Method for preparing biochar material loaded with microbial composite flora and reducing methane emission of rice field by using biochar material

Abstract

The invention relates to the technical field of soil remediation and environmental protection, and discloses a method for preparing a biological carbon material loaded with a microbial composite flora and reducing methane emission of a rice field. A compound solution containing an iron element and a sulfur element and the microbial composite flora are fixed to the surface and the interior of the biochar through chemical precipitation and physical adsorption respectively, and the biochar material loaded with the microbial composite flora is obtained. And applying the biological carbon material loaded with the microbial composite flora into the rice field, and realizing the emission reduction of the methane in the rice field by utilizing the oxidative decomposition of oxidation states such as nitrate nitrogen, sulfate radicals and ferric iron on the methane according to the cyclic coupling principle of the carbon element and elements such as nitrogen, sulfur and iron. Compared with a conventional rice field water control or intermittent irrigation methane emission reduction technology, the technology is simpler and more convenient, and methane emission of the rice field in the waterflooding period can be remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the fields of soil remediation technology and environmental protection technology, and in particular to a method for preparing a biochar material loaded with a microbial composite flora and reducing methane emissions from paddy fields. Background Art

[0002] Methane is a potent greenhouse gas that contributes significantly to global warming. Globally, rice paddy methane emissions account for 30% of global agricultural methane emissions, which in turn account for 40% of total methane emissions from human activities. As the world's largest rice producer, my country, with its vast rice planting area and high yields, produces significant methane emissions from rice paddies. This issue has garnered significant international attention. Effectively reducing methane emissions from rice paddies is crucial for my country to fulfill its international emission reduction commitments and address climate change.

[0003] Currently, research on reducing methane emissions from rice paddies focuses on water management, organic matter management, and the breeding of high-yield, low-emission varieties. In terms of water management, optimizing measures such as delayed and intermittent irrigation can reduce methane emissions to levels not seen before returning green manure to the field. Replacing continuous flooding with intermittent flooding not only reduces methane emissions but also increases rice yields. Regarding organic matter management, returning straw to the fields during the dry season in a water-upland rotation can reduce methane emissions from rice paddies. Furthermore, genetic engineering breeding techniques are providing new avenues for breeding high-yield, low-carbon rice varieties.

[0004] However, the above-mentioned rice field methane emission reduction strategies have obvious limitations. From an operational perspective, whether it is the precise control of irrigation time and water volume in water management, or the grasp of the water-land rotation cycle and the timing of straw return in organic matter management, both require high planting technology, which is difficult for ordinary farmers to master and operate. At the same time, during the implementation of water management and organic matter management strategies, they may face the pressure of declining rice yields due to changes in the original environmental conditions for rice growth, making it difficult for farmers to balance the pursuit of economic benefits and the implementation of emission reduction measures. Therefore, there is an urgent need to develop new strategies for reducing rice field methane emissions that are simple, easy to operate, and have little impact on yield. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a biochar material loaded with a microbial composite flora and reducing methane emissions from rice fields, so as to solve the technical problem that existing rice field methane emission reduction schemes are difficult to apply to ordinary farmers due to their high technical requirements and are therefore not easy to promote.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a method for preparing a biochar material loaded with a microbial composite flora, wherein a compound solution containing iron and sulfur elements and the microbial composite flora are fixed to the surface and interior of the biochar by chemical precipitation and physical adsorption, respectively, to obtain a biochar material loaded with a microbial composite flora; the microbial composite flora includes autotrophic iron-oxidizing bacteria, dissimilatory iron-reducing bacteria, sulfate-reducing bacteria, and nitrifying bacteria.

[0007] The principles and advantages of this solution are: 1. Compared to existing rice field methane emission reduction schemes, which are difficult for ordinary farmers to apply due to their high technical requirements, this scheme prepares biochar material loaded with a microbial complex by loading it with iron and sulfur elements onto biochar. Farmers purchase this biochar material and mix it with the rice fields. Based on the principle of cyclic coupling between carbon and other elements such as nitrogen, sulfur, and iron, this scheme utilizes anaerobic oxidation of methane using non-oxygen electron acceptors such as nitrate nitrogen, sulfate, and trivalent iron, thereby achieving methane emission reduction in rice fields. Compared with conventional rice field water control or intermittent irrigation methane emission reduction technologies, this method is simpler, does not require complex and precise technical requirements, is low-cost, and is applicable to all types of rice field operations, making it easy to promote and apply.

