Method for controlling thioether and byproducts thereof in rainwater pipeline overflow sewage through synchronous coagulation-targeted oxidation-photocatalysis

Abstract

The invention relates to a method for controlling thioether and byproducts thereof in rainwater pipeline overflow sewage through synchronous coagulation-targeted oxidation-photocatalysis, and belongs to the technical field of environmental pollution treatment. The method comprises the following steps: firstly, screening an oxidant in a targeted manner according to front track matching and oxidation potential driving principles; then preparing a graphite-phase carbon nitride / titanium dioxide (g-C3N4 / TiO2) heterojunction photocatalyst by adopting a thermal polymerization method and a dipping-pulling method respectively, and loading the graphite-phase carbon nitride / titanium dioxide (g-C3N4 / TiO2) heterojunction photocatalyst in a reaction tank; the overflow sewage is conveyed into a reaction tank, an optimal oxidant and coagulant polyaluminum chloride are added at the same time, and in order to improve the coagulation effect, a coagulant aid is additionally added. The invention provides an effective treatment method for odor-causing substances in overflow sewage, and potential risks of thioether and by-products thereof on the ecological environment can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of water pollution control and sewage treatment, and in particular to a method for controlling sulfide and its byproducts in overflow sewage from a rainwater pipe by synchronous coagulation-targeted oxidation-photocatalysis. Background Art

[0002] The mixing between urban rainwater pipes and sewage pipes has led to a large amount of domestic sewage and industrial wastewater entering the rainwater 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, high-load organic matter produces a large amount of odor-causing organic matter under the action of microorganisms. At present, sulfide has been identified as the main type of odor-causing organic matter in rainwater pipes. On rainy days, rainwater washes these odor-causing substances into the receiving water body. Sulfide is highly irritating and volatile at low concentrations, causing serious sensory and chemical pollution, endangering human health; and reducing water quality and damaging aquatic ecosystems. In addition, sediments have been identified as the main source and reservoir of sulfide. Therefore, simply removing soluble sulfide in overflow sewage without treating the particulate matter in it does not necessarily solve the fundamental problem. The particulate matter will adsorb a large amount of sulfide, and the microorganisms in it may continue to produce odor-causing substances, causing repeated odors in the water body. In addition, analyzing whether sulfide will produce by-products during the removal process is crucial to assessing whether sulfide will continue to affect human health and the water environment. Therefore, only by controlling particulate matter, sulfide and its by-products in overflow sewage at the same time can we fundamentally solve the odor pollution and water quality safety problems of receiving water bodies caused by rainwater pipe drainage.

[0003] At present, the control of pollutants in overflow sewage mainly focuses on conventional pollutants. Patent CN118145775A discloses a method for treating overflow sewage by pre-oxidation coagulation, which proposes to treat overflow sewage by oxidation, coagulation, flocculation and sedimentation in sequence, and can effectively and simultaneously remove COD, ammonia nitrogen, total phosphorus, turbidity, UV in overflow sewage in a short time. 254 However, this method is mainly aimed at COD, ammonia nitrogen, total phosphorus, turbidity and UV 254 Its comprehensive treatment capacity for conventional pollutants such as chlorinated hydrocarbons may be insufficient when faced with complex sewage components, especially for some key pollutants (such as sulfides), the treatment effect is unclear; moreover, this method does not clarify the lasting impact of water treatment on aquatic ecology.

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

[0005] In addition, patent CN116642995B provides an adsorption experimental device for odorous substances, which evaluates the adsorption capacity of specific catalytic materials for odorous substances through adsorption experiments. The 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, the device mainly focuses on the research of a single odorous substance, and its application range is relatively limited. Therefore, in view of the pollution characteristics of rainwater pipe overflow sewage with 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 increasingly serious pollution caused by overflow of rainwater pipes, it is urgent to provide a new method to solve the above technical problems in view of the shortcomings of the above disclosed technologies. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for synergistically treating sulfide and its byproducts in overflow sewage from rainwater pipes based on synchronous coagulation-targeted oxidation-photocatalysis. The present invention aims to efficiently remove sulfide and particulate matter (sulfide adsorbed and containing sulfide-generating microorganisms) in overflow sewage by establishing terminal treatment facilities and adopting synchronous coagulation-targeted oxidation-photocatalysis process, and control the generation of sulfide byproducts, so as to improve water quality and protect aquatic ecosystems, and provide a more comprehensive and efficient solution for urban sustainable development.

