Remediation method for high-concentration organic pollutants in soil

Abstract

The invention relates to the field of environmental remediation, and discloses a remediation method for high-concentration organic pollutants in soil, which comprises the following steps: firstly, injecting a nano zero-valent iron (nZVI) suspension into the contaminated soil for chemical reduction treatment, then adding sodium persulfate for oxidation treatment, and then adding a nano zero-valent iron (nZVI) suspension into the contaminated soil; the complex organic pollutants are converted into biodegradable intermediate products; then, two-stage microbial communities are introduced in sequence, the first-stage microbial community is used for degrading alcohol and ketone intermediate products, the second-stage microbial community is used for degrading organic acid intermediate products, and thorough mineralization of pollutants is achieved. According to the method, the pollutant degradation rate and the final removal effect can be remarkably improved, and the method is suitable for treatment scenes of various high-concentration organic pollutants and has high adaptability and economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of environmental restoration, and in particular to a method for restoring high-concentration organic pollutants in soil. Background Art

[0002] Organic pollutants (such as polycyclic aromatic hydrocarbons, benzene compounds, petroleum hydrocarbons, pesticides, etc.) are highly stable and persistent and can exist in the soil for a long time, posing a serious threat to the ecological environment and human health. Therefore, how to efficiently repair and purify contaminated soil has become an important research topic in the field of environmental science and engineering.

[0003] Traditional soil remediation methods include chemical treatment and biological remediation. However, although a single chemical treatment method can quickly degrade organic pollutants in the soil, it is usually difficult to completely convert pollutants into harmless substances, and it is easy to generate secondary pollutants during the treatment process; in addition, due to the complex chemical properties of pollutants in the soil, single chemical oxidants show low efficiency in treating certain high molecular weight pollutants. On the other hand, bioremediation technology is centered on microbial degradation. Although it is more effective in treating some low-concentration, biodegradable pollutants, when faced with high-concentration pollutants or difficult-to-degrade compounds, the activity of microorganisms is limited, the degradation efficiency is significantly reduced, and it often takes a long time to achieve significant removal of pollutants. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for remediating high-concentration organic pollutants in soil, which can efficiently and thoroughly remove high-concentration organic pollutants in soil, while overcoming the limitations of single chemical treatment or biological remediation methods in terms of degradation efficiency and pollutant mineralization.

[0005] To achieve the above objectives, the present invention is implemented through the following technical scheme: A method for remediating high-concentration organic pollutants in soil, comprising the following steps:

[0006] S1, injecting nano zero-valent iron suspension into the soil for chemical treatment;

[0007] S2, after the nano zero-valent iron treatment, sodium persulfate is added for oxidation treatment;

[0008] S3, introducing the first stage microbial community into the chemically treated soil to promote the biodegradation of alcohol and ketone intermediates;

[0009] S4. After the first stage of biodegradation is completed, the second stage of microbial community is introduced to treat the organic acid intermediates;

[0010] S5. Carry out post-treatment of the soil after the restoration is completed.

[0011] Preferably, the preparation steps of the nano zero-valent iron suspension include:

[0012] Dispersing nano zero-valent iron particles in deionized water to prepare a suspension with a concentration of 10-30 g / L;

[0013] The suspension is subjected to an oscillation treatment, the ultrasonic frequency is 40 kHz, and the oscillation time is 30-60 minutes;

[0014] During the suspension preparation, the pH value of the suspension was adjusted to 6-8.

[0015] Preferably, the nano zero-valent iron particles have an average particle size of 50-100 nm and a purity greater than 99%.

[0016] Preferably, the injection amount of the nano zero-valent iron is controlled at 1-5 L per cubic meter of soil, and the injection depth is 5-20 cm.

[0017] Preferably, the sodium persulfate oxidation treatment comprises the following steps:

[0018] Dissolve sodium persulfate in deionized water to prepare a solution with a concentration of 5-15 g / L;

[0019] The sodium persulfate solution is evenly applied to the contaminated soil treated with nano-zero-valent iron, with the injection depth ranging from 5 to 20 cm and the injection volume controlled at 5 to 10 L per cubic meter of soil;

[0020] During the oxidation treatment, the soil moisture was maintained in the range of 15-20%, and the soil pH was stabilized at 6.5-7.5 by adding phosphate buffer.

[0021] Preferably, the first stage microbial community includes Pseudomonas and Bacillus, and the suspension concentration is 10 6 -10 8 CFU / mL, the addition amount is 10-20L per cubic meter of soil.

[0022] Preferably, during the first stage of microbial degradation, the soil moisture is maintained at 20-25% and the incubation time is 7-14 days.

[0023] Preferably, the second stage microbial community includes Ralstonia and Actinomycetes, and the suspension concentration is 10 6 -10 8 CFU / mL, the addition amount is 10-20L per cubic meter of soil.

[0024] Preferably, the culture temperature of the microorganisms in the second stage is 28-32° C., the culture time is 48 hours, and the incubation time is 7-14 days.

[0025] Preferably, the post-treatment includes physical stabilization and backfilling of the soil.

[0026] The present invention provides a method for remediating high-concentration organic pollutants in soil. It has the following beneficial effects:

[0027] 1. The present invention effectively accelerates the initial degradation process of organic pollutants through chemical treatment with nano zero-valent iron (nZVI) and sodium persulfate. After the nano zero-valent iron reacts with the pollutants for reduction, the pollutants are further oxidized by sodium persulfate to rapidly decompose the pollutants into biodegradable intermediates, thereby significantly increasing the rate of the entire repair process and significantly reducing the pollutant concentration in a relatively short period of time.

