Degradation method of aged petroleum hydrocarbon pollutants in soil

Abstract

The invention relates to the technical field of organic pollutant treatment, in particular to a method for degrading aged petroleum hydrocarbon pollutants in soil. Firstly, low-temperature dielectric barrier plasma treatment with specific parameters is utilized, and a preliminary degradation effect is performed according to the characteristics of the aged petroleum hydrocarbon pollutants; and secondly, by utilizing specific types of compound bacteria microorganisms and by virtue of a good synergistic effect among the pseudomonas aeruginosa, the microbacterium oxydans and the ochrobactrum intermedium in the compound bacteria microorganisms, the degradation efficiency and the degradation rate of the microorganisms on the primary degradation substances are obviously improved, and an intermediate degradation product with smaller molecular weight is generated. In addition, after the compound bacteria microorganisms are introduced, through control of specific conditions, deep degradation of the compound bacteria microorganisms on intermediate degradation products is achieved, and the total degradation rate is greatly increased. Through low-temperature dielectric barrier plasma treatment and'different space coupling 'of compound bacteria and microorganisms, a new idea is provided for treating pollutants through the coupling synergistic effect of the low-temperature dielectric barrier plasma treatment and the compound bacteria and microorganisms.

Description

Technical Field

[0001] This invention relates to the field of organic pollutant treatment technology, and in particular to a method for degrading aged petroleum hydrocarbon pollutants in soil. Background Technology

[0002] Aged petroleum hydrocarbons (A-PHC) are persistent pollutants formed from petroleum hydrocarbons that have existed in the environment for a long time, after physical, chemical, and biological processes. During the aging process, the lighter components (such as low-molecular-weight alkanes) in petroleum hydrocarbons gradually volatilize or degrade, while the remaining high-molecular-weight petroleum hydrocarbons (such as C29-C36 alkanes) have a more stable chemical structure and significantly reduced bioavailability, making them chemically stable. Aged petroleum hydrocarbons accumulate in soil over long periods, easily binding with soil particles to form stable structures that are difficult to desorb and degrade efficiently using conventional methods. Toxic components such as polycyclic aromatic hydrocarbons are enriched in aged petroleum hydrocarbons, increasing their ecotoxicity.

[0003] The aforementioned characteristics of aging petroleum hydrocarbon pollutants result in high environmental hazards, such as soil ecological damage: leading to a reduction of more than 40% in soil microbial community diversity, a 90% reduction in key functional bacteria such as nitrogen-fixing bacteria, and damage to soil fertility and self-purification capacity.

[0004] To address soil pollution caused by aging petroleum hydrocarbons, researchers have developed a low-temperature plasma method for treatment. This method offers rapid degradation and wide applicability, breaking down petroleum hydrocarbons into smaller molecules using high-energy electrons and free radicals. However, it is prone to producing toxic byproducts and poses a potential disturbance to the soil ecosystem. Researchers have also developed a microbial degradation method, which is environmentally friendly and cost-effective, converting pollutants into harmless carbon dioxide and water. However, this method has limited ability to degrade aging petroleum hydrocarbons, exhibiting low degradation efficiency, long degradation cycles, and instability due to the influence of soil environmental factors.

[0005] To address the problems of the aforementioned single remediation methods, researchers have developed combined remediation methods. However, these methods mostly focus on combinations such as electro-microbe and plant-microbe, while the coupling of low-temperature plasma and microorganisms is still in the exploratory stage. Furthermore, the research and application of these methods for aging petroleum hydrocarbons is basically nonexistent. Summary of the Invention

[0006] In view of this, the present invention provides a method for degrading aged petroleum hydrocarbon pollutants in soil. The degradation method provided by the present invention can effectively degrade aged petroleum hydrocarbon pollutants without producing toxic byproducts, and has high degradation efficiency, short degradation cycle and stable degradation effect.

[0007] This invention provides a method for degrading aged petroleum hydrocarbon pollutants in soil, comprising the following steps: Soil containing aged petroleum hydrocarbon pollutants is subjected to low-temperature medium barrier plasma treatment, followed by the addition of compound microorganisms for degradation and deep degradation. The compound microorganisms include Pseudomonas aeruginosa, Microbacterium oxysporum, and Bacillus intermedius.

