Water treatment system, method for producing pure water, and water treatment method

Abstract

The present invention provides a water treatment system for more efficiently removing hardly decomposable organic substances. A pure water production device (1A) (water treatment system) includes: a halogen oxyacid addition unit (21) that adds a halogen oxyacid to water to be treated containing organic substances; and an ion exchanger filling device (14) that is located downstream of the halogen oxyacid addition unit (21) and filled with at least an anion exchanger. The water to be treated after adding the halogen oxyacid is passed through the ion exchanger filling device (14).

Description

Technical Field

[0001] This application is based on Japanese Application No. 2020-152091 filed on September 10, 2020, and Japanese Application No. 2021-137253 filed on August 25, 2021, and claims priority based on these applications. The entire contents of these applications are incorporated herein by reference.

[0002] The present invention relates to a water treatment system, a method for producing pure water, and a water treatment method. Background Art

[0003] With the increasing demand for high-quality pure water, in recent years, methods for decomposing and removing trace amounts of organic substances, particularly hardly decomposable organic substances such as urea, contained in pure water have been studied. Japanese Unexamined Patent Application Publication No. 2011-183275 and Japanese Unexamined Patent Application Publication No. 2012-11356 disclose a method in which sodium bromide and sodium hypochlorite are added to water to be treated containing urea, and the water to be treated is retained in a reaction tank to remove urea. Summary of the Invention

[0004] In the methods disclosed in Japanese Unexamined Patent Application Publication No. 2011-183275 and Japanese Unexamined Patent Application Publication No. 2012-11356, it is necessary to retain the water to be treated in the reaction tank for a long time, and urea cannot be removed efficiently. An object of the present invention is to provide a water treatment system capable of more efficiently removing hardly decomposable organic substances.

[0005] The water treatment system of the present invention includes: a halogen oxyacid addition unit that adds a halogen oxyacid to water to be treated containing an organic substance; and an ion exchanger filling device that is located downstream of the halogen oxyacid addition unit and filled with at least an anion exchanger. The water treatment system passes the water to be treated after adding the halogen oxyacid through the ion exchanger filling device.

[0006] According to the present invention, a water treatment system capable of more efficiently removing hardly decomposable organic substances can be provided.

[0007] The above and other objects, features, and advantages of the present application will become apparent from the following detailed description with reference to the accompanying drawings illustrating the present application. Brief Description of the Drawings

[0008] Figure 1 It is a schematic structural diagram of a pure water production apparatus according to a first embodiment.

[0009] Figure 2 It is a schematic structural diagram of a pure water production apparatus according to a second embodiment.

[0010] Figure 3This is a schematic structural diagram of the pure water production device according to the third embodiment.

[0011] Figure 4 This is a schematic structural diagram of the pure water production device according to the fourth embodiment.

[0012] Figure 5 This is a schematic structural diagram of the pure water production device according to the fifth embodiment.

[0013] Figure 6 This is a schematic structural diagram of the pure water production device according to the sixth embodiment.

[0014] Figure 7 This is a schematic structural diagram of the pure water production device according to the seventh embodiment.

[0015] Figure 8 This is a graph showing the relationship between the space velocity of the water to be treated and the urea removal rate.

[0016] Figure 9 This is a graph showing the relationship between the water passing time of the water to be treated and the urea removal rate. Detailed Embodiments

[0017] Hereinafter, embodiments of the water treatment system, the pure water production method, and the water treatment method of the present invention will be described with reference to the accompanying drawings. Figure 1 The schematic structure of the pure water production device 1A according to the first embodiment of the present invention is shown. The pure water production device 1A is an example of a water treatment system. The pure water production device 1A (primary system) and the downstream subsystem (secondary system) together constitute an ultrapure water production device. The raw water supplied to the pure water production device 1A (hereinafter referred to as the water to be treated) contains organic substances including urea.

[0018] The pure water production device 1A has a filter 11, an activated carbon tower 12, a first ion exchange device 13, an ion exchange body filling device 14, a reverse osmosis membrane device 15, an ultraviolet irradiation device (ultraviolet oxidation device) 16, a second ion exchange device 17, and a degassing device 18. They are arranged in series in this order along the main pipe L1 from upstream to downstream with respect to the flow direction D of the water to be treated. After the water to be treated is boosted by a raw water pump (not shown), it passes through the filter 11 to remove dust and the like with a relatively large particle size, and passes through the activated carbon tower 12 to remove impurities such as high-molecular organic substances. The structure of the filter 11 is not limited, but a sand filter is used in this embodiment. The first ion exchange device 13 has a cation tower (not shown) filled with cation exchange resin, a decarbonation tower (not shown), and an anion tower (not shown) filled with anion exchange resin. They are arranged in series in this order from upstream to downstream. The water to be treated removes cation components through the cation tower, removes carbonic acid through the decarbonation tower, and removes anion components through the anion tower.

[0019] The pure water production apparatus 1A is provided with a halogen oxyacid addition unit 21 that adds a halogen oxyacid to the water to be treated containing urea. The halogen oxyacid sometimes exists as an ion or an acid depending on the pH. The halogen oxyacid is a general term for their forms. In the present embodiment, the halogen oxyacid is hypohalous acid, but it may also be halic acid, perhalic acid, hypohalous acid, etc. In terms of stability, hypohalous acid is preferably used. Further, in the present embodiment, the hypohalous acid is hypobromous acid, but it may also be hypochlorous acid or hypoiodous acid. In addition to the halogen oxyacid, for example, combined chlorine or combined bromine, etc., which can be measured by a general residual chlorine meter, may also be used. In terms of the removal efficiency of urea, a halogen oxyacid is preferred. The halogen oxyacid addition unit 21 includes a storage tank 21a for bromide salt (a supply unit for bromide salt), a storage tank 21b for an oxidizing agent (a supply unit for an oxidizing agent), a retention tank 21c for bromide salt and an oxidizing agent (a mixing unit for bromide salt and an oxidizing agent), and a transfer pump 21d. Examples of the bromide salt include sodium bromide (NaBr) and potassium bromide. Examples of the oxidizing agent include hypochlorite (e.g., sodium hypochlorite (NaClO)), permanganate, hydrogen peroxide, persulfate, etc. Since hypobromous acid is difficult to store for a long time, it is generated by mixing the bromide salt and the oxidizing agent at the time of use. The hypobromous acid generated in the retention tank 21c is pressurized by the transfer pump 21d and added to the water to be treated flowing through the main pipe L1. The bromide salt and the oxidizing agent may be directly supplied to the main pipe L1, and they may be stirred by the flow of the water to be treated in the main pipe L1 to generate hypobromous acid. The hypobromous acid may be continuously added to the water to be treated or intermittently added to the water to be treated. Alternatively, a line mixer, an orifice, etc. may be provided in the main pipe L1, and a turbulent flow may be formed by these devices to mix the bromide salt and the oxidizing agent to generate hypobromous acid. The added halogen oxyacid may be only one kind, or a mixture of two or more kinds of halogen oxyacids may be added.

