JPH11156352A - Method and apparatus for treatment of water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat water efficiently by restraining photorectivation of microorganisms while defects of ultraviolet disinfecting and phtocatalytic disinfection are compensated as a disinfecting method in place of a chlorine disinfection method. SOLUTION: When water to be treated is irradiated with ultraviolet radiation from ultraviolet lamp 2, a photoreactivation phenomenon of microorganism is restrained by irradiating cylindrical platy photocatalytic supports 9 to 12 arranged so that a photocatalyst having titanium dioxide, etc., as a main constituent and water to be treated come to be contact with each other simultaneously with ultraviolet radiation. As the ultraviolet lamp 2, a medium pressure or high pressure mercury lamp is preferably used. Thereby, the photoreactivation phenomenon of the microorganisms is restrained by a disinfection effect of free radicals having intensive oxidation force generated with the photocatalyst irradiated with ultraviolet radiation in addition to a direct disinfection effect of ultraviolet radiation, and effective disinfection can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment method for irradiating treated water with ultraviolet rays in the presence of a photocatalyst and disinfecting the water by killing microorganisms contained in the treated water, and a water treatment apparatus used therefor. It is.

[0002]

2. Description of the Related Art Conventionally, chlorination is generally used for disinfection in water treatment. However, there is a problem of chlorine odor due to residual chlorine and an influence on an ecosystem at a discharge destination, and harmful organic chlorine caused by a reaction with organic matter in water. There are issues that need to be examined, such as the problem of compound by-products, the problem of chlorine-resistant microorganisms such as cryptosporidium, and the problem of transporting and storing chlorinating agents in mountainous treatment plants. Development has been attempted (for example, Shinichiro Ogaki (1992), "Recent Trends in Disinfection Technology", Water Works, Vol. 29, No. 3, 71)
(Naokiyuki Miko et al., 1995) "Treatment characteristics and mechanism of ultraviolet disinfection", Monthly Sewer, Vol. 18, No. 6, page 20).

[0003] Disinfection techniques that can replace chlorine include, for example,
There is a UV disinfection method.

When an organism is irradiated with ultraviolet rays, especially ultraviolet rays having a wavelength of about 254 nm, adjacent pyrimidine bases in the deoxyribonucleic acid (DNA) that controls genetic information, in particular,
It is thought that gene expression and DNA replication do not occur normally and eventually die because thymidine bases undergo photocrosslinking and dimerization (for example, Shigeru Ando et al. (199)
4) "Disinfection of sewage and drainage by ultraviolet light", Water and wastewater, Vol. 36, No. 6, p. 27, etc.). However, organisms damaged on DNA by ultraviolet light have a wavelength of 300 n.
It is known that damage is reduced and recovery occurs when receiving visible light or near-ultraviolet light from m to 600 nm (for example, "Biochemical Dictionary", Tokyo Chemical Dojin; Kashimada Koji et al. (1)
995) "Evaluation of light recovery in ultraviolet irradiation water treatment" Journal of Japan Society on Water Environment, Vol. 18, No. 1, p. 44; Koji Tosa et al. (1997) "Inactivation and light recovery of diarrheagenic Escherichia coli by ultraviolet light" Journal of the Environmental Society, Vol. 20, No. 9, 610
page). This phenomenon is called light recovery.

Therefore, when disinfecting with ultraviolet light,
Many microorganisms that seem to have been killed by ultraviolet irradiation will be revived by light recovery when exposed to sunlight after being released, so it has been required to perform sufficient treatment in consideration of light recovery, In the related art, there is a concern that the processing efficiency may be significantly reduced, such as the extension of the ultraviolet irradiation time.

In recent years, attention has been paid to a photocatalyst as a technique for disinfecting a substance different from ultraviolet rays without adding a chemical such as chlorine.

