Method for decomposing colored wastewater, and treatment apparatus for decomposing colored wastewater.

Abstract

To provide a method for efficiently subjecting colored waste water to decomposition treatment even when waste water is colored in waste water decomposition treatment using a photocatalyst.SOLUTION: A colored waste water decomposition treatment method comprises: a light irradiation step of applying light to a photocatalyst in colored waste water in the presence of dissolved oxygen. The chromaticity of the colored waste water fed to the light irradiation step lies in the range of 50 degrees or more to 1,000 degrees or less, and the photocatalyst has a primary particle diameter of 100 nm or less and a secondary particle diameter of 1 μ or more, and the photocatalyst has a titanium oxide content of 90 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for decomposing colored wastewater and a treatment apparatus for decomposing colored wastewater. [Background technology]

[0002] Wastewater is generated from daily life or business activities, and much of it is discolored. This discoloration is due to naturally occurring organic matter (various organic compounds produced by the decomposition of plant matter in the soil by microorganisms), as well as organic matter from garbage, kitchen waste and its decaying remains, factory wastewater, human waste, and heavy metal ions such as copper, iron, and chromium.

[0003] These wastewaters are treated primarily by the activated sludge process, especially at sewage treatment plants, and the resulting sewage sludge is treated primarily by anaerobic digestion. These methods utilize the decomposition principle by aerobic and anaerobic microorganisms, but other treatments based on various principles are also used as supplementary methods at sewage treatment plants or at various water treatment facilities other than sewage treatment plants.

[0004] Examples of such treatments include precipitation / flotation separation, filtration, membrane separation, ion exchange, physical adsorption, stripping, chlorination, ozone treatment, ultraviolet irradiation, and catalytic / photocatalytic oxidation. Among these, the photocatalytic method involves applying light energy to a photocatalytic substance in a liquid containing the substance to be oxidized and dissolved oxygen, causing the substance to be oxidized and decomposed by its strong oxidizing power. Photocatalysts can be used semi-permanently as long as they do not degrade, and compared to methods that add ozone or chemicals, they reduce the cost of additives, eliminate the need for post-treatment of excess additives, and enable clean and inexpensive treatment. Furthermore, because they are highly active, stable, and inexpensive, many photocatalysts composed of titanium dioxide nanoparticles with a primary particle size of less than 1 μm are being investigated. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-41331

Non-Patent Literature

[0006]

Non-Patent Literature 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the treatment by the above-mentioned photocatalyst, there are still few examples implemented on a practical scale, and most of them remain at the laboratory level. One of the factors that has hindered practical application is the coloring and suspension of the treatment liquid. If the solution as the treatment liquid is colored, the light with the absorption wavelength thereof does not transmit, the irradiation light attenuates in the reaction vessel, and the amount of light that the photocatalyst particles can receive is significantly reduced. Also, the suspension due to the suspended substances in the liquid greatly affects the amount of light received by the photocatalyst particles. Furthermore, the attenuation of the incident light by the photocatalyst fine particles themselves must also be considered. The photocatalyst fine particles (less than 1 μm) suspended in a colloidal state in the liquid absorb light and, depending on the particle size, scatter light complexly (Mie scattering). Thus, there is a problem that the conventional powder fine particle catalyst does not act effectively on the colored and suspended sewage (hereinafter, this is referred to as "colored sewage" in the present invention).

[0008] Under such circumstances, the main object of the present invention is to provide a method for efficiently decomposing and treating colored sewage even when the sewage is colored in the decomposition treatment of sewage using a photocatalyst. Another object of the present invention is to provide a colored sewage decomposition treatment apparatus that can be suitably used for the decomposition treatment method.

Means for Solving the Problems

[0009] The inventors diligently conducted research to solve the above-mentioned problems. As a result, they found that in the decomposition treatment of colored wastewater with a chromaticity in the range of 50 degrees to 1000 degrees, by using a photocatalyst with a primary particle diameter of 100 nm or less, a secondary particle diameter of 1 μm or more, and a titanium dioxide content of 90% by mass or more, and irradiating the photocatalyst with light in the colored wastewater in the presence of dissolved oxygen, the colored wastewater is efficiently decomposed. The present invention was completed by further research based on this finding.

[0010] In other words, the present invention provides inventions in the following embodiments. Item 1. A method for decomposing colored wastewater, The system includes a light irradiation step in which light is irradiated onto the photocatalyst in the colored wastewater in the presence of dissolved oxygen. The chromaticity of the colored wastewater subjected to the light irradiation process is in the range of 50 degrees to 1000 degrees. The photocatalytic material has a primary particle diameter of 100 nm or less and a secondary particle diameter of 1 μm or more. The photocatalytic material has a titanium dioxide content of 90% by mass or more, and is a method for decomposing colored wastewater. Item 2. The method for decomposing colored wastewater according to Item 1, wherein, in the light irradiation step, ultraviolet light is irradiated onto the photocatalyst while stirring the colored wastewater. Item 3. The method for decomposing colored wastewater according to item 1 or 2, wherein the photocatalytic body has a configuration in which a co-catalyst is supported on the surface of the photocatalytic material. Item 4. A method for decomposing colored wastewater according to any one of items 1 to 3, wherein the chromaticity of the colored wastewater subjected to the light irradiation step is in the range of 50 degrees or more and 800 degrees or less. Item 5. A method for decomposing colored wastewater according to any one of items 1 to 4, wherein the chromaticity of the colored wastewater subjected to the light irradiation step is in the range of 70 degrees or more and 700 degrees or less. Item 6. A method for decomposing colored wastewater according to any one of items 1 to 5, wherein the secondary particle size of the photocatalyst is 40 μm or more. Item 7. A discolored wastewater decomposition apparatus for use in the discolored wastewater decomposition method described in any one of items 1 to 6, It has a function to perform a light irradiation process in which light is irradiated onto a photocatalyst in colored wastewater in the presence of dissolved oxygen. The chromaticity of the colored wastewater subjected to the light irradiation process is in the range of 50 degrees to 1000 degrees. The photocatalytic material has a primary particle diameter of 100 nm or less and a secondary particle diameter of 1 μm or more. The aforementioned photocatalytic material has a titanium dioxide content of 90% by mass or more, and is used in a discolored wastewater decomposition treatment device. [Effects of the Invention]

[0011] According to the present invention, a method for efficiently decomposing colored wastewater using a photocatalyst is available, even when the wastewater is colored. Furthermore, according to the present invention, a colored wastewater decomposition apparatus that can be suitably used in the said decomposition method is also available. [Brief explanation of the drawing]

[0012] [Figure 1] These are the UV-VIS spectra of the photocatalyst obtained in Preparation Example 1, when the dispersion concentration in water was changed. [Figure 2] These are the UV-VIS spectra of the photocatalyst obtained in Preparation Example 2, when the dispersion concentration in water was changed. [Figure 3] Figures 1 and 2 show the absorbance at a wavelength of 365 nm plotted against the photocatalyst dispersion concentration. [Figure 4] This is the emission spectrum of the mercury lamp used for UV irradiation of colored wastewater in the example. [Figure 5] This graph shows the relationship between the decomposition treatment time of colored wastewater and the COD retention rate in Example 1 and Comparative Examples 1 and 2 (vertical axis: R254 COD retention rate, horizontal axis: treatment time). [Figure 6]This graph shows the relationship between the decomposition treatment time of colored wastewater and the chromaticity retention rate in Example 1 and Comparative Examples 1 and 2 (vertical axis: R390 chromaticity retention rate, horizontal axis: treatment time). [Figure 7] In Example 2, the graphs show the relationship between the wastewater decomposition treatment time and the remaining percentages of COD, chromaticity, and turbidity (R254, R390, R870) (the vertical axis represents the remaining percentage (R254, R390, R870), and the horizontal axis represents the treatment time). [Figure 8] In Example 3, the graphs show the relationship between the wastewater decomposition treatment time and the remaining percentages of COD, chromaticity, and turbidity (R254, R390, R870) (the vertical axis represents the remaining percentage (R254, R390, R870), and the horizontal axis represents the treatment time). [Figure 9] These are photographs of the wastewater before and after the decomposition treatment in Example 3 (left side: before decomposition treatment, right side: after pre- and post-treatment). [Modes for carrying out the invention]

[0013] The present invention relates to a decomposition treatment method for colored wastewater. In the present invention's method for decomposing colored wastewater, the colored wastewater to be decomposed has a color intensity in the range of 50 degrees to 1000 degrees. The present invention's method for decomposing colored wastewater includes a light irradiation step in which light is irradiated onto a photocatalyst in the colored wastewater in the presence of dissolved oxygen. The photocatalyst is characterized by having a primary particle diameter of 100 nm or less, a secondary particle diameter of 1 μm or more, and a titanium dioxide content of 90% by mass or more. By having these characteristics, the present invention's method for decomposing colored wastewater can efficiently decompose colored wastewater even when the wastewater is colored, in wastewater decomposition treatment using a photocatalyst.

[0014] Furthermore, the colored wastewater decomposition treatment apparatus of the present invention is a wastewater decomposition treatment apparatus for use in a method for decomposing colored wastewater, and is equipped with a function to perform a light irradiation step in which light is irradiated onto a photocatalyst in colored wastewater in the presence of dissolved oxygen, wherein the chromaticity of the colored wastewater subjected to the light irradiation step is in the range of 50 degrees to 1000 degrees, and the photocatalyst has a primary particle diameter of 100 nm or less, a secondary particle diameter of 1 μm or more, and a titanium dioxide content of 90% by mass or more. By having these features, the wastewater decomposition treatment apparatus of the present invention can efficiently decompose colored wastewater even when the wastewater is colored, in wastewater decomposition treatment using a photocatalyst, and can be suitably used in the colored wastewater decomposition treatment method of the present invention described above.

[0015] The following describes in detail the method for decomposing colored wastewater and the treatment apparatus for decomposing colored wastewater according to the present invention. In this specification, numbers connected by "~" represent a numerical range that includes the numbers before and after "~" as the lower limit and upper limit, respectively. If multiple lower limits and multiple upper limits are listed separately, any lower limit and upper limit can be selected and connected by "~".

