Working principle editing EDI system is a scientific water treatment technology, which is mainly used to purify water quality by the selective permeation of ions by exchange membrane under the action of DC electric field. Between a pair of electrodes of electrodialyzer, a plurality of groups of negative membranes, positive membranes and separators (A and B) are alternately arranged to form a concentrated chamber and a weak chamber (i.e., cations can pass through the positive membrane and anions can pass through the negative membrane). Cations in the light chamber water migrate to the negative electrode and pass through the positive membrane, and are intercepted by the negative membrane in the concentrated chamber; Anions in the water migrate to the cathode direction and are intercepted by the anode membrane in the concentrated chamber, so that the number of ions in the water passing through the light chamber gradually decreases and becomes fresh water, while the concentration of dielectric ions in the concentrated chamber continuously rises due to the continuous influx of anions and cations in the concentrated chamber, and becomes concentrated water, thus achieving the purpose of desalination, purification, concentration or refining. [1] 3 System Features Editing Since the industrialization of EDI membrane stack technology in 1986, thousands of EDI systems have been installed all over the world, especially in pharmaceutical, semiconductor, electric power and surface cleaning industries, and also widely used in wastewater treatment, beverages and microorganisms. EDI equipment is applied to reverse osmosis system, replacing traditional mixed bed ion exchange technology (MB-DI) to produce stable ultrapure water. Compared with mixed ion exchange technology, EDI technology has the following advantages: (1) stable water quality; (2) easy realization of full-automatic control; (3) no shutdown due to regeneration; (4) EDI system without chemical regeneration; (5) low operating cost; (6) small plant area; (7) no sewage discharge; (7) EDI working principle: EDI module fills ion exchange resin between anion/cation exchange membranes to form EDI unit. The working principle of EDI is shown in the figure. In EDI module, a certain number of EDI units are separated by grids to form concentrated water chamber and fresh water chamber. And cathode/anode electrodes are arranged at both ends of the cell group. Under the impetus of direct current, the anions and cations in the water flow passing through the fresh water chamber respectively pass through the anion exchange membrane and enter the concentrated water chamber to be removed in the fresh water chamber. The water passing through the concentrated water chamber takes ions out of the system and becomes concentrated water. EDI equipment generally uses secondary reverse osmosis (RO) pure water as EDI feed water. The resistivity of RO pure water is generally 40-2μS/cm(25℃). The resistivity of EDI pure water can be as high as 18 mω cm (25℃), but according to the use of deionized water and system configuration, EDI ultra-pure water is suitable for preparing pure water with resistivity of 1-18.2 mω cm (25℃). 4 Application field editing 1. Semiconductor and electronics industry-ultrapure water 2. Biological and pharmaceutical industry-purified water 3. Power plant-boiler make-up water 4. Surface painting 5. Consumption and cosmetics industry 6. Replacing all kinds of distilled water 7. Other industries with high requirements on water purity [1] 5 Operation impact editing Main factors affecting EDI system operation (1) Influence of EDI inlet water conductivity. Under the same operating current, with the increase of the conductivity of raw water, the removal rate of weak electrolyte by EDI decreases, and the conductivity of effluent also increases. If the conductivity of raw water is low, the content of ions will be low, and the low concentration of ions will make the EMF gradient formed on the surface of resin and membrane in the light chamber large, which will lead to the enhancement of water dissociation degree, the increase of limit current and the generation of more H+ and OH-, thus making the regeneration effect of anion and cation exchange resin filled in the light chamber good. (2) The influence of working voltage and current. With the increase of working current, the quality of produced water becomes better. However, if the current is increased after reaching the highest point, due to the excessive amount of H+ and OH- ions produced by water ionization, a large number of surplus ions act as current-carrying ions to conduct electricity except for regeneration of resin. At the same time, due to the accumulation and blockage of a large number of current-carrying ions in the process of moving, and even reverse diffusion, the quality of produced water decreases. (3) The influence of turbidity and pollution index (SDI). The water production channel of EDI module is filled with ion exchange resin. Excessive turbidity and pollution index will block the channel, resulting in the increase of system pressure difference and the decrease of water production. (4) The