Electro deionization (EDI) is a mature electrically driven membrane demineralization process used to refine industrial process water to ultra-high purity for use in the power, microelectronics, food, chemical, pharmaceutical, and other industries.
CWT's EDI systems utilize high-capacity ion exchange membranes to remove not only residual salts, but also ionizible aqueous species such as carbon dioxide, silica, ammonia and boron.
EDI provides several advantages over more traditional ion-exchange processes by:
-Eliminating the need for expensive and hazardous chemicals used in the ion exchange resin regeneration process.
-Reducing energy and operating expenses
The heart of the EDI process is a stack of components similar to a plate and frame heat exchanger, or filter press. Feed water flows in a thin sheet between ion exchange membranes through the EDI stack where a direct current (DC) electrical field drives salt ions dissolved in the feed water into adjacent concentrating compartments. The feed water compartment also contains mixed bed ion exchange resin beads. This resin facilitates the ionization of certain neutral (ionizable) species such as carbon dioxide or weakly ionized species such as bicarbonate, which are then transferred via the DC field through the semi permeable membranes.
The result is high-purity product water that typically contains silica in the single digit parts per billion (ppb) range, which contains so few ions that product quality is measured by resistance of water in the meg-ohm range. For example, a typical CWT EDI product contains less than 2 ppb silica and measures 16-18 meg-ohm-cm.

The EDI Process (animation)
CWT EDI product water typically meets or exceeds required specifications in the microelectronics and power industries.
Removal efficiencies for species of interest are as follows:
-Ammonia removal >99%
-Boron removal >96%
-Carbon dioxide removal >99%
-Silica removal 95%-99%
-Sodium and chloride removal >99%