Water treatment method and water treatment device

Abstract

While maintaining the ion removal performance of EDI, the increase in the water flow differential pressure and voltage of EDI is suppressed. The water treatment method includes passing water to be treated, which contains an oxidant and dissolved oxygen, through an electrodeionized water production apparatus 24 filled with an ion exchanger. The product of the oxidant concentration (unit: mg / L) and the dissolved oxygen concentration (unit: mg / L) of the water to be treated at an inlet P2 of the electrodeionized water production apparatus 24 is 0.1 or less.

Description

[Technical Field]

[0001] This application is based on and claims priority from Japanese Patent Application No. 2024-46568, filed March 22, 2024, which is incorporated herein by reference in its entirety. The present invention relates to a water treatment method and a water treatment device. [Background technology]

[0002] As the demand for high quality pure water has become more apparent, various methods for removing ions contained in pure water have been studied in recent years. For example, as described in Japanese Patent Application Laid-Open No. 2022-89406, ions can be removed using an electrodeionized water production apparatus (hereinafter referred to as EDI). The EDI is filled with an ion exchanger such as an ion exchange resin. Summary of the Invention

[0003] In EDI, increases in the water flow differential pressure and voltage can occur after a long period of operation. The increase in water flow differential pressure is thought to be caused by oxidative degradation of the ion exchanger. Although the mechanism behind the voltage increase is not entirely clear, the inventors of the present application have found that the increase in voltage and water flow differential pressure is related to both the dissolved oxygen concentration and the oxidant concentration in the water being treated introduced into the EDI.

[0004] An object of the present invention is to provide a water treatment method that can suppress an increase in the water flow differential pressure and voltage of an EDI while maintaining ion removal performance.

[0005] The water treatment method of the present invention comprises treating water to be treated containing an oxidant and dissolved oxygen. UV irradiation equipment, Electrodeionized water production equipment filled with ion exchangers In this order To pass water through and, The product of the oxidant concentration (unit: mg / L) and the dissolved oxygen concentration (unit: mg / L) of the water to be treated at the inlet of the electrodeionization water production equipment. but 0.1 or less and irradiating the water to be treated with ultraviolet light from the ultraviolet irradiation device at an irradiation amount such that:

[0006] According to the present invention, it is possible to provide a water treatment method that can suppress an increase in the water flow differential pressure and voltage of an EDI while maintaining the performance of removing ions.

[0007] The above and other objects, features, and advantages of the present application will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate the present application. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a water treatment device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic configuration diagram of an EDI of the water treatment device shown in FIG. [Figure 3] FIG. 10 is a schematic configuration diagram of an EDI according to a modified example. [Figure 4A] FIG. 1 is a schematic diagram of a test device used in Example 1. [Figure 4B] FIG. 1 is a schematic diagram of a test device used in Example 2. [Figure 5] FIG. 5 is a schematic diagram of the EDI of the test device shown in FIGS. 4A and 4B. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of a water treatment method and a design method for a water treatment device of the present invention will be described with reference to the drawings. In the following description, "water to be treated" refers to water being treated by a certain device, and refers to water at the inlet of the device. However, in a context where a specific property of the water to be treated (e.g., dissolved oxygen concentration or hydrogen peroxide concentration) is of interest, it also includes water at any position upstream of the device, as long as the specific property remains substantially unchanged. "Treated water" refers to water treated by a certain device, and refers to water at the outlet of the device. However, in a context where a specific property of the treated water (e.g., dissolved oxygen concentration or hydrogen peroxide concentration) is of interest, it also includes water at any position downstream of the device, as long as the specific property remains substantially unchanged. Furthermore, in the following description, "adjustment" includes both manual adjustment by an operator and automatic control by a control mechanism of various water quality parameters (e.g., dissolved oxygen concentration, hydrogen peroxide concentration, TOC, etc. of the water to be treated and / or the treated water) and device operating parameters (e.g., pump rotation speed, flow rate, space velocity, SV, etc.) so that they fall within a predetermined value or range.

[0010] Figure 1 shows a schematic configuration of a water treatment device 2 according to one embodiment of the present invention. The water treatment device 2 is a pure water production system (primary pure water system) that, together with an upstream pretreatment device 1 and a downstream subsystem (secondary pure water system) 3, constitutes an ultrapure water production system 4. The raw water supplied to the pretreatment device 1 contains at least dissolved oxygen and organic matter. In the following description, upstream and downstream are defined with respect to the flow direction D of the water to be treated or the treated water.

[0011] The pretreatment device 1 includes a filter 11 for removing relatively large particles such as dust and an activated carbon tower 12 for removing impurities such as polymeric organic matter. The filter 11 can be, for example, a sand filter. The water treatment device 2 includes an intermediate tank 20 for storing treated water from the activated carbon tower 12, a reverse osmosis membrane device (hereinafter referred to as RO device 21), a first deoxygenation device 22, an ultraviolet irradiation device (hereinafter referred to as UV device 23), an electrodeionization water production device (hereinafter referred to as EDI 24), and a second deoxygenation device 25. These tanks and devices 11, 12, 20-25 are arranged in series in this order on a main pipe L1 from upstream to downstream in the flow direction D of the water to be treated. A return pipe L2 branches off from the main pipe L1 downstream of the second deoxygenation device 25 and merges with the intermediate tank 20. A flow rate adjusting valve V1 is provided on the return pipe L2. Between the first deoxygenation device 22 and the UV device 23, a TOC meter 26 for measuring the TOC of the water to be treated by the UV device 23 and a first dissolved oxygen meter 27 (another dissolved oxygen meter) for measuring the dissolved oxygen concentration are disposed. Between the UV device 23 and the EDI 24, a sampling pipe 28 for measuring the hydrogen peroxide concentration of the water to be treated by the EDI 24 and a second dissolved oxygen meter 29 for measuring the dissolved oxygen concentration are disposed. An oxidant concentration meter 30 is connected to the sampling pipe 28. Although not shown, a tank for holding treated water from each device of the pretreatment device 1 and the water treatment device 2, for example, the RO device 21, may be provided. Furthermore, although not shown, a circulation line for returning a portion of treated water from one of the devices of the water treatment device 2 to an upstream tank may be provided in addition to the return pipe L2.

