Method for treating printing and dyeing wastewater by combining novel magnetic charcoal MBC-Fe3O4 composite material and Fenton-like technology

Abstract

The invention discloses a method for treating printing and dyeing wastewater by combining a novel magnetic charcoal MBC-Fe3O4 composite material with a Fenton-like technology. The method comprises the following steps: adding the magnetic charcoal MBC-Fe3O4 composite material into printing and dyeing wastewater while stirring, adjusting the pH value, then adding H2O2, and stirring for adsorption. According to the method, a magnetic charcoal adsorption process and a Fenton-like technology based on Fe3O4-H2O2 are effectively combined, an adsorption-regeneration integrated system is integrated for treating the dye wastewater, the adsorption performance of an MBC-Fe3O4 composite material and the Fenton-like catalyst characteristic of Fe3O4 are fully utilized, the adsorption effect on dye pollutants is achieved, and meanwhile, the adsorption performance of the MBC-Fe3O4 composite material and the Fenton-like catalyst characteristic of Fe3O4 are fully utilized. H2O2 is synchronously added into a reaction system to form a Fe3O4-H2O2 Fenton system, so that the material is regenerated, the treatment capacity of the system is effectively improved, and the treatment cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for treating printing and dyeing wastewater by combining a novel magnetic biochar MBC-Fe3O4 composite material with a Fenton-like technology. Background Art

[0002] Printing and dyeing wastewater is one of the main sources of water pollution in my country, with the characteristics of large water volume changes, deep chromaticity, high alkalinity, and complex composition. Traditional biological treatment methods are difficult to ensure that the effluent meets the discharge standards, and general physical methods (adsorption, membrane separation, etc.) are effective, but the treatment cost is high, which greatly increases the difficulty of treating printing and dyeing wastewater. In contrast, physical adsorption has obvious advantages in site requirements, operation management and treatment effect, and has become one of the main technologies for printing and dyeing wastewater treatment. Activated carbon, as a commonly used adsorbent, is widely used in the deep treatment of industrial wastewater due to its large specific surface area and strong adsorption capacity to ensure that the effluent meets the standards stably. However, the small particle size and light specific gravity of activated carbon lead to its disadvantages such as difficulty in separating it from the treated water during use, easy loss, inability to regenerate, and high cost, which limits its wide application. Biochar is widely used because of its wide source and low cost, but with the increasing demand for adsorption treatment, the activation and regeneration of biochar has also received increasing attention. In recent years, loading magnetic nanomaterials on adsorbent materials to improve their adsorption performance and magnetic separation characteristics has become a research hotspot. However, problems such as complex preparation conditions and difficulty in achieving mass production still exist. At the same time, finding a simple and effective way to regenerate adsorbent materials is also the key to improving adsorbent materials.

[0003] The Fenton process is a homogeneous chemical oxidation water treatment technology with simple process equipment. Its Fenton reagent is composed of a catalyst ferrous salt and an oxidant hydrogen peroxide (H2O2) in a certain ratio. The Fenton process is widely used in the treatment of industrial wastewater (such as pharmaceutical wastewater, printing and dyeing wastewater, landfill leachate, etc.), domestic sewage and drinking water, and has good treatment effects. However, the Fenton process has disadvantages such as the production of a large amount of iron sludge, the need to adjust the pH value before and after the reaction, and the loss of catalysts. Among them, the treatment cost of a large amount of iron sludge can reach 10%-50% of the total operating cost of the wastewater treatment project, so it is very important to reduce the generation of iron sludge. The use of iron-containing solid catalysts can avoid the continuous loss of catalysts during the Fenton reaction. For example, the catalyst Fe3O4 has the characteristics of high abundance, low cost, paramagnetism, and easy separation from the treated wastewater. In addition, the divalent iron and trivalent iron contained in Fe3O4 have positive catalytic activity. Therefore, the heterogeneous Fenton oxidation method is a promising conventional Fenton technology derivative process, also known as Fenton-like technology. Summary of the invention

[0004] Aiming at the deficiencies of the conventional powdered activated carbon (PAC) process and the Fenton process, the purpose of the present invention is to provide a method for treating printing and dyeing wastewater by combining a novel magnetic biochar MBC-Fe3O4 composite material with a Fenton-like technology. This method solves the problems in the activated carbon (PAC) technology, such as the difficulty in separating PAC from the treated water, high cost, and difficulty in regeneration. It also improves the problems of the conventional Fenton process, such as the continuous addition of iron salts and a large amount of sludge production. It has significant advantages such as simplicity, high efficiency, and economy. In addition, magnetic substances can also strengthen the flocculation reaction, improve the sedimentation rate and surface load, reduce the floor area of the sedimentation tank and the dosage of chemicals. The magnetic biochar converted from sewage plant sludge also helps to realize the resource utilization of organic solid waste.

