Water treatment method, water treatment device, and method for designing water treatment device

Abstract

A water treatment method includes the steps of: removing dissolved oxygen from treated water containing dissolved oxygen and organic matter using a first deoxygenation device 33; irradiating the treated water from the first deoxygenation device 33 with ultraviolet light using an ultraviolet irradiation device 34; and passing the treated water from the ultraviolet irradiation device 34 through an ion exchanger filling device 35, which is at least filled with anion exchanger A. The ion exchanger filling device 35 removes hydrogen peroxide generated by ultraviolet irradiation from the ultraviolet irradiation device 34 from the treated water from the ultraviolet irradiation device 34, and the treated water from the ultraviolet irradiation device 34 is passed through the anion exchanger A in the ion exchanger filling device 35 at a space velocity of less than 160 ( / h).

Description

Technical Field

[0001] This application asserts priority based on two Japanese applications filed on June 20, 2023 (Japanese Patent Application No. 2023-100986) and September 8, 2023 (Japanese Patent Application No. 2023-146142). The entire contents of these applications are incorporated herein by reference.

[0002] This invention relates to a water treatment method and a water treatment apparatus, as well as a design method for the water treatment apparatus. Prior Technology

[0003] With increasingly stringent requirements for pure water quality, various methods for decomposing and removing trace organic matter contained in pure water have been explored in recent years. Japanese Patent Application Publication No. 2022-175837 discloses a water treatment device comprising a degassing membrane device, a UV oxidizer (hereinafter referred to as an ultraviolet irradiation device), and an ion exchanger arranged in series. Patent Document 1 further describes reducing the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device to a predetermined range, thereby improving the decomposition efficiency of organic matter in the ultraviolet irradiation device. Summary of the Invention

[0004] [The problem that the invention aims to solve] The inventors of this invention discovered that a decrease in the dissolved oxygen concentration in the water treated by an ultraviolet irradiation device leads to an increase in the hydrogen peroxide concentration. The object of this invention is to provide a water treatment method that can improve the decomposition efficiency of organic matter and suppress the increase in hydrogen peroxide concentration.

[0005] The water treatment method of the present invention comprises: a step of removing dissolved oxygen from treated water containing dissolved oxygen and organic matter by means of a first deoxygenation device; a step of irradiating the treated water of the first deoxygenation device with ultraviolet light by an ultraviolet irradiation device; and a step of passing the treated water of the ultraviolet irradiation device through an ion exchanger filling device filled with at least anion exchangers. The ion exchanger filling device removes hydrogen peroxide generated by ultraviolet irradiation from the treated water of the ultraviolet irradiation device, and the treated water of the ultraviolet irradiation device is passed through the anion exchangers of the ion exchanger filling device at a space velocity of less than 160 (h).

[0006] Another water treatment method of the present invention includes the steps of: removing dissolved oxygen from treated water containing dissolved oxygen and organic matter by means of a first deoxygenation device; irradiating the treated water of the first deoxygenation device with ultraviolet light by an ultraviolet irradiation device; and passing the treated water of the ultraviolet irradiation device through an ion exchanger filling device filled with ion exchanger. The first deoxygenation device adjusts the dissolved oxygen concentration in the treated water of the first deoxygenation device in a manner that lowers the hydrogen peroxide concentration in the treated water of the ion exchanger filling device to a predetermined value.

[0007] According to the present invention, a water treatment method is provided that can improve the decomposition efficiency of organic matter and suppress the increase of hydrogen peroxide concentration.

[0008] The foregoing and other purposes, features, and advantages of this application should become apparent from the following detailed description with reference to the accompanying drawings illustrating this application. Simple Explanation of the Diagram

[0009] [Figure 1] is a schematic diagram of a water treatment apparatus related to the first embodiment of the present invention. [Figure 2] is a schematic diagram of a water treatment apparatus related to the second embodiment of the present invention. [Figure 3A] is a schematic diagram of a water treatment apparatus related to the third embodiment of the present invention. [Figure 3B] is a schematic diagram of the water treatment apparatus related to a variation of the third embodiment. [Figure 4] is a graph showing the relationship between the dissolved oxygen concentration of the water treated by the ultraviolet irradiation device and the hydrogen peroxide concentration and TOC of the outlet water of the ion exchange resin filling device. [Figure 5] is a schematic diagram of the experimental apparatus used in Examples 1 and 2. [Figure 6] is a graph showing the relationship between SV and the hydrogen peroxide concentration in the treated water. [Figure 7] is a graph showing the relationship between the dissolved oxygen concentration and the TOC reduction rate of the inlet water of the ultraviolet irradiation device. [Figure 8] is a schematic diagram of the experimental apparatus used in Example 3. [Figure 9] is a graph showing the relationship between the dissolved oxygen concentration of the water treated by the ultraviolet irradiation device and the hydrogen peroxide concentration and TOC of the water treated by the ion exchange resin filling device. Implementation

[0010] The following description, with reference to the figures, outlines embodiments of the water treatment method and apparatus of the present invention. In this description, "treated water" refers to water treated in an apparatus, typically referring to the outlet water of that apparatus. However, in contexts where specific properties of the treated water (e.g., dissolved oxygen concentration or organic matter concentration) are problematic, it includes water at any location downstream of the apparatus, provided that these specific properties have not substantially changed. Figure 1 shows a schematic configuration of a water treatment apparatus 1 related to a first embodiment of the present invention. The water treatment apparatus 1 includes an upstream pretreatment unit 2 and a downstream pure water production unit 3 (primary system). The water treatment apparatus 1, together with the downstream subsystem (secondary system), constitutes an ultrapure water production apparatus. The raw water supplied to the pretreatment unit 2 contains dissolved oxygen and organic matter. In the following description, upstream and downstream are defined according to the flow direction D of the treated water and the treated water itself.

