Method for decomposing wastewater, and wastewater decomposition treatment apparatus.

Abstract

To provide an efficient sewage decomposition treatment method without generating ozone.SOLUTION: A sewage decomposition treatment method comprises subjecting sewage to ultraviolet irradiation, air bubbling, and agitation at the same time, wherein the sewage to be decomposed has a COD value of 100 mg / L or more and a ratio of a BOD value to a CODCr value (BOD / CODCr) of 0.4 or less, and exhibits property resistant to microbial decomposition, and a wavelength of an ultraviolet ray includes 200 to 350 nm and substantially does not include the wavelength less than 200 nm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for decomposing sewage and a sewage decomposition treatment apparatus.

Background Art

[0002] In the Sewage Law, sewage is defined as "wastewater (hereinafter referred to as'sewage') or rainwater resulting from or incidental to life or business (excluding farming businesses)".

[0003] There are two types of sewer systems: combined sewer systems and separate sewer systems. In a combined sewer system, sewage and rainwater are sent together to a sewage treatment plant, while in a separate sewer system, two pipelines are laid, one for sewage and the other for rainwater. Sewage is sent to a sewage treatment plant, and rainwater is directly discharged into rivers or the sea. At the sewage treatment plant, although there is a difference in whether rainwater is combined or not, the entire amount of sewage is received, treated to meet the general wastewater standards, and then discharged into rivers.

[0004] At a sewage treatment plant, sewage is treated by the activated sludge process after sand is removed in a grit chamber and mud is settled as primary sediment in a primary sedimentation tank. In the activated sludge process, activated sludge containing a large amount of aerobic microorganisms such as bacteria is added, and air is blown in for aeration. During this process, organic substances in the sewage are decomposed by the microorganisms. On the other hand, the microorganisms increase and settle as excess sludge containing a large amount of organic substances in the final sedimentation tank. The excess sludge is sent to the sludge treatment process of the sewage treatment plant, either alone or combined with the primary sediment, for further treatment.

[0005] The treatment of sewage sludge containing organic matter is mainly carried out by digestion treatment. Under anaerobic conditions with little oxygen in the digestion tank, the concentrated sewage sludge is microbially treated and decomposed into methane gas, carbon dioxide, etc. The digested sludge after digestion treatment contains high concentrations of refractory organic substances that cannot be decomposed by aerobic microorganisms using the activated sludge method and cannot be decomposed by anaerobic microorganisms through digestion treatment. The digested sludge is dehydrated by dehydration treatment and solid-liquid separated into dehydrated cake and separated liquid. After appropriate treatment such as drying and incineration, the dehydrated cake can be reused as cement raw materials or fertilizers used in agriculture, etc., or landfilled as waste.

[0006] In this way, sewage is sequentially treated at the sewage treatment plant, but the separated liquid of anaerobic digested sludge is sewage with high concentrations of microbially refractory organic components. Further decomposition treatment of the separated liquid is difficult, and currently, it is returned as reflux water to sedimentation tanks, etc., increasing the burden on the entire sewage treatment system.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, sewage at the sewage treatment plant, including raw sewage before treatment, concentrated separation liquid and separated liquid of sewage sludge, and separated liquid of digested sludge, becomes more difficult to treat as the treatment stage progresses because microbially refractory substances are concentrated. Also, in wastewater treatment facilities, etc. of various factories other than sewage treatment plants, sewage that is difficult to be microbially decomposed may be generated in the treatment process.

[0009] One proposed method for decomposing such wastewater and reducing the burden on the entire system is the application of Advanced Oxidation Process (AOP). In Advanced Oxidation Process, a combination of methods such as ultraviolet irradiation and ozone addition is used to remove organic matter from water, generating hydroxyl radicals with strong oxidizing power, thereby completely decomposing the organic matter. Specifically, for example, Patent Document 1 discloses a technology for decomposing and reducing the volume of sludge in wastewater by applying ozone addition treatment to wastewater simultaneously with ultraviolet irradiation.

[0010] In this method, when the scale of wastewater decomposition treatment is small, a low-pressure mercury lamp emitting ultraviolet light at wavelengths of 185 nm and 254 nm can be used. By irradiating air with 185 nm ultraviolet light, ozone can be generated, and by blowing this ozone into water while simultaneously irradiating it with 254 nm ultraviolet light, hydroxyl radicals can be generated. Therefore, it is possible to perform accelerated oxidation using both ozone and ultraviolet light with only an ultraviolet lamp.

[0011] However, when the scale of wastewater decomposition treatment increases, such as in sewage treatment plants, the ozone generation rate becomes insufficient, making it necessary to generate ozone using additional equipment such as electrical discharge. Furthermore, to prevent the release of excess ozone into the environment exceeding the 0.1 ppm work environment standard due to unconsumable use of the injected ozone, equipment to decompose excess ozone is also required.

