A method for synergistically preparing a straw-based biochar and a functional microbial agent compound fertilizer

Abstract

The application discloses a kind of straw-based biochar and functional microbial agent compound fertilizer synergic preparation method, by process innovation integration and energy cascade utilization, straw pyrolysis, flue gas waste heat recovery, microbial agent nutrient solution preparation, in-situ fermentation load and compound granulation are coupled in one body;Utilize pyrolysis flue gas waste heat preparation and heat microbial agent fermentation nutrient solution, and utilize high-temperature biochar sensible heat directly drive and maintain functional microbial agent in-situ solid-state fermentation and active colonization in biochar pore, realize the depth, uniform load of microbial agent, subsequent compound and drying also make full use of system waste heat;The synergic preparation method greatly reduces energy consumption and cost, fundamentally solves the key technical problems that biochar and microbial agent adaptability is poor, microbial agent survival rate in finished product is low, and stability is poor, and the obtained product microbial agent activity is high, and fertilizer efficiency is durable and stable.

Description

Technical Field

[0001] This invention belongs to the field of agricultural waste resource utilization and novel fertilizer preparation technology, specifically involving a method for the synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer. Background Technology

[0002] With the intensive development of agricultural production, the output of crop straw is enormous, and its resource utilization is currently a research hotspot. Preparing biochar from straw through pyrolysis and carbonization, and using it for soil improvement, carbon sequestration, and emission reduction, is an important technological approach. Simultaneously, combining beneficial microorganisms with nitrogen-fixing, phosphorus-solubilizing, potassium-solubilizing, or biocontrol functions (collectively referred to as functional microbial agents) with fertilizers to prepare microbial fertilizers is also an important direction for the development of green agriculture.

[0003] Currently, the conventional technical route for preparing compound fertilizers by combining biochar with functional microbial agents is usually a "step-by-step method," which involves: first, in location A (or production line A), straw is separately carbonized and ground in a pyrolysis furnace to prepare straw-based biochar powder; second, in location B (or production line B), functional microbial strains are cultured in a separate fermentation tank using a specific culture medium to prepare a high-concentration microbial solution or microbial sludge; finally, the prepared biochar powder, microbial agents (and possibly other nutrients such as nitrogen, phosphorus, potassium, and organic matter) are transported to location C for physical mixing, granulation, and drying to obtain the final product. This "step-by-step method" has technical problems: discrete processes, high energy consumption and costs, and poor compatibility between the physicochemical properties of biochar and microbial agents, leading to unstable survival rates, stability, and field efficacy of the microbial agents in the final product. Specifically:

[0004] (1) Waste of energy and materials: A large amount of waste heat generated during biochar preparation (high-temperature flue gas, sensible heat of high-temperature biochar) is not effectively utilized and is either directly discharged or requires additional energy consumption for cooling; while the fermentation process of microbial agents requires additional energy to maintain a constant fermentation temperature. (2) Long process chain and high cost: The preparation of biochar, microbial agents and compound fertilizers are carried out in different places and links, and the materials need to be transported, transferred and stored multiple times, which increases the logistics, warehousing and packaging costs. (3) Artificially fragmented suitability: The pore structure, pH value, nutrient content and other characteristics of biochar were not optimized for the specific functional microbial agents loaded later when prepared separately, so that biochar only serves as a physical carrier and cannot provide the best colonization microenvironment for functional microbial agents. In the subsequent physical mixing process, the microbial cells are prone to death or reduced activity due to mechanical damage and drying stress. (4) Poor product uniformity: The physical mixing after step-by-step preparation makes it difficult to ensure the uniform distribution of microbial agents inside and between biochar particles, which easily leads to microbial agent "agglomeration" or "blank areas" and affects the uniformity of fertilizer effect.

