A method for treating heavy metals in soil with microorganisms

Abstract

The application discloses a method for treating heavy metals in soil by microorganisms and belongs to the technical field of soil remediation. The method comprises the following steps: (1) soil treatment: plowing the soil contaminated by heavy metals, and the plowing depth is 30-40 cm; (2) heavy metal treatment: adding a heavy metal treatment agent into the soil, plowing again to make the heavy metal treatment agent fully contact with the soil, then irrigating the land to adjust the water content of the soil to 25-30%, covering a layer of plastic film on the surface of the soil after the irrigation is completed, and removing the film after the treatment is completed, so that the problem that the initial growth of microorganisms is inhibited by heavy metals and the heavy metal treatment efficiency is reduced is solved.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to a method for treating heavy metals in soil using microorganisms. Background Technology

[0002] With the development of modern technology, soil pollution is becoming increasingly serious, and heavy metal pollution is a major problem in soil pollution, characterized by its insidious nature, difficulty in degradation, poor mobility, and easy accumulation. The main sources of heavy metals in soil are factory waste and agricultural production, and the increasingly serious nature of heavy metal pollution in soil seriously endangers the ecological environment and human health. Therefore, how to solve soil heavy metal pollution has become a focal issue. Currently, microbial treatment of soil heavy metal pollution, utilizing the adsorption, reduction, and transformation of heavy metals by microorganisms to reduce or remove heavy metal pollutants, has good effects and minimal impact on environmental pollution, making it one of the main technical methods for heavy metal soil remediation. However, in the initial stage of treatment, the amount of microorganisms is small, while the concentration of heavy metals in the soil is high, which reduces the metabolic capacity and activity of microorganisms. The growth and reproduction of microorganisms are inhibited by heavy metals, thus leading to a decrease in the efficiency of microbial treatment of heavy metals.

[0003] Therefore, this invention provides a method for treating heavy metals in soil with microorganisms, which promotes the initial growth and reproduction of microorganisms and solves the problem of the initial growth of microorganisms being inhibited by heavy metals. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a method for treating heavy metals in soil with microorganisms, which solves the problem that the initial growth of microorganisms is inhibited by heavy metals, resulting in a decrease in the efficiency of heavy metal treatment.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] A method for treating heavy metals in soil using microorganisms, the method comprising the following steps:

[0007] (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 30-40cm, and weeds and gravel in the soil are removed.

[0008] (2) Heavy metal treatment: Add heavy metal treatment agent to the soil, turn the soil again to make the heavy metal treatment agent fully contact the soil, then irrigate the land to adjust the soil moisture content to 25-30%, and cover the soil surface with a plastic film after irrigation. Remove the film after treatment is completed.

[0009] Furthermore, the processing time in step (2) is 50-60 days.

[0010] Furthermore, the heavy metal treatment agent in step (2) includes heavy metal treatment agent A and heavy metal treatment agent B, wherein heavy metal treatment agent A and heavy metal treatment agent B are mixed evenly in a mass ratio of 1:1.

[0011] Furthermore, the amount of the heavy metal treatment agent used is per 1m 2 Use 30-40g of heavy metal treatment agent on the soil.

[0012] Furthermore, the preparation method of the heavy metal treatment agent is as follows:

[0013] Preparation method of heavy metal treatment agent A:

[0014] S1: Add glucose to water and stir until completely dissolved to obtain a glucose solution. Then add β-cyclodextrin to the glucose solution and mix well. Heat the solution to 80-90℃, add gelatin, mix well, dry at 0-5℃ for 2-3 hours, and then pulverize to obtain granules A.

[0015] S2: Add cassava starch to water at 70-80℃ for gelatinization. After gelatinization, cool to room temperature, add papain solution, mix well to obtain solution A, spray it on the surface of composite particles, and dry at 20-30℃ for 30-40 minutes to obtain treatment agent A.

[0016] Preparation method of heavy metal treatment agent B:

[0017] S1: Mix soybean meal, diatomaceous earth, and seaweed polysaccharide evenly, place them in a granulator for granulation to obtain solid particles, put the solid particles into the microbial fermentation liquid for adsorption, take them out and air dry them to obtain particles B.

[0018] S2: Add xanthan gum to water, stir evenly, heat the solution to 90-95℃, then add polyvinyl alcohol and glutaraldehyde, mix evenly, and cool to room temperature to obtain a mixed gel; put particle B into the mixed gel until particle B is fully coated, then take it out and dry it at 20-30℃ for 30-40 minutes to obtain heavy metal treatment agent B.

[0019] Furthermore, the mass ratio of glucose, β-cyclodextrin, and gelatin in the heavy metal treatment agent A is (1.2-1.5):(1-1.2):(4-5), and the mass ratio of cassava starch and papain is (10-15):(1-1.2).

