Method and system for repairing composite organic pollutants in soil based on low-temperature plasma-microbubbles

Abstract

The invention discloses a method and a system for repairing composite organic pollutants in soil based on low-temperature plasma-microbubbles, and the method comprises the following steps: controlling a plasma-microbubble reactor and oxygen atmosphere and flow, current power, soil-water proportion and a catalyst; a large number of microbubbles rich in active oxygen species are formed in a soil-water mixture formed after water is added into soil, the mass transfer area of the active oxygen species among air, water and soil is enhanced through the microbubbles, and uniform distribution of the microbubbles in a container of the device is achieved in combination with precise control of mechanical stirring. The purpose that active oxygen substances make full contact with a large amount of soil particles is achieved, efficient mass transfer of active oxygen species is achieved, and efficient remediation of a large amount of contaminated soil is completed.

Description

Technical Field

[0001] This invention relates to a method for remediating complex organic pollutants in soil, particularly a method for remediating complex organic pollutants in soil based on low-temperature plasma-microbubbles, and also to the reaction system used in the above-mentioned remediation method. Background Technology

[0002] Currently, the main methods for degrading organic pollutants in soil using low-temperature plasma are to use needle-plate or plate-type dielectric barrier discharge devices to discharge pollutants into the soil, or to add catalysts to enrich pollutants and catalyze the generation of active species, thereby increasing the utilization efficiency of the active substances generated by the low-temperature plasma device and achieving the goal of efficient pollutant degradation. The main idea of ​​this approach is to treat polluted soil with low-temperature plasma: by applying an external electric field to generate high-energy electrons, molecules in the gas entering the device are ionized, active substances are generated above the soil, and then mass transfer occurs through the phase interface, thus acting on the pollutants.

[0003] However, due to the structural design and operational methods of plasma devices, the mass transfer distance of active substances is significantly affected by soil thickness. When the soil to be remediated is thick, the active substances generated in the gas phase by the plasma device have difficulty penetrating the soil layer to contact and react with pollutants and catalysts. This limits mass transfer and utilization rates. Therefore, such systems can only remediate thinner soil layers, resulting in lower soil remediation volumes. Furthermore, because it takes time for active substances in the gas phase to penetrate the soil layer, and most long-lived reactive oxygen species leave the reaction system before fully reacting with pollutants, the system's efficiency in completing the entire remediation process is low, and the required time is long. In summary, current methods for separating and remediating soil pollutants have very limited effectiveness in practical applications. Summary of the Invention

[0004] Purpose of the invention: In addressing the problems of limited practical application of existing low-temperature plasma technology in soil remediation due to difficulties in mass transfer of active substances, resulting in small soil remediation volume, low efficiency, and long remediation time, the purpose of this invention is to provide a remediation method for complex organic pollutants in soil based on low-temperature plasma-microbubbles, suitable for large-scale soil remediation and with extremely strong remediation effect, and also to provide the reaction system used in the above remediation method.

[0005] Technical solution: The present invention provides a method for remediating complex organic pollutants in soil based on low-temperature plasma-microbubbles, comprising the following steps: (1) Boron-nitrogen doped biochar was prepared by liquid phase impregnation method. Nitrogen source precursor and boron source precursor were mixed with glucose, biochar was added and stirred and sonicated in sequence. After drying, pyrolysis reaction was carried out to obtain the product. (2) Pre-treat the organically contaminated soil to obtain soil samples; (3) Mix the soil sample with water and place it into a low-temperature plasma-microbubble system. Stir, add boron and nitrogen-doped biochar, turn on the oxygen supply switch and adjust the gas flow meter, and then conduct the remediation reaction by applying electricity.

[0006] In step (1), the preparation method of biochar is as follows: after removing impurities and washing the biomass, it is dried in an oven at 70-105℃, placed in a tube furnace, heated to 600-800℃ at a rate of 8-10℃ / min in a N2 atmosphere, and kept under this condition for 3-4h to obtain the biochar.

