A method for degrading mixed antibiotics in sewage by low-temperature microwave plasma

Abstract

The present application proposes a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma, which relates to the technical field of treatment of new pollutants. Microwave energy is emitted by a microwave generating device and transmitted to a first converter. After being converted into a waveguide transmission mode, it is transmitted to a second converter. The second converter converts the microwave energy back into a coaxial cable transmission mode and transmits it to a microwave plasma generator. The argon gas flow is controlled by an argon gas flow controller and the argon gas is transmitted to the microwave plasma generator. The microwave plasma generator uses microwave energy to excite argon gas to obtain microwave plasma. The antibiotic solution is treated with the microwave plasma excited by the microwave plasma generator to obtain a degraded antibiotic solution. The method proposed in the present application adopts a three-layer coaxial microwave plasma jet degradation system to achieve efficient degradation of antibiotics in sewage at low power and low temperature.

Description

Technical Field

[0001] The present application relates to the technical field of novel pollutant treatment, and particularly to a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma. Background Art

[0002] According to the ecological risk assessment report, among more than 226 antibiotics, 20% of the antibiotics are highly toxic, 16% of the antibiotics are extremely toxic to algae, and 44% of the antibiotics are highly toxic to water fleas; more than 50% of the antibiotics have ecological toxicity, and one-third of the antibiotics are highly toxic to fish. Even though the concentration of a single antibiotic in environmental water bodies may be very low, the combined concentration of antibiotics may accumulate, thus causing serious toxicity to aquatic organisms.

[0003] To solve the problem of the impact of antibiotics on environmental water bodies, currently, non-thermal plasma is mainly used to remove antibiotics in water bodies, but it mainly focuses on the treatment of single antibiotics, which oversimplifies the problem of managing antibiotics in water environments. This is because compared with single antibiotics, multiple antibiotics with various interactions may cause greater potential toxicity.

[0004] In addition, various antibiotics always coexist in real sewage, and it cannot be considered that the treatment effect of multiple antibiotics is simply the sum of the removal effects of single antibiotics; although coupling plasma and a catalyst can effectively improve the degradation efficiency, secondary pollution of the catalyst cannot be avoided; and existing experiments are difficult to support the practical application of plasma technology. Summary of the Invention

[0005] The present application provides a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma to solve the above problems.

[0006] In an embodiment of the present application, a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma is proposed. The method is implemented through a degradation system, and the degradation system includes: a microwave generating device, a first converter, a second converter, a microwave plasma generator, and an argon flow controller. The method includes:

[0007] Using the microwave generating device to emit microwave energy, and the power of the microwave energy is 15 - 25 W;

[0008] Transmitting the microwave energy to the first converter, and using the first converter to convert the microwave energy from the coaxial cable transmission mode to the waveguide transmission mode and then transmitting it to the second converter;

[0009] Using the second converter to convert the microwave energy back to the coaxial cable transmission mode and transmitting it to the microwave plasma generator;

[0010] The argon flow rate is controlled by an argon flow controller and the argon is transmitted to the microwave plasma generator, and the argon flow rate is 6-10 L / min;

[0011] The microwave plasma generator uses microwave energy to excite argon to obtain microwave plasma;

[0012] The microwave plasma obtained by excitation of the microwave plasma generator is used to treat the antibiotic solution to obtain a degraded antibiotic solution. The antibiotic solution contains at least two or more kinds of mixed antibiotics. The initial concentration of the antibiotic solution is 10-30 mg / L, the pH value of the antibiotic solution is 2.0-12.0, and the degradation treatment time is 0-30 min.

[0013] Optionally, the microwave plasma generator is an atmospheric pressure low-temperature microwave plasma generator obtained by combining a three-layer coaxial structure and a rectangular waveguide power divider.

[0014] Optionally, the degradation system further includes a protection device. The protection device includes at least a circulator and a water load device. The circulator is connected to the first converter, and the water load device is connected to the circulator; The method further includes:

[0015] Using the circulator to prevent the reflected microwave energy power from being too high and damaging the microwave generating device;

[0016] Using the water load device to absorb the microwave energy reflected back through the circulator.

[0017] Optionally, the degradation system further includes a microwave controller and a power reading device. The power reading device includes a bidirectional coupler and a microwave power meter. The bidirectional coupler is connected between the circulator and the second converter, and the microwave power meter is connected to the bidirectional coupler. The method further includes:

[0018] Using the bidirectional coupler and the microwave power meter to read the incident power and the reflected power of the microwave energy;

[0019] Using the microwave controller to control the power of the microwave energy emitted by the microwave generator.

[0020] Optionally, between the first converter and the microwave generating device, and between the second converter and the microwave plasma generator, coaxial cables are used for connection.

[0021] Optionally, the power of the microwave energy is 20 W, the flow rate of the argon is 8 L / min, the pH value of the antibiotic solution is 2.74, and the initial concentration of the antibiotic solution is 20 mg / L.

[0022] Optionally, during the treatment of the antibiotic solution, high-energy electrons and reactive oxygen species generated by microwave plasma react with the antibiotics to achieve the degradation of the antibiotics.

[0023] Optionally, during the treatment of the antibiotic solution, those generated by microwave plasma ·H, ·O, ·OH, O3 act as reactive species to degrade the antibiotics in the antibiotic solution.

[0024] Optionally, the antibiotics in the antibiotic solution are sulfamethoxazole and oxytetracycline.

[0025] Optionally, the degradation pathway of sulfamethoxazole at least includes hydroxylation of the benzene ring, double-bond reconstruction by hydrogen abstraction, hydroxylation of the isoxazole ring, and cleavage of the sulfonamide bond;

[0026] The degradation pathway of oxytetracycline at least includes hydroxylation, deamination, demethylation, dehydration, and ring cleavage reactions.

[0027] This application has the following advantages: This application proposes a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma, which is realized by a degradation system. The degradation system includes: a microwave generating device, a first converter, a second converter, a microwave plasma generator, and an argon flow controller. The method includes: emitting microwave energy using the microwave generating device, and the power of the microwave energy is 15 - 25 W; transmitting the microwave energy to the first converter, and using the first converter to convert the microwave energy from the coaxial cable transmission mode to the waveguide transmission mode and then transmitting it to the second converter; using the second converter to convert the microwave energy back to the coaxial cable transmission mode and transmitting it to the microwave plasma generator; controlling the argon flow through the argon flow controller and transmitting argon to the microwave plasma generator, and the argon flow is 6 - 10 L / min; the microwave plasma generator uses microwave energy to excite argon to obtain microwave plasma; treating the antibiotic solution with the microwave plasma obtained by exciting through the microwave plasma generator to obtain a degraded antibiotic solution. The antibiotic solution contains at least two or more kinds of mixed antibiotics, the initial concentration of the antibiotic solution is 10 - 30 mg / L, the pH value of the antibiotic solution is 2.0 - 12.0, and the degradation treatment time is 0 - 30 min.

[0028] The method proposed in this application uses a three-layer coaxial microwave plasma jet degradation system to achieve efficient degradation of antibiotics in sewage at low power and low temperature, providing new theoretical and technical support for the management of various antibiotics in sewage. Description of the Drawings

[0029] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the attached drawings required for the description of the embodiments of the present application. Obviously, the attached drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other attached drawings can also be obtained based on these attached drawings.

