Microsphere structure for soil improvement and preparation method and application thereof

Abstract

The invention discloses a microsphere structure for soil improvement and a preparation method and application thereof, and belongs to the technical field of soil treatment. According to the structure, MBBR filler is used as a carrier, the microsphere is composed of an inner core, a middle layer and an outer layer, the inner core contains sodium percarbonate, super absorbent resin and triacontanol, and cooperation of water retention and steam disinfection is achieved; the middle layer is sodium alginate gel, MnO2, humic acid and calcium magnesium phosphate fertilizer are embedded in the middle layer, and the soil microenvironment can be adjusted and nutrients can be supplemented; the outer layer is a temperature-sensitive blended membrane of chitosan and poly (N-isopropylacrylamide), and can respond to the environment to accurately release the components in a controlled manner; in the preparation process, microspheres are constructed in a layered manner through an emulsion method, and then the microspheres are loaded on the MBBR filler; the structure is excellent in performance in soil steam disinfection, the disinfection efficiency can be improved, soil ecological restoration is promoted, and the problems that an existing material is single in function and poor in effect are solved.

Description

Technical Field

[0001] This application belongs to the field of soil remediation technology, specifically relating to a microsphere structure for soil improvement, its preparation method, and its application. Background Technology

[0002] Soil, as the core carrier of agricultural production and ecosystem stability, directly determines crop yield, agricultural product safety, and regional ecological balance. In recent years, due to the combined effects of intensive agricultural planting, industrial pollutant emissions, unreasonable fertilization and pesticide use, and extreme climate, global soils are facing severe challenges of accelerated degradation and functional decline. Soil remediation has become a key issue for ecological environmental protection and sustainable agricultural development. The core challenges of soil remediation lie in multiple dimensions: First, soil pollution is prominent, with a complex interplay of pollution types, including excessive heavy metals, accumulated pesticide and fertilizer residues, and the proliferation of pathogens. This not only damages the soil microbial community structure and reduces soil biological activity but also threatens human health through the food chain. Second, soil physical and chemical properties are deteriorating. Long-term continuous cropping and over-cultivation have led to the destruction of soil aggregate structure, reduced water and fertilizer retention capacity, and problems such as compaction, sandification, acidification, or salinization. This results in nutrient imbalance and poor aeration, hindering crop root development. Third, soil ecological functions are degrading. Under the dual effects of pollution and deterioration of physical and chemical properties, the number of beneficial microorganisms in the soil has sharply decreased, material cycling and energy flow have been hindered, and the soil's self-repair capacity has been lost, forming a vicious cycle of pollution-degradation-decreased productivity.

[0003] To address these issues, existing soil remediation technologies and materials have diversified, but they generally suffer from limitations such as single function, poor synergistic effects, and short duration of action. For example, traditional soil conditioners often focus on remediating single physicochemical indicators, such as applying lime only for soil acidification or using desulfurized gypsum for salinization, failing to simultaneously address pollution control and ecological restoration. Soil water-retaining materials such as straw and peat can increase soil moisture content in the short term, but lack nutrient supply capacity and are prone to decomposition and degradation. Pollution remediation materials such as activated carbon and zeolite have limited adsorption capacity for pollutants and are difficult to achieve targeted remediation and secondary pollution control. Microbial agents are limited by their adaptability to the soil environment, have low survival rates under harsh soil conditions, and are difficult to exert stable remediation effects.

[0004] Therefore, developing an integrated treatment material that combines multiple functions such as pollution purification, physicochemical property improvement, nutrient supply, and ecological restoration, and can adapt to complex soil environments, has become a key requirement for breaking through the current bottlenecks in soil treatment technology and achieving a comprehensive improvement in soil quality. It is of great practical significance for promoting green agricultural development and improving the ecological environment. Summary of the Invention

[0005] To address these issues, this application aims to overcome the shortcomings of existing soil remediation materials, such as limited functionality, poor effectiveness, and short duration of action, by providing a microsphere structure for soil improvement, its preparation method, and its application. This microsphere structure can achieve synergistic effects of multiple functions, including water retention, nutrient provision, and regulation of the soil microenvironment, effectively improving soil quality. Furthermore, it plays a significant role in soil steam sterilization, aiding in the rapid recovery of sterilized soil.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] In the first aspect, a microsphere structure for soil improvement is provided, with MBBR packing material as the reaction carrier, and the microsphere structure is loaded on the surface and internal pores of MBBR packing material.

[0008] Furthermore, the microsphere structure includes a core, an intermediate layer, and an outer layer;

[0009] The core consists of an aqueous phase and an oil phase. The aqueous phase includes sodium percarbonate, superabsorbent resin, and deionized water, while the oil phase is triacontanol.

[0010] The middle layer includes sodium alginate, deionized water, MnO2, humic acid, and calcium magnesium phosphate fertilizer powder;

[0011] The outer layer consists of a blend film formed by crosslinking chitosan and poly(N-isopropylacrylamide) with glutaraldehyde.

[0012] MBBR packing material has a large specific surface area and abundant pore structure, which can provide sufficient attachment sites for microspheres, improving their dispersibility and stability in soil. In the three-layer structure design of the microspheres, the core is mainly responsible for water retention and providing basic active substances, the middle layer is responsible for nutrient supply and microenvironment regulation, and the outer layer plays a role in protection and release control. The blended membrane is thermosensitive due to the presence of poly(N-isopropylacrylamide), which can change the membrane permeability with changes in ambient temperature, such as diurnal temperature difference, seasonal changes, or temperature fluctuations after steam sterilization, thereby regulating the release rate of internal substances and achieving the comprehensive effect of soil and water conservation and soil improvement.

[0013] Furthermore, the mass ratio of sodium carbonate, superabsorbent resin and deionized water in the core is 1:(2-5):(10-20).

[0014] The mass ratio of triacontanol to aqueous phase is (0.05-0.1):1;

[0015] The specific surface area of ​​MBBR packing is 50-500 m² / g.