[0008] 2. This solution, by loading iron, sulfur, and various microorganisms onto biochar, allows multiple substances to synergistically complement the functions of microorganisms, thereby enhancing the rice field methane emission reduction effect from multiple dimensions. The details are as follows: (1) Multiple mechanisms synergistically inhibit methane production: The biochar in this scheme, with its rich pore structure and huge specific surface area, absorbs dissolved organic carbon, reducing the carbon source of methanogens from the source. The loaded autotrophic iron-oxidizing bacteria, dissimilatory iron-reducing bacteria, sulfate-reducing bacteria, and nitrifying bacteria further destroy the anaerobic environment required for the survival of methanogens, reduce substrate supply, and change the soil redox potential by consuming oxygen, competing for electron donors, consuming organic matter, and oxidizing ammonia nitrogen. For example, the oxygen consumption of autotrophic iron-oxidizing bacteria and the improvement of aeration by biochar significantly increase the oxygen content in the soil, greatly compressing the living space of methanogens; the consumption of organic matter by sulfate-reducing bacteria and the adsorption of organic carbon by biochar form a double blow, more thoroughly cutting off the supply of raw materials for methane production.

[0009] (2) Strengthening soil environmental regulation: Biochar improves soil aeration and redox environment, providing more favorable conditions for iron- and sulfur-related compounds and microorganisms to function. The loaded iron-related compounds participate in redox reactions and, together with biochar, regulate the soil carbon metabolism pathway; sulfur-related compounds change the soil redox environment and, together with biochar, create an environment that is unfavorable for the survival of methanogens. At the same time, substances produced by microbial metabolism can also interact with biochar, further optimizing soil structure and fertility. For example, sulfide produced by sulfate-reducing bacteria combines with biochar, enhancing the ability to fix heavy metal ions, stabilizing the soil microbial community, and indirectly inhibiting methane production.

[0010] (3) Prolonging the duration and stability of the effect: The interaction between biochar and iron, sulfur and microorganisms forms a relatively stable system, which enhances the overall adaptability to the complex environmental changes in rice fields and ensures the stability and durability of the methane emission reduction effect.

[0011] (4) A win-win situation for promoting rice growth and reducing emissions and increasing yields: Biochar improves soil aeration, which is beneficial to rice root growth, and the nitrifying bacteria carried by it improve the nitrogen utilization rate of rice. Together, they promote rice growth and development. At the same time, other microorganisms and iron and sulfur-related compounds synergistically reduce methane emissions, achieving the dual goals of reducing emissions and increasing yields. This combination not only reduces the impact of methane emissions from rice fields on the environment, but also increases rice yields, increases farmers' income, and enhances the feasibility and promotion value of technology application.

[0012] Preferably, as an improvement, the method comprises the following steps: Step (1): preparing biochar: pyrolyzing hard biomass materials at high temperature to produce biochar, crushing them, washing them with hydrochloric acid to remove ash, washing them with water to neutrality, and then vacuum drying them to obtain biochar; Step (2): forming an iron sulfide precipitate on the biochar: reacting the biochar with a sodium sulfide solution and a ferric chloride solution in sequence, forming an iron sulfide precipitate on the biochar by a chemical precipitation method, and drying the precipitate at a low temperature in a vacuum to obtain a biochar loaded with the iron sulfide precipitate; Step (3): Adsorbing a microbial complex on biochar: Cultivating the microbial complex into a bacterial suspension, immersing the biochar loaded with iron sulfide precipitate into the bacterial suspension, shaking or stirring for adsorption, filtering and separating, and low-temperature drying to obtain a biochar material loaded with the microbial complex.

