Study on thick cell EDI process for ultra pure water production

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The ultra pure water production using a self-designed thick cell EDI stack is investigated by using one stage reverse osmosis permeates as feed solutions. The results show that the operating conditions including applied voltage, dilute flowrate, concentrate flowrate and feed conductivity significantly influence the resistivity of the EDI product. Under conditions of dilute flowrate of 36 L/h, concentrate flowrate of 3.8 L/h, and applied voltage of 36 V, a product stream with resistivity of 16-18 M · cm is achieved.

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... The effects of operating parameters on EDI performance are shown in Table 1. The main technological parameters determining the performance of EDI technique are the current strength and voltage, flow velocity in the diluate and concentrate compartment, temperature and ions concentration (inside both feed and product water), pressure, and the degree of conversion (Fedorenko 2003, Li et al. 2009, Salem 2000. The amount of ions transported through ion exchange membrane is directly proportional to current density (Ervan andWenten 2002, Kurup et al. 2009) and temperature (Song et al. 2005). ...
Electrodeionization (EDI), which combines electrodialysis (ED) and conventional ion-exchange (IX), is a mature process which has been applied since more than twenty years on commercial use for the production of ultrapure water (UPW). Eliminating chemical regeneration is the main reason for its commercial success. The increase in acceptance of EDI technology has led to an installation of very large plant as the commercial state of the art that produces 1,500 m3/h of water for high pressure steam boiler. More recently, EDI system has found a number of new interesting applications in wastewater treatment, biotechnology industry, and other potential field. Along with further growth and wider applications, the development of stack construction and configuration are also become a concern. In this paper, the principle of EDI process is described and its recent developments, commercial scale, and various applications are pointed out.
Electrodeionization (EDI), which combines the advantages of electrodialysis (ED) and conventional ion-exchange (IX) processes, has been successfully applied in the production of ultrapure water. With an ability to perform continuous and deep deionization process without regenerating chemicals, EDI has found a number of new interesting applications such as in wastewater treatment, separation and purification of biotechnology products, and other potential fields. The growing interest has necessitated the development of EDI stack construction and configuration to achieve a better performance. In addition, several studies have been performed to gain a better understanding of ion transfer mechanism in the EDI system. This paper focuses on the mechanism of ionic separation in EDI including the role of ion-exchange resin (IER) and water dissociation reaction as well as its effects on the deionization process. The main technological parameters determining EDI performance are overviewed. Membrane stack configurations along with their advantages and limitation and their development are also pointed out.
In this paper, the adsorption effects of two kinds of domestic anion exchange resins (201×7 and D407) to NO3 - in water were compared, as well as the adsorption effects of the anion resins mixed with cation exchange resins (001×7and D001) to NO3 - in water and performed the electro-regeneration experiment of the mixed resins were studied, in order to explore the feasibility of treating nitrate-contaminated groundwater by ionic exchange adsorption and electro-regeneration. The results of static adsorption showed that the adsorption quantum of 201×7 and D407 were 59 mg NO3 - /mL resin and 25 mg NO3 - /mL resin, respectively. The results of dynamic adsorption illustrated that the volume ratio between 201×7 and 001×7 was 6:4, there was hardly NO3 - existed of the effluent water and the conductivity of effluent was less than 5 �� s/cm. After the mixed resins were saturated, 10h's static and 80h's dynamic electro-regeneration experiment was performed, the NO3 - -N concentration of the effluent was less than 10mg/L and the regeneration rate of the resins was as high as 60%. The results of static and dynamic experiments illustrated that the intermittent technology of adsorption and electro-regeneration can realize the removal of NO3 - in water and achieve the purpose of reducing the energy consumption and avoiding secondary pollution caused by chemical regeneration. Keywords-ion exchange; volume ratio of the mixed resins; electro- regeneration; nitrate-contaminated
Electrodeionization (EDI) is being applied more and more to produce ultrapure water, especially in the semi-conductor industry. The continuous electrical regeneration of the ion-exchange (IEX) mixed bed is the main advantage of this recent technology. EDI couples two well known effects: electrodialysis and IEX. In spite of its rapid development, there are no established theories, design equations nor clear mechanisms of regeneration and transport. The present research work deals with EDI process efficiency. We have investigated the influence of the applied voltage V and the flow rate Q on cell efficiency by measuring current intensity I, and inlet Cin and outlet Cout concentrations of the treated solution. The efficiency R is defined by: R (%) = 100 (∆C/Cin) Q/Q where C = Cin−Cout and Q∆C = J is the mass transfer flux. The main finding was that an original, empirical, and simple equation between the efficiency R and the flow rate Q is established: R = K′∆VQ−n where n ≈ 0.5 or Log R = Log (K′∆V)−n Log (Q), a linear logarithmic equation between R and Q. The mass transfer flux J = Q∆C is then directly proportional to Q and inversely to Q:J=K⁢Qn≈K⁢Q0.5. This is an important result because it presents strong analogies with the habitual equations of electrochemical hydrodynamics (rotating, porous and packed-bed electrodes). The other interesting results are: (1) the current vs. voltage characteristic curve is constituted of three main linear parts, with an optimal zone (4.5–12 V); and (2) the water dissociation threshold voltage was clearly shown (12 V) and coincides with the beginning of a decrease in efficiency.
The transport of cobalt ion in a continuous electrodeionization (CEDI) system was investigated in terms of electrochemical properties of ion exchange textile. The porous plug model and an extended Nernst-Plank equation were applied to describe the transport of Co2+ through an ion exchange textile. The transport characteristics of Co2+ during CEDI operation suggested the transport mechanism was due mainly to the increased current induced by the high conductivity in the ion exchange textile, not accelerated ionic mobility. This study suggested the important parameter for the high performance of the CEDI system is the conductivity of the ion exchange media.