Rice straw rot-promoting and fertilizer-composite microbial agent and preparation method thereof

Abstract

The application relates to the technical field of agricultural waste resource utilization and microbial fertilizer preparation, and discloses a rice straw rot-promoting and fertilizer-preparing compound microbial agent and a preparation method thereof. The compound microbial agent is a core-shell structure particle, which is composed of a core layer, a shell layer wrapped outside the core layer and a microbial suspension sprayed on the outermost layer. The core layer comprises ammonium sulfate, potassium dihydrogen phosphate, bentonite and sodium lignosulfonate; the shell layer comprises urea-formaldehyde resin powder, sodium lignosulfonate, manganese oxalate dihydrate, sodium tetraborate decahydrate and bentonite; and the suspension comprises soybean crude oil, hydrophobic fumed silica and compound microbial dry powder. The application avoids the premature hydrolysis of the high-molecular skeleton by isolating the internal acid and external alkali micro-environment, uses a borate crosslinking network to improve the physical strength so as to realize nutrient slow release, and releases manganese ions to assist in the degradation of stubborn lignin, combines with a thixotropic oil film to store and protect the microorganism, and improves the storage survival rate and rot-promoting efficiency of the microbial agent.

Description

Technical Field

[0001] This invention relates to the field of agricultural waste resource utilization and microbial fertilizer preparation technology, specifically to a compound microbial agent for promoting the decomposition and fertilizer production of rice straw and its preparation method. Background Technology

[0002] Rice straw is rich in recalcitrant cross-linked polymers such as lignin and cellulose. Currently, it is often inoculated with compound microbial agents to accelerate composting and produce fertilizer, thereby achieving rapid return of agricultural waste to the field and resource utilization. However, existing rice straw composting agents have significant limitations in actual production and application. During conventional granulation and storage, exposed microbial spores are highly susceptible to mechanical stress and fluctuations in environmental humidity, leading to a significant reduction in the effective viable bacteria survival rate of the finished product.

[0003] To address the issue of storage survival rates, some existing technologies attempt to introduce polymeric coating materials to encapsulate and protect the microorganisms and nutrients. However, in the complex temperature, humidity, and acid-base microenvironment of the initial stages of actual composting, these conventional polymeric coating frameworks are often easily eroded, leading to premature hydrolysis and breakage, thus losing their physical barrier function too early. Simultaneously, many existing products involve a simple physical mixture of inorganic nutrients and microorganisms. After being applied to the straw pile, the nutrients are rapidly dissolved and released with moisture. This disordered and rapid release not only easily causes excessively high localized salt concentrations in the early stages but also leads to nutrient depletion in the later stages. This results in a severe mismatch between the nutrient supply cycle and the actual demand cycle for the large-scale proliferation of microorganisms and the secretion of lignin-degrading enzymes in the later stages, thereby limiting the complete disintegration of the deep fibrous tissue of the straw and reducing the overall composting efficiency.

[0004] Therefore, this invention proposes a compound microbial agent for promoting the decomposition and fertilizer production of rice straw and its preparation method to overcome the shortcomings of the prior art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a rice straw composting compound microbial agent and its preparation method, which solves the problems of low survival rate of effective live bacteria during the granulation and storage stage, mismatch between nutrient release and microbial degradation of lignin after application, and premature hydrolysis and failure of polymer coating materials in complex composting environments.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a compound microbial agent for promoting the decomposition and fertilizer production of rice straw, employing the following technical solution:

[0008] A compound microbial agent for promoting the decomposition and fertilizer production of rice straw, wherein the compound microbial agent for promoting the decomposition and fertilizer production of rice straw is a core-shell structure particle, consisting of an inner core layer, an outer shell layer surrounding the core layer, and a microbial suspension sprayed on the outermost layer of the compound microbial agent for promoting the decomposition and fertilizer production of rice straw; the raw materials of the core layer contain the following components in parts by weight: ammonium sulfate 15.0-25.0 parts, potassium dihydrogen phosphate 3.0-8.0 parts, bentonite 16.0-19.0 parts, and sodium lignosulfonate 1.0-3.0 parts; The raw materials of the outer shell layer include the following components in parts by weight: 8.0-15.0 parts of urea-formaldehyde resin powder, 10.0-18.0 parts of sodium lignosulfonate, 4.0-8.0 parts of manganese oxalate dihydrate, 1.0-4.0 parts of sodium tetraborate decahydrate, and 10.0-22.0 parts of bentonite; the raw materials of the microbial suspension include the following components in parts by weight: 3.0-5.0 parts of crude soybean oil, 0.1-0.3 parts of hydrophobic fumed silica, and 0.8-1.5 parts of ultra-high concentration compound bacterial dry powder.

[0009] By employing the above technical solution, utilizing the physical spatial isolation established by the core-shell structure, combined with the peripheral cross-linking and solidification mechanism and the thixotropic regulation of surface fluids, a synergistic effect of nutrient slow release and targeted degradation is achieved. The specific mechanism and process are as follows:

[0010] The core layer, composed of ammonium sulfate and potassium dihydrogen phosphate, forms an inorganic acidic microenvironment, while the outer shell, containing sodium tetraborate decahydrate, dissolves in trace amounts of moisture and provides a slightly alkaline buffer. This internal acidic and external alkaline spatial arrangement not only prevents premature precipitation of internal water-soluble nutrients but also plays a crucial role in skeletal protection. Because urea-formaldehyde resin powder is highly susceptible to hydrolytic breakage of methylene ether bonds under high temperatures and in acidic media, the presence of the slightly alkaline buffer system effectively inhibits this degradation pathway, thus maintaining the integrity of the particle structure during the initial stages of processing and application.

[0011] With the framework system stabilized, the chemical microstructure within the outer shell spontaneously reorganizes. The tetraborate ions released from the dissociation of sodium tetraborate decahydrate transform into tetrahydroxyborate ions under weakly alkaline conditions, and rapidly undergo dehydration condensation with the ortho-free hydroxyl groups on the surrounding sodium lignosulfonate molecular chains, generating a diol borate ester crosslinking network. This crosslinking reaction, combined with the physical filling effect of bentonite particles, significantly enhances the outer shell's resistance to mechanical wear, while simultaneously creating steric hindrance to the outward permeation channels of the internal core layer, thus allowing for reasonable control of the nutrient release rate.

[0012] To address the lignin component in rice straw that is difficult for conventional microorganisms to rapidly decompose, this invention introduces manganese oxalate dihydrate into the outer barrier. This substance is poorly soluble in water under normal conditions, but as the fermentation system enters the start-up phase, microbial metabolism produces acid, leading to acidification of the surrounding local microenvironment. Manganese oxalate is then slowly released as soluble divalent manganese ions by acid erosion. These released manganese ions serve as essential cofactors for manganese peroxidase subsequently secreted by the microorganisms, directly mediating and participating in the oxidative cleavage of the phenolic hydroxyl backbone in the lignin macromolecule, thereby accelerating the disintegration of the underlying fibrous tissue of the straw.

[0013] To ensure that the highly active bacterial strains required for the aforementioned fermentation reaction are protected from damage during processing and uniformly adhere to the particle surface, a rheologically specifically regulated microbial suspension is used as the outermost layer. Residual silanol groups on the surface of hydrophobic fumed silica attract each other through hydrogen bonds in the continuous phase of crude soybean oil, spontaneously forming a three-dimensional flocculated network with a certain yield stress. When the system is in a static or low-shear state, it exhibits high viscosity, preventing the possibility of gravity sedimentation of the ultra-concentrated composite bacterial powder. However, when subjected to the high-pressure atomization shear force of the spraying equipment, the internal hydrogen bond network is rapidly disrupted, causing a sharp drop in system viscosity. This ensures that the microorganisms containing trace amounts of free water can firmly adhere to the outermost periphery of the particles in an extremely thin and uniform thixotropic oil film.

[0014] Preferably, the raw materials of the core layer include 20.0 parts ammonium sulfate, 5.0 parts potassium dihydrogen phosphate, 18.0 parts bentonite, and 2.0 parts sodium lignosulfonate; the raw materials of the outer shell layer include 10.0 parts urea-formaldehyde resin powder, 13.0 parts sodium lignosulfonate, 6.0 parts manganese oxalate dihydrate, 2.0 parts sodium tetraborate decahydrate, and 19.0 parts bentonite; the raw materials of the microbial suspension include 3.8 parts crude soybean oil, 0.2 parts hydrophobic fumed silica, and 0.9 parts ultra-high concentration composite bacterial powder.

[0015] By adopting the above technical solution, the acidity benchmark provided by the core layer and the alkalinity buffer capacity of the outer shell layer reach a dynamic balance under this ratio. The density of the cross-linked network is sufficient to withstand various mechanical shears and thermal stresses in the subsequent processing. Furthermore, the initial viscosity and atomization performance of the suspension fall within the optimal operating range, ensuring the consistency of the finished coating thickness during batch preparation.

