JP7770601B2 - Water treatment method, water treatment device, and design method for water treatment device - Google Patents

Description

The present invention relates to a water treatment method, a water treatment device, and a method for designing a water treatment device.

As demands for higher quality pure water become more apparent, various methods have been investigated in recent years for decomposing and removing trace amounts of organic matter contained in pure water. Patent Document 1 discloses a water treatment device in which a degassing membrane device, a UV oxidation device (hereinafter referred to as an ultraviolet irradiation device), and an ion exchanger are arranged in series. Patent Document 1 further describes that the efficiency of the ultraviolet irradiation device in decomposing organic matter can be increased by lowering the dissolved oxygen concentration in the water to be treated by the ultraviolet irradiation device to a specified range.

Japanese Patent Application Laid-Open No. 2022-175837

The inventors of this application discovered that lowering the dissolved oxygen concentration in water being treated by an ultraviolet irradiation device increases the hydrogen peroxide concentration in the treated water. The objective of the present invention is to provide a water treatment method that can increase the efficiency of organic matter decomposition while suppressing increases in hydrogen peroxide concentration.

The water treatment method of the present invention includes removing dissolved oxygen from water to be treated containing dissolved oxygen and organic matter using a first deoxygenation device, irradiating the treated water from the first deoxygenation device with ultraviolet light using an ultraviolet irradiation device to decompose the organic matter , passing the treated water from the ultraviolet irradiation device through an ion exchanger-packed device filled with at least an anion exchanger, and treating the treated water from the ion exchanger-packed device with a platinum group catalyst supporting a platinum group catalyst . The ion exchanger-packed device removes hydrogen peroxide generated by irradiation with ultraviolet light from the ultraviolet irradiation device from the treated water, and the platinum group catalyst-packed device contacts the treated water from the ion exchanger-packed device with the platinum group catalyst to remove the hydrogen peroxide, and the treated water from the ultraviolet irradiation device is passed through the anion exchanger in the ion exchanger-packed device at a space velocity of less than 160 (/h).

The present invention provides a water treatment method that can increase the decomposition efficiency of organic matter and suppress an increase in hydrogen peroxide concentration.

1 is a schematic configuration diagram of a water treatment device according to a first embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a water treatment device according to a second embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a water treatment device according to a third embodiment of the present invention. FIG. 10 is a diagram showing the relationship between the dissolved oxygen concentration in the water to be treated in the ultraviolet irradiation device and the hydrogen peroxide concentration and TOC in the water at the outlet of the ion exchange resin filling device. FIG. 1 is a schematic diagram of a test device used in Examples 1 and 2. 1 is a graph showing the relationship between SV and the hydrogen peroxide concentration of treated water. 1 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. FIG. 10 is a schematic diagram of a test device used in Example 3. 1 is a graph showing the relationship between the dissolved oxygen concentration in the water to be treated by the ultraviolet irradiation device and the hydrogen peroxide concentration and TOC in the water to be treated by the ion exchange resin filling device.

Embodiments of the water treatment method and water treatment device of the present invention will be described below with reference to the drawings. In the following description, "treated water" refers to water treated by a certain device, and typically refers to the outlet water of that device. However, in contexts where a specific property of the treated water (e.g., dissolved oxygen concentration or organic matter concentration) is of concern, it also includes water at any position downstream of the device, as long as the specific property remains substantially unchanged. Figure 1 shows the schematic configuration of a water treatment device 1 according to a first embodiment of the present invention. The water treatment device 1 has an upstream pretreatment device 2 and a downstream pure water production device 3 (primary system). Together with a downstream subsystem (secondary system), the water treatment device 1 constitutes an ultrapure water production system. The raw water supplied to the pretreatment device 2 contains dissolved oxygen and organic matter. In the following description, upstream and downstream are defined with respect to the flow direction D of the water to be treated or the treated water.

The pretreatment device 2 includes a filter 21 for removing relatively large particles such as dust, 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 system 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 packing device 35, and a second deoxygenation device 36. These devices 21, 22, 31-36 are arranged in series in this order on the mother pipe L1 from upstream to downstream in the direction D of the flow of the water to be treated. Although not shown, tanks may be provided to hold treated water from each device in the pretreatment device 2 and the pure water production system 3, such as the activated carbon tower 22, the ion removal device 31, and the reverse osmosis membrane device 32. Furthermore, although not shown, 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 system 3 to an upstream tank.

