JP2015178107A - Method of producing ultrapure water and ultrapure water production equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for producing pure water by bringing UV oxidation-treated water from a UV oxidation unit into contact with a platinum metal supported catalyst resin which prevent deterioration of the catalyst resin and decompose hydrogen peroxide stably over a long period.SOLUTION: In a method and an apparatus for producing pure water by subjecting to-be-treated water to a UV oxidation treatment in a UV oxidation unit 2 and performing a hydrogen peroxide removal treatment by a hydrogen peroxide removal unit 4 using a platinum-based catalyst, the TOC of feed water to the UV oxidation unit 2 is 5 ppb, and an anion exchange resin tower 3 is arranged in the subsequent stage of the UV oxidation unit 2.

Description

  The present invention relates to a pure water production method and apparatus, and more particularly to a pure water production method and apparatus using an ultraviolet oxidation apparatus and a hydrogen peroxide removal apparatus. In the present invention, pure water includes ultrapure water.

  An ultrapure water manufacturing apparatus for cleaning semiconductors and electronic materials is usually composed of a pretreatment system, a primary pure water system, a subsystem, and the like. Each system consists of devices that remove various impurities such as turbidity, salts, and TOC.

  FIG. 4 is a flowchart showing an example of the ultrapure water production apparatus. As shown in the figure, ultrapure water is a raw water (industrial water, city water, Manufactured by treating wells).

  A pretreatment device 10 comprising agglomeration, pressurized flotation (precipitation), filtration (membrane filtration) device, etc. removes suspended substances and colloidal substances in raw water. In this process, it is also possible to remove high molecular organic substances, hydrophobic organic substances, and the like.

  The primary pure water production apparatus 11 including a reverse osmosis membrane separation device, a deaeration device, and an ion exchange device (such as a mixed bed type or a 4-bed 5-tower type) removes ions and organic components from raw water. The reverse osmosis membrane separation apparatus removes salts and ionic and colloidal TOC. The ion exchange apparatus removes salts and removes the TOC component adsorbed or ion exchanged by the ion exchange resin. In the deaerator, inorganic carbon (IC) and dissolved oxygen are removed.

In the subsystem 12, the primary pure water from the primary pure water production apparatus 11 is passed from the tank 14 to the heat exchanger 16 by the pump 15, and then the ultraviolet (UV) irradiation apparatus (low-pressure UV oxidation apparatus in FIG. 4) 17 is used. Then, it is processed by the ion exchange device 18 and the ultrafiltration (UF) membrane separation device 19 to produce ultrapure water. In the low-pressure UV oxidizer 17, TOC is decomposed to an organic acid and further to CO ₂ by 185 nm UV irradiated from a UV lamp. Organic substances and CO ₂ produced by the decomposition are removed by an ion exchange device (usually a mixed bed type ion exchange device) 18 in the subsequent stage. Fine particles are removed in the UF membrane separation device 19, and ion exchange resin debris flowing out from the ion exchange device 18 is also removed.

  The ultrapure water obtained in this manner is supplied from the pipe 20 to the use point 21, and surplus ultrapure water is returned to the tank 14 through the pipe 22.

  Oxidation treatment by ultraviolet irradiation in the ultraviolet oxidizer 17 decomposes organic substances (TOC component) in the water to produce organic acids and carbonic acid. The oxidative decomposition mechanism of the TOC component in this ultraviolet oxidation apparatus is to oxidize and decompose water to generate OH radicals, and oxidatively decompose the TOC component by this OH radicals. In the ultraviolet oxidation apparatus 17 of the subsystem 12, The amount of UV irradiation is excessive irradiation that can sufficiently oxidatively decompose TOC in water.

  Thus, when there is much ultraviolet irradiation amount, since the OH radical produced | generated by decomposition | disassembly of water will become excess, hydrogen peroxide will be produced | generated when an excess OH radical associates. The produced hydrogen peroxide is decomposed when it comes into contact with the ion exchange resin of the subsequent mixed bed ion exchange apparatus, but at this time, the ion exchange resin is deteriorated. Moreover, the TOC component derived from an ion exchange resin newly produces | generates by decomposition | disassembly of an ion exchange resin, and the quality of the obtained ultrapure water falls. Further, the hydrogen peroxide still remaining after passing water through the mixed bed ion exchanger deteriorates the deaerator and UF membrane in the subsequent stage of the mixed bed ion exchanger.

