A method for synchronously coagulating - targeted oxidation - photocatalyzing to control sulfides and their by - products in stormwater pipeline overflow sewage

Abstract

The present invention relates to a method for synchronously coagulating - targeted oxidation - photocatalyzing to control sulfides and their by - products in the overflow sewage of rainwater pipelines, belonging to the technical field of environmental pollution control. This method first targets and screens oxidants according to the principle of frontier orbital matching and oxidation potential driving; then uses the thermal polymerization method and the dip - coating method to prepare a graphitic carbon nitride / titanium dioxide (g - C<subgt;3< / subgt;N<subgt;4 / TiO<subgt;2) heterojunction photocatalyst and load it into the reaction pool; conveys the overflow sewage to the reaction pool, and simultaneously adds the preferably selected oxidant and the coagulant polyaluminum chloride. To improve the coagulation effect, a flocculation aid is additionally added. The present invention provides an effective method for treating odor - causing substances in overflow sewage, which can reduce the potential risks of sulfides and their by - products to the ecological environment.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution control and sewage treatment, and in particular to a method for synchronously coagulating - targeted oxidation - photocatalysis to control sulfides and their by - products in stormwater overflow sewage. Background Art

[0002] The interconnection between urban stormwater pipes and sewage pipes has led to a large amount of domestic sewage and industrial wastewater entering the stormwater system. On sunny days, various pollutants from sewage, atmospheric particulate matter, and surface runoff accumulate in the pipes, forming a stable water - sediment system; under low - flow and anaerobic conditions, a large amount of odor - causing organic compounds are produced by the action of microorganisms on high - load organic matter. Currently, sulfides have been identified as the main type of odor - causing organic compounds in stormwater pipes. On rainy days, rain washes these odor - causing substances into the receiving water body. Sulfides are highly irritating and volatile at low concentrations, causing serious sensory and chemical pollution, endangering human health; and reducing water quality and damaging the aquatic ecosystem. In addition, sediments have been identified as the main source and storage reservoir of sulfides. Therefore, simply removing dissolved sulfides in overflow sewage without treating the particulate matter therein may not solve the fundamental problem. The particulate matter can adsorb a large amount of sulfides, and the microorganisms therein may continuously produce odor - causing substances, resulting in repeated abnormal odors in the water body. In addition, analyzing whether by - products are generated during the removal of sulfides is crucial for evaluating whether sulfides will continuously affect human health and the water environment. Therefore, simultaneously controlling particulate matter, sulfides, and their by - products in overflow sewage can fundamentally solve the problems of odor pollution and water quality safety of the receiving water body caused by stormwater pipe drainage.

[0003] Currently, the control of pollutants in overflow sewage mainly focuses on conventional pollutants. Patent CN118145775A discloses a method for pre - oxidizing and coagulating overflow sewage, which proposes to treat the overflow sewage successively through oxidation, coagulation, flocculation, and sedimentation, and can efficiently and synchronously remove COD, ammonia nitrogen, total phosphorus, turbidity, and UV in the overflow sewage in a short time. 254 However, this method mainly targets conventional pollutants such as COD, ammonia nitrogen, total phosphorus, turbidity, and UV. 254 Its comprehensive treatment ability may be insufficient when facing complex sewage components, especially the treatment effect on some key pollutants (such as sulfides) is unclear; moreover, the method does not clarify the continuous impact on the water ecosystem after water treatment.

[0004] Patent CN104292239A discloses a method for absorbing dimethyl sulfide by by-products during the production of moxidectin oxidized by sodium hypochlorite solution, and proposes that the by-product dimethyl sulfide and the solvent used are transferred to a sodium hypochlorite absorption kettle together through a condenser, and the dimethyl sulfide is oxidized and absorbed by the sodium hypochlorite solution in the sodium hypochlorite absorption kettle. Within 2-4 hours, the content of dimethyl sulfide in the oxidation reaction can be quickly reduced to ≤1.0%. However, due to the characteristics of the overflow sewage such as fast flow rate and strong impact, this method is difficult to be applied at the end of the rainwater pipeline.

