Electrodialysis involves the passage of electric current through brackish or low salinity water in a chamber in which many closely spaced ion selective membranes are placed, thus dividing the chamber into compartments. The electric current causes the salts to be concentrated in alternate compartments with reduced salt content in the remainder. The constraints of electrodialysis are such that feed-waters up to 2 000 p.p.m. may be processed to give a product with 300 p.pjn. total dissolved solids. Where a high purity product is desired the costs may be unacceptable compared to water obtainable from distillation. A principal disadvantage of electrodialysis is that power consumption is proportional to total dissolved solids and its range of cost and performance effectiveness is with low salinity waters. Also high sodium chloride content in the feed-water will require a product purity of less than 250 p.p.m. which also adds to the cost - this restriction also applies to reverse osmosis.

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