  JP 2007-185587 (Patent No. 5124946) discloses, as a method for removing hydrogen peroxide in ultrapure water, water to be treated containing hydrogen peroxide discharged from an ultraviolet oxidation treatment apparatus of an ultrapure water production apparatus. Is a method of decomposing hydrogen peroxide in water to be treated to 1 ppb or less by bringing the metal nanocolloid particles into contact with a hydrogen peroxide decomposition catalyst supported on an anion exchange resin carrier.

JP2007-185587

  As a result of various studies by the inventor, when hydrogen peroxide is removed by bringing hydrogen peroxide-containing water from an ultraviolet oxidizer into contact with a platinum-based metal-supported catalyst according to Patent Document 1, organic matter in the hydrogen peroxide-containing water is removed. When the acid concentration was high, it was recognized that the hydrogen peroxide decomposition ability of the platinum-based metal-supported catalyst decreased early, and hydrogen peroxide leaked early into the treated water. Thus, when the deterioration of the catalyst is fast, the replacement frequency of the catalyst becomes high when high purity ultrapure water is produced, and the production cost of ultrapure water increases.

  The present invention solves the above-mentioned conventional problems, and prevents deterioration (including suppression) of catalyst resin in a method and apparatus for producing pure water by contacting ultraviolet oxidation water from an ultraviolet oxidation apparatus with a platinum-based catalyst. It is an object of the present invention to provide a pure water production method and apparatus capable of stably decomposing hydrogen peroxide over a long period of time.

  The method for producing pure water according to the present invention is the method for producing pure water, wherein the water to be treated is subjected to an ultraviolet oxidation treatment with an ultraviolet oxidation device and then subjected to a hydrogen peroxide removal treatment with a hydrogen peroxide removal device using a platinum catalyst. The TOC of water supplied to the ultraviolet oxidation device is 5 ppb or less.

  In the method for producing pure water of the present invention, the inorganic carbonate ion concentration of water supplied to the ultraviolet oxidation apparatus is less than 1 ppb, and the inorganic carbonate ion concentration of ultraviolet oxidation treated water treated by the ultraviolet oxidation apparatus is 1 ppb or more. It is preferable.

  In the method for producing pure water according to the present invention, it is preferable that after the ultraviolet oxidation water from the ultraviolet oxidation device is subjected to anion exchange treatment, the hydrogen peroxide removal treatment is performed by the hydrogen peroxide removal device.

  An apparatus for producing pure water according to the present invention is an apparatus for producing pure water comprising an ultraviolet ray oxidizer and a hydrogen peroxide removing device having a platinum-based catalyst provided in a subsequent stage. A means for setting the TOC to 5 ppb or less is provided.

  The pure water production apparatus of the present invention preferably includes an anion exchange means between the ultraviolet oxidation apparatus and the hydrogen peroxide removal apparatus.

  The TOC component in the water to be treated is oxidatively decomposed by the ultraviolet oxidation treatment in the ultraviolet oxidation apparatus, and an organic acid and carbonic acid are generated. In the present invention, by setting the TOC concentration in the feed water to the ultraviolet oxidizer to 5 ppb or less, preferably 3 ppb or less, the organic acid concentration in the effluent water of the ultraviolet oxidizer is lowered and installed in the subsequent stage of the ultraviolet oxidizer. Poisoning (deterioration) of the platinum-based catalyst for removing hydrogen peroxide is prevented, and the life of this catalyst can be kept long.

  In the present invention, it is preferable to remove the organic acid and carbonic acid by anion exchange treatment of the effluent from the ultraviolet oxidizer. By removing the organic acid in this way, the life of the platinum-based catalyst installed in the subsequent stage can be further extended.

In the present invention, when the inorganic carbonate ion concentration of the feed water to the ultraviolet oxidizer is less than 1 ppb, by setting the ultraviolet oxidation treatment conditions so that the inorganic carbonate ion concentration in the effluent of the ultraviolet oxidizer is 1 ppb or more, The proportion of organic matter that is decomposed to CO ₂ increases, and as a result, the amount of hydrogen peroxide generated decreases. Thereby, the lifetime of a platinum-type catalyst can be extended.

