Water treatment method and water treatment system

Abstract

This water treatment method comprises: irradiating water being treated that contains organic matter with ultraviolet rays by using an ultraviolet irradiation device 34; passing the water being treated that is irradiated with the ultraviolet rays through an ion exchanger filling device 35 downstream of the ultraviolet irradiation device 34; and acquiring the total organic carbon concentration and the dissolved oxygen concentration of the water being treated by the ultraviolet irradiation device 34. The irradiation with the ultraviolet rays includes adjusting the irradiation amount of the ultraviolet rays on the basis of the total organic carbon concentration and the dissolved oxygen concentration.

Description

Water treatment method and water treatment system

[0001] This application is based on and claims priority from Japanese Patent Application No. 2025-46509, filed on 21 March 2025. This application is incorporated in its entirety by reference. The present invention relates to a water treatment method and a water treatment system.

[0002] As the demand for high-quality pure water becomes more apparent, various methods for removing impurities from pure water have been investigated in recent years. Japanese Patent Publication No. 6-198279 describes installing a total organic carbon (TOC) meter at the inlet of an ultraviolet irradiation device and controlling the output of the ultraviolet irradiation device based on the total organic carbon (TOC) concentration measured by the TOC meter.

[0003] Pure water typically contains dissolved oxygen. Dissolved oxygen consumes ultraviolet light, reducing the efficiency of organic matter decomposition in ultraviolet irradiation devices. Generally, downstream of ultraviolet irradiation devices, ion exchange packing devices are provided to remove organic matter decomposition products generated by ultraviolet irradiation. However, fluctuations in dissolved oxygen concentration cause fluctuations in the TOC concentration of the treated water from the ion exchange packing device. Therefore, when adjusting the amount of ultraviolet irradiation using only TOC concentration as an indicator of water quality, as described in Japanese Patent Publication No. 6-198279, the TOC concentration of the treated water from the ion exchange packing device is prone to fluctuations.

[0004] The present invention aims to provide a water treatment method that can suppress fluctuations in the TOC concentration of the treated water in an ion exchange packing device by sequentially passing water through an ultraviolet irradiation device and an ion exchange packing device located downstream of it.

[0005] The present invention relates to a water treatment method comprising: irradiating water to be treated containing organic matter with ultraviolet light using an ultraviolet irradiation device; passing the treated water irradiated with ultraviolet light through an ion exchange packing device downstream of the ultraviolet irradiation device; and obtaining the total organic carbon concentration and dissolved oxygen concentration of the treated water from the ultraviolet irradiation device. The irradiation of ultraviolet light includes adjusting the amount of ultraviolet light irradiated based on the total organic carbon concentration and dissolved oxygen concentration.

[0006] According to the present invention, it is possible to provide a water treatment method that can suppress fluctuations in the TOC concentration of the treated water in an ion exchange packing device by sequentially passing water through an ultraviolet irradiation device and an ion exchange packing device located downstream of it.

[0007] The purposes, features, and advantages of this application, as described above and for other purposes, will become apparent from the detailed description below, with reference to the accompanying illustrations of this application.

[0008] This is a schematic diagram of a water treatment system according to the first embodiment of the present invention. This diagram shows the relationship between the TOC concentration of the water to be treated and the amount of ultraviolet irradiation. This diagram shows the relationship between the DO concentration of the water to be treated and the amount of ultraviolet irradiation. This diagram shows the relationship between the TOC concentration, DO concentration, and ultraviolet irradiation of the water to be treated. This is a measurement example showing the relationship between the DO concentration and the TOC concentration reduction rate at the inlet of the ultraviolet irradiation device. This is a schematic diagram of a water treatment system according to the second embodiment of the present invention. This is a schematic diagram of a water treatment system according to a modified example of the second embodiment of the present invention. This is a schematic diagram of a water treatment system according to another modified example of the second embodiment of the present invention. This is a schematic diagram of a water treatment system according to the third embodiment of the present invention. TOC concentration, DO concentration, H ２ O ２ This figure shows the relationship between concentration and ultraviolet irradiation dose. This is a schematic diagram of a water treatment system according to the fourth embodiment of the present invention. This is a schematic diagram of a water treatment system according to the fifth embodiment of the present invention. This is a schematic diagram of the apparatus used in Example 1 and Comparative Examples 1 and 2. This is a schematic diagram of the apparatus used in Example 2. This is a schematic diagram of the apparatus used in Example 3.

[0009] (First Embodiment) Hereinafter, embodiments of the water treatment method and water treatment system of the present invention will be described with reference to the drawings. Figure 1 shows a schematic configuration of a water treatment system 1 according to the first embodiment of the present invention. The water treatment system 1 has an upstream pretreatment device 2 and a downstream pure water production device 3 (primary system). The water treatment system 1, together with a downstream subsystem (secondary system) not shown, constitutes an ultrapure water production system. The raw water supplied to the pretreatment device 2 contains organic matter. In the following description, upstream and downstream are defined with respect to the water flow direction DD in the main pipe L1. Furthermore, "adjustment" includes both the automatic control of various operating parameters (on / off of the device, flow rate, pressure, opening / closing of valves, power consumption, etc.) by a control device and the manual adjustment of these operating parameters by an operator. Furthermore, the water treatment device means any device that adjusts the water quality of the water to be treated, and includes, for example, an ion removal device, a reverse osmosis membrane device, a deoxygenation device, an ultraviolet irradiation device, an ion exchanger filling device, and an electrodeionized water production device (EDI).

[0010] (Configuration of Water Treatment System 1) The pretreatment device 2 includes a filter 21 for removing dust and other particles with relatively large particle sizes, and an activated carbon tower 22 for removing impurities such as high-molecular-weight organic substances and oxidizing agents. For example, a sand filter can be used as the filter 21. The pure water production device 3 includes an ion removal device 31, a reverse osmosis membrane device 32, a first deoxygenation device 33, an ultraviolet irradiation device 34, an ion exchanger filling device 35, and a second deoxygenation device 36. These devices 31 to 36 are arranged in series in this order on the main pipe L1 from upstream to downstream with respect to the flow direction DD of the water to be treated. Although not shown in the figures, tanks may be provided to store the treated water from each of the devices in the pretreatment device 2 and the pure water production device 3, such as the activated carbon tower 22, the ion removal device 31, and the reverse osmosis membrane device 32. Although not shown in the figures, piping may be provided to return a portion of the treated water from any of the devices in the pure water production device 3 to an upstream tank or the like.

[0011] The ion removal device 31 includes a cation column (not shown) filled with cation exchange resin, a decarboxylation column (not shown), and an anion column (not shown) filled with anion exchange resin, which are arranged in series in this order from upstream to downstream. A decarboxylation membrane may be provided instead of the decarboxylation column. A softening device that removes hardness components such as calcium and magnesium may be provided instead of the ion removal device 31.