[0005] Therefore, there is a need for a synergistic preparation method that can overcome the above-mentioned defects, achieve closed-loop energy and material processes, integrate processes, and significantly improve the colonization effect of functional microbial agents in biochar and the stability of the product. Summary of the Invention

[0006] To overcome the problems of discrete processing, high energy consumption, and low survival rate of microbial agents in the existing "step-by-step" process, this invention provides a method for the synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer. In the same integrated production system, the pyrolysis and carbonization of straw, the propagation and fermentation of functional microbial agents, and the in-situ loading and compound granulation of both are spatiotemporally coupled and energy synergistically combined.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for synergistic preparation of a compound fertilizer consisting of straw-based biochar and functional microbial agents includes the following steps: Step S1, raw material pretreatment and strain activation: Crop straw is crushed and dried for pretreatment; at the same time, functional strains are activated and first-stage propagation is carried out to obtain first-stage seed liquid; Step S2, Co-pyrolysis-fermentation: The pretreated straw is fed into a moving bed pyrolysis carbonization reactor for medium-low temperature pyrolysis. The high-temperature flue gas generated by pyrolysis is guided into a biochar quenching-inoculant nutrient solution preparation tower with a built-in spray tower. In the spray tower of the preparation tower, an inorganic salt solution containing nitrogen, phosphorus, potassium and trace elements is used as the spray liquid to quench and wash the high-temperature flue gas, forming a basic nutrient solution for inoculant fermentation that is heated and enriched with water-soluble organic matter in the flue gas. The high-temperature solid biochar obtained by pyrolysis is directly transported to a fermentation-loading integrated reactor. Step S3, in-situ fermentation and biochar loading: The primary seed liquid obtained in step S1 is inoculated into the basic nutrient solution for microbial agent fermentation prepared in step S2. After mixing, it is pumped into the integrated fermentation-loading reactor and thoroughly mixed with the high-temperature biochar in the reactor. The residual heat of the high-temperature biochar is used to start and maintain the in-situ solid-state fermentation process, so that the functional microbial agent actively colonizes in the pores of the biochar during the fermentation process, thus achieving in-situ loading. Step S4, compounding and granulation: After the in-situ fermentation is completed, fertilizer and binder are added to the fermentation-load integrated reactor for in-situ homogenization and compounding. The granulator extrudes / disc granulates the compounded wet material in the reactor to form wet material and then granulates it. Step S5, Waste Heat Drying and Post-treatment: The wet granules obtained in step S4 are transported to a low-temperature drying device that utilizes the waste heat of the flue gas from the pyrolysis carbonization reactor for drying; the drying heat source comes from the medium-temperature flue gas that has been sprayed and rapidly cooled in step S2. The heat of this flue gas is converted into hot air through the heat exchanger of the low-temperature drying device to dry the wet granules at low temperature, thus obtaining the final compound fertilizer product.

[0008] In a preferred embodiment of the present invention, in step S1, the functional bacterial strain is at least one of nitrogen-fixing bacteria, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, photosynthetic bacteria, and biocontrol bacteria.

[0009] In a preferred embodiment of the present invention, in step S2, the pyrolysis temperature of the moving bed pyrolysis carbonization reactor is 350-550℃, and the pyrolysis time is 20-60 minutes.

[0010] In a preferred embodiment of the present invention, in step S2, an inorganic salt spray solution containing nitrogen, phosphorus, potassium and trace elements is prepared according to the nutritional requirements of the target functional strain, and the final pH value after spraying and washing is controlled to be 6.0-7.5.

[0011] In a preferred embodiment of the present invention, in step S3, the in-situ solid-state fermentation time is 24-72 hours, and the fermentation endpoint is judged by the residual sugar concentration in the fermentation broth being lower than 0.5% and / or the cell concentration tending to stabilize.

[0012] In a preferred embodiment of the present invention, in step S4, the added binder is one or more of bentonite, attapulgite, or soluble starch, and the amount added is 2%-5% of the total mass of the wet material.

[0013] In a preferred embodiment of the present invention, in step S5, the temperature of the low-temperature drying is controlled at 45-60°C, and the drying time is 20-40 minutes.

[0014] In a preferred embodiment of the present invention, the functional microbial agent is a compound microbial agent of one or more of the following: Bacillus subtilis, Bacillus thuringiensis, Azotobacter chrysogenum, Bacillus megaterium, and photosynthetic bacteria.

