Electrodialysis operating principle

FIG. 5 Basic operating principles of an electrodialysis process using (A) a couple of monopolar (anionic, a, and cationic, c) membranes or (B) a bipolar membrane. 

Electrodialysis Reversal. Electro dialysis reversal processes operate on the same principles as ED however, EDR operation reverses system polarity (typically three to four times per hour). This reversal stops the buildup of concentrated solutions on the membrane and thereby reduces the accumulation of inorganic and organic deposition on the membrane surface. EDR systems are similar to ED systems, designed with adequate chamber area to collect both product water and brine. EDR produces water of the same purity as ED. 

This review summarizes the monopolar and BPM principles of operation. Moreover, this review presents shortly the main applications in chemical processing, pollution control, and resource recovery, and details the specific applications of electrodialysis with BPMs to food and bio-industries. 

FIGURE 5.4 Principles of operation of two types of membrane water desalination units reverse osmosis and electrodialysis. (From Pryde [22], and reprinted courtesy of Cummings Publishing Co.)... 

A recent innovation by a U.S. manufacturer of ED systems has significantly minimized the need for pretreatment. This innovation, known as electrodialysis reversal (EDR), operates on the same basic principle as the standard electrodialysis unit, except that both the product and the brine cells are identical in construction. At a frequency of 3-4 times/hr, the polarity of the electrodes is reversed and the flows are simultaneously switched by automatic... 

The principle of operation of a multicompartmented electrodialysis unit (11) is shown in Fig. 1.11. The cation and anion permeable membranes carry a fixed charge thus they prevent the migration of species of like charge. In a commercial version of Fig. 1.11, there would be several hundred rather than three compartments, multicompartmentalization being required to achieve electric power economics, since electrochemical reactions take place at the electrodes. 

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