[0012] Under these circumstances, the primary objective of the present invention is to provide a method for efficiently decomposing wastewater without generating ozone. Furthermore, the present invention also aims to provide a wastewater decomposition apparatus that can be suitably used in the aforementioned decomposition method. [Means for solving the problem]

[0013] The inventors diligently conducted research to solve the above-mentioned problems. As a result, COD Cr The value is 100 mg / L or higher, and the BOD value and COD CrRatio to a value (BOD / COD Cr ), in a sewage decomposition treatment method where the ratio is 0.4 or less, that is, the sewage exhibits a property of being difficult to decompose by microorganisms, it has been found that by irradiating the sewage with ultraviolet light in the presence of dissolved oxygen and using ultraviolet light having a wavelength range of 200 to 350 nm and substantially not containing wavelengths less than 200 nm, the sewage can be efficiently decomposed without generating ozone. The present invention has been completed through further studies based on such findings.

[0014] That is, the present invention provides an invention in the following aspects. Item 1. A method for decomposing and treating sewage, comprising: The sewage to be decomposed and treated has a COD Cr value of 100 mg / L or more, and the ratio of the BOD value to the COD Cr value (BOD / COD Cr ) is 0.4 or less, that is, it exhibits a property of being difficult to decompose by microorganisms. In the presence of dissolved oxygen, the sewage is irradiated with ultraviolet light, and the wavelength of the ultraviolet light includes 200 to 350 nm and substantially does not contain wavelengths less than 200 nm. A method for decomposing and treating sewage. Item 2. The method for decomposing and treating sewage according to Item 1, wherein the sewage is sewage generated in a sewage treatment process. Item 3. The method for decomposing and treating sewage according to Item 1 or 2, wherein the sewage contains a dewatering separation liquid of sewage sludge or a dewatering separation liquid after anaerobic digestion of sewage sludge. Item 4. The method for decomposing and treating sewage according to Items 1 to 3, wherein the sewage contains a dewatering separation liquid after solubilizing sewage sludge or a dewatering separation liquid after solubilizing sewage sludge and then further anaerobic digestion. Item 5. A sewage decomposition treatment apparatus for use in the method for decomposing and treating sewage according to any one of Items 1 to 4, comprising: The sewage has a COD Cr value of 100 mg / L or more, and the ratio of the BOD value to the COD Cr value (BOD / COD Cr ) is 0.4 or less, that is, it exhibits a property of being difficult to decompose by microorganisms. A wastewater decomposition treatment apparatus comprising the function of simultaneously irradiating the wastewater with ultraviolet light having a wavelength of 200 to 350 nm and substantially excluding wavelengths less than 200 nm, and supplying oxygen-containing gas. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for efficiently decomposing wastewater without generating ozone. Furthermore, according to the present invention, it is also possible to provide a wastewater decomposition apparatus that can be suitably used in said decomposition method. [Brief explanation of the drawing]

[0016] [Figure 1] This is the emission spectrum of the mercury lamp used for ultraviolet irradiation of wastewater in the example. [Figure 2] This graph shows the UV-VIS spectra of wastewater (diluted 10-fold for spectral measurement) in Example 1 at different decomposition treatment times (before decomposition treatment, after 6 hours of decomposition treatment, after 12 hours of decomposition treatment, and after 18 hours of decomposition treatment, respectively) (the vertical axis is absorbance and the horizontal axis is wavelength). [Figure 3] In Example 1, the graphs show the relationship between the wastewater decomposition treatment time and the remaining percentages (R) of COD (R254), chromaticity (R390), and turbidity (R870) (the vertical axis represents the remaining percentage (R), and the horizontal axis represents the treatment time). [Figure 4] These are photographs of the wastewater before and after the decomposition treatment in Example 1 (left side: before decomposition treatment, right side: after decomposition treatment). [Figure 5] This graph shows the relationship between the wastewater decomposition treatment time and the COD retention rate R254 in Examples 2 and 3 and Comparative Examples 1 and 2 (the vertical axis represents the COD retention rate R254, and the horizontal axis represents the treatment time). [Figure 6] This graph shows the relationship between the transmittance and wavelength of the wavelength-limiting filter used in Comparative Example 3. [Figure 7] These are the UV-VIS spectra before and after treatment in Example 4. [Figure 8] These are the UV-VIS spectra before and after treatment in Comparative Example 3. [Figure 9] In Example 5, 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 10] In Example 6, 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 11] These are photographs of the wastewater before and after the decomposition treatment in Example 6 (left side: before decomposition treatment, right side: after pre- and post-treatment). [Modes for carrying out the invention]

[0017] The decomposition treatment method of the present invention is a method for decomposing wastewater. In the present invention, the wastewater to be decomposed is COD Cr The value is 100 mg / L or higher, and the BOD value and COD Cr Ratio of value (BOD / COD) Cr The wastewater has a dissolved oxygen content of 0.4 or less, meaning it exhibits properties of being poorly decomposable by microorganisms. The wastewater decomposition method of the present invention is characterized by irradiating the wastewater with ultraviolet light in the presence of dissolved oxygen, wherein the ultraviolet light wavelengths include 200 to 350 nm and substantially do not include wavelengths less than 200 nm. By having these characteristics, the wastewater decomposition method of the present invention can efficiently decompose wastewater without generating ozone.

