Soil carbon sequestration-organic pollution control synergistic remediation method by coupling microbial iron reduction with biomass charcoal

Abstract

The invention provides a soil carbon sequestration-organic pollution control synergistic remediation method by coupling microbial iron reduction with biomass charcoal, which comprises the following steps: selecting a composite strain comprising nitrogen-fixing bacteria, phosphate solubilizing bacteria and iron reducing bacteria, mixing the composite strain with biomass charcoal to form a microbial-biomass charcoal compound, applying the microbial-biomass charcoal compound to soil, regulating and controlling soil environmental conditions, and controlling organic pollution. The iron circulation and the carbon sequestration effect of the biomass charcoal are promoted. The method comprises the following specific steps: selecting nitrogen-fixing bacteria consisting of clostridium pasteurianum and rhizobium japonicum, phosphate solubilizing bacteria consisting of bacillus subtilis, flavobacterium or streptomyces, and iron reducing bacteria consisting of geobacterium; preparing biomass charcoal; mixing the composite strain with the biomass charcoal; and applying and adjusting the pH value, the moisture content and the air permeability of the soil. The method is suitable for various kinds of soil, especially soil easily polluted by MCPA, the carbon sequestration capacity of the soil can be effectively improved, and environmental pollution is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of soil restoration and improvement, and in particular to a soil carbon fixation-organic pollution control synergistic restoration method by coupling microbial iron reduction with biochar. Background Art

[0002] Brick red soil has an important agricultural status, and low organic carbon content is one of the bottleneck problems restricting its sustainable agricultural development. Brick red soil is an important soil type in my country's tropical and subtropical regions, distributed in Hainan Island, Leizhou Peninsula in Guangdong, southern Yunnan and other regions. Due to sufficient water and heat, the area is the main production area of ​​tropical crops such as rubber, banana, litchi, and mango in my country. It is also an important southern breeding base and winter "vegetable basket" base in my country. Therefore, ensuring the quality and safety of brick red soil is related to the healthy development of my country's tropical agriculture and the increase in production and income of farmers in tropical areas. However, with the development and acceleration of agriculture, the soil environment faces many challenges. Due to the characteristics of high temperature and humidity, high rainfall intensity, and high multiple cropping index in the area, the organic carbon in brick red soil has the characteristics of low content, fast decomposition, not easy to accumulate, and low carbon balance point. The organic carbon content is in the middle and lower levels of my country's organic carbon grade classification. This makes brick red soil one of the most important low-yield soils in my country, and it needs to rely on a large amount of fertilization to maintain productivity, and agricultural development faces huge challenges. On the one hand, excessive fertilization leads to soil compaction and acidification, and on the other hand, it aggravates organic carbon oxidation and greenhouse gas emissions, making "soil carbon sequestration" and "soil fertility improvement" contradictory issues. For example, in the past 30 years, as a typical brick red soil area, Hainan Island has significantly increased its grain production, but the soil organic carbon content has dropped by 25%. Therefore, the fixation of soil organic carbon is of great significance for maintaining soil fertility, improving soil structure and reducing greenhouse gas emissions. Seeking sustainable farmland management methods to achieve carbon sequestration and sink enhancement in brick red soil is an important task to solve the current dilemma of tropical agricultural development and support my country's "dual carbon" goals.

[0003] The content of soil organic carbon can not only cause low soil fertility, but also make soil microorganisms lack energy and nutrition sources for the decomposition of pesticides, increasing the risk of pesticide residues. In particular, in tropical brick red soil areas with high temperature, high rainfall and high multiple cropping index, the amount of pesticide used is 3.6 times the national average and 5.6 times the average of the three northeastern provinces, posing a potential threat to the quality and safety of local agricultural products and the safety of the ecosystem. Among them, the residual risk of dimethyl tetrachlorophenoxyacetic acid (MCPA) is particularly great. As a hormone-type selective herbicide, it is widely used in the control of broad-leaved weeds in agricultural production around the world. The use of MCPA ranks third among pesticides in the world. In brick red soil areas, MCPA is also commonly used for broad-leaved weed control in rice fields and sugarcane fields, with an application rate of up to 1-2.5 kg / ha. Due to its strong biological toxicity, it can cause oxidative damage to animals / plants, damage to human organs / neurasthenia, and fetal / urogenital teratogenicity. MCPA has been listed as an environmental priority monitoring pollutant by the US Environmental Protection Agency and the European Union. Therefore, while improving the organic carbon of brick red soil, the need for MCPA residue degradation should also be fully considered.