[0005] To achieve the above invention purpose, the technical solution adopted by the present invention is: a method for treating printing and dyeing wastewater by combining a novel magnetic biochar MBC-Fe3O4 composite material with a Fenton-like technology, including the following steps: in the printing and dyeing wastewater, add the magnetic biochar MBC-Fe3O4 composite material under stirring, adjust the pH value, and then add H2O2, and stir and adsorb at 20°C - 25°C for 30 min - 300 min; the magnetic biochar MBC-Fe3O4 composite material is prepared from the biochar (MBC) obtained from sewage plant sludge.

[0006] Further, in the magnetic biochar MBC-Fe3O4 composite material, by mass ratio, Fe3O4:MBC = (1 - 3):1.

[0007] Further, adjust the pH value to 9 - 11.

[0008] Further, the preparation method of the magnetic biochar MBC-Fe3O4 composite material includes the following steps:

[0009] 1) Hydrothermally react the concentrated sludge from the sewage plant, dry it to obtain biochar (MBC);

[0010] 2) In the Fe 3+ / Fe 2+ reaction system, using biochar (MBC) as the carrier, add an alkaline solution medium, and mix and stir at 45°C - 55°C for 20 min - 30 min; in the Fe 3+ / Fe 2+ reaction system, by molar ratio, Fe 3+ :Fe 2+ = 2 mol:1 mol;

[0011] 3) After the reaction, let the obtained product stand and precipitate for 30 min - 40 min, remove the supernatant, and put the residue in an oven and dry it overnight;

[0012] 4) Take out the material, fully crush it, and rinse it with ultrapure water, then magnetically recover it until it is neutral.

[0013] Further, in step 1), the hydrothermal reaction is carried out at 160°C - 240°C for 0.5 h - 5 h; the drying is carried out in an oven at 100°C for 24 h - 26 h.

[0014] Further, the Fe 3+ / Fe 2+ reaction system is the FeCl3 / FeSO4 or FeCl3 / FeCl2 reaction system.

[0015] Further, the lye medium is NaOH.

[0016] Further, the printing and dyeing wastewater is methylene blue wastewater.

[0017] Furthermore, in the methylene blue wastewater, the concentration of methylene blue is 100 mg / L - 250 mg / L.

[0018] Furthermore, the addition amount of the magnetic biochar MBC-Fe3O4 composite material is 0.4 g / L - 0.60 g / L, and the addition amount of H2O2 is 0.3 mL / L - 0.5 mL / L.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. The method for treating printing and dyeing wastewater provided by the present invention is creative in combining the magnetic biochar MBC-Fe3O4 composite material with H2O2 to treat actual printing and dyeing wastewater. It is a physical and chemical treatment method combining adsorption-chemical oxidation regeneration, and no additional iron sludge is generated in the whole reaction system. Moreover, the composite material can be recycled.

[0021] 2. The method for treating printing and dyeing wastewater provided by the present invention makes full use of the adsorption performance of the magnetic biochar MBC-Fe3O4 composite material and the characteristics of Fe3O4 as a Fenton-like catalyst. While the composite material plays an adsorption role on dye pollutants, by synchronously adding H2O2 in the reaction system to form a Fe3O4-H2O2 Fenton-like system, the magnetic biochar MBC-Fe3O4 composite material can be regenerated, effectively degrade the substances adsorbed on the surface of the magnetic biochar MBC-Fe3O4 composite material, restore the adsorption capacity of the biochar (MBC), improve the treatment efficiency of the whole process, achieve the discharge standard of the effluent, reduce the operation cost of the process, and realize the resource utilization of organic solid waste while achieving efficient treatment of printing and dyeing wastewater.