When a photocatalyst represented by a semiconductor catalyst such as titanium dioxide receives light on its surface, a decomposition reaction of water in contact with the surface of the catalyst occurs, and a hydroxyl radical (.OH) having a strong oxidizing power is generated. And superoxide (O
₂ ^-) radical is generated, such as by oxidative decomposition of the compound constituting the living body, it is said to kill (e.g., Shi Matsunaga (1984) "New sterilization method using a semiconductor" chemical and biological, first 22, No. 11, p. 754).

As an example of applying a photocatalyst to wastewater treatment, powder (for example, Japanese Patent Application Laid-Open No. 2-298392;
U.S. Pat. No. 23,680; Japanese Patent Application Laid-Open No. Hei 5-23681; Japanese Patent Application Laid-Open No. Hei 6-134476) are disclosed. There is a problem that separation and recovery of the photocatalyst is very difficult. Separation of photocatalyst
To avoid recovery problems, use floating supports (eg,
JP-A-63-42792; JP-A-6-50234
0, etc.), a magnetic support (for example, JP-A-4-37
No. 1233), a molded article (for example, JP-A-6-134476), a granular carrier (for example, JP-A-8-47687), a porous carrier (for example, JP-A-8-47687). Japanese Patent Application Laid-Open No. 99041;
No. 99789) and use as fillers for fibrous carriers (for example, JP-A-4-141294; JP-A-6-320010) are disclosed. Satisfactory processing efficiency has not been obtained due to poor properties. Furthermore, in order to overcome the problem of poor light transmission due to the filler, a method of coating a light-transmitting support (for example, JP-A-8-257410; JP-A-5-154473) is disclosed. However, practical application is difficult and it has not been implemented yet.

Relying solely on the action of the photocatalyst for killing microorganisms and oxidative decomposition of organic substances in the treated water cannot provide satisfactory results in terms of treatment efficiency. Depending on the species, the elimination of bacteria requires a treatment time of several minutes to several hours using only the action of the photocatalyst (for example, SSBl).
ock etal. (1995) "Chemically enhanced sunlight forki
lling bacteria ", Solar Engineering, Vol.1, p431; M.Bek
boelet (1997) "Photocatalytic bactericidal activity
of TiO ₂ in aqueous suspensions of E.coli ", Water.Sc
i.Tech., Vol.35, p95; Toshiya Watanabe (1995) "Sterilization of microorganisms by photocatalytic reaction and its application", Chemical Industry, December, p. 50; Masaaki Hosomi et al. (1997) "Disinfection effect by ultraviolet light and photocatalyst" Evaluation of the 30th Fall Meeting of the Society of Chemical Engineers, G302). Regarding the oxidative decomposition of organic substances, depending on the type of the compound, a treatment time of about several minutes to several hours is generally required only by the action of the photocatalyst (for example, Katsuhiko Yoshida et al. (1994) "Dioxide by sol-gel method"). Photocatalytic Decomposition of Trichlorethylene in Water Using Titanium Thin Film ”Journal of Japan Society on Water Environment, Vol. 17, No. 5, 32
(4); Akio Iso, et al. (1995) "Eco-friendly Environmental Research (Treatment of Persistent Substances)", Fukushima Prefectural High-Tech Plaza Test Report, 1994, p. 96; PHChen et al. "TiO ₂
photocatalysis to remove the trace organic in drin
king water "Water Supply, Vol.13, p29).

[0010]

SUMMARY OF THE INVENTION The present invention compensates for the disadvantages of conventional UV disinfection and photocatalytic disinfection as an alternative to chlorine disinfection, which has the above-mentioned problems such as the generation of harmful substances, that is, the light of microorganisms. An object of the present invention is to provide an ultraviolet disinfection method utilizing a photocatalyst and a device therefor, which suppresses recovery and enables efficient treatment.

[0011]

The present invention provides the following:
It is as follows.

[0012] In the water treatment method of irradiating the water to be treated with an ultraviolet ray by an ultraviolet ray generating lamp, the water to be treated is irradiated with the ultraviolet light, and at the same time, the ultraviolet light is applied to a photocatalyst carrier arranged so that the photocatalyst and the water to be treated come into contact with each other. A water treatment method characterized by suppressing light recovery of microorganisms by irradiation.

