A method for treating high-cod waste liquid containing paint in the automobile manufacturing industry

Abstract

This invention discloses a method for treating high-COD paint-containing wastewater from the automotive manufacturing industry, belonging to the field of automotive manufacturing wastewater treatment technology. The method first uses Fe3O4 magnetic nanoparticles to load Fe... 2+ Cu 2+ A bimetallic magnetically supported Fenton reagent was prepared by coating a siloxane layer with KH-550 ethanol solution. This reagent was added to the waste liquid, and the pH was adjusted to 2.5–4.5 with H2SO4 solution before ozone pre-oxidation. Rare earth-doped amphoteric ZIF-8 was then added, and the pH was adjusted to 6.5–8.5 with an alkaline solution. The mixture was stirred to form composite flocs and allowed to stand. The flocs were recovered by magnetic separation, and the supernatant was collected. After ultrasonic treatment to break up the remaining flocs, the mixture was filtered through a gradient-pore ceramic membrane module supported on a MnO2–γ-FeOOH gradient catalytic layer. This invention achieves efficient removal of recalcitrant pollutants through bimetallic synergistic catalytic enhanced oxidation and ZIF-8 adsorption, significantly reducing sludge production, ensuring stable membrane operation, and allowing for the recycling of core materials. It is suitable for the deep treatment of high-COD paint-containing wastewater from automotive manufacturing painting processes.

Description

Technical Field

[0001] This invention relates to the field of automobile manufacturing wastewater treatment technology, specifically a method for treating high COD wastewater containing paint from the automobile manufacturing industry. Background Technology

[0002] The painting process in the automotive manufacturing industry generates a large amount of high COD wastewater containing paint. This type of wastewater contains complex components such as acrylic resin, polyurethane resin, pigments, fillers, and organic solvents, and is characterized by high COD concentration, strong biological toxicity, and difficulty in degradation, making it a key and challenging area in the field of industrial wastewater treatment.

[0003] Among existing traditional treatment technologies, the Fenton oxidation method requires large amounts of reagents, producing a large volume of iron sludge, resulting in high subsequent treatment costs, and it is incomplete in degrading recalcitrant resin pollutants. Single ozone oxidation technology has limited ability to break down large molecular pollutants, easily forming intermediate byproducts, leading to difficulties in meeting effluent color and COD standards. Conventional adsorbents such as activated carbon and zeolite have poor selectivity for hydrophobic organic pollutants, are easily saturated, and cannot be regenerated, resulting in high operating costs. Even membrane separation technology, often used for advanced treatment, is prone to rapid flux decline due to paint residue clogging the membrane pores, requiring frequent cleaning and maintenance. With increasingly stringent environmental requirements and the growing demand for cost reduction and efficiency improvement in the automotive industry, traditional processes are no longer sufficient to meet practical application needs in terms of treatment effect, operating cost, and environmental friendliness.

[0004] Therefore, it is necessary to provide a method for treating high COD wastewater containing paint from the automotive manufacturing industry to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for treating high COD wastewater containing paint from the automotive manufacturing industry, in order to solve the technical problems of incomplete COD removal, large sludge production, serious membrane fouling, and low resource utilization in traditional processes.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for treating high COD wastewater containing paint from the automotive manufacturing industry, comprising the following steps:

[0007] 1) Fe3O4 magnetic nanoparticles were dispersed in a FeSO4 solution, and Fe3O4 reacted with Fe... 2+ The mass ratio is 8-12:2-4, and the mixture is stirred under nitrogen protection to allow Fe to... 2+ A chemical bond structure is formed with the hydroxyl groups on the Fe3O4 surface; then a CuSO4 solution is slowly added dropwise, Fe 2+ With Cu 2+The molar ratio was 4–6:1, and stirring continued. The KH-550 ethanol solution was atomized into 5–10 μm droplets using ultrasonic spraying, forming a 5–10 nm siloxane layer on the particle surface. After washing and vacuum drying, the bimetallic magnetically loaded Fenton reagent was obtained.

[0008] Fe in bimetallic magnetically loaded Fenton reagent 2+ With Cu 2+ It can efficiently activate ozone to generate a large number of highly active hydroxyl radicals, enhance the oxidation and ring-breaking ability of large molecules of difficult-to-degrade organic matter such as resin and organic solvent in paint waste liquid, and transform them into easily treatable small molecules. Fe3O4 magnetic nanoparticles serve as a carrier, which not only ensures the uniform dispersion and stable loading of bimetallic ions, but also provides structural support for subsequent magnetic separation and recovery. The siloxane layer further enhances the chemical stability of the reagent and reduces the loss of metal ions during the catalytic process.

[0009] 2) Add the bimetallic magnetically loaded Fenton reagent prepared in step 1) to the waste liquid, stir to disperse the reagent evenly; adjust the pH of the waste liquid to 2.5-4.5 with an acidic solution, and then introduce ozone for reaction;

[0010] 3) Add rare earth-doped amphoteric ZIF-8 to the waste liquid after step 2). The rare earth-doped amphoteric ZIF-8 is modified by hydrophobicity of methyltriethoxysilane and its surface is covered with -Si-CH3 groups. Stir to disperse the reagent evenly, adjust the pH to 6.5-8.5 with alkaline solution, stir to form composite flocs, and let stand.

[0011] 4) Pump the mixture from step 3) into a magnetic separation device, apply an external magnetic field, recover the magnetic composite flocs, and collect the supernatant;

[0012] 5) The supernatant collected in step 4) is subjected to ultrasonic treatment to break up residual fine flocs and promote the process. Towards , Towards Transformation;

[0013] 6) Pass the waste liquid after ultrasonic treatment in step 5) into the ceramic membrane module for filtration.

