Device and method for simultaneous nitrogen fixation by gas-liquid mixed-phase pulsed discharge plasma treatment of pfoa

Abstract

The present application relates to water pollution control and resource technology field, especially to a kind of device and method for degrading perfluorooctanoic acid in water by gas-liquid miscible phase pulse discharge plasma technology and simultaneously converting nitrogen in air into nitrate.The present application includes: high-voltage pulse power supply, needle-plate type plasma reactor and emission spectrometer;The top of needle-plate type plasma reactor is equipped with reactor cover plate, and the bottom is equipped with reactor bottom plate, and the reactor cover plate is provided with through hole communicated with atmosphere;The reactor bottom plate is provided with aeration hole;The reactor cover plate is vertically equipped with high-voltage needle electrode, and the bottom tip of high-voltage needle electrode is located in the gas phase in the reactor, and higher than the liquid level of the solution to be treated;The bottom of needle-plate type plasma reactor is equipped with reactor bottom plate, and the reactor bottom plate is provided with aeration hole for blowing gas;The high-voltage output end of high-voltage pulse power supply is connected with high-voltage needle electrode, and the ground end is connected with round plate ground electrode mounted on the upper part of reactor bottom plate.

Description

Technical Field

[0001] This invention relates to the field of water pollution control and resource utilization technology, and in particular to an apparatus and method for degrading perfluorooctanoic acid (PFOA) in water using gas-liquid mixed-phase pulsed discharge plasma technology and simultaneously converting nitrogen in the air into nitrates. Background Technology

[0002] Perfluorooctanoic acid (PFOA) is a typical perfluoroalkyl substance that has been widely used in the production of fluoropolymers, non-stick coatings, and fire-fighting foams. However, it enters surface water, groundwater, and even the marine environment through industrial wastewater discharge, posing a serious threat to ecosystems and human health. This is due to the extremely high bond energy of the CF bond (approximately 485 kJ·mol⁻¹). - ¹) Perfluorooctanoic acid (PFOA) exhibits extremely high thermal and chemical stability, making it very difficult to degrade in the natural environment. It demonstrates persistence, bioaccumulation, and potential toxicity. Currently, methods for removing PFOA from water mainly include adsorption, biodegradation, photocatalytic oxidation, electrochemical oxidation, and ultrasound. However, these methods generally suffer from drawbacks such as pollutant transfer rather than degradation, slow reaction rates, and demanding conditions.

[0003] Low-temperature plasma technology can generate highly reactive species such as high-energy electrons and active free radicals at room temperature and pressure, demonstrating a significant ability to degrade structurally stable and recalcitrant organic pollutants. Among these, gas-liquid two-phase pulsed discharge plasma can... A high-energy electron region and a strong electric field region are constructed near the liquid interface. At the same time, active species generated in the gas phase diffuse and dissolve into the liquid phase, achieving efficient removal of organic pollutants. Therefore, it has received widespread attention in the field of water treatment.

[0004] In existing studies on the degradation of PFOA by gas-liquid pulse discharge, argon is mostly used as the discharge atmosphere because argon is a monatomic molecule, easily ionized, and has a stable discharge, which facilitates the improvement of PFOA degradation efficiency. However, argon is expensive and cannot form high-value-added byproducts, which contradicts the concept of comprehensive energy utilization under the current "dual carbon" background.

[0005] In contrast, while air is slightly more difficult to ionize as a discharge atmosphere, it requires almost zero raw material cost and can generate high-value-added byproducts such as nitrates. High-energy electrons in plasma can simultaneously dissociate N2 and O2 to generate NO. x Reactive nitrogen species, these species in the atmosphere Upon dissolution at the liquid interface, nitrates / nitrites are formed, thus achieving simultaneous degradation of PFOA and resource recovery through nitrogen fixation. Furthermore, PFOA itself is an anionic surfactant, and its aqueous solution exhibits low surface tension. This characteristic can influence the migration of high-value-added products into the liquid phase, but it has not yet been applied in nitrogen fixation research. Although the discharge stability of air is slightly lower than that of argon, high degradation efficiency can be achieved by optimizing the reactor structure and discharge parameters, while simultaneously producing valuable nitrogen fertilizer solution. Therefore, using air as the working gas to achieve integrated degradation and nitrogen fixation is a more promising technical approach for engineering applications.

