Water treatment method and water treatment apparatus

Abstract

When the water to be treated supplied to the ultraviolet irradiation device has a specific water quality, organic substances are efficiently decomposed. 【Solution means】The water treatment method includes supplying the water to be treated having a total organic carbon concentration of 10 μg / L or less and a dissolved oxygen concentration of 30 μg / L or more to the ultraviolet irradiation device 35 at the inlet portion 35A of the ultraviolet irradiation device 35, and irradiating the water to be treated supplied from the inlet portion 35A to the ultraviolet irradiation device 35 with ultraviolet rays from the ultraviolet irradiation device 35. The hydrogen peroxide concentration of the water to be treated at the inlet portion 35A is 30 μg / L or less.

Description

Technical Field

[0001] The present invention relates to a water treatment method and a water treatment apparatus.

Background Art

[0002] With the increasing demand for high-quality pure water, various methods for decomposing and removing trace amounts of organic substances contained in pure water have been studied in recent years. Patent Document 1 describes a water treatment method in which hydrogen peroxide is added to water to be treated upstream of an ultraviolet irradiation device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The fact that the water to be treated supplied to the ultraviolet irradiation device contains hydrogen peroxide is advantageous for promoting the decomposition of organic substances by the ultraviolet irradiation device. However, the inventor of the present application has found that when the water to be treated supplied to the ultraviolet irradiation device has a specific water quality, an excessive amount of hydrogen peroxide conversely inhibits the decomposition of organic substances by the ultraviolet irradiation device.

[0005] An object of the present invention is to provide a water treatment method capable of efficiently decomposing organic substances when the water to be treated supplied to the ultraviolet irradiation device has a specific water quality.

Means for Solving the Problems

[0006] The water treatment method of the present invention has a total organic carbon concentration at the inlet of the ultraviolet irradiation device is of 10 μg / L or less and a dissolved oxygen concentration isSupplying the water to be treated at 30 μg / L or more to an ultraviolet irradiation device, and irradiating the water to be treated supplied to the ultraviolet irradiation device from an inlet portion with ultraviolet rays from the ultraviolet irradiation device. The hydrogen peroxide concentration of the water to be treated at the inlet portion is 30 μg / L or less. In one aspect, it further includes reducing the dissolved oxygen concentration of the water to be treated at the inlet to less than 1000 μg / L by means of a deoxygenation device provided upstream of the ultraviolet irradiation device. In another aspect, it includes returning a part of the treated water irradiated with ultraviolet rays from the ultraviolet irradiation device upstream of the ultraviolet irradiation device through a return pipe, and within the range where the hydrogen peroxide concentration of the water to be treated at the inlet is 30 μg / L or less, performing at least one of: (A) adjusting the irradiation dose of the ultraviolet rays irradiated from the ultraviolet irradiation device; and (B) adjusting the dissolved oxygen concentration of the water to be treated at the inlet by means of a deoxygenation device provided upstream of the ultraviolet irradiation device. In yet another aspect, it further includes returning a part of the treated water irradiated with ultraviolet rays from the ultraviolet irradiation device upstream of the ultraviolet irradiation device, measuring the hydrogen peroxide concentration of the water to be treated supplied to the ultraviolet irradiation device, and adjusting the amount of the treated water returned upstream of the ultraviolet irradiation device so that the measured hydrogen peroxide concentration is 30 μg / L or less.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a water treatment method capable of efficiently decomposing organic substances when the water to be treated supplied to the ultraviolet irradiation device has specific water quality.

Brief Description of the Drawings

[0008]

Figure 1

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Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments of the water treatment method and water treatment apparatus of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a water treatment apparatus 1 according to a first embodiment of the present invention. The water treatment apparatus 1 has an upstream pretreatment apparatus 2 and a downstream pure water production apparatus 3 (primary system). The water treatment apparatus 1 constitutes an ultrapure water production apparatus together with a downstream subsystem (secondary system). The raw water supplied to the pretreatment apparatus 2 contains dissolved oxygen and organic substances. In the following description, upstream and downstream are defined with respect to the flow direction of water in the main pipe. Further, "adjustment" includes both automatically controlling various operation parameters (such as on / off of the apparatus, flow rate, pressure, opening and closing of valves, power consumption, etc.) by a control device and an operator manually adjusting these operation parameters. The present invention can be applied not only to the water treatment apparatus 1 but also to the subsystem.

[0010] The pretreatment apparatus 2 includes a filter 21 for removing dust and the like having a relatively large particle size, and an activated carbon tower 22 for removing impurities such as high molecular organic substances and oxidants. As the filter 21, for example, a sand filter can be used. The pure water production apparatus 3 has an ion removal apparatus 31, a reverse osmosis membrane apparatus 32, an intermediate tank 33, a first deoxygenation apparatus 34, an ultraviolet irradiation apparatus 35, an ion exchanger filling apparatus 36, and a second deoxygenation apparatus 37. These apparatuses and tanks are arranged in series in this order in the main pipe L1 from upstream to downstream with respect to the flow direction D of the water to be treated. Although not shown, in addition to the intermediate tank 33, tanks for storing the treated water of each apparatus of the pretreatment apparatus 2 and the pure water production apparatus 3, for example, the activated carbon tower 22, the ion removal apparatus 31, and the reverse osmosis membrane apparatus 32 may be provided. A return pipe L2 branches from the main pipe L1 downstream of the second deoxygenation apparatus 37 and joins the intermediate tank 33. Although not shown, in addition to the return pipe L2, a pipe for returning a part of the treated water of any apparatus of the pure water production apparatus 3 to an upstream tank or the like may be provided.

