Rotary coaxial DBD plasma treatment device for degrading micro-plastics in soil

Abstract

The invention belongs to the field of contaminated soil remediation and microplastic pollution treatment, and relates to a rotary coaxial DBD plasma treatment device for degrading microplastics in soil. The device comprises a DBD plasma reactor, a gas supply module, an electrode rotating mechanism and a control module, the DBD plasma reactor comprises an inner electrode, a dielectric layer and an outer layer ground electrode; the inner electrode and the outer-layer ground electrode are coaxially arranged, the dielectric layer is arranged between the inner electrode and the outer-layer ground electrode, a gap is reserved between the dielectric layer and the inner electrode, and the inner electrode and the outer-layer ground electrode are respectively connected with the electrode rotating mechanism; the appearance of the inner electrode is of a truncated cone structure, and the surface of the inner electrode is of a spiral structure evenly distributed in the axial direction. By adopting the device disclosed by the invention, the degradation uniformity and thoroughness of the fixed coaxial DBD reactor can be obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of contaminated soil remediation and microplastic pollution treatment, in particular to a rotating coaxial DBD plasma treatment device for microplastic degradation in soil. BACKGROUND

[0002] With the continuous growth of global plastic production and consumption, microplastics have become a new type of pollutant widely distributed in various interfaces of the environment. Studies have shown that the level of microplastic pollution in soil systems is even higher than that in water and atmospheric systems, and the main sources include agricultural film residues, landfill leaching, sewage irrigation, and atmospheric deposition. Microplastics can exist in the soil environment for a long time due to their small particle size, high chemical stability, and strong migration, leading to a decrease in soil porosity, changes in water retention, and a decrease in microbial diversity, thereby damaging the ecological structure and function of the soil. At the same time, as an adsorption platform, microplastics can enrich heavy metals, persistent organic pollutants (POPs), and pathogenic microorganisms, posing potential risks of transmission through biological chains and harm to human health.

[0003] Existing removal and remediation technologies for soil microplastic pollutants mainly include: physical separation methods such as sieving, flotation, and density separation, but the removal effect is poor for microplastic particles smaller than 100 μm, and the original structure of the soil is easily damaged. Thermal treatment methods such as incineration and pyrolysis can achieve microplastic mineralization, but usually require high temperature (> 400℃) conditions, high energy consumption, high cost, and may produce secondary harmful gas emissions. Chemical oxidation methods such as Fenton reaction, which attack and degrade plastics through hydroxyl radicals (·OH), require a large amount of chemical reagents, and have environmental risks and operational complexity. Biological degradation methods rely on specific microorganisms or enzyme systems for catalytic degradation, with long processing periods and limitations on microplastic types, soil environment, and biological adaptability, making engineering application difficult.

[0004] In recent years, low-temperature plasma technology has been widely studied due to its ability to generate highly active species (such as O3, ·OH, ·O, NO x As a typical low-temperature plasma generation method, dielectric barrier discharge (DBD) can stably and uniformly generate a discharge region rich in active particles, with low discharge temperature, high energy utilization rate, and flexible application of dielectric gas, making it a potential soil pollution remediation method.

[0005] However, when directly applying DBD to treat soil microplastic pollution, the following challenges still exist: limited mass transfer within the soil: the soil is a granular medium system, and gas diffusion and active species penetration are hindered, resulting in limited discharge effect to the surface layer or interstitial region of the soil, and insufficient treatment depth; insufficient coverage of the active discharge area: under the static electrode structure, the discharge area is fixed, and part of the area in the soil sample is in the low reaction zone for a long time, resulting in uneven degradation; strong stability of polymer structure: the C-C main chain bond energy of polymers such as polyethylene (PE) and polypropylene (PP) is relatively high (about 348 kJ / mol), and the degradation rate of active species excited by low-temperature plasma is relatively slow; local overheating and carbonization during treatment: the energy is concentrated locally during discharge, and if the soil sample is unevenly distributed, heat accumulation or carbonization may occur, affecting the overall treatment quality.