[0020] Furthermore, the mass ratio of soybean meal, diatomaceous earth, and seaweed polysaccharide in the micro-heavy metal treatment agent B is (6-8):(3-4):(2-3), and the mass ratio of xanthan gum, polyvinyl alcohol, and glutaraldehyde is (3-4):(1-1.2):(0.15-0.2).

[0021] Furthermore, the particle size of the solid particles in the micro-heavy metal treatment agent B is 2-3 mm.

[0022] Furthermore, the preparation method of the microbial fermentation broth in the micro-heavy metal treatment agent B is as follows:

[0023] Trichoderma harzianum and Bacillus subtilis were inoculated into PDA medium and activated at 23-26℃ for 3-5 days. After activation, mycelial cakes of each strain were picked and added to fermentation broth at a 2% inoculation rate and cultured on a shaker at 25-28℃ and 200-220 r / min. When the effective viable count in each mixed fermentation broth reached (4-5)×10⁻⁶, the inoculum was collected. 6 When the concentration of CFU / mL is reached, fermentation is stopped, and fermentation broths are obtained separately. The fermentation broths are then mixed at a volume ratio of 1:1 to obtain the microbial fermentation broth.

[0024] Furthermore, the fermentation liquid culture medium consists of: 5-6g glucose, 12-15g yeast powder, 0.1-0.2g magnesium sulfate, 0.1-0.15g dipotassium hydrogen phosphate, and 1000ml distilled water. After preparation, it is sterilized by steam at 120℃ for 20-25 minutes.

[0025] The decomposition rate of heavy metal treatment agent A is greater than that of heavy metal treatment agent B. Heavy metal treatment agent A can create a suitable environment for microbial growth in the soil in advance, ensuring an optimal breeding ground for the fermentation broth slowly released by heavy metal treatment agent B, thus promoting rapid growth and reproduction of microorganisms to form a dominant microbial community in the early stages of treatment. Specifically, heavy metal treatment agent B contains microbial fermentation broth. After release, the microorganisms can grow and reproduce in the soil, adsorbing heavy metal ions onto the cell surface or inside the cells through the adsorption of their cell walls and extracellular polymers, thereby reducing the heavy metal content in the soil. However, the initial concentration of heavy metals in heavy metal treatment agent B is low after release. Higher heavy metal concentrations significantly inhibit microbial reproduction and may even lead to microbial death, thus reducing the treatment efficiency of heavy metal treatment agent B. Therefore, spraying a mixed gel on the surface of heavy metal treatment agent B—a three-dimensional network structure formed by cross-linking xanthan gum and polyvinyl alcohol—improves the stability of the mixed gel, slowing down the decomposition rate of treatment agent B and allowing for the slow release of heavy metals from it.

[0026] In addition, heavy metal treatment agent A was also added. Papain on the surface of heavy metal treatment agent A promotes the hydrolysis of gelatin, producing more peptides and amino acids. Together with the glucose in heavy metal treatment agent A, it provides nutrients and carbon source for the microorganisms already exposed in heavy metal treatment agent B, promoting microbial growth and reproduction, increasing microbial activity, and encouraging the secretion of more extracellular polymers to enhance the adsorption capacity for heavy metals. Simultaneously, β-cyclodextrin in heavy metal treatment agent A can chelate heavy metals in the soil, reducing the heavy metal content and preventing excessively high heavy metal concentrations from interfering with the initial growth of microorganisms.

[0027] Therefore, by combining heavy metal treatment agent A and heavy metal treatment agent B, the initial growth and reproduction rate of microorganisms can be effectively improved, thereby increasing the efficiency of microorganisms in treating heavy metals.

[0028] Beneficial effects:

[0029] The combined action of heavy metal treatment agent A and heavy metal treatment agent B prepared in this invention can effectively reduce the content of heavy metals in the soil, solve the problem of heavy metal pollution in the soil, effectively restore the ecological function of the soil, and improve soil quality. Furthermore, the heavy metal treatment particles prepared in this invention are green and pollution-free, and will not have any impact on the environment or subsequent crop planting. Detailed Implementation

[0030] The present invention will be described in detail below with reference to specific embodiments:

[0031] Example 1:

[0032] Microbial fermentation broth:

[0033] After thawing, *Trichoderma harzianum* and *Bacillus subtilis* were inoculated into PDA medium and activated at 23°C for 3 days. Following activation, mycelial cakes from each strain were picked and added at a 2% inoculum to fermentation broth medium and cultured in a shaker at 25°C and 200 rpm. The effective viable count in each mixed fermentation broth medium reached 4 × 10⁻⁶. 6 When the concentration of CFU / mL is around 1, stop fermentation and obtain fermentation broth. Then, mix the fermentation broth at a volume ratio of 1:1 to obtain microbial fermentation broth. The composition of the fermentation broth culture medium is: 5g glucose, 12g yeast powder, 0.g magnesium sulfate, 0.1g dipotassium hydrogen phosphate, and 1000ml distilled water. Sterilize with steam at 120℃ for 20min.

