A polydopamine modified biochar loaded Fe-Cu sodium alginate microsphere and a preparation method thereof

Abstract

The application discloses a preparation method of polydopamine modified biochar loaded Fe-Cu sodium alginate microspheres, and biochar is prepared, the biochar is modified by polydopamine, the polydopamine modified biochar is loaded with Fe-Cu, and finally, the polydopamine modified biochar loaded Fe-Cu sodium alginate microspheres are obtained. The preparation method can be used for different particle sizes of sodium alginate microspheres, the prepared sodium alginate microspheres have the adsorption functions of ammonia nitrogen, nitrate nitrogen, chlorobenzene, phosphorus, chromium ions and lead ions, anaerobic ammonia oxidation granular sludge is prepared by taking the sodium alginate microspheres as a core, the sludge granule is provided with large density and good morphological support, sludge swelling problems are avoided, and the settling performance is improved; the adsorption capacity of the sludge to organic matters, ammonia nitrogen and heavy metals is enhanced, the effect of sewage treatment is improved, meanwhile, the sludge is a biodegradable material, and no secondary pollution is caused in the use process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sewage treatment, and particularly relates to a polydopamine modified biochar loaded Fe-Cu sodium alginate microsphere and a preparation method thereof. BACKGROUND

[0002] When an anaerobic ammonia oxidation process is used to treat nitrogen-containing wastewater, a large amount of N2 produced by anaerobic ammonia oxidation bacteria cannot be released, and gas pockets are formed in the interior of granular sludge or attached to the surface of the granular sludge, resulting in a decrease in the density of the granular sludge, floating, and then loss with the effluent, which not only increases the mass concentration of suspended solids in the effluent, affects the treatment effect, and even causes the collapse of the system. In addition, the anaerobic ammonia oxidation process produces about 11% of nitrate byproducts, which affects the discharge standard of the process. These seriously restrict the large-scale promotion and application of the anaerobic ammonia oxidation process.

[0003] There are many studies on the characteristics of anaerobic ammonia oxidation granular sludge and the removal of nitrate byproducts in the prior art, for example, the existing patent CN201510640931.2 discloses a culture method of anaerobic ammonia oxidation granular sludge with a hydroxyapatite core, and by adding calcium ions and high-concentration phosphate ions in the influent, granular sludge with a hydroxyapatite core, good settling performance, high mechanical strength, large particle size, and dense bacteria load can be cultured, and high-efficiency retention of anaerobic ammonia oxidation bacteria under high flow rate can be realized. However, calcium chloride and high-concentration phosphate are needed to be added during the culture process, and high phosphate concentration is easy to cause inhibition of anaerobic ammonia oxidation bacteria, and the process does not involve deep removal of nitrate byproducts.

[0004] Although the existing public documents disclose the treatment method of adding zero-valent iron powder to realize the removal of nitrate byproducts in the anaerobic ammonia oxidation process, there are still some shortcomings and challenges: (1) Too much iron ion release may have a toxic effect on the microbial community, inhibit the activity of some microorganisms, and affect the biodegradation efficiency of the system. Especially, some sensitive bacteria (such as nitrifying bacteria and denitrifying bacteria) have low tolerance to high-concentration iron ions, which may lead to failure of important biological processes in the system. (2) The chemical properties of Fe powder in wastewater may not be stable and may easily undergo oxidation to form iron hydroxide or other insoluble substances, affecting the long-term stability and effect of the particles in the granules. The dissolution and migration process of iron may cause the destruction of the granule structure, leading to the disintegration or loosening of the sludge granules. (3) Although the introduction of iron powder can improve the settling performance to some extent, it may induce sludge bulking under certain conditions, especially when the iron ion concentration is high, which may cause the sludge flocs to become loose and the granule structure to be unstable. Too much iron salt may cause the sludge to settle faster, but at the same time, it reduces the flexibility of the granules, making them fragile. In summary, although Fe powder can bring certain performance improvement in the activated granular sludge process, its introduction needs to be reasonably designed and controlled to avoid adverse effects on the biodegradation function, settling performance, and subsequent sludge disposal of the system. SUMMARY

[0005] To solve at least one of the above problems, the present application provides a kind of polydopamine modified biochar loaded Fe-Cu sodium alginate microspheres and its preparation method.