[0005] In addition, Patent CN116642995B provides an adsorption experimental device for odor substances, and evaluates the adsorption capacity of specific catalytic materials for odor substances through adsorption experiments. This device mainly focuses on the adsorption capacity of specific catalytic materials and lacks the comprehensive treatment capacity for complex sewage components (such as sulfides and their derivatives); moreover, this device mainly focuses on the research of single odor substances, and its application range is relatively limited. Therefore, in view of the pollution characteristics of rainwater pipeline overflow sewage such as fast flow rate, high pollution load, and complex pollutant components, it is necessary to develop a more efficient and comprehensive pollution control process.

[0006] In the context of the increasingly serious pollution of rainwater pipeline overflow, aiming at the deficiencies in the above-mentioned disclosed technologies, there is an urgent need to provide a new method to solve the above technical problems. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a method for synchronously coagulating-targeted oxidation-photocatalysis to synergistically treat sulfides and their by-products in rainwater pipeline overflow sewage. By establishing a terminal treatment facility and adopting the synchronous coagulation-targeted oxidation-photocatalysis process, the present invention aims to efficiently remove sulfides and particulate matter (adsorbing sulfides and containing microorganisms generated by sulfides) in the overflow sewage, and control the generation of sulfide by-products, so as to improve water quality and protect the aquatic ecosystem, and provide a more comprehensive and efficient solution for urban sustainable development.

[0008] The purpose of the present invention is to provide a method for synchronously coagulating-targeted oxidation-photocatalysis to control sulfides and their by-products in rainwater pipeline overflow sewage, including the following steps:

[0009] (1)Targeted screening of oxidants: Through density functional theory (DFT), combined with the analysis of the frontier orbital distribution of thioether molecules, determine the sulfur atom in the thioether molecule and the functional groups adjacent to it with the highest electron cloud density as the active reaction sites, and measure the highest occupied molecular orbital (HOMO) energy of the active sites of the thioether molecule and the lowest unoccupied molecular orbital (LUMO) energy of the oxidant respectively; Based on the frontier molecular orbital theory, determine that the LUMO energy of the oxidant is lower than the HOMO energy of the active site of the thioether molecule to evaluate the feasibility of electron transfer between the thioether molecule and the oxidant; At the same time, measure the standard oxidation potential E 0 , and verify that the standard Gibbs free energy change ΔG of the oxidation reaction of the oxidant oxidizing thioether is < 0; Screen out the oxidant;

[0010] (2)Mix g-C3N4 / TiO2 powder with silica sol, ball-mill to make a slurry, and use the spraying method to form a uniform coating on the surface of the reaction tank, and perform heat treatment in an air atmosphere;

[0011] (3)Transport the overflow sewage to the treated reaction tank obtained in step (2), add a mixture of the oxidant, coagulant and coagulant aid screened in step (1), and then perform stirring and sedimentation treatment on the mixed liquid, and discharge the water after sedimentation;

[0012] (3)Transport the overflow sewage to the reaction tank, add a mixture of the screened oxidant, coagulant and coagulant aid, and then perform stirring and sedimentation treatment on the mixed liquid, and discharge the water after sedimentation, so as to achieve the removal of thioether and particulate matter and the control of the generation of thioether by-products;

[0013] (4)Use solid-phase microextraction-gas chromatography-mass spectrometry to quantitatively analyze the thioether content in the effluent, and measure the turbidity of the effluent, and calculate the thioether removal rate and turbidity removal rate;

[0014] (5)Use the solid-phase extraction method to extract thioether by-products in the effluent obtained in step (1);

[0015] (6)Use a mass spectrometry detector to identify and semi-quantify thioether by-products in the extract obtained in step (3).

[0016] In some embodiments of the present invention, in step (2), the mass ratio of g-C3N4 / TiO2 powder to silica sol is (1:1) ~ (1:1.5);

[0017] The thickness of the coating is 50~100 μm;

[0018] The temperature of the heat treatment is 300~320 °C, and the time is 100~120 minutes.

[0019] In some embodiments of the present invention, in step (2), the g-C3N4 / TiO2 (graphitic carbon nitride / titanium dioxide heterojunction photocatalyst) is prepared by the following method:

[0020] (a) First, g-C3N4 is synthesized by thermal polymerization. Melamine powder is placed in a crucible, heated to 550 °C at a rate of 5 °C / min under nitrogen protection, held for 2 hours, and then naturally cooled and ground to obtain yellow g-C3N4 powder.