The 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, which are arranged in series from upstream to downstream. A decarbonation membrane may be provided instead of the decarbonation tower. Instead of the ion removal device 31, a softener that removes hardness components such as calcium and magnesium may be arranged upstream, and an electrodeionized water production device (EDI) may be arranged downstream in series.

The reverse osmosis membrane device 32 removes impurities such as ions. In this embodiment, the ion removal device 31 is installed upstream of the reverse osmosis membrane device 32, so the reverse osmosis membrane device 32 mainly removes uncharged substances such as organic matter. Removing organic matter with the reverse osmosis membrane device 32 reduces the load on the downstream ultraviolet irradiation device 34. If the total organic carbon (hereinafter also referred to as TOC) of the water to be treated is high, the TOC reduction effect of the ultraviolet irradiation device 34 will be reduced.

The first deoxygenation device 33 removes oxygen from the water to be treated, reducing the dissolved oxygen concentration in the water. Because the first deoxygenation device 33 is located upstream of the ultraviolet irradiation device 34, the water to be treated with a reduced (adjusted) dissolved oxygen concentration is supplied to the ultraviolet irradiation device 34. The type of first deoxygenation device 33 is not limited as long as it can remove dissolved oxygen; for example, a vacuum degassing device can be used. In general, a vacuum degassing device fills a degassing tower with a gas-liquid contact material to increase the surface area of the water, reduces the gas pressure in the degassing tower with a vacuum pump, and places the pure water to be treated in a vacuum to remove dissolved oxygen. The dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum in the degassing tower using a vacuum pump. Furthermore, degassing performance can be improved by introducing nitrogen. In this case, the dissolved oxygen concentration can be adjusted by adjusting the degree of vacuum and the amount of nitrogen inflow (nitrogen partial pressure). A degassing membrane device may also be used as the first deoxygenation device 33. In this case, a vacuum pump is used, as in the vacuum degassing device, and the dissolved oxygen concentration can be adjusted (controlled) by adjusting the degree of vacuum. These first deoxygenation devices 33 reduce the dissolved oxygen concentration in the water while simultaneously removing volatile organic compounds and carbon dioxide into the gas phase (secondary side), thereby reducing their concentrations in the water. Adjusting (controlling) the degree of vacuum and nitrogen inflow rate in the first deoxygenation device 33 includes, for example, measuring the dissolved oxygen concentration in the water being treated in the ultraviolet irradiation device 34 with a measuring device (not shown) and automatically adjusting (controlling) the degree of vacuum and nitrogen inflow rate in the first deoxygenation device 33 based on the measured value by a control device (not shown), or manually adjusting (controlling) the degree of vacuum and nitrogen inflow rate in the first deoxygenation device 33 by an operator. Alternatively, a platinum catalyst-filled device carrying a platinum catalyst such as palladium (Pd) may be used as the first deoxygenation device 33. The dissolved oxygen concentration in the water being treated can be reduced by contacting the hydrogen-added water with the platinum catalyst. The first deoxidizing device 33 described above may be a single-stage configuration, or a multi-stage configuration in which multiple devices are connected in series.

The ultraviolet irradiation device 34 irradiates the water to be treated with ultraviolet rays. The ultraviolet irradiation device 34 can be a low-pressure ultraviolet irradiation device that generates ultraviolet rays with at least one of the wavelengths of 185 nm and 254 nm, for example.

The ion exchanger packing device 35 removes organic decomposition products generated in the treated water by ultraviolet irradiation. The ion exchanger packing device 35 is packed with at least anion exchanger A and may further be packed with cation exchanger K. Anion exchanger A is preferably of the OH type. Anion exchanger A and cation exchanger K are ion exchange resins, and the ion exchange resins may be either gel or MR type. When using anion exchange resin and cation exchange resin, either a mixed-bed or dual-bed system is acceptable. When using a dual-bed system, the anion exchange resin is preferably located upstream of the cation exchange resin, since trace amounts of organic matter eluted from the anion exchange resin can be removed with the cation exchange resin. The anion exchange resin and cation exchange resin may be either regenerated or non-regenerated. In the case of a regenerated system, a dual-bed system is preferred for ease of regeneration. Note that for convenience, anion exchanger A and cation exchanger K are shown as dual-bed systems, but this does not limit the configuration of the ion exchanger packing device 35. Monolithic or fibrous anion exchanger A and cation exchanger K can also be used. Alternatively, an EDI packed with at least an anion exchange resin can be used. Since EDI is a continuously regenerated type, a regeneration process for the ion exchange resin is not required.

