Electrodeionization

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. 

In some instances, water produced by EDI with 10-18 megohm-cm resistivity can be used directly. Commonly, an EDI system is followed by a mixed-bed polishing filter in order to assure high purity. For customers EDI demineralization means lower water-treatment cost and less risk to downstream equipment and products [8,9]. 

In order to avoid secondary contamination at the C A contacts, the number of these contacts should be minimized by using uniform-size beads in desahnation compartment or beads may be arrangement in such a way that the C A contacts never occur in dilute cell (sparse media [53]). This allows decreased power consumption and increased stack capacity. Or, the beads can be arranged in form of alternating layers where each layer contains only one type of ion-exchange resin. 

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Electrodemineralization includes a number of subset technologies, including electrodialysis (ED), electrodialysis reversal (EDR), and electrodeionization (EDI). Electrodeionization is sometimes termed continuous electrodeionization (CEDI) or continuous deionization (CDI). 

Reverse osmosis/electrodeionization (RO/EDI) plants are available in modular form to suit any desired input-output water quality and flow rate. A RO/EDI system should be capable of producing high-purity water of perhaps 5 to 20 xS/cm conductivity (0.2-0.05 MO/cm resistance). By providing a second EDI stack in series, it is possible to achieve even higher quality of up to 0.055 xS/cm conductivity (18.2 Mfl/cm resistance). 

Osmonics. Electrodeionization. Technical documents and promotional literature. Osmonics, Inc., USA, 1999. 

Electrodeionization systems were first suggested to remove small amounts of radioactive elements from contaminated waters [27], but the principal current application is the preparation of ultrapure water for the electronics and pharmaceutical industries [28], The process is sometimes used as a polishing step after the water has been pretreated with a reverse osmosis unit. 

Figure 10.18 Schematic of the electrodeionization process using mixed-bed ion exchange resin to increase the conduction of the dilute compartments of the electrodialysis stack...

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. 

The main difference between the electrodeionization system with the mixed-bed ion-exchange resins and the system with separate beds is that in mixed-bed electrodeionization systems anions and cations are simultaneously removed from the feed... 

Ganzi, G.C. (1988) Electrodeionization for high purity water production, in New Membrane Materials and Processes for Separation, 84 (eds K.K. Sirkar and... 

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. 

The fifth paper, "A Separative Bioreactor Direct Product Capture and pH Control," presented by Seth Snyder of the Argonne National Laboratory, reviewed development and performance of a novel bioreactor incorporating electrodeionization to simultaneously produce and separate products from both enzymatic and microbially mediated reactions. The sixth paper, " Optimization of Xylose Fermentation in Spent Sulfite Liquor by Saccharomyces cerevisiae 259ST," presented by Steven Helle of the University of British Columbia, provided an overview of an approach to fermentation optimization utilized to identify key process variables limiting use of the SSL for commercial ethanol production. 

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 (CEDI—the continuous process subset of electrodeionization (EDI) that is sometimes referred to as... 

Table 16.6 Continuous electrodeionization recovery as a function of feed water hardness for an E-Cell (GE) module.18...

Continuous electrodeionization systems can achieve 95% rejection of boron and silica, and 99+% rejection of sodium and chloride. This performance is possible due to voltage-induced dissociation of water that effectively regenerates a portion of the resin thereby allowing removal of weakly ionized species such as silica and boron.19 In fact, the boron in the effluent from a CEDI system can be lower than that in the effluent from a mixed-bed ion exchange system.13... 

Continuous electrodeionization is primarily used as an alternative to ion exchange. Because of the extensive pretreatment required by CEDI systems, the technology has grown into a polisher for RO (see Figure 16.18). Continuous deionization can achieve mixed-bed water quality of RO permeate without the need to store and... 

Dey, Avijit, and Bill Loyd, "Unique Design Features of Omexell Spiral Wound Electrodeionization Technology," White paper, Omexell Inc., and Dow Water Solutions. 

Wood, Jonathan, Joseph Gifford, John Arba, and Michael Shaw, "Production of Ultrapure Water by Continuous Electrodeionization," presented at the 12th Aachener Menbran Kolloquium, Aachen, Germany, October, 2008. 

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