[0008] The object of the present invention is to provide a method for controlling sulfide and its byproducts in the overflow sewage of the rainwater pipe by synchronous coagulation-targeted oxidation-photocatalysis, comprising the following steps: (1) Targeted screening of oxidants: Through density functional theory (DFT) and combined with the frontier orbital distribution analysis of thioether molecules, the sulfur atom and its adjacent functional groups in the thioether molecule 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 thioether 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 thioether molecule to evaluate the feasibility of electron transfer between the thioether molecule and the oxidant; at the same time, the standard oxidation potential E of the thioether molecule is determined0 , verify that the standard Gibbs free energy change ΔG of the oxidation reaction of the oxidant to oxidize the thioether is less than 0; screen out the oxidant; (2) Mixing g-C3N4 / TiO2 powder with silica sol, ball milling to form a slurry, spraying to form a uniform coating on the surface of the reaction tank, and heating in an air atmosphere; (3) transporting the overflow sewage to the treated reaction tank obtained in step (2), adding the mixture of the oxidant, coagulant and coagulant aid screened in step (1), and then stirring and precipitating the mixed solution, and discharging the water after precipitation; (3) The overflow sewage is transported to the reaction tank, and a mixture of a screened oxidant, a coagulant and a coagulant aid is added. The mixed solution is then stirred and precipitated, and the water is discharged after precipitation to achieve the removal of sulfide and particulate matter and the control of the generation of sulfide by-products; (4) using solid phase microextraction-gas chromatography-mass spectrometry to quantitatively analyze the sulfide content in the effluent, and measuring the turbidity of the effluent, and calculating the sulfide removal rate and turbidity removal rate; (5) extracting the sulfide byproduct in the water obtained in step (1) using a solid phase extraction method; (6) Identify and semi-quantitate the thioether by-product in the extract obtained in step (3) using a mass spectrometer.

[0009] In some embodiments of the present invention, in step (2), the mass ratio of g-C3N4 / TiO2 powder to silica sol is (1:1) to (1:1.5); The thickness of the coating is 50-100 μm; The heating treatment is performed at a temperature of 300-320° C. and for a time of 100-120 minutes.

[0010] In some embodiments of the present invention, in step (2), the g-C3N4 / TiO2 (graphite phase carbon nitride / titanium dioxide heterojunction photocatalyst) is prepared by the following method: (a) First, g-C3N4 was synthesized by thermal polymerization. Melamine powder was placed in a crucible and heated to 550°C at 5°C / min under nitrogen protection. The temperature was kept at this temperature for 2 hours, and then the mixture was naturally cooled and ground to obtain yellow g-C3N4 powder.

[0011] (b) Synthesis of TiO2 nanoparticles: Tetrabutyl titanate (TBOT) and anhydrous ethanol were mixed in a volume ratio of 1:4, added dropwise to an ethanol-water solution containing nitric acid (pH=3), stirred to form a transparent sol, dried at 80°C, and calcined at 450°C for 2 hours to obtain anatase TiO2 nanoparticles; (c) Construction of g-C3N4 / TiO2 heterostructure: g-C3N4 and TiO2 were dispersed in ethanol at a mass ratio of 1:2, ultrasonically treated for 1 hour, ammonia was added to adjust the pH to 9, hydrothermally reacted at 150°C for 6 hours, centrifuged and washed, and then dried at 60°C to obtain a g-C3N4 / TiO2 heterojunction composite material.

[0012] In the present invention, a g-C3N4 / TiO2 heterojunction photocatalyst is loaded on the surface of a reaction cell, and natural light is used to drive the degradation of sulfide.

[0013] In some embodiments of the present invention, the sulfide includes one or more of dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diethyl disulfide (DEDS) and diethyl trisulfide (DETS).

[0014] In some embodiments of the present invention, in step (3), the oxidant is selected from sodium hypochlorite and / or potassium ferrate.

[0015] In some embodiments of the present invention, in step (3), the coagulant is selected from one or more of polyaluminium chloride, aluminium sulfate and ferric chloride.

[0016] In some embodiments of the present invention, in step (3), the coagulant aid is selected from polyacrylamide and / or calcium oxide.