[0008] Preferably, the content of aged petroleum hydrocarbon pollutants in the soil containing aged petroleum hydrocarbon pollutants is not higher than 40 g / kg; and the particle size of the soil containing aged petroleum hydrocarbon pollutants is less than 500 micrometers.

[0009] Preferably, the input voltage of the cryogenic dielectric barrier plasma treatment is 55~85V, the duty cycle is 45~65%, the pulse frequency is 200~250HZ, and the treatment time is 65~90 minutes.

[0010] Preferably, in the low-temperature dielectric barrier plasma treatment, the dielectric barrier layer used has a relative permittivity of 2.5 to 6.0 and a breakdown strength of not less than 10 kV / mm; the dielectric barrier layer includes quartz glass, alumina ceramic, borosilicate glass or polytetrafluoroethylene.

[0011] Preferably, the thickness of the dielectric barrier layer is 0.5~3mm; the shape of the dielectric barrier layer matches the electrode, and adopts a circular plate structure or a rectangular plate structure; the size of the dielectric barrier layer is larger than the size of the electrode; the discharge spacing of the dielectric barrier layer is 0.5~5mm.

[0012] Preferably, the electrodes used in the cryogenic dielectric barrier plasma treatment are inserted into the soil to be treated in an array and connected in parallel to a power supply; the electrodes are circular or square electrodes.

[0013] Preferably, the mass ratio of *Pseudomonas aeruginosa* to *Aureobacterium intermedius* is 0.9~1.2:0.9~1.2; the mass ratio of *Microbacterium oxysporum* to *Aureobacterium intermedius* is 0.9~1.2:0.9~1.2.

[0014] Preferably, the mass ratio of the pretreated soil to the composite microorganisms is 1000:3~8.

[0015] Preferably, the degradation temperature is 24-32 degrees Celsius, the relative humidity is 40-60%, and the time is more than 30 days.

[0016] Preferably, the temperature for deep degradation is 30-38 degrees Celsius, the relative humidity is 30-50%, and the time is more than 40 days.

[0017] This invention provides a method for degrading aged petroleum hydrocarbon pollutants in soil. The degradation method provided by this invention can effectively degrade aged petroleum hydrocarbon pollutants, without producing toxic byproducts, and exhibits high degradation efficiency, a short degradation cycle, and stable degradation effects. Specifically, this invention achieves the above-mentioned beneficial effects through the following means: First, this invention utilizes low-temperature medium-barrier plasma treatment with specific parameters to perform preliminary degradation of aged petroleum hydrocarbon pollutants, targeting their characteristics. On one hand, it initially breaks down stable structures such as benzene rings in aged petroleum hydrocarbon pollutants, reducing their content in the soil. On the other hand, the pre-degraded substances produced by the aforementioned low-temperature medium-barrier plasma treatment have lower binding force with soil particles, improving the soil's physicochemical properties, increasing desorption efficiency, and facilitating the full utilization of these pollutants by the complex microorganisms. Furthermore, it enhances and maintains the activity of the complex microorganisms. Moreover, the control of these specific parameters simultaneously minimizes damage to the original soil microbial community structure, enzyme activity, and soil fertility, balancing remediation effectiveness with soil ecological protection. This demonstrates good ecological compatibility and aligns with the development trend of green remediation.

[0018] Secondly, this invention utilizes a specific type of composite microbial community. Through the excellent synergistic effect among *Pseudomonas aeruginosa*, *Microbacterium oxysporum*, and *Bacillus intermedius*, the degradation efficiency and rate of the initial degradation substances are significantly improved, producing intermediate degradation products with smaller molecular weights. The composite microbial community in this invention further degrades most of the initial degradation substances. Although the degradation effect is concentrated in this stage, it relies on the initial degradation substances generated by the low-temperature medium-barrier plasma treatment. The two have a good synergistic effect; when used alone, their degradation effects are poor. This is likely because the initial degradation substances produce substances that activate at least one of the microorganisms in the composite microbial community.

[0019] In addition, by introducing compound microorganisms and controlling specific conditions, this invention achieves deep degradation of intermediate degradation products by compound microorganisms, which greatly improves the total degradation rate. At the same time, it metabolizes and degrades byproducts that may be generated by low-temperature plasma treatment, reducing the risk of secondary pollution and filling the gap in existing methods that are not targeted enough for aging petroleum hydrocarbon pollutants.