[0013] Technical Effect: This solution employs the aforementioned setup, loading biochar with iron sulfide precipitate and a compatible microbial community in separate steps. This allows for precise control of iron sulfide formation, prevents microbial activity from being affected by chemical reactions, enhances material structural stability, and optimizes the synergistic effects between microorganisms, iron sulfide, and biochar, thereby more effectively reducing methane emissions from rice paddies. The applicants discovered through experiments that, when biomass homogenate, sulfur, iron, and microbial communities are mixed and fermented to form micro-nano bio-iron sulfide, precise control of the iron sulfide formation process is difficult and can easily lead to iron sulfide aggregation or uneven distribution, impacting its subsequent function. Furthermore, during the mixed culture process, the chemical reaction between the iron and sulfur compounds can generate heat or alter the solution's pH, negatively impacting microbial activity. If, on the other hand, the composite microbial community is loaded first and then the sulfur- and iron-containing compounds are mixed to load the iron sulfide precipitate, the chemical precipitation process can alter reaction conditions such as solution concentration, pH, and temperature, potentially toxic or inhibitory to the loaded microbial community. Moreover, the microbial load comes first and the iron sulfide precipitates later, making it difficult for the two to form an ideal microenvironment and electron transfer system, resulting in poor functional synergy between microorganisms, iron sulfide and biochar, and unable to efficiently participate in soil redox reactions, thereby reducing the overall effect of methane emission reduction.

[0014] Preferably, as an improvement, in step (1), the high-temperature pyrolysis is pyrolysis at 350-370°C for 1-4 hours; after pulverization, the biochar particle size is 0.5-2 mm.

[0015] Technical Effect: This solution utilizes the above-mentioned configuration to achieve biochar with a large specific surface area and a rich pore structure while maintaining good dispersibility. On the one hand, the moderate pore size of biochar within this particle size range provides differentiated microenvironments for different bacterial communities (for example, iron-oxidizing bacteria colonize oxygen-rich surface pores, while sulfate-reducing bacteria are distributed in anaerobic internal pores). This reduces inter-bacterial conflicts and ensures smooth exchange of microorganisms with external substances, reducing the carbon source for methanogens. Furthermore, biochar particles of this size can effectively improve soil aeration and water retention. Larger particles form aeration channels in the soil, increasing soil oxygen content and disrupting the anaerobic environment that methanogens thrive in. Furthermore, their pore structure provides a certain degree of water retention, creating favorable moisture conditions for rice growth, promoting increased rice yields, and achieving a balance between emission reduction and yield increase. Specifically, this solution utilizes medium- and low-temperature pyrolysis to gradually decompose the lignin and cellulose in the biomass, forming abundant mesopores and a small number of micropores. This pore structure provides a large specific surface area, and low- to medium-temperature pyrolysis can retain some oxygen-containing functional groups (such as carboxyl and hydroxyl groups). These functional groups can bind to iron sulfide through electrostatic interactions or coordination bonds, enhancing chemical adsorption capacity and facilitating microbial attachment and physical adsorption of iron sulfide precipitation. The applicants have experimentally found that if the pyrolysis temperature is too high, the high temperature causes micropores to merge into larger pores or close, reducing the specific surface area and weakening physical adsorption capacity. Furthermore, the oxygen-containing functional groups decompose at high temperatures, reducing chemical adsorption sites and, in turn, lowering the loading efficiency of iron sulfide precipitation. If the pyrolysis temperature is too low, the large amount of volatile organic compounds remaining in the biomass will clog the pores, reducing its adsorption capacity. The residual organic matter may be used as a carbon source by methanogens, directly stimulating methane production. Furthermore, if the pyrolysis temperature is too low, the biochar will not form a stable carbon skeleton, which is easily broken down in the soil, resulting in uncontrolled release of the loaded iron sulfide precipitation. If the biochar particle size is too large after pulverization, the effective adsorption sites per unit mass of biochar will be reduced, resulting in a smaller area for microbial colonization. This will also make it difficult for iron sulfide precursors (such as Fe²⁺ and S²⁻) to penetrate the particles, reducing loading efficiency and preventing effective inhibition of methanogenesis through the Fenton reaction. If the biochar particle size is too small after pulverization, ultrafine particles will easily agglomerate due to van der Waals forces, reducing the actual specific surface area utilization rate. Furthermore, fine particles fill soil pores, inhibiting oxygen diffusion and potentially promoting the activity of anaerobic methanogens.

[0016] Preferably, as an improvement, in step (2), the concentration of the sodium sulfide solution is 0.02-0.5 mol / L, and the concentration of the ferric chloride solution is 0.02-0.5 mol / L; the solid-liquid ratio of the biochar mixed with the sodium sulfide solution and the ferric chloride solution is 1:5-10, and the mixing precipitation time is 0-0.5 h.