[0004] At present, some soil improvement methods have been proposed for soil carbon increase or organic pollutant degradation. For example, applying organic fertilizers to increase soil organic carbon; using chemical fertilizers to provide nutrients for the degradation of organic pollutants. However, these methods all have certain limitations. For example, excessive use of chemical fertilizers can lead to soil compaction, environmental pollution and other problems. Moreover, current soil improvement methods rarely consider the dual obstacles of poor organic carbon and serious MCPA residues in brick red soil. The use of microorganisms to drive iron cycle to promote the carbon fixation effect of biochar soil, that is, using nitrogen-fixing bacteria, phosphate-solubilizing bacteria and iron-reducing bacteria to promote the carbon fixation effect and pollutant degradation effect of biochar; due to the low nitrogen and phosphorus nutrients in tropical brick red soil, especially in highly polluted soil. Organic pollutants are carbon-rich pollutants, and microbial degradation of such pollutants requires the absorption of nitrogen and phosphorus from the soil.

[0005] It is a green and sustainable method for soil improvement. However, the current research on how to effectively use specific composite bacteria to achieve this goal is not in-depth enough, and further exploration and optimization of related methods are needed. Summary of the invention

[0006] In view of this, the present invention proposes a soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar to solve the above problems.

[0007] The technical solution of the present invention is achieved as follows: a soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar: including the following technical solutions:

[0008] S1. Select composite bacteria: the composite bacteria include nitrogen-fixing bacteria, phosphate-solubilizing bacteria and iron-reducing bacteria, the nitrogen-fixing bacteria are Clostridium pasteurianum and soybean rhizobium in a mass ratio of 1:1-3, the phosphate-solubilizing bacteria are Bacillus subtilis, Flavobacterium or Streptomyces, and the iron-reducing bacteria are Geobacter;

[0009] S2. Preparing biochar: subjecting the biomass raw material to pyrolysis and carbonization treatment under anaerobic or anoxic conditions;

[0010] S3, mixing the composite bacteria with the prepared biomass charcoal to form a microorganism-biomass charcoal composite;

[0011] S4. Applying the microorganism-biochar complex to target soil and regulating the environmental conditions of the soil to promote the microbial-driven iron cycle and the soil carbon fixation effect of biochar.

[0012] Furthermore, the composite bacteria in S1 include nitrogen-fixing bacteria, phosphate-solubilizing bacteria and reducing bacteria in a mass ratio of (2.5-5.5):(8.1-10.2):(1.3-3.5).

[0013] Furthermore, the effective viable count of the composite bacteria in S1 is ≥ 1×10 9 CFU / g.

[0014] Furthermore, the temperature of the pyrolysis and carbonization treatment of the biomass raw material in S2 is 300-800° C., and the pyrolysis time is 5-10 hours.

[0015] Furthermore, the biomass raw materials in S2 are one or more of crop straw, forestry waste, livestock and poultry manure, waste wood, energy plants or urban organic waste.

[0016] Furthermore, each gram of biochar in S3 contains 10 8 -10 10 microbial cells.

[0017] Furthermore, the application amount in S4 is 3-10 tons of microorganism-biomass charcoal complex per hectare of soil.

[0018] Furthermore, the step of regulating the environmental conditions of the soil includes: adjusting the pH value of the soil to 5.5-8.5, controlling the moisture content of the soil to 40-80%, and maintaining good aeration of the soil.

[0019] Furthermore, the humus in S4 is humic acid, fulvic acid or humin.

[0020] Furthermore, the above method is applicable to different types of soil, including but not limited to paddy field soil, sugarcane field soil and other soils susceptible to MCPA contamination.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Improving soil carbon sequestration capacity: By driving the iron cycle through microorganisms, the combination and stabilization of biochar and soil organic carbon are promoted, the soil carbon sequestration capacity is improved, which is beneficial to maintaining soil fertility and improving soil structure.