[0020] The concentration of the halogen oxyacid is preferably 6 to 200 times by weight of the TOC (total organic carbon) in the water to be treated, and more preferably 30 times by weight or more. If the halogen oxyacid added exceeds 200 times by weight, the load on the subsequent equipment becomes high. As shown in Example 5 described later, depending on the required water quality, by adding 6 times by weight of the halogen oxyacid, it is possible to obtain a sufficient urea removal effect. Further, as will be described in Example 4 later, it is preferred that the concentration of the divalent anion contained in the water to be treated is in the range of 0 to 0.4 mmol / L. The concentration of the halogen oxyacid, the TOC, and the divalent anion concentration in the water to be treated are the values at the inlet of the ion exchanger filling device 14.

[0021] The connection part of the halogen oxyacid addition unit 21 to the main pipe L1, that is, the addition part of the halogen oxyacid to the water to be treated is in the middle of the first ion exchange device 13 and the ion exchanger filling device 14. That is, the ion exchanger filling device 14 is located immediately downstream of the connection part of the halogen oxyacid addition unit 21 to the main pipe L1, and the water to be treated after adding the halogen oxyacid is immediately treated by the ion exchanger filling device 14. "Immediately downstream" means that between the addition part of the halogen oxyacid addition unit 21 and the ion exchanger filling device 14, there is no water treatment device having a liquid contact part made of an organic material. The water treatment device is any device for removing impurities contained in the water to be treated, including filtration membranes such as reverse osmosis membranes, ultrafiltration membranes, and microfiltration membranes, ion exchange devices, degassing devices, etc., but does not include heat exchangers, pumps, valves, meters, etc.

[0022] The ion exchanger filling device 14 is a tower filled with at least an anion exchanger. A cation exchanger can also be filled in the ion exchanger filling device 14. In this case, the cation exchanger and the anion exchanger are filled in a mixed bed, but they can also be filled in a multiple bed. In the latter case, it is preferable that the anion exchanger is on the upstream side of the cation exchanger. As described in Example 1 below, from the viewpoint of urea removal efficiency, it is more preferable that only the anion exchanger is filled in the ion exchanger filling device 14. On the other hand, in the case of filling a cation exchanger and an anion exchanger in a mixed bed, the positively charged eluate flowing out from the anion exchanger can be adsorbed by the cation exchanger. As the anion exchanger and the cation exchanger, it is preferable to use an anion exchange resin and a cation exchange resin, but a monolithic or fibrous anion exchanger and cation exchanger can also be used. The ion exchange resin can be either a gel type or an MR type. The anion exchange resin is not limited and can be either a strongly basic resin or a weakly basic resin. In the case of a strongly basic resin, it can be in the OH form or the Cl form, etc. In addition, the ion exchanger filling device 14 can be an electro-deionized water production device (EDI) filled with an anion exchange resin.

[0023] By bringing the water to be treated after adding the halogen oxyacid into contact with the anion exchanger filled in the ion exchanger filling device 14, urea can be removed efficiently in a short time. Most of the urea is removed within about several seconds to several minutes when the water to be treated passes through the ion exchanger filling device 14. In the conventional reaction tank, a residence time of several hours is required. Therefore, compared with the reaction tank, urea can be removed in an extremely short time. In addition, in the case of the conventional reaction tank, in order to ensure the residence time of the water to be treated, the enlargement of the device is inevitable. However, since the ion exchanger filling device 14 has the same structure as a general ion exchange device, it is also more advantageous than the reaction tank from the viewpoint of the installation area.

[0024] Thus, by bringing the treated water added with a halogen oxyacid, particularly hypohalous acid, into contact with an anion exchanger, the inventors consider the reasons for being able to remove urea efficiently in a short time as follows: By bringing the halogen oxyacid into contact with the anion exchanger, the halogen oxyacid ions are captured by the anion exchanger. As a result, the halogen oxyacid ions are concentrated inside the anion exchanger. In addition, the treated water flows along the voids of the anion exchanger (in the case of resin, the gaps between the resins), so urea is likely to stay in the anion exchanger. As described above, the possibility of contact between the halogen oxyacid ions and urea increases, and urea can be removed in a short time. Therefore, in order to capture the halogen oxyacid ions, the ion exchanger filling device 14 needs to be filled with at least an anion exchanger.

[0025] A reducing agent adding unit 22 is provided between the ion exchanger filling device 14 and the reverse osmosis membrane device 15. The reducing agent adding unit 22 is a removal unit for the halogen oxyacid remaining in the treated water. Hydrogen peroxide is used as the reducing agent, but sulfite can also be used. The reducing agent adding unit 22 has a storage tank 22a for the reducing agent and a transfer pump 22b. The reducing agent is pressurized by the transfer pump 22b and added to the treated water passing through the main pipe L1 between the ion exchanger filling device 14 and the reverse osmosis membrane device 15. The removal unit for the halogen oxyacid is not limited to the reducing agent adding unit 22 as long as it has the same effect. For example, it can be a platinum group metal catalyst carrier such as palladium (Pd), activated carbon, etc. Or, these removal units for the halogen oxyacid can be combined in series.

[0026] The reverse osmosis membrane device 15 removes the excess reducing agent. The removal unit for the reducing agent can be an ion exchange resin, an electro-deionized water production device, an ultraviolet irradiation device, a platinum group metal catalyst carrier, etc., and these reducing agent removal units can be combined in series. The platinum group metal catalyst carrier is composed of a platinum group metal catalyst composed of a platinum group metal supported on an anion exchanger. As the anion exchanger, an anion exchange resin, a monolithic organic porous anion exchanger, etc. can be used. The platinum group metal catalyst decomposes reducing agents such as hydrogen peroxide through its catalytic action. As the platinum group metal, platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), iridium (Ir), etc. can be mentioned, and one of them can be used alone, or two or more of them can be used in combination. Among these platinum group metals, Pt and Pd are preferred, and Pd is further preferred from the viewpoint of cost. The installation position of the platinum group metal catalyst carrier is not particularly limited as long as it is downstream of the adding position of the reducing agent, and it is preferably downstream of the second ion exchange device 17 described later. Since the second ion exchange device 17 removes the anion components, the reducing agent removal performance of the platinum group metal catalyst is improved.

