Water treatment method, beads used in the method, and water treatment device

Abstract

To provide a titanium oxide-containing photocatalytic coating agent for a water treatment device, capable of effectively allowing ultraviolet rays to reach water to be treated, and beads coated with the coating agent, and to provide a water treatment device capable of treating persistent substances by using these coating agent and beads.SOLUTION: The above problem is solved by coating beads near an ultraviolet irradiator in a water treatment device with a highly transparent paint containing a photocatalyst.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a water treatment method for treating hardly decomposable substances, beads used in the method, and a water treatment apparatus.

Background Art

[0002] In some countries overseas such as the United States, sewage is reused. To use sewage as drinking water, in addition to sterilization, it is also necessary to treat hardly decomposable substances whose regulations are becoming stricter year by year. Conventionally known treatment techniques include methods using activated carbon or activated sludge, coagulation sedimentation methods, etc. However, in the case of hardly decomposable substances such as 1,4-dioxane and typical nitrosamines such as NDMA, they have properties such as high water solubility, microbial non-decomposability, low volatility, and low adsorptivity, and it has been difficult to decompose and remove them by the above-mentioned methods. Therefore, for the decomposition and removal of 1,4-dioxane, NDMA, etc., an advanced oxidation process (AOP) is used. This is a treatment method that generates OH (hydroxyl radicals) by the reaction of a plurality of oxidants and water, such as ozone and ultraviolet light, hydrogen peroxide and ultraviolet light, ozone and hydrogen peroxide, promotes the oxidative decomposition reaction, and removes harmful substances. Water treatment apparatuses using this method are known (Patent Documents 1 and 2). However, apparatuses using ozone or hydrogen peroxide require care in handling, and since the apparatuses become large-sized, the installation and maintenance costs may be high. There is a demand for the development of a treatment technology for hardly decomposable substances that can be realized without using ozone or hydrogen peroxide.

[0003] Patent Document 3 describes an invention of a water treatment apparatus including an ultraviolet irradiator having titanium oxide-coated beads arranged around it and an ozone generator, which utilizes the photocatalytic action of titanium oxide. However, since conventional photocatalytic coating agents contain titanium oxide, which is also used as a raw material for white pigments, the beads coated with this become turbid, and there is a problem that ultraviolet rays are scattered on their surfaces. That is, in the conventional technology, the irradiated ultraviolet rays could not pass through the photocatalytic-coated beads, and most of the irradiated ultraviolet rays could not reach the water to be treated. Therefore, a practical technology that can more effectively reach the water to be treated with ultraviolet rays has been desired.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a water treatment method, beads used in the method, and a water treatment apparatus that can effectively reach ultraviolet rays to the water to be treated. Further, by selecting and irradiating the beads coated with the photocatalyst with ultraviolet light of an appropriate wavelength, it is also an object to simply treat hardly decomposable substances with the photocatalyst, which has been difficult in the past.

Means for Solving the Problems

[0006] As a result of intensive research to solve the above problems, the present inventors have recently come to apply beads in a water treatment apparatus with a highly transparent paint containing a photocatalyst, which has been developed for construction (building exterior walls). According to the present invention, since a photocatalytic action can be efficiently obtained, when the coated beads are arranged near an ultraviolet irradiator in a water treatment apparatus, it can be expected that ultraviolet light can reach the water to be treated more effectively than before. Further, in the present invention, it is expected that treatment of hardly decomposable substances and sterilization can be achieved all at once by appropriately adjusting the wavelength of the irradiated ultraviolet light. Based on the above findings, the present inventors have further advanced the research and completed the present invention.

