1、 Basic Definition and Core Principles
EDI (Electrodeionization) is a deep water treatment technology that combines electrodialysis (ED) with ion exchange resin technology. Through the action of an electric field, it efficiently removes ions from water and continuously regenerates the resin, without the need for traditional chemical agents. It can produce high-purity water (close to theoretical pure water). The core principle is as follows:
Ion exchange: Ions in water are adsorbed by ion exchange resin filled in a freshwater chamber.
Electric field driven migration: Under the action of a direct current electric field, cations migrate towards the cathode and pass through the cation exchange membrane (C membrane), while anions migrate towards the anode and pass through the anion exchange membrane (A membrane), entering the concentrated water chamber to purify the water quality of the fresh water chamber.
Resin self regeneration: The H ⁺ and OH ⁻ generated by water electrolysis continuously regenerate the resin, restoring its exchange capacity and achieving continuous operation without stopping the machine for regeneration.
2、 Technical Structure and Key Components
The typical structure of an EDI module consists of multiple compartments, with core components including:
Ion exchange membrane:
Cation exchange membrane (C membrane): allows only cations to pass through and blocks anions.
Anion exchange membrane (A membrane): allows only anions to pass through and blocks cations.
Ion exchange resin:
Filled in a freshwater chamber, it adsorbs ions from water and is divided into cationic resin (H-type) and anionic resin (OH type).
Electrode and electric field:
The anode (positive electrode) and cathode (negative electrode) provide a direct current electric field to drive ion migration; Oxidation reaction occurs near the anode to generate O ₂, and reduction reaction occurs near the cathode to generate H ₂.
Water flow channel:
Freshwater chamber: The water to be treated passes through and produces pure water after removing ions.
Concentrated water chamber: Collect ions migrated from the fresh water chamber to form concentrated water for discharge.
Polar water chamber: an independent channel near the electrode, through which polar water flows to remove electrode reaction products (such as H ₂, O ₂).
3、 Technical advantages
Advantages of traditional ion exchange/electrodialysis comparison
The conductivity of high-purity produced water can reach 0.05-0.5 μ S/cm (close to theoretical pure water), far exceeding traditional resin processes.
Continuous operation, no need for chemical regeneration, water electrolysis, self regenerating resin, eliminating acid-base agents, reducing wastewater discharge and manual operation.
Low operating costs save pharmaceutical expenses, low energy consumption (about 0.3-0.6 kWh/m ³), and simple maintenance.
The compact and efficient equipment has a volume of only 1/3-1/2 of traditional resin systems, with high integration and suitable for modular design.
Environmentally friendly, safe, and free from chemical pollution, in line with the trend of green water treatment, especially suitable for environmentally sensitive scenarios.
4、 Process flow and operation points
Typical process:
Pre treated water (such as RO produced water) → EDI module → high-purity water production
Pre treatment requirement: Most ions (conductivity<20 μ S/cm) need to be removed by reverse osmosis (RO) to prevent the resin from saturating too quickly.
Key control parameters:
Inlet water temperature: 25-35 ℃ (optimal efficiency, ion migration rate decreases at low temperatures).
Working voltage/current: Adjust according to water quality, usually voltage 50-200V, current 0.5-2A.
Concentrated water/extreme water flow rate: The concentrated water flow rate is generally 5-10% of the fresh water flow rate, and the extreme water flow rate is 1-3%. It is necessary to control the concentration of concentrated water ions to prevent membrane fouling.
PH value: The pH of the influent should be between 6-9 to avoid excessive resin load or membrane damage.
5、 Application Fields
EDI technology is widely used in industries that require extremely high water quality, with typical scenarios including:
Electronic semiconductors: Ultra pure water (conductivity ≤ 0.055 μ S/cm) is used for chip manufacturing and wafer cleaning to prevent circuit defects caused by metal ion contamination.
Pharmaceutical industry: Preparation of water for injection (WFI) and purified water (PW) in accordance with USP, EP, Chinese Pharmacopoeia and other standards to ensure drug production safety.
Power industry: Boiler feedwater treatment for thermal/nuclear power plants to avoid scaling and corrosion, and extend equipment life (such as water conductivity<0.1 μ S/cm).
Laboratory and scientific research: The laboratory ultrapure water system (such as resistivity 18.2 M Ω· cm) meets the needs of precision analysis, cell culture, and other applications.
Chemical and New Energy: Production water for lithium battery electrolytes and electronic grade solvents to ensure chemical purity and process stability.
6、 Common Problems and Solutions
Resin pollution and lifespan:
Reason: Insufficient pretreatment leads to organic matter, colloids, or metal ions (such as Fe ³ ⁺, Al ³ ⁺) blocking the resin pores.
Solution: Strengthen pre-treatment (such as activated carbon filtration, softening), and regularly clean the resin with dilute acid/alkali solution (such as 1-2 times a year).
Membrane fouling:
Reason: The concentration of Ca ² ⁺, Mg ² ⁺, CO ∝ ² ⁻ and other substances in the concentrated water chamber is too high, resulting in the formation of calcium carbonate/magnesium precipitates.
Solution: Add scale inhibitors (such as polyphosphate), control the conductivity of concentrated water to be less than 500 μ S/cm, or dilute the ion concentration using concentrated water circulation mode.
Decrease in water quality:
Reason: resin aging, membrane damage, or electrode efficiency degradation.
Solution: Replace resin or membrane components, check electrode connections and voltage stability.
7、 Technological development trends
Energy saving: Developing low voltage and high selectivity membrane materials to reduce energy consumption (such as new nanocomposite membranes).
Miniaturization and Integration: Modular design suitable for decentralized water use scenarios (such as containerized EDI systems for field research).
Intelligent monitoring: integrating online conductivity and flow sensors with PLC control system to achieve fully automatic operation and fault warning.
Concentrated water treatment technology: Combining membrane distillation, evaporation crystallization and other processes to achieve zero discharge of concentrated water and improve environmental benefits.
summary
EDI technology, with its high efficiency, environmental friendliness, and continuous water production characteristics, has become a core technology in the field of high-purity water treatment. With the continuous improvement of water quality requirements in industries such as semiconductors and pharmaceuticals, EDI will continue to innovate in energy-saving membrane materials, intelligent system integration, and other directions, promoting the green and digital transformation of the water treatment industry.
Post time: Jun-09-2025