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In recent decades, mixed bed ion exchange technology has been the standard process for ultra-pure water preparation. Because periodic regeneration is needed, and large quantity of chemicals and pure water must be used during the process of regeneration, which will cause environment issues, acid- and alkali-less ultra-pure water system needs to be developed.

Traditional ion exchange technology can no longer meet the demand for modern industry and environment protection. Therefore, the EDI technology combining membrane, resin and electrochemistry principles becomes a revolution in water treatment technology. It uses electricity instead of acid or alkali for regeneration of ion exchange resin, thus meeting the demand for modern environment protection.

Since industrialization of EDI membrane deposit technology in 1986, several thousand sets of EDI systems have been installed in the world The technology has been vigorous developed in pharmaceutical, semi-conductor, electric power and surface cleaning industry, etc., and widely adopted in waste water treatment, beverage and micro-organism sectors.
EDI device is applied after reverse osmosis system to replace traditional mixing ion exchange technology. EDI technology has following advantages.

1. Stable water quality

2. Easy automatic control

3. Non breakdown for regeneration

4. Not need to chemical regenerate

5. cheap operation cost

6. Small space occupation

7. No sewage discharge
Theory of EDI SYSTEM
EDI device has ion exchange resin between anion and cation ion exchange membrane to form EDI unit. The working principle is shown in following figure. In an EDI component, certain quantities of EDI units are separated by mesh to form dense water chamber, and positive and negative electrodes are setup at the two ends of EDI unit. Driven by DC current, anion and cation ions passing the fresh water chamber penetrate the anion and cation ion exchange membrane to enter dense water chamber, thus they are got rid of from the fresh water chamber. Water passing the dense water chamber brings the ions out of the system to become dense water. EDI device usually adopts RO pure water as EDI feed water. Conductivity of RO pure water is generally 40-2|IS/cm (25 ), while resistivity of EDI pure water can be as high as 18 (25 ). However, according to purpose of deionized water and system configuration, EDI device is suitable for preparing pure water of 1-18.2 (25 ) resistivity.