Photocatalytic treatment method for thiophanate-methyl wastewater

Abstract

The invention discloses a photocatalytic treatment method for thiophanate-methyl wastewater, which belongs to the technical field of wastewater treatment and comprises the following steps: S1, adjusting the pH value of the thiophanate-methyl wastewater to 8-10, adding an inorganic polymer flocculation solution to adjust the pH value to 6-7, stirring, adding an organic polymer flocculation solution for flocculation, standing after stirring, and filtering to obtain filtrate; filter residues and first treatment waste liquid are obtained; s2, mixing the first treated waste liquid with hydrogen peroxide, and performing catalytic wet oxidation to obtain a second treated liquid; s3, a composite photocatalyst is added into the second treatment liquid, ultrasonic treatment is performed for 40-60 min under irradiation of an ultraviolet lamp, standing is performed for 2-4 h, filtering is performed, and filtrate is third treatment liquid; s4, evaporation and concentration are conducted on the third treatment liquid through a membrane distiller, and treatment is completed. According to the discharged water obtained through the treatment method, the COD removal rate is larger than 95%, and the NH3-N removal rate is larger than 93%.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and particularly relates to a photocatalytic treatment method for thiophanate-methyl wastewater. Background Art

[0002] Thiophanate-methyl is a broad-spectrum, systemic, low-toxic fungicide with systemic, preventive and therapeutic effects, and can effectively prevent diseases of a variety of crops.

[0003] The synthesis route for methyl thiophanate primarily uses methyl chloroformate and sodium thiocyanate as raw materials, using N,N-dimethylaniline as a catalyst. Methyl isothiocyanate is first synthesized, and then condensed with o-phenylenediamine. Production wastewater primarily originates from the synthesis of methyl isothiocyanate, product washing, and solvent recovery processes. This wastewater primarily contains organic compounds such as N,N-dimethylaniline, thiocarbamates, methyl thiophanate, and its isomers. It exhibits high COD, high salinity, and significant toxicity, making it highly contaminated, hazardous, and difficult to biodegrade.

[0004] Regarding the treatment methods for methyl thiophanate wastewater, there are currently incineration, physical and chemical methods, and biological treatment methods. Although the incineration method can effectively treat high-concentration organic wastewater, it has problems such as high energy consumption, complex equipment, and easy production of harmful gases (such as hydrogen chloride); physical and chemical methods such as activated carbon adsorption and flocculation precipitation have poor treatment effects alone. Due to the high salinity in the wastewater and the inhibitory effect of fungicide residues on microorganisms, traditional biochemical methods require a large amount of dilution of the wastewater, resulting in low treatment efficiency and large area occupied. Photocatalytic oxidation technology has been used in industrial wastewater treatment in recent years due to its advantages such as high efficiency in degrading organic matter and no secondary pollution.

[0005] Titanium dioxide has the characteristics of small particles, many surface active centers, high catalytic efficiency, and is non-toxic and pollution-free. It is widely popular as a photocatalyst. However, pure titanium dioxide tends to agglomerate during use, resulting in poor catalytic effect and difficulty in separation, leading to poor wastewater purification effect. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for photocatalytic treatment of thiophanate-methyl wastewater, so as to solve the problem of poor photocatalytic treatment effect of thiophanate-methyl wastewater in the prior art.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for photocatalytic treatment of thiophanate-methyl wastewater comprises the following steps:

[0009] S1, adjusting the pH value of the thiophanate-methyl wastewater to 8-10, adding an inorganic polymer flocculation solution to adjust the pH value to 6-7, stirring, adding an organic polymer flocculation solution for flocculation, stirring and then standing, filtering to obtain a filter residue and a first treated waste liquid;

[0010] S2, mixing the first treated waste liquid with hydrogen peroxide and performing catalytic wet oxidation to obtain a second treated liquid;

[0011] S3, adding the composite photocatalyst to the second treatment liquid, ultrasonically treating under ultraviolet light for 40-60 minutes, letting it stand for 2-4 hours, filtering, the filter residue is the recovered composite photocatalyst, and the filtrate is the third treatment liquid;

[0012] S4. The third treatment liquid is evaporated and concentrated by a membrane distiller to complete the treatment.