[0016] Preferably, the ultra-high concentration compound bacterial powder is a mixture of dormant spore powders of *Phanerochaete chrysosporium*, *Trichoderma reesei*, and *Bacillus megaterium*; the mass ratio of the *Phanerochaete chrysosporium*, *Trichoderma reesei*, and *Bacillus megaterium* is 1.5–2.5:1.5–2.5:1.0; and the total effective viable count of the ultra-high concentration compound bacterial powder is ≥1.0 × 10⁻⁶. 10CFU / g.

[0017] By employing the above-mentioned technical solution, the established mass ratio of the three types of microorganisms induces *Procambarus chrysospora* to preferentially destroy the external structure of lignin. Subsequently, the cellulase system secreted by *Trichoderma reesei* penetrates and degrades the internal cellulose polymers, while *Bacillus megaterium* is responsible for decomposing peripheral organic residues and competitively inhibiting the proliferation of other microorganisms. This compound system achieves in-situ synergy in space and sequential degradation in time, effectively improving the bioconversion rate of stubborn high-molecular polymers in rice straw.

[0018] Preferably, the urea-formaldehyde resin powder is a polymer dry powder prepared by an addition reaction and an acidic condensation reaction of formaldehyde aqueous solution and urea; in the reaction system for preparing the urea-formaldehyde resin powder, the initial molar ratio of formaldehyde to urea is 1.20 to 1.50.

[0019] By employing the above technical solution, the initial molar ratio of formaldehyde to urea is limited to this range, controlling the formation ratio of hydroxymethyl groups and cross-linked methylene bonds in the resin molecular chain. This polymer dry powder with a specific degree of cross-linking possesses both the physical toughness and thermal stability required for film coating, reducing the powdering rate during the shell coating process, and keeping the residual free formaldehyde content in the system at an extremely low level, preventing it from penetrating upwards and causing cytotoxicity to the microbial spores coated on the surface.

[0020] Preferably, the moisture content of the rice straw composting compound microbial agent is 1.5% to 1.9%.

[0021] By adopting the above technical solution, the residual water content of the final particle system is strictly controlled within a low lower limit range. On the one hand, this forces the microbial spores attached to the outermost oil film to spontaneously maintain a low-energy dormant metabolic state. On the other hand, it cuts off the pathway for external free water molecules to penetrate into the internal polymer skeleton and induce hydrolysis from the physical source, thus ensuring the long-term storage period of the finished product.

[0022] Secondly, the present invention provides a method for preparing a compound microbial agent for promoting the decomposition and fertilizer production of rice straw, which adopts the following technical solution:

[0023] A method for preparing a compound microbial agent for promoting the decomposition and fertilizer production of rice straw includes the following steps:

[0024] S1. Mix the raw materials of the core layer to obtain core dry powder, and mix the raw materials of the outer shell layer to obtain outer shell powder;

[0025] S2. Put the core dry powder into the granulator and spray pure water to make the core dry powder agglomerate to obtain micro-core particles.

[0026] S3. Continuously and evenly sprinkle shell powder into the granulator and spray pure water at the same time. After the shell powder is completely coated on the surface of the micro-core particles, wet particles with core-shell structure are obtained.

[0027] S4. The core-shell structured wet particles are dried at high temperature and cooled by countercurrent air flow to obtain dried particles.

[0028] S5. Crude soybean oil and hydrophobic fumed silica are mixed by high-speed shear dispersion, and then ultra-high concentration compound bacterial dry powder is added and stirred at low speed to obtain a microbial suspension; the microbial suspension is sprayed onto the surface of dry particles by air atomization to obtain the finished product.

[0029] By adopting the above technical solution, this process route of multi-layer stepwise granulation combined with suspension atomization coating clearly defines the spatial arrangement of internal nutrients and external microbial spores at the physical manufacturing level, significantly reducing the risk of inactivation of highly sensitive microorganisms during mechanical processing. The specific preparation evolution process is as follows:

[0030] In the initial stage of granulation, the core dry powder forms liquid bridges between particles through the injection of pure water within the granulator. The pure water dissolves some of the sodium lignosulfonate and inorganic salts, creating viscous resistance. Combined with capillary adsorption and the mechanical tumbling and extrusion of the granulator, the powder is gradually densified, constructing a micro-core particle skeleton with initial compressive strength. As the micro-core skeleton forms, outer shell powder is continuously sprinkled in and adheres layer by layer to its surface. The simultaneously added water not only triggers the dissociation of sodium tetraborate decahydrate and initiates its chemical condensation reaction with sodium lignosulfonate, but also promotes the absorption of water and crystalline expansion of the bentonite in the powder. The expanded crystalline layers fill the tiny pores between the urea-formaldehyde resin particles, and together they construct a dense physical barrier outside the micro-core.

[0031] The wet granules, now double-coated, then enter the dehydration and curing stage. High-temperature drying drives the free water inside the granules to migrate to the surface and vaporize. The accelerated removal of moisture simultaneously promotes the cross-linking reaction of borate esters in the outer shell layer and causes the overall skeleton to shrink and solidify. Considering that rapid cooling can easily cause the outer layer of the polymer material to become brittle and crack, the subsequent counter-current air cooling slowly and evenly removes residual heat, eliminating the thermal stress concentration caused by the temperature difference between the inside and outside, allowing the granule skeleton to solidify smoothly.

[0032] The oil film coating process at the end of the production line fully utilizes the thixotropic properties of the composite fluid. After initial high-speed shearing of soybean crude oil and hydrophobic fumed silica, polar silanol groups intertwine in the nonpolar continuous phase to form a weak and unstable hydrogen bond network. At the moment the suspension is atomized and sprayed through air, the airflow shear force tears this network, causing a sharp drop in local viscosity, allowing the droplets to spread evenly across the surface of the dry particles. Once spraying is complete and the external shearing force disappears, the spontaneous reconstruction of the hydrogen bond network causes the liquid film viscosity to rapidly recover. This not only prevents the oil phase from flowing and dripping onto the particle surface but also forms a physical sealing film that isolates the microbial spores from air and external moisture, stably fixing them in place.

[0033] Preferably, step S4 is implemented as follows: the core-shell structure wet particles are fed into a rotary drum dryer, the inlet air temperature of the rotary drum dryer is set to 90-110℃ and the outlet air temperature is set to 50-65℃, and the residence time of the core-shell structure wet particles in the rotary drum dryer is controlled so that the moisture content evaporates to 1.5%-1.9%; then the dried particles with the moisture content reduced to 1.5%-1.9% are fed into a cooling drum, and air at 20-30℃ is introduced for countercurrent cooling so that the outlet temperature after cooling is reduced to 28-32℃.

[0034] By employing the above technical solution, gentle heating is achieved through a set inlet and outlet air temperature gradient, avoiding the crusting and internal sealing phenomena caused by excessively rapid evaporation of moisture on the particle surface. This preserves sufficient capillary channels for the outward diffusion of deep moisture. Controlling the terminal moisture content at 1.5%–1.9% and lowering the outlet temperature to 28–32°C prevents the possibility of degradation of polymer components due to continuous heating. Simultaneously, a suitable temperature bed is provided for subsequent microbial live coating, avoiding spore damage caused by residual heat.

[0035] Preferably, step S5 is implemented as follows: soybean crude oil and hydrophobic fumed silica are mixed at a high speed of 2000-3000 r / min for 10-15 min; then the speed is adjusted to a low speed of 80-120 r / min, and ultra-high concentration compound bacterial dry powder is added and stirred for 10-20 min to prepare a microbial suspension; the microbial suspension is uniformly sprayed using an atomizing spray gun at an atomization pressure of 0.3-0.5 MPa.

[0036] By employing the above technical solution, the high-speed, high-shear force applied in the early stage thoroughly breaks up the secondary agglomerates of fumed silica, achieving uniform dispersion at the primary particle level. Switching to a low-speed stirring state establishes a stable mixing flow field, ensuring that the microbial powder is fully wetted in the oil phase while being protected from physical tearing of the spore cell walls by high mechanical shear force. An atomization pressure of 0.3–0.5 MPa can tear the suspension into concentrated micron-sized droplets, ensuring coating coverage.

[0037] Preferably, before step S1, the ultra-high concentration compound bacterial powder is pre-treated as follows: the proportioned microbial dormant spore powder is put into a mixer, and an equal mass of diatomaceous earth is added and stirred evenly; the mixture of diatomaceous earth and microbial dormant spore powder is placed in a 35°C environment and vacuum dried for 12 hours until the moisture content drops to below 5%, and then pulverized and sieved to obtain ultra-high concentration compound bacterial powder.

[0038] By employing the above technical solution, the micro-nano-scale porous structure rich in diatomaceous earth is utilized to allow dormant spores to be successfully embedded deep within its pores during dry physical stirring. This not only allows the inorganic framework of diatomaceous earth to bear the direct grinding stress generated by subsequent mechanical processing, but also, combined with the low-pressure, oxygen-free dehydration environment created by gentle vacuum drying at 35°C, forcibly removes the free bound water from the spore surface, compelling them to completely enter a dormant period of metabolic stagnation.