[0023] (2) Improve soil nutrient status: Nitrogen-fixing bacteria can increase the nitrogen content in the soil, and phosphate-solubilizing bacteria can release the fixed phosphorus in the soil, providing more nutrients for plant growth and promoting plant growth and development.

[0024] (3) Degradation of soil pollutants: To a certain extent, the metabolic activities of microorganisms may help degrade pollutants such as pesticides that may exist in the soil, such as MCPA, reduce the risk of soil pollution, and ensure the safety of the soil ecosystem.

[0025] (4) Wide adaptability: This method is applicable to different types of soils, including but not limited to paddy field soil, sugarcane field soil, and other soils susceptible to MCPA contamination, and has good promotion and application value. DETAILED DESCRIPTION

[0026] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0027] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0028] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0029] Example 1

[0030] A soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar comprises the following steps:

[0031] S1. Select composite bacteria: select Clostridium pasteurianum and Rhizobium sojae as nitrogen-fixing bacteria in a mass ratio of 1:1, select Bacillus subtilis as phosphate-solubilizing bacteria, and select Geobacter as iron-reducing bacteria. Mix nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and iron-reducing bacteria in a mass ratio of 2.5:8.1:1.3 to prepare a composite bacteria, and ensure that the effective viable count of the composite bacteria is 1×109 CFU / g.

[0032] S2. Preparation of biochar: Select crop straw as the biomass raw material, set the pyrolysis carbonization treatment temperature to 400° C. and the pyrolysis time to 10 hours under anaerobic conditions to prepare biochar.

[0033] S3. Forming a microorganism-biomass charcoal composite: mixing the composite bacteria with the prepared biomass charcoal at a ratio of 108 microbial cells per gram of biomass charcoal to form a microorganism-biomass charcoal composite.

[0034] S4. Application and soil environment regulation: Mix the microorganism-biomass charcoal complex and humic acid in a mass ratio of 1:0.2 and apply to paddy soil at a rate of 3 tons per hectare of soil. Adjust the soil pH to 4.5, control the soil moisture content to 50%, and maintain good soil aeration.

[0035] Example 2

[0036] A soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar comprises the following steps:

[0037] S1. Select composite bacteria: select Clostridium pasteurii and Rhizobium sojae as nitrogen-fixing bacteria in a mass ratio of 1:3, select Flavobacterium as phosphate-solubilizing bacteria, and select Geobacter as iron-reducing bacteria. Mix nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and iron-reducing bacteria in a mass ratio of 5.5:10.2:3.5 to prepare a composite bacteria. The effective viable count of the composite bacteria is 1.5×10 9 CFU / g.

[0038] S2. Preparation of biochar: using a mixture of forestry waste and livestock and poultry manure in a mass ratio of 1:1 as a biomass raw material, and subjecting the mixture to pyrolysis and carbonization treatment at a temperature of 600° C. and a pyrolysis time of 5 hours under anoxic conditions to prepare biochar.

[0039] S3, forming a microorganism-biomass carbon composite: the composite bacteria and the prepared biomass carbon are mixed at a ratio of 10 10 The ratio of microbial cells is mixed to form a microbial-biomass charcoal composite.

[0040] S4. Application and soil environment regulation: Mix the microorganism-biochar complex and humic acid at a mass ratio of 1:0.5 and apply to the sugarcane field soil at an application rate of 10 tons per hectare of soil. Adjust the soil pH to 6.5, control the soil moisture content to 100%, and maintain good soil aeration.

[0041] Example 3

[0042] A soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar comprises the following steps:

[0043] S1. Select composite bacteria: select Clostridium pasteurianum and Rhizobium sojae as nitrogen-fixing bacteria in a mass ratio of 1:2, select Streptomyces as phosphate-solubilizing bacteria, and select Geobacter as iron-reducing bacteria. Mix nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and iron-reducing bacteria in a mass ratio of 4:9:2.5 to prepare a composite bacteria. The effective viable count of the composite bacteria is 2×10 9 CFU / g.

[0044] S2. Preparation of biochar: using a mixture of waste wood, energy plants and urban organic waste in a mass ratio of 2:3:1 as a biomass raw material, and pyrolyzing and carbonizing the mixture under anaerobic conditions at a temperature of 500° C. for a pyrolysis time of 8 hours to prepare biochar.