[0013] Furthermore, the composite photocatalyst is prepared by the following steps:

[0014] Water-soluble dihydrochlorin e6 was added to deionized water and stirred evenly in the dark. Then, supported titanium dioxide was added and stirred at 40°C in the dark for 2-4 hours. The mixture was filtered, and the filter cake was washed with deionized water and dried at 80°C to constant weight to obtain a composite photocatalyst.

[0015] Furthermore, the ratio of water-soluble dihydrochlorin e6, deionized water and loaded titanium dioxide is 0.45g:80-120mL:0.45-1g. Using water-soluble dihydrochlorin e6 and loaded titanium dioxide as raw materials, water-soluble dihydrochlorin e6 is loaded on the surface of loaded titanium dioxide through interactions such as hydrogen bonds to obtain a composite photocatalyst.

[0016] Furthermore, the supported titanium dioxide is prepared by the following steps:

[0017] Dissolve tetrabutyl titanate in anhydrous ethanol and stir evenly, then add glacial acetic acid and continue stirring for 2-3 hours. Then add molecular sieves, add anhydrous ethanol and distilled water while stirring, continue stirring for 30-60 minutes, and react at 100°C for 12 hours. After the reaction is completed, cool to room temperature, filter, dry the filter cake, place it in a muffle furnace, heat it to 500°C, and calcine for 3 hours to obtain supported titanium dioxide.

[0018] Furthermore, the usage ratio of tetrabutyl titanate, anhydrous ethanol, glacial acetic acid, molecular sieves and distilled water is 3.3 mL: 30-33 mL: 1 mL: 1.0-1.5 g: 5 mL, and the volume ratio of the anhydrous ethanol added successively is 2:1.

[0019] Furthermore, the molecular sieve is SBA-15 and / or SBA-16.

[0020] Composite TiO2 with mesoporous molecular sieves can not only improve the dispersibility and recyclability of TiO2, but also enhance the effect of photocatalytic degradation of pollutants through synergistic effect with molecular sieves.

[0021] Furthermore, the water-soluble dihydrochlorin e6 is prepared by the following steps:

[0022] Hydroxypropyl chitosan was dissolved in deionized water to obtain a mixture a. EDC·HCl and NHS were added to MES buffer and stirred uniformly. A dimethyl sulfoxide solution of chlorin e6 was added, and the mixture was stirred at room temperature in the dark for 4 hours to obtain a mixture b. The mixture b was added dropwise to the mixture a. After the addition was complete, the mixture was stirred at room temperature in the dark for 24 hours. The reaction product was dialyzed against ultrapure water for 3 days using a dialysis bag with a molecular weight cutoff of 8000-14000 Da. The dialyzed product was freeze-dried to obtain water-soluble chlorin e6.

[0023] Furthermore, the usage ratio of hydroxypropyl chitosan, deionized water, EDC·HCl (1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride), NHS (N-hydroxysuccinimide), MES buffer, dihydrochlorin e6 and dimethyl sulfoxide is 100 mg:100 mL:15 mg:30 mg:5 mL:5-20 mg:5 mL.

[0024] Furthermore, the molecular weight of hydroxypropyl chitosan is 50 kDa-500 kDa, preferably 12 kDa, with a degree of substitution of 85%, and was purchased from Nanjing Bermuda Biotechnology Co., Ltd.

[0025] Furthermore, MES buffer was prepared by dissolving 2-(N-morpholino)ethanesulfonic acid (MES) in deionized water to a final concentration of 20 mmol / L, and adjusting the pH to 6.0 with sodium hydroxide.