[0030] Figure 1 It is a schematic flow chart of the steps of a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma proposed in the embodiments of the present application;

[0031] Figure 2 It is a schematic flow chart of a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma proposed in the embodiments of the present application;

[0032] Figure 3 It is a result graph of the degradation efficiency of treating single and mixed antibiotics in water by low-temperature microwave plasma provided in the embodiments of the present application;

[0033] Figure 4 It is a result graph of the influence of argon gas flow rate on the degradation efficiency of antibiotics provided in the embodiments of the present application;

[0034] Figure 5 It is a result graph of the influence of the initial concentration of antibiotics on the degradation efficiency of antibiotics provided in the embodiments of the present application;

[0035] Figure 6 It is an energy yield graph of antibiotics with different initial concentrations provided in the embodiments of the present application;

[0036] Figure 7 It is a result graph of the influence of different initial pH values on the degradation efficiency of antibiotics proposed in the embodiments of the present application;

[0037] Figure 8 It is a result graph of the influence of microwave power on the degradation efficiency of antibiotics provided in the embodiments of the present application;

[0038] Figure 9 It is a result graph of the change in conductivity during the degradation of antibiotic solutions under different acidity conditions provided in the embodiments of the present application;

[0039] Figure 10 It is a result graph of the mineralization efficiency of antibiotic solutions provided in the embodiments of the present application;

[0040] Figure 11 It is a result graph of the influence of isopropanol on the degradation efficiency of antibiotics provided in the embodiments of the present application;

[0041] Figure 12 It is a schematic diagram of the degradation path of SMX proposed in the embodiments of the present application;

[0042] Figure 13 It is a schematic diagram of an OTC degradation path proposed in an embodiment of the present application. Specific embodiments

[0043] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0044] To address the impact of antibiotics on environmental water bodies, research on treating antibiotics in water bodies using plasma has become increasingly extensive. However, current treatment methods mainly focus on the treatment of single antibiotics, which overly simplifies the problem of managing antibiotics in the water environment. This is because compared with single antibiotics, multiple antibiotics with various interactions may cause greater potential toxicity. For example, the combined toxicity of fluoroquinolones and sulfonamides was studied in zebrafish, and the results showed that the mixture of fluoroquinolones and sulfonamides could cause developmental toxicity, cardiotoxicity, immunotoxicity, and neurotoxicity. The combination of fluoroquinolone drugs and sulfonamide antibiotics could inhibit the activity of acetylcholinesterase in goldfish. The mixture of sulfonamides and tetracyclines might increase the plasma estradiol level in medaka, thus affecting reproductive metabolism. Other studies have also pointed out that the combined action of trimethoprim, sulfamethoxazole, and sulfadiazine would significantly inhibit the growth of microalgae. Even if the concentration of a single antibiotic in environmental water bodies may be very low, the combined concentration of antibiotics may accumulate, thereby causing serious toxicity to aquatic organisms.

[0045] In addition, various antibiotics always coexist in real sewage, and it cannot be considered that the treatment effect of multiple antibiotics is simply the sum of the removal effects of single antibiotics; although coupling plasma and a catalyst can effectively improve the degradation efficiency, secondary pollution of the catalyst cannot be avoided; and existing experiments are difficult to support the practical application of plasma technology.

[0046] Based on this, the present application proposes a device and method for treating mixed antibiotics in sewage by maximizing the degradation ability of the plasma itself. The mixed antibiotics are treated by low-temperature microwave plasma, and the degradation efficiencies of single antibiotics and mixed antibiotics are evaluated. The influencing factors of the antibiotic degradation efficiency are explored and the optimal experimental operation conditions are determined. During the experiment, the total organic carbon is monitored to study the mineralization efficiency of the antibiotics. Different concentrations of isopropanol are used as •OH scavengers to track their roles in the reaction. The main degradation intermediate products generated by the decomposition of antibiotics are identified by high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF / MS), and possible degradation pathways are proposed.

[0047] Referring to Figure 1 , Figure 1 FIG. is a schematic flow chart of the steps of a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma proposed in an embodiment of the present application. The method is implemented by a degradation system, and the degradation system includes: a microwave generating device, a first converter, a second converter, a microwave plasma generator, and an argon flow controller. The method includes the following steps:

[0048] Step 1: The microwave generating device emits microwave energy, and the power of the microwave energy is 15-25 W;

[0049] Step 2: The microwave energy is transmitted to the first converter, and the first converter converts the microwave energy from the coaxial cable transmission mode to the waveguide transmission mode and then transmits it to the second converter;

[0050] Step 3: The second converter converts the microwave energy back to the coaxial cable transmission mode and transmits it to the microwave plasma generator;

[0051] Step 4: The argon flow is controlled by the argon flow controller and the argon is transmitted to the microwave plasma generator, and the argon flow is 6-10 L / min;

[0052] Step 5: The microwave plasma generator uses the microwave energy to excite argon to obtain microwave plasma;

[0053] Step 6: The antibiotic solution is treated by the microwave plasma excited by the microwave plasma generator to obtain a degraded antibiotic solution. The antibiotic solution contains at least two or more mixed antibiotics. The initial concentration of the antibiotic solution is 10-30 mg / L, the pH value of the antibiotic solution is 2.0-12.0, and the degradation treatment time is 0-30 min.

[0054] To clearly illustrate the method for degrading mixed antibiotics in sewage using low-temperature microwave plasma proposed in this application, the following will be described in detail in conjunction with Figure 2 for a detailed description. Figure 2 is a schematic flow chart of a method for degrading mixed antibiotics in sewage using low-temperature microwave plasma proposed in an embodiment of this application.

[0055] In the specific implementation step 1, the microwave plasma generator is obtained by exciting argon with microwave energy. Therefore, first, the microwave energy is emitted by the microwave generating device and transmitted to the microwave plasma generator to obtain microwave plasma by excitation. In the embodiment of this application, the above-mentioned microwave generating device can be a solid-state microwave source (model PA2425-250, purchased from the 13th Research Institute of China Electronics Technology Group Corporation) (refer to Figure 2 for Solid State Microwave Source), or it can be other devices capable of emitting microwave energy. This application does not limit this, and it is only subject to actual requirements.

[0056] In an alternative embodiment of this application, in order to control the power of the microwave energy emitted by the microwave generating device, the microwave generating device is also connected to a microwave controller. The power of the microwave energy emitted by the microwave generating device is controlled through the microwave controller. In this application, the power of the microwave energy is controlled between 15 - 25 W, and it can be 15 W, 20 W, 25 W, etc. The above-mentioned microwave controller can be a device with actual control operations such as a computer (refer to Figure 2 for Computer).

[0057] In the specific implementation step 2, considering that directly transmitting the microwave energy to the microwave plasma generator to excite the microwave plasma may cause varying degrees of damage to both the microwave generating device and the microwave plasma generator, resulting in a decrease in the service life of these two devices, and at the same time, it will also reduce the degradation efficiency. In this application, the microwave energy is first transmitted to the first converter. Since the microwave energy emitted by the microwave generating device is in the coaxial cable transmission mode, which is not conducive to transmission, the first converter is used to convert the microwave energy from the coaxial cable transmission mode to the waveguide transmission mode and then transmitted to the second converter.

[0058] In the specific implementation step 3, since the microwave plasma generator processes the microwave energy in the coaxial cable transmission mode when exciting the microwave energy, when the microwave energy in the waveguide transmission mode is transmitted to the second converter, the second converter converts the microwave energy into the coaxial cable transmission mode and transmits it to the microwave plasma generator for use by the microwave plasma generator.

[0059] In step 2 and step 3, the microwave energy in the coaxial cable transmission mode can be a TEM wave (Transverse Electromagnetic Wave), that is, an electromagnetic wave without electric field and magnetic field components in the propagation direction, and the microwave energy in the waveguide transmission mode can be a TE wave (Transverse Electric Wave), that is, a wave with a magnetic field component but no electric field component in the propagation direction. The function of the first converter and the second converter is to realize the conversion between TEM waves and TE waves, wherein TE10 waves are a specific mode of TE waves, wherein "10" represents the half-wave number of the electric field in the x-direction and the y-direction of the waveguide. The first converter and the second converter in the present application can realize the conversion between TEM waves and TE10 waves in a rectangular waveguide. The conversion between step 2 and step 3 can avoid damage to the microwave generating device and the microwave plasma generator by microwave energy. The first converter can refer to Figure 2 Waveguide Coaxial Converters in Figure 1. The second converter is shown in the same diagram as the first converter, but is located on the right and is not labeled in the diagram.

