JPH10151452A - Sterilization method for water by photocatalyst-ultraviolet ray - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sterilize water such as clean water and sewage effectively using a photocatalyst by controlling the oxidation-reduction potential(ORP) in a treatment tank at a value corresponding to bacteria and viruses to be killed by the quantity of the added photocatalyst. SOLUTION: For example, in the sterilization treatment of colon bacilli in activated sludge treatment water of a sewage treatment plant, while a treatment tank being aerated, a photocatalyst such as titanium dioxide is added to adjust oxidation-reduction potential(ORP) at a prescribed value, and the water is irradiated with ultraviolet rays at prescribed illuminance using a low pressure lamp. Since there exists a correlation between the oxidation-reduction potential(ORP) of the water and the quantity of the added photocatalyst, by controlling the oxidation-reduction potential by the quantity the added photocatalyst, the corresponding illluminance of ultraviolet rays can be determined. The quantity of the photocatalyst to be added and the illuminance of ultraviolet rays can be determined optionally corresponding to the kinds bacteria to be killed, enabling efficient sterilization treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the technical field of water treatment for sterilizing water and purifying underwater contaminants, and more particularly to removing contaminants and fungi in water using a photocatalyst and ultraviolet irradiation. The present invention relates to a method of disinfecting water with a photocatalyst-ultraviolet light for oxidation and / or disinfection.

[0002]

2. Description of the Related Art At present, water is widely used in various industries and households. For example, water is used for water supply, food industry water, washing water, pools, baths, cooling tower water, fish breeding water and the like. As a result, the amount of wastewater used has increased. Since water, such as water and sewage, contains bacteria, viruses, algae, and the like, these have been sterilized and / or oxidized by disinfection to render them harmless.

[0003] Disinfection of water is generally performed by chlorine disinfection using chlorine. However, chlorine disinfection involves problems of chlorine odor and chlorine disinfection by-products of organic chlorides such as trihalomethane.
Alternatively, if chlorinated sewage treatment water is discharged into a river, there is a concern that the chlorine and organic chlorides remaining in the water will have an adverse effect on the fish and shellfish living in the river, thereby affecting the environment.

Therefore, as a disinfection method replacing chlorine disinfection, a disinfection method using a chemical disinfectant such as chloramine, chlorine dioxide, bromine or ozone has come into practical use.

[0005] On the other hand, in recent years, research results on the possibility of carrying out dirt, odor and sterilization by a photocatalyst are described in "Chemical Industry", December 1995 (pp. 9-13 and p. 50-5).
Reported in 4). In this report, when a typical photocatalyst, titanium oxide, is irradiated with light, a hydroxyl radical (OH.) Having extremely large oxidizing power is applied to the catalyst surface.
And superoxide ion (O ²⁻ ) are generated, and oxidative decomposition of organic chlorine compounds that are difficult to decompose by other methods. Also, titanium oxide powder as a photocatalyst is added to a suspension of yeast, Escherichia coli, green algae, etc. It is described that sterilization and algicidal killing can be performed by inputting and irradiating light.

FIG. 1 is a diagram schematically showing a reaction by a photocatalyst. The principle of the sterilization by the photocatalyst is that, as shown in FIG. 1, when the titanium oxide (TiO ₂ ) particles 1 are irradiated with ultraviolet rays (hv), excited electrons (e) are generated in the electronic structure of the titanium oxide.
^- ) And holes (h ⁺ ) as the through holes are generated. Electronic (e
^- ) Reacts with oxygen (O ₂ ) present on the catalyst surface to generate superoxide ions (O ²⁻ ). On the other hand, holes (h
⁺ ) Reacts with water to generate hydroxy radicals (OH.). Hydroxyl radical (OH.) Is considered to have strong oxidizing power and attack and destroy enzymes and coenzymes in the cell membrane of bacteria 2 to kill the bacteria.

