250 L/h EDI Ultra-Pure Water Generation System · Technical Overview

Water resistivity ≥ 18.25 MΩ·cm (25°C) | Pilot-scale validation of the ultrapure water system for production line

Water production rate: 250 L/h; Resistivity: 18.25 MΩ·cm; Dual-stage RO + EDI + Polishing Mixed Bed with Acid-Base Continuous Regeneration; PLC-controlled fully automatic system.

I. Equipment Overview

This equipment is a modular ultrapure water (UPW) generation system designed for pilot-scale production lines, with a rated output capacity of 250 L/h and a stable water resistivity of 18.25 MΩ·cm (at 25°C) – corresponding to the water quality grade defined by the theoretical maximum conductivity of pure water (0.055 μS/cm). The system employs a proven process chain comprising "pre-treatment + dual-stage reverse osmosis (RO) + EDI (Electrodeionization) + polishing mixed bed + UV sterilization + final filtration"; its effluent meets the stringent requirements for trace ions, TOC, particulates, and microorganisms in pilot-scale validation and precision cleaning applications across the electronics, pharmaceutical, and chemical industries.

With equipment as the core design objective, the EDI section employs DC power to drive continuous desalination, while the polishing mixed-bed serves as the final refinement step; together, these technologies overcome the theoretical upper limit of single-stage EDI (typically 5–18 MΩ·cm), ensuring long-term compliance with the 18.25 MΩ·cm specification.

250 L/h rated water output (20°C)

18.25 MΩ·cm – Electrical resistivity (25°C)

≥ 75% overall system recovery rate

0 Acid–Base EDI Continuous Regeneration

II. Process Flow Diagram

To maintain a consistent water quality of 18.25 MΩ·cm, the system employs a six-stage stepwise desalination process. The water quality changes at each stage are as follows:

Raw water → Raw water tank/泵 → Multi-media filtration → Activated carbon filtration → Softener → Protective filter (5 μm) → Primary RO → Secondary RO → RO intermediate water tank → EDI module → Polishing mixed bed → UV disinfection → Final 0.22 μm filtration → Ultra-pure water tank → Water usage point

Water quality at inlet and outlet of each section (typical values)

III. Detailed System Component Overview – System Components

3.1 Pre-treatment Unit

• Raw water tank + raw water pump: Buffers fluctuations in raw water supply and maintains a constant water supply pressure (≥0.25 MPa).

• Multi-media Filter: Quartz sand/anthracite filter media for removing suspended solids, iron and manganese colloids, and reducing the SDI.

• Activated carbon filter: Adsorbs residual chlorine and organic compounds to protect the subsequent RO membrane (residual chlorine concentration must be <0.1 ppm).

• Softener: Sodium-based cation exchange resin for removing Ca²⁺/Mg²⁺ hardness and preventing scaling in RO/EDI systems.

• Security filter: 5 μm melt-blown filter element – intercepts leakage particles from the upstream section, protecting the high-pressure pump and membrane elements.

3.2 Reverse Osmosis (RO) Unit

• Two-stage RO: First-stage desalination ≥98%; second-stage further refined desalination; total desalination rate> 99.5%.

• High-pressure pump: Each stage is equipped with a vertical stainless steel pump, optionally paired with a variable-frequency drive or energy recovery system for energy efficiency.

• Membrane elements: Wound aromatic polyamide composite membranes (e.g., DOW/Times Warford), anti-fouling design.

• Concentrated wastewater recycling: Secondary concentrate can be recycled back into the raw water tank, increasing the overall recovery rate of the pumping system to over 75%.

3.3 EDI Deionization Unit (Core)

• Membrane stack configuration:淡水室(filled with mixed ion-exchange resin)+ concentrate room, separated by alternating anion/cation exchange membranes.

• Operating voltage/current: DC power supply (typically 0–600 V / mA), with constant-current or constant-voltage operation.

• Continuous regeneration: The DC electric field drives the directional migration and removal of ions; the resin does not require acid-or alkali-based regeneration.

• Inlet water conditions: conductivity ≤ 20 μS/cm, hardness <1 ppm, TOC <0.5 ppm, temperature 5–45°C.