[0011] The ion removal device 31 includes a cation tower (not shown) filled with a cation exchange resin, a decarbonation tower (not shown), and an anion tower (not shown) filled with an anion exchange resin, and these are arranged in series in this order from upstream to downstream. A decarbonation membrane may be provided instead of the decarbonation tower. Instead of the ion removal device 31, a softening device for removing hardness components such as calcium and magnesium can be arranged in series on the upstream side, and an electro-deionization water production device (EDI) can be arranged in series on the downstream side. The EDI removes ion components that are inhibitors of the organic matter decomposition treatment in the ultraviolet irradiation device 35.

[0012] The reverse osmosis membrane device 32 removes impurities such as ions. In the present embodiment, since the ion removal device 31 is provided upstream of the reverse osmosis membrane device 32, the reverse osmosis membrane device 32 mainly removes uncharged substances such as organic matter. The reverse osmosis membrane device 32 may be provided in multiple stages. When the total organic carbon concentration of the water to be treated is high, the decomposition efficiency of organic matter in the ultraviolet irradiation device 35 decreases. By removing organic matter with the reverse osmosis membrane device 32, the load on the downstream ultraviolet irradiation device 35 is reduced. A pH adjustment mechanism may be provided in the stage before the reverse osmosis membrane device 32. The treated water of the reverse osmosis membrane device 32 is stored in the intermediate tank 33.

[0013] The first deoxygenation device 34 removes oxygen from the water to be treated and reduces the dissolved oxygen concentration in the water to be treated. At the same time, the first deoxygenation device 34 can also remove volatile organic compounds, carbonic acid, etc. into the gas phase (secondary side) and reduce their concentrations in the water. Since the first deoxygenation device 34 is located upstream of the ultraviolet irradiation device 35, the water to be treated with a reduced (adjusted) dissolved oxygen concentration is supplied to the ultraviolet irradiation device 35. The type of the first deoxygenation device 34 is not limited as long as it can remove dissolved oxygen. 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 water to be treated is placed in a vacuum state, and the dissolved oxygen is removed. The dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum in the degassing tower using a vacuum pump. The degree of vacuum can be adjusted using an inverter connected to the vacuum pump. Furthermore, the degassing performance can be improved by introducing nitrogen. In this case, the dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum and the nitrogen inflow amount (nitrogen partial pressure).

[0014] A degassing membrane device may be used as the first deoxygenation device 34. In this case, a vacuum pump is also used as in the vacuum degassing device, and the dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum. The degree of vacuum can be adjusted using an inverter connected to the vacuum pump. When automatically adjusting the degree of vacuum and the nitrogen inflow amount in the first deoxygenation device 34, for example, the dissolved oxygen concentration in the water to be treated of the ultraviolet irradiation device 35 is measured by a measuring device (not shown), and based on the measured value, a control device (not shown) can adjust the degree of vacuum and the nitrogen inflow amount in the first deoxygenation device 34. As another first deoxygenation device 34, a platinum group catalyst filling device supporting a platinum group catalyst such as palladium (Pd) may be used. By bringing the water to be treated added with hydrogen into contact with the platinum group catalyst, the dissolved oxygen concentration in the water to be treated can be reduced. The first deoxygenation device 34 described above may have a single-stage configuration or a multi-stage configuration in which a plurality of devices are connected in series.

[0015] The ultraviolet irradiation device 35 irradiates the water to be treated with ultraviolet rays to decompose the organic substances contained in the water to be treated. The ultraviolet rays irradiated from the ultraviolet irradiation device 35 react with water to generate hydrogen peroxide. As the ultraviolet irradiation device 35, for example, an ultraviolet irradiation device (for example, a low-pressure ultraviolet irradiation device) that generates ultraviolet rays with at least one of the wavelengths of 185 nm and 254 nm can be used. The irradiation dose of ultraviolet rays is defined by the irradiation energy (unit: kWh / m 3 ) added per unit volume of water. Therefore, the irradiation dose can be adjusted by the number of lighting lamps of the ultraviolet irradiation device 35 and dimming, and can also be adjusted by changing the flow rate of the water to be treated. When automatically adjusting the ultraviolet irradiation dose in the ultraviolet irradiation device 35, for example, the total organic carbon concentration (hereinafter referred to as the TOC concentration) of the water to be treated at the inlet 35A of the ultraviolet irradiation device 35 is measured with a TOC meter (not shown), and based on the measured value, a control device (not shown) can adjust the number of lighting lamps, dimming, and the flow rate of the water to be treated in the ultraviolet irradiation device 35.

