Method for degrading mixed antibiotics in sewage through low-temperature microwave plasma

Abstract

The invention provides a method for degrading mixed antibiotics in sewage through low-temperature microwave plasmas, and relates to the technical field of novel pollutant treatment.The method comprises the steps that a microwave generating device is adopted for emitting microwave energy and transmitting the microwave energy to a first converter, and after the microwave energy is converted into a waveguide transmission mode, the microwave energy is transmitted to a second converter; a second converter is adopted to convert the microwave energy back to a coaxial cable transmission mode and transmit the microwave energy to a microwave plasma generator; the argon flow is controlled through an argon flow controller, and argon is transmitted to the microwave plasma generator; the microwave plasma generator adopts microwave energy to excite argon to obtain microwave plasma; the antibiotic solution is treated through microwave plasmas obtained through excitation of the microwave plasma generator, and the degraded antibiotic solution is obtained. According to the method provided by the invention, a three-layer coaxial microwave plasma jet degradation system is adopted, so that the antibiotics in the sewage are efficiently degraded at low power and low temperature.

Description

Technical Field

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

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

[0003] To address the impact of antibiotics on environmental water, current approaches to remove antibiotics from water are mainly through non-thermal plasma, but they mainly focus on the treatment of a single antibiotic, which oversimplifies the problem of managing antibiotics in aquatic environments. This is because multiple antibiotics with various interactions may cause greater potential toxicity than a single antibiotic.

[0004] In addition, various antibiotics always exist simultaneously in real sewage, and it cannot be assumed that the treatment effect of multiple antibiotics is just the sum of the removal effects of a single antibiotic; although coupling plasma and catalyst together can effectively improve the degradation efficiency, secondary contamination 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 using low-temperature microwave plasma to solve the above-mentioned 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 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 microwave generating device is used to emit microwave energy, wherein the power of the microwave energy is 15-25 W; Transmitting the microwave energy to a first converter, and using the first converter to convert the microwave energy from a coaxial cable transmission mode to a waveguide transmission mode, and then transmitting the microwave energy to a second converter; The second converter is used to convert the microwave energy back into a coaxial cable transmission mode and transmit it to a microwave plasma generator; The argon flow rate is controlled by an argon flow controller and transmitted to the microwave plasma generator, and the argon flow rate is 6-10 L / min; The microwave plasma generator uses microwave energy to excite argon gas to obtain microwave plasma; The antibiotic solution is treated with microwave plasma obtained by exciting a microwave plasma generator to obtain a degraded antibiotic solution, wherein the antibiotic solution includes 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.

[0007] 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.

[0008] Optionally, the degradation system further includes a protection device, 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: The circulator is used to prevent the reflected microwave energy from being too high in power and damaging the microwave generating device; The water load device is used to absorb the microwave energy reflected back by the circulator.

[0009] 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 dual directional coupler is connected between the circulator and the second converter, the microwave power meter is connected to the bidirectional coupler, and the method further includes: Using the dual directional coupler and the microwave power meter to read the incident power and reflected power of microwave energy; The microwave controller is used to control the power of the microwave energy emitted by the microwave generator.

[0010] Optionally, a coaxial line is used to connect the first converter and the microwave generating device, and the second converter and the microwave plasma generator.

[0011] Optionally, the power of the microwave energy is 20 W, the flow rate of the argon gas 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.

[0012] Optionally, during the treatment of the antibiotic solution, high-energy electrons and active oxygen species generated by microwave plasma react with the antibiotics to achieve degradation of the antibiotics.

[0013] Optionally, during the treatment of the antibiotic solution, the , ˙H, ˙O, ˙OH, and O3 act as active species to degrade antibiotics in the antibiotic solution.

[0014] Optionally, the antibiotics in the antibiotic solution are sulfamethoxazole and oxytetracycline.

[0015] Optionally, the degradation pathway of sulfamethoxazole includes at least 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 oxytetracycline at least includes hydroxylation, deamination, demethylation, dehydration and ring cleavage reactions.

[0016] The present application includes the following advantages: The present application proposes a method for degrading mixed antibiotics in sewage by low-temperature microwave plasma, which is achieved by a degradation system, wherein the degradation system includes: a microwave generator, a first converter, a second converter, a microwave plasma generator and an argon flow controller, and the method includes: using the microwave generator to emit microwave energy, wherein 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 a coaxial cable transmission mode to a waveguide transmission mode, and then transmitting it to the second converter; using the second converter to convert the microwave energy back to a coaxial cable transmission mode, and transmitting it to the microwave plasma generator; controlling the argon flow rate by an argon flow controller and transmitting the argon to the microwave plasma generator, wherein the argon flow rate is 6-10 L / min; the microwave plasma generator uses microwave energy to excite argon to obtain microwave plasma; treating an antibiotic solution with the microwave plasma obtained by excitation of the microwave plasma generator to obtain a degraded antibiotic solution, wherein the antibiotic solution includes at least two or more mixed antibiotics, and 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 0-30min.