[0014] Preferably, in step 1), the Fe3O4 magnetic nanoparticles have a particle size of 15–55 nm and an initial specific surface area of ​​70–130 m². 2 / g; the concentration of FeSO4 solution is 0.08–0.12 mol / L, and the concentration of CuSO4 solution is 0.04–0.06 mol / L; under nitrogen protection, Fe3O4 and Fe 2+The initial stirring time for mixing was 15–20 min, and the stirring time after adding CuSO4 was 10–15 min. During ultrasonic spraying, the mass fraction of KH-550 ethanol solution was 4–6 wt%, and the spraying pressure was 0.2–0.4 MPa. After washing the reagent 3–5 times, it was vacuum dried for 1.5–2.5 h at a temperature of 55–65 °C and a vacuum degree of -0.09–-0.07 MPa. The total loading of the prepared bimetallic magnetically loaded Fenton reagent was 10–20 wt%, and the specific surface area was ≥120 m². 2 / g.

[0015] Preferably, in step 2), the initial pH of the waste liquid to be treated is 5.5–9.0, the dosage of the bimetallic magnetically loaded Fenton reagent is 2–6 g / L; the acidic solution used to adjust the pH is an 8%–12% (w / w) H2SO4 solution; the concentration of the introduced ozone is 8–22 mg / L, the flow rate is 0.6–1.4 L / min, the pre-oxidation reaction time is 12–25 min; after the reagent is added, the stirring speed is 180–220 r / min, and the stirring time is 4–6 min.

[0016] Preferably, in step 3), the preparation method of the rare earth-doped amphoteric ZIF-8 includes the following steps:

[0017] 3a) Press Zn 2+ with La 3+ Weigh out zinc salt, lanthanum nitrate, and 2-methylimidazole in a molar ratio of 20–100:1, and dissolve them in DMF solvent to form a mixed solution, wherein Zn 2+ The concentration is 0.1–0.3 mol / L;

[0018] 3b) Transfer the mixed solution to a reaction vessel and react at a constant temperature of 100–140°C for 12–24 h to form La. 3+ Doped ZIF-8 crystal;

[0019] 3c) Collect the precipitate by centrifugation, and wash the precipitate successively with DMF solvent, 50% ethanol aqueous solution, and deionized water to obtain La. 3+ For doped ZIF-8 crystals, the residual DMF solvent content is controlled to be ≤0.01wt%;

[0020] 3d) Disperse the ZIF-8 crystals obtained in step 3c) in ethanol, add 1-2 wt% of methyltriethoxysilane by weight of ZIF-8 crystals, and stir at 50-70°C for 4-6 h to perform hydrophobic modification, forming rare earth-doped amphoteric ZIF-8 with -Si-CH3 groups on the surface.

[0021] 3e) Centrifuge and dry the rare earth-doped amphoteric ZIF-8 obtained in step 3d).

[0022] La in rare earth-doped amphoteric ZIF-8 3+ The doping optimizes the adsorption active sites of ZIF-8, improving the adsorption capacity and selectivity for small molecule organics and residual pigments and fillers generated by pre-oxidation; the -Si-CH3 hydrophobic group formed by methyltriethoxysilane modification enhances the material's affinity for hydrophobic organic pollutants, while avoiding excessive encapsulation by aqueous pollutants; its amphoteric properties can adapt to the adsorption requirements under different pH environments, and after combining with magnetic particles, it forms a structurally stable composite floc, significantly improving solid-liquid separation efficiency.

[0023] Preferably, in step 3), after adding rare earth-doped amphoteric ZIF-8 to the waste liquid treated in step 2), the mixture is stirred at a speed of 140-160 r / min for 2-4 min; in step 3), after adjusting the pH of the waste liquid to 6.5-8.5 with an alkaline solution, the mixture is stirred at a speed of 180-220 r / min for 8-20 min; the subsequent settling time of the flocs is 4-6 min.

[0024] Preferably, in step 4), the conditions for separating the magnetic composite flocs are: an applied magnetic field strength of 0.08–0.22 T, a magnetic field strength gradient of 40–60 T / m, and a separation time of 4–6 min.

[0025] Preferably, in step 5), the ultrasonic treatment power is 700-1100W, the frequency is 15-45kHz, and the treatment time is 4-10min, to ensure that the residual fine flocs are broken down to a particle size ≤5μm.

[0026] The compatibility between ultrasonic power and ozone flow rate in step 2):

[0027] When the ultrasonic power is 700-850W, the ozone flow rate corresponding to step 2) is 1.0-1.4L / min;

[0028] When the ultrasonic power is 850-1100W, the ozone flow rate corresponding to step 2) is 0.6-1.0L / min.

[0029] Preferably, in step 6), the ceramic membrane assembly is a gradient pore size ceramic membrane assembly, wherein the surface pore size is smaller than the inner pore size, the surface pore size is 40-90 nm and the inner pore size is 90-160 nm, and the ceramic membrane surface is loaded with a MnO2-γ-FeOOH gradient catalytic layer.

[0030] Preferably, in step 6), the MnO2-γ-FeOOH gradient catalytic layer is prepared by stepwise loading:

[0031] 6a) First, immerse the ceramic membrane in a mixed solution of KMnO4 and MnSO4, bathe it in a water bath at 55-65℃ for 2-4 hours, and calcine it at 480-520℃ for 1.5-2.5 hours to form a MnO2 layer;

[0032] 6b) The ceramic membrane treated in step 6a) is then immersed in FeCl3 solution, bathed in a water bath at 35-45℃ for 5-7 hours, and calcined at 280-320℃ for 0.5-1.5 hours to form a γ-FeOOH layer;

[0033] The total thickness of the MnO2-γ-FeOOH gradient catalytic layer loaded on the ceramic film surface is 70–130 nm, of which the surface γ-FeOOH loading is 0.6–1.2 mg / cm³. 2 The inner layer MnO2 loading is 0.8–1.4 mg / cm³. 2 .

[0034] The inner MnO2 layer of the MnO2-γ-FeOOH gradient catalytic layer primarily targets the deep degradation of nitrogen-containing organic matter and some aromatic compounds, while the outer γ-FeOOH layer enhances the catalytic oxidation of residual oxidation intermediates such as phenols and aldehydes, achieving precise removal of different types of pollutants. The catalytic layer works synergistically with the gradient pore size ceramic membrane, with the small pore size on the surface ensuring filtration accuracy and the large pore size in the inner layer reducing mass transfer resistance. At the same time, the catalytic reaction can decompose pollutants attached to the membrane surface, delaying membrane clogging and improving membrane operational stability.

