Method for removing perfluoro- and polyfluoroalkyl substances based on co-heating of biomass and contaminated soil

Abstract

This invention provides a method for removing perfluorinated and polyfluoroalkyl (PFOA) compounds based on co-heating of biomass and contaminated soil, belonging to the field of soil treatment technology. The method includes the following steps: mixing biomass with soil containing PFOA compounds to obtain a mixture; co-heating the mixture under an inert gas atmosphere to obtain soil with PFOA compounds removed; wherein, during the co-heating process, the biomass in the mixture pyrolyzes to generate biochar and reducing gases. The reducing gases are used to promote the degradation of PFOA compounds, and the biochar is used to capture undegraded PFOA compounds in situ. This method is characterized by simple operation, high treatment efficiency, excellent energy utilization, and strong environmental safety, and is suitable for large-scale remediation of contaminated soil.

Description

Technical Field

[0001] This invention relates to the field of soil treatment technology, and in particular to a method for removing perfluorinated and polyfluoroalkyl compounds based on co-heating biomass with contaminated soil. Background Technology

[0002] Per- and polyfluoroalkyl compounds (PFAS), as a typical class of persistent organic pollutants, are difficult to degrade under natural conditions due to their strong carbon-fluorine bond structure. They exhibit significant bioaccumulation and potential toxicity, persisting in the soil environment for extended periods and posing a serious threat to ecosystems and human health. Currently, remediation technologies for PFAS-contaminated soils mainly include physical adsorption, chemical oxidation, biodegradation, and pyrolysis. However, these remediation technologies suffer from problems such as incomplete treatment and the potential for secondary pollution in practical applications. Summary of the Invention

[0003] In view of the above, in order to at least partially solve at least one of the aforementioned technical problems, the present invention provides a method for removing perfluorinated and polyfluoroalkyl compounds based on co-heating of biomass and contaminated soil. The technical solution provided by the present invention is as follows.

[0004] According to one embodiment of the present invention, a method for removing perfluorinated and polyfluoroalkyl compounds based on co-heating of biomass and contaminated soil is provided, comprising the following steps:

[0005] Biomass is mixed with soil containing perfluorinated and polyfluoroalkyl compounds to obtain a mixture. The mixture is then subjected to co-heating treatment under an inert gas atmosphere to obtain soil in which perfluorinated and polyfluoroalkyl compounds have been removed. During the co-heating treatment, the biomass in the mixture is pyrolyzed to generate biochar and reducing gas. The reducing gas is used to promote the degradation of perfluorinated and polyfluoroalkyl compounds, and the biochar is used to capture some of the undegraded perfluorinated and polyfluoroalkyl compounds in situ.

[0006] According to an embodiment of the present invention, the mass ratio of biomass to soil containing perfluorinated and polyfluoroalkyl compounds is 1:10 to 1:20.

[0007] According to embodiments of the present invention, the initial concentration of perfluorinated and polyfluoroalkyl compounds in soil containing perfluorinated and polyfluoroalkyl compounds is 0.1-10 mg / kg.

[0008] According to an embodiment of the present invention, the heating temperature during the co-pyrolysis process is 350-450°C, and the heating time is 0.5-1h.

[0009] According to an embodiment of the present invention, before the biomass is mixed with soil containing perfluorinated and polyfluoroalkyl compounds, the process further includes: pulverizing and drying the biomass.

[0010] According to an embodiment of the present invention, in the above drying process, the moisture content of the biomass is controlled to be ≤10%; in the above pulverizing process, the particle size of the biomass is controlled to be 1-5mm.

[0011] According to embodiments of the present invention, the perfluorinated and polyfluoroalkyl compounds are perfluorooctane sulfonic acid; the reducing gas is at least one of hydrogen, carbon monoxide, and methane; and the biomass is at least one of peanut shells, straw, corn, and wheat.