The second deoxygenation device 36 is located downstream of the ion exchanger filling device 35 and can have a configuration similar to that of the first deoxygenation device 33. The second deoxygenation device 36 removes dissolved oxygen, carbon dioxide, etc. from the water to be treated.

(Operation method of water treatment device 1)
Next, a method for operating 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 relatively large-particle 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 cation components, carbonate components, and anion components, 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. In this way, the water to be treated, which contains organic matter and dissolved oxygen and has an adjusted dissolved oxygen concentration, is supplied to the ultraviolet irradiation device 34.

The ultraviolet irradiation device 34, located downstream of the first deoxygenation device 33, irradiates the treated water from the first deoxygenation device 33 with ultraviolet rays. As shown in the following equation 1, dissociated hydrogen radicals (·H) react with dissolved oxygen to form water, and the remaining OH radicals (·OH) decompose organic matter. OH radicals not used to decompose organic matter recombine to form hydrogen peroxide. In other words, by irradiating the water to be treated with ultraviolet rays from the ultraviolet irradiation device 34, hydrogen peroxide is generated in the water to be treated (or the hydrogen peroxide concentration increases).
According to formula 1, it can be understood that a larger amount of oxygen is preferable to increase the efficiency of decomposing organic matter, but in reality, there is an appropriate range for the oxygen concentration for reasons that will be described later.

The treated water from the ultraviolet irradiation device 34 is passed through an ion exchanger packing device 35, which is located downstream of the ultraviolet irradiation device 34 and is packed with at least anion exchanger A. Some of the hydrogen peroxide decomposes into _H2O and _O2 (dissolved oxygen) on the surface of the anion exchanger A. That is, the ion exchanger packing device 35 removes some of the hydrogen peroxide generated by irradiation with ultraviolet light from the ultraviolet irradiation device 34 from the treated water from the ultraviolet irradiation device 34. The ion exchanger packing device 35 also removes organic matter remaining in the treated water from the ultraviolet irradiation device 34. The second deoxygenation device 36 removes dissolved oxygen generated when hydrogen peroxide is decomposed in the ion exchanger packing device 35. The treated water, whose TOC has been reduced and whose increase in hydrogen peroxide has been suppressed in this way, is sent to a subsystem for further treatment.

Conventionally, platinum group catalysts have been used to remove hydrogen peroxide. Platinum group catalysts can decompose hydrogen peroxide with high efficiency, but they are expensive. Therefore, when treating water containing a relatively high concentration of hydrogen peroxide, such as the treated water from the ultraviolet irradiation device 34, with a platinum group catalyst, the platinum group catalyst becomes larger (i.e., a large amount of platinum group catalyst may be required), which can lead to increased costs for the water treatment device 1. In this embodiment, hydrogen peroxide is decomposed using anion exchanger A, eliminating the need for a platinum group catalyst and minimizing increases in operating costs. Note that while the hydrogen peroxide concentration in the treated water from the ultraviolet irradiation device 34 is higher than that in the inlet water of the ultraviolet irradiation device 34, the hydrogen peroxide concentration is on the order of several tens of μg/L, as explained in the examples below, and therefore damage to the anion exchanger A, if any, is limited.

(Regarding the space velocity (SV) of the water to be treated passed through the ion exchanger packing device 35)
As described above, hydrogen peroxide generated by ultraviolet irradiation from the ultraviolet irradiation device 34 is removed by the ion exchanger packing device 35. However, the present inventors discovered that the efficiency of hydrogen peroxide removal from the water to be treated varies significantly depending on the water flow conditions in the ion exchanger packing device 35. In this embodiment, the space velocity (SV) of the treated water in the ultraviolet irradiation device 34, which is passed through the anion exchanger A of the ion exchanger packing device 35, is controlled or adjusted to less than 160 (/h). This control or adjustment may be performed automatically or manually by an operator. This promotes the decomposition reaction of hydrogen peroxide by the anion exchanger A and suppresses an increase in the hydrogen peroxide concentration. While there is no particular lower limit for the SV, if the SV is too low, the amount of organic matter eluted from the ion exchanger in the ion exchanger packing device 35 per unit volume into the treated water increases, leading to an increase in the TOC of the treated water. Therefore, the SV is preferably 40 (/h) or more. Details of the SV will be described in the Examples.

