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 claims priority based on Japanese Patent Application No. 2023-100986, filed on June 20, 2023, and Japanese Patent Application No. 2023-146142, filed on September 8, 2023. The entire contents of these applications are incorporated herein by reference.

[0002] The present invention relates to a water treatment method and a water treatment device, as well as a design method for the water treatment device. Prior Art

[0003] With the increasing demand for pure water quality, various methods for decomposing and removing trace organic matter 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 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 device. Summary of the Invention

[0004] [Problems to be solved by the invention]

[0005] The inventors of this invention have discovered that a decrease in the dissolved oxygen concentration in water being treated by an ultraviolet irradiation device can increase the hydrogen peroxide concentration in the water being treated. The present invention aims to provide a water treatment method that improves the decomposition efficiency of organic matter while suppressing the increase in hydrogen peroxide concentration.

[0006] The water treatment method of the present invention comprises: removing dissolved oxygen from treated water containing dissolved oxygen and organic matter by a first deoxygenation device; irradiating the treated water in the first deoxygenation device with ultraviolet light by an ultraviolet irradiation device; and passing the treated water in the ultraviolet irradiation device through an ion exchanger filling device filled with at least an anion exchanger. The ion exchanger filling device removes hydrogen peroxide generated by irradiation with ultraviolet light from the ultraviolet irradiation device from the treated water in the ultraviolet irradiation device. The treated water in the ultraviolet irradiation device is passed through the anion exchangers of the ion exchanger filling device at a space velocity of less than 160 rpm.

[0007] Another water treatment method of the present invention comprises: removing dissolved oxygen from treated water containing dissolved oxygen and organic matter using a first deoxygenator; irradiating the treated water in the first deoxygenator with ultraviolet light using an ultraviolet irradiation device; and passing the treated water in the ultraviolet irradiation device through an ion exchanger filling device filled with ion exchangers. The first deoxygenator adjusts the dissolved oxygen concentration in the treated water in the ion exchanger filling device so that the hydrogen peroxide concentration in the treated water in the first deoxygenator is lower than a predetermined value.

[0008] According to the present invention, a water treatment method can be provided which can improve the decomposition efficiency of organic matter and suppress the increase of hydrogen peroxide concentration.

[0009] The above contents and other objects, features, and advantages of the present application will become more apparent through the following detailed description with reference to the accompanying drawings which illustrate the present application. Simple diagram description

[0010] [Fig. 1] is a schematic diagram showing the structure of a water treatment device according to the first embodiment of the present invention. [Fig. 2] is a schematic diagram showing the structure of a water treatment device according to a second embodiment of the present invention. [Fig. 3A] is a schematic structural diagram of a water treatment device according to a third embodiment of the present invention. [Fig. 3B] is a schematic diagram showing the structure of a water treatment device according to a modified example of the third embodiment. FIG4 is a graph showing the relationship between the dissolved oxygen concentration of water to be treated in an ultraviolet irradiation device and the hydrogen peroxide concentration and TOC of the water at the outlet of an ion exchange resin filling device. [Figure 5] is a schematic diagram of the test device used in Examples 1 and 2. FIG6 is a graph showing the relationship between SV and the hydrogen peroxide concentration of treated water. FIG7 is a graph showing the relationship between the dissolved oxygen concentration in the inlet water of the ultraviolet irradiation device and the TOC reduction rate. [Figure 8] is a schematic diagram of the experimental device used in Example 3. FIG9 is a graph showing the relationship between the dissolved oxygen concentration of water to be treated in the ultraviolet irradiation device and the hydrogen peroxide concentration and TOC of water treated in the ion exchange resin filling device. Implementation Method

[0011] The following describes embodiments of the water treatment method and water treatment apparatus of the present invention with reference to the accompanying drawings. In the following description, "treated water" refers to water treated in a device, typically the outlet water of the device. However, in contexts where specific properties of the treated water (such as dissolved oxygen concentration or organic matter concentration) are problematic, this term also includes water at any location downstream of the device, as long as the specific properties remain substantially unchanged. Figure 1 schematically illustrates the structure of a water treatment apparatus 1 according to the first embodiment of the present invention. The water treatment apparatus 1 includes an upstream pre-treatment device 2 and a downstream pure water production device 3 (primary system). The water treatment apparatus 1, together with its downstream subsystem (secondary system), constitutes an ultrapure water production device. The raw water supplied to the pre-treatment device 2 contains dissolved oxygen and organic matter. In the following description, upstream and downstream are defined based on the flow direction D of the treated water.