[0016] 1. Method for decomposing colored wastewater In the colored wastewater decomposition treatment method of the present invention, the colored wastewater to be decomposed has a chromaticity of 50 degrees or more and 1000 degrees or less. Chromaticity refers to the degree of pale yellow to yellowish-brown color caused by substances dissolved in water or presenting colloidally. 1 degree of chromaticity is defined as the color obtained by adding 1 mL of chromaticity standard solution (1 mg platinum and 0.5 mg cobalt) to 1000 mL of water. It should be noted that when measuring the chromaticity of turbid water, the result will be affected by the turbidity. Chromaticity measured after removing turbidity by filtration or centrifugation is called "true chromaticity," while chromaticity measured without such pretreatment is called "apparent chromaticity." In the dewatered separated liquid of digested sludge used in the examples of the present invention, filtration (using filter paper with a particle size retention of 1 μm) was performed to remove coarse sediment before the preliminary decomposition treatment, but turbidity remained. To completely remove turbidity, filtration with an even finer 0.22 μm filter paper was performed, but this resulted in a change in the overall shape of the UV-VIS spectrum, indicating that the properties of the actual solution could not be preserved. Therefore, in this invention, the pre-filtration treatment is standardized to use 1 μm filter paper. Accordingly, in this invention, chromaticity is defined as the "apparent chromaticity after 1 μm filtration," which includes the effect of turbidity. In the decomposition treatment method for colored wastewater of this invention, decomposition treatment of colored wastewater means that by applying the decomposition treatment method of this invention to the colored wastewater to be decomposed, the wastewater after decomposition treatment will have at least a lower chromaticity than before decomposition treatment. In colored wastewater, the coloring substance and dissolved oxygen undergo an oxidation reaction, resulting in oxidative decomposition while generating decomposition products such as carbon dioxide.

[0017] In this invention, the wastewater to be decomposed is colored wastewater. As a measure of coloration, a chromaticity measurement is used, and the target is colored wastewater in the chromaticity range of 50 to 1000 degrees. From the viewpoint of clearly demonstrating the effect of adding granular photocatalyst, a more preferable chromaticity range is 50 to 800 degrees, and an even more preferable chromaticity range is 70 to 700 degrees.

[0018] Colored wastewater can be discharged from any facility or process, as long as its color falls within the specified range. For example, it can be wastewater generated in any process at a sewage treatment plant, such as activated sludge treatment, sludge thickening, anaerobic digestion, or sludge dewatering. It can also be wastewater received at wastewater treatment facilities in various factories and other facilities other than sewage treatment plants, or wastewater generated in any of its treatment processes.

[0019] In sewage treatment plants, sludge is sometimes solubilized to reduce the amount of sludge to be treated and to improve process efficiency. The colored wastewater targeted by this invention may be the result of such solubilization treatment. Any method can be used for solubilization, including chemical methods using chemical agents, physicochemical methods utilizing heating or hydrothermal reactions, mechanical methods such as ultrasound and bead mills, and electrochemical methods using electrolysis.

[0020] Wastewater obtained by this solubilization treatment often has a higher color than wastewater that has not undergone solubilization treatment. For example, when no solubilization treatment is performed, the dewatered liquor after anaerobic digestion of sewage sludge has a color of about 500 to 2500 degrees, whereas the dewatered liquor after anaerobic digestion of sewage sludge after solubilization treatment has a color of about 2000 to 4000 degrees. The method of the present invention cannot be directly applied to solutions exceeding 1000 degrees, but the method of the present invention can be applied after dilution to a solution below 1000 degrees or after decomposition by other methods to a solution below 1000 degrees.

[0021] In the present invention, the colored wastewater after decomposition treatment has a lower chromaticity than before decomposition treatment. In the present invention, the decomposition rate of the chromaticity of the colored wastewater before and after decomposition treatment (chromaticity of colored wastewater before decomposition treatment - chromaticity of colored wastewater after decomposition treatment) / (chromaticity of colored wastewater before decomposition treatment) is preferably 10% or more, more preferably 20% or more, and even more preferably 50% or more.

[0022] Furthermore, from the viewpoint of suitably exhibiting the effects of the present invention, the COD value of the colored wastewater to be decomposed is preferably about 100 to 30,000 mg / L, more preferably about 100 to 10,000 mg / L, and even more preferably about 100 to 3,000 mg / L. Furthermore, from the viewpoint of suitably exhibiting the effects of the present invention, the BOD value and COD of the colored wastewater to be decomposed are Cr Ratio of value (BOD / COD) Cr ) is preferably 0.4 or less, more preferably 0.3 or less, and even more preferably 0.25 or less.

[0023] Furthermore, the TOC (Total Organic Carbon) of the colored wastewater to be decomposed is not particularly limited, but is preferably about 30 to 10,000 mg / L, more preferably about 30 to 3,000 mg / L, and even more preferably about 30 to 1,000 mg / L. Furthermore, the ammoniacal nitrogen (NH4-N) of the colored wastewater to be decomposed is not particularly limited, but is preferably about 100 to 5,000 mg / L, more preferably about 100 to 4,000 mg / L, and even more preferably about 100 to 2,000 mg / L. Furthermore, the pH of the colored wastewater to be decomposed is preferably about 5.0 to 9.0, more preferably about 6.0 to 9.0, and even more preferably about 6.0 to 8.5.

[0024] In this invention, water quality tests are conducted on the wastewater before and after decomposition treatment in order to confirm the properties of the colored wastewater to be decomposed and to evaluate the effectiveness of the wastewater decomposition treatment method of this invention. These water quality tests are also used in the examples described later. For each test method, those prescribed by laws and regulations (official methods) are followed, and for others, the wastewater testing methods (Japan Sewerage Association, 2012 edition) are followed. In this invention, these will be referred to as "official methods, etc."

[0025] The method for testing the degree of coloration of wastewater is to perform chromaticity measurement. Methods for measuring and displaying chromaticity include transmitted light measurement, colorimetric method, and display using stimulus values ​​and chromaticity coordinates x,y. In this invention, measurement is performed by the colorimetric method after pretreatment with filtration using glass fiber filter paper with a pore size of 1 μm (GFP), and the unit of expression is "degrees".

[0026] Furthermore, for measuring the COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand), and TOC (Total Organic Carbon) values ​​of wastewater, pretreatment is performed by filtration using glass fiber filter paper with a pore size of 1 μm (GFP), and measurements are taken as soluble BOD, soluble COD, and soluble TOC. In COD measurement, the oxygen demand is determined using potassium dichromate, and the COD Cr It is expressed as a value. In BOD measurement, N-allylthiourea is added and soluble C-BOD (Wastewater Testing Methods 2012 Edition, Part 2, Chapter 1, Section 21-2, Japan Sewerage Association) is measured. Hereafter, unless otherwise specified, in this invention, soluble C-BOD is referred to as BOD (BOD value), and soluble COD Cr The COD (COD value) is denoted as COD, and the soluble TOC (TOC value) is denoted as TOC. Furthermore, chromaticity was analyzed by colorimetric method after GFP filtration, and ammoniacal nitrogen (NH4-N) was analyzed by ion chromatography after 0.45 μm filtration. pH was measured using the glass electrode method.

[0027] In addition to the tests conducted by official methods as described above, the present invention measures the ultraviolet-visible (UV-VIS) spectrum of wastewater using a spectrophotometer to determine surrogate indices for COD, chromaticity, and turbidity. UV-VIS spectra can be measured quickly (within 1 minute) with a small volume of liquid (approximately 3 mL), and it is known that absorbance at specific wavelengths correlates well with water quality values. Therefore, in order to evaluate the decomposition rate by the decomposition treatment method of the present invention over time, the absorbance at the wavelengths shown below is adopted as a surrogate indice, and its rate of change is calculated.

[0028] First, we will use 254nm absorbance (A254) as a substitute index for COD. In JIS K 0807 "Automatic UV absorbance measuring instrument for water quality monitoring", the UV absorbance measurement value at a wavelength of 253.7nm is used as the COD. Mn It has been shown that it is correlated with and used for calculating water pollution load related to total water load regulation. In this invention, COD is used as COD Mn Not COD Cr Although this method is used, the actual dewatered liquid of digested sludge is measured by COD.Cr When A254 was measured, a good linear correlation was observed between the two.

[0029] Next, absorbance at 390 nm (A390) is used as a surrogate index for chromaticity. Among the methods for measuring chromaticity, the transmitted light measurement method (Wastewater Testing Methods 2012 Edition, Part 2, Chapter 1, Section 4, 1, Japan Sewerage Association) measures the degree of pale yellow to yellowish-brown color caused by substances dissolved in water or present in colloidal form, using spectrophotometry. When chromaticity and A390 were measured using a digital turbidimeter (WA-PT-4DG, Kyoritsu Chemical Research Institute) for the dewatered separated liquid of actual digested sludge, a good linear relationship was obtained.

[0030] Furthermore, the absorbance at 870 nm (A870) was used as a surrogate indicator of turbidity. Among the methods for measuring turbidity, the transmitted light measurement method (Wastewater Testing Methods 2012 Edition, Part 2, Chapter 1, Section 5, Item 2, Japan Sewerage Association) involves shining light from one side and measuring the transmitted light. Turbidity (kaolin standard) is determined by utilizing the fact that the degree of light attenuation is related to the concentration of suspended solids in the water. When turbidity (polystyrene standard) and A870 were measured using a digital turbidimeter (WA-PT-4DG, Kyoritsu Chemical Research Institute) for the dewatered separated liquid of actual digested sludge, a good linear relationship was obtained.

[0031] The present invention provides a method for decomposing colored wastewater, comprising a light irradiation step in which light is irradiated onto a photocatalyst in colored wastewater in the presence of dissolved oxygen. The photocatalyst is characterized by having a primary particle diameter of 100 nm or less, a secondary particle diameter of 1 μm or more, and a titanium dioxide content of 90% by mass or more. The present invention provides a method for decomposing colored wastewater, which allows for the effective decomposition of colored wastewater by irradiating a specific photocatalyst in colored wastewater in the presence of dissolved oxygen with light.

[0032] The photocatalyst has a titanium dioxide content of 90% by mass or more, a primary particle diameter of 100 nm or less, and a secondary particle diameter of 1 μm or more. As described later, the structure of the photocatalyst has, for example, a structure in which a co-catalyst is supported on the surface of titanium dioxide as the photocatalytic material.

[0033] The proportion of titanium dioxide in the entire photocatalyst is 90% by mass or more, preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 98% by mass or more.