[0012] The reverse osmosis membrane apparatus 32 removes impurities such as ions. The reverse osmosis membrane apparatus 32 may be installed in multiple stages. If the total organic carbon concentration of the water to be treated is high, the decomposition efficiency of organic matter in the ultraviolet irradiation device 34 decreases. By removing organic matter in the reverse osmosis membrane apparatus 32, the load on the downstream ultraviolet irradiation device 34 is reduced.

[0013] The first deoxygenation device 33 removes oxygen from the water to be treated, thereby reducing the dissolved oxygen concentration in the water. Since the first deoxygenation device 33 is located upstream of the ultraviolet irradiation device 34, the ultraviolet irradiation device 34 is supplied with water to be treated that has a reduced (adjusted) dissolved oxygen concentration. The type of the first deoxygenation device 33 is not limited as long as it can remove dissolved oxygen; for example, a vacuum degasser can be used. Generally, in a vacuum degasser, a gas-liquid contact material to increase the surface area of ​​water is packed into the degassing tower, the gas pressure inside the degassing tower is reduced by a vacuum pump, the water to be treated is placed under vacuum, and dissolved oxygen is removed. The dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum inside the degassing tower using a vacuum pump. Degassing performance can also be improved by introducing nitrogen. A degassing membrane device may be used as the first deoxygenation device 33, or a platinum group catalyst packed device supporting a platinum group catalyst such as palladium (Pd) may be used. The first deoxygenation device 33 described above may be a single-stage configuration or a multi-stage configuration in which multiple devices are connected in series.

[0014] The ultraviolet irradiation device 34 irradiates the water to be treated with ultraviolet light to decompose organic matter contained in the water. As the ultraviolet irradiation device 34, for example, an ultraviolet irradiation device that generates ultraviolet light with a wavelength of at least one of 172 nm, 185 nm, or 254 nm (for example, a low-pressure ultraviolet irradiation device) can be used. The amount of ultraviolet irradiation can be adjusted by the number of lamps on the ultraviolet irradiation device 34 or by dimming (applied voltage). No other water treatment equipment is provided between the first deoxygenation device 33 and the ultraviolet irradiation device 34, and the first deoxygenation device 33 and the ultraviolet irradiation device 34 can be connected only by piping.

[0015] The ion exchanger filling device 35 is located downstream of the ultraviolet irradiation device 34, and treated water irradiated with ultraviolet light is passed through it. The ion exchanger filling device 35 removes decomposition products of organic matter generated in the treated water of the ultraviolet irradiation device 34 by ultraviolet irradiation. The ion exchanger filling device 35 is filled with ion exchange resin, but monolithic or fibrous ion exchangers may also be filled. The ion exchanger filling device 35 may also be an EDI filled with ion exchange resin. Since the EDI is a continuous regeneration type, a regeneration process for the ion exchange resin is unnecessary. No water treatment equipment, especially water treatment equipment for removing organic matter or water treatment equipment for irradiating with ultraviolet light, is provided between the ultraviolet irradiation device 34 and the ion exchanger filling device 35, and the ultraviolet irradiation device 34 and the ion exchanger filling device 35 can be connected only by piping.

[0016] The second deoxygenation unit 36 ​​is located downstream of the ion exchanger packing unit 35 and can have a configuration similar to that of the first deoxygenation unit 33. The second deoxygenation unit 36 ​​removes dissolved oxygen, carbon dioxide, etc. The treated water from the second deoxygenation unit 36 ​​is sent to the subsystem.

[0017] The pure water production apparatus 3 has means for obtaining the total organic carbon concentration (hereinafter referred to as TOC concentration) and dissolved oxygen concentration (hereinafter referred to as DO concentration) of the water to be treated at the inlet 34A of the ultraviolet irradiation apparatus 34, specifically a total organic carbon concentration meter (hereinafter referred to as TOC meter 41) and a dissolved oxygen concentration meter (hereinafter referred to as DO meter 42). The TOC meter 41 and DO meter 42 are installed between the first deoxygenation apparatus 33 and the ultraviolet irradiation apparatus 34, and no other water treatment equipment is installed between the first deoxygenation apparatus 33 and the ultraviolet irradiation apparatus 34. Therefore, it can be considered that the TOC meter 41 and DO meter 42 are measuring the TOC concentration and DO concentration at the inlet 34A of the ultraviolet irradiation apparatus 34. As long as the TOC concentration and DO concentration of the water to be treated at the inlet 34A of the ultraviolet irradiation apparatus 34 can be obtained, the installation location of the TOC meter 41 and DO meter 42 is not limited, and estimating the TOC concentration and DO concentration by other methods is also included in "obtaining". For example, a DO meter 42 may be installed at the inlet of the first deoxygenation device 33, and the DO concentration at the inlet 34A of the ultraviolet irradiation device 34 may be calculated from the measured value of the DO meter 42 and the dissolved oxygen removal rate of the first deoxygenation device 33. Alternatively, if a tank located upstream of the ultraviolet irradiation device 34 (for example, between the reverse osmosis membrane device 32 and the first deoxygenation device 33) and a recirculation line returning to the tank are provided, a TOC meter 41, a DO meter 42 and a flow meter may be installed upstream of the tank, and another TOC meter, a DO meter and a flow meter may be installed in the recirculation line. In this case, the TOC concentration at the inlet 34A of the ultraviolet irradiation device 34 can be estimated from the measured values ​​of the TOC meter 41 upstream of the tank and the TOC meter in the recirculation line, and from the flow meter upstream of the tank and the flow meter in the recirculation line. The DO concentration at the inlet 34A of the ultraviolet irradiation device 34 can be estimated in the same manner.

[0018] The pure water production apparatus 3 has a control unit 34B for the ultraviolet irradiation device 34. The control unit 34B is connected to the TOC meter 41, the DO meter 42, and the ultraviolet irradiation device 34. Based on the TOC concentration measured by the TOC meter 41 and the DO concentration measured by the DO meter 42, the control unit 34B adjusts the amount of ultraviolet radiation emitted from the ultraviolet irradiation device 34, specifically the number of lamps lit in the ultraviolet irradiation device 34 and the dimming (applied voltage).

