Continuous Electrodeionization Technology
Permeate polishing that is cost-effective, dependable and chemical-free.
EDI is a chemical-free, continuous process that uses direct current power to remove ionized and ionizable substances from feedwater. For polishing reverse osmosis (RO) permeate, EDI is a clever alternative to–and a successful substitute for–conventional mixed bed ion exchange (IX). The use of electrodeionization to regenerate resin in mixed beds eliminates the need for hazardous chemicals to be stored and handled. In addition, because EDI only uses electricity as a consumable, this permeate polishing method produces no hazardous waste.
The EDI module includes a series of chambers linked together by ion-exchange membranes and filled with ion exchange resins. Water enters the module and is forced to migrate through the resins and across the membranes by an electrical field applied perpendicular to the flow. As a result, these impurity ions do not remain permanently bound to the media. Still, they accumulate in drainable or recyclable concentrate streams. Finally, the deionized product water is ready for use or further purification.
The advantage of electrodeionization is that the ion exchange beds in EDI systems are constantly regenerated, so they do not deplete as quickly as batch-mode ion exchange beds. Because the concentrates remove the contaminants, the resin is not overworked. As a result, an EDI unit can be used for many years before being replaced. This method usually yields a product with a water resistance more significant than 15 M.cm. In addition to the convenience and reduced downtime associated with cartridge replacement, this technology can be used in place of single-use purification cartridges, and EDI can provide more consistent purity than single-bed ion-exchange systems, which may release weakly bound ions as the media exhausts. When compared to an ion-exchange bed, the smaller resin volumes in an EDI module limit the release of organic contaminants.