[0017] Technical effect: This scheme adopts the above-mentioned setting to facilitate the full loading of iron sulfide precipitation in the pores of biochar. Specifically, the concentration range of sodium sulfide and ferric chloride solution in this scheme can ensure that the molar ratio of Fe³⁺ to S²⁻ is close to 1:1~3:1, thereby ensuring the formation of FeS or FeS2 and avoiding excess ion residue. The solid-liquid ratio of 1:5~10 can ensure that the solution fully infiltrates the pores of biochar, promoting the diffusion and reaction of Fe³⁺ and S²⁻ on the surface and inside of the carbon. The applicant found through experiments that if the concentration of sodium sulfide and ferric chloride solution is too low, the amount of iron sulfide generated will be less than 1%, and a continuous covering layer cannot be formed, resulting in insufficient utilization of the active sites on the biochar surface. Instead, the pores of the biochar itself may adsorb organic carbon, indirectly providing substrates for methanogens and increasing methane release. However, if the concentrations of the sodium sulfide and ferric chloride solutions are too high, Fe⁺ and S⁻ react to rapidly form large iron sulfide particles, which clog the biochar mesopores. This leads to uneven iron sulfide loading and insufficient localized Fe⁺ release, preventing methanogen inhibition through the Fe⁺ / Fe⁺ cycle. Excessive S⁻ may also increase the soil's Eh (redox potential), ultimately promoting methane oxidation in the long term. If the solid-to-liquid ratio is too high (excess solution), the dilution effect reduces the probability of Fe⁺ and S⁻ collisions, decreasing the precipitation rate. Unreacted S⁻ is converted to H₂S in the soil, poisoning plant roots. If the solid-to-liquid ratio is too low (insufficient solution), the biochar's internal pores remain uninfiltrated, leaving only the surface loaded with iron sulfide, causing particles to easily fall off and poor long-term sustained release. Furthermore, insufficient or unevenly distributed iron sulfide loading leads to fluctuating Fe⁺ release rates, making it impossible to stably inhibit methanogen activity.

[0018] Preferably, as an improvement, in step (3), the OD600 of the bacterial suspension is 0.6-1.

[0019] Technical Effect: This scheme utilizes the above-mentioned setup to ensure uniform microbial activity and abundance while ensuring uniform microbial attachment to the biochar. This prevents waste of biochar adsorption sites due to low concentrations, while also preventing microbial aggregation or inadequate adsorption due to high concentrations. This ensures uniform microbial distribution on the biochar surface, promoting full contact between the microorganisms and the surrounding environment, and improving the material's performance in reducing methane emissions in rice fields. The applicants have discovered through experiments that if the bacterial suspension concentration is too high, the bacterial interactions become unbalanced, and excessive iron-oxidizing bacteria rapidly consume Fe₂⁺. This, on the one hand, causes Fe₃⁺ accumulation (>5 mM), inhibiting the activity of iron-reducing bacteria (high Fe₃⁺ concentrations induce cellular oxidative stress). On the other hand, nitrifying bacteria compete with iron-reducing bacteria for electron acceptors, disrupting the Fe-S₂ coupling pathway and reducing methane emission efficiency. Furthermore, Fe₃⁺ hydrolyzes to form Fe(OH)₃ colloids, which clog the biochar pores. Furthermore, excessive sulfate-reducing bacteria lead to excessively high S₂⁻ concentrations, inhibiting the ammonia monooxygenase activity of nitrifying bacteria and poisoning iron-oxidizing bacteria. However, if the concentration of the bacterial suspension is too low, the composite bacterial community cannot form a functional network (such as Fe-SN coupling) at low concentration. When it only relies on a single bacterial community (such as sulfate-reducing bacteria), the methane emission reduction effect is significantly reduced and it is easily affected by environmental fluctuations, further reducing the methane emission reduction effect.

[0020] Preferably, as an improvement, in step (3), the solid-liquid ratio of biochar to bacterial suspension is 1:5-10, and after shaking or stirring for 12-24 hours, the suspension is filtered and separated, and the obtained biochar material loaded with the microbial composite flora is stored at 30-37°C.

