EM bacteria modified corn stalk biochar for ammonia nitrogen pollution remediation and preparation method and application thereof

Abstract

This invention discloses an EM-modified corn straw biochar for ammonia nitrogen pollution remediation, its preparation method, and its application, belonging to the fields of environmental functional materials and water pollution control technology. The modified biochar is prepared by co-culturing and modifying corn straw biochar with an EM bacterial solution containing Bacillus thuringiensis EM-A1; the EM bacteria carry the hydroxylamine oxidoreductase gene. hao and nitric oxide reductase gene norB The modified biochar exhibits a mesoporous surface area increase of over 100% and an average pore size increase of over 8%. The preparation method includes the preparation of raw biochar, activation by EM bacteria, co-cultivation modification, and post-treatment. This invention achieves synergistic operation of an "adsorption-degradation" combined system by actively reshaping the pore structure of biochar through EM bacteria. It possesses both rapid adsorption and continuous degradation capabilities, operates stably and efficiently under wide temperature, wide pH, and high ammonia nitrogen concentrations, and the preparation process is green, mild, and low-cost, making it suitable for the treatment of ammonia nitrogen in decentralized water bodies such as aquaculture wastewater and agricultural runoff.

Description

Technical Field

[0001] This invention relates to the fields of environmental functional materials and water pollution control technology, specifically to an EM bacteria-modified corn straw biochar for ammonia nitrogen pollution remediation, its preparation method, and its application. Background Technology

[0002] Ammonia nitrogen pollution in aquatic bodies mainly originates from excessive application of nitrogen fertilizers in agriculture and discharge of aquaculture wastewater, which are significant contributing factors to eutrophication and ecological damage. Meanwhile, my country generates a large amount of agricultural waste such as corn stalks annually, making the "waste-to-waste" green governance approach a hot research topic in the environmental field. Currently, ammonia nitrogen removal methods in water bodies mainly include physical methods (such as stripping and adsorption), chemical methods (such as breakpoint chlorination), and biological methods (such as nitrification-denitrification). However, physical methods are energy-intensive and adsorbent materials are easily saturated; chemical methods are prone to secondary pollution; and traditional biological methods have poor adaptability to conditions such as low temperature and low carbon-to-nitrogen ratios, making them difficult to apply to decentralized agricultural runoff and aquaculture wastewater.

[0003] Biochar, due to its large specific surface area, well-developed pore structure, and environmental friendliness, is widely used for the adsorption and removal of ammonia nitrogen in water. To further improve adsorption performance, researchers have used chemical methods to modify biochar, with chemically modified biochar technology being the most representative. For example, Nankai University disclosed a method for oxidizing corn stalk biochar with hydrogen peroxide (CN201610021147.8), which increases the adsorption strength of biochar for ammonia nitrogen through oxidation modification; Cong et al. obtained a maximum adsorption capacity of 68.15 mg / g by modifying biogas residue with KMnO4 and 41.00 mg / g by modifying it with NaOH; Kunming University of Science and Technology disclosed a method for physically modifying biochar (CN201610830642.3), which effectively improves the adsorption capacity of biochar for ammonia nitrogen in water by physically modifying biochar through cyclic freezing and thawing. However, the aforementioned chemical and physical modification technologies have the following drawbacks: First, they only have a single physical adsorption function and lack sustainable degradation capabilities. Once the adsorption sites become saturated, the material loses its processing capacity and needs to be regenerated or replaced, making it difficult to cope with continuous pollution loads. Second, they rely on hazardous chemicals or complex processes, posing risks of secondary environmental pollution or high energy consumption. Third, the modification process consumes a large amount of biomass raw materials, limiting the economic viability of large-scale applications.

