A method for combined phytoremediation of lead and cadmium contaminated soil by biochar and actinomycetes

Abstract

The present application relates to the field of soil pollution bioremediation, and particularly relates to a method for bioremediation of lead and cadmium composite contaminated soil by using biochar and actinomycetes, and aims to solve the technical problems of low remediation efficiency of lead and cadmium composite contaminated soil and low field colonization success rate of actinomycetes. The method comprises the following steps: preparing a functionalized biochar matrix by calcium dihydrogen phosphate immersion treatment; selecting an actinomycete strain capable of producing indole acetic acid and ACC deaminase; allowing the microorganism to colonize inside the pore structure of the functionalized biochar matrix; planting a hyperaccumulator, and applying the composite remediation material in a layered manner. The present application can selectively activate lead and cadmium, maintain the supply level of plant absorbable heavy metals, significantly improve the survival rate of actinomycetes in complex soil environment, realize the synergistic effect of reducing the toxicity risk of soil heavy metals and promoting the enrichment and absorption of plants, and improve the remediation uniformity of the remediation system for different depths of soil.

Description

Technical Field

[0001] This invention relates to the field of soil pollution bioremediation technology, and in particular to a combined biochar and actinomycete phytoremediation method for lead-cadmium contaminated soil. Background Technology

[0002] With the acceleration of industrialization and the large-scale development and utilization of mineral resources, the accumulation of heavy metals such as lead and cadmium in the soil environment has become a global environmental governance challenge. Lead-cadmium contaminated soils, due to their high toxicity, strong mobility, and difficulty in natural degradation, pose a serious threat to the quality and safety of agricultural products and human health. Among current soil heavy metal pollution remediation technologies, phytoremediation technology has gradually become a hot research and application area for scholars both domestically and internationally due to its advantages such as low cost, environmental friendliness, and minimal damage to soil structure. Among these technologies, hyperaccumulating plants, which transfer heavy metals from the soil to the aboveground parts through root absorption and then remove them by harvesting the aboveground parts, are considered a green remediation technology with broad application prospects.

[0003] However, single-plant remediation technology faces many limitations in practical applications. Hyperaccumulating plants typically grow slowly, have low biomass, and require high soil fertility and moisture conditions. In barren or severely polluted soil environments, their survival rate and remediation efficiency often fall short of expectations. Therefore, researchers both domestically and internationally are actively exploring technical approaches to enhance phytoremediation effects by adding exogenous amendments or functional microorganisms. Biochar, a type of carbonaceous porous material produced by the pyrolysis of biomass under anaerobic or limited-oxygen conditions, has gained widespread attention in the field of soil heavy metal pollution remediation due to its large specific surface area, well-developed pore structure, and abundant surface functional groups. Biochar can effectively reduce the bioavailability and migration capacity of heavy metals in soil through mechanisms such as adsorption and fixation, ion exchange, and precipitation complexation, thereby mitigating the toxic effects of heavy metals on plants. Meanwhile, actinomycetes, as an important component of the soil microbial community, can produce various plant growth-promoting factors and antibiotic-like substances, significantly promoting root development and aboveground biomass accumulation through pathways such as secreting plant hormones, lysing phosphorus and potassium, and inhibiting soil-borne pathogens.

[0004] In existing technologies, the combined application of biochar and actinomycetes has been explored to enhance phytoremediation effects. Specifically, the addition of biochar provides a beneficial environment for actinomycetes in two ways: firstly, the porous structure of biochar provides a favorable habitat and protective barrier, helping them maintain activity and colonize around the roots in complex soil environments; secondly, the nutrients and water adsorbed on the surface of biochar can sustain the growth needs of actinomycetes, extending their functional lifespan. Simultaneously, actinomycetes improve the soil microenvironment and promote the release of root exudates through metabolic activities, thereby indirectly enhancing the adsorption and fixation effect of biochar on heavy metals. Theoretically, this synergistic effect should achieve the dual goals of reducing soil heavy metal toxicity and promoting plant growth.

[0005] However, with the continuous and in-depth research on related technologies and the gradual implementation of large-scale field trials, some inherent characteristics of the above-mentioned technical solutions at the principle level have gradually revealed deep-seated internal contradictions when dealing with complex and ever-changing actual pollution scenarios. Specifically, the strong adsorption and fixation effect of biochar on heavy metals, while reducing its bioavailability, inevitably weakens the dynamic process of heavy metal migration from the soil solid phase to plant roots. This principle-based constraint is particularly prominent in lead-cadmium co-contaminated soils: lead in soil often exists in relatively stable forms such as carbonate-bound and iron-manganese oxide-bound states, and its background bioavailability is inherently low; while cadmium, although highly reactive, will significantly reduce its concentration gradient in the soil solution if the biochar application rate is too high, leading to a decrease in the absorption rate by plant roots. More importantly, actinomycetes promote the release of plant root exudates, which in some cases accelerates the desorption and release of heavy metals adsorbed on the biochar surface. This dynamic change makes the remediation effect exhibit significant non-linear characteristics, making it difficult to achieve the expected remediation target through simple dosage superposition.

[0006] Furthermore, in actual farmland soil environments, the interaction between biochar and actinomycetes is influenced by multiple factors, including soil pH, organic matter content, ionic strength, and microbial community competition. While the alkaline properties of biochar can improve acidic soils, they may also lead to drastic fluctuations in the soil microbial community structure, affecting the survival and functional expression of actinomycetes. The colonization success rate of actinomycetes in soil is closely related to the species, growth stage, and root exudate composition of the host plant. These intertwined and mutually restrictive factors make it difficult to guarantee the remediation efficiency and stability of existing technologies when facing actual contaminated site conditions, and significant differences exist between reported results from different studies.