[0006] To achieve the above purpose, the following technical means are adopted:

[0007] The first aspect of the present application provides a preparation method of polydopamine modified biochar loaded Fe-Cu sodium alginate microspheres, comprising the following steps:

[0008] (1) Preparation of biochar: biomass material is used, carbonized under nitrogen or inert gas environment at a temperature of 450-600 DEG C, naturally cooled, crushed, and screened by screen mesh to obtain biochar powder with a particle size of 0.5-1 mm, dried and ready for use;

[0009] (2) Polydopamine coating: disperse the biochar powder in Tris buffer solution, uniformly disperse by ultrasonic, and obtain biochar particle suspension; add dopamine in deionized water according to the ratio of 100 mL:1-2 g, stir until completely dissolved; adjust the pH to 8.5-9.0 with sodium hydroxide to obtain dopamine solution; gradually add the dopamine solution to the biochar, monitor with pH meter to ensure the suitability of the reaction environment; stir at room temperature for 12-24 hours, expose to air for oxidation; when the color gradually changes from light yellow to dark brown, it indicates that the polymerization is complete, and the polydopamine coating is gradually deposited on the surface of the biochar particles;

[0010] (3) Fe-Cu ion loading: the polydopamine modified biochar is soaked in a mixed solution of FeCl3 and CuCl2 with a ratio of 1-2 g: 20 mL, and stirred for 4-6 hours; after washing with deionized water and drying, the polydopamine modified biochar loaded with Fe-Cu is obtained;

[0011] (4) Preparation of sodium alginate microspheres: sodium alginate is dissolved in deionized water at a ratio of 1-2 g: 50 mL, and the polydopamine modified biochar loaded with Fe-Cu is mixed with the sodium alginate solution at a ratio of 1-2 g: 100 mL; the mixed solution is dropped into a hardening liquid at a speed of 1.5-2.5 mL / min to form microspheres; the microspheres are placed in the hardening liquid for 30 min, and then taken out after hardening, and washed with water to obtain polydopamine modified biochar loaded with Fe-Cu sodium alginate microspheres.

[0012] In some embodiments of the present application, in step (1), the biomass material is waste sludge or agricultural and forestry waste biomass.

[0013] In some embodiments of the present application, in step (3), the mixed solution of FeCl3 and CuCl2 is prepared by mixing a 0.1-0.2 M FeCl3 solution with a 0.1-0.2 M FeCl3 solution.

[0014] In some embodiments of the present application, in step (4), the hardening liquid is a calcium chloride solution with a concentration of 25-30 g / L.

[0015] In some embodiments of the present application, in step (4), the distance between the mixed solution and the hardening liquid is kept at 3-5 cm when the mixed solution is dropped into the hardening liquid to form microspheres.

[0016] In some embodiments of the present application, in steps (1) and (3), the drying condition is 50-80°C, and the drying time is 10-15 hours.

[0017] The second aspect of the present application provides polydopamine modified biochar loaded with Fe-Cu sodium alginate microspheres prepared by the method according to the first aspect.

[0018] The third aspect of the present application provides the use of polydopamine modified biochar loaded with Fe-Cu sodium alginate microspheres prepared by the method according to the second aspect in preparing anaerobic ammonia oxidation granular sludge. The sodium alginate microspheres prepared by using polydopamine modified activated carbon loaded with iron-copper (Fe-Cu) powder as the core of active granular sludge (AGS) can significantly improve the structural stability, adsorption performance and biocompatibility of the sludge, and provide a slow-release iron ion effect to avoid microbial toxicity.

[0019] The obtained anaerobic ammonia oxidation granular sludge is applied in sewage treatment, and ammonia nitrogen, nitrate nitrogen, COD, phosphorus and heavy metal ions can be effectively removed.

[0020] Advantages of the present application

[0021] Compared with the prior art, the present application has the following advantages: the present application uses polydopamine (PDA) modified activated carbon to load iron-copper (Fe-Cu) powder to make sodium alginate (SA) microspheres, the microspheres formed by sodium alginate can firmly wrap the activated carbon and iron powder, the support structure is stable, and the loss of the core material is reduced. The polydopamine coating enhances the adhesion between materials, so that the internal components of the microspheres are not easy to fall off.

[0022] The use of polydopamine modification and the wrapping of sodium alginate allows the slow release of iron ions from the iron-copper particles, avoiding the inhibition of microbial activity due to excessive iron concentration; and the sustained release of iron ions helps to maintain good phosphorus removal performance, improving the operational stability of the system and preventing the secondary release of phosphorus in application.