[0007] In step (1), the nitrogen source precursor and the boron source precursor are urea and boric acid, respectively, and the mass-volume ratio of the nitrogen source precursor, the boron source precursor, glucose and biochar is 1:1:2~3:20.

[0008] In step (1), the stirring time is 2-4 hours, the ultrasonic time is 2-4 hours, and the pyrolysis reaction is carried out at 700-800℃ for 3-4 hours under a nitrogen atmosphere with a heating rate of 4-5℃ / min.

[0009] In step (2), the pretreatment involves air-drying the organically contaminated soil, removing impurities, and grinding it to obtain a soil sample.

[0010] In step (3), the mass ratio of soil to water is 1:4.5~5.5.

[0011] In step (3), the stirring rate is 800-1200 r / min and the oxygen supply flow rate is 700-900 mL / min.

[0012] In step (3), the output power of the energized reaction is 70-90W and the processing time is 30-120min.

[0013] The system used in the above-mentioned repair method is a low-temperature plasma-microbubble reaction system. The system includes a plasma-microbubble device, as well as an oxygen cylinder, a gas flow meter, a stirring blade speed controller, a high-voltage power supply, and an oscilloscope connected to it.

[0014] The plasma-microbubble device is a quartz barrel reactor with a sealed flange cover at the top. Coaxial cylindrical electrodes are mounted on the flange cover with their lower ends extending into the reactor. Microporous aeration heads are installed at the ends of the electrodes. The high-voltage electrode is connected to a power source, and the low-voltage electrode is grounded. An air inlet is connected to the top of the electrode, and an air outlet is connected to the flange cover. A gas flow meter and an oscilloscope are also provided. The gas flow rate is regulated by the gas flow meter, and the oscilloscope records parameters such as real-time voltage, current, and discharge waveform.

[0015] The coaxial cylindrical electrode is constructed from the inside out as follows: a high-voltage electrode at the center, a ceramic medium surrounding the high-voltage electrode, and a low-voltage electrode. The ceramic medium and the low-voltage electrode form a gas chamber for oxygen to enter. Oxygen enters the gas chamber inside the electrode through the air inlet.

[0016] Invention Principle: This invention utilizes a superior plasma-microbubble reaction system and optimized control of oxygen atmosphere and flow rate, current power, soil-water ratio, and catalyst. This allows for the formation of numerous microbubbles rich in active oxygen species within the soil-water mixture after water is added to the soil. These microbubbles enhance the mass transfer area of ​​active oxygen species between the gas, water, and soil phases. Combined with precise control of mechanical stirring, the microbubbles are evenly distributed within the device container, achieving full contact between active oxygen substances and a large number of soil particles, thus realizing efficient mass transfer of active oxygen species.

