Electrodialysis is to use selective permeability of the ion exchange membrane to separate the electrolyte from the solution driven by the potential difference under the action of DC electric field, thereby achieving the purpose of desalination, concentration, purification of the solution. The core component of electrodialysis is the membrane stack. The membrane stack is mainly composed of electrodes and ion exchange membranes. The adjacent ion exchange membranes are separated by partitions.Showing as the following figure.

Schematic diagram of electrodialysis

The anion membrane only allows the anion to pass through; the cation membrane only allows the cation to pass through. As shown, under the action of a DC electric field, Na+ ions move toward the cathode and Cl- ions move toward the anode. Further, due to the selective permeability of the ion exchange membrane, Cl- ions can only pass through the anion exchange membrane, and Na+ ions can only pass through the cation exchange membrane. In the compartment where both Cl- ions and Na+ ions migrate out, the desalination chamber is referred to as a light chamber, and the compartment where Cl- ions and Na+ ions are moved into is a concentration chamber referred to as a concentrated chamber. The water flows from each of the rich and light compartments are separately collected to produce two main streams, desalinated water and concentrated brine.

Firstly,the electrodialysis membrane used must have high selectivity, low electrical resistance, high exchange capacity, low permeability, good mechanical and chemical properties, high anti-pollution performance and good cleaning recovery.

Secondly,the auxiliary equipment such as separators, electrodes, high-frequency switching power supplies, etc. must be high-performance, high-quality.They have been used at a large number of engineering field for a long time.Good sealing and zero leakage is required. High desalination efficiency with high degree concentration.

Thirdly, there are strict requirements for the control of operating current, voltage, pH, flow, pressure, etc., and strict control of the operating process.This can ensure higher efficiency of desalination and current while ensuring faster desalination rate.

Ensure that the design of the electrodialysis system is more scientific and reasonable, and the performance of the electrodialysis unit is more advanced and optimized.

Diagram of electrodialysis

Due to the large number of electrodialysis membrane reactors, an online cleaning tank and a washing pump are provided to wash the electrodialyzer periodically. When the electrodialysis unit is out of service, it is automatically rinsed for 3 to 5 minutes to remove dirt deposited on the surface of the membrane, so that the device and membrane are effectively maintained.

When the membrane unit is operated for a long period of time, it will accumulate some dirt that is difficult to be washed, such as organic matter, inorganic salt scale, etc., resulting in a decrease in membrane performance. This type of dirt must be cleaned with chemicals to restore film properties. Chemical cleaning is performed by cleaning device that includes two cleaning fluid tanks, cleaning pump, and associated piping, valves, and meters. When the membrane module is contaminated, it can be used for chemical cleaning of the membrane concentration system.

In fact, electrodialysis technology is a mature treatment technology, which has been successfully used in China's metallurgy, chemical industry, papermaking and other industries for many years. Because of the high salt content of electrodialysis (5000mg/l or more), the production water cannot be directly used in the power plant which limits the application of the technology in the power system. However, combined with the reverse osmosis technology, the electrodialysis water is used as the hydration of ordinary reverse osmosis, and the reverse osmosis concentration can continue to enter the electrodialysis concentration. At present, the core equipment of electrodialysis has been domestically produced for many years, and the quality of electrodialysis products has reached or exceeded the imported brands, which not only reduces the investment cost, but also brings great convenience for the promotion and application of electrodialysis technology and after-sales service.