[0011] The pretreatment unit 2 includes a filter 21 for removing larger particles of dust and the like, and an activated carbon tower 22 for removing impurities such as high-molecular-weight organic matter. The filter 21 can be, for example, a sand filter. The pure water production unit 3 includes an ion removal unit 31, a reverse osmosis membrane unit 32, a first deoxygenation unit 33, an ultraviolet irradiation unit 34, an ion exchanger filling unit 35, and a second deoxygenation unit 36. These units 21, 22, and 31-36 are connected in series from upstream to downstream on the main pipe L1 according to the flow direction D of the treated water. Although not shown in the figure, a tank can be provided to hold the treated water from each unit of the pretreatment unit 2 and the pure water production unit 3, such as the activated carbon tower 22, the ion removal unit 31, and the reverse osmosis membrane unit 32. Also, although not shown in the figure, a circulation pipeline can be provided to return a portion of the treated water from any of the units 31-36 of the pure water production unit 3 to the tank on the upstream side.

[0012] The ion removal device 31 includes a cation exchange resin-filled cation tower (not shown), a decarbonation tower (not shown), and an anion exchange resin-filled anion tower (not shown), which are connected in series from upstream to downstream. A decarbonation membrane can also be installed instead of the decarbonation tower. Alternatively, a softening device for removing hardness components such as calcium or magnesium and an electro-deionized water (EDI) device can be connected in series on the upstream and downstream sides to replace the ion removal device 31.

[0013] The reverse osmosis membrane unit 32 removes impurities such as ions. In this embodiment, an ion removal unit 31 is installed upstream of the reverse osmosis membrane unit 32, so the reverse osmosis membrane unit 32 mainly removes non-charged substances such as organic matter. By removing organic matter in the reverse osmosis membrane unit 32, the load on the downstream ultraviolet irradiation unit 34 is reduced. If the total organic carbon (TOC) of the treated water is high, the TOC reduction effect of the ultraviolet irradiation unit 34 will be low.

[0014] The first deoxygenation device 33 removes oxygen from the treated water, thereby reducing the dissolved oxygen concentration in the treated water. The first deoxygenation device 33 is located upstream of the ultraviolet irradiation device 34, so the ultraviolet irradiation device 34 is supplied with treated water whose dissolved oxygen concentration has been reduced (adjusted). The type of the first deoxygenation device 33 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 used to increase the surface area of ​​the water is filled into the degassing tower, and a vacuum pump is used to reduce the gas pressure inside the degassing tower, placing the pure water (used as the treated water) under vacuum to remove dissolved oxygen. The dissolved oxygen concentration can be adjusted (controlled) by adjusting (controlling) the vacuum level inside the degassing tower using a vacuum pump. Furthermore, nitrogen can be introduced to improve degassing performance. In this case, the dissolved oxygen concentration can be adjusted (controlled) by adjusting (controlling) the vacuum level and the nitrogen inflow rate (nitrogen partial pressure). A degassing membrane device can also be used as the first deoxygenation device 33. In this case, a vacuum pump is used in the same manner as the vacuum degassing device, and the dissolved oxygen concentration can be adjusted (controlled) by adjusting (controlling) the vacuum level. This first deoxygenation device 33 can reduce the dissolved oxygen concentration in the water while removing volatile organic compounds and carbonic acid into the gas phase (secondary phase), thereby reducing their concentration in the water. Furthermore, adjusting (controlling) the vacuum level and nitrogen flow rate in the first deoxygenation device 33 includes, for example, measuring the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 using a measuring device (not shown), and automatically adjusting (controlling) the vacuum level and nitrogen flow rate in the first deoxygenation device 33 based on the measured value by a control device (not shown), or manually adjusting (controlling) the vacuum level and nitrogen flow rate in the first deoxygenation device 33 by the operator. As another first deoxygenation device 33, a platinum group catalyst filling device carrying a platinum group catalyst such as palladium (Pd) can also be used. By bringing the treated water containing added hydrogen into contact with a platinum group catalyst, the dissolved oxygen concentration in the treated water can be reduced. The first deoxygenation device 33 described above can be configured as a single section or as multiple sections with multiple devices connected in series.

[0015] The ultraviolet irradiation device 34 irradiates the water being treated with ultraviolet light. As the ultraviolet irradiation device 34, a low-pressure ultraviolet irradiation device that generates ultraviolet light of at least one wavelength, such as 185nm or 254nm, can be used.

[0016] The ion exchanger filling device 35 removes the decomposition products of organic matter generated in the treated water due to ultraviolet irradiation. The ion exchanger filling device 35 is at least filled with anion exchanger A, and may also be further filled with cation exchanger K. Anion exchanger A is preferably in the OH form. Anion exchanger A and cation exchanger K are ion exchange resins, which can also be gel-type or MR-type. When using anion exchange resin and cation exchange resin, either a mixed bed or a multi-bed system can be used. In the case of a multi-bed system, the cation exchange resin can remove trace amounts of dissolved organic matter originating from the anion exchange resin; therefore, it is preferable that the anion exchange resin is located upstream of the cation exchange resin. The anion exchange resin and cation exchange resin can also be either regenerable or non-regenerable. In the case of a regenerable system, a multi-bed system is preferred in terms of ease of regeneration. Furthermore, Figure 1 illustrates the anion exchanger A and cation exchanger K in a multi-bed configuration for simplification, but Figure 1 does not limit the configuration of the ion exchanger filling device 35. Monolithic or even fibrous anion exchanger A and cation exchanger K can also be used. Alternatively, an EDI filled with at least anion exchange resin can be used. Since the EDI is continuously regenerable, a regeneration step of the ion exchange resin is not required.