[0017] The method proposed in this 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, providing new theoretical and technical support for the management of multiple antibiotics in sewage. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0019] Figure 1This is a schematic flow chart of the steps of a method for degrading mixed antibiotics in sewage using low-temperature microwave plasma, as proposed in an embodiment of the present application; Figure 2 It is a schematic flow chart of a method for degrading mixed antibiotics in sewage by using low-temperature microwave plasma proposed in an embodiment of the present application; Figure 3 This is a graph showing the degradation efficiency of single and mixed antibiotics in water treated with low-temperature microwave plasma provided in an embodiment of the present application; Figure 4 This is a result diagram of the effect of argon gas flow rate on antibiotic degradation efficiency provided in an embodiment of the present application; Figure 5 This is a result diagram of the effect of the initial concentration of an antibiotic on the degradation efficiency of the antibiotic provided in an embodiment of the present application; Figure 6 This is an energy yield diagram of antibiotics with different initial concentrations provided in an embodiment of the present application; Figure 7 This is a result diagram of the effect of different initial pH values ​​on the degradation efficiency of antibiotics proposed in the examples of the present application; Figure 8 This is a result diagram of the effect of microwave power on antibiotic degradation efficiency provided by an embodiment of the present application; Fig. 9 This is a result diagram of the change in conductivity of an antibiotic solution during the degradation process at different acidities provided in an embodiment of the present application; Fig.10 This is a mineralization efficiency result diagram of an antibiotic solution provided in an embodiment of the present application; Fig.11 This is a result diagram of the effect of isopropanol on antibiotic degradation efficiency provided in an embodiment of the present application; Fig.12 This is a schematic diagram of a SMX degradation pathway proposed in the examples of this application; Fig.13 This is a schematic diagram of an OTC degradation pathway proposed in an embodiment of the present application. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] In order to address the impact of antibiotics on environmental water bodies, research on antibiotics in plasma treatment of water bodies has become increasingly extensive, but current treatment methods mainly focus on the treatment of single antibiotics, which oversimplifies the problem of managing antibiotics in aquatic environments. This is because multiple antibiotics with various interactions may cause greater potential toxicity compared to single antibiotics. For example, the combined toxicity of fluoroquinolones and sulfonamides was studied in zebrafish, and the results showed that mixtures of fluoroquinolones and sulfonamides can cause developmental toxicity, cardiotoxicity, immunotoxicity, and neurotoxicity. Fluoroquinolones combined with sulfonamide antibiotics can inhibit the activity of acetylcholinesterase in goldfish. A mixture of sulfonamides and tetracyclines may increase plasma estradiol levels in medaka, thereby affecting reproductive metabolism. Other studies have also pointed out that the combined effects of trimethoprim, sulfamethoxazole, and sulfadiazine significantly inhibit the growth of microalgae. Even though the concentration of a single antibiotic in environmental water bodies may be low, the combined concentration of antibiotics may accumulate, causing serious toxicity to aquatic organisms.

[0022] In addition, various antibiotics always exist simultaneously in real sewage, and it cannot be assumed that the treatment effect of multiple antibiotics is just the sum of the removal effects of a single antibiotic; although coupling plasma and catalyst together can effectively improve the degradation efficiency, secondary contamination of the catalyst cannot be avoided; and existing experiments are difficult to support the practical application of plasma technology.

[0023] Based on this, this application proposes a device and method for treating mixed antibiotics in sewage by maximizing the degradation ability of plasma itself. Mixed antibiotics were treated by low-temperature microwave plasma, and the degradation efficiency of single antibiotics and mixed antibiotics was evaluated. The factors affecting the degradation efficiency of antibiotics were explored and the optimal experimental operating conditions were determined. Total organic carbon was monitored during the experiment to study the mineralization efficiency of antibiotics. Different concentrations of isopropanol were used as OH capture agents to track their role in the reaction. The main degradation intermediates produced by the decomposition of antibiotics were identified by high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF / MS), and possible degradation pathways were proposed.

[0024] See also Figure 1 , Figure 1 The present invention is a schematic flow chart of the steps of a method for degrading mixed antibiotics in sewage by using low-temperature microwave plasma, which is proposed in an embodiment of the present invention. The method is implemented by a degradation system, which includes: a microwave generating device, a first converter, a second converter, a microwave plasma generator and an argon gas flow controller. The method includes the following steps: Step 1: using the microwave generating device to emit microwave energy, wherein the power of the microwave energy is 15-25 W; Step 2: transmitting the microwave energy to a first converter, and using the first converter to convert the microwave energy from a coaxial cable transmission mode to a waveguide transmission mode, and then transmitting the microwave energy to a second converter; Step 3: using the second converter to convert the microwave energy back into a coaxial cable transmission mode, and transmitting it to a microwave plasma generator; Step 4: Control the argon flow rate through an argon flow controller and transmit the argon gas to the microwave plasma generator, and the argon flow rate is 6-10 L / min; Step 5: The microwave plasma generator excites argon gas using microwave energy to obtain microwave plasma; Step 6: Treating the antibiotic solution with microwave plasma excited by a microwave plasma generator to obtain a degraded antibiotic solution, wherein the antibiotic solution includes 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.

[0025] In order to clearly illustrate the method for degrading mixed antibiotics in sewage by low-temperature microwave plasma proposed in this application, Figure 2 For detailed explanation, Figure 2 It is a schematic flow chart of a method for degrading mixed antibiotics in sewage by using low-temperature microwave plasma as proposed in an embodiment of the present application.

[0026] When the step 1 is specifically implemented, the microwave plasma generator is obtained by exciting argon gas with microwave energy. Therefore, microwave energy is first emitted by a microwave generating device and transmitted to the microwave plasma generator to excite and obtain microwave plasma. In the embodiment of the present application, the microwave generating device can be a solid-state microwave source (model PA2425-250, purchased from the 13th Institute of China Electronics Technology Group Corporation) (see Figure 2 The Solid State Microwave Source in the embodiment may also be other devices capable of emitting microwave energy. This application is not limited to this and is subject to actual needs.

[0027] In an optional embodiment of the present application, in order to control the power of the microwave energy emitted by the microwave generating device, the microwave generating device is further connected to a microwave controller, and the power of the microwave energy emitted by the microwave generating device is controlled by the microwave controller. In the present application, the power of the microwave energy is controlled between 15-25 W, which can be 15 W, 20 W, 25 W, etc. The above-mentioned microwave controller can be a device with actual control operation such as a computer (see Figure 2 in the computer).

[0028] When specifically implementing step 2, it is considered that directly transmitting microwave energy to the microwave plasma generator to excite microwave plasma may cause varying degrees of damage to both the microwave generating device and the microwave plasma generator, resulting in a reduction in the service life of the two devices, and also reducing the degradation efficiency. In the present application, the microwave energy is first transmitted to the first converter. Since the microwave energy emitted by the microwave generating device is in a coaxial cable transmission mode, it is not conducive to transmission. Therefore, the first converter is used to convert the microwave energy from the coaxial cable transmission mode to a waveguide transmission mode, and then transmitted to the second converter.