[0026] Chlorin e6 is a chlorophyll derivative with a unique molecular structure and optical properties. Under ultraviolet light, it absorbs light energy and converts it into chemical energy, thereby generating reactive oxygen species (such as singlet oxygen and superoxide anions). These reactive oxygen species are highly reactive and can destroy the molecular structure of organic pollutants in wastewater, helping to reduce the COD content in wastewater. However, the poor water solubility of chlorin e6 limits its application in wastewater treatment. Based on this, hydroxypropyl chitosan, a highly water-soluble raw material, was used as the raw material to obtain water-soluble chlorin e6 through an amide reaction between the -NH2 of hydroxypropyl chitosan and the -COOH of chlorin e6.

[0027] Furthermore, the pH regulator in S1 is sodium hydroxide or hydrochloric acid solution.

[0028] Furthermore, the inorganic polymer flocculation solution is a polyferric sulfate solution with a mass concentration of 30% or a polyaluminum chloride solution with a mass concentration of 30%.

[0029] Furthermore, the organic polymer flocculation solution is a polyacrylamide solution with a mass concentration of 0.1-1%, and the dosage of the organic polymer flocculation solution is 0.1-0.5% of the volume of the thiophanate-methyl wastewater.

[0030] Furthermore, the amount of hydrogen peroxide added to S2 is 2-4% of the volume of the first treated waste liquid, and the mass fraction of hydrogen peroxide is 28-30%.

[0031] Furthermore, the catalytic wet oxidation in S2 is carried out at a temperature of 120-150° C. and a pressure of 0.5-1 MPa, and the catalytic wet oxidation is carried out for 30-60 minutes.

[0032] Furthermore, 1-3 grams of composite photocatalyst is added per liter of the second treatment liquid in S3, and the wavelength of the ultraviolet lamp is 365-400 nm.

[0033] Furthermore, the ultrasonic frequency in S3 is 500-1000 kHz.

[0034] Furthermore, the feed liquid temperature of the membrane distiller in S4 is 70-90°C, the flow rate is 50-100 L / h per square meter of membrane, the cooling liquid temperature is 10-50°C, and the membrane component is a hollow fiber membrane made of PTFE material.

[0035] Beneficial effects of the present invention:

[0036] The present invention provides a photocatalytic treatment method for thiophanate-methyl wastewater. The method comprises the following steps: firstly, neutralization, flocculation and filtration are performed to remove part of suspended solids, sulfhydryl compounds and catalyst N,N-dimethylaniline in the wastewater to reduce COD; then catalytic wet oxidation is performed to further reduce COD in the wastewater; finally, pollutants are photocatalytically degraded and membrane distillation is performed to obtain discharge water. The method comprises the following steps: a COD removal rate of more than 95%; and an NH3-N removal rate of more than 93%.

[0037] The present invention adopts ultrasound to assist the photocatalytic reaction, which is beneficial to improving the degradation rate of pollutants in wastewater. The reason is that the mechanical effect caused by ultrasonic radiation accelerates the separation of degradation products on the catalyst surface, regenerates the deactivated surface, and thus improves the activity of the catalyst.

[0038] The present invention uses water-soluble dihydrochlorin e6 and supported titanium dioxide as raw materials to prepare a composite photocatalyst. The supported titanium dioxide is molecular sieve-supported titanium dioxide. The molecular sieve has a high specific surface area and an ordered pore structure, can effectively disperse TiO2 particles, reduce agglomeration, and improve photocatalytic activity and recyclability. The supported titanium dioxide is hydroxypropyl chitosan grafted with dihydrochlorin e6, wherein dihydrochlorin e6 has good photosensitivity. Hydroxypropyl chitosan can adsorb heavy metal ions and organic pollutants in wastewater through electrostatic action or coordination bonds to achieve an adsorption-catalytic effect. The present invention combines the two, and the water-soluble dihydrochlorin e6 and the supported titanium dioxide play a synergistic role, so that the composite photocatalyst has better photocatalytic performance, the organic pollution content in the treated wastewater is lower, and the treatment effect is better. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0040] The technical solution of the present application is illustrated below through specific embodiments and comparative examples.

