A preparation method of a novel environment-friendly fertilizer capable of reducing soil pollution

Abstract

The application relates to the field of agricultural environmental protection technology, in particular to a preparation method of a novel environment-friendly fertilizer capable of reducing soil pollution. 8 The raw material composition comprises, by weight, 50 parts of corn straw biochar, 20 parts of humic acid, 5 parts of bacillus subtilis inoculum with a viable bacterial count of 10 CFU / g, 3 parts of amino acid chelated zinc, 2 parts of sodium carboxymethyl cellulose and 18 parts of deionized water; the application can simultaneously act on heavy metals and organic pollutants in the soil by optimizing the composition of the microbial inoculum and combining with the specific pretreated adsorption carrier, can enhance the fixing capacity for the heavy metals and efficiently degrade the organic pollutants, solves the defects of single pollution reduction function of the existing fertilizer, can effectively cope with the composite pollution scene, and significantly widens the pollution reduction application range of the product.

Description

Technical Field

[0001] This invention relates to the field of agricultural environmental protection technology, specifically to a method for preparing a novel environmentally friendly fertilizer that can reduce soil pollution. Background Technology

[0002] Soil pollution is becoming increasingly prominent in current agricultural production, with complex pollution scenarios involving heavy metals and organic pollutants being common, severely impacting soil ecological functions and crop safety. Existing fertilizer products have significant shortcomings in soil pollution remediation, specifically:

[0003] The pollution reduction function is singular, and the scope of application is limited. Most pollution-reducing fertilizers can only perform simple adsorption of heavy metals or have a certain degradation effect on specific organic pollutants. They are unable to simultaneously address the complex pollution of heavy metals and organic pollutants coexisting in the soil, and cannot meet diverse pollution control needs. Pollution reduction stability is poor, and the risk of secondary pollution is high. Although some fertilizers have a certain pollutant adsorption capacity, the adsorbed pollutants are easily desorbed and released back into the soil when environmental conditions change, such as soil moisture and pH fluctuations, leading to secondary pollution and failing to achieve long-term stable pollution reduction effects. The synergy between pollution reduction and production needs is neglected. Traditional fertilizers often focus on single-effect fertilizer supply, and some pollution-reducing products may even inhibit crop growth. At the same time, most products cannot improve soil acid-base imbalance and fertility decline, making it difficult to meet the comprehensive needs of soil pollution control, crop yield increase, and soil improvement, which does not conform to the goals of sustainable agricultural production. Insufficient adsorption carrier performance restricts pollution reduction efficiency. The adsorption carriers commonly used in existing fertilizers have low adsorption capacity due to the large amount of ash impurities attached to their surfaces and the limited internal pore structure. This results in insufficient adsorption capacity for pollutants, further limiting the overall pollution reduction efficiency and failing to provide an efficient solution for soil pollution remediation. Summary of the Invention

[0004] The primary objective of this invention is to provide a method for preparing a novel environmentally friendly fertilizer that can reduce soil pollution.

[0005] A further objective of this invention is to provide a method for preparing a novel environmentally friendly fertilizer that can reduce soil pollution.

[0006] A method for preparing a novel environmentally friendly fertilizer that can reduce soil pollution includes the following raw material composition and preparation steps; the raw material composition, by weight, is 50 parts corn straw biochar, 20 parts humic acid, and 10 parts viable bacteria. 8 The preparation steps include: 5 parts of Bacillus subtilis inoculum (CFU / g), 3 parts of amino acid chelated zinc, 2 parts of sodium carboxymethyl cellulose, and 18 parts of deionized water;

[0007] (1) Biochar pretreatment: Corn straw biochar was placed in a constant temperature drying oven and dried at 105℃ until the moisture content was ≤5%. Then it was crushed by a universal pulverizer and passed through an 80-mesh standard sieve to obtain pretreated biochar.

[0008] (2) Preparation of microbial inoculum: Bacillus subtilis strain was inoculated into LB liquid medium, which consisted of 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride, and a pH of 7.0. The inoculated medium was placed in a constant temperature shaking incubator at 30°C and 180 rpm for 48 h to obtain a viable count of 10. 8 CFU / g of Bacillus subtilis inoculum;

[0009] (3) Preparation of mixed materials: Pretreated biochar, humic acid, amino acid chelated zinc and sodium carboxymethyl cellulose were added to a double helix mixer and mixed at 300 rpm for 15 min at room temperature to form a solid mixed base. Bacillus subtilis inoculant and deionized water were added to the solid mixed base at a uniform speed and mixed at 250 rpm for 20 min to obtain a uniform wet mixed material.