[0034] Heavy metal treatment agent A:

[0035] S1: Add 1.2g of glucose to 100ml of water and stir until completely dissolved to obtain a glucose solution. Then add 1g of β-cyclodextrin to the glucose solution and mix well. Heat the solution to 80℃, add 4g of gelatin, mix well, dry at 0℃ for 2 hours, and then pulverize to obtain granules A.

[0036] S2: Add 10g of tapioca starch to 100ml of water at 70℃ for gelatinization. After gelatinization, cool to room temperature and add 1g of papain and 10ml of water to prepare a papain solution. Mix well to obtain solution A. Spray it on the surface of the composite particles and dry at 20℃ for 30min to obtain treatment agent A.

[0037] Heavy metal treatment agent B:

[0038] S1: Mix soybean meal, diatomaceous earth, and seaweed polysaccharide evenly in a mass ratio of 6:3:2, place them in a granulator for granulation, and obtain solid particles with a particle size of 2mm. Put the solid particles into the microbial fermentation liquid for adsorption, take them out and air dry them to obtain particles B.

[0039] S2: Add 3g xanthan gum to 100ml of water, stir well, heat the solution to 90℃, then add 1g polyvinyl alcohol and 0.15g glutaraldehyde, mix well and cool to room temperature to obtain a mixed gel; put particle B into the mixed gel until particle B is fully coated, then take it out and dry it at 20℃ for 30min to obtain heavy metal treatment agent B.

[0040] Methods for treating heavy metals in soil using microorganisms:

[0041] (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 30cm, and weeds and gravel in the soil are removed.

[0042] (2) Heavy metal treatment: A heavy metal treatment agent is added to the soil. The heavy metal treatment agent is composed of heavy metal treatment agent A and heavy metal treatment agent B mixed evenly at a mass ratio of 1:1. For every 1 m³ of soil, a heavy metal treatment agent is added. 2 The soil was treated with 30g of heavy metal treatment agent, and then the soil was turned over again to ensure that the heavy metal treatment agent was in full contact with the soil. The land was then irrigated to adjust the soil moisture content to 25%. After irrigation, a plastic film was placed over the soil surface. The film was removed after 50 days of treatment.

[0043] Example 2:

[0044] Microbial fermentation broth:

[0045] After thawing, *Trichoderma harzianum* and *Bacillus subtilis* were inoculated separately into PDA medium and activated at 24℃ for 4 days. Following activation, mycelial cakes from each strain were picked and added at a 2% inoculum to fermentation broth medium and cultured on a shaker at 26℃ and 210 rpm. The effective viable count in each mixed fermentation broth medium reached 4.5 × 10⁻⁶. 6 When the concentration of CFU / mL is around 1, stop fermentation and obtain fermentation broth. Then, mix the fermentation broth at a volume ratio of 1:1 to obtain microbial fermentation broth. The composition of the fermentation broth culture medium is: 5.5g glucose, 14g yeast powder, 0.15g magnesium sulfate, 0.13g dipotassium hydrogen phosphate, and 1000ml distilled water. Sterilize with steam at 120℃ for 22min.

[0046] Heavy metal treatment agent A:

[0047] S1: Add 1.35g of glucose to 112ml of water and stir until completely dissolved to obtain a glucose solution. Then add 1.1g of β-cyclodextrin to the glucose solution and mix well. Heat the solution to 85℃, add 4.5g of gelatin, mix well, dry at 2℃ for 2.5h, and then pulverize to obtain granules A.

[0048] S2: Add 12.5g of cassava starch to 125ml of water at 75℃ for gelatinization. After gelatinization, cool to room temperature and add 1.1g of papain and 11ml of water to prepare a papain solution. Mix well to obtain solution A. Spray it on the surface of the composite particles and dry at 25℃ for 35min to obtain treatment agent A.

[0049] Heavy metal treatment agent B:

[0050] S1: Mix soybean meal, diatomaceous earth, and seaweed polysaccharide evenly in a mass ratio of 7:3.5:2.5, place them in a granulator for granulation, and obtain solid particles with a particle size of 2.5mm. Put the solid particles into the microbial fermentation liquid for adsorption, take them out and air dry them to obtain particles B.