[0021] (b) Synthesis of TiO2 nanoparticles: Tetrabutyl titanate (TBOT) and absolute ethanol are mixed at a volume ratio of 1:4, and the mixture is dropped into an ethanol-aqueous solution containing nitric acid (pH = 3), stirred to form a transparent sol, dried at 80 °C, and then calcined at 450 °C for 2 hours to obtain anatase TiO2 nanoparticles.

[0022] (c) Construction of the g-C3N4 / TiO2 heterostructure: g-C3N4 and TiO2 are dispersed in ethanol at a mass ratio of 1:2, ultrasonicated for 1 hour, the pH is adjusted to 9 by adding ammonia water, and a hydrothermal reaction is carried out at 150 °C for 6 hours. After centrifugation and washing, it is dried at 60 °C to obtain a g-C3N4 / TiO2 heterojunction composite material.

[0023] In the present invention, the g-C3N4 / TiO2 heterojunction photocatalyst is loaded on the surface of the reaction pool, and natural light is used to drive the degradation of thioethers.

[0024] In some embodiments of the present invention, the thioethers include one or more of dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diethyl disulfide (DEDS), and diethyl trisulfide (DETS).

[0025] In some embodiments of the present invention, in step (3), the oxidant is selected from sodium hypochlorite and / or potassium ferrate.

[0026] In some embodiments of the present invention, in step (3), the coagulant is selected from one or more of polyaluminum chloride, aluminum sulfate, and ferric chloride.

[0027] In some embodiments of the present invention, in step (3), the coagulant aid is selected from polyacrylamide and / or calcium oxide.

[0028] In some embodiments of the present invention, in step (3), the mass concentration ratio of the oxidant, coagulant, and coagulant aid is 5:(30 - 32):(0.3 - 0.4).

[0029] In some embodiments of the present invention, in step (5), the specific steps for extracting the thioether by-products in the effluent obtained in step (3) using solid-phase extraction are as follows: Activate the SPE column with methanol and ultrapure water; load the effluent sample and pass it through the column at a flow rate of 9.5 - 10.0 mL / min; then use nitrogen to dry the column at a pressure of 14.5 - 15.0 psi for 70 - 80 min; after the column is dried, elute the sample on the column with methyl tert-butyl ether (MTBE) at a flow rate of 1.8 - 2.0 mL / min, and collect the thioether and its by-product molecules.

[0030] In some embodiments of the present invention, in step (6), the method for identifying and semi-quantifying thioether by-products is as follows: Introduce the thioether by-products in the extract into the GC through an auto-sampler. The temperature program is as follows: The initial column oven temperature is set to 35 °C and maintained for 10 min; then it is heated to 80 °C at a rate of 3 °C / min, and then rapidly heated to 240 °C at a rate of 60 °C / min and maintained at this temperature for 3 min; the injection port temperature is fixed at 250 °C, helium is used as the carrier gas, and the constant flow rate is maintained at 1.93 mL / min; the nickel source temperature is set to 230 °C; mass spectrometry analysis is carried out in the full-scan mode, and the scanning range is set to 30 to 400 m / z; the scanning starts at 3 min and continues until 25 min ends, the interval time is 0.2 s, and the scanning speed is 2000 amu / s.

[0031] The thioether by-products include methanesulfonyl chloride, methyl thiosulfinate, and methylsulfonylmethyl thiosulfonate.

[0032] Specifically, the method of the present invention: First, convey the overflow sewage to the reaction tank, and at the same time add the selected oxidant and the coagulant polyaluminum chloride. The dosage of the oxidant is 10 mg / L, and the dosage of polyaluminum chloride is 60 mg / L; to improve the coagulation effect, an additional 0.6 mg / L of the coagulant aid polyacrylamide is added; the mixed solution is rapidly stirred at 250 rpm for 40 s, then slowly stirred at 100 rpm for 80 s, and finally stirred at a speed of 50 rpm for 3 min, and then precipitated for 10 min to finally obtain the treated effluent; in addition, the present invention also analyzes the thioether and its by-products in the overflow sewage, quantitatively determines the thioether content in the effluent using solid-phase microextraction-gas chromatography-mass spectrometry, and extracts the thioether by-products in 1 L of the treated effluent using solid-phase extraction, and identifies and semi-quantifies its components using gas chromatography-mass spectrometry; during the solid-phase extraction process, first activate the solid-phase extraction column with methanol and ultrapure water, then load the water sample and dry the column, and finally elute the sample with methyl tert-butyl ether and perform gas chromatography-mass spectrometry analysis after concentration.