[0015] In a preferred embodiment of the present invention, in step S3, before the fermentation culture medium is pumped into the reactor and mixed with the high-temperature biochar, a molasses or trehalose solution accounting for 1%-3% of the biochar mass is sprayed onto the surface of the high-temperature biochar in the integrated fermentation-loading reactor.

[0016] An integrated production system for implementing the above-mentioned synergistic preparation method of straw-based biochar and functional microbial agent compound fertilizer includes, in sequence, a straw pretreatment device, a moving bed pyrolysis carbonization reactor, a biochar quenching-microbial agent nutrient solution preparation tower with built-in spray tower, a fermentation-loading integrated reactor, a granulator, and a low-temperature drying device utilizing waste heat from flue gas; wherein, the flue gas outlet of the moving bed pyrolysis carbonization reactor is connected to the flue gas inlet of the preparation tower, and its biochar outlet is connected to the feed inlet of the fermentation-loading integrated reactor through a high-temperature resistant conveying device; the nutrient solution outlet of the preparation tower is connected to the liquid inlet of the fermentation-loading integrated reactor; and the flue gas outlet of the preparation tower is connected to the heat exchanger of the low-temperature drying device.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) Deep energy synergy, significant energy saving and consumption reduction: The waste heat of pyrolysis high-temperature flue gas and the sensible heat of high-temperature biochar are innovatively utilized in two stages: “preparation of nutrient solution by spray tower” and “fermentation in integrated reactor”. The former converts the waste heat into heat of the fermentation medium, while the latter directly uses the sensible heat of biochar to maintain the fermentation temperature, completely eliminating the extra energy consumption of biochar cooling and fermentation heating in the traditional process, and realizing the internal circulation of system energy.

[0018] (2) High integration of processes reduces costs: Key processes such as pyrolysis, flue gas treatment, nutrient solution preparation, fermentation, loading, and compounding are integrated into a few core equipment, resulting in a very short material flow path. This eliminates the need for transportation, storage, and reprocessing of intermediate products, significantly reducing equipment investment, operation, and logistics costs.

[0019] (3) In-situ adaptation optimization enhances the efficacy of microbial agents: The core innovation lies in enabling functional microbial agents to undergo in-situ, dynamic fermentation and loading in the optimal state of "freshly produced" biochar, which still retains residual heat and has open pores. This process forces the microbial cells to actively seek out and colonize the pores of the biochar, forming a "micro-ecological sanctuary," effectively avoiding mechanical damage caused by subsequent physical mixing. The pore structure and surface chemical properties of the biochar are also modified to a certain extent during the in-situ fermentation process, which is more conducive to the survival of the microbial agents. This fundamentally solves the problem of poor compatibility between microbial agents and carriers and low survival rate.

[0020] (4) Good product uniformity and stability: From the start of fermentation, the microbial agent is in uniform contact with and grows in the biochar. Subsequent compounding is also carried out in the same reactor, ensuring that the distribution of microbial agent and nutrients in the final product is highly uniform. The microbial agent loaded inside the pores of the biochar is physically protected and has stronger tolerance to subsequent environmental conditions such as drying and storage, thus extending the product's shelf life and field efficacy. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments or prior art, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This application provides a flowchart of a method for the synergistic preparation of a compound fertilizer consisting of straw-based biochar and functional microbial agents.

[0023] Figure 2 This application provides a schematic diagram of equipment connections for an integrated production system.

[0024] Figure 3 This is a comparison curve showing the change in the survival rate of functional bacteria over time in products prepared by the synergistic preparation method of this application and those prepared by the traditional stepwise method.

[0025] Figure 4 This is a comparison chart showing the change of available potassium content in the soil over time after the application of different fertilizers (example: taking potassium-solubilizing bacteria as an example). Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0027] like Figure 1 As shown in the figure, this invention provides a method for the synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer, comprising the following steps: Step S1, raw material pretreatment and strain activation: Crop straw is crushed and dried for pretreatment; at the same time, functional strains are activated and first-stage propagation is carried out to obtain first-stage seed liquid; the functional strains are at least one of nitrogen-fixing bacteria, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, photosynthetic bacteria, and biocontrol bacteria.