[0007] In summary, how to fully leverage the heavy metal immobilization function of biochar to reduce environmental and ecological risks while maintaining and enhancing the plant's ability to absorb and accumulate heavy metals, and how to ensure the effective colonization and stable functional expression of actinomycetes in complex soil environments, have become key technical challenges currently faced by those skilled in the art. This requires a paradigm shift in technical approach design from "single enhancement" to "synergistic effect," constructing a new joint remediation method that can comprehensively consider multiple objectives and dynamically adapt to complex working conditions. Summary of the Invention

[0008] To address the above shortcomings, this invention provides a combined biochar and actinomycete phytoremediation method for lead-cadmium co-contaminated soil, which can achieve efficient remediation of lead-cadmium co-contaminated soil. The specific technical solution is as follows: A method for combined biochar and actinomycete phytoremediation of lead-cadmium contaminated soil includes applying a biochar-actinomycete composite remediation material to the lead-cadmium contaminated soil for remediation. The preparation of the biochar-actinomycete composite remediation material includes the following steps: A biochar-actinomycete composite remediation system was constructed by mixing a functionalized biochar matrix with a bacterial suspension, such that the water content of the functionalized biochar matrix was 30%–50%, and the bacterial suspension contained actinomycetes, with an inoculum size of 10... 8 ~10 10 CFU / g biochar matrix yields biochar-actinomycete composite remediation material.

[0009] Preferably, the bacterial suspension also includes *Penicillium wansii* (…). Paecilomyces variotii The total inoculum size of the complex consisting of actinomycetes and Paecilomyces wani was 10. 8 ~10 10 CFU / g biochar matrix.

[0010] Preferably, in the biochar-actinomycete composite remediation material, the colonization density of the actinomycetes in the biochar is ≥10. 7 CFU / g biochar matrix.

[0011] Preferably, in the biochar-composite microbial remediation material, the colonization density of the composite microorganisms composed of actinomycetes and Paecilomyces wanensis in the biochar is ≥10. 7 CFU / g biochar matrix.

[0012] Preferably, the preparation of the biochar-actinomycete composite remediation material further includes the following steps: To prepare a compound bacterial agent, an actinomycete strain that secretes plant growth-promoting substances and can produce indoleacetic acid and ACC deaminase was selected. The actinomycete and *Paecilomyces wani* were combined to form the compound bacterial agent. The actinomycete strain was inoculated into Gao's No. 1 liquid medium and cultured with shaking at 28℃~30℃ for 5~7 days at a rotation speed of 150~180 r / min to obtain an actinomycete suspension. The mycelium or spores of the slant culture were inoculated into PDA slant medium to obtain a spore suspension. The spore suspension was inoculated into PDB medium and cultured at 25~30℃ at a rotation speed of 140~160 r / min for 4~6 days to obtain a *Paecilomyces wani* spore suspension.

[0013] Preferably, the actinomycetes are selected from Streptomyces griseus (Streptomyces gravidus). Streptomyces griseus ) or Streptomyces medullaris ( Streptomyces mediterranei One of them.

[0014] Preferably, after mixing, the mixture is placed in a negative pressure environment for 20-40 minutes; after removal, the mixture is mixed with a sodium alginate solution with a concentration of 1-3% (w / v), and then dropped into a calcium chloride solution with a concentration of 2-4% (w / v), reacted for 20-40 minutes, and washed; and then cultured statically at 25℃-28℃ for 3-5 days to allow microorganisms to colonize the pore structure of the biochar.

[0015] Preferably, the preparation of functionalized biochar matrix includes a pyrolysis treatment: lignocellulosic biomass is pyrolyzed under oxygen-limited pyrolysis conditions at 300℃~500℃ for 2~4 hours. After pyrolysis, the biochar is ground to a particle size of 0.5~2 mm to obtain crude biochar. The preparation also includes an impregnation functionalization stage, in which the crude biochar is placed in an impregnation solution comprising a 0.5~2 mol / L calcium dihydrogen phosphate solution for 12~24 hours at an impregnation temperature of 25℃~35℃ to obtain the functionalized biochar matrix.

[0016] Preferably, the impregnation solution further includes a composite solution of 0.1~0.5 mol / L sodium thiosulfate and 0.1~0.5 mol / L ferrous sulfate.

[0017] Preferably, the lignocellulosic biomass raw material is corn stalk or peanut shell, the pyrolysis temperature is 350℃~450℃, and the pyrolysis time is 3h; the impregnation treatment time is 15~20h, the impregnation temperature is 20~40℃, and the mixture is shaken every 1~3h during the impregnation process; after impregnation, vacuum drying is performed at a drying temperature of 80℃~105℃.

[0018] Preferably, the preparation of the biochar-actinomycete composite remediation material further includes the following steps: testing the pH value, organic matter content, clay content, total lead and cadmium content, and available content of the target lead-cadmium contaminated soil before remediation.

[0019] Preferably, the preparation of the biochar-actinomycete composite remediation material further includes the following steps: Hyperaccumulating plants were selected as remediation plants, and the biochar-actinomycete composite remediation material was applied to the top 0-20cm soil layer of the contaminated soil at a rate of 200-500 g / m². 2 After application, till and mix thoroughly, then sow or transplant hyperaccumulating plants. Harvest the plants after 120-180 days of growth.

[0020] Preferably, during the plant growth period, conventional water and fertilizer management is carried out to maintain the soil moisture content at 60% to 80% of the field capacity; 15 to 25 kg of nitrogen fertilizer, 8 to 15 kg of phosphorus fertilizer, and 10 to 20 kg of potassium fertilizer are applied per mu (unit of land area), and the fertilization method is hole application or trench application, with a fertilization depth of 10 to 15 cm.

[0021] Preferably, the biochar-actinomycete composite remediation material is applied in a layered manner: first, 50-70% of the total amount of composite remediation material is evenly spread on the soil surface, and then the soil is tilled and mixed for the first time at a depth of 15-20cm; then, 30-50% of the total amount of composite remediation material is spread on the tilled soil surface, and the soil is tilled and mixed for the second time at a depth of 25-35cm.

[0022] Preferably, the hyperaccumulating plant is Sedum aizoon or Solanum nigrum, and the planting density of Sedum aizoon is 15-25 plants / m². 2 The planting density of the black nightshade is 10-20 plants / m². 2 .

[0023] Preferably, the method further includes the following steps: after the harvest is completed, the heavy metal content of the above-ground parts of the plants is measured. If the lead and cadmium content in the soil still does not reach the expected remediation target, a second crop is planted and harvested 60 to 90 days after the first harvest.

[0024] This invention also provides an application of a combined biochar and actinomycete phytoremediation method for lead-cadmium co-contaminated soil in the remediation of lead-cadmium co-contaminated soil.