[0033] The above technical solution of the present invention has the following advantages compared with the prior art:

[0034] 1. The present invention combines the advantages of three treatment methods: coagulation, targeted oxidation, and photocatalysis. The coagulant PACl destroys the particle stability and promotes their aggregation into sedimentable flocs through synergistic effects such as charge neutralization, adsorption bridging, and net trapping and sweeping, effectively removing the thioether and its by-product molecules adsorbed on the particulate matter in the overflow sewage. The targeted screening oxidant can selectively oxidize specific pollutants or reactants, reducing the influence of other substances on the removal of thioether and its by-product molecules, thereby improving the efficiency and selectivity of the reaction and converting the thioether and its by-product molecules into harmless substances. The g-C3N4 / TiO2 heterojunction photocatalyst, under natural light irradiation, absorbs light energy, excites electrons, and generates active substances, thus accelerating chemical reactions and promoting the complete mineralization of thioether and its by-product molecules and reducing the generation of by-products. The coupling effect of the three exhibits a significant synergistic effect, capable of more efficiently removing pollutants in complex sewage. There is currently no patent on the synchronous coagulation-targeted oxidation-photocatalysis for synergistically controlling thioether and its by-product molecules, and the present invention fills this gap. By synchronously and efficiently removing dissolved and particulate thioether in the overflow sewage, it helps to comprehensively improve the overall water quality of the water body.

[0035] 2. The implementation of the present invention is relatively simple, easy to integrate into existing sewage treatment facilities, and convenient for popularization and application. Moreover, the chemical agent cost is relatively low, achieving a good balance between pollutant removal and economic cost control, providing an efficient, economical, and operable solution for the sewage treatment industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in combination with the drawings, where

[0037] Figure 1 is the graph of the removal rate of thioether in the embodiments and comparative examples of the present invention; among them, (a) is the removal rate of turbidity by synchronous coagulation-oxidation-photocatalysis when sodium hypochlorite, potassium ferrate, and hydrogen peroxide are used as oxidants respectively; (b) is the removal effect of thioether by the synchronous coagulation-oxidation-photocatalysis process when sodium hypochlorite is used as the oxidant; (c) is the removal effect of thioether by the synchronous coagulation-oxidation-photocatalysis process when potassium ferrate is used as the oxidant; (d) is the removal effect of thioether by the synchronous coagulation-oxidation-photocatalysis process when hydrogen peroxide is used as the oxidant.

[0038] Figure 2 is the spectrogram of thioether and its by-product molecules identified by gas chromatography-mass spectrometry in Example 1 of the present invention.

[0039] Figure 3 is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0041] (1). The g-C3N4 / TiO2 (graphitic carbon nitride / titanium dioxide heterojunction photocatalyst) used in the present invention is prepared by the following method:

[0042] (a). First, g-C3N4 is synthesized by thermal polymerization method. Melamine powder is placed in a crucible, heated to 550 °C at a rate of 5 °C / min under nitrogen protection, held for 2 hours, and then ground after natural cooling to obtain yellow g-C3N4 powder.

[0043] (b). Synthesis of TiO2 nanoparticles: Tetrabutyl titanate (TBOT) and absolute ethanol are mixed at a volume ratio of 1:4, and then dropped into an ethanol-aqueous solution containing nitric acid (pH = 3), stirred to form a transparent sol, dried at 80 °C, and then calcined at 450 °C for 2 hours to obtain anatase TiO2 nanoparticles;

[0044] (c). Construction of g-C3N4 / TiO2 heterostructure: g-C3N4 and TiO2 are dispersed in ethanol at a mass ratio of 1:2, ultrasonicated for 1 hour, ammonia water is added to adjust the pH to 9, and hydrothermal reaction is carried out at 150 °C for 6 hours. After centrifugal washing and drying at 60 °C, g-C3N4 / TiO2 heterojunction composite material is obtained.

[0045] (2) The specific operation of the spraying method used in the present invention: g-C3N4 / TiO2 powder and silica sol are mixed to form a slurry, and the slurry is evenly sprayed on the surface of the reaction tank through a spray gun, and heat treatment is carried out in an air atmosphere to enhance the adhesion of the coating.