[0016] Furthermore, in the intermediate layer, the mass ratio of sodium alginate to deionized water is (0.2-0.5):10;

[0017] The total amount of MnO2, humic acid, calcium magnesium phosphate fertilizer powder and the mass ratio of sodium alginate are (1-2):10, and the mass ratio of MnO2, humic acid and calcium magnesium phosphate fertilizer powder is 1:(2-3):(3-5).

[0018] In the core fluid, during the soil steam sterilization stage, although the high-temperature steam introduced from the outside can act on the soil surface, the deeper soil is prone to incomplete sterilization due to insufficient moisture caused by the soil's pore structure. The sodium percarbonate in the core decomposes in the high-temperature sterilization environment, and the generated hydrogen peroxide further decomposes to release water and oxygen. The released water can synergistically increase the overall soil moisture with the external steam, enhancing the steam's penetration into the deeper soil. When soil steam sterilization ends and the ambient temperature drops to room temperature, the permeability of the chitosan-poly(N-isopropylacrylamide) blend membrane on the outer layer of the microspheres increases with decreasing temperature, and the highly absorbent core... The resin begins to exhibit its strong water absorption and swelling properties, rapidly absorbing residual steam condensate and subsequent irrigation water from the soil. Through its three-dimensional network structure, it firmly locks in the water, solving the problem of reduced water retention caused by the damage to soil aggregate structure during high-temperature sterilization. Furthermore, the gel-like substance formed after water locking can slowly release water, providing a continuous water supply to plant roots and microorganisms in the soil and preventing rapid water leakage or evaporation. At the same time, triacontanol in the core is slowly released into the soil as the permeability of the outer membrane increases. By regulating the rate of plant cell division and photosynthetic efficiency, it promotes the development and recovery of plant roots and growth in the sterilized soil.

[0019] In the intermediate layer, sodium alginate and deionized water are mixed in a ratio of (0.2-0.5):10 to form a solution with good gelation properties, providing a stable carrier for the embedded substances. MnO2, humic acid, and calcium magnesium phosphate powder are added in specific proportions. MnO2 is a typical amphoteric oxidant, and its manganese element (Mn...) 4 (⁺) It has a strong electron-acquiring ability and can act as an electron transfer medium in the soil, flexibly participating in reactions under different redox states. The redox potential, a key indicator of the soil microenvironment, directly determines the form of nutrients, the content of harmful substances, and the activity of microorganisms in the soil. MnO2, as an oxidant, can participate in redox reactions in the soil and regulate the redox potential of the soil; humic acid can improve soil structure and enhance the soil's fertilizer retention capacity and buffering performance; calcium magnesium phosphate fertilizer can supplement the soil with nutrients such as calcium, magnesium, and phosphorus. The synergistic effect of the three, with the total amount added and sodium alginate in a ratio of (1-2):10, and the ratio of the three themselves in a ratio of 1:(2-3):(3-5), can achieve the best effect of nutrient supply and microenvironment regulation.

[0020] In the outer layer, the poly(N-isopropylacrylamide) molecule contains both hydrophilic amide groups and hydrophobic isopropyl groups. At room temperature, the amide groups can form hydrogen bonds with water molecules, and the molecular chains are in an extended state, with hydrophilicity dominating and weak interactions between hydrophobic groups in the molecules. However, when the temperature rises above the lower critical dissolution temperature, the heat energy will break the hydrogen bonds between the amide groups and water molecules, weakening the hydrophilicity of the molecules. At this time, in order to reduce contact with water molecules, the hydrophobic isopropyl groups will spontaneously aggregate, leading to a significant enhancement of hydrophobic interactions between molecular chains. This, in turn, causes the molecular chains to shrink and aggregate, ultimately reducing the pore size and making the structure of the blended membrane denser, thus achieving the effect of reducing membrane permeability. This characteristic is well-suited for soil steam sterilization scenarios, and can reduce the premature loss of functional components in the core and intermediate layers during the high-temperature sterilization stage.

[0021] Secondly, a method for preparing microsphere structures for soil improvement includes the following steps:

[0022] Sodium percarbonate and superabsorbent resin are added to deionized water and stirred at 500-600 rpm for 10-30 minutes until homogeneous to obtain the aqueous phase; triacontanol is melted into a transparent liquid in a water bath at 70-80℃ to serve as the oil phase.

[0023] The oil phase is dropped into the aqueous phase under high-speed stirring at 6000-8000 rpm, and stirred for 5-10 minutes to form an O / W emulsion, thus obtaining the core fluid, i.e., the core.

[0024] Sodium alginate is dissolved in deionized water and stirred at 100-300 rpm until clear. MnO2, humic acid, and calcium magnesium phosphate fertilizer powder are added and ultrasonically treated for 5-10 minutes to obtain the intermediate layer liquid, i.e., the intermediate layer.

[0025] Add liquid paraffin and Span-80 to a three-necked flask, heat in a 60-80℃ water bath, and stir at 500-600 rpm until Span-80 dissolves. Add core fluid dropwise, adjust to 8000-10000 rpm, and stir for 5-10 minutes to obtain the colostrum.

[0026] Cool the primary emulsion to room temperature, reduce the stirring speed to 500-600 rpm, add the intermediate layer liquid dropwise, and continue stirring for 20-30 minutes until the sodium alginate gels to obtain the secondary emulsion;

[0027] The poly(N-isopropylacrylamide) prepolymer solution was mixed with the chitosan solution and stirred until homogeneous to obtain the mixed outer layer solution, i.e., the outer layer; the complex emulsion was poured into the mixed outer layer solution and stirred at 300-500 rpm at room temperature for 40-60 minutes. Then, a 0.5% glutaraldehyde solution was added dropwise and reacted at 40°C for 1.5-2 hours to obtain the microsphere emulsion.

[0028] Microspheres were collected by filtration of the microsphere emulsion, washed 2-3 times with petroleum ether and 2-3 times with deionized water, and the surface moisture was drained to obtain the soil steam sterilization microsphere structure, which was then set aside for later use.