[0034] Titanium dioxide is used as an aggregate (secondary particles) of microcrystalline (primary particles) such as anatase, rutile, and brookite. While such microcrystalline aggregates are generally obtained as powdered photocatalysts, the present invention is characterized by its granular form. Specifically, in the present invention, the photocatalyst is a particle with a secondary particle diameter of 1 μm or more. By setting the secondary particle diameter to 1 μm or more, energy loss due to strong wavelength-dependent scattering (Mie scattering) can be suppressed. Generally, particle size measurement and particle number measurement are possible by the light shielding method for particles of 1 μm or more, so light shielding is dominant over Mie scattering, and irradiated light easily penetrates between particles. Therefore, it is possible to achieve both decomposition of dissolved substances in a solution by light irradiation and decomposition by photocatalytic action by light irradiation of the photocatalyst.

[0035] Using highly active powdered photocatalysts as raw materials increases the likelihood of preparing highly active granular photocatalysts. In this case, from the viewpoint of producing secondary particles with a large surface area, it is preferable to keep the heat treatment temperature below 400°C during the granular preparation process. Photocatalysts with a large surface area may have a pore structure. The pore size may be mesopores, macropores, or a combination of both.

[0036] Regarding the primary particle diameter of the photocatalytic medium, there is no limitation as long as it is 100 nm or less. However, from the perspective of increasing the contact between the substance to be treated in water and the photocatalyst surface and enhancing the reaction rate, it is preferably less than 100 nm, and more preferably 50 nm or less. The range of the primary particle diameter of the photocatalytic medium is, for example, about 1 to 100 nm, preferably about 2 to 50 nm. The primary particle diameter of the photocatalytic medium can be confirmed by observation with a transmission electron microscope or measurement of the crystallite diameter by the line broadening method of powder X-ray diffraction. Also, when it is difficult to measure the primary particle diameter, the equivalent primary particle diameter can be estimated from the BET specific surface area measured by the nitrogen adsorption method using the following formula (Ohtani Bunko, Photocatalyst Standard Research Method, Tokyo Tosho (2005), pp. 408-410).

[0037] S = 6 / (ρd) S: BET specific surface area [m 2 g -1 ρ: True density of primary particles [gm -3 d: Primary particle diameter [m] For example, in the case of titanium oxide, ρ is approximately 4 × 106 gm -3 Therefore, when estimating d in units of nm, it can be calculated by the following formula. d[nm]=1500 / S[m 2 g -1

[0038] ​​​From the viewpoint of suppressing the scattering of irradiated light by the photocatalyst, the secondary particle diameter of the photocatalyst of the present invention is 1 μm or larger. Furthermore, a diameter of 40 μm or larger is preferable because it facilitates solid-liquid separation of the photocatalyst. In addition, in the present invention, the secondary particle diameter of the photocatalyst must be set to an upper limit particle diameter that allows for uniform dispersion in the liquid by stirring. Examples of such upper limit particle diameters include 1000 μm or less, preferably 300 μm or less, and more preferably 200 μm or less. There are no restrictions on the shape of the photocatalyst. It may be spherical, such as a perfect sphere or an oblate sphere, polyhedron such as a cube or a rectangular prism, needle-shaped, or irregularly fragmented, or a mixture thereof. In the case of a non-spherical shape, the secondary particle diameter should be within the particle size range described above in terms of the diameter equivalent to a sphere. In the present invention, such a photocatalyst will be referred to as granular. Generally, what is called granular or fine-grained is included here.

[0039] To ensure that the secondary particle size of the granular photocatalyst is within the scope of the present invention, if the secondary particle size of the raw material photocatalyst is appropriate, it can be used as is, and a co-catalyst metal can be supported as needed. If the raw material photocatalyst is in the form of a fine powder or less than 1 μm, it can be granulated or otherwise processed to achieve an appropriate secondary particle size before supporting the metal, or the metal can be supported while the material remains in fine powder form, and then granulated or otherwise processed to achieve an appropriate secondary particle size. If the raw material photocatalyst is in the form of a bead-shaped molded body or larger, for example, 1 mm or larger, it can be crushed and classified to achieve an appropriate secondary particle size, and then a co-catalyst can be supported as needed.

[0040] Any method can be used to granulate the finely powdered photocatalytic material, including stirring (tumbling) granulation, fluidized bed granulation, extrusion granulation, and spray drying granulation. Alternatively, a method may be employed in which the fine particles are formed into lumps by heating, dehydration condensation, or sintering, then crushed to reduce their size, and further classified to obtain an appropriate secondary particle size range. The crushing method is not particularly limited; in addition to manual crushing using a mortar and pestle, crushing machines such as roller mills, hammer mills, rotary mills, and planetary mills may be used.

[0041] In this invention, any method can be used to standardize the secondary particle size of the photocatalytic material, and classification can be performed by methods such as sieving. For example, in the embodiment, granular material that passed through a sieve with a mesh size of 125 μm but did not pass through a sieve with a mesh size of 40 μm was collected. If fine powder generated by operations such as crushing remains attached to the collected granular material, the remaining fine particles can be removed by sieving and water sedimentation.

[0042] Methods for measuring secondary particle size generally include microscopy, sieving, water sedimentation, laser diffraction / scattering, dynamic light scattering, and Coulter counter methods. Furthermore, while there are various definitions of diameter for particles of different shapes, such as major axis diameter, minor axis diameter, equivalent circle diameter, and equivalent spherical diameter, the equivalent spherical diameter will be used in the following explanation. When referring to particle size distribution, there are distribution criteria such as number-based, area-based, volume-based, and weight-based. In the following explanation, the number-based value will be used, but if it is possible to convert from the volume-based or weight-based value to the number-based value, that converted value may be used. From the above perspective, when considering methods for measuring the secondary particle size of the photocatalyst in the present invention, the laser diffraction / scattering method, which directly measures the particle size distribution in a water-dispersed state and obtains the equivalent spherical diameter, can be said to be the optimal measurement method.

[0043] In the present invention, the photocatalyst may consist solely of a photocatalytic substance, or it may contain other components (for example, co-catalysts) for purposes such as enhancing photocatalytic reaction activity.

[0044] Examples of such co-catalysts include platinum, gold, palladium, ruthenium, rhodium, silver, copper, and iridium. Among these, it is particularly preferable to use precious metals such as platinum, palladium, and gold as co-catalysts. Co-catalysts may be used individually or in combination of two or more types.

[0045] In the range where the amount of co-catalyst supported is small, photocatalytic activity increases with increasing support. However, it is known that if the amount of co-catalyst supported is too large, the co-catalyst itself absorbs and scatters light, hindering the photocatalyst's light absorption, or acts as a recombination center for electrons and holes, thereby decreasing photocatalytic activity. The appropriate amount of co-catalyst supported needs to be determined according to the type of co-catalyst metal, the type of photocatalytic material, the primary and secondary particle sizes, and the type of reaction. When supported on titanium oxide fine particles with a primary particle size of 100 nm or less, the range of co-catalyst supported amount is preferably 0.01 to 10 mass%, more preferably 0.01 to 3 mass%, and even more preferably 0.01 to 2 mass%.

[0046] There are no restrictions on the method for supporting a co-catalyst on the surface of a photocatalytic material; known methods such as photodeposition, impregnation, precipitation-precipitation, and colloidal deposition can be employed. Furthermore, when supporting gold, methods such as the gold hydroxo complex solution developed by the present inventors (Patent No. 5740658, Patent No. 6441454) may be used. In the co-catalyst support operation, heat treatment is often required to convert the precursor (nitrate, chloride, hydroxide, acetate, etc.) into the target co-catalyst material (metal, metal oxide). While there are no restrictions on the heat treatment temperature, it is preferable to use a temperature of 400°C or lower, especially when supporting nanoparticles, to prevent thermal aggregation.

[0047] The amount of photocatalyst used and the dispersion concentration (g / L, etc.) of the photocatalyst, obtained by dividing it by the amount of water used to disperse it, should be appropriately set according to the secondary particle size of the photocatalyst used. The amount of oxidation of the substance can be increased according to the amount of light irradiated onto the photocatalyst. From the viewpoint of improving the utilization efficiency of the irradiated light, a higher dispersion concentration of the photocatalyst is preferable, preferably 0.1 g / L or higher, more preferably 1.5 g / L or higher, and even more preferably 2.5 g / L or higher. An example of an upper limit for the dispersion concentration of the photocatalyst is 50 g / L.

[0048] The light source for irradiating the photocatalyst is not particularly limited as long as it contains ultraviolet light with a wavelength of 400 nm or less to which the titanium dioxide photocatalyst responds. For example, it can be selected from fluorescent lamps, black lights, germicidal lamps, low-pressure mercury lamps, high-pressure mercury lamps, xenon lamps, mercury-xenon lamps, halogen lamps, metal halide lamps, LEDs (deep ultraviolet, ultraviolet), laser light, sunlight, etc. These lights may be shone directly onto the photocatalyst, reflected using mirrors, or guided using optical fibers. In the case of sunlight, it may be focused using a concave mirror or the like. Of these light sources, it is preferable to use black lights, germicidal lamps, low-pressure mercury lamps, high-pressure mercury lamps, xenon lamps, mercury-xenon lamps, LEDs (deep ultraviolet, ultraviolet), laser light, etc., as these are light sources capable of irradiating ultraviolet light of the required intensity. In ultraviolet irradiation, the intensity of the irradiated light (irradiance) should be 10 W / m² in the wavelength range of 400 nm or less. 2 Anything above that is acceptable, preferably 100 W / m 2 More preferably 1000 W / m 2 This concludes the explanation. When using a radiometer, it is necessary to check the spectral sensitivity curve and use a product that has spectral sensitivity in the required wavelength range. In the decomposition method of this application using titanium dioxide photocatalyst, measurement probes generally designated for UVC, UVB, and UVA are suitable, and it is more appropriate to sum all measured values. In this invention, the distance between the position closest to the light source on the outer surface of the reaction vessel (quartz beaker, etc.) (side or bottom surface depending on the irradiation direction) and the tip of the lamp fixture was measured, and the irradiance measured by separately placing the lamp fixture and measurement probe at the same distance was taken as the intensity of the irradiated light. In the case of the internal irradiation method, since the surface of the water-cooled jacket housing the lamp is in direct contact with the reaction liquid, the probe was made to be in contact with the surface of the water-cooled jacket, and the irradiance was measured at the position closest to the center of the lamp's light-emitting part.

[0049] In the light irradiation process, it is necessary to carry out the process in the presence of dissolved oxygen in the colored wastewater, and it is desirable that the colored wastewater contains a sufficient concentration of dissolved oxygen to allow the photocatalytic reaction to proceed.

