Layered photocatalysis-biodegradation coupled sewage treatment system and method

Abstract

The invention relates to a layered photocatalysis-biodegradation coupled sewage treatment system and method. The layered photocatalysis-biodegradation coupled sewage treatment system comprises a reactor, a light source and a power supply, a water inlet and a water outlet are formed in the reactor; a partition plate is arranged in the middle of the reactor and is used for dividing the reactor into an upper-layer photocatalytic reactor and a lower-layer biodegradation reactor; small holes for communicating the upper layer and the lower layer are formed in the partition plate; a photocatalyst for photocatalytic degradation is placed in the photocatalytic reactor; the biodegradation reactor is filled with a biofilm filler for biodegradation; the light source is located above the reactor and used for providing light for the photocatalytic reactor. According to the invention, in the degradation process, the toxic action of direct light source and photocatalyst on the biological membrane filler is reduced; physical separation of photocatalysis and biodegradation is achieved, the shading effect of the biological membrane filler is reduced, a light source can be conveniently and efficiently utilized by the photocatalyst, the sewage degradation efficiency is high, and meanwhile the toxicity of a degradation product is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage treatment, in particular to a layered photocatalysis-biodegradation coupling sewage treatment system and method. BACKGROUND

[0002] With the rapid development of urbanization and industrialization, pollutants are discharged into the environment, which has an impact on the ecological environment and human health. In traditional sewage treatment technology, biodegradation of pollutants and photocatalytic degradation of pollutants have played an important role. The efficiency of biodegradation of pollutants is affected by its growth metabolism, pollutant characteristics and environmental conditions, and the degradation effect of high-concentration pollutants is not good. In contrast, photocatalysis can quickly decompose refractory pollutants by generating active oxygen species through the reaction of electron-hole pairs generated by photocatalysts with external substances (such as O2 and H2O), thereby attacking organic compounds to break down pollutants, but this process may cause accumulation of toxic by-products.

[0003] Intimately coupling of photocatalysis and biodegradation (ICPB) as a promising water treatment technology has been greatly developed. This technology combines the characteristics of photocatalytic reaction and biodegradation, and has extraordinary advantages in faster and more thorough purification of most refractory pollutants, while also being economically feasible and environmentally friendly. In the process of simultaneous coupling of photocatalysis and biodegradation, photocatalysis converts refractory compounds into biodegradable products, which helps microorganisms to further utilize the intermediates produced by photocatalysis to convert them into less toxic substances, thereby maintaining the degradation efficiency of pollutants while reducing the toxicity of products.

[0004] The most common ICPB system selects a photocatalytic internal circulation biofilm reaction device, which realizes effective degradation of pollutants by adding photocatalyst-microorganism integrated porous carriers (photocatalysts are fixed on the surface of the carriers, and biofilms grow inside the carriers) to it. The system provides oxygen through an external aeration device to establish a water and carrier gas lift circulation, and under the irradiation of an external light source, the photocatalyst and microorganism on the porous carrier couple to degrade pollutants. In addition, some studies directly mix dispersed photocatalysts with biofilms to construct ICPB systems for degrading pollutants. Although many achievements have been made in the application of ICPB technology, the light-shielding effect of biofilm fillers and the difficulty in separating photocatalysts and biofilms still hinder the practical application of ICPB. SUMMARY

[0005] The present application aims to overcome the above technical deficiencies, provide a layered photocatalysis-biodegradation coupling sewage treatment system and method, solve the technical problems of low photocatalytic efficiency caused by the light shielding effect of the biological membrane filler and the difficulty in separating the photocatalyst and the biological membrane in the ICPB system of the prior art.