[0012] According to embodiments of the present invention, biomass is mixed with soil containing perfluorinated and polyfluoroalkyl (PFAA) compounds and then subjected to co-thermal treatment. During the co-thermal treatment, the biomass undergoes pyrolysis, simultaneously generating biochar and reducing gases. The reducing gases promote the degradation of PFAAs, while the biochar, with its abundant pores and surface active sites, adsorbs and immobilizes in-situ the incompletely degraded PFAAs and their degradation products. This achieves efficient removal of PFAAs through a synergistic mechanism of "degradation + in-situ capture and sequestration." This method is applicable to different initial concentrations and types of PFAAs and is not limited by the type of medium. Whether targeting contaminated soil or a solution system containing PFAAs, the synergistic effect of biochar generation through biomass pyrolysis can be achieved. The pyrolysis process requires no additional energy input, realizing the synergistic utilization of matter and energy, effectively reducing treatment costs. Meanwhile, this method is characterized by simple operation, high efficiency, low energy consumption, and good environmental safety. Biomass materials are inexpensive, readily available, and renewable. There is no leakage of harmful gases during the treatment process, and the properties of the treated medium are stable, which is in line with the concept of green treatment and resource recycling. Attached Figure Description

[0013] Figure 1 A flowchart illustrating the steps of the method for removing perfluorinated and polyfluoroalkyl compounds by co-heating biomass with contaminated soil provided by the present invention;

[0014] Figure 2 A process flow diagram of the method for removing perfluorinated and polyfluoroalkyl compounds by co-heating biomass with contaminated soil provided by the present invention;

[0015] Figure 3 A schematic diagram illustrating the mechanism and effect of the method for removing perfluorinated and polyfluoroalkyl compounds by co-heating biomass with contaminated soil provided by the present invention;

[0016] Figure 4 This is a flowchart illustrating the method for detecting the concentration of perfluorinated and polyfluoroalkyl compounds in soil samples in an embodiment of the present invention. Detailed Implementation

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0018] In the remediation of soils contaminated with perfluorinated and polyfluoroalkyl substances (PFAS), pyrolysis has attracted widespread attention due to its ability to directly destroy the molecular structure of PFAS. However, this method still faces many challenges in practical applications. For example, traditional pyrolysis processes often require treatment times exceeding 2 hours or significantly increased reaction temperatures to achieve effective PFAS degradation, directly leading to a substantial increase in energy consumption and remediation costs. Furthermore, during pyrolysis, some PFAS degradation intermediates may escape in gaseous form, posing a risk of secondary pollution. In addition, existing pyrolysis methods fail to fully utilize the synergistic effects of material transformation during pyrolysis (such as the adsorption and fixation of pollutants by carbonization products) and lack effective stabilization measures for incompletely degraded PFAS, resulting in some residual PFAS still possessing potential ecotoxicity and affecting the long-term environmental safety of the remediation site. Therefore, developing a synergistic treatment technology that combines high-efficiency degradation, stable storage, and low energy consumption has significant technological innovation value and engineering application implications.

[0019] In view of this, this invention proposes a method for removing perfluorinated and polyfluoroalkyl (PFOA) compounds based on the principle of carbon capture and storage (CFS). This method utilizes the pyrolysis of biomass to generate biochar, and under the action of reducing gases generated during pyrolysis, achieves a synergistic effect of "degradation + in-situ capture and storage" of PFOA compounds. This synergistic mechanism not only significantly improves the degradation efficiency of PFOA compounds and reduces energy consumption, but also stably stores incompletely degraded PFOA compounds in biochar, effectively preventing secondary migration and environmental risks, ultimately achieving safe and efficient remediation of contaminated soil.

[0020] Figure 1 The flowchart illustrates the steps of the method for removing perfluorinated and polyfluoroalkyl compounds by co-heating biomass with contaminated soil, as provided by this invention.

[0021] like Figure 1 As shown, the method includes operations S110-S120.

[0022] In operation S110, biomass is mixed with soil containing perfluorinated and polyfluoroalkyl compounds to obtain a mixture.

[0023] In operation S120, the mixture is subjected to co-heating treatment under an inert gas atmosphere to obtain soil in which perfluorinated and polyfluoroalkyl compounds have been removed.