[0020] Furthermore, through the aforementioned parameter control, this invention can adapt to soils with different levels of pollution and textures, making it particularly suitable for aging petroleum hydrocarbon-contaminated sites such as industrial legacy sites. It offers significant engineering application advantages in terms of degradation efficiency, treatment cycle, and secondary pollution control, providing a new technical approach for the remediation of such sites. This invention also provides a novel approach to the synergistic treatment of pollutants through the "non-spatial coupling" of low-temperature medium-barrier plasma treatment and composite microorganisms (the two do not need to occur simultaneously in the same space, but rather work synergistically through mass transfer). Attached Figure Description

[0021] To more clearly illustrate the technical solutions of this invention, the accompanying drawings used in the embodiments of this invention or in the prior art are briefly described below. For those skilled in the art, other drawings can be derived from the following drawings without creative effort, and all such drawings are within the protection scope of this invention.

[0022] Figure 1 The graphs show a comparison of the degradation effects of Examples 1-8 and Comparative Examples 1-5. Detailed Implementation

[0023] This invention provides a method for degrading aged petroleum hydrocarbon pollutants in soil, comprising the following steps: Soil containing aged petroleum hydrocarbon pollutants is subjected to low-temperature medium barrier plasma treatment, followed by the addition of compound microorganisms for degradation and deep degradation. The compound microorganisms include Pseudomonas aeruginosa, Microbacterium oxysporum, and Bacillus intermedius.

[0024] This invention involves subjecting soil containing aged petroleum hydrocarbon contaminants to sequential low-temperature dielectric barrier plasma treatment to obtain pretreated soil. In this invention, the content of aged petroleum hydrocarbon contaminants in the soil is preferably no higher than 40 g / kg, more preferably 0.3~35 g / kg, and even more preferably 1~25 g / kg.

[0025] In this invention, the particle size of the soil containing aged petroleum hydrocarbon pollutants is preferably less than 500 micrometers, and more preferably less than 300 micrometers.

[0026] In this invention, the temperature of the cryogenic dielectric barrier plasma treatment is preferably room temperature (20~37 degrees Celsius), the pressure is preferably atmospheric pressure (1 atmosphere), and the working gas is preferably air.

[0027] In this invention, the input voltage of the cryogenic dielectric barrier plasma treatment is preferably 55~85V, more preferably 60~80V, the duty cycle is preferably 45~65%, more preferably 50~60%, and the pulse frequency is preferably 200~250HZ.

[0028] In this invention, the processing time of the cryogenic dielectric barrier plasma treatment is preferably 65-90 minutes, more preferably 75-80 minutes.

[0029] In this invention, in the low-temperature dielectric barrier plasma treatment, the relative permittivity of the dielectric barrier layer is preferably 2.5 to 6.0, and the breakdown strength is preferably not less than 10 kV / mm; the dielectric barrier layer preferably includes quartz glass, alumina ceramic, borosilicate glass, or polytetrafluoroethylene.

[0030] In this invention, the thickness of the dielectric barrier layer is preferably 0.5~3mm, more preferably 1~2mm; the shape of the dielectric barrier layer is preferably matched with the electrode, more preferably a circular plate structure or a rectangular plate structure; the size of the dielectric barrier layer is preferably larger than the size of the electrode, more preferably 3~10mm on one side; the discharge spacing of the dielectric barrier layer (gas gap between the electrode and the dielectric barrier layer) is preferably 0.5~5mm, more preferably 1~3mm.

[0031] This invention employs the aforementioned dielectric barrier layer to ensure stable blocking discharge and suppress arc generation. The aforementioned dimensions prevent edge discharge. Within the aforementioned discharge spacing range, it ensures the formation of a uniform, stable, and highly active low-temperature plasma at atmospheric pressure, and is less prone to breakdown and arcing.

[0032] In this invention, the electrodes used for cryogenic dielectric barrier plasma treatment are preferably inserted into the soil to be treated in an array and connected in parallel to a power source; the electrodes are preferably circular or square electrodes. The effective range of cryogenic dielectric barrier plasma treatment is the cylindrical (circular electrode) or cubic (square electrode) shape formed by the projected portion between two discharge electrodes.