[0025] The technical solution of this invention achieves synergistic and efficient remediation of lead-cadmium co-contaminated soil based on the following technical principles: The functionalized biochar matrix used in this invention is impregnated with a composite impregnation solution of calcium dihydrogen phosphate, sodium thiosulfate, and ferrous sulfate to form a phosphorus-containing functional layer on the biochar surface. This phosphorus-containing functional layer can form lead phosphate precipitate with lead ions in the soil environment, which has a low solubility product, while providing sufficient adsorption sites for cadmium ions. The iron-sulfur components can form amorphous FeS microdomains, which have a dual immobilization effect on cadmium through lattice intercalation and cadmium-sulfur precipitation. Compared with unfunctionalized biochar, the functionalized biochar matrix has a 40%–60% higher adsorption capacity for lead and a 20%–35% higher adsorption capacity for cadmium.

[0026] The actinomycete strain used in this invention promotes root elongation and branching by producing indoleacetic acid, increasing the contact area between roots and soil, thereby enhancing the root system's ability to capture heavy metals; it reduces the content of ACC, a precursor of ethylene, in plants by producing ACC deaminase, alleviating the inhibitory effect of ethylene accumulation caused by heavy metal stress on plant growth; and it indirectly increases the effective concentration of lead and cadmium on the plant root surface by secreting siderophores to chelate iron ions in the soil and inhibiting the competitive adsorption between lead and cadmium and iron ions. *Penicillium wannii* ( Paecilomyces variotii Under iron-deficient conditions, it can efficiently secrete isohydroxamic acid-type siderophores, with siderophore production reaching over 80% of siderophore units. The secreted siderophores can not only chelate Fe... 3+ It can improve the iron nutrition of plants and also work with Cd. 2+ Pb 2+ It forms soluble complexes, effectively increasing the effective concentration of heavy metals in the rhizosphere microdomain, creating favorable conditions for absorption by the roots of hyperaccumulating plants.

[0027] The biochar-actinomycete composite remediation system constructed in this invention achieves spatial isolation and protection for actinomycetes by colonizing the porous structure of a functionalized biochar matrix, thus preventing competitive inhibition from native soil microbial communities. Simultaneously, the organic acids and enzymes produced by the metabolic activities of the actinomycetes can regulate the release rate of adsorbed heavy metals on the surface of the functionalized biochar matrix, matching it with the absorption rate of plant roots and avoiding phytotoxic effects caused by a single large release of heavy metals. The layered loading structure with calcium alginate encapsulation significantly improves the survival rate of microorganisms. This is attributed to the rapid fixation effect of the outer passivation layer, which creates a low-toxicity microenvironment around the particles, while the calcium alginate gel matrix provides high water retention and a physical barrier, doubly ensuring the survival and slow release of the internal microbial agents. Higher survival rates and longer-lasting functional expression ultimately further enhance the removal rate of lead and cadmium in the soil.

[0028] The layered application method adopted in this invention achieves a three-dimensional distribution of functionalized biochar matrix in the soil profile by incorporating composite remediation material into the soil through two tillages. This creates a concentration gradient that varies from the surface to the deeper layers, providing differentiated heavy metal activation effects for plant roots at different soil depths and improving the remediation efficiency of the system for deeper soil layers.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention achieves selective activation treatment of heavy metals in lead-cadmium co-contaminated soil through the design of functionalized biochar matrix, which not only ensures that the environmental risks of lead and cadmium are controllable, but also maintains the supply level of plant-absorbable heavy metals.

[0030] 2. This invention significantly improves the survival rate and functional expression stability of actinomycetes in complex soil environments through a spatial isolation colonization strategy, solving the technical problem of low colonization success rate of actinomycetes under field conditions.

[0031] 3. This invention achieves a synergistic effect of reducing the risk of heavy metal toxicity in soil and promoting plant enrichment and absorption by constructing a biochar-actinomycete composite remediation system, thus solving the problem of conflicting objectives in single technical routes.

[0032] 4. This invention improves the uniformity of the remediation system for soils at different depths by optimizing the layered application method, thereby enhancing the reliability of the overall remediation effect. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments 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 based on these drawings without creative effort.

[0034] Figure 1 A schematic diagram of the overall process of the combined biochar and actinomycete phytoremediation method for lead-cadmium contaminated soil provided by the present invention. Figure 2 This is a schematic diagram illustrating the preparation process and structure of the functionalized biochar matrix in this invention; Figure 3 This is a schematic diagram of the structure of the biochar-actinomycete composite remediation system in this invention; The attached figures are labeled as follows: 1. Functionalized biochar matrix; 2. Crude biochar; 3. Phosphorus-containing functional layer; 4. Actinomycete suspension; 5. Streptomyces griseus or Streptomyces thaliana; 6. Biochar-actinomycete composite remediation material; 7. Porous structure. Detailed Implementation

[0035] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0036] Penicillium wanensis ( Paecilomyces variotii Purchased from the China Industrial Microbial Culture Collection Center (CICC).

[0037] Example 1 S1. Physicochemical property analysis of the target lead-cadmium contaminated soil: A 1000m² area was selected. 2 Using a lead-cadmium contaminated site as an experimental field, representative soil samples were collected to determine the soil pH, organic matter content, clay content, and total and available lead-cadmium content. The soil pH was determined using a potentiometric method, with deionized water mixed at a water-to-soil ratio of 2.5:1 before pH measurement. The organic matter content was determined using a potassium dichromate external heating method, with quantitative analysis of the oxidation degree of soil organic matter by potassium dichromate under silver sulfate catalysis. Clay content was determined using a laser particle size analyzer to analyze particle size distribution and identify the proportion of particles smaller than 0.002 mm. The total lead and cadmium content was determined using aqua regia digestion-inductively coupled plasma mass spectrometry (ICP-MS). Specifically, 0.5000 g of air-dried soil sample was pulverized and sieved, then placed in a digestion tube. 10 mL of aqua regia (a mixture of concentrated hydrochloric acid and concentrated nitric acid at a volume ratio of 3:1) was added, and the sample was digested at 180 °C for 2 h. After digestion, the sample was cooled to room temperature and diluted to a 50 mL volumetric flask with deionized water. The sample was then shaken well before analysis. The available lead and cadmium content was determined using DTPA extraction. 10.00 g of sieved soil sample was placed in a 250 mL Erlenmeyer flask, and 50 mL of DTPA extractant (0.005 mol / L DTPA, 0.1 mol / L triethanolamine, 0.01 mol / L calcium chloride, pH 7.3) was added. The sample was shaken at 180 rpm for 2 h at room temperature. After filtration, the lead and cadmium concentration of the filtrate was determined using ICP-MS.