[0006] In view of the problems existing in the above-mentioned technologies, there is an urgent need to develop a reaction device and method that uses air as the working gas and utilizes gas-liquid pulsed discharge plasma to simultaneously achieve efficient degradation of PFOA and nitrogen resource utilization, thereby taking into account both the removal of organic pollutants and the in-situ production of nitrogen fertilizer. Summary of the Invention

[0007] To address the technical problem that existing technologies have not fully utilized the characteristic of PFOA to significantly alter the surface tension of the gas-liquid interface, thereby affecting the migration of active nitrogen to the liquid phase and the generation of nitrates in an air atmosphere, this invention provides a device and method for treating PFOA and simultaneously fixing nitrogen in a gas-liquid mixed-phase pulsed discharge plasma. This method achieves continuous and stable discharge in an air atmosphere, efficiently degrading PFOA, while simultaneously converting nitrogen in the air into resource-usable nitrates, thus achieving the synergistic purpose of pollutant removal and simultaneous nitrogen fixation.

[0008] The technical means employed in this invention are as follows: A device for simultaneous nitrogen fixation of PFOA by gas-liquid mixed-phase pulsed discharge plasma treatment includes: a high-voltage pulsed power supply, a needle-plate plasma reactor, and an emission spectrometer; Furthermore, the top of the needle-plate plasma reactor is equipped with a reactor cover plate, and the reactor cover plate is provided with a through hole that communicates with the atmosphere. Furthermore, a high-pressure needle electrode is vertically mounted on the reactor cover plate, with the bottom tip of the high-pressure needle electrode located in the gas phase inside the reactor and above the liquid surface of the solution to be treated. Furthermore, the bottom of the reactor is equipped with a reactor bottom plate, and the reactor bottom plate is provided with aeration holes for blowing air in. Furthermore, a circular plate ground electrode is installed at the bottom of the needle-plate plasma reactor, and the circular plate ground electrode is immersed in the solution to be treated; Furthermore, the high-voltage output terminal of the high-voltage pulse power supply is connected to the high-voltage needle electrode, and the grounding terminal is connected to the circular plate grounding electrode mounted on the upper part of the reactor bottom plate. Furthermore, an emission spectrometer is installed on one side of the needle-plate plasma reactor; Furthermore, the aeration holes on the bottom plate of the reactor are used to introduce gas during the treatment process to supplement oxygen and nitrogen, providing raw materials for the generation of reactive oxygen species and reactive nitrogen species.

[0009] Furthermore, the needle-plate spacing between the high-voltage needle electrode and the circular plate ground electrode is 8-12mm, preferably 8mm.

[0010] Furthermore, the discharge voltage of the high-voltage pulse power supply is 16-20kV, preferably 18kV, and the discharge polarity is positive – connected to the high-voltage pulse power supply.

[0011] Furthermore, the method for simultaneous nitrogen fixation of PFOA via gas-liquid mixed-phase pulsed discharge plasma treatment includes the following steps: S51. Inject the solution containing perfluorooctanoic acid into the reactor, so that the circular plate ground electrode is completely submerged and the tip of the high-pressure needle electrode is above the liquid surface. S52. Air is blown into the solution through the aeration holes; S53. Turn on the high-voltage pulse power supply to generate plasma in the gas-liquid interface region to degrade perfluorooctanoic acid. S54. During the process, perfluorooctanoic acid in the solution is decomposed, while nitrogen and oxygen in the air are converted into nitrate ions under the action of plasma, thus achieving simultaneous nitrogen fixation.

[0012] Furthermore, in step S53, the degradation rate of PFOA continued to increase with treatment time at different initial concentrations.

[0013] Furthermore, during the discharge process in step S54, nitrate (NO3) - The amount of ) generated increases significantly with processing time.

[0014] Furthermore, the nitrates produced during simultaneous nitrogen fixation in step S54, which are then used as liquid nitrogen fertilizer, can be recycled as chemical raw materials.

[0015] The features of this invention are as follows: 1. Improved discharge stability due to air bubbles in the liquid: Air is introduced into the liquid phase through aeration holes. The generated bubbles preferentially discharge under the influence of the electric field, thus maintaining the continuous stability of the discharge. At the same time, the presence of bubbles can promote the migration of PFOA in the solution to the gas-liquid interface, enhancing its enrichment at the interface, which is beneficial to subsequent degradation reactions.