It is a block diagram which shows the pure water manufacturing method and apparatus which concern on embodiment. It is explanatory drawing of an Example and a comparative example. It is explanatory drawing of an Example and a comparative example. It is a block diagram of an ultrapure water manufacturing apparatus.

Hereinafter, the present invention will be described in more detail with reference to FIG. In the embodiment of FIG. 1, the water to be treated is treated by the ultraviolet oxidation device 2 and then the hydrogen peroxide removal treatment is performed by the hydrogen peroxide removal device 4 having a platinum catalyst. As this treated water, primary pure water from a primary pure water production apparatus is suitable. The quality of primary pure water from the primary pure water production equipment is usually
Electrical specific resistance: 18 MΩ · cm or more (metal ion concentration: 5 ng / L or less, residual ion concentration: 10 ng / L or less)
Number of fine particles: 5 or less fine particles of 0.1 μm or more in 1 mL
It is.

  The inorganic carbonate ion concentration in the water to be treated such as primary pure water is preferably less than 1 ppb. When the concentration of inorganic carbonate ions in the water to be treated is 1 ppb or more, decarbonation treatment is performed by using a decarboxylation device such as a decarboxylation tower, anion exchange device, vacuum degassing device, or degassing membrane device alone or in combination. Thus, the inorganic carbonic acid concentration is preferably less than 1 ppb.

When the TOC concentration in the water to be treated such as primary pure water is 5 ppb or less, the water to be treated is supplied to the ultraviolet oxidizer 2 as it is. When the TOC concentration in the water to be treated is more than 5 ppb, the TOC reducing means 1 sets the TOC concentration to 5 ppb or less, preferably 3 ppb or less. As the TOC reduction means, a UV oxidation apparatus, an ion (mainly anion) exchange apparatus, an organic substance adsorption apparatus using activated carbon, an accelerated oxidation treatment apparatus (an oxidation accelerator such as UV oxidation + H ₂ O ₂ or persulfuric acid), or the like is used. Among them, a UV oxidation device and an ion exchange device are preferable.

  The TOC component is oxidatively decomposed by the ultraviolet oxidation treatment in the ultraviolet oxidation apparatus 2 to produce an organic acid and carbonic acid, and hydrogen peroxide is produced. In the present invention, by setting the TOC concentration in the feed water to the ultraviolet oxidizer 2 to 5 ppb or less, preferably 3 ppb or less, the organic acid concentration in the effluent water of the ultraviolet oxidizer 2 is lowered, The installed platinum catalyst for removing hydrogen peroxide is prevented from being poisoned, and the life of the catalyst can be kept long.

In the present invention, when the inorganic carbonate ion concentration of the feed water to the ultraviolet oxidizer 2 is less than 1 ppb, the treatment conditions of the ultraviolet oxidizer 2 so that the inorganic carbonate ion concentration in the effluent of the ultraviolet oxidizer 2 is 1 ppb or more ( For example, it is preferable to set input power, water flow rate, and the like. Thus, the proportion of organic material is increased to be decomposed into CO _2, the amount of this result the organic acid is reduced. Thereby, the lifetime of a platinum-type catalyst can be extended. Note that the inorganic carbonate ion concentration of water supplied to the ultraviolet oxidizer 2 is less than 1 ppb in order to reduce the load on the subsequent processing.

In order to prevent the organic acid in the effluent from the ultraviolet oxidizer 2 from poisoning the catalyst, it is preferable to pass the effluent from the ultraviolet oxidizer 2 through the anion exchange means 3 to remove the organic acid. . The anion exchange means is preferably an anion exchange resin, particularly a strongly acidic anion exchange resin, and the anion exchange resin may be used in a state mixed with a cation exchange resin. Carbonic acid is removed together with the organic acid by the anion exchange treatment. The water flow SV to the anion exchange resin is preferably about 10 to 200 h ⁻¹ .

  The effluent water from the anion exchange means 3 is passed through the hydrogen peroxide removing device 4 to remove hydrogen peroxide. As this hydrogen peroxide removing device 4, a device using a platinum catalyst is employed. The platinum-based catalyst is preferably a platinum-based metal colloidal particle, particularly a nano-colloidal particle supported on a carrier.

  Examples of platinum-based metals include ruthenium, rhodium, palladium, osmium, iridium, and platinum. These platinum group metals can be used singly, in combination of two or more, can be used as two or more alloys, or can be a refinement of a naturally produced mixture. It is also possible to use the product without separating it into a single unit. Among these, platinum, palladium, a platinum / palladium alloy alone or a mixture of two or more of them is particularly suitable because of its strong catalytic activity.