[0028] Step S2, Co-pyrolysis-fermentation: The pretreated straw is fed into a moving bed pyrolysis carbonization reactor for medium- and low-temperature pyrolysis. The high-temperature flue gas generated by pyrolysis is guided into a biochar quenching-inoculant nutrient solution preparation tower with a built-in spray tower. In the spray tower, an inorganic salt solution containing nitrogen, phosphorus, potassium, and trace elements is used as the spray liquid to quench and wash the high-temperature flue gas, forming a heated and enriched basic nutrient solution for inoculant fermentation. The high-temperature solid biochar obtained from pyrolysis is directly transported to a fermentation-loading integrated reactor. In this embodiment, the spray tower is built into the biochar quenching-inoculant nutrient solution preparation tower, receiving the high-temperature flue gas discharged from the pyrolysis reactor and completing the quenching and washing and nutrient solution preparation.

[0029] Step S3, in-situ fermentation and biochar loading: The primary seed liquid obtained in step S1 is inoculated into the basic nutrient solution for microbial fermentation prepared in step S2. After mixing, it is pumped into the integrated fermentation-loading reactor and thoroughly mixed with the high-temperature biochar in the reactor. The residual heat of the high-temperature biochar is used to start and maintain the in-situ solid-state fermentation process, so that the functional microbial agent actively colonizes in the pores of the biochar during the fermentation process, thus achieving in-situ loading.

[0030] Step S4, compounding and granulation: After the in-situ fermentation is completed, fertilizer and binder are added to the fermentation-load integrated reactor for in-situ homogenization and compounding. The granulator then extrudes / discs the compounded wet material in the reactor to form wet material and granulates it.

[0031] Step S5, Waste Heat Drying and Post-treatment: The wet granules obtained in Step S4 are transported to a low-temperature drying device utilizing the waste heat of the flue gas from the pyrolysis carbonization reactor for drying. The drying heat source comes from the medium-temperature flue gas that has undergone rapid cooling via spraying in Step S2. The heat of this flue gas is converted into hot air through a heat exchanger to dry the wet granules at a low temperature, obtaining the final compound fertilizer product. The moisture content meets the requirements. After drying, the granules are cooled and sieved. Qualified granules are metered and packaged to obtain the straw-based biochar and functional microbial agent compound fertilizer product.

[0032] In step S2, the residual heat of the high-temperature flue gas heats the spray liquid to the optimal fermentation temperature range (25-45℃) for the functional strains. At the same time, some water-soluble organic acids, phenols and other substances in the flue gas are absorbed into the spray liquid, forming a basic nutrient solution for bacterial fermentation that is rich in carbon source and heat. The high-temperature solid biochar obtained by pyrolysis is directly transported to a fermentation-loading integrated reactor with a temperature control jacket for temporary storage.

[0033] In step S2, the pyrolysis temperature of the moving bed pyrolysis carbonization reactor is 350-550℃, and the pyrolysis time is 20-60 minutes.

[0034] In step S2, the inorganic salt spray solution containing nitrogen, phosphorus, potassium and trace elements is formulated according to the nutritional requirements of the target functional strain, and the final pH value after spraying and washing is controlled to be 6.0-7.5.

[0035] In step S3, the residual heat of the high-temperature biochar is used to rapidly bring the temperature of the mixed system to and maintain it at the optimal fermentation temperature of the functional strain, thus initiating the in-situ solid-state fermentation process. During this process, the functional strains utilize the nutrient solution and the organic nutrients adsorbed on the surface of the biochar to proliferate. Driven by the fermentation dynamics, the bacterial cells actively migrate and colonize the rich porous structure and surface of the high-temperature biochar formed by the residual heat drying, thereby achieving in-situ, deep, and uniform loading of the bacterial agent.

[0036] In step S3, the integrated fermentation-loading reactor has stirring, aeration, temperature control and pH monitoring functions; during the fermentation process, circulating water is introduced through the jacket for fine-tuning of the temperature, and aerobic or facultative anaerobic fermentation conditions are maintained through intermittent low-pressure sterile air aeration.