[0016] The ion exchanger filling device 36 removes the decomposition products of organic substances generated in the treated water of the ultraviolet irradiation device 35 by ultraviolet irradiation. The ion exchanger filling device 36 is filled with an ion exchange resin, but a monolithic or fibrous ion exchanger may be filled. The ion exchanger filling device 36 may be an EDI filled with an ion exchange resin. Since EDI is a continuous regeneration type, the regeneration process of the ion exchange resin becomes unnecessary.

[0017] The second deoxygenation device 37 is located downstream of the ion exchanger filling device 36 and can have the same configuration as the first deoxygenation device 34. The second deoxygenation device 37 removes dissolved oxygen, carbonic acid, etc. in the water to be treated.

[0018] The treated water of the second deoxygenation device 37 is sent to the subsystem. The return pipe L2 that branches downstream of the second deoxygenation device 37 adjusts the flow rate of the pure water supplied to the subsystem. For this purpose, a valve V1 for flow rate adjustment is arranged in the return pipe L2. Since it is preferable to provide the return pipe L2 at the most downstream position of the pure water production device 3, it branches from the main pipe L1 downstream of the second deoxygenation device 37, but other return pipes branching from the main pipe L1 upstream of the second deoxygenation device 37 may be provided.

[0019] As described above, since the ultraviolet irradiation device 35 generates hydrogen peroxide from water, the water flowing on the downstream side of the ultraviolet irradiation device 35 contains hydrogen peroxide. Also, the water containing hydrogen peroxide is returned to the intermediate tank 33 by the return pipe L2. However, since no hydrogen peroxide removing means is provided between the intermediate tank 33 and the ultraviolet irradiation device 35, the water flowing through the section between the intermediate tank 33 and the inlet of the subsystem contains hydrogen peroxide. In other words, the water to be treated supplied to the ultraviolet irradiation device 35 contains hydrogen peroxide. On the other hand, since the hydrogen peroxide contained in the raw water is substantially removed by the activated carbon tower 22, the water flowing through the section between the ion removal device 31 and the intermediate tank 33 does not substantially contain hydrogen peroxide. Therefore, the hydrogen peroxide concentration of the water to be treated supplied to the ultraviolet irradiation device 35 is higher than the hydrogen peroxide concentration of the water flowing through the section between the ion removal device 31 and the intermediate tank 33. In this embodiment, since no hydrogen peroxide removing means (for example, the hydrogen peroxide removing device 38 or the reducing agent adding device of the second embodiment) is provided between the intermediate tank 33 and the inlet of the subsystem, the hydrogen peroxide concentration of the water flowing through the section between the outlet of the ultraviolet irradiation device 35 and the inlet of the subsystem and the water flowing through the return pipe L2 is also higher than the hydrogen peroxide concentration of the water flowing through the section between the ion removal device 31 and the intermediate tank 33. Note that the ion exchanger filling device 36 removes a trace amount of hydrogen peroxide, but the removal efficiency is extremely low. The hydrogen peroxide removing means refers to a means having a higher hydrogen peroxide removal efficiency than the ion exchanger filling device 36.

[0020] (Water treatment method) Next, a water treatment method using the water treatment apparatus 1 will be described. As described above, in the present embodiment, the water to be treated sequentially flows through each apparatus constituting the pretreatment apparatus 2 and the pure water production apparatus 3, and pure water is produced. In particular, in the present embodiment, the water to be treated having a specific water quality (hereinafter referred to as specific water quality) of total organic carbon concentration of 10 μg / L or less and dissolved oxygen concentration of 30 μg / L or more is supplied to the ultraviolet irradiation apparatus 35 at the inlet portion 35A of the ultraviolet irradiation apparatus 35. The water to be treated supplied from the inlet portion 35A of the ultraviolet irradiation apparatus 35 to the ultraviolet irradiation apparatus 35 is irradiated with ultraviolet rays from the ultraviolet irradiation apparatus 35. Since the energy cost increases when the ultraviolet irradiation amount is high, the ultraviolet irradiation amount is 0.1 kWh / m 3 The following is preferable, and 0.08 kWh / m 3 The following is more preferable, and 0.06 kWh / m 3 The following is even more preferable. Since the decomposition efficiency of organic substances decreases when the ultraviolet irradiation amount is too low, the ultraviolet irradiation amount is preferably 0.02 kWh / m 3 or more. Since the load on the subsequent ion exchanger filling apparatus 36 and the ultraviolet irradiation amount can be small when the total organic carbon concentration is low, the total organic carbon concentration is preferably 5 μg / L or less.