[0028] 2. The present invention adopts a multi-stage microbial community control strategy, introduces appropriate microbial communities according to different intermediate products of pollutants, and realizes efficient degradation of intermediate products. In the first stage, the microbial community degrades alcohol and ketone intermediate products, and in the second stage, the microbial community specifically mineralizes organic acid intermediate products. This staged treatment method significantly improves the efficiency and effect of microbial remediation.

[0029] 4. The present invention not only accelerates the initial degradation of pollutants during the repair process, but also promotes the complete mineralization of intermediate products through the combined action of chemical and biological composite treatment. The concentration of residual pollutants is extremely low, close to complete removal, and the efficient transformation of pollutants from complex structures to simple harmless substances is achieved, ensuring the thoroughness and long-term stability of the repair.

[0030] 5. The synergistic effect of chemical treatment and biological remediation in the present invention greatly improves the degradation rate and efficiency of pollutants and shortens the remediation time, which can significantly reduce the treatment cost in practical applications. Higher degradation efficiency means reduced energy consumption and labor input during the remediation cycle, thus showing greater advantages in terms of economy and environmental sustainability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flow chart of the method. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Please see attached Figure 1The present invention provides a method for remediating high-concentration organic pollutants in soil, which degrades and removes organic pollutants in soil in stages and efficiently through the synergistic effect of chemical treatment and biological remediation. This example will describe each step and its mechanism of action in detail.

[0034] Step S1: Chemical treatment of nano-zero-valent iron suspension

[0035] 1. Preparation of Nano Zero-Valent Iron Suspension:

[0036] Nano zero-valent iron (nZVI) particles with an average particle size of 50-100 nm and a purity greater than 99% are dispersed in deionized water to prepare a suspension with a concentration of 10-30 g / L. The suspension is treated with an ultrasonic device with an oscillation frequency of 40 kHz and an oscillation time of 30-60 minutes to ensure uniform dispersion of the nanoparticles in the solution. The pH value of the suspension is adjusted to 6-8 by adding an appropriate amount of pH regulator to improve the stability of the nZVI particles and prevent agglomeration.

[0037] 2. Nano-Zero-Valent Iron Injection Process:

[0038] The nZVI suspension was injected into the contaminated soil using an injection system, with the injection volume controlled at 1-5L per cubic meter of soil and the injection depth at 5-20cm. After injection, the soil was mechanically mixed to ensure uniform distribution of nZVI in the soil.

[0039] Nano-zero-valent iron undergoes redox reactions with organic pollutants in the soil, converting high molecular weight organic pollutants (such as polycyclic aromatic hydrocarbons, petroleum hydrocarbons, etc.) into low molecular weight intermediates (such as alcohols, ketones and organic acids), thereby reducing the toxicity of pollutants and improving their biodegradability. This process effectively breaks the chemical bonds in the pollutant molecules, making them easier to handle in the subsequent bioremediation stage.

[0040] Step S2: Oxidation treatment with sodium persulfate

[0041] 1. Preparation and application of sodium persulfate solution:

[0042] Sodium persulfate is dissolved in deionized water to prepare a solution with a concentration of 5-15 g / L. The sodium persulfate solution is applied to the contaminated soil that has been treated with nZVI by uniform spraying or injection, with the injection depth controlled at 5-20 cm and the injection volume at 5-10 L per cubic meter of soil.

[0043] 2. Reaction condition control:

[0044] During the oxidation process, the soil moisture was maintained at 15-20%, and the pH value of the soil was stabilized at 6.5-7.5 by adding phosphate buffer. The reaction time was set to 24-48 hours to ensure that sodium persulfate could effectively oxidize the intermediates in the soil.

[0045] Sodium persulfate decomposes in the soil to generate active sulfate free radicals (SO4 - ), which has strong oxidizing properties and can further degrade intermediates such as alcohols and ketones formed during nZVI treatment, converting them into smaller organic acids. This process greatly improves the degradability of pollutants and provides suitable conditions for the subsequent bioremediation stage.

[0046] Step S3: Introduction and degradation of the first stage microbial community

[0047] 1. Selection and cultivation of microbial communities:

[0048] Pseudomonas and Bacillus were selected as the first stage microbial community and their suspension concentration was adjusted to 10 6 -10 8 CFU / mL. The cultured microbial suspension was evenly added to the chemically treated soil at a volume of 10-20L per cubic meter of soil.

[0049] 2. Degradation condition control:

[0050] During this stage, the soil moisture is maintained at 20-25% and the incubation time is 7-14 days to ensure that the microorganisms grow and reproduce under optimal conditions.

[0051] The first stage microorganisms use alcohols and ketones as carbon sources and decompose these intermediates into simpler organic acids and carbon dioxide through their metabolic enzymes. This decomposition reaction reduces the complexity and toxicity of pollutants and lays the foundation for the treatment of microorganisms in the second stage.

[0052] Step S4: Introduction and degradation of the second stage microbial community

[0053] 1. Selection and cultivation of microbial communities:

[0054] After the first stage of biodegradation is completed, the second stage of microbial community, including Ralstonia and Actinomycetes, is introduced. The suspension concentration is maintained at 10 6 -10 8 CFU / mL and injected into the soil at a volume of 10-20L per cubic meter of soil.

[0055] 2. Degradation condition control:

[0056] In the second stage, the microbial culture temperature is controlled at 28-32°C, the culture time is 48 hours, and the incubation time is 7-14 days to ensure that the microorganisms decompose organic acid intermediates under optimal metabolic conditions.

[0057] Ratna and actinomycetes can efficiently decompose organic acid compounds and completely mineralize them into harmless carbon dioxide and water. The microbial metabolism process at this stage is the final step of the entire remediation method, ensuring the complete removal of pollutants and achieving complete remediation of contaminated soil.