[0013] The above water treatment method, wherein a medium pressure or high pressure mercury lamp is used as the ultraviolet ray generating lamp.

A water treatment apparatus for irradiating treated water with ultraviolet light, comprising: a photocatalyst carrier arranged so that the photocatalyst and the treated water come into contact with each other; and a light source for irradiating the carrier with ultraviolet light. A water treatment apparatus, comprising irradiating treated water simultaneously and / or to the treated water via a photocatalyst and / or to the photocatalyst via the treated water.

The above-mentioned water treatment apparatus, wherein one or both surfaces of a cylindrical or plate-like support is coated with a photocatalyst as the photocatalyst support.

The above-mentioned water treatment apparatus, wherein a photocatalyst containing titanium dioxide as a main component is used as the photocatalyst.

[0017] The water treatment apparatus according to any one of the above-mentioned items, mainly intended for sterilization and disinfection of microorganisms.

The water treatment apparatus according to any one of the above items (1) to (4), wherein a medium pressure or high pressure mercury lamp is used as a light source for irradiating the ultraviolet rays.

As a result of repeated studies on methods that can be used in combination with ultraviolet disinfection among methods of disinfection using an action mechanism different from that of ultraviolet light, when the water to be treated is irradiated with ultraviolet light in the presence of a photocatalyst, the direct The present inventors have found that the disinfection can be performed extremely effectively by the synergistic effect of the terrible killing and the indirect killing by the oxidizing power generated by the photocatalysis, and have completed the present invention. According to the present invention, light recovery that was problematic in disinfection of ultraviolet light alone was suppressed, and the low disinfection efficiency that was a problem in disinfection of photocatalyst alone was overcome,
Extremely effective and efficient water disinfection is possible.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The photocatalyst coated in an ultraviolet irradiation reaction tank is not particularly limited as long as it is a semiconductor material having photocatalytic activity. For example, Ag, Al, As, Ba,
Bi, Cd, Co, Cr, Cu, Fe, Ga, In, M
o, Nb, Ni, Pb, Sb, Se, Si, Sn, S
Any of r, Te, Ti, W, Zn, and Zr, or oxides, sulfides, and phosphides of these metals.

Further, the above-mentioned metal or compound can be used alone, or may be a mixture of two or more kinds.
Considering the use conditions such as the intensity of activity as a photocatalyst and the spectral distribution of a lamp used as a light source, or the ease of immobilization to a support to be coated, the stability of the immobilized film, the durability, etc. Things can be adopted. In general, among the photocatalysts, titanium oxide is preferable in that knowledge on economics, processability, a production method, and physicochemical properties is accumulated.

In order to improve the catalytic activity of the photocatalyst, A
g, Au, Cu, Fe, Mb, Ni, Pd, Pr, R
Metals such as d, Rh, Ru, Sn, V, and Zn, or oxides of these metals may be supported.

Generally, the activity of the photocatalyst is as follows:
It is said that the crystal structure and the specific surface area of the catalyst substance influence. For example, titanium oxide can have two kinds of tetragonal crystal structures, namely, an anatase phase and a rutile phase, and these crystal structures are dependent on the calcination temperature at the time of film production. Phase transition is 600-7
It is said to start in the temperature range of 00 ° C (for example,
Kato Kazumi (1995) "Structural Control of Titanium Oxide Coating Film and Improvement of Photochemical Properties by Chemically Modified Alkoxide Method", Ceramics, Vol. 30, No. 11, 1021
page). Generally, the anatase phase has a higher activity as a photocatalyst than the rutile phase (for example, Katsuhiko Yoshida et al. (1994)
"Photocatalytic degradation of trichlorethylene in water using titanium dioxide thin film by sol-gel method" Journal of Japan Society on Water Environment, 1
7, No. 5, p. 324), it is preferable to use anatase-type titanium oxide, but it is not always necessary to use 100% anatase, and the anatase-type titanium oxide exists to the extent that anatase-type crystal form can be detected. It should just be.