[0041] Preparation Example 1

[0042] A composite photocatalyst is prepared by the following steps:

[0043] 0.45 g of water-soluble dihydrochlorin e6 was added to 80 mL of deionized water and stirred evenly in the dark. Then 0.45 g of supported titanium dioxide was added and stirred at 40°C in the dark for 2 h. The mixture was filtered, the filter cake was washed with deionized water, and dried at 80°C to constant weight to obtain a composite photocatalyst.

[0044] The supported titanium dioxide is prepared by the following steps:

[0045] 3.3 mL of tetrabutyl titanate was dissolved in 20 mL of anhydrous ethanol and stirred evenly, then 1 mL of glacial acetic acid was added and stirring was continued for 2 h. Then 1.0 g of molecular sieve SBA-15 was added, and 10 mL of anhydrous ethanol and 5 mL of distilled water were added while stirring. Stirring was continued for 30 min. The mixture was reacted at 100 ° C for 12 h. After the reaction was completed, it was cooled to room temperature, filtered, and the filter cake was dried and placed in a muffle furnace and heated to 500 ° C. It was calcined for 3 h to obtain supported titanium dioxide.

[0046] The water-soluble dihydrochlorin e6 is prepared by the following steps:

[0047] 1 g of hydroxypropyl chitosan (molecular weight 12 kDa, degree of substitution 85%, purchased from Nanjing Bermuda Biotechnology Co., Ltd.) was dissolved in 1000 mL of deionized water to obtain a mixture a. 0.15 g of EDC·HCl and 0.03 g of NHS were added to 50 mL of MES buffer and stirred uniformly. A mixed solution consisting of 0.05 g of dihydrochlorin e6 and 50 mL of dimethyl sulfoxide was added, and the mixture was stirred at room temperature in the dark for 4 h to obtain a mixture b. The mixture b was added dropwise to the mixture a. After the addition was complete, the mixture was stirred at room temperature in the dark for 24 h. The reaction product was dialyzed against ultrapure water for 3 days using a dialysis bag with a molecular weight cutoff of 8000a. The dialyzed product was freeze-dried to obtain water-soluble dihydrochlorin e6.

[0048] MES buffer was prepared by dissolving 2-(N-morpholino)ethanesulfonic acid (MES) in deionized water to a final concentration of 20 mmol / L and adjusting the pH to 6.0 with sodium hydroxide.

[0049] Preparation Example 2

[0050] A composite photocatalyst is prepared by the following steps:

[0051] 0.45 g of water-soluble dihydrochlorin e6 was added to 120 mL of deionized water and stirred evenly in the dark. Then 1 g of supported titanium dioxide was added and stirred at 40°C in the dark for 4 h. The mixture was filtered and the filter cake was washed with deionized water and dried at 80°C to constant weight to obtain a composite photocatalyst.

[0052] The supported titanium dioxide is prepared by the following steps:

[0053] 3.3 mL of tetrabutyl titanate was dissolved in 22 mL of anhydrous ethanol and stirred evenly, then 1 mL of glacial acetic acid was added and stirring was continued for 3 h. Then 1.5 g of molecular sieve SBA-16 was added, and 11 mL of anhydrous ethanol and 5 mL of distilled water were added while stirring. Stirring was continued for 60 min. The mixture was reacted at 100 ° C for 12 h. After the reaction was completed, it was cooled to room temperature, filtered, and the filter cake was dried and placed in a muffle furnace and heated to 500 ° C. It was calcined for 3 h to obtain supported titanium dioxide.

[0054] The water-soluble dihydrochlorin e6 is prepared by the following steps:

[0055] 1 g of hydroxypropyl chitosan (molecular weight 12 kDa, degree of substitution 85%, purchased from Nanjing Bermuda Biotechnology Co., Ltd.) was dissolved in 1000 mL of deionized water to obtain a mixture a. 0.15 g of EDC·HCl and 0.03 g of NHS were added to 50 mL of MES buffer and stirred uniformly. A mixed solution consisting of 0.2 g of dihydrochlorin e6 and 50 mL of dimethyl sulfoxide was added, and the mixture was stirred at room temperature in the dark for 4 h to obtain a mixture b. The mixture b was added dropwise to the mixture a. After the addition was complete, the mixture was stirred at room temperature in the dark for 24 h. The reaction product was dialyzed against ultrapure water for 3 days using a dialysis bag with a molecular weight cutoff of 14,000 Da. The dialyzed product was freeze-dried to obtain water-soluble dihydrochlorin e6.