[0045] S3, forming a microorganism-biomass carbon composite: the composite bacteria and the prepared biomass carbon are mixed at a ratio of 10 9 The ratio of microbial cells is mixed to form a microbial-biomass charcoal composite.

[0046] S4. Application and soil environment regulation: Mix the microorganism-biochar complex and humic acid in a mass ratio of 1:0.4 and apply it to the soil susceptible to MCPA contamination at a rate of 6 tons per hectare of soil. Adjust the soil pH to 5.5, control the soil moisture content to 80%, and maintain good soil aeration.

[0047] Comparative Example 1

[0048] The MCPA-contaminated soil without any treatment was selected as a comparative example. After 3 months, a comparative test was performed with the soil in the example.

[0049] Test Example 1-Determination of soil carbon sequestration capacity

[0050] Steps:

[0051] 1. Collecting soil samples: In the soil treated in Examples 1-3 and the comparative soil, appropriate soil samplers were used to sample according to the sampling depth (20 cm) and sampling point distribution to ensure that the collected soil samples were representative.

[0052] 2. Pretreatment of soil samples: Air-dry the collected soil samples to remove impurities such as stones and plant roots, then grind the soil samples into fine powder using a mortar or grinder, and sieve (0.15 mm sieve) to make the soil particles uniform to ensure the accuracy of the analysis results.

[0053] 3. Elemental analysis: Accurately weigh 10 mg of pre-treated soil sample, put it into the sample boat of the element analyzer, and send the sample boat into the combustion furnace of the element analyzer. Under the action of high temperature 900-1200℃ and oxygen flow, the carbon in the soil is oxidized into carbon dioxide, and other elements (nitrogen, hydrogen, etc.) are also converted into corresponding gases. After these gases are separated by the chromatographic column, they enter the detector for detection. According to the peak area or signal intensity of carbon dioxide detected by the detector, it is compared with the standard substance of known concentration to calculate the carbon content in the soil sample.

[0054] 4. Calculate carbon sequestration capacity: Based on the carbon content in the soil sample, combined with parameters such as soil bulk density, sampling area and sampling depth, calculate the carbon storage per unit area of ​​soil, which is used as an indicator of soil carbon sequestration capacity.

[0055] Carbon sequestration capacity (g / kg) = soil carbon content (g / kg) × soil bulk density (kg / m 3 )×sampling depth (m).

[0056] 5. Test results:

[0057] Table 1:

[0058]

[0059]

[0060] In the above results, the microorganisms added in the embodiment group act synergistically with the biochar, providing a more favorable living environment and carbon source for the microorganisms, promoting the growth, reproduction and metabolic activities of the microorganisms, thereby enhancing the carbon fixation capacity of the soil. Biochar itself is rich in carbon, and has a highly aromatic structure, high stability, is not easily decomposed by microorganisms in the soil, and can store carbon for a long time. Its porous structure can also adsorb organic matter in the soil, reduce the mineralization and decomposition of organic carbon, and provide a habitat for microorganisms, promote the contact and conversion of microorganisms and organic carbon, and further improve the soil carbon fixation capacity. The change in the redox state of iron will affect the decomposition and conversion of organic matter in the soil, and the appropriate iron cycle process will help to form a stable soil aggregate structure, protect the organic carbon in the soil from being easily decomposed, thereby promoting soil carbon fixation. In the embodiment, the iron cycle driven by microorganisms optimizes the soil environment to a certain extent, which is beneficial to soil carbon fixation.

[0061] Test Example 2- Determination of soil nutrient content

[0062] 1. Determination of total nitrogen content: Kjeldahl method;

[0063] 2. Determination of effective phosphorus content: molybdenum antimony colorimetric method;

[0064] 3. Determination of available potassium content: ammonium acetate extraction-flame photometry.

