JP2008302308A - Photocatalyst and method for manufacturing thereof, method and apparatus for water treatment using thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocatalyst capable for remarkably improving photocatalyst activity, its production method, a water treatment method, and apparatus using the photocatalyst. <P>SOLUTION: The photocatalyst consists of a silver chloride deposited on a material containing a conductive substance and the silver chloride is preferable to be produced by depositing silver on the material containing a conductive substance and carrying out electrooxidation. Further, the silver chloride produced in such a manner is separated from the material containing the conductive substance to obtain the photocatalyst and the production method is carried out by at first depositing silver on the material containing the conductive substance and next forming silver chloride from silver by electrooxidation. Further, in a water treatment method for removing a harmful substance from water containing the harmful substance, the photocatalyst is brought into contact with water containing the harmful substance. The apparatus for removing the harmful substance from water containing the harmful substance has an introduction inlet 1 for water containing the harmful substance and a wastewater port 4, the photocatalyst 2 in the inside, and a light source 3 for irradiating the photocatalyst with light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a photocatalyst exhibiting photocatalytic activity with high efficiency, a method for producing the photocatalyst, and a water treatment method and apparatus using the photocatalyst.
The photocatalyst of the present invention can be applied to water treatment of industrial wastewater, municipal sewage, tap water, biomass and the like in various chemical processes such as pharmaceuticals, pharmaceuticals, agricultural chemicals, foods, and semiconductors. In particular, harmful substances are oxidizable pollutants such as organic substances (organic substances), oxidation treatment of water containing ammonia, detoxification (low molecular weight or conversion to stable substances), pests such as bacteria and protozoa The present invention relates to a method and an apparatus for sterilization (inactivation) of water containing algae, killing algae, decolorization, and deodorization.

Table 1 shows examples of applications of the present invention and application fields corresponding to the applications.

In recent years, awareness of environmental pollution has been increasing. In particular, recognition of water (treatment) is high, and the emergence of water treatment methods that can obtain more effective and high-quality water quality is expected.
As a conventional water treatment method, treatment of an organic substance (organic matter) in water will be described.
Conventionally, an activated carbon method, an ozone method, an electrolysis method, and the like are known as methods for removing organic substances in water. However, these processing methods have the following problems.
The activated carbon method has a relatively high treatment efficiency, but the regeneration of the activated carbon is complicated and expensive.
The ozone method has relatively good effects of decolorization, deodorization and decomposition as organic substance treatment, and other sterilization effects exist, but ozone is expensive to produce, and unused ozone is used as waste ozone. Because it is released, it is necessary to take measures against secondary pollution to the environment of leaked waste ozone.
Although the electrolysis method has a relatively good decolorization efficiency as an organic matter treatment, it cannot provide a sufficient effect for organic matter decomposition. In addition, the cost is high.

On the other hand, the present inventors have proposed a novel method using a photocatalyst (eg, Japanese Patent Publication No. 2-55117, Japanese Patent No. 3202863).
Japanese Patent Publication No. 2-55117 aims to accelerate the reaction by blowing air or oxygen in the presence of a peroxide such as hydrogen peroxide.
Japanese Patent No. 3202863 promotes the reaction by making the photocatalyst into a linear article such as a fiber to increase the area of the photocatalyst.
There is also a proposal for promoting silver sterilization by supporting silver on a photocatalyst material (Japanese Patent Laid-Open No. 10-235346).
All of these photocatalysts use titanium oxide (TiO ₂ ).

These conventional photocatalyst methods are effective depending on the application and required performance, but the method using titanium oxide as a photocatalyst is in principle performance when it is in an oxygen-deficient state (a state where the oxygen concentration in water is reduced). Will fall. Therefore, in such a case, a phenomenon in which the quality of the treated water is deteriorated due to a decrease in water treatment efficiency or instability is caused.
Under such circumstances, even if the treated water (load) conditions change, such as sudden hypoxia, stabilization of long-term performance (maintaining performance above a certain level for a long time), facilitation of maintenance management, etc. The appearance of a more practically effective method was expected depending on the application and required performance.
Japanese Examined Patent Publication No. 2-55117 Japanese Patent No. 3202863 JP 10-235346 A

  The present invention relates to the development of a more effective (high performance) photocatalyst in view of the above prior art, and a photocatalyst capable of remarkably improving the photocatalytic activity by supporting silver chloride on a base material and a method for producing the same. Another object of the present invention is to provide a water treatment method and apparatus that can remove harmful pollutants in water with high efficiency.