[0027] The ultraviolet irradiation device 16 irradiates the water to be treated with ultraviolet rays. As the ultraviolet irradiation device 16, for example, an ultraviolet lamp including at least one wavelength among 254 nm, 185 nm, and 172 nm can be used. The anion exchanger (and cation exchanger) filled in the ion exchanger filling device 14 deteriorates due to contact with halogen oxyacids as oxidants, and organic substances flow out into the water to be treated. This organic substance is decomposed by the reverse osmosis membrane device 15, the ultraviolet irradiation device 16, and the second ion exchange device 17 (cation exchanger). This will be described in detail below.

[0028] Since the oxidation action of halogen oxyacids such as hypobromous acid is strong, for example, it is easy to deteriorate the membrane formed of an organic material. Therefore, originally, as in the present embodiment, when halogen oxyacids are brought into contact with an organic structure such as an anion exchanger, it is likely to cause a decrease in the water quality of the water to be treated due to the peeling of the organic material, so it is not preferable. On the other hand, the inventors of the present application found that by bringing the water to be treated after adding halogen oxyacids into contact with an anion exchanger, urea can be removed in a short time and with high efficiency. Therefore, regardless of the problem that the possibility of peeling of the organic material increases in the present embodiment, the water to be treated after adding halogen oxyacids is intentionally brought into contact with the anion exchanger. As a result, in order to remove the organic substances that may be generated in the subsequent processes, a reverse osmosis membrane device 15, an ultraviolet irradiation device 16, and a second ion exchange device 17 are provided.

[0029] In other words, the following description can also be made. In the present embodiment, an anion exchanger is essential for removing urea, and thus the anion exchanger of the ion exchanger filling device 14 is intentionally brought into contact with a halogen oxoacid. However, for other water treatment devices (such as organic membranes) having a liquid contact portion made of an organic material, even if they are brought into contact with a halogen oxoacid, it is of no help in removing urea or the contribution to urea removal is small. In addition, if the halogen oxoacid is brought into contact, the treatment performance of other components will decrease due to the deterioration of the organic material. Therefore, these water treatment devices are arranged at the subsequent stage of the ion exchanger filling device 14 so as not to be in contact with a high-concentration halogen oxoacid. That is to say, in the present embodiment, between the addition portion of the halogen oxoacid to the water to be treated and the ion exchanger filling device 14, there is no water treatment device having a liquid contact portion made of an organic material that comes into contact with the water to be treated after the addition of the halogen oxoacid. On the downstream side of the ion exchanger filling device 14, due to the consumption of the halogen oxoacid in the ion exchanger filling device 14 and the decomposition of the halogen oxoacid based on the reducing agent, the halogen oxoacid concentration of the water to be treated is significantly reduced. Therefore, even if there is deterioration of the water quality of the water to be treated caused by the peeling and elution of the organic material of each water treatment device on the downstream side of the ion exchanger filling device 14, particularly on the downstream side of the reducing agent addition unit 22, it is limited. All in all, in the present embodiment, by limiting the water treatment device having a liquid contact portion made of an organic material that comes into contact with a halogen oxoacid to only the device essential for urea removal, both the improvement of the urea removal efficiency and the suppression of the outflow of the organic material are achieved.

[0030] The second ion exchange device 17 located downstream of the ultraviolet irradiation device 16 is a regenerative ion exchange resin tower filled with an anion exchange resin and a cation exchange resin. The decomposition products of the organic matter generated in the water to be treated by ultraviolet irradiation are removed by the second ion exchange device 17. Thereafter, dissolved oxygen, carbonic acid, etc. in the water to be treated are removed by the degassing device 18.

[0031] Next, refer to Figures 2 - 7 Other embodiments of the pure water manufacturing device of the present invention will be described. The structures and effects for which the description is omitted are the same as those of the first embodiment. From the second to the sixth embodiments, it can be seen that the halogen oxoacid addition unit 21 and the ion exchanger filling device 14 are assembled into the pure water manufacturing device as inseparable components, and in addition, the degree of freedom of the installation position of this component is high.

[0032] (Second Embodiment)

[0033] In Figure 2The schematic structure of the pure water production apparatus 1B according to the second embodiment is shown. A halogen oxyacid is added to the treated water in the activated carbon tower 12. Subsequently, the ion exchanger filling device 14 is provided between the addition section of the halogen oxyacid and the first ion exchange device 13. That is, on the main pipe L1, in the flow direction D of the water to be treated, from the upstream to the downstream, the activated carbon tower 12, the addition section of the halogen oxyacid, the ion exchanger filling device 14, the addition section of the reducing agent, and the first ion exchange device 13 are arranged in series in this order. In the present embodiment, since there is also no water treatment device having a liquid contact portion made of an organic material between the addition section of the halogen oxyacid and the ion exchanger filling device 14, deterioration of the quality of the water to be treated due to peeling and elution of the organic material is prevented. In addition, components derived from the oxidizing agent (in the present embodiment, bromide ions, chloride ions, and Na ions) and components derived from the reducing agent can be removed not only by the reverse osmosis membrane device 15 and the second ion exchange device 17 but also by the first ion exchange device 13. Therefore, the load on the water treatment device subsequent to the first ion exchange device 13 can be reduced.

[0034] (Third Embodiment)

[0035] In Figure 3 the schematic structure of the pure water production apparatus 1C according to the third embodiment is shown. The halogen oxyacid is added at two locations, upstream and downstream of the filtration device 11. Specifically, the halogen oxyacid addition unit 21 is connected to the downstream of the filtration device 11. A reaction tank 20 is provided upstream of the filtration device 11, and the other halogen oxyacid addition unit 23 is connected to the reaction tank 20. Although not shown in the figure, the other halogen oxyacid addition unit 23 may not be connected to the upstream of the reaction tank 20. The halogen oxyacid addition unit 21 and the other halogen oxyacid addition unit 23 share the storage tanks 21a, 21b, the retention tank 21c, and the transfer pump 21d, but these devices may also be provided separately in the halogen oxyacid addition unit 21 and the other halogen oxyacid addition unit 23. The halogen oxyacid is added to the water to be treated in the reaction tank 20, and after the water to be treated has been retained in the reaction tank 20 for a given time, it is sent to the filtration device 11. Although the water to be treated with a high halogen oxyacid concentration is supplied to the filtration device 11, since the filtration device 11 is a sand filtration device, deterioration due to contact with the halogen oxyacid does not occur. In addition, since the halogen oxyacid can be removed by the activated carbon tower 12, it is not necessary to provide the reducing agent addition unit 22.