[0017] The second deoxygenation device 36 can be located downstream of the ion exchanger filling device 35 and has the same structure as the first deoxygenation device 33. The second deoxygenation device 36 removes dissolved oxygen, carbonic acid, etc. from the water being treated.

[0018] (Operation method of water treatment device 1) Next, the operation method of the water treatment device 1 described above will be explained. First, the water to be treated (raw water) is supplied to the pretreatment device 2. The pretreatment device 2 removes larger particles of dust or high-molecular-weight organic matter and other impurities from the water to be treated. The cation exchange tower, anion exchange tower, and decarbonation tower of the ion removal device 31 remove cationic components and carbonic and anionic components from the water to be treated, respectively. The first deoxygenation device 33 removes a portion of the dissolved oxygen from the water to be treated, which contains dissolved oxygen and organic matter. In this way, the water to be treated, which contains organic matter and dissolved oxygen and whose dissolved oxygen concentration has been adjusted, is supplied to the ultraviolet irradiation device 34.

[0019] The ultraviolet irradiation device 34, located downstream of the first deoxygenation unit 33, irradiates the treated water of the first deoxygenation unit 33 with ultraviolet light. As shown in reaction formula 1 below, the dissociated hydrogen radicals (·H) react with dissolved oxygen to form water, while the remaining OH radicals (·OH) decompose organic matter. The OH radicals not used for the decomposition of organic matter will re-bond to form hydrogen peroxide. That is, by irradiating the treated water with ultraviolet light from the ultraviolet irradiation device 34, hydrogen peroxide will be generated in the treated water (or the concentration of hydrogen peroxide will increase).

[0020] [Number 1] Furthermore, according to reaction formula 1, while it is understandable that more oxygen is better in order to improve the decomposition efficiency of organic matter, in reality, the oxygen concentration is kept within an appropriate range for the reasons described later.

[0021] The treated water from the ultraviolet irradiation device 34 is passed through an ion exchanger filling device 35 located downstream of the ultraviolet irradiation device 34 and filled with at least anion exchanger A. A portion of the hydrogen peroxide decomposes into H2O and O2 (dissolved oxygen) on the surface of the anion exchanger A. That is, the ion exchanger filling device 35 removes a portion of the hydrogen peroxide generated by ultraviolet irradiation from the ultraviolet irradiation device 34 from the treated water. Furthermore, the ion exchanger filling device 35 removes residual organic matter from the treated water of the ultraviolet irradiation device 34. The second deoxygenation device 36 removes dissolved oxygen generated during the decomposition of hydrogen peroxide in the ion exchanger filling device 35. Thus, the treated water, with its TOC reduced and hydrogen peroxide increase suppressed, is sent to the subsystem for further treatment.

[0022] Previously, platinum group catalysts were used to remove hydrogen peroxide. While platinum group catalysts can decompose hydrogen peroxide efficiently, they are expensive. Therefore, when treating water containing a high concentration of hydrogen peroxide, such as the water treated by the ultraviolet irradiation device 34, with platinum group catalysts, the catalysts may need to be large-scale (i.e., a large amount of platinum group catalyst may be required), leading to an increase in the cost of the water treatment device 1. In this embodiment, since anion exchanger A is used to decompose hydrogen peroxide, platinum group catalysts are not required, thus suppressing the increase in operating costs. Furthermore, although the hydrogen peroxide concentration in the water treated by the ultraviolet irradiation device 34 is higher than that in the inlet water of the ultraviolet irradiation device 34, the hydrogen peroxide concentration is only in the tens of μg / L range, as explained in the embodiments described later, and the damage to anion exchanger A is limited even if it occurs.

[0023] (Regarding the space velocity (SV) of the water being treated in the ion exchanger filling device 35) As mentioned above, hydrogen peroxide generated by ultraviolet irradiation from the ultraviolet irradiation device 34 is removed by the ion exchanger filling device 35. However, the inventors of this invention have discovered that the removal efficiency of hydrogen peroxide in the treated water varies significantly depending on the water flow conditions of the ion exchanger filling device 35. In this embodiment, the space velocity (SV) of the treated water in the ultraviolet irradiation device 34, where the anion exchanger A is passed through the ion exchanger filling device 35, is controlled and adjusted to be below 160 ( / h). The control or adjustment can be performed automatically or manually by the user. This promotes the decomposition reaction of hydrogen peroxide using the anion exchanger A and inhibits the rise in hydrogen peroxide concentration. There is no particular limitation on the lower limit of SV, but if SV is too low, the amount of organic matter dissolved from the ion exchanger in the ion exchanger filling device 35 into each unit volume of treated water will increase, leading to an increase in the TOC of the treated water. Therefore, SV is preferably set to 40 ( / h) or higher. Details regarding SV are explained in the implementation examples.