3.4 Polishing and Final Finishing Unit

• Polished mixed-bed: Nuclear-grade cation and anion resins (mixed in a 1:1 ratio) – increased resistivity from ~17 MΩ·cm to 18.25 MΩ·cm.

• UV sterilizer (185/254 nm): 254 nm germicidal action; 185 nm degradation of TOC <5 ppb.

• Terminal filter: 0.22 μm (or 0.1 μm) bag-type filter element, which intercepts particles and bacteria to ensure the purity of the point-of-use water.

• Ultra-pure water tank: Made of PE or stainless steel (inert material); equipped with a nitrogen-sealed or breathing filter to prevent secondary contamination; features a recirculation design.

IV. EDI Working Principle

EDI (Electrodeionization) is a coupled technology combining electrodialysis and ion exchange. Under the influence of a direct current electric field:

1. The anions and cations in the freshwater chamber migrate directionally toward the positive and negative electrodes, respectively, under the influence of the electric field;

2. Cations pass through the cation-selective membrane, while anions pass through the anion-selective membrane into the adjacent concentrate chamber;

3. The ion exchange resin filled in the freshwater chamber accelerates ion conduction and captures migrating ions;

4. Water undergoes slight hydrolysis (water cleavage) on the resin surface, generating H⁺/OH⁻ ions, thereby regenerating the resin in situ and enabling continuous self-regeneration;

5. The concentrated stream, after ion enrichment, is discharged or recycled; the freshwater chamber continuously produces high-purity water.

Compared to traditional mixed-bed systems, EDI does not consume acids or bases, eliminates the discharge of acidic or alkaline wastewater, and allows for continuous operation – making it the mainstream approach in green ultrapure water technology. However, it requires a high inlet water purity; therefore, a two-stage RO pre-treatment system is necessary; for the final stage (resistivity of 18.25 MΩ·cm), a polishing mixed-bed system is still employed as a backup.

V. Main Technical Specifications

VI. Product Water Quality Indicators

The produced water meets the typical requirements for laboratory/industrial-scale ultrapure water (closely aligning with GB/T 11446.1 EW-Ⅰ and ASTM D1193 Type I):

If the pilot-scale process imposes extremely stringent requirements on metal ions (e.g., Cu, Fe, Zn) or boron (B), a dedicated boron-and metal-removal fine-column may be installed after the polishing stage, or a degassing membrane (membrane degassing) may be added to further reduce dissolved oxygen and CO₂ levels.

VII. Equipment Features & Advantages

Process and Water Quality

• Two-stage RO + EDI + polishing mixed-bed system – stable resistivity of 18.25 MΩ·cm

• Continuous water production with minimal water quality fluctuations, ideal for long-term pilot-scale operation

• Low TOC, low particulate matter, and low microbial contamination risk

Operation and Cost

• EDI acid–base regeneration – no waste acid or base discharge – environmentally friendly

• High level of automation, minimal human intervention, and low operational and maintenance costs

• Modular integration – compact footprint, facilitating the setup and relocation of pilot-scale workshops

VIII. Automatic Control and Monitoring

• PLC + Touchscreen HMI: One-touch start/stop, automatic flushing, fault self-diagnosis and alarm.

• Online instruments: water resistivity/conductivity meter, flowmeter, pressure transmitter, RO feedwater conductivity, pH (optional).

• Safety Interlock: Low-pressure/high-pressure protection, pump dry-run protection, water tank level linkage, and EDI water shortage power-off protection.

• Data logging: Historical storage of operational parameters; supports USB/Ethernet export for ease of pilot-scale testing.

IX. Installation, Commissioning and Maintenance

X. Typical Application Areas

• Pilot-scale validation line: Pilot-scale scale-up of ultrapure water supply and water quality validation for new processes and new materials.

• Electronic semiconductors: High-purity water for cleaning, development, and wet processing applications (sensitive to trace metals).

• Pharmaceuticals and Biotechnology: Pre-treatment of Water for Injection (WFI), formulation preparation, and laboratory analysis.

• Chemicals and Energy: Applications requiring high-purity water – e.g., battery materials, catalysts, surface treatment, etc.

• Analytical testing: ICP-MS, HPLC, TOC analysis, and other trace-level detection methods – requiring ultrapure water.