[0024] According to an embodiment of the present invention, biomass and soil containing perfluorinated and polyfluoroalkyl compounds are uniformly mixed in a predetermined ratio to form a mixture, ensuring sufficient contact between the two. Subsequently, the mixture is subjected to co-heating treatment under an inert gas atmosphere; during this process, the biomass in the mixture undergoes pyrolysis, simultaneously generating biochar and reducing gases. The generated reducing gases (such as hydrogen, carbon monoxide, etc.) further act on the perfluorinated and polyfluoroalkyl compounds in the soil, promoting their degradation and transformation through reduction reactions; simultaneously, the biochar formed by biomass pyrolysis, with its abundant porous structure and surface active sites, adsorbs and immobilizes in situ the perfluorinated and polyfluoroalkyl compounds that have not yet been completely degraded. Finally, soil free of perfluorinated and polyfluoroalkyl compounds is obtained.

[0025] This method utilizes a dual mechanism of "degradation + in-situ capture and storage" through reducing gases and biochar, significantly improving the degradation efficiency of perfluorinated and polyfluoroalkyl compounds and suppressing secondary pollution. Furthermore, the pyrolysis of biomass into biochar requires no additional energy input, achieving synergistic utilization of matter and energy, thus effectively reducing overall remediation costs. Simultaneously, this method is characterized by its simplicity, high efficiency, low energy consumption, and good environmental safety. Moreover, its synergistic treatment effect is unaffected by the soil medium, making it suitable for the remediation of large-scale organically contaminated soils.

[0026] In some embodiments, the mass ratio of biomass to soil containing perfluorinated and polyfluoroalkyl compounds is 1:10 to 1:20, for example, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, but not limited to the values ​​listed.

[0027] According to embodiments of the present invention, this ratio ensures that biomass pyrolysis generates sufficient biochar to cover the pollution load of perfluorinated and polyfluoroalkyl (PFAA) compounds, while avoiding the increased energy consumption and potential impact on the subsequent utilization of remediated soil caused by excessive biomass (e.g., greater than 1:20). Preferably, the mass ratio of biomass to soil containing PFAA compounds is 1:20. At this ratio, biomass pyrolysis can generate sufficient reducing gases (e.g., H2, CO, CH4), enhancing the degradation rate and removal rate of PFAA compounds by strengthening the chemical reduction pathway. Simultaneously, the generated biochar can adsorb and in-situ seal incompletely degraded PFAA compounds and their intermediate products, effectively reducing the risk of secondary release. This ratio ensures remediation effectiveness while balancing energy consumption control and process economy, achieving a balance between remediation efficiency, environmental safety, and technical feasibility.

[0028] In some embodiments, the initial concentration of perfluorinated and polyfluoroalkyl compounds in the soil is 0.1-10 mg / kg, for example, 0.1 mg / kg, 0.3 mg / kg, 0.5 mg / kg, 0.8 mg / kg, 1 mg / kg, 2 mg / kg, 3 mg / kg, 4 mg / kg, 5 mg / kg, 6 mg / kg, 7 mg / kg, 8 mg / kg, 9 mg / kg, or 10 mg / kg, but not limited to the listed values. In some embodiments, the heating temperature during the co-heat treatment process is 350-450°C, for example, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, or 450°C, but not limited to the listed values. The heating time is 0.5-1 hour, for example, 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, or 1 hour, but is not limited to the listed values.

[0029] According to embodiments of the present invention, co-heating treatment within a temperature range of 350-450℃ effectively promotes the degradation of perfluorinated and polyfluoroalkyl compounds (PFACs) by utilizing the reducing gases (such as H2, CO, and CH4) released during biomass pyrolysis, while avoiding the damage to the physicochemical properties (such as structure and nutrients) of the soil matrix caused by high temperatures (such as above 500℃). This temperature window balances reaction efficiency and process economy, facilitating the sustainable use of remediated soil. Within a heating time range of 0.5-1 h, the "degradation + in-situ capture and sequestration" process of biomass pyrolysis and PFACs can essentially reach a dynamic equilibrium, ensuring both effective removal and stabilization of PFACs and meeting the requirements of rapid engineering remediation. This approach demonstrates good process operability and potential for large-scale application.

[0030] In some embodiments, the co-heat treatment process of the present invention is carried out in a closed reaction device that is resistant to high temperatures (e.g., 350-450°C) and corrosion.

[0031] According to embodiments of the present invention, the closed reaction apparatus not only effectively prevents the leakage of perfluorinated and polyfluoroalkyl compounds and their degradation products, avoiding secondary pollution, but also helps maintain the stability and concentration of the reducing atmosphere within the reaction system, thereby continuously promoting the degradation of perfluorinated and polyfluoroalkyl compounds. Furthermore, this design optimizes the heat and mass transfer processes within the reaction apparatus, improving energy utilization efficiency.