[0010] (4) Granulation and drying: The wet mixture is fed into the extrusion granulator, the granulation temperature is set to 60℃ and the die diameter is 2mm. After extrusion granulation, the granules are placed in a hot air circulating drying oven at 50℃ and dried until the moisture content is ≤8%. After cooling to room temperature, they are screened to obtain basic pollution-reducing and environmentally friendly fertilizer.

[0011] Preferably, the number of viable bacteria in the raw material composition is 10. 8 Replace 5 parts of Bacillus subtilis inoculum with a live bacteria count of 10 CFU / g. 8 Three portions of Bacillus subtilis inoculum with a CFU / g concentration and a live bacteria count of 10... 8 The combination of two parts of Pseudomonas aeruginosa inoculum agent with CFU / g; the preparation method of the Pseudomonas aeruginosa inoculum agent is to inoculate the Pseudomonas aeruginosa strain into LB liquid medium, the LB liquid medium being composed of 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride and pH 7.0, and then placing the inoculated medium in a constant temperature shaking incubator at 30℃ and 180 rpm for 48 h.

[0012] Preferably, the pretreatment step of the biochar is adjusted as follows: corn straw biochar is placed in a 1 mol / L hydrochloric acid solution and soaked at room temperature for 2 hours, with stirring once every 30 minutes during the soaking period; after soaking, the biochar is repeatedly rinsed with deionized water until the pH value of the eluent is 7.0, and then the rinsed biochar is placed in a 105℃ constant temperature drying oven to dry until the moisture content is ≤5%, and then crushed with a universal pulverizer and passed through an 80-mesh standard sieve to obtain acid-washed activated biochar.

[0013] Preferably, 2 parts of disodium ethylenediaminetetraacetate are added to the raw material composition, and the amount of deionized water is adjusted to 16 parts. In the preparation step of the mixture, disodium ethylenediaminetetraacetate, acid-washed activated biochar, humic acid, amino acid chelated zinc, and sodium carboxymethyl cellulose are added to a double helix mixer and mixed together with other solid raw materials.

[0014] Preferably, the amino acid chelated zinc is added to the twin-helix mixer simultaneously with the pretreated biochar, humic acid, and sodium carboxymethyl cellulose in the mixture preparation step.

[0015] Preferably, the Bacillus subtilis inoculant and the Pseudomonas inoculant are added together at a uniform rate to the solid mixed base during the preparation step of the mixed material.

[0016] Preferably, in the microbial agent preparation step, the oscillation speed of the constant temperature oscillation incubator is maintained at 180 rpm, and the incubation temperature is maintained at 30°C.

[0017] Preferably, in the granulation and drying steps, the die diameter of the extrusion granulator is set to 2 mm, and the granulation temperature is set to 60°C.

[0018] Preferably, the hydrochloric acid solution is used to soak the biochar for 2 hours, with stirring every 30 minutes to ensure uniform soaking.

[0019] Preferably, the disodium ethylenediaminetetraacetate, acid-washed activated biochar, humic acid, amino acid chelated zinc, and sodium carboxymethyl cellulose are mixed at room temperature and at a speed of 300 rpm for 15 minutes.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. This invention optimizes the composition of microbial agents and combines them with a pretreated adsorption carrier to simultaneously target heavy metals and organic pollutants in the soil. It enhances the fixation capacity for heavy metals and efficiently degrades organic pollutants, overcoming the shortcomings of existing fertilizers with only one pollution reduction function. It can effectively address complex pollution scenarios and significantly broaden the scope of application for pollution reduction of the product.

[0022] 2. On the one hand, this invention effectively removes surface ash impurities and expands the internal pore structure of biochar by performing specific pretreatment, thereby significantly improving adsorption capacity and adsorption efficiency. On the other hand, it introduces an environmentally friendly chelating agent to form an adsorption and chelation synergistic mechanism with the adsorption carrier, which can firmly fix pollutants and prevent them from desorbing when the soil environment changes, thereby achieving a long-term stable pollution reduction effect and completely eliminating the risk of secondary pollution.

[0023] 3. This invention uses humic acid and amino acid components to construct an environmentally friendly nutrient system. While efficiently reducing pollution, it can provide sufficient and high-quality nutrients for crop growth, effectively promoting crop growth and solving the problem of traditional pollution reduction products easily "suppressing yield". At the same time, it can adjust the soil pH value to a suitable range for crop growth, improve key fertility indicators such as soil urease activity, improve soil ecological structure, enhance soil sustainable production capacity, and achieve a triple synergy of pollution control, yield increase and soil improvement.