[0051] S2: Add 3.5g xanthan gum to 140ml of water, stir well, heat the solution to 95℃, then add 1g polyvinyl alcohol and 0.18g glutaraldehyde, mix well and cool to room temperature to obtain a mixed gel; put particle B into the mixed gel until particle B is fully coated, then take it out and dry it at 25℃ for 35min to obtain heavy metal treatment agent B.

[0052] Methods for treating heavy metals in soil using microorganisms:

[0053] (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 35cm, and weeds and gravel in the soil are removed.

[0054] (2) Heavy metal treatment: A heavy metal treatment agent is added to the soil. The heavy metal treatment agent is composed of heavy metal treatment agent A and heavy metal treatment agent B mixed evenly at a mass ratio of 1:1. For every 1 m³ of soil, a heavy metal treatment agent is added. 2 The soil was treated with 35g of heavy metal treatment agent, and then the soil was turned over again to ensure that the heavy metal treatment agent was in full contact with the soil. The land was then irrigated to adjust the soil moisture content to 28%. After irrigation, a plastic film was placed over the soil surface and the film was removed after 55 days of treatment.

[0055] Example 3:

[0056] Microbial fermentation broth:

[0057] After thawing, *Trichoderma harzianum* and *Bacillus subtilis* were inoculated into PDA medium and activated at 26°C for 5 days. Following activation, mycelial cakes from each strain were picked and added at a 2% inoculum to fermentation broth and cultured in a shaker at 28°C and 220 rpm. The effective viable count in each mixed fermentation broth reached 5 × 10⁻⁶. 6 When the concentration of CFU / mL is around 1, stop fermentation and obtain fermentation broth. Then, mix the fermentation broth at a volume ratio of 1:1 to obtain microbial fermentation broth. The composition of the fermentation broth culture medium is: 6g glucose, 15g yeast powder, 0.2g magnesium sulfate, 0.15g dipotassium hydrogen phosphate, and 1000ml distilled water. The medium is then sterilized by steam at 120℃ for 25min.

[0058] Heavy metal treatment agent A:

[0059] S1: Add 1.5g of glucose to 125ml of water and stir until completely dissolved to obtain a glucose solution. Then add 1.2g of β-cyclodextrin to the glucose solution and mix well. Heat the solution to 90℃, add 5g of gelatin, mix well, dry at 5℃ for 2 hours, and then pulverize to obtain granules A.

[0060] S2: Add 15g of tapioca starch to 150ml of water at 70℃ for gelatinization. After gelatinization, cool to room temperature and add 1.2g of papain and 12ml of water to prepare a papain solution. Mix well to obtain solution A. Spray it on the surface of the composite particles and dry at 30℃ for 40min to obtain treatment agent A.

[0061] Heavy metal treatment agent B:

[0062] S1: Mix soybean meal, diatomaceous earth, and seaweed polysaccharide evenly in a mass ratio of 8:4:3, place them in a granulator for granulation, and obtain solid particles with a particle size of 3mm. Put the solid particles into the microbial fermentation liquid for adsorption, take them out and air dry them to obtain particles B.

[0063] S2: Add 4g xanthan gum to 120ml of water, stir well, heat the solution to 90℃, then add 1.2g polyvinyl alcohol and 0.2g glutaraldehyde, mix well and cool to room temperature to obtain a mixed gel; put particle B into the mixed gel until particle B is fully coated, then take it out and dry it at 30℃ for 40min to obtain heavy metal treatment agent B.

[0064] Methods for treating heavy metals in soil using microorganisms:

[0065] (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 40cm, and weeds and gravel in the soil are removed.

[0066] (2) Heavy metal treatment: A heavy metal treatment agent is added to the soil. The heavy metal treatment agent is composed of heavy metal treatment agent A and heavy metal treatment agent B mixed evenly at a mass ratio of 1:1. For every 1 m³ of soil, a heavy metal treatment agent is added. 2 The soil was treated with 40g of heavy metal treatment agent, and then the soil was turned over again to ensure that the heavy metal treatment agent was in full contact with the soil. The land was then irrigated to adjust the soil moisture content to 30%. After irrigation, a plastic film was placed over the soil surface. The film was removed after 60 days of treatment.

[0067] Comparative Example 1:

[0068] This comparative example is compared with Example 1, the only difference being the raw materials used to prepare heavy metal treatment agent A; specifically, glucose is not added. The specific method is as follows:

[0069] S1: Add 1g of β-cyclodextrin to 100ml of water and stir until completely dissolved to obtain a β-cyclodextrin solution. Then heat the β-cyclodextrin solution to 80℃, add 4g of gelatin, mix evenly, dry at 0℃ for 2h, and then pulverize to obtain granules A.