[0035] Preferably, the treatment method further includes step 7): adding the magnetic composite flocs recovered in step 4) to the analytical tank, adding acidic analytical solution at a solid-liquid ratio of 1:8 to 12, stirring to ensure thorough analytical of the magnetic composite flocs, recovering the bimetallic magnetically loaded Fenton reagent by magnetic field separation, washing to neutral and then reusing; then backwashing the ceramic membrane, the backwash waste liquid entering the ZIF-8 recovery tank, adding a mixture of ethanol and EDTA, stirring, centrifuging to separate the rare earth-doped amphoteric ZIF-8, drying and reusing;

[0036] Preferably, in step 7), the acidic eluent is an H2SO4 solution with a concentration of 0.08–0.12 mol / L, the stirring speed during the eluent process is 180–220 r / min, and the time is 15–25 min; the volume ratio of the ethanol to EDTA mixture is 5–8:1, the EDTA concentration is 0.05–0.15 mol / L, the centrifugation speed is 2800–3200 r / min, and the time is 4–6 min.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] 1. This invention utilizes bimetallic magnetically loaded Fenton reagent containing Fe 2+ With Cu 2+The catalytic effect significantly improves the generation efficiency and stability of hydroxyl radicals. Combined with the strong oxidizing properties of ozone, it rapidly disrupts the chemical structure of macromolecular pollutants such as resins and pigments, transforming recalcitrant organic matter into easily treatable small molecules, laying the foundation for subsequent advanced treatment. The coating design of the siloxane layer enhances the stability of the reagent, while the magnetic carrier provides structural support for subsequent efficient separation and recovery.

[0039] 2. This invention utilizes rare-earth-doped amphoteric ZIF-8, which, due to its high specific surface area and amphoteric adsorption properties, can capture small molecule organic matter and residual pigments generated during pre-oxidation. 3+ The doping further optimizes the adsorption active sites, while the -Si-CH3 hydrophobic groups formed by methyltriethoxysilane modification effectively enhance the material's antifouling ability. The composite flocs formed with magnetic particles can be rapidly separated via magnetic separation, reducing sludge retention and secondary pollution. Ultrasonic treatment not only breaks up residual fine flocs, preventing clogging of the ceramic membrane, but also promotes... Towards , Towards The valence state transformation continuously maintains the activity of the catalytic system.

[0040] 3. This invention utilizes a gradient pore size ceramic membrane: a small pore size on the surface ensures filtration accuracy, while a large pore size in the inner layer reduces mass transfer resistance. The surface-loaded MnO2-γ-FeOOH gradient catalytic layer further degrades residual recalcitrant pollutants, achieving a synergistic effect between filtration and catalysis. The combined ultrasonic and backwashing cleaning method effectively delays membrane fouling and extends membrane lifespan. The resource recovery step, through acidic desorption and EDTA complexation, enables the efficient recovery and reuse of bimetallic magnetically loaded Fenton reagent and rare-earth-doped amphoteric ZIF-8, significantly reducing reagent consumption and operating costs, while also reducing sludge discharge. Attached Figure Description

[0041] Figure 1 This is a bar chart showing the COD removal rate of the treatment methods provided in Examples 1-3 and Comparative Examples 1-6 of the present invention.

[0042] Figure 2 Bar charts showing the sludge production of the treatment methods provided in Examples 1-3 and Comparative Examples 1-6 of the present invention;

[0043] Figure 3 This is a bar chart showing the membrane flux maintenance rate of the treatment methods provided in Examples 1-3 and Comparative Examples 1-6 of the present invention;

[0044] Figure 4 This is a bar chart showing the removal rate of core pollutants in the treatment methods provided in Examples 1-3 and Comparative Examples 1-6 of the present invention.

[0045] Figure 5This is a bar chart showing the processing cost of the processing methods provided in Embodiments 1-3 and Comparative Examples 1-6 of the present invention. Detailed Implementation

[0046] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment provides a method for treating high-COD paint-containing wastewater in the automotive manufacturing industry. The specific steps are as follows:

[0049] 1) Weigh 10g of Fe3O4 magnetic nanoparticles and disperse them in 100mL of 0.1mol / L FeSO4 solution. The Fe3O4 and Fe... 2+ The mass ratio was 10:3, and the mixture was stirred at 200 rpm for 18 min under nitrogen protection to allow Fe to... 2+ It forms a chemical bond structure with the hydroxyl groups on the Fe3O4 surface; 50 mL of 0.05 mol / L CuSO4 solution is slowly added dropwise, Fe... 2+ With Cu 2+ The molar ratio was 5:1, and stirring was continued for 12 min. A 5 wt% KH-550 ethanol solution was atomized into 8 μm droplets using ultrasonic spraying at a pressure of 0.3 MPa, forming an 8 nm siloxane layer on the particle surface. The particles were washed four times with deionized water and vacuum dried at 60 °C and -0.08 MPa for 2 h to obtain a bimetallic magnetically loaded Fenton reagent with a total loading of 15 wt% and a specific surface area of ​​135 m². 2 / g.

[0050] 2) Take 1L of the waste liquid to be treated, add 4g / L of the bimetallic magnetically loaded Fenton reagent prepared in step 1), stir at 200r / min for 5min to disperse evenly; adjust the pH to 3.5 with 10wt% H2SO4 solution, introduce ozone at a concentration of 15mg / L and a flow rate of 1.0L / min, and react for 18min.

[0051] 3) Add 2.5 g / L rare earth-doped amphoteric ZIF-8 and La to the waste liquid treated in step 2). 3+ The doping amount was 1.2 wt%, the grafting degree was 1.4 mmol / g, and the mixture was stirred at 150 r / min for 3 min to disperse it evenly. The pH was adjusted to 7.5 with 10 wt% NaOH solution, and the mixture was stirred at 200 r / min for 14 min to form composite flocs. The mixture was then allowed to stand for 5 min.

[0052] 4) Pump the mixture from step 3) into a magnetic separation device, apply a magnetic field of 0.15T with a gradient of 50T / m, separate for 5 minutes, recover the magnetic composite flocs, and collect the supernatant.