[0004] In recent years, immobilizing functional microorganisms on the surface of biochar to construct an "adsorption-biodegradation" composite system has become a new direction, with the most representative being the immobilized microorganism-biochar composite system technology. For example, Hunan University disclosed a biochar-immobilized EM bacteria composite material and its preparation method (CN202310408982.7). Biomass materials are immersed in a mixed solution of phosphoric acid and zinc chloride for chemical pretreatment, followed by calcination to obtain biochar. This biochar is then mixed and cultured with an EM bacteria suspension to obtain the biochar-immobilized EM bacteria composite material, which is used for in-situ remediation of eutrophic polluted sediment. Ocean University of China has disclosed a method for immobilizing salt- and cold-tolerant composite bacterial strains (CN201510086209). This method uses biochar balls as a carrier to immobilize anaerobic ammonia-oxidizing bacteria, denitrifying bacteria, and petroleum-degrading bacteria that have undergone salt and cold tolerance acclimatization. This method is applied to the purification of ammonia nitrogen and petroleum hydrocarbon-polluted water bodies under low-temperature and high-salt conditions. In addition, the team also disclosed a method for immobilizing cold-tolerant ammonia-oxidizing bacteria with biochar balls (CN201810359264.4), which was applied in the Liaohe River wetland and achieved an ammonia nitrogen degradation efficiency of up to 96% in water bodies at 15℃. However, this technology still has the following drawbacks: First, most existing biochar preparation processes require chemical pretreatment or complex nano-modification, with stringent modification conditions. Furthermore, the immobilized strains used are often of a single genus or a few species, resulting in a limited population structure and environmental adaptability. This makes it difficult to maintain high degradation activity when water quality fluctuates significantly in actual water bodies. Second, the immobilization strength of the bacteria on the biochar surface is insufficient. The simple co-cultivation method with microorganisms has weak binding force, making it prone to cell detachment and loss under dynamic water flow conditions, leading to decreased treatment efficiency and poor long-term operational stability. Third, existing research generally uses biochar only as an inert carrier, failing to recognize the structural modification function of microorganisms on the carrier material itself. Moreover, there is a lack of systematic utilization of the molecular genetic basis of EM bacteria, making it difficult to guide further improvement of synergistic performance from a mechanistic perspective.

[0005] In addition, the technology of directly applying EM bacteria to remove ammonia nitrogen from water bodies has been extensively studied. El-Nakieb et al. reported that EM bacteria achieved an ammonia nitrogen removal rate of over 96% in textile industrial wastewater; Chen et al. screened a highly efficient denitrifying EM strain, EM-H8, with an ammonia nitrogen removal rate of 5.94 mg / L / h; Ding Chenyu et al. isolated Bacillus thuringiensis EM-A1, which achieved a removal rate of 97.13% for 1000 mg / L ammonia nitrogen; and another patent discloses the application of Bacillus thuringiensis LUY3 (CN202311529684.X) in the treatment of ammonia nitrogen in aquaculture wastewater and urban domestic sewage. However, this technology has the following drawbacks: First, free EM bacteria are easily lost in dispersed water bodies and it is difficult to maintain an effective bacterial density in the system for a long time, requiring continuous addition and resulting in high operating costs; Second, free bacteria have limited tolerance to coexisting pollutants in the aquatic environment (such as heavy metals and organic matter); Third, the composite form of EM bacteria and materials is simple, only remaining at the level of a simple combination of "microorganisms + carriers", lacking a system design from the perspective of "synergistic symbiosis" between materials and microorganisms.

[0006] In summary, current technologies lack a modified material that can optimize the pore structure of biochar, leverage the efficient degradation capabilities of microorganisms, and possess both rapid adsorption and continuous degradation functions, strong environmental adaptability, stable operation, and green economy. Summary of the Invention

[0007] (a) The problems to be solved by the present invention are: (1) solving the technical problem that existing chemically modified or physically modified biochar materials only have a single physical adsorption function and lack continuous degradation ability; (2) solving the technical problem that existing chemically modified biochar technology relies on hazardous chemicals, has the risk of secondary pollution, and has high cost; (3) solving the technical problem that the strain population structure in existing immobilized microorganism-biochar composite systems is single and the environmental adaptability is limited; (4) solving the technical problem that free bacteria are easily lost, the tolerance of coexisting pollutants is limited, and the strain-material composite form is single in existing EM bacteria direct application technology.