[0046] Example 1: Synchronous coagulation-sodium hypochlorite oxidation-photocatalytic treatment of overflow sewage

[0047] (1) Water quality characteristics of overflow sewage: The concentration of DMDS is 5.82 ± 1.23 μg / L, the concentration of DMTS is 4.19 ± 1.69 μg / L, the concentration of DEDS is 0.037 ± 0.016 μg / L, the concentration of DETS is 0.016 ± 0.011 μg / L, the turbidity is 57.7 ± 1.70 NTU, the concentration of dissolved organic carbon (DOC) is 12.9 ± 0.71 mg / L, and the concentration of total nitrogen (TN) is 24.6 ± 0.31 mg / L.

[0048] (2)Oxidant Targeted Screening: Among the oxidants sodium hypochlorite, potassium ferrate, and hydrogen peroxide (H2O2), based on the principles of frontier orbital matching (kinetics) and oxidation potential driving (thermodynamics) between the oxidants and the sulfur ether and its by-product molecules, sodium hypochlorite was selected as the optimal oxidant, and potassium ferrate as the sub-optimal oxidant.

[0049] The results of the frontier orbital matching analysis are as follows: When sodium hypochlorite is used as the oxidant, the energy level difference ΔE between the LUMO energy (-3.42 eV) of ClO⁻ and the HOMO energy (-5.23 eV) of sulfur ether (such as dimethyl sulfide) is 1.81 eV, meeting the frontier orbital matching principle (ΔE < 2.0 eV); when potassium ferrate is used as the oxidant, the energy level difference ΔE between the LUMO energy (-4.05 eV) of Fe(VI) and the HOMO energy (-5.23 eV) of sulfur ether (such as dimethyl sulfide) is 1.18 eV, meeting the frontier orbital matching principle (ΔE < 2.0 eV); when H2O2 is used as the oxidant, the energy level difference ΔE between the LUMO energy (-1.56 eV) of H2O2 and the HOMO energy (-5.23 eV) of sulfur ether (such as dimethyl sulfide) is 3.67 eV, not meeting the frontier orbital matching principle (ΔE < 2.0 eV).

[0050] The results of the oxidation potential driving analysis are as follows: When sodium hypochlorite is used as the oxidant, assuming that sulfur ether (such as dimethyl sulfide) is completely oxidized by ClO⁻ to sulfate (SO4 2- ), and ClO⁻ is reduced to Cl⁻, the reaction formula is (CH3)2S + 8ClO⁻ → SO4 2- + 8Cl⁻, the E 0 (+0.89V) of ClO⁻ is significantly higher than the sulfur ether oxidation threshold (-0.5 V), ΔE = +1.39V (corresponding to ΔG 0 = -nFΔE = −16×96485×1.39 ≈ −2150 kJ / mol < 0), meeting the thermodynamic spontaneous condition; when potassium ferrate is used as the oxidant, assuming that sulfur ether (such as dimethyl sulfide) is completely oxidized by Fe(VI) to sulfate (SO4 2- ), and Fe(VI) is reduced to Fe(III), the reaction formula is 3(CH3)2S + 8Fe(VI) → 3SO4 2- + 8Fe(III), the E 0 (+0.72V) of Fe(VI) is significantly higher than the sulfur ether oxidation threshold (-0.5V), ΔE = +1.22V (corresponding to ΔG 0=-nFΔE = -24 × 96485 × 1.22 ≈ -2824 kJ / mol (<0), which satisfies the thermodynamic spontaneous condition; the reaction between H2O2 and thioether does not conform to the reaction kinetics, so the thermodynamic analysis is no longer carried out; in summary, the electron transfer barrier between ClO⁻ and thioether is the lowest, indicating the optimal reaction kinetics. Therefore, sodium hypochlorite is the optimal oxidant, and potassium ferrate is the sub-optimal oxidant.

[0051] (3) Loading of g-C3N4 / TiO2 heterojunction photocatalyst: Mix g-C3N4 / TiO2 powder and silica sol in a mass ratio of 1:1 to make a slurry, and evenly spray the slurry on the surface of the reaction tank through a spray gun to form a coating with a thickness of 75 μm. Heat it in an air atmosphere at 300 °C for 2 hours to enhance the adhesion of the coating.

[0052] (4) Preparation of reagents: Prepare a NaClO stock solution with a concentration of 10 g / L; prepare a PAM stock solution with a concentration of 0.1 g / L; prepare a PACl stock solution with a concentration of 60 g / L.