[0060] When the step 4 is specifically implemented, another important substance for the microwave plasma generator to generate microwave plasma is argon. Therefore, the high-purity argon is passed through an argon flow controller, the transmission flow of the argon is limited to a certain extent, and then transmitted to the microwave plasma generator for use by the microwave plasma generator. In the present application, the argon flow controller can be a mass flow controller (see Figure 2 Mass Flow Controllers in ), high purity argon is usually stored in argon cylinders, see Figure 2 The argon gas flow controller and the argon gas bottle, as well as the argon gas flow controller and the microwave plasma generator, are connected through a gas transmission pipeline to transmit argon gas. In the embodiment of the present application, the argon gas flow rate is controlled between 6-10 L / min, which can be 6 L / min, 8 L / min, 10 L / min, etc.

[0061] When the step 5 is specifically implemented, after the microwave energy and the argon gas are transmitted to the microwave plasma generator, the microwave plasma generator excites the argon gas with the microwave energy to obtain a microwave plasma (see Figure 2 In the present application, the microwave plasma generator may be a microwave plasma jet. Figure 2 The device directly connected to the argon flow controller through the gas pipeline is not marked in the figure.

[0062] In step 6 of the specific implementation, the microwave plasma generated by the microwave plasma generator is used to treat the antibiotic solution to obtain the degraded antibiotic solution. During the treatment, the antibiotic solution (refer to Figure 2 Antibiotic Solution therein) is placed below the microwave plasma generator so that the microwave plasma can react with the antibiotic solution. Secondly, the antibiotic solution is placed on a magnetic stirrer (refer to Figure 2 Magnetic Stirrers therein) so that during the degradation process, the antibiotic can react fully with the microwave plasma by stirring to improve the degradation efficiency.

[0063] In the embodiment of the present application, the above-mentioned antibiotic solution is a sewage solution containing at least two or more mixed antibiotics, including but not limited to sewage solutions discharged from hospitals, sewage solutions discharged from pharmaceutical factories, sewage solutions discharged from chemical or biochemical reagent factories, etc. The antibiotics contained in the solution can be sulfonamides (such as Sulfamethoxazole (SMX), Sulfapyridine (SPD), and Sulfadimethoxine (SMO), etc.), tetracyclines (such as Sulfamethoxazole (SMX), Sulfapyridine (SPD), and Sulfadimethoxine (SMO)), quinolones (such as Norfloxacin (NOR), Ciprofloxacin (CIP), and Ofloxacin (OFL), etc.), macrolides (such as Erythromycin (ERY), Azithromycin (AZI), Roxithromycin (ROX), and Clarithromycin (CLA), etc.), β-lactams (such as Cefalexin (CFX), etc.), lincomycins (such as lincomycin), trimethoprims, and so on.

[0064] In the embodiments of the present application, the concentration of the above-mentioned antibiotic solution is 10 - 30 mg / L, which can be 10 mg / L, 20 mg / L, 30 mg / L, etc. The pH value of the antibiotic solution is 2.0 - 12.0, which can be 2.38, 2.74, 3.48, 6.04, 6.50, 7.21, 10.52, 10.60, 11.24, etc. The time for treating the antibiotic with microwave plasma is 0 - 30 min, which can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc.

[0065] In an alternative embodiment of the present application, the above-mentioned microwave plasma generator is an atmospheric pressure low-temperature microwave plasma generator obtained by combining a three-layer coaxial structure and a rectangular waveguide power divider. Compared with a two-layer coaxial structure, the microwave plasma generator with a three-layer coaxial structure can excite a longer and wider plasma, which is attributed to a stronger electric field distribution and a larger electron density. At the same time, the length and diameter of the plasma jet are achieved by adjusting the microwave input power and gas flow rate of the inner and outer coaxial. In addition, when the microwave plasma generator adopted in the present application generates microwave plasma, it does not generate high-temperature microwave plasma, but generates low-temperature microwave plasma. This low-temperature microwave plasma can be directly touched by hand. Therefore, a cooling device is not required during the entire degradation process, reducing additional energy consumption. Since low-temperature microwave plasma is generated, the actually input microwave energy is also relatively low. The excitation of microwave plasma can be achieved with a power range of 15 - 25 w. There will be no thermal effect due to the temperature increase of the mixed antibiotics, nor will the antibiotic solution evaporate. The degradation of antibiotics in the antibiotic solution by microwave plasma can be accurately monitored to obtain accurate degradation results.

[0066] In an alternative embodiment of the present application, the above-mentioned degradation system further includes a protection device. The above-mentioned protection device at least includes a circulator (refer to Figure 2 Circulator in Figure 2 ), and a water load device (refer to

[0067] Based on the above embodiments, the degradation system proposed in the present application further includes a microwave controller (refer to Figure 2 Computer in Figure 2a Dual Directional Coupler) and a microwave power meter, the dual directional coupler is connected between the circulator and the second converter, the microwave power meter (not shown in the figure) is connected to the dual directional coupler, and the method further includes: using the dual directional coupler and the microwave power meter to read the incident power and the reflected power of the microwave energy; using the microwave controller to control the power of the microwave energy emitted by the microwave generator.

[0068] Based on the above embodiments, between the above first converter and the above microwave generating device, and between the above second converter and the above microwave plasma generator, coaxial cables are used for connection, and coaxial cables are used to transmit microwave energy, and the microwave energy transmitted by the coaxial cables all belongs to the coaxial cable transmission mode.

[0069] In an alternative embodiment of the present application, the optimal degradation parameters in the method for degrading mixed antibiotics in sewage by low-temperature microwave plasma are as follows: the power of the microwave energy is 20 W, the flow rate of argon is 8 L / min, the pH value of the antibiotic solution is 2.74, the concentration of the antibiotic solution is 20 mg / L. Under these conditions, the mixed antibiotics are degraded, the degradation time is 30 min, and the degradation efficiency of the mixed antibiotics can reach more than 99%.

[0070] In an alternative embodiment of the present application, during the process of treating the antibiotic solution, high-energy electrons and reactive oxygen species generated by the microwave plasma react with the antibiotics to achieve the degradation of the antibiotics.

[0071] In an alternative embodiment of the present application, during the process of treating the antibiotic solution, generated by the microwave plasma 、˙H, ˙O, ˙OH, O3 are used as reactive species to degrade the antibiotics in the antibiotic solution.

[0072] In a preferred embodiment of the present application, the antibiotics in the antibiotic solution are sulfamethoxazole and oxytetracycline.

[0073] Based on the above embodiments, the degradation pathway of the above sulfamethoxazole at least includes hydroxylation of the benzene ring, double bond reconstruction by hydrogen abstraction, hydroxylation of the isoxazole ring, and cleavage of the sulfonamide bond; the degradation pathway of the above oxytetracycline at least includes hydroxylation, deamination, demethylation, dehydration, and ring cleavage reactions.

[0074] The reagents used in this example are all commercially available and are purchased from Shanghai Aladdin Technology Co., Ltd., Chengdu Kelong Chemical Reagent Factory, and Sigma-Aldrich Technology Co., Ltd. The experimental instruments used are all commercially available and are purchased from the 13th Research Institute of China Electronics Technology Group Corporation, Chengdu Euler Microwave Component Co., Ltd., Chengdu Maipinhuineng Technology Co., Ltd., Chengdu Maipinhuineng Technology Co., Ltd., Chengdu Euler Microwave Component Co., Ltd., China Electronics Technology Siyuan Instrumentation (Anhui) Co., Ltd., Zhengzhou Ketan Instrument and Equipment Co., Ltd., Shanghai Leici Instrument Co., Ltd., and Shanghai Youke Instrument Co., Ltd.