[0029] Liquid core liquid is dropwise added to a system containing liquid paraffin and Span-80. High-speed stirring at 8000-10000 rpm disperses the core liquid into uniformly sized micro-droplets using shear force. At this point, liquid paraffin acts as the continuous phase, and the micro-core droplets act as the dispersed phase, forming a stable water-in-oil (O / W) primary emulsion, laying the foundation for core formation. The stirring speed is then reduced to 500-600 rpm to avoid damaging the droplets. Next, a liquid intermediate layer, including sodium alginate solution, MnO2, humic acid, and calcium magnesium phosphate fertilizer powder, is added dropwise. The sodium alginate gelation reaction is triggered by the system environment without the need for additional gelling agents, transforming the liquid intermediate layer into a gel-like outer shell. The core droplets are then fixed within the gel shell, forming a complex emulsion.

[0030] The complex emulsion is poured into a mixed outer layer solution, which includes a poly(N-isopropylacrylamide) prepolymer and a chitosan solution. The poly(N-isopropylacrylamide) imparts thermosensitive properties to the mixed outer layer solution. A stirring speed of 300-500 rpm ensures the complex emulsion is uniformly dispersed in the mixed outer layer solution, and then a glutaraldehyde solution is added dropwise. Glutaraldehyde acts as a crosslinking agent, causing a chemical crosslinking reaction between the outer chitosan and poly(N-isopropylacrylamide) to form a stable solid blend membrane that completely encapsulates the core droplet and the gel interlayer. This membrane retains the thermosensitive properties of poly(N-isopropylacrylamide), allowing its permeability to adjust with temperature changes, and it coats the surface of the complex emulsion, forming a microsphere structure. Finally, by filtration and washing, residual liquid on the surface is removed, yielding solid, three-layered microspheres.

[0031] Through high-speed stirring and the action of emulsifier (Span-80), the core liquid is dispersed into non-coalescing micro-droplets, each droplet being an independent microsphere core unit, thus avoiding liquid agglomeration that would prevent it from forming.

[0032] The physical curing of sodium alginate in the middle layer and the chemical curing of glutaraldehyde in the outer layer provide a solid support structure for the droplet from the inside out, ultimately fixing the liquid core inside the microsphere.

[0033] Adding a 1% sodium alginate solution and stirring at 30-40℃ allows the sodium alginate to act as a binder, ensuring that the microspheres are firmly loaded onto the surface and internal pores of the MBBR filler. Pre-freezing at -80℃ rapidly freezes the moisture in the microspheres, reducing the damage to the microsphere structure caused by ice crystals. Freeze-drying, on the other hand, sublimates the moisture under low-temperature vacuum conditions, maintaining the porous structure and stability of the microspheres, while also preserving the structure and properties of the outer temperature-sensitive blend membrane.

[0034] Furthermore, the mass ratio of liquid paraffin to Span-80 is 10:(1-2).

[0035] Furthermore, the mass ratio of poly(N-isopropylacrylamide) prepolymer to chitosan solution in the mixed outer layer liquid is 1:3, and the mass ratio of chitosan to 1% acetic acid solution in the chitosan solution is 1:50.

[0036] Furthermore, the poly(N-isopropylacrylamide) prepolymer solution is prepared by dissolving N-isopropylacrylamide and ammonium persulfate in 5 mL of water and stirring at 60-80°C for 30-45 minutes, wherein the mass ratio of N-isopropylacrylamide to ammonium persulfate is 100:(1-3).

[0037] Thirdly, the application of a microsphere structure for soil improvement involves loading the microsphere structure onto MBBR packing material and further applying it to the soil steam sterilization process.

[0038] The method for loading microspheres onto MBBR packing includes: mixing dried microspheres with MBBR packing, adding a 1% sodium alginate solution, stirring at 30-40℃ for 1-2 hours to uniformly load the microspheres onto the surface and internal pores of the MBBR packing, and then pre-freezing at -80℃ for 2 hours and freeze-drying for 18-20 hours until completely dry.

[0039] Furthermore, the mass ratio of microspheres to MBBR filler is 1:(5~20).

[0040] Furthermore, the mass ratio of sodium alginate solution to microspheres is 1:10.

[0041] The outer thermosensitive blend membrane regulates the release rate of internal substances according to changes in soil temperature. Under suitable conditions, the superabsorbent resin in the core absorbs and retains moisture, providing sufficient water to the soil; sodium percarbonate slowly releases oxygen, improving soil aeration; and triacontanol promotes plant growth. The middle layer of sodium alginate gel slowly degrades, releasing MnO2, humic acid, and calcium magnesium phosphate fertilizer. MnO2 regulates the soil's redox environment, humic acid improves soil structure and nutrient retention capacity, and calcium magnesium phosphate fertilizer replenishes nutrients, thus helping the disinfected soil quickly restore its ecological function.

[0042] Beneficial technical effects:

[0043] The microsphere structure for soil improvement provided in this application comprises a core, a middle layer, and an outer layer. The core consists of sodium percarbonate, an aqueous phase of superabsorbent polymer (SAP), and an oil phase of tridecanoic acid (TCA). During the soil steam sterilization stage, the water produced by the decomposition of sodium percarbonate, in synergy with the externally introduced steam, significantly increases the overall soil moisture and effectively enhances the steam's penetration into deeper soil layers, ensuring thorough sterilization even in deeper soil layers. The released oxygen improves soil aeration, creating more favorable conditions for soil microbial activity and aiding in a more thorough sterilization process. After sterilization, the water locked in by the SAP solves the problem of decreased water retention caused by the destruction of soil aggregate structure during high-temperature sterilization. Its transformation from a solid state absorbing water to a gel-like substance allows for the slow release of water, continuously providing sufficient moisture to plant roots and microorganisms in the soil, preventing rapid water leakage or evaporation, and maintaining stable soil moisture. TCA, as a plant growth regulator, is slowly released to promote vegetation recovery, effectively promoting the development and growth recovery of plant roots in the sterilized soil.