[0029] When step 3 is specifically implemented, since the microwave plasma generator processes the microwave energy in the coaxial cable transmission mode when exciting microwave energy, when the microwave energy in the waveguide transmission mode is transmitted to the second converter, the microwave energy is converted into the coaxial cable transmission mode by the second converter and transmitted to the microwave plasma generator for use by the microwave plasma generator.

[0030] 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.

[0031] 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 2The 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.

[0032] 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.

[0033] When the step 6 is implemented, the antibiotic solution is treated with microwave plasma excited by a microwave plasma generator to obtain a degraded antibiotic solution. Figure 2 The Antibiotic Solution in the microwave plasma generator is placed under the microwave plasma generator to allow the microwave plasma to react with the antibiotic solution. Figure 2 Magnetic Stirrers in the reactor are placed so that during the degradation process, the antibiotics can be fully reacted with the microwave plasma by stirring to improve the degradation efficiency.

[0034] In the embodiment of the present application, the above-mentioned antibiotic solution is a sewage solution including 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 (Sulfamethoxazole, SMX), sulfapyridine (Sulfapyridine, SPD) and sulfadimethoxine (Sulfadimethoxine, SMO), etc.), tetracyclines (such as sulfamethoxazole (Sulfamethoxazole, SMX), sulfapyridine (Sulfapyridine, SPD) and sulfadimethoxine (Sulfadimethoxine, SMO)), quinolones (such as norfloxacin (NOR), ciprofloxacin (Ciprofloxacin, CIP) and ofloxacin (OFL), etc.), macrolides (such as erythromycin (Erythromycin, ERY), azithromycin (AZI), roxithromycin (ROX) and clarithromycin (CLA), etc.), β-lactams (such as cefalexin (CFX), etc.), lincomycins (such as lincomycin, etc.), trimethoprim, etc.

[0035] In the embodiments of the present application, the concentration of the 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.

[0036] In an optional 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, a 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 greater 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 of the inner and outer coaxial. In addition, when the microwave plasma generator used 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, so no cooling device is required in the entire degradation process, reducing additional energy consumption. Since low-temperature microwave plasma is generated, the actual input microwave energy is also low, and the excitation of microwave plasma can be achieved in the power range of 15-25 w, and there will be no mixed antibiotics due to the increase in temperature. Thermal effect, there will be no evaporation of antibiotic solution, can accurately monitor the situation of microwave plasma degradation of antibiotics in antibiotic solution, and obtain accurate degradation results.

[0037] In an optional embodiment of the present application, the above-mentioned degradation system further includes a protection device, and the above-mentioned protection device at least includes a circulator (see Figure 2 Circulator) and water load device (see Figure 2 The circulator is connected to the first converter, the water load device is connected to the circulator, and the circulator and the first converter, as well as the water load device and the circulator are electrically connected; the method further includes: using the circulator to prevent the reflected microwave energy from being too high in power and damaging the microwave generating device; and using the water load device to absorb the microwave energy reflected back by the circulator to prevent damage to the microwave generating device.

[0038] Based on the above embodiments, the degradation system proposed in the present application further includes a microwave controller (see Figure 2 Computer) and a power reading device, the power reading device comprising a dual directional coupler (see Figure 2 The method further comprises: using the dual directional coupler and the microwave power meter to read the incident power and reflected power of the microwave energy; and using the microwave controller to control the power of the microwave energy emitted by the microwave generator.

[0039] Based on the above embodiment, a coaxial line is used to connect the first converter and the microwave generating device, and the second converter and the microwave plasma generator, and the coaxial line is used to transmit microwave energy, and the microwave energy transmitted by the coaxial line belongs to the coaxial cable transmission mode.

[0040] In an optional embodiment of the present application, the optimal degradation parameters in the method of low-temperature microwave plasma degradation of mixed antibiotics in wastewater are as follows: the power of microwave energy is 20 W, the flow rate of argon gas is 8 L / min, the pH value of the antibiotic solution is 2.74, and the concentration of the antibiotic solution is 20 mg / L. Under these conditions, the mixed antibiotics are degraded for 30 min, and the degradation efficiency of the mixed antibiotics can reach more than 99%.

[0041] In an optional embodiment of the present application, during the treatment of the antibiotic solution, high-energy electrons and active oxygen species generated by microwave plasma react with the antibiotics to achieve degradation of the antibiotics.

[0042] In an optional embodiment of the present application, during the treatment of the antibiotic solution, the microwave plasma is used to generate , ˙H, ˙O, ˙OH, and O3 act as active species to degrade antibiotics in the antibiotic solution.

[0043] In a preferred embodiment of the present application, the antibiotics in the antibiotic solution are sulfamethoxazole and oxytetracycline.

[0044] 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.

[0045] The reagents used in this example are all commercially available and purchased from Shanghai Aladdin Technology Co., Ltd., Chengdu Kelon Chemical Reagent Factory, and Sigma-Aldrich Technology Co., Ltd. The experimental instruments used are all commercially available and purchased from the 13th Institute of China Electronics Technology Group Corporation, Chengdu Euler Microwave Components Co., Ltd., Chengdu Maipin Huineng Technology Co., Ltd., Chengdu Maipin Huineng Technology Co., Ltd., Chengdu Euler Microwave Components Co., Ltd., China Electronics Cosine Technology (Anhui) Co., Ltd., Zhengzhou Ketan Instrument Equipment Co., Ltd., Shanghai Leici Instrument Co., Ltd., and Shanghai Youke Instrument Co., Ltd.

[0046] 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 the present application, the following examples are used to illustrate.

[0047] Example 1: Determination of antibiotic concentration in water after microwave plasma treatment Microwave plasma will produce physical effects and different chemically active species, using physical and chemical effects to efficiently treat pollutants. Therefore, in order to improve the utilization efficiency of active species, the applicant determined the degradation efficiency of antibiotics based on single treatment and mixed treatment.