[0012] The RO device 21 removes impurities such as organic matter. If the TOC of the water to be treated by the UV device 23 is high, the TOC reduction effect of the UV device 23 may be reduced. Removing organic matter with the RO device 21 reduces the load on the downstream UV device 23 and prevents a decrease in the TOC reduction effect. Because the RO device 21 removes ions, the ion load on the downstream EDI 24 is also reduced. The RO device 21 may be provided in multiple stages. Although not shown, an ion removal device consisting of a cation tower, an anion tower, and a decarbonation tower, or an ion removal device consisting of a cation tower and a decarbonation tower, or a device for adjusting the pH of the water to be treated by the RO device 21 may be provided before the RO device 21.

[0013] The first deoxygenation device 22 removes oxygen from the water to be treated, thereby reducing the dissolved oxygen concentration of the water. Because the first deoxygenation device 22 is located upstream of the UV device 23, the UV device 23 is supplied with water to be treated whose dissolved oxygen concentration has been reduced (adjusted). The type of the first deoxygenation device 22 is not limited as long as it can remove dissolved oxygen; for example, a vacuum degassing device can be used. The vacuum degassing device is equipped with a vacuum pump 22A. In general, a vacuum degassing device fills a degassing tower with a gas-liquid contact material to increase the surface area of ​​the water, and the gas pressure in the degassing tower is reduced by the vacuum pump 22A, placing the water to be treated in a vacuum state and removing dissolved oxygen. The dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum in the degassing tower using the vacuum pump 22A. The degree of vacuum can be adjusted, for example, by controlling the rotation speed of the vacuum pump 22A using an inverter installed in the vacuum pump 22A. Furthermore, degassing performance can be improved by introducing nitrogen into the degassing tower. In this case, the dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum and the amount of nitrogen inflow (amount of sweep gas).

[0014] A membrane degassing device may be used as the first deoxygenation device 22. In this case, a vacuum pump 22A is used, as in the vacuum degassing device, and the dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum. These first deoxygenation devices 22 reduce the dissolved oxygen concentration in the water to be treated and simultaneously discharge volatile organic substances, carbon dioxide, etc. into the gas phase (secondary side), thereby reducing the concentrations of volatile organic substances, carbon dioxide, etc. in the water to be treated.

[0015] Alternatively, a platinum catalyst-filled device carrying a platinum catalyst such as palladium (Pd) may be used as the first deoxygenation device 22. By bringing the hydrogen-added water into contact with the platinum catalyst, the oxygen in the water reacts with the hydrogen to form water. This reduces the dissolved oxygen concentration. The first deoxygenation device 22 described above may have a single stage or a multi-stage configuration in which multiple deoxygenation devices are connected in series. The installation location of the first deoxygenation device 22 is not limited as long as it is upstream of the EDI 24, and it may be between the UV device 23 and the EDI 24 or upstream of the RO device 21.

[0016] The UV device 23 irradiates the water to be treated with ultraviolet rays. The UV device 23 may be, for example, a low-pressure ultraviolet irradiation device that generates ultraviolet rays with at least one of wavelengths of 185 nm and 254 nm. Organic matter in the water to be treated is oxidized and decomposed by the ultraviolet rays. Considering the deterioration of the performance of the ultraviolet oxidation treatment and the load on the EDI 24, a decarbonation device may be provided upstream of the UV device 23.

[0017] UV irradiation generates organic decomposition products in the treated water from the UV device 23. These decomposition products consist of organic acids and carbonic acid, which are removed by the EDI 24. The EDI 24 is a continuous regeneration system, eliminating the need for a regeneration process for the ion exchange resin. Figure 2 shows a schematic diagram of the EDI 24. The EDI 24 includes, in order from the anode chamber 24B, an anode chamber 24B equipped with an anode 24A, a first concentration chamber 24C, a first small deionization chamber 24D, a second small deionization chamber 24E, a second concentration chamber 24F, and a cathode chamber 24G equipped with a cathode 24H. The first concentration chamber 24C may also serve as the anode chamber 24B, and the second concentration chamber 24F may also serve as the cathode chamber 24G. The first small deionization chamber 24D and the second small deionization chamber 24E are connected in series with the first small deionization chamber 24D on the upstream side and the second small deionization chamber 24E on the downstream side in terms of the flow direction of the water to be treated. The first concentrating chamber 24C and the second concentrating chamber 24F are arranged in parallel. The anode chamber 24B and the cathode chamber 24G are connected in series with the cathode chamber 24G on the upstream side and the anode chamber 24B on the downstream side in terms of the flow direction of the water supplied to the electrode chambers.

