A method for degrading gatifloxacin in wastewater based on cathode micro-arc plasma electrolysis technology

Abstract

The application belongs to the technical field of wastewater treatment, and particularly relates to a method for degrading gatifloxacin in wastewater based on a cathode micro-arc plasma electrolysis technology. The method comprises the following steps: placing the wastewater in an electrolysis reactor, using a titanium rod as a cathode, a platinum sheet as an anode, applying a pulse direct current voltage with a voltage of 320V to 360V and a frequency of 150Hz, forming a gas film on the surface of the cathode and initiating plasma micro-arc discharge, degrading the gatifloxacin in the wastewater by active substances generated by the discharge, and the treatment time being 8 minutes to 12 minutes; wherein the wastewater comprises wastewater containing gatifloxacin. The method provided by the application can achieve nearly complete removal of gatifloxacin in an aqueous solution within 8 minutes under the condition of 100mg·L ‑1 GAT, 340V, pH=7.8, 0.5mol·L ‑1 KCl, and has great potential in treating high-concentration medical wastewater.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for degrading gatifloxacin in wastewater based on cathode micro-arc plasma electrolysis technology. Background Technology

[0002] Gatifloxacin (GAT), a fourth-generation fluoroquinolone, is widely used in clinical practice. Its broad-spectrum antibacterial activity makes it effective against a variety of Gram-positive and Gram-negative bacteria. However, due to its limited metabolic degradation and low excretion efficiency, the persistent presence of GAT has raised concerns—this substance has been detected in various water bodies, from wastewater treatment plants to surface water and groundwater systems. The widespread presence of fluoroquinolone antibiotics in water bodies and wastewater has made antimicrobial resistance in aquatic microbial communities a major ecological problem. The persistent presence of GAT in water bodies is mainly due to its structural characteristics and pH distribution. As an amphoteric fluoroquinolone, GAT exists primarily in a zwitterionic form under near-neutral pH conditions. Its quinolone core structure contains a piperazine group and a 1-cyclopropyl substituent, which endows it with potent antibacterial activity but also results in low biodegradability and strong adsorption, limiting the removal efficiency of conventional wastewater treatment. Biological treatment processes, such as aerobic and anaerobic processes, are often slow and frequently inhibited by toxic byproducts such as antibiotics and heavy metals—substances that accumulate and hinder microbial activity. On the other hand, while physical adsorption can effectively remove pollutants, it merely transfers them to a solid surface, leading to secondary treatment issues, such as the need for frequent regeneration or disposal of spent adsorbents.

[0003] Advanced oxidation processes (AOPs) have become a significant pathway for the degradation of persistent fluoroquinolone antibiotics. Mainstream processes such as ozone treatment, photocatalysis, electrochemical oxidation, and the Fenton reaction have all demonstrated good performance. For example, ozone treatment achieves 99% GAT removal within 4 minutes at pH 10; enhanced O3 / S (IV) systems complete approximately 87% antibiotic degradation within 5 minutes. With optimization of conditions such as pH, current density, and iron catalyst dosage, electro-Fenton (EF) and photoelectric Fenton (PEF) processes can achieve complete antibiotic removal. However, these traditional AOP technologies still have limitations in practical applications. Photocatalysis faces three major challenges: low light energy utilization, catalyst deactivation, and poor catalyst recovery and reuse rates. Furthermore, ozone oxidation is limited by its selectivity for specific molecular structures, leading to incomplete mineralization and high capital and operating costs. The Fenton process is limited to a narrow optimal pH range (typically 2 to 3) and produces iron sludge, potentially causing secondary waste emissions. The necessary addition of hydrogen peroxide also poses safety hazards during storage and transportation.

[0004] Non-thermal plasma (NTP) technology has been extensively studied as an alternative to antibiotic degradation. Glow discharge (GD), dielectric barrier discharge (DBD), and corona discharge (CD) technologies can generate reactive oxygen species without the need for additional chemicals. Studies have confirmed that GD technology can accelerate redox reactions. DBD technology has been shown to be highly efficient and energy-saving. For example, Lou et al. found that using DBD / Cl2 treatment increased the removal rate of levofloxacin from 77.8% to 97.5%, while reducing energy consumption by approximately 64%. Studies have shown that corona discharge is simple to operate and inexpensive. Water quality parameters such as pH and conductivity significantly affect NTP performance. Existing plasma technologies often employ anodic discharge to maintain degradation efficiency; however, the anode is prone to oxidation, dissolution, and corrosion in strong oxidizing environments, leading to electrode deactivation and affecting operational stability. Summary of the Invention

[0005] To address the problem in existing plasma wastewater treatment technologies where the anode is prone to oxidation, dissolution, and corrosion under strong oxidizing environments, leading to electrode deactivation and affecting operational stability, this invention provides a method for degrading gatifloxacin in wastewater based on cathode micro-arc plasma electrolysis technology. This method completely removes gatifloxacin at a concentration of 100 mg / L within 10 minutes. To achieve the above objective, this invention employs the following technical solution.