[0075] In order to clearly illustrate the degradation efficiency and influencing factors of the method for degrading mixed antibiotics in sewage by low-temperature microwave plasma proposed in this application for mixed antibiotics in water, the following examples will be used for illustration.

[0076] Example 1: Determination of the concentration of antibiotics in water after microwave plasma treatment

[0077] Microwave plasma will produce physical effects and different chemically active species, and use physical and chemical actions to efficiently treat pollutants. Therefore, in order to improve the utilization efficiency of active species, the applicant measured the degradation efficiency of antibiotics based on single treatment and mixed treatment.

[0078] The concentration of the antibiotic stock solution was configured to be 1 g / L, and the antibiotics selected were sulfamethoxazole (SMZ) and oxytetracycline (OTC). The specific operation is as follows: The SMZ and OTC drugs were separately dissolved in 0.1 mol / L acetic acid solution to prepare stock solutions with a concentration of 1 g / L, and stored in a refrigerator at 4°C for a storage period of one week. The standard solutions used in the degradation experiment were diluted from the stock solution to meet the needs of analysis. The resistivity of the deionized water used in the experiment was 18.2 MΩ.

[0079] The physical and chemical properties of sulfamethoxazole (SMZ) and oxytetracycline (OTC) used are shown in Table 1.

[0080] Table 1 Physical and chemical properties of sulfamethoxazole and oxytetracycline

[0081]

[0082] The concentration of the antibiotic solution after plasma treatment was determined using an ultra-high performance liquid chromatograph (Water, ACQUITY UPLC H-class) equipped with a UV (Ultraviolet Radiation) detector and a T3 chromatographic column (2.1 mm × 100 mm, 1.8 µm). The mobile phase was 0.1% formic acid aqueous solution (phase A) and methanol (phase B). Table 2 shows the mobile phase gradient settings, and the flow rate was maintained at 0.3 mL / min, which allowed the simultaneous determination of two antibiotics in one sample. The sample injection volume was 10 µL, and the retention time was 10 min. The column temperature was maintained at room temperature, and the concentrations of SMX and TOC were detected at 264 nm and 268 nm, respectively.

[0083] Table 2 Construction of the mobile phase for detecting the residual antibiotic concentration in aqueous solution by UPLC

[0084]

[0085] Subtract the ratio of the antibiotic concentration in the water body after microwave plasma treatment measured by the above method to the antibiotic concentration in the initial water body from 1 to obtain the efficiency of microwave plasma in degrading the mixed antibiotics in the water body. In all examples of this application, unless otherwise specified, the initial concentration of a single antibiotic was 10 mg / L, and the initial concentration of the mixed antibiotics was 20 mg / L.

[0086] 12 mL of sulfamethoxazole, oxytetracycline, and mixed antibiotic solutions were respectively placed in 10 mL glass beakers and directly treated under a room temperature microwave plasma jet to evaluate their respective degradation efficiencies. The results of the degradation efficiencies of the antibiotics treated alone and in combination are shown in Figure 3 , Figure 3 which is a graph showing the degradation efficiency results of a low-temperature microwave plasma for treating single and mixed antibiotics in water provided by an example of this application. Figure 3 The abscissa of [] is the treatment time (in minutes), and the ordinate is the degradation efficiency. Compared with the treatment of single antibiotics (SMX or OTC), the degradation efficiency of the mixed antibiotics (SMX + OTC) was improved at different treatment times, and the highest reached 100%. The range of the improvement in the degradation efficiency of SMX + OTC compared to single SMX was 6.17% - 11.13%, and the improvement in the degradation efficiency compared to single OTC was 10.21% - 26.28%. This may be because when treating high-concentration antibiotics, a higher degradation efficiency is produced compared to treating low-concentration antibiotics, as more antibiotic molecules participate in the reaction with the active reactants.

[0087] Example 2: Influence of different experimental parameters on the antibiotic degradation efficiency

[0088] To maximize the utilization of the energy of microwave plasma, the applicant explored the experimental parameters affecting the degradation efficiency of antibiotic solutions, such as microwave power, gas flow rate for generating plasma, concentration and pH value of the initial solution. The degradation efficiency of antibiotics in the antibiotic solution was measured under different experimental parameters.

[0089] Example 2A: Influence of Argon Flow Rate on Antibiotic Degradation Efficiency

[0090] Pure argon gas was used to excite a three - layer coaxial microwave plasma to treat the mixed solutions of two antibiotics, SMX, OTC, and SMX + OTC respectively. The treatment concentration of individual antibiotics was 10 mg / L, and the concentration of the mixed antibiotic solution was 20 mg / L. The reaction time was 0 - 30 min. The microwave input power was maintained at 20 w. The gas flow rate is an important parameter affecting the degradation efficiency, which affects the degradation of antibiotics mainly in two aspects. First, it affects the direct interaction between the plasma and the antibiotics, such as the direct collision between high - energy electrons and antibiotic molecules. Second, it indirectly affects the degradation efficiency of the target by changing the content of ROS (Reactive Oxygen Species) in water.

[0091] The experimental results are presented Figure 4 , Figure 4 is a graph showing the influence of argon flow rate on antibiotic degradation efficiency provided in the examples of this application. Figure 4 Part (a) shows the influence of argon flow rate on the SMX solution, Figure 4 Part (b) shows the influence of argon flow rate on the OTC solution, Figure 4 Part (c) shows the influence of argon flow rate on the SMX + OTC solution, Figure 4The abscissa is the treatment time (in minutes), and the ordinate is the degradation efficiency. The results show that regardless of the gas flow rate, the degradation efficiency increases with the extension of the treatment time. After the same treatment time, with the increase of the gas flow rate, the treatment effects of SMX, OTC, and SMX+OTC first increase and then decrease, and the treatment effect is the best at 8 L / min. Under the same experimental conditions for SMX and OTC solutions, SMX is more easily degraded. When the treatment time is 5 min, the degradation efficiency has exceeded half, reaching 57.57%±1.27; when the treatment time is extended to 12 min, the degradation efficiency is 90.20% ± 1.53; when the treatment time is increased to 20 min, the degradation efficiency basically reaches 100%. At gas flow rates of 6 L / min and 10 L / min, the degradation efficiencies of the SMX solution after 30 min of treatment are 94.56% ± 2.31 and 100% respectively. At the optimal flow rate of 8 L / min, the degradation efficiencies of OTC reach 52.86% ± 2.96 and 93.97% ± 1.32 at 10 min and 20 min respectively; when the treatment time is extended to 30 min, it basically reaches the state of 100% treatment. At 6 L / min and 10 L / min, the degradation efficiencies of the OTC solution after being treated by microwave plasma for 30 min are 89.76% ± 1.76 and 97.10% ± 1.26 respectively. When treating the mixed solution of SMX and OTC with microwave plasma, the best degradation efficiency is obtained. When the gas flow rate is 8 L / min, the degradation efficiencies of the mixed solution with an initial concentration increased to 20 mg / L after being treated for 10 min and 20 min are 63.3.% ± 2.03 and 94.27% ± 1.50 respectively; the degradation efficiency reaches 98.62% ± 1.23 at 25 min, and it is basically completely treated; even when treating the mixed antibiotics for 30 min at the minimum flow rate of 6 L / min, the degradation efficiency is 90.37% ± 2.46. When the gas flow rate is too small, microwave plasma is not conducive to generating high-energy electrons and ROS in surface discharge, thus directly reducing the degradation efficiency of antibiotics. On the other hand, when the gas flow rate is too large, the residence time of free radicals becomes shorter, and they do not have time to react completely with pollutants, reducing the degradation efficiency. In addition, too large a flow rate will also generate larger bubbles in the water and reduce the contact between ROS and antibiotic molecules. Therefore, an argon flow rate of 8 L / min was selected in the subsequent experiments.