  There is no particular limitation on the method for producing platinum-based metal colloidal particles, and examples thereof include a metal salt reduction reaction method and a combustion method. Among these, the metal salt reduction reaction method can be suitably used because it is easy to produce and stable metal nanocolloid particles can be obtained. According to the metal salt reduction reaction method, for example, 0.1 to 0.4 mmol / L aqueous solution of platinum-based metal chloride, nitrate, sulfate, metal complex, etc., alcohol, citric acid or a salt thereof, formic acid, acetone Platinum metal nanocolloid particles can be produced by adding a reducing agent such as acetaldehyde 4 to 20 equivalent times and boiling for 1 to 3 hours. Also, dissolve 1 to 2 mmol / L of a platinum metal salt such as hexachloroplatinic acid or potassium hexachloroplatinate in an aqueous polyvinylpyrrolidone solution, add a reducing agent such as ethanol, and heat to reflux for 2 to 3 hours in a nitrogen atmosphere. Thus, nano colloidal particles of platinum-based metal can be produced.

  The average particle diameter of the platinum-based metal nanocolloid particles is preferably 1 to 50 nm, more preferably 1.2 to 20 nm, and still more preferably 1.4 to 5 nm. This particle size is a value obtained from electron microscope imaging.

  Examples of the carrier for supporting the platinum-based metal nanocolloid particles include magnesia, titania, alumina, silica-alumina, zirconia, activated carbon, zeolite, diatomaceous earth, and ion exchange resin. Among these, an anion exchange resin can be particularly preferably used. The platinum-based metal nanocolloid particles have an electric double layer and are negatively charged. Therefore, the platinum-based metal nanocolloid particles are stably supported on the anion exchange resin and are difficult to peel off. Platinum-based metal nanocolloid particles supported on an anion exchange resin exhibit a strong catalytic activity for the decomposition and removal of hydrogen peroxide. The exchange group of the anion exchange resin is preferably in the OH form. In the OH-type anion exchange resin, the resin surface becomes alkaline and promotes decomposition of hydrogen peroxide.

  The amount of platinum-based metal nanocolloid particles supported on the anion exchange resin is preferably 0.01 to 0.2% by weight, and more preferably 0.04 to 0.1% by weight.

By bringing hydrogen peroxide-containing water into contact with a hydrogen peroxide decomposition catalyst in which platinum-based metal nanocolloid particles are supported on a carrier, hydrogen peroxide in water is converted into 2H ₂ O ₂ →
Decomposed by 2H ₂ O + O ₂ reaction. The method for contacting the hydrogen peroxide-containing water with the hydrogen peroxide decomposition catalyst is not particularly limited, but it is preferable to pass the water through a hydrogen peroxide decomposition apparatus filled with the hydrogen peroxide decomposition catalyst. The water flow direction can be either an upward flow or a downward flow, but is preferably a downward flow in which the catalyst does not flow.

The water flow rate of the hydrogen peroxide-containing water to the hydrogen peroxide removal catalyst is preferably a space velocity SV of 100 to 2,000 h ⁻¹ , more preferably 500 to 1,500 h ⁻¹ . Since the platinum-based catalyst has a very high decomposition rate of hydrogen peroxide, hydrogen peroxide is sufficiently decomposed even when the water passing space velocity SV is 100 h ⁻¹ or more. However, when the water passing space velocity SV exceeds 2,000 h ⁻¹ , the pressure loss of the water passing becomes excessive, and the decomposition and removal of hydrogen peroxide may be insufficient.

  Since the platinum-based metal nanocolloid particles supported on the anion exchange resin have a large specific surface area, the reaction rate of hydrogen peroxide decomposition is very high, and the water passing space velocity can be increased. Since the amount of water passing is larger than the amount of the catalyst, the amount of the hydrogen peroxide decomposition catalyst to be used can be reduced, and the processing cost can be reduced. Even in the case of a catalyst in which platinum-based metal nanocolloid particles are supported on an anion exchange resin, hydrogen peroxide acts on the anion exchange resin because it decomposes rapidly upon contact with the platinum-based metal nanocolloid particles. There is nothing. Therefore, there is no possibility that the anion exchange resin is attacked by hydrogen peroxide and organic carbon (TOC) is eluted.

