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Desalination
Published in Frank R. Spellman, Hydraulic Fracturing Wastewater, 2017
Electrodeionization (EDI) involves ion exchange resins, ion exchange membranes, and a direct electrical current (DC) (Figure 7.21). The distinguishing characteristic of an EDI system, as compared to a standard ED system, is that its desalting compartments are filled with an ion exchange resin. Ions are transported to the ion exchange resin by diffusion; they are then transported through the resin by the current. The current flows through the ion exchange resin because this is the path of least resistance. This process is capable of removing weakly ionized species and desalting water to very low concentrations. The advantage of EDI over desalting technologies is that its use decreases chemical usage by as much as 90% and the volume of the chemical wastestream by approximately 50%. EDI also has a smaller footprint and reduced operating and capital costs.
Electro-membrane processes for the removal of trace toxic metal ions from water
Published in Alberto Figoli, Jan Hoinkis, Jochen Bundschuh, Membrane Technologies for Water Treatment: Removal of Toxic Trace Elements with Emphasis on Arsenic, Fluoride and Uranium, 2016
Svetlozar Velizarov, Adrian Oehmen, Maria Reis, João Crespo
Electrodeionization (EDI) is a hybrid process combining ion-exchange with electrodialysis by introducing ion-exchange resins into the electrodialysis chambers. The combination allows for treating very dilute electrolyte solutions, while the ion-exchange resin beads inside the chambers are continuously regenerated in-situ by hydrogen and hydroxide ions produced by water electrolysis occurring in the two external electrode compartments (Monzie et al., 2005). Therefore, the EDI process has received increasing attention in the purification of solutions containing toxic metal ions (Dzyako and Belyakov, 2004; Grebenyuk et al., 1998; Mahmoud and Hoadley, 2012; Spoor et al., 2002a; 2002b).
Electromembrane Processes in Water Purification and Energy Generation
Published in Sundergopal Sridhar, Membrane Technology, 2018
Sujay Chattopadhyay, Jogi Ganesh Dattatreya Tadimeti, Anusha Chandra, E. Bhuvanesh
Ultrapure water is usually recommended for electronic and pharmaceutical industries. Electrodeionization (EDI) is a unique technique that can provide ultrapure water at very low cost. This is a hybrid separation process involving the ion exchange resins and ion exchange membranes. EDI technique has gained tremendous attention these days because it can deliver ultrapure water as well as recover some precious ionic species from contaminated water. The technique is independent of the nature of the electrolytes that are present in the feed solution (Arar et al., 2014). Usually, weakly-ionized species, such as CO2 and boron, pose difficulties during separation via RO and ED. EDI is capable of continuous removal of these species to a very high degree of removal. Crucial process parameters that influence the efficiency of an EDI module are current density, flow velocity both in feed and concentrate streams, temperature and TDS of the feed solution. Laktionov et al. (1999) introduced ion exchange textile as conducting spacers in ordinary electrodialysis and experimented on a pilot scale to prepare ultrapure water. The pressure drop was found to be much lower with ion exchange spacers relative to commonly used resin beads. Thus, it becomes cost effective. Strathmann (2010) gave a detailed description of ED technique and the appropriate modifications required to make ED process a continuous operation instead of a batch process. In some cases, the continuous electro-deionization unit contains mixed bed resins in the diluate chamber, while in another set of design, cation and anion exchange resins are placed in separate chambers with a partition of bipolar membrane between them. Detailed description of this technique may be found elsewhere (Strathmann, 2010; Laktionov et al., 1999).
Recent developments of electromembrane desalination processes
Published in Environmental Technology Reviews, 2018
Derya Y. Koseoglu-Imer, Ahmet Karagunduz
Electrodeionization (EDI) is a technique in which ion exchange media and ED system are combined. The transport of species causes the potential gradient between the ion-exchanger bed and membranes [31]. In EDI stack, the diluate or concentrate cells have specific ion exchange filler which can be a bed of ion-exchange resin granules, ion-exchange textile, conducting spacer or organic porous ion exchange material. In any case, the primary distinction from ED system is the deionization mechanism: the electro-migration of salt particles in EDI system is occured by ion-exchange media and the salt ions are exchanged with H+ and OH− groups in the ion-exchange media [32]. A shematic diagram of EDI mechanism is shown in Figure 2. In the system, there are basically three compartments named as electrode compartment, concentrating and diluting compartments. Therefore, it contains two ion selective membranes: anion permeable and cation permeable membranes. The membranes are located in between concentrating and diluting compartments. During operation, the feed water enters the diluting compartment of EDI module, ions are attracted to their respective counter electrodes under an electrical field. Then, ions are exchanged with H+ and OH− ions and moved through the anion exchanger and cation exchanger resins. Anions in diluting compartment are passed by AEM to concentrating compartment also cations by CEM which can then be drained or be recycled. Feed water turns the deionized product water and it can then be used directly or undergo further treatment for enhanced water purity [33,34]. The mechanism removal of ions in an EDI cell has two stages: (i) diffusion of cations to the strong cation exchanger and dissemination of the anions to the strong anion exchanger; and (ii) ionic conduction of the solid phase to the border of the membranes. Because the ion concentration within the solid is very high, the process that controls ion removal is the ion diffusion rate of the aqueous phase to the surface of the solid ion exchange, which depends of three factors: (1) surface between solid and solution; (2) thickness of the liquid layer through which ions diffuse; and (3) concentration gradient between the solid and liquid phase [35]. Thus, EDI process can be summarized by three simultaneous stages: (1) ion exchange stage between resin beads and impurity ions in diluating compartment; (2) transportation of ions via an applied external electric field through AEM and CEM; (3) regeneration of resin beads by electricity [36].