[0007] That is, the present invention includes the following inventions in order to solve the above problems. [1] In a water treatment apparatus provided with an ultraviolet irradiator for irradiating water to be treated containing hardly decomposable substances with ultraviolet light, A water treatment method, characterized in that beads coated with a transparent or translucent paint containing titanium oxide are arranged around the ultraviolet irradiator. [2] The transparent or translucent paint containing titanium oxide has a transmittance of 50% to 80% with respect to the wavelength region of 340 nm to 380 nm, which is a wavelength region near the band gap, when measured by an ultraviolet-visible spectrophotometer. The method according to [1]. [3] The light source of the ultraviolet irradiator includes a mercury ultraviolet lamp, an LED lamp, an excimer lamp, or a combination thereof selected from the group consisting of a low-pressure mercury lamp, a medium-pressure mercury lamp, and a high-pressure mercury lamp. The method according to [1] or [2]. [4] The method according to any one of [1] to [3], characterized in that the hardly decomposable substance contains one or more selected from the group consisting of 1,4-dioxane, dioxin, nitrosoamine, and phenol. [5] The beads are beads in which a transparent or translucent resin layer containing no photocatalyst is formed with glass beads or glass containing at least one selected from the group consisting of soda glass, soda-lime glass, quartz glass, crystallized glass, and heat-resistant glass as a core, and the method according to any one of [1] to [4]. [6] Beads coated with a transparent or translucent paint containing titanium oxide, which are characterized by being used in a water treatment apparatus containing a hardly decomposable substance. [7] A water treatment apparatus comprising an ultraviolet irradiator for irradiating ultraviolet rays to water to be treated containing a hardly decomposable substance, and beads coated with a transparent or translucent paint containing titanium oxide being disposed around the ultraviolet irradiator.

Advantages of the Invention

[0008] According to the present invention, for example, when the beads laminated and filled near an ultraviolet lamp in a water treatment apparatus are coated with the coating agent of the present invention, fine titanium oxide particles dispersed in the coating agent absorb ultraviolet rays and can promote chemical reactions (oxidation, reduction reactions). On the other hand, since the portion other than the particles is transparent or translucent, the irradiated ultraviolet rays can permeate the water to be treated without being attenuated as compared with the prior art. That is, as compared with the prior art, the probability that ultraviolet rays reach not only the bead layer near the ultraviolet irradiator but also the photocatalyst-coated beads laminated and filled in the outer layer is significantly improved. Even in an apparatus having no ozone or hydrogen peroxide generator, etc., the treatment of hardly decomposable substances can be efficiently performed by the action of the photocatalyst and ultraviolet rays. Also, by appropriately adjusting the irradiation wavelength of ultraviolet light, etc. within a desired range, it is possible to provide a water treatment method capable of achieving both the intended sterilization and the treatment of hardly decomposable substances at once, and a water treatment apparatus using the method. Furthermore, since the method of the present invention can be changed to one using the present invention only for a part (bead part) of the ultraviolet irradiation equipment of an existing water treatment apparatus during maintenance or inspection, there is an advantage that a significant apparatus change (such as an increase in the floor area) is not required.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] [Water Treatment Apparatus Equipped with Ultraviolet Irradiator] The water treatment apparatus of the present invention includes an ultraviolet irradiator for irradiating ultraviolet light to water to be treated containing hardly decomposable substances and / or water to be treated that requires sterilization. Preferably, the water treatment apparatus of the present invention includes an ultraviolet irradiator for irradiating ultraviolet light to water to be treated containing hardly decomposable substances, and more preferably, beads coated with a transparent or translucent paint containing titanium oxide are arranged around the ultraviolet irradiator (specifically, refer to FIGS. 2 to 3 of Patent Document 3 described above). Particularly preferably, it is a water treatment apparatus in which the beads are stacked (for example, refer to FIG. 2 of this specification), but it is not limited thereto. The casing of the water treatment device is, for example, a metal container such as stainless steel or aluminum, or a resin container such as polytetrafluoroethylene (PTFE) or polyvinyl chloride (PVC), but is not limited thereto. Among these, it is preferable to use a stainless steel container in consideration of corrosion resistance. When using a resin container, it is preferable to use a PTFE container with extremely high resistance to ultraviolet rays. When the beads are stacked, preferably 1 to 6 layers, more preferably 2 to 5 layers, and even more preferably 3 to 4 layers are stacked, but not limited thereto. When TERSUS EN described later is used as the coating agent for the glass beads, it is preferably stacked in 1 to 3 layers, but not limited thereto. Such a device is already well-established in the art for the transparent or translucent paint containing titanium oxide described later and the parts other than the beads coated with the paint. For example, it is possible to refer to the devices described in Patent Documents 1 to 3 above.

[0011] The ultraviolet irradiator included in the water treatment device of the present invention preferably includes, as a light source, a mercury ultraviolet lamp, an LED lamp, an excimer lamp, or a combination thereof selected from the group consisting of a low-pressure mercury lamp, a medium-pressure mercury lamp, and a high-pressure mercury lamp. Among these, a widely used low-pressure mercury lamp or an LED lamp with a high degree of freedom in reactor structure is preferable, but not limited thereto. The wavelength of the ultraviolet ray irradiated in the present invention is preferably a wavelength of about 220 m to about 280 nm. More preferably, it is a wavelength of about 250 nm to about 270 nm.

