In semiconductor fabrication, the use of reverse osmosis (RO) is considered essential to achieve the
purity levels necessary for wafer production.
In power plants, increased recognition of the effect of ultrapure water quality on system component life has resulted in demand for membrane systems which can render an even higher purity of water than mixed-bed deionization systems alone can achieve (e.g. lower TOC, particles, etc.). Such high levels of demineralization can be obtained using electrodeionization (EDI). EDI combines ionexchange resins, ion-exchange membranes, and a direct (DC) electric field. Basically, EDI is an electrodialysis (ED) process modified by the addition ofion-exchange resin. When EDI is used for the production of high purity water, the ion-exchange resin beads enhance mass transfer, facilitate water splitting, and reduce stack resistance.
The ionexchange resin exchanges ions with the incoming feed stream. The DC electrical field splits water into hydrogen and hydroxyl ions, which, in turn, continuously regenerate the ion-exchange resins. The exchanged ions are transferred through the membranes to the brine stream and flushed from the system.1,2 Compared to conventional ion exchange, EDI has the advantage of being a continuous process with constant stable product quality, which is able to produce ultra high purity water without the need for acid or caustic regeneration.
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