Core Process Overview :
Tap Water → Pretreatment → Primary RO Reverse Osmosis → Secondary RO Reverse Osmosis → EDI Electrodeionization → Terminal Polishing → Ultrapure Water
Step 1: Pretreatment — The "Basic Line of Defense" for Ultrapure Water Preparation
As raw water, tap water contains various impurities such as sediment, rust, colloids, residual chlorine, organic matter, and calcium and magnesium ions. If it directly enters subsequent core equipment, it will cause membrane clogging and equipment damage, seriously affecting the purity of ultrapure water and the service life of the system. The core of pretreatment is "rough purification", which removes most large-particle impurities and lays the foundation for subsequent deep purification. It is an indispensable first step in ultrapure water preparation and the cornerstone of ensuring long-term stable operation of the system.
Specific Steps :
Multimedia Filtration: Uses filter media such as quartz sand and anthracite to intercept large-particle impurities (particle size ≥ 5μm) such as sediment, rust, and suspended solids in tap water, reduces raw water turbidity, purifies water quality, and reduces the processing burden of subsequent processes. It is the first line of defense in pretreatment.
Activated Carbon Filtration: Uses the developed pore structure of activated carbon to adsorb residual chlorine, odors, and macromolecular organic matter in tap water, and also removes some colloidal impurities, avoiding oxidative corrosion of subsequent RO membranes by residual chlorine, further improving the cleanliness of raw water, and preparing for the reverse osmosis link.
Softening Filtration: Through ion exchange resin, replaces calcium and magnesium ions in tap water, converts hard water into soft water, prevents scaling of subsequent equipment from the source, avoids clogging of RO membranes and EDI modules, extends the service life of core equipment, and it is recommended to control the effluent hardness ≤ 0.1mg/L.
Precision Filtration (Security Filtration): Uses a 5μm precision filter element to intercept tiny impurities not removed in the previous steps, ensuring that the water entering the RO reverse osmosis system meets the water inlet requirements (SDI pollution index < 3), completely protecting the RO membrane from scratches and clogging. It is the last key process in pretreatment.
Water Quality Standards After Pretreatment: Turbidity ≤ 0.1 NTU, residual chlorine ≤ 0.05 mg/L, SDI ≤ 3, hard water turned soft, no obvious impurities, which can directly enter the RO reverse osmosis link, adapting to the pretreatment needs of industrial ultrapure water in most industries.
Step 2: RO Reverse Osmosis — The "Core Purification" for Ultrapure Water Preparation
Although the water after pretreatment has removed large-particle impurities, it still contains a large number of ions, small-molecular organic matter, microorganisms, etc., which cannot meet the water needs of high-end fields. RO (Reverse Osmosis) is the core link in ultrapure water preparation, known as the "gatekeeper of water purification". Its core function is to deeply remove more than 98% of ions, organic matter, and microorganisms in water, realizing the key leap from tap water to pure water, and it is one of the core technologies in ultrapure water preparation.
Double-stage RO reverse osmosis is essential for high-end ultrapure water (single-stage can be used for ordinary pure water to adapt to different water quality needs). Specific steps:
Primary RO Reverse Osmosis: Driven by a high-pressure pump, the pretreated water passes through the RO membrane (pore size only 0.1-1nm, equivalent to one millionth of a hair), intercepting most cations (Na+, Ca2+,Mg2+), anions (Cl-, SO42-), organic matter, microorganisms and other impurities in the water. The product water conductivity is ≤ 10 μS/cm, the desalination rate can reach more than 98%, providing qualified inlet water for the secondary reverse osmosis.
Secondary RO Reverse Osmosis: Performs secondary deep purification on the primary RO product water, further removing residual trace ions and small-molecular organic matter, ensuring that the product water conductivity is ≤ 5 μS/cm and SiO2 ≤ 200 ppb, providing the optimal inlet water conditions for the subsequent EDI electrodeionization link, avoiding trace impurities affecting the EDI product water purity. It is an essential step in ultrapure water preparation for high-end industries such as semiconductors and pharmaceuticals, which can greatly improve the stability of the final ultrapure water.
Key Reminder: The RO membrane is a core consumable, and its quality directly determines the reverse osmosis effect. It is recommended to select high-quality RO membrane elements, and perform regular cleaning and maintenance, which can effectively extend the service life and reduce operating costs. It is also one of the core points in the operation and maintenance of the ultrapure water system.