[0038] The physicochemical properties analysis results of the soil at this site are as follows: pH value is 5.8, organic matter content is 18.5 g / kg, clay content is 32%, total lead is 486 mg / kg, total cadmium is 3.2 mg / kg, available lead content is 98 mg / kg, and available cadmium content is 0.85 mg / kg.

[0039] S2. Preparation of Functionalized Biochar Matrix: This includes three stages: pyrolysis, grinding and granulation, and calcium dihydrogen phosphate impregnation for functionalization. In the pyrolysis stage, corn stalks were selected as the biomass raw material. The corn stalks were cut into 2cm lengths and placed in a high-temperature resistant quartz tube of a tubular pyrolysis furnace. Nitrogen gas was introduced at a flow rate of 100mL / min to replace the air in the furnace. The temperature was then increased from room temperature to the target pyrolysis temperature at a rate of 5℃ / min. The pyrolysis temperature was set to 400℃, and the pyrolysis time was set to 3 hours. After pyrolysis, the heating device was turned off, and the material was allowed to cool naturally to below 100℃ before being removed to obtain crude biochar. In the grinding and granulation stage, the crude biochar was ground in a ball mill using zirconia balls as the grinding media at a ball-to-material ratio of 10:1 for 30 minutes. After grinding, the biochar was sieved, and biochar particles with a diameter of 0.5~2mm were selected as raw materials for subsequent functionalization treatment. In the calcium dihydrogen phosphate impregnation functionalization stage, biochar particles were impregnated in a 1 mol / L calcium dihydrogen phosphate solution at 30°C for 18 hours. During impregnation, the particles were manually shaken every 2 hours to ensure sufficient contact between the biochar particles and the impregnation solution. After impregnation, vacuum drying was performed in a vacuum drying oven at 90°C and a vacuum level of -0.08 MPa for 7 hours, until the biochar particles reached a constant weight, yielding the functionalized biochar matrix.

[0040] S3. Cultivation of Actinomycete Inoculum: *Streptomyces griseus*, a strain capable of producing indoleacetic acid and ACC deaminase, was selected as the strain. The activation and propagation process of the strain is as follows: Glycerol tubes of the bacterial culture, taken from a -80℃ ultra-low temperature freezer, were aseptically streaked onto Gao's No. 1 solid medium plates and incubated at 28℃ for 8 days. After colony formation, typical colonies were selected for microscopic examination for confirmation. After confirmation, single colonies were inoculated into Gao's No. 1 liquid medium and cultured at 28℃ with shaking for 6 days at a rotation speed of 160 r / min to obtain an actinomycete suspension. The composition of Gao's No. 1 liquid medium was: 20 g / L soluble starch, 1 g / L potassium nitrate, 0.5 g / L sodium chloride, 0.5 g / L dipotassium hydrogen phosphate, 0.01 g / L magnesium sulfate heptahydrate, 0.01 g / L ferrous nitrate, 15 g / L agar, with a pH of 7.3. The culture medium preparation process is as follows: Weigh each component according to the formula and place it in deionized water. After stirring evenly, adjust the pH value to 7.3, dispense it into 250 ml Erlenmeyer flasks, add 100 ml of culture medium to each flask, autoclave at 121℃ for 20 min, cool to room temperature, and then inoculate the activated actinomycete strain in a clean bench.

[0041] S4. Construction of a biochar-actinomycete composite remediation system: Place 100g of functionalized biochar matrix in a sterilized 2000ml beaker, add sterile water to adjust the moisture content to 35%, then add the actinomycete suspension cultured in Gao's No. 1 liquid medium, mix the functionalized biochar matrix and the actinomycete suspension to make the final inoculum size 10g. 9 CFU / g biochar matrix was stirred evenly with a sterile glass rod. The mixed material was then placed in a sterile polypropylene tray and spread to a thickness of 3 cm. It was incubated statically at 26℃ for 4 days. During the incubation period, the material was turned once daily with a sterile glass rod to ensure adequate oxygen supply. After actinomycete colonization, the colonization density of actinomycetes in the functionalized biochar matrix was detected using fluorescence microscopy. The specific detection method was as follows: 1g of the colonized functionalized biochar matrix was placed in 9ml of sterile physiological saline, eluted by shaking for 30 minutes, and then serially diluted. 10... -5 ~10 -7 0.1 ml of each dilution solution was spread onto Gao's No. 1 solid culture medium plates and incubated at 28°C for 7-10 days. Colony forming units were counted, and the total colony density was determined to be 2.3 × 10⁻⁶. 7 CFU / g biochar matrix. Fluorescence microscopy observation involved staining live cells with a staining solution, followed by observation of the green fluorescence intensity under a fluorescence microscope to determine the colonization status of the actinomycetes.

[0042] S5. Planting and Remediation Treatment: Biochar-actinomycete composite remediation material was evenly applied to the top 0-20cm soil layer of the lead-cadmium contaminated soil using a layered application method, at a rate of 350g / m³. 2 The specific application process is as follows: First, evenly spread 60% of the total amount of composite remediation material on the soil surface, then perform the first tilling and mixing, with a tilling depth of 18cm; then spread the remaining 40% of the total amount of composite remediation material on the tilled soil surface, and perform a second tilling and mixing, with a tilling depth of 30cm. After tilling, sow or transplant *Sedum aizoon*, with a planting density of 20 plants / m². 2During the plant growth period, routine water management was implemented to maintain soil moisture content at 70% of field capacity. Soil moisture was monitored in real-time using soil moisture sensors and precisely replenished via a drip irrigation system. Fertilizer was applied using furrow application, with 20 kg of nitrogen fertilizer, 10 kg of phosphorus fertilizer, and 15 kg of potassium fertilizer per acre, at a depth of 12 cm. Fertilization was carried out 15 days, 45 days, and 75 days after planting. After 150 days of growth, the *Sedum aizoon* plants were harvested. The above-ground parts of the plants were cut off at ground level, collected, sealed in plastic bags, and sent for heavy metal content testing. After harvesting, the heavy metal content of the above-ground parts of the plants was measured, and soil samples were collected to analyze the remediation effect. Based on the test results, it was determined whether a second round of remediation treatment was needed. If the lead and cadmium content in the soil still did not reach the expected remediation target, a second crop was planted and harvested 75 days after the first harvest.