[0006] To achieve the above technical purpose, the technical scheme provided by the present application is: In a first aspect, the present application provides a layered photocatalysis-biodegradation coupling sewage treatment system, comprising a reactor, and a light source and a power source connected thereto; the reactor is provided with a water inlet and a water outlet; a partition plate is arranged in the middle of the reactor, and the partition plate is used to divide the reactor into an upper photocatalytic reactor and a lower biodegradation reactor; a small hole for communication between the upper and lower layers is formed in the partition plate; a photocatalyst for photocatalytic degradation is placed in the photocatalytic reactor; a biological membrane filler for biodegradation is filled in the biodegradation reactor; the light source is located above the reactor and is used to provide light for the photocatalytic reactor.

[0007] In a second aspect, the present application provides a photocatalysis-biodegradation coupling sewage treatment method, which is carried out by using the above-mentioned system.

[0008] Compared with the prior art, the present application has the following beneficial effects: The present application constructs a layered photocatalysis-biodegradation coupling sewage treatment system, which effectively reduces the direct light of the light source and the toxic effect of the photocatalyst on the biological membrane filler during the degradation process due to the physical separation of the light-shielding partition plate; the physical separation of photocatalysis and biodegradation is realized, which not only reduces the light shielding effect of the biological membrane filler, but also facilitates the more efficient use of the light source by the photocatalyst, improves the resource availability; tests have found that the present application has high sewage degradation efficiency and low degradation product toxicity, reduces the secondary treatment of photocatalytic toxic products, and is especially suitable for sulfonamide antibiotic sewage treatment. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a structural schematic diagram of the layered photocatalysis-biodegradation coupling sewage treatment system of the present application; Among them, 1-reaction tank, 101-partition plate, 102-photocatalytic reactor, 103-biodegradation reactor, 104-water inlet, 105-water outlet; 2-photocatalyst; 3-biological membrane filler; 4-aeration device, 401-aeration pump, 402-flow meter, 403-aeration diffuser; 5-light source; 6-agitator; 7-power supply; Figure 2 is the removal efficiency of sulfamethoxazole in batch tests of the present application; Figure 3 is the growth curve of E. coli under different conditions of the present application. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] Current common ICPB systems suffer from drawbacks such as the light-blocking effect of biofilm packing and the difficulty in separating and reusing photocatalysts and biofilms. This invention constructs a layered photocatalysis-biodegradation coupled wastewater treatment system. Through physical separation, the photocatalytic and biodegradation zones are separated, ensuring simultaneous photocatalysis and biodegradation while significantly reducing the light-blocking effect of the biofilm packing and solving the problem of difficult separation between photocatalysts and biofilm packing. The application of this system expands the selection range of photocatalysts and biofilms to facilitate the removal of recalcitrant pollutants from wastewater. These features not only enhance the potential for resource recovery and utilization but also possess broad commercial prospects and application potential. This invention's system can couple the degradation of sulfonamide antibiotics and other substances in water, and has advantages such as simple operation and easy separation of photocatalysts and biofilms.

[0012] Firstly, see [the following] Figure 1 This invention provides a layered photocatalytic-biodegradation coupled wastewater treatment system, including a reactor 1, and a connected light source 5 and a power supply 7; the reactor 1 is provided with an inlet and an outlet; a partition plate 101 is provided in the middle of the reactor 1, which is used to divide the reactor 1 into an upper photocatalytic reactor 102 and a lower biodegradation reactor 103; small holes are opened on the partition plate 101 for communication between the upper and lower layers; a photocatalyst 2 for photocatalytic degradation is placed in the photocatalytic reactor 102; the biodegradation reactor 103 is filled with a biofilm packing material 3 for biodegradation; the light source 5 is located above the reactor and is used to provide illumination to the photocatalytic reactor 102.

[0013] Preferably, photocatalyst 2 is ZnO / g-C3N4 photocatalyst gel microspheres.

[0014] The photocatalyst of this invention is a gel microsphere, which is easy to disperse evenly in the photocatalytic reactor, fully receive light, does not affect the influent and effluent during the wastewater treatment process, and is easy to recycle after treatment.