[0070] S2: Add 10g of tapioca starch to 100ml of water at 70℃ for gelatinization. After gelatinization, cool to room temperature and add 1g of papain to 10ml of water to prepare a papain solution. Mix well to obtain solution A. Spray the solution onto the surface of the composite particles and dry at 20℃ for 30min to obtain treatment agent A.

[0071] The method of treating heavy metals in soil with microorganisms in this comparative example is the same as that in Example 1.

[0072] Comparative Example 2:

[0073] This comparative example is compared with Example 1, the only difference being the raw materials used to prepare heavy metal treatment agent A. Specifically, β-cyclodextrin is not added, and the specific method is as follows:

[0074] S1: Add 1.2g of glucose to 100ml of water and stir until completely dissolved to obtain a glucose solution. Then heat the glucose solution to 80℃, add 4g of gelatin, mix well, dry at 0℃ for 2 hours, and then pulverize to obtain granules A.

[0075] S2: Add 10g of tapioca starch to 100ml of water at 70℃ for gelatinization. After gelatinization, cool to room temperature and add 1g of papain to 10ml of water to prepare a papain solution. Mix well to obtain solution A. Spray the solution onto the surface of the composite particles and dry at 20℃ for 30min to obtain treatment agent A.

[0076] The method of treating heavy metals in soil with microorganisms in this comparative example is the same as that in Example 1.

[0077] Comparative Example 3:

[0078] This comparative example is compared with Example 1, the only difference being the raw materials used to prepare heavy metal treatment A. Specifically, papain and tapioca starch are not added. The specific method is as follows:

[0079] S1: Add 1.2g of glucose to 100ml of water and stir until completely dissolved to obtain a glucose solution. Then add 1g of β-cyclodextrin to the glucose solution and mix well. Heat the solution to 80℃, add 4g of gelatin, mix well, dry at 0℃ for 2 hours, and then pulverize to obtain heavy metal treatment agent A.

[0080] The method of treating heavy metals in soil with microorganisms in this comparative example is the same as that in Example 1.

[0081] Comparative Example 4:

[0082] This comparative example is compared with Example 1, the only difference being the raw materials used to prepare heavy metal treatment agent B. Specifically, the mixed gel is replaced with gelatin, and the specific method is as follows:

[0083] S1: Mix soybean meal, diatomaceous earth, and seaweed polysaccharide evenly in a mass ratio of 6:3:2, place them in a granulator for granulation, and obtain solid particles with a particle size of 2mm. Put the solid particles into the microbial fermentation liquid for adsorption, take them out and air dry them to obtain particles B.

[0084] S2: Add 3g of gelatin to 100ml of water, stir well, heat the solution to 90℃, then add 0.15g of glutaraldehyde, mix well, and cool to room temperature to obtain gelatin gel; put particle B into the gelatin gel until particle B is fully coated, then take it out and dry it at 20℃ for 30min to obtain heavy metal treatment agent B.

[0085] The method of treating heavy metals in soil with microorganisms in this comparative example is the same as that in Example 1.

[0086] Comparative Example 5:

[0087] This comparative example is compared with Example 1, the only difference being the preparation process of heavy metal treatment agent B. Specifically, particles B are not coated with a mixed gel. The specific method is as follows:

[0088] S1: Mix soybean meal, diatomaceous earth, and seaweed polysaccharide evenly in a mass ratio of 6:3:2, place them in a granulator for granulation, and obtain solid particles with a particle size of 2mm. Put the solid particles into the microbial fermentation broth for adsorption, and take them out and air dry to obtain heavy metal treatment agent B.

[0089] The method of treating heavy metals in soil with microorganisms in this comparative example is the same as that in Example 1.

[0090] Comparative Example 6:

[0091] This comparative example is compared with Example 1, the only difference being that heavy metal treatment agent A is not added to the heavy metal treatment agent, that is, only heavy metal treatment agent B is added, and the specific method is as follows;

[0092] (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 30cm, and weeds and gravel in the soil are removed.

[0093] (2) Heavy metal treatment: Add heavy metal treatment agent B to the soil at a concentration of 1 m³. 2 The soil was treated with 30g of heavy metal treatment agent B, and the soil was turned over again to ensure that the heavy metal treatment agent was in full contact with the soil. Then the land was irrigated to adjust the soil moisture content to 25%. After irrigation, a plastic film was placed on the soil surface and the film was removed after 50 days of treatment.

[0094] In this comparative example, the microbial treatment agent B is the same as in Example 1.

[0095] Comparative Example 7:

[0096] This comparative example is compared with Example 1, the only difference being that the heavy metal treatment agent is made by uniformly mixing heavy metal treatment agent A and heavy metal treatment agent B at a mass ratio of 2:1, as follows:

[0097] (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 30cm, and weeds and gravel in the soil are removed.