[0018] Furthermore, the wastewater decomposition treatment apparatus of the present invention is a wastewater decomposition treatment apparatus for use in a wastewater decomposition treatment method, wherein the wastewater to be decomposed is COD Cr The value is 100 mg / L or higher, and the BOD value and COD Cr Ratio of value (BOD / COD) CrThe wastewater treatment apparatus of the present invention is characterized by having a 0.4 or less ozone content, that is, exhibiting properties of being poorly decomposable by microorganisms, and by having the function of simultaneously irradiating the wastewater with ultraviolet light containing wavelengths of 200 to 350 nm and substantially excluding wavelengths less than 200 nm, and supplying oxygen-containing gas. By having these characteristics, the wastewater decomposition treatment apparatus of the present invention can efficiently decompose wastewater without generating ozone, and can be suitably used in the wastewater decomposition treatment method of the present invention described above.

[0019] The wastewater decomposition treatment method and wastewater decomposition treatment apparatus of the present invention will be described in detail below. 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 may be selected and connected by "~".

[0020] 1. Method for decomposing and treating wastewater In the wastewater decomposition treatment method of the present invention, the wastewater to be decomposed is COD Cr The value (chemical oxygen demand using potassium dichromate as the oxidizing agent) is 100 mg / L or higher, and the BOD value (biological oxygen demand) and COD are also... 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 decomposition treatment method of the present invention, decomposition treatment means that by applying the decomposition treatment method of the present invention to the wastewater to be decomposed, the wastewater after decomposition treatment will have a COD value that is at least lower than that before decomposition treatment, and the rate of reduction will be 10% or more.

[0021] In the present invention, the wastewater to be decomposed 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 dewatered liquor separated from anaerobic digested sludge is wastewater in which difficult-to-decompose organic components are concentrated at high concentrations. Further decomposition treatment of this dewatered liquor 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 dewatered liquor can be used as the wastewater to be decomposed.

[0022] The wastewater targeted in this invention is wastewater that exhibits properties that make it difficult to decompose by microorganisms. Wastewater with a large difference between COD (Chemical Oxygen Demand) and 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] In the present invention, the COD value of the wastewater after decomposition treatment is lower than that of the wastewater before decomposition treatment. In the present invention, the decomposition rate of the COD value of the wastewater before and after decomposition treatment ((COD value of wastewater before decomposition treatment - COD value of wastewater after decomposition treatment) / (COD value of wastewater before decomposition treatment)) is 10% or more, preferably 20% or more, and more preferably 40% or more.

[0029] In the present invention, 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 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, 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.

[0030] Furthermore, in the present invention, it is preferable that the color of the wastewater after decomposition treatment is lower than that before decomposition treatment. In the present invention, the decomposition rate of the color of the wastewater before and after 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 decomposition treatment is lower than that before decomposition treatment. In the present invention, the decomposition rate of the TOC value of the wastewater before and after 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 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 decomposition treatment is preferably around 5.5 to 8.5, more preferably around 6.0 to 8.5, and even more preferably around 6.0 to 8.0.

[0031] In this invention, water quality tests are conducted on wastewater before and after decomposition treatment in order to confirm the properties of the 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."

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The wastewater decomposition method of the present invention comprises a decomposition treatment step in which ultraviolet light is irradiated onto the wastewater to be 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. The wastewater decomposition method of the present invention comprises a decomposition treatment step in which ultraviolet light of a specific wavelength is irradiated onto the specific wastewater in the presence of dissolved oxygen, thereby enabling efficient decomposition of the wastewater while suppressing the generation of ozone due to ultraviolet irradiation.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 irradiating it with ultraviolet light, the wastewater can be irradiated with ultraviolet light in the presence of dissolved oxygen. The supply of oxygen-containing gas carried out in conjunction with ultraviolet irradiation is done in order to include a sufficient concentration of dissolved oxygen in the wastewater decomposition treatment method of the present invention.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] In the wastewater decomposition treatment method of the present invention, the decomposition treatment time is not particularly limited as long as the wastewater decomposition treatment 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 wastewater decomposition treatment progresses. For example, it is about 5 to 80°C, preferably about 10 to 60°C.

[0050] By performing the wastewater decomposition treatment method of the present invention as a preliminary decomposition treatment, and then applying the colored wastewater decomposition treatment method using a photocatalyst as a subsequent decomposition treatment to the resulting colored wastewater, the color of the colored wastewater can be efficiently reduced, and the decomposition treatment can be further advanced.

