Continuous electrodeionization membranes

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. 

In this chapter only electromenbrane separation processes such as electrodialysis, electrodialysis with bipolar membranes and continuous electrodeionization will be discussed. 

Continuous electrodeionization is widely used today for the preparation of high-quality deionized water for the preparation of ultrapure water in the electronic industry or in analytical laboratories. The process is described in some detail in the patent literature and company brochures [29]. There are also some variations of the basic design as far as the distribution of the ion-exchange resin is concerned. In some cases the diluate cell is filled with a mixed bed ion-exchange resin, in other cases the cation- and anion-exchange resins are placed in series in the cell. More recently, bipolar membranes are also being used in the process. 

Grabowskij, A., Zhang, G., Strafhmann, H. and Eigenberger, G. (2006) The production of high purity water by continuous electrodeionization with bipolar membranes. Journal of Membrane Science, 281, 297. 

In this chapter, the impact of other membrane technologies on the operation of RO systems is discussed. Technologies considered include microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) as pretreatment to RO, and continuous electrodeionization (CEDI) as post-treatment to RO. This chapter also describes the HERO (high efficiency RO—Debasish Mukhopadhyay patent holder, 1999) process used to generate high purity water from water that is difficult to treat, such as water containing high concentrations of silica. 

Continuous electrodeionization technology uses mixed bed ion exchange resins and selectively permeable membranes to extract dissolved salts from water under the influence of an electric field. This field drives the ions away from the products flow and continuously regenerates the resin beads, avoiding the need for chemical regeneration. The combination of reverse osmosis and electrodeionization is claimed to be the safest and most reliable way to produce purified water. 

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