[0039] Preferably, before step S1, the urea-formaldehyde resin powder in the outer shell powder is prepared as follows: formaldehyde aqueous solution and urea are mixed evenly, an alkaline solution is added to adjust the pH of the system to 8.0-8.5, and the temperature is raised to 70-80℃ and reacted at a constant temperature for 40-60 min; then an acidic solution is added to adjust the pH of the system to 4.5-5.5, and the temperature is raised to 80-90℃ for a condensation reaction for 60-120 min; after the reaction is completed, the pH is adjusted to 7.5-8.0 with an alkaline solution to terminate the reaction, and the reaction solution is sent to a centrifugal spray drying tower for spray drying at an inlet air temperature of 150-170℃ and an outlet air temperature of 80-90℃ to obtain urea-formaldehyde resin powder.

[0040] By employing the above technical solution, the preparation process of this resin powder is based on a two-stage chemical transformation. The first stage is a nucleophilic addition reaction under alkaline conditions, where the amino group in the urea molecule adds to the formaldehyde carbonyl group, generating intermediates such as monohydroxymethylurea and dihydroxymethylurea. The main reaction process can be described as: H2N-CO-NH2 + CH2O → H2N-CO-NH-CH2OH. As the reaction progresses to the second stage, the system enters an acidic environment, triggering a condensation reaction. A large amount of dehydration condensation occurs between the hydroxymethyl group and the amino group, or between hydroxymethyl groups themselves, forming stable methylene bonds and methylene ether bonds. The main crosslinking reaction can be described as: R-NH-CH2OH + H2N-R' → R-NH-CH2-NH-R' + H2O. Finally, the continuous growth of the polymer chain segments is terminated by alkaline neutralization, and the solvent is removed by instantaneous high-temperature spray drying. The liquid polymer is directly converted into a polymer dry powder with a fixed molecular weight distribution and a spatial crosslinking network, laying a stable mechanical foundation for film formation and coating.

[0041] This invention provides a compound microbial agent for promoting the decomposition and fertilizer production of rice straw and its preparation method. It has the following beneficial effects:

[0042] 1. This invention constructs a core layer containing ammonium sulfate and potassium dihydrogen phosphate, and an outer shell layer containing sodium tetraborate decahydrate, creating an acidic-alkaline microenvironment gradient within the particles. This spatial isolation and buffering system effectively inhibits the hydrolytic breakage of the outer urea-formaldehyde resin powder under heated or acidic conditions, preventing premature precipitation of internal nutrients and ensuring the structural stability of the composite particle skeleton during processing and long-term storage.

[0043] 2. This invention utilizes the tetrahydroxyborate ions dissociated from sodium tetraborate decahydrate to undergo a dehydration condensation reaction with sodium lignosulfonate in the outer shell layer. The resulting borate ester crosslinking network fills the bentonite, enhancing the outer shell layer's resistance to mechanical wear. Simultaneously, it creates steric hindrance to the outward permeation channels of internal water-soluble nutrients, achieving a physical slow-release effect of fertilizer nutrients.

[0044] 3. This invention introduces manganese oxalate dihydrate into the outer shell layer, which works synergistically with a complex of microorganisms such as *Procambarus chrysospora* in the outermost layer. During the initial acidification of the microenvironment in straw fermentation, manganese oxalate is slowly released as it is eroded by the acid, releasing free divalent manganese ions. These ions, as essential cofactors for the secretion of manganese peroxidase by microorganisms, directly participate in and accelerate the oxidative decomposition of stubborn lignin macromolecules in rice straw, thus improving the overall fermentation efficiency.

[0045] 4. The outermost layer of this invention uses a thixotropic microbial suspension constructed from hydrophobic fumed silica and crude soybean oil. Under static conditions, the system relies on a hydrogen bond network to maintain high viscosity to prevent the ultra-concentrated composite bacterial powder from settling due to gravity. However, when subjected to shear force during atomization spraying, the viscosity rapidly decreases, thereby forming a uniformly thick sealing oil film on the outermost periphery of the particles, cutting off the path of external moisture penetration and effectively reducing the inactivation rate of microbial spores. Attached Figure Description

[0046] Figure 1 The bar chart shows the suspension test results of the present invention, wherein (a) is a comparison test chart of the thixotropic index of the suspension system of each experimental group, (b) is a comparison test chart of the oil separation rate of the suspension after standing for 24 hours in each experimental group, and (c) is a comparison test chart of the relative standard deviation of the total number of effective viable bacteria in the finished product particles of each experimental group.

[0047] Figure 2 The graphs are line graphs showing the test results of microenvironment indicators and enzyme activities of the present invention. Among them, (a) is a comparison graph of the pH value changes of the microenvironment of the mixture of Example 1 and Comparative Example 4 during the culture period, (b) is a comparison graph of the changes in the concentration of soluble manganese ions in the mixture, and (c) is a comparison graph of the changes in the activity of manganese peroxidase.

[0048] Figure 3The bar chart shows the test results of gas emission during particle drying according to the present invention. (a) is a comparative test chart of the cumulative emission concentration of formaldehyde in wet particles of each experimental group during the drying period, and (b) is a comparative test chart of the cumulative emission concentration of ammonia in wet particles of each experimental group during the drying period.

[0049] Figure 4 The bar chart shows the granulation quality and physical and mechanical properties test results of the present invention. Among them, (a) is a comparison chart of the sphericity of the target particle size of 2 to 4 mm after granulation in each experimental group, (b) is a comparison chart of the average compressive strength of the unoiled semi-finished particles in each experimental group, and (c) is a comparison chart of the wear resistance pulverization rate of the unoiled semi-finished particles in each experimental group.

[0050] Figure 5 This is a line graph showing the error of the rice straw degradation agronomic effect test results of the present invention. Detailed Implementation

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0053] Sodium lignosulfonate, CAS No. 8061-51-6, is a natural high molecular weight polymer derivative with a weight average molecular weight of 8,000 to 12,000, a sulfonic acid group mass fraction ≥10.0%, a reducing agent mass fraction ≤7.0%, and a moisture content ≤5.0%.

[0054] Hydrophobic fumed silica, CAS No. 68909-20-6, is a solid nanomaterial modified with hexamethyldisilazane, with a specific surface area of ​​150 to 250 m². 2 / g, with a primary particle size of 10 to 20 nm and a carbon mass fraction of 2.5% to 3.5%.

[0055] Manganese oxalate dihydrate, chemical formula MnC2O4·2H2O, CAS number 6556-16-7, purity ≥98.0%, manganese mass fraction ≥29.5%.

[0056] Crude soybean oil, CAS No. 8001-22-7, is obtained by pressing soybeans without refining, decolorizing and deodorizing. It has an acid value ≤3.0mgKOH / g and moisture and volatile matter ≤0.2%.

[0057] Bentonite, whose main component is montmorillonite, CAS number 1302-78-9, is a calcium-based bentonite with a cation exchange capacity ≥60mmol / 100g and is pulverized through a 200-mesh sieve.

[0058] The standard strain of *Procambarus chrysosporus* with accession number ATCC 24725 was used.

[0059] Trichoderma reesei was obtained using the standard strain with accession number ATCC 56765.

[0060] Bacillus megaterium was obtained using the standard strain with accession number ATCC 14581.

[0061] Preparation Example 1: This preparation example provides a method for preparing urea-formaldehyde resin powder, including the following steps:

[0062] 182.4 g of a 37% formaldehyde aqueous solution and 100.0 g of urea were added to a reaction vessel and mixed thoroughly. At this point, the molar ratio of formaldehyde to urea was 1.35. A 10% sodium hydroxide solution was added to adjust the pH of the system to 8.2, and the temperature was raised to 75°C. The reaction was carried out at this temperature for 50 minutes with stirring. Subsequently, a 10% formic acid solution was added to adjust the pH of the system to 5.0, and the temperature was raised to 85°C for polycondensation. The reaction was carried out at this temperature for 90 minutes with stirring. A 10% sodium hydroxide solution was added to adjust the pH of the system to 7.8 to terminate the reaction. The resulting reaction solution was sent to a centrifugal spray drying tower with the inlet air temperature set at 160°C and the exhaust air temperature at 85°C. The urea-formaldehyde resin powder was obtained by spray drying.

[0063] Preparation Example 2: This preparation example provides a method for preparing urea-formaldehyde resin powder, including the following steps:

[0064] 162.2 g of a 37% formaldehyde aqueous solution and 100.0 g of urea were added to a reaction vessel and mixed thoroughly. At this point, the molar ratio of formaldehyde to urea was 1.20. A 10% sodium hydroxide solution was added to adjust the pH of the system to 8.0, and the temperature was raised to 70°C. The mixture was then kept at this temperature for 40 minutes under stirring. Subsequently, a 10% formic acid solution was added to adjust the pH of the system to 4.5, and the temperature was raised to 80°C for polycondensation. The mixture was kept at this temperature for 60 minutes under stirring. The reaction was terminated by adding a 10% sodium hydroxide solution to adjust the pH of the system to 7.5. The resulting reaction solution was then sent to a centrifugal spray drying tower with an inlet air temperature of 150°C and an outlet air temperature of 80°C. The urea-formaldehyde resin powder was obtained by spray drying.