[0098] (2) Heavy metal treatment: A heavy metal treatment agent is added to the soil. The heavy metal treatment agent is composed of heavy metal treatment agent A and heavy metal treatment agent B mixed evenly at a mass ratio of 2:1. For every 1 m³ of soil, a heavy metal treatment agent is added. 2The soil was treated with 30g of heavy metal treatment agent, and then the soil was turned over again to ensure that the heavy metal treatment agent was in full contact with the soil. The land was then irrigated to adjust the soil moisture content to 25%. After irrigation, a plastic film was placed over the soil surface. The film was removed after 50 days of treatment.

[0099] In this comparative example, heavy metal treatment agent A and heavy metal treatment agent B are the same as in Example 1.

[0100] Comparative Example 8:

[0101] This comparative example is compared with Example 1, the only difference being that the heavy metal treatment agent is made by uniformly mixing heavy metal treatment agent A and heavy metal treatment agent B at a mass ratio of 1:2, as follows:

[0102] (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 30cm, and weeds and gravel in the soil are removed.

[0103] (2) Heavy metal treatment: A heavy metal treatment agent is added to the soil. The heavy metal treatment agent is composed of heavy metal treatment agent A and heavy metal treatment agent B mixed evenly at a mass ratio of 1:2. For every 1 m³ of soil, a heavy metal treatment agent is added. 2 The soil was treated with 30g of heavy metal treatment agent, and then the soil was turned over again to ensure that the heavy metal treatment agent was in full contact with the soil. The land was then irrigated to adjust the soil moisture content to 25%. After irrigation, a plastic film was placed over the soil surface. The film was removed after 50 days of treatment.

[0104] In this comparative example, heavy metal treatment agent A and heavy metal treatment agent B are the same as in Example 1.

[0105] Comparative Example 9:

[0106] This comparative example is compared with Example 1, the difference being that microbial fermentation broth is used instead of heavy metal treatment agent B. The specific method is as follows:

[0107] (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 30cm, and weeds and gravel in the soil are removed.

[0108] (2) Heavy metal treatment: Add heavy metal treatment agent A and microbial fermentation broth to the soil, per 1m 2 The soil was treated with 15g of heavy metal treatment agent A and 15g of microbial fermentation liquid, and then the soil was turned over again to ensure that the heavy metal treatment agent was in full contact with the soil. The land was then irrigated to adjust the soil moisture content to 25%. After irrigation, a plastic film was placed on the soil surface and the film was removed after 50 days of treatment.

[0109] The microbial fermentation broth used in this comparative example is the same as that prepared in Example 1.

[0110] experiment:

[0111] Experimental setup: Soil uncontaminated with heavy metals was excavated as the experimental soil, with each experimental group having a soil area of ​​2m². 2 The soil layer was 30cm thick, and then heavy metal ions were added to simulate heavy metal contaminated soil. The specific details are as follows:

[0112] Aqueous solutions of CuSO4, ZnSO4, and Pb(NO3)2 were prepared and then added to the soil to introduce Cu into the soil. 2 + Zn 2+ Pb 2 The initial concentration was 100 mg / kg. After standing for two days, the mixture was stirred evenly before the experiment was conducted.

[0113] Experimental group 1 used heavy metal treatment agent A and heavy metal treatment agent B prepared in Example 1;

[0114] Comparative groups 1-5 used heavy metal treatment agent A and heavy metal treatment agent B prepared in comparative examples 1-5 respectively; the heavy metal treatment methods are as follows:

[0115] (1) Heavy metal treatment: A heavy metal treatment agent is added to the soil. The heavy metal treatment agent is composed of heavy metal treatment agent A and heavy metal treatment agent B mixed evenly at a mass ratio of 1:1. For every 1 m³ of soil, a heavy metal treatment agent is added. 2 After applying 30g of heavy metal treatment agent to the soil, the soil is turned over to ensure that the heavy metal treatment agent is in full contact with the soil. Then, the land is irrigated to adjust the soil moisture content to 25%. After irrigation, a plastic film is placed on the soil surface. The film is removed after 50 days of treatment.

[0116] Comparative group 6 used only the heavy metal treatment agent B prepared in Example 1, at a dosage of 1 m 2 Use 30g of heavy metal treatment agent B on the soil.

[0117] Comparative groups 7 and 8 used heavy metal treatment agent A and heavy metal treatment agent B prepared in Example 1. The heavy metal treatment agent in comparative group 7 was a mixture of heavy metal treatment agent A and heavy metal treatment agent B at a mass ratio of 2:1, and the heavy metal treatment agent in comparative group 8 was a mixture of heavy metal treatment agent A and heavy metal treatment agent B at a mass ratio of 1:2.

