Ultraviolet irradiation and sodium hypochlorite synergistic sewage treatment process

Abstract

The invention relates to the technical field of sewage treatment, in particular to an ultraviolet irradiation and sodium hypochlorite synergistic sewage treatment process which specifically comprises the following steps: S1, performing light treatment on sewage by using an ultraviolet lamp, and controlling the ultraviolet dosage to be 15-25mJ / cm < 2 >, the wavelength of the ultraviolet lamp to be 254nm and the irradiation time to be 1-5min; s2, adding modified sodium hypochlorite into the sewage treated in the step S1 under the condition of not stopping illumination of the ultraviolet lamp to obtain a treated water body; s3, sodium thiosulfate is added into the water body obtained in the step S2, redundant chlorine elements in the water body are removed, and a finally-treated water sample is obtained. Through the synergistic effect of ultraviolet irradiation and modified sodium hypochlorite, the adding amount of sodium hypochlorite is reduced (the sodium hypochlorite can reach the standard only by 1 mg / L), meanwhile, the contact reaction time is shortened to 1 min, and the comprehensive energy consumption is reduced by 30%-40%. In addition, residual chlorine is accurately neutralized by sodium thiosulfate in a controlled amount, excessive medicament residues are avoided, and the green chemical process requirements are met.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and specifically to a sewage treatment process that synergistically uses ultraviolet light irradiation and sodium hypochlorite. Background Art

[0002] If various pathogenic microorganisms surviving in sewage cannot be sufficiently removed through disinfection, these pathogens may enter the receiving water body and cause various waterborne diseases, posing risks to the ecosystem and human health. Currently, the commonly used sewage disinfection technologies mainly include chemical disinfection methods (such as sodium hypochlorite, chlorine dioxide, ozone, etc.) and physical disinfection methods (such as ultraviolet light). Among them, sodium hypochlorite is the most commonly used disinfectant in sewage treatment plants. However, when it reacts with the natural organic matter (NOM) present in sewage, a large amount of toxic disinfection by-products (DBPs) will be produced, which have potential adverse effects on the water environment and human health. Compared with traditional chemical disinfection, although ultraviolet disinfection hardly produces disinfection by-products that are "carcinogenic, teratogenic, and mutagenic", its disinfection effect is unstable in practical applications, and there is a phenomenon of photoreactivation of inactivated microorganisms. The existence of these problems limits the application and development of the above single disinfection methods in the process of sewage disinfection. Therefore, combined disinfection processes have emerged.

[0003] Currently, the commonly used disinfection processes in sewage treatment plants are chlorine disinfection and ultraviolet disinfection. However, problems such as the accumulation of disinfection by-products, photoreactivation of microorganisms, and low disinfection efficiency brought about during the disinfection process limit the further application and development of the disinfection process. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a sewage treatment process that synergistically uses ultraviolet light irradiation and sodium hypochlorite.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A sewage treatment process that synergistically uses ultraviolet light irradiation and sodium hypochlorite, comprising the following steps:

[0007] S1. Using an ultraviolet lamp to irradiate the sewage, controlling the ultraviolet dose to be 15 - 25 mJ / cm 2 , the wavelength of the ultraviolet lamp is 254 nm, and the irradiation time is 1 - 5 min;

[0008] S2. Without stopping the ultraviolet light irradiation, adding modified sodium hypochlorite to the sewage treated in step S1 to obtain the treated water body;

[0009] S3. Adding sodium thiosulfate to the water body obtained in step S2 to remove the excess chlorine element in the water body to obtain the finally treated water sample;

[0010] Among them, the preparation of modified sodium hypochlorite includes the following steps:

[0011] S21. Dissolve chitosan in a dilute acetic acid solution and stir until completely dissolved to form a chitosan solution;

[0012] S22. Dissolve ethylenediaminetetraacetic acid in deionized water to obtain an EDTA solution and slowly add it to the chitosan solution. Stir while adding to make the solution mix evenly to form a chitosan-EDTA complex solution;

[0013] S23. Add 3-5 parts of the chitosan-EDTA complex solution and 5-8 parts of the modified photoassistant solvent to 20-30 parts of sodium hypochlorite solution to obtain a mixed solution;

[0014] S24. Add sodium bicarbonate to the mixed solution to control the pH of the mixed solution at 6.8-7.5. The addition process is carried out under stirring conditions at 25-30 °C to finally obtain modified sodium hypochlorite.

[0015] The preparation of the modified photoassistant solvent includes the following steps:

[0016] S231. Add 3-5 parts of nano-zinc oxide to 20-25 parts of absolute ethanol and ultrasonically treat it at a frequency of 40 kHz for 20-30 min to obtain a nano-zinc oxide solution;

[0017] S232. Add 1-2 parts of cetyltrimethylammonium bromide to the nano-zinc oxide solution and stir in a water bath at 60 °C for 1-2 h to obtain a CTAB-nano-zinc oxide solution;

[0018] S233. Add 4-6 parts of potassium persulfate to the CTAB-nano-zinc oxide solution and stir for 2-3 h to finally obtain the modified photoassistant solvent.

[0019] Preferably, the mass ratio of chitosan to ethylenediaminetetraacetic acid in steps S21 and S22 is 3:1.

[0020] Preferably, the stirring speed during the preparation of the modified photoassistant solvent is 300-350 r / min.

