Electrodeionization (EDI) is a process of continuous demineralization of water using ion-exchange resins, ion-selective membranes and direct electric current (strength field). The resulting water is deeply demineralized, with a resistance of 12 to 18 MΩ * cm, as after ion-exchange filters of mixed action of the FSD type.

The main carrier force of the electrodeionization processes is the potential difference of a constant electric field (electric voltage) on both sides of the membrane channel formed by an anion-exchange and cation-exchange membrane filled with an ion-exchange resin (a mixture of cation and anion exchange resin). It is the constant voltage that ensures the transfer of dissolved ions from the desalinated water stream through ion-selective membranes to the discharged stream of concentrated water, thereby causing continuous regeneration of the ion exchanger. The source water for these CEDI systems is the permeate (desalinated flow) of reverse osmosis systems, with a salinity of 0.1-10 mg/l.

Application:

– pharmaceuticals;

– energy;

– semiconductor production.

The electrodeionization process is carried out in a cell, which consists of alternating cavities separated by anion- and cation-selective membranes. Semi-permeable ion-exchange membranes are arranged so that they form parallel chambers bounded by electrodes (cathode and anode) on both sides. The source water enters a series of dilution chambers (clean water chambers). A constant electric current is passed through all the chambers, causing the ions to migrate towards the respective electrodes. A cation exchange membrane separates the dilution chamber from the concentration chamber. The concentrate is recirculated in the concentration chambers, promoting mixing and turbulence of the flow over the membrane surface and maintaining electrical conductivity. The delution chambers into which the source water is supplied are filled with ion-exchange resins of the same size and having a spherical shape. The electrical current makes it possible for the ions to move continuously through the ion exchange resin, i.e. from the feed water stream to the concentrate stream. The electric current also decomposes water molecules into hydrogen cations and hydroxyl anions. Ions entering the delution chamber pass through the ion exchange resins and ion exchange membranes in the direction of the electrical potential gradient and enter the concentrate chamber. The concentration of ions in the dilution chamber will decrease (water demineralization occurs), and in the concentration chamber it will increase (brine concentrate is formed).

Advantages of the EDI process compared to mixed bed filters:

– no need for chemicals;

– continuous mode of operation;

– stability of water quality;

– lack of drains;

– reduction of capital and operating costs.