[0008] (II) Technical Solution To achieve the above objectives, the present invention provides an EM-modified corn straw biochar for ammonia nitrogen pollution remediation. The modified biochar is prepared by co-culturing corn straw biochar with an EM bacterial solution containing Bacillus thuringiensis EM-A1 strain. The EM bacteria carry the hydroxylamine oxidoreductase encoding gene hao and the nitric oxide reductase encoding gene norB. The mesoporous specific surface area of ​​the modified biochar is increased by more than 100% compared with that before modification, and the average pore size is increased by more than 8%.

[0009] Specifically, the modified biochar has an average pore size of 5.61 nm ± 0.5 nm, a mesoporous specific surface area of ​​≥ 16.15 m² / g, an equilibrium adsorption capacity for ammonia nitrogen that is at least 120% higher than before modification, and a maximum monolayer adsorption capacity of ≥ 28.0 mg / g.

[0010] Furthermore, the EM bacteria also carry ABC efflux pump encoding genes patA and patB, as well as mobile genetic elements; the mobile genetic elements include transposases and at least one insertion sequence selected from IS3, IS30, and IS1380.

[0011] Furthermore, the adsorption process of ammonia nitrogen by the modified biochar conforms to a pseudo-second-order kinetic model, with chemisorption as the dominant process; its adsorption thermodynamic parameters ΔH are 9.39 kJ / mol ± 1 kJ / mol, and ΔG are 8.57–8.93 kJ / mol.

[0012] This invention also provides a method for preparing the above-mentioned EM-modified corn straw biochar, comprising the following steps: S1. Preparation of raw biochar: Corn stalks are crushed, sieved, and then pyrolyzed and carbonized at 400℃ under low oxygen conditions. After cooling, they are washed until neutral, dried, and sieved to obtain raw corn stalk biochar. S2. EM bacterial activation: Mix EM bacterial solution with brown sugar and ammonia-free water at a volume ratio of 1:1:20, and activate and culture at 25–30℃ and 150–180rpm for 24 h to obtain activated EM bacterial solution. S3. Co-culture modification: The original corn straw biochar obtained in step S1 and the activated EM bacterial solution obtained in step S2 are mixed at a solid-liquid ratio of 1:3 and cultured in the dark at 20–30℃ for 48 h to allow EM bacteria to colonize the surface of the biochar and reshape the pore structure. S4. Post-treatment: After the culture is completed, wash to remove the unadsorbed free cells, and vacuum dry at 40℃ for 24 h to obtain EM bacteria modified corn straw biochar.

[0013] Preferably, the pyrolysis carbonization time in step S1 is 2 h, the drying temperature is 105℃, and the sieving is through a 200-mesh sieve; the EM bacterial solution in step S2 contains Bacillus thuringiensis EM-A1 strain, and the brown sugar and ammonia-free water are both sterile.

[0014] Furthermore, during the co-culture process described in step S3, EM bacteria drive the directional transformation of biochar micropores into mesopores through the secretion of extracellular polymers, physical cell penetration, and chemical dissolution by metabolites, thereby increasing the specific surface area and average pore size of the mesopores.

[0015] This invention also provides the application of the above-mentioned EM bacteria modified corn straw biochar in the removal of ammonia nitrogen from water bodies. The modified biochar is added to water bodies containing ammonia nitrogen, and ammonia nitrogen is rapidly enriched through adsorption. At the same time, the loaded EM bacteria are used for in-situ biodegradation, thereby achieving the regeneration of adsorption sites and continuous removal.

[0016] Specifically, the water body is aquaculture wastewater, farmland runoff, eutrophic lake water, or landscape water body; the dosage of the modified biochar is 1–10 g / L, the treatment temperature is 15–35℃, the pH is 4–10, and the removal rate of ammonia nitrogen is ≥90%.