[0024] 4. The raw materials used in this invention are widely available and cost-controllable. The preparation process is clear and easy to operate, without relying on complex or special equipment, and is easy to scale up. The product has significant technical advantages in terms of pollution reduction, fertilizer supply, and soil improvement. It can effectively solve the pain points of existing technologies, meet the actual needs of agricultural environmental protection and production, and has good prospects for industrial application and promotion value. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0026] Example 1:

[0027] The specific steps are as follows:

[0028] Raw material composition (by weight): 50 parts corn stalk biochar, 20 parts humic acid, and 10 live bacteria. 8 Five parts of Bacillus subtilis inoculant (CFU / g), three parts of amino acid chelated zinc, two parts of sodium carboxymethyl cellulose, and 18 parts of deionized water.

[0029] Preparation steps:

[0030] (1) Biochar pretreatment: Corn straw biochar was placed in a constant temperature drying oven and dried at 105℃ until the moisture content was ≤5%. Then it was crushed with a universal pulverizer and passed through an 80-mesh standard sieve to obtain pretreated biochar.

[0031] (2) Preparation of microbial inoculum: Bacillus subtilis strain was inoculated into LB liquid medium, which consisted of 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride, and a pH of 7.0. The inoculated medium was placed in a constant temperature shaking incubator at 30°C and 180 rpm for 48 h to obtain a viable count of 10. 8 Bacillus subtilis inoculum agent at CFU / g.

[0032] (3) Preparation of the mixture: Pretreated biochar, humic acid, amino acid chelated zinc, and sodium carboxymethyl cellulose were added together to a twin-helix mixer and mixed at 300 rpm for 15 min at room temperature to form a solid mixture. Bacillus subtilis inoculant and deionized water were added to the solid mixture at a uniform speed and mixed at 250 rpm for 20 min to obtain a uniform wet mixture.

[0033] (4) Granulation and drying: The wet mixture is fed into an extrusion granulator. The granulation temperature is set to 60℃ and the die diameter is 2mm. After extrusion granulation, the granules are placed in a hot air circulating drying oven at 50℃ and dried until the moisture content is ≤8%. After cooling to room temperature, they are screened to obtain basic pollution-reducing and environmentally friendly fertilizer.

[0034] In addition, corn stalk biochar is prepared by pyrolyzing corn stalks at 500-600℃ in an inert gas atmosphere for 2 hours, with a carbonization rate of ≥35% and a specific surface area of ​​140-160 m² before pretreatment. 2 / g, ash content ≤8%;

[0035] Humic acid: derived from lignite, purified by alkali dissolution and acid precipitation, with a humic acid purity ≥85%, organic matter content ≥90%, and pH value 7.0-8.0.

[0036] Example 2:

[0037] Based on the technical solution of Example 1, the single Bacillus subtilis inoculant in Example 1 mainly plays a role in heavy metal passivation and soil microbial community regulation, but its ability to degrade polycyclic aromatic hydrocarbon organic pollutants in the soil is limited, and it cannot cope with the combined pollution scenarios of heavy metals and organic pollutants. Therefore, Example 2 optimizes the composition of the microbial inoculant, while the dosage of other raw materials and preparation steps are completely consistent with Example 1, with the specific adjustments as follows:

[0038] Raw material adjustment (microbial agent optimization only): The viable count in Example 1 was increased to 10. 8 Five doses of Bacillus subtilis inoculum with a CFU / g concentration were replaced with a live bacteria count of 10. 8 Three portions of Bacillus subtilis inoculum with a CFU / g concentration and a live bacteria count of 10... 8 The combination of two CFU / g Pseudomonas inoculum agents. The preparation method of the Pseudomonas inoculum agent is the same as that of the Bacillus subtilis inoculum agent, which is also carried out by shaking culture in LB liquid medium at 30°C and 180 rpm for 48 h.

[0039] Pseudomonas has a specific ability to degrade polycyclic aromatic hydrocarbon organic pollutants in soil. It works synergistically with the heavy metal passivation function of Bacillus subtilis to achieve dual pollution reduction of heavy metals and organic pollutants in soil at the same time. This effectively makes up for the deficiency of insufficient degradation ability of organic pollutants in Example 1 and broadens the scope of application of fertilizer for pollution reduction.

[0040] Furthermore, the strain of Bacillus subtilis is Bacillus subtilis, which has the ability to passivate lead and cadmium ions. After being cultured in LB liquid medium for 48 hours, the viable count stabilized at 10. 8 CFU / g; This strain can achieve a degradation rate of over 60% for polycyclic aromatic hydrocarbons (PAHs) within 48 hours at 30℃, and has no antagonistic effect when combined with Bacillus subtilis.