[0012] Specifically, examples of the water treatment device that can preferably use the photocatalyst coating agent of the present invention include, for example, Trojan UVFit and UVSwift of Trojan, which have a structure as shown in FIG. 1 described later, for wastewater and drinking water treatment devices, ultraviolet sterilization systems such as Wedeco Spektron and Wedeco LBX of Xylem, ULTRATRON of ULTRAAQUA TM and MONORAYTM Examples include, but are not limited to, an ultraviolet sterilization system or the like. In addition, the water treatment apparatus using the method of the present invention may further include mechanisms known in the art of water treatment, such as an activated carbon adsorber for treating organometallic compounds and an ozone generator for ozone treatment.

[0013] [Transparent or translucent photocatalyst coating agent, beads] The coating agent used in the present invention preferably contains fine particles of titanium oxide as a photocatalyst and is transparent or translucent. More preferably, it is transparent. The transparency can be measured, for example, by the method described in the examples below. For example, when measured by an ultraviolet-visible spectrophotometer, the transmittance is preferably 50% to 80%, more preferably 60% to 80% with respect to the wavelength range of 340 nm to 380 nm, which is near the band gap, but is not limited thereto, and the transparency can be appropriately measured by methods known in the art. More preferably, the coating agent is one in which the fine particles of titanium oxide do not aggregate and the particles are uniformly dispersed in the coating agent, but is not limited thereto. The coating agent is preferably coated on each bead in 1 to 5 layers, more preferably 2 to 3 layers, but is not limited thereto. As the photocatalyst coating agent used in the present invention, for example, the TERSUS series (TERSUS EN, EG, IN, etc.) manufactured by Shin-Etsu Chemical Co., Ltd. can be used. Preferably, TERSUS EN can be used, but is not limited thereto. Another or further preferred characteristic of the coating agent of the present invention is that almost no organic solvent is used and / or no organic resin is included. In addition, the photocatalyst coating agent of the present invention may further contain photocatalysts other than titanium oxide, such as tin oxide, strontium titanate, and other components known in the art.

[0014] The beads treated with the photocatalytic coating agent of the present invention contain glass, preferably transparent or translucent glass. For example, beads containing one or more selected from the group consisting of soda glass, soda-lime glass, quartz glass, crystallized glass, and heat-resistant glass, or beads having a transparent or translucent resin layer containing no photooxidation catalyst formed on the surface of glass as a core are included. Among them, it is preferable to use glass beads made of quartz glass with less ultraviolet absorption. Further, for beads having a transparent or translucent resin layer containing no photooxidation catalyst formed on the surface of glass as a core, the glass used as the core can preferably be the glass that becomes the material of the beads. As the resin layer, it is preferable to use a resin having high transparency, less ultraviolet absorption, and high resistance to ultraviolet rays, such as cycloolefin polymer and cycloolefin copolymer. Preferably, the beads treated with the coating agent are used in a water treatment apparatus containing a hardly decomposable substance. More preferably, they are used around an ultraviolet irradiator in the water treatment apparatus. Even more preferably, they are stacked and filled around the ultraviolet irradiator in the water treatment apparatus. Regarding the arrangement of the beads, it may be a fixed bed densely filled around the ultraviolet irradiator in the casing to such an extent that the beads cannot move freely, or a so-called fluidized bed that can move inside the casing to some extent by the water flow of the water to be treated. From the viewpoint of suppressing the peeling of the coating layer by a transparent or translucent paint containing titanium oxide and extending the life of the coated beads, it is preferable to use a fixed bed. In addition, as a method for confirming that the beads have been treated with the photocatalytic coating agent of the present invention, in addition to the method of comparing the weights of the beads before and after being coated with the photocatalytic coating agent, it can also be confirmed by observing the state of the bead surface with an electron microscope or the like. In addition, it can be confirmed by methods commonly used in the art.