[0021] Technical Effect: This solution utilizes the aforementioned setup to ensure full contact between the biochar and the bacterial suspension, allowing the microorganisms to evenly distribute and penetrate deep into the biochar pores, ensuring effective microbial attachment to the biochar surface and within its pores. Furthermore, limiting the material's storage temperature effectively maintains the activity and metabolic capacity of the microorganisms, ensuring that the material, when applied to rice fields, can quickly exert its methane-inhibiting effects.

[0022] Preferably, as an improvement, the present invention further provides a biochar material loaded with a microbial complex, which is prepared by the above method.

[0023] Preferably, as an improvement, the present invention also provides a method for reducing methane emissions from rice fields by using a biochar material loaded with a microbial complex, wherein the biochar material is cultured with rice field mud by air bubbling for 7 to 15 days and then applied to the rice field.

[0024] Technical Effect: This solution utilizes the aforementioned configuration to fully activate microorganisms and encourage them to fully penetrate the pores of biochar and firmly adhere, forming a more stable structure. This prevents the microorganisms from detaching from the biochar once they enter the complex environment of the rice paddy, ensuring their continued function and stable suppression of methane production. During co-cultivation with paddy mud, the microorganisms interact with substances in the mud, adjusting their metabolic pathways. This not only allows the microorganisms to more quickly integrate into the paddy ecosystem after application, reducing the risk of decreased activity or death due to environmental changes, but also better inhibits the methane production mechanisms in the paddy field, improving the targeted and effective methane reduction. The applicants have discovered through experiments that if biochar is applied directly to rice paddies, the microorganisms require a longer time to adapt to the environment and find suitable habitats and nutrient sources. During this period, methanogens may already be actively producing methane. However, the microbial complex, not yet fully adapted to the environment, is unable to effectively and promptly suppress these activities. This results in a lack of significant methane reduction in the initial application period, impacting the overall efficiency and effectiveness of the reduction.

[0025] Preferably, as an improvement, the paddy field mud is mud 0 to 5 cm away from the rice root system, and the mass volume ratio of the biochar material to the paddy field mud is 1:5 to 1:20.

[0026] Technical Effect: The mud area 0-5 cm from the rice roots, due to its favorable hypoxic conditions and enriched root secretions, becomes the primary habitat for methanogens and the core area of methane emissions from rice paddies. This setup allows the biochar-loaded microbial complex to precisely "target" and inhibit methanogens. Specifically, autotrophic iron-oxidizing and sulfate-reducing bacteria alter the mud's redox environment by consuming dissolved oxygen and competing for electron donors, disrupting the anaerobic environment previously suitable for methanogens. This significantly reduces the activity and abundance of methanogens in the mud, thereby reducing methane emissions. The optimal mass-to-volume ratio of biochar to paddy mud in this solution ensures thorough mixing of the biochar with the rice root mud, forming an effective "methane reduction barrier" around the roots, effectively blocking the active methane production chain of methanogens and reducing methane production and emissions. The applicants discovered through experiments that when biochar is grown in blank rice paddy mud, the microbial complex cannot accurately locate the key areas and key bacterial communities responsible for methane emissions. When applied to rice paddies, the complex struggles to quickly suppress the highly active methanogens around the roots, causing them to continue to multiply and produce methane, effectively preventing methane emissions from the paddy fields.

[0027] Preferably, as an improvement, the bubbling air culture method is to add 0.5-1.0 g / L of glucose and sodium acetate respectively to the mixture of biochar material and rice field mud, and culture the mixture by bubbling air for 7-15 days; during the bubbling air culture process, the dissolved oxygen concentration of the cultivation system is greater than 2 mg / L.

[0028] Technical effect: This solution adopts the above-mentioned setting, which is convenient for providing nutrition for microorganisms and bacterial communities, promoting their rapid growth and reproduction and shortening the culture cycle. Cultivating for 7 to 15 days can give the microorganisms enough time to adapt to the culture environment and complete growth, reproduction and stable combination with biochar. During this period, the microorganisms can make full use of the added carbon source and nutrients in the rice field mud to maintain a high activity state. The applicant found through experiments that if the culture time is too short, the growth of the number of microorganisms is limited and has not yet reached the optimal activity state, resulting in a weak inhibitory effect on methanogens. For example, nitrifying bacteria may not have yet reproduced in large numbers and established stable nitrification, and cannot effectively consume ammonia nitrogen, so that the nitrogen source available to methanogens is not fully reduced, making it difficult to effectively inhibit methane production.