As a method for immobilizing the photocatalyst particles on the support, a known method can be employed. For example, a method in which a sol in which a photocatalytic substance or a precursor thereof is suspended in a solvent such as water, alcohol, or toluene is applied to the surface of a support and fixed, or in order to increase the specific surface area of the coating, A material to which a high molecular organic substance such as polyethylene glycol is added is coated on the surface of the support, dried, and fired.
An immobilization method and the like can be mentioned. As a method of applying the sol to the support, a known coating method, spraying method, and dipping method can be adopted. The support coated with the sol is dried at 150 to 1000 ° C., preferably 300 to
Firing in a heating furnace at 700 ° C. for 30 minutes to 2 hours. In particular, when titanium oxide is used as the photocatalyst, it is preferable to perform calcination at a temperature lower than the phase transition temperature to the rutile phase, and more preferably, to gradually heat from room temperature to the calcination temperature.

The material of the support to be coated with the photocatalyst may be selected according to the ease of coating the photocatalyst substance to be used. However, in order to control the disinfection efficiency, light, especially ultraviolet light, is efficiently used. A transmissive light-transmitting support, preferably quartz glass, is used.

The shape of the support coated with the photocatalyst is not particularly limited as long as it can be easily mounted in the reaction tank of the ultraviolet disinfection apparatus to be mounted and can suppress the pressure loss of flowing water as much as possible. For example, cylindrical, square tubular, plate,
Lattice shape and the like. Further, in order to increase the contact between the water to be treated and the photocatalyst, the shape of the support may be provided with irregularities for the purpose of causing turbulence in flowing water.

The support can be coated with a photocatalyst on one or both sides of the support surface. However, from the viewpoint of disinfection efficiency or economy, the entire surface or a part of the surface which comes into contact with the water to be treated is coated with the photocatalyst. Preferred supports are suitable.

As an ultraviolet disinfection device for mounting a photocatalyst, for example, there is a water channel type internal irradiation type ultraviolet disinfection device as shown in FIGS. 1 (a) and 1 (b). This is a device for immersing an ultraviolet ray generating lamp 2 in the flow path of the water to be treated and irradiating ultraviolet rays from inside the flowing water. The ultraviolet ray generating lamp 2 is inserted in a protective tube 3 for waterproofing.

As a mode for mounting a support coated with a photocatalyst in this apparatus, for example, FIG.
(H). That is, FIG.
As shown in FIGS. 1D and 1E, the surface of the protective tube 3 of the ultraviolet light generating lamp 2 which is in contact with the treated water is coated with the photocatalyst 9 in advance.
In addition to the protective tube 3 as described above, one or both surfaces of the support are coated with a photocatalyst, and are arranged so as to surround the ultraviolet light generating lamp 2 as lattice-shaped supports 10 and 11 assembled in a cylindrical, square cylindrical or well shape. As shown in FIG. 1 (f), (g), a plate-like support 1 in which one or both surfaces of the support is coated with a photocatalyst.
As shown in FIG. 1, a configuration in which the device is disposed vertically or horizontally between the ultraviolet ray generating lamps 2, a configuration in which it is previously supported on the inner wall surface and / or the bottom surface of the ultraviolet radiation reaction tank 7 as shown in FIG. And / or a form in which two or more of these are arranged along the bottom surface as a plate-like carrier 12 or the like. Among the mounting examples, the form in which the protective tube 3 of the ultraviolet ray generating lamp 2 is coated in advance with a photocatalyst can be applied without deteriorating the performance such as hydraulic characteristics of the existing ultraviolet disinfection apparatus. Since the deposition of dirt on the surface can be expected to be reduced by coating the photocatalyst 3 with the photocatalyst 3, cleaning of the protection tube 3 which is indispensable for operation in an existing apparatus becomes unnecessary or its frequency can be reduced. It is preferable for the reason. Alternatively, a plate-shaped carrier coated with a photocatalyst and disposed vertically between the ultraviolet light generating lamps 2 is preferable from the viewpoint of ease of mounting on an existing ultraviolet light disinfection device and easy maintenance.

