Microbial fertilizer capable of reducing effectiveness of cadmium and preparation process of microbial fertilizer

Abstract

The invention provides a microbial fertilizer capable of reducing cadmium effectiveness and a preparation process thereof. The microbial fertilizer is prepared from the following raw materials in parts by weight: 20-30 parts of lactic acid, 20-30 parts of citric acid, 10-25 parts of starch, 15-20 parts of L-lysine, 15-25 parts of sodium tripolyphosphate, 0.1-1 part of lanthanum nitrate, 20-25 parts of fruit shells, 16-32 parts of a microbial agent and 5-20 parts of bone meal. According to the microbial fertilizer capable of reducing the effectiveness of cadmium and the preparation process of the microbial fertilizer, compared with polylactic acid, modified polylactic acid is adopted, so that the toughness and strength of the material are improved, the material is more durable in a soil environment, the hydrophilicity of the material is improved, the attachment and growth environment of microorganisms is improved, and the activity of the microorganisms is facilitated; by adjusting the grafting proportion, slow release of microorganisms can be achieved, the effectiveness and stability of the microorganisms in soil are prolonged, and it is ensured that the microorganisms continuously play a role in the remediation process.

Description

Technical Field

[0001] The present invention relates to the technical field of soil pollution treatment, and particularly relates to a microbial fertilizer capable of reducing the availability of cadmium and a preparation process thereof. Background Art

[0002] With the rapid development of industrialization and urbanization, the problem of soil pollution is becoming increasingly serious. Among them, cadmium and cadmium pollution are particularly prominent. Cadmium and cadmium are harmful heavy metals. Long-term accumulation in the soil will cause great harm to the ecological environment and human health. Cadmium and cadmium mainly come from industrial wastewater, waste gas emissions, and solid waste stacking. These pollutants accumulate in the soil, resulting in cadmium exceeding the standard, which in turn affects soil quality and the balance of the ecosystem. Cadmium and cadmium pollution have an inhibitory effect on the growth of crops, reducing the yield and quality of agricultural products. At the same time, through the food chain, it poses a potential threat to human health, such as causing skin diseases, respiratory diseases, etc.

[0003] The chemical reduction method is currently the most widely used remediation technology for cadmium pollution. However, this method has deficiencies in terms of post-remediation stability, high cost, poor operational convenience, and also has a certain negative impact on the environment.

[0004] Therefore, it is necessary to provide a microbial fertilizer capable of reducing the availability of cadmium and a preparation process thereof to solve the above technical problems. Summary of the Invention

[0005] The present invention provides a microbial fertilizer capable of reducing the availability of cadmium and a preparation process thereof, which solves the problems of insufficient stability, high cost, poor operational convenience, and negative environmental impact.

[0006] To solve the above technical problems, a microbial fertilizer capable of reducing the availability of cadmium provided by the present invention is composed of the following raw materials in parts by weight: 20 - 30 parts of lactic acid, 20 - 30 parts of citric acid, 10 - 25 parts of starch, 15 - 20 parts of L-lysine, 15 - 25 parts of sodium tripolyphosphate, 0.1 - 1 part of lanthanum nitrate, 20 - 25 parts of fruit shell, 16 - 32 parts of microbial inoculum, and 5 - 20 parts of bone meal;

[0007] The microbial inoculum component is a mixture of 5 - 10 parts of Geobacter lovleyi, 5 - 10 parts of Bacillus polymyxa, and 5 - 10 parts of Bacillus subtilis.

[0008] Preferably, the microbial inoculum further includes: 1 - 2 parts of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl, and ester functional groups.

[0009] Preferably, the preparation method of the modified polylactic acid includes the following steps:

[0010] S11, add the dehydrated L-lactic acid, diphenyl ether and stannous chloride into a three-necked flask and stir thoroughly, evacuate with a circulating water pump, raise the temperature to 150-200°C at a heating rate of 10°C / min, and react for 3h;

[0011] S12. After the reaction is completed, the obtained sample is distilled, and after the solvent is evaporated, a certain amount of acetone is added to dissolve it, and then the obtained solution is precipitated in a large amount of water and filtered. The obtained polylactic acid is vacuum dried to constant weight to obtain a white powdery product;

[0012] S13, dissolving polylactic acid in tetrahydrofuran heated to 50°C, introducing N2, stirring thoroughly, heating to 66°C and then starting constant temperature reflux, and adding acrylic acid and dibenzoyl peroxide in 4 portions within 2 minutes;

[0013] S14. After the reaction is completed, 50 mL of 95% ethanol solution is added to the reaction product solution. After a white precipitate appears, the precipitate and the solution are poured into a sand core crucible with constant weight for suction filtration. The precipitate is washed twice with 95% ethanol, and the precipitate and the sand core crucible are placed in a 50° C. constant temperature oven and dried to constant weight to obtain a crude graft copolymer.