[0051] 2. Method for decomposing colored wastewater In the method for decomposing colored wastewater, the colored wastewater to be decomposed preferably has a color intensity in the range of 50 degrees to 1000 degrees. The 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 method for decomposing colored wastewater can efficiently decompose colored wastewater even when the wastewater is colored, in wastewater decomposition treatment using a photocatalyst.

[0052] In other words, the present invention provides a method for decomposing colored wastewater, which includes a light irradiation step in which light is irradiated onto a photocatalyst in the colored wastewater obtained by the wastewater decomposition treatment method of the present invention in the presence of dissolved oxygen, wherein 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 applying this method, colored wastewater can be efficiently decomposed.

[0053] Chromaticity refers to the degree of pale yellow to yellowish-brown color caused by substances dissolved in water or presenting colloidally. 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 is important to note 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 sludge separation liquid used in the examples of this invention, filtration (using filter paper with a particle size of 1 μm) was performed to remove coarse precipitates before the decomposition treatment, but turbidity remained. When further filtration with finer 0.22 μm filter paper was performed to completely remove the turbidity, a change was observed in the overall shape of the UV-VIS spectrum, indicating that the properties of the actual liquid could not be preserved. Therefore, in this invention, the filtration pretreatment is standardized to use 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. In the method for decomposing colored wastewater, the 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 less 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.

[0054] In the decomposition treatment method for colored wastewater, 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.

[0055] The colored wastewater can be any type of wastewater, regardless of the type of facility or process it is discharged from, as long as its color falls within the above-mentioned range. For example, it can be wastewater generated in any of the processes at a sewage treatment plant, such as activated sludge treatment, sludge concentration, 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 the treatment processes. As described above, the colored wastewater decomposition method of the present invention can be applied to the obtained colored wastewater after performing the wastewater decomposition method of the present invention.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 The ratio is preferably 0.4 or less, more preferably 0.3 or less, and even more preferably 0.25 or less.

[0060] 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.

[0061] 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."

[0062] 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".

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] The 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 and a secondary particle diameter of 1 μm or more, and a titanium dioxide content of 90% by mass or more. The method for decomposing colored wastewater allows for the effective decomposition of the colored wastewater by irradiating a specific photocatalyst in the colored wastewater in the presence of dissolved oxygen with light.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] While there are no restrictions on the primary particle size of the photocatalyst as long as it is 100 nm or less, it is preferable that it be less than 100 nm, and more preferably 50 nm or less, from the viewpoint of increasing contact between the substance to be treated in water and the photocatalyst surface and thereby increasing the reaction rate. The primary particle size range of the photocatalyst is, for example, about 1 to 100 nm, preferably about 2 to 50 nm. The primary particle size of the photocatalyst can be confirmed by observation with a transmission electron microscope or by crystallite size measurement by line broadening method of powder X-ray diffraction. If it is difficult to measure the primary particle size, the equivalent primary particle size can be estimated from the BET specific surface area measured by the nitrogen adsorption method using the following formula (Fumio Otani, Standard Research Methods for Photocatalysis, Tokyo Tosho (2005), pp. 408-410).

[0074] 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 dioxide, ρ is approximately 4 × 10⁶ gm -3 Therefore, when d is estimated in units of nm, it can be calculated using the following formula. d[nm] = 1500 / S[m] 2 g -1 ]

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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%.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] In the decomposition treatment method for colored wastewater, the decomposition treatment time is not particularly limited once the decomposition treatment of the colored wastewater has progressed. 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 should also be about 0.1 to 100 hours, preferably about 0.5 to 50 hours. Furthermore, the decomposition treatment temperature is not particularly limited once the decomposition treatment of the colored wastewater has progressed. For example, it is about 5 to 80°C, preferably about 10 to 60°C.

[0093] 3. Wastewater decomposition treatment equipment The wastewater decomposition apparatus of the present invention is a wastewater decomposition apparatus for use in a wastewater decomposition treatment method, wherein the wastewater to be decomposed is COD Cr The value is 100 mg / L or higher, and the BOD value and COD Cr Ratio of value (BOD / COD) CrThe material exhibits properties of being microbially resilient, with a value of 0.4 or less, and is characterized by the simultaneous irradiation of the wastewater with ultraviolet light containing wavelengths of 200-350 nm and substantially excluding wavelengths less than 200 nm, and the supply of oxygen-containing gas. A batch reactor that does not add or remove wastewater during the reaction may be used, or a continuous tank reactor may be employed in which the wastewater before treatment is introduced into a tank-type reaction vessel at a constant flow rate and the treated solution is discharged at a constant flow rate.

[0094] Details regarding wastewater, ultraviolet irradiation, oxygen gas supply, etc., are as described in "1. Wastewater Decomposition Treatment Method" above.