[0041] Example 3:

[0042] Based on the technical solution of Example 2, the pretreated biochar used in Example 2 is a conventionally dried and pulverized product. Its surface is covered with ash impurities and its pore structure is limited, resulting in insufficient adsorption capacity for heavy metal ions and organic pollutant molecules, thus affecting the overall pollution reduction efficiency. Therefore, Example 3 optimizes the biochar pretreatment process. The remaining raw material amounts and preparation steps are completely consistent with Example 2, with the specific adjustments as follows:

[0043] Optimization of biochar pretreatment: The biochar pretreatment steps in Example 2 were adjusted as follows: First, corn stalk biochar was placed in a 1 mol / L hydrochloric acid solution and soaked at room temperature for 2 hours, stirring once every 30 minutes to ensure uniform acid washing. After soaking, the biochar was repeatedly rinsed with deionized water until the pH of the eluent was 7.0. Then, the rinsed biochar was placed in a 105℃ constant temperature drying oven and dried until the moisture content was ≤5%. Subsequently, it was pulverized using a universal pulverizer and passed through an 80-mesh standard sieve to obtain acid-washed activated biochar.

[0044] Hydrochloric acid washing can effectively remove ash impurities adhering to the surface of biochar, while expanding its internal pore structure, increasing the specific surface area of ​​the biochar from 150 m² in Example 2. 2 / g increased to 280m 2 / g increases the adsorption sites for heavy metal ions (such as lead ions and cadmium ions) and organic pollutant molecules, further improving the fertilizer's adsorption efficiency for pollutants and enhancing the pollution reduction effect.

[0045] Example 4:

[0046] Based on the technical solution of Example 3, which uses acid washing to activate biochar to achieve efficient adsorption of pollutants, the adsorbed heavy metal ions are prone to desorption when soil moisture changes or pH fluctuates, leading to the risk of secondary pollution. Therefore, Example 4 enhances the stabilization effect of heavy metals by adding an environmentally friendly chelating agent. The remaining preparation steps are completely consistent with Example 3, with the specific adjustments as follows:

[0047] Raw material adjustment (addition of chelating agent): Based on the raw materials in Example 3, 2 parts of disodium ethylenediaminetetraacetate were added. To ensure consistent moisture content of the mixture to meet granulation requirements, the amount of deionized water was simultaneously adjusted to 16 parts. In the mixture preparation step, disodium ethylenediaminetetraacetate, along with acid-washed activated biochar, humic acid, amino acid chelated zinc, and sodium carboxymethyl cellulose, were added to a twin-screw mixer to participate in the mixing with other solid raw materials.

[0048] Disodium EDTA can form stable chelates with free lead and cadmium ions in the soil, preventing them from being absorbed by plants or migrated with water. This chelation effect synergizes with the adsorption of acid-washed activated biochar, constructing a multi-layered heavy metal control mechanism of adsorption, chelation, and fixation. This effectively solves the problem of easy desorption of heavy metals after adsorption in Example 3, achieving a comprehensive and stable pollution reduction effect.

[0049] Disodium ethylenediaminetetraacetate: analytical grade, purity ≥99%, chelating capacity ≥220mg / g (calculated as CaCO3).

[0050] Comparative Example 1: Fertilizer Preparation Without Biochar

[0051] This comparative example is used to verify the core role of biochar as an adsorption carrier. Its raw material composition and preparation steps are missing only the acid-washed and activated biochar in Example 4, as follows:

[0052] Raw material composition (by weight): 20 parts humic acid, 10 live bacteria 8 Three portions of Bacillus subtilis inoculum agent with a CFU / g concentration and a viable count of 10cFU / g 8 The mixture consists of 2 parts CFU / g Pseudomonas inoculum, 3 parts amino acid chelated zinc, 2 parts sodium carboxymethyl cellulose, 2 parts disodium EDTA, and 60 parts deionized water. The amount of deionized water was increased to 60 parts to compensate for the volume loss caused by the missing biochar, ensuring the mixture reaches the same moisture level as in Example 4, thus meeting the requirements for subsequent granulation.

[0053] Preparation steps: The preparation steps are completely consistent with those in Example 4, except that the biochar pretreatment step is removed. Humic acid, amino acid chelated zinc, sodium carboxymethyl cellulose, and disodium EDTA from the above raw materials are directly added to a double helix mixer. The subsequent microbial agent addition, mixing, granulation, and drying steps are the same as in Example 4.

[0054] Comparative Example 2: Fertilizer Preparation Without Microbial Agents

[0055] This comparative example is used to verify the key role of the compound microbial agent in the degradation of organic pollutants and the regulation of soil microbial communities. Its raw material composition and preparation steps are missing only the compound microbial agent in Example 4, as follows:

[0056] Raw material composition (by weight): 50 parts acid-washed activated corn stalk biochar, 20 parts humic acid, 3 parts amino acid chelated zinc, 2 parts sodium carboxymethyl cellulose, 2 parts disodium EDTA, and 20 parts deionized water. The amount of deionized water was adjusted to 20 parts to compensate for the reduced liquid volume due to the absence of microbial inoculants, ensuring that the moisture content of the mixture was consistent with that in Example 4.

