A method for remediation of polycyclic aromatic hydrocarbon contaminated soil

Abstract

The application relates to a method for repairing polycyclic aromatic hydrocarbon (PAHs) contaminated soil, and the specific steps are as follows: S1, surfactant elution treatment of the PAHs contaminated soil to obtain elution treated soil; S2, modification of biochar by using a modified solution to obtain modified biochar; S3, mixing and feeding the modified biochar, MoS2 and single persulfate obtained in the step S2 into the elution treated soil obtained in the step S1 to complete the repair of the PAHs contaminated soil. Compared with the prior art, the surfactant, biochar and MoS2 technology are comprehensively applied to the repair of the PAHs contaminated soil, the solubility and bioavailability of the PAHs are enhanced by using the surfactant first, then the modified biochar is combined with the MoS2 or PMS system to form a composite repair system, and the removal efficiency and repair effect of the PAHs can be improved.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to a method for remediating polycyclic aromatic hydrocarbon (PAH) contaminated soil. Background Technology

[0002] Existing research indicates that surfactants play a significant role in the remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soil. Nonionic surfactants such as TX100 and Tween80 are examples. [1] It has been proven to effectively improve the solubility and biodegradability of PAHs. The effect of the nonionic surfactant Twcen80 on the absorption of phenanthrene and pyrene by ryegrass was studied using a hydroponic system simulation. The results showed that when the initial concentrations of phenanthrene and pyrene in the culture medium were 1.00 mg·L⁻¹, the absorption of phenanthrene and pyrene by PAHs was significantly improved. -1 and 0.12 mg·L -1 At that time, 0–105.6 mg·L -1 Within a certain range, low concentrations of Twcen80 can promote the absorption of phenanthrene and pyrene by roots and leaves. However, current research is mostly limited to the effects of surfactant application on the remediation of PAH-contaminated environments in the rhizosphere, with limited research on the action process and mechanism of surfactants. Plant-surfactant combined rhizosphere remediation technology will become a new research focus in the field of rhizosphere remediation of PAH-contaminated soils. In addition, certain specific biosurfactants such as lactic acid glycerides and BS29 bio-emulsion have also shown good effects. [2-5] These surfactants promote the release of PAHs from the soil and their biodegradation by increasing their water solubility.

[0003] Surfactants can significantly increase the solubility of polycyclic aromatic hydrocarbons (PAHs), thereby improving their elution efficiency from soil. Studies have shown that different types of surfactants have varying elution effects on PAHs. For example, Triton X-100 exhibited the highest gravimetric solubility in removing acetylnaphthalene and fluorescein. Furthermore, the elution effect can be further optimized by adjusting factors such as surfactant concentration, elution time, and solid-liquid ratio. [9] .

[0004] Surfactants can alter the surface charge and absorption potential energy of soil, thereby affecting the occurrence or solubility of pollutants. This alteration helps to improve the desorption capacity of pollutants from the soil and promote their bioremediation.

[0005] In the removal of heavy metals and radionuclides, surfactants also involve mechanisms of dissolution, complexation, and ion exchange. These mechanisms also apply to the removal of polycyclic aromatic hydrocarbons (PAHs), making pollutants easier to remove by forming stable complexes or ion exchange complexes.

[0006] Surfactants not only exhibit good remediation effects when used alone, but they can also be combined with other remediation techniques, such as chemical, biological, or physical techniques, to enhance overall remediation efficiency. For example, in the intensive remediation of hydrophobic organic pollutants (HOCs) in soils, surfactants are often used to improve the treatment efficiency of other remediation technologies.

[11] .

[0007] Although traditional surfactants exhibit high elution rates during remediation, they may cause secondary pollution to the soil. Therefore, researchers are exploring novel environmentally friendly surfactants, such as the gemini anionic surfactant AGS, and nonionic surfactants Tween-80 and Triton X-100, in order to find remediation technologies that are both environmentally friendly and economical.

