Water treatment method and water treatment device

Abstract

To provide a water treatment method that includes irradiating water to be treated with ultraviolet light to which a sulfur compound containing a peroxide group has been added, and that is capable of suppressing a dissolved oxygen concentration.SOLUTION: A water treatment method includes: adding a sulfur compound containing a peroxide group to water to be treated that contains an organic matter; irradiating the water to which the sulfur compound has been added with ultraviolet light; and acquiring a first index value related to a dissolved oxygen concentration in the water to be treated irradiated with ultraviolet light, in which at least one of a concentration of the sulfur compound to be added and an amount of ultraviolet light irradiation is adjusted based on the first index value.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As the demand for high-quality pure water has become apparent in recent years, various methods for decomposing and removing trace amounts of organic substances contained in pure water have been studied. A typical such method is an organic substance decomposition and removal step by ultraviolet oxidation treatment. Patent Document 1 discloses a technique for adding a sulfur compound containing a peroxide group to water to be treated and then irradiating the water to be treated with ultraviolet light to decompose and remove the organic substances contained in the water to be treated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventor of the present application has found that the higher the addition amount of the sulfur compound containing a peroxide group and the irradiation amount of ultraviolet light, the higher the dissolved oxygen concentration in the water to be treated after ultraviolet irradiation, which affects the treated water quality. An object of the present invention is to provide a water treatment method including irradiating water to be treated added with a sulfur compound containing a peroxide group with ultraviolet light and capable of suppressing the dissolved oxygen concentration.

Means for Solving the Problems

[0005] The water treatment method of the present invention includes adding a sulfur compound containing a peroxide group to the water to be treated containing organic substances, irradiating the water to be treated to which the sulfur compound has been added with ultraviolet light, and obtaining a first index value related to the dissolved oxygen concentration in the water to be treated irradiated with ultraviolet light, and adjusting at least one of the concentration of the sulfur compound to be added and the irradiation amount of ultraviolet light based on the first index value.

Effects of the Invention

[0006] According to the present invention, it is possible to provide a water treatment method that includes irradiating water to be treated to which a sulfur compound containing a peroxide group has been added with ultraviolet light and can suppress the dissolved oxygen concentration.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0008] Hereinafter, embodiments of the water treatment apparatus and the water treatment method of the present invention will be described with reference to the drawings. The water to be treated supplied to the water treatment apparatus of the present invention is not particularly limited. For example, any treated water in the water treatment system can be used as the water to be treated. When the water treatment system uses reclaimed water or recovered water as raw water, it is also possible to use any treated water in another system that produces reclaimed water or recovered water as the water to be treated.

[0009] (First Embodiment) FIG. 1 shows a schematic configuration of a water treatment apparatus 1 according to the first embodiment of the present invention. The water treatment apparatus 1 (primary system) constitutes an ultrapure water production apparatus together with a downstream subsystem (secondary system). The raw water supplied to the water treatment apparatus 1 contains organic substances. The water treatment apparatus 1 includes a raw water tank 11, a filter 12, an activated carbon tower 13, an ion removal device 14, a sulfur compound addition means 15, an ultraviolet irradiation device 16 (ultraviolet oxidation device), a reverse osmosis membrane device 17, an ion exchanger filling device 18, and a deaeration device 19. These facilities 11 to 19 are arranged in series in the order of the facilities 11 to 19 along the main pipe L1 from upstream to downstream with respect to the flow direction D of the water to be treated. The water to be treated stored in the raw water tank 11 is pressurized by a raw water pump (not shown), and then relatively large-sized dust and the like are removed by the filter 12, and impurities such as high-molecular organic substances are removed by the activated carbon tower 13. The configuration of the filter 12 is not limited, but in this embodiment, a sand filter is used.

[0010] The ion removal device 14 includes a cation tower (not shown) filled with a cation exchanger, a decarbonation tower (not shown), and an anion tower (not shown) filled with an anion exchanger, which are arranged in series in this order from upstream to downstream. The cation tower removes cation components from the water to be treated, the decarbonation tower removes carbonic acid from the water to be treated, and the anion tower removes anion components from the water to be treated. A decarbonation membrane may be provided instead of the decarbonation tower. Instead of the ion removal device 14, a softening device for removing hardness components such as calcium and magnesium can be arranged in series upstream, and an electro-deionized water production device (EDI) can be arranged in series downstream. Examples of the ion exchangers for the cation exchanger and the anion exchanger include ion exchange resins and monolithic or fibrous ion exchangers.