  The concentration of hydrogen peroxide contained in the treated water in contact with the hydrogen peroxide decomposition catalyst is preferably 5 ppb (weight ratio) or less, and more preferably 1 ppb (weight ratio) or less. If the concentration of hydrogen peroxide contained in ultrapure water is 5 ppb (weight ratio) or less, it is possible to perform treatments such as cleaning using ultrapure water without adversely affecting semiconductor and liquid crystal components. .

  When the present invention is applied to the ultrapure water production apparatus of FIG. 4, an anion exchange resin tower and a hydrogen peroxide removal apparatus are arranged in this order between the low pressure UV oxidation apparatus 17 and the mixed bed ion exchange apparatus 18. It is preferable to install them in series.

[Experimental Examples 1-3]
A synthetic primary pure water obtained by adding IPA (isopropyl alcohol) to ultrapure water was treated according to the flow of FIG.

That is, IPA is injected into ultrapure water by an IPA addition device 5 comprising a tank and a pump to prepare a quantitative primary IP water containing IPA containing a TOC concentration of 3, 5 or 10 ppb. 6 kW, UV wavelength 185 nm) at 10 L / min. The effluent from the ultraviolet oxidizer 7 was passed through the strongly acidic anion exchange resin tower 8 at SV = 100 h ⁻¹ , and further Pt-supported anion exchange resin (manufactured by Nippon Sheet Glass Co., Ltd., average particle diameter of Pt nanocolloid 10 nm) Water was passed through the catalyst tower 9 packed with NO at SV = 1000 h ⁻¹ . Table 1 shows the change over time in the hydrogen peroxide concentration in the effluent water of the ultraviolet oxidizer 7, and Table 2 shows the change over time in the hydrogen peroxide concentration in the treated water from the Pt catalyst tower 9.

[Experimental Examples 4 to 6]
As shown in FIG. 3, the anion exchange resin tower 8 was omitted, and the treatment was performed in exactly the same manner as in Experimental Examples 1 to 3, except that the effluent water from the ultraviolet oxidizer 7 was directly passed through the Pt catalyst tower 9. went. Table 3 shows changes with time in the hydrogen peroxide concentration in the treated water from the Pt catalyst tower 9.

  As shown in Table 1, the hydrogen peroxide concentration in the effluent of the ultraviolet oxidizer 7 was the same regardless of whether the TOC concentration in the feed water to the ultraviolet oxidizer 7 was 3, 5, or 10 ppb.

  As shown in Table 2, in the flow of FIG. 2 in which the ultraviolet oxidizer effluent was brought into contact with the anion exchange resin and then passed through the Pt catalyst tower 9, the hydrogen peroxide resolution was not reduced even at the ultraviolet oxidizer inlet TOC = 10 ppb. Maintained high over time.

  As shown in Table 3, in the flow of FIG. 3 in which the effluent from the ultraviolet oxidizer is passed through the Pt catalyst tower 9 as it is, when the ultraviolet oxidizer inlet TOC = 10 ppb, the hydrogen peroxide resolution has already decreased 15 days after the passage. ing. From this result, if the treated water hydrogen peroxide concentration <1 ppb is required, the hydrogen peroxide decomposition catalyst should be replaced once every 2 to 3 months, even considering that the SV used in the actual machine is 1/10. Will be needed. In the case of producing ultrapure water with TOC ≦ 5 ppb, it is possible to ensure performance for one year or more with an actual machine without replacing the hydrogen peroxide decomposition catalyst.

  From these results, the TOC decomposition product by the ultraviolet oxidation device reduces the hydrogen peroxide resolution of the platinum-based catalyst, but the TOC of the water supply of the ultraviolet oxidation device is set to 5 ppb or less, and preferably at the front stage of the hydrogen peroxide decomposition catalyst device. It was recognized that the frequency of replacement of the platinum-based hydrogen peroxide decomposition catalyst was significantly reduced by removing the TOC decomposition product with an anion exchange resin.

[Experimental Examples 7 to 10]
In Experimental Examples 5 and 6, the result when the ultraviolet ray irradiation amount of the ultraviolet oxidation device 7 is changed so that the inorganic carbonate ion concentration of the effluent water (UV treated water) of the ultraviolet oxidation device 7 becomes as shown in Table 4 Is shown together with the results of Experimental Examples 5 and 6.