[0008] Biochar is a highly efficient adsorbent material, and its adsorption capacity for pollutants can be enhanced by introducing different functional groups. For example, ammonia activation can increase the amino groups on the surface of biochar, while plasma activation helps to increase oxygen-containing functional groups. [6] In addition, metal impregnation technology has also been used to increase the specific surface area and catalytic active sites of biochar, thereby enhancing its catalytic performance.

[0009] Acid-base modification involves treating biochar with acid or alkali solutions to alter its specific surface area and pore volume, and to introduce surface functional groups, thereby improving its adsorption performance. For example, modifying wood-based biochar with ammonia can introduce amino functional groups on its surface, which have a strong affinity for certain contaminants, such as copper ions.

[0010] Physical modification methods mainly include high-temperature calcination. High-temperature calcination (heating at 800℃~900℃ for 1~2 hours) can remove organic matter and other impurities from the pores of biochar, change its pore structure, increase its specific surface area, and thus enhance its adsorption capacity.

[0011] Chemical modification methods include treating biochar with different chemical reagents. For example, biochar can be modified with acidic and basic chemical reagents such as HNO3, H2SO4, H3PO4, Na2CO3, NH3·H2O, NaOH, and Ca(OH)2. By pretreatment, mixing, and impregnation, the acidity and alkalinity of the biochar surface can be directionally controlled, which can significantly change its surface properties and adsorption performance.

[0012] Biomodification methods utilize microorganisms or other biological materials to treat biochar. For example, by immobilizing Yarrowia lipolytica Tzyx3 on biochar to form a biochar agent, the removal efficiency of polycyclic aromatic hydrocarbons such as naphthalene, phenanthrene, and pyrene in water can be significantly improved.

[0013] Preparing composite materials is also an effective modification method. For example, loading P-doped g-C3N4 onto biochar can significantly improve the photocatalytic degradation efficiency of naphthalene, with a removal rate of 76.41%, a first-order kinetic rate constant of 0.0084 min^-1, which is 3.1 times that of pure g-C3N4.

[0014] Iron-loaded biochar has also been used to enhance research on the removal mechanism of polycyclic aromatic hydrocarbons (PAHs) in constructed wetlands. This modification method enhances the removal capacity of biochar for PAHs by adding iron.

[0015] These studies demonstrate that different modification methods can significantly improve the removal efficiency of biochar for polycyclic aromatic hydrocarbons.

[0016] MoS2, as a metastable metallic material, exhibits excellent catalytic performance in activated persulfate (PMS) systems. PMS is an effective sulfate radical precursor capable of generating highly oxidizing SO4. - • Free radicals are used to degrade recalcitrant organic compounds. MoS2 can activate PMS not only through thermal activation and acoustic activation, but also through photoactivation to further enhance its catalytic efficiency.

[0017] MoS2, as a heterogeneous metal catalyst, can effectively activate PMS (polystyrene-methyl) to generate highly oxidizing reactive oxygen species, thereby removing recalcitrant organic matter from water. Studies have shown that MoS2 nanosheets can significantly improve the activation efficiency of PMS through the piezoelectric effect. When compressive strain is applied, MoS2 nanosheets can generate hydroxyl radicals (·OH), which are further converted into SO42-. - • Free radicals, thereby enhancing the activation effect of PMS ( Figure 3 ).

[0018] In the US / MoS2NFs / PMS system, the combination of ultrasound (US) and MoS2 nanoflowers (NFs) further enhanced the activation efficiency of PMS. Experimental results showed that this combined system had a higher degradation efficiency compared to the single system, revealing the synergistic effect of US and MoS2 on PMS activation. Density functional theory calculations further elucidated the charge distribution in polarized MoS2 nanosheets under different strains and explained the piezoelectric catalytic properties of MoS2 nanosheets and the reaction pathway between PMS and the active edge support of MoS2. Figure 4 ).

[0019] MoS2 has also demonstrated excellent performance in removing specific pollutants. For example, studies have shown that MoS2 enhances Fe... 2+ Activated PMS systems can effectively remove sulfamethoxazole (SMX) and reduced hexavalent chromium (Cr(VI)) from solution. [7]In addition, MoS2 has been used to activate PMS to remove organic pollutants such as tetracycline (TC).