[0006] As a novel plasma oxidation technology, cathode micro-arc plasma electrolysis (CMPE) has been designed and developed. The core innovation of CMPE lies in the fact that plasma discharge occurs at the cathode rather than the anode, which greatly avoids the oxidation and corrosion problems present in traditional designs. The main mechanism of this degradation technology is the synergistic effect of ultraviolet light, shock waves, and various reactive oxygen species (such as •OH, •O₂⁻, etc.). The device has a simple structure, low energy consumption, and flexible operation, opening up new avenues for wastewater treatment. Based on this, this invention provides a method for degrading gatifloxacin in wastewater based on cathode micro-arc plasma electrolysis technology, comprising the following steps:

[0007] Wastewater is placed in an electrolytic reactor, with a titanium rod as the cathode and a platinum sheet as the anode. A pulsed DC voltage of 320V~360V and a frequency of 140Hz~160Hz is applied to form a gas film on the surface of the cathode and trigger plasma discharge. The active substances generated by the discharge degrade gatifloxacin in the wastewater. The treatment time is 8~12 minutes.

[0008] The wastewater includes wastewater containing gatifloxacin.

[0009] This invention achieves rapid and efficient degradation of gatifloxacin by combining cathode discharge with the aforementioned physical and chemical oxidation effects. It also avoids the problems of oxidation, dissolution, corrosion, and deactivation of the anode in existing anodic discharge systems, thereby improving the operational stability of the device and the performance of electrode recycling. This solves the problem in existing plasma wastewater treatment technologies where the anode is prone to oxidation, dissolution, and corrosion in a strong oxidizing environment, leading to electrode deactivation and affecting operational stability.

[0010] Furthermore, the initial concentration of the wastewater containing gatifloxacin is 50 mg·L⁻¹. -1 ~150mg·L -1 .

[0011] Furthermore, the initial pH value of the wastewater containing gatifloxacin is 7-9.

[0012] Furthermore, the electrolytic reactor contains an auxiliary electrolyte with a concentration of 0.04 mol·L⁻¹. -1 ~0.06 mol·L -1 .

[0013] Furthermore, the auxiliary electrolyte is KCl.

[0014] Furthermore, the titanium rod is cylindrical, with a length of 40mm~60mm and a diameter of 4mm~6mm; the platinum sheet is rectangular, with a length of 40mm~60mm and a width of 20mm~30mm.

[0015] Furthermore, the cathode is polished and rinsed with 500-1500 grit sandpaper before use.

[0016] Furthermore, the distance between the cathode and the anode is 15mm to 25mm.

[0017] Furthermore, the plasma discharge process generates ultraviolet light, shock waves, and ultrasonic cavitation effects, while also producing active substances such as •OH, •O2⁻, H2O2, and O3. Through the synergistic effect of physical effects and active substances, the rapid degradation of gatifloxacin is achieved.

[0018] Furthermore, the role of the main active substance was verified through free radical capture experiments, and the degradation pathway of gatifloxacin was deduced based on liquid chromatography-mass spectrometry (LC-MS) analysis.

[0019] Furthermore, the wastewater also includes wastewater containing fluoroquinolone antibiotics.

[0020] The present invention also provides an apparatus for implementing the method, comprising an electrolytic reactor.

[0021] The electrolytic reactor is provided with a cathode and an anode, which are arranged opposite to each other; the cathode and anode are connected to a pulse power supply, which is used to apply a pulsed DC voltage to form a gas film on the surface of the cathode and trigger plasma discharge.

[0022] The electrolysis reactor is also movably equipped with a circulating cooling device and a condensing device. The circulating cooling device is connected to the condensing device. The circulating cooling device is used to remove the heat generated during the plasma discharge process to control the reaction temperature. The condensing device is used to condense and recover the gaseous products generated during the plasma discharge process.

[0023] The electrolysis reactor is connected to an OES emission spectrometer, which is used to monitor the emission spectrum during the plasma discharge process in real time.