[0015] Although the photocatalytic action of titanium oxide and the like is known, its mechanism of action is as follows. When a photocatalyst such as titanium oxide is irradiated with light (such as ultraviolet light), e in the conduction band of titanium oxide -(Electrons) also generate h+ (holes) in the valence band. Then, O2 in the air, e - and moisture, h+ each undergo reduction and oxidation reactions. O2 on the photocatalyst surface - (superoxide ion), OH (hydroxyl radical), two types of highly reactive oxygen species with high decomposition power are generated. These reactive oxygen species can decompose various refractory substances including 1,4-dioxane (preferably, refractory organic substances), and furthermore, effects of removing dirt and bad odors, and antibacterial effects can also be obtained. In addition, in order to confirm that the beads treated with the photocatalyst coating agent of the present invention have photocatalytic activity (undergo redox reactions), methods, reagents, and kits known in the art can be used. For example, in the examples described later, a method using methylene blue (MB) is used. When ultraviolet light (wavelength: 260 to 270 nm) is irradiated on the photocatalyst, a redox reaction occurs. By utilizing the fact that when blue methylene blue is reduced, it becomes colorless leucomethylene blue, the presence or absence of photocatalytic activity can be confirmed. In addition, methods such as a method using methyl orange (MO) and a method using methyl red (MR) can be used. In addition, various other conventionally known methods for measuring photocatalytic activity can be applied.

[0016] [Refractory substances] By the method of using the photocatalyst coating agent of the present invention, efficient decomposition and removal of refractory substances from the water to be treated are possible. Examples of such refractory substances include 1,4-dioxane, hydrazine, dioxin, nitrosoamine, humic substances (humic acid, fulvic acid, humin, etc.), and phenol. Preferably, 1,4-dioxane and NDMA, which are typical nitrosoamines, but are not limited thereto. The concentration of the hardly decomposable substance decomposable by the method of the present invention in the water to be treated is not particularly limited, and may be, for example, 10 μg / L to 200 mg / L, 10 μg / L to 50 mg / L, 10 μg / L to 1 mg / L, or 10 μg / L to 0.2 mg / L, but is not limited thereto. Further, an example of another preferable concentration is about 0.01 to 0.1 mg / L, but is not limited thereto.

Example

[0017] Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0018] <Method for calculating transmittance (transparency) of beads> In order to calculate the transparency (transmittance at 340 to 380 nm) of the beads used in the following experiment, the average absorbance from 340 to 380 nm was calculated by the following method.

Equation

Equation

Equation

[0019] [Example 1] Examination of Coating Conditions of Photocatalyst Coating Agent <Material> · Spherical glass beads (manufactured by AS ONE, material: soda glass, particle size 5 mm, average weight 0.1713 g) · Spherical quartz glass beads (AS ONE, material: quartz glass, particle size 5 mm, average weight 0.1701 g) · Titanium oxide-containing photocatalyst coating agent (manufactured by Shin-Etsu Chemical Co., Ltd., TERSUS EN) · Methylene blue (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0020] In order to establish the conditions for coating the surface of the glass beads with a uniform titanium oxide (TiO2) layer using the photocatalyst coating agent, the following two coating methods were examined.

[0021] (1) Spray coating Spherical glass beads or spherical quartz glass beads with a particle size of 5 mm were spread out in a petri dish (inner diameter: 5.2 cm), and the weight was measured. Next, the glass beads were transferred to the tea-containing part of a commercially available tea strainer (wire mesh part: approximately 25 mesh to 1 mm width), and the undiluted solution of a titanium oxide-containing coating agent (hereinafter simply referred to as the coating agent) was sprayed and applied to the entire glass beads without dilution using an airbrush (manufactured by VENTCY, Rechargeable Airbrush, Double Action Set, Automatic Power, Integrated Compressor, nozzle diameter: 0.3 mm). It was confirmed that the coating agent was applied to the entire glass beads, and they were left for at least one day and up to three days until the solvent component in the coating agent completely volatilized and dried. Note that the drying was carried out in the atmosphere of the laboratory in a dark place to avoid the adhesion of dust etc. to the surface of the coating layer. After drying, the above process was repeated a plurality of times to obtain glass beads coated with 1 to 4 layers of the coating agent. The coated glass beads were transferred to another container and immersed in an aqueous solution of 50 ppm methylene blue (MB) for one day. Since titanium oxide has the property of adsorbing methylene blue, the concentration of the methylene blue aqueous solution will be reduced without photocatalytic decomposition. Therefore, in this example, the external factors were excluded by immersing the coated beads in the methylene blue aqueous solution in advance.

