Electrodialysis reversal

F. H. WeUer, ed.. Electrodialysis (ED) and Electrodialysis Reversal (EDR) Technology, Ionics, Inc., Watertown, Mass. 

Electrodialysis Reversal. Electro dialysis reversal processes operate on the same principles as ED however, EDR operation reverses system polarity (typically three to four times per hour). This reversal stops the buildup of concentrated solutions on the membrane and thereby reduces the accumulation of inorganic and organic deposition on the membrane surface. EDR systems are similar to ED systems, designed with adequate chamber area to collect both product water and brine. EDR produces water of the same purity as ED. 

The use of reverse osmosis (RO), electrodialysis reversal (EDR) and other membrane techniques, and evaporation or demineralization may be applicable when a reduction in the TDS content of the MU water source is required. 

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). 

Electrodialysis reversal is a development of ED and is also employed either in its own right for the production of basic pure water or as a component in a larger system for very pure or ultrapure water. 

Electrodialysis reversal can produce water of below 5 pS/cm conductivity (sometimes lower) the membranes are essentially impervious to fouling, and the polarity reversal provides an excellent membrane and cell compartment cleaning mechanism. This technology lends itself to an all-membrane approach (triple-membrane process) for the production of high-purity water employing UF/EDR/RO. 

In addition to these three treatments, there are several alternative treatment technologies applicable to the treatment of common metals wastes. These technologies include electrolytic recovery, electrodialysis, reverse osmosis, peat adsorption, insoluble starch xanthate treatment, sulfide precipitation, flotation, and membrane filtration.1516... 

AC, activated carbon CA, citric acid EDR, electrodialysis reversal EDTA, ethylenediamine-tetraacetic acid MF, microfiltration UF, ultrafiltration. 

In the practical application of electrodialysis there are two main process operation modes. The first one is referred to as the unidirectional electrodialysis and the second as electrodialysis reversal [22]. In a unidirectional operated electrodialysis system the electric field is permanently applied in one direction and the diluate and concentrate cells are also permanently fixed over the period of operation. Unidirectional operated electrodialysis plants are rather sensitive to membrane fouling and scaling and often require a substantial feed-solution pretreatment and stack-cleaning procedures in the form of periodical rinsing of the stack with acid or detergent solutions. The unidirectional operating concept is mainly used today for applications in the... 

Membrane separation techniques, which are used mainly in industrial processes, include dialysis, electrodialysis, reverse osmosis, ultrafiltration,... 

FIGURE 40 (a) Electrodialysis and (b) electrodialysis reversal (EDR). Cation exchange membrane indicated by C and anion exchange membrane by A (Ionics Inc.)... 

Other methods to achieve bitartrate stability, rarely used in the North Coast, are addition of metatartaric acid, electrodialysis, reverse osmosis, and ion exchange. Concern with potential bitartrate instability varies from winery to winery. Some enologists prefer to keep the processing of wine to a minimum. They rely solely on cool fermentation and winter storage temperatures to precipitate excess bitartrates. They trust their customers will overlook any additional bitartrate crystals that precipitate out in bottled wines. 

Enoch et al. [90] used electrodialysis reversal (EDR) to prepare boiler makeup water for Dutch power stations from several types of surface waters. EDR uses automatic reversal of electrode polarity at regular time intervals to minimize membrane scaling. The EDR unit contained 200 anion and cation exchange membrane pairs, each with a surface area of 0.47 m. Polarity reversal occurred every 15, 20, or 25 min. Samples of surface water were desalted by 96% at an energy consumption of 1 kWh/m of product water and at a current density (8.3 A/cm ) that was 80% of the limiting current density (current density when the surface water cation concentration at the membrane surface drops to zero). 

A recent innovation by a U.S. manufacturer of ED systems has significantly minimized the need for pretreatment. This innovation, known as electrodialysis reversal (EDR), operates on the same basic principle as the standard electrodialysis unit, except that both the product and the brine cells are identical in construction. At a frequency of 3-4 times/hr, the polarity of the electrodes is reversed and the flows are simultaneously switched by automatic... 

Mansouri, M., Electrodialysis reversal units used as predemineralizer in boiler... 

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