[0043] Example 2 S1. Physicochemical property analysis of the target lead-cadmium contaminated soil: A 2000m² site of lead-cadmium contaminated soil was selected. 2 As an experimental field, representative soil samples were collected, and the soil pH, organic matter content, clay content, total lead and cadmium content, and available form content were measured. The measurement methods were the same as in Example 1. The soil physicochemical properties were as follows: pH 6.2, organic matter content 22.3 g / kg, clay content 28%, total lead 325 mg / kg, and total cadmium 2.8 mg / kg.

[0044] S2. Same as Example 1.

[0045] S3. Cultivation of actinomycete inoculum: *Streptomyces thaliana*, a strain capable of producing indoleacetic acid and ACC deaminase, was selected as the strain. The cultivation conditions and methods were the same as in Example 1.

[0046] S4. Same as Example 1.

[0047] S5. Planting and Remediation: After tilling, sow or transplant black nightshade seedlings at a density of 15 plants / m². 2 Harvesting and effect evaluation were conducted after 180 days of growth. Other conditions and methods were the same as in Example 1.

[0048] Example 3 In step S2, during the impregnation functionalization stage, the biochar particles are impregnated in a composite impregnation solution. The composite impregnation solution consists of a 1 mol / L solution of calcium dihydrogen phosphate, a 0.3 mol / L solution of sodium thiosulfate, and a 0.2 mol / L solution of ferrous sulfate. Other conditions and methods are the same as in Example 1.

[0049] Example 4 Step S3 involves cultivating the compound bacterial agent: *Streptomyces griseus* and *Penicillium wani*, which are capable of producing indoleacetic acid and ACC deaminase, are selected.Paecilomyces variotii ( ) to form a compound bacterial agent.

[0050] The activation and propagation process of *Penicillium wani* is as follows: The slant culture was taken from a 4℃ refrigerator. Under aseptic conditions, a small amount of mycelium or spores was picked up with an inoculation loop and streaked onto potato dextrose agar (PDA) slant medium. The medium composition was: 6 g / L potato extract powder, 20 g / L glucose, and 20 g / L agar. The medium was autoclaved at 121℃ for 20 min. The slant was then incubated at 28℃ for 5 days. After a large number of yellowish-brown to olive-green powdery conidia grew on the surface of the slant, microscopic examination was performed for confirmation. Following confirmation, the slant surface was repeatedly rinsed with 10 ml of sterile water in a laminar flow hood to elute the spores into a sterile Erlenmeyer flask containing glass beads. The flask was then shaken at 180 r / min for 20 min on a shaker to ensure complete spore dispersion. Finally, the spore suspension was filtered through four layers of sterile gauze to remove mycelial fragments. Spores were counted using a hemocytometer under an optical microscope, and the spore suspension concentration was adjusted to 1×10⁻⁶. 8 Each milliliter of the above spore suspension was used as an inoculum stock solution. The spore suspension was inoculated at a 1% (v / v) inoculation rate into potato dextrose liquid (PDB) medium, composed of 6 g / L potato extract powder and 20 g / L glucose. The medium was dispensed into 250 mL Erlenmeyer flasks, with 100 mL of medium added to each flask. The flasks were autoclaved at 121°C for 20 min and cooled to room temperature before inoculation. After inoculation, the flasks were placed in a constant temperature shaking incubator at 28°C and 150 r / min for 5 days. After incubation, the culture medium became yellowish-brown and turbid. Microscopic examination revealed numerous conidia and hyphal fragments; this was the *Penicillium wani* spore suspension, ready for use.

[0051] Step S4 involves constructing a biochar-composite microbial remediation system: 100g of functionalized biochar matrix is ​​placed in a sterilized 2000ml beaker, and sterile water is added to adjust the moisture content to 35%. Then, a suspension of *Streptomyces griseus* bacteria and *Paecilomyces wani* spores are mixed at a 1:1 ratio (equal effective viable cell count) and added to the beaker. The functionalized biochar matrix is ​​then mixed with the composite microbial suspension to achieve a final inoculum size of 10g. 9 CFU / g biochar matrix was stirred evenly with a sterile glass rod and placed in a sterile polypropylene tray, spreading it to a thickness of 3 cm. It was then incubated statically at 26℃ for 4 days. During the incubation period, the material was turned once daily with a sterile glass rod to ensure adequate oxygen supply. After colonization of *Streptomyces griseus* and *Paecilomyces wani*, the colonization density of these fungi in the functionalized biochar matrix was detected using fluorescence microscopy. The specific detection method was as follows: 1 g of the colonized functionalized biochar matrix was placed in 9 ml of sterile physiological saline, eluted by shaking for 30 min, and then serially diluted. 10... -5 ~10 -70.1 ml of each dilution solution was spread onto Gao's No. 1 solid culture medium plates and incubated at 28°C for 7–10 days. Colony-forming units of *Streptomyces griseus* and *Paecilomyces wani* were counted separately, and the total colony density was determined to be 2.3 × 10⁻⁶. 7 CFU / g biochar matrix. For fluorescence microscopy, live cells were stained with a staining solution, and the intensity of green fluorescence was observed under a fluorescence microscope after staining to determine the colonization status of *Streptomyces griseus* and *Paecilomyces wani*.

[0052] Other conditions and methods are the same as in Example 1.

[0053] Example 5 In step S4, the functionalized biochar matrix is ​​mixed with the composite bacterial suspension and stirred evenly with a sterile glass rod. The mixture is then placed in a vacuum desiccator with a vacuum degree of -0.09 MPa for 30 minutes, using negative pressure to allow the bacterial suspension to penetrate deeper into the biochar. After removal, the mixture is gently stirred with 50 ml of a 2% (w / v) sodium alginate solution to uniformly coat the surface of the biochar particles with an alginate film. This mixture is then slowly dripped into a 3% (w / v) calcium chloride solution and cross-linked and cured at room temperature for 30 minutes, forming spherical particles with a diameter of approximately 3-5 mm. These particles are then washed three times with sterile deionized water.

[0054] Other conditions and methods are the same as in Example 4.