[0022] (2) Impregnation Coating Similar to the spray coating in (1), spherical glass beads or spherical quartz beads with a particle size of 5 mm were spread out in a petri dish (inner diameter: 5.2 cm), and the weight was measured. Next, the coating agent stock solution in an amount sufficient to immerse all the glass beads was dispensed, and it was left for at least one full day and up to 3 days until the solvent component in the coating agent completely volatilized and dried. Note that the drying was carried out in a dark place in the laboratory atmosphere to avoid the adhesion of dust or the like to the surface of the coating layer. When laminating and applying the coating agent, after the above complete drying, the dispensing and drying of the coating agent were repeated to obtain glass beads coated with 1 to 4 layers by coating. The coated beads were transferred to another container and immersed in an aqueous solution of 50 ppm methylene blue (MB) for one day.

[0023] <Confirmation of methylene blue decomposition ability (photocatalytic activity)> To measure the photocatalytic activity of the glass beads coated by the methods in (1) and (2) above respectively, a decomposition test of methylene blue was conducted instead of the refractory substance. That is, after leaving the coated glass beads standing in the laboratory atmosphere in a dark place for one day, the surface of the glass beads was washed with pure water, the moisture was gently wiped off, and the glass beads were spread out in a petri dish with an inner diameter of 5.2 cm for measurement so that they formed a single layer. 10 mL of an aqueous solution of 50 ppm methylene blue (MB) was dispensed into the petri dish containing the glass beads, and UV-LED light with a central wavelength of 280 nm was irradiated for 1 hour. The MB aqueous solution after UV-LED light irradiation was dispensed into a glass measuring cell with an optical path length of 1 cm, and the absorbance was measured using an absorptiometer (manufactured by SHIMADZU, model number: UV-1800). MB showed an absorbance peak at wavelengths of 260 to 270 nm, and showed the highest value at a wavelength of 264 nm in all the measurement results. Based on the absorbance of the MB aqueous solution measured in this way, a calibration curve of the MB concentration was created, the MB concentration in the aqueous solution was calculated, and further the decomposition rate (%) of MB was calculated using the following calculation formula. The results are as shown in Figure 3.

Equation

[0024] [Example 2] Confirmation of ultraviolet light transmission when beads coated with a photocatalyst coating agent in 1 layer were stacked in 1 to 3 layers Spherical quartz glass beads impregnated and coated with only 1 layer of the photocatalyst coating agent by the method of Example 1 were immersed in a 50 ppm MB aqueous solution for one day. After one day, the surface of the spherical quartz glass beads was washed with pure water, and the moisture was gently wiped off. The quartz glass beads were spread out in a tall beaker with an inner diameter of 5.2 cm for measurement so that there were 1, 2, and 3 layers respectively. 15 mL of a 50 ppm MB aqueous solution was dispensed into this tall beaker and irradiated with UV-LED light with a wavelength of 270 nm for 10, 20, 30, 40, 50, and 60 minutes respectively. Also, the concentration of the MB aqueous solution after UV-LED light irradiation was measured using an absorptiometer in the same manner as in Example 1. The concentration of MB was calculated from the calibration curve created based on the absorbance measurement, and the changes in the MB concentration and the decomposition rate of MB depending on the irradiation time of the UV-LED light and the number of stacked layers when the quartz glass beads were stacked were determined. The results were as shown in Figure 4 and Tables 1 to 3.

[0025]

Table 1

[0026]

Table 2

[0027]

Table 3

[0028] As is clear from Fig. 4 and Tables 1 to 3, in this experiment, as the number of laminated layers of the photocatalyst-coated quartz glass beads increased from 1, 2, to 3 layers, the MB decomposition rate improved from about 39% - 50% to about 82% - 91%. The increase in the MB decomposition rate according to the number of laminated layers of the photocatalyst-coated quartz glass beads is because ultraviolet light reaches the beads in the lower layer, which can be said to be a surprising effect. That is, in the case of the conventional turbid titanium oxide coating agent, even if the titanium oxide-coated beads are laminated, ultraviolet light does not reach the beads in the lower layer. Therefore, even if several layers of titanium oxide-coated beads are laminated, it is considered that the MB decomposition rate does not change. In addition, since a positive correlation was also observed between the irradiation time of ultraviolet light and the MB decomposition rate, it was also found that the necessary photocatalytic ability can be obtained by adjusting the irradiation time.

