A combined remediation agent and remediation method for soil contaminated with high concentrations of TNT.

Abstract

This invention discloses a combined remediation agent and method for high-concentration TNT contaminated soil. The combined remediation agent includes a bioremediation agent and a chemical remediation agent. The bioremediation agent includes activated sludge and glycerol, while the chemical remediation agent is a sodium percarbonate solution or a hydrogen peroxide solution activated with sodium bicarbonate. The TNT-contaminated soil is first subjected to biological pre-reduction degradation using the bioremediation agent, followed by chemical oxidation remediation using the chemical remediation agent. This invention provides a microbial-chemical combined remediation method for high-concentration TNT contaminated soil, achieving a TNT degradation rate of ≥95% in soils with initial TNT concentrations exceeding 1000 mg / kg. The remediation agent residue is low, causing minimal damage to soil structure and function, and is environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation technology, specifically to a combined remediation agent and remediation method for soil contaminated with high concentrations of TNT. Background Technology

[0002] TNT is one of the most synthesized and used explosives by humans. During its synthesis, use, and disposal, large amounts of TNT enter the environment, causing soil and groundwater pollution. Environmental TNT pollution has adverse effects on humans, plants, and microorganisms. Long-term exposure to TNT contaminated environments can lead to skin irritation, liver dysfunction, increased cataract size, and anemia, in addition to potential mutagenic and carcinogenic effects in humans. TNT is highly toxic to terrestrial plants, affecting germination rates, reducing plant biomass, and causing abnormal plant growth.

[0003] Currently, remediation methods for TNT-contaminated soil are mainly classified into physical, chemical, microbial, and phytoremediation methods. Physical methods primarily involve pyrolysis, but these are costly and cause significant damage to soil structure and function. Chemical methods involve oxidizing TNT in the soil, but oxidation alone has low utilization of reactive oxygen species (ROS), and the TNT degradation residues contain high levels of benzene compounds. Microbial methods utilize microbial agents for biodegradation, but this method has a long timeframe, and high TNT concentrations inhibit microbial growth. Phytoremediation involves planting vegetation in TNT-contaminated soil, but the remediation period is long, and the residual TNT content in the soil is high. Therefore, developing remediation methods with high TNT removal rates, capable of mineralizing benzene compounds, with minimal damage to soil function and structure, and high utilization of ROS has enormous application potential in the remediation of TNT-contaminated sites.

[0004] Currently, methods for treating soil contaminated with high concentrations of TNT are relatively limited, and there are no reports of combining microbial and chemical methods. Patent CN 103143558B discloses an anaerobic-aerobic remediation method for TNT-contaminated soil. This method involves air-drying and grinding the soil to be remediated into granules; adding water and the soil granules to a biological sludge reactor, mixing thoroughly, adding nutrient solution and surfactants, and inoculating with anaerobic microorganisms (such as sludge from the anaerobic treatment stage of domestic sewage or organic wastewater); and finally, adding humus for aerobic remediation. However, this remediation method involves soil grinding, and the initiation and control of the anaerobic stage require specialized equipment and nitrogen filling. The control process is complex, the overall cycle is long, and its widespread application for treating large quantities of contaminated soil is difficult. Summary of the Invention

[0005] In view of the above-mentioned prior art, the purpose of this invention is to provide a combined remediation agent and remediation method for soil contaminated with high concentration of TNT.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of this invention provides a combined remediation agent for soil contaminated with high concentrations of TNT. The combined remediation agent includes a bioremediation agent and a chemical remediation agent. The bioremediation agent includes activated sludge and a bio-enhancing agent. The chemical remediation agent is a sodium percarbonate solution or a hydrogen peroxide solution activated with sodium bicarbonate.

[0008] Preferably, the activated sludge is activated sludge from an urban wastewater treatment plant.

[0009] Preferably, the bio-enhancing agent is glycerol, and the mass ratio of activated sludge to glycerol is (0.5-5):(1-3).

[0010] Preferably, the sodium percarbonate solution has a mass fraction of 1-5%.

[0011] As a preferred method, the preparation method of hydrogen peroxide solution activated with sodium bicarbonate is as follows: sodium bicarbonate is added to hydrogen peroxide solution, and the mass fraction of hydrogen peroxide in the resulting solution is 0.3-3%, and the molar ratio of sodium bicarbonate to hydrogen peroxide is 1:(10-20).

[0012] A second aspect of this invention provides a combined remediation method for soil contaminated with high concentrations of TNT, comprising the following steps:

[0013] (1) Bio-pre-reduction degradation: Add glycerol to TNT-contaminated soil and stir evenly. Dilute activated sludge with water, add it to the TNT-contaminated soil with added glycerol and stir evenly to carry out the reaction.