In order to solve the above problems, the present invention provides a photocatalyst characterized in that silver chloride is supported on a material containing a conductive substance.
In the photocatalyst, silver chloride is preferably generated by electrolytic oxidation by supporting silver on a material containing a conductive substance.
In the present invention, the photocatalyst is characterized in that silver chloride obtained by carrying out electrolytic oxidation by supporting silver on a material containing a conductive substance is separated from the material containing the conductive substance. It is what.
Furthermore, in the present invention, in the method for producing a photocatalyst, the photocatalyst is produced by first supporting silver on a material containing a conductive substance and then forming silver chloride from the silver by electrolytic oxidation. This is a manufacturing method.
In the method for producing a photocatalyst, the support of silver on a material containing a conductive substance can be performed by electrolytic reduction deposition.

Further, in the present invention, in a water treatment method for removing harmful substances from water containing harmful substances, water containing harmful substances is brought into contact with any one of the photocatalysts under light irradiation. It is a method.
In the water treatment method, the water containing a harmful substance may be in an oxygen-poor state.
Further, according to the present invention, an apparatus for removing harmful substances from water containing harmful substances has an inlet and a water outlet for water containing the harmful substances, and includes any one of the above photocatalysts and light to the photocatalyst. The water treatment apparatus is characterized by having a light source for irradiation.

According to the present invention, the following effects can be achieved.
(1) A highly active AgCl photocatalyst was produced by carrying silver on the surface of a material containing a conductive substance.
(2) The photocatalyst can be formed by supporting silver on a material containing at least a conductive substance and then performing electrolytic oxidation.
(3) The photocatalyst exhibits high activity even in an oxygen-poor state such that the oxygen concentration in water is, for example, 1 to 3 mg / L or less.
(4) Since this photocatalyst exhibits highly active oxidizing power even in anoxic conditions from the concentration range of oxygen content in the natural state (normal state), oxidation, disinfection (deactivation), decolorization, deodorization, etc. It was applicable to a wide range of uses and fields of use.
(5) From the above, the practicality of the photocatalytic technology has further increased.

The present invention has been invented based on the following four findings.
(1) When the photocatalyst is irradiated with light, a hole (h ⁺ ) is generated in the valence band and an electron (e ⁻ ) is generated in the conduction band by photoexcitation, and this hole has a strong oxidizing power. It is useful as an environmental pollution purification material because it can decompose and detoxify various oxidizable contaminants. For example, when the photocatalyst is titanium oxide (TiO ₂ ), holes generated on the surface of TiO ₂ are about +3.0 V (vs. NHE), which is 1.5 times the oxidizing power of ozone. It is. (Ebara Times, No. 180, p.3-14, 1998)
(2) As a conventional photocatalyst, for example, to increase the efficiency of the photocatalytic reaction of TiO ₂ , it is important to prevent recombination of holes and electrons (acceleration of charge separation). Conventionally, for this purpose, oxygen present around the photocatalyst as an electron acceptor (electron acceptor) performs this function, but electron transfer by oxygen is not always sufficient (electron transfer by oxygen is slow). That is, the use of oxygen for the electron acceptor becomes the rate-determining factor of the photocatalytic reaction activity so far, and reduces the overall rate of the photocatalytic reaction.
Thus, since TiO ₂ of the conventional photocatalyst must coexist with oxygen, the photocatalyst cannot be used in principle in an oxygen-poor state, and therefore there is a limit in application development.

(3) above to a material containing a conductive material (eg: SnO ₂₎ silver chloride (AgCl) supported on (AgCl / SnO ₂₎ and the light irradiation, showing a high activity (marked photocatalysis). Further, when particulate AgCl is separated from the AgCl / SnO ₂ and light is irradiated to the particulate AgCl in the same manner, high activity is exhibited. Although details of this reaction mechanism are under intensive study and details are unknown, active species (eg, OH radicals) are generated by holes generated by photoexcitation of AgCl due to light irradiation on the AgCl surface, It is considered to show activity. This photocatalyst has the property of exhibiting high activity even in an oxygen-free state where oxygen is not present or in a state where oxygen is low (anoxic state).
(4) a photocatalyst of the present invention (Example: AgCl / SnO _2, particulate AgCl) is the material (SnO ₂₎ surface containing a conductive material, first by supporting Ag, then, the Ag in KCl electrolyte solution Practically effective AgCl can be formed by electrolytic oxidation.

The photocatalyst of the present invention has (1) a material containing a conductive substance (eg SnO ₂ ) on which AgCl (particulate) is supported, or (2) the AgCl (particulate) contains a conductive substance. including material (eg: SnO ₂₎ has been separated (desorbed) from photocatalyst exerts an oxidizing effect giving its energy by light absorption in the other reactants (object to be processed), various chemical Reactions such as oxidation reaction, sterilization (inactivation), decolorization reaction, and deodorization reaction are induced to decompose and remove harmful substances (pollutants) in water (detoxification: low molecular weight or conversion to stable substances).

Next, the present invention will be described in detail.
AgCl support material (base material)
The base material may be any material as long as it can support AgCl which is the photocatalyst of the present invention. As such a material, any material containing a conductive substance may be used, and a known conductive substance or a non-conductive substance containing a conductive substance can be used. The significance of using a material containing a conductive substance which is a feature of the present invention is that the photocatalyst of the present invention can be easily produced. That is, the photocatalyst can be easily manufactured by using the material as an electrode. For example, AgCl can be effectively formed by first depositing silver (Ag) on the surface of the material by electrolytic reduction and then performing electrolytic oxidation.