[0024] As described above, in addition to controlling or even adjusting the spatial velocity (SV) of the treated water flowing through the ultraviolet irradiation device 34 of the anion exchanger A in the ion exchanger filling device 35 to be below 160 ( / h), the water treatment device 1 can also be designed in such a way that the spatial velocity (SV) of the treated water flowing through the ultraviolet irradiation device 34 of the anion exchanger A in the ion exchanger filling device 35 is below 160 ( / h). For example, for a water treatment device 1 that includes a first deoxygenation device for removing dissolved oxygen from treated water containing dissolved oxygen and organic matter, an ultraviolet irradiation device located downstream of the first deoxygenation device and irradiating the treated water of the first deoxygenation device with ultraviolet light, and an ion exchanger filling device located downstream of the ultraviolet irradiation device and filled with at least anion exchanger, the water treatment device 1 can be designed in such a way that the spatial velocity of the treated water flowing through the ultraviolet irradiation device of the anion exchanger in the ion exchanger filling device is below 160 ( / h). As a method for designing the water treatment apparatus 1 to ensure that the spatial velocity of the treated water from the ultraviolet irradiation device is less than 160 ( / h), the flow rate of the treated water toward the ion exchanger filling device 35 can be determined based on factors such as the raw water flow rate, the treated water flow rate, and the treated water quality. Then, by ensuring that the spatial velocity of the treated water from the ultraviolet irradiation device is less than 160 ( / h), the amount of resin filled in the ion exchanger filling device 35 (e.g., the cross-sectional area of ​​the ion exchanger filling device 35, the layer height of the ion exchange resin, etc.) and the number of towers of the ion exchanger filling devices 35 when they are arranged side by side can be determined.

[0025] SV is calculated based on anion exchanger A. For example, if the ion exchanger filling device 35 is filled only with anion exchanger A, SV is calculated based on the volume of the anion exchanger filling section. Specifically, if the volume of the anion exchanger filling section is set as V (m3) and the flow rate of the water to be treated is set as q (m3 / h), then SV ( / h) = q / V. If the ion exchanger filling device 35 is filled with both anion exchanger A and cation exchanger K in a mixed bed, SV is calculated based only on the volume of anion exchanger A. If the ion exchanger filling device 35 is filled with both anion exchanger A and cation exchanger K in a mixed bed, SV is calculated based on the total volume of anion exchanger A, that is, only on the volume of anion exchanger A when it is assumed to be filled with both anion exchanger A and cation exchanger K in a mixed bed.

[0026] SV can be adjusted using several methods. If the flow channel area of ​​the anion exchanger filling section is set to A, and the height (layer thickness) of the anion exchanger filling section in the flow direction is set to h, then since V = A × h, SV becomes q / (A × h). Therefore, SV can be adjusted by adjusting at least one of the flow rate q, the flow channel area A, and the layer thickness h. Alternatively, although the diagram is omitted, a circulation piping can be installed downstream of the ion exchanger filling device 35, branching from the main pipe L1 and converging back into the main pipe L1 upstream of the ion exchanger filling device 35. During normal operation, a circulation operation is performed to return a portion of the treated water to the upstream side using the circulation piping. When the SV of the ion exchanger filling device 35 reaches a predetermined value, the opening degree of the valve installed in the circulation piping is adjusted to reduce the flow rate (or the valve is closed). The flow rate of the ion exchanger filling device 35 is reduced only by the reduction component of the flow rate in the circulation piping, so SV can also be adjusted by this method. The opening and closing of the valve and the degree of opening can be adjusted by the operator or by a control device. Alternatively, multiple ion exchanger filling devices 35 can be arranged in parallel, with water flowing through only a portion of the ion exchanger filling devices 35 during normal operation, and water flowing through the other ion exchanger filling devices 35 when the SV of the circulating ion exchanger filling device 35 is above a predetermined value.

[0027] (Regarding dissolved oxygen concentration) Since ultraviolet light irradiated by ultraviolet irradiation device 34 is easily absorbed by oxygen, if the dissolved oxygen concentration in the treated water is high, the reaction shown in reaction formula (1) is not easily generated, thus reducing the efficiency of OH free radical generation. The first deoxygenation device 33 adjusts the dissolved oxygen concentration in the treated water of ultraviolet irradiation device 34 to below 1000 μg / L. In this way, ultraviolet light is not easily consumed by dissolved oxygen, thereby increasing the efficiency of OH free radical generation and thus increasing the efficiency of organic matter decomposition. As described in the following embodiments, reducing the dissolved oxygen concentration too much will not achieve the TOC reduction effect. Furthermore, reducing the dissolved oxygen concentration may lead to the need for larger scale of the first deoxygenation device 33 or an increase in operating costs. On the other hand, as can be understood from reaction formula (1), a fixed amount of dissolved oxygen is required to improve the efficiency of organic matter decomposition (or to efficiently generate OH free radicals). As mentioned above, the dissolved oxygen concentration is preferably 1 μg / L or more, and more preferably 5 μg / L or more. Details are explained in the embodiments.

[0028] (Regarding TOC) If the TOC and dissolved oxygen concentrations in the water treated by the ultraviolet irradiation device 34 are high, the hydrogen peroxide concentration in the water treated by the ultraviolet irradiation device 34 may also increase. Therefore, it is preferable to adjust the dissolved oxygen concentration in the water treated by the ultraviolet irradiation device 34 as described above, and to adjust the TOC in the water treated by the ultraviolet irradiation device 34 to below 5 μg / L. The TOC can be adjusted by an ion removal device located upstream of the ultraviolet irradiation device 34. Examples of ion removal devices include a reverse osmosis membrane device 32 and an ion removal device 31.