[0044] The sodium alginate gel layer in the middle layer is embedded with MnO2, humic acid and calcium magnesium phosphate fertilizer powder. When the soil temperature decreases after disinfection, the membrane permeability of the outer blended membrane increases, and the sodium alginate gel layer in the middle layer of the microsphere structure releases the embedded substances: MnO2, as a typical amphoteric oxidant, allows the +4 manganese ions to flexibly participate in reactions under different redox states, regulating the soil microenvironment; humic acid improves soil structure and fertilizer retention capacity; and calcium magnesium phosphate fertilizer replenishes nutrients such as calcium, magnesium and phosphorus, quickly repairing the damage to soil fertility caused by disinfection.

[0045] A blend membrane composed of outer chitosan and poly(N-isopropylacrylamide) crosslinked with glutaraldehyde, under high-temperature steam sterilization conditions, as the temperature rises above the low critical dissolution temperature of poly(N-isopropylacrylamide), the thermal energy breaks the hydrogen bonds between the amide groups and water molecules, weakening the hydrophilicity of the molecules. To reduce contact with water molecules, the hydrophobic groups spontaneously aggregate, leading to a significant enhancement of hydrophobic interactions between molecular chains, resulting in adaptive shrinkage of the membrane structure. This reduces the premature loss of sodium percarbonate, superabsorbent resin, triacontanol in the core layer, and MnO2, humic acid, and calcium magnesium phosphate fertilizer in the intermediate layer. After sterilization, as the temperature decreases, poly(N-isopropylacrylamide) forms hydrogen bonds with water molecules, with hydrophilicity becoming dominant, and the molecular chains expand, increasing membrane permeability. This allows the release of core and intermediate layer components, ensuring a sustained and stable soil improvement effect after sterilization, accelerating the recovery of the soil ecosystem after sterilization, and ultimately achieving soil steam sterilization and improvement. Attached Figure Description

[0046] Figure 1 This is a flowchart of a method for preparing microsphere structures for soil improvement.

[0047] Figure 2 This is a schematic diagram of a microsphere structure used for soil improvement.

[0048] Figure labels: 1. Kernel; 2. Intermediate layer; 3. Outer layer. Detailed Implementation

[0049] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application will be provided below.

[0050] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0051] Example 1

[0052] like Figure 1 As shown, this embodiment provides a method for preparing microsphere structures for soil improvement, including the following steps:

[0053] 1. Weigh sodium percarbonate and superabsorbent resin and add them to deionized water. Stir at 580 rpm for 25 minutes until homogeneous to obtain an aqueous phase. The mass ratio of sodium percarbonate, superabsorbent resin and deionized water is 1:4:10. Weigh triacontanol and melt it into a transparent liquid in a water bath at 78°C to obtain the oil phase. Add the oil phase dropwise to the aqueous phase under high-speed stirring at 7500 rpm and stir for 8 minutes to form an O / W emulsion to obtain the core liquid. The mass ratio of triacontanol to the aqueous phase is 0.08:1.

[0054] 2. Weigh out sodium alginate and dissolve it in deionized water. Stir at 100 rpm until clear. Add MnO2, humic acid, and calcium magnesium phosphate fertilizer powder. Sonicate for 8 minutes to obtain the intermediate layer liquid.

[0055] The mass ratio of sodium alginate to deionized water is 0.4:10; the total amount of MnO2, humic acid, calcium magnesium phosphate fertilizer powder and the mass ratio of sodium alginate are 1.8:10, and the mass ratio of MnO2, humic acid and calcium magnesium phosphate fertilizer powder is 1:2.8:4.5.

[0056] 3. Weigh out liquid paraffin and Span-80 and add them to a three-necked flask. Stir at 580 rpm in a 75°C water bath until Span-80 dissolves. Add core fluid dropwise and stir at 9000 rpm for 8 minutes to obtain the primary emulsion. The mass ratio of liquid paraffin to Span-80 is 10:1.8.

[0057] 4. Cool the primary emulsion to room temperature, reduce the stirring speed to 580 rpm, add the intermediate layer liquid dropwise, and continue stirring for 28 minutes until the sodium alginate gels to obtain the secondary emulsion;

[0058] 5. Prepare poly(N-isopropylacrylamide) prepolymer solution by dissolving N-isopropylacrylamide and ammonium persulfate in 5 mL of water and stirring at 75°C for 40 minutes. Weigh out the poly(N-isopropylacrylamide) prepolymer solution and mix it with chitosan solution, stir evenly to obtain the mixed outer layer solution.

[0059] The mass ratio of poly(N-isopropylacrylamide) prepolymer to chitosan solution in the mixed outer layer liquid is 1:3; the mass ratio of chitosan to 1% acetic acid solution in the chitosan solution is 1:50; and the mass ratio of N-isopropylacrylamide to ammonium persulfate is 100:2.5.

[0060] The double emulsion was poured into the mixed outer layer liquid and stirred at 450 rpm at room temperature for 55 minutes. Then, a 0.5% glutaraldehyde solution was added dropwise, and the mixture was reacted at 40°C for 1.8 hours to obtain a microsphere emulsion. The mass ratio of the amount of glutaraldehyde solution added to the mass of the mixed outer layer liquid was 2.5:10.

[0061] 6. Collect the microspheres by filtration of the microsphere emulsion, wash three times with petroleum ether and three times with deionized water, drain the surface moisture, and obtain the microsphere structure for soil improvement, as described above. Figure 2 As shown, for future reference.

[0062] An application of a microsphere structure for soil improvement, wherein the microsphere structure is loaded onto MBBR packing material, the MBBR packing material having a specific surface area of ​​400 m² / g; further applied in soil steam sterilization process. The method for loading the microsphere structure onto MBBR packing material includes: mixing dried microspheres with MBBR packing material, simultaneously adding a 1% (w / w) sodium alginate solution, stirring at 38°C for 1.8 hours to uniformly load the microspheres onto the surface and internal pores of the MBBR packing material, then pre-freezing at -80°C for 2 hours followed by freeze-drying for 19 hours until completely dry, the mass ratio of microspheres to MBBR packing material is 1:10, and the mass ratio of sodium alginate solution to microspheres is 1:10.

