Electrodialysis process configuration

Bipolar cell configurations have been examined and are used in various electrochemical operations which include fuel cells [9,10], batteries [11-20], electrochemical capacitors [21], chlorate and chlor-alkali cells [22-27], electrowinning of metals [28-30], fused salt electrolysis of A1 and Mg [31-36], electrodialysis [37], and electroorganic processes [38]. 

Concentration polarisation is not generally severe in dialysis and diffusion dialysis because of the low fluxes involved (lower than in reverse osmosis) and also because the mass transfer coefficient of the low molecular solutes encountered is of the same order of magnitude as in reverse osmosis. In carrier mediated processes and in membrane contactors the effect of concentration polarization may become moderate mainly due to the flux through the membrane. Finally, the effect of concentration polarisation may become ver severe in electrodialysis. In the following sections concentration polarization will be described more in detail. In some module configurations such as plate-and-frame and spiral wound spacer materials are used in the feed compartment (see chapter VIII). These spacers effect the mass transfer coefficient and can be considered as turbulence promoters. 

Figure 8.1.4(c) introduces through the example of dialysis (see Section 4.3.1) a countercurrent flow configuration of a membrane device where two separate feed streams tu-e entering the separator as in the separation system type (2). In the electrodialysis (Section 3.4.2.S) process of selective transport of ions through an ion exchange membrane, the liquid solutions on two sides of any ion exchange membrane are sometimes in countercurrent flow. 

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