[0017] Based on this, the optimal ratio of boron and nitrogen source precursors was selected, and boron-nitrogen-doped biochar was designed and prepared in a targeted manner. Boron doping introduced electron-deficient centers, while nitrogen doping introduced electron-rich regions. The combination of the two activated the sp2+ sites on the biochar. 2 The hybridized carbon lattice narrows the bandgap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals within the carbon framework, thereby enhancing the catalyst's electron transfer capability and promoting its adsorption and activation of long-lived active species generated by plasma. The entire process continuously converts long-lived active oxygen species in the microbubbles into ·OH at the interface, achieving high utilization of active oxygen species. This combination allows for the remediation of more soil in a shorter time, improving the practical application of low-temperature plasma technology in soil remediation.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The remediation method of the present invention has a large soil remediation capacity, high efficiency and short time, and has a strong practical application capability. The degradation rate of various types of pollutants can reach 90% or more within 1 hour; (2) When the system of the present invention is applied to soil pollutant treatment, the precise control of mechanical stirring is combined to achieve the uniform distribution of the above-mentioned microbubbles in the device container, further improving the remediation rate and remediation effect. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the plasma-microbubble reaction system of the present invention; wherein, 1-plasma-microbubble device, 2-oxygen cylinder, 3-gas flow meter, 4-stirring blade speed controller, 5-high voltage power supply, 6-oscilloscope; Figure 2This is a schematic diagram of the plasma-microbubble device of the present invention, wherein 11-reactor, 12-flange cover, 13-high voltage electrode, 14-ceramic medium, 15-low voltage electrode, 16-stirring blade, 17-microporous aerator, and 18-motor. Figure 3 This is a schematic diagram of the method for remediating complex organic pollutants in soil based on low-temperature plasma-microbubbles according to the present invention; Figure 4 This is a comparison of the performance of the low-temperature plasma-microbubble-based method for remediating complex organic pollutants in soil in different catalytic systems. Figure 5 This is a comparison of the performance of the method for remediating complex organic pollutants in soil based on low-temperature plasma-microbubbles in this invention in degrading p-nitrochlorobenzene in different ratios of boron and nitrogen source precursor systems; Figure 6 This is a comparison of the performance of the low-temperature plasma-microbubble-based method for remediating complex organic pollutants in soil at different current powers. Figure 7 This is a comparison chart of the performance of the low-temperature plasma-microbubble-based method for remediating complex organic pollutants in soil in this invention in degrading p-nitrochlorobenzene at different soil-water ratios. Figure 8 This is a comparison of the performance of the low-temperature plasma-microbubble-based method for remediating complex organic pollutants in soil under different oxygen flow rates. Figure 9 This is a performance comparison chart of the remediation method for complex organic pollutants in soil based on low-temperature plasma-microbubbles according to the present invention on complex organic pollutants in soil. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the embodiments. The test materials used in the embodiments can all be purchased through conventional means.

[0021] Example 1 The present invention provides a method for remediating complex organic pollutants in soil based on low-temperature plasma-microbubbles, comprising the following steps: (1) Preparation of boron-nitrogen-doped biochar: Straw, animal skeletons and other common biomass were cleaned and removed of impurities. They were then dried in an oven at 105°C. The dried biomass was placed in a tube furnace and heated to 600°C at a rate of 10°C / min in a N2 atmosphere. The temperature was maintained for 4 hours to obtain biochar. Boron-nitrogen-doped biochar was prepared by liquid-phase impregnation. Urea and boric acid in a mass ratio of 1:1 were weighed as nitrogen source precursor and boron source precursor, respectively. They were mixed with glucose and dissolved in deionized water. Biochar was weighed and added to the above mixed solution. The mixture was stirred and sonicated for 4 hours each. After being stirred and evaporated to a paste in an 80°C water bath, the mixture was transferred to an oven and dried at 70°C until completely dry. Finally, the mixture was pyrolyzed at 800°C for 3 hours in a nitrogen atmosphere at a heating rate of 5°C / min to obtain boron-nitrogen-doped biochar. (2) Soil pretreatment: After the composite organic polluted soil is air-dried, impurities are removed, it is ground and filtered through a 40-mesh sieve to obtain soil samples to be treated; (3) Preparation before remediation: Add the soil sample obtained in step 2 and water to the plasma-microbubble reaction system at a ratio of 1:5, and then add 0.5% of the boron-nitrogen-doped biochar obtained in step 1 of the composite organic polluted soil mass. Turn on the motor and stir for 5 minutes at a stirring speed of 800-1200 r / min. Turn on the oxygen cylinder and adjust the flow meter to 800 mL / min. (4) Soil remediation: Turn on the plasma device and adjust the input voltage and current control device power to 80 W. The remediation is completed after 30-120 min of reaction.

[0022] like Figure 1 As shown, the plasma-microbubble reaction system of the present invention includes a plasma-microbubble device 1, and connected thereto an oxygen cylinder 2, a gas flow meter 3, a stirring blade speed controller 4, a high-voltage power supply 5, and an oscilloscope 6.