[0015] A further preferred embodiment of the preparation steps for ZnO / g-C3N4 photocatalyst gel microspheres includes: S11, heating urea to 480-520℃ and keeping for 1.8-2.2h to obtain g-C3N4; adding zinc acetate and urea in a molar ratio of 1:(2-4) into an ethylene glycol aqueous solution, ultrasonic dissolving to obtain a first mixed solution, and hydrothermally reacting, washing and drying the first mixed solution to obtain a ZnO precursor; S12, dispersing g-C3N4 and the ZnO precursor in anhydrous ethanol in a mass ratio of 1:1, drying to obtain a solid sample, and heating the solid sample to 480-520℃ and keeping for 1.8-2.2h to obtain a ZnO / g-C3N4 photocatalyst; S13, dispersing the ZnO / g-C3N4 photocatalyst in ultrapure water in a concentration of 280-320mg / L, mixing with a 3wt% sodium alginate solution in a volume ratio of 1:1 to obtain a second mixed solution; and dropping the second mixed solution into an anhydrous CaCl2 solution to obtain ZnO / g-C3N4 photocatalyst gel microspheres through solidification.

[0016] It can be understood that g-C3N4 and the ZnO precursor in step S12 are added into anhydrous ethanol only to make them uniformly mixed, and the ethanol is finally dried, so the amount of ethanol can be used to completely wet g-C3N4 and the ZnO precursor.

[0017] More preferably, in step S11, the ethylene glycol aqueous solution is prepared by mixing ethylene glycol and ultrapure water in a volume ratio of 1:1; the concentration of zinc acetate in the first mixed solution is 0.08-0.12mol / L; and the hydrothermal reaction is carried out at 150-170℃ for 11-13h.

[0018] More preferably, the heating rate of urea and the heating rate of the solid sample are both 13-14℃ / min. In the present application, by controlling the heating temperature and the heating rate, ZnO and g-C3N4 are combined under the premise of lower energy consumption.

[0019] More preferably, the mass concentration of the anhydrous CaCl2 solution is 1.5-2.5%; and the volume ratio of the second mixed solution to the anhydrous CaCl2 solution is 1:(18-22).

[0020] Preferably, the biofilm filler 3 comprises a polyethylene carrier (K1 carrier) and a biofilm grown on the polyethylene carrier.

[0021] The present application realizes effective degradation of pollutants by setting the biofilm filler and forming an ICPB system through photocatalytic degradation, and effectively reduces the toxicity of degradation products.

[0022] Further preferably, the preparation steps of the biofilm filler comprise: S21, In a moving bed biofilm reactor filled with polyethylene carrier, activated sludge is inoculated and the first synthetic wastewater is introduced for cultivation. S22, after the biofilm grows on the polyethylene carrier, the activated sludge is removed and the second synthetic wastewater is introduced to continue the cultivation to obtain the biofilm packing material.

[0023] More preferably, in step S21, the filling rate of the polyethylene carrier is 35-45%; the COD of the first synthetic wastewater is ≥400 mg / L. -1 NH4 + -N content in 80 mg / L -1 The above applies; the cultivation time is one week, the hydraulic retention time is 24 hours, and the activated sludge is replaced daily.

[0024] Further preferably, in step S22, the conditions for continued cultivation include: using a 4-hour cyclic cultivation method, which includes a 60-minute influent time, a 175-minute aerobic reaction time, and a 5-minute effluent time, with the COD in the second synthetic wastewater ≥ 350 mg / L. -1 NH4 + -N content in 60 mg / L -1 above.

[0025] More preferably, in step S22, the culture time is continued for more than 45 days. In this invention, the biofilm stabilizes after 45 days of continued culture and can be used as a biofilm packing material.

[0026] Preferably, the partition 101 includes a movable black glass panel.

[0027] This invention uses a movable black glass plate as a partition, which facilitates reactor installation and has good corrosion resistance.

[0028] In a further preferred embodiment, the partition 101 also includes a support layer, such as a support mesh, located beneath the black glass plate to enhance structural stability.

[0029] Preferably, it also includes an aeration device 4 for supplying dissolved oxygen into the reactor.