A more preferable material of the base material is a conductive substance (effective as an electrode). The material is practically effective because it can be supported by Ag and formed by electrolysis of AgCl through a series of operations. That is, since AgCl can be produced more easily and effectively, it can be used more suitably.
This material may be a metal oxide such as SnO ₂ , Al, W, stainless steel, zinc, or a carbon-based material such as metal or carbon black.
The base material has a plate shape, a net shape, a sheet shape, a tube shape, a column shape, a rod shape (bar shape), a linear shape, a fiber shape, a filter shape, a granular shape, and a spherical shape.
Selection of the material type and shape of the base material includes the following Ag loading (addition) method and conditions, AgCl formation method and conditions, application destination (use) of the photocatalyst, light source type, device shape, scale, required specifications, etc. You can make an appropriate decision after review.

AgCl formation
In the photocatalyst AgCl of the present invention, Ag is first supported (added) on a material containing a conductive substance, and then AgCl is formed from the Ag.
(A) Ag loading The Ag loading (addition) method may be any method as long as AgCl can be formed by loading on a material containing a conductive substance. Any material can be used as long as it can form AgCl that exhibits the photocatalytic performance.
Such a method of supporting Ag includes: (a) a method of depositing Ag carrier crystal fine particles on a material containing a conductive substance by electrolytic reduction; and (b) a solution containing a silver compound containing at least a conductive substance. There is a method in which a material is impregnated and added by heat treatment.

Among the above-mentioned supporting methods, the method (a) is practically effective since a conductive material such as SnO ₂ is used as a base material, so that Ag supporting by electrolytic method and subsequent formation of AgCl can be performed by a series of operations. Is.
That is, since AgCl can be produced more easily and effectively, it can be used more suitably.
The supporting form is not particularly limited as long as AgCl can be formed from the supporting Ag, and the Ag particle diameter is 0.1 μm to 500 μm, preferably 1 μm to 50 μm, more preferably 1 μm to 4 μm.

(B) formation of AgCl AgCl is a Ag, Cl ^- effectively formed by electrolytic oxidation in an electrolytic solution containing.
This electrolytic solution includes KCl. When electrolytic oxidation is performed at a concentration of 0.01 M to 10 M KCl, preferably 0.1 M to 1 M KCl, the generation of AgCl from Ag becomes effective. A highly active photocatalyst formed on the material is produced.

The photocatalyst of the present invention includes (1) a material containing a conductive substance formed with AgCl (eg, AgCl / SnO ₂ ), (2) a material obtained by detaching particulate AgCl from the above (1), Can be used.
These photocatalysts can be determined by considering the advantages (characteristics) of each photocatalyst based on the application destination (use) of the photocatalyst, the device shape and operating conditions, the type of light source, method of use, scale, and required specifications. I can do it. The advantages (characteristics) of each photocatalyst are shown below.
A material in which AgCl is formed on a material containing a conductive substance (eg, AgCl / SnO ₂ ) is, as described above, a plate shape, a net shape, a sheet shape, a tube shape, a column shape, a rod shape (bar shape), a linear shape, Since various shapes such as a fiber shape and a filter shape can be formed, the photocatalytic reaction device can be fixed to any place. As a result, (a) the degree of freedom in designing the photocatalytic reaction device is expanded, and (b) there is an advantage that maintenance and maintenance of the device are facilitated.

  On the other hand, particulate AgCl has a small apparent specific gravity and a large surface area. Thereby, in a photocatalytic reaction apparatus, since it can be used as a floating state in to-be-processed water, there exists an advantage which can perform the light irradiation to a photocatalyst, and the contact of a photocatalyst and a to-be-processed object more effectively. That is, the particulate AgCl can be used in a floating state as shown in FIGS. In this case, the floating state of the photocatalyst can be easily obtained by using microbubbles as bubbles by introducing air, and the floating state can be easily obtained. Further, the contact efficiency between the object to be processed and the surface of the photocatalyst by the microbubbles can be improved (average residence time can be reduced). (Increase) effect can be processed effectively. That is, the particulate AgCl is in a form in which the particulate AgCl can be suitably used when used under air bubbles by air supply (introduction) as shown in FIGS.

Usually, the form of a photocatalyst in which AgCl is formed on a material containing a conductive substance (eg, AgCl / SnO ₂ ) is easy to handle, maintain, and maintain the degree of freedom in designing the reactor. It is preferable from the point.
The suitable particle size of AgCl can be selected from the presence or absence of the base material of the photocatalyst, its shape, application destination (use), device shape, operating conditions, scale, required specifications, etc. The particle size is controlled by the electrolytic oxidation conditions Is possible.
The particle size is 0.1 μm to 500 μm, preferably 1 μm to 50 μm, more preferably 1 μm to 5 μm.
Suitable electrolytic oxidation conditions, concentration, electrolytic current, and formation time can be appropriately determined by appropriately conducting preliminary tests depending on the form of AgCl used.