[0063] Example 2

[0064] like Figure 1 As shown, this embodiment provides a method for preparing microsphere structures for soil improvement, including the following steps:

[0065] 1. Weigh sodium percarbonate and superabsorbent resin and add them to deionized water. Stir at 500 rpm for 10 minutes until homogeneous to obtain the aqueous phase. The mass ratio of sodium percarbonate, superabsorbent resin and deionized water is 1:2:15. Weigh triacontanol and melt it into a transparent liquid in a 70℃ water bath to obtain the oil phase. Add the oil phase dropwise to the aqueous phase under high-speed stirring at 6000 rpm and stir for 5 minutes to form an O / W emulsion to obtain the core liquid. The mass ratio of triacontanol to the aqueous phase is 0.05:1.

[0066] 2. Weigh out sodium alginate and dissolve it in deionized water. Stir at 150 pm until clear. Add MnO2, humic acid, and calcium magnesium phosphate fertilizer powder. Sonicate for 5 minutes to obtain the intermediate layer liquid.

[0067] The mass ratio of sodium alginate to deionized water is 0.2:10; the total amount of MnO2, humic acid, calcium magnesium phosphate fertilizer powder and the mass ratio of sodium alginate are 1:10, and the mass ratio of MnO2, humic acid and calcium magnesium phosphate fertilizer powder is 1:2:3.

[0068] 3. Weigh out liquid paraffin and Span-80 and add them to a three-necked flask. Stir at 500 rpm in a 60°C water bath until Span-80 dissolves. Add core fluid dropwise and stir at 8000 rpm for 5 minutes to obtain the primary emulsion. The mass ratio of liquid paraffin to Span-80 is 10:1.

[0069] 4. Cool the primary emulsion to room temperature, reduce the stirring speed to 500 rpm, add the intermediate layer liquid dropwise, and continue stirring for 20 minutes until the sodium alginate gels to obtain the secondary emulsion;

[0070] 5. Prepare poly(N-isopropylacrylamide) prepolymer solution by dissolving N-isopropylacrylamide and ammonium persulfate in 5 mL of water and stirring at 60°C for 30 minutes. Weigh out the poly(N-isopropylacrylamide) prepolymer solution and mix it with chitosan solution, stir evenly to obtain the mixed outer layer solution.

[0071] The mass ratio of poly(N-isopropylacrylamide) prepolymer to chitosan solution in the mixed outer layer liquid is 1:3; the mass ratio of chitosan to 1% acetic acid solution in the chitosan solution is 1:50; and the mass ratio of N-isopropylacrylamide to ammonium persulfate is 100:1.

[0072] The double emulsion was poured into the mixed outer layer liquid and stirred at 300 rpm at room temperature for 40 minutes. Then, a 0.5% glutaraldehyde solution was added dropwise, and the mixture was reacted at 40°C for 1.5 hours to obtain a microsphere emulsion. The mass ratio of the amount of glutaraldehyde solution added to the mass of the mixed outer layer liquid was 1:10.

[0073] 6. Collect the microspheres by filtration of the microsphere emulsion, wash twice with petroleum ether and twice with deionized water, drain the surface moisture, and obtain the microsphere structure for soil improvement, for later use.

[0074] An application of a microsphere structure for soil improvement, wherein the microsphere structure is loaded onto MBBR packing material, the MBBR packing material having a specific surface area of ​​50 m² / g; further applied in soil steam sterilization process. The method for loading the microsphere structure onto MBBR packing material includes: mixing dried microspheres with MBBR packing material, simultaneously adding a 1% (w / w) sodium alginate solution, stirring at 30°C for 1 hour to uniformly load the microspheres onto the surface and internal pores of the MBBR packing material, then pre-freezing at -80°C for 2 hours followed by freeze-drying for 18 hours until completely dry; the mass ratio of microspheres to MBBR packing material is 1:5; the mass ratio of sodium alginate solution to microspheres is 1:10.

[0075] Example 3

[0076] like Figure 1 As shown, this embodiment provides a method for preparing microsphere structures for soil improvement, including the following steps:

[0077] 1. Weigh sodium percarbonate and superabsorbent resin and add them to deionized water. Stir at 600 rpm for 30 minutes until homogeneous to obtain the aqueous phase. The mass ratio of sodium percarbonate, superabsorbent resin and deionized water is 1:5:18. Weigh triacontanol and melt it into a transparent liquid in an 80℃ water bath to obtain the oil phase. Add the oil phase dropwise to the aqueous phase under high-speed stirring at 8000 rpm and stir for 10 minutes to form an O / W emulsion to obtain the core liquid. The mass ratio of triacontanol to the aqueous phase is 0.1:1.

[0078] 2. Weigh out sodium alginate and dissolve it in deionized water. Stir at 200 rpm until clear. Add MnO2, humic acid, and calcium magnesium phosphate fertilizer powder. Sonicate for 10 minutes to obtain the intermediate layer liquid. The mass ratio of sodium alginate to deionized water is 0.5:10. The total amount of MnO2, humic acid, and calcium magnesium phosphate fertilizer powder added is in the mass ratio of sodium alginate to 2:10, and the mass ratio of MnO2, humic acid, and calcium magnesium phosphate fertilizer powder is 1:3:5.

[0079] 3. Weigh out liquid paraffin and Span-80 and add them to a three-necked flask. Stir at 600 rpm in an 80°C water bath until Span-80 dissolves. Add core liquid dropwise and stir at 10,000 rpm for 10 minutes to obtain the primary emulsion. The mass ratio of liquid paraffin to Span-80 is 10:2.