[0053] 5) The supernatant collected in step 4) is subjected to ultrasonic treatment at a power of 900W, a frequency of 30kHz, and a time of 7min to break up the residual fine flocs to a particle size of ≤5μm.

[0054] 6) The waste liquid after ultrasonic treatment in step 5) is passed into the ceramic membrane module and cross-flow filtration is used. The pressure is 0.25 MPa, the flow rate on the membrane surface is 1.2 m / s, the temperature is 28℃, and the reaction time is 25 min. The ceramic membrane is ultrasonically treated with 500W for 3 min every 3 h, and backwashing with 0.15 MPa is applied for 1.5 min at the same time.

[0055] 7) Add the magnetic composite flocs recovered in step 4) to the analytical cell, add 0.1 mol / L H2SO4 analytical solution at a solid-liquid ratio of 1:10, stir at 200 r / min for 20 min, and use magnetic field separation to recover the bimetallic magnetically loaded Fenton reagent. Wash until neutral for later use. Backwash the ceramic membrane, and put the backwash waste liquid into the ZIF-8 recovery cell. Add a mixture of ethanol and EDTA at a volume ratio of 6:1 and an EDTA concentration of 0.1 mol / L. After stirring, centrifuge at 3000 r / min for 5 min to separate the rare earth-doped amphoteric ZIF-8. Dry it for later use.

[0056] Example 2

[0057] This embodiment provides a method for treating high-COD paint-containing wastewater in the automotive manufacturing industry. The specific steps are as follows:

[0058] 1) Weigh 12g of Fe3O4 magnetic nanoparticles and disperse them in 100mL of 0.12mol / L FeSO4 solution. The Fe3O4 and Fe... 2+ The mass ratio was 12:4, and the mixture was stirred at 220 rpm for 20 min under nitrogen protection to allow Fe to... 2+ It forms a chemical bond structure with the hydroxyl groups on the Fe3O4 surface; 50 mL of 0.06 mol / L CuSO4 solution is slowly added dropwise, Fe... 2+ With Cu 2+ The molar ratio was 6:1, and stirring was continued for 15 min. A 6 wt% KH-550 ethanol solution was atomized into 10 μm droplets using ultrasonic spraying at a pressure of 0.4 MPa, forming a 10 nm siloxane layer on the particle surface. The particles were washed five times with deionized water and vacuum dried at 65 °C and -0.07 MPa for 2.5 h to obtain a bimetallic magnetically loaded Fenton reagent with a total loading of 20 wt% and a specific surface area of ​​142 m². 2 / g.

[0059] 2) Take 1L of the waste liquid to be treated, add 6g / L of the bimetallic magnetically loaded Fenton reagent prepared in step 1), stir at 220r / min for 6min to disperse evenly; adjust the pH to 4.5 with 12wt% H2SO4 solution, introduce ozone at a concentration of 22mg / L and a flow rate of 1.4L / min, and react for 25min.

[0060] 3) Add 3.5 g / L of rare earth-doped amphoteric ZIF-8 and La to the waste liquid treated in step 2). 3+ The doping amount was 2.0 wt%, the grafting degree was 1.8 mmol / g, and the mixture was stirred at 160 r / min for 4 min to disperse it evenly. The pH was adjusted to 8.5 with 10 wt% NaOH solution, and the mixture was stirred at 220 r / min for 20 min to form composite flocs. The mixture was then allowed to stand for 6 min.

[0061] 4) Pump the mixture from step 3) into a magnetic separation device, apply a magnetic field of 0.22T with a gradient of 60T / m, separate for 6 minutes, recover the magnetic composite flocs, and collect the supernatant.

[0062] 5) The supernatant collected in step 4) is subjected to ultrasonic treatment at a power of 1100W, a frequency of 45kHz, and a time of 10min to break up the residual fine flocs to a particle size of ≤5μm.

[0063] 6) The waste liquid after ultrasonic treatment in step 5) is passed into the ceramic membrane module and cross-flow filtration is used. The pressure is 0.35 MPa, the flow rate at the membrane surface is 1.7 m / s, the temperature is 35℃, and the reaction time is 35 min. The ceramic membrane is ultrasonically treated with 600W for 4 min every 4 h, and backwashing with 0.18 MPa is applied for 2 min at the same time.

[0064] 7) Add the magnetic composite flocs recovered in step 4) to the analytical cell, add 0.12 mol / L H2SO4 analytical solution at a solid-liquid ratio of 1:12, stir at 220 r / min for 25 min, and use magnetic field separation to recover the bimetallic magnetically loaded Fenton reagent. Wash until neutral for later use. Backwash the ceramic membrane, and put the backwash waste liquid into the ZIF-8 recovery cell. Add a mixture of ethanol and EDTA at a volume ratio of 8:1 and an EDTA concentration of 0.15 mol / L. After stirring, centrifuge at 3200 r / min for 6 min to separate the rare earth-doped amphoteric ZIF-8. Dry it for later use.

[0065] Example 3

[0066] This embodiment provides a method for treating high-COD paint-containing wastewater in the automotive manufacturing industry. The specific steps are as follows:

[0067] 1) Weigh 8g of Fe3O4 magnetic nanoparticles and disperse them in 100mL of 0.08mol / L FeSO4 solution. The Fe3O4 and Fe... 2+The mass ratio was 8:2, and the mixture was stirred at 180 rpm for 15 min under nitrogen protection to allow Fe to be produced. 2+ It forms a chemical bond structure with the hydroxyl groups on the Fe3O4 surface; 50 mL of 0.04 mol / L CuSO4 solution is slowly added dropwise, Fe... 2+ With Cu 2+ The molar ratio was 4:1, and stirring was continued for 10 min. A 4 wt% KH-550 ethanol solution was atomized into 5 μm droplets using ultrasonic spraying at a pressure of 0.2 MPa, forming a 5 nm siloxane layer on the particle surface. The particles were washed three times with deionized water and vacuum dried at 55 °C and -0.09 MPa for 1.5 h to obtain a bimetallic magnetically loaded Fenton reagent with a total loading of 10 wt% and a specific surface area of ​​122 m². 2 / g.