Light source The light source is not limited as long as it can exhibit photocatalytic action when irradiated to the photocatalyst, such as a discharge lamp such as a mercury lamp or a xenon lamp, a fluorescent lamp such as a germicidal lamp, a black light or a fluorescent lamp, or a filament lamp such as an incandescent lamp. , Artificial light sources such as light emitting diodes (LEDs) and laser light, sunlight, and the like can be used, and can be used by appropriately selecting the application destination (use), apparatus shape, apparatus scale, photocatalyst type, required specifications, and the like.
For example, for sterilization applications, a sterilization lamp or a low-pressure mercury lamp is preferred. This is because the sterilization effect by the sterilization line from the germicidal lamp is added to the photocatalytic action, and ozone is generated by using the low-pressure mercury lamp, so that the bactericidal action by the ozone is added and a synergistic effect is obtained. It can be selected and used, and is preferable for sterilization and deodorizing applications.

In general, the treated water contains an oxygen concentration of about 8.8 mg / L (20 ° C., atmospheric pressure) in a natural state (normal state), but the photocatalyst of the present invention has an oxygen concentration of 1 mg / L to 3 mg / L or less in water. It acts similarly even in an anoxic state and is a major feature of the present invention.
The oxygen concentration is a value at 20 ° C. and atmospheric pressure, and varies depending on temperature, pressure, and water treatment method.
In general, in the aerobic treatment, an oxygen concentration of 1 to 3 mg / L (20 ° C., in the atmosphere) is necessary. However, in the present invention, even in a state where a normal aerobic treatment below the concentration is not possible in principle. I can do it.
The photocatalyst of the present invention exhibits high activity. Although details of this reaction mechanism are under intensive study and details are unknown, it is considered as follows. It is considered that active species (eg, OH radicals) are generated due to holes generated by photoexcitation of AgCl due to light irradiation to AgCl, and show high activity. Since the conduction band of AgCl is at a position considerably higher than the conduction band of titanium oxide (TiO ₂ ), which is known as a conventional photocatalyst, it is considered that the generated protons act effectively as an electron acceptor.

The photocatalyst of the present invention is one in which silver is first supported on a material containing a conductive substance and then produced by electrolytic oxidation. AgCl produced in this way has a small apparent specific gravity in the crystal structure, It is considered that it exhibits high performance as a photocatalyst because it is in the form of particles with a large surface area and high purity.
Here, the light irradiation to AgCl / conductive material has higher performance than particulate AgCl. The reason for this is that when a conductive substance (eg, SnO ₂ ) is used, excited electrons generated by light irradiation to AgCl are efficiently transferred from the conduction band of AgCl to the conductive substance (eg, SnO ₂ ). This is considered to be because holes in the AgCl valence band effectively act on the reaction.

Example 1
Production of photocatalyst; according to the following steps.
(1); preform (SnO ₂₎ supported SnO ₂ of Ag onto immersed in 0.2 M-NaClO ₄ and 0.2 mM-AgClO ₄ solution, introducing Ar from the solution under performs electrolytic reduction ( Ag / SnO ₂ ).
(Counter electrode: −1.0 V is applied for 60 minutes between brushy carbon and working electrode SnO ₂ )
(2); Ag / from SnO ₂ of Ag formed Ag / SnO ₂ of AgCl was immersed in 0.2 M-KCl electrolyte solution, carrying out electrolytic oxidation (AgCl / SnO _2).
(Counter electrode: between brassie carbon and SnO _2, 60 minutes electrolytic oxidation at + 0.9 mA)

Results SEM photograph, particle size distribution and X-ray analysis of photocatalyst (AgCl / SnO ₂ ) In the production of photocatalyst, the surface was examined by SEM photograph observation, X-ray analysis (XRD) and particle size distribution measurement.
FIG. 3 is an SEM photograph of (a): Ag / SnO ₂ and (b): AgCl / SnO ₂ (the photocatalyst of the present invention), and an enlarged view of the AgCl part is shown in the upper right part of (b). . Note that the base of FIG. 3 is SnO ₂ .
FIG. 4 shows the XRD pattern. In FIG. 4, ● represents SnO _2, ○ represents Ag, × represents AgCl, (a) Ag / SnO ₂ , (b) AgCl / SnO ₂ , and (c) AgCl / SnO after one month of use. ₂ .
FIG. 5 shows the particle size distribution of (a): Ag / SnO ₂ and (b): AgCl / SnO ₂ (the photocatalyst of the present invention).
From these photographs, XRD pattern and particle size distribution, 1 μm to 3 μm (average particle size: 1.5 μm) of Ag particles are supported on SnO ₂ by electrolytic reduction, and 1 μm to 4 μm (average particle size) by the following electrolytic oxidation. It was observed that AgCl (diameter: 2.1 μm) was formed on SnO ₂ .
Formation of Ag to AgCl FIG. 6 shows the formation (change amount,%) from Ag to AgCl in the Ag / SnO ₂ . The electrolytic oxidation time is 10 minutes to 180 minutes, and it can be seen from FIG. 6 that 90% (or more) of Ag to AgCl is formed by electrolytic oxidation for 60 minutes or more.

