Pure water production device and pure water production method

Abstract

To provide a pure water production device that efficiently removes refractory organic materials such as urea.SOLUTION: A pure water production device 1A has: hypohalous acid addition means 21 that adds hypohalous acid to target water containing organic materials; and an ultraviolet irradiation device 15 that is on the downstream side of the hypohalous acid addition means 21 and irradiates the target water having hypohalous acid added thereto with ultraviolet rays.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a pure water producing apparatus and a pure water producing method. [Background technology]

[0002] As the demand for higher quality pure water becomes more apparent, various methods for decomposing and removing trace amounts of organic matter contained in pure water have been investigated in recent years. As a representative of such methods, a process for decomposing and removing organic matter by ultraviolet oxidation treatment has been introduced.

[0003] Patent Documents 1 to 3 disclose methods for removing organic matter by adding hydrogen peroxide to water to be treated and irradiating the water with ultraviolet light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5512357 specification [Patent Document 2] Japanese Patent Application Publication No. 5-305297 [Patent Document 3] Japanese Patent Application Publication No. 10-277572 Summary of the Invention [Problem to be solved by the invention]

[0005] Hydrogen peroxide cannot sufficiently remove persistent organic substances such as urea. An object of the present invention is to provide a pure water production system that can more effectively remove persistent organic substances. [Means for solving the problem]

[0006] The pure water producing apparatus of the present invention comprises a hypohalous acid adding means for adding hypohalous acid to water to be treated that contains organic matter, and an ultraviolet ray irradiating device located downstream of the hypohalous acid adding means for irradiating ultraviolet rays onto the water to be treated to which the hypohalous acid has been added. A pipe connected to the inlet of the ultraviolet irradiation device, an addition point provided in the pipe to which a pH adjusting solution is added, and a pH adjusting means for adjusting the pH of the water to be treated to 3 or more and 8 or less and, have The addition point and the ultraviolet irradiation device are connected only by this piping. In another aspect, the pure water production system has a pipe in which an ultraviolet irradiation device is installed, and an addition point provided in the pipe to which hypohalous acid is added, and the addition point and the ultraviolet irradiation device are connected only by the pipe. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a pure water producing apparatus that can more effectively remove persistent organic substances. [Brief explanation of the drawings]

[0008] [Figure 1A] FIG. 1 is a schematic diagram showing the configuration of a pure water production system according to embodiment 1A. [Figure 1B] FIG. 1 is a schematic diagram of a pure water production system according to embodiment 1B. [Figure 1C] FIG. 1C is a schematic diagram showing the configuration of a pure water production system according to embodiment 1C. [Figure 2A] FIG. 2 is a schematic diagram of a pure water producing system according to embodiment 2A. [Figure 2B] FIG. 10 is a schematic diagram of a pure water producing system according to embodiment 2B. [Figure 3A] FIG. 3 is a schematic diagram of a pure water producing system according to embodiment 3A. [Figure 3B] FIG. 10 is a schematic diagram of a pure water producing system according to embodiment 3B. [Figure 4] FIG. 1 is a schematic diagram of a test device used in Example 1. [Figure 5] 3 is a graph showing the relationship between the pH of the water to be treated and the urea removal rate in Example 1. [Figure 6] 1 is a graph showing the relationship between the hypobromous acid concentration in the water to be treated and the urea removal rate in Example 1. [Figure 7] FIG. 1 is a schematic diagram of a test device used in Example 2. [Figure 8] FIG. 10 is a schematic diagram of a test device used in Example 3. [Figure 9] FIG. 10 is a schematic diagram of a test device used in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Embodiments 1A to 1C) Hereinafter, embodiments of the pure water production system and method of the present invention will be described with reference to the drawings. Fig. 1A shows a schematic configuration of a pure water production system 1A according to embodiment 1A of the present invention. The pure water production system 1 (primary system) constitutes an ultrapure water production system together with an upstream pretreatment system and a downstream subsystem (secondary system). The raw water produced in the pretreatment system (hereinafter referred to as "water to be treated") contains organic matter including urea.

[0010] The pure water production system 1A includes a filter 11, an activated carbon tower 12, a first ion exchanger 13, a reverse osmosis membrane device 14, an ultraviolet irradiation device (ultraviolet oxidation device) 15, a second ion exchanger 16, and a degassing device 17, which are arranged in series along a mother pipe L1 from upstream to downstream in the flow direction D of the water to be treated. The water to be treated is pressurized by a raw water pump (not shown), and then relatively large particles such as dust are removed from the water to be treated by the filter 11. Impurities such as high molecular weight organic matter are removed from the water to be treated by the activated carbon tower 12. The first ion exchanger 13 includes a cation tower (not shown) filled with a cation exchange resin, a decarbonation tower (not shown), and an anion tower (not shown) filled with anion exchange resin, which are arranged in series in this order from upstream to downstream. The water to be treated has cationic components removed in the cation tower, carbonate removed in the decarbonation tower, and anionic components removed in the anion tower. Ionic components are then further removed from the water to be treated by the reverse osmosis membrane device 14.