[0021] Preferably, the addition amount of the modified sodium hypochlorite is 1-3 mg / L.

[0022] Preferably, the addition amount of sodium thiosulfate is 0.1-0.2 mg / L.

[0023] Preferably, in step S1, the ultraviolet lamp uses a low-pressure mercury lamp with a power of 30 W and a lamp tube spacing of 5 cm.

[0024] Preferably, the stirring speed during the preparation of the modified sodium hypochlorite is 250-300 r / min.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The present invention utilizes modified sodium hypochlorite, which can generate reactive oxygen species and sulfate radicals under the action of ultraviolet light, and synergistically attacks the microbial membrane structure with hypochlorous acid to oxidize and degrade complex organic substances, reducing the ineffective consumption of sodium hypochlorite and stabilizing the effective chlorine concentration, thereby further improving the degradation efficiency.

[0027] 2. The present invention adopts a treatment process of first ultraviolet light and then the synergistic action of ultraviolet light and modified sodium hypochlorite to inactivate fecal coliforms. The inactivation effect can be stably maintained above 1.8-lg, 1.4-lg, and 2.0-lg, which is more stable than simultaneous disinfection with ultraviolet light and modified sodium hypochlorite.

[0028] 3. The synergistic action of ultraviolet light and modified sodium hypochlorite in the present invention reduces the dosage of sodium hypochlorite (only 1 mg / L is required to meet the standard), and at the same time shortens the contact reaction time to 1 minute, reducing the comprehensive energy consumption by 30%-40%. In addition, sodium thiosulfate accurately controls the amount to neutralize residual chlorine, avoiding excessive drug residues and meeting the requirements of green chemical processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart of the synergistic sewage treatment process of ultraviolet light and sodium hypochlorite of the present invention;

[0030] Figure 2 It is a schematic diagram of the bactericidal effect after adding modified sodium hypochlorite to the water samples treated in Examples 1-6 of the present invention and reacting for 1 minute. The abscissa is the dosage of modified sodium hypochlorite (mg / L), corresponding to Examples 1-6 respectively;

[0031] Figure 3 It is a schematic diagram of the bactericidal effect after adding modified sodium hypochlorite to the water samples treated in Examples 1-6 of the present invention and reacting for 3 minutes. The abscissa is the dosage of modified sodium hypochlorite (mg / L), corresponding to Examples 1-6 respectively;

[0032] Figure 4 It is a schematic diagram of the bactericidal effect after adding modified sodium hypochlorite to the water samples treated in Examples 1-6 of the present invention and reacting for 5 minutes. The abscissa is the dosage of modified sodium hypochlorite (mg / L), corresponding to Examples 1-6 respectively;

[0033] Figure 5 It is a comparison diagram of the bactericidal effects after adding modified sodium hypochlorite to the water samples treated in Examples 1-6 of the present invention and reacting for 1 minute, 3 minutes, and 5 minutes. The abscissa is the dosage of modified sodium hypochlorite (mg / L), corresponding to Examples 1-6 respectively;

[0034] Figure 6Schematic diagram of the sterilization effect after adding modified sodium hypochlorite to the water samples treated in Comparative Examples 1-6 of the present invention. The abscissa is the dosage of modified sodium hypochlorite (mg / L), corresponding to Comparative Examples 1-6 respectively;

[0035] Figure 7 Three-dimensional fluorescence spectrogram of the raw water before treatment in the present invention;

[0036] Figure 8 Three-dimensional fluorescence spectrogram of the water sample after treatment in Example 1 of the present invention;

[0037] Figure 9 Three-dimensional fluorescence spectrogram of the water sample after treatment in Comparative Example 1 of the present invention;

[0038] Figure 10 Line graph of the photoreactivation rate of fecal coliforms in the water sample after treatment in Example 1 of the present invention;

[0039] Figure 11 Line graph of the photoreactivation rate of fecal coliforms in the water sample after treatment in Comparative Example 1 of the present invention;

[0040] Figure 12 For the water sample after treatment in Example 1 of the present invention, NH 4 + -N and TP removal effect line graph, where the abscissa is the dosage of modified sodium hypochlorite (mg / L);

[0041] Figure 13 For the water sample after treatment in Comparative Example 1 of the present invention, NH 4 + -N and TP removal effect line graph, where the abscissa is the dosage of modified sodium hypochlorite (mg / L);

[0042] Figure 14 Line graph of the turbidity change of the water sample after treatment in Example 1 of the present invention, where the abscissa is the dosage of modified sodium hypochlorite (mg / L);

[0043] Figure 15 Line graph of the turbidity change of the water sample after treatment in Comparative Example 1 of the present invention, where the abscissa is the dosage of modified sodium hypochlorite (mg / L);

[0044] Figure 16 For the water sample after treatment in Example 1 of the present invention, the change line graph of COD and UV 254 where the abscissa is the dosage of modified sodium hypochlorite (mg / L);

[0045] Figure 17 For the water sample after treatment in Comparative Example 1 of the present invention, the change line graph of COD and UV 254 where the abscissa is the dosage of modified sodium hypochlorite (mg / L). Detailed implementation manners

[0046] The present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] Please refer to Figure 1-17 , the present invention provides a technical solution:

[0048] The sewage in the following examples and comparative examples is the secondary effluent of a sewage treatment plant in Changchun. A total of 28 L of water is randomly taken and evenly divided into 14 parts for use in Examples 1-6 and Comparative Examples 1-8.