[0048] The concentration of the antibiotic stock solution was 1 g / L, and the antibiotics selected were sulfamethoxazole (SMZ) and oxytetracycline (OTC). The specific operation was as follows: SMZ and OTC drugs were dissolved in 0.1 mol / L acetic acid solution, respectively, to prepare a stock solution with a concentration of 1 g / L, and stored in a refrigerator at 4°C. The storage period was one week. The standard solution used in the degradation experiment was diluted from the stock solution to meet the needs of the analysis. The resistivity of the deionized water used in the experiment was 18.2 MΩ.

[0049] The physicochemical properties of sulfamethoxazole (SMZ) and oxytetracycline (OTC) used are shown in Table 1.

[0050] Table 1 Physical and chemical properties of sulfamethoxazole and oxytetracycline

[0051] The concentration of 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 column (2.1 mm × 100 mm, 1.8 µm). The mobile phases were 0.1% formic acid in water (phase A) and methanol (phase B). Table 2 shows the mobile phase gradient setting, 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.

[0052] Table 2 Construction of mobile phase for detecting residual antibiotic concentration in aqueous solution by UPLC

[0053] The efficiency of microwave plasma degradation of mixed antibiotics in water is obtained by subtracting the ratio of the concentration of antibiotics in water after microwave plasma treatment and the concentration of antibiotics in water initially measured by the above method from 1. In all embodiments of the present application, unless otherwise specified, the initial concentration of a single antibiotic is 10 mg / L, and the initial concentration of mixed antibiotics is 20 mg / L.

[0054] 12 mL of sulfamethoxazole, oxytetracycline and mixed antibiotic solution were placed in 10 mL glass beakers respectively and placed directly under the room temperature microwave plasma jet to evaluate their respective degradation efficiencies. The degradation efficiency results of antibiotics treated alone and mixed are shown in Figure 3 , Figure 3 This is a graph showing the degradation efficiency of single and mixed antibiotics in water treated with low-temperature microwave plasma provided in an embodiment of the present application. Figure 3 The horizontal axis is the treatment time (in minutes), and the vertical axis is the degradation efficiency. Compared with the single antibiotic treatment (SMX or OTC), the degradation efficiency of the mixed antibiotics (SMX+OTC) was improved at different treatment times, and the highest could reach 100%. The degradation efficiency of SMX+OTC was improved by 6.17%-11.13% compared with that of SMX alone, and by 10.21%-26.28% compared with that of OTC alone. This may be due to the fact that the treatment of high concentrations of antibiotics produces higher degradation efficiency compared with the treatment of low concentrations of antibiotics, because more antibiotic molecules are involved in the reaction with the active reactants.

[0055] Example 2: Effect of different experimental parameters on antibiotic degradation efficiency In order to maximize the use of microwave plasma energy, the applicant explored the experimental parameters that affect the degradation efficiency of the antibiotic solution, such as microwave power, gas flow rate for generating plasma, concentration of the initial solution, and pH value. The degradation efficiency of the antibiotic in the antibiotic solution was measured under different experimental parameters.

[0056] Example 2A: Effect of Argon Flow Rate on Antibiotic Degradation Efficiency Pure argon was used to excite three-layer coaxial microwave plasma to treat the mixed solutions of SMX, OTC and SMX + OTC antibiotics. The treatment concentration of the single antibiotic was 10 mg / L, the concentration of the mixed antibiotic solution was 20 mg / L, and 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 mainly affects the degradation of antibiotics in two aspects. First, by affecting the direct interaction between plasma and antibiotics, such as the direct collision between high-energy electrons and antibiotic molecules. Secondly, by changing the content of ROS (Reactive Oxygen Species) in water, the degradation efficiency of the target is indirectly affected.

[0057] Experimental results participation Figure 4 , Figure 4 This is a result diagram of the effect of argon gas flow rate on antibiotic degradation efficiency provided in an embodiment of the present application. Figure 4 Part (a) shows the effect of argon flow rate on SMX solution. Figure 4Part (b) shows the effect of argon flow rate on OTC solution. Figure 4 Part (c) shows the effect of argon flow rate on SMX+OTC solution. Figure 4 The horizontal axis is the treatment time (in minutes), and the vertical axis 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 gas flow rate, the treatment effects of SMX, OTC and SMX+OTC first increase and then decrease, and the treatment effect is best at 8 L / min. Under the same experimental conditions of 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 the gas flow rates of 6 L / min and 10 L / min, the degradation efficiencies of SMX solution treated for 30 min are 94.56%±2.31 and 100%, respectively. At the optimal flow rate of 8 L / min, the degradation efficiency of OTC reached 52.86% ± 2.96 and 93.97% ± 1.32 at 10 min and 20 min, respectively; when the treatment time was extended to 30 min, it basically reached 100% treatment. At 6 L / min and 10 L / min, the degradation efficiency of OTC solution treated with microwave plasma for 30 min was 89.76% ± 1.76 and 97.10% ± 1.26, respectively. The best degradation efficiency was obtained when the mixed solution of SMX and OTC was treated with microwave plasma. When the gas flow rate is 8 L / min, the degradation efficiency of the mixed solution with an initial concentration of 20 mg / L after being treated for 10 min and 20 min is 63.3.% ± 2.03 and 94.27% ± 1.50 respectively; the degradation efficiency reaches 98.62% ± 1.23 at 25 min, which is basically completely treated; even at the minimum flow rate of 6 L / min, the degradation efficiency of the mixed antibiotics after 30 min is 90.37% ± 2.46. When the gas flow rate is too small, microwave plasma is not conducive to the generation of high-energy electrons and ROS in surface discharge, which directly reduces 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 there is no time to completely react with pollutants, which reduces the degradation efficiency. In addition, excessive flow rate will also produce larger bubbles in water and reduce the contact between ROS and antibiotic molecules. Therefore, in subsequent experiments, the argon flow rate was selected as 8 L / min.