[0023] The biocompatibility of polydopamine promotes the rapid attachment and growth of microbial communities on the surface of the microspheres, accelerating the maturation of granular sludge in application; the porous structure on the surface of the microspheres provides more attachment sites for microorganisms, promoting the formation of biofilms and improving the organic matter degradation efficiency of the system.

[0024] The porous structure of activated carbon in the sodium alginate microspheres enhances the adsorption capacity of organic matter, ammonia nitrogen and heavy metals, improving the effect of sewage treatment. The iron-copper particles wrapped by polydopamine promote the catalytic oxidation-reduction reaction, improving the COD degradation and phosphorus precipitation effect.

[0025] Sodium alginate and polydopamine are both biodegradable materials, and will not remain in the environment for a long time in use, and have high recycling and regeneration potential, meeting the requirements of sustainable development.

[0026] When it is used as the core to prepare sludge particles, the sodium alginate microspheres provide a larger density and good morphological support for the sludge particles, avoid the problem of sludge swelling, and improve the settling performance; this helps to form compact and stable sludge particles, improve the settling speed of sludge and the separation efficiency. The core structure of the polydopamine-activated carbon-iron-copper microspheres enables the granular sludge to have stronger resistance, which can cope with sudden organic load or pollutant concentration fluctuations in wastewater treatment; this enhanced particle stability helps to extend the operation cycle of the sludge system and reduce the frequency of shutdown maintenance. The catalytic effect of the iron-copper particles can effectively promote the electron transfer in the denitrification process, improve the denitrification efficiency. The synergistic effect of polydopamine and activated carbon enhances the removal of phosphorus, ensures the simultaneous removal of nitrogen and phosphorus, and improves the effluent water quality. It does not cause secondary pollution during sludge aging or disposal, which is conducive to environmental protection; the core material is easy to recover and regenerate, and the structure of the microspheres is convenient for recovery after wastewater treatment through sedimentation or screening, reducing the loss of core materials. The recovered microspheres can restore the adsorption capacity through simple regeneration treatment (such as acid washing, alkali washing, high-temperature sintering, etc.), further reducing the operation cost. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Pictures of Fe-Cu loaded polydopamine modified biochar in Example 1 of the present application are shown;

[0028] Figure 2 Pictures of Fe-Cu loaded polydopamine modified biochar in Example 1 of the present application are shown;

[0029] Figure 3 Pictures of Fe-Cu loaded polydopamine modified biochar in Example 1 of the present application are shown;

[0030] Figure 4 Pictures of Fe-Cu loaded polydopamine modified biochar in Example 1 of the present application are shown;

[0031] Figure 5 The structure of the anaerobic continuous stirred reactor in Example 2 of the present application is shown; wherein 1, stirring reaction cavity; 2, motor; 3, stirring shaft; 4, stirring fan blade; 5, water inlet pipe; 6, water outlet pipe; 7, nitrogen pipe;

[0032] Figure 6 The average regeneration rate comparison chart of the treated sodium alginate microspheres under different regeneration treatment methods in Example 2 of the present application is shown;

[0033] Figure 7 The removal effect of ammonia nitrogen after the formation of stable activated granular sludge in the reactor in Example 3 is shown;

[0034] Figure 8 The removal of nitrate after the formation of stable activated granular sludge in the reactor in Example 3 is shown.

[0035] Figure 9 Pictures of anaerobic activated granular sludge recovered after wastewater treatment in Example 3 are shown. DETAILED DESCRIPTION

[0036] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present application, and are not intended to limit the scope of what the inventors regard as their application nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (for example, amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is weight average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric. Standard abbreviations can be used, e.g., kb (kilobase), bp (base pair), dNTP (deoxynucleotide triphosphate), PCR (polymerase chain reaction), cP (centipoise), rpm (revolutions per minute), and the like.

[0037] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this application belongs. As used herein, the following reference works are incorporated by reference: all publications and patent documents (including issued patents) cited in this application. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many of the specific details given herein. Such experimentation will not require undue experimentation given the benefit of the disclosure herein.

[0038] The technical solutions of the present application are further described in detail below in conjunction with the specific embodiments.