[0030] In a further preferred embodiment, the aeration device 4 includes an aeration pump 401, which is connected to an aeration diffuser 403 via a pipeline. The aeration diffuser 403 is located at the bottom of the biodegradation reactor 103. A flow meter 402 is installed on the pipeline.

[0031] Preferably, the reactor also includes a stirrer 6 connected to the power supply 7. The stirrer is used to stir the wastewater in the photocatalytic reactor and the biodegradation reactor. The stirrer 6 includes one or more of a magnetic stirrer and a mechanical stirrer. Specifically, a magnetic stirrer can be installed in the biodegradation reactor 103, and a mechanical stirrer can be installed in the photocatalytic reactor 102.

[0032] Secondly, the present invention provides a photocatalytic-biodegradation coupled wastewater treatment method, which utilizes the above-mentioned system.

[0033] Preferably, the wastewater treatment conditions include: a photocatalyst concentration of 200–400 mg / L. -1 The biofilm packing material has a filling ratio of 4–10%; the aeration rate is 0.1–0.3 L / min. -1 The stirring speed is 200-400 rpm.

[0034] Preferably, the wastewater contains sulfonamide antibiotics.

[0035] The main advantages of this invention are: (1) The present invention innovatively constructs a layered photocatalytic-biodegradation coupled wastewater treatment system. Due to the physical separation of the opaque glass plate, the direct light source and the toxic effect of the photocatalyst on the biofilm packing are effectively reduced during the degradation process. (2) In the coupling process, the present invention realizes the physical separation of photocatalysis and biodegradation, which not only reduces the light-blocking effect of biofilm filler, but also facilitates the photocatalyst to make more efficient use of light source and improves resource availability.

[0036] (3) The use of the layered photocatalysis-biodegradation coupling device in this invention helps to separate the photocatalyst and biofilm filler, enhancing the potential for resource reuse.

[0037] The present invention will be further described in detail below through specific embodiments.

[0038] Example 1 S1, Preparation of photocatalyst: S11, urea was first heated to 500 °C at a heating rate of 13.5 °C / min and heated at this temperature for 2 h to obtain g-C3N4. 0.01 mol of zinc acetate and 0.03 mol of urea were added to 100 mL of ethylene glycol ultrapure water with a volume ratio of 1:1. After sonication at 100 W for 30 minutes to dissolve the mixture, the resulting first mixed solution was transferred to a 100 mL Teflon-lined stainless steel high-pressure reactor and heated to 160 °C for 12 h. The resulting material was then washed with ultrapure water and dried at 60 °C for 12 h to obtain the ZnO precursor.

[0039] S12, g-C3N4 and ZnO precursor were dispersed in anhydrous ethanol at a weight ratio of 1:1 and dried at 60 °C until the ethanol evaporated completely. The resulting sample was heated to 500 °C at a heating rate of 13.5 °C / min and kept at that temperature for 2 h to obtain ZnO / g-C3N4 photocatalyst.

[0040] S13, Immobilization of the photocatalyst: A 3% sodium alginate solution was sterilized at 121 °C for 30 min and then cooled for later use. Subsequently, the ZnO / C3N4 photocatalyst was dispersed in 10 mL of ultrapure water at a concentration of 300 mg / L, and mixed with the cooled sodium alginate solution at a ratio of 1:1 (v:v) to obtain a second mixed solution. 6 mL of the second mixed solution was added dropwise to 120 mL of anhydrous CaCl2 solution (2wt%) at a rate of 10 mL / min. After curing for 12 h, ZnO / g-C3N4 photocatalyst gel microspheres were obtained.