[0050] In the light irradiation process, the dissolved oxygen concentration in the colored wastewater is not particularly limited, but is preferably 1 mg / L or more, more preferably 1.5 mg / L or more, and even more preferably 2 mg / L or more. The upper limit for the dissolved oxygen concentration in the colored wastewater is 200 mg / L or less. A higher dissolved oxygen concentration allows for a higher reaction rate, and since dissolved oxygen is consumed by the oxidation reaction, it is necessary to replenish it to prevent a decrease in dissolved oxygen concentration. For this reason, it is effective to constantly blow in oxygen-containing gas (e.g., air) using aeration devices such as diffusers, diffusers, or diffusers. Efficiency can be increased by subdividing bubbles using aeration devices made of materials such as sintered ceramics or synthetic resins with fine pore sizes.

[0051] For example, under atmospheric pressure, when air is blown into water, the upper limit of the dissolved oxygen concentration in the water is 14.2 mg / L at 0°C and 8.8 mg / L at 20°C. Since the dissolved oxygen concentration can be increased in proportion to the partial pressure of oxygen in the gas phase, bubbling pure oxygen will result in an upper limit of five times that of air bubbling (44 mg / L at 20°C), and if it is possible to pressurize the gas phase in the apparatus, the dissolved oxygen concentration can be increased according to that pressure. Alternatively, oxygen gas can be diluted with air or other gases to produce a gas with a higher oxygen concentration than air. In practice, the gas to be blown in and the blowing conditions should be selected within the limits of the apparatus configuration and acceptable costs.

[0052] In the light irradiation process, it is preferable to irradiate the photocatalyst with light while stirring it in colored wastewater. The stirring should be performed in the colored wastewater with a strength appropriate to the size and amount of the photocatalyst so that it is dispersed in the colored wastewater.

[0053] For small-scale laboratory-scale implementations, stirring methods include manual stirring with a stirring rod, stirring with a shaker, stirring with a magnetic stirrer and magnetic rotor, stirring with a stirring motor and stirring blades, and stirring by creating a water flow in a tank using a pump. When using a magnetic stirrer, it is preferable to stir while keeping the magnetic rotor submerged in the liquid using a fish clip or spinner flask, as rotating the magnetic rotor at the bottom of the container may cause part of the photocatalyst to be crushed and disintegrated. It should be noted that if the stirring method for colored wastewater (reaction solution) is inappropriate or the stirring is too strong, part of the photocatalyst may disintegrate, causing the photocatalytic material to detach as powder smaller than 1 μm, making light transmission difficult.

[0054] For large-scale implementations such as sewage treatment facilities, any of the various stirring devices, such as impellers, water jets, or bubbles, may be used. To effectively increase the dissolved oxygen concentration in the liquid and promote the reaction, it is preferable to employ either a magnetic stirring system, a water jet stirring system, or an impeller system.

[0055] In the method for decomposing colored wastewater of the present invention, the decomposition treatment time is not particularly limited as long as the decomposition treatment of colored wastewater progresses. For example, in the case of a batch reactor, it is about 0.1 to 100 hours, preferably about 0.5 to 50 hours. In the case of a continuous tank reactor, the residence time can also be about 0.1 to 100 hours, preferably about 0.5 to 50 hours. Furthermore, the decomposition treatment temperature is not particularly limited as long as the decomposition treatment of colored wastewater progresses. For example, it is about 5 to 80°C, preferably about 10 to 60°C.

[0056] As described above, in the colored wastewater decomposition method of the present invention, the colored wastewater to be decomposed can be discharged from any facility or process, as long as its chromaticity is within the above range. However, for wastewater with a chromaticity exceeding 1000 degrees (for example, wastewater exhibiting properties of poor microbial decomposition), the efficiency of the decomposition treatment decreases. Such highly colored wastewater is typically wastewater generated in the sewage treatment process (specifically, wastewater exhibiting properties of poor microbial decomposition generated in the treatment process at a sewage treatment plant). At a sewage treatment plant, wastewater is treated sequentially, but the separated liquid after dewatering of anaerobic digested sludge is wastewater with a high concentration of poorly decomposable organic components. Further decomposition treatment of this separated liquid is difficult, and currently, it is returned as wastewater to grit tanks, etc., placing a heavy burden on the entire sewage treatment system.

[0057] For wastewater with a color intensity exceeding 1000 degrees, it is effective to apply another decomposition treatment method as a preliminary treatment before applying the colored wastewater decomposition treatment method of the present invention, thereby reducing the color intensity of the colored wastewater to a range of 50 degrees to 1000 degrees, and then applying the colored wastewater decomposition treatment method of the present invention as a subsequent treatment. Below, a preliminary decomposition treatment method for wastewater that can be suitably performed prior to the colored wastewater decomposition treatment method of the present invention will be described.

[0058] 2. Preliminary decomposition treatment method preceding the decomposition treatment method for colored wastewater As a preliminary decomposition treatment method preceding the decomposition treatment method for colored wastewater, it is preferable to employ the following preliminary decomposition treatment method for wastewater. The wastewater to be subjected to preliminary decomposition treatment is, for example, a COD value of 100 mg / L or more, and a BOD value and COD Cr Ratio of value (BOD / COD) Cr The ozone content is 0.4 or less, meaning it exhibits properties of being poorly decomposable by microorganisms. This wastewater pre-decomposition treatment method is characterized by irradiating the wastewater with ultraviolet light in the presence of dissolved oxygen, with the ultraviolet light wavelengths including 200-350 nm and substantially excluding wavelengths less than 200 nm. By having these characteristics, this wastewater pre-decomposition treatment method can efficiently pre-decompose wastewater without generating ozone.

[0059] In other words, prior to the decomposition treatment method for colored wastewater of the present invention, the COD value is 100 mg / L or more, and the BOD value and COD Cr Ratio of value (BOD / COD) Cr A pre-decomposition treatment method for wastewater exhibiting properties of poor microbial decomposition, where the ratio is 0.4 or less, is characterized by irradiating the wastewater with ultraviolet light in the presence of dissolved oxygen, wherein the ultraviolet wavelength includes 200 to 350 nm and substantially does not include wavelengths less than 200 nm. By applying this pre-decomposition treatment method for wastewater, colored wastewater can be obtained, and the resulting colored wastewater can be used as the colored wastewater to be decomposed in the present invention.

[0060] In the wastewater pre-decomposition treatment method of the present invention, the wastewater to be subjected to pre-decomposition treatment has a COD value (chemical oxygen demand) of 100 mg / L or more, and the BOD value and COD Cr Ratio of value (BOD / COD) Cr The COD value is 0.4 or less, meaning it exhibits properties of being poorly decomposable by microorganisms. In the wastewater pre-decomposition treatment method of the present invention, pre-decomposition treatment means that by applying the pre-decomposition treatment method of the present invention to the wastewater to be pre-decomposed, the wastewater after pre-decomposition treatment will have a COD value that is at least lower than that before pre-decomposition treatment, and the rate of reduction will be 10% or more.

[0061] In the present invention, the wastewater targeted for preliminary decomposition treatment is typically wastewater generated in the sewage treatment process (specifically, wastewater generated in the treatment process at a sewage treatment plant, which exhibits properties of being difficult to decompose by microorganisms). As described above, wastewater is treated sequentially at a sewage treatment plant, but the separated liquid after dewatering of anaerobic digested sludge is wastewater with a high concentration of difficult-to-decompose organic components. Further decomposition treatment of this separated liquid is difficult, and currently it is returned as wastewater to grit tanks, etc., placing a heavy burden on the entire sewage treatment system. In the present invention, such separated liquid can be used as wastewater targeted for preliminary decomposition treatment.

[0062] The wastewater targeted in this invention is wastewater that exhibits properties that make it difficult to decompose by microorganisms. Wastewater with a large ratio of COD (Chemical Oxygen Demand) to BOD (Biochemical Oxygen Demand) can be said to have properties that make it difficult to decompose by microorganisms. In this invention, COD Cr Values ​​above 100 mg / L, BOD value and COD Cr Ratio of value (BOD / COD) Cr Wastewater with a value of 0.4 or less is defined as wastewater exhibiting properties that make microbial decomposition difficult.

[0063] Wastewater that is difficult to decompose microbially can be discharged at any facility or process, as long as its COD and BOD values ​​are within the above ranges. For example, wastewater generated at any of the processes in a sewage treatment plant, such as activated sludge treatment, sludge concentration, anaerobic digestion, or sludge dewatering, is acceptable. Furthermore, wastewater received at wastewater treatment facilities in various factories and other facilities, or wastewater generated at any of the treatment processes, is also acceptable.

[0064] Specific examples of wastewater to be decomposed in the present invention include dewatered filtrate (dewatered liquid) of sewage sludge (primary sedimentation sludge, excess sludge, mixed sludge, etc.), dewatered filtrate after anaerobic digestion of sewage sludge, dewatered filtrate after solubilization treatment of sewage sludge, dewatered filtrate after solubilization treatment of sewage sludge and further anaerobic digestion, and dewatered filtrate after anaerobic digestion of sewage sludge and subsequent solubilization treatment. The wastewater subjected to decomposition treatment may be of only one type or a mixture of two or more types of wastewater. Typically, the wastewater to be decomposed in the present invention includes at least one of the above-mentioned dewatered filtrates.

[0065] In sewage treatment plants, sludge is sometimes solubilized to reduce sludge volume and improve process efficiency. As mentioned above, the wastewater that is difficult to decompose by microorganisms, which is the target of this invention, may have undergone such solubilization treatment. Any method can be used for solubilization treatment, and examples include chemical methods using chemical agents, physicochemical methods using heating or hydrothermal reactions, mechanical methods such as ultrasound and bead mills, and electrochemical methods by electrolysis.

[0066] From the viewpoint of suitably exhibiting the effects of the present invention, the COD of the wastewater to be decomposed. Cr The values ​​are preferably around 100 to 30,000 mg / L, more preferably around 100 to 10,000 mg / L, and even more preferably around 100 to 3,000 mg / L. Furthermore, from the viewpoint of suitably exhibiting the effects of the present invention, the BOD value and COD of the wastewater to be decomposed should be considered. Cr Ratio of value (BOD / COD) Cr The ratio is 0.4 or less, preferably 0.3 or less, and more preferably 0.25 or less.