[0017] In some embodiments of the present invention, in step (3), the mass concentration ratio of the oxidant, the coagulant and the coagulant aid is 5: (30-32): (0.3-0.4).

[0018] In some embodiments of the present invention, in step (5), the specific steps of extracting the sulfide byproduct in the effluent obtained in step (3) by solid phase extraction are as follows: using methanol and ultrapure water to activate the SPE column; loading the effluent sample and passing it through the column at a flow rate of 9.5~10.0mL / min; then using nitrogen to dry the column at a pressure of 14.5~15.0 psi for 70~80min; after the column is dried, eluting the sample on the column with methyl tert-butyl ether (MTBE) at a flow rate of 1.8~2.0 mL / min to collect the sulfide and its byproduct molecules.

[0019] In some embodiments of the present invention, in step (6), the method for identifying and semi-quantitating thioether by-products is as follows: the extract thioether 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 min; 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 min; the injection port temperature is fixed at 250°C, helium is used as the carrier gas, and a constant flow rate of 1.93 mL / min is maintained; 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 min and lasts until 25 min, with an interval of 0.2 s and a scan speed of 2000 amu / s; The thioether by-products include methanesulfonyl chloride, methyl methylthiosulfinate and methylsulfonyl methylthiosulfinate.

[0020] Specifically, the method of the present invention is as follows: first, the overflow sewage is transported to a reaction tank, and the screened oxidant and coagulant polyaluminium chloride are added at the same time, wherein the addition amount of the oxidant is 10 mg / L, and the addition amount of the polyaluminium chloride is 60 mg / L; in order to improve the coagulation effect, 0.6 mg / L of coagulant aid polyacrylamide is additionally added; the mixed solution is rapidly stirred at 250 rpm for 40 seconds, then slowly stirred at 100 rpm for 80 seconds, and finally stirred at 50 rpm for 3 minutes, and then precipitated for 10 minutes to finally obtain the treated effluent; in addition, the present invention also analyzes the sulfide and its by-products in the overflow sewage, and uses solid phase microextraction-gas chromatography-mass spectrometry to quantify the sulfide content in the effluent, and uses solid phase extraction to extract 1 The sulfide by-products in the effluent after L treatment were identified and semi-quantified by gas chromatography-mass spectrometry. During the solid phase extraction process, the solid phase extraction column was first activated with methanol and ultrapure water, then the water sample was loaded and the column was dried, and finally the sample was eluted with methyl tert-butyl ether and concentrated before gas chromatography-mass spectrometry analysis.

[0021] The above technical solution of the present invention has the following advantages compared with the prior art: 1. The present invention combines the advantages of three treatment methods: coagulation, targeted oxidation and photocatalysis. The coagulant PACl destroys the stability of particles and promotes their aggregation into settleable flocs through synergistic effects such as charge neutralization, adsorption bridging, and net capture and sweeping, effectively removing sulfide and its by-product molecules adsorbed by particles in overflow sewage; the targeted screened oxidant can selectively oxidize specific pollutants or reactants, reduce the influence of other substances on the removal of sulfide and its by-product molecules, thereby improving the efficiency and selectivity of the reaction and converting sulfide and its by-product molecules into harmless substances; the g-C3N4 / TiO2 heterojunction photocatalyst absorbs light energy, excites electrons and produces active substances under natural light, thereby accelerating chemical reactions, promoting the complete mineralization of sulfide and its by-product molecules, and reducing the generation of by-products; the coupling of the three shows a significant synergistic effect, which can more efficiently remove pollutants in complex sewage. At present, there is no patent on the synergistic control of sulfide and its by-product molecules by synchronous coagulation-targeted oxidation-photocatalysis, and the present invention fills this gap. By simultaneously and efficiently removing soluble and particulate sulfides in overflow sewage, it helps to achieve a comprehensive improvement in the overall water quality of the water body.

[0022] 2. The present invention is relatively simple to implement and can be easily integrated into existing sewage treatment facilities, making it easy to promote and apply. In addition, the cost of the reagents is low, achieving a good balance between pollutant removal and economic cost control, and providing an efficient, economical and operable solution for the sewage treatment industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein: Figure 1 It is a result diagram of the removal rate of sulfide in the embodiments of the present invention and the comparative example; wherein, (a) is the removal rate of turbidity by simultaneous coagulation-oxidation-photocatalysis when sodium hypochlorite, potassium ferrate and hydrogen peroxide are used as oxidants respectively; (b) is the removal effect of sulfide by the simultaneous coagulation-oxidation-photocatalysis process when sodium hypochlorite is used as the oxidant; (c) is the removal effect of sulfide by the simultaneous coagulation-oxidation-photocatalysis process when potassium ferrate is used as the oxidant; (d) is the removal effect of sulfide by the simultaneous coagulation-oxidation-photocatalysis process when hydrogen peroxide is used as the oxidant.