[0095] The wastewater decomposition apparatus of the present invention has the function of simultaneously irradiating with ultraviolet light having a wavelength of 200 to 350 nm and substantially excluding wavelengths less than 200 nm, and supplying oxygen-containing gas, and is capable of decomposing the aforementioned wastewater, but there are no particular restrictions on the specific configuration. The wastewater decomposition apparatus of the present invention, for example, comprises an ultraviolet 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 with ultraviolet light from within the liquid (internal irradiation type), or it can be installed outside and irradiate with ultraviolet light through the vessel wall from the bottom or side of the reaction vessel (external irradiation type).

[0096] 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.

[0097] 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 ultraviolet 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.

[0098] The configurations of the agitator section and the gas injection section can be those described in "1. Method for Decomposing Wastewater" above. [Examples]

[0099] 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.

[0100] <Example 1> For wastewater A, we used the dewatered separated liquid obtained after solubilization treatment of sewage sludge at a sewage treatment plant, followed by anaerobic digestion, and then pre-treated with filtration using Kiriyama filter paper 5C (particle size retention 1 μm). As shown in Table 1, the soluble COD of wastewater A was... Cr The value is 2300 mg / L, the BOD value is 150 mg / L, and the BOD / COD ratio is 0.07. Since the BOD / COD value of wastewater A is less than 0.4, it indicates that it is poorly biodegradable by microorganisms.

[0101] The decomposition treatment of wastewater A was carried out by the following method. A quartz beaker (9 cm in diameter, 20 cm in height) was used as the reaction vessel, and 180 mL of wastewater A was added. A PTFE bubbler (AS ONE Corporation, 6 cm in diameter, pore size 5-100 μm, average 40 μm) was placed at the bottom of the beaker. Air (1000 mL / min) controlled by a mass flow controller was injected into wastewater A in a foamy form from a gas injection filter, and wastewater A was stirred at 600 rpm using a stirring blade type agitator (DLAB Scientific, OS20) to ensure sufficient contact of the foam with the solution and 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 side of the beaker, and air cooling was performed by fan blowing.

[0102] Figure 1 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, and since it transmits zero ultraviolet light with a wavelength of 210 nm or less, the emission line at a wavelength of 185 nm, which is seen in ordinary mercury lamps, does not appear in the spectrum. For this reason, no ozone is generated while using this lamp, and no ozone odor was detected during the work. 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 to be 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 a distance of 2.2 cm from the tip of the lamp fixture to the side of the quartz beaker, which served as the reaction vessel, was 192 W / m². 2 (UVC probe), 580W / m 2 (UVB probe), 435W / m 2 (UVA probe). The ultraviolet light effective for the wastewater decomposition method of this invention corresponds to UVC and UVB, with a total of 772 W / m². 2 (Wavelengths were 220-315 nm.)

[0103] Solution analysis for evaluating the decomposition rate was performed using a spectrophotometer (UV-1800, Shimadzu Corporation). A portion of wastewater A, sampled for analysis, was diluted 10-fold with deionized distilled water and placed in a quartz cell with a path length of 10 mm. The absorbance was measured in the wavelength range of 190 to 900 nm.

[0104] In the decomposition reaction of a certain pure substance, the decomposition rate equation is investigated by plotting the residual rate C / C0 against the decomposition time, with the concentration before decomposition being C0 and the concentration at each time being C. When the residual rate C / C0 is equal to 1, the decomposition rate is 1-C / C0. For example, when the residual rate is 0.6 (60%), the decomposition rate is 0.4 (40%). In this invention, since the wastewater to be decomposed does not contain a specific pure substance, it is not possible to express a concentration residual rate. However, R254, R390, and R870, calculated using the following formulas from alternative indicators of COD, chromaticity, and turbidity, will be called the COD residual rate, chromaticity residual rate, and turbidity residual rate, respectively.

[0105] 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)

[0106] Light irradiation was performed continuously for 6 hours, followed by stopping and analysis of the solution. This procedure was repeated three times, for a total of 18 hours of irradiation. Figure 2 shows the change in UV-VIS spectrum (data after 10-fold dilution at the time of spectral measurement) with respect to treatment time, and Figure 3 shows the change in R254, R390, and R870 with respect to treatment time. Figure 4 shows photographs of the solutions before and after treatment, and Table 1 shows the analytical values ​​of these solutions using official methods.

[0107] [Table 1]

[0108] The graph shown in Figure 2 indicates that absorbance decreases across the entire measurement wavelength range with increasing treatment time, suggesting that the decomposition of wastewater progresses over time.

[0109] Figure 3 shows the results of plotting the absorbance changes at wavelengths of 254 nm, 390 nm, and 870 nm against treatment time, calculated as the remaining percentages of COD, chromaticity, and turbidity relative to the absorbance before treatment. The reason for using a logarithmic vertical axis 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 such cases, plotting the reaction time on the horizontal axis and the remaining percentage of substance concentration (C / C0) on the vertical axis (logarithmic axis) results in a straight line, confirming a first-order reaction. The results in Figure 3 show that R254 is a straight line, indicating that the decomposition of the COD component follows a first-order rate equation and that there are no particular inhibiting or promoting factors. In contrast, the change in R390 shows that the decomposition of the chromatic component is accelerated after 6 hours. The change in R870 shows that the decomposition of the turbidity component proceeds faster than the COD decomposition from the beginning and is further accelerated after 6 hours. The decomposition rate decreases after 12 hours, which is thought to be because the decomposition rate has increased and the turbidity components have almost completely disappeared.