[0033] After obtaining the pretreated soil, the present invention adds a compound microbial mixture to the pretreated soil for degradation and deep degradation. In the present invention, the mass ratio of Pseudomonas aeruginosa to Aristobacterium intermedius is preferably 0.9~1.2:0.9~1.2, more preferably 1:1.

[0034] In this invention, the mass ratio of Microbacterium oxidans to Bacillus intermedia is preferably 0.9~1.2:0.9~1.2, more preferably 1:1.

[0035] In this invention, the preferred mass ratio of Pseudomonas aeruginosa, Microbacterium oxysporum, and Bacillus intermedius is 1:1:1.

[0036] In this invention, the mass ratio of the pretreated soil to the composite microorganisms is preferably 1000:3~8, more preferably 1000:4~7, and even more preferably 1000:5~6.

[0037] In this invention, the degradation temperature is preferably 24-32 degrees Celsius, more preferably 27 degrees Celsius, the relative humidity is preferably 40-60%, more preferably 52%, and the time is preferably more than 30 days, more preferably 35-50 days.

[0038] In this invention, the temperature for deep degradation is preferably 30-38 degrees Celsius, more preferably 36 degrees Celsius, the relative humidity is preferably 30-50%, more preferably 40%, and the time is preferably more than 40 days, more preferably 40-85 days.

[0039] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments.

[0040] Example 1: This embodiment provides a method for degrading aged petroleum hydrocarbon pollutants in soil, the specific steps of which are as follows: Soil containing 5 g / kg of aged petroleum hydrocarbon contaminants was cleaned, ground, and filtered through a sieve to ensure a particle size no larger than 500 micrometers. The soil was then spread evenly in a plasma reactor, ready for cryogenic dielectric barrier plasma treatment. Under ambient temperature, pressure, and air atmosphere conditions, the input voltage was controlled at 60-80V, the duty cycle at 65%, the pulse frequency at 250Hz, and the treatment time was 70 minutes. The dielectric barrier layer (quartz glass) used had a relative permittivity of 4.5, a breakdown strength of 18kV / mm, a thickness of 1mm, and a circular flat structure matching the electrodes. Its dimensions extended 3mm beyond the electrodes on one side, and the discharge spacing was 3mm. The electrodes were inserted into the soil in an array, connected to a power source, and subjected to cryogenic dielectric barrier plasma treatment to obtain pretreated soil.

[0041] A compound microbial culture was prepared, with *Pseudomonas aeruginosa* and *Bacillus intermedius* in a 1:1 mass ratio, and *Microbacterium oxysporum* and *Bacillus intermedius* in a 1:1 mass ratio. The compound microbial culture was added to the pretreated soil, maintaining a mass ratio of 1000:5. Degradation was carried out at 27°C and 52% relative humidity for 35 days, followed by further degradation at 36°C and 40% relative humidity for 45 days. Samples were taken to test the concentration of aged petroleum hydrocarbon pollutants in the soil.

[0042] Example 2: This embodiment provides a method for degrading aged petroleum hydrocarbon pollutants in soil, the specific steps of which are as follows: Soil containing 35 g / kg of aged petroleum hydrocarbon contaminants was cleaned, ground, and filtered through a sieve to ensure a particle size no larger than 500 micrometers. The soil was then spread evenly in a plasma reactor, ready for cryogenic dielectric barrier plasma treatment. Under ambient temperature, pressure, and air atmosphere conditions, the input voltage was controlled at 60-80V, the duty cycle at 45%, the pulse frequency at 200Hz, and the treatment time was 65 minutes. The dielectric barrier layer (quartz glass) used had a relative permittivity of 6.0, a breakdown strength of 23kV / mm, a thickness of 2mm, and a circular flat structure matching the electrodes. Its dimensions extended 6mm beyond the electrodes on one side, and the discharge spacing was 4mm. The electrodes were inserted into the soil in an array, connected to a power source, and subjected to cryogenic dielectric barrier plasma treatment to obtain pretreated soil.