[0024] Figure 2 This is the molecular spectrum of sulfide and its by-products identified by gas chromatography-mass spectrometry in Example 1 of the present invention.

[0025] Figure 3 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0026] The present invention is 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 implement it, but the embodiments are not intended to limit the present invention.

[0027] (1) The g-C3N4 / TiO2 (graphite phase carbon nitride / titanium dioxide heterojunction photocatalyst) used in the present invention is prepared by the following method: (a) First, g-C3N4 was synthesized by thermal polymerization. Melamine powder was placed in a crucible and heated to 550°C at 5°C / min under nitrogen protection. The temperature was kept at this temperature for 2 hours, and then the mixture was naturally cooled and ground to obtain yellow g-C3N4 powder.

[0028] (b) Synthesis of TiO2 nanoparticles: Tetrabutyl titanate (TBOT) and anhydrous ethanol were mixed in a volume ratio of 1:4, added dropwise to an ethanol-water solution containing nitric acid (pH=3), stirred to form a transparent sol, dried at 80°C, and calcined at 450°C for 2 hours to obtain anatase TiO2 nanoparticles; (c) Construction of g-C3N4 / TiO2 heterostructure: g-C3N4 and TiO2 were dispersed in ethanol at a mass ratio of 1:2, ultrasonically treated for 1 hour, ammonia was added to adjust the pH to 9, hydrothermally reacted at 150°C for 6 hours, centrifuged and washed, and then dried at 60°C to obtain a g-C3N4 / TiO2 heterojunction composite material.

[0029] (2) The specific operation of the spraying method used in the present invention is as follows: g-C3N4 / TiO2 powder is mixed with silica sol to form a slurry, the slurry is evenly sprayed on the surface of the reaction tank through a spray gun, and a heating treatment is performed in an air atmosphere to enhance the adhesion of the coating.

[0030] Example 1: Simultaneous coagulation-sodium hypochlorite oxidation-photocatalytic treatment of overflow sewage (1) Characteristics of overflow sewage water quality: DMDS concentration was 5.82±1.23 μg / L, DMTS concentration was 4.19±1.69 μg / L, DEDS concentration was 0.037±0.016 μg / L, DETS concentration was 0.016±0.011 μg / L, turbidity was 57.7±1.70 NTU, dissolved organic carbon (DOC) concentration was 12.9±0.71 mg / L, and total nitrogen (TN) concentration was 24.6±0.31 mg / L.

[0031] (2) Targeted screening of oxidants: Among the oxidants sodium hypochlorite, potassium ferrate, and hydrogen peroxide (H2O2), sodium hypochlorite was selected as the optimal oxidant and potassium ferrate as the suboptimal oxidant based on the frontier orbital matching (kinetics) and oxidation potential drive (thermodynamics) principles between the oxidant and the thioether and its by-product molecules.

[0032] The results of frontier orbital matching analysis are as follows: when sodium hypochlorite is used as the oxidant, the energy level difference between the LUMO energy of ClO⁻ (-3.42 eV) and the HOMO energy of sulfide (such as dimethyl sulfide) (-5.23 eV) is ΔE=1.81 eV, which meets the frontier orbital matching principle (ΔE<2.0 eV); when potassium ferrate is used as the oxidant, the energy level difference between the LUMO energy of Fe(VI) (-4.05 eV) and the HOMO energy of sulfide (such as dimethyl sulfide) (-5.23 eV) is ΔE=1.18 eV, which meets the frontier orbital matching principle (ΔE<2.0 eV); when H2O2 is used as the oxidant, the energy level difference between the LUMO energy of H2O2 (-1.56 eV) and the HOMO energy of sulfide (such as dimethyl sulfide) (-5.23 eV) is ΔE=3.67 eV, which does not meet the frontier orbital matching principle (ΔE<2.0 eV).