[0019] (Water Treatment Method) Next, a water treatment method using the water treatment system 1 will be described. As described above, in this embodiment, water to be treated containing organic matter is sequentially passed through each of the devices constituting the pretreatment device 2 and the pure water production device 3 to produce pure water. Specifically, the water treated in the pretreatment device 2 is introduced into the pure water production device 3, sequentially treated in the ion removal device 31, the reverse osmosis membrane device 32, and the first deoxygenation device 33, and then sent to the ultraviolet irradiation device 34. The TOC concentration of the water to be treated at the inlet 34A of the ultraviolet irradiation device 34 is obtained by the TOC meter 41, and the DO concentration is obtained by the DO meter 42. The ultraviolet irradiation device 34 irradiates the water to be treated containing organic matter with ultraviolet light. The water to be treated after being irradiated with ultraviolet light is passed through the ion exchanger filling device 35 downstream of the ultraviolet irradiation device 34, and the treated water from the ion exchanger filling device 35 is further treated in the second deoxygenation device 36 and sent to the subsystem.

[0020] The control method in the control unit 34B, specifically the method for adjusting the amount of ultraviolet irradiation of the ultraviolet irradiation device 34, will be explained in more detail below. Control in the control unit 34B can be performed, for example, by PID (Proportional Integral Derivative) control. Here, the terms are defined as follows. Water treated by UV irradiation device 34: Water at the inlet 34A of UV irradiation device 34 Treated water from ion exchanger filling device 35: Water at the outlet 35A of ion exchanger filling device 35 Treated water TOC concentration: TOC concentration of the water treated by UV irradiation device 34 Treated water DO concentration: DO concentration of the water treated by UV irradiation device 34 Treated water TOC concentration: TOC concentration of the water treated by ion exchanger filling device 35 Target TOC concentration: A predetermined target value for the TOC concentration of the treated water TOC concentration TOC concentration reduction rate: (TOC1 - TOC2) / TOC1 × 100 (%) when the TOC concentration of the water treated is TOC1 and the TOC concentration of the treated water is TOC2 Target TOC concentration reduction rate: A predetermined target value for the TOC concentration reduction rate

[0021] Ultraviolet irradiation is performed to decompose organic matter, and it is common to install an ion exchange packing device 35 downstream of the ultraviolet irradiation device 34 to remove the decomposition products of organic matter generated during this process. The ultraviolet irradiation device 34 and the ion exchange packing device 35 function together as an organic matter removal device. In normal applications, there is no problem as long as the treated water TOC concentration is below the target TOC concentration, but in the case of ultrapure water used for cleaning wafers, for example, it has been pointed out that fluctuations in the treated water TOC concentration may affect the yield of the final product. The treated water from the pure water production device 3 is sent to a subsystem for further treatment, but fluctuations in the treated water TOC concentration also affect the TOC concentration of the treated water in the subsystem. For this reason, it is important not only to keep the treated water TOC concentration below the target TOC concentration but also to suppress temporal fluctuations.

[0022] Next, the relationship between the TOC concentration of the treated water, the DO concentration of the treated water, and the ultraviolet irradiation dose will be explained with reference to Figures 2A to 2C. Figure 2A conceptually shows the relationship between the TOC concentration of the treated water and the ultraviolet irradiation dose, and Figure 2B conceptually shows the relationship between the DO concentration of the treated water and the ultraviolet irradiation dose. The vertical axis shows the ultraviolet irradiation dose required to control the TOC concentration of the treated water to the target TOC concentration. As shown in Figure 2A, there is generally a positive correlation between the TOC concentration of the treated water and the ultraviolet irradiation dose. Since dissolved oxygen absorbs ultraviolet light, the organic matter decomposition efficiency of the ultraviolet irradiation device 34 decreases when the DO concentration is high. Therefore, the higher the DO concentration of the treated water, the higher the ultraviolet irradiation dose needs to be, and as shown in Figure 2B, there is generally a positive correlation between the DO concentration of the treated water and the ultraviolet irradiation dose.

[0023] For example, if the TOC concentration of the water to be treated fluctuates, the amount of ultraviolet irradiation can be adjusted according to Figure 2A. If the TOC concentration of the water to be treated increases from T1 to T2, the amount of ultraviolet irradiation can be increased from U1 to U2. However, if the DO concentration of the water to be treated fluctuates at this time, it becomes difficult to control the TOC concentration of the treated water to the target TOC concentration. When the TOC concentration of the water to be treated increases from T1 to T2, if the DO concentration of the water to be treated increases from D1 to D2 as shown in Figure 2B, the amount of ultraviolet irradiation U2 is insufficient, and the TOC concentration of the treated water may exceed the target TOC concentration. Conversely, if the DO concentration of the water to be treated decreases from D1 to D3, the amount of ultraviolet irradiation U2 becomes excessive, and the TOC concentration of the treated water may fall below the target TOC concentration. In the latter case in particular, since irradiation is performed with an amount greater than necessary, the power consumption of the ultraviolet irradiation device 34 will also increase unnecessarily.

[0024] In this embodiment, when irradiating with ultraviolet light using the ultraviolet irradiation device 34, the control unit 34B adjusts the amount of ultraviolet irradiation, specifically the number of lamps lit by the ultraviolet irradiation device 34 and the dimming (applied voltage), based on both the TOC concentration and the DO concentration of the water to be treated. In other words, the amount of ultraviolet irradiation required to control the TOC concentration of the treated water to the target TOC concentration is a function f(T, D) of the TOC concentration T and DO concentration D of the water to be treated (f means function; the same applies hereafter). Figure 2C shows the relationship between the TOC concentration, DO concentration and the amount of ultraviolet irradiation of the water to be treated. The amount of ultraviolet irradiation in the region S enclosed by the TOC concentrations T1 to T2 and the DO concentrations D2 to D3 of the water to be treated is the function f(T, D) shown in region S1. If the DO concentration of the water to be treated is not considered, only one-dimensional control between points A and B is possible, and therefore the ultraviolet intensity can only be adjusted between U1 and U2. The same applies when adjusting the UV intensity based solely on the DO concentration of the treated water, without considering the TOC concentration of the treated water.

[0025] The combination of the function f(T) of the TOC concentration in the treated water and the function f(D) of the DO concentration in the treated water can also be considered as a single water quality parameter. If we abbreviate f(T) as A and f(D) as B, the combinations of function f(T) and function f(D) are A×B, A / B, B / A, A+B, A-B, B-A, A B , B AIt can take various forms, such as those listed above. For example, when the combination of functions f(T) and f(D) takes the form of a product, the function becomes f(T, D) = f(T) × f(D), and the amount of ultraviolet irradiation can be calculated based on the product of functions f(T) and f(D). Functions f(T) and f(D) can be determined separately. For example, an approximate value of the amount of ultraviolet irradiation can be obtained based on f(T), and then corrected to a more appropriate value considering the DO concentration of the treated water using f(D). As long as f(T) is a function of the TOC concentration of the treated water, it can take any form, and as long as f(D) is a function of the DO concentration of the treated water, it can take any form, allowing for more precise adjustment. Functions f(T, D) and functions f(T) and f(D) can be obtained from experiments or from operating data of an actual plant.