[0057] Preparation steps: The preparation steps are completely consistent with those in Example 4, except that the microbial agent preparation step is removed. No microbial agents are added during the preparation of the mixed materials. The remaining biochar pretreatment, solid raw material mixing, granulation and drying steps are the same as those in Example 4.

[0058] Comparative Example 3: Preparation of environmentally friendly fertilizers that replace traditional chemical fertilizers

[0059] This comparative example is used to verify the role of the environmentally friendly nutrient system composed of humic acid and amino acid chelated zinc in the present invention in fertilizer efficiency, soil improvement and synergistic pollution reduction. Its raw material composition is only changed by replacing the environmentally friendly nutrient components in Example 4 with traditional chemical fertilizers, as follows:

[0060] Raw material composition (by weight): 50 parts acid-washed activated corn stalk biochar, 10 parts urea, 8 parts potassium dihydrogen phosphate, 5 parts zinc sulfate, 2 parts sodium carboxymethyl cellulose, 2 parts disodium ethylenediaminetetraacetate, and 16 parts deionized water. Among these, urea, potassium dihydrogen phosphate, and zinc sulfate are traditional fertilizers, and their total weight is consistent with the total weight of humic acid and amino acid chelated zinc in Example 4, ensuring a comparable nutrient supply.

[0061] Preparation steps: The preparation steps are completely consistent with those in Example 4, except that urea, potassium dihydrogen phosphate, and zinc sulfate are used instead of humic acid and amino acid chelated zinc in the preparation of the mixture, and are added to the mixer together with other solid raw materials. All other steps remain unchanged.

[0062] Comparative Example 4: Preparation of fertilizer from unactivated biochar

[0063] This comparative example is used to verify the effect of biochar activation process on adsorption effect. The only difference in raw material composition and preparation steps is that the acid-washed activated biochar in Example 4 is replaced with unactivated biochar, as follows:

[0064] Raw material composition (by weight): exactly the same as in Example 4, namely 50 parts corn straw biochar, 20 parts humic acid, and 10 live bacteria. 8 Three portions of Bacillus subtilis inoculum agent with a CFU / g concentration and a viable count of 10cFU / g 8 Two parts of Pseudomonas aeruginosa inoculum (CFU / g), three parts of amino acid chelated zinc, two parts of sodium carboxymethyl cellulose, two parts of disodium EDTA, and 16 parts of deionized water.

[0065] Preparation steps: The preparation steps are basically the same as those in Example 4, except that the preparation step of "acid washing and activating biochar" is replaced with the pre-treatment biochar preparation step in Example 1. That is, the corn straw biochar is only dried at 105°C and crushed through an 80-mesh sieve, without hydrochloric acid washing and subsequent rinsing steps. All other steps are the same as in Example 4.

[0066] The results of the optimization experiment on the parameters of biomass carbon acid washing are shown in Table 1 below:

[0067]

[0068] The data above shows that soaking in 1 mol / L hydrochloric acid for 2 hours yields the best cost-effectiveness in terms of biochar specific surface area and Pb removal rate. Therefore, this parameter should be selected as in Example 3. Treatment with 1.5 mol / L hydrochloric acid, although increasing the biochar specific surface area (290 m²), also resulted in a lower Pb removal rate. 2 The removal rate of Pb (59.2%) was slightly higher than that of 1.0 mol / L, but there were significant shortcomings:

[0069] (1) The purchase cost of 1.5 mol / L hydrochloric acid is 30% higher than that of 1.0 mol / L, and rinsing to neutral requires an additional 40% of deionized water;

[0070] (2) High concentrations of hydrochloric acid increase the corrosiveness of equipment by 25%, and long-term use will increase production and maintenance costs;

[0071] (3) The marginal gains in Pb removal rate and specific surface area are only 0.5% and 3.6%, respectively, which are far from enough to cover the increase in cost and operating costs. Therefore, soaking in 1 mol / L hydrochloric acid for 2 hours is the most cost-effective method, balancing the pollution reduction effect, production cost and operational feasibility.

[0072] The results of the raw material ratio optimization experiment are shown in Table 2 below:

[0073]

[0074] The data above shows that when 50 parts biochar and 20 parts humic acid are combined, the pollution reduction effect and fertilizer effect are balanced, and the Pb removal rate is 58.7%. Therefore, this ratio was chosen.

[0075] The results of the comparative experiment on the dosage of disodium ethylenediaminetetraacetate are shown in Table 3 below:

[0076]

[0077] The data above shows that 2 parts of disodium EDTA can achieve the lowest desorption rate and the highest fresh weight of wheat, so this dosage was chosen.