As described above, in addition to controlling or adjusting the space velocity (SV) of the treated water of the ultraviolet irradiation device 34, which is passed through the anion exchanger A of the ion exchanger packing device 35, to less than 160 (/h), the water treatment device 1 may also be designed so that the space velocity (SV) of the treated water of the ultraviolet irradiation device 34, which is passed through the anion exchanger A of the ion exchanger packing device 35, is less than 160 (/h). For example, the water treatment device 1 may include a first deoxygenation device that removes dissolved oxygen from the treated water containing dissolved oxygen and organic matter, an ultraviolet irradiation device located downstream of the first deoxygenation device that irradiates the treated water of the first deoxygenation device with ultraviolet light, and an ion exchanger packing device located downstream of the ultraviolet irradiation device and packed with at least anion exchanger. The water treatment device 1 is designed so that the space velocity of the treated water of the ultraviolet irradiation device, which is passed through the anion exchanger of the ion exchanger packing device, is less than 160 (/h). In the water treatment device 1, one method for designing the ultraviolet irradiation device so that the space velocity of the treated water is less than 160 (/h) is to determine the flow rate of the water to be treated to the ion exchanger packing device 35 based on the raw water flow rate, treated water flow rate, treated water quality, etc. Then, the amount of resin to be packed in the ion exchanger packing device 35 (e.g., the cross-sectional area of the ion exchanger packing device 35, the height of the ion exchange resin layer, etc.), and the number of columns of the ion exchanger packing devices 35 if they are arranged in parallel, etc., are determined so that the space velocity of the treated water in the ultraviolet irradiation device is less than 160 (/h).

SV is calculated for anion exchanger A. For example, if the ion exchanger packing device 35 is packed with only anion exchanger A, SV is calculated for the volume of the anion exchanger packing section. Specifically, if the volume of the anion exchanger packing section is V (m ³ ) and the flow rate of the water to be treated is q (m ³ /h), SV (/h) = q/V. If the ion exchanger packing device 35 is packed with multiple beds of anion exchanger A and cation exchanger K, SV is calculated for only the volume of anion exchanger A. If the ion exchanger packing device 35 is packed with a mixed bed of anion exchanger A and cation exchanger K, SV is calculated for the total volume of anion exchanger A, that is, for only the volume of anion exchanger A when it is assumed that multiple beds of anion exchanger A and cation exchanger K are packed.

SV can be adjusted in several ways. 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 (flow direction) is h, then V = A × h, and therefore SV = q/(A × h). Therefore, SV can be adjusted by adjusting at least one of the flow rate q, flow area A, and layer thickness h. Alternatively, although not shown, a circulation pipe may be provided that branches off from the main pipe L1 downstream of the ion exchanger-filled device 35 and merges with the main pipe L1 upstream of the ion exchanger-filled device 35. During normal operation, a portion of the treated water is circulated back to the upstream side through the circulation pipe. When the SV of the ion exchanger-filled device 35 exceeds a predetermined value, the valve on the circulation pipe is adjusted to reduce the flow rate (or the valve is closed). The flow rate of the ion exchanger-filled device 35 decreases by the same amount as the flow rate in the circulation pipe, so SV can also be adjusted using this method. The valve opening and closing and the valve opening may be adjusted by the operator or by a control device. Alternatively, multiple ion exchanger packing devices 35 may be installed in parallel, with water passing through only some of the ion exchanger packing devices 35 during normal operation, and when the SV of the circulating ion exchanger packing device 35 exceeds a predetermined value, water may also be passed through the other ion exchanger packing devices 35.

(Regarding dissolved oxygen concentration)
Because ultraviolet light emitted from the ultraviolet irradiation device 34 is easily absorbed by oxygen, a high dissolved oxygen concentration in the water being treated makes it difficult for the reaction shown in Equation (1) to occur, resulting in a decrease in the efficiency of OH radical generation. The first deoxygenation device 33 adjusts the dissolved oxygen concentration in the water being treated by the ultraviolet irradiation device 34 to less than 1,000 μg/L. This reduces the consumption of ultraviolet light by dissolved oxygen, improving the efficiency of OH radical generation and the decomposition efficiency of organic matter. As described in the examples below, excessively reducing the dissolved oxygen concentration does not achieve the desired TOC reduction effect. Furthermore, lowering the dissolved oxygen concentration may result in an increase in the size of the first deoxygenation device 33 and increased operating costs. On the other hand, as can be seen from Equation (1), a certain amount of dissolved oxygen is required to increase the decomposition efficiency of organic matter (or to efficiently generate OH radicals). Therefore, a dissolved oxygen concentration of 1 μg/L or higher is preferable, and 5 μg/L or higher is more preferable. Details will be described in the examples.