[0026] In this embodiment, the amount of ultraviolet irradiation is adjusted based on the TOC concentration and DO concentration of the treated water, making it easy to suppress fluctuations in the TOC concentration of the treated water. In the method of adjusting the amount of ultraviolet irradiation based on the TOC concentration and DO concentration of the treated water, the adjustment is made after the water quality of the treated water has changed, so the TOC concentration of the treated water is prone to fluctuations.

[0027] The target TOC concentration and the target TOC concentration reduction rate vary depending on the design and operation of the water treatment system 1, and are not necessarily constant values. As shown in Figure 2C, if the target TOC concentration is low or the target TOC concentration reduction rate is high, it is necessary to increase the amount of ultraviolet irradiation, and the amount of ultraviolet irradiation needs to be adjusted, for example, within the range of region S2. If the target TOC concentration is high or the target TOC concentration reduction rate is low, it is necessary to decrease the amount of ultraviolet irradiation, and the amount of ultraviolet irradiation needs to be adjusted, for example, within the range of region S3. Therefore, when the target TOC concentration is a variable, the amount of ultraviolet irradiation required to control the treated water TOC concentration to the target TOC concentration R1 is a function f(T, D, R1) or f(T) × f(D) × f(R1). When the TOC concentration reduction rate is a variable, the amount of ultraviolet irradiation required to control the TOC concentration reduction rate to the target TOC concentration reduction rate R2 is a function f(T, D, R2) or f(T) × f(D) × f(R2). The functions f(T, D, R1), f(T, D, R2), f(R1), and f(R2) may be obtained from experiments or from operating data of an actual plant. The target TOC concentration R1 and the TOC concentration reduction rate R2 may be stored in the control unit 34B in advance, or the operator may input them into the control unit 34B.

[0028] The amount of ultraviolet irradiation can also be adjusted based on the difference between the TOC concentration of the treated water and the target value, and the difference between the DO concentration of the treated water and the target value. Alternatively, the amount of ultraviolet irradiation can also be adjusted based on the ratio of the TOC concentration of the treated water to the target value, and the ratio of the DO concentration of the treated water to the target value. The target values ​​for the TOC concentration of the treated water and the target values ​​for the DO concentration of the treated water are, for example, combinations of TOC concentration and DO concentration of the treated water when a desirable treated water TOC concentration is obtained, and these may be stored in advance in the control unit 34B, or the operator may input them into the control unit 34B.

[0029] The DO concentration of the treated water is not particularly limited, but the effect of this embodiment is greater when it is 1000 μg / L or less. Figure 3 shows the relationship between the DO concentration at the inlet of the ultraviolet irradiation device and the TOC concentration reduction rate when water with a TOC concentration of 5 μg / L is sequentially passed through the ultraviolet irradiation device and the ion exchange packing device. When the TOC concentration reduction rate is almost constant when the DO concentration exceeds 1000 μg / L, the amount of ultraviolet irradiation can be adjusted based only on the TOC concentration of the treated water. In other words, in this range, it is possible to adjust the amount of ultraviolet irradiation based on both the TOC concentration and the DO concentration of the treated water, but the need for this is small. On the other hand, when the DO concentration is 1000 μg / L or less, the TOC concentration reduction rate tends to increase as the DO concentration decreases, so it is effective to adjust the amount of ultraviolet irradiation based on both the TOC concentration and the DO concentration of the treated water. The effect of this embodiment is greater when the DO concentration of the treated water is 500 μg / L or less, and the effect of this embodiment is even greater when it is 100 μg / L or less. While there is no lower limit to the DO concentration of the treated water, a lower concentration of 1 μg / L or less increases the load required to reduce the DO concentration (e.g., larger vacuum pump for the first deoxygenation device 33, increased power costs), so a concentration of 1 μg / L or more is preferable, and 5 μg / L or more is more preferable. Similarly, while there is no particular limit to the TOC concentration of the treated water, the lower the TOC concentration, the greater the influence of the DO concentration. Therefore, a TOC concentration of 10 μg / L or less, and even more so, 5 μg / L or less, enhances the effectiveness of this embodiment.

[0030] (Second Embodiment) Figure 4 shows a schematic configuration of a water treatment system 1 according to a second embodiment of the present invention. Configurations and effects that are not described are the same as in the first embodiment. The water treatment system 1 of this embodiment has a flow meter 43 for measuring the flow rate of water to be treated that flows through the ultraviolet irradiation device 34. The flow meter 43 is connected to the control unit 34B. The installation position of the flow meter 43 is not limited as long as the flow rate of the water to be treated that flows through the ultraviolet irradiation device 34 is the same. If the flow rate of the water to be treated in the ultraviolet irradiation device 34 and the flow rate of the treated water are the same, at least one of the flow rate of the water to be treated in the ultraviolet irradiation device 34 and the flow rate of the treated water may be measured by at least one flow meter 43. In this embodiment, the flow meter 43 is provided downstream of the second deoxygenation device 36, but it can also be provided at any position from the ion removal device 31 to the second deoxygenation device 36, for example.

[0031] When irradiating with ultraviolet light using the ultraviolet irradiation device 34, the control unit 34B can adjust the power of the ultraviolet irradiation device 34 based on the TOC concentration of the water to be treated, the DO concentration of the water to be treated, and the flow rate F of the water to be treated that flows through the ultraviolet irradiation device 34. The amount of ultraviolet irradiation is the energy per unit volume (unit: kWh / m³). 3 Since it is defined as ), the power of the ultraviolet irradiation device 34 can be adjusted in proportion to the flow rate F. Specifically, the ultraviolet irradiation amount P (kWh / m³) is determined by the function f(T, D, F) or f(T) × f(D) × f(F). 3 ) and determine the flow rate F (m 3 The power W (kW) of the ultraviolet irradiation device 34 can be determined by multiplying by ( / h). The power of the ultraviolet irradiation device 34 can also be adjusted based on the difference or ratio between the flow rate F and the reference flow rate. The reference flow rate may be stored in the control unit 34B in advance, or the operator can input it into the control unit 34B. Based on the power W, the number of lamps lit by the ultraviolet irradiation device 34 and the dimming (applied voltage) can be adjusted. In this embodiment, even if the flow rate fluctuates, the amount of ultraviolet irradiation can be maintained at an appropriate level by adjusting the power of the ultraviolet irradiation device 34, making it easy to suppress fluctuations in the TOC concentration of the treated water.