[0018] The first small deionization compartment 24D is filled with anion exchange resin A, and the second small deionization compartment 24E is filled with cation exchange resin C on the upstream side and anion exchange resin A on the downstream side with respect to the flow direction of the water to be treated. The anode compartment 24B is filled with cation exchange resin C, and the first and second concentrating compartments 24C and 24F and the cathode compartment 24G are filled with anion exchange resin A. The cation exchange resin C is filled with a strongly acidic cation exchange resin with at least an H-type ion exchange group, and the anion exchange resin A is filled with a strongly basic anion exchange resin with at least an OH-type ion exchange group. It is not necessary to fill the anode compartment 24B, the cathode compartment 24G, and the first and second concentrating compartments 24C and 24F with ion exchange resins, but it is preferable to fill these spaces with ion exchange resins in order to reduce the DC voltage applied between the anode 24A and the cathode 24H during operation of the EDI 24. Each chamber of the EDI 24 may be filled with a fibrous or monolithic ion exchanger instead of the ion exchange resin.

[0019] The anode chamber 24B and the first concentrating chamber 24C are adjacent to each other across a cation exchange membrane CM, the first concentrating chamber 24C and the first small deionizing chamber 24D are adjacent to each other across an anion exchange membrane AM, the first small deionizing chamber 24D and the second small deionizing chamber 24E are adjacent to each other across an anion exchange membrane AM, the second small deionizing chamber 24E and the second concentrating chamber 24F are adjacent to each other across a cation exchange membrane CM, and the second concentrating chamber 24F and the cathode chamber 24G are adjacent to each other across an anion exchange membrane AM. In the portion of the second small deionizing chamber 24E filled with anion exchange resin A, an anion exchange membrane AM is disposed on the second small deionizing chamber 24E side of the cation exchange membrane CM.

[0020] With a DC voltage applied between the anode 24A and the cathode 24H, water to be treated is supplied to the first small deionization compartment 24D, concentrating compartment feed water is supplied to the first and second concentrating compartments 24C and 24F, and electrode compartment feed water is supplied to the cathode compartment 24G. The anionic components of the water to be treated supplied to the first small deionization compartment 24D are adsorbed by the anion exchange resin A, thereby progressing deionization (demineralization). The treated water from the first small deionization compartment 24D is supplied to the second small deionization compartment 24E, where the cationic and anionic components are adsorbed by the cation exchange resin C and the anion exchange resin A, respectively, thereby further progressing deionization (demineralization). The treated water (deionized water) from the second small deionization compartment 24E is discharged from the EDI 24. The anion components adsorbed on the anion exchange resin A finally flow into the first concentration compartment 24C, and the cation components adsorbed on the cation exchange resin C finally flow into the second concentration compartment 24F, and both are discharged together with the concentrated water. The electrode chamber feed water supplied to the cathode chamber 24G passes through the cathode chamber 24G and is then supplied to the anode chamber 24B, from which it is discharged as electrode water. The current flowing between the anode 24A and the cathode 24H of the EDI 24 is 0.1 to 2 A / dm per effective membrane area of ​​the ion exchange membrane. 2 Increasing the current can improve the ion removal rate, but this may accelerate the deterioration of the ion exchange resin due to hydrogen peroxide.

[0021] FIG. 3 shows a schematic diagram of a modified EDI 241. The anode 24A, anode chamber 24B, first concentrating chamber 24C, second concentrating chamber 24F, cathode chamber 24G, and cathode 24H are configured the same as those of the EDI 24 shown in FIG. 2. In this modified example, the first small distillation chamber 24D and the second small distillation chamber 24E of the EDI 24 shown in FIG. 2 are replaced with a single distillation chamber 24J. The distillation chamber 24J is packed with a mixed bed of anion exchange resin and cation exchange resin (the symbol M in the figure indicates mixed bed packing). The anion exchange resin and cation exchange resin packed in the distillation chamber 24J may be the same as those in the EDI 24. The first concentrating chamber 24C may also serve as the anode chamber 24B, and the second concentrating chamber 24F may also serve as the cathode chamber 24G. The anode chamber 24B and the first concentrating chamber 24C are adjacent to each other across a cation exchange membrane CM, the first concentrating chamber 24C and the deionizing chamber 24J are adjacent to each other across an anion exchange membrane AM, the deionizing chamber 24J and the second concentrating chamber 24F are adjacent to each other across a cation exchange membrane CM, and the second concentrating chamber 24F and the cathode chamber 24G are adjacent to each other across an anion exchange membrane AM. The following description is directed to EDI 24, but is equally applicable to EDI 241.

[0022] The configuration of the EDI 24 is not limited to the above-described embodiment. The EDI 24 may be filled with at least one of anion exchange resin and cation exchange resin. If both are filled, either a mixed-bed or multi-bed configuration is acceptable. The EDI 24 may also be filled with an ion exchanger other than ion exchange resin, such as a monolithic or fibrous ion exchanger. Multiple units may be arranged in parallel, with the first concentration compartment 24C, the first small distillation compartment 24D, the second small distillation compartment 24E (or distillation compartment 24J instead of the first and second small distillation compartments 24D and 24E), and the second concentration compartment 24F constituting a single unit. In this case, adjacent concentration compartments can be shared. The greater the number of units, the higher the voltage of the EDI 24, making it easier to achieve the effects of the present invention.