[0016] 2. Enhanced interfacial reaction through surface discharge: The strong electric field between the high-voltage needle electrode and the circular plate ground electrode induces streamer discharge in the gas phase. The discharge channel propagates axially and impacts the liquid surface, forming a high-energy-density discharge region at the gas-liquid interface. As a surface-active substance, PFOA easily accumulates at the gas-liquid interface to form a molecular layer, which is then directly attacked by high-energy electrons and active species, accelerating its decomposition.

[0017] 3. Simultaneous generation of reactive oxygen and nitrogen: During discharge in an air atmosphere, high-energy electrons collide with O2 and N2 to generate reactive species such as ·OH, O3, NO, and NO2. ROS accelerates the decomposition of PFOA, while RNS converts inert... N2 is converted into NO3. - -N enables the dual function of degrading pollutants and simultaneously fixing nitrogen.

[0018] 4. PFOA alters the gas-liquid microenvironment to promote nitrogen fixation: PFOA molecules enriched at the interface reduce the surface tension of water, affecting the formation and collapse of microbubbles. Smaller, more stable bubbles increase the gas-liquid contact area and mass transfer efficiency, thereby improving the efficiency of N2 activation. Simultaneously, PFOA molecules act as "energy acceptors," absorbing energy from high-energy electrons more effectively than water molecules, and indirectly transferring energy to nitrogen molecules through the degradation of intermediate products (such as the formed F atoms), thus enhancing the nitrogen fixation reaction.

[0019] Compared with the prior art, the present invention has the following advantages: 1. The device and method for treating PFOA and simultaneously fixing nitrogen in gas-liquid mixed-phase pulsed discharge plasma provided by the present invention rapidly decomposes PFOA: The present invention utilizes the synergistic effect of gas-liquid interface enrichment and surface discharge, and the PFOA degradation rate exceeds 90% within 30 min, with a treatment efficiency significantly higher than that of traditional methods. 2. The gas-liquid mixed-phase pulsed discharge plasma treatment device and method for PFOA and simultaneous nitrogen fixation provided by the present invention achieves stable and continuous discharge in an air atmosphere to achieve the nitrogen fixation target: The present invention utilizes aeration holes set on the bottom plate to blow gas into the liquid phase, and combines online spectral monitoring technology to detect the generation and distribution of nitrogen and oxygen active intermediates in real time, providing a basis for optimizing discharge parameters and realizing the continuous conversion of nitrogen into nitrogen fertilizer. 3. The gas-liquid mixed-phase pulsed discharge plasma treatment device and method for PFOA treatment and simultaneous nitrogen fixation provided by the present invention achieves efficient simultaneous nitrogen fixation: while degrading pollutants, more than 651 mg / L of nitrate can be generated within 30 min, realizing the coupling of pollutant treatment and resource recovery. 4. The gas-liquid mixed-phase pulsed discharge plasma treatment device and method for PFOA and simultaneous nitrogen fixation provided by the present invention significantly shortens the perfluorocarbon chain: the carbon chain length of PFOA is greatly reduced after treatment, its persistence and bioaccumulation are significantly reduced, and the risk to the water environment is greatly reduced. 5. The gas-liquid mixed-phase pulsed discharge plasma treatment device and method for PFOA and simultaneous nitrogen fixation provided by this invention has outstanding resource value: the treated liquid contains high concentrations of nitrates, which can be recycled as liquid nitrogen fertilizer or chemical raw materials for the production of industrial products such as fertilizers and explosives. It can also be used for irrigation of ecological forests and urban green spaces, achieving carbon emission reduction and economic closed loop, and is an important development direction for green water treatment technology. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the device structure of the present invention; Figure 2 This is a graph showing the degradation rate of perfluorooctanoic acid (PFOA) over time at different initial concentrations according to the present invention. Figure 3 This is a graph showing the formation of nitrate and nitrite ions during surface discharge in water according to the present invention. Figure 4 This is a graph showing the formation of nitrate and nitrite ions in the PFOA solution of the present invention during the discharge process; Figure 5 This is an energy efficiency curve of nitrogen fixation in water and PFOA solution according to the present invention; Figure 6 This is a graph showing the effect of different concentrations of PFOA solution on nitrate formation according to the present invention; Figure 7 This is a graph showing the effect of different concentrations of PFOA solution on nitrite formation according to the present invention.