FIG. 2 shows the results of a test in which Escherichia coli was sterilized by suspending titanium oxide powder as a photocatalyst. E. coli solution was adjusted number of E. coli in 10 ⁵ cells / ml in pure water placed in a beaker, and suspended it to titanium oxide powder, wavelength 36
When a fluorescent lamp containing a large amount of ultraviolet light near 0 nm is irradiated, as shown in FIG. 2, the number of viable bacteria almost disappears in about 60 minutes, and sterilization is performed. However, it can be seen that the decrease in the number of viable bacteria is small without irradiation.

[0008] A problem in sterilizing treatment using a photocatalyst is that sterilization efficiency is low. That is, the light energy incident on the photocatalyst is usually converted to chemical energy necessary for sterilization by only a few percent or less, and the rest becomes heat. In addition, the effective amount of titanium oxide, which is a photocatalyst, is unknown, and if it is intended to be applied in a fluidized bed,
There is a problem that it is very difficult to recover and separate the photocatalyst from the fine particles. For this reason, photocatalysts have been put into practical use by forming a titanium oxide thin film on the tile surface and using it as a bactericidal tile, or by forming a titanium oxide thin film on hollow glass beads. It is known that these glass beads are used for techniques such as floating the water on water to decompose crude oil spilled to the sea.However, the use of photocatalysts for disinfection of water is difficult because of its practical application. Not implemented.

[0009] In recent years, a method of disinfecting water without using a chemical disinfectant, which has been put to practical use in recent years, is a disinfection method using ultraviolet rays. The advantages of UV disinfection without the use of a chemical disinfectant are the relatively simple equipment, the absence of residual substances and the difficulty of producing by-products. Therefore, since chlorine does not remain in water as in the case of chlorination, even if the treated water is directly discharged into a river, the fish and shellfish living in the river are not affected at all. UV sterilization is effective against Escherichia coli, general bacteria, mold, yeast, viruses, etc., and unlike the chemical disinfectant, even if the UV irradiation dose exceeds the design value, there is no problem of excessive injection, and operation management is easy. There is also an advantage that it is.

[0010] The principle of ultraviolet sterilization is that ultraviolet rays are 100 to 3
It is a kind of light having a wavelength of 80 nm (nanometer),
Among them, the wavelength of 253.7 nm is most easily absorbed by DNA (deoxyribonucleic acid) of bacteria, viruses, algae, etc., and the absorbed ultraviolet rays impair the DNA necessary for maintaining life and transmitting genetic information, thereby hindering regeneration. It is believed to kill.

[0011] However, there are various issues to be studied in order to effectively utilize ultraviolet sterilization. For example,
When ultraviolet absorbing substances or contaminants are present in water, the irradiation efficiency of ultraviolet rays is deteriorated, and there is a drawback that ultraviolet rays cannot reach pathogenic microorganisms.

It is 310 for pathogenic microorganisms etc.
When irradiated with visible light or near ultraviolet light of ~ 490 nm,
Pathogenic microorganisms have the disadvantage that the damage is recovered by the light recovery ability by the action of the light recovery enzyme. That is, as shown in FIG. 3, Escherichia coli sterilized by ultraviolet irradiation recovers light by visible light. This light recovery phenomenon is well known, and it is considered that some bacteria recover light when exposed to sunlight in the discharged water after disinfection by ultraviolet sterilization. Further, there is a drawback that ultraviolet irradiation is hindered by dirt formed on the sewage contact surface of the quartz tube protecting the ultraviolet lamp. That is, there are inorganic stains mainly composed of magnesium and calcium, and organic stains mainly composed of oil.

It is considered that by solving these various problems, ultraviolet sterilization can be used effectively.

[0014]

Accordingly, the present invention provides a method of disinfecting water such as water and sewage using a photocatalyst as a disinfection method in which by-products such as chlorine and trihalomethane do not exist in treated water. It is an object of the present invention to provide a sterilization method capable of performing such a method.