[0011] The pure water production apparatus 1A includes a hypohalous acid adding means 21 that adds hypohalous acid to the water to be treated. In this embodiment, the hypohalous acid is hypobromous acid, but it may also be hypochlorous acid or hypoiodous acid. The hypohalous acid adding means 21 includes a sodium bromide (NaBr) storage tank 21a (sodium bromide supply means), a sodium hypochlorite (NaClO) storage tank 21b (sodium hypochlorite supply means), a sodium bromide and sodium hypochlorite stirring tank 21c (sodium bromide and sodium hypochlorite mixing means), and a transfer pump 21d. Because hypobromous acid is difficult to store for long periods of time, it is produced by mixing sodium bromide and sodium hypochlorite according to the timing of use. The hypobromous acid produced in the agitation tank 21c (mixing means) is pressurized by the transfer pump 21d and added to the water to be treated passing through the main pipe L1 between the reverse osmosis membrane device 14 and the ultraviolet irradiation device 15. Sodium bromide and sodium hypochlorite may be supplied directly to the main pipe L1 and agitated by the flow of the water to be treated in the main pipe L1 to produce hypobromous acid.

[0012] The ultraviolet irradiation device 15, located downstream of the hypohalous acid addition means 21, irradiates the water to be treated with added hypohalous acid with ultraviolet light. For example, an ultraviolet lamp containing at least one of the wavelengths of 254 nm or 185 nm can be used as the ultraviolet irradiation device 15. The ultraviolet light preferably contains a wavelength component of 185 nm, which has high energy and excellent decomposition ability for organic matter. UV irradiation promotes the decomposition of organic matter (urea) by hypobromous acid. However, because hypochlorous acid is more easily decomposed by ultraviolet light than hypobromous acid, irradiation with a large amount of ultraviolet light accelerates the decomposition reaction of hypochlorous acid, resulting in unnecessary energy consumption. Furthermore, there is a possibility that hypochlorous acid for generating hypobromous acid will be insufficient, preventing the hypobromous acid generation reaction from proceeding.

[0013] A conventional method for removing organic matter involves adding hydrogen peroxide to water to be treated. Hydroxyl radicals are generated from hydrogen peroxide by ultraviolet irradiation, and the hydroxyl radicals promote the oxidative decomposition of organic matter. However, as explained in Example 1, hypohalous acid is far more effective than hydrogen peroxide in removing persistent organic matter such as urea. Therefore, according to this embodiment, the concentration of persistent organic matter such as urea in ultrapure water supplied to a point-of-use can be reduced.

[0014] The second ion exchanger 16, located downstream of the ultraviolet irradiation device 15, is a regenerative ion exchange resin tower filled with anion exchange resin and cation exchange resin. Decomposition products of organic matter generated in the water to be treated by ultraviolet irradiation are removed by the second ion exchanger 16. Thereafter, dissolved oxygen in the water to be treated is removed by the degassing device 17.

[0015] As will be described in detail in Example 1, the urea removal rate is significantly improved when the pH of the water to be treated is 8 or less. For this reason, the pure water production system 1A has a pH adjustment means 22 upstream of the ultraviolet irradiation device 15. The pH adjustment means 22 has a storage tank 22a for a pH adjustment solution, such as sulfuric acid or hydrochloric acid, and a transfer pump 22b. The pH adjustment solution is pressurized by the transfer pump 22b and added to the water to be treated passing through the mother pipe L1 between the reverse osmosis membrane device 14 and the ultraviolet irradiation device 15. The pH adjustment means 22 adjusts the pH of the water to 8 or less, preferably 7 or less, more preferably 5 or less, and even more preferably 4 or less. The lower limit of the pH is not limited from the perspective of the urea removal rate, but it is preferably 3 or more in consideration of the impact on downstream equipment.