[0067] As a result of solubilization treatment, the wastewater obtained shows increased COD and BOD, and the difference between COD and BOD also increases, making it even more difficult to decompose than before solubilization treatment. For example, without solubilization treatment, the dewatered liquor after anaerobic digestion of sewage sludge has a COD of about 300-3000 mg / L and a BOD of about 10-500 mg / L, whereas the dewatered liquor after anaerobic digestion of sewage sludge after solubilization treatment has a COD of about 500-5000 mg / L and a BOD of about 10-500 mg / L. The decomposition method of the present invention can be applied even to wastewater with such high COD levels.

[0068] In the present invention, the COD value of wastewater after the preliminary decomposition treatment is lower than that before the preliminary decomposition treatment. In the present invention, the decomposition rate of the COD value of wastewater before and after the preliminary decomposition treatment ((COD value of wastewater before preliminary decomposition treatment - COD value of wastewater after preliminary decomposition treatment) / (COD value of wastewater before preliminary decomposition treatment)) is 10% or more, preferably 20% or more, and more preferably 40% or more.

[0069] In the preliminary decomposition treatment, the chromaticity of the wastewater to be decomposed is not particularly limited, but is preferably around 50 to 10,000 degrees, more preferably around 50 to 7,000 degrees, and even more preferably around 70 to 4,000 degrees. Chromaticity refers to the degree of pale yellow to yellowish-brown color caused by substances dissolved in water or presenting colloidally. One degree of chromaticity is defined as the color obtained by adding 1 mL of chromaticity standard solution (1 mg of platinum and 0.5 mg of cobalt) to 1,000 mL of water. It should be noted that when measuring the chromaticity of turbid water, the result will be affected by the turbidity. Chromaticity measured after removing turbidity by filtration or centrifugation is called "true chromaticity," while chromaticity measured without such pretreatment is called "apparent chromaticity." In the dewatered separated liquid of digested sludge used in the examples of the present invention, filtration (using filter paper with a particle size retention of 1 μm) was performed to remove coarse sediment before the preliminary decomposition treatment, but turbidity remained. When filtration was performed with an even finer 0.22 μm filter paper to completely remove turbidity, a change was observed in the overall shape of the UV-VIS spectrum, indicating that the properties of the actual solution could not be preserved. Therefore, in this invention, the pre-filtration treatment is standardized to be performed with 1 μm filter paper. Accordingly, the chromaticity in this invention is defined as the "apparent chromaticity after 1 μm filtration," which includes the effect of turbidity. Furthermore, the TOC (Total Organic Carbon) of the wastewater to be decomposed is not particularly limited, but is preferably about 30 to 10,000 mg / L, more preferably about 30 to 3,000 mg / L, and even more preferably about 30 to 1,000 mg / L. Furthermore, the ammoniacal nitrogen (NH4-N) of the wastewater to be decomposed is not particularly limited, but is preferably about 100 to 5,000 mg / L, more preferably about 100 to 4,000 mg / L, and even more preferably about 100 to 2,000 mg / L. Furthermore, the pH of the wastewater to be decomposed is preferably around 5 to 9, more preferably around 6 to 9, and even more preferably around 6 to 8.5.

[0070] Furthermore, in the present invention, it is preferable that the color of the wastewater after the preliminary decomposition treatment is lower than that before the preliminary decomposition treatment. In the present invention, the decomposition rate of the color of the wastewater before and after the preliminary decomposition treatment is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more. Furthermore, in the present invention, it is preferable that the TOC value of the wastewater after the preliminary decomposition treatment is lower than that before the preliminary decomposition treatment. In the present invention, the decomposition rate of the TOC value of the wastewater before and after the preliminary decomposition treatment is preferably 10% or more, more preferably 20% or more, and even more preferably 40% or more. In the present invention, the decomposition rate of ammoniacal nitrogen (NH4-N) in the wastewater before and after the preliminary decomposition treatment is preferably 10% or more, more preferably 40% or more, and even more preferably 80% or more. Furthermore, in the present invention, the pH of the wastewater after the preliminary decomposition treatment is preferably about 5.5 to 8.5, more preferably about 6.0 to 8.5, and even more preferably about 6 to 8.0.

[0071] In this invention, in order to confirm the properties of the wastewater to be subjected to the preliminary decomposition treatment and to evaluate the effectiveness of the preliminary decomposition treatment method for wastewater in this invention, water quality tests of the wastewater are conducted before and after the preliminary decomposition treatment. These water quality tests are also used in the examples described later. For each test method, those prescribed by laws and regulations (official methods) are followed, and for others, the wastewater testing methods (Japan Sewerage Association, 2012 edition) are followed. In this invention, these will be referred to as "official methods, etc."

[0072] For measuring COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand), and TOC (Total Organic Carbon) values ​​of wastewater, pretreatment is performed by filtration using glass fiber filter paper with a pore size of 1 μm (GFP), and measurements are taken as soluble BOD, soluble COD, and soluble TOC. In COD measurement, the oxygen demand is determined using potassium dichromate, and then the COD Cr It is expressed as a value. In BOD measurement, N-allylthiourea is added and soluble C-BOD (Wastewater Testing Methods 2012 Edition, Part 2, Chapter 1, Section 21-2, Japan Sewerage Association) is measured. Hereafter, unless otherwise specified, in this invention, soluble C-BOD is referred to as BOD (BOD value), and soluble COD CrThe COD (COD value) is denoted as COD, and the soluble TOC (TOC value) is denoted as TOC. Furthermore, chromaticity was analyzed by colorimetric method after GFP filtration, and ammoniacal nitrogen (NH4-N) was analyzed by ion chromatography after 0.45 μm filtration. pH was measured using the glass electrode method.

[0073] In addition to the tests conducted by official methods as described above, the present invention measures the ultraviolet-visible (UV-VIS) spectrum of wastewater using a spectrophotometer to determine surrogate indices for COD, chromaticity, and turbidity. UV-VIS spectra can be measured quickly (within 1 minute) with a small volume of liquid (approximately 3 mL), and it is known that absorbance at specific wavelengths correlates well with water quality values. Therefore, in order to evaluate the decomposition rate by the pre-decomposition treatment method of the present invention over time, the absorbance at the wavelengths shown below is adopted as a surrogate indice, and its rate of change is calculated.

[0074] First, we will use 254nm absorbance (A254) as a substitute index for COD. In JIS K 0807 "Automatic UV absorbance measuring instrument for water quality monitoring", the UV absorbance measurement value at a wavelength of 253.7nm is used as the COD. Mn It has been shown that it is correlated with and used for calculating water pollution load related to total water load regulation. In this invention, COD is used as COD Mn Not COD Cr Although this method is used, the actual dewatered liquid of digested sludge is measured by COD. Cr When A254 was measured, a good linear correlation was observed between the two.

[0075] Next, 390nm absorbance (A390) is used as a surrogate index for chromaticity. Among the methods for measuring chromaticity, the transmitted light measurement method (Wastewater Testing Methods 2012 Edition, Part 2, Chapter 1, Section 4, Item 1, Japan Sewerage Association) measures the degree of pale yellow to yellowish-brown color caused by substances dissolved in water or present in colloidal form, using spectrophotometric analysis. When chromaticity and A390 were measured using a digital turbidimeter (WA-PT-4DG, Kyoritsu Chemical Research Institute) for the dewatered separated liquid of actual digested sludge, a good linear relationship was obtained.

[0076] Furthermore, the absorbance at 870 nm (A870) was used as a surrogate indicator of turbidity. Among the methods for measuring turbidity, the transmitted light measurement method (Wastewater Testing Methods 2012 Edition, Part 2, Chapter 1, Section 5, Item 2, Japan Sewerage Association) involves shining light from one side and measuring the transmitted light. Turbidity (kaolin standard) is determined by utilizing the fact that the degree of light attenuation is related to the concentration of suspended solids in the water. When turbidity (polystyrene standard) and A870 were measured using a digital turbidimeter (WA-PT-4DG, Kyoritsu Chemical Research Institute) for the dewatered separated liquid of actual digested sludge, a good linear relationship was obtained.

[0077] The wastewater pre-decomposition treatment method of the present invention comprises a pre-decomposition treatment step in which ultraviolet light is irradiated onto the wastewater to be pre-decomposed in the presence of dissolved oxygen, and the ultraviolet light is characterized in that it includes wavelengths of 200 to 350 nm and substantially does not include wavelengths less than 200 nm. By comprising a pre-decomposition treatment step in which ultraviolet light of a specific wavelength is irradiated onto the specific wastewater in the presence of dissolved oxygen, the wastewater pre-decomposition treatment method of the present invention makes it possible to efficiently pre-decompose the wastewater while suppressing the generation of ozone due to ultraviolet irradiation.

[0078] In the present invention, the wavelength range of ultraviolet light irradiated onto the wastewater should include 200 to 350 nm and substantially exclude wavelengths less than 200 nm. Preferably, it includes 200 to 315 nm and substantially excludes wavelengths less than 200 nm. More preferably, it includes 220 to 315 nm and substantially excludes wavelengths less than 200 nm. Even more preferably, it includes 250 to 315 nm and substantially excludes wavelengths less than 200 nm.

[0079] Here, "ultraviolet light substantially does not contain wavelengths below 200 nm" means that the irradiation intensity of the strongest wavelength below 200 nm is 1 / 10 or less of the irradiation intensity of the strongest wavelength between 200 and 315 nm. Any ultraviolet light (light) that meets this condition can be monochromatic light of a specific wavelength, light consisting of emission lines of multiple wavelengths, or light having a continuous spectrum.

[0080] In ultraviolet irradiation, the intensity of the irradiated light (irradiance) is 10 W / m² in the wavelength range of 350 nm or less. 2 Anything above that is acceptable, preferably 50W / m 2 More preferably 250 W / m 2 That concludes the explanation. When using a radiometer probe, it is necessary to check the spectral sensitivity curve and use a product that has spectral sensitivity in the required wavelength range. In the decomposition method of the present invention, measurement probes generally designated for UVC and UVB fall into this category, and it is more appropriate to sum both measurement values. In the present invention, the distance between the position closest to the light source on the outer surface of the reaction vessel (quartz beaker, etc.) (the side or bottom surface depending on the irradiation direction) and the tip of the lamp fixture was measured, and the irradiance measured by separately placing the lamp fixture and the measurement probe at the same distance was taken as the intensity of the irradiated light.