[0029] Preferably, as an improvement, during the bubbling air culture process, the dissolved oxygen concentration in the culture system is greater than 2 mg / L.

[0030] Technical Effect: This solution adopts the above-mentioned configuration to ensure the aerobic respiration needs of aerobic microorganisms (such as nitrifying bacteria and autotrophic iron-oxidizing bacteria). These microorganisms change the redox potential of the mud by consuming oxygen, inhibiting the anaerobic environment required for the survival of methanogens and effectively blocking methane production. The applicant found through experiments that if the dissolved oxygen concentration is too low, the aerobic respiration of aerobic microorganisms is severely inhibited, and metabolic activity slows down or even stagnates. Autotrophic iron-oxidizing bacteria cannot carry out iron oxidation reactions normally and cannot effectively increase the redox potential of the mud, allowing the anaerobic environment in which the methanogens are located to be maintained, multiplying in large numbers and continuously producing methane. At the same time, insufficient dissolved oxygen will also affect the efficiency of microorganisms in utilizing carbon sources, resulting in slow growth and a decrease in the number of microorganisms, further weakening the ability to inhibit methanogens and reducing the methane emission reduction effect of biochar materials. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following examples and experimental examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used are all commercially available.

[0032] Example 1 This method provides a method for preparing biochar material loaded with a microbial complex. A compound solution containing iron and sulfur elements and the microbial complex are fixed to the surface and interior of the biochar through chemical precipitation and physical adsorption, respectively. The method specifically includes the following steps: Step (1): Preparation of biochar: Coconut shell, almond and other hard biomass materials are used as raw materials and pyrolyzed at 350-370°C for 1-4h to prepare biochar. After pyrolysis, the biochar is crushed to a particle size of 0.5-2 mm, pickled with 0.1 mol / L hydrochloric acid to remove ash, washed with water to neutrality, and dried under vacuum conditions for later use.

[0033] Step (2): forming an iron sulfide precipitate on the biochar: reacting the biochar with a 0.02-0.5 mol / L sodium sulfide solution and a 0.02-0.5 mol / L ferric chloride solution in a solid-liquid ratio of 1:5-10, with the mixing precipitation time being 0-0.5 h, forming an iron sulfide precipitate on the biochar by a chemical precipitation method, and vacuum drying at low temperature for later use.

[0034] Step (3): Adsorbing a microbial complex on biochar: Select target bacteria including chemoautotrophic iron-oxidizing bacteria, dissimilatory iron-reducing bacteria, sulfate-reducing bacteria, and nitrifying bacteria (wherein, autotrophic iron-oxidizing bacteria, dissimilatory iron-reducing bacteria, sulfate-reducing bacteria, and nitrifying bacteria are mixed in equal proportions), and culture them in a suitable culture medium until the logarithmic growth phase OD600 is 0.6-1.0; immerse the biochar in the above-mentioned cultured bacterial suspension (bacterial suspension concentration is about 1×10^8 CFU / mL), with the solid-liquid ratio of biochar to bacterial suspension being 1:5-10, and shake or stir for 12-24 hours; filter and separate, separate the biochar adsorbed from the bacterial suspension, dry it at low temperature, and store it at 30-37°C.

[0035] Examples 2-3 and Comparative Examples 1-12 are basically the same as Example 1, with the differences shown in Table 1.

[0036] Table 1 Differences between Examples 1 to 3 and Comparative Examples 1 to 12

[0037] This proposal also provides a method for reducing methane emissions from rice paddies using a biochar material loaded with a microbial complex. The biochar material loaded with iron sulfide precipitate and a microbial complex is incubated with paddy mud using a bubble air method for 7-15 days before being applied to the paddy field. The paddy mud is defined as the mud 0-5 cm from the rice roots, and the mass-to-volume ratio of the biochar material to the paddy mud is 1:5-1:20. The bubble air method involves adding 0.5 g / L each of glucose and sodium acetate to the biochar material and incubating for 7-15 days using a bubble air method. During the bubble air method, the dissolved oxygen concentration in the culture system is maintained at greater than 2 mg / L.