[0024] Furthermore, the voltage applied by the pulsed power supply is sufficient to cause the water near the surface of the titanium cathode to evaporate due to Joule heating, forming a continuous gas film layer and triggering plasma micro-arc discharge.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a method for degrading gatifloxacin in wastewater based on cathode micro-arc plasma electrolysis technology. The method involves placing wastewater in an electrolysis reactor, using a titanium rod as the cathode and a platinum sheet as the anode, and applying a pulsed DC voltage of 320V~360V with a frequency of 140Hz~160Hz. This causes a gas film to form on the surface of the cathode and triggers plasma micro-arc discharge. The active substances generated by the discharge degrade gatifloxacin in the wastewater, with a treatment time of 8 to 12 minutes. The wastewater includes wastewater containing gatifloxacin. This invention fundamentally changes the plasma initiation location and reaction mechanism through cathodic micro-arc plasma electrolysis, thereby solving the problem of anodic oxidation corrosion. Traditional technologies rely on the anode to generate plasma, and the anode is directly subjected to oxidation, dissolution, and corrosion in a highly oxidizing plasma environment. In contrast, this invention uses a titanium rod cathode as the plasma initiating electrode, forming a gas film on the cathode surface and inducing micro-arc discharge. This transfers the highly oxidizing plasma region to the cathode side, allowing the anode to only act as a counter electrode to conduct current without being exposed to the highly oxidizing plasma environment. Under these conditions, the platinum anode undergoes only conventional electrochemical reactions, avoiding electrode deactivation caused by anodic oxidation corrosion and significantly improving the system's operational stability. At the same time, the plasma generated by the cathode can still effectively degrade gatifloxacin through active substances in the solution (such as •OH, •O2⁻, etc.), achieving a synergistic effect of efficient degradation and electrode stability.

[0026] This invention achieves rapid and efficient degradation of gatifloxacin by combining cathode discharge with the aforementioned physical and chemical oxidation effects. It also avoids the problems of oxidation, dissolution, corrosion, and deactivation of the anode in existing anodic discharge systems, thereby improving the operational stability of the device and the performance of electrode recycling. This solves the problem in existing plasma wastewater treatment technologies where the anode is prone to oxidation, dissolution, and corrosion in a strong oxidizing environment, leading to electrode deactivation and affecting operational stability.

[0027] 2. This invention details the mechanism of gatifloxacin (GAT) degradation via the CMPE process. The invention investigated the effects of the following key operating parameters: applied voltage, initial concentration, initial pH, and type of auxiliary electrolyte. Free radical capture experiments revealed the main active substances, and possible degradation pathways of GAT were derived based on liquid chromatography-mass spectrometry (LC-MS). This invention contributes to a deeper understanding of the CMPE treatment process for fluoroquinolone antibiotics and provides crucial information for the further development of plasma-based wastewater treatment technologies.

[0028] 3. This invention evaluated the degradation efficiency of gatifloxacin (GAT) using cathode micro-arc plasma electrolysis (CMPE). The study found that the process efficiency was affected by several key parameters, including initial concentration, pH, applied voltage, and auxiliary electrolyte. Degradation efficiency was improved under higher pH and increased applied voltage conditions; however, degradation efficiency decreased with increasing initial GAT concentration. Furthermore, KCl was the most effective auxiliary electrolyte, exhibiting a significantly higher degradation rate than KNO3 and K2SO4. At 380V, nearly 85% of GAT was degraded in just 2 minutes. However, after 6 minutes, the degradation efficiency stabilized at all voltage levels, indicating that voltage increases above 340V did not significantly improve performance. The optimized conditions for achieving nearly 100% GAT degradation within 8 minutes using CMPE were: 100 mg / L GAT concentration, 340V applied voltage, 0.05 mol / L KCl concentration, and pH 7.8. The degradation process mainly involves hydroxyl radicals (•OH), superoxide radicals (•O2⁻), and photogenerated holes (h). + Active substances such as piperazine ring and cyclopropyl group are degraded through pathways including the breaking of the piperazine ring and cyclopropyl group, defluorination, decarboxylation, transformation of the quinolone ring, and mineralization into small molecules such as CO2 and H2O. Attached Figure Description

[0029] Figure 1 In this invention, ultraviolet-visible spectrophotometry is used to monitor the changes in gatifloxacin (GAT) concentration during CMPE; wherein: (a) UV-Vis spectra of GAT treated with CMPE under different time conditions; (b) Degradation rate calculated based on the 282 nm absorption peak. Conditions: [GAT] = 100 mg / L, [pH] = 7.8, [applied voltage] = 340 V, [KCl] = 0.05 mol / L.