[0036] The structure of the reaction tank 20 is basically the same as that of the conventional reaction tank. That is, the reaction tank 20 has a flow path (not shown) inside, and urea is removed while the water to be treated flows along the flow path for a given time. However, in the present embodiment, since halogen oxyacid is added again to the water to be treated flowing out of the reaction tank 20, it is not necessary to remove urea in the reaction tank 20. Generally, as the urea concentration decreases, the urea removal efficiency tends to decrease. For example, the time required to reduce the urea concentration to 10% of the original concentration is of the same order as the time required to reduce it from 10% to 1%. In the present embodiment, since the reaction tank 20 only needs to roughly remove urea, a long residence time is not required. Therefore, compared with the prior art, the treatment of urea can be carried out in a short time, and the miniaturization of the reaction tank 20 becomes possible. On the other hand, the amount of urea treated by the ion exchanger filling device 14 is greatly reduced by the reaction tank 20, so the load on the ion exchanger filling device 14 is reduced. As a result, the replacement frequency of the anion exchanger (and cation exchanger) is reduced, and the amount of organic substances generated due to the deterioration of the anion exchanger (and cation exchanger) is also reduced. In addition, the halogen oxyacid adding unit 21 of the present embodiment is connected to the main pipe L1 at the outlet of the filtration device 11. However, the position of the connection part of the halogen oxyacid adding unit 21 is not limited to this, and the halogen oxyacid adding unit 21 may also be connected to the main pipe L1 at the position of other embodiments.

[0037] The reaction tank 20 may also be omitted. In addition, either the halogen oxyacid adding unit 21 or the other halogen oxyacid adding unit 23 may be provided alone, or both may be provided. For example, when the reaction tank 20 is provided and only the other halogen oxyacid adding unit 23 is provided as the halogen acid adding unit, the halogen oxyacid not consumed in the reaction tank 20 can be brought into contact with the anion exchanger filled in the ion exchanger filling device 14. In addition, in the present embodiment, as in the second embodiment, the components derived from the oxidant and the components derived from the reductant can also be removed by the first ion exchange device 13.

[0038] (Fourth Embodiment)

[0039] In Figure 4The schematic structure of the pure water production apparatus 1D according to the fourth embodiment is shown. The halogen oxyacid is added upstream of the filtration device 11. Subsequently, the ion exchanger filling device 14 is disposed between the addition section of the halogen oxyacid and the filtration device 11. That is, on the main pipe L1, in the flow direction D of the water to be treated, from the upstream toward the downstream, the addition section of the halogen oxyacid, the ion exchanger filling device 14, the filtration device 11, the activated carbon tower 12, and the first ion exchange device 13 are arranged in series in this order. In addition, since the filtration device 11 is a sand filtration device, as described above, it is difficult to be affected by the above-mentioned halogen oxyacid. Therefore, the filtration device 11 may be disposed between the addition section of the halogen oxyacid and the ion exchanger filling device 14. In the present embodiment, in the case where a small amount of pulverized matter flows out from the anion exchanger of the ion exchanger filling device 14, it can be removed by the downstream filtration device 11. In addition, since the halogen oxyacid can be removed by the activated carbon tower 12, it is not necessary to provide the reducing agent addition unit 22. In the present embodiment, as in the third embodiment, the reaction tank 20 can also be provided upstream of the ion exchanger filling device 14. In addition, in the present embodiment, as in the second embodiment, the components derived from the oxidizing agent and the components derived from the reducing agent can also be removed by the first ion exchange device 13.

[0040] (Fifth Embodiment)

[0041] In Figure 5 the schematic structure of the pure water production apparatus 1E according to the fifth embodiment is shown. The filtration device is integrated with the ion exchanger filling device 114. Specifically, sand and the ion exchanger are filled in a common tower in a multiple-bed mixed-bed manner. In the present embodiment, cost reduction of the apparatus and reduction of the installation area of the apparatus can be achieved. In addition, in the present embodiment, as in the second embodiment, the components derived from the oxidizing agent and the components derived from the reducing agent can also be removed by the first ion exchange device 13. Since the halogen oxyacid can be removed by the activated carbon tower 12, it is not necessary to provide the reducing agent addition unit 22.

[0042] (Sixth Embodiment)

[0043] In Figure 6The schematic structure of the pure water production device 1F according to the sixth embodiment is shown. The pure water production device 1F of this embodiment includes a dissolved oxygen adjustment unit (deoxygenation device 18A, dissolved oxygen meter 19). The deoxygenation device 18A is provided upstream of the halogen oxyacid addition unit 21, specifically between the first ion exchange device 13 and the ion exchange medium filling device 14. The addition part of the halogen oxyacid is provided between the deoxygenation device 18A and the ion exchange medium filling device 14. The deoxygenation device 18A adjusts the dissolved oxygen concentration of the water to be treated at the inlet of the ion exchange medium filling device 14 to be 0.1 mg / L or more and 1 mg / L or less. A dissolved oxygen meter 19 is provided between the deoxygenation device 18A and the ion exchange medium filling device 14. The dissolved oxygen meter 19 measures the dissolved oxygen concentration of the water to be treated at the outlet of the deoxygenation device 18A. The dissolved oxygen concentration measured by the dissolved oxygen meter 19 is sent to the control device 24 of the deoxygenation device 18A. The control device 24 controls the deoxygenation device 18A based on this dissolved oxygen concentration so that the dissolved oxygen concentration measured by the dissolved oxygen meter 19 is 0.1 mg / L or more and 1 mg / L or less. As a result, the dissolved oxygen concentration of the water to be treated at the inlet of the ion exchange medium filling device 14 is controlled to be 1 mg / L or less.