[0020] MoS2 can also be combined with other materials to form composites, thereby improving its catalytic performance. For example, the Fe3O4 / MoS2 composite material, synthesized via a hydrothermal method, exhibits excellent ability to degrade 2,4-dichlorophenoxyacetic acid (2,4-D). [8] Furthermore, the CoFe2O4@MoS2 composite material also exhibited efficient tetracycline degradation capabilities.

[0021] MoS2 not only performs exceptionally well in laboratory research but also shows potential for application in practical environmental remediation. For example, the piezoelectric activation effect of MoS2 nanoflowers on persulfate. [9] It can promote the degradation of waterborne organic pollutants and provide a new approach to utilizing natural mechanical energy in environmental remediation.

[0022] The combination of MoS2 and persulfate systems has significant advantages in water treatment. By catalytically activating PMS to generate strong oxidizing free radicals, it effectively degrades recalcitrant organic pollutants.

[10] Meanwhile, the combined application of MoS2 with other materials further enhances its catalytic performance and environmental remediation potential.

[0023] MoS2, as a heterogeneous metal catalyst, can effectively activate PMS to remove recalcitrant organic matter from water. In the MoS2 / Fe... 2+ In the PMS system, the degradation rate of sulfamethoxazole (SMX) reached 88.5% after 6 minutes of reaction, which is much higher than that of Fe. 2+ The degradation rate of SMX by PMS or MoS2 / PMS systems at 6 minutes. MoS2 can accelerate Fe... 2+ Activation of PMS and persulfate (PDS) generates a large number of reactive oxygen species (ROS), such as ·OH and SO42-. - · and 1O2. Therefore, the introduction of MoS2 effectively promotes the free radical (·OH, SO42-) - The formation of ·), 1O2 and Fe(IV) improves the efficiency of the PMS activation process.

[0024] Increasing the defect density of active sites, edge sites, and basal planes, as well as regulating the electronic structure and crystal phase, are effective strategies to improve the intrinsic catalytic activity and overall catalytic performance of MoS2. Doping iron-based catalysts with multiple metals has proven to be an effective way to improve persulfate activation performance. For example, by introducing MoS2 onto the surface of FeCo nanoboxes, a highly efficient persulfate activation catalyst (FeCo@MoS2) with better catalytic performance was successfully synthesized. Layered MoS2 with the strongest piezoelectric activity was synthesized and screened using different methods, and its catalytic performance was further improved by loading it onto a porous ceramic support. MoS2 exhibits excellent catalytic performance in activating single persulfate systems, especially with Fe... 2+ When used in combination with metal ions, the degradation efficiency can be significantly improved. Summary of the Invention

[0025] The purpose of this invention is to provide a method for remediating polycyclic aromatic hydrocarbon (PAH) contaminated soil. This invention integrates surfactants, biochar, and MoS2 technology for the remediation of PAH-contaminated soil. First, surfactants are used to enhance the solubility and bioavailability of PAHs. Then, modified biochar is combined with a MoS2 or PMS system to form a composite remediation system, which can improve the removal efficiency and remediation effect of PAHs.

[0026] The objective of this invention can be achieved through the following technical solutions:

[0027] A method for remediating polycyclic aromatic hydrocarbon (PAH) contaminated soil, comprising the following specific steps:

[0028] S1. Polycyclic aromatic hydrocarbon contaminated soil is treated by surfactant elution to obtain eluted soil.

[0029] S2. Modify the biochar using a modification solution to obtain modified biochar;

[0030] S3. The modified biochar, MoS2 and persulfate obtained in step S2 are mixed and added to the eluted soil obtained in step S1 to complete the remediation of polycyclic aromatic hydrocarbon contaminated soil.

[0031] Furthermore, in step S1, the polycyclic aromatic hydrocarbons include PHE, PYR, and BaP.