[0038] In rice cultivation boxes (each example was repeated three times, starting 25 days after cultivation), gas was collected using an acrylic static chamber to measure greenhouse gas emission fluxes. Gas sampling began on the first day after application to the rice fields, and continued at intervals until the rice harvest. Gas sampling was performed using a static chamber method, and methane emissions under different treatments were measured using gas chromatography. The results are shown in Table 2: Table 2 Methane emissions from paddy soil after different treatments (mg / m 2 / h)

[0039] Experimental data shows that biochar loaded with microorganisms can significantly reduce methane emissions from rice paddies, especially in early-stage paddy fields. The applicants discovered through experiments that factors such as biochar pyrolysis temperature, biochar particle size, the solid-to-liquid ratio during adsorption of iron sulfide and microorganisms, the concentrations of sodium sulfide and ferric chloride solutions, the OD value of the microbial culture, and the adsorption oscillation time of the microbial culture all significantly affect the activity of methanogens in the soil and, consequently, the effectiveness of methane reduction.

[0040] Specifically, if the pyrolysis temperature is too low (as in Comparative Example 1), on the one hand, it is likely to leave residual organic matter, affecting its adsorption capacity. On the other hand, the low pyrolysis temperature destabilizes the biochar skeleton, preventing the effective release of adsorbed iron sulfide, both of which will reduce the methane emission reduction effect. If the pyrolysis temperature is too high (as in Comparative Example 2), the biochar's specific surface area and active adsorption sites are reduced, thereby reducing the iron sulfide loading efficiency and the methane emission reduction effect. In the high-temperature pyrolysis of hard biomass materials into biochar, the slow pyrolysis process generally requires a longer pyrolysis time due to the continuous flow of heating and cooling materials in and out of the cooling process. Compared with temperature, pyrolysis time actually has a smaller impact on the quality of pyrolyzed biochar.

[0041] If the particle size is too small (as in Comparative Example 3), the ultrafine particles are prone to agglomeration due to van der Waals forces, reducing the actual specific surface area utilization. Furthermore, the fine particles fill soil pores, inhibiting oxygen diffusion and potentially promoting the activity of anaerobic methanogens. If the particle size is too large (as in Comparative Example 4), the effective adsorption sites per unit mass of biochar are reduced, resulting in a smaller area for microbial colonization. Furthermore, it is difficult for iron sulfide precursors (such as Fe²⁺ and S²⁻) to penetrate the particles, reducing loading efficiency and making it impossible to effectively inhibit methanogenesis through the Fenton reaction, thereby reducing methane emissions reduction effectiveness.

[0042] During the iron sulfide precipitation stage on the biochar, if the sodium sulfide and ferric chloride solution concentrations are too low (as in Comparative Example 5), the resulting iron sulfide production is too low, resulting in insufficient loading and reduced methane emission reduction effectiveness. If the sodium sulfide and ferric chloride solution concentrations are too high (as in Comparative Example 6), the high concentrations of Fe³⁺ and S²⁻ rapidly generate large iron sulfide particles, which clog the biochar mesopores. This leads to uneven iron sulfide loading and insufficient localized Fe²⁺ release, preventing the Fe²⁺ / Fe³⁺ cycle from inhibiting methanogens. The precipitation of iron-sulfur compounds on the biochar surface is a chemical precipitation reaction, which typically completes quickly, and the precipitation time has little impact on the results.

[0043] During the adsorption of a complex microbial community on biochar, if the bacterial concentration is too low (as in Comparative Example 7), the complex community cannot form a functional network at low concentrations. Relying solely on a single bacterial community significantly reduces the methane emission reduction effect. If the bacterial concentration is too high (as in Comparative Example 8), the methane emission reduction efficiency will be reduced due to an imbalance in the interaction between the bacterial communities. If the oscillation time is too short (as in Comparative Example 9), a small number of microorganisms will enter the pores of the biochar, while the majority of the microorganisms will be retained on the surface and easily washed off by water, reducing its load stability and, in turn, the methane emission reduction effect. If the oscillation time is too long (as in Comparative Example 10), the continuous high shear force will cause mechanical damage to the microorganisms and reduce their activity.