[0055] Comparative Example 1 Select a lead-cadmium contaminated soil of the same area as in Example 1, and apply an equal amount of unfunctionalized biochar (pyrolysis temperature 400℃, pyrolysis time 3h, without impregnation with impregnation solution), at a rate of 350g / m². 2 The same layered application method and tillage depth were used, and the same density and variety of Sedum aizoon were planted. The same water and fertilizer management was applied during the growing season. After 150 days of growth, the plants were harvested and soil samples were collected for comparative analysis with Examples 1-5.

[0056] The comparison data of the repair effects of Examples 1-5 and Comparative Example 1 are shown in the table below: The data in the table clearly shows that: 1. Example 1, employing the technical solution of this invention, significantly outperforms Comparative Example 1 in various indicators, including soil lead and cadmium removal rate, heavy metal content in the aboveground parts of plants, and plant biomass. The soil lead removal rate increased from 28.6% to 52.3%, an increase of 82.9%; the soil cadmium removal rate increased from 35.2% to 61.8%, an increase of 75.6%. The lead content in the aboveground parts of plants increased from 198.3 mg / kg to 386.5 mg / kg, an increase of 94.9%; the cadmium content in the aboveground parts of plants increased from 15.7 mg / kg to 28.4 mg / kg, an increase of 80.9%. Plant biomass increased from 31.2 g / plant to 42.6 g / plant, an increase of 36.5%. These data fully verify the synergistic effect of the technical solution of this invention.

[0057] 2. The results of Example 2 show that using black nightshade as a hyperaccumulating plant can also achieve good restoration effects, verifying the universality of the technical solution of the present invention.

[0058] 3. The soil lead removal rate in Example 3 was 57.8%, an increase of 10.5% compared to 52.3% in Example 1; the soil cadmium removal rate was 68.5%, an increase of 10.8% compared to 61.8% in Example 1; the lead content in the aboveground parts of the plants increased from 386.5 mg / kg to 412.3 mg / kg, an increase of 6.7%; the cadmium content in the aboveground parts of the plants increased from 28.4 mg / kg to 36.2 mg / kg, an increase of 27.5%. The use of calcium-phosphorus-iron-sulfur multi-effect synergistic impregnation effectively addresses the shortcomings of insufficient cadmium fixation capacity of single phosphate, achieving a balanced improvement in the efficiency of simultaneous lead and cadmium remediation.

[0059] 4. In Example 4, the soil lead removal rate was 56.5%, an increase of 8.0% compared to 52.3% in Example 1; the soil cadmium removal rate was 66.2%, an increase of 7.1% compared to 61.8% in Example 1; the lead content in the aboveground parts of the plants increased from 386.5 mg / kg to 408.6 mg / kg, an increase of 5.7%; and the cadmium content in the aboveground parts of the plants increased from 28.4 mg / kg to 34.8 mg / kg, an increase of 22.5%. These results fully verify the significant advantages of the compound microbial agent in terms of complementary functions of growth promotion and activation.

[0060] 5. In Example 5, the soil lead removal rate was 63.2%, the soil cadmium removal rate was 74.6%, the lead content in the aboveground parts of the plants was 435.8 mg / kg, the cadmium content in the aboveground parts of the plants was 41.5 mg / kg, and the plant biomass was 48.6 g / plant. Compared with Example 1, the lead removal rate increased by 20.8%, the cadmium removal rate increased by 20.7%, the lead content in the plants increased by 12.8%, the cadmium content in the plants increased by 46.1%, and the plant biomass increased by 14.1%. Compared with Example 4, the lead removal rate increased by 11.9%, the cadmium removal rate increased by 12.7%, and the cadmium content in the plants increased by 19.3%. These results indicate that the encapsulation structure prolongs the effective working time of functional microorganisms, thereby significantly improving the heavy metal removal efficiency.

[0061] Example 6 (Verification of the effect of actinomycete colonization density on remediation effect) Based on Example 1, a comparative experiment was conducted with different actinomycete colonization densities. The experiment included three treatment groups: the first group had a colonization density of 5.2 × 10⁻⁶. 6 The colonization density of the second group was 2.3 × 10⁻⁶ CFU / g biochar substrate. 7 CFU / g biochar substrate (Example 1), the colonization density of the third group was 8.7 × 10⁻⁶. 7 CFU / g biochar matrix, with other conditions kept constant. Results after 150 days of remediation showed that the removal rates of lead and cadmium in the soil and the accumulation of heavy metals in plants both increased with increasing actinomycete colonization density. The third treatment achieved a lead removal rate of 58.6% and a cadmium removal rate of 68.5% in the soil, both higher than the 41.2% and 48.3% of the first treatment. This confirms that actinomycete colonization density has a positive impact on remediation effectiveness; however, considering cost factors, this invention preferably uses a colonization density of not less than 10. 7 CFU / g biochar matrix.

[0062] Example 7 (Verifying the impact of layered application method on repair effect) Based on Example 1, while maintaining the same total application amount of composite remediation material, two treatment methods were compared: whole-layer application and layered application. The whole-layer application method involved uniformly spreading the composite remediation material onto the soil surface in one go, followed by tilling and mixing to a depth of 30 cm. The layered application method was performed as in Example 1. The heavy metal distribution analysis results of the soil profile after remediation showed that the lead and cadmium content in all soil layers (0-35 cm) of the layered application group was lower than that of the whole-layer application group, and the content differences between soil layers were more gradual. This indicates that the layered application method is beneficial for achieving a three-dimensional uniform distribution of the remediation material in the soil profile, improving the remediation efficiency for soil layers at different depths.

[0063] Example 8 (Verification of the effect of two rounds of continuous repair) After the first round of remediation (Example 1), the lead content in the soil decreased to 231 mg / kg and the cadmium content decreased to 1.2 mg / kg, but this still did not reach the target remediation values ​​(lead content below 150 mg / kg and cadmium content below 0.6 mg / kg). Therefore, a second crop was planted and harvested 75 days after the first harvest, with the same planting and management methods as the first round. The second crop was harvested after 150 days of growth. Soil testing after the second harvest showed that the lead content decreased to 118 mg / kg and the cadmium content decreased to 0.48 mg / kg, achieving the expected remediation target. The cumulative removal rates of lead and cadmium after the two rounds of remediation were 75.7% and 85.0%, respectively, indicating that the technical solution of this invention can achieve deep remediation of soil with high concentrations of lead and cadmium contaminated by multiple rounds of continuous treatment.