[0016] As will be described in detail in Example 1, the TOC removal rate can be significantly improved by adding hypohalous acid at a concentration of 30 times by weight or more, preferably 60 times by weight or more, more preferably 120 times by weight or more, and even more preferably 250 times by weight or more relative to the TOC content of the water being treated upstream of the hypohalous acid addition means 21. Therefore, the pure water production system 1A includes a TOC analyzer 18, such as a TOC meter, that measures the TOC content of the water being treated upstream of the hypohalous acid addition means 21. The location of the TOC analyzer 18 is not limited as long as it is upstream of the hypohalous acid addition means 21, but it is preferably located immediately before the hypohalous acid is added. Therefore, the TOC analyzer 18 is installed between the reverse osmosis membrane device 14 and the hypohalous acid addition means 21. The amount of hypohalous acid added is not limited from the perspective of the TOC removal rate, but it is preferably 2000 times by weight or less relative to the TOC content, taking into account the impact on downstream equipment. Alternatively, a urea analyzer, such as a urea concentration meter, may be used as the TOC analyzer 18. In this case, the urea removal rate is greatly improved by adding hypohalous acid in an amount 5 times by weight or more, preferably 12 times by weight or more, more preferably 25 times by weight or more, and even more preferably 50 times by weight or more relative to the urea concentration in the water to be treated upstream of the hypohalous acid adding means 21. The amount of hypohalous acid to be added is not limited from the viewpoint of the urea removal rate, but it is preferable to set it to 400 times by weight or less of urea, taking into account the impact on downstream equipment.

[0017] FIG. 1B shows a schematic configuration of a pure water production system 1B according to embodiment 1B of the present invention. In this embodiment, another ultraviolet irradiation device 15a is installed in series downstream of the ultraviolet irradiation device 15, specifically between the ultraviolet irradiation device 15 and the second ion exchange device 16. The remaining configuration is the same as that of embodiment 1A. The downstream ultraviolet irradiation device 15a removes hypohalous acid remaining in the water to be treated by photolysis. This reduces the load on the second ion exchange device 16 and suppresses oxidative degradation of the resin in the second ion exchange device 16. Similar to the ultraviolet irradiation device 15, the other ultraviolet irradiation device 15a can be an ultraviolet lamp emitting at least one of the wavelengths of 254 nm and 185 nm.

[0018] FIG. 1C shows a schematic configuration of a pure water production system 1C according to embodiment 1C of the present invention. In this embodiment, a reducing agent addition means 23 is installed downstream of the ultraviolet irradiation device 15, and a reverse osmosis membrane device 19 is installed downstream of the reducing agent addition means 23 and upstream of the second ion exchange device 16. The remaining configuration is the same as embodiment 1A. The reducing agent addition means 23 removes hypohalous acid remaining in the water to be treated. Examples of reducing agents that can be used include hydrogen peroxide and sodium sulfite. The reducing agent addition means 23 includes a reducing agent storage tank 23a and a transfer pump 23b. The reducing agent is pressurized by the transfer pump 23b and added to the water to be treated passing through the mother pipe L1 between the ultraviolet irradiation device 15 and the reverse osmosis membrane device 19. The reverse osmosis membrane device 19 removes excess reducing agent. The reducing agent removal means may be an ion exchange resin, an electrodeionization device, or the like. Alternatively, these reducing agent removal means may be combined in series.

[0019] The means for removing hypohalous acid is not limited to those of embodiments 1B and 1C, and other ultraviolet irradiation device 15a and reducing agent adding means 23 are examples of means for removing hypohalous acid, so that other means for removing hypohalous acid (oxidizing agent removing means) having a similar effect may be used, such as a platinum group catalyst such as palladium (Pd), activated carbon, etc. Alternatively, these means for removing hypohalous acid may be combined in series.

[0020] (Embodiments 2A to 2B) FIG. 2A shows a schematic configuration of a pure water production system 2A according to embodiment 2A of the present invention. In this embodiment, hydrogen peroxide is used for the oxidative decomposition of compounds such as organic substances. The water to be treated contains anions as well as any compounds that can be oxidatively decomposed by hydrogen peroxide. The pure water production system 2A includes a filter 11, an activated carbon tower 12, a first ion exchanger 13, a reverse osmosis membrane device 14, an ultraviolet irradiation device 15, a second ion exchanger 16, and a degassing device 17, which are arranged in series along a main pipe L1 from upstream to downstream in the flow direction D of the water to be treated. These devices 11 to 17 have the same configuration as embodiments 1A to 1C. In this embodiment, a hydrogen peroxide addition means 24 is provided between the reverse osmosis membrane device 14 and the ultraviolet irradiation device 15. The hydrogen peroxide addition means 24 includes a hydrogen peroxide storage tank 24a and a transfer pump 24b. The hydrogen peroxide is pressurized by the transfer pump 24b and added to the water to be treated passing through the mother pipe L1 between the reverse osmosis membrane device 14 and the ultraviolet irradiation device 15. The water to be treated to which hydrogen peroxide has been added is irradiated with ultraviolet light by the ultraviolet irradiation device 15. This generates hydroxyl radicals from the hydrogen peroxide, which promote the oxidative decomposition of organic matter. As mentioned above, hydrogen peroxide is not very efficient at removing persistent organic matter such as urea, but is effective in the oxidative decomposition of general compounds that are not persistent. A catalyst tower 20 filled with a platinum-group catalyst support is provided downstream of the second ion exchange device 16 (anion removal device), i.e., between the second ion exchange device 16 and the degassing device 17.