[0023] The second deoxygenation device 25 is located downstream of the EDI 24 and can have a configuration similar to that of the first deoxygenation device 22. The second deoxygenation device 25 removes dissolved oxygen, carbon dioxide, etc. from the water to be treated.

[0024] (Operation method of water treatment device 2) Next, we will explain how to operate the water treatment device 2 described above. First, water to be treated (raw water) is supplied to the pretreatment device 1. The pretreatment device 1 removes impurities such as relatively large-particle dust and high-molecular-weight organic matter from the water to be treated. The RO device 21 removes impurities such as organic matter and ions from the water treated by the pretreatment device 1. The first deoxygenation device 22 removes a portion of the dissolved oxygen from the water treated by the RO device 21. The UV device 23 irradiates the water treated by the first deoxygenation device 22 with ultraviolet light. As shown in Equation 1, water dissociates into hydrogen radicals (·H) and OH radicals (hydroxyl radicals), and the OH radicals decompose the organic matter. The OH radicals not used to decompose the organic matter recombine to form hydrogen peroxide. Therefore, by irradiating the water to be treated with ultraviolet light from the UV device 23, hydrogen peroxide is generated in the water treated by the UV device 23 (or the hydrogen peroxide concentration increases). [ka]

[0025] Next, the treated water from the UV device 23 is passed through the EDI 24. The EDI 24 mainly removes the decomposition products of organic matter remaining in the treated water from the UV device 23. Some of the hydrogen peroxide is decomposed into H2O and O2 (dissolved oxygen) on the surface of the anion exchange resin A. The second deoxygenation device 25 removes the dissolved oxygen generated by the EDI 24 and the dissolved oxygen that was not reacted in the UV device 23. The treated water, with its TOC and dissolved oxygen reduced in this way, is sent to subsystem 3 for further treatment.

[0026] (Hydrogen peroxide and dissolved oxygen concentrations at the inlet of EDI24) Because voltage is applied to the EDI 24, the increase in differential pressure due to oxidative degradation of the ion exchanger becomes significant, and the voltage also increases significantly. Therefore, in this embodiment, the hydrogen peroxide concentration and dissolved oxygen concentration of the water to be treated at the inlet P2 of the EDI 24 are adjusted so that the product of the hydrogen peroxide concentration (unit: mg / L) and the dissolved oxygen concentration (unit: mg / L) of the water to be treated at the inlet P2 of the EDI 24 is 0.1 or less. This suppresses increases in the water flow differential pressure and voltage of the EDI 24. The hydrogen peroxide concentration can be measured using an absorbance method using the phenolphthalein method or an online concentration meter. A hydrogen peroxide concentration meter 30 capable of measuring the hydrogen peroxide concentration online is connected to the sampling pipe 28. The dissolved oxygen concentration can be measured using a second dissolved oxygen meter 29. The water flow differential pressure is the differential pressure between the inlet and outlet of the dilution chamber, i.e., the pressure at inlet P3 of first dilution chamber 24D minus the pressure at outlet P4 of second dilution chamber 24E, and the voltage is a DC voltage applied between anode 24A and cathode 24H of EDI 24. The ratio of the hydrogen peroxide concentration to the dissolved oxygen concentration is not limited. For example, the hydrogen peroxide concentration may be adjusted to 0.1 mg / L or less and the dissolved oxygen concentration to 1 mg / L or less, or the hydrogen peroxide concentration may be adjusted to 1 mg / L or less and the dissolved oxygen concentration to 0.1 mg / L or less, or both may be adjusted to approximately 0.33 mg / L or less. The hydrogen peroxide concentration and the dissolved oxygen concentration are preferably adjusted so that the product of the hydrogen peroxide concentration (unit: mg / L) and the dissolved oxygen concentration is 0.05 or less, and more preferably 0.01 or less. For example, both the hydrogen peroxide concentration and the dissolved oxygen concentration may be adjusted to 0.1 mg / L or less, or may be adjusted to 0.05 mg / L or less.

[0027] The increase in water flow differential pressure in the EDI 24 is caused by oxidative degradation of the ion exchange resin. Specifically, oxidative degradation of the ion exchange resin causes it to swell, narrowing the gaps between the ion exchange resins and increasing the pressure loss in the desalination compartment. Therefore, the water flow differential pressure is one indicator of oxidative degradation of the ion exchange resin. In this embodiment, the ion exchange resin is oxidized and degraded by hydrogen peroxide, but similar oxidative degradation can also occur with oxidizing agents other than hydrogen peroxide, such as halogen oxoacids. Halogen oxoacids include hypohalous acids, halogen acids, perhalogen acids, and halogenous acids, while hypohalous acids include hypobromous acid, hypochlorous acid, and hypoiodous acid. Note that the mechanism behind the voltage increase is not entirely clear, but it is possible that oxidative degradation of the ion exchange resin is a factor.

[0028] The dissolved oxygen concentration of the water to be treated in the EDI 24 can be adjusted mainly by the first deoxygenation device 22. Furthermore, as can be seen from Equation 1, the rate of dissolved oxygen consumption varies depending on the amount of ultraviolet light irradiation, so the dissolved oxygen concentration of the water to be treated in the EDI 24 can also be adjusted by the amount of ultraviolet light irradiation from the UV device 23.