[0032] Further, in step S1, the polycyclic aromatic hydrocarbon contaminated soil is ground and sieved, a surfactant solution is added, and the soil is obtained after elution treatment by shaking and centrifugation extraction.

[0033] Further, in step S1, the surfactant is C12-ED3A3Na, and the concentration of the surfactant is 6000 mg / L and the pH is 11.72.

[0034] Furthermore, in step S1, the elution time is 4 hours.

[0035] Further, in step S2, the biochar is prepared as follows:

[0036] Weigh an appropriate amount of pine sawdust, dry it, and sieve it. Immerse the sieved sawdust powder in NaOH solution and wash it until the pH value is stable. Then immerse it in HCl solution, repeat the process several times, and dry it for later use. Heat it to 400℃ at a heating rate of 5℃ / min and then anaerobically calcine it at a constant temperature for 2 hours to obtain biochar.

[0037] Further, in step S2, the solid-liquid ratio of the biochar and the modified solution is 1 g:(20-1000 mL).

[0038] Further, in step S2, the modified solution includes HNO3, H3PO4, Ca(OH)2 and NH3·H2O.

[0039] Furthermore, the modified solution is H3PO4.

[0040] Furthermore, in step S3, the modified biochar, MoS2 and persulfate obtained in step S2 are evenly spread on the soil after elution treatment obtained in step S1, and then plant seedlings are transplanted, watered, and managed in the field. Repeating the sowing 2-5 times can remediate the soil contaminated with polycyclic aromatic hydrocarbons in situ.

[0041] Furthermore, in step S3, the amount of modified biochar obtained in step S2 is 4-5 kg / m³. 2 The dosage of persulfate is 4–6 kg / m³. 2 The mixing depth is 10–20 cm, and the MoS2 dosage is 2–3 kg / m³. 2 The mixing depth is 10-20cm.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] 1. This invention combines modified biochar with a MoS2 or PMS system to form a composite remediation system. The effectiveness of this composite system is verified through experiments, and parameters are continuously optimized based on practical applications. For example, the removal efficiency of surfactants is tested under different concentrations and temperatures, as well as the optimal ratio and contact time of biochar and MoS2.

[0044] 2. By utilizing composite surfactants to enhance biochar-loaded MoS2 or monopersulfate systems, the remediation effect of polycyclic aromatic hydrocarbon (PAH) contaminated soils was significantly improved through multifaceted synergistic effects. This method is not only highly efficient and environmentally friendly, but also widely applicable to the remediation of PAH-contaminated soils of different types and degrees.

[0045] 3. In the process of studying the adsorption of heavy metals by biochar, this invention found that carboxyl, hydroxyl, and amino groups contribute significantly. Therefore, HNO3, H3PO4, Ca(OH)2 and NH3·H2O were selected as acid and alkali modification solutions to regulate the surface functional groups of biochar.

[0046] 4. Optimizing the ratio of nonionic and chelating surfactants in the remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soil requires comprehensive consideration of multiple factors, including surfactant type, concentration, elution time, solid-liquid ratio, and their combined effects. Nonionic surfactants such as Triton X-100, AEO-9, and Tween80 have shown good results in treating naphthalene-contaminated soil. Chelating surfactants such as sodium N-lauroyl ethylenediamine triacetate (LED3A) and C... 12 -ED3A3Na also showed high efficiency in treating soils contaminated with a combination of heavy metals and polycyclic aromatic hydrocarbons (PAHs); the concentration of surfactants significantly affected the elution effect. For example, Triton X-100 effectively removed PAHs at a concentration of 8 g / L. Meanwhile, the nonionic surfactant Brij30 significantly improved PAH desorption at lower doses, while C12E8 did not enhance PAH removal at any dose; the combination of nonionic and chelating surfactants may produce a synergistic effect.

[13] For example, when chelating surfactant LED3A is used in combination with nonionic surfactants, it can effectively remove cadmium and pyrene from soil simultaneously; chelating surfactants such as ED3A are environmentally safe, biodegrade rapidly, and are virtually nontoxic to mammals and aquatic plants and animals.