[0081] Examples of light sources capable of emitting such ultraviolet light include low-pressure mercury lamps, high-pressure mercury lamps, xenon lamps, mercury-xenon lamps, electrodeless discharge lamps, and deep ultraviolet LEDs. Furthermore, by using optical filters such as bandpass filters in conjunction with such light sources, it is possible to irradiate only ultraviolet light of a single wavelength or a specific wavelength range.

[0082] From the standpoint of increasing the intensity of the irradiated light, it is currently preferable to use ozone-free low-pressure mercury lamps and high-pressure mercury lamps. Low-pressure mercury lamps have their main emission peaks at wavelengths of 185 nm and 254 nm. High-pressure mercury lamps are light sources with their main emission peaks at wavelengths of 254 nm and 365 nm, and inherently include emission at a wavelength of 185 nm. Ozone-free low-pressure mercury lamps and high-pressure mercury lamps use ozone-free quartz glass (glass made by adding heavy metals to fused quartz glass to prevent the transmission of ultraviolet light with wavelengths below 240 nm) in the lamp bulb, so that light with wavelengths below 200 nm is not emitted.

[0083] Furthermore, the ultraviolet irradiation of wastewater is carried out in the presence of dissolved oxygen. Specifically, by supplying oxygen-containing gas to the wastewater while performing ultraviolet irradiation, the wastewater can be irradiated with ultraviolet light in the presence of dissolved oxygen. The supply of oxygen-containing gas, which is carried out in conjunction with ultraviolet irradiation, is done in the wastewater pre-decomposition treatment method of the present invention to ensure that the wastewater contains a sufficient concentration of dissolved oxygen.

[0084] The dissolved oxygen concentration in wastewater is not particularly limited, but is preferably 1 mg / L or higher, more preferably 1.5 mg / L or higher, and even more preferably 2 mg / L or higher. The upper limit for the dissolved oxygen concentration in wastewater is 200 mg / L or lower. A higher dissolved oxygen concentration allows for a higher reaction rate, and since dissolved oxygen is consumed by the oxidation reaction, it is necessary to replenish it to prevent a decrease in dissolved oxygen concentration. For this reason, it is effective to constantly blow in oxygen-containing gas (e.g., air) using aeration devices such as diffusers, diffusers, or diffusers. Efficiency can be increased by subdividing bubbles using aeration devices made of materials such as sintered ceramics or synthetic resins with fine pore sizes.

[0085] For example, under atmospheric pressure, when air is blown into water, the upper limit of the dissolved oxygen concentration in the water is 14.2 mg / L at 0°C and 8.8 mg / L at 20°C. Since the dissolved oxygen concentration can be increased in proportion to the partial pressure of oxygen in the gas phase, bubbling pure oxygen will result in an upper limit of five times that of air bubbling (44 mg / L at 20°C), and if it is possible to pressurize the gas phase in the apparatus, the dissolved oxygen concentration can be increased according to that pressure. Alternatively, as an oxygen-containing gas, oxygen gas can be diluted with air or other gas to produce a gas with a higher oxygen concentration than air, which can then be blown in. In practice, the oxygen-containing gas to be blown in and the blowing conditions should be selected within the limits of the apparatus configuration and allowable costs.

[0086] Furthermore, it is desirable to agitate the wastewater along with ultraviolet irradiation and the supply of oxygen-containing gas. This agitation is performed to supply sufficient dissolved oxygen to the wastewater.

[0087] Any method of stirring is acceptable as long as it can stir the water with a strength appropriate to the volume and viscosity of the liquid. For small-scale laboratory implementations, methods include manual stirring with a stirring rod, stirring using a shaker, stirring using a magnetic stirrer and magnetic rotor, stirring using a stirring motor and stirring blades, and stirring by creating a water flow in a tank with a pump.

[0088] For large-scale implementations such as sewage treatment facilities, any of the various stirring devices, such as impellers, water jets, or bubbles, may be used. To effectively increase the dissolved oxygen concentration in the liquid and promote the reaction, it is preferable to employ either a magnetic stirring system, a water jet stirring system, or an impeller system.

[0089] In the wastewater pre-decomposition treatment method of the present invention, the pre-decomposition treatment time is not particularly limited as long as the wastewater pre-decomposition treatment is progressing, for example, in the case of a batch reactor, it is about 0.1 to 100 hours, preferably about 0.5 to 50 hours. In the case of a continuous tank reactor, the residence time can also be about 0.1 to 100 hours, preferably about 0.5 to 50 hours. Furthermore, the pre-decomposition treatment temperature is not particularly limited as long as the wastewater pre-decomposition treatment is progressing, for example, it is about 5 to 80°C, preferably about 10 to 60°C.

[0090] 3. Wastewater decomposition treatment equipment The wastewater decomposition treatment apparatus of the present invention is a colored wastewater decomposition treatment apparatus for use in a method for decomposing colored wastewater, and is equipped with a function to perform a light irradiation step in which light is irradiated onto a photocatalyst in colored wastewater in the presence of dissolved oxygen, wherein the chromaticity of the colored wastewater subjected to the light irradiation step is in the range of 50 degrees to 1000 degrees, the photocatalyst has a primary particle diameter of 100 nm or less and a secondary particle diameter of 1 μm or more, and the photocatalyst has a titanium dioxide content of 90% by mass or more.

[0091] Details regarding colored wastewater, photocatalysts, ultraviolet irradiation, dissolved oxygen, etc., are as described in "1. Method for Decomposing Colored Wastewater" above.

[0092] The wastewater decomposition apparatus of the present invention has a function to perform a light irradiation step in which light is irradiated onto the photocatalyst in colored wastewater in the presence of dissolved oxygen, and there are no particular restrictions on the specific configuration as long as it can treat the colored wastewater. For example, the wastewater decomposition apparatus of the present invention comprises a light irradiation unit, a stirring unit, and a gas injection unit in a reaction vessel. The ultraviolet irradiation unit can be installed inside the reaction vessel and immersed in the wastewater to irradiate light from within the liquid (internal irradiation type), or it can be installed outside and irradiate light through the vessel wall from the bottom or side of the reaction vessel (external irradiation type).

[0093] In the case of an external irradiation type apparatus, the entire reactor should be constructed from a material that can transmit the required ultraviolet wavelength, or a window plate should be attached to the irradiation section. Such a material can be any of borosilicate glass or quartz glass, but from the viewpoint of transmitting ultraviolet light at a wavelength of around 250 nm, quartz glass is preferred.

[0094] In the case of internal irradiation, the reactor does not need to transmit ultraviolet light, so from that perspective, it can be made of any material. An outer casing may be required to immerse the light irradiation lamp in the liquid, and the material for this should be selected in the same way as the window plate material for external irradiation devices.

[0095] The configurations of the stirring device section and the gas injection section can be those described in "1. Method for Decomposing Colored Wastewater" above. [Examples]

[0096] The present invention will be described in detail below with reference to examples and comparative examples. However, the present invention is not limited to the examples.

[0097] <Example 1 of photocatalyst preparation> (Preparation of granular Pt / TiO2 (platinum-supported titanium oxide granules)) Platinum was supported onto titanium dioxide powder, and then granulated to form granular Pt / TiO2. The titanium dioxide powder used was AEROXIDE® TiO2P25 (hereinafter referred to as P25) manufactured by Nippon Aerosil, with an average primary particle size of 21 nm (catalog value). The detailed procedure for this preparation is shown below.

[0098] (1) Plasma loading onto titanium dioxide powder by photoprecipitation method 400 mL of a 50 vol% methanol aqueous solution was placed in a spinner flask (Chemglass Life Science, CLS-1400) with a nominal capacity of 500 mL, and 8 g of titanium dioxide powder (P25) was added. 1.23 mL of chlorplatinic acid aqueous solution (0.1 mol / L) was added, and dissolved oxygen in the flask and solution was removed by bubbling nitrogen gas (500 mL / min) through a PFA tube connected to the side arm cap for 30 minutes while stirring with a magnetic stirrer (approximately 350 rpm).

[0099] After stopping the nitrogen gas flow and sealing the container, light (wavelength 365 nm) from a handy UV lamp (AS ONE, SLUV-8) was shone from the side while stirring continued. Gas sampling was performed using a gas-tight syringe from a septum attached to the nitrogen gas outlet channel connected to the side arm cap on the opposite side, and analyzed by TCD gas chromatography (molecular sieve 5A column) to confirm the generation of hydrogen. After 1 hour of light irradiation, it was confirmed that hydrogen was steadily generated due to the completion of the photodeposition reaction of Pt onto titanium dioxide.

[0100] After the photoprecipitation reaction was complete, the precipitate was collected by centrifugation, redispersed with water, and the precipitate was collected again. This process was repeated a total of three times, and the mixture was dried at 100°C to obtain a photocatalyst composed of platinum-supported titanium oxide (Pt / TiO2). In the photocatalyst, the amount of platinum supported on the titanium oxide was 0.3% by weight.

[0101] (2) Classification of photocatalysts The prepared photocatalytic material became lumpy after drying, with uneven particle size. This was classified by the following crushing, sieving, and water sedimentation procedures. The photocatalytic material was crushed in an agate mortar, and particles that passed through a 125 μm sieve but not a 40 μm sieve were collected. These were placed in a crucible and calcined in a muffle furnace at 400°C for 1 hour.

[0102] As it stands, fine particles generated during grinding remain attached, preventing complete removal of particles smaller than 40 μm. Therefore, the attached fine particles were removed by the following water sedimentation procedure. The sieved secondary particles of 40-125 μm were placed in a screw-cap vial (AS ONE No. 8), 100 mL of water was added, the lid was closed and shaken, and then allowed to stand. Leaving the particles that had completely settled, the supernatant, which still contained some fine particles and was slightly suspended, was discarded up to a depth of 8.5 cm from the water surface. Water was added again to a total volume of 100 mL, shaken, allowed to stand, and the supernatant was discarded. This procedure was repeated 7 times. With each repetition, the suspension in the supernatant disappeared, and a completely clear supernatant was obtained. Finally, after discarding the supernatant, the contents were transferred to a Teflon® evaporating dish with a small amount of water, heated to approximately 40°C, and dried to obtain a photocatalyst with secondary particle diameters of 40-125 μm. Laser diffraction and scattering measurements revealed that the average secondary particle size of this photocatalyst in its aqueous dispersion state was 86 μm. Measurements of the nitrogen adsorption surface area, powder X-ray diffraction, and transmission electron microscopy of the prepared photocatalyst confirmed that the primary particle size of titanium dioxide in the prepared photocatalyst remained unchanged from that of the raw material P25 powder. Therefore, the prepared granular Pt / TiO2 had an average primary particle size of 21 nm, a titanium dioxide content of 99.7% (Pt 0.3 wt%), and an average secondary particle size of 86 μm.