[0021] Figure 2 schematically shows the relationship between the TOC concentration, dissolved oxygen concentration (hereinafter referred to as DO concentration), and hydrogen peroxide concentration (hereinafter referred to as H2O2 concentration) at the inlet 35A of the ultraviolet irradiation device 35, and the organic matter decomposition performance of the ultraviolet irradiation device 35. Generally, since hydrogen peroxide is an oxidation promoter, the decomposition of organic matter is promoted by adding hydrogen peroxide to the water to be treated in the ultraviolet irradiation device 35. For example, when the DO concentration is less than 30 μg / L, the decomposition of organic matter is promoted regardless of the TOC concentration. Even when the DO concentration is 30 μg / L or more, if the TOC concentration is greater than 10 μg / L, the decomposition of organic matter is promoted. On the other hand, in the case of water with a specific water quality, an excessive concentration of hydrogen peroxide reduces the decomposition efficiency of organic matter by ultraviolet light. This is considered to be because hydrogen peroxide becomes an inhibitor of the decomposition of organic matter by ultraviolet light. Therefore, for the water to be treated with a specific water quality, a lower H2O2 concentration promotes the decomposition of organic matter more easily. The H2O2 concentration is preferably 30 μg / L or less, more preferably 20 μg / L or less, even more preferably less than 10 μg / L, and still more preferably 5 μg / L or less. However, for reasons to be described later, the H2O2 concentration is preferably greater than 1 μg / L, and more preferably 2 μg / L or more.

[0022] For the water to be treated without specific water quality, it is effective to add hydrogen peroxide for the decomposition of organic substances (or not to perform the treatment to reduce the H2O2 concentration). However, for example, in order to reduce the DO concentration to less than 30 μg / L, it may be necessary to increase the cost of the first deoxygenation device 34 or the power consumption of the vacuum pump, and in some cases, it may be desirable to set the DO concentration to 30 μg / L or more. Regarding the TOC concentration, in order to suppress the cost increase and operating cost of the upstream ion removal device 31 and reverse osmosis membrane device 32, it may be reasonable for the value at the inlet 35A of the ultraviolet irradiation device 35 to be a certain large value. Thus, whether the water to be treated of the ultraviolet irradiation device 35 has specific water quality depends on the design of the water treatment device 1, the design of the entire ultrapure water production device including subsystems, the water quality of the raw water, etc., and may not be determined only from the viewpoint of the organic matter decomposition performance of the ultraviolet irradiation device 35. However, when the water to be treated at the inlet 35A of the ultraviolet irradiation device 35 has specific water quality, an operation to reduce the H2O2 concentration is preferred.

[0023] (DO concentration) The DO concentration of the water to be treated at the inlet 35A of the ultraviolet irradiation device 35 is not limited as long as it is 30 μg / L or more, but it is preferably less than 1000 μg / L. As described in Example 3 below, by setting it to less than 1000 μg / L, the decomposition performance of organic substances by ultraviolet rays is improved. The DO concentration of the water to be treated at the inlet 35A of the ultraviolet irradiation device 35 is more preferably 500 μg / L or less, and even more preferably 100 μg / L or less. The DO concentration of the water to be treated can be adjusted by the first deoxygenation device 34 provided upstream of the ultraviolet irradiation device 35. The DO concentration can be measured online, for example, with a DO concentration meter (not shown) provided between the first deoxygenation device 34 and the ultraviolet irradiation device 35.

[0024] In order to increase the decomposition efficiency of organic substances, the irradiation amount of ultraviolet rays irradiated from the ultraviolet irradiation device 35 can be adjusted (Method A). In addition, since dissolved oxygen has the property of absorbing ultraviolet rays, when the DO concentration is low, the ultraviolet rays absorbed by the dissolved oxygen decrease, and the decomposition efficiency of organic substances increases. Therefore, in order to increase the decomposition efficiency of organic substances, the DO concentration of the water to be treated can also be adjusted by the first deoxygenation device 34 (Method B). Method A and Method B may be executed in combination, or only either one may be executed, but it is preferably performed within a range in which the H2O2 concentration of the water to be treated at the inlet portion 35A of the ultraviolet irradiation device 35 is 30 μg / L or less. A sampling pipe L3 for hydrogen peroxide is provided at an arbitrary position between the intermediate tank 33 and the ultraviolet irradiation device 35 (in this embodiment, between the first deoxygenation device 34 and the ultraviolet irradiation device 35), and the H2O2 concentration of the water to be treated at the inlet portion 35A of the ultraviolet irradiation device 35 can be measured from the water collected by the sampling pipe L3. The H2O2 concentration may be measured online with an H2O2 concentration meter (not shown) provided at an arbitrary position between the intermediate tank 33 and the ultraviolet irradiation device 35 (for example, between the first deoxygenation device 34 and the ultraviolet irradiation device 35). When adjusting the irradiation amount of ultraviolet rays by Method A, usually the irradiation amount of ultraviolet rays is increased, but the irradiation amount of ultraviolet rays may be decreased within a range in which the decomposition efficiency of organic substances does not decrease significantly. When adjusting the DO concentration of the water to be treated by Method B, usually the DO concentration of the water to be treated is decreased, but the DO concentration of the water to be treated may be increased within a range in which the decomposition efficiency of organic substances does not decrease significantly.