[0043] A compound microbial contaminant was prepared, with a mass ratio of *Pseudomonas aeruginosa* and *Bacillus intermedius* of 1.2:0.9, and a mass ratio of *Microbacterium oxysporum* and *Bacillus intermedius* of 1.2:0.9. The compound microbial contaminant was added to the pretreated soil, maintaining a mass ratio of 1000:4.6. Degradation was carried out at 27°C and 52% relative humidity for 30 days, followed by deep degradation at 36°C and 40% relative humidity for 50 days. Samples were taken to test the concentration of aged petroleum hydrocarbon pollutants in the soil.

[0044] Example 3: This embodiment provides a method for degrading aged petroleum hydrocarbon pollutants in soil, the specific steps of which are as follows: Soil containing 15 g / kg of aged petroleum hydrocarbon contaminants was cleaned, ground, and filtered through a sieve to ensure a particle size no larger than 500 micrometers. The soil was then spread evenly in a plasma reactor, ready for cryogenic dielectric barrier plasma treatment. Under ambient temperature, pressure, and air atmosphere conditions, the input voltage was controlled at 60-80V, the duty cycle at 50%, the pulse frequency at 210Hz, and the treatment time was 90 minutes. The dielectric barrier layer (quartz glass) used had a relative permittivity of 2.5, a breakdown strength of 13kV / mm, a thickness of 2.2mm, and a circular flat structure matching the electrodes. Its dimensions extended 3mm beyond the electrodes on one side, and the discharge spacing was 5mm. The electrodes were inserted into the soil in an array, connected to a power source, and subjected to cryogenic dielectric barrier plasma treatment to obtain pretreated soil.

[0045] A compound microbial culture was prepared, with a mass ratio of *Pseudomonas aeruginosa* and *Bacillus intermedius* of 1.2:1, and a mass ratio of *Microbacterium oxysporum* and *Bacillus intermedius* of 1.2:1. The compound microbial culture was added to the pretreated soil, maintaining a mass ratio of 1000:4.1. Degradation was carried out at 30°C and 60% relative humidity for 40 days, followed by deep degradation at 38°C and 30% relative humidity for 45 days. Samples were taken to test the concentration of aged petroleum hydrocarbon pollutants in the soil.

[0046] Example 4: This embodiment provides a method for degrading aged petroleum hydrocarbon pollutants in soil, the specific steps of which are as follows: Soil containing 0.3 g / kg of aged petroleum hydrocarbon contaminants was cleaned, ground, and filtered through a sieve to ensure a particle size no larger than 500 micrometers. The soil was then spread evenly in a plasma reactor, ready for cryogenic dielectric barrier plasma treatment. Under ambient temperature, pressure, and air atmosphere conditions, the input voltage was controlled at 60-80V, the duty cycle at 55%, the pulse frequency at 220Hz, and the treatment time was 80 minutes. The dielectric barrier layer (polytetrafluoroethylene) used had a relative permittivity of 4.0, a breakdown strength of 11kV / mm, a thickness of 0.5mm, and a circular flat structure matching the electrodes, extending 8mm beyond the electrodes on one side, with a discharge spacing of 2mm. The electrodes were inserted into the soil in an array, connected to a power source, and subjected to cryogenic dielectric barrier plasma treatment to obtain pretreated soil.

[0047] A compound microbial culture was prepared, with a mass ratio of *Pseudomonas aeruginosa* and *Bacillus intermedius* of 0.9:1, and a mass ratio of *Microbacterium oxysporum* and *Bacillus intermedius* of 0.9:1. The compound microbial culture was added to the pretreated soil, maintaining a mass ratio of 1000:7.3. The culture was degraded for 50 days at 32°C and 40% relative humidity, followed by further degradation for 45 days at 38°C and 30% relative humidity. Samples were taken to test the concentration of aged petroleum hydrocarbon pollutants in the soil.

[0048] Example 5: This embodiment provides a method for degrading aged petroleum hydrocarbon pollutants in soil, the specific steps of which are as follows: Soil containing 1 g / kg of aged petroleum hydrocarbon contaminants was cleaned, ground, and filtered through a sieve to ensure a particle size no larger than 500 micrometers. The soil was then spread evenly in a plasma reactor, ready for cryogenic dielectric barrier plasma treatment. Under ambient temperature, pressure, and air atmosphere conditions, the input voltage was controlled at 60-80V, the duty cycle at 60%, the pulse frequency at 240Hz, and the treatment time was 80 minutes. The dielectric barrier layer (borosilicate glass) used had a relative permittivity of 5.0, a breakdown strength of 10kV / mm, a thickness of 2mm, and a rectangular flat structure matching the electrodes, extending 10mm beyond each side of the electrodes, with a discharge spacing of 2.5mm. The electrodes were inserted into the soil in an array, connected to a power source, and subjected to cryogenic dielectric barrier plasma treatment to obtain pretreated soil.