[0030] Figure 2 This invention illustrates the effect of CMPE on the degradation efficiency of GAT at different initial concentrations over time; wherein: (a) represents the degradation efficiency; (b) Degradation kinetics; Conditions: pH = 7.8, applied voltage = 340V, KCl = 0.05mol / L.

[0031] Figure 3 This invention illustrates the effect of initial pH value on GAT degradation efficiency; wherein: (a) represents the degradation efficiency; (b) Degradation kinetics; Conditions: pH=3, 7.8 and 10, [GAT]=100mg / L, [KCl]=0.05mol / L, [Applied voltage]=340V.

[0032] Figure 4 This invention illustrates the effect of different supporting electrolytes on GAT degradation efficiency; wherein: (a) represents the degradation efficiency; (b) Degradation kinetics; Conditions: [GAT] = 100 mg / L, [pH] = 7.8, [Applied voltage] = 340 V.

[0033] Figure 5 This invention illustrates the effect of different voltages on GAT degradation efficiency; wherein: (a) represents the degradation efficiency; (b) Degradation kinetics; Conditions: [GAT] = 100 mg / L, [pH] = 7.8, [KCl] = 0.05 mol / L.

[0034] Figure 6 The chemical oxygen demand (COD) of GAT degradation under different voltages in this invention is given; wherein the reaction conditions are: [GAT] = 100 mg / L, [pH] = 7.8, [KCl] = 0.05 mol / L.

[0035] Figure 7 This represents the average current efficiency of GAT degradation under different voltages in this invention.

[0036] Figure 8 This invention relates to the effect of active substance scavenging agents on the degradation of GAT in the CMPE process.

[0037] Figure 9 The image shows the liquid chromatography-mass spectra of GAT after 4 minutes of CMPE process operation in this invention; wherein the conditions are: [GAT]=100mg / L, [pH]=7.8, [applied voltage]=340V, [KCl]=0.05mol / L.

[0038] Figure 10 This describes the degradation pathway of GAT after 4 minutes in the CMPE process of this invention; wherein the conditions are: [GAT]=100mg / L, [pH]=7.8, [applied voltage]=340V, [KCl]=0.05mol / L.

[0039] Figure 11 This is a structural diagram of the device for degrading gatifloxacin in wastewater according to the present invention.

[0040] In the diagram, 1-pulse power supply, 2-OES emission spectrometer, 3-electrolysis reactor, 4-cathode, 5-anode, 6-circulating cooling device, and 7-condensation equipment.

[0041] Figure 12 The images show the surface morphology and XRD pattern of the oxide film on the pure titanium cathode surface after CMPD treatment in this invention; wherein: (a) shows the surface morphology; (b) is the XRD pattern. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but this should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art, and the materials, reagents, etc. used in the following embodiments are commercially available unless otherwise specified.

[0043] The materials used in the following embodiments are as follows: Gatifloxacin (C 19 H 22 FN3O4 (GAT) was purchased from Beijing Higher Education Research Technology Co., Ltd. Electrolytes potassium chloride (KCl, 99.8%), potassium sulfate (K2SO4, 99.5%), and potassium nitrate (KNO3, 99.5%) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Potassium hydroxide (KOH, 95%) and hydrochloric acid (HCl, 36%) were used to adjust the pH of the solution and were also purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0044] The ultrapure water used in this invention was produced by a laboratory ultrapure water system (Ike, Advanced-IV-04). All reagents selected from the supplier were analytical grade and were not pretreated before use in the experiments.

[0045] Example This invention provides a device for degrading gatifloxacin in wastewater (e.g., Figure 11 As shown in the figure, it includes electrolysis reactor 3.

[0046] The electrolysis reactor 3 is equipped with a cathode 4 and an anode 5, which are arranged opposite to each other. The cathode 4 and anode 5 are connected to a pulse power supply 1 (WHYH-40kW). The pulse power supply 1 is used to apply a pulsed DC voltage to form a gas film on the surface of the cathode and trigger plasma micro-arc discharge.

[0047] The electrolysis reactor 3 is also movably equipped with a circulating cooling device 6 and a condensing device 7. The circulating cooling device 6 and the condensing device 7 are connected. The circulating cooling device 6 is used to remove the heat generated during the plasma discharge process to control the reaction temperature, and the condensing device 7 is used to condense and recover the gaseous products generated during the plasma discharge process. The circulating cooling device 6 and the condensing device 7 can be conventional equipment in this field.