[0011] Between the ion removal device 14 and the ultraviolet irradiation device 16, there is provided a sulfur compound adding means 15 for adding a sulfur compound containing a peroxide group (hereinafter sometimes simply referred to as a sulfur compound) to the water to be treated. The sulfur compound adding means 15 includes a sulfur compound adding line 15a, a storage tank 15b for the sulfur compound connected to one end of the adding line 15a, and a transfer pump 15c for the sulfur compound. The other end of the adding line 15a is connected to the main pipe L1 between the ion removal device 14 and the ultraviolet irradiation device 16. Examples of the sulfur compound containing a peroxide group include sodium peroxydisulfate (Na2S2O8), ammonium peroxydisulfate ((NH4)2S2O8), potassium peroxydisulfate (K2S2O8), etc., and these are used alone or in combination. The addition concentration of the sulfur compound is preferably adjusted according to the total organic carbon (TOC) in the water to be treated. For this purpose, a TOC meter (not shown) can be provided between the ion removal device 14 and the sulfur compound adding means 15.

[0012] The ratio of the concentration of the sulfur compound to the TOC of the water to be treated (more precisely, the TOC of the water to be treated in the section between the connection part with the main pipe L1 of the addition line 15a and the ion removal device 14) (hereinafter referred to as the concentration ratio) is preferably about 10 to 5000 times. If the concentration ratio is less than 10, the generation of sulfate radicals is insufficient, and the decomposition efficiency of the organic matter in the water to be treated decreases. If the concentration ratio is more than 5000, the concentration of the sulfur compound remaining without being used for the decomposition of the organic matter increases, and the sulfur compound is used wastefully. In addition, the load of the sulfur compound to be treated by the reverse osmosis membrane device 17 may increase, or the damage to the ion exchanger filling device 18 may increase.

[0013] The ultraviolet irradiation device 16 irradiates the water to be treated with ultraviolet rays. As the ultraviolet irradiation device 16, for example, an ultraviolet lamp including at least one of wavelengths of 365 nm, 254 nm, 185 nm, and 172 nm can be used. The sulfur compound containing a peroxide group generates sulfate radicals in the water to be treated by ultraviolet irradiation. Sulfate radicals have a faster decomposition rate of organic matter than, for example, hydroxyl radicals generated by irradiating water with ultraviolet rays, and efficiently decompose the organic matter contained in the water to be treated.

[0014] Between the ultraviolet irradiation device 16 and the reverse osmosis membrane device 17, a dissolved oxygen meter 21 (dissolved oxygen concentration acquisition means) and a TOC meter 22 (TOC acquisition means) are provided. The dissolved oxygen meter 21 acquires the dissolved oxygen concentration in the water to be treated irradiated with ultraviolet rays. The TOC meter 22 acquires the TOC in the water to be treated irradiated with ultraviolet rays. The installation position of the dissolved oxygen meter 21 is not limited to the immediate vicinity of the outlet of the ultraviolet irradiation device 16 and can be set at any position in the subsequent stage of the ultraviolet irradiation device 16. For example, the dissolved oxygen concentrations obtained are different when the dissolved oxygen meter 21 is installed upstream and downstream of the degassing device 19. However, since the dissolved oxygen removal rate of the degassing device 19 is known, the dissolved oxygen concentration obtained can be used as the first index value described below regardless of whether the dissolved oxygen meter 21 is installed upstream or downstream of the degassing device 19. Similarly, the installation position of the TOC meter 22 is not limited to the immediate vicinity of the outlet of the ultraviolet irradiation device 16 and can be set at any position in the subsequent stage of the ultraviolet irradiation device 16. In the following description, the measured value of the dissolved oxygen meter 21 (dissolved oxygen concentration in the water to be treated irradiated with ultraviolet rays) may be referred to as the first index value, and the measured value of the TOC meter 22 (TOC in the water to be treated irradiated with ultraviolet rays) may be referred to as the second index value. The first index value is an index value related to the dissolved oxygen concentration, and the second index value is an index value related to the TOC.