[0029] Because hydrogen peroxide is primarily generated by ultraviolet irradiation, the hydrogen peroxide concentration in the water being treated by the EDI 24 can be adjusted primarily by the amount of ultraviolet irradiation from the UV device 23. The amount of ultraviolet irradiation can be adjusted by at least one of the number of ultraviolet lamps turned on, dimming, and the flow rate of the water being treated. Furthermore, because ultraviolet light emitted from the UV device 23 is easily absorbed by oxygen, a high dissolved oxygen concentration in the water being treated by the UV device 23 reduces the efficiency of OH radical generation, making it difficult for OH radicals to recombine with each other, resulting in a decrease in the hydrogen peroxide concentration. Conversely, a low dissolved oxygen concentration in the water being treated by the UV device 23 increases the efficiency of OH radical generation, promoting the hydrogen peroxide concentration. Therefore, the hydrogen peroxide concentration in the water being treated by the EDI 24 can also be adjusted by the first deoxygenation device 22. While the hydrogen peroxide concentration and dissolved oxygen concentration in the water being treated by the EDI 24 can be adjusted by at least one of the amount of ultraviolet irradiation from the first deoxygenation device 22 and the amount of ultraviolet irradiation from the UV device 23, it is preferable to use both the first deoxygenation device 22 and the amount of ultraviolet irradiation from the UV device 23 in combination.

[0030] Since oxidation degradation of ion exchange resins is caused by oxidizing agents such as hydrogen peroxide, it has been thought that reducing the concentration of oxidizing agents in the EDI 24 treatment water is an effective way to prevent oxidation degradation of ion exchange resins. -Even if the oxidant concentration in the water being treated by EDI24 is high, if the dissolved oxygen concentration is low, it is possible to suppress the increase in the water flow differential pressure and voltage of EDI24.-If the oxidant concentration in the water being treated by EDI24 is low, it is possible to suppress the increase in water flow differential pressure and voltage of EDI24, regardless of whether the dissolved oxygen concentration is high or low. -When the oxidant concentration and dissolved oxygen concentration of the water to be treated by EDI24 are high, it is difficult to suppress the increase in the water flow differential pressure and voltage of EDI24. This makes it possible to increase the degree of freedom in the operating conditions for suppressing increases in the water flow differential pressure and voltage of the EDI24.

[0031] (Regarding the space velocity (SV) of the treated water for EDI24) The SV of the water to be treated in the EDI 24 is preferably 100 to 400 ( / h) per unit of the EDI 24. If the SV is small, the size of the EDI 24 will be large, and if the SV is large, the size of the EDI 24 can be made small, but the flow rate will be too fast and the differential pressure of the water passing through will be high. If the SV is large, the load on the EDI 24 will also increase, and if the water to be treated contains an oxidant, oxidation degradation will be more likely to progress. The SV can be adjusted in several ways. If the flow area of ​​the first and second small deionization chambers 24D and 24E is A, the total length of the flow path is h, and the total volume is V, then V = A × h, and therefore SV = q / V = q / (A × h). Therefore, if the flow rate q, the flow path area A, and the total flow path length are long h The SV can be adjusted by adjusting at least one of the above.

[0032] (TOC and dissolved oxygen concentration in the inlet water of UV device 23) The hydrogen peroxide generated by the UV device 23 correlates with the TOC and dissolved oxygen concentration of the water being treated by the UV device 23. Specifically, if the TOC and dissolved oxygen concentration of the water being treated by the UV device 23 are high, the hydrogen peroxide concentration of the water being treated by the UV device 23 may be high. By keeping the product of the TOC (unit: mg / L) and the dissolved oxygen concentration (unit: mg / L) of the water being treated at the inlet P1 of the UV device 23 at 0.01 or less, it is possible to suppress an increase in the water flow differential pressure and voltage of the EDI 24. In other words, adjusting the product of the dissolved oxygen concentration and TOC of the water being treated by the UV device 23 can achieve the same effect as adjusting the product of the hydrogen peroxide concentration and the dissolved oxygen concentration of the water being treated by the EDI 24. TOC can be measured by the TOC meter 26, and the dissolved oxygen concentration can be measured by the first dissolved oxygen meter 27. The ratio of TOC to dissolved oxygen concentration is not limited. For example, the TOC may be adjusted to 0.01 mg / L or less and the dissolved oxygen concentration to 1 mg / L or less, or the TOC may be adjusted to 1 mg / L or less and the dissolved oxygen concentration to 0.01 mg / L or less, or both may be adjusted to 0.1 mg / L or less. The product of the dissolved oxygen concentration and the TOC is preferably 0.005 or less. For example, it is preferable to set the TOC to 0.01 mg / L or less and the DO to 0.1 mg / L or less or 0.05 mg / L or less. The TOC can be adjusted, for example, by changing the recovery rate of the RO device 21 or the amount of water circulated within the water treatment device 2. For example, if a portion of the water supplied from the second deoxygenation device 25 to the subsystem 3 is returned to the inlet of the UV device 23, the TOC of the water to be treated by the UV device 23 can be reduced by adjusting the valve V1 on the return pipe L2 to increase the flow rate of the returned water, or the TOC can be increased by decreasing the flow rate. Even in this case, the hydrogen peroxide concentration and the dissolved oxygen concentration of the water to be treated by the EDI 24 can be adjusted by the above-mentioned method, so that the options for adjusting the water quality of the water to be treated by the EDI 24 are increased.