Step 3: EDI Electrodeionization — The "Deep Desalination" for Ultrapure Water Preparation
The water treated by double-stage RO reverse osmosis has reached the pure water standard, but there are still residual trace ions, which cannot meet the scenarios with extremely high purity requirements such as semiconductors and laboratories (requiring resistivity ≥ 15 MΩ·cm). EDI (Electrodeionization) is the core technology for deep desalination of ultrapure water, which does not require acid-base regeneration, is environmentally friendly and efficient, can completely remove trace ions in pure water, and realize the leap from pure water to ultrapure water. It is the mainstream deep desalination method in modern ultrapure water preparation, replacing the traditional ion exchange mixed bed process, and solving the pain points of high pollution and cumbersome operation and maintenance of the traditional process.
Core Principle of EDI Electrodeionization: Driven by an electric field, trace ions in pure water migrate directionally through ion exchange membranes, and at the same time, self-regeneration is realized with the help of ion exchange resin, without adding acid-base chemical reagents. It is not only environmentally friendly but also can realize continuous and stable water production, avoiding the problems of frequent regeneration of the traditional ion exchange process and the generation of a large amount of chemical wastewater, which is in line with the development trend of green and environmental protection industry.
Water Quality Standards After EDI Treatment: Resistivity can reach 15-18.2 MΩ·cm (25℃), TOC ≤ 1 ppb, microorganisms ≤ 10 CFU/mL, basically meeting the primary ultrapure water standard, which can meet the basic water needs of most high-end industries, and its performance directly determines the purity level of the final ultrapure water.
Step 4: Terminal Polishing — The "Ultimate Guarantee" for Ultrapure Water
The ultrapure water treated by EDI has met the needs of most industries, but for extremely harsh scenarios such as semiconductor wafer cleaning, lithography, and pharmaceutical water for injection, terminal polishing is still required to completely remove residual trace particles, organic matter, and dissolved gases, ensuring that the ultrapure water meets international standards, avoiding product defects and experimental errors caused by tiny impurities. It is the ultimate guarantee for the qualification of ultrapure water purity, which can further improve the stability of water quality and adapt to the harsh requirements of high-end scenarios.
Specific Steps of Terminal Polishing:
The polishing mixed bed is the terminal precision processing unit of the ultrapure water system, which deeply purifies the EDI produced water to 18.2M Ω· cm, stabilizes water quality, eliminates fluctuations, and ensures the ultimate water purity at the terminal.
UV Sterilization: Uses 185nm + 254nm dual-wavelength UV lamps. On the one hand, it kills residual microorganisms in the water; on the other hand, it decomposes trace organic matter (TOC) in the water into CO? and water, ensuring TOC ≤ 1 ppb, avoiding product quality or experimental results affected by organic pollution, and preventing water quality pollution by microbial metabolites.
Ultrafiltration (UF): Uses a 0.1μm ultrafiltration membrane to intercept nano-scale particles, colloidal silica, bacterial fragments, etc., in the water, ensuring that the particle content ≤ 1 piece/mL (particle size ≥ 0.1 μm), especially suitable for the harsh requirements of the semiconductor industry, avoiding tiny particles adhering to the wafer surface, leading to chip short circuits and performance failure.
Degassing Treatment: Removes dissolved gases (O2, CO2, etc.) in the water through a degassing membrane or nitrogen-sealed circulation system, ensuring that the dissolved gas ≤ 10 ppb, avoiding bubbles forming on the wafer surface affecting the lithography and etching effects, and preventing the decrease of ultrapure water resistivity caused by CO2 dissolution, ensuring water quality stability. It is one of the key difficulties in semiconductor ultrapure water preparation.
After terminal polishing, the final ultrapure water is produced, and the core indicators fully meet international standards: resistivity 18.2 MΩ·cm (25℃, theoretical maximum purity), TOC ≤ 1 ppb, microorganisms ≤ 10 CFU/mL, particle content ≤ 1 piece/mL (particle size ≥ 0.1 μm), dissolved gas ≤ 10 ppb. It can be directly used in various harsh scenarios such as semiconductors, pharmaceuticals, photovoltaics, and high-end laboratories, realizing the complete transformation from tap water to ultrapure water, and meeting the high-end water needs of different industries.