Applications of electrodialysis

The use of ED can be used in the treatment of process solutions from plating baths containing chromium [6]. Dilute rinse water solutions can be concentrated by the removal of the CrOv ions across an anion exchange membrane into the chromic acid concentrate. ED is also used as a method of purification of plating solutions by the removal of contaminant ions which are picked up during the plating operation. 

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Efficient separation or pretreatment in the influent streams can include activated carbon absorption to reduce or prevent such problems. Principal applications of electrodialysis include ... 

Treatment of brackish waters in the production of potable supplies has been the largest application of electrodialysis. Costs associated with electrodialysis processes depend on such factors as the total dissolved solids (TDS) in the feed, the level of removal of TDS (percent rejection), and the size of the plant. In brackish water treatment, operating costs for very large ED installations (on the order of millions of gallons a day) have been between 40 cents to 50 cents per 1,000 gallons for brackish feed waters, which compares favorably with RO costs. 

Audinos, R., Roson, J.P., and Jouret, C. 1979. Application of electrodialysis to the elimination of certain grape juice and wine components. Connaissance de la Vigne et du Vin 13, 229-239. 

Bazinet, L., Lamarche, F., Labrecque, R., Toupin, R., Boulet, M., and Ippersiel, D. 1997. Electroacidification of soybean proteins for the production of isolate. Food Technol. 51(9), 52-56, 58, 60. Bazinet, L., Lamarche, F., and Ippersiel, D. 1998. Bipolar-membrane electrodialysis Applications of electrodialysis in the food industry. Trends in Food Sci. Technol. 9, 107-113. 

Habova, V., Melzoch, K., Rychtera, M., Pribyl, L., and Mejta, V. 2001. Application of electrodialysis for lactic acid recovery. Czech J. Food Sci. 19, 73-80. 

Nomura, Y., Iwahara, M., and Hongo, M. 1987a. Application of electrodialysis fermentation to L-lysine fermentation. Nippon Nogei Kagaku Kaishi 61, 1293-1295. 

Paronetto, L. 1941. The application of electrodialysis to wines. Annuar. Staz. Sper. Viticolt. Enol. Conegliano 10, 123-149. 

In the United States, electrodialysis was developed primarily for desalination of water, with Ionics being the industry leader. In Japan, Asahi Glass, Asahi Chemical (a different company), and Tokuyama Soda developed the process to concentrate seawater [8], This application of electrodialysis is confined to Japan, which has no domestic salt sources. Electrodialysis membranes concentrate the salt in seawater to about 18-20% solids, after which the brine is further concentrated by evaporation and the salt recovered by crystallization. 

The second major application of electrodialysis is the production of table salt by concentration of seawater [8], This process is only practiced in Japan, which has no other domestic salt supply. The process is heavily subsidized by the... 

Electrodialysis is by far the largest use of ion exchange membranes, principally to desalt brackish water or (in Japan) to produce concentrated brine. These two processes are both well established, and major technical innovations that will change the competitive position of the industry do not appear likely. Some new applications of electrodialysis exist in the treatment of industrial process streams, food processing and wastewater treatment systems but the total market is small. Long-term major applications for ion exchange membranes may be in the nonseparation areas such as fuel cells, electrochemical reactions and production of acids and alkalis with bipolar membranes. 

Exceeding the limiting current density in practical applications of electrodialysis can affect the efficiency of the process severely by increasing the electrical resistance of the solution and causing water dissociation, which leads to changes of the pH values ofthe solution causing precipitation of metal hydroxide on the membrane surface. 

In the practical application of electrodialysis there are two main process operation modes. The first one is referred to as the unidirectional electrodialysis and the second as electrodialysis reversal [22]. In a unidirectional operated electrodialysis system the electric field is permanently applied in one direction and the diluate and concentrate cells are also permanently fixed over the period of operation. Unidirectional operated electrodialysis plants are rather sensitive to membrane fouling and scaling and often require a substantial feed-solution pretreatment and stack-cleaning procedures in the form of periodical rinsing of the stack with acid or detergent solutions. The unidirectional operating concept is mainly used today for applications in the... 

Wisniewski, J. and G. Wisniewska (1997). Application of electrodialysis and cation exchange technique to water and acid recovery. Environ. Protection Eng., 23, 3-4, 35-45. 

Electrodialysis is a membrane-based process which can be used for separation, removal, or concentration of ionic species present in aqueous solutions. These operations are accomplished by the selective transport of ions through an ion exchange membrane under the influence of a direct current. One of the earliest applications of electrodialysis was the desalting of brackish water. However, since the 1970s, extensive studies have been performed on the application of electrodialysis for waste-water treatment, especially in the electroplating and metal-finishing industries. 

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. 

Bazinet L, Lamarche E, and Ippersiel D. Bipolar-membrane electrodialysis An application of electrodialysis for the food industry. Trends Food Sci. Tech. 1998 9 107-113. 

A great advantage of electrochemical reactions compared with chemical conversions is the effective contribution to pollution control. The direct electron transfer from the electrode to the substrate avoids the problem of separation and waste treatment of the frequently toxic end products of the chemical oxidants or reductants. Furthermore, by electrodialysis, organic acids or bases can be regenerated from their salts without the use of sulfuric acid or sodium hydroxide, for example, which lead to the coproduction of sodium salts or sulfates as waste [79]. At the same time, inorganic acids and bases, necessary for chemical production, are provided by this process. An application of electrodialysis has been demonstrated in the preparation of methoxyacetic acid by oxidation of methoxyethanol at the nickel hydroxide electrode [80]. Finally, unwanted side products can be converted into the wanted product, which increases the economy of the process and reduces the problem of waste separation and treatment. This is accomplished in the manufacture of chloroacetic acid by chlorination of acetic acid. There the side product dichloroacetic acid, formed by overchlorination, is cathodically converted to chloroacetic acid [81]. 