[0014] (2) Chemical oxidation remediation: Add chemical remediation agent to the soil in step (1). The chemical remediation agent is sodium percarbonate solution or hydrogen peroxide solution activated with sodium bicarbonate. Stir to form mud and carry out the reaction. After the reaction, filter out the water from the mud and dry it.

[0015] Preferably, in step (1), the amount of glycerol added is 1-3% of the soil mass, the amount of activated sludge added is 0.5-5% of the soil mass, and the dilution ratio of activated sludge is 1-10 times.

[0016] Preferably, in step (1), the reaction time is 2-7 days and the reaction temperature is 25-40℃.

[0017] Preferably, in step (2), the amount of chemical remediation agent added is 2-5 times the soil volume.

[0018] Preferably, in step (2), the reaction time is 12-48h, the reaction temperature is 25-40℃, and the mud is stirred every 2-6h during the process.

[0019] The glycerol added during the pre-reduction degradation stage of this invention functions as both a surfactant and an electron donor. As a surfactant, glycerol promotes the dissolution of bound TNT in the soil, enhancing its bioavailability and facilitating its reduction by organisms. Compared to other nonionic biosurfactants such as rhamnolipids and Tween 80, glycerol is inexpensive and readily available, utilizing industrial-grade crude glycerol or waste glycerol. As an electron donor, readily biodegradable glycerol aims to deplete oxygen in the soil solution, rapidly creating localized anaerobic conditions and promoting the growth of anaerobic microorganisms. Activated sludge provides active microbial strains; the proliferating microorganisms, through cometabolism, reduce the difficult-to-oxidize and degrade TNT to nitroaniline compounds for further biodegradation. Compared to single or combined degrading microbial strains, activated sludge contains a large number of anaerobic, aerobic, and facultative microorganisms, exhibiting strong adaptability to the soil environment. It requires no special preparation, is inexpensive and readily available, and can also serve as a method for disposing of excess activated sludge.

[0020] The chemical remediation agent added during the chemical oxidation stage of this invention, namely sodium percarbonate solution or sodium bicarbonate activated hydrogen peroxide solution, maintains a slightly alkaline soil condition. Under this condition, highly reactive percarbonate ions are generated, which decompose to produce superoxide anion free radicals, carbonate free radicals, etc., which can destroy the benzene ring structure of TNT biological pre-reduction products, further oxidizing the biological pre-reduction products, and oxidizing some TNT degradation products into carbon dioxide and water, thereby further reducing the biotoxicity of the treated soil. Before use, the hydrogen peroxide is activated and then added to the soil, which facilitates uniform contact between the oxidant and the activator, improves activation efficiency, and also inhibits the catalytic decomposition of hydrogen peroxide by metal ions in acidic soil. After the chemical oxidation stage, excess hydrogen peroxide can automatically decompose to produce oxygen and water. Carbonate and bicarbonate ions are common anions in soil and will not cause secondary pollution problems.

[0021] This invention uses a combination of bioremediation and chemical remediation agents to remediate TNT-contaminated soil. Compared with single bioremediation methods, such as anaerobic-aerobic microbial remediation, this invention has the advantages of a shorter remediation cycle, more thorough TNT degradation, simpler technology and equipment, and easier large-scale application. Compared with single chemical oxidation remediation, this invention has a higher overall TNT degradation rate. The nitroaniline produced by biological pre-reduction of TNT reacts with reactive oxygen species faster than TNT itself. Therefore, for the same remediation target, less chemical remediation agent is needed, resulting in lower cost and less damage to soil structure.

[0022] The beneficial effects of this invention are:

[0023] This invention provides a microbial chemical combination remediation method for soil contaminated with high concentrations of TNT. The method achieves a TNT degradation rate of ≥95% in soil with an initial TNT concentration exceeding 1000 mg / kg. The method is easy to operate, has a short time cycle, low cost, and is easy to promote on a large scale.

[0024] The combined remediation agent provided by this invention can automatically decompose the residual oxidant hydrogen peroxide after the reaction, glycerol can serve as a carbon source and be decomposed by microorganisms, and sodium bicarbonate is a common component of soil, so its residue in the soil will not cause harm. The remediation agent has a small residual amount, causes little damage to soil structure and function, and is environmentally friendly. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0026] As described in the background section, single chemical oxidation has low utilization of reactive oxygen species, and the residues of TNT degradation contain high levels of benzene compounds. Bioremediation using microorganisms in activated sludge requires specialized equipment, the control process is complex, the overall cycle is long, and it is difficult to promote the treatment of large amounts of contaminated soil.

[0027] Based on this, the present invention combines bioremediation and chemical remediation for the treatment of soil contaminated with high concentrations of TNT. It utilizes activated sludge and glycerol for biological pre-reduction of the soil, followed by chemical oxidation of the soil using sodium percarbonate. Currently, sodium percarbonate is mainly used for the treatment of soil pollution such as petroleum hydrocarbons, phthalates, tetracyclines, and pesticide pollution, and there are no reports on its use in treating TNT-contaminated soil.