Further, as an ultraviolet disinfection device for mounting a photocatalyst, for example, a pipeline type external irradiation type ultraviolet disinfection device as shown in FIG. 2 can be mentioned. The water to be treated flows into the apparatus through the inflow port 14, and flows through the water pipe 13 made of an ultraviolet light transmitting material such as quartz glass or fluororesin.
After being irradiated with ultraviolet rays from an ultraviolet ray generating lamp 2 disposed outside the tube, the ultraviolet rays are discharged from an outlet 15. Examples of the form of mounting the photocatalyst on this device include a form in which a photocatalytic coating is applied to the inner wall of the water pipe 13 and a form in which a photocatalyst carrier is inserted inside the water pipe 13.

The light source to be mounted on the apparatus of the present invention is not particularly limited as long as it has an ability to generate ultraviolet rays. For example, a low / medium / high pressure mercury lamp, a germicidal lamp, a black lamp, a xenon lamp, etc. Is mentioned. The mercury lamp exemplified here is an ultraviolet ray generating lamp suitably used for ultraviolet sterilization, and is generally classified into a low pressure, a medium pressure, and a high pressure based on a difference in a mercury vapor pressure filled in a lamp tube. Among them, the low-pressure mercury lamp generates very efficiently ultraviolet rays having a wavelength of about 254 nm, which can directly kill microorganisms. On the other hand, a medium-pressure mercury lamp and a high-pressure mercury lamp have the property of generating ultraviolet light having a wavelength of 400 nm or less that can activate a photocatalyst together with ultraviolet light having a wavelength of about 254 nm. It is more preferred to use.

Operational control factors for effectively using the apparatus of the present invention include suspended solids concentration (SS), ultraviolet transmittance, dissolved oxygen concentration (DO), redox potential ( ORP), the amount of inflow water, and the like. Since a large amount of SS may cause a significant decrease in treatment efficiency due to a decrease in the UV transmittance of the water to be treated, remove it from the influent as much as possible and / or monitor the UV transmittance of the treated water as much as possible. It is desirable to control the amount of inflow water so that a predetermined amount of ultraviolet light can be secured. When DO is increased, ozone is generated by ultraviolet rays and O
₂ ^- due to generation promotion, because it can be expected that further enhance the disinfection effect, or in advance air aerated flowing water to the apparatus, it is desirable or oxygen-enriched. Since the water quality at the time of inflow of the treated water changes every moment, to observe the disinfection effect over time, monitor the ORP in the treated water,
What is necessary is just to feed back to the control of the amount of treated water and the like.

[0033]

EXAMPLES Examples and comparative examples of the present invention will be described.

In the following Examples and Comparative Examples, the effect of accelerating the UV disinfection efficiency by the photocatalyst was confirmed using the small UV disinfection apparatus shown in FIG. This apparatus is a cylindrical reaction vessel in which an ultraviolet ray generating lamp 2 waterproofed by a protective tube 3 made of quartz glass is inserted. One end of the reaction vessel has an inlet 14 for the water to be treated and the other end has a water inlet. An outlet 15 is provided so that the water to be treated flows in one direction in the reaction tank. Furthermore, in order to investigate the effect of the photocatalyst, a cylindrical inner tube 16 carrying the photocatalyst on the inner wall was inserted so as to be in contact with the inner wall of the reaction tank.

[0035]

Example 1 A sol prepared from titanium alkoxide was applied to the inner wall of a glass cylindrical intubation 16, dried at room temperature, heated and fired to form a cylindrical intubation 16 coated with a titania photocatalyst on the inner wall. .