[0006] Some coaxial DBD reactors have been used for pollutant degradation, for example: Chinese patent CN114918242A discloses a microplastic contaminated soil remediation device and method based on coaxial DBD plasma technology, which proposes a soil remediation device based on static coaxial DBD discharge, but this technology still uses a fixed electrode structure, and the uniformity of soil exposure is limited, and the complete degradation rate of microplastics is low. This device is still a laboratory-scale device, and there is still a certain gap to practicality. Other similar technologies, such as the plasma-assisted waste treatment method disclosed in WO2020178651A1, mainly focus on surface contamination treatment, and the degradation effect of microplastics embedded in the soil is insufficient.

[0007] Therefore, due to the limited time and area of soil sample exposure to the plasma active region based on the existing coaxial discharge structure, full coverage treatment cannot be achieved, resulting in uneven and incomplete degradation, and other problems; it is difficult to promote polymer chain scission reactions and accelerate the degradation process, resulting in insufficient degradation completeness and efficiency, which makes it difficult to achieve the desired effect of degrading microplastics in soil using the existing rotating coaxial dielectric barrier discharge plasma reactor. SUMMARY

[0008] In view of the above defects or improvement needs of the prior art, the present application provides a rotating coaxial DBD plasma treatment device for degrading microplastics in soil, which solves the problem of poor treatment effect in the process of traditional DBD plasma treatment of soil.

[0009] To achieve the above-mentioned purpose, the present application provides a rotating coaxial DBD plasma reactor, comprising: a DBD plasma reactor, a gas supply module, an electrode rotating mechanism, and a control module; the gas supply module is connected to the plasma reactor, and the DBD plasma reactor, the gas supply module, and the electrode rotating mechanism are connected to the control module.

[0010] The DBD plasma reactor comprises an inner electrode, a dielectric layer, and an outer ground electrode; the inner electrode and the outer ground electrode are coaxially arranged, the dielectric layer is arranged between the inner electrode and the outer ground electrode, and a gap is left between the inner electrode and the outer ground electrode; the inner electrode and the outer ground electrode are respectively connected with the electrode rotating mechanism; wherein the outer shape of the inner electrode is a truncated cone structure, and the surface is a spiral structure uniformly distributed along the axial direction.

[0011] Preferably, the diameter of the inner electrode gradually increases from the first end to the end along the axial direction; wherein the diameter of the end of the inner electrode is 2.6-8mm, the diameter of the first end of the inner electrode is 2-5mm, and the conical angle is 0.7-1.7°. The conical angle is about 1.5°.

[0012] Preferably, the surface of the inner electrode is a spiral groove structure or a spiral protrusion structure uniformly distributed along the axial direction, the spiral angle is 20°-45°, and the pitch is 1 / 10-5 / 1 of the length of the inner electrode.

[0013] Preferably, the surface of the inner electrode is provided with a micron-level protrusion array or a micro-groove array, the array size is 10-100μm, and the array spacing is 50-200μm.

[0014] Preferably, the DBD plasma reactor is covered with a heating module, and the heating module is connected with the control module.

[0015] Preferably, the heating module comprises a heating system, a temperature control sensor, and a PID closed-loop regulation unit.

[0016] The heating system is covered on the outer ground electrode of the DBD plasma reactor, and is used for heating the DBD plasma reactor; the temperature control sensor is arranged on the outer ground electrode of the DBD plasma reactor, and is used for detecting the actual temperature of the DBD plasma reactor; the PID closed-loop regulation unit is connected with the heating system and the temperature control sensor, and is used for feedback adjusting the temperature of the heating system according to the collected actual temperature data.

[0017] Preferably, the heating system is a resistance heating band or a silicon carbide heating sleeve, which is wrapped around the outer ground electrode of the DBD plasma reactor.

[0018] Preferably, the electrode rotating mechanism comprises two rotating mechanisms, which are respectively connected with the inner electrode and the outer ground electrode.

[0019] Each electrode rotating mechanism comprises a stepping motor, a bearing and a shaft coupling; one end of the shaft coupling is connected to an output shaft of the stepping motor, and the other end is connected to the bearing; the other end of the bearing is connected to the inner electrode or the outer electrode.

[0020] Preferably, the gas supply module comprises a gas source bottle, a mass flow controller MFC and a pressure regulating valve; one end of the pressure regulating valve is connected to the gas source bottle, and the other end is connected to an inlet end of the mass flow controller MFC; the mass flow controller MFC is connected to a discharge cavity gas inlet of the DBD plasma reactor and connected to the control module.