[0058] Example 2B: Effect of initial antibiotic concentration on antibiotic degradation efficiency The initial concentration of the antibiotic solution has a significant effect on the degradation efficiency. The degradation experiment and the determination of the antibiotic concentration 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.

[0059] Experimental results refer to Figure 5 , Figure 5 This is a result diagram of the effect of the initial concentration of an antibiotic on the degradation efficiency of the antibiotic provided in an embodiment of the present application. Figure 5 Part (a) shows the effect of the initial concentration of antibiotics on the SMX solution. Figure 5 Part (b) shows the effect of the initial concentration of antibiotics on the OTC solution. Figure 5 Part (c) shows the effect of the initial antibiotic concentration on the SMX+OTC solution. Figure 5 The horizontal axis is the treatment time (in minutes), and the vertical axis is the degradation efficiency.

[0060] The results showed that lower initial concentrations showed higher treatment efficiency. The treatment effect of mixed antibiotics was better than that of single antibiotics. At initial concentrations of 10 mg / L, 20 mg / L and 30 mg / L, the degradation efficiencies of SMX and OTC reached 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, the degradation efficiencies obtained were 100%, 100% and 79.92% ± 1.32 at initial concentrations of 10 mg / L, 20 mg / L and 30 mg / L, respectively. The amount of ROS generated in a period of time by microwave plasma discharge under fixed experimental conditions is limited. If the concentration of antibiotics in water is too low, ROS will not be fully utilized, resulting in energy waste. On the contrary, too high an antibiotic concentration will result in a large amount of byproducts. Therefore, the competition between byproducts and target antibiotic molecules will intensify the scarcity of ROS, resulting in insufficient antibiotic degradation.

[0061] At the same time, the G 50 Energy yield, results see Figure 6 , Figure 6 is an energy yield diagram of antibiotics with different initial concentrations provided in the examples of the present application, Figure 6The horizontal axis is the initial concentration of the antibiotic solution (in mg / L), and the vertical axis is the energy yield (in mg / kWh). The results show that whether it is a single antibiotic or a mixed antibiotic, the energy yield first increases and then decreases with the increase in concentration. Moreover, mixed antibiotics significantly improve the energy efficiency of antibiotics. When the initial concentration is 10 mg / L, 20 mg / L and 30 mg / L, the energy yield of the mixed antibiotics increases by 12.80-18.28 mg / kWh, 17.70-31.57 mg / kWh and 21.60-31.77 mg / kWh, respectively.

[0062] Example 2C: Effect of initial pH value of antibiotics on antibiotic degradation efficiency Since different pH values ​​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, carried out degradation experiments and determination of antibiotic concentrations using the treatment method in Example 1, and used H2SO4 / NaOH to adjust the pH values ​​of the SMX solution to 2.38, 6.04, and 11.24, respectively, the pH values ​​of the OTC solution to 3.48, 7.21, and 10.60, respectively, and the pH values ​​of the mixed solution of SMX+OTC to 2.74, 6.50, and 10.52, respectively. The pH values ​​of the antibiotic solutions before and after degradation were detected using a digital acidometer.

[0063] Experimental results refer to Figure 7 , Figure 7 This is a graph showing the effect of different initial pH values ​​on the degradation efficiency of antibiotics proposed in an embodiment of the present application. Figure 7 Part (a) shows the degradation efficiency of SMX at different pH values. Figure 7 Part (b) shows the degradation efficiency of OTC at different pH values. Figure 7 Part (c) shows the degradation efficiency of SMX+OTC at different pH values. Figure 7 Part (d) shows the pH variation trend of SMX at different times. Figure 7 Part (e) shows the pH value variation trend of OTC at different times. Figure 7 Part (f) shows the pH value variation trend of SMX+OTC at different times. Figure 7 The horizontal axis is the processing time (in minutes). Figure 7 The ordinate of part (d) is pH value, and the ordinate of the rest is degradation efficiency.

[0064] Obviously from Figure 7From parts (a) to (c), it can be seen that higher degradation efficiencies of SMX, OTC, and SMX + OTC mixed solutions can be obtained under weak acid conditions, followed by solutions close to neutral, and alkaline environments are the least conducive to 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 at pH 3.48 was 93.97 ± 1.32, and at pH 7.21, the degradation efficiency reached 90.25 ± 1.32 at 30 min, while at pH 10.60, even if the reaction time was extended to 30 min, the degradation efficiency was still only 72.67 ± 1.84. The mixed solution of SMZ and OXY also achieved the best degradation efficiency under acidic conditions, because under acidic conditions, hydrated electrons react with hydrogen ions to generate hydrogen radicals, which further generate ˙OH, thereby increasing the generation of ˙OH.

[0065] In addition, the pH trend of the antibiotic solution was monitored during the microwave plasma treatment, and the results showed that Figure 7 Part (d) to part (f). As can be seen from the figure, whether it is a single antibiotic or a mixed antibiotic, the pH value of the solution is basically stable in acidic and alkaline environments. Only in a near-neutral environment will the pH value of the solution decrease with reaction time. On the one hand, the reactive nitrogen (RNS) produced by the expansion of plasma in the air causes the acidity of the solution to increase. On the other hand, the acidic intermediate NOR (norfloxacin) produced by degradation is also a factor in the change of the pH value of the solution.

[0066] Example 2D: Effect of microwave power on antibiotic degradation efficiency The degradation experiment and the determination of antibiotic concentration were carried out using the treatment method in Example 1, wherein 15 W, 20 W and 25 W microwave powers were selected to treat the antibiotic solution, respectively, to explore the effect of different microwave powers on the antibiotic degradation efficiency. Figure 8 , Figure 8 This is a result diagram of the effect of microwave power on antibiotic degradation efficiency provided in an embodiment of the present application. Figure 8 Part (a) is the degradation efficiency of SMX at different powers. Figure 8 Part (b) shows the degradation efficiency of OTC at different powers. Figure 8 Part (c) shows the degradation efficiency of SMX+OTC at different powers. Figure 8 The horizontal axis is the treatment time (in minutes), and the vertical axis is the degradation efficiency.