[0068] 2) Take 1L of the waste liquid to be treated, add 2g / L of the bimetallic magnetically loaded Fenton reagent prepared in step 1), stir at 180r / min for 4min to disperse evenly; adjust the pH to 2.5 with 8wt% H2SO4 solution, introduce ozone at a concentration of 8mg / L and a flow rate of 0.6L / min, and react for 12min.

[0069] 3) Add 1.5 g / L rare earth-doped amphoteric ZIF-8 and La to the waste liquid treated in step 2). 3+ Doping amount 0.5wt%, grafting degree 1.0mmol / g, stirred at 140r / min for 2min to disperse evenly; pH ​​adjusted to 6.5 with 10wt% NaOH solution, stirred at 180r / min for 8min to form composite flocs, and allowed to stand for 4min.

[0070] 4) Pump the mixture from step 3) into a magnetic separation device, apply a magnetic field of 0.08T with a gradient of 40T / m, separate for 4 minutes, recover the magnetic composite flocs, and collect the supernatant.

[0071] 5) The supernatant collected in step 4) is subjected to ultrasonic treatment at a power of 700W, a frequency of 15kHz, and a time of 4min to break up the residual fine flocs to a particle size of ≤5μm.

[0072] 6) The waste liquid after ultrasonic treatment in step 5) is passed into the ceramic membrane module and cross-flow filtration is used. The pressure is 0.15MPa, the flow rate at the membrane surface is 0.8m / s, the temperature is 20℃, and the reaction time is 15min. The ceramic membrane is ultrasonically treated with 400W for 2min every 2h, and backwashing with 0.12MPa is applied for 1min at the same time.

[0073] 7) Add the magnetic composite flocs recovered in step 4) to the analytical cell, add 0.08 mol / L H2SO4 analytical solution at a solid-liquid ratio of 1:8, stir at 180 r / min for 15 min, and use magnetic field separation to recover the bimetallic magnetically loaded Fenton reagent. Wash until neutral for later use. Backwash the ceramic membrane, and put the backwash waste liquid into the ZIF-8 recovery cell. Add a mixture of ethanol and EDTA at a volume ratio of 5:1 and an EDTA concentration of 0.05 mol / L. After stirring, centrifuge at 2800 r / min for 4 min to separate the rare earth-doped amphoteric ZIF-8. Dry it for later use.

[0074] Comparative Example 1

[0075] The only difference between this comparative example and Example 1 is that in step 1), the preparation of the single-metal magnetically loaded Fenton reagent is carried out without the addition of CuSO4 solution; the remaining steps are completely consistent with Example 1.

[0076] Expected performance: lacking Fe 2+ and Cu 2+ The bimetallic catalysis reduced the oxidation efficiency of the Fenton reaction, resulting in insufficient decomposition of recalcitrant organic matter and lower COD and core pollutant removal rates compared to Example 1. In the monometallic catalytic system, the reagent reaction was incomplete, leading to an increase in sludge production. The membrane flux maintenance rate was less affected, but the overall treatment effect was weaker than that of Example 1. Since the resource recovery process was not changed, the reagent recovery rate was close to that of Example 1, but the unit treatment cost indirectly increased due to insufficient oxidation efficiency.

[0077] Comparative Example 2

[0078] The only difference between this comparative example and Example 1 is that step 3) of adding rare earth-doped amphoteric ZIF-8 is missing, and only pH adjustment and stirring flocculation are performed. The remaining steps are completely consistent with Example 1.

[0079] Expected performance: Lacking the adsorption effect of rare earth-doped amphoteric ZIF-8, it cannot effectively capture small molecule organic matter and residual pigments generated during pre-oxidation, resulting in a significant decrease in COD removal rate and core pollutant removal rate; relying solely on conventional flocculation, the floc structure formed is loose, with poor settling performance and increased sludge production; unadsorbed fine pollutants easily clog the ceramic membrane, leading to a decrease in membrane flux maintenance rate; without the participation of ZIF-8, subsequent resource recovery only involves bimetallic magnetically loaded Fenton reagent, and the overall treatment effect and operational stability are inferior to Example 1.

[0080] Comparative Example 3

[0081] The only difference between this comparative example and Example 1 is that the ultrasonic treatment in step 5) is missing; the rest of the steps are completely consistent with Example 1.

[0082] Expected performance: Residual fine flocs are not broken up and are easily deposited on the ceramic membrane surface and block the membrane pores, resulting in a significant decrease in membrane flux maintenance and an increase in membrane cleaning frequency; the lack of ultrasound to promote the conversion of metal ion valence states leads to a slight decrease in the efficiency of subsequent catalytic reactions, and a slight decrease in COD removal rate and core pollutant removal rate; sludge production is similar to that of Example 1, but membrane maintenance costs increase and the overall process operation stability deteriorates.

[0083] Comparative Example 4

[0084] The only difference between this comparative example and Example 1 is that step 6) uses a common ceramic membrane without the MnO2-γ-FeOOH gradient catalytic layer; the rest of the steps are completely consistent with Example 1.

[0085] Expected performance: Ordinary ceramic membranes only have filtration function and lack deep catalytic degradation effect, so they cannot further decompose residual recalcitrant pollutants. The COD removal rate and core pollutant removal rate are lower than those in Example 1. There is no catalytic layer on the membrane surface to decompose attached pollutants, the membrane fouling rate is accelerated, and the membrane flux maintenance rate is reduced. The sludge production is similar to that in Example 1, but the difficulty of achieving the effluent quality standard is increased, and the membrane maintenance frequency and cost are increased.

[0086] Comparative Example 5

[0087] The only difference between this comparative example and Example 1 is that the resource recovery in step 7) is missing, and the bimetallic magnetically loaded Fenton reagent and ZIF-8 are used only once. The remaining steps are completely consistent with Example 1.

