Complex microbial inoculant for repairing heavy metal-organic pollutant combined polluted soil as well as preparation method and application of complex microbial inoculant

Abstract

The invention discloses a complex microbial inoculant for repairing heavy metal-organic pollutant combined polluted soil as well as a preparation method and application thereof, and belongs to the technical field of preparation of soil repairing microbial inoculants. The preparation method comprises the following steps: firstly, modifying starch by using glucosidase, then loading a composite strain, glucosidase and an enzymolysis product (oligosaccharide or monosaccharide) into the modified starch, and finally, clathrating the substances by using phosphorus-doped ferrihydrite with a hierarchical pore structure, so that the activity and stability of the obtained composite microbial agent can be remarkably improved; the efficient remediation of the heavy metal and organic pollutant combined polluted soil is realized, and the problems existing in the current common complex microbial inoculants are effectively solved; the raw materials are simple and easy to obtain, and the preparation process is simple and suitable for large-scale popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation bacterial agent preparation, and more specifically relates to a composite bacterial agent for remediating soil contaminated by heavy metals and organic pollutants, and a preparation method and application thereof. Background Art

[0002] With the acceleration of my country's industrialization and urbanization, the problem of heavy metal pollution in soil is becoming increasingly serious. In addition to heavy metal pollution, organic pollutants also exist in the soil. Heavy metal-organic pollutant complex pollution has different pollution characteristics from single factor pollution, and often has associated and comprehensive characteristics. Heavy metals and organic pollutants have complex interactive complex effects in the soil. Therefore, the difficulty of controlling complex pollution has increased significantly.

[0003] Traditional soil remediation methods such as physical and chemical methods often have problems such as high cost and unsatisfactory treatment effects. The technology of using microorganisms to repair soil heavy metal pollution has gradually developed and has become an important method for heavy metal contaminated soil treatment. However, existing microbial agents are often only targeted at single heavy metal contaminated soils, and the treatment effect on heavy metal-organic pollutant composite contaminated soils is still poor. In addition, the commonly used microbial agents have low stability and activity in the soil, which limits their remediation effect.

[0004] Therefore, it is of great significance to develop a composite bacterial agent with good treatment effect, high stability and the ability to treat heavy metal-organic pollutant combined pollution. Summary of the invention

[0005] The purpose of the present invention is to provide a composite bacterial agent for repairing soil contaminated by heavy metals and organic pollutants, and a preparation method and application thereof, so as to solve the problems existing in the above-mentioned prior art and achieve efficient treatment of soil contaminated by heavy metals and organic pollutants.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing a composite bacterial agent for repairing soil contaminated by heavy metals and organic pollutants, comprising the following steps:

[0008] Starch is modified by glucosidase to obtain a starch-enzyme suspension; a composite bacterial suspension is added to the starch-enzyme suspension for oscillation and mixing, and enzyme-bacteria composite-loaded modified starch is obtained by freeze-drying; the enzyme-bacteria composite-loaded modified starch, phosphate-doped ferrihydrite and carboxymethyl cellulose are ground and mixed to obtain the composite bacterial agent.

[0009] The present invention first utilizes glucosidase to modify starch, then loads composite bacteria, glucosidase and enzymolysis product (oligosaccharide or monosaccharide) into modified starch, and finally realizes inclusion of the above-mentioned substances with phosphorus-doped ferrihydrite of multi-level pore structure; wherein, the enzymolysis product (oligosaccharide or monosaccharide) of glucosidase-modified starch can be combined with heavy metals to form a complex, thereby reducing the activity of heavy metals; the combination of composite bacteria, glucosidase and enzymolysis product (oligosaccharide or monosaccharide) can realize full passivation of heavy metals and organic pollutants, significantly increase the activity of the obtained composite bacterial agent, and solve the problem that the currently commonly used composite bacterial agents have low activity, poor treatment effect, and can only realize the passivation of heavy metals. The surface of modified starch contains a large number of active groups, which can significantly increase the binding strength of composite bacteria, glucosidase and enzymolysis product (oligosaccharide or monosaccharide) with phosphorus-doped ferrihydrite, improve the loading effect, and in addition, can also significantly improve the activity and stability of composite bacteria, glucosidase and enzymolysis product (oligosaccharide or monosaccharide), and solve the problem that the currently commonly used composite bacterial agents have poor stability. In addition to acting as a carrier to improve the stability of active ingredients, phosphate-doped ferrihydrite can also effectively passivate heavy metals in the soil. By reducing the bioavailability of heavy metals, it can significantly alleviate the stress of heavy metals on soil microorganisms and reduce the risk of heavy metal transmission in the food chain.