[0015] The reverse osmosis membrane device 17 removes sulfur compounds containing peroxide groups remaining in the treated water of the ultraviolet irradiation device 16. Sulfur compounds containing peroxide groups have strong oxidizing power. Therefore, when the treated water of the ultraviolet irradiation device 16 containing a high concentration of sulfur compounds is supplied to the ion exchanger filling device 18, oxidative degradation of the ion exchanger and elution of organic substances therefrom occur, increasing the TOC of the treated water of the ion exchanger filling device 18. In this embodiment, since the reverse osmosis membrane device 17 supplies the water to be treated with a reduced concentration of sulfur compounds to the ion exchanger filling device 18, an increase in the TOC of the treated water of the ion exchanger filling device 18 is prevented. Since the reverse osmosis membrane device 17 is hardly affected by oxidative degradation, it is preferable as a means for removing sulfur compounds.

[0016] The sulfur compound concentration of the water to be treated passed through the reverse osmosis membrane device 17 is not particularly limited, but is preferably 400 mg / L or less, more preferably 100 mg / L or less, and even more preferably 20 mg / L or less from the viewpoint of suppressing the load on the ion exchanger filling device 18. If the sulfur compound concentration exceeds 400 mg / L, oxidative degradation of the reverse osmosis membrane device 17 may occur, and the load on the ion exchanger filling device 18 may also increase. The sulfur compound concentration of the treated water of the reverse osmosis membrane device 17, that is, the inlet water of the ion exchanger filling device 18, is preferably 0.5 mg / L or less. Thereby, while preventing oxidative degradation of the ion exchanger, the ionized organic substances can be efficiently removed by the ion exchanger filling device 18.

[0017] The sulfur compound concentration in the water to be treated after ultraviolet irradiation may vary depending on the concentration of the added sulfur compound. When a high sulfur compound concentration is expected, two or more reverse osmosis membrane devices 17 (not shown) may be provided in series. Alternatively, a sulfur compound removing means (not shown) may be provided upstream of the ion exchanger filling device 18. The sulfur compound removing means is not particularly limited, and examples thereof include a reducing agent, activated carbon, and a platinum group catalyst. When activated carbon or a catalyst is disposed upstream of the reverse osmosis membrane device 17, they may deteriorate themselves when the sulfur compound concentration is high. When a reducing agent is added upstream of the reverse osmosis membrane device 17, the amount of the reducing agent added increases, and the cost of the chemical agent becomes high. Therefore, it is preferable to provide the sulfur compound removing means between the reverse osmosis membrane device 17 and the ion exchanger filling device 18. Thereby, the ion load on the ion exchanger filling device 18 is also reduced.

[0018] The ion exchanger filling device 18 is a regenerative ion exchange tower filled with an anion exchanger and a cation exchanger. The decomposition products of the organic substances generated in the water to be treated by ultraviolet irradiation are removed by the ion exchanger filling device 18. Although not shown, EDI may be provided instead of the ion exchanger filling device 18. Since EDI is a continuous regeneration type, the regeneration process of the ion exchanger is unnecessary.

[0019] The deaerator 19 removes gases such as dissolved oxygen and carbonic acid contained in the water to be treated. The deaerator 19 is not limited as long as it can remove gases such as dissolved oxygen and carbonic acid. For example, a vacuum deaerator can be used. Generally, in a vacuum deaerator, a gas-liquid contact material for increasing the surface area of water is filled in a deaeration tower, the gas pressure in the deaeration tower is reduced by a vacuum pump, the water to be treated is placed in a vacuum state, and dissolved oxygen is removed. The dissolved oxygen concentration can be adjusted (controlled) by adjusting (controlling) the degree of vacuum in the deaeration tower using a vacuum pump. Furthermore, the deaeration performance can be improved by introducing nitrogen. In this case, the dissolved oxygen concentration can be adjusted (controlled) by adjusting (controlling) the degree of vacuum and the nitrogen inflow rate (nitrogen partial pressure).

[0020] (Operation method of water treatment device 1) As can be understood from the above description, by increasing at least either the concentration of the sulfur compound containing a peroxide group or the amount of ultraviolet irradiation, the generation amount of sulfate radicals can be increased and the TOC can be reduced. On the other hand, the inventor of the present application has found that the higher the addition amount of the sulfur compound and the amount of ultraviolet irradiation, the higher the dissolved oxygen concentration in the water to be treated after ultraviolet irradiation. This relationship is schematically shown in FIG. 2. It is considered that dissolved oxygen is generated in the process of irradiating the sulfur compound containing a peroxide group with ultraviolet rays to generate sulfate radicals. Since dissolved oxygen becomes an impurity depending on the use of the treated water, it may be desirable to reduce the dissolved oxygen concentration so that the treated water does not contain more dissolved oxygen than the specified value. However, when the dissolved oxygen concentration is reduced, the load on the deaerator 19 increases, resulting in an increase in the operating cost due to an increase in the power of the vacuum pump.