[0044] The deoxygenation device 18A is a device that removes oxygen from the water to be treated and reduces the dissolved oxygen concentration of the water to be treated. Therefore, it is the same as or similar to the degassing device 18 in the first to fifth embodiments. Therefore, in this embodiment, the degassing device 18 is omitted, but the degassing device 18 can also be provided at the same position as in the first to fifth embodiments. The type of the deoxygenation device 18A is not limited. For example, a vacuum degassing device can be used. Generally, in a vacuum degassing device, a gas-liquid contact material for increasing the surface area of water is filled in a degassing tower, the gas pressure in the degassing tower is reduced by a vacuum pump, the pure water as the water to be treated is set to a vacuum state, and the dissolved oxygen is removed. The dissolved oxygen concentration can be controlled by adjusting the vacuum degree in the degassing tower using a vacuum pump. Furthermore, the degassing performance can be improved by introducing nitrogen. In this case, the dissolved oxygen concentration can be controlled by adjusting the vacuum degree and the nitrogen inflow amount (nitrogen partial pressure). A deoxygenation device using a deoxygenation membrane can also be used. In this case, a vacuum pump is also used as in the vacuum degassing device, and the dissolved oxygen concentration can be controlled by adjusting the vacuum degree. These deoxygenation devices 18A can be arranged in series in two or more stages. As other deoxygenation devices 18A, a structure in which hydrogen (H2) is added to the water to be treated and the water to be treated is brought into contact with a palladium (Pd) catalyst can also be used. Through the palladium catalyst, oxygen and hydrogen react to form water, thereby removing oxygen.

[0045] Since the resin filled in the ion exchanger filling device 14 is a liquid contact part made of an organic material, if an oxidizing agent such as a halogen oxyacid comes into contact with such a liquid contact part, the resin as the liquid contact part will undergo oxidative deterioration, and the treated water quality will deteriorate. In addition, the resin swells due to oxidative deterioration, resulting in an increase in the differential pressure of the passing water pressure. The inventor found that if the dissolved oxygen concentration exceeds 1 mg / L, the oxidation of the oxidizing agent is promoted, resulting in conditions such as a decrease in water quality and an increase in the differential pressure of the passing water pressure. By adjusting the dissolved oxygen concentration of the water to be treated to 1 mg / L or less, the oxidizing power of the oxidizing agent is reduced, and the oxidative deterioration of the resin can be alleviated. The lower limit of the dissolved oxygen concentration of the water to be treated is not particularly limited, but preferably 0.1 mg / L or more. If the dissolved oxygen concentration is less than 0.1 mg / L, the effect of preventing the oxidative deterioration of the liquid contact part is small and limited even if there is any. In addition, since reducing the dissolved oxygen concentration to less than 0.1 mg / L will lead to the enlargement of the vacuum pump of the deoxidizing device 18A and an increase in the power cost of the vacuum pump, it is not preferred.

[0046] As described above, several embodiments have been described, but the pure water production device of the present invention is not limited to these. For example, in the first to sixth embodiments, the first ion exchange device 13 may be omitted, and an EDI may be provided between the reverse osmosis membrane device 15 and the ultraviolet irradiation device 16. In addition, in all of the above embodiments, multiple reverse osmosis membrane devices 15 may be provided in multiple stages or in series. In this case, a halogen oxyacid addition unit 21, an ion exchanger filling device 14, and a reducing agent addition unit 22 may be provided in this order between the pre-stage reverse osmosis membrane device and the post-stage reverse osmosis membrane device. In the sixth embodiment, the installation location of the dissolved oxygen adjustment unit (deoxidizing device 18A, dissolved oxygen meter 19) is not particularly limited. For example, multiple reverse osmosis membrane devices 15 may be provided in series, and a dissolved oxygen adjustment unit, a halogen oxyacid addition unit 21, an ion exchanger filling device 14, and a reducing agent addition unit 22 may be provided in the middle. In other words, in Figure 6 it is possible to provide another reverse osmosis membrane device 15 between the first ion exchange device 13 and the deoxidizing device 18A. In this case, the first ion exchange device 13 may be omitted.

[0047] In addition, for example, the halogen oxyacid addition unit 21, the ion exchanger filling device 14, and the reducing agent addition unit 22 may also be provided downstream of the reverse osmosis membrane device 15. The second ion exchange device 17 may be an electro-deionized water production device (EDI). In addition, the present invention can also be used for the treatment of recycled water and the treatment of wastewater.

[0048] (Seventh Embodiment)

[0049] Furthermore, the technical idea shown in the sixth embodiment can be extended to a water treatment system in which an oxidizing agent containing a halogen oxyacid or an oxidizing agent other than a halogen oxyacid is added to the water to be treated. That is, general water treatment devices (reverse osmosis membranes, ion exchange resins, etc.) used in the water treatment system are oxidatively deteriorated when an oxidizing agent flows in, and their treatment performance is significantly reduced. Therefore, an oxidizing agent removal unit such as an activated carbon tower is usually provided upstream of the water treatment device or downstream of the addition section of the oxidizing agent to the water to be treated. However, if the activated carbon deteriorates over time, the oxidizing agent removal performance decreases, so the oxidizing agent may flow into the downstream water treatment device. In addition, since the activated carbon itself is oxidatively deteriorated, organic substances are eluted, which sometimes becomes a load on the subsequent device. As a result, the downstream water treatment device deteriorates, causing a decrease in the quality of pure water. In addition, for the purpose of sterilizing the water treatment device, a bactericide (oxidizing agent) may be passed through the water treatment device to such an extent that the water treatment device deteriorates. However, depending on the conditions, the water treatment device may be oxidatively deteriorated by the bactericide. The method of removing the oxidizing agent by adding a reducing agent is different from that of an activated carbon tower, etc. Although the possibility of equipment deterioration over time is low, the remaining reducing agent becomes a load on the subsequent water treatment device. In the advanced oxidation process (AOP) using an oxidizing agent, the remaining oxidizing agent may also deteriorate the resin, etc. of the subsequent water treatment device.

[0050] In Figure 7The schematic structure of the pure water production apparatus 1G according to the seventh embodiment is shown. In the present embodiment, instead of the first ion exchange apparatus 13 of the sixth embodiment, a softening apparatus 25 is provided. Further, instead of the halogen oxyacid addition unit 21, a more general oxidant addition unit 27 is provided. The softening apparatus 25 is an apparatus that removes hardness components such as calcium and magnesium, and usually, ion exchange resins are filled therein. Generally, the reverse osmosis membrane apparatus 15 promotes oxidative degradation caused by residual chlorine or the like in the presence of hardness, and thus the softening apparatus 25 is provided upstream of the reverse osmosis membrane apparatus 15. The installation location of the softening apparatus 25 is not limited as long as it is upstream of the reverse osmosis membrane apparatus 15. An EDI 26 is provided between the reverse osmosis membrane apparatus 15 and the ultraviolet irradiation apparatus 16. When an oxidant leaks into the treated water of the reverse osmosis membrane apparatus 15, the treated water containing the oxidant is passed through the EDI 26. However, since the dissolved oxygen concentration of the water to be treated is adjusted to 1 mg / L or less by the deoxygenation apparatus 18A, oxidative degradation of the resin filled in the EDI 26 is suppressed, and stable treated water quality can be obtained. In addition, in the present embodiment, the softening apparatus 25 and the EDI 26 are not essential. Although not shown in the figure, the pure water production apparatus may also be provided with a filter 11, an activated carbon tower 12, a first ion exchange apparatus 13, a deoxygenation apparatus 18A, a dissolved oxygen meter 19, a reverse osmosis membrane apparatus 15, an ultraviolet irradiation apparatus (ultraviolet oxidation apparatus) 16, a second ion exchange apparatus 17, and a degassing apparatus 18 in this order, and an oxidant addition unit 27 may be provided between the dissolved oxygen meter 19 and the reverse osmosis membrane apparatus 15.