[0033] The results of the oxidation potential driven analysis are as follows: When sodium hypochlorite is used as the oxidant, assuming that the sulfide (such as dimethyl sulfide) is completely oxidized by ClO⁻ to sulfate (SO4 2- ), ClO⁻ is reduced to Cl⁻, the reaction formula is (CH3)2S+8ClO⁻→SO4 2- +8Cl⁻,ClO⁻ of E 0 (+0.89 V) is significantly higher than the thioether oxidation threshold (-0.5 V), ΔE = +1.39 V (corresponding to ΔG 0 = -nFΔE = −16×96485×1.39 ≈ −2150 kJ / mol<0, satisfying the thermodynamic spontaneous condition; when potassium ferrate is used as the oxidant, assuming that the sulfide (such as dimethyl sulfide) is completely oxidized by Fe(VI) to sulfate (SO4 2- ), Fe(VI) is reduced to Fe(III), the reaction formula is 3(CH3)2S + 8Fe(VI)→ 3SO4 2- + 8Fe(III), Fe(VI) 0 (+0.72V) is significantly higher than the thioether oxidation threshold (-0.5V), ΔE = +1.22V (corresponding to ΔG 0 =-nFΔE = -24 × 96485 × 1.22 ≈ -2824 kJ / mol<0), which meets the thermodynamic spontaneous conditions; the reaction of H2O2 and thioether does not conform to the reaction kinetics, so no thermodynamic analysis is performed; in summary, the electron transfer barrier between ClO⁻ and thioether is the lowest, indicating the optimal reaction kinetics, so sodium hypochlorite is the optimal oxidant and potassium ferrate is the suboptimal oxidant.

[0034] (3) Loading of g-C3N4 / TiO2 heterojunction photocatalyst: g-C3N4 / TiO2 powder and silica sol were mixed in a mass ratio of 1:1 to form a slurry. The slurry was evenly sprayed on the surface of the reaction tank by a spray gun to form a coating with a thickness of 75 μm. The coating was heated at 300 °C for 2 h in an air atmosphere to enhance the adhesion of the coating.

[0035] (4) Reagent preparation: Prepare NaClO stock solution with a concentration of 10 g / L; prepare PAM stock solution with a concentration of 0.1 g / L; prepare PACl stock solution with a concentration of 60 g / L.

[0036] (5) Simultaneous coagulation-sodium hypochlorite oxidation-photocatalysis for simultaneous treatment of overflow sewage: 1 mL / L PACl mother liquor, 1 mL / L PAM mother liquor and 1 mL / L NaClO mother liquor were added at the same time, and the concentrations of coagulant PACl, coagulant aid PAM and oxidant NaClO were controlled to be 60 mg / L, 0.6 mg / L and 10 mg / L respectively; the reaction solution was stirred, firstly the mixture was stirred rapidly at 250 rpm for 40 s, then the stirring speed was reduced to 100 rpm and continued to stir for 80 s, and finally the stirring speed was reduced to 50 rpm and stirred for 3 min; the quencher sodium thiosulfate was added to terminate the oxidation reaction; after the above steps, the precipitate was allowed to settle for 15 min to separate the flocculants, and the concentration and turbidity of the supernatant thioether were measured. The experimental results are shown in Figure 1 When PACl-NaClO was used for simultaneous treatment, the removal rate of the total sulfide concentration reached 100%, the reduction rate of turbidity reached 95.6%, and the removal effects of sulfide and particulate matter were good.

[0037] (6) Solid phase extraction for thioether byproducts: 1 L of the water obtained in step (5) was taken and the thioether byproducts were enriched using an SPE column. At the beginning of the experiment, each SPE column was activated with methanol and ultrapure water in turn to ensure that the resin surface was fully wetted and to maximize its adsorption activity. The activation process included passing 5.0 mL of methanol through the column at a flow rate of 5.0 mL / min, followed by passing 5.0 mL of ultrapure water through the column at the same rate. This step was repeated once more. Another 5.0 mL of methanol was passed through the column at a flow rate of 5.0 mL / min to ensure full activation. Then, the sample was loaded and 1.0 L of water sample was passed through the column at a flow rate of 10.0 mL / min. After the sample was loaded, the column was dried using nitrogen at a pressure of 15.0 psi for 80 min. After the column was dried, the sample on the column was eluted with 10.0 mL of methyl tert-butyl ether (MTBE) at a flow rate of 2.0 mL / min to collect the thioether byproducts. The column was then blown with nitrogen at a flow rate of 10.0 mL of MTBE containing thioether byproducts was concentrated to 1.0 mL; the final concentrated sample was used for GC-MS analysis.