[0049] Example 1

[0050] A sewage treatment process combining ultraviolet light irradiation and sodium hypochlorite:

[0051] S1. The sewage is irradiated with ultraviolet light by using an ultraviolet lamp, and the ultraviolet dose is controlled to be 15 mJ / cm 2 , the wavelength of the ultraviolet lamp is 254 nm, the irradiation time is 1 min, the ultraviolet lamp used is a low-pressure mercury lamp, the power is 30 W, and the lamp tube spacing is 5 cm;

[0052] S2. Without stopping the ultraviolet light irradiation, modified sodium hypochlorite is added to the sewage treated in step S1, and the addition amount is 0.5 mg / L to obtain the treated water body;

[0053] S3. Sodium thiosulfate is added to the water body obtained in step S2, and the addition amount is 0.1 mg / L to remove the excess chlorine element in the water body to obtain the finally treated water sample;

[0054] Among them, the preparation of the modified sodium hypochlorite includes the following steps:

[0055] S21. Chitosan is dissolved in a dilute acetic acid solution and stirred at a speed of 250 r / min until completely dissolved to form a chitosan solution. The mass ratio of chitosan to ethylenediaminetetraacetic acid in the following step S22 is 3:1;

[0056] S22. Ethylenediaminetetraacetic acid is dissolved in deionized water to obtain an EDTA solution and slowly added to the chitosan solution. While adding, it is stirred at a speed of 250 r / min to make the solution mix evenly to form a chitosan-EDTA complex solution;

[0057] S23. 30 g of the chitosan-EDTA complex solution and 50 g of the modified photosensitizer solvent are added to 200 g of the sodium hypochlorite solution to obtain a mixed solution;

[0058] S24. Add sodium bicarbonate to the mixed solution, control the pH of the mixed solution at 6.8, and during the addition process, stir under the conditions of 25 °C and a rotation speed of 250 r / min to finally obtain modified sodium hypochlorite;

[0059] The preparation of the modified photo-assisted solvent includes the following steps:

[0060] S231. Add 30 g of nano-zinc oxide to 200 g of absolute ethanol, and ultrasonically treat it at a frequency of 40 kHz for 20 min to obtain a nano-zinc oxide solution;

[0061] S232. Add 10 g of cetyltrimethylammonium bromide to the nano-zinc oxide solution, and stir in a water bath at 60 °C at a rotation speed of 300 r / min for 1 h to obtain a CTAB-nano-zinc oxide solution;

[0062] S233. Add 40 g of potassium persulfate to the CTAB-nano-zinc oxide solution, and stir at a rotation speed of 300 r / min for 2 h to finally obtain the modified photo-assisted solvent.

[0063] Example 2

[0064] An ultraviolet light irradiation and sodium hypochlorite synergistic sewage treatment process:

[0065] S1. Use an ultraviolet lamp to irradiate the sewage, control the ultraviolet dose at 25 mJ / cm 2 , the wavelength of the ultraviolet lamp is 254 nm, the irradiation time is 5 min, the ultraviolet lamp used is a low-pressure mercury lamp, the power is 30 W, and the lamp tube spacing is 5 cm;

[0066] S2. Without stopping the ultraviolet light irradiation, add the modified sodium hypochlorite to the sewage treated in step S1, and the addition amount is 1 mg / L to obtain the treated water body;

[0067] S3. Add sodium thiosulfate to the water body obtained in step S2, and the addition amount is 0.2 mg / L to remove the excess chlorine element in the water body to obtain the finally treated water sample;

[0068] Among them, the preparation of the modified sodium hypochlorite includes the following steps:

[0069] S21. Dissolve chitosan in a dilute acetic acid solution, and stir at a rotation speed of 300 r / min until completely dissolved to form a chitosan solution. The mass ratio of chitosan to ethylenediaminetetraacetic acid in the following step S22 is 3:1;

[0070] S22. Dissolve ethylenediaminetetraacetic acid in deionized water to obtain an EDTA solution, and slowly add it to the chitosan solution. While adding, stir the solution at a speed of 300 r / min to make the solution mix evenly, forming a chitosan-EDTA complex solution;

[0071] S23. Add 50 g of the chitosan-EDTA complex solution and 80 g of the modified photoauxiliary solvent to 300 g of sodium hypochlorite solution to obtain a mixed solution;

[0072] S24. Add sodium bicarbonate to the mixed solution to control the pH of the mixed solution at 7.5. During the addition process, stir under the conditions of 30 °C and a rotation speed of 300 r / min to finally obtain the modified sodium hypochlorite;

[0073] The preparation of the modified photoauxiliary solvent includes the following steps:

[0074] S231. Add 50 g of nano-zinc oxide to 250 g of absolute ethanol, and ultrasonically treat it at a frequency of 40 kHz for 30 min to obtain a nano-zinc oxide solution;

[0075] S232. Add 20 g of cetyltrimethylammonium bromide to the nano-zinc oxide solution, and stir in a water bath at 60 °C at a rotation speed of 350 r / min for 2 h to obtain a CTAB-nano-zinc oxide solution;

[0076] S233. Add 60 g of potassium persulfate to the CTAB-nano-zinc oxide solution, and stir at a rotation speed of 350 r / min for 3 h to finally obtain the modified photoauxiliary solvent.