(About TOC)
If the TOC and dissolved oxygen concentration in the water to be treated by the ultraviolet irradiation device 34 are high, the hydrogen peroxide concentration in the water to be treated by the ultraviolet irradiation device 34 may become high. For this reason, it is preferable to adjust the dissolved oxygen concentration in the water to be treated by the ultraviolet irradiation device 34 as described above, and also to adjust the TOC in the water to be treated by the ultraviolet irradiation device 34 to 5 μg/L or less. 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.

(Hydrogen peroxide removal rate)
The hydrogen peroxide removal rate of the ion exchanger loading device 35 is preferably 10% or higher. This reduces the possibility of the hydrogen peroxide concentration exceeding the allowable value at the point of use, for example. Because subsystems generally include an ultraviolet irradiation device, a hydrogen peroxide removal rate below 10% may reduce the TOC reduction effect of the subsystem's ultraviolet irradiation device. This is because hydrogen peroxide may inhibit the TOC reduction effect of the downstream ultraviolet irradiation device. Generally, supplying hydrogen peroxide to an ultraviolet irradiation device promotes the generation of OH radicals, but this may reduce the TOC reduction effect depending on the conditions. On the other hand, as described in the examples, the hydrogen peroxide removal rate can be increased by reducing the SV. However, reducing the SV to increase the hydrogen peroxide removal rate may lead to an increase in the size of the ion exchanger loading device 35 and an increase in the TOC content of the treated water. Therefore, the upper limit of the hydrogen peroxide removal rate is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less.

Second Embodiment
FIG. 2 shows a schematic configuration of a water treatment device 1 according to a second embodiment of the present invention. The water treatment device 1 of this embodiment includes a platinum group catalyst loading device 37 located downstream of the ion exchanger loading 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 loading device 37 supports a platinum group catalyst such as palladium (Pd) and may have the same configuration as the platinum group catalyst loading device described as an example of the first deoxygenation device 33. Contacting the water to be treated with the platinum group catalyst can further reduce the hydrogen peroxide concentration in the water to be treated. A hydrogen addition section (not shown) may be provided upstream of the platinum group catalyst loading device 37 to reduce the dissolved oxygen concentration. Alternatively, an ion exchanger supporting a metal catalyst such as palladium may be loaded into the EDI. In this case, hydrogen generated at the cathode of the EDI can be used to contact the metal catalyst.

As mentioned above, platinum group catalysts are generally expensive, but because most of the hydrogen peroxide is removed by the ion exchanger packing device 35 installed upstream of the platinum group catalyst packing device 37, the hydrogen peroxide concentration in the water supplied to the platinum group catalyst packing device 37 downstream of the ion exchanger packing device 35 is reduced. This makes it possible to reduce the size of the platinum group catalyst packing device 37, and also helps prevent increases in the cost of the water treatment device 1.

(Third embodiment)
Next, the third embodiment will be described, focusing on differences from the first embodiment. The omitted configuration and effects are the same as those of the first embodiment. FIG. 3( a) shows a schematic configuration of a water treatment device 1 according to a third embodiment of the present invention. The water treatment device 1 of this embodiment includes a dissolved oxygen concentration measuring device 38 that measures the dissolved oxygen concentration in the water to be treated in the ultraviolet irradiation device 34, a hydrogen peroxide concentration measuring device 39 that measures the hydrogen peroxide concentration in the treated water in the ion exchanger filling device 35, and a TOC measuring device 40 that measures the TOC in the treated water in the ion exchanger filling device 35. The hydrogen peroxide concentration measuring device 39 and the TOC measuring device 40 are installed downstream of the second deoxidizer 36, but they can also be installed between the ion exchanger filling device 35 and the second deoxidizer 36. In this embodiment, too, it is preferable to adjust the TOC in the water to be treated in the ultraviolet irradiation device 34 to 5 μg/L or less.

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

As shown in FIG. 3(b), in this embodiment, as in the second embodiment, a platinum group catalyst loading device 37 for removing hydrogen peroxide can be provided downstream of the ion exchanger loading device 35. In particular, when the ion exchanger loading device 35 contains an anion exchanger, hydrogen peroxide is removed by the ion exchanger loading device 35 as described above, reducing the load on the platinum group catalyst loading device 37 for removing hydrogen peroxide. This enables treatment at a high flow rate (high SV) and reduces treatment costs. The hydrogen peroxide concentration measuring device 39 and TOC measuring device 40 are provided downstream of the second deoxidizer 36, but they can also be provided between the ion exchanger loading device 35 and the platinum group catalyst loading device 37 or between the platinum group catalyst loading device 37 and the second deoxidizer 36.

