Continuous electrodeionization

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

The major advantage of the spiral configuration over a plate-and-frame configuration is that there is minimal leakage associated with the spiral configuration. The spiral wound module does not require periodic tightening of nuts and bolts to prevent leaks, unlike plate-and-frame modules. Limitations of the spiral configuration include inferior current and flow distribution relative to plate-and-frame modules, as well as difficulty in assembly and field membrane replacement.17 

A CEDI system can produce up to 18-megohm-cm water at 90-95% water recovery. Recovery by the CEDI system is a function of the total hardness in the feed water to the system. In general, 95% recovery can be realized at a feed water hardness of less than 0.1 ppm as calcium carbonate.16 This is typically attained if the pretreatment to the CEDI consists of either 2-pass RO or sodium-cycle softening followed by RO. Recovery that is achievable is a function of the feed 

Feed Water Hardness (ppm as CaCQ,) CEDI Recovery (%) 

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 

Equations 16.1 and 16.2 show the reactions at the cathode and anode, respectively. These equations indicate that hydrogen and oxygen gases are produced at the electrodes. Typically, 7.5 ml/min of hydrogen and 2.7 ml/ min of oxygen are produced at 25°C and 14.7 psig. Equation 16.3 indicates that chlorine gas may also be generated at the anode. Concentrations of 

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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). 

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. 

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

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... 

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. 

Continuous electrodeionization for high-purity water production... 

Wood, J., Power generation Continuous electrodeionization for power plants. Filtration and Separation, 2008.45(5) 17-19. 

J. Wood, J. Gifford, J. Arha, M. Shaw, Production of ultrapure water hy continuous electrodeionization, Desalination 250 (2010) 973—976. 

A. Grabowski, G. Zhang, H. Strathmaim, G. Eigenherger, Production of high purity water by continuous electrodeionization with bipolar memhranes influence of concentrate and protection compartment, Sep. Purif. Technol. 60 (2008) 86—95. 

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