[0053] (5) Simultaneous coagulation-sodium hypochlorite oxidation-photocatalytic synchronous treatment of overflow sewage: Add 1 mL / L of PACl stock solution, 1 mL / L of PAM stock solution and 1 mL / L of NaClO stock solution simultaneously, and control the concentrations of the coagulant PACl, the coagulant aid PAM and the oxidant NaClO to be 60 mg / L, 0.6 mg / L and 10 mg / L respectively; Stir the reaction solution, first quickly stir the mixture at a speed of 250 rpm for 40 s, then reduce the stirring speed to 100 rpm and continue stirring for 80 s, and finally reduce the stirring speed to 50 rpm and stir for 3 min; Add the quenching agent sodium thiosulfate to terminate the oxidation reaction; After the above steps, precipitate for 15 min to separate the flocs, and measure the concentration and turbidity of thioether in the supernatant. The experimental results are shown in Figure 1 , and it is obtained that when PACl-NaClO is synchronously treated, the removal rate of the total thioether concentration reaches 100%, and the reduction rate of turbidity reaches 95.6%. The removal effects of thioether and particulate matter are both good.

[0054] (6) Solid-phase extraction for extracting sulfide by-products: Take 1 L of the effluent obtained in step (5), and use an SPE column to enrich the sulfide by-products; at the beginning of the experiment, each SPE column is activated with methanol and ultrapure water in sequence to ensure that the resin surface is fully wetted and its adsorption activity is maximized; the activation process includes passing 5.0 mL of methanol through the column at a flow rate of 5.0 mL / min, and then passing 5.0 mL of ultrapure water through the column at the same flow rate; this step is repeated once; then use 5.0 mL of methanol to pass through the column at a flow rate of 5.0 mL / min to ensure full activation; then, load the sample, and pass 1.0 L of the water sample through the column at a flow rate of 10.0 mL / min; after the sample loading is completed, use nitrogen to dry the column at a pressure of 15.0 psi for 80 min; after the column is dried, elute the sample on the column with 10.0 mL of methyl tert-butyl ether (MTBE) at a flow rate of 2.0 mL / min, and collect the sulfide by-products; then use nitrogen blowing to concentrate 10.0 mL of MTBE containing sulfide by-products to 1.0 mL; the finally concentrated sample is used for GC-MS analysis.

[0055] (7) Identification and semi-quantification of sulfide by-products: Use a Shimadzu gas chromatograph equipped with a mass spectrometry detector (GC-MS, Kyoto, Japan) and an RTx-5MS chromatographic column (30 m, inner diameter 0.25 μm, film thickness 0.25 μm, Restek Corporation, Bellefonte, USA) to determine the sulfide by-products; the extract is introduced into the GC through an autosampler and separated according to the following temperature program: the initial column oven temperature is set at 35 °C and maintained for 10 min; then it is heated to 80 °C at a rate of 3 °C / min, and then quickly heated to 240 °C at a rate of 60 °C / min and maintained at this temperature for 3 min; the inlet temperature is fixed at 250 °C, helium is used as the carrier gas, and the constant flow rate is maintained at 1.93 mL / min; the nickel source temperature is set at 230 °C; mass spectrometry analysis is carried out in the full scan mode, and the scanning range is set at 30 to 400 m / z; the scanning starts at 3 min and continues until 25 min, the interval time is 0.2 s, and the scanning speed is 2000 amu / s; the experimental results are shown in Figure 2 , as can be seen from the figure: The identified by-products of sulfide are methanesulfonyl chloride, methyl thiosulfinate, and methylsulfonylmethyl thiosulfonate, and the peak areas of methanesulfonyl chloride, methyl thiosulfinate, and methylsulfonylmethyl thiosulfonate are 1.1×10 6 , 9.2×10 6 and 2.0×10 6 .

[0056] Example 2: Simultaneous coagulation-potassium ferrate oxidation-photocatalytic treatment of overflow sewage

[0057] (1) The water quality characteristics of the overflow sewage, the preparation and loading of the g-C3N4 / TiO2 heterojunction photocatalyst, the targeted screening of oxidants, and the extraction and identification of sulfide by-products and the semi-quantitative steps are the same as those in Example 1.

[0058] (2) Reagent preparation: Prepare potassium ferrate with a concentration of 10 g / L; prepare the PAM mother liquor with a concentration of 0.1 g / L; prepare the PACl mother liquor with a concentration of 60 g / L.