[0014] S15. Pour the crude graft copolymer into a Soxhelt extractor, use acetone as solvent, extract for 16 hours, reflux 5 to 6 times per hour to remove the homopolymer, and bake the residue after extraction in a constant temperature oven at 50°C to constant weight to obtain a pure graft copolymer, which is modified polylactic acid.

[0015] Preferably, the preparation method of the microbial agent comprises the following steps:

[0016] S21, placing Bacillus lovrei, Bacillus polymyxa and Bacillus subtilis in a seed culture medium, and culturing them at a temperature of 25 to 30° C. and a shaking speed of 100 to 200 r / min for 1 to 2 days to obtain corresponding seed solutions;

[0017] S22, inoculating the seed liquid into a fermentation medium at a volume ratio of 4-8%, and shaking and culturing for 2-4 days at a temperature of 25-33° C. and a shaking speed of 100-150 r / min to obtain a corresponding fermentation bacterial liquid;

[0018] S23. The modified polylactic acid and the fermentation solution are fully mixed in a mass ratio of 1:2.5, shaken at a temperature of 30°C and a shaker speed of 200 r / min, then placed in a constant temperature incubator at 30°C for fermentation for 48 hours, and finally dried at a constant temperature of 50°C to obtain the corresponding microbial agent.

[0019] Preferably, the components of the seed culture medium are as follows: 10 g of sucrose, 5 g of peptone, 0.01 g of FeSO4·7H2O, 0.5 g of MgSO4·7H2O, and 1 L of distilled water.

[0020] Preferably, the components of the fermentation culture medium are as follows: 20 g of corn flour, 10 g of sucrose, 2 g of peptone, 2 g of yeast extract, 2 g of NaCl, 0.5 g of MgSO4, and 1 L of distilled water.

[0021] Preferably, a constant temperature device is required in step S14. The constant temperature device includes a constant temperature box body. A driving motor is fixedly installed on the back of the constant temperature box body. A lead screw is fixedly installed at the output end of the driving motor. A threaded sleeve is threadedly connected to the outer side of the lead screw. A support plate is fixedly installed on the outer side of the threaded sleeve.

[0022] Preferably, sliding sleeves are fixedly installed at both ends of the bottom of the support plate. A support plate is slidably connected to the inner side of the sliding sleeve. Both support plates are fixedly installed on the inner side of the constant temperature box body. A control switch is fixedly installed on one side of the constant temperature box body. The control switch is electrically connected to the driving motor.

[0023] Preferably, a door body is rotatably connected to the front of the constant temperature box body. Support feet are fixedly installed around the bottom of the constant temperature box body.

[0024] To solve the above problems, the present invention also provides a preparation process for a microbial fertilizer capable of reducing the availability of cadmium. The method includes the following steps:

[0025] S31. Prepare modified polylactic acid;

[0026] S32. Prepare a microbial inoculant;

[0027] S33. Weigh each raw material according to the ratio, and then perform a drying treatment. After the dried raw materials are fully mixed evenly, add them to an air flow pulverizer, and control the fineness of the pulverized material to be between 200 and 300 mesh. Granulate the pulverized material to obtain a solid microbial soil conditioner.

[0028] Compared with the related technology, a microbial fertilizer capable of reducing the availability of cadmium and its preparation process provided by the present invention have the following beneficial effects:

[0029] The present invention provides a microbial fertilizer capable of reducing cadmium availability and its preparation process. By using modified polylactic acid, compared with polylactic acid, the toughness and strength of the material are improved, making it more durable in the soil environment, increasing the hydrophilicity of the material, improving the attachment and growth environment of microorganisms, contributing to the activity of microorganisms. By adjusting the grafting ratio, the slow release of microorganisms can be achieved, extending their effectiveness and stability in the soil, and ensuring that microorganisms continuously play a role in the remediation process;

[0030] Through the cooperation of microorganisms such as Geobacter lovleyi, Bacillus polymyxa, and Bacillus subtilis, they have better adaptability and survival ability, can act synergistically, promote the transformation and fixation of chromium, and reduce environmental pollution;

[0031] Moreover, the microbial soil conditioner has a low cost, is easy to produce and apply on a large scale, and is also relatively simple to use, and can be applied to the remediation of different types of soil chromium pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a micrograph of Geobacter lovleyi in the microbial agent provided by the present invention;

[0033] Figure 2 It is a micrograph of Bacillus polymyxa in the microbial agent provided by the present invention;

[0034] Figure 3 It is a micrograph of Bacillus subtilis in the microbial agent provided by the present invention;

[0035] Figure 4 It is a schematic structural diagram of a preferred embodiment of a constant temperature device for the microbial fertilizer capable of reducing cadmium availability provided by the present invention;

[0036] Figure 5 For Figure 4 The schematic structural diagram of another perspective shown;

[0037] Figure 6 For Figure 4 The schematic structural diagram of the bottom of the tray shown;

[0038] Reference numerals in the figure: 1, constant temperature box body; 11, door body; 12, support feet; 2, drive motor; 21, lead screw; 22, threaded sleeve; 23, tray; 24, sliding sleeve; 3, support plate; 4, control switch. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The present invention will be further described below with reference to the drawings and embodiments.