[0037] In step S3, the in-situ solid-state fermentation time is 24-72 hours, and the fermentation endpoint is judged by the residual sugar concentration in the fermentation broth being lower than 0.5% and / or the cell concentration tending to stabilize.

[0038] In step S4, after the in-situ fermentation in step S3 reaches the peak cell concentration, the calculated amount of nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer, micronutrient fertilizer and necessary binder are directly added to the fermentation-loading integrated reactor. The mixture is stirred in the reactor to achieve in-situ homogeneous mixing of biochar-microbial agent complex and chemical nutrients to form wet material. The wet material is discharged from the bottom of the reactor and granulated by an extrusion granulator or a disc granulator to obtain wet granules.

[0039] In step S4, the added binder is one or more of bentonite, attapulgite, or soluble starch, and the amount added is 2%-5% of the total mass of the wet material.

[0040] In step S5, the temperature for low-temperature drying is controlled at 45-60℃, and the drying time is 20-40 minutes.

[0041] The functional microbial agent is a compound microbial agent containing one or more of the following: Bacillus jellyoides, Bacillus subtilis, Azotobacter chrysogenum, Bacillus megaterium, and photosynthetic bacteria. Bacillus jellyoides is used for potassium solubilization, while Bacillus subtilis is used for biocontrol.

[0042] In step S3, before pumping the fermentation medium into the reactor and mixing it with the high-temperature biochar, a molasses or trehalose solution accounting for 1%-3% of the biochar mass is sprayed onto the surface of the high-temperature biochar in the integrated fermentation-loading reactor to further increase the active sites and initial nutrients on the biochar surface and promote the colonization of functional bacteria.

[0043] like Figure 2 As shown, the present invention also provides an integrated production system for implementing the above-mentioned synergistic preparation method of straw-based biochar and functional microbial agent compound fertilizer. The system includes, in sequence, a straw pretreatment device, a moving bed pyrolysis carbonization reactor, a biochar quenching-microbial agent nutrient solution preparation tower with a built-in spray tower, a fermentation-loading integrated reactor, a granulator, and a low-temperature drying device utilizing waste heat from flue gas. The flue gas outlet of the moving bed pyrolysis carbonization reactor is connected to the flue gas inlet of the preparation tower, and its biochar outlet is connected to the feed inlet of the fermentation-loading integrated reactor via a high-temperature resistant conveying device. The nutrient solution outlet of the preparation tower is connected to the liquid inlet of the fermentation-loading integrated reactor. The flue gas outlet of the preparation tower is connected to the heat exchanger of the low-temperature drying device. The heat exchanger converts the heat from the medium-temperature flue gas discharged from the preparation tower into hot air for drying, achieving cascade utilization of waste heat.

[0044] Straw pretreatment equipment crushes and dries crop straw to obtain straw raw materials that meet the requirements for pyrolysis, preparing them for subsequent carbonization.

[0045] Biochar quenching-inoculant nutrient solution preparation tower with built-in spray tower: high-temperature flue gas is quenched and washed with nitrogen, phosphorus, potassium and inorganic salt spray solution, and the waste heat is recovered to heat the nutrient solution; water-soluble organic matter in flue gas is enriched to prepare basic nutrient solution for inoculant fermentation; the cooled medium-temperature flue gas is output for subsequent drying.

[0046] Fermentation-Loading Integrated Reactor: Receives high-temperature biochar and microbial nutrient solution, completing functional microbial inoculation, in-situ solid-state fermentation, and colonization of the microbial agent within the biochar pores. Subsequently, fertilizers and binders can be added in-situ to complete homogenization and compounding. Granulator: Extrudes / disc-granulates the mixed wet material from the reactor to form wet granules.

[0047] Low-temperature drying equipment utilizing flue gas waste heat: Utilizing the waste heat of the medium-temperature flue gas output from the preparation tower, the waste heat is converted into hot air via a heat exchanger and dried at a low temperature of 45–60℃ to obtain the finished compound fertilizer. High-temperature resistant conveying equipment: Directly conveys the high-temperature biochar produced by the pyrolysis reactor to the fermentation-loading integrated reactor, retaining the sensible heat of the biochar.