[0047] 5. This invention optimizes the ratio of nonionic and chelating surfactants based on the following steps: Preliminary screening: Selecting nonionic and chelating surfactants with high elution efficiency. Concentration optimization: Determining the optimal concentration through experiments to achieve the highest elution efficiency. Compounding experiments: Exploring the compounding ratio of nonionic and chelating surfactants to find the optimal combination. Environmental assessment: Ensuring that the selected surfactants are environmentally safe and have good biodegradability.

[0048] 6. The preparation method and type of biochar have a significant impact on the removal efficiency of polycyclic aromatic hydrocarbons (PAHs). Different preparation methods result in different physicochemical properties of biochar, thus affecting its adsorption and degradation capacity for PAHs. Pyrolysis: Biochar prepared by high-temperature pyrolysis typically has larger pores and specific surface area, which helps to improve its adsorption capacity. Hydrothermal carbonization: This method uses high-temperature liquid water as a medium, which can simultaneously dissolve organic and inorganic matter, thus the prepared biochar may have higher chemical activity and adsorption capacity. Gasification and microwave pyrolysis: These methods can also prepare biochar with different pore structures and surface properties, thus affecting its PAH removal efficiency.

[0049] 7. Biochar from different raw material sources varies in pore size, porosity, and specific surface area, which affects its adsorption and degradation capacity for PAHs. For example, rice husk biochar has been shown to have a high capacity for PAH degradation in immobilized microbial agents. Biochar made from yew and Bridal Wreath exhibits high adsorption efficiency in removing PAHs from urban stormwater runoff, especially under 300℃ combustion conditions, where the adsorption efficiency for pyrene can reach 88%. Biochar can remove PAHs not only through physical adsorption but also through biodegradation by immobilized microbial agents. For example, biochar immobilized with Yeastia lipolytica to form an agent shows a significant synergistic effect in removing naphthalene, phenanthrene, and pyrene from water.

[12] .

[0050] 8. In persulfate monosulfate (PMS) systems, cobalt ions (Co2+) have been shown to have the best activation performance. However, the high biotoxicity of cobalt ions can lead to secondary pollution problems, thus requiring measures to control their toxicity. To effectively activate PMS and control toxicity, other transition metal ions can be considered as alternatives. For example, iron ions (Fe2+) and manganese ions (Mn2+) have also been extensively studied for PMS activation.

[14] Furthermore, they are less toxic than cobalt ions. In particular, iron and manganese ions are gradually becoming alternatives to cobalt oxides due to their environmental friendliness and low cost. In the process of activating PMS using transition metal ions, the optimal molar ratio of metal ions to PMS is a crucial factor determining the activation effect. For example, the optimal activation molar ratio of PMS to Fe2+ is 1:1, and adding the activator gradually during the addition of metal ions yields better degradation results than adding it all at once. Attached Figure Description

[0051] Figure 1 C 12 The effect of ED3A3Na concentration on phenanthrene removal rate;

[0052] Figure 2 The effect of elution time on phenanthrene removal rate;

[0053] Figure 3 The mechanism by which MoS2 nanosheets enhance the activation effect of PMS;

[0054] Figure 4 The reaction pathway between PMS and the MoS2 active edge carrier;

[0055] Figure 5 The data show the adsorption of Cr(VI) by biochar before and after acid-base modification, and the fitting results of the Langmuir and Freundlich isotherm models. Detailed Implementation

[0056] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0057] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features described herein can be combined with each other.