[0017] Furthermore, the modified biochar forms an "adsorption-degradation" combined system during the removal of ammonia nitrogen: the adsorption module rapidly captures ammonia nitrogen through the optimized mesoporous structure, while the degradation module converts ammonia nitrogen into nitrogen gas through the hydroxylamine oxidoreductase and nitric oxide reductase of EM bacteria. The two work together to achieve long-term stable operation.

[0018] Furthermore, when the modified biochar treats high-concentration ammonia nitrogen wastewater, the EM bacteria discharge toxic intermediate metabolites through the ABC effluent pump encoding genes patA / patB, maintaining degradation activity; and achieve genetic plasticity through mobile genetic elements, adapting to fluctuations in temperature, pH and pollutant concentration.

[0019] The beneficial effects of this invention are as follows: (1) This invention uses EM bacteria for biomodification, which enables the material to adsorb ammonia nitrogen while simultaneously utilizing the loaded EM bacteria for in-situ biodegradation, continuously freeing up adsorption sites, achieving a positive cycle, and significantly extending the service life of the material; (2) This invention uses EM bacteria for biomodification without using any toxic chemical reagents. The modification conditions are room temperature, normal pressure, and neutral, and the entire process is clean and pollution-free; the raw material, corn stalks, is agricultural waste, and EM bacteria and sugar sources are readily available in the market, reducing the preparation cost by more than 60% compared to chemical modification; (3) The EM bacteria used in this invention are a composite bacterial group, which allows it to operate in a wide temperature range of 15–35℃, a wide acid-base range of pH 4–10, and 1000 It can maintain high degradation activity even under high ammonia nitrogen shock of mg / L, and is suitable for the treatment of rural non-point source pollution with dispersed and highly fluctuating characteristics; (4) The present invention enables EM bacteria to fully colonize the surface of biochar through light-shielded co-cultivation. At the same time, EM bacteria actively optimize the pore structure of biochar, increasing the mesoporous surface area by 129%, providing more sufficient and stable attachment space for bacteria, enhancing the binding strength between bacteria and carrier, and significantly improving the ability to resist scouring and loss under dynamic water flow conditions. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a process flow diagram for preparing EM-modified corn straw biochar according to the present invention.

[0022] Figure 2 The image shows a comparison of the infrared spectra of raw biochar and biochar modified with EM bacteria.

[0023] Figure 3 The metagenomic analysis results of the EM strain of this invention include KEGG functional annotation map, COG functional classification map, species abundance pie chart and insertion sequence distribution map. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0025] Example 1: Preparation of EM-modified corn straw biochar This embodiment provides a specific method for preparing EM bacteria-modified corn straw biochar.

[0026] S1. Preparation of raw biochar: Corn stalks were air-dried, crushed, and passed through a 100-mesh sieve. The stalks were then placed in a muffle furnace and pyrolyzed at 400℃ under low-oxygen conditions for 2 hours. After natural cooling, the biochar was removed, repeatedly washed with deionized water until neutral, dried at 105℃, and passed through a 200-mesh sieve to obtain raw corn stalk biochar. The average pore size of the raw biochar was measured to be 5.12 nm, and the mesoporous specific surface area (BJH adsorption branch) was 7.04 m² / g.

[0027] S2. EM bacterial activation: Mix commercially available EM bacterial solution (containing strains such as Bacillus thuringiensis EM-A1) with brown sugar and ammonia-free water at a volume ratio of 1:1:20, and activate and culture at 30℃ and 150 rpm for 24 h to obtain activated EM bacterial solution.

[0028] S3. Co-cultivation modification: The raw corn straw biochar obtained in step S1 and the activated EM bacterial solution obtained in step S2 were mixed at a solid-liquid ratio of 1:3 (g / mL), placed in a light-proof container, and incubated at 25℃ for 48 h. During this process, EM bacteria colonized the surface of the biochar and drove the directional transformation of the biochar micropores into mesopores through the secretion of extracellular polymers, physical penetration of bacterial cells, and chemical dissolution by metabolites.