[0078] Performance Testing and Results Analysis

[0079] The test conditions are as follows:

[0080] Test soil: Selected composite polluted farmland soil with Pb content of 50 mg / kg, Cd content of 2 mg / kg, Cu content of 30 mg / kg, Zn content of 80 mg / kg, PAHs content of 10 mg / kg (pH=5.8, organic matter content 1.2%).

[0081] Crop planted: wheat. 10 kg of soil was taken from each treatment group and placed in plastic pots (30 cm in diameter and 25 cm in height). 15 seeds were sown in each pot. After emergence, the seedlings were thinned to 10 plants per pot. The growth cycle was 90 days. During this period, the soil moisture content was maintained at 70% of field capacity.

[0082] Fertilizer application rate: Each treatment group was evenly fertilized at a rate of 20g / pot, while the control group (no fertilizer) was not fertilized.

[0083] The test metrics and methods are shown in Table 4 below:

[0084]

[0085] The test results are shown in Table 5 below:

[0086]

[0087] This performance test used farmland soil contaminated with lead, cadmium, copper, zinc, and polycyclic aromatic hydrocarbons as the research object. The soil pH was 5.8 and the organic matter content was 1.2%. Wheat was planted in the soil, and a 90-day growth cycle was set. Each fertilization treatment group was fertilized at a dosage of 20 grams per pot, with the unfertilized group serving as a control. The technical effect of the environmentally friendly fertilizer of this invention was verified through multi-dimensional indicators. The specific analysis is as follows:

[0088] (1) The heavy metal removal rate directly reflects the fertilizer's ability to treat heavy metal pollution in soil. The test results show that the heavy metal removal effect of each example is significantly better than that of the comparative example and the control group, and shows a gradual optimization trend: 1 Comparison between examples: Example 1 uses a single Bacillus subtilis agent and conventional biochar, and its lead, cadmium, copper and zinc removal rates are 42.3%, 38.5%, 35.1% and 32.8%, respectively; Example 2 optimizes the single agent into a compound agent of Bacillus subtilis and Pseudomonas, and the heavy metal removal rate is slightly improved, with lead at 43.1%, cadmium at 39.2%, copper at 36.5% and zinc at 34.2%, reflecting the optimization effect of the compound agent on the microbial environment; Example 3 further uses a single agent of Bacillus subtilis and Pseudomonas, and the heavy metal removal rate is slightly improved, with lead at 43.1%, cadmium at 39.2%, copper at 36.5% and zinc at 34.2%, reflecting the optimization effect of the compound agent on the microbial environment; Example 3 further optimizes the heavy metal removal rate of the single agent into a compound agent of Bacillus subtilis and Pseudomonas, and the heavy metal removal rate is 32.3%, 38.5%, 35.1% and 32.8%, respectively. Replacing the standard biochar with acid-washed activated biochar significantly improved the heavy metal removal rate, with lead at 58.7%, cadmium at 55.3%, copper at 52.8%, and zinc at 49.5%. This indicates that hydrochloric acid washing can remove surface ash from biochar and expand its pore structure, increasing the specific surface area of ​​biochar from 150 square meters per gram to 280 square meters per gram, thus significantly enhancing its adsorption capacity for heavy metal ions. In Example 4, disodium ethylenediaminetetraacetate was added to the biochar based on Example 3, achieving the highest heavy metal removal rate, with lead at 72.5%, cadmium at 68.9%, copper at 65.3%, and zinc at 61.2%. This demonstrates that the chelating agent and activated biochar form an "adsorption-chelation" synergistic mechanism, which can further enhance the heavy metal fixation effect. 2. Comparison with Comparative Examples: Comparative Example 1, lacking biochar, had the lowest heavy metal removal rate, with lead at 21.5%, cadmium at 18.7%, copper at 16.3%, and zinc at 14.5%, only one-third to one-quarter of that in Example 4, indicating that biochar is the core carrier for fertilizer adsorption of heavy metals. Comparative Example 4, using unactivated biochar, had heavy metal removal rates of 50.2% for lead, 45.7% for cadmium, 42.1% for copper, and 38.9% for zinc, significantly lower than Example 3, verifying the key role of biochar activation process in adsorption performance. Comparative Example 3, using traditional fertilizer instead of environmentally friendly nutrients, had heavy metal removal rates of 40.3% for lead, 36.8% for cadmium, 33.2% for copper, and 30.1% for zinc, close to Example 1 but far lower than Example 4, indicating that the environmentally friendly nutrient system composed of humic acid and amino acid chelated zinc can synergistically improve pollution reduction. The control group, without fertilizer, had a heavy metal removal rate of only about 5%, further proving the necessity and effectiveness of the fertilizer of this invention in the treatment of heavy metal pollution.