[0029] (Regarding hydrogen peroxide removal rate) The hydrogen peroxide removal rate of the ion exchanger filling device 35 is preferably 10% or higher. This reduces, for example, the possibility that the hydrogen peroxide concentration at the point of use may exceed the permissible value. The subsystem generally includes an ultraviolet (UV) irradiation device; therefore, if the hydrogen peroxide removal rate is below 10%, the TOC reduction effect of the UV irradiation device may decrease. This is because hydrogen peroxide may hinder the TOC reduction effect of the downstream UV irradiation device. Generally, supplying hydrogen peroxide to the UV irradiation device promotes the generation of OH radicals, but depending on the conditions, this may reduce the TOC reduction effect. On the other hand, as described in the embodiment, although the hydrogen peroxide removal rate can be increased by reducing SV, reducing SV to increase the hydrogen peroxide removal rate may lead to an increase in the size of the ion exchanger filling device 35 and an increase in the TOC of the treated water. Therefore, the upper limit of the hydrogen peroxide removal rate is preferably set to 50% or lower, more preferably 40% or lower, and particularly preferably 30% or lower.

[0030] (Second Implementation) Figure 2 shows a schematic configuration of a water treatment apparatus 1 related to a second embodiment of the present invention. The water treatment apparatus 1 of this embodiment has a platinum group catalyst filling device 37 located downstream of the ion exchanger filling device 35 and upstream of the second deoxygenation device 36. The second embodiment is identical to the first embodiment except for this point. The platinum group catalyst filling device 37 carries a platinum group catalyst such as palladium (Pd) and can have the same configuration as the platinum group catalyst filling device described in the example of the first deoxygenation device 33. By contacting the treated water with the platinum group catalyst, the concentration of hydrogen peroxide in the treated water can be further reduced. In addition, to reduce the dissolved oxygen concentration, a hydrogen addition section (not shown) can be provided upstream of the platinum group catalyst filling device 37. Alternatively, an ion exchanger carrying a metal catalyst such as palladium can be filled into the EDI as an alternative configuration. In this case, hydrogen generated at the cathode of the EDI can be used as hydrogen to contact the metal catalyst.

[0031] As mentioned above, platinum group catalysts are generally expensive. However, since most of the hydrogen peroxide is removed by the ion exchanger filling device 35 located upstream of the platinum group catalyst filling device 37, the concentration of hydrogen peroxide in the supply water to the platinum group catalyst filling device 37 downstream of the ion exchanger filling device 35 is reduced. This allows for miniaturization of the platinum group catalyst filling device 37 and also reduces the increase in cost of the water treatment device 1.

[0032] (Third Implementation) Next, the third embodiment will be described focusing on the differences from the first embodiment. The omitted components and effects are the same as in the first embodiment. Figure 3A shows a schematic configuration of the water treatment apparatus 1 related to the third embodiment of the present invention. The water treatment apparatus 1 of this embodiment includes: a dissolved oxygen concentration measuring device 38 for measuring the dissolved oxygen concentration in the treated water of the ultraviolet irradiation device 34; a hydrogen peroxide concentration measuring device 39 for measuring the hydrogen peroxide concentration in the treated water of the ion exchanger filling device 35; and a TOC measuring device 40 for measuring the TOC in the treated water of the ion exchanger filling device 35. The hydrogen peroxide concentration measuring device 39 and the TOC measuring device 40 are disposed downstream of the second deoxygenation device 36, or may be disposed between the ion exchanger filling device 35 and the second deoxygenation device 36. In this embodiment, the TOC in the treated water of the ultraviolet irradiation device 34 should also be adjusted to 5 μg / L or less.

[0033] The ion exchanger filling device 35 is filled with ion exchangers. Unlike the first and second embodiments, the ion exchanger filling device 35 is not primarily for the removal of hydrogen peroxide, but rather for the removal of organic matter. Therefore, it is preferable to include both anion exchangers and cation exchangers. However, the ion exchanger filling device 35 may also include only either anion exchangers or cation exchangers.

[0034] As shown in Figure 3B, in this embodiment, similar to the second embodiment, a platinum group catalyst filling device 37 for removing hydrogen peroxide can be installed downstream of the ion exchanger filling device 35. In particular, when the ion exchanger filling device 35 includes anion exchangers, as described above, hydrogen peroxide is removed in the ion exchanger filling device 35, thus reducing the hydrogen peroxide removal load on the platinum group catalyst filling device 37. This allows for high flow rate (high SV) processing, reducing processing costs. The hydrogen peroxide concentration measuring device 39 and the TOC measuring device 40 are installed downstream of the second deoxygenation device 36, or they can be installed between the ion exchanger filling device 35 and the platinum group catalyst filling device 37, or between the platinum group catalyst filling device 37 and the second deoxygenation device 36.

[0035] Figure 4 schematically illustrates the relationship between the dissolved oxygen concentration of the water treated by the ultraviolet irradiation device 34 and the hydrogen peroxide concentration and TOC of the outlet water of the ion exchanger filling device 35. As mentioned above, ultraviolet light is easily absorbed by oxygen. Therefore, if the dissolved oxygen concentration in the water treated by the ultraviolet irradiation device 34 is high, the reaction shown in equation (1) is less likely to occur. As a result, the efficiency of OH radical generation decreases, and the hydrogen peroxide concentration decreases. On the other hand, if the dissolved oxygen concentration in the water treated by the ultraviolet irradiation device 34 is low, the reaction shown in equation (1) will be promoted, OH radicals will increase, and thus the hydrogen peroxide concentration will increase.