[0021] In this embodiment, based on at least either the dissolved oxygen concentration in the water to be treated acquired by the dissolved oxygen meter 21 or the TOC in the water to be treated acquired by the TOC meter 22, at least either the concentration of the sulfur compound added to the water to be treated from the sulfur compound adding means 15 or the irradiation amount of the ultraviolet rays irradiated from the ultraviolet irradiation device 16 is adjusted or controlled. The ultraviolet irradiation amount means the irradiation energy of the ultraviolet rays irradiated to the water to be treated per unit volume. Whether to use the dissolved oxygen concentration or TOC as an index depends on the use of the treated water, the values of the dissolved oxygen concentration and TOC, and the like. For example, when the TOC is not too high (when the TOC does not affect the control of the concentration of the sulfur compound added to the water to be treated or the irradiation amount of the ultraviolet rays), only the dissolved oxygen concentration can be used as an index. Specifically, when the standard value (upper limit value) of the dissolved oxygen concentration (the first index value) is set as the first standard value, at least either the concentration of the sulfur compound added or the ultraviolet irradiation amount is adjusted or controlled so that the first index value is lower than the first standard value. Also, when the dissolved oxygen concentration is not too high (when the dissolved oxygen concentration does not affect the control of the concentration of the sulfur compound added to the water to be treated or the irradiation amount of the ultraviolet rays), only the TOC can be used as an index. Specifically, when the standard value (upper limit value) of the TOC (the second index value) is set as the second standard value, at least either the concentration of the sulfur compound added or the ultraviolet irradiation amount is adjusted or controlled so that the second index value is lower than the second standard value. The standard value is determined in consideration of water quality guarantee values, the treatment performance of subsequent devices, and the like.

[0022] As shown in FIG. 2, the dissolved oxygen concentration and the TOC have a negative correlation, and when one is reduced, the other increases. Therefore, when reducing both the dissolved oxygen concentration and the TOC, it is preferable to adjust or control the concentration of the sulfur compound and the ultraviolet irradiation amount so that only one of the dissolved oxygen concentration and the TOC does not decrease extremely. At least either the concentration of the sulfur compound added or the ultraviolet irradiation amount is controlled so that the first index value is lower than the first standard value and the second index value is lower than the second standard value. Since the concentration of the sulfur compound and the ultraviolet irradiation amount can be adjusted independently, by using the adjustment of both in combination, both the dissolved oxygen concentration and the TOC can be controlled with higher precision.

[0023] Whether to prioritize the sulfur compound concentration or the UV irradiation dose can be determined by the load on the subsequent device of the UV irradiation device 16 and the operating cost. When there is no margin in the load on the reverse osmosis membrane device 17 or the ion exchanger filling device 18 with respect to the sulfur compound, or when it is desired to suppress the installation base of the reverse osmosis membrane device 17, it is preferable to preferentially control the UV irradiation dose. When there is a margin in the load on the reverse osmosis membrane device 17 or the ion exchanger filling device 18 with respect to the sulfur compound, or when it is desired to suppress the power of the UV irradiation device 16, it is preferable to preferentially control the sulfur compound concentration.

[0024] The adjustment or control of the sulfur compound concentration and the UV irradiation dose may be performed manually or may be performed automatically by providing a control device. In FIG. 1, the control device 23 is shown by a broken line. The control device 23 is connected to the dissolved oxygen meter 21, the TOC meter 22, the UV irradiation device 16, and the transfer pump 15c of the sulfur compound addition means 15. The control device 23 stores, in addition to the first reference value and the second reference value, information (priority information) on which of the sulfur compound concentration and the UV irradiation dose is to be prioritized. The dissolved oxygen concentration in the water to be treated is input to the control device 23 from the dissolved oxygen meter 21, and the TOC in the water to be treated is input from the TOC meter 22. The control device 23 controls either or both of the UV irradiation device 16 and the transfer pump 15c based on the dissolved oxygen concentration, the TOC, the first reference value, the second reference value, and the priority information.