[0023] like Figure 2 and 3 As shown, the main body is a quartz barrel reactor 11 with a top-sealed flange cover 12. The high-voltage electrode 13 is connected to the high-voltage power supply 5, the low-voltage electrode 15 is grounded, the top of the electrode is connected to an air inlet, the end of the electrode is equipped with a microporous aeration head 17, the flange cover 12 is connected to an air outlet, the plasma-microbubble device 1 is connected to the oxygen cylinder 2 through the gas flow meter 3, the stirring blade speed controller 4 is connected to the stirring blade 16 through the motor 18, and is connected to the oscilloscope 6 to record parameters such as real-time voltage, current and discharge waveform.

[0024] A coaxial cylindrical electrode is mounted on a flange cover with its lower end extending into the reactor 11. Its structure, from the inside out, consists of a high-voltage electrode 13 in the middle, a ceramic medium 14 enclosing the high-voltage electrode, and a low-voltage electrode 15. A gas chamber is located between the ceramic medium 14 and the grounded low-voltage electrode 15, through which oxygen enters the gas chamber. After the power is switched on, under the influence of the electric field between the high-voltage and grounded electrodes, high-energy electrons collide with oxygen molecules inelastically, inducing their excitation and dissociation, producing ozone and other reactive oxygen species. The oxygen, rich in reactive oxygen species, forms microbubbles at the bottom of the reactor through the microporous aeration head 17 at the electrode end, and is dispersed throughout the container by mechanical stirring. Under the action of added boron-nitrogen-doped biochar, a large number of hydroxyl radicals are generated, efficiently degrading pollutants in the soil.

[0025] Regarding the repair method in Example 1, a plasma-microbubble system was used to degrade p-nitrochlorobenzene under conditions of no boron-nitrogen-doped biochar, with boron-doped biochar, with nitrogen-doped biochar, and with boron-nitrogen-doped biochar.

[0026] Specifically, 300g of fish bones were washed, dried in an oven at 105℃, and then placed in a tube furnace. The temperature was increased to 600℃ at a rate of 10℃ / min under a N2 atmosphere and maintained for 4 hours to obtain 30g of biochar. This biochar was divided into three equal portions. One portion was prepared by dissolving 0.5g of urea and 1.5g of glucose in deionized water; another portion by dissolving 0.5g of boric acid and 1.5g of glucose in deionized water; and the third portion by dissolving 0.5g of urea, 0.5g of boric acid, and 1.5g of glucose in deionized water. After mixing the three solutions thoroughly, 10g of biochar was added to each portion, and the mixture was stirred and sonicated for 4 hours each. The mixture was then evaporated in an 80℃ water bath until it reached a paste-like consistency. Afterward, it was transferred to an oven and dried completely at 70℃. Finally, it was pyrolyzed at 800℃ for 3 hours under a nitrogen atmosphere at a heating rate of 5℃ / min to obtain 12g of boron-doped biochar, 12g of nitrogen-doped biochar, and 12.5g of boron-nitrogen-doped biochar.

[0027] In the laboratory, 200g of soil contaminated with p-nitrochlorobenzene at a concentration of 200mg / kg was prepared. 1L of water was measured using a graduated cylinder and poured into a quartz container. The contaminated clay was poured into the container while stirring, the flange cover was closed, and the motor was turned on for stirring at 800 rpm for 5 minutes. Stirring was then stopped, the flange cover was opened, the catalytic system was adjusted, and stirring was continued at 800 rpm for another 5 minutes. The oxygen cylinder was turned on, and the flow meter was set to a flow rate of 800ml / min. The high-voltage power supply was turned on and set to 80W. This state was maintained for 2 hours to complete the soil remediation. Samples were taken at 0, 15, 30, 60, and 120 minutes, and the concentration of p-nitrochlorobenzene was measured after extraction. Experiments were conducted sequentially under the following conditions: no boron-nitrogen-doped biochar, 1g of the above-mentioned boron-doped biochar, 1g of the above-mentioned nitrogen-doped biochar, and 1g of the above-mentioned boron-nitrogen-doped biochar.