[0065] Preparation Example 3: This preparation example provides a method for preparing urea-formaldehyde resin powder, including the following steps:

[0066] 202.7 g of a 37% formaldehyde aqueous solution and 100.0 g of urea were added to a reaction vessel and mixed thoroughly. At this point, the molar ratio of formaldehyde to urea was 1.50. A 10% sodium hydroxide solution was added to adjust the pH of the system to 8.5, and the temperature was raised to 80°C. The mixture was then kept at this temperature for 60 minutes under stirring. Subsequently, a 10% formic acid solution was added to adjust the pH of the system to 5.5, and the temperature was raised to 90°C for polycondensation. The mixture was kept at this temperature for 120 minutes under stirring. The reaction was terminated by adding a 10% sodium hydroxide solution to adjust the pH of the system to 8.0. The resulting reaction solution was then sent to a centrifugal spray drying tower with an inlet air temperature of 170°C and an outlet air temperature of 90°C. The urea-formaldehyde resin powder was obtained by spray drying.

[0067] Preparation Example 4: This preparation example provides a method for preparing ultra-high concentration compound bacterial dry powder, including the following steps:

[0068] The effective viable bacteria count is ≥3.0×10⁻⁶. 10 CFU / g of dormant spore powders of *Phanerochaete chrysosporium*, *Trichoderma reesei*, and *Bacillus megaterium* were added to a horizontal mixer at a mass ratio of 2.0:2.0:1.0 and mixed thoroughly. An equal mass of diatomaceous earth (passed through a 300-mesh sieve) was added to the mixed powders, and the mixture was stirred at 100 rpm for 30 minutes. The mixture was then placed in a vacuum drying oven at 35°C and dried for 12 hours until the moisture content dropped below 5%. The dried mixture was then pulverized and passed through a 100-mesh sieve to obtain a total viable count ≥1.0 × 10⁻⁶. 10 Compound bacterial powder with CFU / g.

[0069] Preparation Example 5: This preparation example provides a method for preparing ultra-high concentration compound bacterial dry powder, including the following steps:

[0070] The effective viable bacteria count is ≥3.0×10⁻⁶. 10 CFU / g of dormant spore powders of *Phanerochaete chrysosporium*, *Trichoderma reesei*, and *Bacillus megaterium* were added to a horizontal mixer at a mass ratio of 1.5:1.5:1.0 and mixed thoroughly. An equal mass of diatomaceous earth (passed through a 300-mesh sieve) was added to the mixed powders, and the mixture was stirred at 100 rpm for 30 minutes. The mixture was then placed in a vacuum drying oven at 35°C and dried for 12 hours until the moisture content dropped below 5%. The dried mixture was then pulverized and passed through a 100-mesh sieve to obtain a total viable count ≥1.0 × 10⁻⁶. 10 Compound bacterial powder with CFU / g.

[0071] Preparation Example 6: This preparation example provides a method for preparing ultra-high concentration compound bacterial dry powder, including the following steps:

[0072] The effective viable bacteria count is ≥3.0×10⁻⁶. 10CFU / g of dormant spores of *Phanerochaete chrysosporium*, *Trichoderma reesei*, and *Bacillus megaterium* were mixed evenly in a horizontal mixer at a mass ratio of 2.5:2.5:1.0. An equal mass of diatomaceous earth (passed through a 300-mesh sieve) was added to the mixed powder, and the mixture was stirred at 100 rpm for 30 minutes. The mixture was then dried in a vacuum drying oven at 35°C for 12 hours until the moisture content dropped below 5%. The dried product was then pulverized and passed through a 100-mesh sieve to obtain a total viable count ≥1.0 × 10⁻⁶. 10 Compound bacterial powder with CFU / g.

[0073] Example 1: This example provides a compound microbial agent for promoting the decomposition and fertilizer production of rice straw and its preparation method, including the following steps:

[0074] Step 1: At 25°C, 20.0 kg of ammonium sulfate, 5.0 kg of potassium dihydrogen phosphate, 18.0 kg of bentonite, and 2.0 kg of sodium lignosulfonate were added to a horizontal ribbon mixer and stirred for 12 minutes to obtain the core dry powder. 10.0 kg of urea-formaldehyde resin powder obtained in Preparation Example 1, 13.0 kg of sodium lignosulfonate, 6.0 kg of manganese oxalate dihydrate, 2.0 kg of sodium tetraborate decahydrate, and 19.0 kg of bentonite were added to another horizontal ribbon mixer and stirred for 12 minutes to obtain the outer shell powder.

[0075] Step 2: Put the core dry powder obtained in Step 1 into a disc granulator with an inclination angle of 45 degrees and a rotation speed of 35 rpm; spray 9.0 kg of pure water at a temperature of 25℃ evenly onto the surface of the powder in the granulator through a pneumatic atomizing nozzle, and keep the equipment running for 10 minutes to make the powder agglomerate to obtain micro-core particles.

[0076] Step 3: While the disc granulator continues to run, continuously and evenly sprinkle the shell powder obtained in Step 1 into the granulator, and simultaneously spray 4.5 kg of pure water at a temperature of 25°C through a pneumatic atomizing nozzle. After the shell powder is completely coated on the surface of the micro-core particles, continue running for 5 minutes to obtain core-shell structured wet particles.

[0077] Step 4: The core-shell structured wet granules are fed into a co-current rotary drum dryer via a belt conveyor. The dryer inlet air temperature is set to 100℃ and the outlet air temperature to 55℃. The residence time of the granules in the dryer is controlled to be 20 minutes, so that the moisture content of the granules is reduced to 1.8%. Then the granules are sent to the cooling drum, where 25℃ air is introduced for counter-current cooling, so that the outlet temperature of the granules is reduced to 30℃.

[0078] Step 5: Add 3.8 kg of crude soybean oil and 0.2 kg of hydrophobic fumed silica to a twin-shaft mixing tank equipped with a high-speed shear disperser and a low-speed stirring paddle. Turn on the high-speed shear disperser and shear mix at 2500 rpm for 12 minutes. Then turn off the high-speed shear disperser, turn on the low-speed stirring paddle and set the speed to 100 rpm, add 0.9 kg of the compound bacterial powder obtained in Preparation Example 4, and stir at low speed for 15 minutes to obtain a suspension. Send the dried particles cooled in Step 4 into a rotary drum coating machine, and use an air atomizing spray gun to evenly spray the pre-prepared suspension onto the particle surface at an atomization pressure of 0.4 MPa to obtain the finished product.

[0079] Example 2: This example provides a compound microbial agent for promoting the decomposition and fertilizer production of rice straw and its preparation method, including the following steps:

[0080] Step 1: At 20°C, 25.0 kg of ammonium sulfate, 8.0 kg of potassium dihydrogen phosphate, 16.0 kg of bentonite, and 1.0 kg of sodium lignosulfonate were added to a horizontal ribbon mixer and stirred for 15 minutes to obtain the core dry powder. 8.0 kg of urea-formaldehyde resin powder obtained in Preparation Example 2, 10.0 kg of sodium lignosulfonate, 4.0 kg of manganese oxalate dihydrate, 1.0 kg of sodium tetraborate decahydrate, and 22.0 kg of bentonite were added to another horizontal ribbon mixer and stirred for 15 minutes to obtain the outer shell powder.

[0081] Step 2: Put the core dry powder obtained in Step 1 into a disc granulator with an inclination angle of 40 degrees and a rotation speed of 30 rpm; spray 10.0 kg of pure water at a temperature of 20℃ evenly onto the surface of the powder in the granulator through a pneumatic atomizing nozzle, and keep the equipment running for 12 minutes to make the powder agglomerate to obtain micro-core particles.

[0082] Step 3: While the disc granulator continues to run, continuously and evenly sprinkle the shell powder obtained in Step 1 into the granulator, and simultaneously spray 4.0 kg of pure water at a temperature of 20°C through a pneumatic atomizing nozzle. After the shell powder is completely coated on the surface of the micro-core particles, continue running for 5 minutes to obtain core-shell structured wet particles.

[0083] Step 4: The core-shell structured wet granules are fed into a co-current rotary drum dryer via a belt conveyor. The dryer inlet air temperature is set to 90℃ and the outlet air temperature to 50℃. The residence time of the granules in the dryer is controlled to be 25 minutes, so that the moisture content of the granules is reduced to 1.9%. Then the granules are sent to the cooling drum, where 20℃ air is introduced for counter-current cooling, so that the outlet temperature of the granules is reduced to 28℃.

[0084] Step 5: Add 3.0 kg of crude soybean oil and 0.1 kg of hydrophobic fumed silica to a twin-shaft mixing tank equipped with a high-speed shear disperser and a low-speed stirring paddle. Turn on the high-speed shear disperser and shear mix at 2000 rpm for 10 minutes. Then turn off the high-speed shear disperser, turn on the low-speed stirring paddle and set the speed to 80 rpm, add 0.8 kg of the compound bacterial powder obtained in Preparation Example 5, and stir at low speed for 10 minutes to obtain a suspension. Send the dried particles cooled in Step 4 into a rotary drum coating machine, and use an air atomizing spray gun to evenly spray the pre-prepared suspension onto the particle surface at an atomization pressure of 0.3 MPa to obtain the finished product.