[0010] The composite bacterial species in the composite bacterial species suspension are Bacillus subtilis, Bacillus megaterium, Bacillus jelly-like and Bacillus laterosporus; the mass ratio of Bacillus subtilis, Bacillus megaterium, Bacillus jelly-like and Bacillus laterosporus is 1-2:1-3:1:2-3; the live bacterial content in the composite bacterial species suspension is 2×10 8 ~5×10 9 CFU / mL.

[0011] The invention combines Bacillus subtilis, Bacillus megaterium, Bacillus gelatinus and Bacillus laterosporus and controls the dosage ratio of each strain, thereby improving soil structure, improving soil microecological environment, significantly improving the passivation of heavy metals and organic pollutants, and realizing effective remediation of soil contaminated by heavy metal-organic pollutants composite.

[0012] Preferably, the modification comprises: mixing starch and a buffer to obtain a starch suspension; and adding glucosidase to the starch suspension for modification.

[0013] Optionally, the starch includes one or more of corn starch, potato starch, sweet potato starch and wheat starch; the buffer includes sodium acetate buffer;

[0014] Preferably, the pH value of the buffer solution is 5.1 to 5.5; the dosage ratio of the starch to the buffer solution is 1 g:3 to 5 mL; and the concentration of the glucosidase after adding glucosidase to the starch suspension is 150 to 200 U / g.

[0015] Preferably, the modification temperature is 50-60° C., and the modification time is 10-12 h.

[0016] Preferably, the volume ratio of the starch-enzyme suspension to the composite bacterial suspension is 2 to 3:1.

[0017] Preferably, the temperature of the oscillating mixing is 20 to 25° C., and the time of the oscillating mixing is 2 to 3 hours; the temperature of the freeze-drying is -20 to -10° C., and the time of the freeze-drying is 1 to 2 hours.

[0018] The present invention does not need to perform an enzyme inactivation treatment step after starch modification. The composite bacteria can be directly loaded after starch modification. The activity of the enzyme during the composite bacteria loading process is reduced by the temperature difference between modification and oscillation mixing. Under the premise that the enzyme is not inactivated, the multi-level pore structure of the modified starch is not further destroyed by the enzyme, thereby ensuring that the modified starch has a high loading amount.

[0019] Preferably, the particle size of the phosphorus-doped ferrihydrite is 60-80 meshes; the mass ratio of the modified starch, phosphorus-doped ferrihydrite and carboxymethyl cellulose loaded by the enzyme-bacteria composite is 4-5:10-15:1-3.

[0020] Preferably, the particle size of the composite bacterial agent is 100-150 meshes.

[0021] The second technical solution of the present invention: providing a composite bacterial agent prepared by the preparation method of the composite bacterial agent for repairing soil contaminated by heavy metals and organic pollutants.

[0022] The third technical solution of the present invention is to provide the application of the composite bacterial agent in repairing soil contaminated by heavy metals and organic pollutants.

[0023] The present invention discloses the following technical effects:

[0024] 1. The present invention firstly uses glucosidase to modify starch, then loads the composite bacteria, glucosidase and enzymolysis products (oligosaccharides or monosaccharides) into the modified starch, and finally uses phosphorus-doped ferrihydrite with a multi-level pore structure to achieve inclusion of the above substances, which can significantly improve the activity and stability of the obtained composite bacterial agent, realize the efficient remediation of soil contaminated by heavy metals and organic pollutants, and effectively solve the problems existing in the currently commonly used composite bacterial agents;

[0025] 2. The raw materials used in the present invention are simple and easy to obtain, the preparation process is simple, and it is suitable for large-scale promotion and application. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] The present invention first describes the raw materials used in the following examples and comparative examples:

[0032] Glucosidase and amylase were purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0033] Bacillus subtilis, Bacillus megaterium, Bacillus gelatinosa and Bacillus laterosporus were purchased from Shandong Yitai Biotechnology Co., Ltd.