[0012] The pretreatment device 2 includes a filter 21 for removing larger particles of dust and other impurities, and an activated carbon tower 22 for removing impurities such as high-molecular organic matter. A sand filter, for example, 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 21, 22, 31-36 are arranged in series on the main pipe L1, in the direction D of the treated water flow, from upstream to downstream. Although not shown in the figure, tanks for storing treated water from each device 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, may also be provided. Furthermore, although not shown in the figure, a circulation line may be provided to return a portion of the treated water from any of the devices 31-36 of the pure water production device 3 to the upstream tank.

[0013] Ion removal device 31 comprises a cation tower (not shown) filled with cation exchange resin, a decarbonation tower (not shown), and an anion tower (not shown) filled with anion exchange resin, arranged in series from upstream to downstream. A decarbonation membrane can be installed in place of the decarbonation tower. Alternatively, a softening device for removing hardness components such as calcium and magnesium and an electrical deionized water generator (EDI) can be installed in series on both the upstream and downstream sides of ion removal device 31.

[0014] The reverse osmosis membrane device 32 removes impurities such as ions. In this embodiment, an ion removal device 31 is installed upstream of the reverse osmosis membrane device 32, so the reverse osmosis membrane device 32 primarily removes non-charged substances such as organic matter. Removing organic matter in the reverse osmosis membrane device 32 reduces the load on the downstream ultraviolet irradiation device 34. If the total organic carbon (TOC) content of the treated water is high, the TOC reduction effect of the ultraviolet irradiation device 34 will be reduced.

[0015] The first deaerator 33 removes oxygen from the treated water, thereby reducing the dissolved oxygen concentration in the treated water. The first deaerator 33 is located upstream of the ultraviolet irradiation device 34, so the ultraviolet irradiation device 34 is supplied with treated water after its dissolved oxygen concentration has been reduced (adjusted). The type of first deaerator 33 is not limited, as long as it can remove dissolved oxygen. For example, a vacuum deaerator can be used. Generally, a vacuum deaerator fills a deaerator tower with a gas-liquid contact material that increases the surface area of ​​the water. A vacuum pump is used to reduce the gas pressure within the tower, placing the pure water being treated under a vacuum state to remove dissolved oxygen. The dissolved oxygen concentration can be adjusted (controlled) by controlling the vacuum level within the tower using a vacuum pump. Furthermore, the deaeration performance can be enhanced by introducing nitrogen. In this case, the dissolved oxygen concentration can be adjusted (controlled) by adjusting the vacuum level and the amount of nitrogen inflow (nitrogen partial pressure). A deaerator membrane device can also be used as the first deaerator 33. In this case, a vacuum pump is used similarly to the vacuum degassing device, and the dissolved oxygen concentration can be adjusted (controlled) by adjusting (controlling) the vacuum level. The first deoxygenator 33 reduces the dissolved oxygen concentration in the water while simultaneously removing volatile organic compounds and carbonic acid into the gas phase (secondary side), thereby reducing their concentrations in the water. Furthermore, adjusting (controlling) the vacuum level and nitrogen inflow rate in the first deoxygenator 33 includes, for example, measuring the dissolved oxygen concentration in the treated water in the ultraviolet irradiation device 34 using a measuring device (not shown). Based on the measured value, a control device (not shown) automatically adjusts (controls) the vacuum level and nitrogen inflow rate in the first deoxygenator 33, or manually by an operator. Alternatively, a platinum-group catalyst-filled device carrying a platinum-group catalyst such as palladium (Pd) can be used as the first deoxygenator 33. By allowing the treated water to be treated with hydrogen to contact the platinum group catalyst, the dissolved oxygen concentration in the treated water can be reduced. The first deoxygenation device 33 described above can be constructed as a single stage or as multiple stages with multiple devices connected in series.

[0016] The ultraviolet irradiation device 34 irradiates the water to be treated with ultraviolet rays. As the ultraviolet irradiation device 34, a low-pressure ultraviolet irradiation device that generates ultraviolet rays of at least one wavelength of, for example, 185 nm or 254 nm can be used.