[0015]

In order to effectively sterilize using the photocatalyst, it is important that the photocatalyst be irradiated with ultraviolet rays instead of visible light as light energy. Then, the oxidation-reduction potential (OR
P) varies depending on the amount of the photocatalyst added, and it has been found that the ultraviolet irradiance (μW · S / cm ² ) necessary for sterilizing various bacteria can be determined according to the value of the oxidation-reduction potential (ORP). Further, by controlling the value of the oxidation-reduction potential (ORP) in the water treatment tank, it is possible to shorten the ultraviolet irradiation time required for sterilizing various bacteria, and to reduce the phenomenon of light recovery, which is a disadvantage of ultraviolet sterilization. Knowing that it can be prevented, the present inventors completed the method for sterilizing water with photocatalyst-ultraviolet light of the present invention.

The gist of the present invention is as follows.

(1) In a water disinfection method for oxidizing and / or disinfecting pollutants, fungi and the like in treated water by irradiating ultraviolet rays with photocatalyst particles present in the water treatment tank, the amount of the photocatalyst depends on the amount of photocatalyst added. A method for disinfecting water with a photocatalyst-ultraviolet light, wherein an oxidation-reduction potential (ORP) in a treatment tank is controlled to a value corresponding to bacteria and viruses to be disinfected.

(2) Oxidation-reduction potential (ORP) in the processing tank
3. The method for sterilizing water with a photocatalyst-ultraviolet ray as described in 1 above, wherein the value is controlled to a value that can prevent the light recovery phenomenon of the bacteria to be sterilized.

(3) The method for sterilizing water with photocatalyst-ultraviolet light as described in (1) or (2) above, wherein the photocatalyst particles are porous particles.

(4) The photocatalyst particles described above, wherein the surface of a substrate such as glass is coated with a photocatalyst.
Or a method for disinfecting water with a photocatalyst-ultraviolet light according to 2.

(5) The method for sterilizing water with photocatalyst-ultraviolet light as described in any one of (1) to (4) above, wherein the inside of the treatment tank is aerated.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The photocatalytic activity used in the present invention is
Semiconductor materials such as titanium oxide
Titanium oxide is a rutile type belonging to tetragonal system, anatase
There are three types of crystals, zeite and orthorhombic brookite
Among them, in particular, anatase-type titania (TiO 2)
_Two) Is preferred because of its high photoactivity and high bactericidal effect.
Other semiconductor materials can be used. For example, oxidation
As a substance having photoactivity comparable to titanium, titanium
Strontium acid (SrTiO_Three) And potassium niobate
(K_FourNbO₁₇). Other cadmium sulfide
(CdS), potassium tantalate (K TaO_Three), Oxidation
Niobium (Nb_TwoO_Five) And zinc oxide (ZnO).
You.

Ultraviolet rays were irradiated to treated water in which a photocatalyst was added to treated water and treated water to which no photocatalyst was added, and a comparative experiment was conducted on the E. coli bactericidal effect.

As the treated water, activated sludge treated water at a sewage treatment plant was used. Escherichia coli number of 2 × 10 ⁴ cells / ml was present in the treated water, and the irradiation intensity of ultraviolet rays was changed using a medium-pressure ultraviolet lamp, and 0.5 g / l of titanium dioxide was added as a photocatalyst. The treated water in the case of no addition was irradiated with ultraviolet rays to measure the survival rate of Escherichia coli. During ultraviolet irradiation, aeration was performed and the amount of active oxygen in water was 2 mg / l. FIG. 4 shows the results.
As shown in FIG. 4, the same irradiation intensity (mW · S / cm ² )
It can be seen that the germicidal effect of the photocatalyst-ultraviolet method (marked with ▲) according to the present invention, in which the photocatalyst was added, was significantly higher than the case without the photocatalyst (marked with ○). This means that the photocatalyst-ultraviolet method according to the present invention requires 30 to 4 times less ultraviolet light to sterilize Escherichia coli than the ultraviolet method without a photocatalyst.
This means that it can be reduced by 0%.

As described above, when the amount of ultraviolet radiation necessary for sterilizing Escherichia coli was reduced, that is, the reason for shortening the ultraviolet radiation time was investigated, the oxidation-reduction potential (ORP) caused by adding a photocatalyst to the treated water was determined. It is based on the rise, and if the oxidation-reduction potential (ORP) of the treated water is controlled by the amount of the photocatalyst added, the ultraviolet irradiance (μW · S / cm ² ) necessary for sterilizing various bacteria can be determined. I found it.