[0067] Microwave power is one of the important factors affecting the degradation efficiency of antibiotics. The initial concentrations of SMX and OTC antibiotics were 10 mg / L, the initial concentration of SMX+OTC mixed antibiotics was 20 mg / L, the argon flow rate was 8 L / min, the initial pH values ​​were 2.38, 3.48 and 2.74, and the microwave input powers were 15 W, 20 W and 25 W, respectively. The results showed that the degradation efficiency of antibiotics increased with the increase of microwave power. Figure 8 Part (a) shows that after 15 min of treatment with SMX solution, the degradation efficiency increased 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. When the treatment time was extended to 25 min, the degradation efficiency increased 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 increased from 56.93% ± 1.69 at 15 W to 79.82% ± 2.03 at 20 W, and then increased to 82.11% ± 1.35 at 25 W. After extending the treatment time to 30 min, the degradation efficiency increased from 91.62% ± 2.22 at 15 W to 97.34% ± 1.66 at 20 W, and then increased to 101.66% ± 1.52 at 25 W. For the SMX+OTC mixed antibiotic solution, Figure 8 Part (c) shows that after 15 min of treatment, the degradation efficiency increased 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. When the treatment time was extended to 25 min, the degradation efficiency increased 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 was extended to 30 min, the degradation efficiency increased from 96.67% ± 1.86 at 15 W to 100% at 20 W-25 W. The results show that as the input power increases, the degradation efficiency also increases to 100% at 20 W-25 W. The results show that as the input power increases, the degradation efficiency also increases. The physicochemical effects in discharge are enhanced with the increase of input energy. On the other hand, higher voltage can also accelerate electrons in the plasma, emit more intense ultraviolet light and stronger shock waves, all of which can improve the efficiency of antibiotic degradation.

[0068] Example 2E: Changes in conductivity of antibiotic solution during degradation at different acidities The applicant selected antibiotic solutions with different initial pH values ​​(the initial pH values ​​of SMZ solution were 2.38, 6.04 and 11.24, and the initial pH values ​​of OXY solution were 3.48, 7.21 and 10.60, respectively), and used a conductivity meter to monitor the changes in their conductivity during microwave plasma treatment. Fig. 9 , Fig. 9 This is a result diagram of the change in conductivity of an antibiotic solution during the degradation process under different acidities provided in an embodiment of the present application. Fig. 9 Part (a) shows the conductivity variation trend of SMX during degradation at different acidities. Fig. 9 Part (b) shows the conductivity variation trend of OTC during degradation at different acidities. Fig. 9 The horizontal axis is the treatment time (in minutes), and the vertical axis is the conductivity (in μs / cm). Since organic compounds will produce many inorganic free ions during the degradation process, such as ammonium ions (NH4 + ), sulfate (SO4 2+ ), sulfite (SO3 2+ ), nitrate (NO3 - ), nitrite (NO2 - ) and hydrogen ions (H3O + ), therefore, the conductivity of the antibiotic solution increases with the treatment time. In this case, NO3 - and NO2 -The ions may be generated by microwave plasma or may be degradation products of SMX and OTC. When the initial pH value of SMX solution was 2.38, the conductivity increased from 1331 µs / cm ± 5.56 to 1688.33 µs / cm ± 9.61; when the pH value was 6.04, the conductivity increased from 682.66 µs / cm ± 8.08 to 878.66 µs / cm ± 5.50; when the pH value was 11.24, the conductivity increased from 1698.33 µs / cm± 17.61 to 1928.33 µs / cm±6.03; the conductivity increased the most under acidic conditions, about 357.33 µs / cm. The conductivity of the OTC solution increased from 73.9 µs / cm ± 5.21 to 149.67 µs / cm ± 1.53 when the initial pH value was 3.48; from 365.33 µs / cm ± 5.51 to 503.33 µs / cm ± 3.51 when the pH value was 7.21; and from 489 µs / cm ± 2.64 to 638 ± 4.00 when the pH value was 10.60. The conductivity increased the most under alkaline conditions, which was about 149 µs / cm. However, the increase in conductivity is not conducive to the formation of ˙OH, which will eventually inhibit the degradation efficiency of antibiotics.

[0069] Example 3: Mineralization efficiency of antibiotics Another important indicator for evaluating the removal performance of antibiotic pollutants is mineralization efficiency. The applicant used a TOC (vario TOC cube, elementar, Germany) analyzer to measure the total organic carbon (TOC) before and after SMX and OTC treatment. 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 can be found in Fig.10 , Fig.10 This is a mineralization efficiency result diagram of an antibiotic solution provided in an embodiment of the present application. Fig.10 The horizontal axis is the processing time (in minutes), and the vertical axis is the mineralization efficiency.

[0070] Generally, the removal rate of TOC is lower than the corresponding degradation efficiency, which indicates that some intermediate byproducts are produced during the degradation process. When the treatment time is 15 min, the mineralization efficiency 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 is extended to 30 min, the mineralization efficiency increases to 60.03% ± 4.03, 36.75% ± 2.79 and 66.16% ± 3.80, respectively. The mineralization efficiency of the mixed antibiotics has been significantly improved, increasing by 6.13% and 29.41%, respectively. This shows that microwave plasma can degrade antibiotics into small molecular organic matter and small molecular inorganic matter. However, under these experimental conditions, some intermediates produced during the degradation process cannot be further mineralized.

[0071] Example 4: Effect of Hydroxyl Radical Scavengers on Antibiotic Degradation Efficiency In order to study the contribution of reactive oxygen radicals to the degradation efficiency of antibiotics, since the lifetime of OH in the liquid phase is usually about 10 - 9 seconds, so it is difficult to quantify the amount of ˙OH generated in microwave plasma. Usually, isopropyl alcohol (IPA) is used as a scavenger of ˙OH to indirectly evaluate their important role in the degradation of antibiotic solutions. Therefore, different volumes (5 μL, 10 μL, 20 μL) of isopropyl alcohol were added to the antibiotic solutions, and the presence of hydroxyl radicals was indirectly verified by quenching experiments.