LB medium (1% tryptone, 1% Na
Cl, 0.5% yeast extract), and cultured with shaking overnight at 37 ° C using sterile saline.
After dilution by a factor of 00, a test bacterial solution containing approximately 10 ⁷ E. coli per ml was prepared.

This test bacterium solution was flowed into the reaction tank from the inflow port 14 of the apparatus shown in FIG. 3A by a water flow pump, and treated water was recovered at the outflow port 15 of the apparatus. UV generating lamp 2
, A 400 W high-pressure mercury lamp was used. The irradiation intensity of the ultraviolet light having a wavelength of 254 nm transmitted through the quartz glass protective tube 3 at the position corresponding to the distance between the cylindrical intubation tube 16 inserted in the reaction tank and the ultraviolet light generating lamp 2 was measured by the US Spectronic.
s Corporation UV intensity meter model DS-254E
It measured using.

By changing the inflow rate into the reaction tank in various ways, the samples irradiated with ultraviolet rays with different ultraviolet irradiation doses on the test bacterial solution were transferred to two glass test tubes, respectively.
One was allowed to stand in a dark place, and the other was irradiated with visible light using a 15 W white fluorescent lamp for 60 minutes to recover the light. After UV irradiation,
The number of viable bacteria in the sample that had been allowed to stand in the dark or irradiated with visible light was determined by the most probable number method (MPN) described in the “Water Water Test Method (1993 version)” or “Sewage Test Method (1984 version)”.
Method). The results are shown in FIG. In the figure, the horizontal axis plots the UV irradiation dose, and the vertical axis plots the survival rate after the treatment. The UV irradiation dose represents the product of the UV irradiation intensity at the wavelength of 254 nm and the residence time of the test bacterial solution in the reaction tank. The survival rate is a value obtained by dividing the number of viable bacteria in a sample irradiated with ultraviolet light or a sample irradiated with visible light after irradiation with ultraviolet light by the number of viable bacteria in the test bacterial solution before the treatment.

As apparent from FIG. 4, 1.5 mW · s
/ Cm ² or more, the survival rate immediately after ultraviolet irradiation (marked with ○ in the figure) attenuated below the detection limit, and the survival rate 60 minutes after visible light irradiation (marked with Δ in the figure) was irradiated with ultraviolet light. Although the value was slightly larger than the survival rate immediately after, the light recovery was slight, and the light recovery did not occur when irradiated with ultraviolet rays of 3 mW · s / cm ² or more. That is, it was shown that when a high-pressure mercury lamp was used as a light source in the present invention, complete disinfection with light recovery suppressed was possible.

[0040]

Comparative Example 1 The same experiment as in Example 1 was performed using a cylindrical intubation 16 having no titanium dioxide photocatalytic coating. The results are shown in FIG.

As apparent from FIG. 5, 1.5 mW · s
Although the survival rate immediately after the irradiation with ultraviolet rays (marked with a circle in the figure) attenuated below the detection limit as in Example 1 due to the irradiation of ultraviolet rays of / cm ² or more, the light recovery was extremely significant 60 minutes after irradiation with visible light. And light recovery was observed even when irradiated with ultraviolet light of 15 mW · s / cm ² or more. That is, when ultraviolet irradiation was performed in the absence of a photocatalyst, it was impossible to completely suppress light recovery within the range examined, so that the water treatment method of the present invention is extremely effective. it is obvious.

[0042]

Example 2 A sol prepared from a titanium alkoxide was applied to the inner wall of a cylindrical inner tube 16 made of glass, dried at room temperature, heated and fired to form a cylindrical inner tube 16 coated with a titania photocatalyst on the inner wall. .

LB medium (1% tryptone, 1% Na
Cl, 0.5% yeast extract), and cultured with shaking overnight at 37 ° C using sterile saline.
After dilution by a factor of 00, a test bacterial solution containing approximately 10 ⁷ E. coli per ml was prepared.