[0089] (2) As a typical organic pollutant, the degradation rate of polycyclic aromatic hydrocarbons (PAHs) is the core indicator for measuring the ability of fertilizers to cope with compound pollution. The test results highlight the key role of compound microbial agents: 1. Comparison between examples: Example 1 contains only Bacillus subtilis and this bacterium does not have the function of degrading PAHs, so the PAH degradation rate is only 35.2%; Example 2 introduces Pseudomonas and this bacterium can specifically degrade PAHs, so the PAH degradation rate jumps to 62.5%, an increase of 77.6%, which directly proves the ability of Pseudomonas to degrade organic pollutants; Example 3 uses activated biochar, and the PAH degradation rate is 64.1%, which is slightly higher than that of Example 2. The reason is that activated biochar can provide better attachment sites for microorganisms and promote the reproduction of microbial communities; Example 4 adds chelating agents, and the PAH degradation rate is further increased to 78.3%. It is speculated that after the chelating agent fixes heavy metals, it can reduce the toxic inhibition of heavy metals on microorganisms and enhance the activity of microbial communities. 2. Comparison with comparative examples: Comparative example 2, lacking microbial inoculant, had a polycyclic aromatic hydrocarbon (PAH) degradation rate of only 22.3%, far lower than that of the examples, indicating that the compound microbial inoculant is the core functional component for PAH degradation; Comparative example 1, lacking biochar, had a PAH degradation rate of 40.2%, lower than examples 2 to 4, indicating that biochar has an auxiliary synergistic effect on microbial PAH degradation; The control group, without fertilizer, had a PAH degradation rate of only 8.5%, with almost no natural degradation ability, highlighting the significant advantages of the fertilizer of this invention for the treatment of organic pollution.

[0090] (3) Fertilizer efficiency is measured by wheat fresh weight, while soil improvement is measured by pH value and urease activity. These two indicators are important manifestations of fertilizer practicality. The test results show that the fertilizer of this invention can take into account both pollution reduction and crop growth and soil quality improvement: 1. Wheat fresh weight: The highest wheat fresh weight in Example 4 was 56.3 grams per pot, while in Examples 1 to 3 it was 45.6 grams per pot, 48.2 grams per pot, and 51.8 grams per pot, respectively, showing a gradual optimization trend; the wheat fresh weights in Comparative Examples 1 to 3 were 32.8 grams per pot, 38.5 grams per pot, and 42.1 grams per pot, respectively, all lower than those in the Examples; the control group was only 28.3 grams per pot, less than half of that in Example 4. This result proves that by optimizing the raw material composition, including compound microbial agents, activated biochar, and environmentally friendly nutrients, this invention can effectively provide nutrients for crops, promote growth, and solve the problem of "yield suppression" of traditional pollution reduction products. 2. Soil pH: The initial soil pH was slightly acidic at 5.8. After planting in Example 4, the pH rose to 6.8, approaching neutral. Examples 1-3 showed pH values ​​of 6.3, 6.4, and 6.5 respectively. Comparative Examples 1-3 showed pH values ​​of 6.1, 6.2, and 6.3 respectively, while the control group's pH decreased to 5.7. Neutral soil is more conducive to crop root absorption and microbial activity, indicating that the fertilizer of this invention can improve acidic soil and enhance the soil ecological environment. 3. Urease Activity: Urease activity reflects the soil's nitrogen conversion capacity, a core fertility indicator. Example 4 showed a maximum activity of 1.8 mg / g / day. Examples 1-3 showed activity of 1.2 mg / g / day, 1.3 mg / g / day, and 1.5 mg / g / day respectively. Comparative Examples 1-3 showed activity of 0.9 mg / g / day, 1.0 mg / g / day, and 1.1 mg / g / day respectively, while the control group's activity was only 0.6 mg / g / day. This result indicates that the fertilizer of this invention can increase soil enzyme activity, enhance soil fertility, and provide a sustainable nutrient supply for crop growth.

[0091] (4) The heavy metal desorption rate is directly related to the risk of secondary pollution. The test results show that the present invention can effectively reduce this risk: the heavy metal desorption rate of Example 4 is the lowest at 0.8%, with almost no heavy metal desorption; Example 3 is 5.1%, and Examples 1 and 2 are 8.5% and 8.2% respectively; Comparative Example 1 lacks biochar, and Comparative Example 3 uses traditional fertilizer, both of which have relatively high desorption rates of 12.3% and 15.6% respectively; Comparative Example 4 uses unactivated biochar, with a desorption rate of 4.8%, which is higher than that of Example 3; the control group has a rate as high as 20.5%, which poses a serious risk of secondary pollution. The results prove that the disodium ethylenediaminetetraacetate added in Example 4 can form a stable chelate with heavy metals. Combined with the adsorption effect of activated biochar, a multi-layered heavy metal control mechanism of adsorption, chelation, and fixation is constructed, which completely solves the problem of easy desorption of heavy metals after adsorption and eliminates the hidden danger of secondary pollution.