[0032] Next, an example will be described in which the flow rate of water to be treated that flows through at least one water treatment device varies. The flow rate of water to be treated that flows through at least one water treatment device may vary, for example, according to the amount of ultrapure water used at the use point 67. Figures 5A to 5B show a schematic configuration of a water treatment system 1 according to a modification of the second embodiment. Configurations and effects that are not described are the same as in the second embodiment. In the configuration shown in Figure 5A, a first intermediate tank 51 is provided between the ion removal device 31 and the reverse osmosis membrane device 32, and a first pump 52 is provided between the first intermediate tank 51 and the reverse osmosis membrane device 32. A second intermediate tank 53 is provided between the reverse osmosis membrane device 32 and the ultraviolet irradiation device 34, and a second pump 54 is provided between the second intermediate tank 53 and the ultraviolet irradiation device 34. A first circulation line L2 is provided that branches off from between the reverse osmosis membrane device 32 and the second intermediate tank 53 and merges with the first intermediate tank 51. A second circulation line L3 is provided, branching off from between the second deoxygenation device 36 and subsystem 6 and joining to the second intermediate tank 53. The subsystem 6 downstream of the pure water production device 3 includes a third intermediate tank 61, a third pump 62, a second ultraviolet irradiation device 63, a second ion exchange device 64, a deaeration device 65, and a membrane filtration device 66, with a use point 67 provided downstream of the membrane filtration device 66. Furthermore, a third circulation line L4 is provided to return the ultrapure water not used at the use point 67 to the third intermediate tank 61. In the configuration shown in Figure 5B, a fourth intermediate tank 55, a fourth pump 56, and an EDI 57 are further provided between the reverse osmosis membrane device 32 and the second intermediate tank 53 compared to the configuration shown in Figure 5A. Also, a fourth circulation line L5 is provided, branching off from between the EDI 57 and the second intermediate tank 53 and joining to the fourth intermediate tank 55.

[0033] By providing a first intermediate tank 51, a second intermediate tank 53, a third intermediate tank 61 (and a fourth intermediate tank 55 in Figure 5B), and first to third circulation lines L2 to L4 (and a fourth circulation line L5 in Figure 5B), the water treatment flow rate in each device can be kept constant. For example, in Figure 5A, if the amount of water treated by subsystem 6 decreases and the water level in the third intermediate tank 61 rises, the flow rates of the first circulation line L2 and the second circulation line L3 can be increased to reduce the amount of water supplied to the third intermediate tank 61. However, increasing the flow rates of the first circulation line L2 and the second circulation line L3 ultimately leads to the wasteful consumption of power by the first pump 52 and the second pump 54. In particular, the first pump 52, located upstream of the reverse osmosis membrane device 32, has high power consumption, which is a constraint in reducing the overall power consumption of the water treatment system 1.

[0034] In this modified example, the rotational speed of at least one of the first pump 52, the second pump 54, and the third pump 62 is controlled by an inverter, and the rotational speeds of these pumps 52, 54, and 62 are adjusted according to the flow rate to be processed. For example, if the required supply amount from the reverse osmosis membrane apparatus 32 to the ultraviolet irradiation apparatus 34 decreases, power consumption can be reduced by lowering the rotational speed of the first pump 52 with an inverter, instead of increasing the flow rate of the first circulation line L2.

[0035] However, if the processing flow rate of the reverse osmosis membrane device 32 changes, for example, the TOC concentration of the treated water in the ultraviolet irradiation device 34 will fluctuate. Also, if the flow rates of the ultraviolet irradiation device 34, the ion exchanger packing device 35, and the second deoxygenation device 36 change, the TOC concentration of the water passing through the second circulation line L3 will fluctuate, and the TOC concentration of the treated water in the ultraviolet irradiation device 34 will also fluctuate. This is because when the processing flow rate is low, the elution concentration of organic matter from the ion exchanger packing device 35 increases. Elution of organic matter can occur whether the ion exchanger packing device 35 is a mixed-bed type or a multi-bed type, but it is more pronounced in the multi-bed type. The same applies to the DO concentration; if the processing flow rate of the second deoxygenation device 36 changes, the processing performance changes, causing fluctuations in the DO concentration of the treated water in the ultraviolet irradiation device 34. Furthermore, the TOC concentration and DO concentration of the treated water in the second ultraviolet irradiation device 63 of subsystem 6 also fluctuate. This modified version makes it easy to maintain constant water quality even when the flow rate fluctuates, by controlling the amount of ultraviolet irradiation based on the flow rate of the ultraviolet irradiation device 34.

[0036] In this modified example, the rotational speeds of the first pump 52 and the second pump 54 (and a fifth pump 56 in Figure 5B) are controlled by an inverter, and the rotational speed of the third pump 62 can be kept constant (Pattern 1). Alternatively, the rotational speed of the first pump 52 (and a fifth pump 56 in Figure 5B) is controlled by an inverter, and the rotational speeds of the second pump 54 and the third pump 62 can be kept constant (Pattern 2). In Pattern 1, the processing flow rate of the second ultraviolet irradiation device 63 is constant, and in Pattern 2, the processing flow rates of the ultraviolet irradiation device 34 and the second ultraviolet irradiation device 63 are constant. Since fluctuations in the processing flow rates of the ion exchange device and degassing device affect the water quality of the treated water, it is preferable to control the flow rates of the ion exchange device and degassing device near the use point 67 to be as constant as possible. In Patterns 1 and 2, the processing flow rates of each device in subsystem 6 are constant, and the processing flow rate of subsystem 6 is adjusted by the circulation rate of the third circulation line L4, so the water quality at the use point 67 tends to be stable. In Pattern 2, the flow rates of the ultraviolet irradiation device 34, the ion exchanger filling device 35, and the second deoxygenation device 36 are constant, making it easier to stabilize the water quality at the use point 67. In this case, a TOC meter 47 and a DO meter 48 may be installed at the inlet of the second ultraviolet irradiation device 63, and the control unit 63B may adjust the amount of ultraviolet irradiation from the second ultraviolet irradiation device 63 based on the TOC concentration measured by the TOC meter 47 and the DO concentration measured by the DO meter 48. Even if the water flow rates of the first pump 52 and the second pump 54 fluctuate, the water quality at the use point 67 can be further stabilized. Alternatively, instead of the TOC meter 47 and the DO meter 48, a TOC meter, a DO meter, and a flow meter may be installed at the inlet of the third intermediate tank 61 of the main pipe L1, and a TOC meter, a DO meter, and a flow meter may be installed in the third circulation line L4. In this case, the TOC concentration at the inlet of the second ultraviolet irradiation device 63 can be estimated from the measurements of the TOC meter upstream of the third intermediate tank 61 and the TOC meter on the third circulation line L4, as well as the flow meter upstream of the third intermediate tank 61 and the flow meter on the third circulation line L4. The DO concentration at the inlet of the second ultraviolet irradiation device 63 can be estimated in the same manner.

