Ultrapure water (UPW) is produced through a combined process of multi-stage physical filtration, membrane separation, electrochemical deionization, ultraviolet oxidation, and adsorption to almost completely remove impurities such as ions, organic matter, particles, microorganisms, and dissolved gases from water. The final product has a resistivity approaching the theoretical limit of 18.25 MΩ·cm at 25°C.
1. Pretreatment Stage
- Multi-media filter: Removes sediment, rust, and suspended solids via screening and interception.
- Activated carbon filter: Adsorbs residual chlorine, organic compounds, and odors.
- Water softener (optional): Removes calcium and magnesium ions via cation exchange to prevent scaling.
- Security filter (5 μm): Protects subsequent components by trapping residual particles.
2. Reverse Osmosis (RO) – Core Desalination
Under high pressure (2–6 MPa), water molecules pass through a semi-permeable RO membrane (pore size ≈ 0.0001 μm), rejecting 98–99% of salts, bacteria, viruses, colloids, and macromolecular organics.
3. Electrodeionization (EDI) – Deep Deionization
Combines ion-exchange resin and a DC electric field to continuously remove trace ions. Water ionization regenerates the resin without chemicals, producing high-purity water (5–18 MΩ·cm).
4. Polishing Stage
- Polishing mixed bed: Nuclear-grade resin for final ion removal to reach 18.2 MΩ·cm.
- UV oxidation (185 nm & 254 nm): Degrades TOC and kills bacteria.
- Degassing membrane / vacuum degassing: Removes dissolved CO₂, O₂, and other gases.
5. Terminal Filtration
0.22 μm ultrafiltration / microfiltration removes residual particles and microorganisms for sterile, particle-free ultrapure water.
Complete Process Flow
Raw Water → Pretreatment → RO → EDI → Polishing Mixed Bed → UV Oxidation → Degassing → Terminal UF → Ultrapure Water (18.25 MΩ·cm)
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