[0040] First Embodiment

[0041] Please refer to Figure 1 、Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 , wherein, Figure 1 is the micrograph of Geobacter lovleyi in the microbial inoculant provided by the present invention; Figure 2 is the micrograph of Bacillus polymyxa in the microbial inoculant provided by the present invention; Figure 3 is the micrograph of Bacillus subtilis in the microbial inoculant provided by the present invention; Figure 4 is the schematic structural diagram of a preferred embodiment of a constant temperature device for a microbial fertilizer capable of reducing the availability of cadmium provided by the present invention; Figure 5 is Figure 4 the schematic structural diagram of another perspective shown in Figure 6 is Figure 4 the schematic structural diagram of the bottom of the pallet shown in . A microbial fertilizer capable of reducing the availability of cadmium and its preparation process are composed of the following raw materials in parts by weight: 20 - 30 parts of lactic acid, 20 - 30 parts of citric acid, 10 - 25 parts of starch, 15 - 20 parts of L-lysine, 15 - 25 parts of sodium tripolyphosphate, 0.1 - 1 part of lanthanum nitrate, 20 - 25 parts of fruit shell, 16 - 32 parts of microbial inoculant, 5 - 20 parts of bone meal;

[0042] The microbial inoculant component is a mixture of 5 - 10 parts of Geobacter lovleyi, 5 - 10 parts of Bacillus polymyxa and 5 - 10 parts of Bacillus subtilis.

[0043] The microbial inoculant further includes: 1 - 2 parts of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl and ester functional groups.

[0044] The preparation method of the modified polylactic acid includes the following steps:

[0045] S11. Add dehydrated and dried L-lactic acid, diphenyl ether and stannous chloride to a three-necked flask, stir well, evacuate with a circulating water pump, raise the temperature to 150 - 200 °C at a rate of 10 °C / min, and react for 3 h;

[0046] S12. After the reaction is completed, distill the obtained sample, add a certain amount of acetone to dissolve it after evaporating the solvent, then precipitate the obtained solution in a large amount of water and filter it. The obtained polylactic acid is dried in vacuum to constant weight to obtain a white powdery product;

[0047] S13. Dissolve the polylactic acid in tetrahydrofuran heated to 50 °C, introduce N2, stir well, raise the temperature to 66 °C and then start constant temperature reflux, and add acrylic acid and benzoyl peroxide in 4 portions within 2 min;

[0048] S14. After the reaction is completed, 50 mL of 95% ethanol solution is added to the reaction product solution. After a white precipitate appears, the precipitate and the solution are poured into a sand core crucible with constant weight for suction filtration. The precipitate is washed twice with 95% ethanol, and the precipitate and the sand core crucible are placed in a 50° C. constant temperature oven and dried to constant weight to obtain a crude graft copolymer.

[0049] S15. Pour the crude graft copolymer into a Soxhelt extractor, use acetone as solvent, extract for 16 hours, reflux 5 to 6 times per hour to remove the homopolymer, and bake the residue after extraction in a constant temperature oven at 50°C to constant weight to obtain a pure graft copolymer, which is modified polylactic acid.

[0050] The preparation method of the microbial agent comprises the following steps:

[0051] S21, placing Bacillus lovrei, Bacillus polymyxa and Bacillus subtilis in a seed culture medium, and culturing them at a temperature of 25 to 30° C. and a shaking speed of 100 to 200 r / min for 1 to 2 days to obtain corresponding seed solutions;

[0052] S22, inoculating the seed liquid into a fermentation medium at a volume ratio of 4-8%, and shaking and culturing for 2-4 days at a temperature of 25-33° C. and a shaking speed of 100-150 r / min to obtain a corresponding fermentation bacterial liquid;

[0053] S23. The modified polylactic acid and the fermentation solution are fully mixed in a mass ratio of 1:2.5, shaken at a temperature of 30°C and a shaker speed of 200 r / min, then placed in a constant temperature incubator at 30°C for fermentation for 48 hours, and finally dried at a constant temperature of 50°C to obtain the corresponding microbial agent.

[0054] The components of the seed culture medium are as follows: 10 g sucrose, 5 g peptone, 0.01 g FeSO4·7H2O, 0.5 g MgSO4·7H2O, and 1 L distilled water.

[0055] The ingredients of the fermentation medium are as follows: 20 g corn flour, 10 g sucrose, 2 g peptone, 2 g yeast extract, 2 g NaCl, 0.5 g MgSO4, and 1 L distilled water.