[0037] (Third Embodiment) Figure 6 shows a schematic configuration of a water treatment system 1 according to the third embodiment of the present invention. The configuration and effects, which are not described, are the same as those of the first embodiment. In this embodiment, a hydrogen peroxide concentration meter (hereinafter referred to as H2O2 meter 44) is provided to measure the hydrogen peroxide concentration of the water to be treated by the ultraviolet irradiation device 34 (hereinafter referred to as the water to be treated H2O2 concentration). When the ultraviolet irradiation device 34 irradiates with ultraviolet light, the control unit 34B can adjust the amount of ultraviolet irradiation based on the water to be treated TOC concentration, the water to be treated DO concentration, and the water to be treated H2O2 concentration H. The amount of ultraviolet irradiation to control the treated water TOC concentration to the target TOC concentration is a function f(T, D, H) or f(T) × f(D) × f(H). The function f(T, D, H) or the function f(H) may be obtained from experiments or from operating data of an actual plant.

[0038] The difference between the TOC concentration of the treated water and the target value, the difference between the DO concentration of the treated water and the target value, and the H of the treated water 2 The amount of ultraviolet irradiation can also be adjusted based on the difference in the O2 concentration from the target value. Alternatively, the amount of ultraviolet irradiation can also be adjusted based on the ratio of the TOC concentration of the treated water to the target value, the ratio of the DO concentration of the treated water to the target value, and the ratio of the H2O2 concentration of the treated water to the target value. The target values ​​for the TOC concentration of the treated water, the target values ​​for the DO concentration of the treated water, and the target values ​​for the H2O2 concentration of the treated water are, for example, combinations of the TOC concentration of the treated water, the DO concentration of the treated water, and the H2O2 concentration of the treated water when a desirable TOC concentration of treated water is obtained, and these may be stored in advance in the control unit 34B, or the operator may input them into the control unit 34B.

[0039] Fig. 7 conceptually shows the relationship between the TOC concentration of water to be treated, the DO concentration of water to be treated, the H₂O₂ concentration, and the ultraviolet irradiation dose for controlling the TOC concentration of treated water to a target TOC concentration. In general, hydrogen peroxide acts as an oxidation accelerator, so adding hydrogen peroxide to the water to be treated in the ultraviolet irradiation device 34 promotes the decomposition of organic substances. Referring to Fig. 7, when the DO concentration of the water to be treated is low, the decomposition of organic substances is promoted regardless of the TOC concentration of the water to be treated, so it is preferable to reduce the ultraviolet irradiation dose as the H₂O₂ concentration increases. When the DO concentration of the water to be treated is high and the TOC concentration is high, the decomposition of organic substances is also promoted, so it is preferable to reduce the ultraviolet irradiation dose as the H₂O₂ concentration increases. In contrast, when the DO concentration of the water to be treated is high and the TOC concentration of the water to be treated is low, an excessively high concentration of hydrogen peroxide reduces the decomposition efficiency of organic substances by ultraviolet rays. This is considered to be because hydrogen peroxide acts as an inhibitor of the decomposition of organic substances by ultraviolet rays. In this case, it is preferable to increase the ultraviolet irradiation dose as the H₂O₂ concentration increases. As described above, since the relationship between the H₂O₂ concentration and the ultraviolet irradiation dose has both positive and negative correlations, it is preferable to adjust the ultraviolet irradiation dose in combination with the TOC concentration of the water to be treated and the DO concentration of the water to be treated.

[0040] (Fourth Embodiment) Fig. 8 shows a schematic configuration of a water treatment system 1 according to a fourth embodiment of the present invention. Configurations and effects whose description is omitted are the same as those of the first embodiment. In this embodiment, an illuminance meter 45 that measures the ultraviolet irradiation dose of the ultraviolet irradiation device 34 is provided. Since the lamp of the ultraviolet irradiation device 34 is installed in water, the illuminance meter 45 is also installed in water. The lamp of the ultraviolet irradiation device 34 gradually deteriorates as the lighting time increases, so the irradiation dose decreases even when the same voltage is applied. The illuminance reduction rate α relative to a new lamp is obtained from the measurement value of the illuminance meter 45, and by multiplying the function f obtained in each of the above embodiments by 1 / (1-α), the number of lit lamps and dimming (applied voltage) can be adjusted with higher accuracy.

[0041] (Fifth Embodiment) FIG. 9 shows a schematic configuration of a water treatment system 1 according to a sixth embodiment of the present invention. Configurations and effects that are omitted from description are the same as those in the first embodiment. A subsystem 6 downstream of the pure water production apparatus 3 comprises a second intermediate tank 61, a third pump 62, a second ultraviolet irradiation device 63, a second ion exchange device 64, a degassing device 65, and a membrane filtration device 66, and a point of use 67 is provided downstream of the membrane filtration device 66. Furthermore, a circulation line L4 is provided for returning ultrapure water that has not been used at the point of use 67 to the second intermediate tank 61. In this embodiment, a second TOC meter 46 is provided between the membrane filtration device 66 and the point of use 67. The second TOC meter 46 acquires the TOC concentration of treated water at the point of use 67. The second TOC meter 46 is connected to a control unit 34B.

[0042] TOC meters generally have a blank value. The blank value is the TOC concentration derived from the TOC meter itself, and a TOC meter does not output a value lower than the blank value. That is, the TOC meter outputs the total value of the TOC concentration of the water to be measured and the TOC concentration derived from the TOC meter. Therefore, if the ultraviolet irradiation dose is controlled based on the TOC concentration measured by the TOC meter 41, the irradiation dose may become excessive, leading to the possibility of unnecessary energy consumption. In this embodiment, the ultraviolet irradiation dose of the ultraviolet irradiation device 34 is adjusted based on the difference between the TOC concentration of water to be treated at the inlet of the ultraviolet irradiation device 34 and the TOC concentration of treated water at the point of use 67, and the DO concentration of the water to be treated. Specifically, the control unit 34B calculates a TOC concentration TOC3 by subtracting the measured TOC concentration value measured by the second TOC meter 46 from the measured TOC concentration value measured by the TOC meter 41. The TOC concentration TOC3 is substantially equal to the TOC concentration of the target water itself at the inlet of the ultraviolet irradiation device 34. The control unit 34B adjusts the ultraviolet irradiation dose of the ultraviolet irradiation device 34 based on the TOC concentration TOC3 and the DO concentration of the water to be treated. Therefore, more efficient ultraviolet treatment is achieved, which also leads to reduction in power consumption of the ultraviolet irradiation device 34 and downsizing of the device. This embodiment is also applicable to the second ultraviolet irradiation device 63 of the subsystem 6.