[0056] The MES buffer was prepared in the same manner as in Example 1.

[0057] Example 1

[0058] A method for photocatalytic treatment of thiophanate-methyl wastewater comprises the following steps:

[0059] S1, adjusting the pH value of the thiophanate-methyl wastewater to 9, adding a 30% mass concentration of polyferric sulfate solution or a 30% mass concentration of polyaluminium chloride solution to adjust the pH value to 6, stirring for 20min, adding a 0.1% mass concentration of polyacrylamide solution for flocculation, the polyacrylamide solution dosage is 0.1% of the volume of the thiophanate-methyl wastewater, stirring and standing, filtering to obtain a filter residue and a first treated waste liquid;

[0060] S2. Mixing the first treated waste liquid with hydrogen peroxide for catalytic wet oxidation, wherein the amount of hydrogen peroxide added is 2% of the volume of the first treated waste liquid, the mass fraction of hydrogen peroxide is 28%, and the catalytic wet oxidation is carried out at a temperature of 120° C. and a pressure of 1 MPa for 30 minutes to obtain a second treated liquid;

[0061] S3. Add the composite photocatalyst of Preparation Example 1 to the second treatment liquid, add 1 gram of the composite photocatalyst per liter of the second treatment liquid, irradiate with ultraviolet light, the wavelength of the ultraviolet light is 365-400 nm, ultrasonically treat for 40 minutes, and the ultrasonic frequency is 500 kHz. Let it stand for 2 hours and filter. The filter residue is the recovered composite photocatalyst, and the filtrate is the third treatment liquid;

[0062] S4. The third treatment liquid is evaporated and concentrated by a membrane distiller to complete the treatment.

[0063] The feed liquid temperature of the membrane distiller is 70°C, the flow rate is 50L / h per square meter of membrane, the cooling liquid temperature is 10°C, and the membrane component is a hollow fiber membrane made of PTFE material with a pore size of 0.45um, a porosity of 80%, and a membrane thickness of 0.25mm.

[0064] Example 2

[0065] A method for photocatalytic treatment of thiophanate-methyl wastewater comprises the following steps:

[0066] S1, adjusting the pH value of the methyl thiophanate wastewater to 10, adding a 30% mass concentration of polyaluminium chloride solution to adjust the pH value to 7, stirring for 30min, adding a 0.5% mass concentration of polyacrylamide solution for flocculation, the polyacrylamide solution dosage is 0.3% of the volume of the methyl thiophanate wastewater, stirring and standing, filtering to obtain a filter residue and a first treated waste liquid;

[0067] S2. Mixing the first treated waste liquid with hydrogen peroxide for catalytic wet oxidation, wherein the amount of hydrogen peroxide added is 3% of the volume of the first treated waste liquid, the mass fraction of hydrogen peroxide is 29%, and the catalytic wet oxidation is carried out at a temperature of 130° C. and a pressure of 0.8 MPa for 40 minutes to obtain a second treated liquid;

[0068] S3, adding the composite photocatalyst of Preparation Example 1 to the second treatment liquid, adding 2 grams of composite photocatalyst per liter of the second treatment liquid, irradiating with ultraviolet light, the wavelength of the ultraviolet light is 365-400nm, ultrasonically treating for 50 minutes, the ultrasonic frequency is 800kHz, standing for 3 hours, filtering, the filter residue is the recovered composite photocatalyst, and the filtrate is the third treatment liquid;

[0069] S4. The third treatment liquid is evaporated and concentrated by a membrane distiller to complete the treatment.