[0058] Example 1

[0059] This embodiment provides a method for treating polycyclic aromatic hydrocarbon (PAH) contaminated soil with surfactants, and the specific steps are as follows:

[0060] Soil contaminated with polycyclic aromatic hydrocarbons (PHE, PYR, BaP) was ground through a 60-mesh (0.42 mm) sieve. 0.5 g of contaminated soil was placed in a 50 mL centrifuge tube, and 10 mL of surfactant solution was added. Each treatment was repeated three times. The centrifuge tubes were placed in a constant-temperature shaker and horizontally shaken for 24 h (25℃, 150 r / min). The centrifuge tubes were then centrifuged at high speed (3... 000 r / min, 10 min), let stand, take 2 mL of supernatant and ultrasonically extract with 10 mL of extraction solvent (hexane and dichloromethane volume ratio of 1:1) for 1 h, take 5 mL of the lower layer extract and pass it through a solid phase extraction column (SPE, the solid phase extraction column is filled from bottom to top with 1 g each of anhydrous sodium sulfate, silica gel, Florisil and anhydrous sodium sulfate), activate the SPE column with 5 mL of hexane, after purification, rinse the rotary evaporator flask and SPE column 3 times with a mixture of hexane and dichloromethane volume ratio of 9:1, place the purified liquid on a rotary evaporator and concentrate it again to 2 mL, add 1 mL of acetonitrile and concentrate to less than 1 mL, make up to 1 mL with acetonitrile, and determine by liquid chromatography.

[0061] Example 2

[0062] This embodiment provides an optimized method for treating polycyclic aromatic hydrocarbon (PAH) contaminated soil with surfactants. The specific steps are as follows:

[0063] S1, Single-factor experiment on the concentration of the novel chelating surfactant C12-ED3A3Na

[0064] Soil was treated with a novel chelating surfactant, C12-ED3A3Na, with a elution time of 4 h, a water-to-soil ratio of 20:1, a temperature of 25 °C, a pH of 11.72 for the C12-ED3A3Na solution, and concentrations of C12-ED3A3Na of 0 mg / L, 500 mg / L, 1000 mg / L, 2000 mg / L, 4000 mg / L, 6000 mg / L, and 8000 mg / L.

[0065] like Figure 1 As shown, when the concentration of C12-ED3A3Na is less than 1000 mg / L, the removal rate of phenanthrene increases rapidly with increasing concentration; when C 12 When the concentration of -ED3A3Na continued to increase to 2000 mg / L, the removal rate of phenanthrene actually decreased, and then decreased again with C. 12 As the concentration of -ED3A3Na increases, the removal rate of phenanthrene continues to rise, and when C... 12 When the concentration of -ED3A3Na is 6000 mg / L, the removal rate of phenanthrene reaches its highest point, at 85.44%; further increasing the concentration of C... 12 With increasing C3A3Na concentration, the removal rate of phenanthrene decreased again. Overall, the removal rate of phenanthrene decreases with increasing C3A3Na concentration. 12 The concentration of -ED3A3Na increases, reaching a high point, and then increases C. 12 The removal rate of phenanthrene at the -ED3A3Na concentration actually decreases. This is because C 12 As the concentration of -ED3A3Na increases, the number of micelles in the aqueous phase increases, and its ability to solubilize phenanthrene becomes stronger, thus increasing the phenanthrene removal rate; however, when C... 12 When the concentration of -ED3A3Na increases to a certain extent, the solution viscosity increases, and micelles are easily adsorbed into the soil, resulting in a decrease in the removal rate of phenanthrene.

[0066] Single-factor experiment on elution time of S2, a novel chelating surfactant C12-ED3A3Na.

[0067] Soil was treated with a novel chelating surfactant, C12-ED3A3Na, at a concentration of 6000 mg / L, a water-to-soil ratio of 20:1, a temperature of 25℃, a pH of 11.72, and elution times of 20 min, 40 min, 60 min, 240 min, 480 min, and 600 min.

[0068] Figure 2 The data showed that within 240 minutes of elution, the phenanthrene removal rate increased rapidly, reaching a peak at 240 minutes. However, with further extension of the elution time, the phenanthrene removal rate actually decreased. This is likely due to the interaction between phenanthrene, surfactant, and soil. In the initial stage of elution, the surfactant rapidly desorbs phenanthrene from the soil and dissolves it in surfactant micelles, while the adsorption rate of surfactant micelles into the soil is relatively slow; therefore, the phenanthrene removal rate increases. However, in the later stages of elution, many of the soluble phenanthrene surfactant micelles are also adsorbed into the soil, leading to a decrease in the phenanthrene removal rate.