[0039] Example 1 Preparation of sodium alginate microspheres

[0040] The preparation steps of sodium alginate microspheres are as follows:

[0041] (1) Preparation of biochar: Biomass material: waste sludge is used. A tube furnace or high-temperature furnace is used to prevent combustion in a nitrogen or inert gas environment. The furnace temperature is raised to 500°C and maintained for 3 hours to ensure complete carbonization of the biomass. It is naturally cooled to room temperature. The prepared biochar is crushed and sieved using a screen to obtain biochar powder with a particle size of 0.5-1 mm to ensure uniformity. Dry at 60°C for 12 hours to remove moisture.

[0042] (2) Polydopamine coating: The biochar powder obtained in (1) is dispersed in Tris buffer solution, and is uniformly dispersed by ultrasonic to obtain a biochar particle suspension; in a 250 mL beaker, 100 mL of deionized water is added, 1 g of dopamine is added, and stirring is performed until complete dissolution; sodium hydroxide is used to adjust the pH to 8.5-9.0; the dopamine solution is gradually added to the biochar, and a pH meter is used to monitor to ensure the suitability of the reaction environment; stirring is maintained for 24 hours, and oxidation is performed in air; when the color gradually changes from light yellow to dark brown, it indicates that the polymerization is complete, and the polydopamine coating is gradually deposited on the surface of the biochar particles to form a polydopamine modified biochar.

[0043] (3) Fe-Cu ion loading: 10 g of the polydopamine modified biochar is soaked in 200 mL of a mixed solution of 0.1 M FeCl3 and 0.1 M CuCl2, stirring is performed at 300 rpm for 2 hours; deionized water is used for washing 3 times to remove unbound metal ions, and then drying is performed at 60°C for 12 hours to obtain Fe-Cu loaded polydopamine modified biochar, as shown in Figure 1 .

[0044] (4) Preparation of sodium alginate microspheres: 2 g of sodium alginate is dissolved in 100 mL of deionized water, and stirring is performed until complete dissolution. 1 g of the Fe-Cu loaded polydopamine modified biochar is mixed with the sodium alginate solution, and stirring is performed until uniform; the mixed solution is dropped into a hardening solution of calcium chloride with a concentration of 30 g / L at a rate of 2 mL / min using a dropper, and the drop distance is maintained at 3-5 cm to form microspheres. The microspheres are left to stand in the hardening solution for 30 minutes to ensure complete hardening of the microspheres. The hardened microspheres are taken out of the calcium chloride solution and placed in deionized water for washing 3 times to remove excess sodium alginate and calcium ions. The washed microspheres are dried at 60°C for 12 hours until the microspheres are completely dried. The polydopamine modified biochar loaded Fe-Cu sodium alginate microspheres are obtained.

[0045] The different particle sizes of the prepared sodium alginate microspheres are as shown in Figure 2 , the SEM image of the porous structure on the surface of the sodium alginate microspheres is as shown in Figure 3 , and the XDR image of the sodium alginate microspheres is as shown in Figure 4 .

[0046] The sodium alginate microspheres prepared in this example are used for adsorption tests of ammonia nitrogen, nitrate nitrogen, chlorobenzene, phosphorus, chromium ions and lead ions, and the results are as shown in Table 1.

[0047] Table 1: Results of ammonia nitrogen adsorption and nitrate nitrogen adsorption of sodium alginate microspheres

[0048]

[0049] Example 2 Cultivation of ANAMMOX granular sludge

[0050] The steps for cultivating ANAMMOX granular sludge are as follows:

[0051] (1) Take the ANAMMOX strain Bacillus DMF-4 (CGTCC No. M2022413) preserved on April 11, 2022, in the China General Microbiological Culture Collection Center, and cultivate it in an anaerobic medium at 30°C for 1-2 weeks to activate it; the anaerobic medium comprises NH4Cl: 1000 mg / L, NaNO3: 500 mg / L, KH2PO4: 50 mg / L, KCl: 50 mg / L, NaHCO3: 100 mg / L, and 2 mL / L of a trace element solution, wherein the trace elements include H3BO3R, MnC12, ZnSO4, Na3MoO4, and H2SeO3. Bacillus sp.

