Compound bacterial fertilizer for heavy metal contaminated soil remediation and preparation method thereof

Abstract

The invention provides a compound bacterial fertilizer for heavy metal contaminated soil remediation and a preparation method thereof. The compound bacterial fertilizer comprises the following components in parts by weight: 5-20 parts of a compound bacterial agent, 5-15 parts of modified coal gangue, 30-60 parts of dunaliella salina powder modified charcoal and 5-15 parts of an auxiliary agent. The prepared compound bacterial fertilizer can increase the content of organic matters in soil, adsorb free heavy metals, reduce the content level of heavy metal elements and efficiently repair heavy metal contaminated soil, is applied to growth tests of crops, promotes heavy metals of the crops to reach the standard, and meets nutrient requirements and safety requirements of growth.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, and in particular relates to a compound microbial fertilizer for the remediation of heavy metal contaminated soil and its preparation method. Background Technology

[0002] Soil is the cornerstone of human agricultural production and the health of ecosystems. However, with the rapid development of industry and agriculture, soil heavy metal pollution has become a serious global environmental problem. Heavy metals such as cadmium, lead, chromium, mercury, and metalloid arsenic enter the soil environment through mining, industrial emissions, wastewater irrigation, and the irrational use of chemical fertilizers and pesticides. These heavy metals are highly toxic, persistent, and bioaccumulative, not only damaging soil structure and microbial communities and inhibiting crop growth, but also potentially accumulating through the food chain, ultimately harming human health and causing various chronic diseases.

[0003] Current soil heavy metal remediation technologies mainly include three categories: physical remediation, chemical remediation, and bioremediation. Among them, bioremediation has become a research hotspot due to its environmental friendliness and low cost. Microbial remediation utilizes specific functional microorganisms (such as Bacillus and Pseudomonas) to reduce the bioavailability and mobility of heavy metals in the soil through adsorption, precipitation, redox reactions, or biotransformation, making it an important means of achieving soil ecological restoration. However, existing bio-fertilizers still face several technical bottlenecks: First, the heavy metal fixation effect is unstable, often relying on single modifying materials or microbial strains, lacking synergistic effects, and making it difficult to address complex heavy metal pollution; second, functional microorganisms struggle to maintain high activity and colonization capacity in complex and harsh soil environments, resulting in unstable remediation effects and long remediation cycles.

[0004] Therefore, how to develop a compound microbial fertilizer that combines the functions of efficient heavy metal fixation, soil structure improvement, and crop nutrient supply is an urgent problem to be solved in this invention. Summary of the Invention

[0005] The purpose of this invention is to provide a compound microbial fertilizer for the remediation of heavy metal contaminated soil and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides a compound microbial fertilizer for the remediation of heavy metal contaminated soil, characterized in that the compound microbial fertilizer comprises the following components in parts by weight: 5-20 parts of compound microbial agent, 5-15 parts of modified coal gangue, 30-60 parts of modified biochar from Dunaliella salina powder, and 5-15 parts of additives.

[0007] As a further improvement, the modified coal gangue is silane coupling agent modified coal gangue.

[0008] As a further improvement, the silane coupling agent includes mercaptosilane coupling agents and aminosilane coupling agents.

[0009] As a further improvement, the mercaptosilane coupling agent is γ-mercaptopropyltrimethoxysilane or γ-mercaptopropyltriethoxysilane; the aminosilane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0010] Preferably, the mercaptosilane coupling agent is γ-mercaptopropyltrimethoxysilane; the aminosilane coupling agent is γ-aminopropyltriethoxysilane.

[0011] As a further improvement, the synthesis of the modified coal gangue includes the following steps: (1) Grind and sieve the coal gangue, then wash the sieved coal gangue stepwise with an inorganic acid solution. After the washing is completed, post-processing is performed to obtain intermediate one. (2) Then, intermediate one was dispersed in an inorganic acid solution and heated to 60-80℃. Potassium permanganate solution was added and stirred to react. After the reaction was completed, it was post-processed to obtain intermediate two. (3) Add intermediate two to an organic solvent, then add hydrazine hydrate to it and reflux, then add mercaptosilane coupling agent and continue reflux, then post-process to obtain intermediate three; (4) Add intermediate three to an organic solvent and add an aminosilane coupling agent, stir and reflux for 1-3 hours, filter to obtain solid suspension, and then process to obtain modified coal gangue.

[0012] As a further improvement, the step-by-step acid washing step in step (1) is as follows: the sieved coal gangue is first mixed and stirred with a sulfuric acid solution with a mass concentration of 15-30% for 10-20 minutes, washed with deionized water until the pH value of the washing liquid is neutral, and dried to obtain dried coal gangue; then the dried coal gangue is added to a hydrochloric acid solution with a mass fraction of 15-20%, and heated and stirred in a water bath at 30-50℃ for 10-15 hours.