[0051] Therefore, the water treatment system includes: a water treatment apparatus having a liquid contact portion made of an organic material; an oxidant addition unit located upstream of the water treatment apparatus that adds an oxidant to the water to be treated; and a deoxygenation apparatus located upstream of the water treatment apparatus that adjusts the dissolved oxygen concentration at the inlet of the water treatment apparatus to 1 mg / L or less. Examples of the water treatment apparatus include a reverse osmosis membrane apparatus, an ion exchange apparatus filled with ion exchange resins, or an EDI. Further, the water treatment method includes: adding an oxidant to the water to be treated using an oxidant addition unit upstream of a water treatment apparatus having a liquid contact portion made of an organic material; and adjusting the dissolved oxygen concentration at the inlet of the water treatment apparatus to 1 mg / L or less using a deoxygenation apparatus located upstream of the water treatment apparatus. The oxidant is not limited to halogen oxyacids such as hypohalous acids, and may be permanganic acid, hydrogen peroxide, persulfuric acid, or the like, or may be a bactericide used in the water treatment apparatus. Further, the water to be treated may contain free chlorine, combined chlorine, combined bromine, or the like.

[0052] In addition, although the oxidant addition unit 27 is omitted and no oxidant is added by the oxidant addition unit 27, the present invention can also be applied when the water to be treated contains an oxidant. Alternatively, in the sixth embodiment, the halogen oxyacid addition unit 21 and the reducing agent addition unit 22 can also be deleted. In this case, the oxidative degradation of the ion exchange resin filled in the reverse osmosis membrane device 15 and the EDI 26 is suppressed by the dissolved oxygen adjustment unit (deoxidation device 18A, dissolved oxygen meter 19).

[0053] Therefore, the water treatment system includes: a water treatment device that is supplied with the water to be treated containing an oxidant and has a liquid contact portion made of an organic material; and a deoxidation device that is located upstream of the water treatment device and adjusts the dissolved oxygen concentration of the water to be treated at the inlet of the water treatment device to 1 mg / L or less. In addition, the water treatment method includes the following steps: supplying the water to be treated containing an oxidant to the water treatment device having a liquid contact portion made of an organic material; and adjusting the dissolved oxygen concentration of the water to be treated at the inlet of the water treatment device to 1 mg / L or less.

[0054] (Example 1)

[0055] The treated water prepared by adding halogen oxyacids to ultrapure water was passed through a column of a simulated ion exchange device, and the urea removal rate was measured. 100 mL of ion exchange resin was packed in the column, and the treated water was passed through at a flow rate of 12 L / h (SV 120 ( / h)). The addition amount of urea was adjusted so that the urea concentration was 80 μg / L. As the halogen oxyacid, hypobromous acid was added at a concentration of 2 mg-Cl2 / L (chlorine conversion concentration). NaBr was selected as the bromide salt, and NaClO was selected as the oxidant. Hypobromous acid was generated by mixing NaBr and NaClO. The concentration of hypobromous acid was measured as follows: glycine was added to the sample water to change free chlorine to combined chlorine, and then it was measured using a free chlorine reagent with a residual salt concentration meter (manufactured by HANNA). In Comparative Example 1, only 100 mL of cation exchange resin was packed in the column. In Example 1-1, only 100 mL of anion exchange resin was packed in the column. In Example 1-2, anion exchange resin and cation exchange resin were mixed and packed in the column in a volume ratio of 2:1 and a total of 100 mL. AMBERJET 1024H type (manufactured by Organo Corporation) was used as the cation exchange resin, and AMBERJET 4002OH type (manufactured by Organo Corporation) was used as the anion exchange resin. When the urea concentration of the treated water at the inlet side of the column was set as C1 and the urea concentration of the treated water of the column was set as C2, the urea removal rate was obtained as (C1 - C2) / C1 × 100 (%). The urea concentration was measured by ICP-MS (inductively coupled plasma mass spectrometry). The urea removal rate was 98% in Example 1-1, 95% in Example 1-2, and 0.5% in the comparative example. It can be seen that by bringing the treated water containing hypobromous acid into contact with the anion exchanger, urea can be efficiently removed.

[0056] (Example 2)

[0057] Using the same device as in Example 1, the urea removal rate was obtained with the space velocity of the treated water supplied to the column as a parameter. Specifically, the urea removal rates for multiple SVs (120, 240, 500, 1000, 1200) (unit ( / h)) were obtained under the conditions of Example 1-1. The addition amount of the anion exchange resin was set to 100 mL for all SVs, and the flow rate of the treated water was changed. In Figure 8The relationship between SV and the urea removal rate is shown. The smaller the SV, the longer the contact time between the water to be treated and the anion exchanger, thus improving the urea removal rate. The larger the SV, the lower the urea removal rate, but even at SV 1200 ( / h), a removal rate of 44% can be achieved. According to the required water quality of pure water, even such a level can obtain sufficient effects. Therefore, it is preferable that the water to be treated is supplied to the ion exchanger filling device 14 at a space velocity SV of 1200 ( / h) or less. When a urea removal rate of 70% or more is desired, it is preferably set to SV 500 ( / h) or less, and when a urea removal rate of 90% or more is desired, it is preferably set to SV 240 ( / h).