[0032] In some embodiments, the biomass is further subjected to crushing and drying before being mixed with soil containing perfluorinated and polyfluoroalkyl compounds.

[0033] According to embodiments of the present invention, pulverization can increase the specific surface area of ​​biomass, promote its uniform contact with contaminated soil, and avoid incomplete local reactions; drying reduces the interference of moisture on the pyrolysis process, which is conducive to the effective transfer of heat and the rapid release of reducing gases (such as H2, CO, CH4).

[0034] In some implementations, after the biomass is dried, its moisture content needs to be controlled to be ≤10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, but is not limited to the values ​​listed.

[0035] According to embodiments of the present invention, controlling the moisture content of biomass to below 10% can reduce the energy consumed by moisture evaporation in the initial stage of biomass pyrolysis and improve the pyrolysis reaction efficiency. At the same time, a low moisture content (≤10%) can avoid the dilution interference of water vapor on reducing atmospheres (such as H2, CO, CH4), ensure the efficient degradation of perfluorinated and polyfluoroalkyl compounds, and promote the formation of a more stable pore structure in biochar, thereby enhancing its adsorption performance.

[0036] In some embodiments, the biomass is pulverized to control its particle size to 1-5 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm, but not limited to the listed values. Controlling the biomass particle size within the 1-5 mm range is beneficial for achieving uniform mixing with contaminated soil particles and enhancing heat and mass transfer efficiency.

[0037] In some embodiments, perfluorinated and polyfluoroalkyl compounds include, but are not limited to, perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonic acid (PFHxS), perfluorobutane sulfonic acid (PFBS), and perfluorononanoic acid (PFNA). PFOS is preferably used as a representative pollutant for verification in this invention. Elution tests with an ammonia-methanol solution at a volume ratio of 2:98 showed no desorption of PFOS encapsulated in biochar. This indicates that biochar generated through biomass co-pyrolysis has a strong capacity for encapsulating PFOS, effectively mitigating its secondary migration and release into the environment and meeting long-term stabilization requirements. Therefore, the remediated soil can be returned to the environment or utilized as a resource without further treatment.

[0038] In some embodiments, the biomass is at least one of peanut shells, straw, corn, and wheat.

[0039] According to embodiments of the present invention, the aforementioned biomass materials are widely available and inexpensive. Under heating conditions of approximately 400°C, they can be simultaneously converted into biochar with a large surface area and strong adsorption capacity, providing an ideal carrier for the efficient capture and stable storage of perfluorinated and polyfluoroalkyl compounds, thus offering the dual benefits of resource utilization and environmental remediation. Preferably, peanut shells are used as biomass, and the peanut shell biochar generated from its pyrolysis exhibits superior adsorption performance, showing the best capture and storage effect on PFOS, with a removal rate exceeding 90% during the synergistic degradation process.

[0040] In some implementations, using optimal process parameters (heating temperature 400℃, heating time 0.5h, biomass to contaminated soil mass ratio 1:20, and peanut shells as biomass material), a perfluorooctane sulfonic acid (PFOS) removal rate of over 99% can be achieved. This result is far superior to the removal efficiency of pyrolysis alone (typically only 20%-40%). Even when using straw as biomass material, the total removal rate under these process conditions can still reach 69.24%-79.9%, significantly demonstrating the synergistic effect of "degradation + in-situ capture and storage".

[0041] Figure 2 The process flow diagram of the method for removing perfluorinated and polyfluoroalkyl compounds by co-heating biomass with contaminated soil provided by the present invention is shown.

[0042] like Figure 2 As shown, biomass was first pretreated by selecting agricultural waste such as straw and peanut shells, which were crushed, dried, and then thoroughly mixed with soil containing perfluorinated and polyfluoroalkyl compounds (PFACs). The mixture was placed in a closed reaction apparatus, heated to 400℃, and held at that temperature for 0.5 hours. During this process, a reducing atmosphere and biochar were generated from the pyrolysis of biomass. The reducing atmosphere promoted the degradation of PFACs, while the biochar could capture in situ the incompletely degraded PFACs and their intermediates, achieving a synergistic effect of "degradation + in-situ capture and sequestration". After the reaction, the mixture was naturally cooled to room temperature. The PFACs in the resulting soil were either degraded into harmless substances or stabilized by the biochar. Eluent washing with an ammonia-methanol solution at a volume ratio of 2:98 verified that the PFACs sealed in the biochar did not desorb, indicating that the method has a reliable stabilization effect.