[0070] The feed liquid temperature of the membrane distiller is 80°C, the flow rate is 80L / h per square meter of membrane, the coolant temperature is 20°C, and the membrane component is a hollow fiber membrane made of PTFE material with a pore size of 0.45um, a porosity of 80%, and a membrane thickness of 0.25mm.

[0071] Example 3

[0072] A method for photocatalytic treatment of thiophanate-methyl wastewater comprises the following steps:

[0073] S1, adjusting the pH value of the thiophanate-methyl wastewater to 10, adding a 30% mass concentration of polyaluminium chloride solution to adjust the pH value to 7, stirring for 40min, adding a 1% mass concentration of polyacrylamide solution for flocculation, the polyacrylamide solution is stirred in an amount of 0.5% of the volume of the thiophanate-methyl wastewater and then allowed to stand, filtered to obtain a filter residue and a first treated waste liquid;

[0074] S2. Mixing the first treated waste liquid with hydrogen peroxide for catalytic wet oxidation, wherein the amount of hydrogen peroxide added is 4% of the volume of the first treated waste liquid, the mass fraction of hydrogen peroxide is 30%, and the catalytic wet oxidation is carried out at a temperature of 150° C. and a pressure of 1 MPa for 60 minutes to obtain a second treated liquid;

[0075] S3, adding the composite photocatalyst of Preparation Example 1 to the second treatment liquid, adding 3 grams of composite photocatalyst per liter of the second treatment liquid, irradiating with ultraviolet light, the wavelength of the ultraviolet light is 365-400nm, ultrasonic treatment for 60min, the ultrasonic frequency is 1000kHz, standing for 4h, filtering, the filter residue is the recovered composite photocatalyst, and the filtrate is the third treatment liquid;

[0076] S4. The third treatment liquid is evaporated and concentrated by a membrane distiller to complete the treatment.

[0077] The feed liquid temperature of the membrane distiller is 90°C, the flow rate is 100L / h per square meter of membrane, the coolant temperature is 50°C, and the membrane component is a hollow fiber membrane made of PTFE material with a pore size of 0.45um, a porosity of 80%, and a membrane thickness of 0.25mm.

[0078] Example 4

[0079] The method for photocatalytic treatment of thiophanate-methyl wastewater is different from that in Example 1 only in that the composite photocatalyst in Example 1 is replaced by the product obtained in Preparation Example 2.

[0080] Example 5

[0081] The method for photocatalytic treatment of thiophanate-methyl wastewater is different from that of Example 1 only in that 2 grams of the composite photocatalyst of Preparation Example 1 is added per liter of the second treatment liquid.

[0082] Comparative Example 1

[0083] The method for photocatalytic treatment of thiophanate-methyl wastewater is different from that in Example 1 only in that the composite photocatalyst in Example 1 is replaced with supported titanium dioxide, and the preparation process of supported titanium dioxide is the same as that in Preparation Example 1.

[0084] Comparative Example 2

[0085] The photocatalytic treatment method for methyl thiophanate wastewater is different from that in Example 1 only in that the composite photocatalyst in Example 1 is replaced with water-soluble dihydrochlorin e6, and the preparation process of water-soluble dihydrochlorin e6 is the same as that in Preparation Example 1.

[0086] Comparative Example 3

[0087] The photocatalytic treatment method for thiophanate-methyl wastewater is different from that in Example 1 only in that the ultrasonic treatment for 40 min in S3 is adjusted to stirring for 40 min at a speed of 100 r / min.

[0088] The methyl thiophanate wastewater photocatalytic treatment method of Examples 1-5 and Comparative Examples 1-3 was used to treat methyl thiophanate production wastewater in Anhui Province. The water quality of the methyl thiophanate production wastewater was: pH 8, COD content 4000 mg / L, and NH3-N content 1500 mg / L. The treated discharge water was tested and the COD removal rate and NH3-N removal rate were calculated. The results are shown in Table 1:

[0089] Table 1

[0090]

[0091] It can be seen from the data recorded in Table 1 that the photocatalytic treatment methods for thiophanate-methyl wastewater provided by Examples 1 to 5 have better treatment effects, which are significantly better than those of Comparative Examples 1 to 3.

