Water Quality Output

Resistivity >15 MΩ·cm

Industry Standards

Ultrapure water quality is categorized into five industry standards: 18 MΩ·cm, 15 MΩ·cm, 10 MΩ·cm, 2 MΩ·cm, and 0.5 MΩ·cm, to differentiate between various water qualities.

Ion Exchange Method

The process is as follows:

Raw water → Raw water booster pump → Multi-media filter → Activated carbon filter → Water softener → Precision filter → Cation resin filter bed → Anion resin filter bed → Mixed bed of cation and anion resins → Microporous filter → Point of use

Batch Ion Exchange

This method involves mixing ion exchange resin with the raw water to be treated and stirring appropriately to achieve exchange equilibrium, ensuring the water quality meets design requirements after equilibrium. This method is typically used for small-scale production or experimental needs.

Fixed Bed Ion Exchange

This is a commonly used ion exchange method where ion exchange resin is placed in an exchange column, and the raw water to be treated flows through the resin bed at a certain velocity to achieve exchange. This method features simple equipment and easy operation, making it suitable for production of various scales. However, the resin utilization rate is low, and regeneration costs are high.

Two-Stage Reverse Osmosis Method

The process is as follows:

Raw water → Raw water booster pump → Multi-media filter → Activated carbon filter → Water softener → Precision filter → Primary reverse osmosis → pH adjustment → Intermediate water tank → Secondary reverse osmosis → Pure water tank → Pure water pump → Microporous filter → Point of use

EDI Method

Advantages of EDI Ultrapure Water Equipment Technology

EDI ultrapure water equipment is widely accepted in industries, microelectronics, power generation, and laboratories. Its applications in surface cleaning, surface coating, electrolysis, chemical industry, and solar photovoltaics are increasingly extensive.

EDI can replace traditional mixed ion exchange technology (MB-DI) to produce stable deionized water. Compared to mixed ion exchange technology, EDI offers the following advantages:

1. The amount of ion exchange resin used is small, approximately 5% of that used in traditional ion exchange methods.

2. Ion exchange resin does not require chemical regeneration with acids or alkalis, saving large amounts of acids, alkalis, and cleaning water, significantly reducing labor intensity.

3. No discharge of waste acid or alkali solutions, making it a clean production technology and an environmentally friendly product.

4. The process is easily automated, ensuring stable water quality. Combined with RO and other water treatment technologies, it can form a complete pure and ultrapure water production line.

5. High water quality output, meeting national electronic grade water Class I standards, with resistivity of 15–18 MΩ·cm and bacterial endotoxin content less than 0.1 mg/L, fully satisfying the requirements of the Chinese Pharmacopoeia and the United States Pharmacopoeia for pharmaceutical water.

6. Excellent removal capability for weakly ionized substances (such as carbon dioxide, silicon, boron, ammonia, etc.), making it more suitable for ultrapure water needs.

7. Continuous pure water production process, eliminating the need for duplicate setups like ion exchange beds where one is in use while another is regenerated.

Working Principle of EDI

The EDI module (membrane stack) is the core of EDI operation. A simple EDI membrane stack mainly consists of two electrodes with opposite charges and multiple module unit pairs. A membrane unit pair consists of a freshwater chamber (D-chamber) filled with cation and anion exchange resins, a cation membrane, an anion membrane, and a concentrate chamber (C-chamber). The EDI membrane stack contains multiple membrane unit pairs. Inside each membrane stack, there are two electrodes with a voltage of 600V, which is the necessary voltage for each membrane stack. The positive electrode carries a positive voltage, and the negative electrode carries a negative voltage, with current passing through 30 membrane units between the positive and negative electrodes. Each freshwater chamber contains cation and anion resins, equivalent to an 8-kilometer-thick mixed bed. A cation membrane separates the freshwater chamber from the concentrate chamber in the direction of the cathode, while on the other side, an anion membrane also separates the freshwater chamber from the concentrate chamber. The membranes used in EDI are very different from those used in reverse osmosis. Reverse osmosis membranes allow small molecular contaminants, ions, and water to pass through, while EDI membranes, like ion exchange resins, are made of polystyrene material and only allow ions with appropriate charges to pass through, with water essentially unable to pass. The resins are continuously regenerated through water dissociation.

In the electric field, water molecules in the feed water dissociate into H+ and OH-, which are attracted by opposite charges. H+ moves through the cation resin toward the cathode, and OH- moves through the anion resin toward the anode. This movement of H+ and OH- regenerates the resin. The cation membrane allows H+ to pass into the concentrate chamber, and the anion membrane allows OH- to pass into the concentrate chamber, where H+ and OH- combine to form water. The flow of water in the concentrate chamber carries away cations and anions from the water. The membranes prevent ions of opposite charges from entering the freshwater chamber. As water flows through the freshwater chamber, ions are removed by the resin, resulting in pure water on the effective side (freshwater chamber).

The operation process is as follows:

Raw water → Raw water booster pump → Multi-media filter → Activated carbon filter → Water softener → Precision filter → Primary reverse osmosis unit → Intermediate water tank → Intermediate water pump → EDI system → Microporous filter → Point of use

Process Flow

1. Pretreatment system → Reverse osmosis system → Intermediate water tank → Rough mixed bed → Fine mixed bed → Pure water tank → Pure water pump → UV sterilizer → Polishing mixed bed → Precision filter → End user (≥18 MΩ·cm) (Traditional process).

2. Pretreatment → Reverse osmosis → Intermediate water tank → Water pump → EDI unit → Purified water tank → Pure water pump → UV sterilizer → Polishing mixed bed → 0.2 or 0.5 μm precision filter → End user (≥18 MΩ·cm) (New process).

3. Pretreatment → Primary reverse osmosis → Dosing unit (pH adjustment) → Intermediate water tank → Secondary reverse osmosis (positively charged reverse osmosis membrane) → Pure water tank → Pure water pump → EDI unit → UV sterilizer → 0.2 or 0.5 μm precision filter → End user (≥17 MΩ·cm) (New process).

4. Pretreatment → Reverse osmosis → Intermediate water tank → Water pump → EDI unit → Pure water tank → Pure water pump → UV sterilizer → 0.2 or 0.5 μm precision filter → End user (≥15 MΩ·cm) (New process).

5. Pretreatment system → Reverse osmosis system → Intermediate water tank → Pure water pump → Rough mixed bed → Fine mixed bed → UV sterilizer → Precision filter → End user (≥15 MΩ·cm) (Traditional process). Each of the above processes has its own advantages, and you can choose the one that suits your needs based on your specific situation. With the advancement of science, many new processes have replaced old ones. Using reverse osmosis to produce high-purity water has become widespread and is the current standard process.