[0029] S4. Post-treatment: After the culture is completed, the modified biochar is washed three times with sterile water to remove unadsorbed free bacteria, and then dried in a vacuum drying oven at 40℃ for 24 h to obtain EM bacteria modified corn straw biochar.

[0030] The modified biochar prepared in this embodiment had an average pore size of 5.61 nm and a mesoporous specific surface area of ​​16.15 m² / g, representing increases of 9.5% and 129% respectively compared to the original biochar. The modified biochar exhibited an equilibrium adsorption capacity of approximately 25 mg / g for ammonia nitrogen, a 127% increase compared to the original biochar (approximately 11 mg / g), with a maximum monolayer adsorption capacity of 28.0 mg / g. Adsorption kinetics fitting showed a pseudo-second-order kinetic model with a correlation coefficient R² = 0.988, indicating that chemisorption was the dominant process. Thermodynamic analysis showed ΔH = 9.39 kJ / mol and ΔG = 8.57–8.93 kJ / mol (288.15–308.15 K), indicating that the energy input required for adsorption was reduced and the temperature dependence was weakened after modification.

[0031] Example 2: Molecular genetic characteristics analysis of EM bacteria In this embodiment, metagenomic sequencing analysis was performed on the Bacillus thuringiensis EM-A1 strain among the EM bacteria used.

[0032] EM bacterial culture was inoculated into an inorganic salt medium with ammonia nitrogen as the sole nitrogen source. After culturing at 25°C and 150 rpm, the bacterial cells were collected, and genomic DNA was extracted and sequenced on the DNBSEQ-T7 platform. After quality control and assembly, a non-redundant gene set was obtained, and species and functional gene annotation was performed using databases such as NR, KEGG, COG, and CARD.

[0033] The results showed that the strain was *Bacillus thuringiensis*, with over 99% identity to the ammonia nitrogen-degrading strain EM-A1 (MW551532.1). KEGG annotation revealed that the strain carried the hydroxylamine oxidoreductase gene *hao* (1,134 reads) and the nitric oxide reductase gene *norB* (1,470 reads), indicating a complete ammonia nitrogen metabolic pathway capable of converting ammonia nitrogen into nitrogen gas via heterotrophic nitrification-aerobic denitrification. COG functional classification further revealed the strain's metabolic characteristics: carbohydrate transport and metabolism (Class G, 4,892 genes) had the highest abundance, indicating the strain's efficient carbon source utilization capacity; amino acid transport and metabolism (Class E, 3,275 genes) was the second most abundant, demonstrating its strong nitrogen assimilation capacity; energy production and conversion (Class C, 1,612 genes) were also relatively abundant, providing a continuous ATP supply for the ammonia nitrogen degradation process. These functional characteristics collectively constitute the metabolic basis for the strain's efficient nitrogen removal. CARD annotations showed that the ABC efflux pump genes patA (79,034 reads) and patB (22,704 reads) were the most abundant, enabling the timely excretion of toxic metabolic intermediates such as hydroxylamine and nitrite from the cell. Analysis of mobile genetic elements revealed that transposases accounted for 22.72%, and insertion sequences such as IS3, IS30, and IS1380 accounted for 10.59%, 10.00%, and 8.1%, respectively, providing a genetic basis for the amplification, recombination, and horizontal transfer of nitrogen metabolism-related genes, enabling the strain to rapidly optimize gene expression under environmental stress.

[0034] Example 3: Performance test of EM bacteria in degrading ammonia nitrogen This example investigates the effects of temperature, pH, and initial ammonia nitrogen concentration on the degradation performance of EM bacteria.

[0035] EM bacterial culture was inoculated into an inorganic salt medium (MSM) with ammonia nitrogen as the sole nitrogen source at a volume ratio of 1:100. The initial ammonia nitrogen concentration was 100 mg / L. The culture was carried out under constant temperature and shaking conditions. Samples were taken at regular intervals to determine the residual ammonia nitrogen concentration and bacterial growth density.