[0021] The second ion exchange device 16 is an ion exchange tower filled with at least an anion exchanger such as an anion exchange resin, and removes at least anions from the water to be treated to which hydrogen peroxide has been added. The ion exchange tower is preferably a regenerative type. In this embodiment, the second ion exchange device 16 is filled with an anion exchange resin. The second ion exchange device 16 may also be filled with a cation exchange resin. In this case, the anion exchange resin and the cation exchange resin may be packed in a multi-bed configuration or a mixed-bed configuration. A regenerative multi-bed ion exchange tower is particularly preferred because of its ease of regeneration. In the case of a multi-bed configuration, either the anion exchange resin or the cation exchange resin may be located upstream in the flow direction D of the water to be treated. Alternatively, an anion tower filled with an anion exchange resin and a cation tower filled with a cation exchange resin may be separately provided. The second ion exchange device 16 may have any configuration as long as it functions as an anion removal means for removing anions from the water to be treated containing hydrogen peroxide and anions.

[0022] The platinum group catalyst carrier packed in the catalyst tower 20 is an anion exchanger, or in this embodiment, an anion exchange resin, carrying a platinum group catalyst made of a platinum group metal. The platinum group catalyst carrier removes hydrogen peroxide contained in the water to be treated from which anions have been removed. A monolithic organic porous anion exchanger can also be used as the anion exchanger. The platinum group catalyst decomposes hydrogen peroxide through its catalytic action. Examples of platinum group metals include platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir). These metals may be used alone or in combination of two or more. Among these platinum group metals, Pt and Pd are preferred, with Pd being even more preferred from a cost perspective.

[0023] Excess hydrogen peroxide that is added to the water to be treated but not used to decompose compounds is decomposed into water and oxygen and removed by contact with the platinum group catalyst. As will be explained in Example 2 below, the efficiency of the platinum group catalyst in removing hydrogen peroxide improves as the amount of anion components contained in the water to be treated decreases. For this reason, in this embodiment, a second ion exchange device 16 is placed upstream of the platinum group catalyst.

[0024] It has traditionally been thought that hydrogen peroxide oxidizes and deteriorates ion exchangers, so platinum group catalysts are placed before the ion exchanger to limit the amount of hydrogen peroxide that comes into contact with the ion exchanger. However, in the experiments conducted this time, almost no damage to the anion exchanger by hydrogen peroxide was confirmed. This is thought to be because the concentration of hydrogen peroxide used in pure water production is low, and is not a concentration that would damage the anion exchanger. Furthermore, because hydrogen peroxide is ultimately decomposed by the platinum group catalyst, it does not affect the quality of the ultrapure water supplied to the point of use.

[0025] FIG. 2B shows a schematic configuration of a pure water production system 2B according to embodiment 2B of the present invention. In this embodiment, the second ion exchanger 16a is packed with an anion exchanger and a platinum group catalyst carrier, and the other configurations are the same as those of embodiment 2A. That is, while the second ion exchanger 16 and the catalyst tower 20 are installed separately in embodiment 2A, in this embodiment, the anion exchanger and the platinum group catalyst carrier are packed in a single ion exchange tower (second ion exchanger 16a). This allows for a more compact pure water production system 2B. As in embodiment 2A, the second ion exchanger 16a may also be packed with a cation exchanger. That is, the second ion exchanger 16a may be a regenerative ion exchange tower in which the anion exchanger, the cation exchanger, and the platinum group catalyst carrier are packed separately from each other. In this case, the position of the cation exchanger is not limited as long as the platinum group catalyst carrier is located downstream of the anion exchanger. Specifically, the anion exchanger, cation exchanger, and platinum group catalyst carrier can be packed in the second ion exchange device 16a in the following order from upstream to downstream in the flow direction D of the water to be treated. (1) Anion exchanger / Platinum catalyst support / Cation exchanger (2) Cation exchanger / anion exchanger / platinum group catalyst support (3) Anion exchanger / cation exchanger / platinum group catalyst carrier As mentioned above, since the platinum group catalyst support is an anion exchanger, it is preferable that the platinum group catalyst support and the anion exchanger are packed adjacent to each other ((1) or (2)). This allows the platinum group catalyst support and the anion exchanger to be handled together during regeneration, simplifying the regeneration procedure. In addition, by replacing part of the area where the anion exchanger was previously packed with the platinum group catalyst support, it is easy to use an existing ion exchange tower.