[0080] 4. Cool the primary emulsion to room temperature, reduce the stirring speed to 600 rpm, add the intermediate layer liquid dropwise, and continue stirring for 30 minutes until the sodium alginate gels to obtain the secondary emulsion;

[0081] 5. Prepare poly(N-isopropylacrylamide) prepolymer solution by dissolving N-isopropylacrylamide and ammonium persulfate in 5 mL of water and stirring at 80°C for 45 minutes. Weigh the poly(N-isopropylacrylamide) prepolymer solution and mix it with chitosan solution, stir evenly, and obtain the mixed outer layer solution.

[0082] The mass ratio of poly(N-isopropylacrylamide) prepolymer to chitosan solution in the mixed outer layer liquid is 1:3; the mass ratio of chitosan to 1% acetic acid solution in the chitosan solution is 1:50; and the mass ratio of N-isopropylacrylamide to ammonium persulfate is 100:3.

[0083] The double emulsion was poured into the mixed outer layer liquid and stirred at 500 rpm at room temperature for 60 minutes. Then, a 0.5% glutaraldehyde solution was added dropwise, and the mixture was reacted at 40°C for 2 hours to obtain a microsphere emulsion. The mass ratio of the amount of glutaraldehyde solution added to the mass of the mixed outer layer liquid was 3:10.

[0084] 6. Collect the microspheres by filtration of the microsphere emulsion, wash them three times with petroleum ether and three times with deionized water, drain off the surface moisture, and obtain the microsphere structure for soil improvement, for later use.

[0085] An application of a microsphere structure for soil improvement, wherein the microsphere structure is loaded onto MBBR packing material, the MBBR packing material having a specific surface area of ​​500 m² / g; further applied in soil steam sterilization process. The method for loading the microsphere structure onto MBBR packing material includes: mixing dried microspheres with MBBR packing material, simultaneously adding a 1% (w / w) sodium alginate solution, stirring at 40°C for 2 hours to uniformly load the microspheres onto the surface and internal pores of the MBBR packing material, then pre-freezing at -80°C for 2 hours followed by freeze-drying for 20 hours until completely dry; the mass ratio of sodium alginate solution to microspheres is 1:10; the mass ratio of microspheres to MBBR packing material is 1:20.

[0086] Example 4

[0087] like Figure 1 As shown, this embodiment provides a method for preparing microsphere structures for soil improvement, including the following steps:

[0088] 1. Weigh sodium percarbonate and superabsorbent resin and add them to deionized water. Stir at 550 rpm for 20 minutes until homogeneous to obtain an aqueous phase. The mass ratio of sodium percarbonate, superabsorbent resin and deionized water is 1:3:20. Weigh triacontanol and melt it into a transparent liquid in a 75°C water bath to obtain the oil phase. Add the oil phase dropwise to the aqueous phase under high-speed stirring at 7000 rpm and stir for 7 minutes to form an O / W emulsion to obtain the core liquid. The mass ratio of triacontanol to the aqueous phase is 0.07:1.

[0089] 2. Weigh out sodium alginate and dissolve it in deionized water. Stir at 300 rpm until clear. Add MnO2, humic acid, and calcium magnesium phosphate fertilizer powder. Sonicate for 7 minutes to obtain the intermediate layer liquid. The mass ratio of sodium alginate to deionized water is 0.3:10. The total amount of MnO2, humic acid, and calcium magnesium phosphate fertilizer powder added is 1.5:10, and the mass ratio of MnO2, humic acid, and calcium magnesium phosphate fertilizer powder is 1:2.5:4.

[0090] 3. Weigh out liquid paraffin and Span-80 and add them to a three-necked flask. Stir at 550 rpm in a 70°C water bath until Span-80 dissolves. Add core fluid dropwise and stir at 9000 rpm for 7 minutes to obtain the primary emulsion. The mass ratio of liquid paraffin to Span-80 is 10:1.5.

[0091] 4. Cool the primary emulsion to room temperature, reduce the stirring speed to 550 rpm, add the intermediate layer liquid dropwise, and continue stirring for 25 minutes until the sodium alginate gels to obtain the secondary emulsion;

[0092] 5. Preparation of poly(N-isopropylacrylamide) prepolymer solution: N-isopropylacrylamide and ammonium persulfate were dissolved in 5 mL of water and stirred at 70°C for 35 minutes. The poly(N-isopropylacrylamide) prepolymer solution was weighed and mixed with a chitosan solution, and stirred until homogeneous to obtain a mixed outer layer. The mass ratio of poly(N-isopropylacrylamide) prepolymer solution to chitosan solution in the mixed outer layer was 1:3; the mass ratio of chitosan to 1% acetic acid solution in the chitosan solution was 1:50; and the mass ratio of N-isopropylacrylamide to ammonium persulfate was 100:2.

[0093] The double emulsion was poured into the mixed outer layer liquid and stirred at 400 rpm at room temperature for 50 minutes. Then, a 0.5% glutaraldehyde solution was added dropwise, and the mixture was reacted at 40°C for 1.7 hours to obtain a microsphere emulsion. The mass ratio of the amount of glutaraldehyde solution added to the mass of the mixed outer layer liquid was 2:10.

[0094] 6. Collect the microspheres by filtration of the microsphere emulsion, wash twice with petroleum ether and three times with deionized water, drain the surface moisture, and obtain the microsphere structure for soil improvement, for later use.

[0095] An application of microsphere structures for soil improvement, wherein the microsphere structures are loaded onto MBBR packing material, and the MBBR packing material has a specific surface area of ​​300 m². 2 / g; further applied in soil steam sterilization processes. The method of loading microspheres onto MBBR packing includes: mixing dried microspheres with MBBR packing, adding 1% sodium alginate solution by mass, stirring at 35°C for 1.5 hours to uniformly load the microspheres onto the surface and internal pores of the MBBR packing, then pre-freezing at -80°C for 2 hours and freeze-drying for 19 hours until completely dry, with the mass ratio of sodium alginate solution to microspheres being 1:10; and the mass ratio of microspheres to MBBR packing being 1:15.

[0096] Comparative Example 1

[0097] Compared to Example 1, the mass ratio of sodium percarbonate, superabsorbent resin and deionized water is 1:1:10.