[0058] Step S5: Post-processing

[0059] 1. Physical stabilization and backfilling of soil:

[0060] After bioremediation is completed, the soil is physically stabilized, including drying and screening, to remove unreacted chemicals and microbial residues. The treated soil is then backfilled to its original location, and site preparation and vegetation restoration are carried out to restore the original ecological functions of the soil.

[0061] 2. Site management and environmental monitoring:

[0062] Regular monitoring of the repaired soil, including testing of the soil's physical and chemical properties and residual pollutant concentrations, is carried out to ensure the durability of the repair effect and the ecological safety of the soil.

[0063] The present invention combines the chemical reduction treatment of nano zero-valent iron with the strong oxidation treatment of sodium persulfate to effectively reduce the toxicity of high molecular weight organic pollutants in the soil and convert them into biodegradable intermediates. In addition, through the dynamic regulation of multi-stage microbial communities, efficient decomposition and thorough mineralization of intermediates are achieved. The creativity of the present invention lies in its unique chemical-biological composite remediation strategy, which solves the problem of low efficiency and long time for traditional remediation methods to treat high-concentration organic pollutants, significantly improves the efficiency and integrity of soil remediation, and has good practical value and promotion prospects.

[0064] In order to better understand the present invention, the above method is described in detail below in conjunction with specific embodiments.

[0065] Example 1: Remediation of petroleum contaminated soil

[0066] Pollutant type: The main pollutant in the soil is petroleum hydrocarbon, with a pollution concentration of 1000 mg / kg.

[0067] 1.nZVI chemical treatment:

[0068] The concentration of nano zero-valent iron is 20g / L, the particle size is 50nm, the injection volume is 3L per cubic meter of soil, and the injection depth is 10cm.

[0069] The suspension was treated by ultrasonic agitation for 40 minutes at a frequency of 40 kHz.

[0070] 2. Sodium persulfate oxidation treatment:

[0071] The concentration of sodium persulfate is 10g / L, the injection volume is 7L per cubic meter of soil, and the injection depth is 10cm.

[0072] The soil moisture was maintained at 18%, the pH value was controlled at 7.0, and the reaction time was 48 hours.

[0073] 3. The first stage of bioremediation:

[0074] Pseudomonas and Bacillus were selected, and the concentration of microbial suspension was 10 7 CFU / mL, the amount added per cubic meter of soil is 15L.

[0075] Incubation conditions: soil moisture was 22%, incubation time was 10 days, and temperature was maintained at 22°C.

[0076] 4. Second stage bioremediation:

[0077] Select Ralstonia and Actinomycetes, the concentration of microbial suspension is 10 7 CFU / mL, the amount added per cubic meter of soil is 15L.

[0078] Incubation conditions: soil moisture was 24%, incubation time was 14 days, and temperature was maintained at 30°C.

[0079] Restoration effect: After 24 days of restoration, the concentration of petroleum hydrocarbons in the soil was reduced to below 5 mg / kg, meeting the national standard.

[0080] Example 2: Remediation of pesticide-contaminated soil

[0081] Pollutant type: The main pollutant in the soil is organophosphorus pesticides, with a pollution concentration of 1500 mg / kg.

[0082] 1.nZVI chemical treatment:

[0083] The concentration of nano zero-valent iron is 15g / L, the particle size is 80nm, the injection volume is 4L per cubic meter of soil, and the injection depth is 12cm.

[0084] The suspension was treated by ultrasonic oscillation for 30 minutes at a frequency of 40 kHz.

[0085] 2. Sodium persulfate oxidation treatment:

[0086] The concentration of sodium persulfate is 12 g / L, the injection volume is 5 L per cubic meter of soil, and the injection depth is 12 cm.

[0087] The soil moisture was maintained at 20%, the pH value was controlled at 7.5, and the reaction time was 36 hours.

[0088] 3. The first stage of bioremediation:

[0089] Pseudomonas was selected, and the concentration of microbial suspension was 10 6 CFU / mL, the amount added per cubic meter of soil is 12L.

[0090] Incubation conditions: soil moisture was 23%, incubation time was 7 days, and temperature was maintained at 25°C.

[0091] 4. Second stage bioremediation:

[0092] Select R. leucoderma, the concentration of microbial suspension is 10 8 CFU / mL, the amount added per cubic meter of soil is 18L.

[0093] Incubation conditions: soil moisture was 25%, incubation time was 10 days, and temperature was maintained at 28°C.

[0094] Restoration effect: After 17 days of restoration, the concentration of organophosphorus pesticides in the soil dropped to below 3 mg / kg.

[0095] Example 3: Remediation of benzene contaminated soil

[0096] Pollutant type: The main pollutant in the soil is benzene organic matter, with a pollution concentration of 2000 mg / kg.

[0097] 1.nZVI chemical treatment:

[0098] The concentration of nano zero-valent iron is 25g / L, the particle size is 100nm, the injection volume is 5L per cubic meter of soil, and the injection depth is 15cm.

[0099] The suspension was treated by ultrasonic oscillation for 60 minutes at a frequency of 40 kHz.

[0100] 2. Sodium persulfate oxidation treatment:

[0101] The concentration of sodium persulfate is 15g / L, the injection volume is 6L per cubic meter of soil, and the injection depth is 15cm.

[0102] The soil moisture was maintained at 17%, the pH value was controlled at 6.8, and the reaction time was 48 hours.

[0103] 3. The first stage of bioremediation:

[0104] Pseudomonas was selected, and the concentration of microbial suspension was 10 8 CFU / mL, the amount added per cubic meter of soil is 20L.