Therefore, the oxidation-reduction potential (OR
The change in P) was investigated by adding anatase-type titania particles to water as photocatalytic particles. As a result, in the case where no anatase type titania particles were added, +100 mV (Ag / A
gCl), but the oxidation-reduction potential increased in accordance with the amount of the added anatase-type titania particles, and increased to +250 to +300 mV when about 0.5 g / l was added.

As described above, the oxidation-reduction potential (O
Since (RP) is correlated with the amount of photocatalyst added, it can be seen that if the oxidation-reduction potential is controlled by the amount of photocatalyst added, the ultraviolet irradiance (μW · S / cm ² ) can be determined accordingly. Therefore, according to the present invention, the amount of the photocatalyst to be added and the ultraviolet illuminance can be arbitrarily determined according to various bacteria to be sterilized, so that the sterilization can be performed efficiently.

The photocatalyst to be added to the treated water includes photocatalyst particles, porous particles obtained by granulating and sintering photocatalyst particles, and a coating in which the surface of a substrate such as quartz glass or glass is coated with the photocatalyst. Particles can be used.
Quartz glass is most desirable because it transmits ultraviolet light. The photocatalyst can be coated by a CVD method or the like. The use of the porous particles and the coated particles has an advantage that the separation and recovery operations are easier than using the photocatalyst fine particles.

When the inside of the water treatment tank is aerated during the sterilization treatment of water by the photocatalyst-ultraviolet method of the present invention, the dissolved oxygen (DO) in the water treatment tank increases, and the contact between the photocatalyst particles and the treated water is good. Therefore, it is possible to further improve the sterilization efficiency.

Next, an experiment was conducted on the effect of light recovery of Escherichia coli when sterilizing Escherichia coli in water by the photocatalyst-ultraviolet method of the present invention.

As the experimental conditions, in order to sterilize 99% of Escherichia coli, in the case where no photocatalyst was added, a low-pressure lamp was used to irradiate an ultraviolet ray with an ultraviolet illuminance of 7.0 mW · S / cm ^2. In the photocatalyst-ultraviolet method according to the above, the oxidation-reduction potential (ORP) is increased by +2 while performing aeration.
A photocatalyst was added so as to have a voltage of 50 mV or more, and ultraviolet irradiation with an ultraviolet illuminance of 4.5 mW · S / cm ² was performed using a low-pressure lamp. The treated water subjected to the sterilization treatment was irradiated with visible light for 180 minutes, and the effect of light recovery during that time was examined by examining the sterilization rate. The result is shown in FIG. As shown in FIG. 5, a photorecovery phenomenon occurred in the ultraviolet method without the addition of a photocatalyst (conventional method) (circle in the figure), but a photorecovery phenomenon was observed in the photocatalyst-ultraviolet method of the present invention in which a photocatalyst was added. None (● in the figure).

As described above, the light recovery phenomenon, which was difficult to be prevented by the conventional ultraviolet method, can be effectively prevented by the photocatalyst-ultraviolet method of the present invention, and the efficiency of the sterilization treatment has been remarkably improved.

[0033]

An embodiment of the present invention will be described.

Three types of containers each containing Escherichia coli, yeast and bacteriophage in the treated water were prepared. The oxidation-reduction potential (ORP) of the treated water to be sterilized is determined by adding titanium oxide photocatalyst particles to the treated water, whereby ORP = 150 to 200 mV and ORP = 200 to 30 respectively.
0 mV and ORP = 300 to 400 mV were controlled to three kinds of oxidation-reduction potentials. Next, the treated water in the container was irradiated with ultraviolet rays using a low-pressure ultraviolet lamp. UV illuminance (μW ·) required to sterilize various bacteria (but sterilization rate 99%)
S / cm ² ). The results are as shown in Table 1 below.