[0026] 2A and 2B, hydrogen peroxide adding means 24 is provided upstream of ultraviolet irradiation device 15, but hydrogen peroxide adding means 24 can be omitted. The second ion exchange devices 16, 16a can achieve the same effect because hydrogen peroxide is generated in the water to be treated by irradiating it with ultraviolet light from ultraviolet irradiation device 15. Furthermore, although not shown, an electrodeionization device with a deionization chamber filled with a platinum group catalyst carrier may be used as the second ion exchange device 16, 16a.

[0027] (Third Embodiments 3A to 3B) Embodiments 3A and 3B have a configuration that combines Embodiments 1A to 1C and Embodiments 2A and 2B. Therefore, for the configuration and effects of each device, please refer to the above-mentioned embodiments. FIG. 3A shows a schematic configuration of a pure water production system 3A according to Embodiment 3A of the present invention. The pure water production system 3A includes a filter 11, an activated carbon tower 12, a first ion exchange device 13, a reverse osmosis membrane device 14, an ultraviolet irradiation device 15, a second ion exchange device 16, a catalyst tower 20 (platinum group catalyst carrier), and a degassing device 17, which are arranged in series along a mother pipe L1 from upstream to downstream with respect to the flow direction D of the water to be treated. These devices 11 to 17 and 20 have the same configuration as in Embodiment 2A. The pure water production system 3A also includes a hypohalous acid addition means 21 that adds hypohalous acid to the water to be treated. The hypohalous acid adding means 21 has the same configuration as in embodiments 1A to 1C, and adds hypohalous acid to the water to be treated between the reverse osmosis membrane device 14 and the ultraviolet irradiation device 15. Furthermore, like embodiments 1A to 1C, the pure water producing system 3A has a pH adjusting means 22 upstream of the ultraviolet irradiation device 15. Furthermore, like embodiments 1A to 1C, the pure water producing system 3A has a TOC analyzing means 18, such as a TOC meter, that measures the TOC of the water to be treated upstream of the hypohalous acid adding means 21.

[0028] In this embodiment, as in Embodiments 1A to 1C, hypohalous acid is added to the water to be treated to remove persistent organic matter such as urea. The pH of the water to be treated is then adjusted to 3 to 8, preferably 3 to 5, by pH adjustment means 22. Ultraviolet light generated by ultraviolet irradiation device 15 promotes the decomposition of persistent organic matter (urea) by hypobromous acid. Because hypohalous acid has strong oxidizing power, it may oxidize and deteriorate the ion exchanger in the downstream second ion exchange device 16. Therefore, hydrogen peroxide is added to the water to be treated to remove any remaining hypohalous acid. For this purpose, the pure water production system 3A includes hydrogen peroxide addition means 24 located downstream of the ultraviolet irradiation device 15, more specifically, between the ultraviolet irradiation device 15 and the second ion exchange device 16. In other words, the hydrogen peroxide addition means 24 adds hydrogen peroxide to the water to be treated that has been irradiated with ultraviolet light. As in Embodiments 2A to 2C, the hydrogen peroxide adding means 24 includes a hydrogen peroxide storage tank 24a and a transfer pump 24b. While hypohalous acid can be removed using, for example, sulfite, hydrogen peroxide is preferred because this increases the load on the downstream ion exchanger. After the hypohalous acid is removed using hydrogen peroxide, excess hydrogen peroxide is removed using a platinum group catalyst, as in Embodiments 2A and 2B. Since anion components are removed in advance using the second ion exchanger 16, the efficiency of hydrogen peroxide removal using the platinum group catalyst is improved.

[0029] FIG. 3B shows a schematic configuration of a pure water production system 3B according to embodiment 3B of the present invention. In this embodiment, the second ion exchanger 16a is packed with an anion exchanger and a platinum group catalyst carrier, and the other configurations are the same as those of embodiment 3A. That is, in this embodiment, like embodiment 2B, the anion exchanger and the platinum group catalyst carrier are packed in a single ion exchange tower (second ion exchanger 16a). The second ion exchanger 16a may also be packed with a cation exchanger. For details, see embodiment 2B.