[0036] In this embodiment, this principle is used to adjust the hydrogen peroxide concentration in the water treated by the ion exchanger filling device 35. The first deoxygenation device 33 adjusts the dissolved oxygen concentration measured in the dissolved oxygen concentration measuring device 38 by adjusting the hydrogen peroxide concentration measured in the hydrogen peroxide concentration measuring device 39 to a predetermined value. For example, when the operator manually operates the first deoxygenation device 33, if the hydrogen peroxide concentration measured in the hydrogen peroxide concentration measuring device 39 exceeds the standard value, or if it is judged that the concentration is likely to exceed the standard value, the output of the vacuum pump of the first deoxygenation device 33 is reduced, thereby increasing the dissolved oxygen concentration in the water treated by the first deoxygenation device 33. The change in dissolved oxygen concentration can be confirmed in the dissolved oxygen concentration measuring device 38. When the first deoxygenation device 33 is in automatic operation, the output (dissolved oxygen concentration) of the vacuum pump of the first deoxygenation device 33 is adjusted by the control device (not shown) according to the measured value of the hydrogen peroxide concentration measuring device 39, so that the hydrogen peroxide concentration measured in the hydrogen peroxide concentration measuring device 39 is within an appropriate range.

[0037] On the other hand, if the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 is too high, the ultraviolet light will be excessively absorbed by oxygen, thus reducing the efficiency of OH radical generation. Consequently, if the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 is higher than required, as shown in Figure 4, the TOC in the water treated by the ion exchanger filling device 35 will increase. Conversely, if the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 is low, the TOC in the water treated by the ion exchanger filling device 35 will decrease. That is, the hydrogen peroxide concentration and TOC in the water treated by the ion exchanger filling device 35 are in a relationship where an increase in one leads to a decrease in the other.

[0038] The first deoxygenation device 33 adjusts the dissolved oxygen concentration measured in the dissolved oxygen measuring device 38 based on the hydrogen peroxide concentration measured in the hydrogen peroxide concentration measuring device 39 and the TOC measured in the TOC measuring device 40, specifically, by bringing both below a predetermined value. The predetermined value for the hydrogen peroxide concentration is preferably 40 μg / L. As mentioned above, if an ultraviolet irradiation device is installed downstream, a high hydrogen peroxide concentration may hinder the TOC reduction effect of the downstream ultraviolet irradiation device. Furthermore, if a hydrogen peroxide removal method is installed downstream, the load on the hydrogen peroxide removal method will increase. The specific value of TOC is not particularly limited, but is preferably, for example, 2 μg / L, and more preferably 1 μg / L. The first deoxygenation device 33 adjusts the dissolved oxygen concentration to above 20 μg / L and below 100 μg / L, more preferably above 20 μg / L and below 60 μg / L, and even more preferably above 20 μg / L and below 40 μg / L.

[0039] (Example 1) Ultraviolet light was irradiated onto the treated water containing dissolved oxygen and organic matter. The irradiated water was then passed through an ion exchange resin filling device to evaluate the hydrogen peroxide removal performance. Figure 5 shows a schematic diagram of the experimental setup. A first membrane degassing device 41 and a second membrane degassing device 42 were connected in series, with an ultraviolet irradiation device 43 and an ion exchange resin filling device 44 located downstream. A dissolved oxygen meter (Orbisphere, manufactured by HACH Corporation) was installed between the second membrane degassing device 42 and the ultraviolet irradiation device 43 to measure the dissolved oxygen concentration of the inlet water of the ultraviolet irradiation device 43. The ion exchange resin filling device 44 was configured as a mixed bed, with anion exchange resin (AMBERJET4002OH type, manufactured by Organo Corporation) filling the upstream side and cation exchange resin (AMBERJET1024H type, manufactured by Organo Corporation) filling the downstream side. The TOC concentration in the inlet water of the first membrane degassing device 41 was 2 μg / L, and the hydrogen peroxide concentration was 10 μg / L.

[0040] The dissolved oxygen concentration in the inlet water of the ultraviolet irradiation device 43 is adjusted to 20 μg / L, 60 μg / L, and 100 μg / L. The dissolved oxygen concentration is adjusted using the following methods: bypassing either the first membrane degassing device 41 or the second membrane degassing device 42; adjusting the vacuum level of the first membrane degassing device 41 and the second membrane degassing device 42 using a vacuum pump inverter; and stopping the vacuum pump and supplying oxygen. The treated water prepared in this way is supplied to the ultraviolet irradiation device 43. A low-pressure ultraviolet oxidation device JPW (manufactured by Photoscience Co., Ltd., Japan) is used as the ultraviolet irradiation device 43, and the treated water is irradiated with ultraviolet light at an irradiation dose of 0.07 kWh / m³. Furthermore, the flow rate of water flowing into the ion exchange resin filling device 44 is changed by using the discharge line 45 installed at the inlet of the ion exchange resin filling device 44, and the SV relative to the anion exchange resin is changed to 60, 80, 100, 120, 140, 160, 180 ( / h).