[0028] like Figure 4 The plasma-microbubble system exhibits low utilization of long-lived reactive oxygen species without catalyst addition. Increasing the doping of a single atom type significantly improves the post-catalyst degradation efficiency. The effect of boron doping is attributed to the generation of -OBO- groups after incorporation into the carbon matrix, which disrupts the electroneutrality of the carbon lattice and provides charge sites conducive to oxidant adsorption and activation. The effect of nitrogen doping is attributed to the donation of electrons by nitrogen atoms to the carbon framework, introducing locally electron-rich regions, enhancing the polarity of adjacent carbon atoms, and promoting electron transfer between the catalyst and oxidant. Furthermore, boron-nitrogen co-doping reshapes the overall electronic environment of the catalyst, increasing the density of electron-rich sites on the surface. Electrons are more easily transferred to the long-lived reactive oxygen species generated by the plasma-microbubble device, catalyzing the generation of highly oxidizing hydroxyl radicals and improving the overall degradation rate of the system.

[0029] Regarding the remediation method in Example 1, urea and boric acid in molar ratios of 1:1, 1:2, 1:3, 2:1, and 3:1 were used as boron and nitrogen source precursors to prepare catalysts. The five boron and nitrogen-doped biochars were coupled using a plasma-microbubble system to degrade nitrochlorobenzene.

[0030] Specifically, 100g of beef bones were washed, dried in an oven at 105℃, and then placed in a tube furnace. The temperature was increased to 600℃ at a rate of 10℃ / min under a N2 atmosphere and maintained for 4 hours to obtain 10g of biochar. Different masses of urea, boric acid, and 1.5g of glucose were weighed, dissolved in deionized water, and mixed thoroughly. Biochar was added to the mixture, stirred, and sonicated for 4 hours each. The mixture was then evaporated in an 80℃ water bath until a paste was formed, transferred to an oven, and dried completely at 70℃. Finally, the catalyst precursor was pyrolyzed at 800℃ for 3 hours under a nitrogen atmosphere at a heating rate of 5℃ / min to obtain 12.5g of boron-nitrogen-doped biochar. By controlling the mass of urea to be 0.5, 0.33, 0.25, 0.66, and 0.75g, and the mass of boric acid to be 0.5, 0.66, 0.75, 0.33, and 0.25g, five different catalysts were obtained.

[0031] In the laboratory, 250g of soil contaminated with p-nitrochlorobenzene at a concentration of 200mg / kg was prepared. 1.25L of water was measured using a graduated cylinder and poured into a quartz container. The contaminated clay was poured into the container while stirring, the flange was closed, and the motor was turned on for stirring at 1200 rpm for 5 minutes. Stirring was then stopped, the flange was opened, and 1.25g of the aforementioned boron-nitrogen-doped biochar was added. Stirring was continued at 1200 rpm for another 5 minutes. An oxygen cylinder was turned on, and the flow meter was set to a flow rate of 800ml / min. A high-voltage power supply was turned on at a current of 80W, and this state was maintained for 2 hours to complete soil remediation. Samples were taken at 0, 15, 30, 60, and 120 minutes, and the concentration of p-nitrochlorobenzene was measured after extraction. Five boron-nitrogen catalysts were then tested using the same method.

[0032] like Figure 5 Overall, the boron-nitrogen doped catalyst with a urea to borate molar ratio of 1:1 showed better performance. This is likely due to the fact that nitrogen provides abundant Lewis base sites and electrons under this condition, enhancing the adsorption and activation of long-lived active species generated by plasma; and the appropriate amount of boron, as a Lewis acid site, can regulate the electron cloud density of the carbon framework and promote electron transfer. Therefore, a boron-nitrogen doped catalyst with a urea to borate molar ratio of 1:1 was subsequently selected.

[0033] Regarding the repair method of Example 1, the method was used to degrade p-nitrochlorobenzene under current power conditions of 40, 60, 80, 100, and 120 W.