[0077] Example 3

[0078] An ultraviolet light irradiation and sodium hypochlorite synergistic sewage treatment process:

[0079] S1. Use an ultraviolet lamp to irradiate the sewage, control the ultraviolet dose at 20 mJ / cm 2 , the wavelength of the ultraviolet lamp is 254 nm, the irradiation time is 2 min, the ultraviolet lamp used is a low-pressure mercury lamp, the power is 30 W, and the lamp tube spacing is 5 cm;

[0080] S2. Without stopping the ultraviolet light irradiation, add the modified sodium hypochlorite to the sewage treated in step S1, and the addition amount is 2 mg / L to obtain the treated water body;

[0081] S3. Add sodium thiosulfate to the water body obtained in step S2, and the addition amount is 0.12 mg / L to remove the excess chlorine element in the water body to obtain the finally treated water sample;

[0082] Among them, the preparation of the modified sodium hypochlorite includes the following steps:

[0083] S21. Dissolve chitosan in a dilute acetic acid solution and stir at a speed of 260 r / min until completely dissolved to form a chitosan solution. The mass ratio of chitosan to ethylenediaminetetraacetic acid in the following step S22 is 3:1;

[0084] S22. Dissolve ethylenediaminetetraacetic acid in deionized water to obtain an EDTA solution and slowly add it to the chitosan solution. While adding, stir at a speed of 260 r / min to make the solution mix evenly, forming a chitosan-EDTA complex solution;

[0085] S23. Add 40 g of the chitosan-EDTA complex solution and 40 g of the modified photosensitizer solvent to 220 g of sodium hypochlorite solution to obtain a mixed solution;

[0086] S24. Add sodium bicarbonate to the mixed solution to control the pH of the mixed solution at 7. The addition process is carried out under stirring conditions at 26 °C and a speed of 260 r / min, and finally modified sodium hypochlorite is obtained;

[0087] The preparation of the modified photosensitizer solvent includes the following steps:

[0088] S231. Add 40 g of nano-zinc oxide to 210 g of absolute ethanol and ultrasonically treat it at a frequency of 40 kHz for 22 min to obtain a nano-zinc oxide solution;

[0089] S232. Add 15 g of cetyltrimethylammonium bromide to the nano-zinc oxide solution and stir in a water bath at 60 °C at a speed of 310 r / min for 1.5 h to obtain a CTAB-nano-zinc oxide solution;

[0090] S233. Add 50 g of potassium persulfate to the CTAB-nano-zinc oxide solution and stir at a speed of 310 r / min for 2.5 h to finally obtain the modified photosensitizer solvent.

[0091] Example 4

[0092] A sewage treatment process synergistically using ultraviolet light irradiation and sodium hypochlorite:

[0093] S1. Use an ultraviolet lamp to irradiate the sewage, control the ultraviolet dose to be 17 mJ / cm 2 , the wavelength of the ultraviolet lamp is 254 nm, the irradiation time is 3 min, the ultraviolet lamp used is a low-pressure mercury lamp, the power is 30 W, and the lamp tube spacing is 5 cm;

[0094] S2. Without stopping the ultraviolet light irradiation, add the modified sodium hypochlorite to the sewage treated in step S1, and the addition amount is 3 mg / L to obtain the treated water body;

[0095] S3. Add sodium thiosulfate to the water body obtained in step S2 at an addition amount of 0.14 mg / L to remove the excess chlorine element in the water body, and obtain the finally treated water sample;

[0096] Among them, the preparation of the modified sodium hypochlorite includes the following steps:

[0097] S21. Dissolve chitosan in a dilute acetic acid solution and stir at a speed of 270 r / min until completely dissolved to form a chitosan solution. The mass ratio of chitosan to ethylenediaminetetraacetic acid in the following step S22 is 3:1;

[0098] S22. Dissolve ethylenediaminetetraacetic acid in deionized water to obtain an EDTA solution and slowly add it to the chitosan solution. While adding, stir at a speed of 270 r / min to make the solution mix evenly to form a chitosan-EDTA complex solution;

[0099] S23. Add 45 g of the chitosan-EDTA complex solution and 60 g of the modified photoauxiliary solvent to 240 g of sodium hypochlorite solution to obtain a mixed solution;

[0100] S24. Add sodium bicarbonate to the mixed solution to control the pH of the mixed solution at 7.1. The addition process is carried out under the stirring condition of 27°C and a speed of 270 r / min, and finally obtain the modified sodium hypochlorite;

[0101] The preparation of the modified photoauxiliary solvent includes the following steps:

[0102] S231. Add 45 g of nano-zinc oxide to 220 g of absolute ethanol and ultrasonically treat it at a frequency of 40 kHz for 24 min to obtain a nano-zinc oxide solution;

[0103] S232. Add 15 g of cetyltrimethylammonium bromide to the nano-zinc oxide solution and stir in a water bath at 60°C at a speed of 320 r / min for 1.5 h to obtain a CTAB-nano-zinc oxide solution;

[0104] S233. Add 45 g of potassium persulfate to the CTAB-nano-zinc oxide solution and stir at a speed of 320 r / min for 2.5 h to finally obtain the modified photoauxiliary solvent.