Example 2
FIG. 1 is an example in which water treatment using the photocatalyst of the present invention is applied to treatment of water containing a hardly biodegradable organic substance.
FIG. 1 shows a treatment process of water containing a hardly biodegradable organic substance comprising a photocatalytic reaction step A and a biological treatment step B using the photocatalyst of the present invention.
The photocatalytic reaction step A is carried out by the photocatalytic reaction device of the present invention, and the biological treatment step B is carried out by a biological treatment device.
Treated water 1 containing various organic substances, for example, humin-based COD, agricultural chemicals, organic biodegradable organic substances such as organochlorine compounds, is introduced into the photocatalytic reactor A.
The main structure of the photocatalytic reaction apparatus A includes the photocatalyst 2 and the light source 3 of the present invention shown in FIG. In FIG. 2, reference numeral 4 is treated water (outlet) treated by the photocatalyst 2.
In FIG. 1 and FIG. 2, the same symbols indicate the same meaning.

In the photocatalytic reactor A, the organic matter to be treated in the water to be treated 1 is subjected to an oxidizing action by the photocatalyst 2 activated by light irradiation from the light source 3, and the easily decomposable organic matter is a harmless gas of CO ₂ and H ₂ O. And is released into the atmosphere 5. In addition, the hardly decomposable organic substance is converted into a readily biodegradable organic substance and remains in water.
Next, the water 4 containing an easily biodegradable organic substance is sent to the biological treatment apparatus B. Here, the readily biodegradable organic substance having a low molecular weight reduced by the photocatalytic reaction apparatus A is treated by a living body in the apparatus B which is brought into an aerobic condition by air blowing 6, and biologically low molecular weight is reduced. Converted into harmless substances.
The biological treatment that can be used here includes biological filtration, fluidized medium biological treatment, honeycomb contact material biological treatment, and activated sludge treatment, and can be selected according to specifications and the like as appropriate. This example is biofiltration for biofilm treatment.

In the case where a high-concentration organic substance to be treated is contained in a high concentration or when high-efficiency treatment is performed, the biologically treated water 7 is not directly used as the outlet treated water 8, but is circulated 9 in the photocatalytic reactor A. It is preferable to improve the removal rate.
This is because the undegraded, hardly biodegradable organic material after decomposing the readily biodegradable organic material in the biological treatment process is converted again into an easily biodegradable organic material by performing an oxidation reaction with a photocatalyst again. is there.
In this way, the water 1 containing a hardly biodegradable organic substance is effectively treated by performing preliminary treatment in the photocatalytic reaction apparatus A of the present invention in the previous step and then performing biological treatment B in the subsequent step. Can be processed.

Example 3
The coagulation sedimentation treatment water (COD: 98 mg / L, chromaticity 150 degree | times) of a urine treatment facility was introduce | transduced into the treatment process of FIG. 1, and COD and chromaticity were investigated.
Treatment conditions Treated water treatment amount: 10 L / day.
Photocatalytic reactor; model of FIG.
Size: The size of the reactor in the model of FIG. 2 is 3L.
Light source: germicidal lamp (intensity 2.5 mW / cm ² ).
Photocatalyst: The photocatalyst produced in Example 1 is used.
Biological treatment system Method: Aerobic biofiltration Biological filtration rate: 110m / day

COD and Color Removal Performance FIG. 7 shows the values of 60-day operation for COD.
In FIG. 7, ◯ represents the value of the present invention, and ● represents the value as a comparative example, where the light source is turned off and only the biological treatment apparatus is used. In FIG. 7, ↓ indicates 1 mg / L.
FIG. 7 shows the following.
When biological treatment is performed from the beginning, the organic substance removal performance varies greatly and is low. This is considered to be because, depending on the type of the organic matter to be introduced, for example, when a more highly biodegradable organic matter (high molecular weight organic matter) is introduced at a high concentration temporarily, the removal performance decreases.
In contrast to this, first, by reducing the molecular weight of a large number of organic substances contained in water using the photocatalytic reaction device of the present invention and then biologically treating it, highly purified water can be stably obtained (water having a high ultimate cleanliness). ), Highly reliable water can be obtained continuously for a long time.
Table 2 shows the chromaticity. The method of the comparative example is as described above. The numerical values in Table 2 are chromaticity (degrees).