[0021] Preferably, the system further comprises a tail gas purification module.

[0022] The tail gas purification module comprises a lye washing tower, an activated carbon filter and a tail gas detection unit; wherein a gas inlet of the lye washing tower is sealingly connected to a discharge cavity gas inlet of the DBD plasma reactor, and a gas outlet is connected to an inlet of the activated carbon filter; an outlet of the activated carbon filter is connected to the tail gas detection unit.

[0023] Overall, compared with the prior art, the scheme provided by the present application mainly has the following beneficial effects:

[0024] 1、The rotating coaxial DBD plasma reactor of the present application adopts an inner electrode with a truncated conical structure and a spiral groove structure on the surface, and combines an electrode rotating mechanism, which can effectively guide the axial rotation flow of the gas and promote the dynamic agitation of the soil particles in the discharge area, significantly improve the contact frequency of the discharge active species and the soil particles, and effectively improve the degradation uniformity and completeness of the fixed coaxial DBD reactor. At the same time, the outer layer rotates clockwise and the center rotates counterclockwise slowly in combination with the electrode rotating mechanism, forming a double-rotation-flow superposition agitation effect, which significantly improves the dynamic mixing effect of the soil sample, further improves the uniformity of the reaction zone and the overall treatment depth, effectively prevents the problem of particle deposition and clogging, and ensures the long-term stable operation of the system.

[0025] 2、The present application preferably designs the inner electrode with a stepped diameter increasing structure along the axial direction, forming a non-uniform electric field and a turbulent flow transition gas flow, which not only enhances the radial and axial mass transfer efficiency, but also effectively deepens the active species penetration depth in the soil, greatly improves the complete degradation ability of microplastic pollutants, and avoids the phenomenon of surface carbonization and internal residue.

[0026] 3、The application preferably prepares a micron-level protrusion array or a micro-groove array on the inner electrode surface, induces a high-density micro-plasma generation zone (Micro-DBD), locally enhances the electric field intensity, and makes the generation rate of high-activity species such as ozone and hydroxyl radicals increase by more than 30%, thereby accelerating the breaking and oxidation reaction of the high-energy bonds of micro-plastics and improving the degradation rate and mineralization degree.

[0027] 4、The application provides a rotating coaxial DBD plasma treatment system for micro-plastic degradation in soil, which adopts the rotating coaxial DBD plasma reactor, and is provided with a heating module on the surface, so that the plasma reactor cavity promotes the chain breaking of micro-plastics and the synergistic mineralization reaction of active species in a high-temperature environment, greatly shortens the treatment time, and realizes the rapid and complete degradation of micro-plastics. Meanwhile, the control module and the machine learning optimization module are introduced, a plurality of operation data such as discharge parameters, temperature and tail gas components can be collected in real time, the discharge power, the rotating speed and the heating curve are dynamically adjusted based on historical and real-time data, the system adaptive optimization and the energy optimal distribution are realized, compared with the traditional fixed parameter control mode, the treatment efficiency can be significantly improved, the energy consumption can be reduced, and the stability and robustness of long-term operation of the system can be improved.

[0028] 5、The application preferably is provided with a three-stage tail gas purification system, which can effectively remove harmful gases such as ozone and nitrogen oxides generated in the reaction process, ensure that the tail gas emission meets the environmental protection standard, reduce the secondary pollution risk to the environment, and realize a truly green treatment process.

[0029] In summary, the application realizes systematic technical innovation in the aspects of active species generation, mass transfer strengthening, reaction uniformity improvement, energy consumption reduction and intelligent control, and the overall performance is better than that of the existing coaxial DBD or single heating treatment micro-plastic degradation technology, and has wide application prospect and promotion value. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structure sectional view of the rotating coaxial DBD plasma reactor of the application;

[0031] Figure 2 is a structure sectional view of the rotating coaxial DBD plasma reactor of the application;

[0032] Figure 3 is a general structure schematic diagram of the rotating coaxial DBD plasma treatment system for micro-plastic degradation in soil of the application.

[0033] Figure 4 is a general process flow schematic diagram of the micro-plastic degradation in soil of the application.

[0034] Figure 5The soil degradation rate-time curve provided by the embodiment of the present application.