[0041] S2, Cultivation of biofilm packing material: S21. To cultivate biofilm packing material, 600 mL of activated sludge from a municipal wastewater treatment plant was inoculated into a 3 L moving bed biofilm reactor (MBBR). 1200 K1 carriers were added to the reactor, and cultivation was carried out at a 40% filling rate. The cultivation conditions were: 2.4 L of a solution containing 500 mg L of K1 was added to the MBBR at a hydraulic retention time (HRT) of 24 h. - 1 COD, 100 mg / L -1 NH4 + -N synthetic wastewater is used to promote the rapid growth of activated sludge on the carrier. To eliminate microorganisms that do not easily adhere to the carrier, the activated sludge in the reactor is replaced daily.

[0042] After one week of cultivation, a biofilm grew on the K1 carrier (S22), and the activated sludge was removed from the reactor. The reactor then entered the subsequent operation phase, with the MBBR operating at a 4-hour cycle time, including a 60-minute influent time, a 175-minute aerobic reaction time, and a 5-minute effluent time. At this stage, the synthetic wastewater supplied to the reactor contained 400 mg L / L. -1 COD, 75 mg / L -1 NH4 + -N. The biofilm culture is complete when the biofilm grows stably on the K1 support. S3, Assembly of a layered photocatalytic-biodegradation coupled wastewater treatment system: like Figure 1As shown, the system of this invention is a layered reactor with a movable glass plate. The entire reactor is made of plexiglass, with an effective volume of 400 mL. The partition plate 101 includes a movable black glass plate, specifically a black opaque plexiglass plate. The partition plate 101 (glass plate and its supporting layer) evenly divides the 400 mL effective volume, forming an upper photocatalytic reactor 102 and a lower biodegradation reactor 103. 4 mm holes are evenly distributed on the movable black glass plate for communication between the upper and lower layers. An aeration device 4 is installed outside the reactor to supply dissolved oxygen into the reactor 1. An external magnetic stirrer and a mechanical stirrer are added to ensure uniform agitation of the photocatalyst 2 and the biofilm packing 3 within the reactor 1. Furthermore, an LED light is placed on top of the reactor 1 to provide a light source.

[0043] Test Example 1 A 1 ppm sulfamethoxazole solution was selected as the target pollutant, and a 40 W LED lamp was used as the light source. The photocatalyst concentration was 300 mg / L throughout the experiment. -1 The biofilm packing material has a filling ratio of 5% and an aeration rate of 0.2 L / min. -1 The magnetic stirrer and the mechanical stirrer rotate at 300 rpm and 250 rpm, respectively.

[0044] Five sets of experiments were conducted, namely photolysis, adsorption, biodegradation, photocatalytic degradation, and ICPB degradation. The photolysis group was set up to investigate the degradation of sulfamethoxazole under LED light source irradiation alone. In the adsorption group, the adsorption of sulfamethoxazole on inactivated biofilms and photocatalysts was investigated under dark conditions. The biodegradation, photocatalytic degradation, and ICPB degradation groups were compared through single biodegradation and photocatalytic degradation coupled with ICPB degradation, respectively, to explore the advantages of ICPB coupled degradation of sulfamethoxazole. It is particularly noteworthy that the biodegradation group was conducted under dark conditions to protect the biofilm packing material from light exposure, while the photocatalytic degradation and ICPB degradation groups were conducted under light conditions. Photolysis group: LED light source only + photocatalytic reactor (no photocatalyst) + biodegradation reactor (no biofilm packing). Adsorption group: dark conditions + photocatalytic reactor (containing photocatalyst) + biodegradation reactor (containing inactivated biofilm packing); Biodegradation group: Dark conditions only + biodegradation reactor (including biofilm packing); Photocatalytic degradation group: LED light source + photocatalytic reactor (including photocatalyst) only; ICPB degradation group: LED light source + photocatalytic reactor (including photocatalyst) + biodegradation reactor (including biofilm packing).

[0045] Experimental results are as follows Figure 2 As shown, the removal efficiencies of sulfamethoxazole in the adsorption, photolysis, and biodegradation systems were 5.3%, 7.0%, and 10.2%, respectively. This indicates that the physical separation of the photocatalyst from the biofilm packing has almost no effect on the degradation of sulfamethoxazole in the adsorption, photolysis, and biodegradation systems.