[0105] Incubation conditions: soil moisture was 20%, incubation time was 14 days, and temperature was maintained at 20°C.

[0106] 4. Second stage bioremediation:

[0107] Actinomycetes were selected and the concentration of microbial suspension was 10 8 CFU / mL, the amount added per cubic meter of soil is 12L.

[0108] Incubation conditions: soil moisture was 22%, incubation time was 10 days, and temperature was maintained at 28°C.

[0109] Restoration effect: After 24 days of restoration, the concentration of benzene pollutants in the soil dropped to below 7 mg / kg.

[0110] Example 4: Remediation of soil contaminated by polycyclic aromatic hydrocarbons

[0111] Pollutant type: The main pollutant in the soil is polycyclic aromatic hydrocarbons (PAHs), with a pollution concentration of 1800 mg / kg.

[0112] 1.nZVI chemical treatment:

[0113] The concentration of nano zero-valent iron is 20g / L, the particle size is 60nm, the injection volume is 4L per cubic meter of soil, and the injection depth is 10cm.

[0114] The suspension was treated by ultrasonic agitation for 40 minutes at a frequency of 40 kHz.

[0115] 2. Sodium persulfate oxidation treatment:

[0116] The concentration of sodium persulfate is 10g / L, the injection volume is 6L per cubic meter of soil, and the injection depth is 10cm.

[0117] The soil moisture was maintained at 15%, the pH value was controlled at 6.5, and the reaction time was 48 hours.

[0118] 3. The first stage of bioremediation:

[0119] Bacillus was selected, and the concentration of microbial suspension was 10 7 CFU / mL, the amount added per cubic meter of soil is 15L.

[0120] Incubation conditions: soil moisture was 23%, incubation time was 10 days, and temperature was maintained at 24°C.

[0121] 4. Second stage bioremediation:

[0122] Actinomycetes were selected and the concentration of microbial suspension was 10 7 CFU / mL, the amount added per cubic meter of soil is 12L.

[0123] Incubation conditions: soil moisture was 24%, incubation time was 14 days, and temperature was maintained at 30°C.

[0124] Restoration effect: After 28 days of restoration, the concentration of PAHs in the soil was reduced to below 5 mg / kg.

[0125] Example 5: Remediation of soil contaminated by chlorinated organic compounds

[0126] Pollutant type: The main pollutants in the soil are chlorinated organic matter, with a pollution concentration of 1200 mg / kg.

[0127] 1.nZVI chemical treatment:

[0128] The concentration of nano zero-valent iron is 15g / L, the particle size is 50nm, the injection volume is 3L per cubic meter of soil, and the injection depth is 8cm.

[0129] The suspension was treated by ultrasonic oscillation for 30 minutes at a frequency of 40 kHz.

[0130] 2. Sodium persulfate oxidation treatment:

[0131] The concentration of sodium persulfate is 10g / L, the injection volume is 5L per cubic meter of soil, and the injection depth is 8cm.

[0132] The soil moisture was maintained at 18%, the pH value was controlled at 7.0, and the reaction time was 36 hours.

[0133] 3. The first stage of bioremediation:

[0134] Pseudomonas and Bacillus were selected, and the concentration of microbial suspension was 10 6 CFU / mL, the amount added per cubic meter of soil is 12L.

[0135] Incubation conditions: soil moisture was 20%, incubation time was 7 days, and temperature was maintained at 22°C.

[0136] 4. Second stage bioremediation:

[0137] Select R. leucoderma, the concentration of microbial suspension is 10 8 CFU / mL, the amount added per cubic meter of soil is 18L.

[0138] Incubation conditions: soil moisture was 25%, incubation time was 12 days, and temperature was maintained at 30°C.

[0139] Restoration effect: After 19 days of restoration, the concentration of chlorinated organic matter in the soil dropped to below 4 mg / kg.

[0140] In order to better highlight the technical advantages of the present invention, the above method is described in detail below through comparative experiments combined with specific embodiments.

[0141] Comparative experiment 1: Comparison of the effects of nano-zero-valent iron (nZVI) treatment

[0142] Experimental materials: contaminated soil (pollutant type is petroleum hydrocarbon, concentration is about 1500 mg / kg), nano zero-valent iron (nZVI, average particle size 50-100 nm, purity >99%), sodium persulfate, Pseudomonas and Bacillus microbial communities.

[0143] Experimental group (the present invention group):

[0144] S1: Use nZVI suspension with a concentration of 20 g / L, injection volume of 3 L per cubic meter of soil, and injection depth of 10 cm.

[0145] Subsequent steps are performed according to the method of the present invention: sodium persulfate oxidation treatment (S2), two-stage bioremediation (S3 and S4), and post-treatment (S5).

[0146] Comparative Example 1 (without nZVI group):

[0147] S1: No nZVI suspension was added and the chemical reduction treatment stage was skipped directly.

[0148] The subsequent treatment steps were consistent with the experimental group: sodium persulfate oxidation treatment (S2), two-stage bioremediation (S3 and S4), and post-treatment (S5).

[0149] Experimental procedures

[0150] 1. Soil sample preparation:

[0151] Contaminated soil samples were collected in the contaminated area and divided into two groups, respectively used for the experimental group and comparative example 1. After homogenization, each group of samples was loaded into experimental reactors of the same specifications.

[0152] 2. Nano-zero-valent iron treatment (experimental group only):

[0153] After the nZVI suspension was prepared to a concentration of 20 g / L, it was treated with ultrasound for 40 minutes to ensure its uniform dispersion.

