1. The basic principle, characteristics and scope of application of electrodialysis
The electrodialysis method used in the desalination of brackish water is abbreviated as ED. It is a membrane separation technology that uses an ion exchange membrane to separate the anions and cations in the salt water under the action of an electric field, thereby reducing the salt concentration in the fresh water chamber to obtain fresh water. Electrodialysis device utilizes the directional migration of ions under the action of an electric field, and achieves the purpose of desalination through a selective permeability ion exchange membrane. Under the action of an external DC electric field, the ions in the water migrate in a direction (the cation exchange membrane only allows cations to pass through, and the anion exchange membrane only allows anions to pass through), so that most of the ions in one kind of water migrate to another kind of water. This technology is relatively mature, and has the main advantages of simple process, high salt removal rate, low water production cost, convenient operation, and no environmental pollution. In the 1950s, the United States and the United Kingdom began to use this method for brackish water desalination, and in the 1980s, China used this method for brackish water desalination, industrial pure water and ultrapure water manufacturing.
The main components of an electrodialyser are anion and cation exchange membranes, separators and electrodes. The compartment formed by the partition plate is the channel through which the liquid flows, the compartment through which the fresh water passes is the desalination chamber, and the compartment through which the concentrated water passes is the concentration chamber. The anion and cation exchange membranes and the concentrated and fresh water separators are alternately arranged, repeated and superimposed, and a pair of end electrodes are added to form an electrodialyzer. Electrodialyzers can be assembled in three ways: one-stage and one-stage (large water production, for large and medium-sized), one-stage multi-stage (higher desalination rate, small water production, for small and medium-sized), and multi-stage and multi-stage. There are vertical and horizontal installation methods.
2. Application characteristics of electrodialysis method in brackish water desalination project
(1) The removal rate of soluble inorganic salts such as iron, magnesium, calcium, potassium, chloride and other toxicological indicators arsenic and fluoride by electrodialysis reaches 66 percent to 93 percent , which can meet the needs of brackish water desalination;
(2) The removal rate of oxygen consumption, NH32N, NO-32N, NO22N and silicon by electrodialysis is low, only 15 percent to 45 percent . However, due to the low content of the above indicators in the raw water, the removal rate is low, but it can still meet the requirements Hygienic requirements for drinking water;
(3) The removal rate of SO2-4 by electrodialysis is 63.8 percent , which is used to desalinate SO-42Na type and SO4·Cl2Na type water, which is difficult to meet the sanitary requirements of drinking water;
(4) The energy consumption of the electrodialysis process is closely related to the salt content of the feed water. The higher the salt content of the feed water, the greater the energy consumption. Therefore, electrodialysis is more suitable for desalination of low-salt brackish water. In addition, due to the inability of electrodialysis to remove organic matter and bacteria in water, and the large energy consumption of equipment operation, its application in brackish water desalination projects is limited. replaced by the device.