[0056] When the microbial soil conditioner is applied to cadmium - contaminated soil, the microbial inoculant therein begins to exert its unique functions. Protected by modified polylactic acid, the microorganisms quickly adapt to the soil environment and start their work. First of all, Bacillus polymyxa and Bacillus subtilis effectively adsorb cadmium ions in the soil with the help of their cell walls and secreted extracellular polysaccharides. This adsorption not only reduces the bioavailability and mobility of cadmium, decreases the harm of metallic cadmium to the soil ecosystem, but also lays the foundation for the subsequent bioremediation process. At the same time, through the quorum - sensing system, Bacillus polymyxa and Bacillus subtilis can produce and respond to signal molecules such as N - acyl - homoserine lactone. These signal molecules accelerate the reproduction rate of Geobacter lovleyi. Geobacter lovleyi can transform divalent cadmium ions into complexed cadmium through its metabolic pathway. When the number of Geobacter lovleyi increases, the reduction rate of cadmium ions becomes faster, thereby improving the remediation efficiency of soil cadmium pollution. To further enhance this remediation process, acrylic acid is introduced into the modified polylactic acid. This chemical substance can form a protective layer on the polylactic acid molecular chain, shielding the signal molecules, reducing the contact between signal molecules and other reactive substances, slowing down the degradation or decomposition reaction of signal molecules, thus improving the chemical stability of signal molecules and enabling signal molecules to continuously act in the environment, providing a persistent communication mechanism for the synergistic action of microorganisms. Under the action of Geobacter lovleyi, the polylactase can specifically hydrolyze the ester bonds in the modified polylactic acid, thereby initiating its degradation process. On the other hand, the esterase secreted by Bacillus polymyxa and Bacillus subtilis can precisely cut the ester bonds of the modified polylactic acid, significantly enhancing the degradation rate of the modified polylactic acid. In addition, under the guidance of signal molecules, Bacillus polymyxa and Bacillus subtilis also synthesize polymerase. This process enhances the hydrophilicity of the modified polylactic acid, making the modified polylactic acid more easily become the target of enzymes, facilitating the subsequent enzymatic hydrolysis and ensuring the efficient degradation of the modified polylactic acid. The degradation products of the modified polylactic acid, such as lactic acid, can serve as the carbon source for microorganisms, promoting the growth and metabolism of microorganisms, and further enhancing the quorum - sensing behavior of the microbial population. The enhancement of the quorum - sensing behavior of the microbial population not only increases the concentration and activity of signal molecules, but also promotes the interaction between microorganisms, forming a dynamic remediation cycle, further improving the remediation efficiency of contaminated soil and the ecological restoration ability;

[0057] In summary, through the application of the microbial soil conditioner, combined with the special design of modified polylactic acid and the synergistic effect among Bacillus polymyxa, Bacillus subtilis, and Geobacter lovleyi, the process of contaminated soil remediation has been significantly accelerated. It not only effectively reduces the cadmium ion pollution but also promotes the restoration of the soil ecosystem and the healthy growth of the microbial community. This method meets the requirements of environmental protection and sustainable development, ensuring the safety and environmental friendliness of microbial agents in the soil remediation process and providing a green and sustainable solution for soil remediation;

[0058] The microbial fertilizer reduces the activity of heavy metals in the soil, decreases the absorption of heavy metals by plant roots, contains macromolecular anionic groups, reduces the penetration ability of soil heavy metals to the roots, and the conduction of heavy metals in root cells, thus reducing the harm of heavy metals;

[0059] This product adopts the spraying granulation process and has the characteristics of uniform granulation, round particles, bright color, stable quality, comprehensive nutrients, easy dissolution, and easy absorption. Scientific use of this product can meet the nutritional needs of crop growth, improve the micro-ecological environment in the crop root zone, provide important energy for the growth and reproduction of microorganisms, and the large amount of active organic matter contained can also improve the soil, enhance soil air permeability, promote crop root activity, and better improve soil fertility.

[0060] This product can be used as a base fertilizer or top dressing (can be flushed), and is widely applicable to paddy and dryland crops such as field crops, fruits, and vegetables.

[0061] In step S14, a constant temperature device is required. The constant temperature device includes a constant temperature box body 1. A driving motor 2 is fixedly installed on the back of the constant temperature box body 1. The output end of the driving motor 2 is fixedly installed with a lead screw 21. A threaded sleeve 22 is threadedly connected to the outer side of the lead screw 21. A support plate 23 is fixedly installed on the outer side of the threaded sleeve 22.

[0062] Both ends of the bottom of the support plate 23 are fixedly installed with sliding sleeves 24. The inner side of the sliding sleeves 24 is slidably connected to a support plate 3. Both of the support plates 3 are fixedly installed on the inner side of the constant temperature box body 1. A control switch 4 is fixedly installed on one side of the constant temperature box body 1. The control switch 4 is electrically connected to the driving motor 2.

[0063] A door body 11 is rotatably connected to the front of the constant temperature box body 1. Support feet 12 are fixedly installed around the bottom of the constant temperature box body 1.