[0043] Figure 3 A schematic diagram illustrating the mechanism and effect of the method for removing perfluorinated and polyfluoroalkyl compounds by co-heating biomass with contaminated soil provided by the present invention.

[0044] like Figure 3As shown, taking PFOS-contaminated soil as an example, the PFOS-contaminated soil was mixed with biomass and then co-treated at 400℃ for 0.5 h to convert the biomass into biochar, while simultaneously forming a reducing atmosphere. During this process, the reducing atmosphere degrades PFOS into short-chain perfluorinated and polyfluoroalkyl compounds, while the in-situ generated biochar, through its porous structure and surface functional groups, efficiently adsorbs and stably stores undegraded PFOS and intermediate products (such as short-chain perfluorinated and polyfluoroalkyl compounds), achieving a synergistic effect of "degradation + in-situ capture and storage".

[0045] Figure 4 This is a flowchart illustrating the method for detecting the concentration of perfluorinated and polyfluoroalkyl compounds in soil samples in an embodiment of the present invention.

[0046] like Figure 4 As shown, 10 mL of ammonia-methanol mixed solution (ammonia:methanol = 2:98) was added to the sample to be tested. The sample was vortexed for 1 min to ensure thorough dispersion, followed by sonication for 20 min. Then, the sample was centrifuged at 5000 r / min for 5 min, and the supernatant was transferred to a new centrifuge tube. This process of vortexing for 1 min, sonicating for 20 min, and centrifuging for 5 min was repeated twice, with the supernatant transferred to a new centrifuge tube after each centrifugation. One mL of the supernatant was filtered through a 0.22 μm membrane, and the filtrate was collected in a sample vial. Finally, the sample was analyzed using liquid chromatography-mass spectrometry (LC-MS).

[0047] The present invention will be described in detail below with reference to specific embodiments. It should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Unless otherwise expressly stated, the experimental materials, raw materials, and reagents used in the following embodiments and in the specification of the present invention are all commercially available conventional products.

[0048] Example 1

[0049] Peanut shells were selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 1 mg / kg was added to 0.05 g of crushed peanut shells, making the biomass-to-contaminated soil mass ratio 1:20. The mixture was thoroughly mixed to obtain a homogeneous mixture. The mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 2 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 100%.

[0050] Example 2

[0051] Peanut shells were selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 10 mg / kg was added to 0.05 g of crushed peanut shells, making the biomass-to-contaminated soil mass ratio 1:20. The mixture was thoroughly mixed to obtain a homogeneous mixture. The mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, it was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 99.14%.

[0052] Example 3

[0053] Peanut shells were selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 10 mg / kg was mixed with 0.1 g of crushed peanut shells, making the biomass-to-contaminated soil mass ratio 1:10. The mixture was thoroughly mixed to obtain a homogeneous mixture. The mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 99.32%.

[0054] Example 4

[0055] Straw was selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 10 mg / kg was added, along with 0.05 g of crushed straw, making the biomass-to-contaminated soil mass ratio 1:20. The mixture was thoroughly mixed to obtain a homogeneous mixture. This mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 86.66%.

[0056] Example 5

[0057] Straw was selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 10 mg / kg was added, along with 0.1 g of crushed straw, making the biomass-to-contaminated soil mass ratio 1:10. The mixture was thoroughly mixed to obtain a homogeneous mixture. This mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 93.07%.

[0058] Example 6

[0059] Peanut shells were selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 0.1 mg / kg was mixed with 0.05 g of crushed peanut shells, making the biomass-to-contaminated soil mass ratio 1:20. The mixture was thoroughly mixed to obtain a homogeneous mixture. The mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 97.06%.

[0060] Example 7

[0061] Straw was selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 0.1 mg / kg was added to 0.05 g of crushed straw, making the biomass-to-contaminated soil mass ratio 1:10. The mixture was thoroughly mixed to obtain a homogeneous mixture. The mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, it was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 83.25%.