[0072] Different volumes of IPA were added to single antibiotics (initial concentration of 10 mg / L) and mixed antibiotics (initial concentration of 20 mg / L) at an argon flow rate of 8 L / min, a power of 20 W, and a volume of 12 mL. The degradation efficiency was shown in Fig.11 As shown, Fig.11 This is a graph showing the effect of isopropanol on the degradation efficiency of antibiotics provided in an embodiment of the present application. Fig.11 Part (a) shows the effect of IPA on the degradation efficiency of SMX. Fig.11 Part (b) shows the effect of IPA on the degradation efficiency of OTC. Fig.11 Part (c) shows the effect of IPA on the degradation efficiency of SMX+OTC. Fig.11 The horizontal axis is the treatment time (in minutes), and the vertical axis is the degradation efficiency.

[0073] When 5 µL 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 the degradation efficiency at 30 min decreased to 57.59% ± 2.46. When the amount of IPA added was 10 µL, the degradation efficiency after 20 min of reaction was 31.71% ± 1.67, and the degradation efficiency after 30 min of treatment was 48.47% ± 1.86. When IPA was further increased to 20 µL, the degradation efficiency of SMX solution treated for 20 min and 30 min was 21.00% ± 1.74 and 33.28% ± 1.96, respectively. When 1.0 µL 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. The degradation efficiency at 30 min decreased from 100% to 38.58% ± 1.21. When the amount of IPA added was 2.5 µL, the degradation efficiency after 20 min of reaction was 5.38% ± 0.65, and the degradation efficiency after 30 min of treatment was 34.39% ± 1.58. When IPA was further 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, the degradation efficiency after adding 5 µL IPA for 10 min and 20 min 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 after 30 min was 58.13% ± 2.60; the degradation efficiency after adding 10 µL IPA for 10 min and 20 min was 6.44% ± 0.43 and 16.99% ± 2.63, respectively, and the degradation efficiency after 30 min was 28.33% ± 2.03; when IPA was further increased to 20 µL, the degradation efficiency after 20 min and 30 min was only 5.73% ± 0.69 and 11.60% ± 2.03, respectively. These results indicate that the addition of OH scavengers can significantly inhibit the degradation of antibiotics. The degradation efficiency of OTC solution under microwave plasma is lower than that of single SMX solution and OTC + SMX mixed solution, so the amount of IPA added to the OTC solution should be less.The inhibitory effect of mixed antibiotics after adding IPA is the most obvious, indicating that the ˙OH generated by microwave plasma is fully utilized during the reaction. Therefore, ˙OH plays the most important oxidative role in the process of microwave plasma removal of antibiotics.

[0074] Example 5: Possible pathways of degradation of SMX and OTC Example 5A: Determination of byproducts and degradation pathways of sulfamethoxazole Any change in the chemical structure of SMX is considered as the removal of the pollutant. The formation of various compounds during the treatment can be correlated with the contribution of various plasma-generated reactants 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, the intermediate products of SMZ solution treated with microwave plasma for 30 min were analyzed by HPLC-QQQ / MS using positive-negative ion mode. In this example, the degradation products of SMX and OTC were detected using an Agilent LC1290 high performance liquid chromatograph and an Agilent 6470 triple quadrupole (QQQ) tandem mass spectrometer. Separation was performed using an Agilent, EC-C18 column (3.0 x 150 mm, 2.7 μm) at 35°C. 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 mobile phase flow rate was 0.4 mL / min and the injection volume was 10 μL. The 6470 QQQ mass spectrometer was equipped with a positive and negative ESI source. The gas flow was set to 12 L / min, the temperature was set to 150 °C, the nebulizer pressure was 30 Psi, the scan time was 350 ms, and the scan step size was 0.1 amu. The sheath gas flow 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 spectrum acquisition range was 50-1000 mass / charge (m / z). For MS 2 , two precursors were selected for each cycle based on abundance. Fragmentation analysis was performed 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 negative and positive ion modes are shown in Tables 3 and 4, respectively: Table 3 Mobile phase ratio of negative ions

[0075] Table 4 Mobile phase ratio of positive ions

[0076] Possible intermediates were identified based on the m / z values ​​of the substances, and the degradation pathway of sulfamethoxazole was inferred based on the intermediates in each time period. During the plasma treatment of SMZ solution, a series of intermediates were formed and then degraded simultaneously with the target compound. Based on the identified degradation intermediates, the proposed SMX degradation pathway is expressed as Fig.12 , Fig.12 This is a schematic diagram of the degradation pathway of SMX proposed in the embodiment of the present application. Four main degradation pathways have been observed according to the attack site and type of free radicals. Although microwave plasma discharge can produce a variety of substances ( , ˙H, ˙O, ˙OH, O3, etc.), which contribute to the removal of pollutants to varying degrees. However, free radical capture experiments show that ˙OH plays an important role in the degradation of SMX, with a reaction rate constant of 8.5 × 10 9 .