[0041] The hydrogen peroxide concentrations in the inlet water and treated water of the ion exchange resin packed unit 44 were determined, and the hydrogen peroxide removal performance of the ion exchange resin packed unit 44 was evaluated. The hydrogen peroxide concentration was determined using the phenolphthalein reduction method and spectrophotometry. Figure 6 shows the relationship between SV and the hydrogen peroxide concentration in the treated water, and the relationship between SV and the hydrogen peroxide removal rate. The hydrogen peroxide removal rate was calculated from the hydrogen peroxide concentration H1 of the inlet water and the hydrogen peroxide concentration H2 of the treated water using the formula shown in Figure 5.

[0042] The hydrogen peroxide concentration H1 in the inlet water of the ion exchange resin filling device 44 (the treated water of the ultraviolet irradiation device 43) was 41 μg / L when the dissolved oxygen concentration in the inlet water of the ultraviolet irradiation device 43 was 20 μg / L, 32 μg / L when the dissolved oxygen concentration was 60 μg / L, and 29 μg / L when the dissolved oxygen concentration was 100 μg / L. It was observed that the hydrogen peroxide concentration tended to increase as the dissolved oxygen concentration decreased. However, by keeping the SV relative to the anion exchanger below 160 ( / h), the hydrogen peroxide concentration H2 in the treated water could be reduced. By keeping the SV below 120 ( / h), the hydrogen peroxide removal rate was approximately 10% or more; by keeping it below 100 ( / h), the hydrogen peroxide removal rate was approximately 20%. The SV was preferably below 100 ( / h), more preferably below 90 ( / h), and especially preferably below 80 ( / h).

[0043] (Example 2) With the SV of the anion exchanger fixed at 80 ( / h), the dissolved oxygen concentration was adjusted to 1, 5, 10, 20, 60, 100, 1000, and 8000 μg / L to evaluate the removal performance of organic matter (TOC reduction rate). In cases with high dissolved oxygen concentrations, oxygen was supplied to the treated water through a degassing membrane. Figure 7 shows the relationship between the dissolved oxygen concentration in the inlet water of the UV irradiation device 43 and the TOC reduction rate. The TOC reduction rate was calculated from the TOC (T1) at the inlet of the UV irradiation device 43 and the TOC (T2) of the treated water in the ion exchange resin filling device 44 using the formula shown in Figure 5. The TOC was measured using a Sievers TOC meter M500e (manufactured by SUEZ). The TOC reduction rate does not change significantly within the dissolved oxygen concentration range of 1000–8000 μg / L. Below 1000 μg / L, it increases as the concentration decreases further, reaching saturation around 10 μg / L, and showing little change within the range of 1–10 μg / L. Therefore, the dissolved oxygen concentration in the inlet water of the ultraviolet irradiation device 43 is preferably below 1000 μg / L, more preferably below 100 μg / L, particularly preferably below 60 μg / L, and most preferably below 20 μg / L.

[0044] (Example 3) Ultraviolet light was irradiated onto the treated water containing dissolved oxygen and organic matter, and then the irradiated water was passed through an ion exchanger filling device to evaluate the removal performance of hydrogen peroxide and organic matter. Figure 8 is a schematic diagram of the test device. Using the same method as in Example 1, the dissolved oxygen concentration in the treated water of the ultraviolet irradiation device 43 was adjusted to 20 μg / L, 50 μg / L, 100 μg / L, and 1000 μg / L. The SV of the ion exchanger filling device 44 was set to 50 ( / h). As in Examples 1 and 2, the ultraviolet irradiation device was used to irradiate the treated water with ultraviolet light at an irradiation dose of 0.07 kWh / m³. The ion exchange resin filling device 44 was filled with a combined bed of cation exchange resin and anion exchange resin, as in Example 1. The TOC in the inlet water of the first membrane degassing device 41 was 2 μg / L. The concentration of hydrogen peroxide in the treated water of the ion exchange resin filling device 44 was measured using a hydrogen peroxide monitor (OROXIDE manufactured by Organo Corporation), and the TOC in the treated water of the ion exchange resin filling device 44 was measured using the same TOC meter as in Example 2.

[0045] Figure 9 illustrates the relationship between the dissolved oxygen concentration of the water being treated by the ultraviolet irradiation device 43 and the hydrogen peroxide concentration of the water being treated by the ion exchange resin filling device 44. The hydrogen peroxide concentration is 33 μg / L when the dissolved oxygen concentration is 20 μg / L, 28 μg / L when the dissolved oxygen concentration is 50 μg / L, 23 μg / L when the dissolved oxygen concentration is 100 μg / L, and 21 μg / L when the dissolved oxygen concentration is 1000 μg / L. It was observed that the hydrogen peroxide concentration tends to increase as the dissolved oxygen concentration decreases. Therefore, it is known that by adjusting the dissolved oxygen concentration of the water being treated by the ultraviolet irradiation device 43, the hydrogen peroxide concentration of the water being treated by the ion exchange resin filling device 44 can be adjusted.