[0049] A compound microbial culture was prepared, with *Pseudomonas aeruginosa* and *Bacillus intermedius* in a 1:1 ratio and *Microbacterium oxysporum* and *Bacillus intermedius* in a 1:1.2 ratio. The compound microbial culture was added to the pretreated soil, maintaining a pretreated soil to compound microbial culture ratio of 1000:4.8. The culture was subjected to degradation at 24°C and 60% relative humidity for 35 days, followed by deep degradation at 30°C and 50% relative humidity for 40 days. Samples were taken to test the concentration of aged petroleum hydrocarbon pollutants in the soil.

[0050] Example 6: This embodiment provides a method for degrading aged petroleum hydrocarbon pollutants in soil, the specific steps of which are as follows: Soil containing 10 g / kg of aged petroleum hydrocarbon contaminants was cleaned, ground, and filtered through a sieve to ensure a particle size no larger than 500 micrometers. The soil was then spread evenly in a plasma reactor, ready for cryogenic dielectric barrier plasma treatment. Under ambient temperature, pressure, and air atmosphere conditions, the input voltage was controlled at 60-80V, the duty cycle at 50%, the pulse frequency at 210Hz, and the treatment time was 85 minutes. The dielectric barrier layer (alumina ceramic) used had a relative permittivity of 3.0, a breakdown strength of 14kV / mm, a thickness of 2.2mm, and a rectangular flat structure matching the electrodes. Its dimensions extended 4.5mm beyond the electrodes on one side, and the discharge spacing was 4mm. The electrodes were inserted into the soil in an array, connected to a power source, and subjected to cryogenic dielectric barrier plasma treatment to obtain pretreated soil.

[0051] A compound microbial culture was prepared, with *Pseudomonas aeruginosa* and *Bacillus intermedius* in a 1:1 mass ratio, and *Microbacterium oxysporum* and *Bacillus intermedius* in a 1:1 mass ratio. The compound microbial culture was added to the pretreated soil, maintaining a mass ratio of 1000:5.5. The culture was subjected to degradation at 25°C and 50% relative humidity for 35 days, followed by further degradation at 35°C and 45% relative humidity for 45 days. Samples were taken to test the concentration of aged petroleum hydrocarbon pollutants in the soil.

[0052] Example 7: This embodiment provides a method for degrading aged petroleum hydrocarbon pollutants in soil, the specific steps of which are as follows: Soil containing 25 g / kg of aged petroleum hydrocarbon contaminants was cleaned, ground, and filtered through a sieve to ensure a particle size no larger than 500 micrometers. The soil was then spread evenly in a plasma reactor, ready for cryogenic dielectric barrier plasma treatment. Under ambient temperature, pressure, and air atmosphere conditions, the input voltage was controlled at 60-80V, the duty cycle at 55%, the pulse frequency at 230Hz, and the treatment time was 70 minutes. The dielectric barrier layer (alumina ceramic) used had a relative permittivity of 3.0, a breakdown strength of 18kV / mm, a thickness of 1.5mm, and a rectangular flat structure matching the electrodes. Its dimensions extended 7mm beyond the electrodes on one side, and the discharge spacing was 2mm. The electrodes were inserted into the soil in an array, connected to a power source, and subjected to cryogenic dielectric barrier plasma treatment to obtain pretreated soil.

[0053] A compound microbial culture was prepared, with a mass ratio of *Pseudomonas aeruginosa* and *Bacillus intermedius* of 1:0.9, and a mass ratio of *Microbacterium oxysporum* and *Bacillus intermedius* of 1:0.9. The compound microbial culture was added to the pretreated soil, maintaining a mass ratio of 1000:5. Degradation was carried out at 27°C and 55% relative humidity for 38 days, followed by deep degradation at 38°C and 50% relative humidity for 40 days. Samples were taken to test the concentration of aged petroleum hydrocarbon pollutants in the soil.