[0035] In all the drawings, the same reference signs are used to indicate the same elements or structures, wherein: 101-soil, 102-drying box, 103-vibrating screen equipment machine, 104-crusher, 105-soil sample cabin, 106-control module, 107-temperature control sensor, 108-DBD plasma reactor, 109-mass flow controller MFC, 110-gas source bottle, 111-discharge high-voltage power supply device, 112-alkali absorption tower, 301-inner electrode, 302-gap, 303-medium layer, 304-outer layer ground electrode. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0037] The present application provides a rotating coaxial DBD plasma treatment device for microplastic degradation in soil, which comprises a DBD plasma reactor, a gas supply module, an electrode rotating mechanism and a control module. The gas supply module is connected to the plasma reactor and is used to accurately deliver reaction gas, dynamically control flow and pressure, ensure gas purity and safety stability. The plasma reactor, the electrode rotating mechanism and the gas supply module are all connected to the control module.

[0038] As shown in Figure 1 The present application provides a structure sectional view of a rotating coaxial DBD plasma reactor, which comprises an inner electrode 301, a medium layer 303 and an outer layer ground electrode 304.

[0039] The inner electrode 301 and the outer layer ground electrode 304 are coaxially arranged, the medium layer 303 is arranged between the inner electrode 301 and the outer layer ground electrode 304 and has a gap 302 with the inner electrode, and the inner electrode 301 and the outer layer ground electrode 304 are respectively connected to the electrode rotating mechanism. The gap 302 simultaneously serves as a soil channel and a discharge area.

[0040] Among them, the inner electrode is a high-voltage electrode, the outer shape is a truncated cone structure, and the surface is a spiral structure uniformly distributed along the axial direction. As shown in Figure 1As shown, the cross-sectional view of the inner electrode is trapezoidal, and its shape is that of a cone with the tip removed, i.e., a truncated cone structure. The internal high-voltage electrode is processed into a spiral structure that extends along the electrode axis. This spiral structure can prolong the gas residence time when rotating, and at the same time, the spiral edge will induce a field strength enhancement effect, thereby enhancing the processing effect.

[0041] In some implementations, such as Figure 2 As shown, the diameter of the inner electrode increases axially from its tip to its tip, creating a transition between a non-uniform electric field and turbulent airflow along the axial direction. Specifically, the diameter of the inner electrode tip is 2.6-8 mm, the diameter of the inner electrode tip is 2-5 mm, and the cone angle is 0.7-1.7°. This structural design effectively promotes the multi-layered distribution and permeation mass transfer of active species in both radial and axial directions, significantly improving the treatment effect of deep microplastic particles within the soil.

[0042] In some embodiments, the surface of the inner electrode has a spiral groove structure or spiral protrusions that are uniformly distributed along the axial direction, the spiral angle is 20° to 45°, and the pitch is 1 / 10 to 5 / 1 of the length of the inner electrode.

[0043] In some embodiments, to enhance the partial discharge intensity, the surface of the inner electrode is further prepared with a micron-scale protrusion array or microgroove array (array size of 10-100 μm and array spacing of 50-200 μm), which can induce a high-density micro-plasma region (Micro-DBD), significantly increase the generation rate of highly active species such as O3, ·O, and ·OH, and accelerate the breaking and mineralization reaction of microplastic polymer chains.

[0044] In some embodiments, the electrode rotation mechanism comprises two rotating mechanisms, connected to the inner electrode and the outer ground electrode respectively. Each electrode rotation mechanism consists of a stepper motor, a ceramic bearing, and a coupling; one end of the coupling is connected to the output shaft of the stepper motor, and the other end is connected to the bearing. The bearing is used to support the rotating components, reduce friction and wear, transmit and distribute loads, provide axial positioning, and absorb shock. The inner ring of the bearing is connected to the rotating shaft, and the outer ring is connected to a fixed base.