[0036] Temperature gradient experiments (15℃, 25℃, 35℃) showed that the degradation rate was highest at 25℃ (83.5%), and remained above 70% at 15℃ and 35℃, indicating that EM bacteria have wide temperature adaptability. pH gradient experiments (pH=4, 7, 10) showed that the degradation rate was highest under neutral conditions (pH=7) (82.35%), and some activity was maintained under strongly acidic or alkaline conditions. Initial ammonia nitrogen concentration experiments (100–1000 mg / L) showed that EM bacteria completely degraded 100 mg / L ammonia nitrogen within 8 h; even at a high concentration of 1000 mg / L, 100% removal was still achieved. This wide adaptability is consistent with the presence of ABC efflux pump genes and mobile genetic elements in metagenomic analysis.

[0037] Example 4: The treatment effect of EM-modified biochar on actual aquaculture wastewater This embodiment applies the modified biochar prepared in Example 1 to the treatment of actual aquaculture wastewater.

[0038] Wastewater from aquaculture farm was collected, with an initial ammonia nitrogen concentration of 85–120 mg / L and a pH of 7.2–7.8. 5 g of modified biochar was added to 1 L of wastewater, and the mixture was treated with shaking at 25℃ and 150 rpm for 24 h. After treatment, the ammonia nitrogen concentration in the water was measured.

[0039] The results showed that the ammonia nitrogen concentration in the treated water decreased to below 8.5 mg / L, with a removal rate exceeding 90%. Simultaneously, no nitrite accumulation was detected in the treated wastewater, indicating that ammonia nitrogen was effectively converted into nitrogen gas or other harmless forms. In the control experiment, the treatment group with only raw biochar (without EM bacteria) showed an ammonia nitrogen removal rate of only about 45% after 24 hours, and the adsorbed material was clearly saturated; the treatment group with only free EM bacteria showed an ammonia nitrogen removal rate of approximately 60% after 24 hours, and the bacteria migrated with the water flow, making it difficult for them to remain in the system. The modified biochar of this invention possesses both rapid adsorption and continuous biodegradation functions, resulting in a significantly better treatment effect than the control.

[0040] Example 5: Validation of the wide adaptability of EM-modified biochar This embodiment tests the ammonia nitrogen removal performance of modified biochar under simulated environmental conditions.

[0041] Low temperature conditions (15℃): 1.0 g of the modified biochar from Example 1 was added to 50 mL of ammonia nitrogen solution with a concentration of 50 mg / L, and the mixture was shaken at 15℃ and 200 rpm until equilibrium was reached. The results showed that the equilibrium adsorption capacity was approximately 22 mg / g, and the removal rate was approximately 88%, indicating that the material maintained good performance at low temperatures.

[0042] High pH conditions (pH=10): 1.0 g of modified biochar was added to 50 mL of ammonia nitrogen solution with a concentration of 50 mg / L (pH adjusted to 10 with NaOH), and the mixture was shaken at 25℃ and 200 rpm until equilibrium was reached. The results showed that the equilibrium adsorption capacity was approximately 20 mg / g, and the removal rate was approximately 80%.

[0043] High-concentration shock (200 mg / L): 1.0 g of modified biochar was added to 50 mL of ammonia nitrogen solution with a concentration of 200 mg / L, and the mixture was shaken at 25℃ and 200 rpm until equilibrium was reached. The results showed that the equilibrium adsorption capacity was approximately 28 mg / g, the removal rate was approximately 70%, and the EM bacteria maintained their degradation activity after adaptation.