[0046] On the other hand, it was observed that the TOC in the treated water of the ion exchange resin filling device 44 tends to decrease as the dissolved oxygen concentration of the treated water of the ultraviolet irradiation device 43 decreases. If the target value for the hydrogen peroxide concentration in the treated water of the ion exchange resin filling device 44 is set to 30 μg / L and the target value for TOC is set to 1.0 g / L, then when the dissolved oxygen concentration of the treated water of the ultraviolet irradiation device 43 is 20 μg / L, the TOC is below the standard value, but the hydrogen peroxide concentration exceeds the standard value. When the dissolved oxygen concentration of the treated water of the ultraviolet irradiation device 43 is 100 μg / L and 1000 μg / L, the hydrogen peroxide concentration is below the standard value, but the TOC exceeds the standard value. When the dissolved oxygen concentration of the treated water of the ultraviolet irradiation device 43 is 50 μg / L, both the hydrogen peroxide concentration and the TOC are below the standard value. Furthermore, the standard value is used to illustrate one example of this embodiment. As described above, the dissolved oxygen concentration is preferably set to 20 μg / L or more and 100 μg / L or less.

[0047] While several preferred embodiments of the invention have been shown and described in detail, it should be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims. The invention may also be applied, for example, to a subsystem of an ultrapure water production apparatus.

[0048] 1: Water treatment equipment 2: Pre-treatment device 3: Pure water production equipment 21: Filter 22: Activated Carbon Tower 31: Ion removal device 32: Reverse osmosis membrane device 33: First Deoxygenation Unit 34: Ultraviolet irradiation device 35: Ion exchanger filling device 36: Second deaerator 37: Platinum group catalyst filling device 38: Dissolved oxygen concentration measuring device 39: Hydrogen peroxide concentration measuring device 40: TOC measuring device 41: First membrane degassing unit 42: Second membrane degassing unit 43: Ultraviolet irradiation device 44: Ion exchange resin packing device H1: Hydrogen peroxide concentration H2: Hydrogen peroxide concentration T1:TOC T2:TOC A: Anion exchanger K: Cation exchanger L1: Main pipe D: Circulation Direction

Claims

1. A water treatment method comprising the following steps: removing dissolved oxygen from treated water containing dissolved oxygen and organic matter using a first deoxygenation device; irradiating the treated water of the first deoxygenation device with ultraviolet light using an ultraviolet irradiation device to decompose the organic matter; passing the treated water of the ultraviolet irradiation device through an ion exchanger filling device filled with at least anion exchangers; and treating the treated water of the ion exchanger filling device through a platinum group catalyst filling device carrying a platinum group catalyst; the ion exchanger filling device removing hydrogen peroxide generated by irradiation from the ultraviolet light of the ultraviolet irradiation device from the treated water of the ultraviolet irradiation device; the platinum group catalyst filling device contacting the treated water of the ion exchanger filling device with the platinum group catalyst to remove the hydrogen peroxide; the treated water of the ultraviolet irradiation device being passed through the anion exchangers of the ion exchanger filling device at a space velocity of less than 160 ( / h).

2. As in request item 1, the water treatment method, wherein, The ultraviolet irradiation device processes water through the anion exchanger in the ion exchanger filling device at a spatial velocity of 120 ( / h) or less.

3. As in request item 1, the water treatment method, wherein, The dissolved oxygen concentration in the water supplied from the first deoxygenation device to the ultraviolet irradiation device is less than 1000 μg / L.

4. The water treatment method as described in Request 1, wherein, The dissolved oxygen concentration in the water supplied from the first deoxygenation device to the ultraviolet irradiation device is 1 μg / L or more and 100 μg / L or less.

5. The water treatment method as described in Request 1, wherein, The total organic carbon in the water being treated, supplied from an ion removal device located upstream of the ultraviolet irradiation device, is less than 5 μg / L.

6. The water treatment method as described in request item 2, wherein, The hydrogen peroxide removal rate of this ion exchanger filling device is over 10%.

7. The water treatment method described in any of requests 1 to 6, wherein, The treated water from the ion exchanger filling device is treated by a second deoxygenation device located downstream of the ion exchanger filling device.

8. A water treatment apparatus comprising: a first deoxygenation device for removing dissolved oxygen from treated water containing dissolved oxygen and organic matter; an ultraviolet (UV) irradiation device located downstream of the first deoxygenation device for irradiating the treated water of the first deoxygenation device with UV light to decompose the organic matter; an ion exchanger filling device located downstream of the UV irradiation device and filled with at least anion exchanger for removing hydrogen peroxide generated by UV irradiation from the treated water of the UV irradiation device; and a platinum group catalyst filling device located downstream of the ion exchanger filling device for carrying platinum group catalyst and contacting the treated water of the ion exchanger filling device with the platinum group catalyst to remove the hydrogen peroxide; wherein the space velocity of the treated water of the UV irradiation device passing through the anion exchanger of the ion exchanger filling device is less than 160 ( / h).

9. A method for designing a water treatment apparatus, the water treatment apparatus comprising: a first deoxygenation device for removing dissolved oxygen from treated water containing dissolved oxygen and organic matter; an ultraviolet irradiation device located downstream of the first deoxygenation device for irradiating the treated water of the first deoxygenation device with ultraviolet light to decompose the organic matter; an ion exchanger filling device located downstream of the ultraviolet irradiation device and filled with at least anion exchanger for removing hydrogen peroxide generated by irradiation with ultraviolet light from the treated water of the ultraviolet irradiation device; and a platinum group catalyst filling device located downstream of the ion exchanger filling device for carrying platinum group catalyst and contacting the treated water of the ion exchanger filling device with the platinum group catalyst to remove the hydrogen peroxide; the method for designing the water treatment apparatus comprises the step of designing the water treatment apparatus such that the space velocity of the treated water of the ultraviolet irradiation device passing through the anion exchanger of the ion exchanger filling device is less than 160 ( / h).

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