[0052] (2) Under an anaerobic environment, inoculate the activated ANAMMOX strain Bacillus DMF-4 (CGTCC No. M2022413) into the culture medium at a volume fraction of 5%, and the culture medium comprises NH4Cl: 1000 mg / L, NaNO3: 500 mg / L, KH2PO4: 50 mg / L, KCl: 50 mg / L, NaHCO3: 100 mg / L, and a trace element solution. Add 10% (mass volume fraction) of the polydopamine-modified biochar loaded with Fe-Cu sodium alginate microspheres prepared in Example 1; Bacillus sp.

[0053] (3) Use an anaerobic continuous stirring reactor to cultivate and monitor the sodium alginate microspheres, sludge, and water obtained after step (2), and maintain the reactor at a constant temperature of 30°C during the cultivation process. Use a nitrogen gas sealing system to avoid air entering, so that the reactor is in an anoxic state. Regularly check the airtightness of the reactor, and supplement nitrogen gas as necessary to maintain the anaerobic environment. Detect the NH4 + and NO3 - concentrations in the culture medium every week to ensure that they are within the ranges of 100-1000 mg / L and 50-300 mg / L, respectively. Ensure that the reactor temperature is stable and avoid fluctuations.

[0054] After 3 weeks of continuous cultivation, collect the ANAMMOX granular sludge with the sodium alginate microsphere core using gravity sedimentation or centrifugation.

[0055] The anaerobic continuous stirring reactor is, for example, Figure 5 ​​As shown, including stirring reaction cavity 1, motor 2, with motor 2 connected stirring shaft 3, the end of stirring shaft 3 is provided with stirring fan blade 4, stirring reaction cavity 1 wall is connected with water inlet pipe 5, water outlet pipe 6, nitrogen pipe 7.

[0056] The settling ratio of the sludge particles was about 30%, the settling time was about 6 min, and the degree of granulation was 91%. A series of characterization analyses were performed on the metal element distribution, metal valence, surface phase and crystal structure, specific surface area, and magnetic saturation strength of the sludge particles. The metal element distribution is shown in Table 2, and the distribution of each element is relatively uniform, and the loading condition is good.

[0057] Table 2 Metal element distribution in granular sludge

[0058]

[0059] XRD analysis was performed, and it was found that the metals and compounds were mainly FeS, CuFe2S3, (Cu, Fe)S2, and FeS 2， Cu, etc.

[0060] The specific surface area of the sludge particles was 331 m 3 g-1, the total pore volume was 1.72 cm 3 g-1, the micropore volume was 1.09 cm 3 g-1, and the average pore size was 32 nm.

[0061] The sludge particles were characterized by magnetic hysteresis loop, and it was found that the saturation magnetization was 15.62 emu g-1. The material has magnetism and has magnetic separation capacity, and can be conveniently recycled and used in other water treatment processes. After the microspheres in the sewage treatment are recovered by sedimentation or screening, the recovered microspheres are regenerated to restore the adsorption capacity, and the average regeneration rate of the microspheres treated by different methods such as acid washing, alkali washing, high temperature, crosslinking, and elution is as Figure 6 shown.

[0062] The results show that: through regeneration treatment by acid washing, alkali washing, high temperature, crosslinking, etc., the regeneration rate reaches about 90%, and the regeneration rate by elution method is slightly lower, about 70%.

[0063] Example 3 Treatment effect of anaerobic ammonia oxidation granular sludge on sewage in an anaerobic continuous stirring reactor

[0064] The anaerobic ammonia oxidation granular sludge cultured in Example 2 was inoculated into a stirring reactor as Figure 3The stirring reaction cavity of the shown anaerobic continuous stirring reactor, the water inlet pipe into the reactor into sewage, sewage water index is ammonia nitrogen: 35-60 mg / L, nitrate nitrogen: 18-23 mg / L. Start the motor, stir the anaerobic ammonia oxidation granular sludge in the stirring reaction cavity, so that it reacts with the sewage, within 60 days of reaction, take the sewage in the water pipe every day for detection, the results are shown in Figure 7 and Figure 8 shown.

[0065] The results show that: after the anaerobic ammonia oxidation granular sludge treatment, the average removal rate of ammonia nitrogen in 60 days is 91.9%; the average removal rate of nitrate nitrogen is 89%.

[0066] The recovered anaerobic active granular sludge after sewage treatment is shown in Figure 9 .