[0017] The ion exchanger filling device 35 removes decomposition products of organic matter generated in the treated water by ultraviolet irradiation. The ion exchanger filling device 35 is filled with at least anion exchanger A and may further be filled with cation exchanger K. Anion exchanger A is preferably in the OH form. Anion exchanger A and cation exchanger K form ion exchange resins, which can be either gel-type or MR-type. When using both anion exchange resin and cation exchange resin, a mixed bed or a multiple bed configuration is possible. When using a multiple bed configuration, the cation exchange resin can be used to remove trace amounts of organic matter eluted from the anion exchange resin. Therefore, it is preferable to position the anion exchange resin upstream of the cation exchange resin. The anion exchange resin and cation exchange resin can be either regenerative or non-regenerative. In the case of a regenerative configuration, a multiple bed configuration is preferred for ease of regeneration. In addition, FIG1 shows anion exchangers A and cation exchangers K as a duplex bed for simplicity. However, FIG1 does not limit the configuration of the ion exchanger-filled device 35. Monolithic or even fibrous anion exchangers A and cation exchangers K may also be used. Alternatively, an EDI filled with at least an anion exchange resin may be used. EDI is a continuously regenerating method, eliminating the need for a regeneration step for the ion exchange resin.

[0018] The second deoxygenator 36 can be located downstream of the ion exchanger filling device 35 and has the same structure as the first deoxygenator 33. The second deoxygenator 36 removes dissolved oxygen, carbonic acid, etc. from the water to be treated.

[0019] (Operation Method of Water Treatment Device 1) Next, the operating method of the water treatment device 1 described above will be described. First, the water to be treated (raw water) is supplied to the pretreatment device 2. The pretreatment device 2 removes impurities such as large-sized dust particles and high-molecular-weight organic matter from the water to be treated. The cation tower, anion tower, and decarbonation tower of the ion removal device 31 remove cations, carbonates, and anions, respectively, from the water to be treated. 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. The treated water, which now contains organic matter and dissolved oxygen and has an adjusted dissolved oxygen concentration, is then supplied to the ultraviolet irradiation device 34.

[0020] The ultraviolet irradiation device 34, located downstream of the first deaerator 33, irradiates the treated water from the first deaerator 33 with ultraviolet light. As shown in the following reaction equation 1, 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 to decompose organic matter re-bond to form hydrogen peroxide. In other words, by irradiating the treated water with ultraviolet light from the ultraviolet irradiation device 34, hydrogen peroxide is generated in the treated water (or its concentration is increased).

[0021] [Number 1] Furthermore, according to Reaction Formula 1, in order to improve the decomposition efficiency of organic matter, it can be understood that more oxygen is better, but in fact, there is an appropriate range of oxygen concentration for the reasons described below.

[0022] The treated water from the ultraviolet irradiation device 34 is passed through an ion exchanger-filled 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 on the surface of the anion exchanger A into H₂O and O₂ (dissolved oxygen). In other words, the ion exchanger-filled device 35 removes a portion of the hydrogen peroxide generated by the ultraviolet rays from the ultraviolet irradiation device 34 from the treated water. Furthermore, the ion exchanger-filled device 35 removes organic matter remaining in the treated water from the ultraviolet irradiation device 34. The second deoxygenator 36 removes dissolved oxygen generated during the decomposition of hydrogen peroxide in the ion exchanger-filled device 35. Thus, the treated water, with its TOC reduced and the increase of hydrogen peroxide suppressed, is sent to a subsystem for further treatment.

[0023] Conventionally, platinum-group catalysts have been used to remove hydrogen peroxide. While platinum-group catalysts can decompose hydrogen peroxide efficiently, they are expensive. Therefore, when using platinum-group catalysts to treat water containing a high concentration of hydrogen peroxide, such as the water treated by the ultraviolet irradiation device 34, the platinum-group catalyst may become larger (i.e., a large amount of platinum-group catalyst may be required), resulting in an increase in the cost of the water treatment device 1. In this embodiment, since the hydrogen peroxide is decomposed by the anion exchanger A, the use of a platinum-group catalyst is eliminated, thereby suppressing increases in operating costs. Furthermore, while the hydrogen peroxide concentration in the water treated by the ultraviolet irradiation device 34 is higher than that in the water inlet to the ultraviolet irradiation device 34, as described in the Examples below, the hydrogen peroxide concentration is only on the order of tens of μg / L, so damage to the anion exchanger A, if any, is limited.

[0024] (Regarding the space velocity (SV) of the water to be treated passing through the ion exchanger-filled device 35) As described above, hydrogen peroxide generated by ultraviolet radiation from the ultraviolet irradiation device 34 is removed by the ion exchanger-filled device 35. However, the inventors of this invention have discovered that the efficiency of removing hydrogen peroxide from the treated water varies significantly depending on the conditions for passing water through the ion exchanger-filled device 35. In this embodiment, the space velocity (SV) of the treated water in the ultraviolet irradiation device 34, which passes through the anion exchanger A in the ion exchanger-filled device 35, is controlled or even adjusted to be less than 160 sph / h. This control or adjustment can be performed automatically or manually by the user. This promotes the decomposition reaction of hydrogen peroxide by the anion exchanger A and suppresses the increase in hydrogen peroxide concentration. The lower limit of the SV is not particularly limited, but if the SV is too low, the amount of organic matter eluted from the ion exchangers in the ion exchanger-filled device 35 into the treated water per unit volume increases, leading to an increase in the TOC of the treated water. Therefore, the SV is preferably set to 40 sph / h or higher. Details about SV are described in the Examples.