[0092] Example 2B: Influence of the initial concentration of antibiotics on the degradation efficiency of antibiotics

[0093] The initial concentration of the antibiotic solution has a significant impact on the degradation efficiency. Degradation experiments and antibiotic concentration measurements were carried out using the treatment method in Example 1. The initial concentrations of the SMX solution, OTC solution, and SMX + OTC solution were 5 mg / L, 10 mg / L, 20 mg / L, and 30 mg / L, respectively.

[0094] The experimental results are shown in Figure 5 , Figure 5 which is a graph showing the effect of the initial antibiotic concentration on the antibiotic degradation efficiency provided by the embodiment of the present application. Figure 5 Part (a) shows the effect of the initial antibiotic concentration on the SMX solution, Figure 5 Part (b) shows the effect of the initial antibiotic concentration on the OTC solution, Figure 5 Part (c) shows the effect of the initial antibiotic concentration on the SMX + OTC solution. Figure 5 The abscissa represents the treatment time (in minutes), and the ordinate represents the degradation efficiency.

[0095] The results show that a lower initial concentration exhibits a higher treatment efficiency. The treatment effect of the mixed antibiotics is better than that of the individual antibiotics. When the initial concentrations are 10 mg / L, 20 mg / L, and 30 mg / L, the degradation efficiencies of SMX and OTC reach 100%, 94.42% ± 1.63, 70.80% ± 2.25 and 100%, 91.02% ± 1.94, 62.19% ± 1.65, respectively. For the mixed solution of SMX and OTC, when the initial concentrations are 10 mg / L, 20 mg / L, and 30 mg / L, the obtained degradation efficiencies are 100%, 100%, and 79.92% ± 1.32, respectively. Under fixed experimental conditions, the number of ROS generated by microwave plasma discharge is limited within a certain period of time. If the concentration of antibiotics in water is too low, the ROS will not be fully utilized, resulting in energy waste. On the contrary, too high an antibiotic concentration will lead to a large number of by-products. Therefore, the competition between the by-products and the target antibiotic molecules will exacerbate the scarcity of ROS, resulting in insufficient degradation of the antibiotics.

[0096] At the same time, the G 50 energy yields of different initial antibiotic concentrations under microwave plasma treatment were also measured. The results are shown in Figure 6 , Figure 6 which is a graph of the energy yield of antibiotics with different initial concentrations provided by the embodiment of the present application. Figure 6The abscissa is the initial concentration of the antibiotic solution (in mg / L), and the ordinate is the energy yield (in mg / kWh). The results show that whether treating a single antibiotic or a mixed antibiotic, the energy production first increases and then decreases with the increase in concentration. Moreover, the mixed antibiotic significantly improves the energy efficiency of the antibiotic. When the initial concentrations are 10 mg / L, 20 mg / L, and 30 mg / L, the energy yields of the mixed antibiotic increase by 12.80 - 18.28 mg / kWh, 17.70 - 31.57 mg / kWh, and 21.60 - 31.77 mg / kWh, respectively.

[0097] Example 2C: Influence of the initial pH value of the antibiotic on the antibiotic degradation efficiency

[0098] Since different pH values can induce changes in ions and conductivity in the solution, thereby affecting the degradation reaction, the applicant explored the degradation efficiency of antibiotics at different initial pH values. Degradation experiments and determination of antibiotic concentration were carried out using the treatment method in Example 1. The pH values of the SMX solution were adjusted to 2.38, 6.04, and 11.24 using H2SO4 / NaOH, the pH values of the OTC solution were adjusted to 3.48, 7.21, and 10.60, and the pH values of the SMX + OTC mixed solution were adjusted to 2.74, 6.50, and 10.52. The pH values of the antibiotic solution before and after degradation were detected using a digital pH meter.

[0099] The experimental results are shown in Figure 7 , Figure 7 which is a graph showing the influence of different initial pH values on the antibiotic degradation efficiency proposed in the examples of this application. Figure 7 Part (a) in it is the degradation efficiency of SMX at different pH values, Figure 7 Part (b) in it is the degradation efficiency of OTC at different pH values, Figure 7 Part (c) in it is the degradation efficiency of SMX + OTC at different pH values, Figure 7 Part (d) in it is the pH change trend of SMX at different times, Figure 7 Part (e) in it is the pH value change trend of OTC at different times, Figure 7 Part (f) in it is the pH value change trend of SMX + OTC at different times, Figure 7 The abscissa of Figure 7 is the treatment time (in minutes),

[0100] Obviously, from Figure 7It can be seen from parts (a) to (c) that higher degradation efficiencies of SMX, OTC, and the SMX + OTC mixed solution can be obtained under weak acid conditions, followed by near-neutral solutions, and the alkaline environment is the most unfavorable for antibiotic degradation. At pH values of 2.38, 6.04, and 11.24, the degradation efficiencies of SMX at 15 min reached 91.53 ± 1.40, 95.22 ± 1.52, and 68.32 ± 1.44 respectively, and reached 87.16 ± 1.63 when the reaction time was extended to 30 min. The degradation efficiency of OTC was 93.97 ± 1.32 at pH 3.48, reached 90.25 ± 1.32 at 30 min at pH 7.21, and only reached 72.67 ± 1.84 even when the reaction time was extended to 30 min at pH 10.60. The best degradation efficiency of the SMZ and OXY mixed solution was also obtained under acidic conditions. Because under acidic conditions, hydrated electrons react with hydrogen ions to generate hydrogen radicals, which further generate ˙OH, thus increasing the generation of ˙OH.

[0101] In addition, the change trend of the pH value of the antibiotic solution was also monitored during the microwave plasma treatment process, and the results are shown in Figure 7 parts (d) to (f) in. It can be seen from the figure that whether it is treating single antibiotics or mixed antibiotics, the pH value of the solution is basically stable in acidic and alkaline environments, and only the pH value of the solution will decrease with the reaction time in the near-neutral environment. On the one hand, the reactive nitrogen species (RNS) generated by the plasma expanding in the air lead to an increase in the acidity of the solution. On the other hand, the acidic intermediate product NOR (norfloxacin) generated by degradation is also a factor affecting the change of the solution pH value.

[0102] Example 2D: Effect of microwave power on antibiotic degradation efficiency

[0103] The degradation experiment and the determination of antibiotic concentration were carried out using the treatment method in Example 1, in which microwave powers of 15 W, 20 W, and 25 W were respectively selected to treat the antibiotic solution to explore the effect of different microwave powers on the antibiotic degradation efficiency. The experimental results are shown in Figure 8 , Figure 8 which is a result diagram showing the effect of microwave power on antibiotic degradation efficiency provided in the embodiments of the present application. Figure 8 Part (a) in shows the degradation efficiency of SMX at different powers, Figure 8 Part (b) in shows the degradation efficiency of OTC at different powers, Figure 8 Part (c) in shows the degradation efficiency of SMX + OTC at different powers, Figure 8 The abscissa of which is the treatment time (unit: minute), and the ordinate is the degradation efficiency.