[0069] Therefore, the extraction efficiency of PAHs is highest when the concentration of C12-ED3A3Na is 6000 mg / L and the elution time is 4 h.

[0070] Example 3

[0071] This embodiment provides a method for preparing biochar, the specific steps of which are as follows:

[0072] Pine sawdust was selected as the raw material for biochar preparation. An appropriate amount of pine sawdust was weighed and dried at 105℃. The dried sawdust was pretreated to remove soluble substances and reduce errors in subsequent experiments. At a solid-liquid ratio of 20 / L, the sawdust powder, after passing through a 100-mesh sieve, was immersed in a 0.05mol / L NaOH solution and stirred thoroughly for 24 hours. Then, it was washed with deionized water until the pH value stabilized. Subsequently, it was immersed in a 0.05mol / L HCl solution, and the above experimental operation was repeated. Finally, it was dried in a 60℃ oven for later use. An aluminum box (50mm in diameter and 30mm in height) containing an appropriate amount of dried sawdust was placed in a box-type atmosphere furnace. First, N2 was introduced for 30 minutes to purge the oxygen from the pyrolysis furnace. Then, heating was carried out at a rate of 5℃ / min, and the temperature was maintained at 400℃ for 2 hours. Afterward, N2 was continued until it naturally cooled to approximately 100℃. The resulting biochar was collected and stored in a desiccator for subsequent experimental use. The resulting biochar was named AB400.

[0073] Example 4

[0074] This embodiment provides a method for modifying biochar with different modification solutions, and the specific steps are as follows:

[0075] HNO3 modification: AB400 (biochar) was placed in a 20% HNO3 solution at a solid-liquid ratio of 1 g / L and stirred continuously at 25°C for 12 h. The mixture was then filtered, washed with deionized water until the pH reached approximately 7, and then dried in a vacuum drying oven at 105°C for 48 h. The resulting product was denoted as AB400HNO3.

[0076] H3PO4 modification: AB400 was placed in a 2mol / L H3PO4 solution at a solid-liquid ratio of 1g / 100mL and stirred continuously at 25℃ for 8h. Then it was filtered, washed with deionized water until the pH was about 7, and then dried in a vacuum drying oven at 105℃ for 48h. The resulting product was denoted as AB400H3PO4.

[0077] Ca(OH)2 modification: AB400 was placed in the supernatant of a saturated Ca(OH)2 solution at a solid-liquid ratio of 1g / 100mL and soaked at 25℃ for 48h. Then it was filtered, washed with deionized water until the pH was about 7, and then dried in a vacuum drying oven at 105℃ for 48h. The resulting product was denoted as AB400Ca(OH)2.

[0078] NH3·H2O modification: AB400 biochar was placed in a 12.5% ​​NH3·H2O solution at a solid-liquid ratio of 1g / 20mL and impregnated at 25℃ for 8h. Then it was filtered, washed with deionized water until pH=7, and then dried in a vacuum drying oven at 105℃ for 48h. The resulting product was denoted as AB400NH4OH.

[0079] A comparison of the adsorption capacity of biochar before and after modification for Cr(VI) is shown in the figure. Figure 5 The fitted isothermal adsorption parameters are shown in Table 1. It can be seen that the Langmuir correlation coefficients (0.974, 0.982, 0.966, 0.986, 0.952) for AB400, AB400HNO3, AB400H3PO4, AB400Ca(OH)2, and AB400NH4OH are all superior to those for Freundlich (0.925, 0.961, 0.922, 0.980, 0.932). This indicates that the Langmuir adsorption model is more suitable for the adsorption of Cr(VI) by biochar. Since the surface of biochar has a porous structure and the oxygen-containing functional groups it carries are related to the composite ionic radius (width = 99, height = 17, dpi = 110), this indicates that the adsorption process of Cr(VI) by biochar is monolayer adsorption.