[0025] As described above, in addition to controlling or even adjusting the space velocity (SV) of the treated water flowing through the ultraviolet irradiation device 34 of the anion exchanger A in the ion exchanger-filled device 35 to be less than 160 sph / h, the water treatment device 1 may also be designed such that the space velocity (SV) of the treated water flowing through the ultraviolet irradiation device 34 of the anion exchanger A in the ion exchanger-filled device 35 is less than 160 sph / h. For example, in a water treatment device 1 comprising a first deoxygenator for removing dissolved oxygen from water to be treated containing dissolved oxygen and organic matter, an ultraviolet irradiation device located downstream of the first deoxygenator and irradiating the treated water of the first deoxygenator with ultraviolet light, and an ion exchanger-filled device located downstream of the ultraviolet irradiation device and filled with at least anion exchangers, the water treatment device 1 may be designed such that the space velocity of the treated water flowing through the ultraviolet irradiation device of the anion exchanger in the ion exchanger-filled device is less than 160 sph / h. As a method for designing the water treatment system 1 so that the space velocity of the water being treated by the ultraviolet irradiation device is less than 160 sph / h, the flow rate of the treated water to the ion exchanger-filled device 35 can be determined based on, for example, the raw water flow rate, the treated water flow rate, and the treated water quality. Furthermore, the amount of resin to be filled in the ion exchanger-filled device 35 (e.g., the cross-sectional area of ​​the ion exchanger-filled device 35, the layer height of the ion exchange resin, etc.), and the number of ion exchanger-filled devices 35 in parallel when the ion exchanger-filled devices 35 are arranged, can be determined so that the space velocity of the water being treated by the ultraviolet irradiation device is less than 160 sph / h.

[0026] SV is calculated based on anion exchanger A. For example, if the ion exchanger-filled device 35 is filled only with anion exchanger A, SV is calculated for the volume of the anion exchanger-filled portion. Specifically, if the volume of the anion exchanger-filled portion is V (m³) and the flow rate of the treated water is q (m³ / h), SV ( / h) = q / V. If the ion exchanger-filled device 35 is filled with a multi-bed of anion exchangers A and cation exchangers K, SV is calculated only for the volume of anion exchanger A. If the ion exchanger-filled device 35 is filled with a mixed bed of anion exchangers A and cation exchangers K, SV is calculated for the total volume of anion exchanger A, that is, only for the volume of anion exchanger A assuming a multi-bed filled with anion exchangers A and cation exchangers K.

[0027] SV can be adjusted using several methods. If the flow area of ​​the anion exchanger-filled section is A and the height (layer thickness) of the anion exchanger-filled section in the flow direction is h, then since V = A × h, SV = q / (A × h). Therefore, SV can be adjusted by adjusting at least one of the flow rate q, the flow area A, or the layer thickness h. Alternatively, although not shown, a circulation pipe can be provided that branches from the main pipe L1 downstream of the ion exchanger-filled device 35 and converges with the main pipe L1 upstream of the ion exchanger-filled device 35. During normal operation, a portion of the treated water is returned upstream using the circulation pipe. When the SV of the ion exchanger-filled device 35 exceeds a predetermined value, the flow rate is reduced (or closed) by adjusting the opening of a valve in the circulation pipe. Since the flow rate of the ion exchanger-filled device 35 is reduced by only the amount of flow reduction in the circulation pipe, this method also allows for adjustment of SV. 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-filled units 35 can be arranged in parallel. During normal operation, water is passed through only some of the ion exchanger-filled units 35. When the SV of the circulating ion exchanger-filled unit 35 exceeds a predetermined value, water is passed through the remaining ion exchanger-filled units 35.