[0064] Compared with the related technology, a microbial fertilizer capable of reducing cadmium availability and its preparation process provided by the present invention have the following beneficial effects:

[0065] By using modified polylactic acid, compared with polylactic acid, the toughness and strength of the material are improved, making it more durable in the soil environment, increasing the hydrophilicity of the material, improving the attachment and growth environment of microorganisms, contributing to the activity of microorganisms. By adjusting the grafting ratio, the slow release of microorganisms can be achieved, extending its effectiveness and stability in the soil, and ensuring that microorganisms continuously play a role in the remediation process;

[0066] Through the cooperation of microorganisms such as Geobacter lovleyi, Bacillus polymyxa, and Bacillus subtilis, they have better adaptability and survival ability, can act synergistically, promote the transformation and fixation of cadmium, and reduce environmental pollution;

[0067] And the microbial soil conditioner has a low cost, is easy to produce and apply on a large scale, and is also relatively simple to use, and can be applied to the remediation of cadmium pollution in different types of soil.

[0068] To solve the above problems, the present invention also provides a preparation process of a microbial fertilizer that can reduce the availability of cadmium, and the method includes the following steps:

[0069] S31. Prepare modified polylactic acid;

[0070] S32. Prepare a microbial inoculant;

[0071] S33. Weigh each raw material according to the ratio, then perform a drying treatment, fully mix the dried raw materials evenly and add them to an air flow pulverizer, control the fineness of the pulverized material to be between 200 and 300 meshes, and granulate the pulverized material to obtain a solid microbial soil conditioner.

[0072] Example Two

[0073] This example discloses a microbial fertilizer that can reduce the availability of cadmium, which is composed of the following raw materials in parts by weight: 20 parts of lactic acid, 20 parts of citric acid, 10 parts of starch, 15 parts of L-lysine, 15 parts of sodium tripolyphosphate, 0.1 part of lanthanum nitrate, 20 parts of fruit shell, 16 parts of microbial inoculant, 5 parts of bone meal, a mixture of 5 parts of Geobacter lovleyi, 5 parts of Bacillus polymyxa, and 5 parts of Bacillus subtilis. The microbial inoculant component also includes: 1 part of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl, and ester functional groups.

[0074] The preparation methods of the modified polylactic acid and the microbial inoculant in this example are the same as those in Example One. The preparation method of a microbial fertilizer that can reduce the availability of cadmium in this example is the same as that in Example One.

[0075] Example Three

[0076] This example discloses a microbial fertilizer that can reduce the availability of cadmium, which is composed of the following raw materials in parts by weight: 30 parts of lactic acid, 30 parts of citric acid, 25 parts of starch, 20 parts of L-lysine, 25 parts of sodium tripolyphosphate, 1 part of lanthanum nitrate, 25 parts of fruit shell, 32 parts of microbial inoculum, and 20 parts of bone meal. The microbial inoculum component is a mixture of 10 parts of Geobacter lovleyi, 10 parts of Bacillus polymyxa, and 10 parts of Bacillus subtilis. The microbial inoculum component also includes: 2 parts of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl, and ester functional groups.

[0077] The preparation methods of the modified polylactic acid and the microbial inoculum in this example are the same as those in Example 1. The preparation method of a microbial fertilizer that can reduce the availability of cadmium in this example is the same as that in Example 1.

[0078] Example 4

[0079] This example discloses a microbial fertilizer that can reduce the availability of cadmium ions, which is composed of the following raw materials in parts by weight: 25 parts of lactic acid, 25 parts of citric acid, 18 parts of starch, 17 parts of L-lysine, 22 parts of sodium tripolyphosphate, 0.5 part of lanthanum nitrate, 23 parts of fruit shell, 25 parts of microbial inoculum, and 12 parts of bone meal. The microbial inoculum component is a mixture of 8 parts of Geobacter lovleyi, 8 parts of Bacillus polymyxa, and 8 parts of Bacillus subtilis. The microbial inoculum component also includes: 1 part of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl, and ester functional groups.

[0080] The preparation methods of the modified polylactic acid and the microbial inoculum in this example are the same as those in Example 1. The preparation method of a microbial fertilizer that can reduce the availability of cadmium in this example is the same as that in Example 1.

[0081] Example 5

[0082] This example discloses a microbial fertilizer that can reduce the availability of cadmium ions, which is composed of the following raw materials in parts by weight: 28 parts of lactic acid, 27 parts of citric acid, 15 parts of starch, 19 parts of L-lysine, 18 parts of sodium tripolyphosphate, 0.8 part of lanthanum nitrate, 21 parts of fruit shell, 19 parts of microbial inoculum, and 18 parts of bone meal. The microbial inoculum component is a mixture of 6 parts of Geobacter lovleyi, 6 parts of Bacillus polymyxa, and 6 parts of Bacillus subtilis. The microbial inoculum component also includes: 1 part of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl, and ester functional groups.