Figure 4 conceptually shows the relationship between the dissolved oxygen concentration in the water being treated in the ultraviolet irradiation device 34 and the hydrogen peroxide concentration and TOC in the outlet water of the ion exchanger filling device 35. As mentioned above, ultraviolet light is easily absorbed by oxygen, so if the dissolved oxygen concentration in the water being treated in 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 being treated in the ultraviolet irradiation device 34 is low, the reaction shown in equation (1) is promoted, and the OH radicals increase, resulting in an increase in the hydrogen peroxide concentration.

In this embodiment, this principle is used to adjust the hydrogen peroxide concentration in the treated water from the ion exchanger filling device 35. The first deoxygenation device 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, so that the hydrogen peroxide concentration measured by the hydrogen peroxide concentration measuring device 39 is lower than a predetermined value. For example, when an operator manually operates the first deoxygenation device 33, if the hydrogen peroxide concentration measured by the hydrogen peroxide concentration measuring device 39 exceeds the target value or determines that it is likely to exceed the target value, the output of the vacuum pump of the first deoxygenation device 33 is reduced, thereby increasing the dissolved oxygen concentration in the treated water from the first deoxygenation device 33. Changes in the dissolved oxygen concentration can be confirmed by the dissolved oxygen concentration measuring device 38. When the first deoxygenation device 33 is operated automatically, a control device (not shown) adjusts the output (dissolved oxygen concentration) of the vacuum pump of the first deoxygenation device 33 according to the measurement value of the hydrogen peroxide concentration measuring device 39 so that the hydrogen peroxide concentration measured by the hydrogen peroxide concentration measuring device 39 is within an appropriate range.

On the other hand, if the dissolved oxygen concentration in the water being treated in the ultraviolet irradiation device 34 is too high, ultraviolet light is absorbed excessively by oxygen, reducing the efficiency of OH radical generation. As a result, if the dissolved oxygen concentration in the water being treated in the ultraviolet irradiation device 34 is higher than necessary, the TOC in the treated water in the ion exchanger filling device 35 will increase, as shown in Figure 4. Conversely, if the dissolved oxygen concentration in the water being treated in the ultraviolet irradiation device 34 is low, the TOC in the treated water in the ion exchanger filling device 35 will decrease. In other words, the hydrogen peroxide concentration and TOC in the treated water in the ion exchanger filling device 35 have a relationship in which an increase in one causes a decrease in the other.

The first deoxidizer 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 so that both are below a predetermined value. The predetermined 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 means is installed downstream, the load on the hydrogen peroxide removal means will increase. The predetermined TOC value is not particularly limited, but is preferably 2 μg/L, and more preferably 1 μg/L. The first deoxidizer 33 adjusts the dissolved oxygen concentration to between 20 μg/L and 100 μg/L, more preferably between 20 μg/L and 60 μg/L, and even more preferably between 20 μg/L and 40 μg/L.

Example 1
Hydrogen peroxide removal performance was evaluated by irradiating water containing dissolved oxygen and organic matter with ultraviolet light and then passing the UV-irradiated water through an ion exchange resin-filled device. Figure 5 shows a schematic diagram of the test equipment. 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-filled device 44 located downstream. A dissolved oxygen meter (Orbisphere, manufactured by HACH) was installed between the second membrane degassing device 42 and the ultraviolet irradiation device 43 to measure the dissolved oxygen concentration of the water at the inlet to the ultraviolet irradiation device 43. The ion exchange resin-filled device 44 was packed with multiple beds of anion exchange resin (AMBERJET4002OH, manufactured by Organo Corporation) upstream and cation exchange resin (AMBERJET1024H, manufactured by Organo Corporation) downstream. The TOC concentration in the inlet water to the first membrane degassing device 41 was 2 μg/L, and the hydrogen peroxide concentration was 10 μg/L.

The dissolved oxygen concentration in the inlet water of 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 in the first membrane degassing device 41 and the second membrane degassing device 42 using a vacuum pump inverter, or stopping the vacuum pump and supplying oxygen. The water to be treated prepared in this manner was supplied to the ultraviolet irradiation device 43. A low-pressure ultraviolet oxidation device JPW (manufactured by Japan Photoscience Co., Ltd.) was used as the ultraviolet irradiation device 43, and the water to be treated was irradiated with ultraviolet light at an irradiation dose of 0.07 kWh/ ^m³ . The flow rate of water to the ion exchange resin packing device 44 was changed using a blow line 45 provided at the inlet of the ion exchange resin packing device 44, and the SV for the anion exchange resin was changed to 60, 80, 100, 120, 140, 160, and 180 (/h).