[0033] (Control device) The hydrogen peroxide concentration and dissolved oxygen concentration of the water to be treated at inlet P2 of EDI 24 can be automatically controlled, and for this purpose, water treatment device 2 may be equipped with control device 31. Control device 31 can be provided, for example, as part of a computer that controls water treatment device 2 or ultrapure water production device 4, or as part of its functions. Control device 31 is connected to second dissolved oxygen meter 29, oxidant concentration meter 30, first deoxygenation device 22, and UV device 23. As described above, second dissolved oxygen meter 29 measures the dissolved oxygen concentration of the water to be treated at inlet P2 of EDI 24. Oxidant concentration meter 30 measures the oxidant concentration (e.g., hydrogen peroxide concentration) of the water to be treated at inlet P2 of EDI 24. The control device 31 controls the quality of the water to be treated at the inlet P2 of the EDI 24 so that the product of the oxidant concentration (unit: mg / L) measured by the oxidant concentration meter 30 and the dissolved oxygen concentration (unit: mg / L) measured by the second dissolved oxygen meter 29 is 0.1 or less, preferably 0.01 or less. Specifically, the control device 31 controls at least one of the output of the vacuum pump 22A of the first deoxygenation device 22 and the amount of ultraviolet light irradiation from the UV device 23 based on the oxidant concentration and the dissolved oxygen concentration. For more specific control methods, please refer to the explanation of the operating method of the water treatment device 2 described above.

[0034] The control device 31 may be connected to the TOC meter 26, the first dissolved oxygen meter 27, the RO device 21, and the valve V1 of the return pipe L2. As described above, the TOC meter 26 measures the TOC of the water to be treated at the inlet P1 of the UV device 23. The first dissolved oxygen meter (another dissolved oxygen meter) 27 measures the dissolved oxygen concentration of the water to be treated at the inlet P1 of the UV device 23. The control device 31 controls the water quality of the water to be treated at the inlet P1 of the UV device 23 so that the product of the TOC (unit: mg / L) measured by the TOC meter 26 and the dissolved oxygen concentration (unit: mg / L) measured by the first dissolved oxygen meter 27 is 0.01 or less, preferably 0.005 or less. Specifically, the control device 31 controls the recovery rate of the RO device 21, the flow rate of the return pipe L2, the speed of the vacuum pump 22A of the first deoxygenation device 22, and the like based on the TOC and dissolved oxygen concentration. outputFor more specific control methods, please refer to the explanation of the method for operating the water treatment device 2 described above.

[0035] Example 1 Using the test equipment shown in Figure 4A, water containing hydrogen peroxide and dissolved oxygen was passed through a first deoxygenation device 22 and an EDI 24. A membrane degassing device was used as the first deoxygenation device 22. The first deoxygenation device 22 was placed upstream of the EDI 24 to adjust the dissolved oxygen concentration of the water. Hydrogen peroxide was also added to the water upstream of the EDI 24. The hydrogen peroxide concentration of the water being treated at the EDI 24 was measured using sample water from a sampling pipe 28 installed between the first deoxygenation device 22 and the EDI 24. The dissolved oxygen concentration of the water being treated at the EDI 24 was measured using a second dissolved oxygen meter 29 installed between the first deoxygenation device 22 and the EDI 24. Figure 5 shows a schematic configuration of the EDI 24 used. The basic configuration is the same as that shown in Figure 2, but the first and second concentration compartments 24C and 24F were filled with anion exchange resin A and cation exchange resin C in a mixed bed (MB) configuration. The specifications and operating conditions of EDI24 are as follows. A cell refers to a compartment separated by an ion exchange membrane, such as a concentration compartment or a deionization compartment. A pressure gauge PI was installed at the inlet of the first small deionization compartment 24D and the outlet of the second small deionization compartment 24E, and the difference in measured values ​​ΔP (water flow differential pressure) was calculated. (a) EDI specifications -Cation exchange membrane CM: Astom homogeneous cation exchange membrane (Neosepta) -Anion exchange membrane AM: Astom homogeneous anion exchange membrane (Neosepta) - Anion exchange resin A: DuPont strong basic anion exchange resin (Amberlite) -Cation exchange resin C: DuPont strong acid cation exchange resin (Amberlite) -Cell opening area: 10cm x 10cm = 100cm 2 =1dm 2 -Cell thickness: 1cm -Cell volume: 100mL -Anode plate material: Pt - Cathode plate material: Stainless steel (b) EDI operating conditions -Water flow rate: 36L / h -Demineralization room SV:180( / h) -Current: 1A / dm 2

[0036] Table 1 shows the water flow differential pressure and voltage across the electrodes of EDI24 after 1,500 hours of operation. DO indicates dissolved oxygen. The water flow differential pressure and voltage were normalized to the measurements in Example 1-1. The hydrogen peroxide concentration was measured by absorbance using the phenolphthalein method. The dissolved oxygen concentration was measured using an Orbisphere dissolved oxygen meter manufactured by HACH. In Examples 1-1 to 1-3, there was almost no increase in the water flow differential pressure or voltage, while in Comparative Examples 1-1 to 1-3, there was an increase in the water flow differential pressure and voltage. This demonstrates that the increase in the water flow differential pressure and voltage of EDI24 can be suppressed by keeping the product of the hydrogen peroxide concentration and the dissolved oxygen concentration of the water being treated by EDI24 at 0.1 or less.