[0103] (3) Measurement of UV-VIS spectrum A spectrophotometer (Shimadzu Corporation, UV-1800) was used to measure the UV-VIS spectrum. To measure the granular photocatalyst while stirring it and maintaining its shape, a hole was drilled in the cover of the measurement chamber and the following equipment was installed so that no ambient light could leak in. A magnetic stirrer was placed in the center of the optical path in the measurement chamber, and a 100 mL quartz beaker was placed on top of it. 80 mL of water was added to the quartz beaker, and a predetermined amount of granular Pt / TiO2 was added. A spinner flask (Corning Corporation, nominal capacity 125 mL, diameter 5 cm) was placed above the center of the beaker so that the stirring blade rotated in the liquid and the measurement light passed underneath it.

[0104] Figure 1 shows the results of measuring UV-VIS spectra while stirring at 500 rpm, varying the dispersion concentration of granular photocatalyst. The absorbance on the vertical axis is shown converted to per 1 cm of optical path length. When measured with water alone without photocatalyst, the absorbance is a constant value of zero, and there is almost no noise, indicating no interference from the stirring blades to the measurement light. Increasing the dispersion concentration of the photocatalyst increases the absorbance, but it remains constant regardless of wavelength, indicating that shielding phenomena are dominant rather than bandgap absorption or Mie scattering. As the amount of photocatalyst increases, the movement of particles affects the noise, but when comparing the average values ​​against wavelength from two measurements, they were in perfect agreement.

[0105] <Example of photocatalyst preparation 2> (Preparation of powdered Pt / TiO2 (platinum-supported titanium oxide fine powder)) Under the same conditions as in Preparation Example 1, platinum was supported on titanium dioxide powder (Nippon Aerosil, P25). The resulting photocatalytic mass was then crushed in an agate mortar, and the portion that passed through a 40 μm sieve was collected. This was further ground in an agate mortar until it became a fine powder, yielding Pt / TiO2 with a secondary particle size of less than 40 μm. The average secondary particle size of the powdered Pt / TiO2 fine particles in water after ultrasonic dispersion, as measured by a dynamic light scattering particle size distribution analyzer, was 0.12 μm. The powdered Pt / TiO2 had an average primary particle size of 21 nm and a titanium dioxide content of 99.7%, the same as the granular Pt / TiO2 in Preparation Example 1, but the average secondary particle size was significantly different, being less than 1 μm.

[0106] A spectrophotometer (Shimadzu Corporation, UV-1800) was used to measure the UV-VIS spectrum. A standard 1 cm square quartz cell was used, and a dispersion of pre-ultrasonically dispersed powdered Pt / TiO2 was added. No stirring was performed during the measurement to maintain a stable dispersion state.

[0107] Figure 2 shows the results of measuring UV-VIS spectra at varying dispersion concentrations of powdered Pt / TiO2. Unlike the case of granular photocatalysts, high absorbance was observed even at low dispersion concentrations. Furthermore, a significant wavelength dependence was observed, with the high absorbance below 400 nm being attributed to the bandgap absorption of TiO2. The fact that absorbance does not become zero above 400 nm suggests that scattering phenomena such as Mie scattering are also involved.

[0108] Figure 3 shows the results of plotting the absorbance at a wavelength of 365 nm for Figures 1 and 2 against the photocatalyst dispersion concentration. A linear relationship was obtained for both granular and powdered photocatalysts, but the slopes differed significantly, with the granular Pt / TiO2 having a slope 1 / 150th that of the powdered Pt / TiO2. Since absorbance is the logarithm of the reciprocal of transmittance, there is a very large difference in transmittance between the two.

[0109] <Example 3 of photocatalyst preparation> (Preparation of granular Au / TiO2 (gold-supported titanium oxide granules)) Gold was supported onto titanium dioxide powder by precipitation-precipitation loading, and then granulated to obtain granular Au / TiO2. The titanium dioxide powder used was the same P25 as used in Preparation Example 1, with an average primary particle size of 21 nm (catalog value). The detailed procedure for this preparation example is shown below. 0.63 mmol of chloroauric acid (HAuCl4·4H2O) was dissolved in 1 L of distilled water, heated to 70°C, and NaOH aqueous solution was added dropwise to adjust the pH to 7. 4.0 g of titanium dioxide (P25) powder was added to this mixture and stirred at 70°C for 1 hour. After this, the mixture was cooled to room temperature, the precipitate was thoroughly washed with distilled water, dried, and calcined in air at 400°C for 4 hours to obtain a photocatalyst consisting of gold-supported titanium dioxide (Au / TiO2). The amount of gold supported, calculated from the amount of chloroauric acid added, is 3.0% by weight, but in this preparation method, some of the added gold is lost during washing. The amount of gold supported in the actual sample, determined by ICP emission spectroscopy, was 1.5% by weight. Therefore, the titanium dioxide content of the Au / TiO2 photocatalyst was 98.5%. Classification of the photocatalyst and removal of fine particles were performed in the same manner as in Preparation Example 1, yielding photocatalysts with secondary particle sizes of 40–125 μm.

[0110] <Example 1> As wastewater A', the dewatered separated liquid obtained after solubilization treatment of sewage sludge and anaerobic digestion at a sewage treatment plant was pre-treated by filtration using Kiriyama filter paper 5C (retaining particle size 1 μm). The soluble COD of this wastewater A' was calculated. Cr The values ​​were 2200 mg / L and the chromaticity was 3600 degrees. Furthermore, when granular Pt / TiO2 from Preparation Example 1 was directly added to wastewater A' and the photocatalyst was irradiated with light in the presence of dissolved oxygen, no effect of accelerating the decomposition treatment of wastewater A' was observed.

[0111] Next, 300 mL of a solution obtained by diluting wastewater A' with water 10 times was designated as colored wastewater A. COD of colored wastewater A CrThe values ​​were 220 mg / L and the color was 360 degrees. To 300 mL of this colored wastewater A, 0.9 g of granular Pt / TiO2 from Preparation Example 1 was added and decomposition treatment was carried out by the following method. A separable flask type photochemical reactor (Sen special light source) was used as the reaction vessel, and 300 mL of colored wastewater A was added. Air (1000 mL / min) with a flow rate controlled by a mass flow controller was injected into the test solution in a foamy manner from a gas injection filter (Fuji Rika Kogyo F335-01, pore size 5~10 μm), and dissolved oxygen was supplied to colored wastewater A by stirring (350 rpm) using a stirrer (Tokyo Rika Kikai, SPZ-1000). For light irradiation, a 100 W high-pressure mercury lamp (HL100G, Sen special light source) was set in the water-cooled jacket in the center of the photochemical reactor and the reaction solution in the separable flask was internally irradiated.

[0112] Figure 4 shows the emission line spectrum of the mercury lamp used in the example (data provided by Sen Special Light Source). The lamp bulb is made of ozone-free quartz glass, which has zero transmittance for ultraviolet light below 210 nm. Therefore, the emission line at 185 nm, which is seen in ordinary mercury lamps, does not appear in the spectrum. An illuminance / luminance / irradiance meter (Delta Ohm, HD2302.01) was used to measure the intensity of the irradiated light (irradiance). Three types of probes were connected and measured according to the wavelength range of ultraviolet light being measured (UVC, UVB, UVA). LP471UVC was used for UVC measurement. The measurement wavelength range of this probe is 220-280 nm. LP471UVB was used for UVB measurement. The measurement wavelength range of this probe is 280-315 nm. LP471UVA was used for UVA measurement. The measurement wavelength range of this probe is 315-400 nm. The irradiance measured at the center height of the lamp's light-emitting part, in contact with the side of the water-cooled jacket where the lamp is installed, was 248 W / m². 2 (UVC probe), 557W / m 2 (UVB probe), 330W / m 2 (UVA probe) was used. The total amount of ultraviolet radiation was 1135 W / m². 2 (Wavelengths were 220-400 nm.)

[0113] Solution analysis for evaluating the decomposition rate was performed using a spectrophotometer (UV-1800, Shimadzu Corporation). A portion of the wastewater sample (test solution) was placed in a quartz cell with a path length of 10 mm, and absorbance was measured in the wavelength range of 190-900 nm. The following values ​​were calculated as indicators of COD decomposition, chromaticity reduction, and turbidity reduction.

[0114] COD retention rate: R254 = (254nm absorbance at each time point) / (254nm absorbance of wastewater before treatment) Chromaticity retention rate: R390 = (390nm absorbance at each time point) / (390nm absorbance of wastewater before treatment) Turbidity retention rate: R870 = (870nm absorbance at each time point) / (870nm absorbance of wastewater before treatment)

[0115] The photocatalyst dispersion concentration is 3.0 g / L. As described above, the soluble COD of colored wastewater A after 10-fold dilution before decomposition. Cr The value was 220 mg / L, and the chromaticity was 360 degrees. Light irradiation was performed continuously for 3 hours, after which it was stopped. During this time, 5 mL of the liquid was sampled every 30 minutes and analyzed using a spectrophotometer.

[0116] Figure 5 shows the results of plotting the absorbance change at a wavelength of 254 nm as the COD retention rate, based on the absorbance before treatment, against the treatment time. Similarly, Figure 6 shows the results of plotting the absorbance change at a wavelength of 390 nm as the chromatic retention rate, based on the absorbance before treatment, against the treatment time. The reason for using a logarithmic vertical axis here is that the oxidative decomposition reaction of organic pollutants in water generally follows a first-order reaction rate equation with respect to the organic pollutant concentration. In this case, plotting the reaction time on the horizontal axis and the retention rate of the substance concentration (C / C0) on the vertical axis (logarithmic axis) results in a straight line, confirming a first-order reaction.

[0117] <Comparative Example 1> The decomposition treatment of colored wastewater A was carried out in the same manner as in Example 1, except that only colored wastewater A was used without adding a photocatalyst and the solution was stirred with a magnetic stirrer. The results of plotting the COD and the remaining chromaticity against the treatment time are shown in Figures 5 and 6, respectively.