[0025] Method A and Method B can be executed according to the TOC concentration in the water to be treated or treated water of the ultraviolet irradiation device 35. Specifically, a TOC meter is arranged at the inlet side of the ultraviolet irradiation device 35 (for example, between the first deoxygenation device 34 and the ultraviolet irradiation device 35) and the outlet side of the ultraviolet irradiation device 35 (for example, the outlet of the second deoxygenation device 37). Then, when the TOC concentration of the water to be treated of the ultraviolet irradiation device 35 exceeds a predetermined value, or when the TOC concentration of the treated water of the ultraviolet irradiation device 35 exceeds a predetermined value, at least one of Method A and Method B, preferably both, can be executed. Note that even when the TOC concentration of the water to be treated or treated water of the ultraviolet irradiation device 35 does not exceed a predetermined value, at least one of Method A and Method B can be executed.

[0026] The first deoxygenation device 34 and the ultraviolet irradiation device 35 are also means for adjusting the H2O2 concentration of the water to be treated at the inlet portion 35A of the ultraviolet irradiation device 35 to 30 μg / L or less. Since ultraviolet rays generate hydrogen peroxide from water, increasing the irradiation amount of ultraviolet rays increases the generation amount of hydrogen peroxide. When the DO concentration is low, the ultraviolet rays absorbed by dissolved oxygen decrease, so more hydrogen peroxide is generated even when the irradiation amount of ultraviolet rays is the same. A part of the generated hydrogen peroxide is returned upstream of the ultraviolet irradiation device 35 through the return pipe L2. Therefore, the H2O2 concentration of the water to be treated at the inlet portion 35A of the ultraviolet irradiation device 35 can be adjusted by at least one of the first deoxygenation device 34 and the ultraviolet irradiation device 35. As described above, the H2O2 concentration of the water to be treated at the inlet portion 35A of the ultraviolet irradiation device 35 can be measured from the water collected through the sampling pipe L3. When the measured H2O2 concentration exceeds a predetermined reference value (for example, 25 μg / L) lower than 30 μg / L, the H2O2 concentration in the water to be treated can be adjusted by adjusting at least one of the irradiation amount of ultraviolet rays and the DO concentration.

[0027] As described above, the hydrogen peroxide contained in the raw water is almost completely removed in the activated carbon column 22. Therefore, the hydrogen peroxide present at the inlet 35A of the ultraviolet irradiation device 35 is almost limited to that generated in the ultraviolet irradiation device 35 and returned upstream of the ultraviolet irradiation device 35 by the return pipe L2. Thus, the flow rate of the return water can be changed so that the H2O2 concentration of the water to be treated becomes 30 μg / L or less. Specifically, the H2O2 concentration of the water to be treated at the inlet 35A of the ultraviolet irradiation device 35 is measured with the sampling pipe L3, and when the measured H2O2 concentration exceeds a predetermined reference value (for example, 25 μg / L) lower than 30 μg / L, the flow rate of the treated water returned from the return pipe L2 to upstream of the ultraviolet irradiation device 35 is reduced. Thereby, the H2O2 concentration of the water to be treated at the inlet 35A of the ultraviolet irradiation device 35 can be adjusted to 30 μg / L or less. For example, when the irradiation amount of ultraviolet rays is increased to increase the decomposition efficiency of organic substances, the H2O2 concentration in the treated water increases. In this case, in order to suppress the increase in the H2O2 concentration of the water to be treated at the inlet 35A of the ultraviolet irradiation device 35, the opening degree of the valve V1 can be throttled to reduce the flow rate of the return water.

[0028] However, the flow rate of the return water is originally determined so as to cope with fluctuations in the amount of ultrapure water used at the use point and the flow rate of pure water supplied to the subsystem associated therewith. If the flow rate of the return water is decreased to lower the H2O2 concentration at the inlet 35A of the ultraviolet irradiation device 35, it may become difficult to cope with fluctuations in the amount of ultrapure water used at the use point. Therefore, in order to enable appropriate adjustment of the flow rate of pure water supplied to the subsystem, the H2O2 concentration at the inlet 35A of the ultraviolet irradiation device 35 is preferably greater than 1 μg / L, and more preferably 2 μg / L or more. Although it is also effective to lower the irradiation amount of ultraviolet rays in order to lower the H2O2 concentration at the inlet 35A of the ultraviolet irradiation device 35, the decomposition efficiency of organic substances in the ultraviolet irradiation device 35 decreases. Thus, if the H2O2 concentration at the inlet 35A of the ultraviolet irradiation device 35 is lowered to 1 μg / L or less, it may be disadvantageous from another viewpoint.