[0104] Microwave power is one of the important factors affecting the degradation efficiency of antibiotics. The initial concentrations of SMX and OTC antibiotics are 10 mg / L, the initial concentration of the SMX+OTC mixed antibiotic is 20 mg / L, the argon gas flow rate is 8 L / min, the initial pH values are 2.38, 3.48, and 2.74 respectively, and the microwave input powers are 15 W, 20 W, and 25 W respectively. The results show that the degradation efficiency of antibiotics increases with the increase of microwave power. Figure 8 Part (a) shows that after treating the SMX solution for 15 min, the degradation efficiency increases from 85.27% ± 1.50 at 15 W to 92.65% ± 1.67 at 20 W, and then to 95.84% ± 1.62 at 25 W. After extending the treatment time to 25 minutes, the degradation efficiency increases from 96.23% ± 1.45 at 15 W to 98.29% ± 0.99 at 20 W, and then to 100% at 25 W. Figure 8 Part (b) shows that after treating the OTC solution for 15 min, the degradation efficiency increases from 56.93% + 1.69 at 15 W to 79.82% ± 2.03 at 20 W, and then to 82.11% ± 1.35 at 25 W. After extending the treatment time to 30 minutes, the degradation efficiency increases from 91.62% ± 2.22 at 15 W to 97.34% ± 1.66 at 20 W, and then to 101.66% ± 1.52 at 25 W. For the SMX+OTC mixed antibiotic solution, as Figure 8 Part (c) shows that after treating for 15 min, the degradation efficiency increases from 78.13% + 2.07 at 15 W to 83.78% + 1.30 at 20 W, and then to 87.11% ± 1.54 at 25 W. After extending the treatment time to 25 min, the degradation efficiency increases from 94.97% ± 2.63 at 15 W to 97.95% ± 1.87 at 20 W, and then to 98.79% ± 0.57 at 25 W. When the treatment time is extended to 30 min, the degradation efficiency increases from 96.67% ± 1.86 at 15 W to 100% at 20 W - 25 W. The results show that with the increase of the input power, the degradation efficiency also increases to 100% at 20 W - 25 W. The results show that with the increase of the input power, the degradation efficiency also increases. The physicochemical effects in the discharge are enhanced with the increase of the input energy. On the other hand, a higher voltage can also accelerate the electrons in the plasma, emitting stronger ultraviolet light and stronger shock waves, which are all factors that can improve the antibiotic degradation efficiency.

[0105] Example 2E: Conductivity changes of antibiotic solutions during degradation at different acidities

[0106] The applicant selected antibiotic solutions with different initial pH values (the initial pH of the SMZ solution was 2.38, 6.04, and 11.24 respectively, and the initial pH of the OXY solution was 3.48, 7.21, and 10.60 respectively), and used a conductivity meter to monitor the conductivity changes during the microwave plasma treatment process. The experimental results are shown in Figure 9 , Figure 9 which is a result diagram showing the conductivity changes of antibiotic solutions during degradation at different acidities provided in the examples of this application. Figure 9 Part (a) shows the conductivity change trend of SMX during degradation at different acidities. Figure 9 Part (b) shows the conductivity change trend of OTC during degradation at different acidities. Figure 9 The abscissa of is the treatment time (in minutes), and the ordinate is the conductivity (in μs / cm). Since many inorganic free ions such as ammonium (NH4 + ), sulfate (SO4 2+ ), sulfite (SO3 2+ ), nitrate (NO3 - ), nitrite (NO2 - ), and hydronium ion (H3O + ) are generated during the degradation of organic compounds, the conductivity of the antibiotic solution increases with the prolongation of the treatment time. In this case, NO3 - and NO2 -Ions may be generated by microwave plasma or be degradation products of SMX and OTC. When the initial pH value of the SMX solution was 2.38, the conductivity increased from 1331 µs / cm ± 5.56 to 1688.33 µs / cm ± 9.61; when the pH was 6.04, the conductivity increased from 682.66 µs / cm ± 8.08 to 878.66 µs / cm ± 5.50; when the pH was 11.24, the conductivity increased from 1698.33 µs / cm ± 17.61 to 1928.33 µs / cm ± 6.03; the increase in conductivity was the largest under acidic conditions, about 357.33 µs / cm. When the initial pH value of the OTC solution was 3.48, the conductivity increased from 73.9 µs / cm ± 5.21 to 149.67 µs / cm ± 1.53; when the pH was 7.21, the conductivity increased from 365.33 µs / cm ± 5.51 to 503.33 µs / cm ± 3.51; when the pH was 10.60, the conductivity increased from 489 µs / cm ± 2.64 to 638 ± 4.00; the increase in conductivity was the largest under alkaline conditions, about 149 µs / cm. However, the increase in conductivity is not conducive to the formation of ˙OH and will ultimately inhibit the degradation efficiency of antibiotics.

[0107] Example 3: Mineralization efficiency of antibiotics

[0108] Since another important indicator for evaluating the removal performance of antibiotic pollutants is the mineralization efficiency. The applicant used a TOC (vario TOC cube, produced by elementar company, Germany) analyzer to measure the total organic carbon (TOC) before and after the treatment of SMX and OTC. Microwave plasma was used to treat single antibiotic (SMX, OTC) and mixed antibiotic (SMX + OTC) solutions, and the mineralization efficiency at 15 min and 30 min was measured. The experimental results are shown in Figure 10 , Figure 10 which is a graph showing the mineralization efficiency results of an antibiotic solution provided in the examples of this application. Figure 10 The abscissa of

[0109] Generally, the removal rate of TOC is lower than the corresponding degradation efficiency, indicating that some intermediate by-products are generated during the degradation process. When the treatment time was 15 min, the mineralization efficiencies of SMX, OTC, and the mixed solution of SMX + OT reached 31.21% ± 2.78, 19.89% ± 2.59, and 39.20% ± 3.36, respectively. When the treatment time was extended to 30 min, the mineralization efficiencies increased to 60.03% ± 4.03, 36.75% ± 2.79, and 66.16% ± 3.80, respectively. The mineralization efficiency of the mixed antibiotics increased significantly, by 6.13% and 29.41% respectively. This indicates that microwave plasma can degrade antibiotics into small molecule organic substances and small molecule inorganic substances. However, under these experimental conditions, some intermediate products generated during the degradation process cannot be further mineralized.

[0110] Example 4: Effect of hydroxyl radical scavenger on the degradation efficiency of antibiotics

[0111] To study the contribution of reactive oxygen free radicals to the degradation efficiency of antibiotics, since the lifetime of ˙OH in the liquid phase is usually about 10 - 9 seconds, it is difficult to quantify the amount of ˙OH generated in microwave plasma. Generally, isopropyl alcohol (IPA) is used as a scavenger for ˙OH to indirectly evaluate their important role in the degradation of antibiotic solutions. Therefore, different volumes (5 μL, 10 μL, 20 μL) of IPA were added to the antibiotic solutions, and the presence of hydroxyl radicals was indirectly verified through quenching experiments.

[0112] At an argon flow rate of 8 L / min, a power of 20 W, and a volume of 12 mL, different volumes of IPA were added to single antibiotics (initial concentration of 10 mg / L) and mixed antibiotics (initial concentration of 20 mg / L) respectively, and the degradation efficiency is as Figure 11 shown, Figure 11 is a graph showing the effect of isopropyl alcohol on the degradation efficiency of antibiotics provided in an embodiment of the present application, Figure 11 in part (a) is the effect of IPA on the degradation efficiency of SMX, Figure 11 in part (b) is the effect of IPA on the degradation efficiency of OTC, Figure 11 in part (c) is the effect of IPA on the degradation efficiency of SMX + OTC, Figure 11 The abscissa is the treatment time (in minutes), and the ordinate is the degradation efficiency.