[0025] As shown by the dashed line in FIG. 1, metal ion addition means 24 may be provided upstream of the ultraviolet irradiation device 16. The metal ions are not limited as long as they are other than alkali metals, and examples include ions such as iron, copper, silver, gold, and manganese. The presence of metal ions in the water to be treated promotes the activation of sulfur compounds and improves the organic matter treatment performance. As will be described in detail in the examples, adding metal ions tends to increase the dissolved oxygen concentration in the water to be treated. That is, compared with the case where no metal ions are added, the degree of change in the dissolved oxygen concentration and TOC in the water to be treated becomes larger. Since this embodiment can appropriately control both the dissolved oxygen concentration and TOC, a particularly large effect can be obtained when metal ions are added. Note that the metal ions may originally be contained in the water to be treated.

[0026] Hereinafter, other embodiments of the present invention will be described. Hereinafter, the differences from the first embodiment will be mainly described. The configurations and effects for which the description is omitted are the same as those of the first embodiment.

[0027] (Second Embodiment) FIG. 3 shows a schematic configuration of the water treatment apparatus 1 according to the second embodiment of the present invention. In this embodiment, as the first index value, the amount of change in the dissolved oxygen concentration in the water to be treated before and after ultraviolet irradiation is used. As the second index value, the amount of change in TOC in the water to be treated before and after ultraviolet irradiation is used.

[0028] A first dissolved oxygen meter 21 and a first TOC meter 22 are provided between the ultraviolet irradiation device 16 and the reverse osmosis membrane device 17. A second dissolved oxygen meter 25 and a second TOC meter 26 are provided between the ion removal device 14 and the ultraviolet irradiation device 16. The first dissolved oxygen meter 21 and the first TOC meter 22 are the same as the dissolved oxygen meter 21 and the TOC meter 22 of the first embodiment. The second dissolved oxygen meter 25 acquires the dissolved oxygen concentration in the water to be treated before ultraviolet irradiation. The second TOC meter 26 acquires the TOC in the water to be treated before ultraviolet irradiation. The first dissolved oxygen meter 21 and the second dissolved oxygen meter 25 are connected to a differentiator 27, and the differentiator 27 calculates the difference in the dissolved oxygen concentration acquired by the first dissolved oxygen meter 21 and the second dissolved oxygen meter 25, that is, the concentration of the dissolved oxygen generated by the ultraviolet irradiation device 16. The first TOC meter 22 and the second TOC meter 26 are connected to a differentiator 28, and the differentiator 28 calculates the difference in TOC acquired by the first TOC meter 22 and the second TOC meter 26, that is, the amount of organic matter decomposed by the ultraviolet irradiation device 16 (TOC reduction amount). In FIG. 3, for convenience, the differentiators 27 and 28 are shown as independent devices, but they may be incorporated as software in the control unit of the water treatment device 1 or the like. In this embodiment as well, it is possible to control the dissolved oxygen concentration and TOC in the same manner as in the first embodiment.

[0029] (Third Embodiment) FIG. 4 shows a schematic configuration of the water treatment apparatus 1 according to the third embodiment of the present invention. Another ultraviolet irradiation device 16A is provided downstream of the ultraviolet irradiation device 16. When the TOC of the water to be treated is high (for example, 10 μg / L or more), the organic substances in the water to be treated can be effectively decomposed by providing a plurality of stages of ultraviolet irradiation devices 16 and 16A. In the upstream ultraviolet irradiation device 16, ultraviolet oxidation decomposition treatment using a sulfur compound containing a peroxide group is performed. In the downstream ultraviolet irradiation device 16A, since almost no sulfur compound remains, normal ultraviolet oxidation decomposition treatment is performed. In such a case, in the upstream ultraviolet irradiation device 16, hardly decomposable TOC components (for example, urea, etc.) are decomposed, and in the downstream ultraviolet irradiation device 16A, normal TOC components are decomposed. If the dissolved oxygen concentration in the water to be treated supplied to the downstream ultraviolet irradiation device 16A is high, the organic substance removal performance of the downstream ultraviolet irradiation device 16A decreases. Therefore, it is preferable to adjust the ultraviolet irradiation amount of the upstream ultraviolet irradiation device 16 and the concentration of the sulfur compound to be added to suppress the dissolved oxygen concentration in the water to be treated of the downstream ultraviolet irradiation device 16A. In the present embodiment, a deaeration device 19A is provided between the upstream ultraviolet irradiation device 16 and the downstream ultraviolet irradiation device 16A to reduce the dissolved oxygen concentration. The deaeration device 19A can also be omitted.