[0034] Preparation of Bacillus subtilis suspension:

[0035] 1. Strain processing and cultivation: Primary culture: open the freeze-dried strain tube under sterile conditions, add an appropriate amount of nutrient broth medium to melt and disperse the strain. Take a small amount of strain suspension and inoculate it into a nutrient broth medium test tube, and culture it at 37°C for 24 hours; Subculture: use an inoculation loop to take the primary culture suspension and streak it on a nutrient agar medium plate, and continue to culture to obtain the second generation. Then pick a typical colony and inoculate it into the nutrient broth medium to obtain the third generation culture;

[0036] 2. Spore formation and inspection: Inoculate the third generation culture on the surface of the nutrient agar medium in the Roche flask and culture for 7 days; use an inoculation loop to take a bacterial sample and stain it with the improved spore staining method. The spore formation rate under microscopic examination must reach more than 95%;

[0037] 3. Prepare spore suspension: add sterile distilled water to the Roche flask, gently scrape off the bacterial moss, and wash repeatedly; concentrate the washed bacterial suspension in a sterile conical flask containing glass beads and shake to obtain a uniform spore suspension.

[0038] Preparation of Bacillus megaterium suspension:

[0039] 1. Activation of bacterial strains: Take the freeze-dried bacterial strain tube, open it under sterile operation, add appropriate amount of nutrient broth medium to melt and disperse the bacterial strain; inoculate it into the nutrient broth medium test tube, and culture it at 37℃ for 24h;

[0040] 2. Transfer and cultivation: streak the culture onto a nutrient agar plate and culture at 37°C; pick a typical bacterial colony and inoculate it into a nutrient broth medium and continue culturing;

[0041] 3. Spore formation and inspection: Inoculate the culture on the surface of nutrient agar medium in a Roche flask and culture for 7 days; stain with the improved spore staining method, and the spore formation rate under microscopic examination must reach more than 95%;

[0042] 4. Prepare spore suspension: add sterile distilled water to the Roche flask, gently scrape off the bacterial moss, and wash repeatedly; concentrate the washed bacterial suspension in a sterile conical flask containing glass beads and shake to obtain a uniform spore suspension.

[0043] Preparation of jelly-like Bacillus suspension

[0044] 1. Activation of bacterial strains: inoculate the bacterial strains into liquid fermentation medium and culture at 37°C for 46 hours to generate a large number of spores;

[0045] 2. Preparation of spore suspension: Add sterile distilled water to the culture medium and scrape fresh spores with an inoculating loop; mix the spore suspension with glass beads and shake to disperse the spores; filter to remove the hyphae and centrifuge to precipitate the spores. Repeat the operation to prepare a spore suspension of the desired concentration.

[0046] Preparation of Bacillus laterosporus suspension:

[0047] 1. Strain activation: Take the Bacillus laterosporus strain and inoculate it on a slant culture medium under sterile conditions for activation culture.

[0048] 2. Preparation of bacterial suspension: Wash the slope with sterile water to obtain seed solution, i.e., preliminary bacterial suspension; the concentration of bacterial solution can be adjusted, such as by using a turbidimeter or turbidometer, to ensure that the bacterial suspension reaches the required turbidity;

[0049] 3. Spore formation and inspection: Cultivate the bacterial suspension under appropriate conditions, such as on a nutrient agar plate at 35-37°C; smear, stain, and examine the spore rate under a microscope to ensure that the required ratio is reached;

[0050] 4. Preparation of spore suspension: Use sterile water to wash off the mixture of spores and bacteria to make a suspension.

[0051] The formula of nutrient broth medium is: 1000 mL of distilled water, 20 g of glucose, 15 g of peptone, 5 g of sodium chloride, 0.5 g of beef extract and 20 g of agar.

[0052] The liquid fermentation medium formula is: molasses 12g / L, K2HPO4 0.8g / L and MgSO4 0.3g / L.