[0105] Example 5

[0106] A sewage treatment process with the synergistic effect of ultraviolet light irradiation and sodium hypochlorite:

[0107] S1. Use an ultraviolet lamp to irradiate the sewage, control the ultraviolet dose to be 21 mJ / cm 2 , the wavelength of the ultraviolet lamp is 254 nm, the irradiation time is 4 min, the ultraviolet lamp used is a low-pressure mercury lamp, the power is 30 W, and the lamp tube spacing is 5 cm;

[0108] S2. Without stopping the ultraviolet light irradiation, add modified sodium hypochlorite to the sewage treated in step S1 at an addition amount of 4 mg / L to obtain the treated water body;

[0109] S3. Add sodium thiosulfate to the water body obtained in step S2 at an addition amount of 0.17 mg / L to remove the excess chlorine element in the water body and obtain the finally treated water sample;

[0110] Among them, the preparation of the modified sodium hypochlorite includes the following steps:

[0111] S21. Dissolve chitosan in a dilute acetic acid solution and stir at a speed of 280 r / min until completely dissolved to form a chitosan solution. The mass ratio of chitosan to ethylenediaminetetraacetic acid in the following step S22 is 3:1;

[0112] S22. Dissolve ethylenediaminetetraacetic acid in deionized water to obtain an EDTA solution and slowly add it to the chitosan solution. While adding, stir at a speed of 280 r / min to make the solution mix evenly to form a chitosan-EDTA complex solution;

[0113] S23. Add 45 g of the chitosan-EDTA complex solution and 70 g of the modified photocatalytic co-solvent to 270 g of sodium hypochlorite solution to obtain a mixed solution;

[0114] S24. Add sodium bicarbonate to the mixed solution and control the pH of the mixed solution at 7.2. The addition process is carried out under the stirring condition of 28 °C and a speed of 280 r / min to finally obtain the modified sodium hypochlorite;

[0115] The preparation of the modified photocatalytic co-solvent includes the following steps:

[0116] S231. Add 40 g of nano-zinc oxide to 230 g of absolute ethanol and ultrasonically treat it at a frequency of 40 kHz for 27 min to obtain a nano-zinc oxide solution;

[0117] S232. Add 16 g of cetyltrimethylammonium bromide to the nano-zinc oxide solution and stir in a water bath at 60 °C at a speed of 330 r / min for 1.5 h to obtain a CTAB-nano-zinc oxide solution;

[0118] S233. Add 50 g of potassium persulfate to the CTAB-nano-zinc oxide solution and stir at a speed of 330 r / min for 2.5 h to finally obtain the modified photocatalytic co-solvent.

[0119] Example 6

[0120] A sewage treatment process combining ultraviolet light irradiation and sodium hypochlorite:

[0121] S1. Treat the sewage with ultraviolet light, control the ultraviolet dose to 24 mJ / cm 2 , the wavelength of the ultraviolet lamp is 254 nm, the irradiation time is 5 min, the ultraviolet lamp used is a low-pressure mercury lamp, the power is 30 W, and the tube spacing is 5 cm;

[0122] S2. Without stopping the ultraviolet light irradiation, add modified sodium hypochlorite to the sewage treated in step S1, and the addition amount is 5 mg / L to obtain the treated water body;

[0123] S3. Add sodium thiosulfate to the water body obtained in step S2, and the addition amount is 0.18 mg / L to remove the excess chlorine element in the water body and obtain the finally treated water sample;

[0124] Among them, the preparation of the modified sodium hypochlorite includes the following steps:

[0125] S21. Dissolve chitosan in a dilute acetic acid solution and stir at a speed of 290 r / min until completely dissolved to form a chitosan solution. The mass ratio of chitosan to ethylenediaminetetraacetic acid in the following step S22 is 3:1;

[0126] S22. Dissolve ethylenediaminetetraacetic acid in deionized water to obtain an EDTA solution and slowly add it to the chitosan solution. While adding, stir at a speed of 290 r / min to make the solution mix evenly to form a chitosan-EDTA complex solution;

[0127] S23. Add 45 g of the chitosan-EDTA complex solution and 75 g of the modified photoassistant solvent to 280 g of the sodium hypochlorite solution to obtain a mixed solution;

[0128] S24. Add sodium bicarbonate to the mixed solution to control the pH of the mixed solution at 7.4. The addition process is carried out under stirring conditions at 28 °C and a speed of 290 r / min to finally obtain the modified sodium hypochlorite;

[0129] The preparation of the modified photoassistant solvent includes the following steps:

[0130] S231. Add 45 g of nano-zinc oxide to 240 g of absolute ethanol and ultrasonically treat it at a frequency of 40 kHz for 28 min to obtain a nano-zinc oxide solution;

[0131] S232. Add 18 g of cetyltrimethylammonium bromide to the nano-zinc oxide solution and stir at a speed of 340 r / min in a water bath at 60 °C for 1.8 h to obtain a CTAB-nano-zinc oxide solution;

[0132] S233. Add 55 g of potassium persulfate to the CTAB-nano-zinc oxide solution and stir at a speed of 340 r / min for 2.8 h to finally obtain the modified photoassistant solvent.

[0133] Comparative Example 1

[0134] Comparative Example 1 differs from Example 1 only in that in this comparative example, the ultraviolet light irradiation treatment in step S1 is omitted, and modified sodium hypochlorite is added directly while irradiating with light.