[0030] Example 1 To confirm the effects of embodiments 1A to 1C, the urea removal rate was measured using the test equipment shown in FIG. 4. An oxidizing agent was added to ultrapure water, and urea was added downstream as a persistent organic substance. The amount of urea added was adjusted so that the TOC of the water to be treated upstream of the ultraviolet irradiation device was 16 μg / L and the urea concentration was 80 μg / L. An ultraviolet irradiation device from Japan Photo Science Co., Ltd. was used, and the irradiation dose was 0.70 kWh / m 3 The water was irradiated with ultraviolet light at 1000 kJ / L. A 300 mL non-regenerative mixed-bed ion exchanger (hereinafter referred to as the ion exchanger) was installed downstream of the ultraviolet irradiation device to remove ionic components. Urea meters (ORUREA, manufactured by Organo) were installed at the inlet side of the ultraviolet irradiation device and the outlet side of the ion exchanger to measure the urea concentration. In Example 1, hypobromous acid was added as an oxidizing agent at a concentration of 2 mg-Cl2 / L (chlorine equivalent concentration). As in Examples 1A to 1C, hypobromous acid was generated by mixing NaBr and NaClO. The concentration of hypobromous acid was measured using a residual salt concentration meter (manufactured by HANNA) with a free chlorine reagent after adding glycine to the sample water to convert free chlorine to combined chlorine. In Comparative Example 1-1, no oxidizing agent was added. In Comparative Example 1-2, hydrogen peroxide was added as an oxidizing agent at a concentration of 2 mg / L. The pH of the water to be treated was set to 7. The urea removal rate was calculated as (C1-C2) / C1 x 100 (%), where C1 is the urea concentration in the water to be treated at the inlet side of the ultraviolet irradiation device and C2 is the urea concentration in the treated water of the ion exchange device.

[0031] The urea removal rate was 61.5% in Example 1, 3.2% in Comparative Example 1-1, and 4.0% in Comparative Example 1-2. This shows that the addition of hypobromous acid significantly improves the urea removal rate. Furthermore, it was found that the addition of hydrogen peroxide slightly improves the urea removal rate, but the effect is limited compared to hypobromous acid.

[0032] Next, to evaluate the effect of the pH of the water to be treated on the urea removal rate, the urea removal rate was measured at pH values ​​of 4, 5, 7, 8, and 9. The pH was adjusted by adding sulfuric acid to the water to be treated, but the other conditions were the same as in the above-mentioned examples. The results are shown in Figure 5. The urea removal rate increases as the pH decreases. The urea removal rate can be improved by setting the pH to 8 or less, preferably 7 or less, more preferably 5 or less, and even more preferably 4 or less.

[0033] Furthermore, we measured the urea removal rate when the hypobromous acid concentration in the treated water was 0, 0.5, 1.0, 2.0, 4.0, and 6.0 mg-Cl2 / L. The results are shown in Figure 6. The urea removal rate increases as the hypobromous acid concentration increases. The urea removal rate can be improved by increasing the hypobromous acid concentration to 0.5 mg-Cl2 / L or higher, preferably 1.0 mg-Cl2 / L or higher, more preferably 2.0 mg-Cl2 / L or higher, and even more preferably 4.0 mg-Cl2 / L or higher. However, the urea removal rate does not change significantly at hypobromous acid concentrations above 4.0 mg-Cl2 / L. Figure 6 also shows the weight ratio of hypobromous acid to TOC.

[0034] Example 2 To confirm the effects of Embodiments 2A and 2B, the hydrogen peroxide concentration of treated water was measured using the test equipment shown in FIG. 7. In Example 2-1, as shown in FIG. 7(a), hydrogen peroxide was added to ultrapure water, and carbon dioxide was added downstream as an anion load. Water to be treated was sequentially passed through a regenerative ion exchange device packed with multiple beds of anion exchange resin and cation exchange resin, and through a Pd catalyst carrier, and the hydrogen peroxide concentration of the treated water (water at the outlet of the Pd resin tower) was measured. In Example 2-2, as shown in FIG. 7(a), water to be treated was prepared in the same manner, passed through a regenerative ion exchange device packed with anion exchange resin, Pd catalyst carrier, and cation exchange resin in this order, and the hydrogen peroxide concentration of the treated water (water at the outlet of the regenerative ion exchange device) was measured. Comparative Example 2 is not shown, but the regenerative ion exchange device was omitted in Example 2-1. That is, the water to be treated was passed through the Pd catalyst carrier without removing anionic components from the water to be treated, and the hydrogen peroxide concentration of the treated water (water at the outlet of the Pd catalyst carrier) was measured.