[0022] 3. The method for treating printing and dyeing wastewater provided by the present invention uses the chemical co-precipitation method to prepare the magnetic biochar MBC-Fe3O4 composite material. Utilizing the magnetism of Fe3O4 in the composite material, the composite material can be rapidly recycled (within 30 s) under the action of an external magnetic field. During the treatment process of methylene blue wastewater, the treatment effect remains basically unchanged after 6 times of repeated use, and no additional iron sludge is generated in the treatment process.

[0023] 4. The method for treating printing and dyeing wastewater provided by the present invention organically combines the advantages of the biochar process and the conventional Fenton process, solves the problems in the traditional activated carbon (PAC) technology, such as the difficulty and high cost of separating PAC from the treated water and the difficulty of regeneration, and improves the problems of the conventional Fenton process, such as the continuous addition of iron salts and the large amount of sludge production. The present invention has significant advantages such as simplicity, high efficiency, and economy, and can be widely applied to the field of printing and dyeing wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a comparison chart of the treatment effects of composite materials with different Fe3O4 / MBC mass ratios on the concentration of methylene blue dye.

[0025] Figure 2 It is a comparison chart of the treatment effects of composite materials with different Fe3O4 / MBC mass ratios on the COD of methylene blue.

[0026] Figure 3 It is the treatment effect diagram of the methylene blue wastewater dye concentration when the magnetic biochar MBC-Fe3O4 composite material of the present invention is reused.

[0027] Figure 4 It is the treatment effect diagram of the COD of methylene blue wastewater when the magnetic biochar MBC-Fe3O4 composite material of the present invention is reused. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] Example 1 A magnetic biochar MBC-Fe3O4 composite material (1) A magnetic biochar MBC-Fe3O4 composite material with a Fe3O4 / MBC mass ratio of 1

[0030] The preparation method is as follows:

[0031] 1. Take the concentrated sludge from the sewage treatment plant and conduct a hydrothermal reaction at 200 °C for 2 h. After the reaction, dry the product in an oven at 100 °C for 24 h to obtain biochar (MBC).

[0032] 2. Add FeCl3 (7.8 g, 28 mmol) and FeSO4 (3.9 g, 14 mmol) to 400 mL of water, mix well at a temperature of 50 °C, then add biochar (MBC) (0.25 g), and continuously stir for 60 min. Then, add NaOH solution (100 mL, 4 mol / L, within 10 min) dropwise to the mixed solution, and then continue the reaction for 20 min.

[0033] 3. After the reaction is completed, let the resulting reaction solution stand and precipitate for 30 min, remove the supernatant, and place the residue in an oven to dry overnight at 100 °C.

[0034] 4. Take out the material, thoroughly crush it, repeatedly rinse it with ultrapure water until neutral, and at the same time magnetically recover it with a neodymium iron boron magnet to obtain a magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4:MBC = 1:1.

[0035] 5. Place the obtained material in an oven and dry it at 100 °C until constant weight, then seal and store it.

[0036] (2) Magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4 / MBC of 2

[0037] The preparation method is as follows:

[0038] 1. Take the concentrated sludge from the sewage treatment plant and conduct a hydrothermal reaction at 200 °C for 2 h. After the reaction, dry the product in an oven at 100 °C for 24 h to obtain biochar (MBC).

[0039] 2. Add FeCl3 (7.8 g, 28 mmol) and FeSO4 (3.9 g, 14 mmol) to 400 mL of water, mix well at a temperature of 50 °C, then add biochar (MBC) (0.125 g), and continuously stir for 60 min. Then, add NaOH solution (100 mL, 4 mol / L, within 10 min) dropwise to the mixed solution, and then continue the reaction for 20 min.

[0040] 3. After the reaction is completed, let the resulting reaction solution stand and precipitate for 30 min, remove the supernatant, and place the residue in an oven to dry overnight at 100 °C.

[0041] 4. Take out the material, thoroughly crush it, repeatedly rinse it with ultrapure water until neutral, and at the same time magnetically recover it with a neodymium iron boron magnet to obtain a magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4:MBC = 2:1.

[0042] 5. The obtained material is placed in an oven and dried at 100 °C until constant weight, then sealed and stored.

[0043] (III) Magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4 / MBC of 3

[0044] The preparation method is as follows:

[0045] 1. Take the concentrated sludge from the sewage treatment plant and carry out hydrothermal reaction at 200 °C for 2 h. After the reaction, dry the product in an oven at 100 °C for 24 h to obtain biochar (MBC).