[0110] Photographs of the liquid before and after a total of 18 hours of treatment (Figure 4) show that the opaque brown liquid color changed to a transparent yellow after treatment. Table 1 shows the soluble COD. Cr Official analysis confirmed that the TOC value was reduced by approximately 50%, and the chromaticity was reduced by 78%. Furthermore, ammoniacal nitrogen (NH4-N) was reduced by 87%, which is thought to be due to the ammonia stripping effect caused by air bubbling.

[0111] <Example 2> For wastewater B, we used the dewatered separated liquid of digested sludge that had not undergone solubilization treatment at a sewage treatment plant, pre-treated by filtration using Kiriyama filter paper 5C (particle size retention 1 μm). Solubility COD of wastewater B Cr The values ​​are 1600 mg / L, the BOD value is 350 mg / L, and the BOD / COD ratio is 0.22. Since the BOD / COD value of wastewater B is less than 0.4, it indicates that it is poorly biodegradable by microorganisms.

[0112] The decomposition treatment of wastewater B was carried out by the following method. A quartz beaker (nominal volume 100 mL) was used as the reaction vessel, and 50 mL of wastewater B was added. Air (400 mL / min) controlled by a mass flow controller was injected into wastewater B in a foamy form from a gas injection filter (Fuji Rika Kogyo F335-01, pore size 5-10 μm), and wastewater B was stirred at 350 rpm using a stirring blade type agitator (SPZ-1000, Tokyo Rika Kikai) to supply dissolved oxygen to the liquid. Light irradiation was carried out in the same manner as in Example 1, except that the irradiation distance was increased. The irradiance measured at the distance from the tip of the lamp fixture to the side of the quartz beaker (6.5 cm) was 69 W / m². 2 (UVC probe), 225W / m 2 (UVB probe), 138W / m 2 (UVA probe). The ultraviolet light effective for the wastewater decomposition method of this invention corresponds to UVC and UVB, with a total of 294 W / m². 2 The wavelength was 220-315 nm. Light irradiation was performed for 3 hours, and a portion of the treated solution was sampled every hour and analyzed with a spectrophotometer. Figure 5 shows the change in COD retention rate R254 with respect to treatment time.

[0113] <Comparative Example 1> Except for supplying nitrogen (400 mL / min) to the gas injection filter and irradiating with light for 1 hour, the decomposition treatment of wastewater B was carried out in the same manner as in Example 2. Figure 5 shows the change in the COD residual rate R254 with respect to treatment time.

[0114] <Example 3> In Comparative Example 1, after 1 hour of light irradiation, the gas supplied to the gas injection filter was changed to oxygen (400 mL / min), and light irradiation was performed for 2 hours to decompose wastewater B. Figure 5 shows the change in COD residual rate R254 with respect to treatment time.

[0115] <Comparative Example 2> Except for not turning on the mercury lamp and not performing light irradiation, the same procedure as in Example 2 was followed for 3 hours of decomposition treatment on wastewater B. Figure 5 shows the change in the COD residual rate R254 with respect to the treatment time.

[0116] As shown in Figure 5, the reaction was slower in Comparative Example 1, where nitrogen was bubbled, compared to Example 2, where air was bubbled, indicating insufficient dissolved oxygen. In Example 3, where the bubbling gas was switched to oxygen, the reaction proceeded sufficiently. However, since the slope of the graph is almost the same in the 2-3 hour interval between Example 2 (air) and Example 3 (oxygen), it was shown that it is not always necessary to use oxygen gas to supply sufficient dissolved oxygen and accelerate the reaction, and that bubbling with air is sufficient. Furthermore, since no decrease in COD was observed in Comparative Example 2, where no light was irradiated, it was shown that light irradiation is necessary along with oxygen supply.

[0117] <Example 4> For wastewater C, 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 (retaining particle size 1 μm), and then diluted 10 times with water. Solubility COD of wastewater C solution Cr The value is 220 mg / L, the BOD value is 11 mg / L, and the BOD / COD ratio is 0.05. Since the BOD / COD value of wastewater C is less than 0.4, it indicates that it is poorly biodegradable by microorganisms.