[0046] In the ICPB system, the degradation rate of sulfamethoxazole reached 86.6%, which is not much different from the removal rate of sulfamethoxazole in the photocatalytic degradation group (87.9%), demonstrating the good degradation efficiency of the stratified ICPB system.

[0047] Test Example 2 Escherichia coli K12 was selected to test the antibacterial activity of sulfamethoxazole (SMX) and its photocatalytic, biochemical, and ICPB conversion products. The toxicity assessment experiment consisted of five groups: a control group, a sulfamethoxazole group, a biodegradation effluent group, a photocatalytic degradation effluent group, and an ICPB degradation effluent group. The measurement volume was 150 mL, and each group was tested in parallel.

[0048] (1) Control group: 148 mL of sterilized LB medium was used as a negative control; (2) SMX group: SMX was added to 148 mL of sterilized LB medium to make the concentration 1 mg L. -1 ; (3) Biodegradation effluent group: 148 mL LB medium was prepared using the solution after the biodegradation experiment; (4) Photocatalytic degradation of water: 148 mL of LB medium was prepared using the solution after the photocatalytic reaction. (5) ICPB degradation effluent group: 148 mL LB medium was prepared using the solution after the ICPB experimental reaction.

[0049] The biodegradation, photocatalytic degradation, and ICPB degradation effluent groups were prepared from the reaction solutions after each experimental reaction. After centrifugation, the reaction solutions were filtered through a 0.22 μm syringe filter. Tryptone, yeast extract, and sodium chloride were then added to the reaction solutions according to the LB medium formula. After dissolution, the pH was adjusted to 7.4 using 1 M sodium hydroxide solution to prepare the corresponding culture medium solutions. All culture medium solutions inoculated with *E. coli* were placed in an incubator and shaken at 30℃, 120 rpm. Samples of 2 mL (11% of the total volume) were taken at 0, 2, 4, 6, 8, 10, 12, and 24 h. The optical density of the samples was measured at 600 nm using a UV spectrophotometer. A curve showing the change in optical density over time was plotted, which represents the growth curve of *E. coli*.

[0050] Experimental results are as follows Figure 3 As shown, the toxicity of the degradation products from the ICPB system is significantly lower than that from photocatalytic degradation products, demonstrating the advantage of the ICPB system in reducing the toxicity of recalcitrant pollutants.

[0051] Based on the combined results of Experiments 1 and 2, the layered photocatalytic-biodegradation coupled wastewater treatment system of this invention significantly reduces the toxicity of degradation products while maintaining high degradation efficiency of sulfamethoxazole, thus reducing the need for secondary treatment of toxic photocatalytic products. After the experiment, the photocatalyst and biofilm packing material are easily separated, facilitating the subsequent resource utilization of both the photocatalyst and microorganisms.

[0052] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A layered photocatalytic-biodegradation coupled wastewater treatment system, characterized in that, This includes the reactor, as well as the connected light source and power supply; The reactor is provided with an inlet and an outlet; a partition plate is provided in the middle of the reactor to divide the reactor into an upper photocatalytic reactor and a lower biodegradation reactor; small holes are provided on the partition plate for communication between the upper and lower layers; The photocatalytic reactor contains a photocatalyst for photocatalytic degradation. The biodegradation reactor is filled with biofilm packing material for biodegradation. The light source is located above the reactor and is used to provide illumination to the photocatalytic reactor.

2. The layered photocatalytic-biodegradation coupled wastewater treatment system according to claim 1, characterized in that, The photocatalyst is ZnO / g-C3N4 photocatalyst gel microspheres.