[0118] Comparative group 9 used treatment agent A prepared in Example 1 and microbial fermentation broth, and its heavy metal treatment method is as follows:

[0119] (1) Heavy metal treatment: Add heavy metal treatment agent A and microbial fermentation broth to the soil, per 1m 2The soil was treated with 15g of heavy metal treatment agent A and 15g of microbial fermentation liquid, and then the soil was turned over again to ensure that the heavy metal treatment agent was in full contact with the soil. The land was then irrigated to adjust the soil moisture content to 25%. After irrigation, a plastic film was placed on the soil surface and the film was removed after 50 days of treatment.

[0120] Blank groups are not processed.

[0121] Sampling: After processing, a five-point sampling method was used to collect soil samples from the topsoil, the top 10cm layer, and the top 20cm layer. The collected soil samples were then mixed, and the heavy metals (Cu) in the mixed soil were tested. 2+ Zn 2+ Pb 2+ The content of ) is shown in Table 1:

[0122] Table 1

[0123] Experimental group 1 38.41 52.05 25.25 Comparison Group 1 51.04 65.87 38.05 Comparison Group 2 50.51 64.02 37.86 Comparison Group 3 55.13 71.44 45.84 Comparison Group 4 56.12 73.65 48.02 Comparison Group 5 59.66 76.23 52.81 Comparison Group 6 66.33 82.66 58.18 Comparison Group 7 45.87 60.58 32.31 Comparison Group 8 52.15 67.56 40.45 Comparison Group 9 63.52 79.45 54.45 Blank group 97.21 98.24 96.35

[0124] Analysis of Table 1 yields the following results:

[0125] 1. Compared with experimental group 1, the difference between control groups 1-3 and experimental group 1 lies in the raw materials used to prepare heavy metal treatment agent A. Control group 1 did not add glucose, resulting in a reduced initial carbon source for microorganisms, lower microbial activity, and slower microbial growth and reproduction rates. This led to a decrease in the efficiency of heavy metal treatment in control group 1, resulting in a higher heavy metal content. Control group 2 did not add β-cyclodextrin, resulting in a higher heavy metal content. This is because β-cyclodextrin can chelate heavy metals in the soil, reducing their content and thus creating a lower heavy metal content in the initial growth environment for microorganisms. However, the absence of β-cyclodextrin in control group 2 resulted in a higher heavy metal content in the initial growth environment for microorganisms, inhibiting their growth and reproduction, thus reducing the efficiency of heavy metal treatment. Control group 3 did not add papain or cassava starch. The decomposition rate of heavy metal treatment agent A was slower, meaning that when heavy metal treatment agent B began to release microorganisms, heavy metal treatment agent A did not create a favorable growth environment for them. This resulted in the inhibition of microbial growth and reproduction by heavy metals in the initial stage, leading to a decrease in the efficiency of heavy metal treatment.

[0126] 2. Compared to experimental group 1, control group 4 used gelatin instead of mixed gel. Gelatin is degraded by microorganisms more quickly than mixed gel, leading to a faster release of microorganisms from heavy metal treatment agent B. At this point, the soil heavy metal content was high, and heavy metal treatment agent A had not yet been properly decomposed. The microbial growth environment was poor, and growth was inhibited, resulting in low heavy metal treatment efficiency. In control group 5, unlike experimental group 1, particles B were not coated with mixed gel. The microorganisms were released too quickly, and heavy metal treatment agent A was not properly decomposed. The microorganisms were in an environment with high heavy metal content, inhibiting their growth and reproduction, resulting in low heavy metal treatment efficiency.

[0127] 3. Compared to experimental group 1, control group 6 did not add heavy metal treatment agent A, meaning only heavy metal treatment agent B was added. After the microorganisms were released, their growth and reproduction were inhibited by the higher heavy metal content in the surrounding environment, resulting in poor heavy metal treatment efficiency. Compared to experimental group 1, control group 7 used a mixture of heavy metal treatment agent A and heavy metal treatment agent B at a mass ratio of 2:1. The larger amount of heavy metal treatment agent A led to the rapid reproduction and growth of other microorganisms in the soil, making them the dominant species and affecting the microorganisms released from heavy metal treatment agent B. Furthermore, the smaller amount of heavy metal treatment agent B resulted in a lower content of microorganisms in the soil, leading to poor heavy metal treatment. Compared to experimental group 1, control group 8 used a mixture of heavy metal treatment agent A and heavy metal treatment agent B at a mass ratio of 1:2. The smaller amount of heavy metal treatment agent A resulted in less of the substances beneficial to microbial growth released from its decomposition, leading to a lower microbial growth rate than in experimental group 1 and poorer heavy metal treatment effect.