[0035] In both Examples 2-1 and 2-2 and Comparative Example 2, hydrogen peroxide and carbon dioxide were added to achieve a hydrogen peroxide concentration of 100 μg / L and a carbon dioxide concentration of 1.5 mg / L. The amount of water passed through the regenerative ion exchange device and Pd catalyst carrier was 36 L / h. The hydrogen peroxide removal rate was calculated as (C1 - C2) / C1 × 100 (%), where C1 is the hydrogen peroxide concentration in the water at the inlet side of the ion exchange device, and C2 is the hydrogen peroxide concentration in the treated water from the Pd catalyst carrier (Example 2-1, Comparative Example 2) or the regenerative ion exchange device (Example 2-2). The hydrogen peroxide removal rate was 99% or higher in both Examples 2-1 and 2-2, and 60% in Comparative Example 2. This confirmed that hydrogen peroxide could be removed more efficiently by first removing anionic components before passing the water through the Pd catalyst carrier.

[0036] Example 3 In order to confirm the effects of Embodiments 3A and 3B, Comparative Examples 3-1 to 3-5 and Examples 3-1 and 3-2 were carried out using the test equipment shown in Figures 8 and 9. An overview is shown in Table 1.

[0037] [Table 1]

[0038] First, Comparative Examples 3-1 to 3-3 were performed using the test equipment shown in FIG. 8(a). Urea was added to ultrapure water as a persistent organic substance, and carbon dioxide was added as an anion load. The water to be treated was then irradiated with ultraviolet light using an ultraviolet irradiation device. In Comparative Example 3-1, no oxidizing agent was added to the water to be treated. In Comparative Example 3-2, hydrogen peroxide was added as an oxidizing agent at a concentration of 2 mg / L, and in Comparative Example 3-3, hypobromous acid was added as an oxidizing agent at a concentration of 2 mg-Cl2 / L. As in Examples 3A to 3C, hypobromous acid was generated by mixing NaBr and NaClO. The urea concentration was 80 μg / L (TOC 16 μg / L), and the carbonate concentration was 2 mg / L. The urea concentration was measured using a urea concentration meter (ORUREA, manufactured by Organo Corporation). The process up to ultraviolet irradiation was the same as in Example 1. A regenerative double-bed ion exchanger (capacity 300 mL) was installed downstream of the ultraviolet irradiation device to remove ionic components. The urea removal rates were determined using the same method as in Example 1, and were 3% in Comparative Example 3-1, 4% in Comparative Example 3-2, and 60% in Comparative Example 3-3, which are almost the same results as in Example 1. In Comparative Example 3-3, the hypobromous acid concentration in the treated water after UV irradiation was 1 mg-Cl / L. Meanwhile, the TOC minus the urea content measured using a urea meter (ORUREA) was 0.8 μg / L in Comparative Examples 3-1 and 3-2, but 40 μg / L in Comparative Example 3-3. This is because the hypobromous acid remaining after UV irradiation from the UV irradiation device deteriorated the ion exchanger in the downstream ion exchange device.

[0039] Next, as Comparative Example 3-4, as shown in Figure 8(b), 2 mg / L of hydrogen peroxide was added to the treated water at the outlet side of the UV irradiation device, and similar measurements were performed. The urea removal rate was similar to that of Comparative Example 3-3. The hypobromous acid concentration in the treated water after hydrogen peroxide addition was less than 0.01 mg-Cl2 / L. Comparing Comparative Examples 3-3 and 3-4, it can be seen that hypobromous acid was removed by hydrogen peroxide. The hydrogen peroxide concentration was 1 mg / L at both the inlet and outlet of the ion exchange device, and the TOC of the ion exchange device-treated water minus the urea content was 0.8 μg / L. This suggests that TOC elution due to resin degradation did not occur at a hydrogen peroxide concentration of around 1 mg / L.

[0040] Next, in Comparative Example 3-5, a Pd catalyst carrier was placed before the ion exchanger, as shown in Figure 9(a). The hydrogen peroxide concentration at the outlet of the Pd catalyst carrier and the treated water from the ion exchanger was 0.4 mg / L, and the hydrogen peroxide removal rate was 60%. The carbonate concentration at the inlet of the Pd catalyst carrier was 2 mg / L. This shows that when anions (carbonate) are not removed at the inlet side of the Pd catalyst carrier, the hydrogen peroxide removal rate is not very high (60%).