[0118] The decomposition treatment of wastewater C was carried out by the following method. A quartz beaker (nominal volume 200 mL) was used as the reaction vessel, and 100 mL of wastewater C was added. The reaction vessel was placed inside a quartz rectangular water tank with dimensions of 10 cm in length, width, and height, and the water temperature was kept constant using a cooling coil through which tap water was circulated. A colored glass filter (5 cm square) for wavelength limiting was installed by leaning it against the inner wall of the water tank. When the colored glass filter was used, the light irradiated from outside the water tank using the same mercury lamp and light fixture as in Example 1 was ensured to pass all of it through the glass filter and reach the reaction vessel. An experiment without the colored glass filter was also conducted using the same apparatus. The glass filter used was UV-37 (Toshiba Glass), and the transmittance of the filter in the wavelength range of 200 to 900 nm was measured with a spectrophotometer, and the results are shown in Figure 6. Air (200 mL / min), whose flow rate was controlled by a mass flow controller, was injected in a foamy manner through a gas injection filter (Fuji Rika Kogyo F335-01, pore size 5-10 μm), while wastewater C was stirred with a magnetic stirrer (500 rpm) to supply dissolved oxygen to the liquid. The same mercury lamp and luminaire as in Example 1 were used, and irradiation was performed for 0.5 hours each. When a colored glass filter was not used, the irradiance measured at the distance (2.5 cm) from the tip of the lamp luminaire through the wall of the quartz water tank to the side of the quartz beaker, which served as the reaction vessel, was 126 W / m². 2 (UVC probe), 407W / m 2 (UVB probe), 361W / m 2 (UVA probe). The ultraviolet light effective for the wastewater decomposition method of this invention corresponds to UVC and UVB, with a total of 533 W / m². 2 (Wavelengths were 220-315 nm). When a colored glass filter was used, the irradiation intensity decreased by the amount of transmittance shown in Figure 6 at each wavelength.

[0119] In Example 4, without using a colored glass filter, wastewater C was directly irradiated with light from a high-pressure mercury lamp having the wavelength distribution shown in Figure 1. After 30 minutes of irradiation, the UV-VIS spectra of wastewater C before and after treatment are shown in Figure 7. Compared to the dotted line before the reaction, the solid line after the reaction shows a decrease in absorbance across the entire wavelength range, confirming that the decomposition reaction is progressing. The COD decomposition rate, determined by R254 after 1 hour of treatment based on the decomposition rate, was 16.8%.

[0120] <Comparative Example 3> Except for limiting the irradiation wavelength by using a UV-37 (Toshiba Glass) colored glass filter, the decomposition treatment of wastewater C was carried out in the same manner as in Example 4. The transmission spectrum of the colored glass filter measured with a spectrophotometer (UV-1800, Shimadzu Corporation) is shown in Figure 6, and the UV-VIS spectra of wastewater C before and after treatment are shown in Figure 8. As shown in the figures, the UV-37 filter is irradiated with light with wavelengths exceeding 350 nm. The emission line at a wavelength of 365 nm is the strongest with this lamp, and the transmittance of the UV-37 filter is also high, indicating that ultraviolet light at a wavelength of 365 nm is sufficiently irradiated in terms of intensity. However, in Figure 8, no difference is observed between the dotted pre-treatment spectrum and the solid post-treatment spectrum, indicating that irradiation with light at wavelengths exceeding 350 nm is not effective for the decomposition reaction.

[0121] The results from Example 4 and Comparative Example 3 above demonstrate that an ultraviolet irradiation wavelength range of 200 nm to 350 nm is effective for the decomposition of wastewater that is difficult to decompose microbially, while ultraviolet light with wavelengths exceeding 350 nm and visible light are ineffective. Furthermore, by substantially excluding wavelengths below 200 nm from the irradiated ultraviolet light, the generation of ozone due to ultraviolet irradiation can be suppressed, allowing for the decomposition of wastewater.

[0122] <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.

[0123] (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).

[0124] 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.

[0125] 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.

[0126] (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.

[0127] 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. Based on laser diffraction and scattering measurements, the average secondary particle size of this photocatalyst in its dispersed state in water was 86 μm.

[0128] Measurements of the nitrogen adsorption surface area, powder X-ray diffraction, and transmission electron microscope results 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.

[0129] <Example of photocatalyst preparation 2> (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.

[0130] <Example 5> For wastewater D', we used the dewatered separated liquid obtained after solubilization treatment of sewage sludge at a sewage treatment plant, followed by anaerobic digestion, and then pre-treated by filtration using Kiriyama filter paper 5C (particle size retention 1 μm). Solubility COD of wastewater D' Cr The values ​​are 2200 mg / L, the chromaticity is 3600 degrees, the BOD value is 150 mg / L, and the BOD / COD ratio is 0.07. Since the BOD / COD value of wastewater D' is less than 0.4, it indicates poor microbial degradation.

[0131] The preliminary decomposition treatment of wastewater D' 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 D' was added. Air (500 mL / min) controlled by a mass flow controller was injected into the wastewater D' in a foamy form through a gas injection filter (Fuji Rika Kogyo F335-01, pore size 5-10 μm), and the wastewater D' 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, which served as 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.)