[0135] Comparative Example 2

[0136] Comparative Example 2 differs from Comparative Example 1 only in that in this comparative example, the addition amount of modified sodium hypochlorite is 1 mg / L.

[0137] Comparative Example 3

[0138] Comparative Example 3 differs from Comparative Example 1 only in that in this comparative example, the addition amount of modified sodium hypochlorite is 2 mg / L.

[0139] Comparative Example 4

[0140] Comparative Example 4 differs from Comparative Example 1 only in that in this comparative example, the addition amount of modified sodium hypochlorite is 3 mg / L.

[0141] Comparative Example 5

[0142] Comparative Example 5 differs from Comparative Example 1 only in that in this comparative example, the addition amount of modified sodium hypochlorite is 4 mg / L.

[0143] Comparative Example 6

[0144] Comparative Example 6 differs from Comparative Example 1 only in that in this comparative example, the addition amount of modified sodium hypochlorite is 5 mg / L.

[0145] Comparative Example 7

[0146] Comparative Example 7 differs from Example 1 only in that in this comparative example, modified photo-assisted solvent is not added.

[0147] Comparative Example 8

[0148] Comparative Example 8 differs from Example 1 only in that in this comparative example, unmodified sodium hypochlorite solution is added.

[0149] Performance test:

[0150] 1. Inactivation effect test on fecal coliform

[0151] The treated water samples obtained from Examples 1 - 6 and Comparative Examples 1 - 6 were tested according to the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB18918 - 2002)". The bactericidal effects after adding modified sodium hypochlorite and reacting for 1 min in Examples 1 - 6 are shown in the appendixFigure 2 , the bactericidal effect after adding modified sodium hypochlorite and reacting for 3 minutes is shown in the appendix Figure 3 , the bactericidal effect after adding modified sodium hypochlorite and reacting for 5 minutes is shown in the appendix Figure 4 , appendix Figure 5 is a comparison chart of the bactericidal effects at three reaction times. From the appendix Figure 2-4 it can be seen that when using the combined disinfection method of ultraviolet first and then ultraviolet with modified sodium hypochlorite, only 1 mg / L of modified sodium hypochlorite needs to be added and the contact reaction time is 1 minute, and the fecal coliform count in the effluent can be reduced to 480 CFU / L, meeting the first-class A discharge standard of "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB18918 - 2002)". As shown in the appendix Figure 6 , when using the simultaneous disinfection method of ultraviolet and modified sodium hypochlorite, the dosage of modified sodium hypochlorite needs to be increased to 3 mg / L to meet the requirements of the above standard after disinfection.

[0152] The experimental results show that if an ideal disinfection effect is to be achieved, the combined disinfection method of ultraviolet first and then ultraviolet with modified sodium hypochlorite can significantly reduce the dosage of modified sodium hypochlorite, and at the same time show stronger microbial inactivation ability than the simultaneous disinfection method of ultraviolet and modified sodium hypochlorite. This is because during the combined disinfection process of ultraviolet first and then ultraviolet with modified sodium hypochlorite, ultraviolet light causes a certain degree of damage to the fecal coliform cells, which increases the possibility of modified sodium hypochlorite penetrating the cell wall and oxidizing the internal proteins or phosphodehydrogenase in the cells, thus improving the disinfection efficiency. When ultraviolet and modified sodium hypochlorite coexist in the water body, the hydrolysis products (HClO / ClO-) of modified sodium hypochlorite will generate active oxygen free radicals (HO · ), chlorine atoms (Cl·), Cl 2 ·- and O ·- , which can be used to degrade the pollutants present in the water, and this is considered a new advanced oxidation process (AOP). The strongly oxidizing free radicals generated by the above AOP can be quickly consumed by the organic matter in the secondary effluent, losing the opportunity to contact and oxidize with microorganisms, resulting in a worse bactericidal effect. Therefore, to obtain an ideal disinfection effect, it is necessary to further increase the dosage of sodium hypochlorite.

[0153] 2. Three-dimensional fluorescence spectroscopy analysis

[0154] The change law of the organic matter components in the water samples before and after combined disinfection was measured using three-dimensional fluorescence spectroscopy. The results are shown in the appendix Figure 7-9 , where the appendix Figure 7 is the three-dimensional fluorescence spectrum diagram of the raw water before treatment, and the appendix Figure 8 is the three-dimensional fluorescence spectrum diagram of the water sample after treatment in Example 1, and the appendix Figure 9It is the three-dimensional fluorescence spectrogram of the water sample after being treated in Comparative Example 1. The peak value of the three-dimensional fluorescence spectrogram at an excitation wavelength of 250 - 280 nm and an emission wavelength < 380 nm is related to substances of dissolved microbial metabolites (Region IV); the peak value at an excitation wavelength > 280 nm and an emission wavelength > 380 nm is related to humic acid substances (Region V). The content of this substance in the water sample can be inferred using the fluorescence intensity value in the figure, so as to explore the change rules of each organic component before and after disinfection.

[0155] Figure 5 The experimental results show that in the combined disinfection method, when using the simultaneous disinfection method of ultraviolet and modified sodium hypochlorite, the fluorescence intensities in Region IV and Region V are significantly reduced compared with the raw water. This indicates that the dissolved microbial metabolites and humic acid substances in the water sample are oxidized and decomposed and lose their fluorescence, resulting in a significant reduction in these two organic components. Under the condition of ultraviolet first and then the synergistic disinfection of ultraviolet and modified sodium hypochlorite, the reduction of dissolved microbial metabolites and humic acid substances is significantly weaker than that of the simultaneous disinfection of ultraviolet and modified sodium hypochlorite, which allows more oxidants to participate in the disinfection process and improves the disinfection efficiency.