[0029] (Second Embodiment) Figure 3 shows a schematic configuration of the water treatment apparatus 1 according to the second embodiment of the present invention. The water treatment apparatus 1 of the present embodiment has a hydrogen peroxide removal device 38 located downstream of the ultraviolet irradiation device 35 and the ion exchanger filling device 36 and upstream of the second deoxygenation device 37. The second embodiment is the same as the first embodiment except for this point. The hydrogen peroxide removal device 38 removes a part of hydrogen peroxide from the treated water irradiated with ultraviolet rays from the ultraviolet irradiation device 35. A part of the treated water from which a part of hydrogen peroxide has been removed is returned upstream of the ultraviolet irradiation device 35 through the return pipe L2. Therefore, the hydrogen peroxide removal device 38 and the return pipe L2 are means for adjusting the H2O2 concentration of the water to be treated at the inlet 35A of the ultraviolet irradiation device 35 to 30 μg / L or less. In the present embodiment, since the return water passing through the return pipe L2 contains almost no hydrogen peroxide, in order to suppress an increase in the H2O2 concentration of the water to be treated at the inlet 35A of the ultraviolet irradiation device 35, the opening degree of the valve V1 can be increased and the flow rate of the return water can be increased.

[0030] The hydrogen peroxide removal device 38 is a platinum group catalyst filling device in which a platinum group catalyst made of a platinum group metal is supported on an anion exchanger (for example, resin). Examples of the platinum group metal include platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), iridium (Ir), etc. One of these may be used alone, or two or more of them may be used in combination. Among these platinum group metals, Pt and Pd are preferable, and Pd is preferable from the viewpoint of cost. By bringing the water to be treated into contact with the platinum group catalyst, the H2O2 concentration in the water to be treated can be reduced. In addition, in order to reduce the DO concentration, a hydrogen addition part (not shown) may be provided upstream of the platinum group catalyst filling device. As an alternative configuration, an ion exchanger carrying a metal catalyst such as Pd may be filled in the EDI. In this case, hydrogen generated at the cathode of the EDI can be used as hydrogen that comes into contact with the metal catalyst.

[0031] In each of the above-described embodiments, the H2O2 concentration is adjusted to 30 μg / L or less. However, if the hydrogen peroxide concentration of the water to be treated at the inlet portion 35A of the ultraviolet irradiation device 35 is 30 μg / L or less even without adjustment, adjustment of the hydrogen peroxide concentration is unnecessary. As described above, in the first embodiment, since the water flowing between the activated carbon tower 22 and the intermediate tank 33 contains almost no hydrogen peroxide, the hydrogen peroxide present at the inlet portion 35A of the ultraviolet irradiation device 35 is almost limited to that generated by the ultraviolet irradiation device 35 and returned upstream of the ultraviolet irradiation device 35 by the return pipe L2. Since the hydrogen peroxide concentration depends on the ultraviolet irradiation amount of the ultraviolet irradiation device 35, the flow rate of the return water passing through the return pipe L2, etc., there are cases where adjustment of the hydrogen peroxide concentration is unnecessary. In the second embodiment, the water flowing between the activated carbon tower 22 and the intermediate tank 33 contains almost no hydrogen peroxide, and by providing the hydrogen peroxide removal device 38, the water flowing through the return pipe L2 also contains almost no hydrogen peroxide. Therefore, regardless of the ultraviolet irradiation amount of the ultraviolet irradiation device 35, the flow rate of the return water passing through the return pipe L2, etc., the hydrogen peroxide concentration of the water to be treated at the inlet portion 35A of the ultraviolet irradiation device 35 is almost zero (30 μg / L or less). Therefore, in the second embodiment, adjustment of the hydrogen peroxide concentration is basically unnecessary.

[0032] (Example 1) Using the test apparatus shown in FIG. 4, the TOC concentration reduction rate was measured. The test apparatus was arranged with a deoxygenation device (deaeration membrane device) 41, an ultraviolet irradiation device 42, and an ion exchange resin column 43 in this order along the flow direction D of the water to be treated. A part of the treated water of the ultraviolet irradiation device 42 was supplied to the ion exchange resin column 43, and the rest was drained from the blow line. The TOC concentration (T1) of the water to be treated between the deoxygenation device 41 and the ultraviolet irradiation device 42 and the TOC concentration (T2) of the treated water of the ion exchange resin column 43 were measured with a TOC meter, respectively. The definition of the TOC concentration reduction rate is shown in FIG. 4.

[0033] The raw water was adjusted to a TOC concentration of 10 μg / L, a DO concentration of 100 μg / L, and an H2O2 concentration of 5 μg / L. Hydrogen peroxide was added upstream of the deoxygenation device 41, and the H2O2 concentration of the water to be treated supplied to the deoxygenation device 41 was adjusted to 5 μg / L (without hydrogen peroxide addition), 30 μg / L, 100 μg / L, and 200 μg / L. By adjusting the degree of vacuum inside the deaeration membrane with the vacuum pump of the deoxygenation device 41, the DO concentration of the water to be treated supplied to the ultraviolet irradiation device 42 was adjusted to 5 μg / L, 30 μg / L, and 100 μg / L (vacuum pump off). By adjusting the supply flow rate of the water to be treated to the ultraviolet irradiation device 42, the ultraviolet irradiation dose was adjusted to 0.06 kWh / m 3 、 0.1 kWh / m 3 。 The H2O2 concentration was measured by the absorbance method. Other test conditions are shown below. · Ultraviolet irradiation device 42: Low-pressure ultraviolet irradiation device JPW (manufactured by Nippon Photo Science Co., Ltd.) · Ion exchange resin column 43: A total of 300 mL of cation exchange resin AMBERJET 1024H form (manufactured by Organo Corporation) and anion exchange resin AMBERJET 4002OH form (manufactured by Organo Corporation) were mixed bed filled at a volume ratio of 1:2 · SV of ion exchange resin: 60 ( / h) · TOC meter… M500e (manufactured by VEOLIA) · Dissolved oxygen meter… Orbisphere 510 (manufactured by Hach)