[0132] The light irradiation was stopped after 6 hours, and the solution was analyzed. This procedure was repeated four times, for a total of 24 hours of irradiation. For the first three irradiations (18 hours of irradiation), the photocatalyst was not added, and a preliminary decomposition treatment was performed to obtain colored wastewater D. The COD of colored wastewater D, calculated from R254, was 330 mg / L, and the chromaticity, calculated from R390, was 260 degrees.

[0133] Next, in the fourth irradiation, 0.54 g of granular Au / TiO2 from Preparation Example 2 was added to perform the post-decomposition treatment of colored wastewater D. The photocatalyst dispersion concentration was 3.0 g / L. The granular Au / TiO2 used was the same as in Preparation Example 1, with 1.5 wt% Au supported on TiO2 by the precipitation-precipitation method, and the particle size range was standardized to 40-125 μm.

[0134] Figure 9 shows the COD retention rate R254, chromaticity retention rate R390, and turbidity retention rate R870 plotted against time for wastewater D' and colored wastewater D. 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 for the colored wastewater decomposition treatment method. Therefore, when granular Au / TiO2 from Preparation Example 2 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.

[0135] <Example 6> As wastewater E', we used the dewatered separated liquid obtained after solubilization treatment of sewage sludge at a sewage treatment plant, followed by anaerobic digestion, and then 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 5 without diluting wastewater E'. The soluble COD of wastewater E' is shown in Table 2. Cr The value was 2200 mg / L, and the chromaticity was 3400 degrees.

[0136] The light irradiation process involved stopping the irradiation after 6 hours and then analyzing the solution, repeating this procedure five times for a total of 30 hours of irradiation. For the first three irradiations (18 hours of irradiation), the photocatalyst was not added, and a preliminary decomposition treatment was performed to obtain colored wastewater E. The COD of colored wastewater E, calculated from R254, was 770 mg / L, and the chromaticity, calculated from R390, was 680 degrees.

[0137] Next, in the fourth and fifth irradiations, 0.54 g of granular Pt / TiO2 from Preparation Example 1 was added to perform a post-treatment decomposition of colored wastewater E. The photocatalyst dispersion concentration was 3.0 g / L.

[0138] Figure 10 shows the COD retention rate R254, chromaticity retention rate R390, and turbidity retention rate R870 plotted against time for wastewater E' and colored wastewater E. 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 wavelengths of 200-350 nm without adding a photocatalyst. With 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 for the decomposition treatment method of colored wastewater. Therefore, when granular Pt / TiO2 was added and decomposition was carried out 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 11 shows photographs of the wastewater before and after a total of 30 hours of treatment, including both the initial and final stages. The liquid, which was a dark brown color before treatment, became almost transparent after 30 hours of treatment. Table 2 shows the analytical values ​​of the wastewater before and after decomposition.

[0139] [Table 2]

[0140] As shown in Table 2, it was found that the photocatalytic decomposition treatment of colored wastewater E in Example 6 could decompose 96% of the chromaticity and 71% of the COD. Furthermore, when the decomposition treatment of colored wastewater E' was carried out with the addition of a photocatalyst after the decomposition treatment without the photocatalyst, it was found that not only could 90% and 85% of the COD and TOC of wastewater E', 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 treating wastewater by decomposing it, The wastewater subject to decomposition treatment is COD Cr The value is 100 mg / L or higher, and the BOD value and COD Cr Ratio of values ​​(BOD / COD) Cr A method for treating wastewater, wherein the ) is 0.4 or less, that is, exhibits properties of being poorly decomposable by microorganisms, and in the presence of dissolved oxygen, ultraviolet irradiation and oxygen-containing gas supply are performed simultaneously on the wastewater, the wavelength of the ultraviolet light includes 200 to 350 nm, and 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.

2. The wastewater decomposition treatment method according to claim 1, wherein the wastewater is wastewater generated in a sewage treatment process.

3. The wastewater decomposition treatment method according to claim 1 or 2, wherein the wastewater includes a dewatered and separated liquid from sewage sludge, or a dewatered and separated liquid obtained after anaerobic digestion of sewage sludge.

4. The wastewater decomposition method according to claims 1 to 3, wherein the wastewater includes a dewatered separated liquid obtained after solubilizing sewage sludge, or a dewatered separated liquid obtained after solubilizing sewage sludge and then anaerobic digestion.

5. A wastewater decomposition apparatus for use in the wastewater decomposition treatment method described in any one of claims 1 to 4, The aforementioned wastewater is COD Cr The value is 100 mg / L or higher, and the BOD value and COD Cr Ratio of values ​​(BOD / COD) Cr ) is 0.4 or less, that is, it exhibits properties of being poorly degradable by microorganisms. A wastewater decomposition treatment apparatus comprising the function of simultaneously irradiating the wastewater with ultraviolet light having a wavelength including 200 to 350 nm, and the irradiation intensity of the strongest wavelength below 200 nm being 1 / 10 or less of the irradiation intensity of the strongest wavelength between 200 and 315 nm, and supplying oxygen-containing gas.

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