[0059] (3) Simultaneous coagulation-potassium ferrate oxidation-photocatalytic treatment of overflow sewage: Add 1 mL / L of the PACl mother liquor, 1 mL / L of the PAM mother liquor and 1 mL / L of the potassium ferrate mother liquor simultaneously, and control the concentrations of the coagulant PACl, the coagulant aid PAM and the oxidant potassium ferrate to be 60 mg / L, 0.6 mg / L and 10 mg / L respectively; Stir the reaction solution, first stir the mixture at a speed of 250 rpm for 40 s, then reduce the stirring speed to 100 rpm and continue stirring for 80 s, and finally reduce the stirring speed to 50 rpm and stir for 3 min; Add the quenching agent sodium thiosulfate to terminate the oxidation reaction; After the above steps, precipitate for 15 min to separate the flocs, and measure the concentration and turbidity of sulfide in the supernatant.

[0060] (4) Process treatment effect: The removal rates of DMDS, DMTS, DEDS and DETS are 76.7%, 91.8%, 100% and 97.0% respectively, and the turbidity is reduced by 85.8% ( Figure 1 ), and the peak areas of the sulfide by-products methylsulfonyl chloride, methyl thiosulfinate and methylsulfonylmethyl thiosulfonate are 0, 9.4×10 6 and 2.7×10 6 respectively; Compared with Example 1, when treating overflow sewage by simultaneous coagulation-potassium ferrate oxidation-photocatalysis, the removal efficiency of sulfide and the turbidity are slightly lower than those of the simultaneous coagulation-sodium hypochlorite oxidation-photocatalytic process, and the generation amounts of the sulfide by-products methyl thiosulfinate and methylsulfonylmethyl thiosulfonate are slightly higher than those of the simultaneous coagulation-sodium hypochlorite oxidation-photocatalytic process.

[0061] Comparative Example 1: Simultaneous coagulation-hydrogen peroxide oxidation-photocatalytic treatment of overflow sewage

[0062] (1) The water quality characteristics of the overflow sewage, the preparation and loading of the g-C3N4 / TiO2 heterojunction photocatalyst, and the extraction and identification of sulfide by-products and the semi-quantitative steps are the same as those in Example 1.

[0063] (2) Reagent preparation: Prepare hydrogen peroxide with a concentration of 10 g / L; prepare the PAM mother liquor with a concentration of 0.1 g / L; prepare the PACl mother liquor with a concentration of 60 g / L.

[0064] (3) Synchronous coagulation - hydrogen peroxide oxidation - photocatalytic treatment of overflow sewage: Add 1 mL / L of PACl mother liquor, 1 mL / L of PAM mother liquor and 1 mL / L of hydrogen peroxide mother liquor simultaneously, and control the concentrations of the coagulant PACl, the coagulant aid PAM and the oxidant hydrogen peroxide to be 60 mg / L, 0.6 mg / L and 10 mg / L respectively; Stir the reaction solution. First, quickly stir the mixture at a speed of 250 rpm for 40 s, then reduce the stirring speed to 100 rpm and continue stirring for 80 s, and finally reduce the stirring speed to 50 rpm and stir for 3 min; Add the quenching agent sodium thiosulfate to terminate the oxidation reaction; After the above steps, precipitate for 15 min to separate the flocs, and measure the concentration and turbidity of thioether in the supernatant.

[0065] (4) Treatment effect of the process: The removal rates of DMDS, DMTS, DEDS and DETS reached 26.0%, 20.4%, 22.1% and 18.5% respectively, and the turbidity decreased by 87.6% ( Figure 1 ); The peak areas of thioether by-products methanesulfonyl chloride, methyl thiosulfinate and methylsulfonylmethyl thiosulfonate were all 0; Compared with Example 1, when treating overflow sewage by synchronous coagulation - hydrogen peroxide oxidation - photocatalysis, the removal efficiency of thioether was much lower than that of synchronous coagulation - sodium hypochlorite oxidation - photocatalysis and synchronous coagulation - potassium ferrate oxidation - photocatalysis processes.

[0066] Obviously, the above embodiments are only examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of this invention.