[0065] 4. Test results:

[0066] sample Total nitrogen content (g / kg) Available phosphorus content (mg / kg) Available potassium content (mg / kg) Example 1 1.85 35.2 185 Example 2 2.10 42.5 210 Example 3 2.35 50.0 230 Comparative Example 1.20 20.5 120

[0067] As can be seen from the above results, nitrogen-fixing bacteria can convert nitrogen in the air into ammonia nitrogen that can be used by plants, increasing the nitrogen content in the soil. Phosphate-solubilizing bacteria can decompose insoluble phosphorus compounds in the soil, releasing effective phosphorus for plant absorption and utilization. In the embodiment group, the addition and activity enhancement of these microorganisms directly promoted the supply of nitrogen and phosphorus nutrients in the soil. Biochar has a large specific surface area and pore structure, which can adsorb nutrient ions (ammonium ions, phosphate ions, etc.) in the soil and reduce nutrient leaching. At the same time, biochar can be used as a slow-release carrier of nutrients, slowly releasing nutrients according to the concentration gradient of nutrients in the soil, improving the effectiveness and supply durability of nutrients. The addition of microorganism-biochar complex and humus improves the physical and chemical properties of the soil, including soil pH, air permeability, water retention, etc. The appropriate soil environment is conducive to the activity of microorganisms in the soil and the transformation process of nutrients, among which aerobic microorganisms are more active in well-ventilated soil, which helps the mineralization of organic nitrogen and the release of phosphorus, thereby increasing the nutrient content of the soil.

[0068] Test Example 3-Determination of MCPA Residue

[0069] Steps:

[0070] 1. Soil sample collection and pretreatment: Select the soil treated in Examples 1-3 and the soil sample of the comparative example, take 20g of the soil sample and place it in a stoppered conical flask, add 100ml of acetonitrile-water mixed solution (volume ratio is 80:20), shake and extract on an oscillator for 50 minutes, then filter with filter paper, and collect the filtrate in a clean container. The residue is extracted again with the extraction solvent, and the two filtrates are combined. Use C 18 The solid phase extraction column was used for purification and the eluate was collected.

[0071] 2. Determination by High Performance Liquid Chromatography

[0072] Column selection: C 18 Reversed phase chromatography columns;

[0073] Mobile phase: a 50:50 volume ratio methanol-water mixture with a pH value of 2.5-4.0;

[0074] The flow rate was controlled at 1.5 mL / min;

[0075] Detection wavelength: 240nm;

[0076] The column temperature was set at 30°C;

[0077] The MCPA residues in soil samples were calculated according to the standard curve equation.

[0078] 3. Measurement results

[0079] sample MCPA residue (mg / kg) Degradation rate (%) Example 1 0.35 82.5 Example 2 0.25 87.5 Example 3 0.10 95.0 Comparative Example 2.00 -

[0080] The microorganisms added in the present invention may have the ability to degrade MCPA, and some microorganisms can decompose MCPA molecules into small molecules by secreting specific enzymes, and then mineralize into harmless substances such as carbon dioxide, water and inorganic salts. In an embodiment, the interaction between the microbial community and MCPA is enhanced, which accelerates the degradation process of MCPA. The redox substances (ferrous ions, ferric ions, etc.) produced during the iron cycle driven by iron-reducing bacteria participate in the degradation reaction of MCPA. Ferrous ions have certain reducibility, can react with MCPA molecules for electron transfer, change the chemical structure of MCPA, and make it easier to be further degraded by microorganisms or other chemical processes. Biochar has a certain adsorption capacity for MCPA, and can adsorb MCPA in the soil to its surface, reduce the concentration of MCPA in the soil solution, reduce the direct toxicity of MCPA to soil organisms on the one hand, and enrich MCPA on the surface of biochar on the other hand, which is conducive to the contact between microorganisms and MCPA and promotes the degradation of MCPA by microorganisms. At the same time, biochar may change the microenvironment of the soil, including local pH value, redox potential, etc., creating more favorable conditions for the degradation of MCPA.

[0081] In summary, the method of promoting biochar soil improvement by microbial driven iron cycle has significant effects on soil carbon fixation, nutrient improvement and MCPA residue degradation. Example 3 showed the best performance in all aspects, and its success may be attributed to the synergistic effect between the microbial-biochar complex, humus and microbial driven iron cycle. These results provide a strong experimental basis for the application of this method in the fields of soil improvement, sustainable agricultural development and contaminated soil remediation, while the carbon fixation capacity, nutrient content and MCPA residue of the comparative soil are not as good as those of the soil treated in the example.