[0038] (7) Identification and semi-quantification of thioether by-products: The thioether by-products were determined using a Shimadzu gas chromatograph (GC-MS, Kyoto, Japan) equipped with a mass spectrometer detector and an RTx-5MS column (30 m, inner diameter 0.25 μm, film thickness 0.25 μm, Restek Corporation, Bellefonte, USA). The extract was introduced into the GC through an autosampler and separated according to the following temperature program: the initial column oven temperature was set to 35 °C and maintained for 10 min; then the temperature was 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 min; the injection port temperature was fixed at 250 °C, and helium was used as the carrier gas at a constant flow rate of 1.93 mL / min; the nickel source temperature was set to 230 °C; mass spectrometry analysis was performed in full scan mode, with the scan range set to 30 to 400 m / z; the scan was from 3 min and lasted until 25 min, with an interval of 0.2 s and a scanning speed of 2000 amu / s. The experimental results are shown in Figure 2 As shown in the figure, the identified thioether byproducts are methanesulfonyl chloride, methyl methylthiosulfinate and methyl sulfonyl methylthiosulfonate. The peak areas of methanesulfonyl chloride, methyl methylthiosulfinate and methyl sulfonyl methylthiosulfonate are 1.1×10 6 , 9.2×10 6 and 2.0×10 6 .

[0039] Example 2: Simultaneous coagulation-potassium ferrate oxidation-photocatalytic treatment of overflow sewage (1) The overflow sewage water quality characteristics, preparation and loading of g-C3N4 / TiO2 heterojunction photocatalyst, targeted screening of oxidants, extraction and identification of thioether byproducts, and semi-quantitative steps are the same as in Example 1.

[0040] (2) Reagent preparation: prepare potassium ferrate at a concentration of 10 g / L; prepare PAM stock solution at a concentration of 0.1 g / L; prepare PACl stock solution at a concentration of 60 g / L.

[0041] (3) Simultaneous coagulation-potassium ferrate oxidation-photocatalytic treatment of overflow sewage: 1 mL / L PACl mother liquor, 1 mL / L PAM mother liquor and 1 mL / L potassium ferrate mother liquor were added simultaneously, and the concentrations of coagulant PACl, coagulant aid PAM and oxidant potassium ferrate were controlled to be 60 mg / L, 0.6 mg / L and 10 mg / L, respectively; the reaction solution was stirred, firstly, the mixture was rapidly stirred at a speed of 250 rpm for 40 s, then the stirring speed was reduced to 100 rpm and continued to stir for 80 s, and finally the stirring speed was reduced to 50 rpm and stirred for 3 min; the quencher sodium thiosulfate was added to terminate the oxidation reaction; after the above steps, the flocculants were separated by settling for 15 min, and the concentration and turbidity of the sulfide in the supernatant were measured.

[0042] (4) Process treatment effect: The removal rates of DMDS, DMTS, DEDS and DETS were 76.7%, 91.8%, 100% and 97.0% respectively, and the turbidity was reduced by 85.8% ( Figure 1 ), the peak areas of the thioether byproducts methanesulfonyl chloride, methyl methylthiosulfinate and methylsulfonylmethylthiosulfonate were 0, 9.4×10 6 and 2.7×10 6 Compared with Example 1, when the overflow sewage is treated by simultaneous coagulation-potassium ferrate oxidation-photocatalysis, the removal efficiency and turbidity of thioether are slightly lower than those of the simultaneous coagulation-sodium hypochlorite oxidation-photocatalysis process, and the production amount of thioether by-products methyl methyl thiosulfinate and methyl sulfonyl methyl thiosulfonate is slightly higher than that of the simultaneous coagulation-sodium hypochlorite oxidation-photocatalysis process.

[0043] Comparative Example 1: Simultaneous coagulation-hydrogen peroxide oxidation-photocatalytic treatment of overflow sewage (1) The overflow sewage water quality characteristics, the preparation and loading of g-C3N4 / TiO2 heterojunction photocatalyst, the extraction and identification of sulfide byproducts, and the semi-quantitative steps are the same as in Example 1.

