Electromembrane desalination

Among electrochemical methods of water purification, one can also list the various electromembrane technologies, electrodialysis in particular. The simplest elec-trodialyzer consists of three compartments separated by semipermeable membranes (usually, cation- and anion-exchange membranes). The water to be purified is supplied to the central (desalination) compartment. In the outer (concentration) compartments, electrodes are set up between which a certain potential difference is applied. Under the effect of the electric field, ions pass througfi the membranes so that the concentration of ionic contaminants in the central compartment decreases. 

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. 

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. 

Linkov VM. Electromembrane reactors for desalination and disinfection of aqueous solutions. Water Research Commission of South Africa. Report Number 964/1/02. 

D. Raucq, G. Pourcelly and C. Gavach, Production of sulfuric acid and caustic soda from sodium sulfate by electromembrane processes. Comparison between electroelectrodialysis and electrodialysis on bipolar membrane, Desalination, 1993, 91, 163— 175 S. Mazrou, H. Kerdjoudi, A.T. Cherif and J. Molenat, Sodium hydroxide and hydrochloric acid generation from sodium chloride and rock salt by electroelectrodialysis, J. Appl. Electrochem., 1997, 27, 558 A.T. Cherif, J. Molenat and A. Elmidaoui, Nitric acid and sodium hydroxide generation by electrodialysis using bipolar membranes. J Appl. Electrochem., 1997, 27, 1069-1074. 

S. Resbeut, G. Pourcelly, R. Sandeaux and C. Gavach, Electromembrane prosesses for waste stream treatment of phenylalanine solutions, Desalination, 1998, 120, 235. 

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]. 

Strathmann, H., Grabowski, A., Eigenberger, G. (2006). Electromembrane processes, efficient and versatile tools in a sustainable industrial development. Desalination, 199, 1-3. 

Raucq D, Pourcelly G, Gawich G. Production of sulfur acid and caustic soda from sodium sulfate by electromembrane process. Comparison between electro-electrodialysis and electrodialysis on bipolar membrane. Desalination 1993 91(12) 163—75. 

Grebenyuk, VD., Chebotareva, R.D., Linkov, N.A. Linkov, VM. (1998) Electromembrane extraction of Zn from Na-containing solutions using hybrid electrodialysis-ion exchange method. Desalination, 115, 255-263. 

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