Several Methods for Preparing Pure Water

The demand for ultrapure water has increased with the development of the semiconductor industry, leading to higher requirements for ultrapure water quality. This has greatly promoted the development of pure water technology, with membrane technology being widely applied. Advanced water treatment technologies such as microfiltration, ultrafiltration, electrodialysis, and reverse osmosis have developed rapidly. Membrane-based pure water production has replaced traditional ion exchanger systems, solving the TOC (Total Organic Carbon) problem and meeting the pure water quality requirements of the electronics industry.

I. Fine Filtration Pure Water Treatment

This uses filter membranes made of special materials, offering high filtration precision. Common types include microfiltration membranes and cartridge filters.

II. Ultrafiltration Pure Water Treatment

This is a type of membrane filtration that removes large molecules, colloids, bacteria, etc. It offers high filtration precision, with ultrafiltration membranes being the most common. Ultrafiltration membranes cannot remove ions from water, meaning they do not have desalination capabilities. They are used for pretreatment of reverse osmosis or fine treatment after reverse osmosis, and can also be used alone.

III. Reverse Osmosis Pure Water Treatment

Reverse osmosis (RO) is a membrane separation technology developed in the 1960s. Its principle is that raw water passes through a reverse osmosis membrane under high pressure, causing the solvent in the water to diffuse from a high concentration to a low concentration, thus achieving separation, purification, and concentration. Reverse osmosis can remove bacteria, viruses, colloids, organic matter, and over 98% of dissolved salts from water. This method features low operating costs, simple operation, high automation, and stable effluent quality. Compared with other traditional water treatment methods, it has significant advantages and is widely used in various industries related to water treatment.

IV. Ion Exchange Pure Water Treatment

Various inorganic salts in water ionize to generate cations and anions. When these cations pass through a hydrogen-type ion exchanger layer, the cations in the water are replaced by hydrogen ions; this is the desalination principle of a cation exchange bed. Similarly, various inorganic salts in water ionize to generate cations and anions. When these anions pass through an OH-type ion exchanger layer, the anions in the water are replaced by OH- ions; this is the desalination principle of an anion exchange bed. A mixed-bed ion exchange device is an ion exchange unit in which cation and anion exchange resins are mixed in a certain proportion and packed into the same exchange column. The uniformly mixed resin layer, with cation and anion resins arranged in a close-knit, interleaved pattern, resembles a multi-bed exchange system. Therefore, a mixed-bed exchange system can be considered as an infinite number of multi-bed exchanges operating in series. Because hydrogen ions and hydroxide ions entering the water after mixed-bed ion exchange immediately generate water molecules with very low ionization, the formation of counterions, which is rare in cation or anion exchanges, allows the exchange reaction to proceed very thoroughly. Therefore, the effluent quality of a mixed-bed exchange system is superior to that of a multi-bed exchange system composed of cation and anion exchange resins connected in series, producing finished water with a very high purity.

V. EDI Pure Water Treatment

This new desalination process combines electrodialysis and ion exchange. The equipment leverages the advantages of both electrodialysis and mixed-bed ion exchange, compensating for their respective shortcomings. It utilizes ion exchange for deep treatment without the need for chemical regeneration. The H+ and OH- generated by ionization are used to regenerate the resin. EDI has high requirements for the influent quality; it must be reverse osmosis permeate or water of equivalent quality. It can continuously produce qualified ultrapure water that meets user requirements, with stable water production, no need for chemical regeneration, and no chemical emissions, making it a green and environmentally friendly product.