[0085] Example 3: This example provides a compound microbial agent for promoting the decomposition and fertilizer production of rice straw and its preparation method, including the following steps:

[0086] Step 1: At 30°C, 15.0 kg of ammonium sulfate, 3.0 kg of potassium dihydrogen phosphate, 19.0 kg of bentonite, and 3.0 kg of sodium lignosulfonate were added to a horizontal ribbon mixer and stirred for 10 minutes to obtain the core dry powder. 15.0 kg of urea-formaldehyde resin powder obtained in Preparation Example 3, 18.0 kg of sodium lignosulfonate, 8.0 kg of manganese oxalate dihydrate, 4.0 kg of sodium tetraborate decahydrate, and 10.0 kg of bentonite were added to another horizontal ribbon mixer and stirred for 10 minutes to obtain the outer shell powder.

[0087] Step 2: Put the core dry powder obtained in Step 1 into a disc granulator with an inclination angle of 50 degrees and a rotation speed of 45 rpm; spray 8.0 kg of pure water at a temperature of 30°C evenly onto the surface of the powder in the granulator through a pneumatic atomizing nozzle, and keep the equipment running for 8 minutes to make the powder agglomerate to obtain micro-core particles.

[0088] Step 3: While the disc granulator continues to run, continuously and evenly sprinkle the shell powder obtained in Step 1 into the granulator, and simultaneously spray 6.0 kg of pure water at a temperature of 30°C through a pneumatic atomizing nozzle. After the shell powder is completely coated on the surface of the micro-core particles, continue running for 5 minutes to obtain core-shell structured wet particles.

[0089] Step 4: The core-shell structured wet granules are fed into a co-current rotary drum dryer via a belt conveyor. The dryer inlet air temperature is set to 110℃ and the outlet air temperature to 60℃. The residence time of the granules in the dryer is controlled to be 15 minutes, so that the moisture content of the granules is reduced to 1.5%. Then the granules are sent to the cooling drum, where 30℃ air is introduced for counter-current cooling, so that the outlet temperature of the granules is reduced to 32℃.

[0090] Step 5: Add 5.0 kg of crude soybean oil and 0.3 kg of hydrophobic fumed silica to a twin-shaft mixing tank equipped with a high-speed shear disperser and a low-speed stirring paddle. Turn on the high-speed shear disperser and shear mix at 3000 rpm for 15 minutes. Then turn off the high-speed shear disperser, turn on the low-speed stirring paddle and set the speed to 120 rpm, add 1.5 kg of the compound bacterial powder obtained in Preparation Example 6, and stir at low speed for 20 minutes to obtain a suspension. Send the dried particles cooled in Step 4 into a rotary drum coating machine, and use an air atomizing spray gun to evenly spray the pre-prepared suspension onto the particle surface at an atomization pressure of 0.5 MPa to obtain the finished product.

[0091] Example 4: This example provides a compound microbial agent for promoting the decomposition and fertilizer production of rice straw and its preparation method, including the following steps:

[0092] Step 1: At 25°C, 20.0 kg of ammonium sulfate, 5.0 kg of potassium dihydrogen phosphate, 18.0 kg of bentonite, and 2.0 kg of sodium lignosulfonate were added to a horizontal ribbon mixer and stirred for 12 minutes to obtain the core dry powder. 10.0 kg of urea-formaldehyde resin powder obtained in Preparation Example 1, 13.0 kg of sodium lignosulfonate, 6.0 kg of manganese oxalate dihydrate, 2.0 kg of sodium tetraborate decahydrate, and 19.0 kg of bentonite were added to another horizontal ribbon mixer and stirred for 12 minutes to obtain the outer shell powder.

[0093] Step 2: Put the core dry powder obtained in Step 1 into a disc granulator with an inclination angle of 45 degrees and a rotation speed of 35 rpm; spray 11.0 kg of pure water at a temperature of 25℃ evenly onto the surface of the powder in the granulator through a pneumatic atomizing nozzle, and keep the equipment running for 10 minutes to make the powder agglomerate to obtain micro-core particles.

[0094] Step 3: While the disc granulator continues to run, continuously and evenly sprinkle the shell powder obtained in Step 1 into the granulator, and simultaneously spray 5.0 kg of pure water at a temperature of 25°C through a pneumatic atomizing nozzle. After the shell powder is completely coated on the surface of the micro-core particles, continue running for 5 minutes to obtain core-shell structured wet particles.

[0095] Step 4: The core-shell structured wet granules are fed into a co-current rotary drum dryer via a belt conveyor. The dryer inlet air temperature is set to 110℃ and the outlet air temperature to 65℃. The residence time of the granules in the dryer is controlled to be 18 minutes, so that the moisture content of the granules is reduced to 1.7%. Then the granules are sent to the cooling drum, where 25℃ air is introduced for counter-current cooling, so that the outlet temperature of the granules is reduced to 30℃.

[0096] Step 5: Add 3.8 kg of crude soybean oil and 0.2 kg of hydrophobic fumed silica to a twin-shaft mixing tank equipped with a high-speed shear disperser and a low-speed stirring paddle. Turn on the high-speed shear disperser and shear mix at 2500 rpm for 12 minutes. Then turn off the high-speed shear disperser, turn on the low-speed stirring paddle and set the speed to 100 rpm, add 0.9 kg of the compound bacterial powder obtained in Preparation Example 4, and stir at low speed for 15 minutes to obtain a suspension. Send the dried particles cooled in Step 4 into a rotary drum coating machine, and use an air atomizing spray gun to evenly spray the pre-prepared suspension onto the particle surface at an atomization pressure of 0.4 MPa to obtain the finished product.

[0097] Comparative Example 1:

[0098] Compared to Example 1, the difference lies in the granulation space structure, which is altered, eliminating the distinction between the core and the outer shell. Specifically, all raw materials from the core dry powder formulation and the outer shell powder formulation in step one are simultaneously added to a horizontal ribbon mixer and stirred for 15 minutes to obtain a mixed dry powder. This mixed dry powder is then fed into a disc granulator, where 13.5 kg of pure water at 25°C is sprayed through a pneumatic atomizing nozzle for overall granulation. The equipment is kept running for 15 minutes to obtain homogeneous wet granules. Step three of Example 1 is omitted, and the homogeneous wet granules are directly subjected to the drying and cooling process in step four. All other steps remain the same.

[0099] Comparative Example 2:

[0100] Compared to Example 1, the difference lies in the spatial distribution of the urea-formaldehyde resin powder. Specifically, 10.0 kg of urea-formaldehyde resin powder from the outer shell powder formulation in Step 1 is transferred to the core dry powder formulation and mixed with ammonium sulfate, potassium dihydrogen phosphate, bentonite, and sodium lignosulfonate in a horizontal ribbon mixer; the outer shell powder formulation no longer contains urea-formaldehyde resin powder. Everything else remains the same.

[0101] Comparative Example 3:

[0102] Compared to Example 1, the difference lies in the change of the rheological formulation of the suspension. Specifically, in step five, hydrophobic fumed silica was not added; instead, 3.8 kg of crude soybean oil and 0.9 kg of compound bacterial powder were mixed and stirred to prepare the suspension. All other steps remained the same.

[0103] Comparative Example 4:

[0104] Compared to Example 1, the difference lies in the alteration of the chemical form and solubility characteristics of the manganese source in the shell region. Specifically, the 6.0 kg of manganese oxalate dihydrate in the shell powder formulation of step one was replaced with 5.66 kg of manganese sulfate monohydrate. All other steps remained the same.

[0105] Comparative Example 5:

[0106] Compared to Example 1, the difference lies in the removal of the slightly alkaline crosslinking network builder in the shell region. Specifically, sodium tetraborate decahydrate was not added to the shell powder formulation in step one, while the remaining component ratios and operating procedures were the same as in Example 1.

[0107] Test Example 1:

[0108] Test objective: To verify the rheological properties of hydrophobic fumed silica in suspension and its effect on coating uniformity.

[0109] The experimental steps are as follows:

[0110] The experimental subjects were the suspensions and final product particles prepared in Examples 1 to 4, as well as the suspension and final product particles prepared in Comparative Example 3.

[0111] Each prepared suspension sample was transferred into a rotational rheometer equipped with a coaxial cylindrical test rotor. The shear rate was set to 0.1 s⁻¹ at room temperature. -1 and 100s -1 The apparent viscosity of the systems was measured separately. (0.1 s⁻¹) -1 Divide the viscosity test value below by 100s -1 The viscosity test value is used to calculate the thixotropic index of the suspension.

[0112] Take 100 mL of each suspension sample and inject it into a 100 mL stoppered graduated cylinder, then seal it. Let it stand at room temperature for 24 hours, read the volume of the clear oil layer that has precipitated at the top of the graduated cylinder, and calculate the oil separation rate.