[0034] Specifically: 100g of walnut shells were washed, dried in an oven at 105℃, and then placed in a tube furnace. The temperature was increased to 600℃ at a rate of 10℃ / min under a N2 atmosphere and maintained at this temperature for 4 hours to obtain 10g of biochar. 0.5g of urea, 0.5g of boric acid, and 1.5g of glucose were weighed and dissolved in deionized water and mixed thoroughly. The biochar was weighed and added to the above mixture, stirred and sonicated for 4 hours each. The mixture was then evaporated in an 80℃ water bath until it became a paste, transferred to an oven, and dried completely at 70℃. Finally, it was pyrolyzed at 800℃ for 3 hours under a nitrogen atmosphere at a heating rate of 5℃ / min to obtain 12.5g of boron-nitrogen-doped biochar.

[0035] In the laboratory, 200g of soil contaminated with p-nitrochlorobenzene at a concentration of 200mg / kg was prepared. 1L of water was measured using a graduated cylinder and poured into a quartz container. The contaminated clay was poured into the container while stirring, the flange cover was closed, and the motor was turned on for stirring at 900 rpm for 5 minutes. Stirring was then stopped, the flange cover was opened, and 1g of the boron-nitrogen-doped biochar was added. Stirring was continued at 900 rpm for another 5 minutes. The oxygen cylinder was turned on, and the flow meter was adjusted to a flow rate of 800ml / min. This condition was maintained for 2 hours to complete soil remediation. Samples were taken at 0, 15, 30, 60, and 120 minutes, and the concentration of p-nitrochlorobenzene was measured after extraction. Experiments were conducted using this method at current power levels of 40, 60, 80, 100, and 120W.

[0036] like Figure 6 The degradation rate of p-nitrochlorobenzene by the plasma-microbubble system coupled with boron-nitrogen biochar first increased and then decreased with the current power of the plasma-microbubble device. This is because increasing the current power can enhance the discharge intensity of the plasma, improve its ionization effect on oxygen, and enhance the generation of reactive oxygen species. However, excessively high current power can easily lead to an increase in system temperature, reducing the existence time of long-lived reactive species such as ozone and hydrogen peroxide in the system, and further reducing their conversion efficiency by the catalyst. Therefore, a current power of 80W is preferred.

[0037] Regarding the remediation method of Example 1, the method was used to degrade p-nitrochlorobenzene under soil-to-water ratios of 1:2, 1:3, 1:4, 1:5, and 1:6.

[0038] Specifically, 100g of coconut shells were washed, dried in an oven at 105℃, and then placed in a tube furnace. The temperature was increased to 600℃ at a rate of 10℃ / min under a N2 atmosphere and maintained for 4 hours to obtain 10g of biochar. 0.5g of urea, 0.5g of boric acid, and 1.5g of glucose were weighed and dissolved in deionized water and mixed thoroughly. The biochar was then added to the mixture and stirred and sonicated for 4 hours each. The mixture was then evaporated in an 80℃ water bath until it became a paste, transferred to an oven, and dried completely at 70℃. Finally, it was pyrolyzed at 800℃ for 3 hours under a nitrogen atmosphere at a heating rate of 5℃ / min to obtain 12.5g of boron-nitrogen-doped biochar.

[0039] In the laboratory, 300g of soil contaminated with p-nitrochlorobenzene at a concentration of 200mg / kg was prepared. Water was measured using a graduated cylinder and poured into a quartz container. Contaminated clay was poured into the container while stirring, the flange cover was closed, and the motor was turned on for stirring at 900 rpm for 5 minutes. Stirring was then stopped, the flange cover was opened, and 1.5g of the aforementioned boron-nitrogen-doped biochar was added. Stirring was continued at 900 rpm for another 5 minutes. An oxygen cylinder was turned on, and the flow meter was set to a flow rate of 800ml / min. A high-voltage power supply was turned on at a current of 80W, and this state was maintained for 2 hours to complete soil remediation. Samples were taken at 0, 15, 30, 60, and 120 minutes, and the concentration of p-nitrochlorobenzene was measured after extraction. Experiments were then conducted sequentially with water volumes of 600, 900, 1200, 1500, and 1800ml.