[0088] Expected performance: The bimetallic magnetically loaded Fenton reagent and rare earth-doped amphoteric ZIF-8 cannot be recycled and reused, resulting in a zero reagent recovery rate; reagent consumption increases significantly, leading to a substantial increase in treatment costs; performance indicators such as COD removal rate, core pollutant removal rate, sludge production, and membrane flux maintenance rate are similar to those in Example 1, but due to the lack of resource recovery, the process economy and environmental performance are significantly inferior to those in Example 1.

[0089] Comparative Example 6

[0090] The comparative example uses a conventional treatment process: 8 g / L FeSO4 and 4 g / L H2O2 (conventional Fenton) are added to the waste liquid, the pH is adjusted to 3.5 and the reaction is carried out for 30 min; 5 g / L PAC and 1 g / L PAM are added for flocculation and the mixture is allowed to stand for 30 min; the supernatant is filtered using a conventional ultrafiltration membrane, and the remaining conditions are the same as in Example 1.

[0091] Expected performance: The conventional Fenton reaction produces a large amount of iron sludge, with sludge production far exceeding that of Example 1; the flocs formed by PAC-PAM flocculation have poor adsorption selectivity and cannot effectively remove specific recalcitrant pollutants, resulting in significantly lower COD removal rates and core pollutant removal rates compared to Example 1; ordinary ultrafiltration membranes have weak antifouling capabilities and are easily clogged by flocs and residual pollutants, leading to low membrane flux maintenance, high membrane cleaning frequency, and high maintenance costs; there is no reagent recovery design, resulting in high treatment costs; the overall process has poor adaptability to high COD wastewater containing paint, and insufficient effluent water quality stability.

[0092] Performance testing methods:

[0093] 1. COD removal rate (%)

[0094] The potassium dichromate method was used for determination.

[0095] ① Take 20 mL of waste liquid before and after treatment, add them to 500 mL Erlenmeyer flasks respectively, add 10 mL of 0.25 mol / L potassium dichromate standard solution and 30 mL of sulfuric acid-silver sulfate solution (mass ratio 100:1), and heat under reflux for 2 h;

[0096] ② After cooling, add 90 mL of water and titrate with 0.1 mol / L ferrous ammonium sulfate standard solution until the solution turns reddish-brown. Record the volume consumed.

[0097] ③ Calculate the COD value using the formula: COD mg / L = (V0 - V1) × C × 8 × 1000 / V2, where V0 is the blank consumption volume, V1 is the sample consumption volume, C is the ferrous ammonium sulfate concentration, and V2 is the sampling volume;

[0098] ④ Removal rate = (Initial COD - Post-treatment COD) / Initial COD × 100%.

[0099] 2. Sludge production (g / L)

[0100] ① Collect sludge generated in all stages of the treatment process, including magnetic separation flocs and membrane cleaning residue, filter it with medium-speed qualitative filter paper with a diameter of 12.5cm, and collect the filter cake;

[0101] ② Transfer the filter cake to a pre-weighed porcelain crucible, dry it in a 105℃ forced-air drying oven for 2 hours, then calcine it in a 600℃ muffle furnace for 30 minutes to remove organic matter. After cooling, weigh it with an electronic balance with an accuracy of 0.1 mg.

[0102] ③ Sludge production = mass of dried sludge (g) / volume of treated waste liquid (L).

[0103] 3. Membrane flux maintenance rate (%)

[0104] ① Membrane flux determination: The gravimetric method was used. Under the set operating pressure of 0.25 MPa as in Example 1, the mass of filtrate that permeated through the ceramic membrane was collected within 60 seconds. The flux was calculated according to the formula: J = (m / ρ) / (A×t), where m is the mass of filtrate, ρ is the density of water, A is the effective area of ​​the membrane, and t is the time.

[0105] ② Initial flux: Record the stable flux value within the first 30 minutes of membrane operation;

[0106] ③ Flux after 3 hours: The stable flux value measured under the same operating conditions after 3 hours of continuous operation;

[0107] ④ Maintenance rate = (flux after 3 hours / initial flux) × 100%.

[0108] 4. Removal rate of core pollutants (%)

[0109] Determined by high performance liquid chromatography (HPLC):

[0110] ① Resin: Acrylic resin, polyurethane resin: The chromatographic column is a C18 column with a diameter of 250 mm × 4.6 mm and a thickness of 5 μm. The mobile phase is methanol-water with a volume ratio of 85:15. The flow rate is 1.0 mL / min. The detection wavelength is 254 nm. The column temperature is 30 °C.

[0111] ② Pigments such as titanium dioxide: The chromatographic column is a silica gel column with a diameter of 250 mm × 4.6 mm and a thickness of 5 μm. The mobile phase is acetonitrile-ethyl acetate with a volume ratio of 70:30. The flow rate is 1.0 mL / min. The detection wavelength is 450 nm. The column temperature is 30 °C.

[0112] ③ The waste liquid before and after treatment was filtered through a 0.22μm filter membrane and then measured on an instrument. The pollutant concentration was calculated using the external standard method based on the peak area.

[0113] ④ Removal rate = (initial concentration - post-treatment concentration) / initial concentration × 100% The arithmetic mean of resin and pigment removal rates is taken.

[0114] 5. Reagent recovery rate (%)

[0115] ① Bimetallic magnetically loaded Fenton reagent: Collect the reagent that has been separated by magnetic field and washed to neutrality in the resource recovery step, dry it under vacuum at 60℃ to constant weight, and record the weight as m1; the dosage is recorded as m0, and the recovery rate = (m1 / m0) × 100%;

[0116] ② Rare earth-doped amphoteric ZIF-8: Collect the ZIF-8 after analysis with ethanol-EDTA mixture, centrifugation and drying, and record the weight as n1; the dosage is recorded as n0, and the recovery rate = (n1 / n0) × 100%;

[0117] ③ The final drug recovery rate is the arithmetic mean of the two above.

