Pure water systems, ultrapure water systems, water softeners

Types and Quality of Water

Our surroundings on Earth are filled with water. It falls as rain, flows into rivers, pours into the sea, evaporates to form clouds (especially as typhoons), and returns to the ground as rain, circulating continuously. Also, when we turn a tap, tap water flows out, which we use for daily drinking and cooking. Factories that produce various goods also use large amounts of water. Water is an indispensable substance for us humans. There are also various types of water.

• Naturally occurring water such as river water, groundwater, and seawater
• Industrial water
• Tap water
• Hard water / Soft water
• Pure water / Distilled water
• Ultrapure water, etc.

Normally, river water is properly treated before being used. There are various types of treatment methods, and the type of water obtained depends on the method used.

Industrial water and tap water contain substances other than water, though in amounts less than 1 g per liter. The substances present can be classified into inorganic substances, organic substances, fine particles, and microorganisms. On the other hand, using these waters in industrial fields can sometimes cause problems. In particular, inorganic substances such as calcium and magnesium, referred to as hardness components, and silica (silicic acid) can affect industrial and manufactured products.

Also, regarding tap water, looking at the requirements for tasty water presented by the "Delicious Water Research Committee" established by the Ministry of Health and Welfare at the time, it is clear that various components need to be dissolved in the water. The actual tap water in Tokyo is close to meeting these requirements. Additionally, the hardness of European mineral water is higher than that of Japanese tap water; for example, the Evian website lists its hardness as 304 mg/L.

"Pure water system" for producing pure water

One of the key industrial products that plays an important role in removing the components contained in water to produce pure water is called 'ion exchange resin.' Table salt is a substance made up of positively charged sodium ions and negatively charged chloride ions, and when dissolved in water, it exists in a dispersed state. Many substances that dissolve in water are in a similar state, and by introducing cation exchange resins that adsorb positive ions and anion exchange resins that adsorb negative ions, the ions in the water are captured, resulting in 'pure water' with few impurities.

A 'pure water system' for producing pure water is composed of the following equipment. Industrial water or tap water is first filtered to remove suspended solids, and then passed through a demineralization tower filled with ion exchange resin to remove impurities from the water, thereby producing 'pure water.' Generally, the '2B3T type' or the 'mixed bed type' is used.

2B3T Type

Mixed-Bed Type

The '2B3T system' produces pure water by filling two demineralization towers with cation and anion resins and passing the water through a decarbonation tower as well. There are also cases where a single tower, called a 'mixed-bed system,' is used with a mixture of cation and anion resins.

There are various configurations for the demineralization towers of pure water systems, and they are selected based on their intended use, required water quality, and cost.

Example Configuration of a Pure Water System

	Remove positive ions with a strongly acidic cation resin and remove negative ions with a strongly basic anion resin.
	Remove cations with a strong acid cation resin, remove anions with a type II or weak base anion resin, and further remove anions with a strong base type I anion resin.
	Remove positive ions with a strongly acidic cation resin, remove negative ions with a Type II anion resin, and remove all ions with a mixed-bed resin.
	Remove cations with a strong acid cation resin, further remove anions with Type II, and further remove anions with a strong base Type I anion resin.
	All ions are removed using a mixed bed of strongly acidic cation resin and strongly basic anion resin.

c: cation, A: anion, M: mixed bed *A decarbonation tower may also be present.

Ion exchange resins are useful for producing pure water, but they need to be periodically regenerated with chemicals. During this regeneration process, pure water cannot be produced, and there are safety concerns associated with the use of chemicals such as hydrochloric acid and caustic soda.

In recent years, there are cases where pure water production systems using “RO + EDI,” which do not require chemical regeneration, are employed. In this system, water that has been filtered through materials such as activated carbon is passed through a filter called an RO membrane to remove ions and fine particles. After this, a combination of ion exchange resins and ion exchange membranes is used to further remove ions using electrical power in a process called EDI: Electrodeionization, or continuous pure water production with electrical regeneration. Because there is no need to use chemicals, this system has become widely used in recent years.

Example configuration of the latest pure water system

This allows the production of 'pure water' with almost no impurities, but there are cases where 'ultrapure water' with even higher purity is used.
It is particularly required for water used in the electronics industry. In semiconductors and liquid crystal components, even trace amounts of impurities can affect product quality. For this reason, components are washed using extremely high-purity water.

In the field of pharmaceuticals, ultrapure water is used not only for cleaning medical devices but also as injection solutions and purified water. The pure water used here is strictly regulated in terms of quality according to the Japanese Pharmacopoeia and similar standards overseas.

In nuclear power plants, electricity is generated by producing steam in the reactor to turn the turbines, and after converting the steam back into water, it is returned to the reactor. At this stage, the water is thoroughly purified and returned as ultrapure water to suppress corrosion of the materials that make up the power generation equipment.
The production of this ultrapure water uses a system that combines multiple treatment facilities. An example of the configuration of an ultrapure water production system used in the electronics industry is shown below.

Example configuration of the latest ultrapure water system

First, raw water such as industrial water is treated with pretreatment equipment like activated carbon and coagulation filtration to remove residual chlorine, suspended matter, and organic substances. Next, similar to pure water production systems, an RO membrane and EDI are used to remove ionic components, and ultraviolet light is applied to kill microorganisms, producing pure water. This pure water is then passed through equipment called a subsystem, where organic substances are decomposed by ultraviolet oxidation, ions are removed using ion exchange resins, and finally fine particles are removed by ultrafiltration membranes to produce "ultrapure water," which is used for washing electronic material wafers.

The ion exchange resins used in this subsystem are of high purity, containing very low amounts of impurities such as metals and organic substances, in order to achieve high-quality water (such as our HG series).

Furthermore, there are also challenges in ultrapure water production systems. Ultraviolet lamps are used to kill microorganisms and to oxidatively decompose organic substances. While UV lamps are effective for these purposes, they also produce hydrogen peroxide by decomposing water. This hydrogen peroxide is a troublesome substance for ion exchange resins. In particular, when cation exchange resins come into contact with hydrogen peroxide, they undergo oxidation reactions, leading to a decline in water quality. Therefore, in the final stage of the subsystem, highly oxidation-resistant cation exchange resins are sometimes used (such as in our UL series).

Additionally, pure water and ultrapure water are widely used in universities and research laboratories. In research and chemical analysis, water is analyzed. If the water used for cleaning equipment or performing analytical procedures is not clean, the measurement results will be unstable. Therefore, for example, to determine whether the sodium concentration is higher than 1 ppm, the pure water used must have a concentration lower than this value. Ultrapure water used in electronic materials must meet levels below the detection limit of analytical instruments, so it is naturally necessary for the water to be extremely pure, which requires advanced processing.