[0048] Example 1: Using wheat straw as raw material and Bacillus spp. as functional strain, a straw-based biochar potassium-solubilizing bacteria compound fertilizer was prepared. The synergistic preparation method is as follows: Figure 2 The process is carried out in the integrated system shown, and the specific steps are as follows: Step S1, Raw Material Pretreatment and Inoculum Activation: Wheat straw with a moisture content of approximately 15% was crushed into 1-3 cm pieces using a crusher. The *Bacillus cereus* (ACCC 03112) inoculum was activated on a slant agar and then inoculated into an Erlenmeyer flask containing 100 mL of liquid seed culture medium. The flask was incubated at 30°C and 180 rpm for 24 hours on a shaker to obtain primary seed culture with a viable count of approximately 5 × 10⁻⁶ cells / mL. 8 CFU / mL.

[0049] Step S2, Co-pyrolysis-fermentation: Crushed wheat straw is fed into a moving bed pyrolysis carbonization reactor at a feed rate of 100 kg / h. The pyrolysis temperature is controlled at 450℃, and the pyrolysis time is 30 minutes. The generated high-temperature flue gas at approximately 450℃ is introduced into a biochar quenching-inoculant nutrient solution preparation tower with an internal spray tower. The spray solution is a pre-prepared salt solution containing ammonium sulfate, potassium dihydrogen phosphate, magnesium sulfate, sodium chloride, and trace elements (pH adjusted to 7.0). The spray flow rate is automatically adjusted according to the flue gas temperature, quenching the flue gas to below 80℃. After absorbing the waste heat and some water-soluble organic matter from the flue gas, the temperature of the spray solution stabilizes at 35℃, forming the basic nutrient solution for inoculant fermentation. Simultaneously, the high-temperature biochar obtained from pyrolysis at approximately 400℃ (yield of approximately 30%, i.e., 30 kg / h) is directly fed into the integrated fermentation-loading reactor via a high-temperature resistant conveying device.

[0050] Step S3, In-situ Fermentation and Biochar Loading: The primary seed culture obtained in Step S1 was inoculated into the basal nutrient solution prepared in Step S2 at an inoculum rate of 5% (v / v), and mixed thoroughly. This mixture was then pumped entirely into the integrated fermentation-loading reactor and mixed with 30 kg of high-temperature biochar within the reactor. Upon mixing, the system temperature rapidly increased from room temperature to 38°C (the optimal temperature range for the target bacteria) due to the high sensible heat of the biochar. Slow stirring (20 rpm) and intermittent aeration (10 minutes every 2 hours, 0.2 vvm) were initiated in the reactor. Fermentation proceeded for 48 hours. During this period, *Bacillus mucilaginosus* proliferated vigorously using the nutrients adsorbed on the surface of the nutrient solution and biochar, and actively migrated and colonized into the pores of the biochar.

[0051] Step S4, Mixing and Granulation: After fermentation, add the following directly to the reactor: urea (equivalent to 4 kg N), superphosphate (equivalent to 3 kg P2O5), potassium sulfate (equivalent to 2 kg K2O), zinc sulfate 0.5 kg, and bentonite 6 kg. Start rapid stirring (60 rpm) for 20 minutes to ensure all materials are mixed evenly. Granulate the mixed wet material using a two-roll extrusion granulator to a particle size of 3-5 mm.

[0052] Step S5, Waste Heat Drying and Post-treatment: The medium-temperature flue gas from the spray tower, at approximately 80°C, is heated to 55°C via a flue gas-air heat exchanger. This hot air is then introduced into a belt-type low-temperature drying device to dry the wet particles for 30 minutes, ensuring the final moisture content of the particles is below 10%. After drying, the particles are cooled and sieved. Particles meeting the specified size are packaged to obtain the final product. Testing shows that the viable count of Bacillus subtilis in the product is ≥2.0 × 10⁻⁶. 8 CFU / g, total nutrients (N+P2O5+K2O) ≥9%, organic matter (as biochar) ≥25%.

