Continuous Electrodeionization Technology

Permeate polishing that is cost-effective, dependable and chemical-free.

EDI is a continuous, chemical-free process that uses DC power to remove ionized and ionizable substances from feedwater. EDI is a clever alternative to–and successful substitute for–conventional mixed bed ion exchange (IX) for polishing reverse osmosis (RO) permeate. Using electrodeionization to regenerate resin in mixed beds avoids the need to store and handle dangerous chemicals. This method of permeate polishing does not produce a hazardous waste stream because EDI’s only consumable is electricity.

The EDI module is made up of a series of chambers separated by ion exchange membranes and filled with ion exchange resins. Water enters the module where ions are forced to migrate through the resins and over the membranes by an applied electrical field at right angles to the flow. These impurity ions are not permanently linked to the media but rather gather in concentrate streams that can be drained or recycled. The deionized product water can be utilized right away or it can be treated further to improve its purity.

The advantage of electrodeionization is that the ion exchange beds in EDI systems are continually regenerated, which means they do not deplete as quickly as batch-mode ion exchange beds. Because the contaminants are eliminated by the concentrates, the resin is not overworked. An EDI unit can last for many years before it needs to be replaced. Using this method, product water resistivity of >15 is typically produced. Single-use purification cartridges can be replaced with this technology, and EDI can give more consistent purity than single-bed ion-exchange systems, which may liberate weakly bound ions as the media exhausts in addition to the practical advantages and reduced downtime of not changing cartridges. In comparison to an ion-exchange bed, the smaller volumes of resin in an EDI module limit the release of organic contaminants.