[0043] (Example) A DO concentration of less than 5 μg / L, H ２ O ２To prepare the treated water, IPA (isopropyl alcohol) was added to ultrapure water with a concentration of less than 10 μg / L to achieve a TOC concentration of 3 μg / L. As shown in Figure 10A, the treated water was sequentially passed through the ultraviolet irradiation device 34 and the ion exchanger packing device 35, and the amount of ultraviolet irradiation was adjusted so that the treated water TOC concentration was 0.5 μg / L (hereinafter referred to as the standard example). A TOC meter 41 and a DO meter 42 were installed between the IPA and oxygen addition points and the ultraviolet irradiation device 34. The treated water TOC concentration stabilized at 0.52 μg / L, and the amount of ultraviolet irradiation when the treated water TOC concentration stabilized was 0.06 kWh / m³ 3 The TOC concentration of the treated water at this time was used as the target TOC concentration in the examples and comparative examples described below. Other test conditions are shown below. ・Ultraviolet irradiation device 34: Low-pressure ultraviolet oxidation device JPW (manufactured by Nippon Photo Science) ・Ion exchange packing device 35: Resin tower / ion exchange packing device 35 with a mixed bed of cation exchange resin AMBERJET 1024H (manufactured by Organo Corporation) and anion exchange resin AMBERJET 4002OH (manufactured by Organo Corporation) in a volume ratio of 1:2, SV (space velocity): 60 / h ・TOC meter 41: M500e (manufactured by VEOLIA) ・DO meter 42: Orbisphere 510 (manufactured by Hach)

[0044] Next, in the apparatus shown in Figure 10A, the amount of IPA added was increased to raise the TOC concentration of the treated water from 3 μg / L to 4 μg / L. The DO concentration of the treated water was also increased from less than 5 μg / L to 30 μg / L. The DO concentration of the treated water was adjusted by supplying oxygen gas to the dissolution membrane. In Example 1, the UV irradiation dose was adjusted based on the measurements of TOC meter 41 and DO meter 42. Specifically, a function of irradiation dose as shown in Figure 2C was obtained in advance, and the UV irradiation dose was calculated by applying the TOC concentration and DO concentration of the treated water to this function. In Comparative Example 1, the UV irradiation dose was adjusted based only on the measurement of TOC meter 41. Specifically, a function of TOC concentration and UV irradiation dose as shown in Figure 2A was obtained in advance, and the irradiation dose was calculated by applying the TOC concentration of the treated water to this function. In Comparative Example 2, the UV irradiation dose was adjusted based only on the measurement of DO meter 42. Specifically, a function between the DO concentration of the treated water and the amount of ultraviolet irradiation, as shown in Figure 2B, was obtained in advance, and the irradiation amount was calculated by applying the DO concentration of the treated water to this function. The irradiation amount was adjusted by changing the number of lamps lit and the dimming (applied voltage) of the lamps.

[0045] The results are shown in Table 1. In Comparative Examples 1 and 2, the TOC concentration of the treated water increased significantly compared to the target TOC concentration of 0.5 μg / L, and stable treated water quality could not be obtained. On the other hand, Example 1 showed a treated water TOC concentration similar to that of the reference example, and stable treated water quality could be obtained even when the TOC concentration and DO concentration of the treated water were changed.

[0046]

[0047] In Example 2, using the apparatus shown in Figure 10B, the amount of IPA added was increased to raise the TOC concentration of the treated water from 3 μg / L to 4 μg / L. The DO concentration of the treated water was also increased from less than 5 μg / L to 30 μg / L. Furthermore, the flow rate of the treated water was reduced by 40% compared to Example 1. The flow rate of the treated water was adjusted by blowing a portion of the treated water, with its TOC and DO concentrations adjusted, before it reached the ultraviolet irradiation device 34. A flow meter 43 was installed downstream of the ion exchanger packing device 35, and the amount of ultraviolet irradiation was controlled based on the TOC concentration of the treated water, the DO concentration of the treated water, and the flow rate of the treated water in the ion exchanger packing device 35. The treated water TOC concentration was 0.53 μg / L, which was approximately the same as that obtained in the reference example and Example 1.

[0048] In Example 3, using the apparatus shown in Figure 10C, the amount of IPA added was increased to raise the TOC concentration of the treated water from 3 μg / L to 4 μg / L. The DO concentration of the treated water was also increased from less than 5 μg / L to 30 μg / L. Furthermore, H2O2 was added to the treated water to adjust the H2O2 concentration to 100 μg / L. An H2O2 meter 44 was installed between the hydrogen peroxide addition point and the ultraviolet irradiation device 34, and the amount of ultraviolet irradiation was controlled based on the TOC concentration, DO concentration, and H2O2 concentration of the treated water. The treated water TOC concentration was 0.49 μg / L, which was approximately the same as that obtained in the reference example and Examples 1 and 2.

[0049] Although embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples. The water to be treated by the ultraviolet irradiation device 34 is the treated water from the first deoxygenation device 33, but it may also be the treated water from, for example, an activated carbon device, a degasser, an ion exchanger packing device, or a reverse osmosis membrane device. The ultraviolet irradiation device 34 and the ion exchanger packing device 35 are provided in the pure water production device 3 (primary system), but the present invention can be similarly applied to an ultraviolet irradiation device and an ion exchanger packing device provided in a subsystem (secondary system). However, the effects of the present invention are greater when applied to a pure water production device 3 with high TOC concentration and DO concentration of the treated water.

[0050] In the above-described embodiment, the amount of ultraviolet irradiation is adjusted based on at least the total organic carbon concentration and dissolved oxygen concentration of the water to be treated in the ultraviolet irradiation device 34, but the amount of ultraviolet irradiation can also be adjusted based on at least the total organic carbon concentration of the water to be treated in the ultraviolet irradiation device 34. In one modified example, the amount of ultraviolet irradiation may be adjusted based on the total organic carbon concentration of the water to be treated in the ultraviolet irradiation device 34 and the total organic carbon concentration of the treated water at the use point 67. That is, the water treatment method in this modified example includes irradiating water to be treated containing organic matter with ultraviolet light using the ultraviolet irradiation device 34, passing the treated water irradiated with ultraviolet light through the ion exchange packing device 35 downstream of the ultraviolet irradiation device 34, and obtaining the total organic carbon concentration of the water to be treated in the ultraviolet irradiation device 34 and the total organic carbon concentration of the treated water at the use point 67. The irradiation with ultraviolet light includes adjusting the amount of ultraviolet irradiation based on the total organic carbon concentration of the water to be treated in the ultraviolet irradiation device 34 and the total organic carbon concentration of the treated water at the use point 67.