[0053] The slant culture medium formula is: peptone 10g, beef extract 15g, sodium chloride 15g, agar 18g and distilled water 1000mL, and the pH value is adjusted to 7.2.

[0054] The formula of nutrient agar medium is: 10 g of peptone, 3 g of beef extract, 5 g of sodium chloride, 15 g of agar and 1000 mL of distilled water, and the pH value is adjusted to 7.2.

[0055] Example 1

[0056] 10 g corn starch and 40 mL sodium acetate buffer with a pH value of 5.2 were mixed to obtain a starch suspension; glucosidase was added to the starch suspension to ensure that the concentration of glucosidase in the starch suspension after addition was 150 U / g, and the starch suspension was modified by heating in a water bath at 50° C. After modification for 10 h, a composite bacterial suspension was added thereto (the mass ratio of Bacillus subtilis, Bacillus megaterium, Bacillus gelatinus and Bacillus laterosporus was 2:3:1:2, and the content of live bacteria in the bacterial suspension was 4×10 8CFU / mL), wherein the volume ratio of the modified mixed solution to the composite bacterial suspension is 3:1, and the mixture is shaken and mixed at 20°C for 2.5h, and then the precipitate is centrifuged and washed with pure water and then freeze-dried at -15°C for 1h to obtain an enzyme-bacteria composite-loaded modified starch; the modified starch is ground and mixed with phosphate-doped ferrihydrite with a particle size of 80 mesh and carboxymethyl cellulose, wherein the mass ratio of the enzyme-bacteria composite-loaded modified starch, phosphate-doped ferrihydrite and carboxymethyl cellulose is 4:10:1, and a composite bacterial agent with a particle size of 120 mesh is obtained.

[0057] Example 2

[0058] 20 g of wheat starch and 80 mL of sodium acetate buffer with a pH value of 5.4 were mixed to obtain a starch suspension; glucosidase was added to the starch suspension to ensure that the concentration of glucosidase in the starch suspension after addition was 180 U / g, and the starch suspension was modified by heating in a water bath at 55° C. After modification for 10 h, a composite bacterial suspension was added thereto (the mass ratio of Bacillus subtilis, Bacillus megaterium, Bacillus gelatinus and Bacillus laterosporus was 1:2:1:2, and the content of live bacteria in the bacterial suspension was 1×10 9 CFU / mL), wherein the volume ratio of the modified mixed solution to the composite bacterial suspension is 2:1, and the mixture is shaken and mixed at 25°C for 3 hours, and then the precipitate is centrifuged and washed with pure water and then freeze-dried at -15°C for 1 hour to obtain an enzyme-bacteria composite-loaded modified starch; the modified starch is ground and mixed with phosphate-doped ferrihydrite with a particle size of 60 mesh and carboxymethyl cellulose, wherein the mass ratio of the enzyme-bacteria composite-loaded modified starch, phosphate-doped ferrihydrite and carboxymethyl cellulose is 5:12:2, and a composite bacterial agent with a particle size of 140 mesh is obtained.

[0059] Example 3

[0060] 10 g of potato starch and 50 mL of sodium acetate buffer with a pH value of 5.2 were mixed to obtain a starch suspension; glucosidase was added to the starch suspension to ensure that the concentration of glucosidase in the starch suspension after addition was 200 U / g, and the starch suspension was modified by heating in a water bath at 60° C. After modification for 12 h, a composite bacterial suspension was added thereto (the mass ratio of Bacillus subtilis, Bacillus megaterium, Bacillus gelatinus and Bacillus laterosporus was 2:2:1:3, and the content of live bacteria in the bacterial suspension was 3×10 9CFU / mL), wherein the volume ratio of the modified mixed solution to the composite bacterial suspension is 3:1, and the mixture is shaken and mixed at 22°C for 2h, and then the precipitate is centrifuged and washed with pure water and then freeze-dried at -20°C for 1.5h to obtain an enzyme-bacteria composite-loaded modified starch; the modified starch is ground and mixed with phosphate-doped ferrihydrite with a particle size of 70 mesh and carboxymethyl cellulose, wherein the mass ratio of the enzyme-bacteria composite-loaded modified starch, phosphate-doped ferrihydrite and carboxymethyl cellulose is 5:15:2.5, and a composite bacterial agent with a particle size of 150 mesh is obtained.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that "glucosidase" is replaced by "amylase", and the rest is the same as Example 1.