[0156] 3. Photoreactivation test of fecal coliform

[0157] The influence of different photoreactivation light intensities on the photoreactivation of fecal coliform is shown in the appendix Figure 10-11 as follows, where the appendix Figure 10 is the line graph of the photoreactivation rate of fecal coliform in the water sample treated in Example 1, and the appendix Figure 11 is the line graph of the photoreactivation rate of fecal coliform in the water sample treated in Comparative Example 1. It can be seen from the appendix Figure 10-11 that the photoreactivation rate of fecal coliform in the water sample after combined disinfection treatment increases with the increase of photoreactivation light intensity or the extension of illumination time. When the photoreactivation illumination time is 8 h and the photoreactivation light intensities are 15 μmol / cm 2 , 30 μmol / cm 2 and 45 μmol / cm 2 , the photoreactivation rates of fecal coliform in the disinfection method of ultraviolet first and then the synergistic action of ultraviolet and modified sodium hypochlorite are 16.88%, 21.09% and 26.96% respectively. This shows that the stronger the photoreactivation light intensity, the greater the energy provided for the damaged bacteria to photoreactivate, and the corresponding photoreactivation ability is also stronger. In the simultaneous disinfection method of ultraviolet and modified sodium hypochlorite, when the photoreactivation light intensities are 15 μmol / cm 2 and 30 μmol / cm 2 , the photoreactivation rates of fecal coliform are not much different, being 25.8% and 24.64% respectively. As the photoreactivation light intensity increases to 45 μmol / cm 2 , the photoreactivation rate increases to 30.81%.

[0158] The comparison results show that the reactivation rate of fecal coliforms disinfected by ultraviolet and modified sodium hypochlorite simultaneously is higher than that disinfected by ultraviolet first and then by the synergistic action of ultraviolet and modified sodium hypochlorite. This may be because the damage degree of fecal coliforms disinfected by ultraviolet first and then by the synergistic action of ultraviolet and modified sodium hypochlorite is greater, resulting in most microorganisms losing the repair function of DNA dimers, thus effectively inhibiting the occurrence of microbial photoreactivation and ensuring the safety and stability of the effluent microbial indicators.

[0159] 4. Changes in NH 4 + -N and TP in the secondary effluent quality indicators

[0160] The removal effects of combined disinfection methods on NH 4 + -N and TP are shown in Figure 12-13 , after treatment by the combined disinfection method, the TP content in the water sample is between 0.06 - 0.09 mg / L, which is already at a relatively low level and has not changed significantly, while the NH 4 + -N content has decreased. Among them, for disinfection by ultraviolet first and then by the synergistic action of ultraviolet and modified sodium hypochlorite, the NH 4 + -N removal rate is 30.3%; for simultaneous disinfection by ultraviolet and modified sodium hypochlorite, the NH 4 + -N removal rate is 48.5%.

[0161] The experimental data show that simultaneous disinfection by ultraviolet and modified sodium hypochlorite shows stronger NH 4 + -N removal ability than disinfection by ultraviolet first and then by the synergistic action of ultraviolet and modified sodium hypochlorite. This is because during the simultaneous disinfection by ultraviolet and modified sodium hypochlorite, on the one hand, modified sodium hypochlorite converts NH 4 + -N in the sewage into chloramine through substitution reaction, and ultraviolet light can effectively cleave the N-Cl bond of chloramine, and the reaction formula is: NH 2 Cl + hv → NH 2 · + ·Cl. On the other hand, the hydrolysis products (HClO / ClO - ) of modified sodium hypochlorite will generate reactive chlorine species (RCS) such as hydroxyl radicals (·OH) and ·Cl under ultraviolet irradiation, which is a new advanced oxidation process. In this process, the generated ·OH and ·Cl can react with NH 4 + -N, thus removing NH 4 + -N from the water body. The reaction formula is: ·OH + NH 3 →NH 2 +H2 O, ·Cl + NH 3 → NH 2 + H + + Cl - 。

[0162] 5. Changes in turbidity in the secondary effluent quality indicators

[0163] Appendix Figure 14-15 The figure shows the changes in turbidity of the secondary effluent from the sewage treatment plant after combined disinfection treatment. The experimental results show that disinfection by ultraviolet first and then the synergistic action of ultraviolet and modified sodium hypochlorite hardly affects the turbidity of the water sample. When disinfecting with ultraviolet and modified sodium hypochlorite simultaneously, the turbidity increases slightly with the increase in the dosage of modified sodium hypochlorite. The reason for the increase in turbidity may be that the strongly oxidizing free radicals generated in the advanced oxidation process can destroy the pollutants existing in the water body, break and separate the larger particles in the sewage into multiple smaller particles, playing a certain role in slime stripping. In addition, factors affecting turbidity such as the shape, size and refractive index of particulate matter in the water body have changed after disinfection, resulting in an increase in the turbidity of the effluent after disinfection.