[0034] Figure 5 shows the relationship between the H2O2 concentration and the TOC concentration reduction rate at an ultraviolet irradiation dose of 0.06 kWh / m 3 。 Figure 6 shows the relationship at an ultraviolet irradiation dose of 0.1 kWh / m 3Shows the relationship between the H2O2 concentration and the reduction rate of the TOC concentration. Referring to Fig. 5, when the DO concentration is 5 μg / L, as the H2O2 concentration increases, the reduction rate of the TOC concentration improves and saturates at about 100 μg / L. When the DO concentration is 30 μg / L, the reduction rate of the TOC concentration is almost constant up to an H2O2 concentration of 30 μg / L, but gradually decreases when it exceeds 30 μg / L. In particular, the reduction rate of the TOC concentration significantly decreased at an H2O2 concentration of 200 μg / L. When the DO concentration is 100 μg / L, a similar trend to the case of a DO concentration of 30 μg / L is obtained, and the reduction rate of the TOC concentration significantly decreased at an H2O2 concentration of 100 μg / L. From the above, it was found that when the DO concentration is 30 μg / L or more, by adjusting the H2O2 concentration to 30 μg / L or less, a decrease in the performance of decomposing organic substances by ultraviolet rays can be suppressed. Also, as shown in Fig. 6, since the tendency does not change even in the case of an ultraviolet irradiation dose of 0.1 kWh / m 3 , it was found that by adjusting the H2O2 concentration to 30 μg / L or less regardless of the ultraviolet irradiation dose, organic substances can be efficiently decomposed.

[0035] (Example 2) Under the same conditions as in Example 1 (DO concentration: 30 μg / L, irradiation dose: 0.1 kWh / m 3 ), the TOC concentration was adjusted to 10 μg / L, 30 μg / L, and 50 μg / L. The H2O2 concentration of the water to be treated supplied to the deoxygenation device 41 was adjusted to 5 μg / L (without hydrogen peroxide addition), 30 μg / L, 100 μg / L, and 200 μg / L. Fig. 7 shows the relationship between the H2O2 concentration and the reduction rate of the TOC concentration. When the TOC concentration is 10 μg / L, the reduction rate of the TOC concentration is almost constant up to an H2O2 concentration of 30 μg / L, but gradually decreases when it exceeds 30 μg / L. When the TOC concentrations are 30 μg / L and 50 μg / L, the reduction rate of the TOC concentration improves as the H2O2 concentration increases. From the above, it was found that when the TOC concentration is 10 μg / L or less, by adjusting the H2O2 concentration to 30 μg / L or less, a decrease in the performance of decomposing organic substances by ultraviolet rays can be suppressed.

[0036] (Example 3) Under the same conditions as in Example 1 (H2O2 concentration: 30 μg / L, ultraviolet irradiation dose: 0.1 kWh / m 3) The DO concentration was adjusted to 5 μg / L, 30 μg / L, 100 μg / L, 1000 μg / L, and 10000 μg / L. Fig. 8 shows the relationship between the DO concentration and the TOC concentration reduction rate. For DO concentrations of 5 μg / L, 30 μg / L, and 100 μg / L, it is the same as in Example 1. Looking at the range where the DO concentration is 30 μg / L or more, the TOC concentration reduction rate is the highest at a DO concentration of 30 μg / L, and the TOC concentration reduction rate decreases as the DO concentration increases. From the above, it was found that the DO concentration is preferably 1000 μg / L or less.

Explanation of Symbols

[0037] 1 Water treatment device 2 Pretreatment device 3 Pure water production device 31 Ion removal device 32 Reverse osmosis membrane device 33 Intermediate tank 34 First deoxygenation device 35 Ultraviolet irradiation device 36 Ion exchanger filling device 37 Second deoxygenation device 38 Hydrogen peroxide removal device

Claims

1. Supplying the ultraviolet irradiation device with treated water having a total organic carbon concentration of 10 μg / L or less and a dissolved oxygen concentration of 30 μg / L or more at the inlet of the ultraviolet irradiation device; Irradiating the treated water supplied from the inlet to the ultraviolet irradiation device with ultraviolet rays from the ultraviolet irradiation device; Reducing the dissolved oxygen concentration of the treated water at the inlet to less than 1000 μg / L by a deoxygenation device provided upstream of the ultraviolet irradiation device; and A water treatment method in which the hydrogen peroxide concentration of the treated water at the inlet is 30 μg / L or less.