This test bacterium solution was introduced into the reaction tank from the inflow port 14 of the apparatus shown in FIG. 3A by a water flow pump, and treated water was recovered at the outflow port 15 of the apparatus. UV generating lamp 2
, A 15 W low-pressure mercury lamp was used. The irradiation intensity of the ultraviolet light having a wavelength of 254 nm transmitted through the protective tube 3 made of quartz glass at a position corresponding to the distance between the cylindrical insertion tube 16 inserted in the reaction tank and the ultraviolet light generating lamp 2 was measured by Spectronics of the United States.
It measured using the UV intensity meter model DS-254E made from Corporation.

By changing the inflow rate into the reaction tank in various ways, the samples after irradiation with the ultraviolet rays to the test bacterial solution were transferred to two glass test tubes, respectively.
One was allowed to stand in a dark place, and the other was irradiated with visible light using a 15 W white fluorescent lamp for 60 minutes to recover the light. After UV irradiation,
The number of viable bacteria in the sample that had been allowed to stand in the dark or irradiated with visible light was determined by the most probable number method (MPN) described in the “Water Water Test Method (1993 version)” or “Sewage Test Method (1984 version)”.
Method). The results are shown in FIG. In the figure, the horizontal axis plots the UV irradiation dose, and the vertical axis plots the survival rate after the treatment. The ultraviolet irradiation dose represents the product of the ultraviolet irradiation intensity at the wavelength of 254 nm and the residence time of the test bacterial solution in the reaction tank. The survival rate is a value obtained by dividing the number of viable bacteria in a sample irradiated with ultraviolet light or a sample irradiated with visible light after irradiation with ultraviolet light by the number of viable bacteria in the test bacterial solution before the treatment.

As is clear from FIG. 6, 8 mW · s / c
by m ² or more ultraviolet radiation, survival rate after UV irradiation (figure ○ mark) has been attenuated below the detection limit, the survival rate after visible light irradiation for 60 minutes (in the drawing ■ marks) is two orders of magnitude Light recovery was slightly observed. However, when the present embodiment using a low-pressure mercury lamp as a light source and the first embodiment using a high-pressure mercury lamp as a light source are compared, the first embodiment has a higher disinfection effect. This is because the two embodiments merely compare the light intensity at the wavelength of 254 nm, but when the light intensity at the wavelength of 254 nm is constant between the low-pressure mercury lamp and the high-pressure mercury lamp, the activity of the photocatalyst is increased. 400nm effective for
Comparing the sum of the light intensities in the entire wavelength range below, it is considered that this is due to the fact that there are more high pressure mercury lamps than low pressure mercury lamps. It is considered that the use of a mercury lamp enables sterilization that is not inferior to a high-pressure mercury lamp.

[0047]

Comparative Example 2 The same experiment as in Example 2 was conducted using a cylindrical intubation 16 having no titanium dioxide photocatalytic coating. The results are shown in FIG.

As is clear from FIG. 7, 8 mW · s / c
The survival rate immediately after the ultraviolet irradiation (marked with a circle in the figure) attenuated below the detection limit in the same manner as in Example 2 due to the ultraviolet irradiation of m ² or more, but survived 60 minutes after irradiation with visible light (in the figure). ■ mark)
Increased by 3 to 4 digits, and light recovery was remarkably observed. 15m
Significant light recovery was observed even when irradiated with ultraviolet light of W · s / cm ² or more. Since the degree of light recovery in Comparative Example 2 was approximately one to two orders of magnitude higher than in Example 2, it is clear that the present invention has an effect of suppressing light recovery even when a low-pressure mercury lamp is used as a light source. is there.

[0049]

According to the present invention, the light recovery phenomenon which has been a problem in the disinfection method using ultraviolet rays is almost completely suppressed,
It can be disinfected very effectively. In addition, practical use of photocatalyst alone was difficult due to low disinfection effect,
The present invention can be effectively disinfected by acting in synergy with the disinfection effect of ultraviolet rays by combining with the ultraviolet ray disinfection.