[0113] When 5 μL of IPA was added to the SMZ solution and treated with microwave plasma for 5 min, the degradation efficiency decreased from 57.57% ± 1.27 to 6.62 ± 1.16. When the treatment time was extended to 20 min, the degradation efficiency decreased from 100% to only 48.84 ± 3.19, and at 30 min, the degradation efficiency decreased to 57.59% ± 2.46. When the amount of IPA added was 10 μL, the degradation efficiency after reacting for 20 min was 31.71% ± 1.67, and the degradation efficiency at 30 min of treatment was 48.47% ± 1.86. When the IPA was continuously increased to 20 μL, the degradation efficiencies of the SMX solution treated for 20 min and 30 min were 21.00% ± 1.74 and 33.28% ± 1.96, respectively. When 1.0 μL of IPA was added to the OTC solution and treated with microwave plasma for 10 min, the degradation efficiency decreased from 52.86% ± 2.96 to 4.19% ± 0.18. When the treatment time was extended to 20 min, the degradation efficiency decreased from 93.97% ± 1.32 to only 10.22% ± 1.66, and at 30 min, the degradation efficiency decreased from 100% to 38.58% ± 1.21. When the amount of IPA added was 2.5 μL, the degradation efficiency after reacting for 20 min was 5.38% ± 0.65, and the degradation efficiency at 30 min of treatment was 34.39% ± 1.58. When the IPA was continuously increased to 5.0 μL, the degradation efficiencies of the OTC solution treated for 20 min and 30 min were 2.49% ± 0.47 and 33.02% ± 1.92, respectively. For the SMX + OTC mixed solution, when 5 μL of IPA was added and treated for 10 min and 20 min, the degradation efficiencies decreased from 63.3% ± 2.03 and 94.27% ± 1.50 to 11.20% ± 1.44 and 30.49% ± 2.11, respectively, and the degradation efficiency at 30 min was 58.13% ± 2.60; when 10 μL of IPA was added and treated for 10 min and 20 min, the degradation efficiencies were 6.44% ± 0.43 and 16.99% ± 2.63, respectively, and the degradation efficiency at 30 min was 28.33% ± 2.03; when the IPA was continuously increased to 20 μL, the degradation efficiencies of the treatment for 20 min and 30 min were only 5.73% ± 0.69 and 11.60% ± 2.03, respectively. These results show that adding ˙OH scavengers can significantly inhibit the degradation of antibiotics. The degradation efficiency of the OTC solution under the action of microwave plasma is lower than that of the single SMX solution and the OTC + SMX mixed solution. Therefore, less IPA should be added when treating the OTC solution.The inhibitory effect of the mixed antibiotics is most obvious after the addition of IPA, indicating that they fully utilize the •OH generated by microwave plasma during the reaction process. Therefore, •OH plays the most important oxidation role in the process of removing antibiotics by microwave plasma.

[0114] Example 5: Possible degradation pathways of SMX and OTC

[0115] Example 5A: Determination of by-products and degradation pathways of sulfamethoxazole

[0116] Any change in the chemical structure of SMX is regarded as the removal of pollutants. The formation of various compounds during the treatment process can be correlated with the contribution of various reactants generated by the plasma to the removal of pollutants, and provide information on the interaction between degradation products and target pollutants. To further determine the degradation pathway of SMX, HPLC-QQQ / MS analysis was performed on the intermediate products of the SMZ solution treated with microwave plasma for 30 min, using positive and negative ion modes. In this example, an Agilent LC1290 high-performance liquid chromatograph and an Agilent 6470 triple quadrupole (QQQ) tandem mass spectrometer were used to detect the degradation products of SMX and OTC. Separation was carried out at 35 °C using an Agilent, EC-C18 chromatographic column (3.0 x 150 mm, 2.7 μm). The mobile phase consisted of water (+ 0.1 % formic acid) and acetonitrile (ACN), with a gradient from 20 % ACN to 80 % ACN over 20 minutes. The flow rate of the mobile phase was 0.4 mL / min, and the injection volume was 10 μL. The 6470 QQQ mass spectrometer was equipped with positive and negative ESI sources. The gas flow rate was set at 12 L / min, the temperature was set at 150 °C, the nebulizer pressure: 30 Psi, the scan time was 350 ms, and the scan step: 0.1 amu. The sheath gas flow rate was 12 L / min, and the temperature was 350 °C. The capillary voltage was 3500 V, and the nozzle voltage was 135 V. The mass spectrometry acquisition range was 50 - 1000 mass / charge (m / z). For MS 2 , two precursors were selected according to abundance for each cycle. Fragmentation analysis was carried out using a collision cell voltage of 0 - 25 V. The analysis was performed in positive ion mode ((+)ESI) and negative ion mode ((-)ESI). The mobile phase ratios for the negative ion mode and positive ion mode are shown in Tables 3 and 4 respectively:

[0117] Table 3 Mobile phase ratio for negative ions

[0118]

[0119] Table 4 Mobile phase ratio for positive ions

[0120]

[0121] Possible intermediates were determined based on the m / z values of the substances, and the degradation pathway of sulfamethoxazole was deduced from the intermediate products at each time period. During the process of plasma treatment of the SMZ solution, a series of intermediate products were formed and then degraded simultaneously with the target compound. Based on the determined degradation intermediates, the proposed SMX degradation pathway is represented as Figure 12 , Figure 12 which is a schematic diagram of an SMX degradation pathway proposed in an embodiment of the present application. Four main degradation pathways have been observed according to the attack sites and types of free radicals. Although microwave plasma discharge can generate various substances ( , •H, •O, •OH, O3, etc.), which contribute to the removal of pollutants to varying degrees. However, through free radical trapping experiments, it is known that •OH plays an important role in the degradation of SMX, and the reaction rate constant is 8.5 × 10 9 .

[0122] Based on the detected m / z ratios of the transformation intermediates and fragments, four possible pathways for the degradation mechanism of SMX in a room-temperature microwave plasma system were proposed. Path 1 involves the hydroxylation of the benzene ring with hydroxyl radicals first. The hydroxylation reaction based on the hydroxyl radical site occurs in two steps. The first step is the formation of a C-O single bond between the target compound and the radical, resulting in the cleavage of the C-Cπ bond. This leaves an unpaired electron on the adjacent carbon atom. The second step involves the extraction of hydrogen and the reconstruction of the double bond, which is the result of the attack of ˙OH on the same carbon atom as in the first step, thus forming the intermediate S1, m / z = 269a. This reaction has been reported in studies focusing on the degradation of sulfamethoxazole, and this degradation pathway subsequently produces other products. ˙OH generates intermediate products S2 (dihydroxylated, m / z = 285) and S3 (trihydroxylated, m / z = 301) through continuous attack on the benzene ring. The nitro group at the C14-N17 position on the benzene ring is replaced by ˙OH to form the intermediate S4. Path 2 corresponds to the cleavage of the C11-S7 bond, possibly due to the attack of ˙OH on the sulfur atom, thus producing sulfamic acid S5 (m / z = 178) and aniline radical. The aniline radical can react with SMX to form S6 (m / z = 344) through the aniline dimerization pathway. Path 3 involves the attack of ˙OH on the C4 atom of the isoxazole ring first. This reaction causes the double bond to break, leaving an unpaired electron on the C5 atom. After extracting hydrogen from the C4 atom, the double bond is reconstructed to form S7 (m / z = 269b). The formation of this product has also been observed in studies on advanced oxidation processes such as ozone oxidation. The continuous reaction of ˙OH with C5 can lead to the formation of the dihydroxylated S8, namely m / z = 287, which is converted to the intermediate S9 with m / z = 133 through substitution. Path 4 is that the S-N bond of SMX is attacked by radicals to produce sulfanilic acid S10 (m / z = 173). The continuous reaction causes the S-C bond to break and the sulfonic acid group to be removed to form the compound S11 aniline (m / z = 94), and radical addition produces the compound S12 o-hydroxyaniline (m / z = 94). The continuous reaction causes the benzene ring to open to form small-molecule enol compounds S13 and S14 methyl ethanol.