[0040] like Figure 7 The degradation rate of nitrochlorobenzene by the plasma-microbubble system coupled with boron-nitrogen biochar first increased and then decreased with the water-to-soil ratio of the plasma-microbubble device. This is because too little water results in a low liquid level, making it difficult for active oxygen species in the bubbles to fully contact the pollutants. Secondly, insufficient water reduces heat dissipation from the plasma electrodes, leading to increased electrode temperature, decreased conductivity, and unstable discharge. Conversely, too much water can cause excessive dispersion of pollutants, reducing reaction efficiency. Therefore, a soil-to-water ratio of 1:5 is preferred.

[0041] Regarding the remediation method of Example 1, the method was used to degrade p-nitrochlorobenzene at oxygen flow rates of 200, 400, 600, 800, and 1000 ml / min.

[0042] Specifically, 100g of tree branches were washed, dried in an oven at 105℃, and then placed in a tube furnace. The temperature was increased to 600℃ at a rate of 10℃ / min under a N2 atmosphere and maintained at this temperature for 4 hours to obtain 10g of biochar. 0.5g of urea, 0.5g of boric acid, and 1.5g of glucose were weighed and dissolved in deionized water and mixed thoroughly. The biochar was then added to the mixture, stirred, and sonicated for 4 hours each. The mixture was then evaporated in an 80℃ water bath until it reached a paste-like consistency, transferred to an oven, and dried completely at 70℃. Finally, it was pyrolyzed at 800℃ for 3 hours under a nitrogen atmosphere at a heating rate of 5℃ / min to obtain 12.5g of boron-nitrogen-doped biochar.

[0043] In the laboratory, 200g of soil contaminated with p-nitrochlorobenzene at a concentration of 200mg / kg was prepared. 1L of water was measured using a graduated cylinder and poured into a quartz container. The contaminated clay was poured into the container while stirring, the flange cover was closed, and the motor was turned on for stirring at 900 rpm for 5 minutes. Stirring was then stopped, the flange cover was opened, and 1g of the boron-nitrogen-doped biochar was added. Stirring was continued at 900 rpm for 5 minutes. Oxygen was introduced through an oxygen cylinder, and the high-voltage power supply was turned on at a current of 80W. This state was maintained for 2 hours to complete soil remediation. Samples were taken at 0, 15, 30, 60, and 120 minutes, and the concentration of p-nitrochlorobenzene was measured after extraction. Experiments were conducted sequentially at oxygen flow rates of 200, 400, 600, 800, and 1000 ml / min using the same method.

[0044] like Figure 8 The degradation rate of p-nitrochlorobenzene by the plasma-microbubble system coupled with boron-nitrogen biochar first increased and then decreased with the oxygen flow rate of the plasma-microbubble device. This is because the increase in oxygen flow rate simultaneously increases the amount of reactive oxygen species entering the system. However, since the cross-sectional area of ​​the discharge region of the device is fixed, the increase in flow rate also simultaneously increases the flow velocity, leading to a decrease in the degree of oxygen ionization. Therefore, an oxygen flow rate of 800 ml / min is preferred.

[0045] The remediation method of Example 1 was used to remediate composite organic soil containing tetracycline, toluene, atrazine, p-nitrochlorobenzene and 2,4-dichlorophenol.

[0046] Specifically: 100g of straw was cleaned and washed, then dried in an oven at 105℃. The dried straw was then placed in a tube furnace and heated to 600℃ at a rate of 10℃ / min under a N2 atmosphere, and maintained at this temperature for 4 hours to obtain 10g of biochar. 0.5g of urea, 0.5g of boric acid, and 1.5g of glucose were weighed and dissolved in deionized water. After mixing thoroughly, the biochar was weighed and added to the mixture. The mixture was stirred and sonicated for 4 hours each. After evaporation into a paste in an 80℃ water bath, the mixture was transferred to an oven and dried at 70℃ until completely dry. Finally, it was pyrolyzed at 800℃ for 3 hours under a nitrogen atmosphere at a heating rate of 5℃ / min to obtain 12.5g of boron-nitrogen-doped biochar.