[0092] This invention optimizes core technologies, including the construction of composite microbial agents, biomass carbon acid washing and activation, and the addition of environmentally friendly chelating agents. Combined with an environmentally friendly nutrient system composed of humic acid and amino acid-chelated zinc, it achieves highly efficient treatment of complex soil pollution, simultaneously increasing heavy metal removal rates to a maximum of 72.5% for lead, 68.9% for cadmium, and a maximum polycyclic aromatic hydrocarbon degradation rate of 78.3%. It also balances fertilizer efficiency and soil improvement, promoting crop growth, with wheat fresh weight reaching a maximum of 56.3 grams per pot, adjusting soil pH to neutral, and increasing soil fertility and urease activity to a maximum of 1.8 mg / g / day. Furthermore, it eliminates the risk of secondary pollution, with a heavy metal desorption rate as low as 0.8%. Compared with comparative examples and traditional methods, this invention's technical solution has significant advantages and practicality, effectively addressing the pain points of existing fertilizers such as single-purpose pollution reduction, insufficient fertilizer efficiency, and secondary pollution. It is suitable for the ecological restoration and agricultural production of complex polluted soils.

[0093] The commercially available control group consisted of mainstream pollution-reducing fertilizers, such as heavy metal adsorption organic fertilizers. The test data are shown in Table 6 below:

[0094]

[0095] The data above shows that the present invention is significantly superior to commercially available products in terms of pollution reduction efficiency, fertilizer efficiency, and secondary pollution control, and represents a significant improvement.

[0096] The long-term follow-up test data based on Example 4 are shown in Table 7 below:

[0097]

[0098] The data above shows that the fertilizer of this invention still maintains high pollution reduction efficiency after one year, and the heavy metal desorption rate is still less than 2%, proving its long-term stable pollution reduction effect.

[0099] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A method for preparing a new environment-friendly fertilizer capable of reducing soil pollution, characterized in that, The raw material composition and preparation steps are as follows: The raw material composition, by weight, is 50 parts corn straw biochar, 20 parts humic acid, and 10 parts viable bacteria. 8 Three portions of Bacillus subtilis inoculum agent with a CFU / g concentration and a viable count of 10cFU / g 8 Two parts of Pseudomonas aeruginosa inoculum (CFU / g), three parts of amino acid chelated zinc, two parts of sodium carboxymethyl cellulose, two parts of disodium EDTA, and 16 parts of deionized water. The preparation steps include: (1) Preparation of acid-washed activated biochar: Corn straw biochar was placed in a 1 mol / L hydrochloric acid solution and soaked at room temperature for 2 hours, with stirring once every 30 minutes during the soaking period; after soaking, the biochar was repeatedly rinsed with deionized water until the pH of the eluent was 7.0, and then the rinsed biochar was placed in a 105℃ constant temperature drying oven to dry until the moisture content was ≤5%, and then crushed with a universal pulverizer and passed through an 80-mesh standard sieve to obtain acid-washed activated corn straw biochar; (2) Preparation of compound microbial inoculants: Bacillus subtilis strain and Pseudomonas strain were inoculated into LB liquid medium, which consisted of 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride, and a pH of 7.

0. The inoculated medium was placed in a constant temperature shaking incubator at 30°C and 180 rpm for 48 h, respectively, and the viable count was 10. 8 CFU / g of Bacillus subtilis and Pseudomonas aeruginosa inoculants; (3) Preparation of mixed materials: Acid-washed activated corn straw biochar, humic acid, amino acid chelated zinc, sodium carboxymethyl cellulose, and disodium ethylenediaminetetraacetate were added to a double helix mixer and mixed at 300 rpm for 15 min at room temperature to form a solid mixed base. Bacillus subtilis inoculant, Pseudomonas inoculant and deionized water were added to the solid mixed base at a uniform speed and mixed at 250 rpm for 20 min to obtain a uniform wet mixed material. (4) Granulation and drying: The wet mixture is fed into the extrusion granulator, the granulation temperature is set to 60℃ and the die diameter is 2mm. After extrusion granulation, the granules are placed in a hot air circulating drying oven at 50℃ and dried until the moisture content is ≤8%. After cooling to room temperature, they are screened to obtain basic pollution-reducing and environmentally friendly fertilizer.

2. The method of claim 1, wherein the new eco-friendly fertilizer capable of reducing soil pollution is prepared by mixing the soil pollution reducing agent with the fertilizer. The method for preparing the Pseudomonas inoculum is as follows: Pseudomonas strains are inoculated into LB liquid medium, which consists of 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride and pH 7.

0. The inoculated medium is then placed in a constant temperature shaking incubator at 30°C and 180 rpm for 48 h.

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