[0044] (2) Reagent preparation: prepare hydrogen peroxide at a concentration of 10 g / L; prepare PAM stock solution at a concentration of 0.1 g / L; prepare PACl stock solution at a concentration of 60 g / L.

[0045] (3) Simultaneous coagulation-hydrogen peroxide oxidation-photocatalytic treatment of overflow sewage: 1 mL / L PACl mother liquor, 1 mL / L PAM mother liquor and 1 mL / L hydrogen peroxide mother liquor were added simultaneously, and the concentrations of coagulant PACl, coagulant aid PAM and oxidant hydrogen peroxide were controlled to be 60 mg / L, 0.6 mg / L and 10 mg / L, respectively; the reaction solution was stirred, firstly, the mixture was rapidly stirred at a speed of 250 rpm for 40 s, then the stirring speed was reduced to 100 rpm and continued to stir for 80 s, and finally the stirring speed was reduced to 50 rpm and stirred for 3 min; the quencher sodium thiosulfate was added to terminate the oxidation reaction; after the above steps, the flocculants were separated by settling for 15 min, and the concentration and turbidity of the thioether in the supernatant were measured.

[0046] (4) Process treatment effect: The removal rates of DMDS, DMTS, DEDS and DETS were 26.0%, 20.4%, 22.1% and 18.5% respectively, and the turbidity was reduced by 87.6% ( Figure 1 ); the peak areas of thioether byproducts methanesulfonyl chloride, methyl methylthiosulfinic acid methyl ester and methylsulfonyl methylthiosulfonate are all 0; compared with Example 1, when the overflow sewage is treated by simultaneous coagulation-hydrogen peroxide oxidation-photocatalysis, the removal efficiency of thioether is much lower than that of simultaneous coagulation-sodium hypochlorite oxidation-photocatalysis and simultaneous coagulation-potassium ferrate oxidation-photocatalysis processes.

[0047] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for controlling sulfide and its byproducts in overflow sewage from rainwater pipes 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 thioether molecules, the sulfur atom and its adjacent functional groups in the thioether molecule 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 thioether molecule and the lowest unoccupied molecular orbital LUMO energy of the oxidant are determined 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 thioether molecule to evaluate the feasibility of electron transfer between the thioether molecule and the oxidant; at the same time, the standard oxidation potential E of the thioether molecule is determined 0 , verify that the standard Gibbs free energy change ΔG of the oxidation reaction of the oxidant to oxidize the thioether is less than 0; screen out the oxidant; (2) Mixing g-C3N4 / TiO2 powder with silica sol, ball milling to form a slurry, spraying to form a uniform coating on the surface of the reaction tank, and heating in an air atmosphere; (3) transporting the overflow sewage to the treated reaction tank obtained in step (2), adding the mixture of the oxidant, coagulant and coagulant aid screened in step (1), and then stirring and precipitating the mixed solution, and discharging the water after precipitation; (4) using solid phase microextraction-gas chromatography-mass spectrometry to quantitatively analyze the sulfide content in the effluent, and measuring the turbidity of the effluent, and calculating the sulfide removal rate and turbidity removal rate; (5) extracting the sulfide byproduct in the water obtained in step (3) using a solid phase extraction method; (6) Identify and semi-quantitate the thioether by-product in the extract obtained in step (5) using a mass spectrometer.

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 50-100 μm; The heating treatment is performed at a temperature of 300-320° C. and for a time of 100-120 minutes.

4. The method according to claim 1, characterized in that The sulfide includes one or more of dimethyl disulfide, dimethyl trisulfide, diethyl disulfide and diethyl trisulfide.

5. The method according to claim 1, characterized in that In step (3), the oxidant is selected from sodium hypochlorite and / or potassium ferrate.

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

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

8. 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).

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

10. The method according to claim 1, characterized in that In step (6), the method for identifying and semi-quantitating the thioether by-product is as follows: the extract thioether by-product is 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 min; 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 min; the injection port temperature is fixed at 250°C, helium is used as the carrier gas, and a constant flow rate of 1.93 mL / min is maintained; 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 min and lasts until 25 min, with an interval of 0.2 s and a scan speed of 2000 amu / s; The thioether by-products include methanesulfonyl chloride, methyl methylthiosulfinate and methylsulfonyl methylthiosulfinate.

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