[0154] The suspension was injected into the soil of the experimental group with the injection depth controlled at 10 cm and then stirred evenly to ensure that nZVI was evenly distributed in the soil.

[0155] 3. Sodium persulfate oxidation treatment (S2):

[0156] Sodium persulfate solution with a concentration of 10 g / L was added to the two groups of soil respectively, with an injection volume of 5 L per cubic meter of soil and an injection depth of 10 cm.

[0157] The soil moisture was controlled at 18%, the pH value was stabilized at 7.0, and the reaction time was 48 hours.

[0158] 4. Two-stage bioremediation:

[0159] S3 (first stage microbial remediation): Pseudomonas and Bacillus were introduced into the two groups, respectively, and the concentration of microbial suspension was 10 7 CFU / mL, the amount added per cubic meter of soil is 15L, and the incubation time is 10 days.

[0160] S4 (second stage microbial remediation): Then, R. leucoderma and Actinomycetes were introduced, with a suspension concentration of 10 7 CFU / mL, the amount added per cubic meter of soil is 15L, and the incubation time is 14 days.

[0161] 5. Data collection:

[0162] Two groups of soil samples were taken every 48 hours to analyze the changes in the concentrations of organic pollutants and intermediates (such as alcohols, ketones, and organic acids).

[0163] The experimental results are shown in the following table:

[0164]

[0165] From the data in the above table, we can get:

[0166] During the entire treatment process, the initial pollutant concentration of the experimental group decreased significantly faster than that of comparative example 1. On the 10th day, the pollutant concentration of the experimental group dropped to 100 mg / kg, while comparative example 1 still had 600 mg / kg of residue.

[0167] The experimental group produced more intermediates (alcohols, ketones, organic acids), while comparative example 1 produced fewer intermediates in the initial stage, which affected the efficiency of subsequent microbial treatment.

[0168] By the 24th day, the final pollutant concentration in the experimental group dropped below 5 mg / kg, while the residual concentration in comparative example 1 was still 50 mg / kg.

[0169] Mechanism of action of nano zero-valent iron (nZVI): nZVI reacts with organic pollutants through redox reactions, destroying the molecular structure of pollutants and converting them into intermediate products that are more easily biodegradable. This process significantly accelerates the initial degradation rate of pollutants and provides better conditions for subsequent chemical oxidation and biodegradation.

[0170] Advantages of intermediate product generation: Since a large number of intermediate products (such as alcohols and ketones) are generated during the nZVI treatment process, these intermediates are easier to be decomposed and utilized by subsequently introduced microorganisms, thereby improving the efficiency of bioremediation and forming a synergistic effect of chemical-biological composite remediation.

[0171] Limitations of Comparative Example 1: In the absence of nZVI, the molecular structure of the pollutant in Comparative Example 1 remains intact, which limits the effects of sodium persulfate and microorganisms, resulting in low pollutant degradation efficiency and insufficient intermediate product generation, thereby hindering the progress of the subsequent remediation stage.

[0172] The present invention significantly improves the initial degradation efficiency of pollutants by introducing nano zero-valent iron (nZVI) and promotes the generation of biodegradable intermediates. These intermediates make the subsequent bioremediation process more efficient and achieve complete mineralization of pollutants.

[0173] Compared with traditional chemical or biological single treatment methods, the chemical-biological composite remediation strategy of the present invention shows significant advantages in the overall removal rate and degradation rate of pollutants, especially achieving significant degradation of high-concentration organic pollutants in a short period of time.

[0174] Comparative experiment 2: Comparison of the effects of sodium persulfate oxidation treatment

[0175] Experimental materials: contaminated soil (the main pollutant is petroleum hydrocarbons, with an initial concentration of about 1500 mg / kg), nano zero-valent iron (nZVI, average particle size 50-100 nm, purity >99%), sodium persulfate, Pseudomonas and Bacillus microbial communities.

[0176] Experimental group (the present invention group):

[0177] S1: First, use nZVI suspension (20 g / L) with an injection volume of 3 L per cubic meter of soil and an injection depth of 10 cm.

[0178] S2: After nZVI treatment, sodium persulfate solution was added at a concentration of 10 g / L and the injection volume was 5 L per cubic meter of soil.

[0179] Subsequent steps: two-stage bioremediation (S3 and S4) and post-processing (S5).

[0180] Comparative Example 2 (group without sodium persulfate):

[0181] S1: nZVI suspension (20 g / L) was also used, with an injection volume of 3 L per cubic meter of soil and an injection depth of 10 cm.

[0182] The sodium persulfate treatment in stage S2 was skipped and no oxidant was added.

[0183] Subsequent steps: two-stage bioremediation (S3 and S4) and post-processing (S5).

[0184] Experimental procedures

[0185] 1. Soil sample preparation:

[0186] Contaminated soil samples were collected and divided into an experimental group and a comparative group 2 to ensure that the two groups of samples had the same initial concentrations of pollutants and physicochemical properties.

[0187] Each group of samples was evenly distributed in a separate reactor for subsequent processing.

[0188] 2. Nano-Zero-Valent Iron Treatment (S1):

[0189] Both groups were injected with nZVI suspension (20 g / L) under the same conditions, with an injection depth of 10 cm and stirred evenly.

[0190] 3. Sodium persulfate oxidation treatment (S2, experimental group only):

[0191] Sodium persulfate solution was added to the soil of the experimental group at a concentration of 10 g / L and an injection volume of 5 L per cubic meter of soil.

[0192] The soil moisture was controlled at 18%, and the pH was stabilized at 7.0 using phosphate buffer, and the reaction time was 48 h.

[0193] Comparative Example 2 skips this step.