[0044] The above results show that the modified biochar of the present invention has good treatment effect under wide temperature, wide pH and high concentration shock conditions, and is suitable for complex working conditions of decentralized rural non-point source pollution.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An EM-modified corn straw biochar for ammonia nitrogen pollution remediation, characterized in that, The modified biochar is prepared by co-culturing and modifying corn straw biochar with EM bacterial solution containing Bacillus thuringiensis EM-A1 strain; the EM bacteria carry the hydroxylamine oxidoreductase encoding gene hao and the nitric oxide reductase encoding gene norB; the mesoporous specific surface area of ​​the modified biochar increases by more than 100% compared with that before modification, and the average pore size increases by more than 8%.

2. The EM-modified corn straw biochar for ammonia nitrogen pollution remediation according to claim 1, characterized in that, The modified biochar has an average pore size of 5.61 nm ± 0.5 nm, a mesoporous specific surface area of ​​≥ 16.15 m² / g, an equilibrium adsorption capacity for ammonia nitrogen that is at least 120% higher than that before modification, and a maximum monolayer adsorption capacity of ≥ 28.0 mg / g.

3. The EM-modified corn straw biochar for ammonia nitrogen pollution remediation according to claim 1, characterized in that, The EM bacteria also carry ABC efflux pump encoding genes patA and patB, as well as mobile genetic elements; the mobile genetic elements include transposases and at least one insertion sequence selected from IS3, IS30, and IS1380.

4. The EM-modified corn straw biochar for ammonia nitrogen pollution remediation according to claim 1, characterized in that, The adsorption process of ammonia nitrogen by the modified biochar conforms to a pseudo-second-order kinetic model, with chemisorption as the dominant process; its adsorption thermodynamic parameters ΔH are 9.39 kJ / mol ± 1 kJ / mol, and ΔG are 8.57–8.93 kJ / mol.

5. A method for preparing EM-modified corn straw biochar as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of raw biochar: Corn stalks are crushed, sieved, and then pyrolyzed and carbonized at 400℃ under low oxygen conditions. After cooling, they are washed until neutral, dried, and sieved to obtain raw corn stalk biochar. S2. EM Bacterial Activation: Mix EM bacterial solution with brown sugar and ammonia-free water at a volume ratio of 1:1:20, and activate and culture at 25–30℃ and 150–180 rpm for 24 h to obtain activated EM bacterial solution. S3. Co-culture modification: The original corn straw biochar obtained in step S1 and the activated EM bacterial solution obtained in step S2 are mixed at a solid-liquid ratio of 1:3 and cultured in the dark at 20–30℃ for 48 h to allow EM bacteria to colonize the surface of the biochar and reshape the pore structure. S4. Post-treatment: After cultivation, wash away unadsorbed free cells and vacuum dry at 40℃ for 24 h to obtain EM bacteria modified corn straw biochar.

6. The method for preparing EM-modified corn straw biochar according to claim 5, characterized in that, In step S1, the pyrolysis and carbonization time is 2 h, the drying temperature is 105℃, and the sieving is through a 200-mesh sieve; in step S2, the EM bacterial solution contains Bacillus thuringiensis EM-A1 strain, and the brown sugar and ammonia-free water are both sterile.

7. The method for preparing EM-modified corn straw biochar according to claim 5, characterized in that, During the co-culture process described in step S3, EM bacteria drive the directional transformation of biochar micropores into mesopores through the secretion of extracellular polymers, physical cell penetration, and chemical dissolution by metabolites, thereby increasing the specific surface area and average pore size of the mesopores.

8. The application of EM-modified corn straw biochar as described in any one of claims 1-4 in the removal of ammonia nitrogen from water bodies, characterized in that, The modified biochar is added to water containing ammonia nitrogen, where ammonia nitrogen is rapidly enriched through adsorption. At the same time, the loaded EM bacteria are used for in-situ biodegradation, thereby regenerating the adsorption sites and achieving continuous removal.

9. The application according to claim 8, characterized in that, The water body is aquaculture wastewater, farmland runoff, eutrophic lake water, or landscape water body; the dosage of the modified biochar is 1–10 g / L, the treatment temperature is 15–35℃, the pH is 4–10, and the removal rate of ammonia nitrogen is ≥90%.

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