[0118] 6. Treatment cost (RMB / ton of water)

[0119] ① Reagent costs: Calculate the consumption of bimetallic magnetic Fenton reagent, ZIF-8, acid-base regulator, ozone generator, etc., and calculate based on market unit price, such as Fenton reagent at 120 yuan / kg and ZIF-8 at 300 yuan / kg;

[0120] ② Energy consumption cost: including the power of stirring equipment, ultrasonic device, magnetic separation system, membrane module, vacuum drying, etc. (kW × operating time (h) × electricity cost (yuan / kWh), calculated at 0.8 yuan;

[0121] ③ Membrane maintenance cost: The ceramic membrane replacement cycle is calculated at 3000 hours, and the unit price of the membrane is 8000 yuan / m. 2 This is allocated to each ton of water;

[0122] ④ Total treatment cost = (chemical cost + energy cost + membrane maintenance cost) / water volume treated in tons.

[0123] The performance test data is as follows:

[0124]

[0125] Based on the above data, it can be seen that the COD removal rate of Examples 1-3 reached 94.2% to 98.5%, and the removal rate of the core pollutant resin pigment was 95.1% to 98.7%. Compared with the COD removal rate of 75.3% and the core pollutant removal rate of 78.5% in Comparative Example 6, which combined traditional Fenton and ultrafiltration processes, the COD removal rate was increased by more than 25%, and the removal rate of the core pollutant was also significantly better than Comparative Examples 1-5, which lacked the key process.

[0126] The sludge production of Examples 1-3 was only 0.9-1.5 g / L, which was not only much lower than 4.8 g / L of Comparative Example 6, but also 17%-64% lower than 1.8 g / L of Comparative Example 1 without bimetallic catalysis and 2.5 g / L of Comparative Example 2 without ZIF-8. This is due to the efficient catalysis of bimetallic magnetically supported Fenton reagent, which reduced reagent loss, and the rapid separation of magnetic composite flocs, which reduced sludge retention.

[0127] The membrane flux maintenance rates of Examples 1-3 reached 85.7% to 92.3%, which is 18% to 104% higher than that of Comparative Example 3 (79.2% without ultrasonic treatment), Comparative Example 4 (66.5% using ordinary ceramic membrane), and Comparative Example 6 (45.2% using conventional ultrafiltration membrane). Among them, the catalyst layer is the core factor for membrane antifouling. The membrane flux maintenance rate of Comparative Example 4, which lacks ultrasonic treatment, is significantly lower than that of Comparative Example 3, which only lacks ultrasonic-assisted treatment. This fully demonstrates the synergistic antifouling effect of ultrasonic breaking up of residual flocs, gradient pore size membrane structure, and MnO2-γ-FeOOH catalyst layer, which together delay membrane fouling.

[0128] The reagent recovery rates in Examples 1-3 remained stable at 82.4%–88.6%. The bimetallic magnetically loaded Fenton reagent and rare-earth-doped amphoteric ZIF-8 could be recycled more than 5 times, resulting in a treatment cost of only 15.3–23.8 yuan / ton of water. This is 27% lower than the 32.8 yuan / ton of water in Comparative Example 5, which omitted the resource recovery step, and 16%–46% lower than the 28.5 yuan / ton of water in Comparative Example 6, which used a traditional process. It is worth noting that Comparative Example 2, due to the lack of the adsorption function and floc enhancement effect of ZIF-8, not only had a core pollutant removal rate of only 87.2%, but also a membrane flux maintenance rate that dropped to 71.5%. Furthermore, the sludge production did not fully reflect the reduction value of ZIF-8, further confirming the key role of this material in the process.

[0129] Therefore, the performance degradation and index differences of each comparative example clearly demonstrate the necessity of key processes in the embodiments, such as bimetallic synergistic catalysis, ZIF-8 adsorption, ultrasonic assistance, gradient catalytic membrane filtration, and resource recovery: Comparative Example 1, due to the lack of Fe... 2+ and Cu 2+ Bimetallic synergistic catalysis reduced the COD removal rate to 82.5%; in Comparative Example 2, omitting ZIF-8 significantly reduced both pollutant removal and membrane operational stability; in Comparative Example 3, the lack of ultrasonic treatment led to residual floc deposition and increased membrane fouling; in Comparative Example 4, the absence of the catalytic layer resulted in accelerated membrane fouling and insufficient deep degradation. In summary, the treatment effect, operational stability, and economic efficiency of this invention are significantly superior to existing technologies.

[0130] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for treating high-COD wastewater containing paint from the automobile manufacturing industry, characterized in that, Includes the following steps: 1) Fe3O4 magnetic nanoparticles were dispersed in a FeSO4 solution, and Fe3O4 reacted with Fe... 2+ The mass ratio is 8-12:2-4, and the mixture is stirred under nitrogen protection to allow Fe to... 2+ A chemical bond structure is formed with the hydroxyl groups on the Fe3O4 surface; then CuSO4 solution is slowly added dropwise, Fe 2+ With Cu 2+ The molar ratio was 4–6:1, and stirring continued. The KH-550 ethanol solution was atomized into 5–10 μm droplets using ultrasonic spraying, forming a 5–10 nm siloxane layer on the particle surface. After washing and vacuum drying, the bimetallic magnetically loaded Fenton reagent was obtained. 2) Add the bimetallic magnetically loaded Fenton reagent prepared in step 1) to the waste liquid, stir to disperse the reagent evenly; adjust the pH of the waste liquid to 2.5-4.5 with an acidic solution, and then introduce ozone for reaction; 3) Add rare earth-doped amphoteric ZIF-8 to the waste liquid after step 2). The rare earth-doped amphoteric ZIF-8 is modified by hydrophobicity of methyltriethoxysilane and its surface is covered with -Si-CH3 groups. Stir to disperse the reagent evenly, adjust the pH to 6.5-8.5 with alkaline solution, stir to form composite flocs, and let stand. 4) Pump the mixture from step 3) into a magnetic separation device, apply an external magnetic field, recover the magnetic composite flocs, and collect the supernatant; 5) The supernatant collected in step 4) is subjected to ultrasonic treatment to break up residual fine flocs and promote the process. Towards , Towards Transformation; 6) Pass the waste liquid after ultrasonic treatment in step 5) into the ceramic membrane module for filtration.