表２の結果により、本発明の光触媒は、脱色に効果的であることがわかる。

The results in Table 2 show that the photocatalyst of the present invention is effective for decolorization.

Example 4
FIG. 8 is an example in which water treatment using the photocatalyst of the present invention is applied to sterilization treatment of water containing pests such as Cryptosporidium. Process).
In a water purification plant using ordinary sedimentation, raw water (treated water) 1 is taken from a river or a well, passed through a rapid mixing basin 11 and a slow mixing basin 12, coagulating sedimentation in a sedimentation basin 13, and sand in a filtration basin 14. Filtration or membrane filtration is performed, and it flows to the subsequent process that continues to the drainage basin 15. 7 is an outlet of the treated water.
In the filtration basin 14, in order to eliminate clogging of the filter medium, the washing is intermittently performed by the reverse water flow, and the washing drain 16 is sent to the drain 17. Further, in the drainage pond 17, the precipitate 18 is sent to the mud pond 19, and the supernatant 20 of the mud pond 19 is sent to the drainage pond 17.

The sediment generated in the sedimentation basin 13 is sent to the drainage basin 19, the supernatant 20 of the drainage basin 19 is sent to the drainage basin 17, a part 21 of the drainage basin 17 is returned to the raw water 1, and becomes turbid Concentrate the quality components.
Here, 22 is a water treatment device (photocatalyst device, main configuration diagram in FIG. 9) using the photocatalyst of the present invention installed in the middle of returning the washing waste water 16 to the raw water 1.
In such a series of water purification processes, pathogenic microorganisms such as Cryptosporidium and Escherichia coli are supplemented together with turbid components including sand and plankton contained in the raw water 1 during coagulation sedimentation and filtration. For this reason, these components are contained in the filtration washing waste water 16, and every time the part 21 of the drainage basin 17 is repeatedly returned, it is concentrated to the raw water side, and even if coagulation sedimentation / filtration is performed, the drainage basin 15 There is a risk of mixing. In the case of microorganisms such as Escherichia coli that do not have chlorine tolerance, the bacteria are killed by sterilization and disinfection by chlorine injection, which is a subsequent process, but for chlorine-resistant organisms such as Cryptosporidium, drinking water is contaminated. Hazard arises, causes serious contamination and is a problem.

In contrast, in the present invention, the photocatalyst device 22 (main configuration diagram: FIG. 9) is provided at the position shown in FIG. Activation). FIG. 9 shows a photocatalytic reaction apparatus, in which a plurality of net-like photocatalysts 2 and ultraviolet lamps 3 manufactured in the same manner as in Example 1 are installed, and the apparatus is sterilized by photocatalyst by stirring water to be treated by a stirring fan F. The effect is promoted. (M) in FIGS. 8 and 9 is a stirring motor.
In this way, pests such as Cryptosporidium and Escherichia coli in the washing waste water 16 are sterilized, and highly safe drinking water can be stably obtained for a long time (ensures safety for a long time).

Example 5
The inactivation of Cryptosporidium was investigated by introducing into the photocatalytic reaction apparatus shown in FIG. 9 test coagulation sediment washing drainage generated from a water purification plant and Cryptosporidium-added treated water to which Cryptosporidium oocyst was added.
Treatment conditions Photocatalytic reaction apparatus: 500 L stainless steel reaction vessel (configuration shown in FIG. 9).
Photocatalyst shape; mesh (4)
Light source: germicidal lamp (irradiation intensity: 2.5 mW / cm ² )
Installed between photocatalysts (6)
Production method of photocatalyst: It was prepared in the same manner as in Example 1.

Water to be treated: Amount of Cryptosporidium added: 1 × 10 ⁶ / L
Turbidity: 20 degrees, usually, the turbidity of washing wastewater from a water purification plant is about 5 to 20 degrees, and 20 degrees is water in a state of high turbidity.
Stirring: 12 times / min
Evaluation method of inactivation: The treated water after treatment was examined for the number of Cryptosporidium oocysts with a microscope after concentration and administered to immunodeficient mice. The inactivation effect of the photocatalyst was examined by counting the number of Cryptosporidium in the stool of the administered mice.
Results The inactivation rate is shown in Table 3.

この結果から、光触媒処理により、洗浄排水中の病原性微生物の殺菌消毒に高い効果があることが認められた。

From this result, it was recognized that the photocatalytic treatment has a high effect on the sterilization and sterilization of pathogenic microorganisms in the washing waste water.