[0022] In the diagram: 1. High-voltage pulse power supply; 2. Needle-plate plasma reactor; 3. Emission spectrometer. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0027] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0028] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0029] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0030] like Figure 1 As shown, the present invention provides an apparatus for simultaneous nitrogen fixation and PFOA treatment using gas-liquid mixed-phase pulsed discharge plasma, comprising: a high-voltage pulse power supply 1, a needle-plate plasma reactor 2, and an emission spectrometer 3; the needle-plate plasma reactor 2 is made of quartz or polymer material, with a reactor cover plate mounted on its top, the reactor cover plate having a through hole communicating with the atmosphere, and a reactor bottom plate mounted on its bottom, the reactor bottom plate having aeration holes; a high-voltage needle electrode is vertically mounted on the reactor cover plate, the tip of the high-voltage needle electrode being located in the gas phase inside the reactor and higher than the liquid level of the solution to be treated; the bottom of the needle-plate plasma reactor 2 is mounted on the reactor bottom plate, the reactor bottom plate having aeration holes for blowing in gas; the high-voltage output terminal of the high-voltage pulse power supply 1 is connected to the high-voltage needle electrode, and the grounding terminal is connected to a circular plate ground electrode mounted on the upper part of the reactor bottom plate; an emission spectrometer 3 is mounted on one side of the needle-plate plasma reactor 2.

[0031] The aeration holes on the bottom plate of the reactor are used to blow in gas, generate stable discharge, and continuously replenish nitrogen and oxygen to provide raw materials for the generation of reactive oxygen species and reactive nitrogen species. The through holes on the reactor cover are for communication with the atmosphere.

[0032] The needle-plate spacing between the high-voltage needle electrode and the circular plate ground electrode is 8-12mm, preferably 8mm.

[0033] The discharge voltage of the high-voltage pulse power supply is 16-20kV, preferably 18kV, and the discharge polarity is positive.

[0034] A method for simultaneous nitrogen fixation of PFOA using gas-liquid mixed-phase pulsed discharge plasma includes the following steps: S51. Inject the solution containing perfluorooctanoic acid into the reactor, so that the circular plate ground electrode is completely submerged and the tip of the high-pressure needle electrode is above the liquid surface. S52. Air is blown into the solution through the aeration holes; S53. Turn on the high-voltage pulse power supply to generate plasma in the gas-liquid interface region to degrade perfluorooctanoic acid. S54. During the process, perfluorooctanoic acid in the solution is decomposed, while nitrogen and oxygen in the air are converted into nitrate ions under the action of plasma, thus achieving simultaneous nitrogen fixation.

[0035] In step S53, the degradation rate of PFOA continued to increase with treatment time at different initial concentrations.

[0036] During the discharge process in step S54, nitrate (NO3) - The amount of ) generated increases significantly with processing time.

[0037] The nitrates produced during simultaneous nitrogen fixation in step S54 can be recycled as liquid nitrogen fertilizer or chemical raw materials.

[0038] Example 1 like Figure 1 As shown, this invention provides a device for simultaneous nitrogen fixation and PFOA treatment using gas-liquid mixed-phase pulsed discharge plasma. The needle-plate plasma reactor 2 is constructed of a quartz cylinder with a radius of 35 mm and a height of 70 mm. A reactor cover made of polymer material is sealed to the top of the needle-plate plasma reactor 2. The cover has two through holes: a small central hole for introducing a high-voltage needle electrode, and another through hole serving both ventilation and sampling functions, and communicating with the atmosphere. The high-voltage needle electrode is made of stainless steel with a radius of curvature of 0.1 mm, perpendicularly passing through the center of the cover, with its tip located 3 mm above the liquid surface. Aeration holes are provided on the reactor bottom plate. A circular plate ground electrode, made of stainless steel, is horizontally placed at the bottom of the needle-plate plasma reactor 2. A high-voltage pulse power supply 1 provides positive polarity pulses at a frequency of 20 Hz. The high-voltage output terminal of the power supply is connected to the high-voltage needle electrode, and the ground terminal is connected to the circular plate ground electrode.

[0039] The processing method in this embodiment is as follows: 50 mL of PFOA solution with a concentration of 120 μmol / L is injected into the needle-plate plasma reactor 2, and the needle-plate spacing is adjusted to 8 mm. Air is introduced into the aeration holes, the high-voltage pulse power supply is turned on, and the discharge voltage is set to 18 kV. During the discharge process, the through holes on the cover plate are open to the atmosphere. The discharge treatment lasts for 30 min.