[0028] This invention provides a combined remediation agent for high-concentration TNT-contaminated soil. The combined remediation agent includes a bioremediation agent and a chemical remediation agent. The bioremediation agent includes activated sludge and glycerol, with a mass ratio of activated sludge to glycerol of (0.5-5):(1-3). The activated sludge is activated sludge from an urban wastewater treatment plant. The chemical remediation agent is a sodium percarbonate solution or a hydrogen peroxide solution activated with sodium bicarbonate, with a mass fraction of 1-5% for the sodium percarbonate solution. The method for activating the hydrogen peroxide solution with sodium bicarbonate is as follows: sodium bicarbonate is added to the hydrogen peroxide solution, resulting in a solution with a hydrogen peroxide mass fraction of 0.3-3%, and a molar ratio of sodium bicarbonate to hydrogen peroxide of 1:(10-20).

[0029] A combined remediation method for soil contaminated with high concentrations of TNT includes the following steps:

[0030] (1) Bio-pre-reduction degradation: Add glycerol to TNT-contaminated soil and stir evenly. The amount of glycerol added is 1-3% of the soil mass. Dilute activated sludge with water 1-10 times. The amount of activated sludge added is 0.5-5% of the soil mass. Add it to the TNT-contaminated soil with added glycerol and stir evenly. React at 25-40℃ for 2-7 days.

[0031] (2) Chemical oxidation remediation: Add 2-5 times the volume of chemical remediation agent to the soil in step (1). The chemical remediation agent is sodium percarbonate solution or hydrogen peroxide solution activated with sodium bicarbonate. Stir to form mud and react at 25-40℃ for 12-48 hours. Stir the mud every 2-6 hours during the reaction. After the reaction, filter out the water from the mud and dry it.

[0032] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0033] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0034] The activated sludge used in this invention was taken from the Xinkaipu Wastewater Treatment Plant in Changsha City, Hunan Province. The activated sludge used in the examples and comparative examples was taken from the same batch, and its composition was not significantly different.

[0035] Example 1

[0036] The TNT content in the soil sample was 3270 mg / kg.

[0037] 1. Biological pre-reduction and degradation treatment of high-concentration TNT contaminated soil:

[0038] (1) Addition of bio-enhancing agent: Add bio-enhancing agent glycerol to TNT-contaminated soil and stir evenly. The amount added is 2% of the soil mass.

[0039] (2) Addition of activated sludge: Dilute the activated sludge 5 times and add it to the TNT-contaminated soil that has been treated with bio-enhancing agent and stir evenly. The amount of activated sludge added is 3% of the soil mass.

[0040] (3) Bio-pre-reduction: The soil solution is sealed and incubated at 30℃ for 6 days to complete the bio-pre-reduction degradation step.

[0041] 2. Chemical oxidative remediation:

[0042] (1) Addition of chemical oxidative remediation agent: Dissolve sodium percarbonate in water to form a sodium percarbonate solution with a mass fraction of 3%. Add the sodium percarbonate solution at a volume of 3 times that of the soil and stir to form a slurry.

[0043] (2) Chemical oxidation remediation reaction control: Soil with added chemical oxidation remediation agent was reacted at 30℃ for 48 hours, and the soil slurry was stirred every 6 hours during the reaction.

[0044] (3) Post-treatment after chemical oxidation remediation: After filtering out the moisture from the soil slurry, let it air dry naturally.

[0045] Example 2

[0046] The TNT content in the soil sample was 3270 mg / kg.

[0047] 1. Biological pre-reduction and degradation treatment of high-concentration TNT contaminated soil:

[0048] (1) Addition of bio-enhancing agent: Add bio-enhancing agent glycerol to TNT-contaminated soil and stir evenly. The amount added is 2% of the soil mass.

[0049] (2) Addition of activated sludge: Dilute the activated sludge 5 times and add it to the TNT-contaminated soil that has been treated with bio-enhancing agent and stir evenly. The amount of activated sludge added is 3% of the soil mass.

[0050] (3) Bio-pre-reduction: The soil solution is sealed and incubated at 30℃ for 6 days to complete the bio-pre-reduction degradation step.

[0051] 2. Chemical oxidative remediation:

[0052] (1) Addition of chemical oxidizing remediation agent: Dilute the hydrogen peroxide solution to a 2% (w / w) hydrogen peroxide solution, according to the molar ratio of HCO3- - Add sodium bicarbonate solid at a ratio of 1:15 (H2O2 = 1, stir to dissolve, and obtain activated hydrogen peroxide solution). Add the activated hydrogen peroxide solution at a volume of 3 times that of the soil and stir to form a slurry.