[0053] Comparative Example: A traditional "step-by-step" method was used to prepare the same product: Wheat straw was first carbonized at 450℃ in a separate pyrolysis unit to obtain biochar, which was then cooled and ground. In another fermentation workshop, *Bacillus subtilis* was fermented on a conventional culture medium for 48 hours. The cooled biochar powder, the fermented bacterial solution (concentrated by centrifugation), fertilizer, binder, etc., were physically mixed in a double-helix mixer for 30 minutes, then granulated and dried with hot air provided by a coal-fired hot air furnace. Testing showed that the initial viable count of the product was approximately 5 × 10⁻⁶. 7 CFU / g.

[0054] Efficacy Verification: Survival Rate Comparison of Microbial Agents: The products obtained in Example 1 and the comparative example were stored at room temperature (25°C) under dry conditions for 6 months, and the viable bacterial count was tested monthly. The test results are plotted as follows. Figure 3As shown in the figure, the product co-prepared according to the present invention exhibits a slow decline in the survival rate of the microbial agent, with the viable bacterial count remaining at 1.5 × 10⁻⁶ after 6 months. 8 CFU / g or higher; while the microbial agents in traditional stepwise products degrade rapidly, with the viable bacterial count decreasing by an order of magnitude after 3 months and falling below 10 after 6 months. 6 CFU / g. This demonstrates that the method of the present invention significantly improves the storage stability of the microbial agent in the finished product.

[0055] Field fertilizer efficiency comparison: Figure 4 In the pot experiment shown (the soil was potassium-deficient), the fertilizer of this invention with equal potassium content, traditional step-by-step fertilizer, ordinary compound fertilizer (without bacteria), and a control without fertilizer were applied. The results showed that the fertilizer of this invention was significantly better than traditional step-by-step fertilizer and ordinary compound fertilizer in promoting soil potassium activation (increasing available potassium content) and crop potassium uptake, verifying its higher biological efficacy.

[0056] Example 2: Using corn stalks as raw material, a multifunctional compound fertilizer was prepared using a compound inoculant of nitrogen-fixing bacteria (such as *Azotobacter chrysogenum*) and biocontrol bacteria (such as *Bacillus subtilis*). In step S2, the pyrolysis temperature was controlled at 500℃. A small amount of yeast extract was added to the spray solution in step S2 to provide an organic nitrogen source. In step S3, the primary seed liquids of the two bacteria were mixed in a 1:1 ratio and inoculated, with a fermentation temperature of 30℃ and a fermentation time of 60 hours. Before the fermentation load, a molasses solution at 2% of its mass was sprayed onto the high-temperature biochar in the reactor. In step S4, the proportion of compound fertilizer was adjusted according to the needs of the target crop (such as vegetables). The remaining steps were the same as in Example 1. The resulting product has nitrogen-fixing, growth-promoting, and soil-borne disease-inhibiting functions.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for the synergistic preparation of a compound fertilizer consisting of straw-based biochar and functional microbial agents, characterized in that, Includes the following steps: Step S1, raw material pretreatment and strain activation: Crop straw is crushed and dried for pretreatment; at the same time, functional strains are activated and first-stage propagation is carried out to obtain first-stage seed liquid; Step S2, Co-pyrolysis-fermentation: The pretreated straw is fed into a moving bed pyrolysis carbonization reactor for medium-low temperature pyrolysis. The high-temperature flue gas generated by pyrolysis is guided into a biochar quenching-inoculant nutrient solution preparation tower with a built-in spray tower. In the spray tower of the preparation tower, an inorganic salt solution containing nitrogen, phosphorus, potassium and trace elements is used as the spray liquid to quench and wash the high-temperature flue gas, forming a basic nutrient solution for inoculant fermentation that is heated and enriched with water-soluble organic matter in the flue gas. The high-temperature solid biochar obtained by pyrolysis is directly transported to a fermentation-loading integrated reactor. Step S3, in-situ fermentation and biochar loading: The primary seed liquid obtained in step S1 is inoculated into the basic nutrient solution for microbial agent fermentation prepared in step S2. After mixing, it is pumped into the integrated fermentation-loading reactor and thoroughly mixed with the high-temperature biochar in the reactor. The residual heat of the high-temperature biochar is used to start and maintain the in-situ solid-state fermentation process, so that the functional microbial agent actively colonizes in the pores of the biochar during the fermentation process, thus achieving in-situ loading. Step S4, compounding and granulation: After the in-situ fermentation is completed, fertilizer and binder are added to the fermentation-load integrated reactor for in-situ homogenization and compounding. The granulator extrudes / disc granulates the compounded wet material in the reactor to form wet material and then granulates it. Step S5, Waste Heat Drying and Post-treatment: The wet granules obtained in step S4 are transported to a low-temperature drying device that utilizes the waste heat of the flue gas from the pyrolysis carbonization reactor for drying; the drying heat source comes from the medium-temperature flue gas that has been sprayed and rapidly cooled in step S2. The heat of this flue gas is converted into hot air through the heat exchanger of the low-temperature drying device to dry the wet granules at low temperature, thus obtaining the final compound fertilizer product.

