Product Introduction

The 2 T/H ultrapure water system combines reverse osmosis (RO) and continuous electrodeionization (EDI) to produce high-purity water from municipal tap water. The process train is: pre-treatment → reverse osmosis → EDI.

Pre-treatment

Pre-treatment conditions the raw water so that it meets the feed requirements of the RO unit, reducing and delaying membrane fouling and extending membrane life. It removes micro-organisms, bacteria, colloids, organic matter, heavy-metal ions, solid particles and free chlorine. The pre-treatment section consists of a sand filter, a carbon filter, an anti-scale dosing unit and a security filter.

• Sand filter — removes mud, sand, impurities and suspended solids from the water and lowers the SDI (silt density index) of the raw water.
• Carbon filter — has a dual function: adsorption and filtration. It removes chemical organic matter, heavy metals, colour, odour and residual chlorine from the water and improves water quality.
• Anti-scale dosing unit — doses a suitable amount (3–5 ppm) of anti-scale agent to inhibit the scaling tendency of calcium, magnesium, carbonate and sulphate ions, helping the membrane remove hardness ions and preventing membrane scaling.
• Security filter — a 5 µm PPF cartridge that intercepts particles larger than 5 µm and extends membrane life.

Reverse Osmosis Unit

The RO membrane has a separation pore size of 10⁻⁶–10⁻⁷ cm and removes organic matter (such as trihalomethane intermediates, colloids, suspended solids, micro-organisms, bacteria, algae and moulds), pyrogens and viruses from the water. After the three stages of pre-treatment, the water is deeply separated by the RO membrane main unit: the fraction beneficial to health passes through while the rest is discharged, giving a desalination rate of 98%. The pure water produced is stored in the pure-water tank. Membrane filtration may be arranged as single-stage or double-stage reverse osmosis.

EDI Unit

Continuous electrodeionization (EDI) uses mixed ion-exchange resin packed in the dilute compartment to adsorb the cations and anions in the feed water. Under a DC voltage these adsorbed ions migrate laterally and pass through the cation- and anion-exchange membranes into the concentrate compartment, where they are removed. As the water travels forward and ions are continuously removed, the conductivity of the solution falls; under the DC voltage the water dissociates to generate enough H⁺ and OH⁻ ions to maintain the system current. Besides migrating laterally, these H⁺ and OH⁻ ions regenerate the ion-loaded resin in place, achieving continuous deep desalination.

Two conditions must be met: the ion content of the feed water must not be too high, and the applied DC voltage must reach a certain value. EDI technology can replace conventional ion-exchange (DI) equipment and produces ultrapure water with a resistivity of up to 10–18 MΩ·cm.

Key Features

• Combined RO + EDI process producing ultrapure water with resistivity up to 10–18 MΩ·cm.
• Continuous operation with stable product-water quality.
• No acid or alkali regeneration and no regeneration wastewater.
• Complete pre-treatment (sand filter, carbon filter, anti-scale dosing and 5 µm security filter) protects the RO membranes.
• 98% desalination rate; single-stage or double-stage RO as required.
• Compact, fully automatic system with on-line monitoring instruments.

Technical Specifications

Process Flow

Raw water is pre-treated by the sand filter and carbon filter, dosed with 3–5 ppm of anti-scale agent and finally protected by a 5 µm security filter. The filtered water is deeply desalinated in the RO main unit with a 98% desalination rate and stored in the pure-water tank; it is then polished in the EDI unit, where dissolved salts are removed continuously, to give ultrapure water with a resistivity of up to 10–18 MΩ·cm at the point of use.

Product Details

Applications

• Ultrapure water for the electronics and semiconductor industry
• Purified water for pharmaceutical production, medical preparations and laboratory use
• Boiler make-up water for power plants and industrial boilers
• Product-formulation water in the beverage, food and cosmetics industries
• Highly purified process water for electroplating and surface treatment