[0037] In Comparative Example 1-4, water to be treated was passed through a resin column packed with resin, and the change in the water flow differential pressure of the resin column was measured. Specifically, a 100 mL resin column was packed with the same type of strongly basic anion exchange resin and strongly acidic cation exchange resin as in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 in a volume ratio of 3:1, and the water to be treated was passed through at a flow rate of 36 L / h. The hydrogen peroxide concentration and dissolved oxygen concentration of the water to be treated were almost equivalent to those of Comparative Example 1-2. As shown in Table 1, the water flow differential pressure after 1500 hours showed almost no change from immediately after the water was passed through. This confirmed that the problem of the present invention, namely, an increase in water flow differential pressure, is particularly pronounced in EDI. Note that, since no voltage was applied in Comparative Example 1-4, values ​​are not listed in Table 1.

[0038] [Table 1]

[0039] Example 2 Using the test equipment shown in FIG. 4B, water to be treated containing hydrogen peroxide and dissolved oxygen was passed through a first deoxygenation device 22, a UV device 23, and an EDI 24. A membrane degassing device was used as the first deoxygenation device 22. The first deoxygenation device 22 was placed upstream of the EDI 24 to adjust the dissolved oxygen concentration of the water to be treated. Water to be treated containing hydrogen peroxide and dissolved oxygen was passed through the first deoxygenation device 22. The TOC of the water to be treated by the UV device 23 was measured using a TOC meter 26 installed between the first deoxygenation device 22 and the UV device 23. The dissolved oxygen concentration of the water to be treated by the UV device 23 was measured using a first dissolved oxygen meter 27 installed between the first deoxygenation device 22 and the UV device 23. The hydrogen peroxide concentration of the water to be treated by the EDI 24 was measured using sample water from a sampling pipe 28 installed between the first deoxygenation device 22 and the EDI 24. The dissolved oxygen concentration of the water to be treated in the EDI 24 was measured by a second dissolved oxygen meter 29 installed between the first deoxygenation device 22 and the EDI 24. The schematic configuration of the EDI 24 is as shown in Figures 4A and 4B, and the specifications and operating conditions of the EDI 24 were the same as those in Example 1. JPW manufactured by Nippon Photo Science Co., Ltd. was used as the UV device 23, and the irradiation amount was 0.06 kWh / m 3 The water to be treated was irradiated with ultraviolet light.

[0040] Table 2 shows the water flow differential pressure and voltage across the electrodes of EDI24 after 1,500 hours of operation. DO indicates dissolved oxygen. The water flow differential pressure and voltage were normalized to the measurements in Example 2-1. In Examples 2-1 to 2-4, almost no increase in water flow differential pressure or voltage was observed, while increases in water flow differential pressure and voltage were observed in Comparative Examples 2-1 and 2-2. This example also demonstrated that increases in water flow differential pressure and voltage across EDI24 could be suppressed by setting the product of the hydrogen peroxide concentration and dissolved oxygen concentration in the water being treated by EDI24 to 0.1 or less. Furthermore, it was confirmed that the product of the hydrogen peroxide concentration and dissolved oxygen concentration in the water being treated by EDI24 was 0.1 or less by setting the product of TOC and dissolved oxygen concentration to 0.01 or less.

[0041] [Table 2]

[0042] (Current density of EDI) Using the EDI24 shown in Figure 5, we measured the differential pressure and voltage across the EDI24 by varying the current density D. The current density D is calculated as D = I / S, where I is the current flowing between the anode and cathode of the EDI24 and S is the opening area of ​​the desalination compartment in the direction of voltage application. The hydrogen peroxide concentration in the EDI24 treated water was 0.1 mg / L or higher, the dissolved oxygen concentration was 3 mg / L or higher, and the product of the hydrogen peroxide and dissolved oxygen concentrations was 0.3 or higher. The differential pressure and voltage were considered to have increased if the values ​​1,500 hours after the start of operation were 10% or higher compared to the values ​​100 hours after the start of operation, and unchanged if they varied less than 10%. The results are shown in Table 3. A tendency for the differential pressure and voltage to increase with increasing current density D was confirmed. In Case 3-1, no increase in the differential pressure or voltage was observed. In Case 3-2, no increase in the differential pressure was observed, but the voltage did increase. In Case 3-3, both the differential pressure and voltage increased. This indicates that when the product of the hydrogen peroxide concentration and the dissolved oxygen concentration exceeds 0.1, D ≥ 0.6 (A / dm 2 ), an increase in the water flow differential pressure due to resin degradation occurs. In other words, when the processing flow rate of the EDI 24 is F and the number of cell sets S of the EDI 24 is N, an increase in the water flow differential pressure due to resin degradation occurs when Z ≥ I / (F / N) = 0.6(A) / (36(L / h) / 1) = 0.0167(A·h / L). Here, a cell set S has a basic configuration in which a concentration compartment, an anion exchange membrane, a deionization compartment, a cation exchange membrane, and another concentration compartment are arranged in the listed order. Adjacent concentration compartments may be shared between adjacent cell sets S. In the example of Figures 2 and 3, the first concentration compartment 24C to the second concentration compartment 24F constitute one cell set S. In other words, the deionization compartment in one cell set S may be divided into a first small deionization compartment 24D and a second small deionization compartment 24E as shown in Figure 2, or may be a single deionization compartment 24J as shown in Figure 3.