[0113] Ten independent production batches were randomly selected from the finished granules prepared in chronological order, with 10g samples weighed from each batch. Sterile physiological saline was added to the samples for shaking and serial dilution. The total number of viable bacteria per gram of granules was determined using the plate spread method. Ten sets of data were collected, and the relative standard deviation was calculated.

[0114] The experimental results are shown in Table 1:

[0115] Table 1: Rheological parameters and viable bacteria distribution data of suspensions in each experimental group

[0116] Experimental group <![CDATA[Low shear viscosity / mPa·s, shear rate 0.1 s -1 > <![CDATA[High shear viscosity / mPa·s, shear rate 100 s -1 > Thixotropic index Oil separation rate after 24 hours of settling / % Relative standard deviation of total viable count / % Example 1 4215 785 5.37 1.15 3.62 Example 2 3982 812 4.90 1.63 4.18 Example 3 4503 741 6.08 0.82 2.94 Example 4 4166 794 5.25 1.37 3.81 Comparative Example 3 985 863 1.14 41.2 26.5

[0117] in conclusion:

[0118] Based on the data in Table 1 and referring to the appendix Figure 1 Examples 1 to 4 show significant differences from Comparative Example 3 in rheological parameters and finished product particle distribution. In Comparative Example 3, the compound bacterial powder was directly dispersed in crude soybean oil, and the suspension was completed in 0.1 s... -1The apparent viscosity was low at low shear rates. Fungal spore powder, due to its greater density than oil, underwent gravitational sedimentation, resulting in an oil separation rate of 41.2% after 24 hours of settling. This physical phase separation affected the material uniformity within the storage tank and pipelines, leading to fluctuations in the viable bacteria concentration extracted by the spray gun during the rotary drum coating process. The relative standard deviation of the total number of viable bacteria on the surface of the finished product particles in Comparative Example 3 was ultimately measured to be 26.5%, indicating uneven distribution of effective viable bacteria among different batches of particles.

[0119] Examples 1 to 4 incorporated hydrophobic fumed silica into the formulation. The hydrophobic and polar groups on its surface interacted in the base oil, forming a three-dimensional network structure with yield stress. This structure improved the suspension's performance in 0.1 seconds. -1 The apparent viscosity at low shear rates slowed down the sedimentation rate of the spore powder, controlling the 24-hour oil separation rate of Examples 1 to 4 between 0.82% and 1.63%. When the suspension containing live bacteria flowed through the high-pressure spray gun, the mechanical shear force broke the existing micro-network, resulting in a decrease in fluid viscosity and the emergence of thixotropic fluid characteristics. Tests showed that the thixotropic index values ​​of Examples 1 to 4 ranged from 4.90 to 6.08. The reduced high shear viscosity allowed the fluid to pass through the atomizing nozzle, and the viscosity gradually recovered as the shear force weakened after the droplets contacted the particle surface. Data showed that the relative standard deviation of the total number of live bacteria in the example groups decreased to 2.94% to 4.18%, improving the concentration fluctuation problem during the live bacteria spraying process and confirming that rheological regulation can affect the coating uniformity in the continuous manufacturing process of compound microbial fertilizer.

[0120] Test Example 2:

[0121] Test objective: To test the correlation between microenvironment pH changes, manganese oxalate dissolution characteristics, and fungal enzyme production patterns over time during cultivation.

[0122] The experimental steps are as follows:

[0123] The experimental subjects were the finished particles prepared in Example 1 and the finished particles in Comparative Example 4.

[0124] Naturally air-dried rice straw was shredded to a length of 2 to 3 cm using a shredder, sterilized under high-pressure steam at 121 degrees Celsius for 20 minutes, and then cooled. Two groups of finished product granules were mixed with the sterilized rice straw at a mass ratio of 1:20. Sterile deionized water was slowly added dropwise to the mixture until the overall moisture content reached 60%.

[0125] The mixture was dispensed into 500 mL wide-mouth culture flasks equipped with breathable membranes and placed in a constant temperature incubator at 30°C for 30 days of continuous incubation. Samples were taken every 3 days during the incubation period, with 5.0 g of the mixture sample weighed each time.

[0126] Add 25 mL of deionized water to the 5.0 g sample and extract on a constant temperature shaker at 150 rpm for 2 hours. Centrifuge the suspension at 4000 rpm for 10 minutes and collect the supernatant. Measure the microenvironmental pH of the extract using a calibrated pH meter.

[0127] A portion of the centrifuged supernatant was filtered through a polyethersulfone aqueous microporous membrane with a pore size of 0.22 micrometers. The concentration of soluble manganese ions in the filtrate was determined using flame atomic absorption spectrometry.

[0128] Take the remaining supernatant and add 2,6-dimethoxyphenol and hydrogen peroxide substrate to the reaction system containing sodium malonate buffer. After reacting at room temperature, measure the increase in absorbance at 469 nm using a UV-Vis spectrophotometer to calculate the activity of manganese peroxidase in the sample.

[0129] The experimental results are shown in Table 2:

[0130] Table 2: Microenvironment and enzyme activity assay data of the mixtures from Example 1 and Comparative Example 4 during the 30-day culture period.

[0131] Culture time / d Example 1 pH Comparative Example 4 pH <![CDATA[Example 1 Manganese ion concentration / mg·L -1 > <![CDATA[Comparative Example 4 Manganese ion concentration / mg·L -1 > <![CDATA[Example 1 Enzyme activity of MnP / U·g -1 > <![CDATA[Specific Activity of 4MnP Enzyme / U·g -1 > 0 7.62 7.58 0.31 18.24 1.05 0.98 3 7.51 7.46 0.45 26.85 1.84 3.42 6 7.18 7.21 0.82 23.11 3.65 7.85 9 6.54 6.48 2.14 18.63 12.41 15.22 12 5.21 5.34 8.76 13.45 27.86 21.04 15 4.75 4.88 18.42 10.28 41.72 23.51 18 4.52 4.67 20.15 8.16 39.54 19.88 21 4.38 4.51 19.68 6.54 33.12 16.43 24 4.3 4.42 17.51 5.22 25.46 12.11 27 4.25 4.38 15.34 4.87 18.91 9.54 30 4.18 4.35 13.68 4.11 13.25 7.66

[0132] in conclusion:

[0133] Based on the data in Table 2 and referring to the appendix Figure 2 The physicochemical properties and enzyme activity changes during the cultivation period differed between Example 1 and Comparative Example 4. During the early fermentation stage (days 0-6), the pH of the extract microenvironment in Example 1 remained in the neutral to slightly alkaline range, resulting in low manganese oxalate solubility and a manganese ion concentration below 0.82 mg / L. Comparative Example 4 used readily soluble manganese sulfate, whose manganese ions dissociated earlier in the rice straw substrate, reaching a concentration of 26.85 mg / L by day 3. In the early fermentation stage, the prematurely dissolved manganese ions readily combined with components in the straw substrate to form precipitates, consuming the soluble manganese source in the system.

[0134] As fermentation time increased, microbial metabolism altered environmental parameters. Microorganisms utilized nitrogen sources and produced organic acids, causing a decrease in the pH of the culture between days 9 and 12. In Example 1, as the environmental pH decreased to a slightly acidic range, the solubility of manganese oxalate increased, and the concentration of soluble manganese ions showed an upward trend after day 12. By day 15, the manganese ion release concentration in Example 1 was measured at 18.42 mg / L, and the manganese peroxidase activity detected concurrently reached 41.72 units / g, demonstrating synchronicity between substrate release and enzyme activity at the time point. In Comparative Example 4, when it entered a slightly acidic environment on day 12, the consumption of free manganese ions in the early stages led to a decrease in the currently available manganese ion concentration to 13.45 mg / L, and its highest tested manganese peroxidase activity was 23.51 units / g. Example 1, through the application of low-solubility manganese salts, combined with pH changes caused by microbial metabolism, influenced the manganese ion release process, adapting the supply of catalytic aids to the microbial enzyme production cycle.

[0135] Test Example 3:

[0136] Test objective: To test the effect of the core-shell spatial distribution structure on the gas release concentration of easily hydrolyzable components during high-temperature drying.

[0137] The experimental steps are as follows:

[0138] The experimental subjects were wet particles from Examples 1 to 4 that had not undergone drying and cooling after the granulation process, as well as wet particles from Comparative Example 1 (which did not distinguish between the core and shell formulations) and wet particles from Comparative Example 2 (which changed the distribution position of the urea-formaldehyde resin powder).

[0139] Weigh 500 grams of each group of wet particle samples and place them flat on the inner tray of a laboratory-grade forced-air drying oven with a sealed gas collection hood.

[0140] Set the inlet air temperature of the drying oven to 100 degrees Celsius, turn on the equipment and maintain hot air circulation to continuously dry the particle samples in the internal tray for 20 minutes.

[0141] Connect calibrated pump-type formaldehyde and ammonia detectors to the exhaust port of the drying oven. Collect the overflow gas from the exhaust pipe during the drying cycle, read and record the cumulative emission concentrations of formaldehyde and ammonia displayed on the equipment, with the test data in milligrams per cubic meter.