The hydrogen peroxide concentrations in the inlet water and treated water of the ion exchange resin charging device 44 were measured to evaluate the hydrogen peroxide removal performance of the ion exchange resin charging device 44. The hydrogen peroxide concentration was measured by absorbance using the phenolphthalein method. Figure 6 shows the relationship between SV and hydrogen peroxide concentration in the treated water, and the relationship between SV and hydrogen peroxide removal rate. The hydrogen peroxide removal rate was calculated using the formula shown in Figure 3 from the hydrogen peroxide concentration H1 in the inlet water of the ion exchange resin charging device 44 and the hydrogen peroxide concentration H2 in the treated water.

The hydrogen peroxide concentration H1 in the inlet water of the ion exchange resin filling device 44 (water treated by 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. There was a tendency for the hydrogen peroxide concentration to increase as the dissolved oxygen concentration decreased. However, by setting the SV for the anion exchanger to less than 160 (/h), the hydrogen peroxide concentration H2 in the treated water could be reduced. Setting the SV to 120 (/h) or less resulted in a hydrogen peroxide removal rate of approximately 10% or more, and setting it to 100 (/h) or less resulted in a hydrogen peroxide removal rate of approximately 20%. An SV of 100 (/h) or less is preferred, with 90 (/h) or less being more preferred, and 80 (/h) or less being even more preferred.

Example 2
The SV for the anion exchanger was fixed at 80 (/h), and 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 where the dissolved oxygen concentration was high, oxygen was supplied to the treated water through a 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 3 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 Corporation). The TOC reduction rate did not change significantly between dissolved oxygen concentrations of 1000 and 8000 μg/L, but increased as the dissolved oxygen concentration decreased below 1000 μg/L, saturated at around 10 μg/L, and did not change significantly between 1 and 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, even more preferably 60 μg/L or less, and even more preferably 20 μg/L or less.

Example 3
The hydrogen peroxide and organic matter removal performance was evaluated by irradiating water containing dissolved oxygen and organic matter with ultraviolet light and then passing the irradiated water through an ion exchanger packing device. Figure 8 is a schematic diagram of the test device. Using the same method as in Example 1, the dissolved oxygen concentration in the water being treated in the ultraviolet irradiator 43 was adjusted to 20 μg/L, 50 μg/L, 100 μg/L, and 1000 μg/L. The SV of the ion exchanger packing device 44 was set to 50 (/h). The water being treated was irradiated with ultraviolet light at an irradiation rate of 0.07 kWh/ ^m3 using the same ultraviolet irradiator as in Examples 1 and 2. The ion exchange resin packing device 44 was packed with multiple beds of the same 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 hydrogen peroxide concentration in the treated water of the ion exchange resin loading device 44 was measured with a hydrogen peroxide monitor (OROXIDE manufactured by Organo Corporation), and the TOC in the treated water of the ion exchange resin loading device 44 was measured with the same TOC meter as in Example 2.

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 charging device 44. The hydrogen peroxide concentration was 33 μg/L when the dissolved oxygen concentration was 20 μg/L, 28 μg/L when it was 50 μg/L, 23 μg/L when it was 100 μg/L, and 21 μg/L when it was 1000 μg/L, showing a tendency for the hydrogen peroxide concentration to increase as the dissolved oxygen concentration was lowered. This demonstrates that the hydrogen peroxide concentration of the water being treated by the ion exchange resin charging device 44 can be adjusted by adjusting the dissolved oxygen concentration of the water being treated by the ultraviolet irradiation device 43.

On the other hand, the TOC in the treated water from the ion exchange resin charging device 44 tended to decrease as the dissolved oxygen concentration of the water being treated from the ultraviolet irradiation device 43 decreased. When the target hydrogen peroxide concentration in the treated water from the ion exchange resin charging device 44 was 30 μg/L and the target TOC value was 1.0 μg /L, when the dissolved oxygen concentration of the water being treated from the ultraviolet irradiation device 43 was 20 μg/L, the TOC was below the target value but the hydrogen peroxide concentration exceeded the target value. When the dissolved oxygen concentration of the water being treated from the ultraviolet irradiation device 43 was 100 μg/L and 1000 μg/L, the hydrogen peroxide concentration was below the target value but the TOC exceeded the target value. When the dissolved oxygen concentration of the water being treated from the ultraviolet irradiation device 43 was 50 μg/L, both the hydrogen peroxide concentration and TOC were below the target value. The guideline values are an example for explaining this embodiment, and as mentioned above, the dissolved oxygen concentration is preferably 20 μg/L or more and 100 μg/L or less.