[0054] Example 8: This embodiment provides a method for degrading aged petroleum hydrocarbon pollutants in soil, the specific steps of which are as follows: Soil containing 20 g / kg of aged petroleum hydrocarbon contaminants was cleaned, ground, and filtered through a sieve to ensure a particle size no larger than 500 micrometers. The soil was then spread evenly in a plasma reactor, ready for cryogenic dielectric barrier plasma treatment. Under ambient temperature, pressure, and air atmosphere conditions, the input voltage was controlled at 55-85V, the duty cycle at 45%, the pulse frequency at 200Hz, and the treatment time was 75 minutes. The dielectric barrier layer (alumina ceramic) used had a relative permittivity of 3.0, a breakdown strength of 20kV / mm, a thickness of 1.5mm, and a rectangular flat structure matching the electrodes. Its dimensions extended 7mm beyond the electrodes on one side, and the discharge spacing was 1.5mm. The electrodes were inserted into the soil in an array, connected to a power source, and subjected to cryogenic dielectric barrier plasma treatment to obtain pretreated soil.

[0055] A compound microbial culture was prepared, with *Pseudomonas aeruginosa* and *Bacillus intermedius* in a mass ratio of 1:1.1, and *Microbacterium oxysporum* and *Bacillus intermedius* in a mass ratio of 1:1.1. The compound microbial culture was added to the pretreated soil, maintaining a mass ratio of 1000:6. Degradation was carried out at 27°C and 42% relative humidity for 35 days, followed by deep degradation at 30–38°C and 45% relative humidity for 43 days. Samples were taken to test the concentration of aged petroleum hydrocarbon pollutants in the soil.

[0056] Comparative Example 1: The preparation method of this comparative example is the same as that of Example 1, except that the cryogenic dielectric barrier plasma treatment is not performed.

[0057] Comparative Example 2: The preparation method of this comparative example is the same as that of Example 1, except that the degradation and deep degradation of the compound microorganisms are not carried out.

[0058] Comparative Example 3: The preparation method of this comparative example is the same as that of Example 1, except that Pseudomonas aeruginosa, Microbacterium oxysporum, and Bacillus intermedius are added in a mass ratio of 3:2:1.

[0059] Comparative Example 4: The preparation method of this comparative example is the same as that of Example 1, except that the input voltage of the low-temperature dielectric barrier plasma treatment is 30~60V, the duty cycle is 30%, and the pulse frequency is 150HZ.

[0060] Comparative Example 5: The preparation method of this comparative example is the same as that of Example 1, except that no deep degradation of the compound microorganisms is performed.

[0061] Test Example 1: The degradation effects of Examples 1-8 and Comparative Examples 1-5 were detected using solvent extraction-chromatographic analysis. The detection method was as follows: Soxhlet extraction was performed for 18 hours using a 1:1 (v / v) hexane-acetone mixed solvent at a reflux rate of 10 times / hour. The results were then analyzed using a 30m × 0.32mm × 0.25μm quartz capillary column (stationary phase: 5% phenyl and 95% methylpolysiloxane). The results are shown in Table 1 and... Figure 1 As shown.

[0062] Table 1. Degradation effects of Examples 1-8 and Comparative Examples 1-5:

[0063] According to Table 1 and Figure 1 It can be seen that the degradation method provided by this invention has high degradation efficiency, completing degradation in 75 days, significantly shortening the degradation cycle compared to existing methods. Furthermore, the degradation effect is ideal, with a degradation rate exceeding 67%. It exhibits good degradation effects on both low-concentration and high-concentration pollutant soils, demonstrating a wide range of applications and broad prospects. Compared to Examples 1-8, Comparative Example 1, lacking low-temperature plasma pretreatment, showed a significant decrease in the degradation efficiency and effect of the composite microorganisms; Comparative Example 2, lacking coupled composite microorganisms, resulted in the disappearance of the synergistic effect of the coupled system, leading to a significant decrease in overall degradation effect; Comparative Example 3, not using the composite microorganisms within the specific proportion range of this invention, resulted in a final degradation effect reverting to conventional levels; Comparative Example 4, with parameters for low-temperature medium barrier plasma treatment outside the scope of this invention, and Comparative Example 5, not undergoing deep degradation under the conditions of this invention, both resulted in poor degradation performance, reverting to conventional levels. In summary, this invention, through specific low-temperature medium-blocking plasma treatment coupled with composite microorganisms, combined with the degradation and deep degradation conditions developed in this invention, not only achieves ideal degradation results, but also breaks the qualitative judgment in this field that the degradation effects of Pseudomonas aeruginosa, Microbacterium oxysporum, and Bacillus intermedius are poor, providing a new technical approach for the degradation and treatment of aged petroleum hydrocarbon pollutants in this field.