[0028] (About dissolved oxygen concentration) Since the ultraviolet rays irradiated from the ultraviolet irradiation device 34 are easily absorbed by oxygen, if the dissolved oxygen concentration in the treated water is high, the reaction shown in reaction formula (1) is not easy to occur, and the generation efficiency of OH radicals is reduced. The first deoxygenation device 33 adjusts the dissolved oxygen concentration in the treated water of the ultraviolet irradiation device 34 to less than 1000 μg / L. In this way, the ultraviolet rays are not easily consumed by dissolved oxygen, which improves the generation efficiency of OH radicals and the decomposition efficiency of organic matter. As described in the embodiment below, reducing the dissolved oxygen concentration too low will not achieve the effect of reducing TOC. In addition, reducing the dissolved oxygen concentration may lead to an increase in the size of the first deoxygenation device 33 or an increase in operating costs. On the other hand, as can be understood from reaction formula (1), in order to improve the decomposition efficiency of organic matter (or in order to efficiently generate OH radicals), a fixed amount of dissolved oxygen is required. As mentioned above, the dissolved oxygen concentration is preferably 1 μg / L or more, and more preferably 5 μg / L or more. The details are described in the embodiment.

[0029] (About TOC) If the TOC and dissolved oxygen concentrations in the water being treated by the ultraviolet irradiation device 34 are high, the hydrogen peroxide concentration in the water being treated by the ultraviolet irradiation device 34 may increase. Therefore, it is preferable to adjust the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 as described above and to adjust the TOC in the water being treated by the ultraviolet irradiation device 34 to 5 μg / L or less. TOC can be adjusted by an ion removal device located upstream of the ultraviolet irradiation device 34. Examples of ion removal devices include the reverse osmosis membrane device 32 and the ion removal device 31.

[0030] (Regarding hydrogen peroxide removal rate) The hydrogen peroxide removal rate of the ion exchanger-filled device 35 is preferably 10% or higher. This can, for example, reduce the possibility of hydrogen peroxide concentrations exceeding allowable values ​​at the point of use. Subsystems typically include ultraviolet irradiation devices. Therefore, if the hydrogen peroxide removal rate is less than 10%, the TOC reduction effectiveness of the subsystem's ultraviolet irradiation device may be reduced. This is because hydrogen peroxide may hinder the TOC reduction effectiveness of the downstream ultraviolet irradiation device. Generally, supplying hydrogen peroxide to the ultraviolet irradiation device promotes the generation of OH radicals, but this can also reduce the TOC reduction effectiveness depending on the conditions. On the other hand, as described in the examples, while the hydrogen peroxide removal rate can be increased by reducing the SV, reducing the SV to increase the hydrogen peroxide removal rate may increase the size of the ion exchanger-filled device 35 and increase the TOC content of the treated water. Therefore, the upper limit of the hydrogen peroxide removal rate is preferably 50% or lower, more preferably 40% or lower, and particularly preferably 30% or lower.

[0031] (Second embodiment) FIG2 schematically illustrates the structure of a water treatment apparatus 1 according to a second embodiment of the present invention. The water treatment apparatus 1 of this embodiment includes a platinum-group catalyst-filled device 37 located downstream of an ion exchanger-filled device 35 and upstream of a second deoxygenator 36. The second embodiment is identical to the first embodiment except for this point. The platinum-group catalyst-filled device 37 carries a platinum-group catalyst such as palladium (Pd) and can have the same structure as the platinum-group catalyst-filled device described in the example of the first deoxygenator 33. Contact of the treated water with the platinum-group catalyst further reduces the concentration of hydrogen peroxide in the treated water. Furthermore, a hydrogen addition unit (not shown) can be provided upstream of the platinum-group catalyst-filled device 37 to lower the dissolved oxygen concentration. Alternatively, an ion exchanger carrying a metal catalyst such as palladium can be filled in the EDI. In this case, hydrogen generated at the cathode of the EDI can be used as hydrogen to contact the metal catalyst.

[0032] As mentioned above, platinum-group catalysts are generally expensive. However, since most of the hydrogen peroxide is removed by the ion exchanger packing device 35 located upstream of the platinum-group catalyst packing device 37, the concentration of hydrogen peroxide in the water supplied to the platinum-group catalyst packing device 37 downstream of the ion exchanger packing device 35 is reduced. This allows the platinum-group catalyst packing device 37 to be miniaturized, and also suppresses an increase in the cost of the water treatment device 1.

[0033] (Third embodiment) Next, the third embodiment will be described, focusing on the differences from the first embodiment. The omitted configuration and effects are the same as those of the first embodiment. Figure 3A schematically illustrates the configuration of a water treatment device 1 according to the third embodiment of the present invention. The water treatment device 1 of this embodiment includes a dissolved oxygen concentration measuring device 38 for measuring the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34; a hydrogen peroxide concentration measuring device 39 for measuring the hydrogen peroxide concentration in the water being treated by the ion exchanger-filled device 35; and a TOC measuring device 40 for measuring the TOC in the water being treated by the ion exchanger-filled device 35. The hydrogen peroxide concentration measuring device 39 and the TOC measuring device 40 are located downstream of the second deoxygenation device 36, or alternatively, between the ion exchanger-filled device 35 and the second deoxygenation device 36. In this embodiment, the TOC in the water being treated by the ultraviolet irradiation device 34 is preferably adjusted to 5 μg / L or less.

