EDI (Electrodeionization)

EDI in the context of water treatment stands for Electrodeionization. It is a high-level water purification technology used to produce ultrapure water, usually after the Reverse Osmosis (RO) process.

Here is the full explanation

Definition of EDI (Electrodeionization)

Electrodeionization (EDI) is the process of removing dissolved ions from water using a combination of ion exchange resin and an electric field.
Unlike conventional deionization that requires chemicals to regenerate the resin, EDI systems do not require additional chemicals because resin regeneration occurs continuously with the help of electricity.

Working Principle of EDI

The EDI process combines three main components:

1. Ion exchange resin - Absorbs positive (cations) and negative (anions) ions from water.

2. Ion exchange membrane - A specialized membrane that passes only certain ions.

3. DC (direct current) electric field - Moves ions through the membrane to be removed from the system.

RO water enters the EDI module → ions such as Ca²⁺, Na⁺, Cl-, SO₄²- are removed → very high purity water (up to 18.2 MΩ-cm resistivity) is produced.

Advantages of EDI over conventional systems

• No need for chemical regeneration (no strong acids and bases).

• Continuous operation without regeneration cycles.

• Environmentally friendly as no chemical waste is generated.

• Stable and high water quality, suitable for semiconductor, pharmaceutical, and power generation industries.

Linkage with RO System

Typically, an ultrapure water treatment system has a sequence like this:

Pretreatment → Reverse Osmosis (RO) → EDI → Polishing filter

EDI serves as the final stage (polishing) to remove residual ions that RO cannot remove.

Common Applications of EDI

• Pharmaceutical industry (making water for injection/WFI)

• Power plant (boiler feed water)

• Electronics and semiconductor industry

• Laboratory and hospital