[0064] Test Example 2: Toxic byproducts were detected in Examples 1-8 and Comparative Examples 1-5. Soil respiration intensity (CO2 release) was determined by alkaline absorption method. Tests were conducted every 15 days (for the last test, if the interval was less than 15 days, the test was conducted at the actual end time) to assess the overall activity of soil microorganisms and thus obtain the production status of toxic byproducts. The results are shown in Table 2.

[0065] Table 2. Toxic byproducts of Examples 1-8 and Comparative Examples 1-5:

[0066] As can be seen from Table 2, the degradation methods provided in Examples 1-8 of this invention do not have significant toxicity accumulation and do not produce toxic byproducts, which is of great significance for the stability of soil conditions. This is due to the good activity of the compound microorganisms under specific conditions and the coupling effect of low temperature medium blocking plasma treatment. Furthermore, stable soil conditions provide good support for the activity and degradation of the compound microorganisms.

[0067] The embodiments of the present invention have been described above; however, these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the above embodiments of the present invention without inventive effort are within the protection scope of the present invention.

Claims

1. A method for degrading aged petroleum hydrocarbon pollutants in soil, characterized in that, Includes the following steps: Soil containing aged petroleum hydrocarbon pollutants is subjected to low-temperature medium barrier plasma treatment, followed by the addition of compound microorganisms for degradation and deep degradation. The compound microorganisms include Pseudomonas aeruginosa, Microbacterium oxysporum, and Bacillus intermedius.

2. The degradation method according to claim 1, characterized in that, The content of aged petroleum hydrocarbon pollutants in the soil containing such pollutants shall not exceed 40 g / kg. The soil containing aged petroleum hydrocarbon pollutants has a particle size of less than 500 micrometers.

3. The degradation method according to claim 1, characterized in that, The input voltage for the cryogenic dielectric barrier plasma treatment is 55~85V, the duty cycle is 45~65%, the pulse frequency is 200~250HZ, and the treatment time is 65~90 minutes.

4. The degradation method according to claim 1, characterized in that, In the aforementioned cryogenic dielectric barrier plasma treatment, the dielectric barrier layer used has a relative permittivity of 2.5 to 6.0 and a breakdown strength of not less than 10 kV / mm; The dielectric barrier layer includes quartz glass, alumina ceramic, borosilicate glass, or polytetrafluoroethylene.

5. The degradation method according to claim 1, characterized in that, The thickness of the dielectric barrier layer is 0.5~3mm; The shape of the dielectric barrier layer matches the electrode, and it adopts a circular plate structure or a rectangular plate structure. The size of the dielectric barrier layer is larger than the size of the electrode; The discharge spacing of the dielectric barrier layer is 0.5~5mm.

6. The degradation method according to claim 1, characterized in that, The electrodes used in the cryogenic dielectric barrier plasma treatment are inserted into the soil to be treated in an array and connected in parallel to the power supply. The electrode is either a circular electrode or a square electrode.

7. The degradation method according to claim 1, characterized in that, The mass ratio of *Pseudomonas aeruginosa* to *Bacillus intermedius* is 0.9–1.2:0.9–1.

2. The mass ratio of *Microbacterium oxysporum* to *Aureobacterium intermedius* is 0.9~1.2:0.9~1.

2.

8. The degradation method according to claim 1, characterized in that, The mass ratio of the pretreated soil to the compound microorganisms is 1000:3~8.

9. The degradation method according to claim 1, characterized in that, The degradation temperature is 24-32 degrees Celsius, the relative humidity is 40-60%, and the time is more than 30 days.

10. The degradation method according to claim 1 or 9, characterized in that, The deep degradation is carried out at a temperature of 30-38 degrees Celsius, a relative humidity of 30-50%, and a time of more than 40 days.

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