[0046] 2. Add FeCl3 (7.8 g, 28 mmol) and FeSO4 (3.9 g, 14 mmol) to 400 mL of water, mix evenly at a temperature of 50 °C, then add biochar (MBC) (0.083 g), and continuously stir for 60 min. Then, add NaOH solution (100 mL, 4 mol / L, within 10 min) dropwise to the mixed solution, and then continue to react for 20 min.

[0047] 3. After the reaction is completed, let the obtained reaction solution stand and precipitate for 30 min, remove the supernatant, and place the residue in an oven and dry it overnight at 100 °C.

[0048] 4. Take out the material, crush it thoroughly, rinse it repeatedly with ultrapure water until neutral, and at the same time recover it magnetically with a neodymium iron boron magnet to obtain a magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4:MBC = 3:1.

[0049] 5. The obtained material is placed in an oven and dried at 100 °C until constant weight, then sealed and stored.

[0050] Example 2 A magnetic biochar MBC-Fe3O4 composite material (I) Magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4 / MBC of 1

[0051] The preparation method is as follows:

[0052] 1. Take the concentrated sludge from the sewage treatment plant and carry out hydrothermal reaction at 200 °C for 2 h. After the reaction, dry the product in an oven at 100 °C for 24 h to obtain biochar (MBC).

[0053] 2. Add FeCl3 (7.8 g, 28 mmol) and FeCl2 (2.8 g, 14 mmol) to 400 mL of water, mix evenly at a temperature of 50 °C, then add biochar (MBC) (0.25 g), and continuously stir for 60 min. Then, add NaOH solution (100 mL, 4 mol / L, within 10 min) dropwise to the mixed solution, and then continue to react for 20 min.

[0054] 3. After the reaction, let the resulting reaction solution stand and precipitate for 30 min, discard the supernatant, and put the residue in an oven and dry it overnight at 100 °C.

[0055] 4. Take out the material, fully crush it, repeatedly rinse it with ultrapure water until neutral, and at the same time magnetically recover it with a neodymium iron boron magnet to obtain a magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4:MBC = 1:1, labeled as Fe3O4 / MBC = 1.

[0056] 5. Put the obtained material in an oven and dry it to constant weight at 100 °C, then store it sealed.

[0057] (2) Magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4 / MBC of 2

[0058] The preparation method is as follows:

[0059] 1. Take the concentrated sludge from the sewage treatment plant and carry out hydrothermal reaction at 200 °C for 2 h. After the reaction, dry the product in an oven at 100 °C for 24 h to obtain biochar (MBC).

[0060] 2. Add FeCl3 (7.8 g, 28 mmol) and FeCl2 (2.8 g, 14 mmol) to 400 mL of water, mix evenly at a temperature of 50 °C, then add biochar (MBC) (0.125 g), and continuously stir for 60 min. Then, add NaOH solution (100 mL, 4 mol / L, within 10 min) dropwise to the mixed solution, and then continue the reaction for 20 min.

[0061] 3. After the reaction, let the resulting reaction solution stand and precipitate for 30 min, discard the supernatant, and put the residue in an oven and dry it overnight at 100 °C.

[0062] 4. Take out the material, fully crush it, repeatedly rinse it with ultrapure water until neutral, and at the same time magnetically recover it with a neodymium iron boron magnet to obtain a magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4:MBC = 2:1, labeled as Fe3O4 / MBC = 2.

[0063] 5. Put the obtained material in an oven and dry it to constant weight at 100 °C, then store it sealed.

[0064] (3) Magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4 / MBC of 3

[0065] The preparation method is as follows:

[0066] 1. Take the concentrated sludge from the sewage treatment plant and carry out hydrothermal reaction at 200 °C for 2 h. After the reaction, dry the product in an oven at 100 °C for 24 h to obtain biochar (MBC).

[0067] 2. Add FeCl3 (7.8 g, 28 mmol) and FeCl2 (2.8 g, 14 mmol) to 400 mL of water, mix well at a temperature of 50 °C, then add magnetic biochar (MBC) (0.083 g), and continuously stir for 60 min. Then, add NaOH solution (100 mL, 4 mol / L, within 10 min) dropwise to the mixed solution, and then continue the reaction for 20 min.

