (H+) or hydroxyl (OH­) ions needed to regenerate the resin from the electrode
reactions; hydrogen ions being generated at the anode and hydroxyl ions at the cathode.
Since the resins are in the electrode compartments, the O2, H2, and Cl2 gas that is created
remains in the product water, which may require an additional gas removal process step. It is
possible that the electrode reaction could produce enough chlorine to reduce the life of the ion
exchange resin, depending upon the amount of chloride in the feed water.
It has been shown that the salt removal by EDI­SB device with 10 mm intermembrane
spacing, is not nearly as good as for a EDI­MB device with 2.5 mm spacing. But the main
disadvantage of the EDI­SB device is that it requires a set of electrodes for each cell. Since
the electrodes are by far the most costly component of a EDI device, this approach is only
cost effective for low flow rate applications where a single cell is sufficient. There have been
some attempts to produce a multi­cell device using bipolar ion exchange membranes, but
these have not been commercialized due to the short life of the bipolar membranes.
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