[0053] (2) Chemical oxidation remediation reaction control: Soil with added chemical oxidation remediation agent was reacted at 30℃ for 48 hours, and the soil slurry was stirred every 6 hours during the reaction.

[0054] (3) Post-treatment after chemical oxidation remediation: After filtering out the moisture from the soil slurry, let it air dry naturally.

[0055] Comparative Example 1

[0056] The TNT content in the soil sample was 3270 mg / kg.

[0057] (1) Addition of bio-enhancing agent: Add bio-enhancing agent glycerol to TNT-contaminated soil and stir evenly. The amount added is 2% of the soil mass.

[0058] (2) Addition of activated sludge: Dilute the activated sludge 5 times and add it to the TNT-contaminated soil that has been treated with bio-enhancing agent and stir evenly. The amount of activated sludge added is 3% of the soil mass.

[0059] (3) Bio-pre-reduction: The soil solution is sealed and incubated at 30℃ for 8 days to complete the bio-pre-reduction degradation step.

[0060] (4) Biological pre-reduction post-treatment: After filtering out the water from the soil slurry, let it air dry naturally.

[0061] Comparative Example 2

[0062] The TNT content in the soil sample was 3270 mg / kg.

[0063] (1) Addition of chemical oxidative remediation agent: Dissolve sodium percarbonate in water to form a sodium percarbonate solution with a mass fraction of 3%. Add the sodium percarbonate solution at a volume of 3 times that of the soil and stir to form a slurry.

[0064] (3) Chemical oxidation remediation reaction control: The reaction was carried out at 30℃ for 8 days, and the soil slurry was stirred every 6 hours during the period.

[0065] (4) Post-treatment after chemical oxidation remediation: After filtering out the moisture from the soil slurry, let it air dry naturally.

[0066] The TNT content in the soil of Examples 1-2 and Comparative Examples 1-2 was detected, and the degradation rate was calculated. The results are shown in Table 1.

[0067] Table 1. Degradation rates of TNT in soil in Examples 1-2 and Comparative Examples 1-2

[0068]

[0069] A comparison of Examples 1 and 2 with Comparative Examples 1 and 2 revealed that the TNT degradation rate using the combined biological pre-reduction and chemical oxidation remediation method of this application is higher than that of single biological reduction or chemical oxidation treatments. Furthermore, the combined biological pre-reduction and chemical oxidation remediation method employed in this invention has a synergistic promoting effect on the degradation of TNT in soil.

[0070] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A combined remediation method for soil contaminated with high concentrations of TNT, characterized in that, Includes the following steps: (1) Biological pre-reduction degradation: Add glycerol to TNT-contaminated soil and stir evenly. Dilute activated sludge with water, add it to the TNT-contaminated soil with added glycerol and stir evenly to carry out the reaction. The activated sludge is activated sludge from an urban wastewater treatment plant, and the mass ratio of highly activated sludge to glycerol is (0.5-5):(1-3). (2) Chemical oxidation remediation: Add chemical remediation agent to the soil in step (1), stir to form mud, react, filter out water from the mud and dry it; wherein, the chemical remediation agent is sodium percarbonate solution or hydrogen peroxide solution activated with sodium bicarbonate. The TNT content in the high-concentration TNT-contaminated soil was 1000-3270 mg / kg.

2. The combined remediation method for high-concentration TNT contaminated soil as described in claim 1, characterized in that, The mass fraction of sodium percarbonate solution is 1%-5%.

3. The combined remediation method for high-concentration TNT contaminated soil as described in claim 1, characterized in that, The method for preparing hydrogen peroxide solution activated with sodium bicarbonate is as follows: sodium bicarbonate is added to hydrogen peroxide solution, and the mass fraction of hydrogen peroxide in the resulting solution is 0.3-3%, and the molar ratio of sodium bicarbonate to hydrogen peroxide is 1:(10-20).

4. The combined remediation method for high-concentration TNT contaminated soil as described in claim 1, characterized in that, In step (1), the amount of glycerol added is 1-3% of the soil mass, the amount of activated sludge added is 0.5-5% of the soil mass, and the dilution ratio of activated sludge is 1-10 times.

5. The combined remediation method for high-concentration TNT contaminated soil as described in claim 1, characterized in that, In step (1), the reaction time is 2-7 days and the reaction temperature is 25-40℃.

6. The combined remediation method for high-concentration TNT contaminated soil as described in claim 1, characterized in that, In step (2), the amount of chemical remediation agent added is 2-5 times the soil volume.

7. The combined remediation method for high-concentration TNT contaminated soil as described in claim 1, characterized in that, In step (2), the reaction time is 12-48h and the reaction temperature is 25-40℃. During this period, the mud is stirred every 2-6h.

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