Electrodeionization and Deionized Water

Electrodeionization (EDI) is a water treatment technology used for producing ultra-pure water. This process utilizes electricity, ion exchange resins and membranes. The two separation technologies; membranes and ion exchange, are combined into one sealed, self-contained unit.

The primary use of electrodeionization (EDI) has focused on Reverse Osmosis (RO) permeate polishing. RO EDI 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 in electrodeionization makes this an attractive technology for use in a wide range of industries including pharmaceutical and power generation to provide very high levels of demineralisation.

Electrodeionization (EDI) works by splitting the water into two streams within the EDI cell; these being known as dilute and concentrate. The electrical current generated in the EDI cell causes 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 compartment. 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 Reverse Osmosis (RO) plant. The dilute quality is commonly > 12 megohm.

The electrical current generated within the electrodeionization (EDI) cell creates H+ and OH- ions, which bring about continuous regeneration of the ion exchange resin within the dilute compartment. The continuous nature of this electrodeionization process leads to the further referencing of this technology as Continuous Electrodeionization (CEDI). This is a very effective process for thus, continuous operation can be achieved without the need for downtime to accommodate regeneration, meaning that the electrodeionization (EDI) process can offer stable product quality and the ability to produce consistent quality high-purity water without the need for chemical regeneration.

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