[0030] (Fourth Embodiment) FIG. 5 shows a schematic configuration of the water treatment apparatus 1 according to the fourth embodiment of the present invention. The water treatment apparatus 1 of the present embodiment has a sulfur compound removing means 29 containing a peroxide group between the reverse osmosis membrane device 17 and the ion exchanger filling device 18. The sulfur compound removing means 29 is not particularly limited, and various means generally used for removing oxidants, such as reducing agents, activated carbon, platinum group metal supported catalysts, etc., can be used.

[0031] The sulfur compound removal means 29 can also be provided between the ultraviolet irradiation device 16 and the reverse osmosis membrane device 17. In that case, however, the load on the sulfur compound removal means 29 increases. When the removal means 29 is activated carbon or a catalyst, there is a possibility that these are oxidatively deteriorated by sulfur compounds and organic substances or the like flow out into the treated water, deteriorating the quality of the treated water. When the removal means 29 is a reducing agent, the amount of the reducing agent added increases, which may increase the chemical cost. In the present embodiment, since most sulfur compounds are removed by the reverse osmosis membrane device 17 and then the remaining sulfur compounds are removed by the removal means 29, this leads to an improvement in the performance of the water treatment apparatus 1 and a reduction in the operating cost.

[0032] (Fifth Embodiment) FIG. 6 shows a schematic configuration of the water treatment apparatus 1 according to the fifth embodiment of the present invention. The water treatment apparatus 1 of the present embodiment has a second reverse osmosis membrane device 17A between the reverse osmosis membrane device 17 and the ion exchanger filling device 18. Even when the sulfur compound concentration is increased to improve the decomposition efficiency of organic substances, the sulfur compound concentration of the treated water of the ultraviolet irradiation device 16 may increase. By arranging the reverse osmosis membrane devices 17 and 17A in series in two or more stages, oxidative deterioration of the ion exchanger in the ion exchanger filling device 18 is suppressed, so that the removal performance of sulfur compounds is improved and the load on the ion exchanger filling device 18 can be reduced. Also in the present embodiment, the sulfur compound removal means 29 of the fourth embodiment can be provided. In this case, the sulfur compound removal means 29 can be arranged between the reverse osmosis membrane devices 17 and 17A arranged in series.

[0033] (Example 1) Using the apparatus shown in Fig. 7(a), ultraviolet rays were irradiated onto the water to be treated containing urea and persulfate (an example of a sulfur compound containing a peroxide group), and the dissolved oxygen concentration in the water to be treated irradiated with ultraviolet rays was measured. Specifically, urea was added to pure water so that the TOC became 6 μg-C / L, and further 10 mg / L of ammonium peroxydisulfate was added as persulfate to prepare the water to be treated. This water to be treated was irradiated with ultraviolet rays using a low-pressure ultraviolet irradiation device JPW (manufactured by Nippon Photo Science Co., Ltd.). A dissolved oxygen meter (Orbisphere 510 manufactured by HACH) was installed in the outlet water line of the ultraviolet irradiation device. The water flow rate to the ultraviolet irradiation device was adjusted to change the ultraviolet irradiation dose (irradiation energy per unit volume), and the dissolved oxygen concentration at each irradiation dose was measured. In Example 1-1, 10 mg / L of ammonium peroxydisulfate was added to the water to be treated. In Example 1-2, 10 mg / L of ammonium peroxydisulfate was added to the water to be treated, and 0.1 mg / L of copper ions (CuSO4) was added. In Example 1-3, 15 mg / L of ammonium peroxydisulfate was added to the water to be treated. No copper ions were added in Examples 1-1 and 1-3.

[0034] The results are shown in Fig. 7(b). In any of the examples, the higher the ultraviolet irradiation dose, the higher the dissolved oxygen concentration in the water to be treated. From the comparison between Examples 1-1 and 1-2, the addition of copper ions increased the dissolved oxygen concentration in the water to be treated. From the comparison between Examples 1-1 and 1-3, the higher the persulfate concentration, the higher the dissolved oxygen concentration in the treated water. From this, it was found that the dissolved oxygen concentration in the water to be treated can be controlled by adjusting the persulfate concentration and the ultraviolet irradiation dose.