[0047] like Figure 9 Overall, this method demonstrates good remediation effects on soils contaminated with complex organic pollutants, achieving an overall degradation rate of approximately 90%. It can be seen that long-lived active substances such as ozone generated by the plasma-microbubble device can react fully with pollutants in the soil within a short time. Combined with the catalytic effect of the catalyst, the pollutants are continuously and thoroughly degraded. The slightly lower degradation rates of p-nitrochlorobenzene and atrazine may be due to the electron-withdrawing substituents in p-nitrochlorobenzene reducing the electron cloud density of the benzene ring, while the triazine ring structure of atrazine results in greater steric hindrance of its substituents. Toluene exhibits the lowest degradation rate, possibly because it lacks active functional groups and has weak reactivity. In summary, this method demonstrates good degradation effects on various pollutants and can be effectively used for the remediation of specific soil types.

Claims

1. A method for remediating complex organic pollutants in soil based on low-temperature plasma-microbubbles, characterized in that, Includes the following steps: (1) Boron-nitrogen doped biochar was prepared by liquid phase impregnation method. Nitrogen source precursor and boron source precursor were mixed with glucose, biochar was added and stirred and sonicated in sequence. After drying, pyrolysis reaction was carried out to obtain the product. (2) Pre-treat the organically contaminated soil to obtain soil samples; (3) Mix the soil sample with water and place it into the low-temperature plasma-microbubble reaction system. Stir, add boron and nitrogen-doped biochar, turn on the oxygen supply switch and adjust the gas flow meter, and then conduct the remediation reaction by applying electricity.

2. The repair method according to claim 1, characterized in that, In step (1), the preparation method of biochar is as follows: after removing impurities and washing the biomass, it is dried in an oven at 70-105℃, placed in a tube furnace, heated to 600-800℃ at a rate of 8-10℃ / min in a N2 atmosphere, and kept under this condition for 3-4h to obtain the biochar.

3. The repair method according to claim 1, characterized in that, In step (1), the nitrogen source precursor and the boron source precursor are urea and boric acid, respectively, and the mass ratio of nitrogen source precursor, boron source precursor, glucose and biochar is 1:1:2~3:

20.

4. The repair method according to claim 1, characterized in that, In step (1), the stirring time is 2-4 hours, the ultrasonic time is 2-4 hours, and the pyrolysis reaction is carried out at 700-800℃ for 3-4 hours under a nitrogen atmosphere with a heating rate of 4-5℃ / min.

5. The repair method according to claim 1, characterized in that, In step (2), the pretreatment involves air-drying the organically contaminated soil, removing impurities, and grinding it to obtain a soil sample.

6. The repair method according to claim 1, characterized in that, In step (3), the mass ratio of soil to water is 1:4.5~5.

5.

7. The repair method according to claim 1, characterized in that, In step (3), the stirring rate is 800-1200 r / min, the oxygen supply flow rate is 700-900 mL / min, the output power of the electro-reaction is 70-90 W, and the processing time is 30-120 min.

8. A system used in the repair method of claim 1, characterized in that, The system is a low-temperature plasma-microbubble reaction system, which includes a plasma-microbubble device and connected to it an oxygen cylinder, a gas flow meter, a stirring blade speed controller, a high-voltage power supply, and an oscilloscope.

9. The system according to claim 8, characterized in that, The plasma-microbubble device is a quartz barrel reactor with a sealed flange cover at the top. Coaxial cylindrical electrodes are mounted on the flange cover with their lower ends extending into the reactor. Microporous aeration heads are installed at the ends of the electrodes. The high-voltage electrode is connected to a power source, the low-voltage electrode is grounded, and an air inlet is connected to the top of the electrode. An air outlet is connected to the flange cover. A gas flow meter and an oscilloscope are also provided.

10. The system according to claim 9, characterized in that, The coaxial cylindrical electrode is constructed from the inside out as follows: a high-voltage electrode at the center, a ceramic medium surrounding the high-voltage electrode, and a low-voltage electrode. The ceramic medium and the low-voltage electrode form a gas chamber for oxygen to enter.

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