Example 6
A 2-naphthol solution widely used as an azo dye is introduced into the photocatalytic reaction vessel 22 composed of the photocatalyst 2 and the light source 3 shown in FIGS. 10 and 11, and the change in 2-naphthol concentration due to the lighting of the light source is measured. Thus, the photocatalytic effect was examined. Further, the poor oxygen state was examined in the same manner.
Reference numeral 23 denotes a glass window for irradiating the photocatalyst 2 with light from the light source 3.
FIG. 10 shows a reaction vessel of AgCl / SnO ₂ : plate-like photocatalyst, and FIG. 11 shows a reaction vessel of AgCl: particulate photocatalyst.
Processing conditions Photocatalytic reaction device: made of 2L stainless steel, configuration of FIGS. 10 and 11 Photocatalyst shape; AgCl / SnO ₂ : Plate shape, AgCl: particulate light source; High-pressure mercury lamp Production method of photocatalyst;
(1) AgCl / SnO ₂ : produced in the same manner as in Example 1.
(2) Particulate AgCl: The above (1) was desorbed in a solution by applying ultrasonic waves. (Average particle size: 2.1 μm)

In FIG. 11, 1 is a liquid to be treated (2-naphthol), 2 is a photocatalyst (AgCl: particulate) in a floating state (dispersed state), 3 is a light source, 22 is a photocatalytic reaction device, and 24 is a photocatalyst 2 in a floating state. This is an air supply tank (air diffuser). Arrows indicate the direction of air flow. The particulate photocatalyst 2 enters a floating state by the bubbles 25 supplied from the lower air diffuser 24, contacts with contaminants in the liquid to be treated, and decomposes 2-naphthol by photocatalytic action.
2-naphthol, 1 × 10 ⁻⁵ M solution Oxygen concentration in water: natural state: 8.8 mg / L and anoxic state: 1.0 mg / L (hereinafter) 2-naphthol concentration measurement method; liquid chromatography Measured by graph

Results Performance of this photocatalyst;
(1) AgCl / SnO ₂ : ◯ and Δ in FIG. 12 indicate those of the present photocatalyst, ○ indicates oxygen concentration in water: 8.8 mg / L, and Δ indicates removal of oxygen concentration in water by degassing (Anoxic state) and the results of the same test, showing the relationship between the ultraviolet irradiation time to the photocatalyst and the 2-naphthol decomposition rate (removal rate).
(2) Particulate AgCl: The black circles in FIG. 12 indicate those of the present photocatalyst, which are used in a suspended state in water as shown in FIG. 11, and the oxygen concentration in the water is 8.8 mg / L, and the ultraviolet rays to the photocatalyst The relationship between irradiation time and 2-naphthol decomposition rate (removal rate) is shown.

Comparative test performance;
In FIG. 12, x is Ag / SnO ₂ (oxygen concentration in water: 8.8 mg / L) for comparison, □ is AgCl (reagent product) for comparison, and ▲ is a conventional photocatalyst (TiO ₂ ) for comparison. This was tested in the same manner by removing the oxygen concentration in water (deoxygenated state) by deaeration.
The results of FIG. 12 show the following.
Conventional photocatalysts lose their photocatalytic performance when they are in an oxygen-poor state. On the other hand, the photocatalyst exhibits high activity in the oxygen-poor state as well as the oxygen state in the natural state.
Since 2-naphthol has been decomposed and removed, the present photocatalyst is effective in decomposing organic substances and decolorizing pigments.

Example 7
An aqueous ammonia solution (2 mg / L as NH ₃ -N) was introduced into a stainless steel photocatalytic reaction vessel 22 composed of the photocatalyst 2 and the light source 3 shown in FIG. The photocatalytic effect was investigated by measuring the change.
The configuration of the photocatalytic reaction device is the same as in Example 6.
The photocatalyst is AgCl / SnO ₂ : plate-like (manufactured in the same manner as in the examples).
The nitrate ion concentration was determined by ion chromatography.

Results FIG. 13 shows the relationship between the ultraviolet irradiation time to the photocatalyst and the nitrate ion concentration.
In FIG. 13, ◯ and Δ are decomposition rates by the photocatalyst of the present invention, ○ is oxygen concentration in water: 8.8 mg / L state, Δ is oxygen concentration in water (anoxic state), and ▲ is for comparison The conventional photocatalyst (TiO ₂ ) is used in an anoxic state (0.5 mg / L).
The following application is possible based on the result of FIG.
The photocatalyst of the present invention quickly oxidizes ammonia in water to nitrate ions. Conventional photocatalysts, such as TiO ₂ (titanium oxide), degrade in performance when they are in an oxygen-poor state, but this photocatalyst is not affected by fluctuations in the oxygen state and can be operated for a long time with high efficiency. Is possible.

Ammonia components in water adversely affect the growth of fish, for example, and cause death at high concentrations, but this method quickly converts ammonia in water to nitric acid (has less adverse effects on fish growth than ammonia). Therefore, it can be suitably used for applications where ammonia is a problem.
In addition, it is possible to effectively treat ammonia and nitrogen-containing substances by general nitric acid reduction methods such as nitric acid nitric acid by denitrifying bacteria under anaerobic conditions, or nitric acid by electrolysis of nitric acid by electrolytic reaction. .