[0077] Based on the m / z ratios of the detected transformation intermediates and fragments, four possible pathways for the degradation mechanism of SMX on a room temperature microwave plasma system were proposed. Path 1 The first is the hydroxylation reaction of the benzene ring with the hydroxyl radical. The hydroxylation reaction based on the hydroxyl radical site is divided into 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 abstraction of hydrogen and the reconstruction of the double bond, which is the result of the ˙OH attack on the same carbon atom as 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 will subsequently produce other products. The ˙OH continues to attack the benzene ring to generate the intermediates S2 (dihydroxylation m / z = 285) and S3 (trihydroxylation m / z = 301). The nitro group at the C14-N17 position on the benzene ring is replaced by ˙OH to generate the S4 intermediate. Pathway 2 corresponds to the cleavage of the C11-S7 bond, probably due to the attack of the sulfur atom by ˙OH, which produces S5 (m / z = 178) aminosulfonic acid and an aniline radical. The aniline radical can react with SMX to form S6 (m / z = 344) via the aniline dimerization pathway. Pathway 3 begins with the attack of ˙OH on the C4 atom of the isoxazole ring, which results in the cleavage of the double bond, leaving an unpaired electron on the C5 atom. The abstraction of hydrogen from the C4 atom restructures the double bond to form S7 (m / z = 269b). The formation of this product has also been observed in studies of advanced oxidation processes such as ozone oxidation. Further reaction of ˙OH with C5 can lead to the formation of dihydroxylated S8, m / z = 287, which is converted to the intermediate S9 m / z = 133 by displacement. Pathway 4 is the attack of the S-N bond of SMX by the radical to produce p-aminobenzenesulfonic acid S10 (m / z = 173). The reaction was continued to cleave the SC bond and remove the sulfonic acid group to form compound S11 aniline (m / z = 94), and free radical addition produced compound S12 o-hydroxyaniline (m / z = 94). The reaction was continued to open the benzene ring to form small molecule enol compounds S13 and S14 methylethanol.

[0078] Example 5B: Determination of byproducts and degradation pathways of oxytetracycline By using a room temperature microwave plasma treatment process, the intermediate products appearing in the degradation process of OTC were analyzed by HPLC-QQQ-MS. 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. The mobile phase ratio is shown in Table 5: Table 5 Determination of mobile phase ratio of OTC intermediates

[0079] like Fig.13 As shown, Fig.13This is a schematic diagram of an OTC degradation pathway proposed in the examples of this 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.

[0080] In pathways 1 and 2, the degradation of OTC starts at different points, including the carbon-carbon double bond, tertiary amino group, and A ring, which are vulnerable to ROS attack. First, OTC undergoes demethylation through a reaction to remove the N-methyl group of OTC, thereby generating O1 (m / z = 447). Next, the generated O1 is demethylated and dehydrated through a reaction to remove the hydroxyl group and N-methyl group of O1, and compound O2 (m / z = 342) is generated due to the cleavage of the C-CONH2 bond. Subsequently, the double bond of O2 is hit by the hydroxyl radical generated in the microwave plasma reaction, and the intermediate O3 (m / z 300) is generated through ring cleavage. It is worth noting that the NC 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 the N-methyl group on the aromatic ring, to produce m / z = 339 (O4). The naphthol ring can be opened by oxidation of ˙OH radicals, and O4 can be decomposed into O5 (m / z = 303). O5 continues to decarboxylate and dehydrate to generate intermediate O6 (m / z = 259). Under further oxidation, the intermediate removes the carbonyl group and is converted into compound O7. The third pathway of OTC decomposition is hydroxylation to generate isomeric compounds O8 (m / z = 477a) and O9 (m / z = 477b), respectively. The intermediates in the OTC degradation process are expected to become low molecular weight organic compounds such as O10, O11 and O12 through other reactions. These organic compounds will then decompose into inorganic substances such as CO2, H2O, NH4 + 、NO3 - wait.

[0081] 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.

[0082] The above is a detailed introduction to the method for low-temperature microwave plasma degradation of mixed antibiotics in wastewater provided by the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for general technicians in this field, according to the ideas of the present application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for degrading mixed antibiotics in sewage by low-temperature microwave plasma, characterized in that: The method is implemented by a degradation system, which includes: a microwave generating device, a first converter, a second converter, a microwave plasma generator and an argon gas flow controller. The method includes: The microwave generating device is used to emit microwave energy, wherein the power of the microwave energy is 15-25 W; Transmitting the microwave energy to a first converter, and using the first converter to convert the microwave energy from a coaxial cable transmission mode to a waveguide transmission mode, and then transmitting the microwave energy to a second converter; The second converter is used to convert the microwave energy back into a coaxial cable transmission mode and transmit it to a microwave plasma generator; The argon flow rate is controlled by an argon flow controller and transmitted to the microwave plasma generator, and the argon flow rate is 6-10 L / min; The microwave plasma generator uses microwave energy to excite argon gas to obtain microwave plasma; The antibiotic solution is treated with microwave plasma obtained by exciting a microwave plasma generator to obtain a degraded antibiotic solution, wherein the antibiotic solution includes 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.

2. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that: 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.

3. 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, which includes at least a circulator and a water load device, wherein the circulator is connected to the first converter, and the water load device is connected to the circulator; the method further includes: The circulator is used to prevent the reflected microwave energy from being too high in power and damaging the microwave generating device; The water load device is used to absorb the microwave energy reflected back by the circulator.

4. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 3, characterized in that: The degradation system further includes a microwave controller and a power reading device, wherein the power reading device includes a bidirectional coupler and a microwave power meter, wherein the dual directional 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: Using the dual directional coupler and the microwave power meter to read the incident power and reflected power of microwave energy; The microwave controller is used to control the power of the microwave energy emitted by the microwave generator.

5. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that: The first converter and the microwave generating device, as well as the second converter and the microwave plasma generator, are connected by coaxial lines.

6. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that: The power of the microwave energy is 20 W, the flow rate of the argon gas 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.

7. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that: In the process of treating the antibiotic solution, the high-energy electrons and active oxygen species generated by microwave plasma react with the antibiotics to achieve degradation of the antibiotics.

8. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that: In the process of treating antibiotic solution, microwave plasma is used to generate , ˙H, ˙O, ˙OH, and O3 act as active species to degrade antibiotics in the antibiotic solution.

9. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 1, characterized in that: The antibiotics in the antibiotic solution are sulfamethoxazole and oxytetracycline.

10. The method for degrading mixed antibiotics in sewage by low-temperature microwave plasma according to claim 9, characterized in that: 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; The degradation pathway of oxytetracycline at least includes hydroxylation, deamination, demethylation, dehydration and ring cleavage reactions.

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