[0035] (Example 2) Using the apparatus shown in Fig. 8(a), ultraviolet rays were irradiated onto the water to be treated containing urea and persulfate, and the dissolved oxygen concentration and TOC in the water to be treated irradiated with ultraviolet rays were measured. The apparatus used was the same as the apparatus shown in Fig. 7(a), except that a TOC meter (Sievers M500e) was installed in the outlet water line of the ultraviolet irradiation device.

[0036] <Example 2-1> Urea was added to pure water so that the TOC became 6 μg-C / L, and further ammonium peroxydisulfate was added at 10 mg / L to prepare the water to be treated. Copper ions were not added. The water to be treated was irradiated with ultraviolet rays using a low-pressure ultraviolet irradiation device JPW. In the same manner as in Example 1, the ultraviolet irradiation dose to the water to be treated was varied in the range of 0.3 to 0.5 kWh / m3. Here, the target dissolved oxygen concentration in the water to be treated after ultraviolet irradiation was set to 100 μg / L or less, and the target TOC was set to 1 μg / L or less. The results are shown in Fig. 8(b). When the ultraviolet irradiation dose was 0.3 kWh / m3, the dissolved oxygen concentration was below the target value, but the TOC exceeded the target value. When the ultraviolet irradiation dose was 0.5 kWh / m3, the TOC was below the target value, but the dissolved oxygen concentration exceeded the target value. In contrast, when the ultraviolet irradiation dose was 0.4 kWh / m3, both the dissolved oxygen concentration and the TOC were below the target values.

[0037] <Example 2-2> Urea was added to pure water so that the TOC became 6 μg-C / L, and ammonium peroxydisulfate was further added to prepare the water to be treated. Copper ions were not added. The water to be treated was irradiated with ultraviolet rays using a low-pressure ultraviolet irradiation device JPW. The ultraviolet irradiation dose to the water to be treated was 0.2 kWh / m3. The addition amount of ammonium peroxydisulfate was varied in the range of 10 to 20 mg / L. The target dissolved oxygen concentration and the target TOC were the same as in Example 2-1. The results are shown in Fig. 8(c). When the addition amount of ammonium peroxydisulfate was 10 mg / L, the dissolved oxygen concentration was below the target value, but the TOC exceeded the target value. When the addition amount of ammonium peroxydisulfate was 20 mg / L, the TOC was below the target value, but the dissolved oxygen concentration exceeded the target value. In contrast, when the addition amount of ammonium peroxydisulfate was 15 mg / L, both the dissolved oxygen concentration and the TOC were below the target values.

[0038] <Example 2-3> In Example 2-1, 0.1 mg / L of CuSO4 was added to the water to be treated. The amount of ultraviolet irradiation to the water to be treated was varied in the range of 0.1 to 0.3 kWh / m3. Here, the target dissolved oxygen concentration in the water to be treated after ultraviolet irradiation was set to 200 μg / L or less, and the target TOC was set to 1 μg / L or less. The results are shown in Fig. 8(b). When the ultraviolet irradiation amount was 0.1 kWh / m3, the dissolved oxygen concentration was below the target value, but the TOC exceeded the target value. When the ultraviolet irradiation amount was 0.3 kWh / m3, the TOC was below the target value, but the dissolved oxygen concentration exceeded the target value. In contrast, when the ultraviolet irradiation amount was 0.2 kWh / m3, both the dissolved oxygen concentration and the TOC were below the target values.

[0039] <Example 2-4> In Example 2-2, 0.1 mg / L of CuSO4 was added to the water to be treated. The amount of ultraviolet irradiation to the water to be treated was set to 0.1 kWh / m3. The addition amount of ammonium peroxydisulfate was varied in the range of 10 to 20 mg / L. The target dissolved oxygen concentration and the target TOC were the same as those in Example 2-1. The results are shown in Fig. 8(c). When the addition amount of ammonium peroxydisulfate was 10 mg / L, the dissolved oxygen concentration was below the target value, but the TOC exceeded the target value. When the addition amount of ammonium peroxydisulfate was 20 mg / L, the TOC was below the target value, but the dissolved oxygen concentration exceeded the target value. In contrast, when the addition amount of ammonium peroxydisulfate was 15 mg / L, both the dissolved oxygen concentration and the TOC were below the target values.

