Electro-De-Ionisation (EDI) is the use of two separation technologies, membranes and ion exchange, combined into one sealed, self-contained unit. The primary use of EDI has focused on RO permeate polishing. This technology is widely used in industry as a final polisher replacing traditional ion exchange units, which require chemical regeneration using base and acid reagents. The lack of chemical usage makes this an attractive technology for use in a wide range of industries including pharmaceutical and power generation.

Within the EDI cell the water is split into 2 streams, dilute and concentrate. The electrical current generated in the EDI cell cause ions present in the dilute stream to migrate across a “bridge” of ion exchange resin beads until they pass through a semi-permeable membrane into the concentrate department. The concentrate stream typically represents around 10% of the EDI feedwater and is rejected, routinely back to front end collection before once again passing through the RO plant. The dilute quality is commonly > 12 megohm.

The electrical current generated within the EDI cell creates H+ and OH- ions, which bring about continuous regeneration of the ion exchange resin within the dilute compartment. As a result continuous operation can be achieved without the need for downtime to accommodate regeneration.

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