  As shown in Table 4, the higher the concentration of inorganic carbonate ions in the effluent water (UV treated water) of the ultraviolet oxidizer 7, the longer the life of the hydrogen peroxide decomposition catalyst, and the water flow is 1 ppb or more, particularly 2 ppb or more. It can be seen that hydrogen peroxide is not detected after 45 days.

DESCRIPTION OF SYMBOLS 1 TOC reduction means 2 Ultraviolet oxidizer 3 Anion exchange means 4 Hydrogen peroxide removal means 7 Low pressure ultraviolet oxidizer

Method for manufacturing ultra-pure water of the present invention includes a primary pure water production system and the secondary pure water producing device, the ultrapure water obtained in the secondary pure water production system is fed to a use point, the use The ultrapure water in the ultrapure water production facility treated with the secondary pure water production equipment is treated with the mixed water of the extra pure water returned from the point and the primary pure water from the primary pure water production equipment. a pure water production method, in the secondary pure water producing device, after the treatment water to ultraviolet oxidation treatment with ultraviolet oxidation device, hydrogen peroxide removal process by the hydrogen peroxide removal apparatus using a platinum catalyst In the method for producing ultrapure water, the TOC of water supplied to the ultraviolet oxidizer is 5 ppb or less.

In the ultra-pure water manufacturing method of the present invention, the inorganic carbonate ion concentration of the water supply to the ultraviolet oxidation device is less than 1ppb, inorganic carbonate ion concentration of ultraviolet oxidation treatment water treated by the ultraviolet oxidation device than 1ppb Preferably there is.

In the method for producing ultrapure water present invention, after the anion exchange treatment to ultraviolet oxidation treatment water from the ultraviolet oxidation device, it is preferable to hydrogen peroxide removal process by the hydrogen peroxide removal equipment.

Ultrapure water Manufacturing equipment of the present invention includes a primary pure water production system and the secondary pure water producing device, the ultrapure water obtained in the secondary pure water production system is fed to a use point, the use This is an ultrapure water production facility where the mixed water of excess ultrapure water returned from the point and primary pure water from the primary pure water production device is treated as secondary water, and is treated in the secondary pure water production device. Te, the secondary pure water producing device includes an ultraviolet oxidation device, provided in a subsequent stage, and hydrogen peroxide removal apparatus having a platinum-based catalyst, means for less 5ppb water supply TOC of the ultraviolet oxidation device It is provided with.

Ultrapure water Manufacturing equipment of the present invention preferably includes an anion exchange means between the ultraviolet oxidation device and hydrogen peroxide removal equipment.

Claims (6)

  In a pure water production method in which water to be treated is subjected to ultraviolet oxidation treatment with an ultraviolet oxidation apparatus and then subjected to hydrogen peroxide removal treatment using a hydrogen peroxide removal apparatus using a platinum catalyst, the TOC of water supplied to the ultraviolet oxidation apparatus is 5 ppb. The manufacturing method of the pure water characterized by the following.   2. The method for producing pure water according to claim 1, wherein an inorganic carbonate ion concentration of water supplied to the ultraviolet oxidation apparatus is less than 1 ppb, and an inorganic carbonate ion concentration of ultraviolet oxidation treated water treated by the ultraviolet oxidation apparatus is 1 ppb. A method for producing pure water, which is as described above.   3. The method for producing pure water according to claim 1, wherein the ultraviolet oxidation water from the ultraviolet oxidation device is subjected to anion exchange treatment, and then the hydrogen peroxide removal treatment is performed by the hydrogen peroxide removal device. A method for producing pure water.   4. The method for producing pure water according to claim 1, wherein the platinum-based catalyst is obtained by supporting a colloidal particle of platinum-based metal on an anion exchange resin. Manufacturing method.   An apparatus for producing pure water comprising an ultraviolet oxidation apparatus and a hydrogen peroxide removal apparatus having a platinum-based catalyst provided in a subsequent stage, comprising means for reducing the TOC of water supplied to the ultraviolet oxidation apparatus to 5 ppb or less. An apparatus for producing pure water characterized by the above.   6. The apparatus for producing pure water according to claim 5, wherein an anion exchange means is provided between the ultraviolet oxidizer and the hydrogen peroxide remover.

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