[0164] 6. Changes in COD and UV in the secondary effluent quality indicators 254 of

[0165] The removal effects of combined disinfection methods on COD and UV 254 are shown in Appendix Figure 16-17 . The experimental results show that the COD in the water sample shows a downward trend after combined disinfection treatment, but the removal effect of UV 254 is not obvious. Among them, when using the disinfection method of ultraviolet first and then the synergistic action of ultraviolet and modified sodium hypochlorite, the COD decreases from 35.42 mg / L to 25.30 mg / L, and the removal rate is 28.6%; UV 254 decreases from 0.175 cm -1 to 0.172 cm -1 , and the removal rate is only 1.7%. When disinfecting with ultraviolet and modified sodium hypochlorite simultaneously, the COD removal rate can reach 42.2%, and the UV 254 removal rate increases to 4%.

[0166] The experimental data show that the simultaneous disinfection of ultraviolet and modified sodium hypochlorite has a more significant removal effect on COD and UV 254 than the synergistic disinfection of ultraviolet first and then the synergistic action of ultraviolet and modified sodium hypochlorite. Whether it is the oxidation and degradation of organic matter by modified sodium hypochlorite or the decomposition of some small-molecule organic matter using ultraviolet energy, it only changes the structure of the organic matter and cannot mineralize the organic matter into CO 2Completely removed from the water body. When ultraviolet and modified sodium hypochlorite are used for disinfection simultaneously, due to the strong activity of the free radicals generated during the advanced oxidation process, macromolecular organic substances with complex structures can be gradually decomposed into small molecule acids and finally transformed into CO 2 Discharged from the water body, significantly achieving the degradation effect on organic substances.

[0167] The experiments in Comparative Examples 7-8 without adding the modified photo-assisted solvent and adding unmodified sodium hypochlorite prove that through the action of ultraviolet light, the modified sodium hypochlorite and the modified photo-assisted solvent of the present application can generate reactive oxygen species and sulfate radicals, synergistically attack the microbial membrane structure with hypochlorous acid, oxidatively degrade complex organic substances, reduce the ineffective consumption of sodium hypochlorite and stabilize the effective chlorine concentration, and further improve the degradation efficiency.

[0168] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A wastewater treatment process using ultraviolet light and sodium hypochlorite, characterized in that: The following steps are involved: S1.Use ultraviolet lamp to treat sewage, and control the ultraviolet dose to 15-25mJ / cm 2 , the wavelength of the UV lamp is 254nm, and the irradiation time is 1-5min; S2. Without stopping the ultraviolet light, adding modified sodium hypochlorite to the wastewater treated in step S1 to obtain treated water; S3. Add sodium thiosulfate to the water obtained in step S2 to remove excess chlorine in the water to obtain a final treated water sample; Wherein, the preparation of the modified sodium hypochlorite comprises the following steps: S21. Dissolving chitosan in a dilute acetic acid solution and stirring until completely dissolved to form a chitosan solution; S22. Dissolve ethylenediaminetetraacetic acid in deionized water to obtain an EDTA solution, and slowly add the solution to the chitosan solution, stirring the solution while adding to mix the solution evenly to form a chitosan-EDTA complex solution; S23. 3-5 parts of chitosan-EDTA complex solution and 5-8 parts of modified light co-solvent are added to 20-30 parts of sodium hypochlorite solution to obtain a mixed solution; S24. Add sodium bicarbonate to the mixed solution, control the pH of the mixed solution to be 6.8-7.5, and add under stirring conditions at 25-30° C. to finally obtain modified sodium hypochlorite.

2. The process for treating sewage by combining ultraviolet light and sodium hypochlorite according to claim 1, characterized in that: The preparation of the modified photo-assisted solvent comprises the following steps: S231. Add 3-5 parts of nano zinc oxide to 20-25 parts of anhydrous ethanol and ultrasonically treat at a frequency of 40kHz for 20-30min to obtain a nano zinc oxide solution; S232. Add 1-2 parts of cetyltrimethylammonium bromide to the nano zinc oxide solution and stir in a water bath at 60° C. for 1-2 h to obtain a CTAB-nano zinc oxide solution; S233. Add 4-6 parts of potassium persulfate into the CTAB-nano zinc oxide solution and stir for 2-3 hours to finally obtain a modified photo-assisted solvent.

3. The process for treating sewage by combining ultraviolet light and sodium hypochlorite according to claim 2, characterized in that: The mass ratio of chitosan to EDTA in steps S21 and S22 is 3:

1.

4. The process for treating sewage by combining ultraviolet light and sodium hypochlorite according to claim 2, characterized in that: The stirring speed during the preparation of the modified photo-assisted solvent is 300-350 r / min.

5. The process for treating sewage by combining ultraviolet light and sodium hypochlorite according to claim 1, characterized in that: The added amount of the modified sodium hypochlorite is 0.5-5 mg / L.

6. The process for treating sewage by combining ultraviolet light and sodium hypochlorite according to claim 1, characterized in that: The added amount of the sodium thiosulfate is 0.1-0.2 mg / L.

7. The process for treating sewage by combining ultraviolet light and sodium hypochlorite according to claim 1, characterized in that: In step S1, the ultraviolet lamp adopts a low-pressure mercury lamp with a power of 30W and a lamp tube spacing of 5cm.

8. The process for treating sewage by combining ultraviolet light and sodium hypochlorite according to claim 1, characterized in that: The stirring speed during the preparation of modified sodium hypochlorite is 250-300 r / min.

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