[0045] In this invention, both the inner and outer electrodes are connected to two rotating motors via insulated couplings. The motors' speed and direction are controlled by a control system, allowing the two electrodes to rotate in opposite directions. During the discharge operation, an AC high voltage of 8–20 kV and a frequency of 5–50 kHz is applied to the reaction module to excite air or oxygen to form abundant plasma active species. To further enhance gas disturbance and particle dynamic mixing, the inner electrode is designed to rotate slowly in the opposite direction to the outer ground electrode, with a rotation speed set at 5–30 rpm. The outer ground electrode rotates clockwise, while the central high-voltage electrode rotates counterclockwise, creating a double-swirling superposition agitation effect, further improving reaction uniformity and overall repair efficiency.

[0046] In some embodiments, the heating system employed by the present application uses heating devices such as resistance heating bands or silicon carbide heating jackets outside the discharge device to heat the rotating coaxial DBD plasma reactor. The present application realizes the rapid and complete decomposition of microplastics in soil at room temperature and pressure by constructing a rotating coaxial DBD discharge and temperature control heating system, combined with intelligent parameter regulation, and effectively mineralizes the microplastics into carbon dioxide and water, thereby achieving green repair and functional recovery of the soil environment.

[0047] For example, the cavity is heated by winding resistance heating bands, the total power is 2-5 kW, the temperature rises at a rate of about 5℃ / min, and the temperature of the reaction cavity is raised to 180-220℃ in a short time. The heating system uses a segmented independent temperature control design, and is equipped with two K-type thermocouples to monitor the surface and internal temperature of the soil, respectively. The heating power is adjusted in real time by a PID closed-loop controller to ensure that the temperature fluctuation is controlled within ±2℃, thereby providing stable temperature conditions for the thermal cracking and plasma synergistic oxidation reaction of microplastics.

[0048] In some embodiments, the heating module includes a heating system, a temperature control sensor, and a PID closed-loop adjustment unit. The heating system is sleeved around the outer ground electrode of the plasma reactor to heat the rotating coaxial DBD plasma reactor. The temperature control sensor is arranged on the outer ground electrode of the plasma reactor to detect the actual temperature of the rotating coaxial DBD plasma reactor. The PID closed-loop adjustment unit is connected to the heating system and the temperature control sensor to feedback and adjust the temperature of the heating system according to the actual temperature data collected.

[0049] The heating system uses a segmented independent temperature control design, and is equipped with two K-type thermocouples to monitor the surface and internal temperature of the soil, respectively. The heating power is adjusted in real time by a PID closed-loop controller.

[0050] As shown in Figure 3 The present application illustrates a general structure schematic diagram of a rotating coaxial DBD plasma treatment system for microplastics degradation in soil. The overall device mainly includes: a DBD plasma reactor 108 (inner electrode 301, gap 302, dielectric layer 303, outer ground electrode 304) as described above, a heating module (including winding resistance heating bands, temperature control sensor 107, and PID closed-loop adjustment unit), a gas supply module (gas source bottle 110, mass flow controller MFC 109, and pressure regulating valve), an exhaust gas purification module (alkali washing tower, activated carbon filter, and exhaust gas detection unit), and a control module 106 (PLC main control unit and human-machine interface HMI). Each module is integrated in an integrated corrosion-resistant steel frame, and a protective cover and an observation window are provided outside the frame for easy on-site operation and maintenance.

[0051] Specifically, the gas supply module includes a gas source bottle 110, a mass flow controller MFC 109, and a pressure regulating valve. The gas source bottle 110 is connected to the inlet end of the pressure regulating valve through a high-pressure hose, and the pressure regulating valve reduces the high-pressure output of the gas source bottle 110 to a stable low pressure, ensuring that the input pressure of the subsequent mass flow controller MFC 109 is within a safe range. The pressure regulating valve is connected to the inlet end of the mass flow controller MFC 109 through a sealed sleeve joint. The outlet end of the mass flow controller MFC 109 can be directly connected to the inlet of the DBD plasma reactor 108 discharge cavity through a pipeline. High-purity air or industrial oxygen is selected as the reaction gas, and the gas flow is controlled within the range of 1-5 L / min, which is precisely adjusted by the mass flow controller MFC 109. The gas is filtered by three-stage dust removal before entering the DBD plasma reactor 108 discharge cavity, ensuring the cleanliness of the gas and the stability and activity of the discharge process. The tail gas purification system is composed of three-stage treatment modules. First, the alkaline absorption tower 112 with 5% NaOH solution is used to remove NOx and O3, then the activated carbon filter is used to adsorb trace organic waste gas, and finally the tail gas online analyzer is used to detect the concentration of O3 and NO2 in real time, ensuring that the tail gas emission meets the environmental protection standards of O3 < 0.05 ppm and NO2 < 0.1 ppm.