[0058] (Example 3)

[0059] Using the same apparatus as in Example 1, the relationship between the urea removal rate and the water passing time of the water to be treated through the ion exchanger filling device 14 was determined. Specifically, urea and hypochlorous acid were added to ultrapure water under the same conditions as in Example 1-1 to prepare the water to be treated. This water to be treated was passed through at a water passing flow rate of 120 L / h until the cumulative supply amount of BrO － reached about 2-fold equivalents of the ion exchange capacity of the anion exchange resin (the water passing time was about 700 hours). The relationship between the water passing time and the urea removal rate is shown in Figure 9 . The anion exchange resin used was non-regenerable, but maintained a good urea removal rate even for long-term water passing. Therefore, by setting the ion exchanger filling device 14 to be non-regenerative, long-term operation can be achieved and regeneration is not required either.

[0060] (Example 4)

[0061] Using the same apparatus as in Example 1, the relationship between the urea removal rate and the sulfate ion concentration of the water to be treated was determined. Specifically, in the same manner as in Example 1-1, 100 mL of ion exchange resin was filled in the column, and the water to be treated was passed through at a flow rate of 12 L / h (SV 120 ( / h)). The addition amount of urea was adjusted so that the urea concentration was 80 μg / L. As the halogen oxyacid, hypobromous acid was added at a concentration of 2 mg-Cl2 / L (chlorine conversion concentration). Furthermore, sulfuric acid was added to this water to be treated. As a result, divalent anions (SO4 2- ) were contained in the water to be treated. The results are shown in Table 1. As the concentration of divalent anions increased, the urea removal rate decreased. This is because if divalent anions coexist, it is difficult for the halogen oxyacid to be captured by the resin. However, even if the urea removal rate is 36%, sufficient effects may sometimes be obtained according to the required water quality. Therefore, the concentration of divalent anions contained in the water to be treated is preferably 0.4 mmol / L or less, and more preferably 0.1 mmol / L or less.

[0062] [Table 1]

[0063] Sulfate ion concentration (mmol / L) Urea removal rate (%) Example 4 - 1 0.001 98 Example 4 - 2 0.01 74 Example 4 - 3 0.1 54 Example 4 - 4 0.2 51 Example 4 - 5 0.4 36

[0064] (Example 5)

[0065] Using the same apparatus as in Example 1, the relationship between the urea removal rate and the halogen oxyacid concentration / TOC ratio (weight ratio) of the water to be treated was determined. Specifically, in the same manner as in Example 1-1, 100 mL of ion exchange resin was packed in the column, and the water to be treated was passed through at a flow rate of 12 L / h (SV120 ( / h)). The addition amount of urea was adjusted so that the urea concentration was 80 μg / L. As the halogen oxyacid, hypobromous acid was added at a concentration of 2 mg-Cl2 / L (chlorine conversion concentration). The results are shown in Table 2. The "hypobromous acid / TOC ratio" in the table is the halogen oxyacid concentration / TOC ratio. The higher the hypobromous acid / TOC ratio, the higher the urea removal rate. However, even when the urea removal rate is 50%, sufficient effects can be obtained according to the required water quality. Therefore, the halogen oxyacid concentration / TOC ratio of the water to be treated is preferably 6 weight times or more, more preferably 30 weight times or more. As described above, in order to suppress the influence on the equipment in the subsequent stage, the halogen oxyacid concentration / TOC ratio is preferably set to 200 weight times or less. In addition, the TOC in this example is the value obtained by converting the urea concentration into TOC.

[0066] [Table 2]

[0067]

[0068] (Example 6)

[0069] Using the same apparatus as in Example 1, the relationships between the dissolved oxygen concentration and the through-water pressure difference of the resin, and between the dissolved oxygen concentration and TOC were determined. Specifically, the treated water prepared by adding hypohalous acid to pure water was passed through the column under the same conditions as in Example 1-1 at a flow rate of 12 L / h (SV 120 ( / h)), and the urea removal rate was measured. The addition amount of urea was adjusted so that the urea concentration was 80 μg / L. As the hypohalous acid, hypobromous acid was added at a concentration of 2 mg-Cl2 / L (chlorine conversion concentration). The dissolved oxygen concentration of the treated water was changed, and the through-water pressure difference and the increase in TOC after 250 hours of water passage were measured. The increase in TOC was determined as the difference between the TOC of the treated water after removing the TOC derived from urea from the TOC of the supply water and the TOC of the treated water, and the TOC of the supply water after removing the TOC derived from urea. The results are shown in Table 3. As described above, the through-water pressure difference is related to the degree of swelling of the resin, so a low through-water pressure difference means that the resin does not swell and maintains soundness. In addition, the lower the through-water pressure difference, the lower the power cost of the pump. The urea removal rates in Examples 6-1, 6-2, and Comparative Example 6 were all 90% or more. By setting the dissolved oxygen to 1 mg / L or less, the increase in TOC was suppressed, and no increase in the through-water pressure difference was confirmed.

[0070] [Table 3]

[0071] Dissolved oxygen concentration (mg / L) Water pressure difference (Mpa) TOC increase (μg / L) Urea removal rate (%) Example 6 - 1 0.2 <0.01 25 ＞90 Example 6 - 2 1 <0.01 95 ＞90 Comparative Example 6 8 ＞0.2 1300 ＞90

[0072] (Example 7)

[0073] Using the same apparatus as in Example 1, the relationships between the dissolved oxygen concentration and the through-water pressure difference of the resin, and between the dissolved oxygen concentration and the TOC were determined. 100 mL of ion exchange resin was filled in the column, and the water to be treated was passed through at a flow rate of 12 L / h (SV 120 ( / h)). Specifically, an anion exchange resin and a cation exchange resin were mixed in a volume ratio of 2:1, totaling 100 mL, and filled in the column as a mixed bed. Hypochlorous acid of 0.1 mg-Cl2 / L was added to the supply water in which oxygen was dissolved in pure water, and the column was passed through with water. AMBERJET 1024 H type (manufactured by Organo Corporation) was used as the cation exchange resin, and AMBERJET 4002 OH type (manufactured by Organo Corporation) was used as the anion exchange resin. The concentration of hypochlorous acid was measured using a residual salt concentration meter (manufactured by HANNA). The TOC of the water to be treated at the column outlet was measured using a TOC meter (M9e manufactured by Sievers Corporation). The dissolved oxygen concentration of the water to be treated was changed, and the through-water pressure difference and the increase in TOC were measured. The increase in TOC was determined as the difference in TOC between the water to be treated at the outlet and inlet of the column. The results are shown in Table 4. In Examples 7-1 to 7-3, no increase in the through-water pressure difference was confirmed, and the TOC was 20 to 40 μg / L. In Comparative Example 7, a through-water pressure difference of 0.2 MPa or more was generated, and the TOC was 100 μg / L.