[0142] The experimental results are shown in Table 3:

[0143] Table 3: Measurement data of cumulative gas emission concentration of wet particles in each experimental group during the drying process at 100 degrees Celsius.

[0144] Experimental group <![CDATA[Formaldehyde cumulative emission concentration / mg·m -3 > <![CDATA[Ammonia cumulative emission concentration / mg·m -3 > Example 1 0.42 1.12 Example 2 0.58 1.34 Example 3 0.35 0.98 Example 4 0.49 1.25 Comparative Example 1 45.63 112.45 Comparative Example 2 68.31 134.72

[0145] in conclusion:

[0146] Based on the data in Table 3 and referring to the appendix Figure 3 The gas release concentrations in Examples 1 to 4 differed from those in Comparative Examples 1 and 2 during the high-temperature drying stage. In Comparative Example 1, no stratified structure was incorporated into the granulation process; the acidic ammonium sulfate and the acid-sensitive urea-formaldehyde resin were distributed in the same wet phase. After drying with hot air at 100°C, the urea-formaldehyde resin degraded in the acidic moisture, producing formaldehyde and ammonia released with the evaporation of moisture. The cumulative emission concentrations of formaldehyde and ammonia reached 45.63 mg / m³ and 112.45 mg / m³, respectively. In Comparative Example 2, the urea-formaldehyde resin in the formulation was transferred to the core region dominated by ammonium sulfate, exacerbating the localized hydrolysis reaction, and the measured formaldehyde emission concentration increased to 68.31 mg / m³. In actual continuous drying operations, the concentrated volatilization of formaldehyde and ammonia directly affects the air quality of the workshop.

[0147] The gas escape concentrations in Examples 1 to 4 were at low levels, with formaldehyde test values ​​ranging from 0.35 to 0.58 mg / m³. In each example, inorganic acidic salts were placed in the core layer of the granules, allowing moisture to evaporate to the periphery through capillary pores. The temperature- and acidity-sensitive urea-formaldehyde resin was distributed in an outer shell layer composed of sodium lignosulfonate and sodium tetraborate decahydrate. The slightly alkaline buffer environment provided by the outer shell layer reduced the probability of resin molecular chain breakage under high-temperature heating. This spatially isolated distribution limited the generation of formaldehyde and ammonia, allowing the fertilizer granules to be continuously dried at temperatures above 100 degrees Celsius, meeting the production process requirements for both hot air drying efficiency and material safety control.

[0148] Test Example 4:

[0149] Test objective: To test the effect of a slightly alkaline crosslinking network builder in the outer shell layer on particle pelleting efficiency, mechanical compressive strength, and wear-resistant pulverization rate.

[0150] The experimental steps are as follows:

[0151] The experimental subjects were unscreened wet granules from the disc granulator of Examples 1 to 4 and dried, unoiled semi-finished granules. At the same time, unscreened wet granules and unoiled semi-finished granules corresponding to Comparative Example 5, in which sodium tetraborate decahydrate was removed from the outer shell, were also selected.

[0152] Weigh 2.0 kg of unscreened wet granules from each group after discharge from the disc granulator. After drying in a laboratory forced-air drying oven, classify and screen the granules using standard test sieves with apertures of 2 mm and 4 mm. Weigh the mass of granules that remain on the 2 mm sieve and pass through the 4 mm sieve, divide this mass by the initial total dried mass, and calculate the pelleting rate percentage for each experimental group.

[0153] One hundred particles with a particle size distribution in the range of 3 to 4 mm were randomly selected from each group of dried semi-finished products. Each sample was placed on the testing platform of a particle strength tester, and the tester was started to apply a load downwards at a uniform speed using the downward-pressing probe. The maximum force value at the moment of fracture of each particle was recorded, and 100 sets of test data were collected. The average compressive strength was calculated, and the test data were expressed in Newtons.

[0154] Weigh 50.0 grams of each group of dried semi-finished product granule samples and put them into an abrasion resistance drum tester equipped with internal baffles. Set the drum speed to 60 revolutions per minute and stop the equipment after running continuously for 10 minutes.

[0155] Remove the remaining material from the drum and pour it onto a 60-mesh standard test sieve with the corresponding aperture for vibratory sieving. Weigh the mass of the powder that falls through the sieve, divide the mass of the falling powder by the total mass of the initial sample, and calculate the percentage of wear-resistant pulverization rate for each group of particles.

[0156] The experimental results are shown in Table 4:

[0157] Table 4: Test data on physical and mechanical properties and pellet quality of unoiled semi-finished pellets in each experimental group

[0158] Experimental group Particle size of 2 to 4 mm, pellet formation rate / % Average compressive strength / N Abrasion resistance pulverization rate / % Example 1 91.5 26.8 0.74 Example 2 89.2 25.2 0.89 Example 3 92.8 27.6 0.61 Example 4 88.6 25.9 0.82 Comparative Example 5 67.3 12.4 5.18

[0159] in conclusion:

[0160] Based on the data in Table 4 and referring to the appendix Figure 4 Examples 1 to 4 differed from Comparative Example 5 in granulation quality and the mechanical properties of the dried particles. The pelleting rate reflects the agglomeration efficiency of the material during the disc granulation stage. Comparative Example 5 removed sodium tetraborate decahydrate from the outer shell formulation, making it difficult to retain free moisture during rolling due to the reliance on physical bonding after adding water to the powder. Many powder particles in this system failed to participate in the agglomeration process, transforming into fine powder or agglomerating into irregular clumps, resulting in a pelleting rate of only 67.3% for the target particle size of 2 to 4 mm. This loose structure problem persisted into the drying process, with the average compressive strength of the semi-finished particles in Comparative Example 5 decreasing to 12.4 Newtons. This level of mechanical strength makes them prone to breakage when subjected to material transport and impacts from equipment on the production line. In the abrasion-resistant drum test for surface strength, the pulverization rate of Comparative Example 5 was 5.18%, indicating that the shedding of powder from the particle surface increased the dust control load in the workshop environment.

[0161] After introducing sodium tetraborate decahydrate into the formulation, the physicochemical morphology of the particle shell region changed in the early stage of granulation. Sodium tetraborate decahydrate dissolved in granulation water created a slightly alkaline liquid medium, promoting the combination of borate ions with free hydroxyl groups on the sodium lignin sulfonate molecular chains to form borate ester chemical cross-linking bonds with a three-dimensional network characteristic. The cross-linking reaction fixed the internal moisture distribution of the material during disc rolling, promoting uniform powder agglomeration and increasing the pelleting rate of Examples 1 to 4 to between 88.6% and 92.8%. After drying, the borate ester chemical cross-linking bonds acted as a skeletal support medium in the shell region, and the average compressive strength data of Examples 1 to 4 reached 25.2 to 27.6 Newtons. The cross-linked shell improved the surface abrasion resistance while increasing the compressive strength, and the abrasion pulverization rate of each example remained in a low range of 0.61% to 0.89%. The shell barrier established by chemical bonding provided mechanical protection for the internal components, meeting the process requirements for particle formation rate and morphological stability in industrial continuous manufacturing.

[0162] Test Example 5:

[0163] Test objective: To test the effect of the final product on the degradation rate of lignin and cellulose in actual rice straw fermentation applications.

[0164] The experimental steps are as follows:

[0165] The experimental subjects were the finished particles prepared in Example 1, the finished particles of Comparative Example 3 without the addition of hydrophobic fumed silica, and the finished particles of Comparative Example 4 with the outer shell manganese oxalate layer replaced by manganese sulfate.

[0166] Naturally air-dried rice straw was collected and cut into 2-3 cm lengths using a shredding device. Samples were taken and the dry basis lignin and cellulose content of the batch of rice straw in its initial state was determined using the Van der Waals washing method.

[0167] Equal masses of rice straw fragments were weighed and placed into fermentation tanks. The finished product granules from Examples 1, 3, and 4 were then added to the fermentation tanks. Water was added to the mixture, and the mixture was turned over to adjust the initial moisture content of the fermentation system to 65%. Ten sampling points were set up in parallel within the pile for each experimental group.

[0168] The mixture was placed under natural temperature composting conditions for continuous fermentation for 40 days. During this period, ventilation and turning of the compost were carried out regularly to maintain an aerobic environment inside the compost pile.

[0169] After fermentation, straw residue samples were collected from each parallel sampling point and dried. The lignin and cellulose content in the residue was determined using the Van der Waals washing method. Based on the initial content data, the absolute degradation rate of lignin and cellulose at each sampling point was calculated, and the average degradation rate and standard deviation of the 10 parallel data points for each group were statistically analyzed.