[0040] Based on the above, the initial concentrations of PFOA were set to 24 μmol / L, 120 μmol / L and 240 μmol / L respectively.

[0041] like Figure 2 As shown, after 30 minutes of discharge, the degradation rates were 86.3%, 90.6%, and 94.6%, respectively. This indicates that the device also has excellent removal capabilities for high concentrations of PFOA, the key to which lies in the enrichment effect of PFOA at the gas-liquid interface and the synergistic attack of high-energy electrons and active species.

[0042] Example 2 Based on Example 1, the present invention also provides a PFOA-synergistic nitrogen fixation method; To verify the synergistic effect of PFOA on nitrogen fixation, two control experiments were set up: Group A consisted of pure water (without PFOA), and the nitrate formation was as follows. Figure 3 As shown; Group B is a 120 μmol / L PFOA solution, and its nitrate formation is as follows. Figure 4 As shown. Discharge conditions were the same as in Example 1 (18 kV, 8 mm, positive polarity). After treatment for 30 min, NO3 in group A... - The concentration was 287.4 mg / L, NO2 - The concentration was 2.97 mg / L, NO3 in group B - The concentration was 651.6 mg / L, NO2 - The concentration was 26.1 mg / L. The presence of PFOA increased the production of nitrate and nitrite by 1.2 times and 7.8 times, respectively, confirming its synergistic promoting effect.

[0043] Compare the energy efficiency of nitrogen fixation in the two solutions, such as Figure 5 As shown, NO3 - -N and NO2 - The total nitrogen fixation energy efficiency was calculated by summing the nitrogen and nitrogen (N) levels. The total nitrogen fixation efficiency gradually increased with increasing discharge time. The nitrogen fixation efficiency tended to stabilize after 10-30 minutes of discharge. The energy efficiency range for group A was 265-384 N mg / kWh, while the nitrogen fixation efficiency range for group B was 758-905 N mg / kWh, significantly higher than that of group A. The presence of PFOA increased the total nitrogen fixation efficiency by 1.4-1.8 times, confirming its synergistic promoting effect.

[0044] The mechanism is as follows: On the one hand, PFOA molecules directly participate in and alter the reaction network of reactive nitrogen species (RNS). RNS, such as ONOOH and NO2·, are significant contributors to PFOA degradation. PFOA reacts with RNS to generate new intermediates, which further decompose, promoting the conversion of nitrogen to nitrates. Furthermore, the PFOA degradation process consumes some hydrated electrons (e) and ·OH, thereby altering the oxidation equilibrium of RNS and causing it to convert more towards nitrates. On the other hand, PFOA alters the solution microenvironment, affecting the reaction equilibrium. As a surfactant, PFOA significantly reduces the surface tension of water, resulting in smaller and more stable microbubbles generated by discharge, increasing the gas-liquid contact area and nitrogen mass transfer efficiency, thus indirectly affecting nitrate formation. In addition, the nitrate ions generated by discharge make the solution acidic (pH drops to 2-3). This acidic environment further enhances the accumulation of PFOA at the gas-liquid interface, forming a positive feedback loop that simultaneously promotes nitrate formation.

[0045] Example 3 Based on Example 2, the present invention also provides the synergistic nitrogen fixation effect of different concentrations of PFOA; Four PFOA concentration gradients were set at 0, 24, 120, and 240 μmol / L, respectively. The discharge conditions were the same as in Example 1 (18 kV, 8 mm, positive polarity). The nitrate formation was as follows: Figure 6 As shown, as the PFOA concentration increased from 24 μmol / L to 120 μmol / L, NO3... - The amount of NO3 formed gradually increases after 30 minutes of discharge. - The concentration of PFOA increased from 352.9 to 651.4 mg / L; when PFOA increased to 240 μmol / L, NO3... - The concentration of PFOA decreased to 282.2 mg / L. This result is attributed to the fact that excess PFOA consumes the reactive species generated by the plasma, creating intense competition with the nitrate formation pathway and thus inhibiting nitrate formation. However, overall, PFOA in the solution still significantly promotes nitrate formation. The formation of nitrite is as follows... Figure 7 As shown, adding PFOA significantly increases NO2. - The yield was measured after 30 min of discharge, with the addition of 24, 120, and 240 μmol / L PFOA and NO2. - The concentrations of nitrogen formed were 32.2, 26.7, and 24.4 mg / L, respectively, which were much higher than the 2.97 mg / L in pure water. Overall, the optimal concentration for PFOA to facilitate nitrogen fixation was 120 μmol / L.