[0044] However, if a composite microbial consortium is first loaded and then mixed with sulfur-containing compounds and iron-containing compounds to precipitate iron sulfide (as in Comparative Example 11), the chemical precipitation process for iron sulfide formation may result in changes in reaction conditions such as solution concentration, pH, and temperature, which can toxic or inhibit the loaded microbial consortium. If micro-nano bio-iron sulfide is formed by mixing a biomass homogenate, sulfur, iron, and microbial consortium for fermentation (as in Comparative Example 12), it is not only difficult to precisely control the iron sulfide formation process, but it can also easily lead to agglomeration or uneven distribution of the iron sulfide, affecting its subsequent function and methane emission reduction effectiveness.

[0045] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A method for preparing a biochar material loaded with a microbial composite flora, characterized by: A compound solution containing iron and sulfur elements and a microbial complex are fixed to the surface and interior of biochar through chemical precipitation and physical adsorption, respectively, to obtain a biochar material loaded with a microbial complex; the microbial complex includes autotrophic iron-oxidizing bacteria, dissimilatory iron-reducing bacteria, sulfate-reducing bacteria, and nitrifying bacteria.

2. The method for preparing a biochar material loaded with a microbial composite flora according to claim 1, characterized in that: The steps include: Step (1): preparing biochar: pyrolyzing hard biomass materials at high temperature to produce biochar, crushing them, washing them with hydrochloric acid to remove ash, washing them with water to neutrality, and then vacuum drying them to obtain biochar; Step (2): forming an iron sulfide precipitate on the biochar: reacting the biochar with a sodium sulfide solution and a ferric chloride solution in sequence, forming an iron sulfide precipitate on the biochar by a chemical precipitation method, and drying the precipitate at a low temperature in a vacuum to obtain a biochar loaded with the iron sulfide precipitate; Step (3): Adsorbing a microbial complex on biochar: Cultivating the microbial complex into a bacterial suspension, immersing the biochar loaded with iron sulfide precipitate into the bacterial suspension, shaking or stirring for adsorption, filtering and separating, and low-temperature drying to obtain a biochar material loaded with the microbial complex.

3. The method for preparing a biochar material loaded with a microbial composite flora according to claim 2, characterized in that: In step (1), the high-temperature pyrolysis is carried out at 350-370°C for 1-4 hours; after crushing, the biochar particle size is 0.5-2 mm.

4. The method for preparing a biochar material loaded with a microbial composite flora according to claim 3, characterized in that: In step (2), the concentration of the sodium sulfide solution is 0.02-0.5 mol / L, and the concentration of the ferric chloride solution is 0.02-0.5 mol / L; the solid-liquid ratio of the biochar mixed with the sodium sulfide solution and the ferric chloride solution is 1:5-10, and the mixing precipitation time is 0-0.5 h.

5. The method for preparing a biochar material loaded with a microbial composite flora according to claim 4, characterized in that: In step (3), the OD600 of the bacterial suspension is 0.6-1.

6. The method for preparing a biochar material loaded with a microbial composite flora according to claim 5, characterized in that: In step (3), the solid-liquid ratio of biochar to bacterial suspension is 1:5-10, and after shaking or stirring for 12-24 hours, the mixture is filtered and separated, and the obtained biochar material loaded with the microbial composite flora is stored at 30-37°C.

7. A biochar material loaded with a microbial complex, characterized by: Prepared by the method according to any one of claims 1 to 6.

8. A method for reducing methane emissions from rice fields using biochar materials loaded with a complex microbial community, characterized by: The biochar material loaded with the microbial composite flora prepared by the method according to any one of claims 1 to 6 is cultured with paddy mud by air bubbling for 7 to 15 days and then applied to the paddy field.

9. The method for reducing methane emissions from rice fields using a biochar material loaded with a microbial composite flora according to claim 8, characterized in that: The paddy field mud is the mud 0-5 cm away from the rice root system, and the mass volume ratio of the biochar material to the paddy field mud is 1:5-1:

20.

10. The method for reducing methane emissions from rice fields using a biochar material loaded with a composite microbial community according to claim 9, characterized in that: The bubbling air culture method comprises adding 0.5 to 1.0 g / L of glucose and sodium acetate respectively to a mixture of biochar material and paddy mud, and culturing the mixture by the bubbling air method for 7 to 15 days; during the bubbling air culture method, the dissolved oxygen concentration of the cultivation system is greater than 2 mg / L.

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