[0062] Example 8

[0063] Corn was selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 0.1 mg / kg was added to 0.05 g of crushed corn, making the biomass-to-contaminated soil mass ratio 1:10. The mixture was thoroughly mixed to obtain a homogeneous mixture. The mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, it was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 91.08%.

[0064] Example 9

[0065] Wheat was selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 0.1 mg / kg was added to 0.05 g of crushed wheat, making the biomass-to-contaminated soil mass ratio 1:10. The mixture was thoroughly mixed to obtain a homogeneous mixture. The mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, it was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 84.27%.

[0066] Example 10

[0067] Straw was selected as the biomass material and pre-treated by crushing to a particle size of 2-3 mm. Then, 10 mL of a PFOS solution with an initial concentration of 2 mg / L was added, along with 0.05 g of crushed straw, making the biomass-to-contaminated soil mass ratio 1:20. The mixture was thoroughly mixed to obtain a homogeneous mixture. This mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 97.75%.

[0068] Comparative Example 1

[0069] One gram of contaminated soil with an initial PFOS concentration of 1 mg / kg was placed in a high-temperature resistant reactor without the addition of any biomass. The mixture was heated to 400°C and held at that temperature for 2 hours. After the reaction was completed, the soil was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 68.5%.

[0070] Comparative Example 2

[0071] One gram of contaminated soil with an initial PFOS concentration of 10 mg / kg was placed in a high-temperature resistant reactor without the addition of any biomass. The reactor was heated to 400°C and held at that temperature for 0.5 hours. After the reaction was completed, the soil was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 18.6%.

[0072] Comparative Example 3

[0073] One mL of a PFOS solution with an initial concentration of 2 mg / kg was placed in a high-temperature resistant reactor without the addition of any biomass. The solution was heated to 400°C and held at that temperature for 0.5 h. After the reaction was completed, the solution was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 27.28%.

[0074] Comparative Example 4

[0075] Peanut shell biochar was pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 10 mg / kg was mixed with 0.025 g of the crushed peanut shell biochar, making the mass ratio 1:40. The mixture was thoroughly mixed to obtain a homogeneous mixture. This mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 73.92%.

[0076] Comparative Example 5

[0077] Peanut shell biochar was pre-treated by crushing to a particle size of 2-3 mm. Then, 1 g of contaminated soil with an initial PFOS concentration of 10 mg / kg was mixed with 0.05 g of the crushed peanut shell biochar, making the mass ratio 1:20. The mixture was thoroughly mixed to obtain a homogeneous mixture. This mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 77.91%.

[0078] Comparative Example 6

[0079] Straw biochar was pre-treated by crushing to a particle size of 2-3 mm. Then, 10 mL of a PFOS solution with an initial concentration of 2 mg / L was added, and 0.05 g of the crushed straw biochar was mixed thoroughly to obtain a homogeneous mixture. The mixture was placed in a high-temperature resistant reactor, heated to 400℃, and held at that temperature for 0.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and samples were taken for testing. The PFOS removal rate was 79.34%.

[0080] The experimental conditions and results of Examples 1-10 and Comparative Examples 1-6 of this invention are summarized in Table 1. In this table, "liquid system" refers to PFOS solution without contaminated soil.

[0081] Table 1 Experimental conditions and results of biomass / biochar remediation of PFOS-contaminated soil

[0082]

[0083] As shown in Table 1, among the above biomass / biochar, peanut shells exhibit excellent performance in removing PFOS. Specifically, under conditions where the initial PFOS concentration is 1-10 mg / kg, the PFOS removal rate exceeds 99% (Examples 1-3); even when the initial PFOS concentration is as low as 0.1 mg / kg, the PFOS removal rate is still as high as 97.06% (Example 6). Therefore, the above demonstrates that peanut shells have a stable and efficient removal capacity for different pollution loads.