[0128] 4. Compared with experimental group 1, control group 9 was treated with heavy metal treatment agent A and microbial fermentation broth. The microorganisms were directly added to the soil. The initial content was low. The heavy metals inhibited the growth of microorganisms. Moreover, heavy metal treatment agent A could not be decomposed well to create a good growth environment for microorganisms, resulting in a reduction in the reproduction of microorganisms, a decrease in the treatment effect of heavy metals, and a higher content of heavy metals in the soil.

[0129] 5. The blank group, which was not treated with the heavy metal treatment agent, had a high content of heavy metals in its soil, while the soil treated with experimental group 1 had a low content of heavy metals. This indicates that the heavy metal treatment agent prepared in experimental group 1 can effectively reduce the content of heavy metals in the soil and has a high treatment efficiency.

[0130] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A method for treating heavy metals in soil using microorganisms, characterized in that, The method includes the following steps: (1) Soil treatment: The soil contaminated with heavy metals is tilled to a depth of 30-40cm; (2) Heavy metal treatment: Add heavy metal treatment agent to the soil, turn the soil again to make the heavy metal treatment agent fully contact the soil, then irrigate the land to adjust the soil moisture content to 25-30%, and cover the soil surface with a plastic film after irrigation. Remove the film after treatment is completed. The heavy metal treatment agent in step (2) includes heavy metal treatment agent A and heavy metal treatment agent B, wherein heavy metal treatment agent A and heavy metal treatment agent B are mixed evenly in a mass ratio of 1:

1. The preparation method of the heavy metal treatment agent is as follows: Heavy metal treatment agent A: S1: Add glucose to water and stir until completely dissolved to obtain a glucose solution. Then add β-cyclodextrin to the glucose solution and mix well. Heat the solution to 80-90℃, add gelatin, mix well, dry at 0-5℃ for 2-3 hours, and then pulverize to obtain granules A. S2: Add cassava starch to water at 70-80℃ for gelatinization. After gelatinization, cool to room temperature, add papain solution, mix well to obtain solution A, spray it on the surface of composite particles, and dry at 20-30℃ for 30-40 minutes to obtain treatment agent A. Heavy metal treatment agent B: S1: Mix soybean meal, diatomaceous earth, and seaweed polysaccharide evenly, place them in a granulator for granulation to obtain solid particles, put the solid particles into the microbial fermentation liquid for adsorption, take them out and air dry them to obtain particles B. S2: Add xanthan gum to water, stir evenly, heat the solution to 90-95℃, then add polyvinyl alcohol and glutaraldehyde, mix evenly and cool to room temperature to obtain a mixed gel; put particle B into the mixed gel until particle B is fully coated, then take it out and dry it at 20-30℃ for 30-40 minutes to obtain heavy metal treatment agent B. The preparation method of the microbial fermentation broth in the heavy metal treatment agent B is as follows: Trichoderma harzianum and Bacillus subtilis were inoculated into PDA medium and activated at 23-26℃ for 3-5 days. After activation, mycelial cakes of each strain were picked and added to fermentation broth at a 2% inoculation rate and cultured on a shaker at 25-28℃ and 200-220 r / min. When the effective viable count in each mixed fermentation broth reached (4-5) × 10⁻⁶, the inoculum was collected. 6 When the concentration of CFU / mL is reached, fermentation is stopped, and fermentation broths are obtained separately. The fermentation broths are then mixed at a volume ratio of 1:1 to obtain the microbial fermentation broth.

2. The method for treating heavy metals in soil using microorganisms according to claim 1, characterized in that, The processing time in step (2) is 50-60 days.

3. The method for treating heavy metals in soil using microorganisms according to claim 2, characterized in that, The amount of the heavy metal treatment agent used is per 1m 2 Use 30-40g of heavy metal treatment agent on the soil.

4. The method for treating heavy metals in soil using microorganisms according to claim 3, characterized in that, The mass ratio of glucose, β-cyclodextrin and gelatin in the heavy metal treatment agent A is (1.2-1.5):(1-1.2):(4-5), and the mass ratio of cassava starch and papain is (10-15):(1-1.2).

5. A method for treating heavy metals in soil using microorganisms according to claim 4, characterized in that, The mass ratio of soybean meal, diatomaceous earth, and seaweed polysaccharide in the heavy metal treatment agent B is (6-8):(3-4):(2-3), and the mass ratio of xanthan gum, polyvinyl alcohol, and glutaraldehyde is (3-4):(1-1.2):(0.15-0.2).

6. A method for treating heavy metals in soil using microorganisms according to claim 5, characterized in that, The particle size of the solid particles in the heavy metal treatment agent B is 2-3 mm.