[0194] 4. Two-stage bioremediation (S3 and S4):

[0195] S3: The first-stage microbial community (Pseudomonas and Bacillus) was introduced into the two groups respectively, with a microbial concentration of 10 7 CFU / mL, the amount added per cubic meter of soil is 15L, and the incubation time is 10 days.

[0196] S4: Then the second stage microbial community (Rattella and Actinomycetes) was introduced at the same concentration of 10 7 CFU / mL, the amount added per cubic meter of soil is 15L, and the incubation time is 14 days.

[0197] 5. Data collection:

[0198] Soil samples were collected every 48 hours to analyze the changes in concentrations of organic pollutants and their intermediates (alcohols, ketones, and organic acids).

[0199] The experimental results are shown in the following table:

[0200]

[0201] From the data in the above table, we can get:

[0202] Initial degradation efficiency: After adding sodium persulfate, the pollutant concentration in the experimental group decreased significantly. On the second day, the concentration dropped to 900 mg / kg, while the concentration in the comparative example 2 dropped to 1100 mg / kg, with a significant difference.

[0203] Intermediate product generation: The experimental group generated a large amount of intermediate products (such as alcohols, ketones, and organic acids) during the oxidation process. The amount of these intermediate products reached 600 mg / kg on the 8th day, while that of comparative example 2 was only 300 mg / kg.

[0204] Comparison of final concentrations: The pollutant concentration in the experimental group dropped to below 3 mg / kg on the 24th day, while that in comparative example 2 still remained at 40 mg / kg.

[0205] The mechanism of sodium persulfate oxidation: Sodium persulfate decomposes in the soil to generate sulfate free radicals (SO4· - ), this free radical has extremely high oxidizing ability and can quickly destroy the molecular structure of organic pollutants and convert them into low molecular weight intermediates (such as alcohols, ketones and organic acids), which are highly biodegradable.

[0206] The role of intermediates: The experimental group produced more intermediates, which provided a good metabolic basis for subsequent microbial remediation, enabling microorganisms to mineralize these degradation products more quickly in the subsequent stages, thereby improving the overall remediation efficiency.

[0207] Limitations of Comparative Example 2: In the absence of sodium persulfate oxidation treatment, the pollutant degradation in Comparative Example 2 relies on nano-zero-valent iron and microbial remediation, but lacks the support of the oxidation treatment stage, resulting in insufficient intermediate product generation and slow pollutant degradation.

[0208] After adding sodium persulfate for oxidation treatment, the present invention not only significantly accelerates the initial degradation rate of pollutants, but also generates a large number of intermediates for further degradation by microorganisms, thereby improving the efficiency of the bioremediation stage. Compared with traditional single chemical treatment or bioremediation methods, the chemical-biological composite remediation strategy of the present invention shows a higher degradation rate, stronger removal ability and more thorough pollutant mineralization effect, significantly improving the overall performance of soil remediation.

[0209] Comparative experiment 3: Comparison of the effects of single microbial remediation and multi-stage microbial remediation

[0210] Experimental materials: contaminated soil (the main pollutants are polycyclic aromatic hydrocarbons, with an initial concentration of about 1800 mg / kg), nano zero-valent iron (nZVI, average particle size 50-100 nm, purity >99%), sodium persulfate, Pseudomonas, Bacillus, Ralstonia and actinomycete microbial communities.

[0211] Experimental group (the present invention group):

[0212] S1 and S2: nZVI suspension (20 g / L) was used first, followed by sodium persulfate oxidation treatment (10 g / L) to ensure that an intermediate product was generated after chemical treatment.

[0213] S3: Introduce the first-stage microbial community (Pseudomonas and Bacillus) to degrade alcohol and ketone intermediates.

[0214] S4: The second stage microbial community (Rattella and Actinomycetes) is then introduced to degrade organic acid intermediates.

[0215] Comparative Example 3 (single microbial group):

[0216] The chemical treatments of steps S1 and S2 are also performed.

[0217] Direct introduction of a single microbial community (Pseudomonas) to treat pollutants and their intermediates at all degradation stages

[0218] Experimental procedures

[0219] 1. Soil sample preparation:

[0220] PAH-contaminated soil samples were collected in the contaminated area and evenly divided into two groups (experimental group and comparative example 3) to ensure that the physical and chemical properties of the samples were consistent.

[0221] The samples were uniformly loaded into individual reactors for subsequent processing steps.

[0222] 2. Chemical treatment stage (S1 and S2):

[0223] Both groups of soil were treated with nZVI (20 g / L) and then with sodium persulfate oxidation (10 g / L) under the same conditions. The reaction time was 48 hours. The soil moisture was controlled at 18% and the pH value was stabilized at 7.0.

[0224] Ensure that chemical treatments generate intermediate products such as alcohols, ketones and organic acids.

[0225] 3. Microbial remediation stage:

[0226] Experimental group (multi-stage microbial remediation):

[0227] S3: First introduce the first stage microbial community (Pseudomonas and Bacillus) at a concentration of 107 CFU / mL, the amount added per cubic meter of soil is 15L, and the incubation time is 10 days.

[0228] S4: Then the second stage microbial community (Rattella and Actinomycetes) was introduced at a concentration of 10 7 CFU / mL, the amount added per cubic meter of soil is 15L, and the incubation time is 14 days.

[0229] Comparative Example 3 (single microorganism remediation):

[0230] A single microbial community (Pseudomonas) was directly introduced at a concentration of 10 7 CFU / mL, the amount added per cubic meter of soil is 30L, and the single incubation time is 24 days.

[0231] 4. Data collection:

[0232] The two groups of samples were sampled every 48 hours to analyze the changes in pollutant concentrations and the concentrations of various intermediate products (alcohols, ketones, and organic acids).