[0098] Comparative Example 2

[0099] Compared to Example 1, MBBR packing was not used.

[0100] Performance testing:

[0101] Pathogen survival rate:

[0102] The soil steam sterilization microsphere structures prepared in the examples and comparative examples were applied to soil. Equal amounts of soil to be sterilized were used to prepare two groups of samples: an experimental group (MBBR packing material with added microspheres) and a control group (without microspheres). Both groups underwent standard steam sterilization treatment to simulate actual sterilization temperature and time. After sterilization, the two soil samples were serially diluted using the dilution plate count method and inoculated onto pathogen-selective culture medium, incubated at 30℃ for 48-72 hours. The number of pathogen colonies on the culture medium was counted and calculated using the formula: "Pathogen survival rate = (number of colonies in the experimental group / number of colonies in the control group) × 100%".

[0103] 72h soil water retention rate:

[0104] The soil steam sterilization microsphere structures prepared in the examples and comparative examples were applied to soil. Equal amounts of soil to be sterilized were used to prepare two groups of samples: an experimental group (MBBR packing material with added microspheres) and a control group (no microspheres added). The initial moisture content was adjusted to saturation, and the initial total mass M1 was recorded. Both groups of soil were placed under the same environmental conditions: temperature 25℃, humidity 50%, and no precipitation, and allowed to stand for 72 hours. After 72 hours, the remaining total mass M2 was recorded. The soil water retention rate at 72 hours was calculated using the formula: 72-hour soil water retention rate = (M2 - soil dry mass) / (M1 - soil dry mass) × 100%.

[0105] To determine the number of beneficial microorganisms, after disinfection, both the experimental and control groups were incubated at 25℃ for 7 days. Soil samples from both groups were then inoculated into culture media using the serial dilution plate counting method and incubated at 30℃ for 72 hours. The number of beneficial microorganism colonies on the culture media was then counted.

[0106] Microsphere shedding rate (after 24 hours of shaking):

[0107] Weigh the total mass of the MBBR packing material after loading microspheres, Mtotal (including packing material and microspheres), and record the initial loaded mass of microspheres, Mmicro (Mmicro = Mtotal - Mpacking material, where Mpacking material is the mass of the blank MBBR packing material). Place the MBBR packing material loaded with microspheres into a conical flask containing deionized water, place it on a shaker, and shake at 150 rpm for 24 hours to simulate soil disturbance. After shaking, filter, collect the MBBR packing material, and dry it to constant weight. Weigh the remaining total mass, Mremaining, and calculate the mass of detached microspheres, Mdetached = Mtotal - Mremaining. Calculate the microsphere detachment rate using the formula: Microsphere detachment rate = (Mdetached / Mmicro) × 100%.

[0108] Triacontanol release rate at room temperature (25℃) (7 days):

[0109] A measured amount of MBBR packing material loaded with microspheres (the total mass of triacontanol in the microspheres, Mtotal alcohol) was weighed and mixed with an equal volume of sterile soil. The mixture was placed in a constant temperature environment at 25°C, and deionized water was added periodically to maintain stable soil moisture. After 7 days, triacontanol released from the soil was extracted using ethanol extraction. The mass of triacontanol in the extract, Mreleased alcohol, was quantitatively determined by high-performance liquid chromatography (HPLC). The triacontanol release rate was calculated using the formula: Triacontanol release rate = (Mreleased alcohol / Mtotal alcohol) × 100%.

[0110] The performance test results of a microsphere structure for soil improvement are shown in Table 1:

[0111] Table 1. Performance test results of soil steam sterilization microsphere structures in Examples 1-4 and Comparative Examples 1-2

[0112] Pathogen survival rate (after disinfection) 72h soil water retention rate Number of beneficial microorganisms Microsphere shedding rate (after 24 hours of shaking) Triacontanol release rate at room temperature (25℃) (7 days) Example 1 4.2% 70% <![CDATA[8.5×10 7 CFU / g]]> 6.8% 65% Example 2 4.8% 62% <![CDATA[7.2×10 7 CFU / g]]> 7.5% 60% Example 3 3.5% 75% <![CDATA[9.8×10 7 CFU / g]]> 4.2% 70% Example 4 3.0% 73% <![CDATA[1.0×10 8 CFU / g]]> 5.5% 68% Comparative Example 1 18% 52% <![CDATA[4.0×10 7 CFU / g]]> 8.2% 55% Comparative Example 2 25% 58% <![CDATA[5.6×10 6 CFU / g]]> - 45%

[0113] Studies using four examples and two comparative examples confirm that this application improves the overall performance of the microsphere structure for soil improvement by optimizing the raw material formulation and manufacturing process. Using MBBR filler as a carrier, a microsphere structure consisting of a core, intermediate layer, and outer layer is loaded. In the core, sodium percarbonate and superabsorbent resin work synergistically in a 1:(2-5) ratio. The superabsorbent resin provides physical water retention, while sodium percarbonate slowly releases active ingredients to aid in steam sterilization. The intermediate layer, containing sodium alginate gel, incorporates MnO2, humic acid, and calcium magnesium phosphate fertilizer in a specific ratio, which regulates the soil microenvironment, improves structure, and replenishes nutrients. The outer layer, a blend of chitosan and poly(N-isopropylacrylamide), is thermosensitive and can precisely control the release of internal components in response to environmental changes. Through the synergistic effect of these three components, the microsphere structure exhibits excellent performance in soil steam sterilization efficiency, soil improvement effect, and stability. In Example 4, the pathogen survival rate of the product was only 3.0%, the soil water retention rate reached 73% after 72 hours, and the number of beneficial microorganisms reached 1.0 × 10⁻⁶. 8 CFU / g.