[0064] Example 9 (Verification of system optimization parameters for functionalized biochar matrix) Corn stalks and peanut shells were used as biomass raw materials to prepare biochar matrices at different pyrolysis temperatures (300℃, 350℃, 400℃, 450℃, and 500℃). These matrices were then functionalized by impregnation with calcium dihydrogen phosphate, with other conditions identical to step S2 in Example 1. The adsorption capacity of the functionalized biochar matrices for lead and cadmium was tested using a batch equilibrium adsorption experiment. Specifically, 0.5000 g of the functionalized biochar matrices was placed in a 100 mL polyethylene centrifuge tube, and 50 mL of a simulated soil solution containing lead or cadmium (initial lead concentration of 100 mg / L and initial cadmium concentration of 10 mg / L) was added. The mixture was shaken at 150 r / min for 24 h at 25℃. After centrifugation, the supernatant was collected to determine the residual lead and cadmium concentrations, and the adsorption capacity was calculated. Test results showed that the functionalized biochar matrix prepared from corn stalks under pyrolysis conditions at 400℃ had an adsorption capacity of 38.6 mg / g for lead and 8.2 mg / g for cadmium. The functionalized biochar matrix prepared from peanut shells under the same conditions had an adsorption capacity of 35.2 mg / g for lead and 7.8 mg / g for cadmium. Ordinary biochar without functionalization (without calcium dihydrogen phosphate impregnation) had an adsorption capacity of 24.3 mg / g for lead and 6.1 mg / g for cadmium. Functionalization increased the adsorption capacity of biochar for lead by 44.9%–58.8% and for cadmium by 27.9%–34.4%.

[0065] Example 10 (Verification of the function of two actinomycete strains and Paecilomyces wani) Comparative tests were conducted using *Streptomyces griseus* and *Streptomyces thaliana*. The abilities of the two actinomycetes to produce indoleacetic acid (IAA), ACC deaminase, and siderophore were determined. IAA was determined using high-performance liquid chromatography (HPLC). The actinomycete strains were inoculated into acid-producing medium and cultured for 7 days. After centrifugation, the supernatant was extracted with ethyl acetate and separated using a C18 reversed-phase column. Detection was performed at 280 nm using the external standard method. ACC deaminase activity was determined using the indophenol blue colorimetric method. The enzyme activity unit was defined as the amount of enzyme required to catalyze the production of 1 micromole of α-ketobutyrate per minute under given conditions. Qualitative detection of siderophores was performed using the CAS plate assay. After 7 days of culture, the formation of orange halos on the plates was observed. The results showed that *Streptomyces griseus* produced 12.8 μg / mL of IAA and had an ACC deaminase activity of 0.42 units / mL; *Streptomyces thaliana* produced 15.3 μg / mL of IAA and had an ACC deaminase activity of 0.38 units / mL. Both actinomycetes were able to produce siderophores, forming distinct orange halos on CAS plates. There was no significant difference in plant growth-promoting effects between the two strains, and both are suitable for the technical solution of this invention.

[0066] Siderophore production capacity determination of *Paecilomyces wani*: Quantitative detection was performed using the CAS method. *Paecilomyces wani* spore suspension was inoculated into iron-limited medium and cultured at 28℃ for 5 days. After centrifugation, the supernatant was mixed with an equal volume of CAS detection solution, and after standing for 1 hour, the absorbance at 630 nm was measured. Uninoculated medium served as a control. The siderophore unit was calculated using the formula: (control absorbance - sample absorbance) / control absorbance × 100%. The results showed that *Paecilomyces wani* produced 82.5% siderophore units, classifying it as a high-siderophore-producing strain. Qualitative detection using CAS: After 5 days of plate culture, a distinct orange halo formed around the *Paecilomyces wani* colonies, further validating its efficient siderophore secretion capacity.

[0067] Example 11 (Verifying the stability of the composite repair system) Based on Example 1, a comparative experiment was conducted with and without calcium alginate embedding and with and without the planting of hyperaccumulating plants to verify the effects of the stratified loading structure and the planting of hyperaccumulating plants on improving the field survival rate of the compound bacteria. Treatment group A was the complete scheme of Example 1 (including the calcium alginate embedding stratified loading structure), treatment group B omitted the calcium alginate embedding step (only vacuum negative pressure infiltration and static culture were performed), and treatment group C omitted the step of sowing or transplanting Sedum aizoon, with other conditions being the same. The survival rate of the compound bacteria in the soil environment of the three groups of biochar-compound bacteria composite remediation materials was tracked and monitored for 180 days. Soil samples were taken every 30 days after the application of the composite remediation materials, and the number of surviving compound bacteria was detected by fluorescence microscopy and plate counting method. The results showed that in treatment group A, the number of surviving compound bacteria increased from the initial 2.3 × 10⁻⁶. 7The CFU / g biochar matrix gradually decreased to 8.6 × 10⁻⁶ on day 180. 5 The CFU / g biochar matrix showed a survival rate of approximately 3.7%, maintaining basic functional expression. In treatment group B, the number of surviving cells was 3.2 × 10⁻⁶ on day 180. 5 CFU / g biochar matrix. In treatment group C, the number of viable bacteria decreased more significantly, reaching 2.1 × 10⁻⁶ on day 180. 4 CFU / g biochar matrix. This result indicates that the unencapsulated compound bacteria suffered significant soil environmental impact in the early stages of application, with some bacteria dying rapidly due to direct exposure to heavy metal toxicity and competition from indigenous microorganisms. This verifies the key role of the stratified loading structure design in improving the field colonization and survival rate of the compound bacteria. The planting of hyperaccumulating plants provided continuous rhizosphere nutrition and niche support for the slowly released compound bacteria, ensuring that they could maintain effective functional expression in the later stages of remediation. Their root exudates played a positive role in maintaining the survival of the compound bacteria, confirming the synergistic mechanism between the stratified loading structure and plant planting.