2. The method according to claim 1, characterized in that, In step 1), the Fe3O4 magnetic nanoparticles have a particle size of 15–55 nm and an initial specific surface area of ​​70–130 m². 2 / g; The concentration of FeSO4 solution is 0.08–0.12 mol / L, and the concentration of CuSO4 solution is 0.04–0.06 mol / L; Under nitrogen protection, Fe3O4 and Fe 2+ The initial stirring time for mixing is 15–20 min, and the stirring time after adding CuSO4 is 10–15 min. During ultrasonic spraying, the mass fraction of the KH-550 ethanol solution is 4–6 wt%, and the spraying pressure is 0.2–0.4 MPa. After being washed 3 to 5 times, the reagent was vacuum dried for 1.5 to 2.5 hours at a temperature of 55 to 65°C and a vacuum degree of -0.09 to -0.07 MPa. The total loading of the bimetallic magnetically loaded Fenton reagent was 10–20 wt%, and the specific surface area was ≥120 m². 2 / g.

3. The method according to claim 1, characterized in that, In step 2), the initial pH of the waste liquid to be treated is 5.5–9.0, and the dosage of bimetallic magnetically loaded Fenton reagent is 2–6 g / L; The acidic solution used to adjust the pH is an 8%–12% (w / w) H2SO4 solution; The ozone concentration introduced is 8–22 mg / L, the flow rate is 0.6–1.4 L / min, and the pre-oxidation reaction time is 12–25 min; After adding the reagent, the stirring speed is 180-220 r / min, and the stirring time is 4-6 min.

4. The method according to claim 1, characterized in that, In step 3), the preparation method of the rare earth-doped amphoteric ZIF-8 includes the following steps: 3a) Press Zn 2+ with La 3+ Weigh out zinc salt, lanthanum nitrate, and 2-methylimidazole in a molar ratio of 20–100:1, and dissolve them in DMF solvent to form a mixed solution, wherein Zn 2+ The concentration is 0.1–0.3 mol / L; 3b) Transfer the mixed solution to a reaction vessel and react at a constant temperature of 100–140°C for 12–24 h to form La. 3+ Doped ZIF-8 crystal; 3c) Collect the precipitate by centrifugation, and wash the precipitate successively with DMF solvent, 50% ethanol aqueous solution, and deionized water to obtain La. 3+ For doped ZIF-8 crystals, the residual DMF solvent content is controlled to be ≤0.01wt%; 3d) Disperse the ZIF-8 crystals obtained in step 3c) in ethanol, add 1-2 wt% of methyltriethoxysilane by weight of ZIF-8 crystals, and stir at 50-70°C for 4-6 h to perform hydrophobic modification, forming rare earth-doped amphoteric ZIF-8 with -Si-CH3 groups on the surface. 3e) Centrifuge and dry the rare earth-doped amphoteric ZIF-8 obtained in step 3d).

5. The method according to claim 1, characterized in that, In step 3), rare earth-doped amphoteric ZIF-8 is added to the waste liquid after step 2), and then stirred at a speed of 140-160 r / min for 2-4 min. In step 3), after adjusting the pH of the waste liquid to 6.5-8.5 with an alkaline solution, continue stirring at a speed of 180-220 r / min for 8-20 min; the subsequent settling time for the flocs is 4-6 min.

6. The method according to claim 1, characterized in that, In step 4), the conditions for separating the magnetic composite flocs are: The applied magnetic field strength was 0.08–0.22 T, the magnetic field strength gradient was 40–60 T / m, and the separation time was 4–6 min.

7. The method according to claim 1, characterized in that, In step 5), the ultrasonic treatment power is 700-1100W, the frequency is 15-45kHz, and the treatment time is 4-10min to ensure that the residual fine flocs are broken down to a particle size ≤5μm. The compatibility between ultrasonic power and ozone flow rate in step 2): When the ultrasonic power is 700-850W, the ozone flow rate corresponding to step 2) is 1.0-1.4L / min; When the ultrasonic power is 850-1100W, the ozone flow rate corresponding to step 2) is 0.6-1.0L / min.

8. The method according to claim 1, characterized in that, In step 6), the ceramic membrane assembly is a gradient pore size ceramic membrane assembly, in which the surface pore size is smaller than the inner pore size. The surface pore size is 40-90 nm and the inner pore size is 90-160 nm. The ceramic membrane surface is loaded with a MnO2-γ-FeOOH gradient catalytic layer.

9. The method according to claim 8, characterized in that, In step 6), the MnO2-γ-FeOOH gradient catalytic layer is prepared by stepwise loading: 6a) First, immerse the ceramic membrane in a mixed solution of KMnO4 and MnSO4, bathe it in a water bath at 55-65℃ for 2-4 hours, and calcine it at 480-520℃ for 1.5-2.5 hours to form a MnO2 layer; 6b) The ceramic membrane treated in step 6a) is then immersed in FeCl3 solution, bathed in a water bath at 35-45℃ for 5-7 hours, and calcined at 280-320℃ for 0.5-1.5 hours to form a γ-FeOOH layer; The total thickness of the MnO2-γ-FeOOH gradient catalytic layer loaded on the ceramic film surface is 70–130 nm, of which the surface γ-FeOOH loading is 0.6–1.2 mg / cm³. 2 The inner layer MnO2 loading is 0.8–1.4 mg / cm³. 2 .

10. The method according to claim 1, characterized in that, The process also includes step 7): adding the magnetic composite flocs recovered in step 4) to the analytical tank, adding acidic analytical solution at a solid-liquid ratio of 1:8 to 12, stirring to ensure thorough analytical of the magnetic composite flocs, recovering the bimetallic magnetically loaded Fenton reagent by magnetic field separation, washing to neutrality and then reusing; then backwashing the ceramic membrane, the backwash waste liquid entering the ZIF-8 recovery tank, adding a mixture of ethanol and EDTA, stirring, centrifuging to separate the rare earth-doped amphoteric ZIF-8, drying and reusing; In step 7), the acidic elution solution is an H2SO4 solution with a concentration of 0.08–0.12 mol / L, and the stirring speed during the elution process is 180–220 r / min and the time is 15–25 min. The volume ratio of ethanol to EDTA mixture is 5–8:1, the EDTA concentration is 0.05–0.15 mol / L, the centrifugation speed is 2800–3200 r / min, and the time is 4–6 min.

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