[0118] <Comparative Example 2> The decomposition treatment of colored wastewater A was carried out in the same manner as in Example 1, except that 0.9 g of powdered Pt / TiO2 from Preparation Example 2 was added to 300 mL of colored wastewater A as a photocatalyst and stirred with a magnetic stirrer. The photocatalyst dispersion concentration was the same as in Example 1, 3.0 g / L, except that the photocatalyst material was powdered Pt / TiO2 instead of granular Pt / TiO2. The results of plotting the COD and the remaining chromaticity against the treatment time are shown in Figures 5 and 6, respectively.

[0119] As shown in Figures 5 and 6, the results indicate that the decomposition reaction was accelerated, as the residual rate of COD and chromaticity was significantly reduced in Example 1, which added granular Pt / TiO2 from Preparation Example 1, compared to Comparative Example 1, which did not contain a photocatalyst. In contrast, Comparative Example 2, which added powdered Pt / TiO2 from Preparation Example 2, showed no significant difference from Comparative Example 1, indicating that the photocatalyst did not have any effect. Colored wastewater A had a high chromaticity of 360 degrees, and its absorbance at 365 nm, the dominant wavelength of the mercury lamp, was also high at 0.39. The results for Comparative Example 2 showed that the addition of powdered photocatalyst did not promote decomposition. In contrast, as shown in Example 1, by adding granular photocatalysts with a secondary particle size of 40-125 μm, the wastewater could be decomposed faster than in Comparative Example 1, which did not contain a photocatalyst.

[0120] <Example 2> For wastewater B', the dewatered separated liquid obtained after solubilization and anaerobic digestion of sewage sludge at a sewage treatment plant was pre-treated by filtration using Kiriyama filter paper 5C (particle size retention 1 μm). Solubility COD of wastewater B' Cr The values ​​are 2200 mg / L, the chromaticity is 3600 degrees, the BOD value is 150 mg / L, and the BOD / COD value is 0.07. Since the BOD / COD value of wastewater B' is less than 0.4, it indicates poor microbial degradation.

[0121] The preliminary decomposition treatment of wastewater B' was carried out by the following method. A large quartz beaker (9 cm in diameter, 20 cm in height) was used as the reaction vessel, and 180 mL of wastewater B' was added. Air (500 mL / min) controlled by a mass flow controller was injected into wastewater B' in a foamy form through a gas injection filter (Fuji Rika Kogyo F335-01, pore size 5-10 μm), and wastewater B' was stirred at 100 rpm using a stirrer (DLAB Scientific, OS20) to supply dissolved oxygen to the liquid. Light irradiation was performed using a 100 W high-pressure mercury lamp (HL100G, Sen special light source) set in a concentrating mirror type lamp fixture (HLR100T-2, Sen special light source), with an irradiation opening of 59 mm in diameter. Light was irradiated from the bottom of the beaker, and air cooling was performed by fan blowing. The irradiance measured at a distance of 2.2 cm from the tip of the lamp fixture to the bottom of the quartz beaker (the reaction vessel) was 192 W / m². 2 (UVC probe), 580W / m 2 (UVB probe), 435W / m 2 (UVA probe) was used. The total amount of ultraviolet radiation was 1207 W / m². 2 (Wavelengths were 220-400 nm.)

[0122] The light irradiation process involved stopping the irradiation after 6 hours and then analyzing the solution, repeating this procedure four times for a total of 24 hours of irradiation. For the first three irradiations (18 hours of irradiation total), the photocatalyst was not added during the preliminary decomposition treatment to obtain colored wastewater B. The COD of colored wastewater B, calculated from R254, was 330 mg / L, and the chromaticity, calculated from R390, was 260 degrees.

[0123] Next, in the fourth irradiation, 0.54 g of granular Au / TiO2 from Preparation Example 3 was added to decompose colored wastewater B. The photocatalytic dispersion concentration was 3.0 g / L. The granular Au / TiO2 used was prepared by supporting 1.5 wt% of Au on TiO2, the same as in Preparation Example 1, using a precipitation-precipitation method, and standardizing the particle size to a range of 40 to 125 μm, similar to Example 1.

[0124] Figure 7 shows the COD retention rate (R254), chromaticity retention rate (R390), and turbidity retention rate (R870) for wastewater B' and colored wastewater B, plotted against time. Since the chromaticity before decomposition is very high at 3600 degrees, adding a photocatalyst would not accelerate the process. Therefore, for the first three irradiations (irradiation time 18 hours), a preliminary decomposition treatment was performed by irradiating with light from a high-pressure mercury lamp containing ultraviolet light with wavelengths of 200-350 nm, without adding a photocatalyst. This preliminary decomposition treatment significantly reduced COD to 85%, chromaticity to 93%, and turbidity to 96% after 18 hours of irradiation. While all values ​​decreased linearly on a logarithmic plot up to 12 hours, the decomposition rate slowed between 12 and 18 hours. The chromaticity after 18 hours of treatment, calculated from R390, was 260 degrees, which falls well within the effective chromaticity range of the decomposition treatment method of the present invention. Therefore, when granular Au / TiO2 from Preparation Example 1 was added and a subsequent decomposition treatment was performed, the remaining rates for COD and chromaticity decreased significantly again between 18 and 24 hours. Finally, after a total of 24 hours of treatment, the decomposition rates of COD, chromaticity, and turbidity calculated from R254, R390, and R870 reached 96%, 98%, and 96%, respectively.

[0125] <Example 3> As wastewater C', the dewatered separated liquid obtained after solubilization treatment of sewage sludge and anaerobic digestion at a sewage treatment plant was pre-treated by filtration using Kiriyama filter paper 5C (retaining particle size 1 μm). The preliminary decomposition treatment was carried out in the same manner as in Example 2 without diluting wastewater C'. As shown in Table 1, the soluble COD of wastewater C' was obtained. Cr The value was 2200 mg / L, and the chromaticity was 3400 degrees.

[0126] The light irradiation was stopped after 6 hours, and the solution was analyzed. This procedure was repeated 5 times, for a total of 30 hours of irradiation. For the first 1 to 3 irradiations (18 hours of irradiation), the photocatalyst was not added, and a preliminary decomposition treatment was performed to obtain colored wastewater C. The COD of colored wastewater C, calculated from R254, was 770 mg / L, and the chromaticity, calculated from R390, was 680 degrees.

[0127] Next, in the fourth and fifth irradiations, 0.54 g of granular Pt / TiO2 from Example 1 was added to decompose colored wastewater C. The photocatalyst dispersion concentration was 3.0 g / L.

[0128] Figure 8 shows the COD retention rate R254, chromaticity retention rate R390, and turbidity retention rate R870 plotted against time for wastewater C' and colored wastewater C. Since the chromaticity before decomposition is very high at 3400 degrees, no acceleration effect can be expected even with the addition of a photocatalyst. Therefore, for the first three irradiations (irradiation time 18 hours), a preliminary decomposition treatment was performed by irradiating with light from a high-pressure mercury lamp containing ultraviolet light with a wavelength of 200-350 nm without adding a photocatalyst. As a result of this preliminary decomposition treatment, after 18 hours of irradiation, 66% of the COD was decomposed, 80% of the chromaticity was decomposed, and 96% of the turbidity was decomposed, showing a linear decrease in concentration on a logarithmic plot. The chromaticity after 18 hours of treatment, calculated from R390, was 680 degrees, which falls within the effective chromaticity range of the decomposition treatment method of the present invention. Therefore, when granular Pt / TiO2 was added as a post-treatment to perform decomposition again, the remaining percentages for COD and chromaticity decreased significantly again between 18 and 30 hours. Comparing the decomposition rates from the slopes of the logarithmic plots of R254 and R390, the addition of granular Pt / TiO2 accelerated the decomposition of COD by 3.7 times and the decomposition of chromaticity by 2.8 times. Figure 9 shows photographs of the wastewater before and after a total of 30 hours of treatment. The liquid, which was a dark brown color before treatment, became almost transparent after 30 hours of pre- and post-treatment. Table 1 shows the analytical values ​​of the wastewater before and after decomposition.

[0129] [Table 1]

[0130] As shown in Table 1, it was found that the post-decomposition treatment of colored wastewater C in Example 3 could decompose 96% of the chromaticity and 71% of the COD. Furthermore, when both the pre-decomposition treatment and the post-decomposition treatment were carried out together, it was revealed that not only could 90% and 85% of the COD and TOC of wastewater C', which are difficult to decompose by microorganisms, be decomposed, but the chromaticity could also be treated with a very high decomposition rate of 99%.

Claims

1. A method for decomposing colored wastewater, The system includes a light irradiation step in which light is irradiated onto the photocatalyst in the colored wastewater in the presence of dissolved oxygen. The chromaticity of the colored wastewater subjected to the light irradiation step is in the range of 260 degrees to 1000 degrees, and the COD value of the colored wastewater is in the range of 100 mg / L to 30000 mg / L. The photocatalytic material has a primary particle diameter of 100 nm or less and a secondary particle diameter of 1 μm or more. The photocatalytic material has a titanium dioxide content of 90% by mass or more, and is a method for decomposing colored wastewater.

2. The method for decomposing colored wastewater according to claim 1, wherein in the light irradiation step, ultraviolet light is irradiated onto the photocatalyst while stirring the colored wastewater.

3. The method for decomposing colored wastewater according to claim 1 or 2, wherein the photocatalytic body has a configuration in which a co-catalyst is supported on the surface of the photocatalytic material.

4. The method for decomposing colored wastewater according to any one of claims 1 to 3, wherein the chromaticity of the colored wastewater subjected to the light irradiation step is in the range of 260 degrees or more and 800 degrees or less.

5. The method for decomposing colored wastewater according to any one of claims 1 to 4, wherein the chromaticity of the colored wastewater subjected to the light irradiation step is in the range of 260 degrees or more and 700 degrees or less.

6. The method for decomposing colored wastewater according to any one of claims 1 to 5, wherein the secondary particle size of the photocatalyst is 40 μm or more.

7. A discolored wastewater decomposition apparatus for use in the discolored wastewater decomposition treatment method described in any one of claims 1 to 6, It has a function to perform a light irradiation process in which light is irradiated onto a photocatalyst in colored wastewater in the presence of dissolved oxygen. The chromaticity of the colored wastewater subjected to the light irradiation step is in the range of 260 degrees to 1000 degrees, and the COD value of the colored wastewater is in the range of 100 mg / L to 30000 mg / L. The photocatalytic material has a primary particle diameter of 100 nm or less and a secondary particle diameter of 1 μm or more. The aforementioned photocatalytic material has a titanium dioxide content of 90% by mass or more, and is used in a discolored wastewater decomposition treatment device.

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