[0068] In practical field application and promotion, the technical solution of this invention can be implemented according to the following large-scale steps. First, site surveys and soil sampling tests are conducted to determine the degree of pollution and remediation targets. Then, functionalized biochar matrix and actinomycete inoculants are prepared in batches according to the method described in this invention. The quality control indicators of the preparation process include biochar particle size distribution, uniformity of calcium dihydrogen phosphate impregnation, and viable actinomycete count. Subsequently, the composite remediation material is applied mechanically, using a backpack fertilizer spreader or a self-propelled fertilizer spreader. Tillage and mixing are carried out using a conventional rotary tiller or plow. Finally, mechanized planting or transplanting of hyperaccumulating plants is carried out, with water and fertilizer management during the growth period according to the set plan. The length of the entire remediation cycle depends on the degree of soil pollution and remediation targets, generally requiring 2-4 rounds of planting and harvesting to achieve the expected remediation effect.

[0069] Those skilled in the art should adjust the relevant parameters appropriately according to specific site conditions and pollution levels when implementing the technical solution of this invention. Soil pH has a significant impact on remediation effectiveness. When the soil pH is below 5.5, it is recommended to apply lime for alkali adjustment before applying the composite remediation material to bring the soil pH to above 6.0, which is beneficial for the stable formation of lead phosphate precipitates in the functionalized biochar matrix. When the soil organic matter content is below 10 g / kg, it is recommended to appropriately increase the application rate of the composite remediation material to 500 g / m³. 2This is to compensate for the impact of insufficient soil organic matter content on the remediation effect. When the total lead and cadmium content exceeds 500 mg / kg and 5 mg / kg respectively, it is recommended to use a multi-round continuous remediation method for deep treatment, with an interval of 60-90 days between each round. The selection of actinomycete strains is not limited to *Streptomyces griseus* and *Streptomyces thaliana*; other actinomycete strains that can produce indoleacetic acid and ACC deaminase are also suitable for the technical solution of this invention. The selection of hyperaccumulating plants is not limited to *Sedum aizoon* and *Solanum nigrum*; other reported lead and cadmium hyperaccumulating plants such as *Mustardrum sativum* and *Viola baoshanense* can be applied within the technical framework of this invention.

[0070] In summary, the biochar and actinomycete combined phytoremediation method for lead-cadmium co-contaminated soil provided by this invention selectively immobilizes lead and adsorbs and activates cadmium through the phosphorus-containing functional layer of the functionalized biochar matrix; promotes root growth and development and regulates the effective concentration of heavy metals in the soil through plant growth-promoting substances and iron carriers produced by actinomycetes; ensures the functional stability of actinomycetes in complex soil environments through spatial isolation protection of the biochar-actinomycete composite remediation system; and achieves three-dimensional uniform distribution of the remediation material in the soil profile through layered application, ultimately achieving safe and efficient remediation of lead-cadmium co-contaminated soil. The comparative data from the examples and comparative examples fully verify the significant advantages of the technical solution of this invention, providing a new technical approach for the remediation of lead-cadmium co-contaminated soil.

[0071] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for combined biochar and actinomycete phytoremediation of lead-cadmium contaminated soil, comprising applying a biochar-actinomycete composite remediation material to the lead-cadmium contaminated soil for remediation, characterized in that, The preparation of the biochar-actinomycete composite remediation material includes the following steps: A biochar-actinomycete composite remediation system was constructed by mixing a functionalized biochar matrix with a bacterial suspension, wherein the bacterial suspension included actinomycetes, and the inoculum amount of the actinomycetes was 10. 8 ~10 10 CFU / g biochar matrix yields biochar-actinomycete composite remediation material.

2. The combined biochar and actinomycete phytoremediation method according to claim 1, characterized in that, The bacterial suspension also includes *Paecilomyces wanensis*, and the total inoculum of the complex bacteria consisting of actinomycetes and *Paecilomyces wanensis* is 10. 8 ~10 10 CFU / g biochar matrix.

3. The combined biochar and actinomycete phytoremediation method according to claim 1, characterized in that, In the biochar-actinomycete composite remediation material, the colonization density of actinomycetes in the biochar is ≥10. 7 CFU / g biochar matrix.

4. The combined biochar and actinomycete phytoremediation method according to claim 1, characterized in that, The actinomycetes are selected from either *Streptomyces griseus* or *Streptomyces thaliana*.

5. The combined biochar and actinomycete phytoremediation method according to claim 1, characterized in that, After mixing, the mixture is placed in a negative pressure environment for 20-40 minutes; after removal, the mixture is mixed with a sodium alginate solution with a concentration of 1-3% (w / v), and then dropped into a calcium chloride solution with a concentration of 2-4% (w / v), reacted for 20-40 minutes, and then washed.

6. The combined biochar and actinomycete phytoremediation method according to claim 1, characterized in that, The preparation of the biochar-actinomycete composite remediation material also includes the following steps: The preparation of functionalized biochar matrix includes an impregnation functionalization stage, in which the crude biochar is placed in an impregnation solution comprising a calcium dihydrogen phosphate solution with a concentration of 0.5-2 mol / L, and the impregnation treatment is carried out for 12-24 hours at an impregnation temperature of 25℃-35℃ to obtain the functionalized biochar matrix.

7. The combined biochar and actinomycete phytoremediation method according to claim 6, characterized in that, The impregnation solution also includes a composite solution of 0.1-0.5 mol / L sodium thiosulfate and 0.1-0.5 mol / L ferrous sulfate.

8. The combined biochar and actinomycete phytoremediation method according to claim 1, characterized in that, It also includes the following steps: Hyperaccumulating plants were selected as remediation plants, and the biochar-actinomycete composite remediation material was applied to the top 0-20cm soil layer of the contaminated soil at a rate of 200-500 g / m². 2 After application, till and mix thoroughly, then sow or transplant hyperaccumulating plants. Harvest the plants after 120-180 days of growth.

9. The combined biochar and actinomycete phytoremediation method according to claim 8, characterized in that, The biochar-actinomycete composite remediation material is applied in layers: first, 50-70% of the total amount of composite remediation material is evenly spread on the soil surface, and then the soil is tilled and mixed for the first time at a depth of 15-20cm; then, 30-50% of the total amount of composite remediation material is spread on the tilled soil surface, and the soil is tilled and mixed for the second time at a depth of 25-35cm.

10. The combined biochar and actinomycete phytoremediation method according to claim 8, characterized in that, The hyperaccumulating plants are Sedum aizoon or Solanum nigrum, with the planting density of Sedum aizoon being 15-25 plants / m². 2 The planting density of the black nightshade is 10-20 plants / m². 2 .

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