[0013] As a further improvement, the compound microbial agent comprises at least two of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus mucilaginosus, Bacillus vesicularis, and Pseudomonas aeruginosa.

[0014] As a further improvement, the compound microbial agent is Bacillus subtilis, Bacillus mucilaginosus, and Bacillus vesicularis; the weight ratio of the added Bacillus subtilis, Bacillus mucilaginosus, and Bacillus vesicularis is (1.5-3):(0.5-2):(0.5-2).

[0015] As a further improvement, the additive is at least one of humic acid, soluble starch, urea, ammonium dihydrogen phosphate, and potassium chloride.

[0016] To enhance the fertilizer efficiency of the compound microbial agent, preferably, the adjuvant is humic acid, soluble starch and ammonium dihydrogen phosphate, with an addition weight ratio of (3-7):(2-5):(1-4).

[0017] This invention also provides a method for preparing a compound microbial fertilizer for the remediation of heavy metal contaminated soil, characterized by comprising the following steps: According to the weight proportions, the compound microbial agent is first mixed with modified biochar, and then the additives and modified coal gangue are added in sequence and mixed again. The mixture is then granulated and screened to obtain microbial fertilizer.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a compound microbial fertilizer for the remediation of heavy metal contaminated soil and its preparation method. The compound microbial fertilizer can increase the organic matter content of the soil, while adsorbing free heavy metals and reducing the elemental content levels of four heavy metal elements: cadmium, lead, copper and zinc. It can efficiently remediate heavy metal contaminated soil. When applied to growth tests in corn fields, it can promote the heavy metal content of corn grains to meet the standards and satisfy the nutrient and safety requirements for corn growth. This invention utilizes a synergistic system of silane coupling agent-modified coal gangue and Dunaliella salina powder-modified biochar. The thiol and amino groups on the surface of the modified coal gangue can strongly capture heavy metal ions through complexation and ion exchange. The porous structure of the Dunaliella salina powder-modified biochar enables physical adsorption and surface binding. Combined with a composite microbial agent, heavy metals are converted into a stable state. The synergistic effect effectively reduces the available heavy metal content in the soil, thereby reducing the heavy metal content in crops to meet safety requirements. The Dunaliella salina powder-modified biochar and modified coal gangue not only adsorb heavy metals and reduce harm, but also replenish the soil with a large amount of organic matter. Combined with humic acid, ammonium dihydrogen phosphate, and other adjuvants, soil fertility is activated, which can improve crop growth quality to a certain extent. Furthermore, the synergy of the two provides a habitat for microorganisms, effectively protecting the activity of the microbial agent and extending its survival time and functional durability in the soil. Detailed Implementation

[0019] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0020] In the following examples, except for modified coal gangue A, modified coal gangue B, Dunaliella salina powder modified biochar, and γ-polyglutamic acid modified biochar, all other compounds and related reagents used were commercially available. Specifically, Bacillus subtilis, Bacillus mucilaginosus, and Bacillus belesii were purchased from Shandong Yihao Biotechnology Co., Ltd.; humic acid was purchased from Shandong Jinshiyuan Chemical Co., Ltd. (item number 023-6533); biochar was purchased from Henan Housen Environmental Protection Technology Co., Ltd. (item number SWT002); Dunaliella salina powder was purchased from Fufeng Sinote Biotechnology Co., Ltd.; soluble starch was purchased from Nantong Yunfeng Starch Co., Ltd. (model NT156); coal gangue was purchased from Shijiazhuang Ruiming Mineral Products Co., Ltd. (item number rm-274); and conventional fertilizer was purchased from Shijiazhuang Baijiaxing Fertilizer Co., Ltd.

[0021] The synthesis of modified coal gangue A includes the following steps: (1) Grind the coal gangue and sieve it through a 200-mesh sieve. Then mix 5g of the sieved coal gangue with 40mL of 20% sulfuric acid solution for 10min. Wash with deionized water until the pH of the washing solution is 7. Dry the coal gangue at 55℃ to obtain the dried coal gangue. Then add the dried coal gangue to 200mL of 18% hydrochloric acid solution and heat it in a 30℃ water bath under reflux for 12h. Filter the solution and dry the sample at 60℃ to obtain intermediate one. (2) Then take 5g of intermediate one and disperse it in 50mL of sulfuric acid solution with a mass fraction of 63% and heat it to 80℃. Then add 15mL of potassium permanganate solution and stir for 30min. After the reaction is completed, wash with deionized water until the pH of the washing solution is 7. Dry the sample at 60℃ to obtain intermediate two. (3) Add 4g of intermediate II to 40mL of methanol and reflux for 30min. Then add 4mL of hydrazine hydrate and reflux for 2h. Next, add 3.8mL of γ-mercaptopropyltrimethoxysilane and continue reflux for 1h. Finally, wash with methanol and deionized water until the pH of the washing solution is 7. Dry at 60℃ to obtain intermediate III. (4) Add intermediate three to 20 mL of toluene and 4.1 mL of γ-aminopropyltriethoxysilane, stir, reflux for 2 h, filter to obtain solid suspension, wash the solid suspension with excess toluene and ethanol respectively, and dry at 60 °C to obtain modified coal gangue A.