[0114] Comparative Example 1 had a 1:1:10 mass ratio of sodium percarbonate, superabsorbent resin, and deionized water in its core. The insufficient proportion of superabsorbent resin weakened the water retention capacity (52% water retention rate after 72 hours), resulted in unstable sodium percarbonate release, decreased disinfection efficiency (18% survival rate of pathogens), and negatively impacted the survival environment of beneficial microorganisms (4.0 × 10⁻⁶). 7 The ratio of superabsorbent polymers (CFU / g) illustrates the important role of a proper proportion of superabsorbent polymers in balancing water retention and disinfection effects.

[0115] Comparative Example 2, due to the absence of MBBR packing material, exhibited poor microsphere dispersibility and easy aggregation, resulting in insufficient disinfection uniformity (pathogen survival rate of 25%), slow nutrient release, and a beneficial microorganism count of only 5.6 × 10⁻⁶. 6 The CFU / g figure fully demonstrates the core role of MBBR packing as a carrier in improving the stability and functionality of microspheres.

[0116] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application 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 this application without departing from the spirit and scope of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the claims of this application.

Claims

1. A microsphere structure for soil improvement, characterized in that, Using MBBR packing as a reaction carrier, the microsphere structure is loaded on the surface and internal pores of the MBBR packing. The microsphere structure includes a core (1), an intermediate layer (2), and an outer layer (3). The core (1) includes an aqueous phase and an oil phase. The aqueous phase includes sodium percarbonate, superabsorbent resin and deionized water, and the oil phase is triacontanol. The intermediate layer (2) includes sodium alginate, deionized water, MnO2, humic acid and calcium magnesium phosphate powder; The outer layer (3) comprises a blend film formed by crosslinking chitosan and poly(N-isopropylacrylamide) with glutaraldehyde.

2. The microsphere structure for soil improvement according to claim 1, characterized in that, The mass ratio of sodium percarbonate, superabsorbent resin and deionized water in the core (1) is 1:(2-5):(10-20). The mass ratio of triacontanol to aqueous phase is (0.05-0.1):1; The specific surface area of ​​the MBBR packing is 50-500 m² / g.

3. The microsphere structure for soil improvement according to claim 1, characterized in that, In the intermediate layer (2), the mass ratio of sodium alginate to deionized water is (0.2-0.5):10; The total amount of MnO2, humic acid, calcium magnesium phosphate fertilizer powder and the mass ratio of sodium alginate are (1-2):10, and the mass ratio of MnO2, humic acid and calcium magnesium phosphate fertilizer powder is 1:(2-3):(3-5).

4. A method for preparing a microsphere structure for soil improvement as described in any one of claims 1-3, characterized in that, Includes the following steps: Sodium percarbonate and superabsorbent resin are added to deionized water and stirred at 500-600 rpm for 10-30 minutes until homogeneous to obtain the aqueous phase; triacontanol is melted into a transparent liquid in a water bath at 70-80℃ to serve as the oil phase. The oil phase is dropped into the aqueous phase under high-speed stirring at 6000-8000 rpm, and stirred for 5-10 minutes to form an O / W emulsion, thus obtaining the core fluid; Sodium alginate was dissolved in deionized water and stirred at 100-300 rpm until clear. MnO2, humic acid, and calcium magnesium phosphate fertilizer powder were added and ultrasonically treated for 5-10 minutes to obtain the intermediate layer liquid. Add liquid paraffin and Span-80 to a three-necked flask, heat in a 60-80℃ water bath, and stir at 500-600 rpm until Span-80 dissolves. Add core fluid dropwise, adjust to 8000-10000 rpm, and stir for 5-10 minutes to obtain the colostrum. Cool the primary emulsion to room temperature, reduce the stirring speed to 500-600 rpm, add the intermediate layer dropwise, and continue stirring for 20-30 minutes until the sodium alginate gels to obtain the secondary emulsion. The poly(N-isopropylacrylamide) prepolymer solution was mixed with the chitosan solution and stirred until homogeneous to obtain a mixed outer layer solution. The complex emulsion was poured into the mixed outer layer solution and stirred at 300-500 rpm at room temperature for 40-60 minutes. Then, a 0.5% glutaraldehyde solution was added dropwise and reacted at 40°C for 1.5-2 hours to obtain a microsphere emulsion. Microspheres were collected by filtration of the microsphere emulsion, washed 2-3 times with petroleum ether and 2-3 times with deionized water, and the surface moisture was drained to obtain the soil steam sterilization microsphere structure.

5. The method for preparing microsphere structures for soil improvement according to claim 4, characterized in that, The mass ratio of the liquid paraffin to Span-80 is 10:(1-2).

6. The method for preparing microsphere structures for soil improvement according to claim 4, characterized in that, The mass ratio of poly(N-isopropylacrylamide) prepolymer to chitosan solution in the mixed outer layer liquid is 1:3, and the mass ratio of chitosan to 1% acetic acid solution in the chitosan solution is 1:

50.

7. The method for preparing microsphere structures for soil improvement according to claim 4, characterized in that, The poly(N-isopropylacrylamide) prepolymer solution is prepared by dissolving N-isopropylacrylamide and ammonium persulfate in 5 mL of water and stirring at 60-80°C for 30-45 minutes, wherein the mass ratio of N-isopropylacrylamide to ammonium persulfate is 100:(1-3).

8. The method for preparing microsphere structures for soil improvement according to claim 4, characterized in that, The mass ratio of the amount of glutaraldehyde solution added to the mass of the mixed outer layer liquid is (1-3):

10.

9. An application of the microsphere structure for soil improvement as described in any one of claims 1-3, characterized in that, The microsphere structure was loaded onto MBBR packing material and applied in the soil steam sterilization process; The method of loading the microsphere structure onto the MBBR packing includes: mixing the dried microspheres with the MBBR packing, adding a 1% sodium alginate solution, stirring at 30-40℃ for 1-2 hours, then pre-freezing at -80℃ for 2 hours and freeze-drying for 18-20 hours until completely dry; the mass ratio of microspheres to MBBR packing is 1:(5~20).

10. The application of the microsphere structure for soil improvement according to claim 9, characterized in that, The mass ratio of sodium alginate solution to microspheres is 1:10.

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