Example 8
FIG. 14 shows a photocatalytic reaction apparatus using the particulate photocatalyst (AgCl) 2 of the present invention in a floating state (dispersed state).
1 is a liquid to be treated, 2 is a particulate photocatalyst in a suspended state (dispersed state), 3 is a light source, 22 is a photocatalytic reaction device, and 26 is a microbubble generator (bubble generator) for making the photocatalyst 2 float. is there.
The arrow indicates the flow direction of the supply air.
The micro-bubble generator 26 is based on a far-centered separation method, whereby bubbles having a diameter of 10 μm to 50 μm are generated.
The particulate photocatalyst 2 is suspended by bubbles (microbubbles) 25 generated from the microbubble generator 26 installed below, and comes into contact with contaminants in the liquid 1 to be treated. A decomposition process is performed.

The photocatalytic reaction device 22 has the light source 3 installed at the center, and the particulate photocatalyst (AgCl) 2 is brought into a floating state by the generation of bubbles 25 from the microbubble generation device 26. Therefore, the photocatalyst 2 is irradiated with light and the photocatalyst 2. And contact efficiency with the object to be processed become more effective. Furthermore, the to-be-processed object in water improves the contact efficiency with the photocatalyst surface (average residence time increases) by microbubbles.
Thus, the present photocatalytic reaction device 22 has an effect due to the floating state of the photocatalyst 2 (the contact efficiency is effective) and an effect of improving the contact efficiency between the object to be treated and the surface of the photocatalyst by the microbubbles 25 (the average residence time is increased). ) Brings about a synergistic effect on the processing efficiency of the object to be processed, so that high-efficiency processing is performed.

The flow block diagram which shows an example of the water treatment apparatus of this invention. The expanded block diagram of the photocatalytic reaction apparatus A of FIG. Prepared in example. 1 (a) Ag / _SnO 2, (b) is a SEM photograph of the AgCl / SnO _2. (A) is Ag / SnO ₂ , (b) is AgCl / SnO ₂ , and (c) is an XRD pattern diagram of AgCl / SnO ₂ after one month of use. Prepared in example. 1 (a) Ag / _SnO 2, (b) is a graph showing the particle size distribution of AgCl / SnO _2. Graph showing the variation of AgCl of Ag in Ag / SnO _2. The flow block diagram which shows the value of COD at the time of driving | running for 60 days of Example 3. FIG. The flow block diagram which shows the other example of the water treatment apparatus of this invention. The expanded block diagram of the photocatalyst apparatus 22 of FIG. The cross-sectional block diagram which used the plate-shaped photocatalyst with the photocatalytic reaction apparatus. The cross-sectional block diagram which used the particulate photocatalyst with the photocatalytic reaction apparatus. The graph which shows the relationship between the ultraviolet irradiation time to a photocatalyst, and 2-naphthol decomposition rate. The graph which shows the relationship between the ultraviolet irradiation time to a photocatalyst, and a nitrification rate. The cross-sectional block diagram which shows the other example of the photocatalytic reaction apparatus using a particulate photocatalyst.

Explanation of symbols

  1: treated water, 2: photocatalyst, 3: light source, 4: photocatalyst treated water, 5: gas, 6: air, 7: biological treated water, 8: treated water, 9: circulating water, 11: rapid mixing pond, 12: slow mixing basin, 13: sedimentation basin, 14: filtration basin, 15: drainage basin, 16: drainage basin, 17: drainage basin, 18: sediment, 19: mud pond, 20: supernatant : Return water, 22: Photocatalyst device, 23: Glass, 24: Air diffuser, 25: Air bubbles, 26: Microbubble generator, A: Photocatalytic reaction device, B: Biological treatment device

Claims (8)

  A photocatalyst characterized in that silver chloride is supported on a material containing a conductive substance.   2. The photocatalyst according to claim 1, wherein the silver chloride is produced by electrolytic oxidation by supporting silver on a material containing a conductive substance.   A photocatalyst characterized in that silver chloride obtained by carrying out electrolytic oxidation by supporting silver on a material containing a conductive substance is separated from the material containing a conductive substance.   In the method for producing a photocatalyst, a method for producing a photocatalyst is characterized in that silver is first supported on a material containing a conductive substance and then silver chloride is formed from the silver by electrolytic oxidation.   5. The method for producing a photocatalyst according to claim 4, wherein the supporting of the silver on the material containing the conductive substance is performed by electrolytic reduction deposition.   A water treatment method for removing harmful substances from water containing harmful substances, wherein the water containing harmful substances is brought into contact with the photocatalyst according to claim 1, 2 or 3 under light irradiation.   The water treatment method according to claim 6, wherein the water containing the harmful substance is in an anoxic state.   An apparatus for removing harmful substances from water containing harmful substances, having an inlet and a drain of water containing the harmful substances, and irradiating the photocatalyst with the photocatalyst according to claim 1, 2, or 3 inside A water treatment apparatus comprising a light source.

Images