[0022] The synthesis of modified coal gangue B includes the following steps: (1) Grind the coal gangue and sieve it through a 200-mesh sieve. Then mix 5g of the sieved coal gangue with 40mL of 20% sulfuric acid solution for 10min. Wash with deionized water until the pH of the washing solution is neutral. Dry it at 60℃ to obtain the dried coal gangue. Then add the dried coal gangue to 200mL of 18% hydrochloric acid solution and heat it in a 30℃ water bath under reflux for 12h. Filter it and dry the sample at 60℃ to obtain intermediate one. (2) Then take 5g of intermediate one and disperse it in 50mL of sulfuric acid solution with a mass fraction of 63% and heat it to 80℃. Then add 15mL of potassium permanganate solution and stir for 30min. After the reaction is completed, wash with deionized water until the pH of the washing solution is neutral. Dry the sample at 60℃ to obtain intermediate two. (3) Add intermediate II to 40 mL of toluene and 4.1 mL of γ-aminopropyltriethoxysilane, stir and reflux for 2 h, filter to obtain solid suspension, wash the solid suspension with excess toluene and ethanol respectively, and dry at 60 °C to obtain γ-aminopropyltriethoxysilane modified coal gangue B.

[0023] The synthesis of Dunaliella salina powder-modified biochar includes the following steps: (1) Soak 200g of biochar in a 1mol / L hydrochloric acid solution for 2h and then sonicate for 15min. Then rinse with deionized water until neutral and dry in an oven at 50℃. Grind and sieve through a 50-mesh sieve to obtain pretreated biochar A. (2) Mix 50g of Dunaliella salina powder with 80mL of deionized water to obtain a suspension. Add 0.3g of cellulase to the suspension and adjust the pH to 4.8 with 0.1mol / L dilute hydrochloric acid solution. Enzymatically hydrolyze at 40℃ for 2h. After the enzymatic hydrolysis is completed, raise the temperature of the system to 80℃ and keep it warm for 15min. After the warming is completed, centrifuge at 6000rpn for 10min, collect the precipitate, and then place it in a vacuum drying oven at 50℃ to dry until the water content is <10% to obtain activated Dunaliella salina powder. (3) Place 100g of pretreated biochar A and 30g of activated Dunaliella salina powder in a mixer and mix for 15min. Then slowly add 20g of 15% sucrose solution and continue mixing until homogeneous. Then vacuum dry at 40℃ and cool naturally to room temperature to obtain Dunaliella salina modified biochar.

[0024] The synthesis of γ-polyglutamic acid modified biochar includes the following steps: (1) Soak 50g of biochar in a 1mol / L hydrochloric acid solution for 1h, then rinse with deionized water until neutral, and then dry in an oven at 50℃. Grind and sieve through a 50-mesh sieve to obtain pretreated biochar B. (2) Add 1.5g of γ-polyglutamic acid to 200mL of deionized water, stir at 20℃ for 10min, add 10g of pretreated biochar B, stir at 50℃ for 10min, add 30mL of glutaraldehyde, continue stirring for 1.5h, filter and wash with deionized water, dry at 40℃, and sieve through 100 mesh to obtain γ-polyglutamic acid modified biochar.

[0025] The preparation methods of Examples 1-3 and Comparative Examples 1-3 include the following steps: According to the weight proportions, the compound microbial agent is first mixed with modified biochar, and then the additives and modified coal gangue are added in sequence and mixed again. After granulation and screening by a granulator, granular compound microbial fertilizer with a diameter of 1-3mm is obtained.

[0026] The components and their contents used in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1 below: Table 1 The compound microbial fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, and the specific methods are as follows: Experimental site: Located in a metal-contaminated area in Handan City, Hebei Province, the site was randomly divided into 7 experimental plots on average; Test crop: Zhengdan 958 maize; Experimental setup: The experimental group used conventional fertilization method plus the compound microbial fertilizer of this invention, with an application rate of 40 kg / mu for the compound microbial fertilizer; the control group used conventional fertilization method plus 40 kg / mu of conventional fertilizer. Test method: After corn harvest, the top 15cm soil was collected using the five-point sampling method, thoroughly mixed, air-dried, and ground through a 100-mesh sieve for the determination of soil organic matter content and heavy metal content. Soil organic matter content: tested according to NY / T 1121.6-2006, potassium dichromate oxidation method; Soil heavy metal content: The soil was treated with microwave digestion according to HJ 803-2016, and the contents of chromium, lead, copper and zinc were measured. Heavy metal content in crops: kernels from different ears of corn were collected after harvest and mixed. The contents of chromium, lead, copper and zinc were determined according to GB 5009.268-2016, ICP-MS-microwave digestion method for plant samples.