[0034] The ion exchanger-filled device 35 is filled with ion exchangers. Unlike the first and second embodiments, the ion exchanger-filled device 35 is primarily intended to remove organic matter rather than hydrogen peroxide. Therefore, it preferably contains both an anion exchanger and a cation exchanger. However, the ion exchanger-filled device 35 may contain only either an anion exchanger or a cation exchanger.

[0035] As shown in FIG3B , in this embodiment, similar to the second embodiment, a platinum-group catalyst-filled device 37 for removing hydrogen peroxide can be installed downstream of the ion exchanger-filled device 35. In particular, when the ion exchanger-filled device 35 includes an anion exchanger, as described above, hydrogen peroxide is removed in the ion exchanger-filled device 35, thereby reducing the hydrogen peroxide removal load on the platinum-group catalyst-filled device 37. This allows treatment at a high flow rate (high SV), thereby reducing treatment costs. The hydrogen peroxide concentration measuring device 39 and the TOC measuring device 40 are installed downstream of the second deoxygenating device 36, and can also be installed between the ion exchanger-filled device 35 and the platinum-group catalyst-filled device 37, or between the platinum-group catalyst-filled device 37 and the second deoxygenating device 36.

[0036] FIG4 schematically shows the relationship between the dissolved oxygen concentration of the water being 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 rays are easily absorbed by oxygen. Therefore, if the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 is high, the reaction shown in reaction formula (1) is not easily generated. As a result, the efficiency of generating OH free radicals decreases, and the concentration of hydrogen peroxide decreases. On the other hand, if the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 is low, the reaction shown in reaction formula (1) is promoted, the number of OH free radicals increases, and the concentration of hydrogen peroxide increases.

[0037] In this embodiment, this principle is used to adjust the hydrogen peroxide concentration in the treated water of the ion exchanger-filled device 35. The first deoxygenator 33 adjusts the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring device 38 based on the hydrogen peroxide concentration measured by the hydrogen peroxide concentration measuring device 39. Specifically, the dissolved oxygen concentration measured by the hydrogen peroxide concentration measuring device 39 is adjusted to keep the dissolved oxygen concentration below a predetermined value. For example, if the operator manually operates the first deoxygenator 33, and the hydrogen peroxide concentration measured by the hydrogen peroxide concentration measuring device 39 exceeds the standard value, or is determined to be highly likely to exceed the standard value, the output of the vacuum pump of the first deoxygenator 33 is reduced, thereby increasing the dissolved oxygen concentration in the treated water of the first deoxygenator 33. Changes in the dissolved oxygen concentration can be confirmed by the dissolved oxygen concentration measuring device 38. When the first deoxygenating device 33 is operated automatically, the control device (not shown) adjusts the output (dissolved oxygen concentration) of the vacuum pump of the first deoxygenating device 33 in response to the measured value of the hydrogen peroxide concentration measuring device 39 so that the hydrogen peroxide concentration measured by the hydrogen peroxide concentration measuring device 39 falls within an appropriate range.

[0038] 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 rays are excessively absorbed by oxygen, reducing the efficiency of OH radical generation. As a result, if the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 exceeds the required concentration, the TOC level in the water being treated by the ion exchanger-filled device 35 increases, as shown in Figure 4. Conversely, if the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 is low, the TOC level in the water being treated by the ion exchanger-filled device 35 decreases. In other words, the hydrogen peroxide concentration and TOC level in the water being treated by the ion exchanger-filled device 35 are in a relationship where one increases while the other decreases.

[0039] The first deoxygenator 33 adjusts the dissolved oxygen concentration measured by the dissolved oxygen measuring device 38 based on the hydrogen peroxide concentration measured by the hydrogen peroxide concentration measuring device 39 and the TOC measured by the TOC measuring device 40, specifically, to keep 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-reducing effect of the downstream ultraviolet irradiation device. Furthermore, if a hydrogen peroxide removal device is installed downstream, the load on the hydrogen peroxide removal device increases. The specific TOC value is not particularly limited; for example, 2 μg / L is preferred, and 1 μg / L is more preferred. The first deoxygenator 33 adjusts the dissolved oxygen concentration to 20 μg / L or more and 100 μg / L or less, more preferably 20 μg / L or more and 60 μg / L or less, and particularly preferably 20 μg / L or more and 40 μg / L or less.