2. The method for synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer according to claim 1, characterized in that, In step S1, the functional bacterial species are at least one of nitrogen-fixing bacteria, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, photosynthetic bacteria, and biocontrol bacteria.

3. The method for synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer according to claim 1, characterized in that, In step S2, the pyrolysis temperature of the moving bed pyrolysis carbonization reactor is 350-550℃, and the pyrolysis time is 20-60 minutes.

4. The method for synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer according to claim 1, characterized in that, In step S2, the inorganic salt spray solution containing nitrogen, phosphorus, potassium and trace elements is formulated according to the nutritional requirements of the target functional strain, and the final pH value after spraying and washing is controlled to be 6.0-7.

5.

5. The method for synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer according to claim 1, characterized in that, In step S3, the in-situ solid-state fermentation time is 24-72 hours, and the fermentation endpoint is judged by the residual sugar concentration in the fermentation broth being lower than 0.5% and / or the cell concentration tending to stabilize.

6. The method for synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer according to claim 1, characterized in that, In step S4, the added binder is one or more of bentonite, attapulgite, or soluble starch, and the amount added is 2%-5% of the total mass of the wet material.

7. The method for synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer according to claim 1, characterized in that, In step S5, the temperature for low-temperature drying is controlled at 45-60℃, and the drying time is 20-40 minutes.

8. The method for synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer according to any one of claims 1-7, characterized in that, The functional microbial agent is a compound microbial agent of one or more of the following: Bacillus subtilis, Bacillus thuringiensis, Azotobacter chrysogenum, Bacillus megaterium, and photosynthetic bacteria.

9. The method for synergistic preparation of straw-based biochar and functional microbial agent compound fertilizer according to claim 1, characterized in that, In step S3, before pumping the fermentation medium into the reactor and mixing it with the high-temperature biochar, a molasses or trehalose solution accounting for 1%-3% of the biochar mass is sprayed onto the surface of the high-temperature biochar in the integrated fermentation-loading reactor.

10. An integrated production system for implementing the synergistic preparation method of straw-based biochar and functional microbial agent compound fertilizer according to any one of claims 1-9, characterized in that, The system includes a straw pretreatment device, a moving bed pyrolysis carbonization reactor, a biochar quenching-inoculant nutrient solution preparation tower with a built-in spray tower, a fermentation-load integrated reactor, a granulator, and a low-temperature drying device utilizing waste heat from flue gas, all connected in sequence. The flue gas outlet of the moving bed pyrolysis carbonization reactor is connected to the flue gas inlet of the preparation tower, and its biochar outlet is connected to the feed inlet of the fermentation-load integrated reactor via a high-temperature resistant conveying device. The nutrient solution outlet of the preparation tower is connected to the liquid inlet of the fermentation-load integrated reactor. The flue gas outlet of the preparation tower is connected to the heat exchanger of the low-temperature drying device.

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