[0043] On the other hand, as explained in Examples 1 and 2, when the product of the hydrogen peroxide concentration and the dissolved oxygen concentration is 0.1 or less, the current density D is 1 A / dm 2 Even when the current density D is 0.14 A / dm, there is no increase in the differential pressure or voltage.2 If it is less than 1A / dm 2 If it is more than 0.6A / dm 2 Exceeds 1A / dm 2 Therefore, in the above embodiment, the current density D is 0.14 A / dm 2 (when Z exceeds 0.0038 A·h / L), and the current density D is 0.6 A / dm 2 When Z is 0.0167 A·h / L or more, a large effect is obtained, and when the current density D is 1 A / dm 2 It can be seen that a particularly large effect is achieved in the above cases (when Z is 0.0278 A·h / L or more).

[0044] [Table 3]

[0045] While 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 therein without departing from the spirit or scope of the appended claims. For example, the present invention may be applied to subsystem 3 of ultra water treatment device 4. [Explanation of symbols]

[0046] 2. Water treatment equipment 21 Reverse osmosis membrane device (RO device) 22 First deoxidizer 23 Ultraviolet irradiation device (UV device) 24 Electrodeionized water production equipment (EDI) 25 Second deoxidizer 31 Control device

Claims

1. A water treatment method in a water treatment device including an electrodeionization water production device filled with an ion exchanger and an ultraviolet irradiation device, passing water to be treated, which contains an oxidant and dissolved oxygen, through the ultraviolet irradiation device and then the electrodeionized water production device; and irradiating the water to be treated with ultraviolet light from the ultraviolet irradiation device at an irradiation amount such that the product of the oxidant concentration (unit: mg / L) and the dissolved oxygen concentration (unit: mg / L) of the water to be treated at the inlet of the electrodeionized water production device is 0.1 or less.

2. The water treatment method according to claim 1 , wherein the product is 0.01 or less.

3. 3. The water treatment method according to claim 1, wherein the oxidizing agent is hydrogen peroxide.

4. 2. The water treatment method according to claim 1, further comprising: providing a deoxygenation device upstream of the electrodeionization device; and passing treated water from the deoxygenation device through the electrodeionization device.

5. The water treatment method according to claim 4 , wherein the dissolved oxygen concentration is adjusted by adjusting at least one of the degree of vacuum and the amount of sweep gas in the deoxidizer.

6. 5. The water treatment method according to claim 4, wherein the ultraviolet irradiation device is provided between the deoxygenation device and the electrodeionized water production device, and the water to be treated is passed through the deoxygenation device, the ultraviolet irradiation device, and the electrodeionized water production device in that order.

7. 7. The water treatment method according to claim 6, wherein the product of the total organic carbon concentration (unit: mg / L) and the dissolved oxygen concentration (unit: mg / L) of the water to be treated at the inlet of the ultraviolet irradiation device is 0.01 or less.

8. adjusting the dissolved oxygen concentration of the water to be treated at the inlet of the ultraviolet irradiation device and the inlet of the electrodeionized water production device by adjusting at least one of the degree of vacuum and the amount of sweep gas of the deoxygenation device; 8. The water treatment method according to claim 7, wherein the oxidant is hydrogen peroxide, and the concentration of the hydrogen peroxide or the dissolved oxygen concentration at the inlet of the electrodeionized water production apparatus is adjusted by adjusting the amount of ultraviolet light irradiation from the ultraviolet irradiation device.

9. 2. The water treatment method according to claim 1, wherein I / (F / N)≧0.0167 (A·h / L), where I is the current flowing between the anode and cathode of the electrodeionized water production device, F is the treatment flow rate of the electrodeionized water production device, and N is the number of cell sets of the electrodeionized water production device.

10. an electrodeionization water production apparatus filled with an ion exchanger and through which water to be treated containing an oxidant and dissolved oxygen is passed; an ultraviolet irradiation device provided upstream of the electrodeionized water production device and through which the water to be treated passes; an oxidant concentration meter for measuring the oxidant concentration of the water to be treated at an inlet of the electrodeionized water production apparatus; a dissolved oxygen meter for measuring the dissolved oxygen concentration of the water to be treated at the inlet of the electrodeionized water production apparatus; a control device for controlling the ultraviolet irradiation amount of the ultraviolet irradiation device, The control device controls the ultraviolet irradiation device so that the treated water is irradiated with ultraviolet rays at an irradiation amount such that the product of the oxidant concentration (unit: mg / L) measured by the oxidant concentration meter and the dissolved oxygen concentration (unit: mg / L) measured by the dissolved oxygen meter is 0.1 or less.

11. A TOC meter for measuring the total organic carbon concentration of the treated water at the inlet of the ultraviolet irradiation device; and another dissolved oxygen meter that measures the dissolved oxygen concentration of the water to be treated at the inlet of the ultraviolet irradiation device, The water treatment device described in claim 10, wherein the control device controls the water quality of the treated water at the inlet of the ultraviolet irradiation device so that the product of the total organic carbon concentration (unit: mg / L) measured by the TOC meter and the dissolved oxygen concentration (unit: mg / L) measured by the other dissolved oxygen meter is 0.01 or less.

12. A water treatment device as described in claim 10 or 11, wherein the oxidizing agent is hydrogen peroxide.

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