The water treatment apparatus of the present invention not only kills microorganisms but also decomposes organic substances in the water to be treated, ie,
It can be expected to greatly reduce OD (chemical oxygen demand) and BOD (biochemical oxygen demand) and to decompose and remove trace harmful substances. The water treatment apparatus of the present invention can be put to practical use not only as a new apparatus equipped with a support coated with a photocatalyst in advance, but also as a simple improvement of mounting a support coated with a photocatalyst on an existing apparatus later. can do.

Further, the water treatment method of the present invention is not only an internal irradiation type of UV disinfection in which an ultraviolet ray generating lamp is disposed in the water stream of the water to be treated, but also an external irradiation type which irradiates ultraviolet rays from outside the water to be treated. It can also be applied to UV disinfection. In an external irradiation type device using a light-permeable water passage through which water to be treated flows, the inner wall of the light-permeable pipe may be coated with a photocatalyst, or the support coated with the photocatalyst is immersed in an open channel through which the water to be treated flows. However, it is also possible to irradiate ultraviolet rays from outside.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an internal irradiation type ultraviolet disinfection device and a mounting form of a photocatalyst-coated support thereon.

FIG. 2 is a diagram illustrating an example of an external irradiation type ultraviolet disinfection device.

FIG. 3 is a view showing an ultraviolet disinfection apparatus used in Examples and Comparative Examples.

FIG. 4 is a diagram showing the survival rate of Escherichia coli immediately after ultraviolet irradiation with a high-pressure mercury lamp in the presence of a photocatalyst and the survival rate after light recovery.

FIG. 5 is a diagram showing the survival rate of Escherichia coli immediately after irradiation with ultraviolet light by a high-pressure mercury lamp and the survival rate after light recovery.

FIG. 6 is a diagram showing the survival rate of Escherichia coli immediately after irradiation with ultraviolet light by a low-pressure mercury lamp in the presence of a photocatalyst and the survival rate after light recovery.

FIG. 7 is a graph showing the survival rate of Escherichia coli immediately after irradiation with ultraviolet rays by a low-pressure mercury lamp and the survival rate after light recovery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Water flowing direction 2 Ultraviolet ray generating lamp 3 Protective tube 4 Relay terminal box 5 Power supply panel 6 Water level adjustment valve 7 Ultraviolet irradiation reaction tank 8 Cross section 9 Photocatalyst 10 Carrier 11 Carrier 12 Carrier 13 Water pipe 14 Inlet 15 Outlet 16 Cylindrical intubation 17 Power supply 18 Cross section

Claims (7)

[Claims] 1. A water treatment method in which water to be treated is irradiated with ultraviolet rays by an ultraviolet ray generating lamp, wherein the water to be treated is irradiated with ultraviolet rays, and the photocatalyst and the water to be treated are disposed on a photocatalyst carrier arranged so as to come into contact with the water. A water treatment method comprising irradiating ultraviolet rays to suppress the light recovery phenomenon of microorganisms. 2. The water treatment method according to claim 1, wherein a medium pressure or high pressure mercury lamp is used as the ultraviolet ray generating lamp. 3. A water treatment apparatus for irradiating treated water with ultraviolet light, comprising: a photocatalyst carrier arranged so that the photocatalyst and the treated water are in contact with each other; and a light source for irradiating the carrier with ultraviolet light. A water treatment apparatus, comprising irradiating a photocatalyst and water to be treated simultaneously and / or to water to be treated via a photocatalyst and / or to a photocatalyst via water to be treated. 4. The water treatment apparatus according to claim 3, wherein one or both sides of a cylindrical or plate-shaped support are coated with a photocatalyst as the photocatalyst support. 5. The water treatment apparatus according to claim 3, wherein a photocatalyst containing titanium dioxide as a main component is used as the photocatalyst. 6. The water treatment apparatus according to claim 3, wherein the main purpose is to sterilize and disinfect microorganisms. 7. The water treatment apparatus according to claim 3, wherein a medium pressure or high pressure mercury lamp is used as a light source for irradiating the ultraviolet rays.