[0051] Specifically, the amount of ultraviolet irradiation required to control the TOC concentration of the treated water to the target TOC concentration is a function f(T1, T2) of the TOC concentration T1 of the water to be treated and the TOC concentration T2 of the use point 67. The combination of the function f(T1) of the TOC concentration of the water to be treated and the function f(T2) of the TOC concentration of the use point 67 can also be considered as a single water quality parameter. That is, the DO concentration D of the water to be treated in the first embodiment can be replaced with the TOC concentration T2 of the use point 67. Furthermore, the dissolved oxygen concentration of the water to be treated in the ultraviolet irradiation device 34 can be obtained, and the amount of ultraviolet irradiation can be adjusted based on the total organic carbon concentration of the water to be treated in the ultraviolet irradiation device 34, the total organic carbon concentration of the treated water at the use point 67, and the dissolved oxygen concentration of the water to be treated in the ultraviolet irradiation device 34.

[0052] If the water treatment system 1 has a plurality of water treatment devices, including an ultraviolet irradiation device 34 and an ion exchange packing device 35 downstream of the ultraviolet irradiation device 34, the water treatment method may include irradiating the water to be treated, which contains organic matter, with ultraviolet light using the ultraviolet irradiation device 34, passing the treated water irradiated with ultraviolet light through the ion exchange packing device 35, obtaining the total organic carbon concentration of the water to be treated in the ultraviolet irradiation device 34, and varying the flow rate of at least one of the plurality of water treatment devices, and the amount of ultraviolet irradiation may be adjusted based on the total organic carbon concentration of the water to be treated in the ultraviolet irradiation device 34. The water treatment device whose flow rate is varied is not limited and may be, for example, at least one water treatment device upstream of the ultraviolet irradiation device 34 among the plurality of water treatment devices or the ultraviolet irradiation device 34. Furthermore, in addition to adjusting the amount of ultraviolet irradiation based only on the total organic carbon concentration, the dissolved oxygen concentration of the water to be treated in the ultraviolet irradiation device 34 may be obtained, and the amount of ultraviolet irradiation may be adjusted based on the total organic carbon concentration and the dissolved oxygen concentration of the water to be treated in the ultraviolet irradiation device 34.

[0053] While several preferred embodiments of the present invention have been described in detail, it should be understood that various changes and modifications are possible without departing from the spirit or scope of the appended claims.

[0054] 1 Water treatment system 34 Ultraviolet irradiation device 34B Control unit 35 Ion exchanger filling device 41 TOC meter (means for obtaining TOC concentration) 42 DO meter (means for obtaining DO concentration)

Claims

1. A water treatment method comprising: irradiating water to be treated containing organic matter with ultraviolet light using an ultraviolet irradiation device; passing the treated water irradiated with ultraviolet light through an ion exchange packing device downstream of the ultraviolet irradiation device; and obtaining the total organic carbon concentration and dissolved oxygen concentration of the treated water from the ultraviolet irradiation device, wherein the irradiation of ultraviolet light includes adjusting the amount of ultraviolet light irradiated based on the total organic carbon concentration and the dissolved oxygen concentration.

2. The water treatment method according to claim 1, wherein the amount of ultraviolet irradiation is adjusted based on a combination of a function of the total organic carbon concentration and a function of the dissolved oxygen concentration.

3. A water treatment method comprising: irradiating water to be treated containing organic matter with ultraviolet light using an ultraviolet irradiation device; passing the water to be treated, which has been irradiated with ultraviolet light, through an ion exchange packing device downstream of the ultraviolet irradiation device; and obtaining the total organic carbon concentration of the water to be treated using the ultraviolet irradiation device and the total organic carbon concentration of the treated water at the point of use, wherein the irradiation of ultraviolet light includes adjusting the amount of ultraviolet light irradiated based on the total organic carbon concentration of the water to be treated and the total organic carbon concentration of the treated water.

4. The water treatment method according to claim 3, comprising obtaining the dissolved oxygen concentration of the water to be treated from the ultraviolet irradiation device, and adjusting the amount of ultraviolet irradiation based on the total organic carbon concentration of the water to be treated, the total organic carbon concentration of the treated water, and the dissolved oxygen concentration.

5. The water treatment method according to claim 1, wherein the power of the ultraviolet irradiation device is adjusted based on the flow rate of the water to be treated that is passed through the ultraviolet irradiation device or the flow rate of the treated water in the ultraviolet irradiation device.

6. A water treatment method using a plurality of water treatment devices, including an ultraviolet irradiation device and an ion exchange packing device downstream of the ultraviolet irradiation device, comprising: irradiating water to be treated containing organic matter with ultraviolet light using the ultraviolet irradiation device; passing the water to be treated irradiated with ultraviolet light through the ion exchange packing device; obtaining the total organic carbon concentration of the water to be treated using the ultraviolet irradiation device; and varying the flow rate of at least one of the plurality of water treatment devices, wherein the irradiation of ultraviolet light includes adjusting the amount of ultraviolet light irradiated based on the total organic carbon concentration.

7. The water treatment method according to claim 6, wherein the flow rate of water to be treated passed through at least one of the water treatment devices located upstream of the ultraviolet irradiation device, or through the ultraviolet irradiation device, is varied.

8. The water treatment method according to claim 6, comprising obtaining the dissolved oxygen concentration of the water to be treated from the ultraviolet irradiation device, wherein the irradiation of ultraviolet light includes adjusting the amount of ultraviolet light irradiation based on the total organic carbon concentration and the dissolved oxygen concentration.

9. The water treatment method according to claim 1, wherein the amount of ultraviolet irradiation of the ultraviolet irradiation device is adjusted based on the hydrogen peroxide concentration of the water to be treated.

10. The water treatment method according to any one of claims 1 to 9, wherein the dissolved oxygen concentration of the water to be treated in the ultraviolet irradiation device is 1000 μg / L or less.

11. The water treatment method according to any one of claims 1 to 9, wherein the water to be treated is passed through a deoxygenation device before being passed through the ultraviolet irradiation device.

12. A water treatment system comprising: an ultraviolet irradiation device for irradiating water to be treated containing organic matter with ultraviolet light; an ion exchange packing device provided downstream of the ultraviolet irradiation device, through which the water to be treated irradiated with ultraviolet light passes; means for obtaining the total organic carbon concentration and dissolved oxygen concentration of the water to be treated at the inlet of the ultraviolet irradiation device; and a control unit for adjusting the amount of ultraviolet light irradiation based on the total organic carbon concentration and the dissolved oxygen concentration.

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