[0067] Example 4 Application of anaerobic ammonia oxidation granular sludge in sewage treatment

[0068] The anaerobic ammonia oxidation granular sludge is used to treat the high ammonia nitrogen wastewater discharged by the chemical enterprises in the industrial park wastewater treatment plant. The water inlet index: chemical oxygen demand (COD): 200-600 mg / L, ammonia nitrogen (NH4 + -N): 300-800 mg / L, total nitrogen (TN): 400-1,000 mg / L. The key parameters are shown in the table, after 3 months of stable operation, the effluent ammonia nitrogen concentration: ≤5 mg / L, total nitrogen removal rate: 90%, COD removal rate: 70%.

[0069]

[0070] This case shows that the anaerobic ammonia oxidation granular sludge has great potential in high ammonia nitrogen wastewater treatment, and is suitable for nitrogen removal of industrial wastewater and municipal wastewater, providing reference for similar projects. This case shows that the anaerobic ammonia oxidation granular sludge has great potential in high ammonia nitrogen wastewater treatment, and is suitable for nitrogen removal of industrial wastewater and municipal wastewater, providing reference for similar projects.

[0071] All the documents mentioned in the present application are cited as references in the present application, just as each document is cited as a reference. In addition, it should be understood that those skilled in the art can make various modifications or modifications to the present application after reading the above teaching of the present application, and these equivalent forms also fall within the scope defined by the present application.

Claims

1. A method for preparing polydopamine-modified biochar-loaded Fe-Cu sodium alginate microspheres, characterized in that: The steps include: (1) Preparation of biochar: Use biomass materials, carbonize them in a nitrogen or inert gas environment at a temperature of 450-600 °C, grind them after natural cooling, sieve them to obtain biochar powder with a particle size of 0.5-1 mm, and dry them for later use; (2) Polydopamine coating: Disperse biochar powder in Tris buffer and disperse it evenly by ultrasound to obtain a biochar particle suspension; gradually add 1-2% dopamine solution by mass volume to the biochar, stir it at room temperature for 12-24 hours, and expose it to air for oxidation. When the color gradually changes from light yellow to dark brown, it indicates that the polymerization is complete and gradually deposits on the surface of the biochar particles to form a polydopamine coating, thereby obtaining polydopamine-modified biochar; (3) Loading of Fe-Cu ions: Soak the polydopamine-modified biochar in a mixed solution of FeCl3 and CuCl2 at a ratio of 1-2 g: 20 mL and stir thoroughly for 4-6 hours; wash with deionized water and dry to obtain the polydopamine-modified biochar loaded with Fe-Cu; (4) Preparation of sodium alginate microspheres: The Fe-Cu loaded polydopamine-modified biochar and a sodium alginate solution with a mass volume ratio of 2-4% are mixed evenly at a ratio of 1-2 g:100 mL; the mixed solution is dripped into the hardening liquid at a rate of 1.5-2.5 mL / min to form microspheres; the microspheres are allowed to stand in the hardening liquid for 30 min, and after hardening, they are taken out from the hardening liquid and rinsed with water to obtain polydopamine-modified biochar loaded with Fe-Cu sodium alginate microspheres.

2. The method for preparing polydopamine-modified biochar-loaded Fe-Cu sodium alginate microspheres according to claim 1, characterized in that: In step (1), the biomass material is waste sludge or agricultural and forestry waste biomass.

3. The method for preparing polydopamine-modified biochar-loaded Fe-Cu sodium alginate microspheres according to claim 1, characterized in that: In step (3), the mixed solution of FeCl3 and CuCl2 is prepared by mixing a FeCl3 solution with a concentration of 0.1-0.2M and a FeCl3 solution with a concentration of 0.1-0.2M.

4. The method for preparing polydopamine-modified biochar-loaded Fe-Cu sodium alginate microspheres according to claim 1, characterized in that: In step (4), the hardening liquid is a 25-30 g / L calcium chloride solution.

5. The method for preparing polydopamine-modified biochar-loaded Fe-Cu sodium alginate microspheres according to claim 1, characterized in that: In step (4), the drop distance of the mixed solution into the hardening solution to form microspheres is maintained at 3-5 cm.

6. The method for preparing polydopamine-modified biochar-loaded Fe-Cu sodium alginate microspheres according to claim 1, characterized in that: In steps (1) and (3), the drying condition is 50-80°C and the drying time is 10-15 hours.

7. Polydopamine-modified biochar loaded with Fe-Cu sodium alginate microspheres prepared according to the method according to any one of claims 1 to 6.

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