Hi) Salt from sea water Another principal application of electrodialysis is the production of common salt from sea water. In the manufacture of salt from this source, generally sea water is first filtered and then warmed with waste heat. Next, this water is slowly passed through the depletion compartments of the multicompartment electrodialysis equipment. Concentration of solids reaches about 20% by weight in the brine collecting in the enrichment compartments. Further processing of this concentrated brine by evaporation yields the salt in solid crystalline state. 

A significant step towards the efficient application of electrodialysis was the introduction of a new operating mode referred to as electrodialysis reversal by Ionics. In this operation mode the flow streams and the polarity in an electrodialysis stack is reversed in certain time intervals [7] and membrane fouling and scaling can be reduced to a minimum. 

The technically and economically most important electrodialytical process used for the separation of ionic components from an aqueous solution is conventional electrodialysis. The main application of electrodialysis is the desalination of brackish water. However, other uses, especially in the food, drug, and chemical process industry as well as in biotechnology and waste water treatment, have recently gained a broader interest. In its basic form electrodialysis can be utilized to perform several general types of separations, such as the separation and concentration of salts, acids, and bases from aqueous solutions, or the separation of monovalent ions from multiple charged components, or the separation of ionic compounds from uncharged molecules. 

Electrodialysis was developed first for the desalination of saline solutions, particularly brackish water. The production of potable water is still currently the most important industrial application of electrodialysis. But other applications, such as the treatment of industrial effluents [45], the production of boiler feed water, demineralization of whey [46], de-acidification of fruit juices [47], etc. are gaining increasing importance with large-scale industrial installations. An application of electrodialysis which is limited regionally to Japan has gained considerable commercial importance. This is the production of table salt from sea water. Diffusion dialysis and the use of bipolar membranes have significantly expanded the application of electrodialysis in recent years [48]. 

Several other potential applications of electrodialysis in wastewater treatment systems which have been studied on a laboratory scale are reported in the literature. In most of these applications the average plant capacity, however, is considerably lower than that in brackish water desalination or table salt production. 

A further application of electrodialysis is the concentration of reverse osmosis brines. Because of limiting membrane selectivity and the osmotic pressure of concentrated salt solutions, the concentration of brine in reverse osmosis desalination plants can not exceed... 

The removal of tartaric acid from wine is another possible application of electrodialysis. In the production of bottled champagne, it is necessary to avoid the formation of crystalline tartar in the wine and tartaric acid must therefore be reduced to a value which does not exceed the solubility limit. This can be done efficiently by electrodialysis. 

Several other applications of electiodialysis in the pharmaceutical industry have been studied on a laboratory scale [51]. Most of these applications are concerned with desalting solutions containing active agents which have to be separated, purified, or isolated from certain substrates [52]. Here, electrodialysis is often in competition with other separation procedures such as dialysis, solvent extraction, etc. In many cases, electrodialysis is the superior process as far as economics and the quality of the product is concerned. Especially the separation of amino acids and other organic acids by electrodialysis seems to be of interest to the pharmaceutical and chemical industry [53]. However, the deionization of cheese whey with an installed capacity of more than 35,000 square meters of membrane area for the production of more than 150,000 tons of desalted lactose per year is economically by far the most important application of electrodialysis in the food industry today. 

Bazinet, L., Lamarche, F., and Ippersiel, D. (1998) Bipolar membrane electrodialysis Applications of electrodialysis in the food industry. Trends in Food Science and Technology 9, 107-113. 

In electrodialysis, there are three categories of costs those that increase with current density (the cost of energy) those that decrease with current density (the cost of membrane replacement and amortization of capital investment) and those that are essentially invariant with current density (cost of chemicals, maintenance, and labor). Because two of these categories of costs vary in opposite directions with current density, there is an economically optimum current density. However, for most applications of electrodialysis, the limiting current density is lower than the ofXimum current density. Therefore, determination of the limiting current density in by the previously described methods is usually the first step in design. 

This paper covers mainly the industrial and medical applications of electrodialysis, ultrafiltration and microfiltration rather than those of reverse osmosis, which have been covered by many authors elsewhere. 

Ion exchange membranes are also being utilized in electrodialysis and electrochemistry. Salt production and desalination are the main applications of electrodialysis. The chlor-aikali process and the adiponitrile process are examples of highly successful ion exchange membrane applications. 

The most important application of electrodialysis is the production of potable water from brackish water [82]. Avery special application is the reverse case, the production of salt. In the latter case the concentrate is the product stream whereas in the former case the diluate stream is the product. Moreover, there is an increasing number of industrial applications where ions have to be removed from.a process stream such as demineralisation of whey, deacidification of fruit juices, production of boiler feed water, removal of organic acids from a fermentation broth.lt is even possible to separate amino acids from each other as will be shown below. 

Pourcelly G, Gavach C (2000) Electrodialysis water splitting - application of electrodialysis with bipolar membranes. In Kemperman AJB (ed) Handbook of bipolar membrane technology. Twenty University Press, Enschede... 

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