[0029] [Example 3] Confirmation of the influence of stirring of the MB aqueous solution on the photocatalytic ability Spherical quartz glass beads impregnated and coated with only one layer of the photocatalyst coating agent by the method of Example 1 were immersed in a 50 ppm MB aqueous solution for one day. After one day, the surface of the quartz glass beads was washed with pure water, the moisture was gently wiped off, and the metal cage was filled with quartz glass beads so that there was one layer. Next, the metal cage together with the quartz glass beads was placed in a 200 mL beaker with an inner diameter of 5.2 cm for measurement, which had a stirrer bar placed in it in advance. 80 mL of a 50 ppm MB aqueous solution was dispensed, and it was placed on a magnetic stirrer (manufactured by Sansho, SR-100). While stirring the MB aqueous solution at about 500 rpm, UV-LED light with a wavelength of 270 nm was irradiated for 10, 30, and 60 minutes respectively. The concentration of the MB aqueous solution after UV-LED light irradiation was measured using an absorptiometer in the same manner as in Example 1. The concentration of MB was calculated from the calibration curve created based on the absorbance measurement, and the changes in the MB concentration and the MB decomposition rate according to the irradiation time of the UV-LED light and the number of laminated layers of the beads were determined. In addition, as a control group, a group irradiated with UV-LED light in a static state without stirring by a magnetic stirrer was prepared. The results were as shown in Fig. 5.

[0030] As is clear from Fig. 5, in the experimental group where UV-LED light was irradiated while stirring the MB solution, the MB decomposition rate was significantly improved. This is considered to be the result of the improvement in the decomposition efficiency due to the diffusion and contact of the photocatalyst on the surface of the quartz glass beads with the unreacted MB molecules on the catalyst surface. That is, since actual water treatment is carried out under the flow of sewage and water to be treated, it is considered that the improvement of mass transfer mobility is effective for the decomposition of pollutants and hardly decomposable substances in water. From the above experimental results, the usefulness of the transparent or translucent photocatalyst coating agent of the present invention became clear.

Industrial Applicability

[0031] The photocatalyst coating agent of the present invention and the beads coated therewith are useful in the field of water treatment devices, particularly water treatment devices for treating hardly decomposable substances.

Explanation of Signs

[0032] 1…Ultraviolet treatment tank 2…Ultraviolet lamp 3…Flow path 4…Flange 5…Inflow pipe 6…Discharge pipe 7…Water to be treated 8…Treated water 9…Pump 10…Signal line 11…Water treatment purification means 12…Control panel 13…Sleeve wiping system 14…Hardly decomposable substance treatment device 15…Water treatment device casing 16…Titanium oxide (TiO2) coated beads 17…Ultraviolet lamp 18…Ultraviolet lamp 19…Lamp protection tube 20…TiO2 coated beads

Claims

Claim 1 A water treatment apparatus comprising an ultraviolet irradiator for irradiating ultraviolet rays to water to be treated containing a hardly decomposable substance, wherein beads coated with a transparent or translucent paint containing titanium oxide are arranged around the ultraviolet irradiator, characterized in that the water treatment method. Claim 2 The transparent or translucent paint containing titanium oxide has a transmittance of 50% to 80% with respect to the wavelength range of 340 nm to 380 nm in the vicinity of the band gap when measured by an ultraviolet-visible spectrophotometer, characterized in that the method according to claim 1. Claim 3 The light source of the ultraviolet irradiator includes a mercury ultraviolet lamp, an LED lamp, an excimer lamp or a combination thereof selected from the group consisting of a low-pressure mercury lamp, a medium-pressure mercury lamp, and a high-pressure mercury lamp, characterized in that the method according to claim 1 or 2. Claim 4 The hardly decomposable substance includes one or more selected from the group consisting of 1,4-dioxane, dioxin, nitrosoamine, and phenol, characterized in that the method according to any one of claims 1 to 3. Claim 5 The beads are glass beads containing one or more selected from the group consisting of soda glass, soda-lime glass, quartz glass, crystallized glass, and heat-resistant glass, or beads formed with a transparent or translucent resin layer containing no photocatalytic oxidant with glass as the core, characterized in that the method according to any one of claims 1 to 4. Claim 6 Beads coated with a transparent or translucent paint containing titanium oxide, characterized in that they are used in a water treatment apparatus containing a hardly decomposable substance. Claim 7 A water treatment apparatus comprising an ultraviolet irradiator for irradiating ultraviolet rays to water to be treated containing a hardly decomposable substance, and beads coated with a transparent or translucent paint containing titanium oxide are arranged around the ultraviolet irradiator, characterized in that the water treatment apparatus.

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