[0040] (Example 1) The hydrogen peroxide removal performance of treated water containing dissolved oxygen and organic matter was evaluated by irradiating it with ultraviolet light and then passing the treated water through an ion exchange resin filling device. Figure 5 is a schematic diagram of the test apparatus. A first membrane degassing device 41 and a second membrane degassing device 42 were arranged 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) was placed between the second membrane degassing device 42 and the ultraviolet irradiation device 43 to measure the dissolved oxygen concentration in the water at the inlet of the ultraviolet irradiation device 43. The ion exchange resin filling device 44 was filled with an anion exchange resin (AMBERJET 4002OH, manufactured by Organo Co., Ltd.) on the upstream side and a cation exchange resin (AMBERJET 1024H, manufactured by Organo Co., Ltd.) on the downstream side in a multi-bed configuration. The TOC concentration in the water at the inlet of the first membrane degassing device 41 was 2 μg / L, and the hydrogen peroxide concentration was 10 μg / L.

[0041] The dissolved oxygen concentration in the water entering the ultraviolet irradiation device 43 was adjusted to 20 μg / L, 60 μg / L, and 100 μg / L. The dissolved oxygen concentration was adjusted by bypassing either the first membrane degassing device 41 or the second membrane degassing device 42, adjusting the vacuum level of each of the first and second membrane degassing devices 41 and 42 using an inverter for the vacuum pump, or stopping the vacuum pump and supplying oxygen. The treated water thus prepared was supplied to the ultraviolet irradiation device 43. A JPW low-pressure ultraviolet oxidation device (manufactured by Japan Photoscience Co., Ltd.) was used as the ultraviolet irradiation device 43, and the treated water was irradiated with ultraviolet light at an irradiation rate of 0.07 kWh / m³. Furthermore, a discharge line 45 provided at the inlet of the ion exchange resin filling device 44 was used to change the flow rate of water flowing into the ion exchange resin filling device 44, and the SV relative to the anion exchange resin was changed to 60, 80, 100, 120, 140, 160, and 180 ( / h).

[0042] The hydrogen peroxide concentrations in the inlet water and treated water of the ion exchange resin filling device 44 were measured, and the hydrogen peroxide removal performance of the ion exchange resin filling device 44 was evaluated. The hydrogen peroxide concentration was measured using the reduced phenolphthalein method and absorbance. Figure 6 shows the relationship between the SV and the hydrogen peroxide concentration in the treated water, and the relationship between the SV and the hydrogen peroxide removal rate. The hydrogen peroxide removal rate was calculated from the hydrogen peroxide concentration H1 of the inlet water of the ion exchange resin filling device 44 and the hydrogen peroxide concentration H2 of the treated water using the formula shown in Figure 5.

[0043] The hydrogen peroxide concentration H1 in the inlet water of the ion exchange resin-filled device 44 (the treated water of the ultraviolet irradiation device 43) was 41 μg / L when the dissolved oxygen concentration 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. A trend was observed where the hydrogen peroxide concentration increased as the dissolved oxygen concentration decreased. However, by reducing the SV relative to the anion exchanger to less than 160 ( / h), the hydrogen peroxide concentration H2 in the treated water could be reduced. By reducing the SV to 120 ( / h) or less, the hydrogen peroxide removal rate was increased to approximately 10% or more, and by reducing it to 100 ( / h) or less, the hydrogen peroxide removal rate was decreased to approximately 20%. The SV is preferably 100 ( / h) or less, more preferably 90 ( / h) or less, and particularly preferably 80 ( / h) or less.

[0044] (Example 2) With the anion exchanger's SV fixed at 80 ( / h), the dissolved oxygen concentration was adjusted to 1, 5, 10, 20, 60, 100, 1000, and 8000 μg / L, and the organic matter removal performance (TOC reduction rate) was evaluated. In cases with high dissolved oxygen concentrations, oxygen was supplied to the treated water via the degassing membrane. Figure 7 shows the relationship between the dissolved oxygen concentration in the water at the inlet of the ultraviolet irradiation device 43 and the TOC reduction rate. The TOC reduction rate was calculated using the formula shown in Figure 5 from the TOC (T1) at the inlet of the ultraviolet irradiation device 43 and the TOC (T2) of the treated water at the ion exchange resin filling device 44. 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, reaching saturation around 10 μg / L. It does not change significantly 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 less than 1000 μg / L, more preferably 100 μg / L or less, particularly preferably 60 μg / L or less, and most preferably 20 μg / L or less.

