1、 EDI (Elctrodei onization) is a pure water manufacturing technology that combines ion exchange technology, ion exchange membrane technology, and ion electromigration technology. It cleverly combines electrodialysis and ion exchange technology, using high voltage at both ends of the electrode to move charged ions in water, and cooperating with ion exchange resin and selective resin membrane to accelerate ion movement and removal, thus achieving the goal of water purification. In the desalination process of EDI, ions are removed through ion exchange membranes under the action of an electric field. At the same time, water molecules generate hydrogen ions and hydroxide ions under the action of an electric field, which continuously regenerate the ion exchange resin to maintain its excellent state.

It utilizes the polarization phenomenon during the electrodialysis process to electrochemically regenerate the ion exchange packed bed, combining the advantages of electrodialysis and ion exchange methods and overcoming their limitations. EDI technology combines two mature water treatment technologies - electrodialysis technology and ion exchange technology, which are referred to as packed bed electrodialysis or electrodeionization technology in China. It mainly replaces traditional ion exchange mixed beds to produce high-purity water, and this water treatment product will become the mainstream equipment in the preparation of high-purity water engineering in this century. The application of this technology and related techniques will bring about fundamental changes in the existing water treatment technology, thereby achieving better environmental and economic benefits

High purity water is crucial for many industrial and commercial projects, such as semiconductor manufacturing and pharmaceuticals. Previously, the purified water used in these industries was obtained through ion exchange. However, membrane systems and membrane treatment processes are becoming increasingly popular as alternatives to pretreatment processes or ion exchange systems. Membrane systems such as electric desalination (EDI) can remove minerals cleanly and work continuously. Moreover, the membrane treatment process is much simpler mechanically than ion exchange systems, and does not require acid or alkali regeneration or wastewater neutralization. The EDI processing is one of the rapidly growing businesses in membrane processing. E D I is a non reverse electrodialysis (ED I) with a special water tank, in which the flow channels are filled with mixed bed ion exchange resin. EDI is mainly used to produce 8-17 megaohms of purified water from water sources with a total dissolved solids (TDS) of 1-20mg/L.

2、 Introduction to the principle of EDI system:

The desalination rate of EDI facilities can reach over 99%. If reverse osmosis equipment is used to preliminarily desalinate water before EDI, and then desalinated by EDI, ultrapure water with a resistivity of over 15M Ω· cm can be produced.

EDI membrane stack is composed of a certain number of units sandwiched between two electrodes. There are two different types of chambers within each unit: the fresh water chamber for desalination and the concentrated water chamber for collecting impurity ions removed. Fill the freshwater chamber with mixed cation and anion exchange resins located between two membranes: the cation exchange membrane that allows only cations to pass through and the anion exchange membrane that allows only anions to pass through.

The resin bed utilizes direct current applied at both ends of the chamber for continuous regeneration. The voltage causes water molecules in the inlet water to decompose into H+and OH -. These ions in the water are attracted by the corresponding electrodes and migrate through the cation and anion exchange resins towards the corresponding membranes. When these ions enter the concentrated water chamber through the exchange membrane, H+and OH - combine to form water. The generation and migration of H+and OH - are the mechanisms by which resins can achieve continuous regeneration.

When impurity ions such as Na+and CI - in the influent adsorb onto the corresponding ion exchange resin, these impurity ions will undergo ion exchange reactions similar to those in a regular mixed bed, and correspondingly displace H+and OH -. Once impurity ions in the ion exchange resin are also added to the migration of H+and OH - towards the exchange membrane, these ions will continuously pass through the tree fingers until they pass through the exchange membrane and enter the concentrated water chamber. These impurity ions cannot further migrate towards the corresponding electrode due to the blocking effect of adjacent compartment exchange membranes, so they can concentrate in the concentrated water chamber, and then the concentrated water containing impurity ions can be discharged from the membrane stack.

For decades, the preparation of pure water has come at the cost of consuming a large amount of acidity and alkalinity. During the production, transportation, storage, and use of acidity and alkalinity, environmental pollution, equipment corrosion, potential harm to human health, and high maintenance costs are inevitable. The use of reverse osmosis greatly reduces the amount of acid and alkali used. The widespread use of reverse osmosis and electric desalination will bring an industrial revolution to the preparation of pure water.

3、 Characteristics of EDI system

The performance of an EDI system is not solely determined by the technical level of the module itself, but also by the rationality of its compatibility with the EDI system and the stability of the incoming water. As a system, EDI system should strive to improve overall safety and stability, which is closely related to the reliability of DC power supply and changes in module internal resistance.

The advantages of EDI system are as follows:

The quality of the produced water is high and stable.

Continuous and uninterrupted water production, without stopping due to regeneration.

No need for chemical regeneration.

Thoughtful stacked design with small footprint.

Low operating and maintenance costs.

No acid or alkali reserves and transportation costs.

Fully automatic operation, no need for dedicated supervision.

4、 Process flowchart of high-purity water