[0233] The experimental results are shown in the following table:

[0234]

[0235] From the data in the above table, we can get:

[0236] Initial advantages of multi-stage remediation: The pollutant concentration in the experimental group dropped to 1200 mg / kg on the second day, while that in comparative example 3 only dropped to 1400 mg / kg. The experimental group generated more intermediates, indicating that the microbial community in the first stage effectively promoted the generation and initial degradation of intermediates.

[0237] Degradation efficiency of intermediate products: The experimental group successfully converted most of the alcohols and ketones into organic acids on the 10th day, and rapidly reduced the concentration of intermediate products in the subsequent second-stage degradation process. However, due to the lack of microorganisms specifically targeting the degradation of organic acids, the intermediate products were retained in the comparative example 3, and the concentration of pollutants decreased slowly.

[0238] Final pollutant removal rate: The experimental group reduced the pollutant concentration to below 5 mg / kg on the 24th day, achieving a significant pollutant mineralization effect; the final concentration of comparative example 3 was still 600 mg / kg, indicating that the effect of single microbial remediation was significantly limited when faced with different types of intermediates.

[0239] Mechanism of action of multi-stage microbial communities: The experimental group used a microbial community that was regulated in stages. The first-stage microorganisms (Pseudomonas and Bacillus) efficiently degraded the alcohol and ketone intermediates generated after chemical treatment, providing suitable substrates for the second stage. The second-stage microorganisms (Rattella and Actinomycetes) thoroughly mineralized the organic acid intermediates, maximizing the degradation rate of pollutants.

[0240] Limitations of a single microbial community: Since Comparative Example 3 uses a single microorganism (Pseudomonas), its degradation mechanism cannot effectively cover different types of intermediates, especially for organic acid intermediates, the degradation efficiency is significantly reduced, resulting in a significant reduction in the repair effect.

[0241] Synergistic effect of microbial communities: The multi-stage microbial communities in the experimental group achieved staged decomposition of pollutants through targeted degradation of intermediate products, greatly improving the final mineralization efficiency and effectively preventing the re-accumulation of organic pollutants in the soil.

[0242] The multi-stage microbial remediation strategy adopted by the present invention greatly improves the degradation rate and final mineralization effect of pollutants. Compared with the traditional single microbial remediation method, the present invention uses a precise microbial community regulation mechanism to enable different types of intermediates to be quickly decomposed under appropriate conditions, thereby greatly improving the pollutant removal efficiency and demonstrating its outstanding advantages in the treatment of various complex organic pollutants.

[0243] Comparative experiment 4: Comparison of the effects of single chemical treatment or biological treatment and chemical-biological combined treatment

[0244] Experimental materials: contaminated soil (the main pollutant is benzene organic matter, with an initial concentration of about 2000 mg / kg), nano zero-valent iron (nZVI, average particle size 50-100 nm, purity >99%), sodium persulfate, Pseudomonas, Bacillus, Ralstonia and actinomycete microbial communities.

[0245] Experimental group settings:

[0246] Experimental group (the present invention group):

[0247] Chemical treatment: nZVI suspension (20 g / L) and sodium persulfate (10 g / L) were used for chemical treatment.

[0248] Bioremediation: A multi-stage microbial community (Pseudomonas, Bacillus, Ralstonia, and Actinomycetes) was introduced for bioremediation.

[0249] Comparative Example 4 (single chemical treatment group):

[0250] Only chemical treatment was performed using nZVI suspension (20 g / L) and sodium persulfate (10 g / L) without any bioremediation stage.

[0251] Comparative Example 5 (single bioremediation group):

[0252] The chemical treatment stage was skipped and a single microbial community (Pseudomonas) was directly introduced for bioremediation.

[0253] Experimental procedures

[0254] 1. Soil sample preparation:

[0255] Soil samples contaminated with benzene organic matter were collected in the polluted area and evenly divided into three groups (experimental group, comparative example 4, and comparative example 5) to ensure that the pollutant concentration and physical and chemical properties of each group of samples were consistent.

[0256] 2. Chemical treatment stage (S1 and S2, applicable to the experimental group and comparative example 4):

[0257] nZVI treatment: nZVI suspension (20 g / L) was injected into the soil at a volume of 4 L per cubic meter of soil and an injection depth of 10 cm.

[0258] Sodium persulfate treatment: After nZVI treatment, sodium persulfate solution (10 g / L) was injected at a rate of 5 L per cubic meter of soil, maintaining soil moisture at 18% and pH at 7.0.

[0259] 3. Bioremediation stage:

[0260] Experimental group (multi-stage microbial remediation):

[0261] S3: Introduce the first stage microbial community (Pseudomonas and Bacillus), the microbial concentration is 10^7 CFU / mL, the addition amount is 15L per cubic meter of soil, and the incubation time is 10 days.

[0262] S4: The second stage microbial community (Rattella and Actinomycetes) was then introduced at a concentration of 10^7 CFU / mL, 15L was added per cubic meter of soil, and the incubation time was 14 days.

[0263] Comparative Example 5 (single bioremediation group):

[0264] A single microbial community (Pseudomonas) was introduced with a concentration of 10^7 CFU / mL, 30L added per cubic meter of soil, and a single incubation time of 24 days.

[0265] 4. Data collection:

[0266] Three groups of soil samples were collected every 48 hours to analyze the changes in the concentrations of pollutants and various intermediate products (such as alcohols, ketones, and organic acids).