[0074] [Table 4]

[0075] Dissolved oxygen concentration (mg / L) Water pressure difference (Mpa) TOC increase (μg / L) Example 7 - 1 <0.005 <0.01 20 Example 7 - 2 0.1 <0.01 20 Example 7 - 3 1 <0.01 40 Comparative Example 7 8 ＞0.2 100

[0076] (Example 8)

[0077] Using EDI instead of the ion exchange resin column, in the same manner as in Example 7, the relationships between the dissolved oxygen concentration and the through-water pressure difference of the EDI, and between the dissolved oxygen concentration and the TOC were evaluated. In the EDI, a first desalination chamber and a second desalination chamber were provided, and the water to be treated was passed through in the order of the first desalination chamber and the second desalination chamber. An anion exchange resin was filled in the first desalination chamber, and a cation exchange resin was filled in the second desalination chamber. An anion exchange resin and a cation exchange resin were filled in the concentration chamber as a mixed bed. Water was passed through at a flow rate of 20 L / h for both the first and second desalination chambers and 5 L / h for the concentration chamber, and the current value was set to 0.5 A. Hypochlorous acid of 0.1 mg-Cl2 / L was added to the supply water in which oxygen was dissolved in pure water, and the EDI was passed through with water. The results are shown in Table 5. The increase in TOC was determined as the difference in TOC between the water to be treated at the outlet and inlet of the EDI. In Examples 8-1 to 8-3, no increase in the through-water pressure difference was confirmed, and the maximum increase in TOC was 2 μg / L. In Comparative Example 8, a through-water pressure difference of 0.1 MPa or more was generated, and the TOC was 14 μg / L.

[0078] [Table 5]

[0079] Dissolved oxygen concentration (mg / L) Water pressure difference (Mpa) TOC increase (μg / L) Example 8 - 1 <0.005 0.02 <1 Example 8 - 2 0.1 0.02 <1 Example 8 - 3 1 0.02 2 Comparative Example 8 8 ＞0.1 14

[0080] Although several preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications can be made without departing from the spirit or scope of the appended claims.

[0081] (Reference numeral description)

[0082] 1A to 1G pure water production devices

[0083] 11 Filter

[0084] 12 Activated carbon tower

[0085] 13 First ion exchange device

[0086] 14 Ion exchanger filling device

[0087] 15 Reverse osmosis membrane device

[0088] 16 Ultraviolet irradiation device (ultraviolet oxidation device)

[0089] 17 Second ion exchange device

[0090] 18 Degassing device

[0091] 18A Deoxidation device

[0092] 19 Dissolved oxygen meter

[0093] 21 Halogen oxyacid addition unit

[0094] 22 Reducing agent addition unit

[0095] 23 Other halogen oxyacid addition units

[0096] 27 Oxidizing agent addition unit.

Claims

1. A water treatment system, comprising: a halogen oxyacid addition unit that adds a halogen oxyacid to water to be treated containing organic matter; and an ion exchanger filling device that is located downstream of the halogen oxyacid addition unit and is filled with at least an anion exchanger, the water treatment system passes the water to be treated after adding the halogen oxyacid through the ion exchanger filling device, the divalent anion concentration of the water to be treated at the inlet of the ion exchanger filling device is 0.4 mmol / L or less.

2. The water treatment system according to claim 1, wherein no water treatment device having a liquid contact portion made of an organic material is provided between the halogen oxyacid addition unit and the ion exchanger filling device.

3. The water treatment system according to claim 1, wherein the water to be treated after adding the halogen oxyacid is supplied to the ion exchanger filling device at a space velocity of 1200 ( / h) or less.

4. The water treatment system according to claim 1, wherein the ion exchanger filling device is non-regenerative.

5. The water treatment system according to claim 1, wherein the water treatment system has a halogen oxyacid removal unit located downstream of the ion exchanger filling device.

6. The water treatment system according to claim 1, wherein the dissolved oxygen concentration of the water to be treated at the inlet of the ion exchanger filling device is 1 mg / L or less.

7. The water treatment system according to claim 6, wherein the water treatment system has a deoxygenation device that is located upstream of the ion exchanger filling device and adjusts the dissolved oxygen concentration of the water to be treated at the inlet of the ion exchanger filling device to 1 mg / L or less.

8. The water treatment system according to claim 7, wherein the water treatment system comprises: a dissolved oxygen meter that measures the dissolved oxygen concentration of the water to be treated at the outlet of the deoxygenation device; and a control device that controls the deoxygenation device based on the dissolved oxygen concentration measured by the dissolved oxygen meter so that the dissolved oxygen concentration measured by the dissolved oxygen meter is 0.1 mg / L or more and 1 mg / L or less.

9. The water treatment system according to claim 1, wherein at the inlet of the ion exchanger filling device, the concentration of the halogen oxyacid in the water to be treated is 6 times the weight of the total organic carbon of the water to be treated or more.

10. The water treatment system according to claim 9, wherein urea is contained in the water to be treated, and the total organic carbon of the water to be treated is a value obtained by converting the urea concentration in the water to be treated into total organic carbon.

11. The water treatment system according to any one of claims 1 to 10, wherein the halogen oxyacid is hypobromous acid.

12. The water treatment system according to claim 1, wherein The water treatment system has a water treatment device, which is supplied with water to be treated containing an oxidant and has a liquid contact portion made of an organic material. The dissolved oxygen concentration of the water to be treated at the inlet of the water treatment device is 0.1 mg / L or more and 1 mg / L or less.

13. The water treatment system according to claim 12, wherein the water treatment system has a deoxidation device located upstream of the water treatment device, which adjusts the dissolved oxygen concentration of the water to be treated at the inlet of the water treatment device to 1 mg / L or less.

14. The water treatment system according to claim 12, wherein the water treatment system has an oxidant addition unit located upstream of the water treatment device, which adds an oxidant to the water to be treated.

15. A method for producing pure water, comprising the following steps: adding a halogen oxyacid to the water to be treated containing an organic substance by using a halogen oxyacid addition unit; and passing the water to be treated after adding the halogen oxyacid through an ion exchanger filling device filled with at least an anion exchanger, wherein the divalent anion concentration of the water to be treated at the inlet of the ion exchanger filling device is 0.4 mmol / L or less.

16. A water treatment method performed by the water treatment system according to claim 1, the water treatment method comprising a step of supplying water to be treated containing an oxidant to a water treatment device having a liquid contact portion made of an organic material, wherein the dissolved oxygen concentration of the water to be treated at the inlet of the water treatment device is 0.1 mg / L or more and 1 mg / L or less.

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