[0083] The preparation methods of the modified polylactic acid and microbial inoculum in this example are the same as those in Example 1. The preparation method of a microbial fertilizer capable of reducing the availability of cadmium ions in this example is the same as that in Example 1.

[0084] Control Group 1

[0085] The difference between this example and Example 1 is that it does not contain Geobacter lovleyi.

[0086] This example discloses a microbial fertilizer capable of reducing the availability of cadmium ions, which is composed of the following raw materials by weight: 23 parts of citric acid, 20 parts of starch, 18 parts of L-lysine, 20 parts of sodium tripolyphosphate, 0.2 part of lanthanum nitrate, 22 parts of fruit shell, 22 parts of microbial inoculum, and 10 parts of bone meal. The components of the microbial inoculum are a mixture of 6 parts of Bacillus polymyxa and 7 parts of Bacillus subtilis. The components of the microbial inoculum also include: 1 part of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl, and ester functional groups.

[0087] The preparation methods of the modified polylactic acid and microbial inoculum in this example are the same as those in Example 1. The preparation method of a microbial fertilizer capable of reducing the availability of cadmium in this example is the same as that in Example 1.

[0088] Control Group 2

[0089] The difference between this example and Example 1 is that it does not contain Bacillus polymyxa and Bacillus subtilis.

[0090] This example discloses a microbial fertilizer capable of reducing the availability of cadmium, which is composed of the following raw materials by weight: 22 parts of lactic acid, 23 parts of citric acid, 18 parts of L-lysine, 20 parts of sodium tripolyphosphate, 0.2 part of lanthanum nitrate, 22 parts of fruit shell, 22 parts of microbial inoculum, and 10 parts of bone meal. The components of the microbial inoculum are 8 parts of Geobacter lovleyi. The components of the microbial inoculum also include: 1 part of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl, and ester functional groups.

[0091] The preparation methods of the modified polylactic acid and microbial inoculum in this example are the same as those in Example 1. The preparation method of a microbial fertilizer capable of reducing the availability of cadmium ions in this example is the same as that in Example 1.

[0092] Control Group 3

[0093] The difference between this example and Example 1 is that it does not contain modified polylactic acid.

[0094] This example discloses a microbial fertilizer that can reduce the availability of cadmium ions, which is composed of the following raw materials in parts by weight: 22 parts of lactic acid, 23 parts of citric acid, 20 parts of starch, 18 parts of L-lysine, 0.2 part of lanthanum nitrate, 22 parts of fruit shell, 22 parts of microbial inoculum, and 10 parts of bone meal. The microbial inoculum is a mixture of 8 parts of Geobacter lovleyi, 6 parts of Bacillus polymyxa, and 7 parts of Bacillus subtilis.

[0095] The preparation methods of the modified polylactic acid and the microbial inoculum in this example are the same as those in Example 1. The preparation method of a microbial fertilizer that can reduce the availability of cadmium ions in this example is the same as that in Example 1.

[0096] Experimental verification: Weigh 2 kg of pollution-free soil, air-dry and crush it, add 4 L of a Cr(VI) standard solution with a concentration of 180 mg / kg, and then stir, air-dry and crush it to obtain simulated polluted soil. Take 8 plastic bottles, add the soil samples passed through a 20-mesh sieve respectively, and then add the microbial soil conditioners of each experimental example group and the control group for remediation. During the remediation period, take out the plastic bottles regularly every 5 days to measure the soil weight and the Cd2+ concentration, and calculate the degradation rate of the modified polylactic acid and the reduction rate of cadmium ions from these data.

[0097] To calculate the degradation rate of the modified polylactic acid, first, the degradation amount of the modified polylactic acid needs to be measured. The weight loss method can be used. Monitor the weight loss of the carrier by weighing, record the weight loss at each sampling, and indirectly reflect the degradation amount. Divide the measured degradation amount of the modified polylactic acid after each sampling by the initial amount of the modified polylactic acid to obtain the degradation rate of the modified polylactic acid.

[0098] To calculate the reduction rate of cadmium ions, the availability of cadmium ions in the initial soil and the availability of cadmium ions after each sampling need to be measured.

[0099] Determination of cadmium ions in soil: Weigh 2.5 g of soil sample into a 250 mL Erlenmeyer flask, add 50 mL of 0.28 M Na2CO3 + 0.5 M NaOH (digestion solution), add 0.4 g of MgCl2, and then add 0.5 mL of 0.5 M phosphate buffer (K2HPO4 / KHPO4), and stir for 5 minutes. Heat the sample to 90 - 95 °C, and continue heating at this temperature for 60 minutes while constantly stirring. Slowly cool to room temperature. Transfer all the samples to a filtration device. The sample passes through a 0.45 μm microfiltration membrane, wash the Erlenmeyer flask with deionized water, collect the filtrate and the rinsing solution in a 250 mL Erlenmeyer flask, and store the filter paper at 4 °C. Slowly add 5.0 M HNO3 drop by drop to the filtrate (while constantly stirring) to adjust the pH to 9.0 ± 0.5. Transfer the sample solution to a 100 mL volumetric flask, make up the volume, and measure.

