Electrodeionization (EDI) is a chemical-free, continuous water purification process that uses a combination of ion exchange membranes, ion exchange resins, and an electric field to remove ionized and ionizable species from water. Applied after reverse osmosis (RO) for further polishing, EDI continuously regenerates the ion exchange resins using electricity, producing high-purity water without chemical consumption or regeneration downtime, making it an environmentally friendly alternative to traditional mixed-bed ion exchange (IX) systems.
How EDI Works
- 1. Ion Transport:
An applied direct current (DC) creates an electric field that forces positively charged ions (cations) to migrate towards the negative electrode and negatively charged ions (anions) towards the positive electrode. - 2. Ion Exchange:
The water flows through a series of chambers containing ion exchange resins and ion-selective membranes. - 3. Membrane Separation:
Cation exchange membranes allow only cations to pass through, while anion exchange membranes permit only anions. - 4. Continuous Regeneration:
Impurity ions are collected in a concentrate stream, and the ion exchange resins are continuously regenerated by the H+ and OH- ions produced by the dissociation of water molecules at the electrodes, eliminating the need for chemical regenerants.
Key Benefits
- Chemical-Free:
No hazardous chemicals are used for regeneration, making it an environmentally friendly process. - Continuous Operation:
Unlike conventional IX systems, EDI operates continuously with no regeneration downtime. - High Purity Water:
Achieves very low levels of conductivity, silica, and other ionizable species. - Space-Saving:
EDI plants often have a compact, modular design.
Common Applications
- Electronics Industry: Produces ultrapure water for rinsing microchips.
- Power Plants: Provides corrosion-free, high-purity boiler feedwater.
- Pharmaceutical and Biotechnology: Ensures high-quality water for sensitive processes.
- Laboratories and Hospitals: Produces water meeting stringent purity standards.
- Food and Beverage: For reusing residual water and chemical production.