[0092] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0093] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for photocatalytic treatment of thiophanate-methyl wastewater, characterized in that: The following steps are involved: S1, adjusting the pH value of the thiophanate-methyl wastewater to 8-10, adding an inorganic polymer flocculation solution to adjust the pH value to 6-7, stirring, adding an organic polymer flocculation solution for flocculation, stirring and then standing, filtering to obtain a filter residue and a first treated waste liquid; S2, mixing the first treated waste liquid with hydrogen peroxide and performing catalytic wet oxidation to obtain a second treated liquid; S3, adding the composite photocatalyst to the second treatment liquid, irradiating with ultraviolet light, ultrasonically treating for 40-60 minutes, letting it stand for 2-4 hours, filtering, and the filtrate is the third treatment liquid; S4, evaporating and concentrating the third treatment liquid through a membrane distiller to complete the treatment; The composite photocatalyst is prepared by the following steps: Water-soluble dihydrochlorin e6 was added to deionized water and stirred evenly in the dark. Then, supported titanium dioxide was added and stirred at 40°C in the dark for 2-4 hours. The mixture was filtered, and the filter cake was washed with deionized water and dried at 80°C to constant weight to obtain a composite photocatalyst.

2. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 1, characterized in that: The usage ratio of water-soluble dihydrochlorin e6, deionized water and supported titanium dioxide is 0.45 g:80-120 mL:0.45-1 g / L.

3. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 1, characterized in that: The supported titanium dioxide is prepared by the following steps: Dissolve tetrabutyl titanate in anhydrous ethanol and stir evenly, then add glacial acetic acid and continue stirring for 2-3 hours. Then add molecular sieves, add anhydrous ethanol and distilled water while stirring, continue stirring for 30-60 minutes, and react at 100°C for 12 hours. After the reaction is completed, cool to room temperature, filter, dry the filter cake, place it in a muffle furnace, heat it to 500°C, and calcine for 3 hours to obtain supported titanium dioxide.

4. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 3, characterized in that: The dosage ratio of tetrabutyl titanate, anhydrous ethanol, glacial acetic acid, molecular sieves and distilled water is 3.3 mL: 30-33 mL: 1 mL: 1.0-1.5 g: 5 mL, and the volume ratio of anhydrous ethanol added successively is 2:

1.

5. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 3, characterized in that: The molecular sieve is SBA-15 and / or SBA-16.

6. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 1, characterized in that: The water-soluble dihydrochlorin e6 is prepared by the following steps: Hydroxypropyl chitosan was dissolved in deionized water to obtain a mixture a. EDC·HCl and NHS were added to MES buffer and stirred uniformly. A dimethyl sulfoxide solution of chlorin e6 was added, and the mixture was stirred at room temperature in the dark for 4 h to obtain a mixture b. The mixture b was added dropwise to the mixture a. After the addition was complete, the mixture was stirred at room temperature in the dark for 24 h. The reaction product was dialyzed against ultrapure water and freeze-dried to obtain water-soluble chlorin e6.

7. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 6, characterized in that: The dosage ratios of hydroxypropyl chitosan, deionized water, EDC·HCl, NHS, MES buffer, dihydrochlorin e6, and dimethyl sulfoxide were 100 mg:100 mL:15 mg:30 mg:5 mL:5-20 mg:5 mL.

8. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 1, characterized in that: The catalytic wet oxidation in S2 is carried out at a temperature of 120-150° C. and a pressure of 0.5-1 MPa, and the catalytic wet oxidation lasts for 30-60 minutes.

9. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 1, characterized in that: 1-3 grams of composite photocatalyst is added to each liter of the second treatment liquid in S3, and the wavelength of the ultraviolet lamp is 365-400nm.

10. The method for photocatalytic treatment of thiophanate-methyl wastewater according to claim 1, characterized in that: The ultrasonic frequency in S3 is 500-1000kHz.

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