[0100] The change in cadmium ion content can be obtained by subtracting the cadmium ion availability after each sampling from the cadmium ion availability in the initial soil. The reduction rate of cadmium ions can be obtained by dividing the change in cadmium ion content by the cadmium ion availability in the initial soil.

[0101] The reduction rates of ionic cadmium in the experimental group and the control group for soil cadmium pollution remediation are shown in Table 1. From the data in Table 1, it can be seen that the microbial soil conditioner formula in the experimental group is significantly superior to the control group in terms of the reduction rate of cadmium ions. This indicates that the mixture of Geobacter lovleyi, Bacillus polymyxa, Bacillus subtilis and modified polylactic acid added in the examples has a significant effect on improving the reduction efficiency of ionic cadmium in the soil. In the experimental group, there are differences in the reduction rates of different examples, which may be related to the different ratios of microbial agents and modified polylactic acid in each example. By optimizing the ratios of these components, the role of the microbial soil conditioner in the cadmium ion reduction process can be further exerted.

[0102] The degradation rates of modified polylactic acid in the experimental group and the control group for soil cadmium pollution remediation are shown in Table 2. The experimental group has an improved degradation rate of modified polylactic acid compared to the control group, which further confirms the promoting effect of Geobacter lovleyi, Bacillus polymyxa, and Bacillus subtilis on the degradation process of modified polylactic acid. In the experimental group, the degradation rate of modified polylactic acid in Example 1 increased most significantly, from 8.24% initially to 33.67% finally. This significant increase may be related to the specific formula ratio in Example 1, indicating that by precisely adjusting the formula ratio, the degradation rate of modified polylactic acid can be further optimized.

[0103] Table 1 Reduction rates of hexavalent chromium in the experimental group and the control group for soil Chromium pollution remediation

[0104] Group 5D 10D 15D 20D Example 1 34.23％ 56.97％ 89.52％ 92.49％ Example 2 22.54％ 40.84％ 60.61％ 76.34％ Example 3 30.68％ 49.66％ 71.58％ 85.88％ Example 4 27.82％ 47.39％ 64.65％ 79.03％ Example 5 28.19％ 48.25％ 64.59％ 81.92％ Control Group 1 0.27％ 0.66％ 0.78％ 0.84％ Control Group 2 8.14％ 13.58％ 14.57％ 15.63％ Control Group 3 9.18％ 18.98％ 22.58％ 36.08％

[0105] Table 2 Degradation rates of modified polylactic acid in the experimental group and the control group for soil Chromium pollution remediation

[0106] Group 5D 10D 15D 20D Example 1 8.24％ 12.56％ 28.74％ 33.67％ Example 2 5.72％ 8.46％ 17.46％ 24.87％ Example 3 7.38％ 10.24％ 23.75％ 28.36％ Example 4 6.34％ 9.85％ 20.98％ 26.68％ Example 5 6.98％ 9.37％ 21.25％ 27.23％ Control Group 1 3.11％ 4.12％ 5.62％ 7.46％ Control Group 2 1.14％ 2.58％ 3.57％ 4.63％ Control Group 3 0％ 0％ 0％ 0％

[0107] After the above effective tests, a microbial fertilizer component in Example 1 of the present invention that can reduce cadmium availability shows significant application effects in both the reduction rate of cadmium ions and the degradation rate of modified polylactic acid. This microbial soil conditioner can effectively exert the cadmium removal efficiency and has practical application value for the remediation of soil cadmium pollution. By optimizing the ratios of components such as the microbial mixture and modified polylactic acid, the effect of the soil conditioner in the process of soil cadmium pollution remediation can be further improved, providing a feasible method for solving soil pollution problems.

[0108] The above are only embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall similarly be included within the patent protection scope of the present invention.

Claims

1. A microbial fertilizer capable of reducing the effectiveness of cadmium, characterized in that: The invention is composed of the following raw materials in parts by weight: 20-30 parts of lactic acid, 20-30 parts of citric acid, 10-25 parts of starch, 15-20 parts of L-lysine, 15-25 parts of sodium tripolyphosphate, 0.1-1 part of lanthanum nitrate, 20-25 parts of fruit shells, 16-32 parts of microbial agents, and 5-20 parts of bone powder; The microbial agent component is a mixture of 5 to 10 parts of Bacillus lovreyi, 5 to 10 parts of Bacillus polymyxa and 5 to 10 parts of Bacillus subtilis.

2. The microbial fertilizer capable of reducing the effectiveness of cadmium according to claim 1, characterized in that: The microbial agent also includes: 1-2 parts of modified polylactic acid; the modified polylactic acid is generated by graft copolymerization of polylactic acid and acrylic acid, and the surface of the modified polylactic acid has hydroxyl, carboxyl and ester functional groups.