[0170] The experimental results are shown in Table 5:

[0171] Table 5: Degradation rate data of rice straw in each experimental group after 40 days of fermentation

[0172] Experimental group Average lignin degradation rate / % Standard deviation of lignin degradation rate / % Average cellulose degradation rate / % Standard deviation of cellulose degradation rate / % Example 1 47.8 1.82 61.4 2.15 Comparative Example 3 32.1 9.45 46.2 12.31 Comparative Example 4 25.6 2.04 40.8 2.58

[0173] in conclusion:

[0174] Based on the data in Table 5 and referring to the appendix Figure 5 The fermentation degradation tests of rice straw in Example 1 differed from those in Comparative Examples 3 and 4. The degradation data of the straw substrate reflected the colonization state and enzymatic reaction of the compound microbial agent. Comparative Example 3 did not contain hydrophobic fumed silica, and the oil suspension underwent physical sedimentation before drum spraying, resulting in differences in the viable bacterial load among different batches and in different areas of the same compost pile. During the 40-day composting process, areas with lower viable bacterial distribution failed to form the required biomass microbial community, leading to a discrete distribution of lignin and cellulose degradation rates in this group, with a standard deviation of 9.45% for lignin degradation. The slower degradation process in some areas lowered the overall average degradation value of this group.

[0175] Comparative Example 4 reflects the impact of the timing of manganese source release on the degradation process. The lignin structure on the surface of rice straw restricts the degradation of internal cellulose, and breaking down this structure requires the participation of lignin-degrading enzymes and metal cofactors. Comparative Example 4 used manganese sulfate as an outer shell additive. In the neutral or slightly alkaline environment at the beginning of composting, manganese sulfate dissociates earlier, and the dissolved manganese ions easily combine with carbonate ions and organic matter in the environment to form precipitates. As fermentation progresses, the microbial metabolic acid production shifts the microenvironment to an acidic stage suitable for fungal secretion of manganese peroxidase, and the free manganese ions in the environment have already been consumed in the early stages. Due to the lack of manganese ion assistance, the enzymatic degradation reaction is limited, and the average lignin degradation rate in this group is 25.6%. The lignin outer shell fails to disintegrate further, hindering the exposure of cellulose, and its average cellulose degradation rate is 40.8%.

[0176] In Example 1, manganese oxalate in the outer shell remained in a solid state during the early stages of composting. Its solubility increased after the microenvironment became acidic, providing a cofactor supplement for the fungal enzyme production cycle. The addition of fumed silica improved the physical stability of the suspension and controlled the uniformity of the live bacteria distribution. The uniform distribution of live bacteria, combined with timely chemical release, resulted in average lignin and cellulose degradation rates of 47.8% and 61.4%, respectively, in Example 1, with relatively concentrated data distribution at each sampling point. The mechanism combining particle physical parameter control with the dissolution equilibrium of sparingly soluble salts altered the biochemical degradation process of the substrate.

[0177] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A compound microbial agent for promoting the decomposition and fertilizer production of rice straw, characterized in that, The rice straw decomposition and fertilizer-making compound microbial agent is a core-shell structure particle, consisting of an inner core layer, an outer shell layer surrounding the core layer, and a microbial suspension sprayed on the outermost layer of the rice straw decomposition and fertilizer-making compound microbial agent. The raw materials of the core layer contain the following components in parts by weight: 15.0-25.0 parts ammonium sulfate, 3.0-8.0 parts potassium dihydrogen phosphate, 16.0-19.0 parts bentonite, and 1.0-3.0 parts sodium lignosulfonate; The raw material of the outer shell layer comprises the following components in parts by weight: 8.0-15.0 parts of urea-formaldehyde resin powder, 10.0-18.0 parts of sodium lignosulfonate, 4.0-8.0 parts of manganese oxalate dihydrate, 1.0-4.0 parts of sodium tetraborate decahydrate, and 10.0-22.0 parts of bentonite. The raw materials of the microbial suspension include the following components in parts by weight: 3.0-5.0 parts of crude soybean oil, 0.1-0.3 parts of hydrophobic fumed silica, and 0.8-1.5 parts of ultra-high concentration compound bacterial powder.

2. The rice straw decomposition and fertilizer-making compound microbial agent according to claim 1, characterized in that, The core layer contains 20.0 parts ammonium sulfate, 5.0 parts potassium dihydrogen phosphate, 18.0 parts bentonite, and 2.0 parts sodium lignosulfonate; the outer shell layer contains 10.0 parts urea-formaldehyde resin powder, 13.0 parts sodium lignosulfonate, 6.0 parts manganese oxalate dihydrate, 2.0 parts sodium tetraborate decahydrate, and 19.0 parts bentonite; the microbial suspension contains 3.8 parts crude soybean oil, 0.2 parts hydrophobic fumed silica, and 0.9 parts ultra-high concentration composite bacterial powder.

3. The rice straw decomposition and fertilizer-making compound microbial agent according to claim 1, characterized in that, The ultra-high concentration compound bacterial powder is a mixture of dormant spore powders of *Phanerochaete chrysosporium*, *Trichoderma reesei*, and *Bacillus megaterium*; the mass ratio of the *Phanerochaete chrysosporium*, *Trichoderma reesei*, and *Bacillus megaterium* is 1.5–2.5:1.5–2.5:1.0; and the total effective viable count of the ultra-high concentration compound bacterial powder is ≥1.0 × 10⁻⁶. 10 CFU / g.

4. The rice straw decomposition and fertilizer-making compound microbial agent according to claim 1, characterized in that, The urea-formaldehyde resin powder is a polymer dry powder prepared by an addition reaction and an acidic condensation reaction of formaldehyde aqueous solution and urea; in the reaction system for preparing the urea-formaldehyde resin powder, the initial molar ratio of formaldehyde to urea is 1.20 to 1.

50.

5. The rice straw decomposition and fertilizer-making compound microbial agent according to claim 1, characterized in that, The moisture content of the rice straw composting compound microbial agent is 1.5% to 1.9%.

6. A method for preparing a compound microbial agent for promoting the decomposition and fertilizer production of rice straw according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix the raw materials of the core layer to obtain core dry powder, and mix the raw materials of the outer shell layer to obtain outer shell powder; S2. Put the core dry powder into the granulator and spray pure water to make the core dry powder agglomerate to obtain micro-core particles. S3. The outer shell powder is continuously and evenly sprinkled into the granulator, and pure water is sprayed simultaneously. After the outer shell powder is completely coated on the surface of the micro-core particles, core-shell structured wet particles are obtained. S4. The core-shell structured wet particles are subjected to high-temperature drying and counter-current air cooling to obtain dried particles; S5. Crude soybean oil and hydrophobic fumed silica are subjected to high-speed shear dispersion and mixing, followed by the addition of ultra-high concentration compound bacterial dry powder and low-speed stirring to obtain a microbial suspension; the microbial suspension is sprayed onto the surface of the dried particles by air atomization to obtain the finished product.

7. The preparation method of the compound microbial agent for promoting the decomposition and fertilizer production of rice straw according to claim 6, characterized in that, The specific implementation method of step S4 is as follows: the core-shell structure wet particles are fed into a rotary drum dryer, the inlet air temperature of the rotary drum dryer is set to 90-110℃ and the outlet air temperature is set to 50-65℃, and the residence time of the core-shell structure wet particles in the rotary drum dryer is controlled so that the moisture evaporates to 1.5%-1.9%; then the dried particles with the moisture content reduced to 1.5%-1.9% are fed into a cooling drum, and air at 20-30℃ is introduced for countercurrent cooling so that the outlet temperature after cooling is reduced to 28-32℃.

8. The preparation method of the compound microbial agent for promoting the decomposition and fertilizer production of rice straw according to claim 6, characterized in that, The specific implementation method of step S5 is as follows: soybean crude oil and hydrophobic fumed silica are mixed at high speed at 2000-3000 r / min for 10-15 min; then the speed is adjusted to 80-120 r / min, and the ultra-high concentration compound bacterial dry powder is added and stirred for 10-20 min to prepare the microbial suspension. The microbial suspension is uniformly sprayed using an atomizing spray gun at an atomization pressure of 0.3–0.5 MPa.

9. The preparation method of the compound microbial agent for promoting the decomposition and fertilizer production of rice straw according to claim 6, characterized in that, Before step S1, the ultra-high concentration compound bacterial powder is pre-treated as follows: the proportioned microbial dormant spore powder is put into a mixer, and an equal mass of diatomaceous earth is added and stirred evenly; the mixture of diatomaceous earth and microbial dormant spore powder is placed in a 35°C environment and vacuum dried for 12 hours until the moisture content drops to below 5%, and then pulverized and sieved to obtain the ultra-high concentration compound bacterial powder.

10. The preparation method of the rice straw decomposition and fertilizer-making compound microbial agent according to claim 6, characterized in that, Before step S1, the urea-formaldehyde resin powder in the outer shell powder is prepared as follows: Mix formaldehyde aqueous solution with urea evenly, add alkaline solution to adjust the pH of the system to 8.0-8.5, heat to 70-80℃ and react at a constant temperature for 40-60 minutes; Then, an acidic solution was added to adjust the pH of the system to 4.5–5.5, and the temperature was raised to 80–90°C to carry out the polycondensation reaction for 60–120 minutes. After the reaction is completed, the pH is adjusted to 7.5-8.0 using an alkaline solution to terminate the reaction. The reaction solution is then sent to a centrifugal spray drying tower and spray dried at an inlet air temperature of 150-170℃ and an outlet air temperature of 80-90℃ to obtain the urea-formaldehyde resin powder.

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