[0068] 4. After the reaction is completed, let the obtained reaction solution stand and precipitate for 30 min, remove the supernatant, and put the residue in an oven to dry overnight at 100 °C.

[0069] 7. Take out the material, fully crush it, repeatedly rinse it with ultrapure water until neutral, and at the same time recover it magnetically with a neodymium iron boron magnet to obtain a magnetic biochar MBC-Fe3O4 composite material with a mass ratio of Fe3O4:MBC = 3:1, marked as Fe3O4 / MBC = 3.

[0070] 10. Put the obtained material in an oven and dry it at 100 °C until it reaches a constant weight, then seal and store it.

[0071] Example 3 Method for treating printing and dyeing wastewater by combining novel magnetic biochar MBC-Fe3O4 composite material with Fenton-like technology (1) Influence of magnetic biochar MBC-Fe3O4 composite materials with different mass ratios on treating printing and dyeing wastewater

[0072] The method is as follows:

[0073] Place a container filled with 500 mL of methylene blue wastewater with a concentration of 200 mg / L in a 20 °C constant temperature water bath. Under mechanical stirring, add 0.25 g of the Fe3O4 / MBC = 1, Fe3O4 / MBC = 2, and Fe3O4 / MBC = 3 composite materials prepared in Example 2 respectively, adjust the pH value to 9, and at the same time add 0.15 mL, 0.15 mL, and 0.2 mL of H2O2 with a concentration of 10 mmol / L respectively. Stir and adsorb at 20 °C for 30 min - 300 min; take samples regularly and measure the methylene blue concentration and COD value in the water.

[0074] The treatment effect comparison of composite materials with different Fe3O4 / MBC mass ratios on the concentration of methylene blue dye in the wastewater is as Figure 1 ; The treatment effect comparison of the methylene blue COD in the wastewater is as Figure 2 .

[0075] Figure 1 and Figure 2It is shown that the addition of H2O2 significantly enhances the degradation effect of the magnetic biochar MBC-Fe3O4 composite on methylene blue wastewater. After 3 hours of reaction, methylene blue was almost completely degraded in the system with the addition of H2O2, while the removal rates of methylene blue by the three composites without the addition of H2O2 were 71.25%, 41.24% and 31.98%, indicating that the introduction of H2O2 greatly improved the degradation efficiency. In addition, the addition of H2O2 also significantly improved the removal effect of COD, and the COD of the treated effluent was stable at 47.72 mg / L, 43.95 mg / L and 43.34 mg / L, much lower than 98.88 mg / L, 194.9 mg / L and 226.47 mg / L in the system without the addition of H2O2. These data fully prove that the synergistic effect of H2O2 and MBC-Fe3O4 can significantly improve the degradation efficiency of pollutants and optimize the wastewater treatment effect. It can be seen that when H2O2 is synchronously added to the system using the magnetic biochar MBC-Fe3O4 composite, the treatment capacity of the system for methylene blue is greatly improved compared with the application of the pure composite material.

[0076] Figure 1 and Figure 2 It is shown that there are obvious differences in the degradation effect of magnetic biochar MBC-Fe3O4 composites with different Fe3O4 / MBC mass ratios on methylene blue. When the composite material is used alone (without the addition of H2O2), the degradation efficiency of methylene blue shows an obvious gradient with the change of the ratio. The removal rate of the most efficient material (Fe3O4 / MBC = 1) reaches 71.25%, which is significantly better than Fe3O4 / MBC = 2 (41.24%) and Fe3O4 / MBC = 3 (31.98%), being 72.76% and 28.97% higher respectively, confirming that optimizing the mass ratio of Fe3O4 to MBC in the material is crucial for improving the treatment effect. It should be noted that after the introduction of H2O2, the three magnetic biochar MBC-Fe3O4 composites with different mass ratios all achieved nearly complete degradation of methylene blue (below the detection limit), and the final COD was stable at a similar level of 47.72 mg / L - 43.34 mg / L, indicating that the strong oxidation effect of H2O2 can effectively make up for the deficiency of the intrinsic activity of the composite material. This phenomenon is particularly reflected in Fe3O4 / MBC = 2 and Fe3O4 / MBC = 3 with poor initial performance, and the improvement amplitude of their COD removal rate is significantly higher than that of Fe3O4 / MBC = 1 when using the composite material alone, indicating that the synergistic effect of H2O2 on low-activity materials is more significant. It can be seen that when the mass ratio of Fe3O4 / MBC in the composite material is 1, the comprehensive efficiency reaches the best. Therefore, the present invention preferably selects the Fe3O4 / MBC mass ratio of 1.