[0123] Example 5B: Determination of the By-products and Degradation Pathways of Oxytetracycline

[0124] By using the room-temperature microwave plasma treatment process, HPLC-QQQ-MS analysis was performed on the intermediate products that appeared during the OTC degradation process. The test method was the same as that in Example 5A. The analytical instrument and parameters for the oxytetracycline degradation intermediates were the same as above, and the mobile phase ratio is shown in Table 5:

[0125] Table 5 Mobile Phase Ratio for Determining OTC Intermediates

[0126]

[0127] As Figure 13 shown Figure 13 is a schematic diagram of an OTC degradation pathway proposed in an embodiment of the present application. The applicant proposed three potential OTC degradation mechanisms, including hydroxylation (+16 Da), deamination (-46 Da), demethylation (-14 Da), dehydration (-18 Da), and ring cleavage-generated ones.

[0128] In pathways 1 and 2, the degradation of OTC starts at different points, including carbon-carbon double bonds, tertiary amines, and ring A vulnerable to ROS attack. First, OTC undergoes demethylation through a reaction to remove the N-methyl of OTC, thereby generating O1 (m / z = 447). Then, the generated O1 undergoes demethylation and dehydration through reactions to remove the hydroxyl group and N-methyl of O1, and at the same time, compound O2 (m / z = 342) is generated due to the cleavage of the C-CONH2 bond. Subsequently, the double bond of O2 is impacted by hydroxyl radicals generated in the microwave plasma reaction, and intermediate O3 (m / z 300) is generated through ring cleavage. It should be noted that the N-C binding energy of OTC is weak. Therefore, in pathway 2, under the action of a strong oxidant (˙OH), OTC undergoes dehydration and demethylation reactions, as well as the shedding of N-methyl on the aromatic ring, generating m / z = 339 (O4). The naphthol ring can be opened by the oxidation of ˙OH radicals, and O4 can be decomposed into O5 (m / z = 303). O5 continues to undergo decarboxylation and dehydration to generate intermediate O6 (m / z = 259). Under further oxidation, the intermediate removes the carbonyl group to be transformed into compound O7. The third path of OTC decomposition is hydroxylation to generate isomeric compounds O8 (m / z = 477a) and O9 (m / z = 477b) respectively. The intermediate products during the OTC degradation process are expected to become low-molecular-weight organic compounds through other reactions, such as O10, O11, and O12. These organic compounds will then decompose into inorganic substances, such as CO2, H2O, NH4 + , NO3 - etc.

[0129] The present application utilizes a degradation system with a three-layer coaxial microwave plasma jet to efficiently degrade mixed antibiotics SMX and OTC in sewage. The biggest advantage of this degradation system is that the ejected plasma is low-temperature contactable, so there is no need for a cooling device during the entire degradation process, and there will be no evaporation of the treated solution. The examples evaluated the degradation efficiency of single antibiotics and mixed antibiotics treated with microwave plasma, respectively. The results showed that mixed antibiotics have better degradation efficiency, and the degradation efficiency of SMX + OTC is 6.17%-11.13% higher than that of single SMX, and 10.21%-26.28% higher than that of single OTC. The good degradation performance is attributed to the full utilization of antibiotics on plasma active substances, and it may also be the mutual reaction of degradation intermediates. Under the same experimental conditions of SMX and OTC solutions, SMX is more easily degraded. When the treatment time is 20 min, the degradation efficiency is basically 100%; the degradation efficiency of OTC is basically 100% at 30 min. For the mixed antibiotics with an initial concentration of 20 mg / L, the degradation efficiency reached 98.62% ± 1.23 when treated for 25 min in a room temperature microwave plasma system. The mineralization efficiencies of SMX, OTC, and SMX+OTC mixed solutions reached 31.21% ± 2.78, 19.89% ± 2.59, and 39.20% ± 3.36, respectively, at 15 min; when the treatment time was extended to 30 min, the mineralization efficiencies increased to 60.03% ± 4.03, 36.75% ± 2.79, and 66.16% ± 3.80, respectively. The mineralization efficiency of the mixed antibiotics was significantly improved, increasing by 6.13% and 29.41%, respectively. In the process of microwave plasma treatment of antibiotic solutions, whether single antibiotics or mixed antibiotics, the pH was basically stable in acidic and alkaline environments, and only in a near-neutral environment would the pH value of the solution decrease with reaction time. Moreover, the conductivity of the antibiotic solution increases with the extension of the treatment time at different acidities. The hydroxyl radical capture experiment shows that the main oxidizing species in the reaction process is ˙OH. The intermediate products in the microwave plasma system reaction process were detected by HPLC-QQQ-MS, and the possible transformation pathways of the degradation of antibiotics SMX and OTC were determined respectively. SMX mainly has four pathways: hydroxylation of the benzene ring, double bond reconstruction of hydrogen abstraction, hydroxylation of the isoxazole ring, and cleavage of the sulfonamide bond. OTC mainly includes hydroxylation, deamination, demethylation, dehydration and ring cleavage reactions, and three potential degradation pathways are proposed. Ultimately, antibiotics are converted from large molecules to small molecules until inorganic ions, CO2 and H2O.

[0130] The above has introduced in detail a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma. Specific examples are used in this article to elaborate on the principle and implementation manner of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A method for degrading mixed antibiotics in sewage by low-temperature microwave plasma, characterized in that, The method is implemented through a degradation system, which includes: a microwave generating device, a first converter, a second converter, a microwave plasma generator, and an argon flow controller. The method includes: Using the microwave generating device to emit microwave energy, and the power of the microwave energy is 20 W; Transmitting the microwave energy to the first converter, and using the first converter to convert the microwave energy from the coaxial cable transmission mode to the waveguide transmission mode, and then transmitting it to the second converter; Using the second converter to convert the microwave energy back to the coaxial cable transmission mode and transmitting it to the microwave plasma generator; Controlling the argon flow through the argon flow controller and transmitting the argon to the microwave plasma generator, and the argon flow is 8 L / min; The microwave plasma generator uses microwave energy to excite argon to obtain microwave plasma. Among them, the microwave plasma generator is an atmospheric pressure low-temperature microwave plasma generator obtained by combining a three-layer coaxial structure and a rectangular waveguide power divider; The microwave plasma obtained by excitation through the microwave plasma generator is used to treat the antibiotic solution to obtain a degraded antibiotic solution. The antibiotics in the antibiotic solution are sulfamethoxazole and oxytetracycline. The initial concentration of the antibiotic solution is 20 mg / L, the pH value of the antibiotic solution is 2.74, and the degradation treatment time is 30 min.

2. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that, The degradation system further includes a protection device, and the protection device at least includes a circulator and a water load device. The circulator is connected to the first converter, and the water load device is connected to the circulator; The method further includes: Using the circulator to prevent the reflected microwave energy power from being too high and damaging the microwave generating device; Using the water load device to absorb the microwave energy reflected back through the circulator.

3. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 2, wherein The degradation system further includes a microwave controller and a power reading device. The power reading device includes a bi-directional coupler and a microwave power meter. The bi-directional coupler is connected between the circulator and the second converter, and the microwave power meter is connected to the bi-directional coupler. The method further includes: Using the bi-directional coupler and the microwave power meter to read the incident power and reflected power of the microwave energy; Using the microwave controller to control the power of the microwave energy emitted by the microwave generator.

4. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that, Between the first converter and the microwave generating device, and between the second converter and the microwave plasma generator, coaxial cables are used for connection.

5. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that, During the treatment of the antibiotic solution, high-energy electrons and reactive oxygen species generated by the microwave plasma react with the antibiotics to achieve the degradation of the antibiotics.

6. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that During the treatment of the antibiotic solution, · , ·H, ·O, ·OH, and O3 are used as active species generated by microwave plasma to degrade the antibiotics in the antibiotic solution. , ·H, ·O, ·OH, and O3 are used as active species generated by microwave plasma to degrade the antibiotics in the antibiotic solution.

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