[0052] Specifically, the control module 106 uses a Siemens S7-1200 series PLC as the main control unit, cooperates with a 10-inch touch human-machine interface (HMI), collects voltage and current signals through an analog input module (Analog Input), and simultaneously monitors the electrode rotation speed in real time through the built-in counter. The multi-channel PID control outputs the heating power command through an analog output module (Analog Output) and transmits it to the heating device. In addition, the HMI can dynamically display data curves, and historical data can be stored in a local Sqlite database, and can be encrypted and uploaded to the cloud through 4G wireless signals, and then analyzed by the AI model on the cloud. The discharge voltage, current, rotation speed, heating temperature, tail gas emission, and other parameters can be monitored and controlled in real time, and the system also has historical data recording, remote networking, and cloud optimization functions. The system can dynamically optimize the rotation speed, discharge power, and heating curve according to the data collected during the processing process, thereby continuously improving the processing efficiency and energy efficiency.

[0053] Specifically, the tail gas purification module includes an alkali scrubber 112, an activated carbon filter, and a tail gas detection unit. The gas inlet of the alkali scrubber 112 is connected to the discharge cavity outlet of the DBD plasma reactor through a sealing connection, the gas outlet of the alkali scrubber 112 is connected to the inlet of the activated carbon filter through a conduit, and the outlet of the activated carbon filter is connected to the tail gas monitoring unit through a quick release joint. Through this connection mode, the tail gas purification module realizes the functions of acid-base neutralization and harmful substance adsorption of the tail gas, and realizes the monitoring function of the tail gas through the sampling probe in the tail gas monitoring unit.

[0054] As shown in Figure 4 , the present application provides a method for degrading microplastics in soil, which uses a system as shown in Figure 3 , and the overall process flow includes the following:

[0055] Step S1: soil pretreatment (drying, vibration, and crushing)

[0056] The soil sample 101 to be treated is first pretreated, including: drying: placing the soil sample 101 in a drying oven 102 and drying at 80-100°C for 4-8 hours to reduce the moisture content of the soil to below 10%, avoiding interference of water with the uniformity of the subsequent discharge and the pyrolysis reaction. Vibration and screening: using a vibrating screen device 103 to screen the dried soil, with a screen aperture of 5mm, to preliminarily remove large lumps and foreign matter. Crushing: for the screened material, a low-temperature crusher 104 is used for further crushing treatment to ensure uniform soil particle size, with a particle size of less than 5mm, to enhance the permeability and action area of the active species of the discharge plasma. The soil sample treated by this step is placed in a soil sample chamber 105, with uniform particle size distribution and stable pore structure, laying a foundation for subsequent rotating plasma discharge and high-temperature synergistic treatment.

[0057] Step S2: rotating coaxial DBD discharge activation

[0058] The soil sample treated by step S1 is loaded into a rotating coaxial DBD plasma reactor, which is composed of a high-pressure inner electrode, a dielectric layer, and a rotatable outer ground electrode. The rotating coaxial DBD plasma reactor drives the outer ground electrode to rotate at a speed of 10-100 rpm through a stepping motor, realizing the full-range dynamic exposure of the soil sample during the discharge process. The inner electrode is designed to rotate slowly in the opposite direction (e.g., the outer layer rotates clockwise and the inner layer rotates counterclockwise at a speed of 5-30 rpm), forming a double-swirl superimposed stirring effect, strengthening the gas disturbance and dynamic mixing of soil particles, and improving the reaction uniformity and overall repair efficiency.

[0059] The air or oxygen is excited to form plasma by applying an alternating high voltage with a peak voltage of 8-20 kV and a frequency of 5-50 kHz through the discharge high-voltage power supply device 111, so as to generate active species such as high-concentration O3, ·O and ·OH, and cover the soil particle surface.

[0060] The heating system is started synchronously, the temperature inside the DBD plasma reactor 108 cavity is heated to 100-50 DEG C through the resistance heating device arranged around the outer electrode, and the preferred range is 180-220 DEG C. The high-temperature heating promotes the microplastic polymer chain rupture and softening, reduces the activation energy, and enhances the plasma degradation rate and thoroughness.