[0045] (Example 3) Water containing dissolved oxygen and organic matter was irradiated with ultraviolet light and then passed through an ion exchanger-filled device to evaluate its hydrogen peroxide and organic matter removal performance. Figure 8 is a schematic diagram of the test apparatus. Using the same method as in Example 1, the dissolved oxygen concentration in the water being treated at the ultraviolet irradiation device 43 was adjusted to 20 μg / L, 50 μg / L, 100 μg / L, and 1000 μg / L. The flow rate of the ion exchanger-filled device 44 was set to 50 h. As in Examples 1 and 2, the water being treated was irradiated with ultraviolet light at a rate of 0.07 kWh / m³. The ion exchange resin-filled device 44 was filled with a multi-bed of cation exchange resin and anion exchange resin, as in Example 1. The TOC content in the water entering the first membrane degassing device 41 was 2 μg / L. The hydrogen peroxide concentration in the treated water of the ion exchange resin filling device 44 was measured using a hydrogen peroxide monitor (OROXIDE manufactured by Organo Co., Ltd.), 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.

[0046] Figure 9 shows 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 at a dissolved oxygen concentration of 20 μg / L, 28 μg / L at a dissolved oxygen concentration of 50 μg / L, 23 μg / L at a dissolved oxygen concentration of 100 μg / L, and 21 μg / L at a dissolved oxygen concentration of 1000 μg / L. A trend is observed where the hydrogen peroxide concentration increases as the dissolved oxygen concentration decreases. This indicates 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.

[0047] Meanwhile, the TOC in the water treated by the ion exchange resin device 44 tends to decrease as the dissolved oxygen concentration of the water being treated by the ultraviolet irradiation device 43 decreases. If the target hydrogen peroxide concentration in the water treated by the ion exchange resin device 44 is set at 30 μg / L and the target TOC is set at 1.0 g / L, when the dissolved oxygen concentration of the water being treated by the ultraviolet irradiation device 43 reaches 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 water being treated by the ultraviolet irradiation device 43 reaches 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 water being treated by the ultraviolet irradiation device 43 reaches 50 μg / L, both the hydrogen peroxide concentration and the TOC are below the standard value. In addition, the standard value is an example used to illustrate this embodiment. As mentioned above, the dissolved oxygen concentration is preferably set to be greater than 20 μg / L and less than 100 μg / L.

[0048] Although several preferred embodiments of the present 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 present invention can also be applied to a subsystem of an ultrapure water production device, for example.

[0049] 1: Water treatment device 2: Pre-processing device 3: Pure water production equipment 21: Filter 22: Activated carbon tower 31: Ion removal device 32: Reverse osmosis membrane device 33: No. 1 deaerator 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 measurement device 41: 1st membrane degassing device 42: Second membrane degassing device 43: Ultraviolet irradiation device 44: Ion exchange resin filling device H1: Hydrogen peroxide concentration H2: Hydrogen peroxide concentration T1:TOC T2:TOC A: Anion exchanger K: cation exchanger L1: mother pipe D: Circulation direction

Claims

1. A water treatment method comprising: 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; and passing the treated water of the ultraviolet irradiation device through an ion exchanger filling device filled with at least anion exchangers; wherein the ion exchanger filling device removes hydrogen peroxide generated by irradiation with ultraviolet light from the treated water of the ultraviolet irradiation device; wherein 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 40 ( / h) or more and less than 100 ( / h).

2. The water treatment method of claim 1, wherein the water system of the ultraviolet irradiation device is circulated through the anion exchanger of the ion exchanger filling device at a space velocity of 40 ( / h) or more and 90 ( / h) or less.

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

4. The water treatment method of claim 1, wherein the dissolved oxygen concentration in the water to be treated supplied from the first deaeration device to the ultraviolet irradiation device is 1 μg / L or more and 100 μg / L or less.

5. The water treatment method of claim 1, wherein the total organic carbon in the water to be 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 of claim 1, wherein the hydrogen peroxide removal rate of the ion exchanger filling device is 10% or more.

7. The water treatment method according to any one of claims 1 to 6, wherein the treated water of 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 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; and an ion exchanger filling device located downstream of the ultraviolet irradiation device and filled with at least anion exchanger; wherein the space velocity of the treated water in the ultraviolet irradiation device through the anion exchanger in the ion exchanger filling device is 40 ( / h) or more and less than 100 ( / 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; and an ion exchanger filling device located downstream of the ultraviolet irradiation device and filled with at least anion exchanger; 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 passing through the anion exchanger of the ion exchanger filling device and the ultraviolet irradiation device is 40 ( / h) or more and less than 100 ( / h).

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