[0082] Test Example 4-Iron reduction index test

[0083] 1. Accurately weigh 5.00g of the treated soil sample into a 100mL stoppered conical flask, add 50mL of 0.5mol / L hydrochloric acid solution, cover the flask tightly, and oscillate on an oscillator for 1h to fully dissolve the ferrous iron in the soil.

[0084] 2. After the shaking is completed, transfer the solution in the conical flask to a centrifuge tube, centrifuge at 3000r / min for 10min, and take the supernatant for later use.

[0085] 3. Pipette 5.00 mL of supernatant into a 50 mL volumetric flask and perform color development and absorbance measurement according to steps 2-4 in the standard curve drawing procedure.

[0086] 4. According to the standard curve regression equation, calculate the ferrous iron content (μg) in 5.00mL supernatant, and then calculate the ferrous iron (Fe(II)) content (mg / kg) in the soil according to the formula:

[0087]

[0088] Where:

[0089] m: ferrous iron content in 5.00 mL of supernatant obtained from the standard curve (μg);

[0090] V: total volume of the extract (mL), 50 mL in this experiment;

[0091] m0: the mass of the soil sample weighed (g), which is 5.00 g in this experiment;

[0092] V1: The volume of supernatant (mL) to be measured, which is 5.00 mL in this experiment.

[0093] 5. Experimental Results

[0094] Group Ferrous iron (Fe(II)) content in soil (mg / kg) Example 1 71.6 Example 2 69.2 Example 3 75.3 Comparative Example 45.7

[0095] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A soil carbon fixation-organic pollution control synergistic remediation method using microbial iron reduction coupled with biochar, characterized in that: The following steps are involved: S1. Select composite bacteria: the composite bacteria include nitrogen-fixing bacteria, phosphate-solubilizing bacteria and iron-reducing bacteria, the nitrogen-fixing bacteria are Clostridium pasteurianum and soybean rhizobium in a mass ratio of 1:1-3, the phosphate-solubilizing bacteria are Bacillus subtilis, Flavobacterium or Streptomyces, and the iron-reducing bacteria are Geobacter; S2. Preparing biochar: subjecting the biomass raw material to pyrolysis and carbonization treatment under anaerobic or anoxic conditions; S3, mixing the composite bacteria with the prepared biochar to form a microorganism-biochar composite; S4. Mix the microorganism-biochar complex and humus in a mass ratio of 1:(0.2-0.5), apply to the target soil, and regulate the environmental conditions of the soil to promote the microbial-driven iron cycle and the soil carbon fixation effect of the biochar.

2. The soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar as claimed in claim 1, characterized in that: The composite bacteria in S1 include nitrogen-fixing bacteria, phosphate-solubilizing bacteria and reducing bacteria in a mass ratio of (2.5-5.5):(8.1-10.2):(1.3-3.5).

3. The soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar as claimed in claim 2, characterized in that: The effective viable count of the composite bacteria in S1 is ≥ 1×10 9 CFU / g.

4. The soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar as claimed in claim 1, characterized in that: The temperature of the pyrolysis and carbonization treatment of the biomass raw material in S2 is 400-600° C., and the pyrolysis time is 5-10 hours.

5. The soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar as claimed in claim 1, characterized in that: The biomass raw materials in S2 are one or more of crop straw, forestry waste, livestock and poultry manure, waste wood, energy plants or urban organic waste.

6. The soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar as claimed in claim 1, characterized in that: Each gram of biochar in S3 contains 10 8 -10 10 microbial cells.

7. The soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar as claimed in claim 1, characterized in that: The application amount in S4 is 3-10 tons of microorganism-biomass charcoal complex per hectare of soil.

8. The soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar as claimed in claim 1, characterized in that: The step of regulating the environmental conditions of the soil includes: adjusting the pH value of the soil to 4.5-6.5, controlling the moisture content of the soil to 50-100%, and maintaining good aeration of the soil.

9. The soil carbon fixation-organic pollution control synergistic remediation method of microbial iron reduction coupled with biochar as claimed in claim 1, characterized in that: The humus in S4 is humic acid, fulvic acid or humin.

10. The method according to any one of claims 1 to 9, characterized in that Suitable for different types of soil, including but not limited to paddy soil, moist iron-alumina soil and other soils.

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