2. The water treatment method according to claim 1, comprising adjusting the hydrogen peroxide concentration of the treated water at the inlet to 30 μg / L or less.

3. The water treatment method according to claim 1, comprising adjusting the dissolved oxygen concentration of the treated water at the inlet to less than 1000 μg / L.

4. Supplying the ultraviolet irradiation device with treated water having a total organic carbon concentration of 10 μg / L or less and a dissolved oxygen concentration of 30 μg / L or more at the inlet of the ultraviolet irradiation device; Irradiating the treated water supplied from the inlet to the ultraviolet irradiation device with ultraviolet rays from the ultraviolet irradiation device; Returning a part of the treated water irradiated with ultraviolet rays from the ultraviolet irradiation device upstream of the ultraviolet irradiation device through a return pipe; Within a range where the hydrogen peroxide concentration of the treated water at the inlet is 30 μg / L or less, (A) Adjusting the irradiation amount of ultraviolet rays irradiated from the ultraviolet irradiation device (B) Adjusting the dissolved oxygen concentration of the treated water at the inlet by a deoxygenation device provided upstream of the ultraviolet irradiation device And performing at least one of the above. A water treatment method.

5. Supplying the ultraviolet irradiation device with treated water having a total organic carbon concentration of 10 μg / L or less and a dissolved oxygen concentration of 30 μg / L or more at the inlet of the ultraviolet irradiation device; Irradiating the treated water supplied from the inlet to the ultraviolet irradiation device with ultraviolet rays from the ultraviolet irradiation device; Returning a part of the treated water irradiated with ultraviolet rays from the ultraviolet irradiation device upstream of the ultraviolet irradiation device; Measuring the hydrogen peroxide concentration of the treated water supplied to the ultraviolet irradiation device; Adjusting the amount of the treated water returned upstream of the ultraviolet irradiation device so that the measured hydrogen peroxide concentration is 30 μg / L or less. A water treatment method in which the hydrogen peroxide concentration of the water to be treated at the inlet is 30 μg / L or less.

6. Removing a part of hydrogen peroxide from the treated water irradiated with ultraviolet rays from the ultraviolet irradiation device by a hydrogen peroxide removal device provided downstream of the ultraviolet irradiation device. Returning a part of the treated water from which a part of the hydrogen peroxide has been removed upstream of the ultraviolet irradiation device. The water treatment method according to any one of claims 1 to 5, comprising:

7. An ultraviolet irradiation device; Means for adjusting the hydrogen peroxide concentration of the water to be treated at the inlet of the ultraviolet irradiation device to 30 μg / L or less. Comprising: The ultraviolet irradiation device irradiates the water to be treated supplied from the inlet with ultraviolet rays. The quality of the water to be treated at the inlet has a total organic carbon concentration of 10 μg / L or less and a dissolved oxygen concentration of 30 μg / L or more. A water treatment device further comprising a deoxygenation device provided upstream of the ultraviolet irradiation device and reducing the dissolved oxygen concentration of the water to be treated at the inlet to less than 1000 μg / L.

8. An ultraviolet irradiation device; Means for adjusting the hydrogen peroxide concentration of the water to be treated at the inlet of the ultraviolet irradiation device to 30 μg / L or less. The ultraviolet irradiation device irradiates the water to be treated supplied from the inlet with ultraviolet rays. The quality of the water to be treated at the inlet has a total organic carbon concentration of 10 μg / L or less and a dissolved oxygen concentration of 30 μg / L or more. A return pipe for returning a part of the treated water irradiated with ultraviolet rays from the ultraviolet irradiation device upstream of the ultraviolet irradiation device. A deoxygenation device provided upstream of the ultraviolet irradiation device. In the range where the hydrogen peroxide concentration of the water to be treated at the inlet is 30 μg / L or less. (A) The ultraviolet irradiation device adjusts the irradiation amount of ultraviolet rays irradiated from the ultraviolet irradiation device. (B) The deoxygenation device adjusts the dissolved oxygen concentration of the water to be treated at the inlet. A water treatment device that performs at least one of the above.

9. An ultraviolet irradiation device; Means for adjusting the hydrogen peroxide concentration of the water to be treated at the inlet of the ultraviolet irradiation device to 30 μg / L or less. The ultraviolet irradiation device irradiates the water to be treated supplied from the inlet with ultraviolet rays. The water quality of the water to be treated at the inlet is such that the total organic carbon concentration is 10 μg / L or less and the dissolved oxygen concentration is 30 μg / L or more. a return pipe that returns a part of the treated water irradiated with ultraviolet rays from the ultraviolet irradiation device upstream of the ultraviolet irradiation device; a sampling pipe for measuring the hydrogen peroxide concentration of the water to be treated supplied to the ultraviolet irradiation device; a water treatment apparatus further comprising a valve for flow rate adjustment provided in the return pipe to adjust the amount of the treated water returned upstream of the ultraviolet irradiation device so that the measured hydrogen peroxide concentration becomes 30 μg / L or less.

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