[0080] Table 1. Fitting results of the isothermal adsorption model for Cr(VI) by acid-base modified biochar.

[0081]

[0082] Depend on Figure 5Table 1 shows that the adsorption capacity of biochar for Cr(VI) before modification is 58.48 mg / g. After modification, biochar modified with H3PO4 (AB400H3PO4) has the strongest adsorption capacity for Cr(VI), with a saturated adsorption capacity of 101.82 mg / g, which is much higher than other modified biochars. However, the adsorption capacity of biochar modified with HNO3, Ca(OH)2 and NH3·H2O for Cr(VI) is reduced.

[0083] Composite surfactants can enhance the adsorption capacity and reactivity of biochar, thereby improving remediation efficiency. However, the concentration and application method of these chemicals must be strictly controlled to avoid creating new secondary pollution. When using composite surfactants to enhance the remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soils with MoS2-loaded biochar or persulfate systems, the selection of remediation technologies, the assessment of secondary pollution risks during the remediation process, and the standardized application of composite surfactants must be comprehensively considered.

[0084] In summary, the method of using composite surfactants to enhance the remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soils with biochar-supported MoS2 or persulfate systems can significantly improve the bioavailability and remediation efficiency of PAHs by selecting appropriate surfactants and optimizing their application conditions. This approach combines the advantages of chemical and biological remediation technologies, providing a new strategy for efficient and environmentally friendly soil remediation.

[0085] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

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Claims

1. A method for remediating polycyclic aromatic hydrocarbon (PAH) contaminated soil, characterized in that, The specific steps are as follows: S1. Polycyclic aromatic hydrocarbon contaminated soil is treated by surfactant elution to obtain eluted soil. S2. Modify the biochar with a modifying solution to obtain modified biochar, wherein the modifying solution is HNO3, H3PO4, Ca(OH)2 or NH3·H2O; S3. The modified biochar, MoS2, and persulfate obtained in step S2 are mixed and added to the eluted soil obtained in step S1 to complete the remediation of polycyclic aromatic hydrocarbon contaminated soil. The amount of modified biochar obtained in step S2 is 4-5 kg / m³. 2 The dosage of persulfate is 4-6 kg / m³. 2 The mixing depth is 10-20cm, and the MoS2 dosage is 2-3 kg / m³. 2 The mixing depth is 10-20cm; In step S1, the surfactant is C12-ED3A3Na, and the concentration of the surfactant is 6000 mg / L and the pH is 11.

72. In step S1, the elution time is 4 hours; In step S2, the biochar is prepared as follows: Weigh an appropriate amount of pine wood chips, dry and sieve them. Immerse the sieved wood chip powder in NaOH solution and wash until the pH value is stable. Then immerse it in HCl solution, repeat the process several times, and dry it for later use. Heat it to 400℃ at a heating rate of 5℃ / min and then anaerobically calcine it at a constant temperature for 2 hours to obtain biochar. In step S3, the modified biochar, MoS2 and persulfate obtained in step S2 are evenly spread on the soil after elution treatment obtained in step S1. Then, plant seedlings are transplanted, watered, and field management is carried out. Repeating the sowing process 2-5 times can remediate the soil contaminated with polycyclic aromatic hydrocarbons in situ.

2. The method for remediating polycyclic aromatic hydrocarbon-contaminated soil according to claim 1, characterized in that, In step S1, the polycyclic aromatic hydrocarbons include PHE, PYR, and BaP.

3. The method for remediating polycyclic aromatic hydrocarbon-contaminated soil according to claim 1, characterized in that, In step S1, the polycyclic aromatic hydrocarbon contaminated soil is ground and sieved, a surfactant solution is added, and the soil is obtained after elution treatment by shaking and centrifugation extraction.

4. The method for remediating polycyclic aromatic hydrocarbon-contaminated soil according to claim 1, characterized in that, In step S2, the solid-liquid ratio of the biochar and the modified solution is 1 g: (20~1000 mL).

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