[0041] Next, similar measurements were performed using the test equipment shown in Figure 9(b) for Examples 3-1 and 3-2. In Example 3-1, a catalyst tower packed with a Pd catalyst carrier was installed downstream of the ion exchanger, and in Example 3-2, the ion exchanger was packed with a Pd catalyst carrier (anion exchange resin, Pd catalyst carrier, and cation exchange resin were packed in this order in the direction of water flow). The hydrogen peroxide concentration at the outlet of the catalyst tower in Example 3-1 and the hydrogen peroxide concentration at the outlet of the ion exchanger in Example 3-2 were both less than 0.01 mg / L, and the hydrogen peroxide removal rate was 99% or more. In Example 3-2, the carbonate concentration of the ion exchanger-treated water was measured and found to be less than 1 μg / L, confirming that the anion components were removed by the ion exchanger.

[0042] When measurements similar to those in Example 1 were carried out by changing the pH of the treated water and the concentration of hypobromous acid, the same results as in Example 1 were obtained. [Explanation of symbols]

[0043] 1A~1C,2A~2C,3A~3C Pure water production equipment 15 Ultraviolet irradiation device 16, 16a, 16b Second ion exchange device (anion removal means) 18 TOC meter (TOC analysis means) 20 Catalyst tower 21 Hypohalous acid addition means 22 pH adjustment means 23 Reducing agent addition means 24 Hydrogen peroxide addition method

Claims

1. a hypohalous acid adding means for adding hypohalous acid to the water to be treated that contains organic matter; an ultraviolet irradiation device located downstream of the hypohalous acid adding means and irradiating ultraviolet light onto the water to be treated to which the hypohalous acid has been added; A pipe connected to an inlet of the ultraviolet irradiation device; an addition point provided in the piping to which a pH adjusting solution is added; a pH adjusting means connected to the addition point and adjusting the pH of the water to be treated to 3 or more and 8 or less; The pure water production apparatus, wherein the addition point and the ultraviolet irradiation device are connected only by the piping.

2. a hypohalous acid adding means for adding hypohalous acid to the water to be treated that contains organic matter; an ultraviolet irradiation device located downstream of the hypohalous acid adding means and irradiating ultraviolet light onto the water to be treated to which the hypohalous acid has been added; A pipe in which the ultraviolet irradiation device is installed; an addition point provided in the piping to which the hypohalous acid is added; The pure water production apparatus, wherein the addition point and the ultraviolet irradiation device are connected only by the piping.

3. 3. The pure water producing apparatus according to claim 1, further comprising a TOC analysis means for measuring the TOC of the water to be treated upstream of the hypohalous acid addition means, wherein the hypohalous acid addition means adds hypohalous acid in an amount 30 times by weight or more of the TOC concentration measured by the TOC analysis means.

4. the organic matter includes urea; 3. The pure water producing apparatus according to claim 1, further comprising a urea analysis means for measuring urea in the water to be treated upstream of the hypohalous acid addition means, wherein the hypohalous acid addition means adds hypohalous acid at a concentration five times by weight or more of the urea concentration measured by the urea analysis means.

5. 5. The water purification system according to claim 1, wherein the hypohalous acid is hypobromous acid.

6. 6. The pure water producing apparatus according to claim 5, wherein the hypohalous acid adding means comprises a sodium bromide supply means, a sodium hypochlorite supply means, and a mixing means for mixing sodium bromide and sodium hypochlorite.

7. 7. The water purifying apparatus according to claim 1, further comprising an ion exchange device located downstream of the ultraviolet irradiation device.

8. 8. The water purifying apparatus according to claim 1, further comprising another ultraviolet irradiation device located downstream of the ultraviolet irradiation device.

9. Adding hypohalous acid to water to be treated that flows through a pipe and contains organic matter; Adding a pH adjusting solution to the water to be treated from an addition point provided in the piping to adjust the pH of the water to be treated to 3 or more and 8 or less; and irradiating the water to be treated, to which the hypohalous acid has been added and the pH has been adjusted, with ultraviolet light by an ultraviolet irradiation device connected to the piping, The method for producing pure water, wherein the addition point and the ultraviolet irradiation device are connected only by the piping.

10. The hypohalous acid is added by a hypohalous acid adding means, 10. The method for producing pure water according to claim 9, wherein the hypohalous acid is added to the piping at an addition point, and the addition point of the hypohalous acid and the ultraviolet irradiation device are connected only by the piping.

11. 11. The method for producing pure water according to claim 9, wherein the water to be treated contains urea.

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