[0061] The treatment is performed for 30-60 minutes under the triple synergy of rotation, discharge and heating, and the treatment time is dynamically adjusted according to the soil pollution level and the microplastic type. The rotating electrode improves the treatment uniformity, the discharge excites high-activity oxidizing species, the heating promotes the chain rupture reaction, and the overall degradation rate is more than 98%.

[0062] Step S3: tail gas absorption and purification

[0063] The tail gas such as O3 and NOx generated in the treatment process is purified through the alkaline absorption tower 112 and the activated carbon filter, so as to ensure that the tail gas meets the standard for emission and avoid secondary environmental pollution.

[0064] Further, sample detection and treatment effect evaluation

[0065] After the treatment, the degradation effect is evaluated through FTIR, TGA, SEM and TOC analysis. If the degradation rate or the TOC index does not meet the standard, the treatment parameters are automatically adjusted and the process is repeated to ensure the repair effect.

[0066] Further, intelligent optimization and system self-learning regulation

[0067] Based on the machine learning model (GBDT, random forest, etc.), the historical and current operation data are analyzed in real time, the rotation speed, the discharge power, the heating program and the gas flow are automatically optimized, the degradation efficiency is gradually improved and the energy consumption is reduced, and the intelligent operation and self-adaptive adjustment of the system are realized.

[0068] Further, the rotating electrode supports rapid replacement and online cleaning, is resistant to high temperature and corrosion, and improves the equipment operation stability and economy.

[0069] Further, the soil structure and porosity change little after the treatment, and the organic matter content is controllable, so that the microplastic removal is ensured while the soil ecological function is maintained, and the subsequent plant recovery and ecological restoration are facilitated.

[0070] The following introduces an example of the present application:

[0071] Take a certain amount of contaminated soil and measure the content of microplastic pollutants in it. First, lay the soil flat in a cool, well-ventilated place, spread it out to allow it to fully contact the air. When the soil moisture content drops to 15%-20% (hand can be crushed), place it in a drying tube and dry at 105°C for 24 hours until constant weight (mass change <0.5%). Select ZS type vibrating sieve machine to sieve the dried soil, first use 18 mesh screen to remove plant residues, plant roots, small stones and other impurities. Then select 100 mesh screen for fine screening, the large soil particles that do not pass need to be sieved again. The sieving work is carried out for 15 minutes. Then use a high-speed pulverizer to crush the soil for 1 minute. Ensure that the soil particle size is ≤0.15mm. Then send the soil from the inlet into the coaxial plasma discharge device.

[0072] The plasma reactor body adopts a quartz glass tube reactor with a coaxial electrode structure. The center electrode has a spiral protrusion structure with a pitch of 3mm, a protrusion height of 1.5mm and an angle of 30°. The outer ground electrode adopts a stainless steel mesh electrode with a micro-protrusion array on the surface. The discharge device is powered by an alternating current pulse power supply with a power supply parameter setting of 15kV and 20kHz. At the same time, the outer ground electrode and the center high-voltage electrode are respectively connected to a stepper motor, and the motor drives the two electrodes to rotate in opposite directions. The rotation speed is set to 50rpm. When working, first start the heating device, set the maximum temperature to 450°C, and at the same time turn on the control module to control and monitor various parameters. Heat until the device temperature reaches 400°C, then start the discharge device and let the motor drive the electrode to rotate. After 2 minutes, add soil for treatment. The tail gas generated by the discharge is treated using a tail gas purification module, and the control module can monitor its pollution level.

[0073] The soil is treated for different times, respectively 15min, 30min, 45min, 60min, 75min, 90min. After the soil is treated by the discharge device, the content of microplastics in it is collected and detected to collect data. The parameters involved are as follows in Table 1

[0074] Table 1: Device working parameters

[0075]

[0076] In combination Figure 5And the above experimental data show that the curve in the figure with the processing time (horizontal axis) and the microplastic degradation rate (vertical axis) is drawn, which shows that under the synergistic effect of spiral rotation coaxial DBD discharge + high temperature heating (experimental group), the degradation rate rapidly rises to more than 90% within 30 minutes, and the degradation rate reaches 99.8% in 45 minutes; The decomposition efficiency is significantly higher than that of high temperature heating (control group). The slope of the curve shows that the synergistic mechanism significantly improves the overall degradation rate and thoroughness. In summary, the device of the application can quickly and completely remove microplastic pollutants in soil under medium energy consumption, while maintaining the stability of the physical and chemical properties of the soil.