[0040] From Examples 2-1 and 2-3, it was found that the higher the ultraviolet irradiation amount, the higher the dissolved oxygen concentration in the water to be treated and the lower the TOC. From Examples 2-2 and 2-4, it was found that the higher the addition amount of ammonium peroxydisulfate, the higher the dissolved oxygen concentration in the water to be treated and the lower the TOC. That is, it was found that in order to control both the dissolved oxygen concentration and the TOC to appropriate values, it is effective to adjust either the ultraviolet irradiation amount or the addition amount of ammonium peroxydisulfate to an appropriate range.

[0041] From Examples 2-3 and 2-4, it was found that when metal ions such as copper ions are added to the water to be treated, the dissolved oxygen concentration in the water to be treated after ultraviolet irradiation becomes higher, while the TOC becomes lower, compared with the case where no metal ions are added. However, referring to Fig. 8(b), the amount of change in the dissolved oxygen concentration (the slope of the graph) with respect to the change in the ultraviolet irradiation dose is larger when copper ions are added than when copper ions are not added. On the other hand, the amount of change in TOC with respect to the change in the ultraviolet irradiation dose is not significantly different between the case where copper ions are added and the case where copper ions are not added. In other words, when no copper ions are added, increasing the ultraviolet irradiation dose effectively reduces the TOC, but the rapid increase in the dissolved oxygen concentration is suppressed. Therefore, when no copper ions are added, it may be more advantageous to preferentially adjust the ultraviolet irradiation dose (or at least adjust the ultraviolet irradiation dose) rather than adjusting the addition amount of ammonium peroxydisulfate. On the other hand, when copper ions are added, as the ultraviolet irradiation dose is increased, the dissolved oxygen concentration increases rapidly and the TOC decreases rapidly, so there is no significant difference in adjusting either the ultraviolet irradiation dose or the addition amount of ammonium disulfate.

Explanation of Signs

[0042] 1 Water treatment apparatus 15 Sulfur compound addition means 16, 16A Ultraviolet irradiation device 17, 17A Reverse osmosis membrane device 18 Ion exchanger filling device 19, 19A Degassing device 21, 25 Dissolved oxygen meter 22, 26 TOC meter 23 Control device 24 Metal ion addition means 29 Sulfur compound removal means

Claims

1. adding a sulfur compound containing a peroxide group to the water to be treated containing organic substances; irradiating the water to be treated to which the sulfur compound has been added with ultraviolet light; obtaining a first index value related to the dissolved oxygen concentration in the water to be treated irradiated with the ultraviolet light; and having; a water treatment method for adjusting at least one of the concentration of the sulfur compound to be added and the irradiation amount of the ultraviolet light based on the first index value.

2. The water treatment method according to claim 1, wherein the first index value is the dissolved oxygen concentration in the water to be treated irradiated with the ultraviolet light.

3. The water treatment method according to claim 1, wherein the first index value is the change amount of the dissolved oxygen concentration in the water to be treated before and after irradiation with the ultraviolet light.

4. obtaining a second index value related to the total organic carbon in the water to be treated irradiated with ultraviolet light; The water treatment method according to claim 1, wherein at least one of the concentration of the sulfur compound to be added and the irradiation amount of the ultraviolet light is adjusted based on the first index value and the second index value.

5. The water treatment method according to claim 4, wherein the second index value is the total organic carbon in the water to be treated irradiated with the ultraviolet light.

6. The water treatment method according to claim 4, wherein the second index value is the change amount of the total organic carbon in the water to be treated before and after irradiation with the ultraviolet light.

7. The water treatment method according to claim 1, further comprising adding metal ions to the water to be treated before irradiation with the ultraviolet light.

8. No metal ions are added to the water to be treated before irradiation with the ultraviolet light, and at least the irradiation amount of the ultraviolet light is controlled based on the first index value. The water treatment method according to claim 1.

9. sulfur compound adding means for adding a sulfur compound containing a peroxide group to the water to be treated containing organic substances; an ultraviolet irradiation device for irradiating the water to be treated to which the sulfur compound has been added with ultraviolet light; acquisition means for acquiring a first index value related to the dissolved oxygen concentration in the water to be treated irradiated with the ultraviolet light; a control device for controlling at least one of the concentration of the sulfur compound to be added and the irradiation amount of the ultraviolet light based on the first index value; A water treatment apparatus having.

10. having acquisition means for acquiring a second index value related to the total organic carbon in the water to be treated irradiated with ultraviolet light; The water treatment apparatus according to claim 9, wherein the control means controls at least one of the concentration of the sulfur compound to be added and the irradiation amount of the ultraviolet rays based on the first index value and the second index value.

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