[0063] Comparative Example 2

[0064] The difference from Example 1 is that the addition of Bacillus subtilis is omitted while the mass ratio of Bacillus megaterium, Bacillus gelatinus and Bacillus laterosporus and the content of live bacteria in the bacterial suspension remain unchanged. The rest is the same as Example 1.

[0065] Comparative Example 3

[0066] The difference from Example 1 is that the addition of Bacillus megaterium is omitted while the mass ratio of Bacillus subtilis, Bacillus gelatinus and Bacillus laterosporus and the content of live bacteria in the bacterial suspension are kept unchanged. The rest is the same as Example 1.

[0067] Comparative Example 4

[0068] The difference from Example 1 is that the addition of Bacillus jelly-like is omitted while the mass ratio of Bacillus subtilis, Bacillus megaterium and Bacillus laterosporus and the content of live bacteria in the bacterial suspension remain unchanged. The rest is the same as Example 1.

[0069] Comparative Example 5

[0070] The difference from Example 1 is that the addition of Bacillus laterosporus is omitted while the mass ratio of Bacillus subtilis, Bacillus megaterium and Bacillus gelatinus and the content of live bacteria in the bacterial suspension remain unchanged. The rest is the same as Example 1.

[0071] Comparative Example 6

[0072] The difference from Example 1 is that the mass ratio of Bacillus subtilis, Bacillus megaterium, Bacillus gelatinosa and Bacillus laterosporus is adjusted to 4:3:1:2, and the rest is the same as Example 1.

[0073] Comparative Example 7

[0074] The difference from Example 1 is that the mass ratio of Bacillus subtilis, Bacillus megaterium, Bacillus gelatinosa and Bacillus laterosporus is adjusted to 2:3:1:5, and the rest is the same as Example 1.

[0075] Comparative Example 8

[0076] The difference from Example 1 is that the addition of phosphorus-doped ferrihydrite is omitted, and the rest is the same as Example 1.

[0077] Comparative Example 9

[0078] The difference from Example 1 is that an enzyme inactivation treatment step is added after the modification, specifically: after the modification is completed, 10 mL of 95% ethanol is quickly added to inactivate the enzyme, and then it is centrifuged for 10 minutes, the supernatant is poured off, and the precipitate containing starch is collected and dried at 40° C. for 48 hours. The dried starch sample is mixed with the composite bacterial suspension. The rest is the same as Example 1.

[0079] Test Example 1

[0080] Test object: Soil in a sewage irrigation area in Heilongjiang;

[0081] Test method: First, the benzo(a)pyrene (BaP) content, heavy metal lead content, organic matter content and soil pH value in the test soil were determined, and then the test soil was divided into 12 parts, and the composite bacterial agents prepared in Examples 1 to 3 and Comparative Examples 1 to 9 were applied respectively, with an application amount of 1.5 g / kg. The soil was cultured for 90 days at a temperature of 25°C and a humidity of 55%. After the culture, the benzo(a)pyrene (BaP) content, heavy metal lead content, organic matter content and soil pH value in the soil were determined. The results are shown in Table 1.

[0082] Table 1 Soil remediation effect

[0083]

[0084] As can be seen from Table 1, the composite bacterial agent obtained by the present invention can significantly reduce the content of benzo(a)pyrene (BaP) and heavy metal lead, improve the passivation of heavy metals and organic pollutants, increase the content of microorganisms and organic matter in the test soil, play a role in improving the soil structure and soil microecological environment, and at the same time adjust the soil pH value to achieve effective remediation of heavy metal-organic pollutant composite contaminated soil.

[0085] Test Example 2

[0086] The soil after the test of Test Example 1 was taken, and the untreated test soil was used as a control group. Lettuces with the same growth were transplanted therein, and 20 lettuces were transplanted in each group to form a parallel comparison. After 6 months, the content of heavy metal lead in each group of lettuces and the yield were measured, and the average value was calculated. The results are shown in Table 2. The growth of the lettuces was observed during the test.