3. A microbial fertilizer capable of reducing the effectiveness of cadmium according to claim 2, characterized in that: The preparation method of the modified polylactic acid comprises the following steps: S11, add the dehydrated L-lactic acid, diphenyl ether and stannous chloride into a three-necked flask and stir thoroughly, evacuate with a circulating water pump, raise the temperature to 150-200°C at a heating rate of 10°C / min, and react for 3h; S12. After the reaction is completed, the obtained sample is distilled, and after the solvent is evaporated, a certain amount of acetone is added to dissolve it, and then the obtained solution is precipitated in a large amount of water and filtered. The obtained polylactic acid is vacuum dried to constant weight to obtain a white powdery product; S13, dissolving polylactic acid in tetrahydrofuran heated to 50°C, introducing N2, stirring thoroughly, heating to 66°C and then starting constant temperature reflux, and adding acrylic acid and dibenzoyl peroxide in 4 portions within 2 minutes; S14. After the reaction is completed, 50 mL of 95% ethanol solution is added to the reaction product solution. After a white precipitate appears, the precipitate and the solution are poured into a sand core crucible with constant weight for suction filtration. The precipitate is washed twice with 95% ethanol, and the precipitate and the sand core crucible are placed in a 50° C. constant temperature oven and dried to constant weight to obtain a crude graft copolymer. S15. Pour the crude graft copolymer into a Soxhelt extractor, use acetone as solvent, extract for 16 hours, reflux 5 to 6 times per hour to remove the homopolymer, and bake the residue after extraction in a constant temperature oven at 50°C to constant weight to obtain a pure graft copolymer, which is modified polylactic acid.

4. The microbial fertilizer capable of reducing the effectiveness of cadmium according to claim 1, characterized in that: The preparation method of the microbial agent comprises the following steps: S21, placing Bacillus lovrei, Bacillus polymyxa and Bacillus subtilis in a seed culture medium, and culturing them at a temperature of 25 to 30° C. and a shaking speed of 100 to 200 r / min for 1 to 2 days to obtain corresponding seed solutions; S22, inoculating the seed liquid into a fermentation medium at a volume ratio of 4-8%, and shaking and culturing for 2-4 days at a temperature of 25-33° C. and a shaking speed of 100-150 r / min to obtain a corresponding fermentation bacterial liquid; S23. The modified polylactic acid and the fermentation solution are fully mixed in a mass ratio of 1:2.5, shaken at a temperature of 30°C and a shaker speed of 200 r / min, then placed in a constant temperature incubator at 30°C for fermentation for 48 hours, and finally dried at a constant temperature of 50°C to obtain the corresponding microbial agent.

5. The microbial fertilizer capable of reducing the effectiveness of cadmium according to claim 4, characterized in that: The components of the seed culture medium are as follows: 10 g sucrose, 5 g peptone, 0.01 g FeSO4·7H2O, 0.5 g MgSO4·7H2O, and 1 L distilled water.

6. The microbial fertilizer capable of reducing the effectiveness of cadmium according to claim 4, characterized in that: The components of the fermentation medium are as follows: 20 g corn flour, 10 g sucrose, 2 g peptone, 2 g yeast extract, 2 g NaCl, 0.5 g MgSO4, and 1 L distilled water.

7. The microbial fertilizer capable of reducing the effectiveness of cadmium and its preparation process according to claim 1, characterized in that: A constant temperature device is required in step S14, and the constant temperature device includes a constant temperature box, a drive motor is fixedly installed on the back of the constant temperature box, a screw rod is fixedly installed on the output end of the drive motor, the outer side surface of the screw rod is threadedly connected with a threaded sleeve, and the outer side surface of the threaded sleeve is fixedly installed with a support plate.

8. The microbial fertilizer capable of reducing the effectiveness of cadmium and its preparation process according to claim 7, characterized in that: Both ends of the bottom of the support plate are fixedly installed with sliding sleeves, the inner side of the sliding sleeve is slidably connected with a support plate, the two support plates are fixedly installed on the inner side of the constant temperature box, and a control switch is fixedly installed on one side of the constant temperature box, and the control switch is electrically connected to the drive motor.

9. The microbial fertilizer capable of reducing the effectiveness of cadmium and its preparation process according to claim 7, characterized in that: The front side of the constant temperature box is rotatably connected with a door body, and supporting feet are fixedly installed around the bottom of the constant temperature box.

10. A process for preparing a microbial fertilizer capable of reducing the effectiveness of cadmium, which is applied to prepare the microbial fertilizer capable of reducing the content of cadmium and chromium as claimed in any one of claims 1 to 9, characterized in that: The method comprises the following steps: S31, preparing modified polylactic acid; S32, preparing a microbial agent; S33, weighing each raw material according to the proportion, and then drying it, mixing the dried raw materials thoroughly and adding them to the air flow mill, controlling the fineness of the crushed material to be between 200 and 300 meshes, granulating the crushed material to obtain a solid microbial soil conditioner.

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