[0077] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the present application and the scope of its equivalent technology, the present application also intends to include these modifications and variations. The above-described embodiments are only preferred embodiments for fully illustrating the present application, and the protection scope is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present application are within the protection scope of the present application.

Claims

1. A rotating coaxial DBD plasma treatment device for the degradation of microplastics in soil, characterized in that, include: The system comprises a DBD plasma reactor, a gas supply module, an electrode rotation mechanism, and a control module; the gas supply module is connected to the plasma reactor, and the DBD plasma reactor, the gas supply module, and the electrode rotation mechanism are all connected to the control module. The DBD plasma reactor includes: an inner electrode, a dielectric layer, and an outer ground electrode; the inner electrode and the outer ground electrode are coaxially arranged, the dielectric layer is disposed between the inner electrode and the outer ground electrode and has a gap with the inner electrode, and the inner electrode and the outer ground electrode are respectively connected to the electrode rotation mechanism; wherein, the inner electrode has a truncated conical shape and a surface with a spiral structure uniformly distributed along the axial direction.

2. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 1, characterized in that, The diameter of the inner electrode gradually increases along the axial direction from the first end to the last end; wherein the diameter of the last end of the inner electrode is 2.6-8mm, the diameter of the first end of the inner electrode is 2-5mm, and the cone angle is 0.7-1.7°.

3. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 1, characterized in that, The surface of the inner electrode is a spiral groove structure or a spiral protrusion structure uniformly distributed along the axial direction, the spiral angle is 20° to 45°, and the pitch is 1 / 10 to 5 / 1 of the length of the inner electrode.

4. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 1, characterized in that, The surface of the inner electrode is provided with a micron-sized protrusion array or a microgroove array, the array size is 10-100μm and the array spacing is 50-200μm.

5. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 1, characterized in that, The DBD plasma reactor is covered with a heating module, which is connected to the control module.

6. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 5, characterized in that, The heating module includes a heating system, a temperature control sensor, and a PID closed-loop control unit; The heating system is covered on the outer ground electrode of the DBD plasma reactor and is used to heat the DBD plasma reactor; the temperature control sensor is located on the outer ground electrode of the DBD plasma reactor and is used to detect the actual temperature of the DBD plasma reactor; the PID closed-loop control unit is connected to the heating system and the temperature control sensor and is used to adjust the temperature of the heating system based on the collected actual temperature data.

7. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 5, characterized in that, The heating system is a resistance heating belt or a silicon carbide heating jacket, which is wrapped around the outer ground electrode of the DBD plasma reactor.

8. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 1, characterized in that, The electrode rotation mechanism includes two rotation mechanisms, which are respectively connected to the inner electrode and the outer ground electrode. Each of the electrode rotation mechanisms includes a stepper motor, a bearing, and a coupling; one end of the coupling is connected to the output shaft of the stepper motor, and the other end is connected to the bearing; the other end of the bearing is connected to the inner electrode or the outer ground electrode.

9. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 1, characterized in that, The gas supply module includes a gas source cylinder, a mass flow controller (MFC), and a pressure regulating valve; one end of the pressure regulating valve is connected to the gas source cylinder, and the other end is connected to the inlet of the mass flow controller (MFC); the mass flow controller (MFC) is connected to the discharge chamber inlet of the DBD plasma reactor and is connected to the control module.

10. The rotating coaxial DBD plasma treatment device for microplastic degradation in soil according to claim 1, characterized in that, The system also includes an exhaust gas purification module; The exhaust gas purification module includes an alkaline scrubbing tower, an activated carbon filter, and an exhaust gas detection unit; wherein, the inlet of the alkaline scrubbing tower is sealed to the inlet of the discharge chamber of the DBD plasma reactor, and the outlet is connected to the inlet of the activated carbon filter; the outlet of the activated carbon filter is connected to the exhaust gas detection unit.

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