[0087] During the test, the leaves of most of the lettuces in the control group turned black one month after transplanting, and most of the lettuces in the control group wilted two months after transplanting; the lettuces transplanted in the soil treated with the composite bacterial agent described in Examples 1 to 3 grew well without lesions.

[0088] Table 2 Yield of crops and heavy metal lead content

[0089] sample Lead content in lettuce (mg / kg) Yield (%) Example 1 0.5 100 Example 2 0.4 100 Example 3 0.5 100 Comparative Example 1 1.5 95 Comparative Example 2 0.9 95 Comparative Example 3 1.2 100 Comparative Example 4 1.2 95 Comparative Example 5 1.6 95 Comparative Example 6 1.6 100 Comparative Example 7 0.8 95 Comparative Example 8 1.8 95 Comparative Example 9 1.9 95 Control group 2.3 25

[0090] The data in the table are all average values, and the yield (%) = number of survivors / number of transplants × 100%.

[0091] From the growth of lettuce and Table 3, it can be seen that the composite bacterial agent obtained by the present invention can effectively repair the soil contaminated by heavy metals and organic pollutants, promote the growth of crops, effectively avoid the occurrence of crop diseases, reduce the content of heavy metals in crops, and increase crop yields.

[0092] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0093] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a composite bacterial agent for repairing soil contaminated by heavy metals and organic pollutants, characterized in that: The steps include: The starch is modified by glucosidase to obtain a starch-enzyme suspension; the composite bacterial suspension is added to the starch-enzyme suspension, and the mixture is shaken and mixed, and the modified starch loaded with enzyme-bacteria composite is obtained by freeze-drying; the modified starch loaded with enzyme-bacteria composite, phosphate-doped ferrihydrite and carboxymethyl cellulose are ground and mixed to obtain the composite bacterial agent; The composite bacterial species in the composite bacterial species suspension are Bacillus subtilis, Bacillus megaterium, Bacillus jelly-like and Bacillus laterosporus; the mass ratio of Bacillus subtilis, Bacillus megaterium, Bacillus jelly-like and Bacillus laterosporus is 1-2:1-3:1:2-3; the live bacterial content in the composite bacterial species suspension is 2×10 8 ~5×10 9 CFU / mL.

2. The preparation method according to claim 1, characterized in that: The modification comprises: mixing starch and buffer to obtain a starch suspension; and adding glucosidase to the starch suspension for modification.

3. The preparation method according to claim 2, characterized in that: The starch includes one or more of corn starch, potato starch, sweet potato starch and wheat starch; and / or the buffer includes sodium acetate buffer, and the pH value of the buffer is 5.1-5.5; and / or the usage ratio of the starch and the buffer is 1g:3-5mL; and / or the concentration of the glucosidase after adding glucosidase to the starch suspension is 150-200U / g.

4. The preparation method according to claim 2, characterized in that: The modification temperature is 50-60° C., and the modification time is 10-12 hours.

5. The preparation method according to claim 1, characterized in that: The volume ratio of the starch-enzyme suspension to the composite bacterial suspension is 2-3:

1.

6. The preparation method according to claim 1, characterized in that: The temperature of the oscillating mixing is 20 to 25° C., and the time of the oscillating mixing is 2 to 3 hours; and / or, the temperature of the freeze-drying is -20 to -10° C., and the time of the freeze-drying is 1 to 2 hours.

7. The preparation method according to claim 1, characterized in that: The particle size of the phosphorus-doped ferrihydrite is 60-80 meshes; and / or the mass ratio of the modified starch, phosphorus-doped ferrihydrite and carboxymethyl cellulose loaded by the enzyme-bacteria composite is 4-5:10-15:1-3.

8. The preparation method according to claim 1, characterized in that: The particle size of the composite bacterial agent is 100-150 meshes.

9. The composite bacterial agent prepared by the method for preparing the composite bacterial agent for repairing soil contaminated by heavy metals and organic pollutants as claimed in any one of claims 1 to 8.

10. Use of the composite bacterial agent according to claim 9 in remediating soil contaminated by heavy metals and organic pollutants.

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