Electromembrane Process Application

Electromembrane processes such as electrolysis and electrodialysis have experienced a steady growth since they made their first appearance in industrial-scale applications about 50 years ago [1-3], Currently desalination of brackish water and chlorine-alkaline electrolysis are still the dominant applications of these processes. But a number of new applications in the chemical and biochemical industry, in the production of high-quality industrial process water and in the treatment of industrial effluents, have been identified more recently [4]. The development of processes such as continuous electrodeionization and the use of bipolar membranes have further extended the range of application of electromembrane processes far beyond their traditional use in water desalination and chlorine-alkaline production. 

The term electromembrane process is used to describe an entire family of processes that can be quite different in their basic concept and their application. However, they are all based on the same principle, which is the coupling of mass transport with an electrical current through an ion permselective membrane. Electromembrane processes can conveniently be divided into three types (1) Electromembrane separation processes that are used to remove ionic components such as salts or acids and bases from electrolyte solutions due to an externally applied electrical potential gradient. (2) Electromembrane synthesis processes that are used to produce certain compounds such as NaOH, and Cl2 from NaCL due to an externally applied electrical potential and an electrochemical electrode reaction. (3) Eletectromembrane energy conversion processes that are to convert chemical into electrical energy, as in the H2/02 fuel cell. 

In summary, electromembrane processes, especially when used as part of hybrid treatment schemes, can provide an efficient removal of toxic metal ions from water. When a target metal exists in water as a mono-valent species, the use of mono-valent (cation- and/or anion-permselective membranes) is especially attractive. Situations, in which ED appears to be less applicable are for waters of very low salinity (conductivity of less than 0.5 mS cm ), for which EDI or DD can be better choices, and, in cases when besides ions, removal of low molecular mass non-charged compounds from the water is desired. In the latter case, pressure-driven membrane processes such as RO or NF may be preferable. 

In conclusion, a greater knowledge of the effect of the key controlling parameters of this powerful separation technique, as well as improvement in membrane life time of the currently available commercial electromembranes and reduction in their costs, would ensure further growth beyond desalination and salt production and foster ED applications in the food sector, as well as in the chemical, pharmaceutical, and municipal effluent treatment areas. This will of course need extensive R D studies and will highly likely result in hybrid processes combining ED to other separation techniques, such as NF, IE, and so on, so as to shorten present downstream and refining procedures. 

Electrodialysis (ED) is used to remove ionized substance from hquids through selective ion-permeable membranes. ED is the most widely commercialized electromembrane technology. Desalination of brackish water is the area of electrodialysis application with the largest number of installations. This chemical-free technology competes with reverse osmosis. Electrodialysis shows better resistance to fouling and scaling. It also has an economical advantage in desalination of low-salinity solutions [13]. Also, it should be kept in mind that because of small material consumption ED is the most environmental friendly process for solution desalination [14]. 

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