influence of hardness. If the residual hardness of inlet water in EDI is too high, it will lead to scaling on the membrane surface of concentrated water channel, decrease the flow rate of concentrated water and decrease the resistivity of produced water; Affect the quality of produced water, and in severe cases, block the concentrated water and polar water channels of the module, resulting in the destruction of the module due to internal heating. (5) The influence of 5)TOC. If the content of organic matter in influent is too high, it will cause organic pollution of resin and selectively permeable membrane, which will lead to the increase of system operating voltage and the decrease of produced water quality. At the same time, it is easy to form organic colloid in the concentrated water channel and block the channel. (7) the influence of CO2 in influent water. HCO3- produced by CO2 in influent water is a weak electrolyte, which easily penetrates the ion exchange resin layer, resulting in the decline of produced water quality. (8) The influence of total anion content (TEA). High TEA will reduce the resistivity of EDI water production, or need to increase EDI operation current, while too high operation current will lead to the increase of system current and residual chlorine concentration in polar water, which is unfavorable to the life of polar membrane. In addition, inlet water temperature, pH value, SiO2 and oxides also affect the operation of EDI system. Control measures of system inlet water quality index (1) Control of inlet water conductivity. Strictly controlling the conductivity during pretreatment to make the conductivity of EDI inlet water less than 40μS/cm can ensure the qualified conductivity of outlet water and the removal of weak electrolyte. (2) Control of working voltage and current. When the system works, it should select the appropriate working voltage and current. At the same time, there is a limit voltage-current point on the voltage-current curve of EDI water purification equipment, which is related to the influent water quality, the performance of membrane and resin and the structure of membrane pair. In order to generate enough H+ and OH- ions to regenerate a certain amount of ion exchange resin, the voltage-current working point of the selected EDI water purification equipment must be greater than the limit voltage-current point. (3) the control of influent CO2. Alkali can be added before RO to adjust pH to remove CO2 to the maximum extent, or degassing tower and degassing membrane can be used to remove CO2. (4) Control of inlet water hardness. Combined with CO2 removal, RO influent can be softened and alkali added. When the salt content of influent water is high, it can be combined with desalination to increase primary RO or nanofiltration. (5)TOC control. Combined with other index requirements, first-class RO is added to meet the requirements. (6) Control of turbidity and pollution index. Turbidity and pollution index are one of the main indexes for influent control of RO system, and the qualified RO effluent can generally meet the influent requirements of EDI. (7)Fe control. The Fe of EDI influent is controlled to be lower than 0.01 mg/L .. If the resin has been poisoned, acid solution can be used for recovery treatment, and the effect is better. [1] (8) EDI system inlet water quality requires comprehensive analysis of the above aspects. The EDI inlet water quality requirements are shown in the table, which can ensure that its outlet water index meets the requirements of high-purity water required by semiconductor manufacturing in the electronics industry. EDI application service EDI technology is widely accepted by pharmaceutical industry, microelectronics industry, power generation industry and laboratories. It is widely used in surface cleaning, surface coating, electrolytic industry and chemical industry. YR-EDI influent requires that the total exchangeable cations (including CO2) should be < 25mg/l (calculated by CaCo3), the PH value should be 5-9, the hardness should be < 0.1 < 0.5 < 0.75 < 1.0, and the recovery rate should be 95%, 90%, 85%, 80% and active SiO2 should be < 0.5mg/ L total organic carbon (TOC) < 0.5mg/L free oxygen < 0.5mg/L YR-EDI technical specification parameters range single module flow rate 7.2-15GPM(1.6-3.4m3/ H) normal recovery rate of 80-95%, temperature of 40-100 f (5to 38 c), inlet pressure of 45-100psi(3.1-6.8Bar), input voltage of 600VDC (maximum), power consumption of 0.32-0.66KW.h/m3, overall dimensions of 12 "wx24" hx19 "d3 2. A group of on-line side monitoring instruments for resistivity and conductivity in Hanna, USA; 3. Power control system: The main electrical components are Schneider, Omron and domestic high-quality devices, which are controlled by PLC, electric ball valves and Schneider electrical components; Performance advantages 1. It can continuously and stably produce high-quality pure water without downtime due to resin regeneration; 2. No pollutant is discharged, which is environmentally friendly and saves investment in waste liquid treatment; 3. The equipment has compact structure, small occupied area and space saving