3. The layered photocatalytic-biodegradation coupled wastewater treatment system according to claim 2, characterized in that, The preparation steps of the ZnO / g-C3N4 photocatalyst gel microspheres include: S11, urea is heated to 480-520℃ and kept at that temperature for 1.8-2.2h to obtain g-C3N4; zinc acetate and urea are added to an aqueous ethylene glycol solution at a molar ratio of 1:(2-4), and dissolved by ultrasonication to obtain a first mixed solution. The first mixed solution is subjected to hydrothermal reaction, washing and drying to obtain the ZnO precursor. S12, g-C3N4 and ZnO precursors were dispersed in anhydrous ethanol at a mass ratio of 1:1, and dried to obtain a solid sample. The solid sample was heated to 480-520℃ and kept at that temperature for 1.8-2.2h to obtain a ZnO / g-C3N4 photocatalyst. S13, ZnO / g-C3N4 photocatalyst was dispersed in ultrapure water at a concentration of 280-320 mg / L, and then mixed with 3 wt% sodium alginate solution at a volume ratio of 1:1 to obtain a second mixed solution; the second mixed solution was dropped into anhydrous CaCl2 solution and solidified to obtain ZnO / g-C3N4 photocatalyst gel microspheres.

4. The layered photocatalytic-biodegradation coupled wastewater treatment system according to claim 3, characterized in that, The ethylene glycol aqueous solution is prepared by mixing ethylene glycol and ultrapure water at a volume ratio of 1:1; the concentration of zinc acetate in the first mixed solution is 0.08–0.12 mol / L; and / or, The hydrothermal reaction is carried out at 150–170°C for 11–13 hours; and / or, During the heating of urea and solid samples, the heating rate is 13–14 °C / min; and / or, The mass concentration of the anhydrous CaCl2 solution is 1.5-2.5%; the volume ratio of the second mixed solution to the anhydrous CaCl2 solution is 1:(18-22).

5. The layered photocatalytic-biodegradation coupled wastewater treatment system according to claim 1, characterized in that, The biofilm packing material includes a polyethylene carrier and a biofilm grown on the polyethylene carrier.

6. The layered photocatalytic-biodegradation coupled wastewater treatment system according to claim 5, characterized in that, The preparation steps of the biofilm packing material include: S21, In a moving bed biofilm reactor filled with polyethylene carrier, activated sludge is inoculated and the first synthetic wastewater is introduced for cultivation. S22, after the biofilm grows on the polyethylene carrier, the activated sludge is removed and the second synthetic wastewater is introduced to continue the cultivation to obtain the biofilm packing material.

7. The layered photocatalytic-biodegradation coupled wastewater treatment system according to claim 6, characterized in that, In step S21, the filling rate of the polyethylene carrier is 35-45%; the COD of the first synthetic wastewater is ≥400 mg / L. -1 NH4 + -N content in 80 mg / L -1 The above applies; the cultivation period is one week, the hydraulic retention time is 24 hours, and the activated sludge is replaced daily. And / or, In step S22, the conditions for continued cultivation include: cultivation using a 4-hour cyclic cultivation method, wherein the 4-hour cyclic cultivation includes a 60-minute influent time, a 175-minute aerobic reaction time, and a 5-minute effluent time; and the COD of the second synthetic wastewater is ≥350 mg / L. -1 NH4 + -N content in 60 mg / L -1 The above; the training period should continue for more than 45 days.

8. The layered photocatalytic-biodegradation coupled wastewater treatment system according to claim 1, characterized in that, The partition includes a movable black glass panel; and / or, It also includes an aeration device for supplying dissolved oxygen into the reactor; and / or, It also includes a stirrer connected to a power source, which is used to stir the wastewater in the photocatalytic reactor and the biodegradation reactor.

9. A photocatalytic-biodegradation coupled wastewater treatment method, characterized in that, The wastewater treatment method is carried out using the system described in any one of claims 1-8.

10. The photocatalytic-biodegradation coupled wastewater treatment method according to claim 9, characterized in that, The conditions for wastewater treatment include: a photocatalyst concentration of 200–400 mg / L. -1 The biofilm packing material has a filling ratio of 4–10%; the aeration rate is 0.1–0.3 L / min. -1 The stirring speed is 200-400 rpm.

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