[0267] The experimental results are shown in the following table:

[0268]

[0269] From the data in the above table, we can get:

[0270] Initial degradation efficiency: In the first 4 days, the pollutant concentration in the experimental group dropped rapidly from 2000 mg / kg to 1200 mg / kg, while that in comparative example 4 (single chemical treatment) dropped to 1400 mg / kg, and that in comparative example 5 (single biological remediation) only dropped to 1800 mg / kg, indicating that the chemical-biological composite treatment showed faster efficiency in the initial degradation.

[0271] Generation and degradation of intermediates: The experimental group generated a large amount of intermediates (alcohols, ketones, organic acids) after chemical treatment, which were rapidly degraded during the bioremediation stage. However, comparative example 4 generated fewer intermediates, and comparative example 5 produced almost no intermediates in the absence of chemical treatment.

[0272] Comparison of final concentrations: The experimental group reduced the pollutant concentration to below 3 mg / kg on the 24th day, while the pollutant concentration of comparative example 4 was still 500 mg / kg, and the pollutant concentration of comparative example 5 was 900 mg / kg, showing the significant advantage of chemical-biological composite treatment in the final pollutant removal rate.

[0273] Chemical-biological synergistic mechanism: The present invention group first converts complex organic pollutants into more easily degradable intermediates (such as alcohols, ketones and organic acids) through the combined chemical treatment of nZVI and sodium persulfate. These intermediates create suitable conditions for subsequent microbial degradation.

[0274] Dynamic regulation of multi-stage microbial communities: The experimental group used a two-stage microbial remediation strategy to achieve efficient mineralization of different types of intermediates. The first-stage microbial community targeted the degradation of alcohols and ketones, and the second-stage microbial community targeted the degradation of organic acids, achieving a synergistic degradation effect of staged treatment.

[0275] Limitations of single treatment methods: Although comparative example 4 (single chemical treatment) can initially degrade pollutants, the lack of subsequent microbial degradation makes it difficult for intermediate products to be completely mineralized. Comparative example 5 (single biological remediation) lacks a chemical pretreatment stage, and the complex molecular structure of the pollutants is difficult to be directly degraded by microorganisms, resulting in low overall degradation efficiency.

[0276] The chemical-biological composite treatment method of the present invention is significantly superior to single chemical treatment and single biological remediation methods in treating high-concentration organic pollutants in soil. Through chemical and biological synergy, the present invention achieves a higher degradation rate and thorough mineralization of pollutants. Experimental data verify the efficient conversion ability of the present invention to intermediate products in the multi-stage treatment process, proving its strong technical advantages and practical application potential in the field of complex soil pollution remediation.

[0277] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for remediating high-concentration organic pollutants in soil, characterized in that: The following steps are involved: S1, injecting nano zero-valent iron suspension into the soil for chemical treatment; S2, after the nano zero-valent iron treatment, sodium persulfate is added for oxidation treatment; S3, introducing the first stage microbial community into the chemically treated soil to promote the biodegradation of alcohol and ketone intermediates; S4. After the first stage of biodegradation is completed, the second stage of microbial community is introduced to treat the organic acid intermediates; S5. Carry out post-treatment of the soil after the restoration is completed.

2. The method for remediating high-concentration organic pollutants in soil according to claim 1, characterized in that: The preparation steps of the nano zero-valent iron suspension include: Dispersing nano zero-valent iron particles in deionized water to prepare a suspension with a concentration of 10-30 g / L; The suspension is subjected to an oscillation treatment, the ultrasonic frequency is 40 kHz, and the oscillation time is 30-60 minutes; During the suspension preparation, the pH value of the suspension was adjusted to 6-8.

3. The method for remediating high-concentration organic pollutants in soil according to claim 2, characterized in that: The nanometer zero-valent iron particles have an average particle size of 50-100 nm and a purity of more than 99%.

4. The method for remediating high-concentration organic pollutants in soil according to claim 1, characterized in that: The injection amount of the nano zero-valent iron is controlled at 1-5L per cubic meter of soil, and the injection depth is 5-20cm.

5. The method for remediating high-concentration organic pollutants in soil according to claim 1, characterized in that: The sodium persulfate oxidation treatment comprises the following steps: Dissolve sodium persulfate in deionized water to prepare a solution with a concentration of 5-15 g / L; The sodium persulfate solution is evenly applied to the contaminated soil treated with nano-zero-valent iron, with the injection depth ranging from 5 to 20 cm and the injection volume controlled at 5 to 10 L per cubic meter of soil; During the oxidation treatment, the soil moisture was maintained in the range of 15-20%, and the soil pH was stabilized at 6.5-7.5 by adding phosphate buffer.

6. The method for remediating high-concentration organic pollutants in soil according to claim 1, characterized in that: The first stage microbial community includes Pseudomonas and Bacillus, and the concentration of the suspension is 10 6 -10 8 CFU / mL, the addition amount is 10-20L per cubic meter of soil.

7. The method for remediating high-concentration organic pollutants in soil according to claim 6, characterized in that: During the first stage of microbial degradation, the soil moisture is maintained at 20-25% and the incubation time is 7-14 days.

8. The method for remediating high-concentration organic pollutants in soil according to claim 1, characterized in that: The second stage microbial community includes Ralstonia and Actinomycetes, and the concentration of the suspension is 10 6 -10 8 CFU / mL, the addition amount is 10-20L per cubic meter of soil.

9. The method for remediating high-concentration organic pollutants in soil according to claim 8, characterized in that: The culture temperature of the microorganisms in the second stage is 28-32° C., the culture time is 48 hours, and the incubation time is 7-14 days.

10. The method for remediating high-concentration organic pollutants in soil according to claim 1, characterized in that: The post-treatment includes physical stabilization and backfilling of the soil.

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