[0035]

[Table 1] As shown in Table 1, the ultraviolet illuminance required for sterilizing various bacteria changes according to the value of the oxidation-reduction potential, and the higher the oxidation-reduction potential, the lower the ultraviolet illuminance. Then, in order to sterilize a specific bacterium, the oxidation-reduction potential is controlled to a specific value, and if the ultraviolet irradiance corresponding to the oxidation-reduction potential is selected and irradiated with ultraviolet light, the intended bacterium can be sterilized. . For this reason, according to the photocatalyst-ultraviolet method of the present invention, it is possible to easily determine the amount of the photocatalyst to be added for sterilizing various bacteria and the amount of the ultraviolet irradiation. In addition, the photocatalyst-ultraviolet method of the present invention to which a photocatalyst is added can significantly reduce the ultraviolet illuminance as compared with the conventional ultraviolet method without adding the photocatalyst particles.

[0036]

According to the present invention, the oxidation-reduction potential (ORP) of treated water is controlled by the amount of photocatalyst added, and the ultraviolet illuminance (μW) is determined based on the value of the oxidation-reduction potential (ORP).
S / cm ² ), so that the amount of the photocatalyst to be added and the UV illuminance can be easily determined to be appropriate values according to various kinds of bacteria to be sterilized, and efficient sterilization treatment Can be performed. In addition, since a photocatalyst is used, sterilization can be performed with a smaller amount of ultraviolet irradiation than in the conventional ultraviolet method, and the light recovery phenomenon, which is a disadvantage of the ultraviolet method, can be prevented.

Although the photocatalyst alone was not practically applicable to disinfection of water because of its low sterilization efficiency, according to the present invention, it is possible to sterilize bacteria, viruses and the like which are resistant to ultraviolet rays. Therefore, the sterilization phenomenon of the photocatalyst can be sufficiently exhibited, and high sterilization efficiency can be obtained.

It should be noted that, without increasing the amount of ultraviolet irradiation, the ORP
Can be controlled to a predetermined value or more, in addition to increasing the amount of the photocatalyst, the following measures can be considered.

(1) ORP is increased by controlling oxygen concentration or oxygen supply amount using oxygen or oxygen-enriched air instead of air for aeration.

(2) ORP is increased by controlling supply amount or supply concentration using ozone (O ₃ ) instead of air for aeration.

(3) The ORP is increased by controlling the concentration and amount of the chemical oxidizing agent such as hydrogen peroxide (H ₂ O ₂ ).

Both methods promote the generation of OH.
P increases and the bactericidal effect increases. However, there is a problem that equipment costs and running costs increase.

The control of ORP by controlling the amount of photocatalyst porous particles or photocatalyst-coated particles can be solved only by initial charging, so that the running cost is the lowest and the processing performance is stable. is there.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a reaction by a photocatalyst.

FIG. 2 is a view showing test results obtained by suspending titanium oxide powder as a photocatalyst and sterilizing Escherichia coli.

FIG. 3 is a graph showing the E. coli survival rate and the maximum recovery value immediately after ultraviolet irradiation.

FIG. 4 is a view showing a sterilizing effect when a photocatalyst is added.

FIG. 5 is a diagram showing the effect of the light recovery phenomenon according to the present invention.

[Explanation of symbols]

1 TiO ₂ particles 2 bacteria

Claims (5)

[Claims] 1. A method of disinfecting water for oxidizing and / or disinfecting pollutants, fungi and the like in treated water by irradiating ultraviolet rays with photocatalytic particles present in a water treatment tank,
The redox potential (OR
A method for disinfecting water by photocatalyst-ultraviolet light, wherein P) is controlled to a value corresponding to bacteria and viruses to be disinfected. 2. The method for sterilizing water with a photocatalyst and ultraviolet rays according to claim 1, wherein the oxidation-reduction potential (ORP) in the treatment tank is controlled to a value that can prevent the light recovery phenomenon of the bacteria to be sterilized. . 3. The method according to claim 1, wherein the photocatalyst particles are porous particles. 4. The method for sterilizing water with photocatalyst-ultraviolet light according to claim 1, wherein the photocatalyst particles are particles obtained by coating the surface of a substrate such as glass with a photocatalyst. 5. The photocatalyst according to claim 1, wherein the inside of the processing tank is aerated.
Disinfection method of water by ultraviolet rays.