[0027] The test results are shown in Tables 2 and 3, where Table 2 is for soil tests and Table 3 is for crop tests, as detailed below: Table 2 Table 3 As can be seen from the test results in Table 2-3, the compound microbial fertilizer prepared by the method provided by the present invention can increase the organic matter content of the soil, while adsorbing free heavy metals and reducing the elemental content levels of four heavy metal elements: chromium, lead, copper and zinc. It can effectively remediate heavy metal-contaminated soil. When applied to the growth test in corn fields, it can promote the heavy metal content of corn kernels to meet the standards and satisfy the nutrient and safety requirements for corn growth.

[0028] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A compound microbial fertilizer for the remediation of heavy metal contaminated soil, characterized in that, The compound microbial fertilizer contains the following components in parts by weight: 5-20 parts compound microbial agent, 5-15 parts modified coal gangue, 30-60 parts modified biochar from Dunaliella salina powder, and 5-15 parts additives.

2. The compound microbial fertilizer for remediation of heavy metal contaminated soil according to claim 1, characterized in that, The modified coal gangue is silane coupling agent modified coal gangue.

3. The compound microbial fertilizer for remediation of heavy metal contaminated soil according to claim 1, characterized in that, The silane coupling agents include mercaptosilane coupling agents and aminosilane coupling agents.

4. The compound microbial fertilizer for remediation of heavy metal contaminated soil according to claim 3, characterized in that, The mercaptosilane coupling agent is γ-mercaptopropyltrimethoxysilane or γ-mercaptopropyltriethoxysilane; the aminosilane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

5. The compound microbial fertilizer for remediation of heavy metal contaminated soil according to claim 1, characterized in that, The synthesis of the modified coal gangue includes the following steps: (1) Grind and sieve the coal gangue, then wash the sieved coal gangue stepwise with an inorganic acid solution. After the washing is completed, post-processing is performed to obtain intermediate one. (2) Then, intermediate one was dispersed in an inorganic acid solution and heated to 60-80℃. Potassium permanganate solution was added and stirred to react. After the reaction was completed, it was post-processed to obtain intermediate two. (3) Add intermediate two to an organic solvent, then add hydrazine hydrate to it and reflux, then add mercaptosilane coupling agent and continue reflux, then post-process to obtain intermediate three; (4) Add intermediate three to an organic solvent and add an aminosilane coupling agent, stir and reflux for 1-3 hours, filter to obtain solid suspension, and then process to obtain modified coal gangue.

6. The compound microbial fertilizer for remediation of heavy metal contaminated soil according to claim 1, characterized in that, The step-by-step acid washing process in step (1) is as follows: the sieved coal gangue is first mixed with a sulfuric acid solution with a mass concentration of 15-30% and stirred for 10-20 minutes, then washed with deionized water until the pH value of the washing solution is neutral, and then dried to obtain dried coal gangue; then the dried coal gangue is added to a hydrochloric acid solution with a mass fraction of 15-20%, and heated and stirred in a water bath at 30-50℃ for 10-15 hours.

7. The compound microbial fertilizer for remediation of heavy metal contaminated soil according to claim 1, characterized in that, The compound microbial agent comprises at least two of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus mucilaginosus, Bacillus vesicularis, and Pseudomonas aeruginosa.

8. The compound microbial fertilizer for remediation of heavy metal contaminated soil according to claim 1, characterized in that, The compound microbial agent consists of Bacillus subtilis, Bacillus mucilaginosus, and Bacillus vesicularis; the weight ratio of Bacillus subtilis, Bacillus mucilaginosus, and Bacillus vesicularis is (1.5-3):(0.5-2):(0.5-2).

9. A compound microbial fertilizer for remediation of heavy metal contaminated soil according to claim 8, characterized in that, The auxiliary agent is at least one of humic acid, soluble starch, urea, ammonium dihydrogen phosphate, and potassium chloride.

10. A method for preparing a compound microbial fertilizer for remediation of heavy metal contaminated soil according to any one of claims 1-9, characterized in that, Includes the following steps: According to the weight proportions, the compound microbial agent is first mixed with modified biochar, and then the additives and modified coal gangue are added in sequence and mixed again. The mixture is then granulated and screened to obtain microbial fertilizer.

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