[0077] (II) Reusability

[0078] The method is as follows:

[0079] At the end of each cycle of the adsorption experiment, the magnetic biochar MBC-Fe2O4 composite material was separated and recovered using a neodymium iron boron magnet. The magnetic biochar MBC-Fe3O4 composite material was appropriately washed with ultrapure water and used for the next cycle reaction according to the method of Example (1). The magnetic biochar MBC-Fe3O4 composite material was repeatedly recovered and used 9 times, and the COD and dye concentration of the effluent were measured for each cycle.

[0080] The treatment effect of the magnetic biochar MBC-Fe3O4 composite material on the dye concentration of methylene blue wastewater during repeated use was as Figure 3 , and the treatment effect on the COD of methylene blue wastewater during repeated use was as Figure 4 .

[0081] Figure 3 and Figure 4 showed that when the magnetic biochar MBC-Fe3O4 composite material was repeatedly used, the treatment effect of the system was stable. Among them, when the mass ratio of Fe3O4 / MBC in the composite material was 1, the repeated use effect of the treatment system for methylene blue wastewater was the best. The treatment effect remained basically unchanged for the first 6 times of repeated use, and the treatment effect decreased slightly for the 7th to 9th times of repeated use.

[0082] It is easy for those skilled in the art to understand that on the premise of no conflict, the above advantageous ways can be freely combined and superimposed. The above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above is only the preferred implementation manner of the present application. It should be noted that for those of ordinary skill in the art in the technical field of the present application, several improvements and modifications can be made without departing from the technical principle of the present application, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A method for treating printing and dyeing wastewater by combining a novel magnetic biochar MBC-Fe3O4 composite material with the Fenton-like technology, characterized in that, The method comprises the following steps: adding the magnetic biochar MBC-Fe3O4 composite material into the printing and dyeing wastewater under stirring, adjusting the pH value, and then adding H2O2, and stirring and adsorbing at 20°C - 25°C for 30 min - 300 min; the magnetic biochar MBC-Fe3O4 composite material is prepared from the biochar MBC obtained from the sewage treatment plant sludge.

2. The method according to claim 1, characterized in that, In the magnetic biochar MBC-Fe3O4 composite material, by mass ratio, Fe3O4:MBC = (1 - 3):

1.

3. The method according to claim 1, wherein Adjust the pH value to 9 - 11.

4. The method according to claim 1, characterized in that, The preparation method of the magnetic biochar MBC-Fe3O4 composite material comprises the following steps: 1) Hydrothermally reacting the concentrated sludge from the sewage treatment plant, and drying to obtain biochar MBC; 2) In Fe 3+ / Fe 2+ reaction system, using biochar MBC as the carrier, adding an alkaline solution medium, mixing and stirring at 45°C - 55°C for 20 min - 30 min; the Fe 3+ / Fe 2+ reaction system, by molar ratio, Fe 3+ :Fe 2+ = 2 mol:1 mol; 3) After the reaction ends, let the obtained product stand and precipitate for 30 min - 40 min, remove the supernatant, and put the residue in an oven to dry overnight; 4) Take out the material, fully crush it, and rinse it with ultrapure water and magnetically recover it to neutral.

5. The method according to claim 4, wherein In step 1), the hydrothermal reaction is carried out at 160°C - 240°C for 0.5 h - 5 h; the drying is carried out in an oven at 100°C for 24 h - 26 h.

6. The method according to claim 4, wherein The described Fe 3+ / Fe 2+ The reaction system is the FeCl3 / FeSO4 or FeCl3 / FeCl2 reaction system.

7. The method according to claim 4, characterized in that, The lye medium is NaOH.

8. The method according to any one of claims 1-7, characterized in that, The printing and dyeing wastewater is methylene blue wastewater.

9. The method according to claim 8, wherein In the methylene blue wastewater, the concentration of methylene blue is 100 mg / L - 250 mg / L.

10. The method according to claim 9, wherein The addition amount of the magnetic biochar MBC-Fe3O4 composite material is 0.4 g / L - 0.60 g / L, and the addition amount of H2O2 is 0.3 mL / L–0.5 mL / L.

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