Overview
EDI (Electrodeionization) ultra-pure water equipment is an advanced water treatment device primarily used for producing ultra-pure water with a resistivity of 15-18.2 MΩ·cm. It integrates the advantages of electrodialysis (ED) and ion exchange technologies. Through the synergistic effect of an electric field and ion exchange resins, it achieves efficient removal of ions in water while avoiding the frequent chemical regeneration required by traditional ion exchange resins. This equipment is widely used in fields with extremely high water quality requirements, such as semiconductors, electronics, pharmaceuticals, laboratories, photovoltaics, and precision machinery, providing stable ultra-pure water for high-end manufacturing and scientific research.
Working Principle
I. Pretreatment Stage
Raw water (usually reverse osmosis (RO) product water or preliminarily treated water) first passes through a precision filter to remove suspended solids, colloids, and other physical impurities, ensuring the water quality entering the EDI module meets requirements (e.g., SDI < 1, residual chlorine < 0.05 mg/L). This prevents contamination of the ion exchange resins and membrane components inside the EDI module.
II. Core Treatment in the EDI Module
The EDI module is the core component of the equipment, consisting of anion/cation exchange resins, anion/cation exchange membranes, and electrodes, divided into freshwater chambers, concentrate chambers, and electrode chambers:
1. Ion Exchange Process:
When raw water enters the freshwater chamber, anions and cations in the water are adsorbed by the corresponding ion exchange resins. After the resins are saturated, the ions migrate to the concentrate chamber through adjacent anion/cation exchange membranes.
2. Electrodialysis Regeneration Process:
A DC electric field is applied across the two ends of the module. Under the electric field, ions adsorbed by the resins are desorbed and migrate to the concentrate chamber through ion exchange membranes. Anion and cation exchange membranes have selective permeability, allowing only anions or cations to pass through, thus achieving directional ion migration and concentration.
3. Water Electrolysis and Resin Regeneration:
Part of the water molecules are electrolyzed into H⁺ and OH⁻ under the electric field. These ions "self-regenerate" the ion exchange resins, restoring their exchange capacity without additional chemical regenerants.
III. Ultra-Pure Water Production and Concentrate Discharge
After treatment in the EDI module, the water flowing out of the freshwater chamber is ultra-pure water with a resistivity of up to 18.2 MΩ·cm. The ion concentration in the concentrate chamber increases significantly; part of the concentrate can be recycled to the pretreatment system, and the remaining concentrate is discharged as wastewater.
Performance Characteristics
I. Ultra-High Purity and Stability
- The resistivity of the produced water can reach up to 18.2 MΩ·cm, with stable water quality and minimal fluctuations, meeting the needs of water-sensitive scenarios such as semiconductor wafer cleaning and biopharmaceutical solution preparation.
- It effectively removes dissolved salts, colloids, organic matter, bacteria, and other impurities in water, with TOC (total organic carbon) reducible to below 10 ppb and silicon content < 1 ppb.
II. Environmentally Friendly
- Eliminates the need for chemical regeneration of traditional ion exchange resins, avoiding the generation and discharge of acid-base waste liquid, which is environmentally friendly.
- Low energy consumption, with operating costs only 30%-50% of those of traditional mixed-bed processes.
III. Automation and Low Maintenance
- High integration allows fully automatic operation via a PLC control system, with real-time monitoring of water quality parameters (e.g., resistivity, flow rate, pressure).
- Modular design facilitates installation and maintenance, with simple and quick replacement of resins or membrane components and a long maintenance cycle (usually 3-5 years for membrane stack replacement).
IV. High Efficiency and Energy Saving
- The electric field-driven ion migration is much more efficient than traditional resin exchange, with a footprint only 1/3-1/2 of that of mixed beds for the same water production capacity.
- Capable of continuous water production without shutdown for regeneration, suitable for 24-hour industrial operations.
Structural Components
I. Pretreatment Unit
- Precision Filter: Typically a 5μm filter element to remove particulate impurities from raw water and protect the EDI module.
- Security Filter(Optional): Some systems are equipped with UV sterilizers or degassing membranes to further remove residual chlorine or CO₂, preventing resin oxidation or carbonate ion interference.
II. EDI Module
- Membrane Stack: Composed of alternating anion/cation exchange membranes, resin layers, and spacers, serving as the core component for ion separation.
- Electrode Assembly: Includes anodes, cathodes, and electrode chambers to provide a DC electric field and discharge electrolytic gases (e.g., H₂, O₂).
- Inlet and Outlet Ports: Including raw water inlet, ultra-pure water outlet, concentrate outlet, and electrode water outlet.
III. Control System
- PLC Control Cabinet: Integrated with water quality monitoring instruments (resistivity meter, conductivity meter), flow sensors, pressure sensors, etc., to automatically adjust operating parameters and trigger alarms in case of faults.
- Human-Machine Interface (HMI): Displays real-time water quality data and operating status, supporting remote monitoring and parameter setting.
IV. Auxiliary Systems
- Concentrate Recycle Pump: Some systems have a concentrate recycling device to improve water recovery (up to 70%-90%).
- Cleaning System: Periodically performs chemical cleaning (e.g., acid cleaning, alkali cleaning) on the EDI module to remove contaminants (e.g., metal oxides, organic matter) from the resin and membrane surfaces.
Application Cases
I. Semiconductor and Electronics Industry
- Application Scenarios: Wafer cleaning in chip manufacturing, photoresist preparation, and rinsing of electronic components.
- Value: The ion content in ultra-pure water directly affects chip yield. EDI equipment ensures water quality meets SEMI standards, supporting the production of advanced processes below 14nm.
II. Pharmaceutical Industry
- Application Scenarios: Preparation of water for injection (WFI), bioreactor cleaning, and drug formulation.
- Value: Complies with FDA and Chinese Pharmacopoeia (ChP) requirements for purified water and WFI, and can be directly used in sterile drug production.
III. Photovoltaic and Optoelectronics Industry
- Application Scenarios: Cleaning of silicon wafers and glass substrates in solar panel production.
- Value: Removes metal ions (e.g., Na⁺, Fe³⁺) and particulate impurities to avoid short circuits in solar cells or reduced light transmittance.
IV. Laboratory and Research Fields
- Application Scenarios: Ultra-pure water preparation in university research laboratories and testing institutions (e.g., for HPLC and ICP-MS analysis).
- Value: Provides stable ultra-pure water to meet the stringent water quality requirements of precision instruments and reduce experimental errors.
Conclusion
EDI ultra-pure water equipment has become an indispensable core device in high-end manufacturing and research due to its high efficiency, environmental friendliness, and stability. With the increasing water quality requirements in semiconductor, new energy, and other industries, EDI technology is evolving toward higher water production efficiency and lower energy consumption, and it will play a key role in more cutting-edge fields in the future.