Claims

1. A method for controlling sulfides and their byproducts in stormwater overflow wastewater by simultaneous coagulation-targeted oxidation-photocatalysis, characterized in that: The following steps are involved: (1) Targeted screening of oxidants: Through density functional theory (DFT) calculations and combined with the analysis of the frontier orbital distribution of sulfide molecules, the sulfur atom in the sulfide molecule and its adjacent functional groups with the highest electron cloud density are determined as the active reaction site, and the highest occupied molecular orbital (HOMO) energy of the active site of the sulfide molecule and the lowest unoccupied molecular orbital (LUMO) energy of the oxidant are measured respectively; based on the frontier molecular orbital theory, the LUMO energy of the oxidant is determined to be lower than the HOMO energy of the active site of the sulfide molecule to evaluate the feasibility of electron transfer between the sulfide molecule and the oxidant; at the same time, the standard oxidation potential (E) of the sulfide molecule is determined. 0 , verify that the standard Gibbs free energy change ΔG of the oxidation reaction of sulfide by the oxidant is less than 0; screen out the oxidant; (2) g-C3N4 / TiO2 powder is mixed with silica sol, ball-milled to form a slurry, and a uniform coating is formed on the surface of the reaction tank by spraying, and then heated in an air atmosphere; (3) transporting the overflow sewage to the reaction tank after treatment in step (2), adding the mixture of the oxidant, coagulant and coagulant aid screened in step (1), and then stirring and settling the mixed solution, and discharging the water after precipitation; (4) quantitatively analyzing the sulfide content in the effluent by solid phase microextraction-gas chromatography-mass spectrometry, measuring the turbidity of the effluent, and calculating the sulfide removal rate and turbidity removal rate; (5) extracting the sulfide byproduct from the water obtained in step (3) using a solid phase extraction method; (6) identifying and semi-quantifying the sulfide byproduct in the extract obtained in step (5) using a mass spectrometer detector; The sulfide includes one or more of dimethyl disulfide, dimethyl trisulfide, diethyl disulfide and diethyl trisulfide; The oxidizing agent is selected from sodium hypochlorite and / or potassium ferrate.

2. The method according to claim 1, characterized in that In step (2), the mass ratio of g-C3N4 / TiO2 powder to silica sol is (1:1) to (1:1.5).

3. The method according to claim 1, characterized in that In step (2), the thickness of the coating is 50 to 100 μm; The heating treatment is performed at a temperature of 300 to 320° C. and for a time of 100 to 120 minutes.

4. The method according to claim 1, wherein In step (3), the coagulant is selected from one or more of polyaluminium chloride, aluminium sulfate and ferric chloride.

5. The method according to claim 1, wherein In step (3), the coagulant aid is selected from polyacrylamide and / or calcium oxide.

6. The method according to claim 1, characterized in that In step (3), the mass concentration ratio of the oxidant, the coagulant and the coagulant aid is 5: (30-32): (0.3-0.4).

7. The method according to claim 1, characterized in that In step (5), the specific steps of extracting the sulfide byproduct from the water obtained in step (4) by solid phase extraction are as follows: using methanol and ultrapure water to activate a solid phase extraction (SPE) column; loading the effluent sample and passing it through the column at a flow rate of 9.5 to 10.0 mL / min; then using nitrogen to dry the column at a pressure of 14.5 to 15.0 psi for 70 to 80 minutes; after the column is dried, eluting the sample on the column with methyl tert-butyl ether at a flow rate of 1.8 to 2.0 mL / min to collect the sulfide byproduct.

8. The method according to claim 1, characterized in that In step (6), the method for identifying and semi-quantifying the sulfide by-products is as follows: the extract sulfide by-products are introduced into the GC through an automatic sampler, and the temperature program is as follows: the initial column oven temperature is set to 35°C and maintained for 10 minutes; then the temperature is increased to 80°C at a rate of 3°C / min, and then rapidly increased to 240°C at a rate of 60°C / min, and maintained at this temperature for 3 minutes; the injection port temperature is fixed at 250°C, and helium is used as the carrier gas to maintain a constant flow rate of 1.93 mL / min; the nickel source temperature is set to 230°C; mass spectrometry analysis is performed in full scan mode, and the scan range is set to 30 to 400 m / z; the scan starts from 3 minutes and lasts until 25 minutes, with an interval of 0.2 seconds and a scan speed of 2000 amu / s; The thioether by-products include methanesulfonyl chloride, methyl methylthiosulfinate, and methylsulfonyl methylthiosulfinate.

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