[0046] In summary, this invention achieves efficient nitrate generation through a PFOA-synergistic nitrogen fixation mechanism while efficiently degrading PFOA (degradation rate > 90% in 30 min). The treated nitrate-rich solution can be recycled as a raw material for Huagong or used as a high-quality liquid nitrogen fertilizer for irrigation of ecological forests or urban green spaces, thus achieving the dual goals of pollutant treatment and resource utilization.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for simultaneous nitrogen fixation and PFOA treatment using gas-liquid mixed-phase pulsed discharge plasma, characterized in that: The device for simultaneous nitrogen fixation of PFOA by gas-liquid mixed-phase pulsed discharge plasma treatment includes: a high-voltage pulse power supply (1), a needle-plate plasma reactor (2), and an emission spectrometer (3). The top of the needle-plate plasma reactor (2) is equipped with a reactor cover plate, and the reactor cover plate is provided with a through hole that communicates with the atmosphere; A high-pressure needle electrode is vertically mounted on the reactor cover plate. The bottom tip of the high-pressure needle electrode is located in the gas phase inside the reactor and is higher than the liquid surface of the solution to be treated. The bottom of the needle-plate plasma reactor (2) is equipped with a reactor bottom plate, and the reactor bottom plate is provided with aeration holes for blowing in gas. The high voltage output terminal of the high voltage pulse power supply (1) is connected to the high voltage needle electrode, and the grounding terminal is connected to the circular plate ground electrode mounted on the upper part of the reactor bottom plate. An emission spectrometer (3) is provided on one side of the needle-plate plasma reactor (2) to monitor the discharge state and guide the adjustment of operating parameters.

2. The apparatus for simultaneous nitrogen fixation of PFOA by gas-liquid mixed-phase pulsed discharge plasma treatment according to claim 1, characterized in that: The aeration holes on the bottom plate of the reactor are used to introduce air during the treatment process, providing raw materials for the generation of reactive oxygen species and reactive nitrogen species. The through holes on the reactor cover plate are used for gas outlets, allowing the reactor interior to communicate with the atmosphere.

3. The apparatus for simultaneous nitrogen fixation and PFOA treatment using gas-liquid mixed-phase pulsed discharge plasma according to claim 1, characterized in that: The needle-plate spacing between the high-voltage needle electrode and the circular plate ground electrode is 8-12 mm.

4. The apparatus for simultaneous nitrogen fixation of PFOA by gas-liquid mixed-phase pulsed discharge plasma treatment according to claim 1, characterized in that: The discharge voltage of the high-voltage pulse power supply is 16-20 kV, and the discharge polarity is positive.

5. A method for simultaneous nitrogen fixation of PFOA using gas-liquid mixed-phase pulsed discharge plasma, employing the apparatus described in claims 1-4, characterized in that: The method includes the following steps: S51. Inject the solution containing perfluorooctanoic acid into the reactor, so that the circular plate ground electrode is completely submerged and the tip of the high-pressure needle electrode is above the liquid surface. S52. Air is blown into the solution through the aeration holes; S53. Turn on the high-voltage pulse power supply to generate plasma in the gas-liquid interface region to degrade perfluorooctanoic acid. S54. During the process, perfluorooctanoic acid in the solution is decomposed, and at the same time, nitrogen in the air is converted into nitrate ions under the action of plasma, thus achieving simultaneous nitrogen fixation.

6. The method for simultaneous nitrogen fixation of PFOA using gas-liquid mixed-phase pulsed discharge plasma according to claim 5, characterized in that: In step S53, the degradation rate of PFOA continuously increases with treatment time at different initial concentrations.

7. The method for simultaneous nitrogen fixation of PFOA using gas-liquid mixed-phase pulsed discharge plasma according to claim 5, characterized in that: In step S54, during the discharge process, nitrate (NO3) - The amount of ) generated increases significantly with processing time.

8. The method for simultaneous nitrogen fixation of PFOA using gas-liquid mixed-phase pulsed discharge plasma according to claim 5, characterized in that: The nitrates produced during simultaneous nitrogen fixation in step S54 can be recycled as liquid nitrogen fertilizer or chemical raw materials.

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