The present invention has been described above using embodiments and examples, but the present invention is not limited to these embodiments and examples. For example, the present invention can also be applied to subsystems of ultrapure water production equipment.

1 Water treatment device 33 First deoxidizer 34 Ultraviolet irradiation device 35 Ion exchanger filling device 36 Second deoxidizer 37 Platinum group catalyst filling device 38 TOC measuring device 39 Hydrogen peroxide concentration measuring device 40 TOC measuring device A Anion exchanger K Cation exchanger

Claims (9)

removing dissolved oxygen from the water to be treated containing dissolved oxygen and organic matter using a first deoxygenation device;
irradiating the treated water from the first deoxygenation device with ultraviolet light by an ultraviolet irradiation device to decompose the organic matter ;
passing the treated water from the ultraviolet irradiation device through an ion exchanger-packed device packed with at least an anion exchanger;
and treating the treated water from the ion exchanger-packed device in a platinum group catalyst-packed device supporting a platinum group catalyst ,
The ion exchanger filling device removes hydrogen peroxide generated by irradiation of ultraviolet rays from the ultraviolet irradiation device from the treated water of the ultraviolet irradiation device,
the platinum group catalyst loading device brings the treated water from the ion exchanger loading device into contact with the platinum group catalyst to remove the hydrogen peroxide;
The water treatment method comprises passing the treated water from the ultraviolet irradiation device through the anion exchanger of the ion exchanger packing device at a space velocity of less than 160 (/h). The water treatment method described in claim 1, wherein the treated water from the ultraviolet irradiation device is passed through the anion exchanger of the ion exchanger packing device at a space velocity of 120 (/h) or less. The water treatment method described in 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. The water treatment method described in 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 1 μg/L or more and 100 μg/L or less. The water treatment method described in claim 1, wherein the total organic carbon content of the water to be treated supplied to the ultraviolet irradiation device from an ion removal device located upstream of the ultraviolet irradiation device is 5 μg/L or less. The water treatment method described in claim 2, wherein the hydrogen peroxide removal rate of the ion exchanger-filled device is 10% or more. The water treatment method described in any one of claims 1 to 6, wherein the treated water from the ion exchanger-filled device is treated in a second deoxygenation device located downstream of the ion exchanger-filled device. a first deoxygenation device that removes dissolved oxygen from the water to be treated that contains dissolved oxygen and organic matter;
an ultraviolet irradiation device located downstream of the first deoxygenation device and irradiating ultraviolet light onto the treated water from the first deoxygenation device to decompose the organic matter ;
an ion exchanger filling device located downstream of the ultraviolet irradiation device, filled with at least an anion exchanger, for removing hydrogen peroxide generated by irradiation of ultraviolet rays from the ultraviolet irradiation device from the treated water of the ultraviolet irradiation device ;
a platinum group catalyst-packing device located downstream of the ion exchanger-packing device, supporting a platinum group catalyst, and bringing treated water from the ion exchanger-packing device into contact with the platinum group catalyst to remove the hydrogen peroxide ;
A water treatment device, wherein the space velocity of the treated water of the ultraviolet irradiation device passed through the anion exchanger of the ion exchanger-packed device is less than 160 (/h). A method for designing a water treatment device comprising: a first deoxygenation device that removes dissolved oxygen from water to be treated that contains dissolved oxygen and organic matter; an ultraviolet irradiation device that is located downstream of the first deoxygenation device and irradiates the water treated by the first deoxygenation device with ultraviolet light to decompose the organic matter ; an ion exchanger-filled device that is located downstream of the ultraviolet irradiation device and is filled with at least an anion exchanger and that removes hydrogen peroxide generated by irradiation of ultraviolet light from the ultraviolet irradiation device from the water treated by the ultraviolet irradiation device; and a platinum group catalyst -filled device that is located downstream of the ion exchanger-filled device and supports a platinum group catalyst and brings the water treated by the ion exchanger-filled device into contact with the platinum group catalyst to remove the hydrogen peroxide ,
A method for designing a water treatment device, comprising designing the water treatment device so that the space velocity of the treated water of the ultraviolet irradiation device passed through the anion exchanger of the ion exchanger filling device is less than 160 (/h).