[0084] Further comparison of different biomass revealed that, under the same treatment conditions, peanut shells exhibited the best PFOS removal efficiency. For example, when the initial PFOS concentration was 0.1 mg / kg and the biomass-to-contaminated soil ratio was 1:10, the PFOS removal rate of peanut shells (97.06%, Example 6) was significantly higher than that of corn (91.08%, Example 8), straw (83.25%, Example 7), and wheat (84.27%, Example 9), indicating that peanut shells are the preferred biomass for this method. Simultaneously, the ratio of biomass to contaminated soil also significantly affected the PFOS removal efficiency: when the initial PFOS concentration was 10 mg / kg, increasing the straw-to-contaminated soil ratio from 1:20 to 1:10 increased the PFOS removal rate from 86.66% to 93.07% (Examples 4-5), demonstrating that appropriately increasing the amount of biomass added helps enhance the PFOS removal effect.

[0085] Comparative experiments further validated the necessity of biomass addition. In the blank experiments (Comparative Examples 1-3), the PFOS removal rate was extremely low without biomass addition, indicating that PFOS pyrolysis alone is insufficient for effective PFOS removal. Furthermore, biomass generally outperformed its corresponding biochar in PFOS removal: at an initial PFOS concentration of 10 mg / kg, peanut shells showed a PFOS removal rate (>99%, Examples 2-3) significantly higher than peanut shell biochar under the same conditions (approximately 73.92%-77.91%, Comparative Examples 4-5); in a liquid system (2 mg / L), straw showed a removal rate (97.75%, Example 10) significantly higher than the corresponding straw biochar (79.34%, Comparative Example 6). These results demonstrate that direct use of biomass is more effective than carbonization in PFOS removal.

[0086] In summary, the method for removing perfluorinated and polyfluoroalkyl compounds (PFOS) based on co-heating of biomass and contaminated soil provided by this invention, when using peanut shells as biomass at a mass ratio of 1:20 with contaminated soil, can achieve a PFOS removal rate of 97.06%-100% within an initial PFOS concentration range of 0.1-10 mg / kg in just 0.5-1 hour. Especially under high-concentration pollution conditions (e.g., an initial PFOS concentration of 10 mg / kg), the removal effect can be further enhanced by appropriately increasing the amount of biomass added. Compared with traditional pyrolysis methods, this method significantly shortens the treatment time and reduces energy consumption, providing an economical and feasible technical path for the resource utilization of agricultural waste and the efficient remediation of PFOS and polyfluoroalkyl compounds.

[0087] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for removing perfluorinated and polyfluoroalkyl compounds based on co-heating of biomass and contaminated soil, characterized in that, Includes the following steps: Biomass is mixed with soil containing perfluorinated and polyfluoroalkyl compounds to obtain a mixture. Under an inert gas atmosphere, the mixture is subjected to co-heat treatment to obtain soil in which perfluorinated and polyfluoroalkyl compounds have been removed; wherein, during the co-heat treatment, the biomass in the mixture is pyrolyzed to generate biochar and reducing gas, the reducing gas is used to promote the degradation of the perfluorinated and polyfluoroalkyl compounds, and the biochar is used to capture the undegraded portion of the perfluorinated and polyfluoroalkyl compounds in situ.

2. The method according to claim 1, characterized in that, The mass ratio of the biomass to the soil containing perfluorinated and polyfluoroalkyl compounds is 1:10 to 1:

20.

3. The method according to claim 1, characterized in that, The initial concentration of perfluorinated and polyfluoroalkyl compounds in the soil containing these compounds is 0.1-10 mg / kg.

4. The method according to claim 1, characterized in that, During the co-pyrolysis process, the heating temperature is 350-450℃ and the heating time is 0.5-1h.

5. The method according to claim 1, characterized in that, Before mixing the biomass with the soil containing perfluorinated and polyfluoroalkyl compounds, the method further includes: pulverizing and drying the biomass.

6. The method according to claim 5, characterized in that, In the drying process, the moisture content of the biomass is controlled to be ≤10%.

7. The method according to claim 5, characterized in that, In the pulverization process, the particle size of the biomass is controlled to be 1-5 mm.

8. The method according to claim 1, characterized in that, The perfluorinated and polyfluoroalkyl compounds are perfluorooctane sulfonic acid.

9. The method according to claim 1, characterized in that, The reducing gas is at least one of hydrogen, carbon monoxide, and methane.

10. The method according to claim 1, characterized in that, The biomass is at least one of peanut shells, straw, corn, and wheat.

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