[0048] The electrolysis reactor 3 includes a glass reaction tank (approximately 1.5L) and a reaction vessel. For example... Figure 11 As shown, an electrolyte was added to the glass reaction vessel, and the degradation of gatifloxacin was carried out using a pulsed DC power supply 1 and the glass reaction vessel. Since a large amount of heat is released into the electrolyte during the experiment, the reaction vessel was placed in a circulating cooling device 6, and a condenser was placed above the reaction vessel to reduce solution evaporation. A 45mm × 5mm pure titanium sheet was used as the cathode 4, and a 5mm × 3mm inert platinum sheet was used as the anode 5. A concentration of 0.05 mol·L⁻¹ was added to the electrolyte. -1 Using KCl as an auxiliary electrolyte allows the conductivity of the electrolyte to reach a similar level.

[0049] The reaction vessel is connected to an OES emission spectrometer 2, which is used to monitor the emission spectrum during the plasma discharge process in real time. Based on this, a method for degrading gatifloxacin in wastewater using cathode micro-arc plasma electrolysis (CMPE) technology is provided, comprising the following steps:

[0050] Wastewater containing gatifloxacin is placed in a glass reaction tank, with a titanium rod as the cathode and a platinum sheet as the anode. A pulsed DC voltage of 320V~360V and a frequency of 150Hz is applied to form a gas film on the surface of the cathode and induce plasma micro-arc discharge. The active substances generated by the discharge degrade the gatifloxacin in the wastewater. The treatment time is 8 minutes to 12 minutes.

[0051] To obtain the specific conditions for the above methods, the following research was conducted: 1. Experimental Procedure In GAT's CMPE processing, the following method is used: Figure 11 The apparatus shown illustrates the process of degrading gatifloxacin in wastewater. Specific parameters are as follows:

[0052] The voltage was maintained within the range of 340V±40V, and the frequency was 150Hz. Ultrapure water was used in all experiments. A titanium rod (50mm long, 5mm in diameter) and a platinum sheet (50mm×25mm) were used as the cathode and anode, respectively, with an electrode spacing of approximately 20mm. Before the degradation experiment, the titanium cathode was polished with 800-grit sandpaper and thoroughly rinsed with ultrapure water.

[0053] The absorbance of the characteristic UV peak of the GAT solution was determined using a UV spectrophotometer (Shengaohua, L5S) at a standard absorption wavelength of 282 nm in 1 nm increments. In addition, the GAT concentration was measured by high-performance liquid chromatography (HPLC, Shimadzu LC-20A; DiamonsilPlus C18 column, 4.6 mm × 250 mm, 5 μm) for mechanistic analysis. The mobile phase consisted of acetonitrile and 0.1% phosphoric acid (80:20 v / v). The pH of the phosphoric acid fraction in the aqueous phase was adjusted to 3.8 with triethylamine. The solution was filtered through a nylon membrane before HPLC analysis. The scan cycle was 20 minutes, and the detection wavelength was 291 nm. To ensure data accuracy, each experiment was performed in triplicate.

[0054] 2. Analytical Methods The time-dependent degradation kinetics of GAT were assessed by monitoring the decrease in GAT concentration over specific time intervals. The experimental data were fitted to the pseudo-first-order kinetic models shown in Equations (1) and (2) to evaluate the degradation kinetic characteristics.

[0055] (1); (2); In the above formula, C 0 and C t The values ​​represent the initial state and the GAT concentration (mg / L) after CMPE treatment, respectively. k app The first-order kinetic rate constant (min) -1 ), t This refers to the degradation treatment time.

[0056] To elucidate the role of active substances in the CMPE process, this invention conducted relevant capture experiments. Quenching experiments were performed using methanol (MeOH), p-benzoquinone (BQ), and ammonium oxalate (AO) to capture •OH, •O₂⁻, and h⁺. Simultaneously, intermediates generated after 4 minutes of treatment were analyzed using liquid chromatography-mass spectrometry (LC-MS, OTOF-QII) to identify key degradation products. The mobile phase was prepared from 0.1% (v / v) aqueous phosphoric acid (pH adjusted to 3.8 with triethylamine) and acetonitrile at an 80:20 (volume ratio) ratio, with a flow rate of 1.0 mL / min. The detection wavelength was set to 291 nm, and the total run time was 20 minutes. The phase composition of the oxide layer on the titanium cathode surface was analyzed using X-ray diffraction (XRD, X'Pert Pro MPD) with Cu Kα radiation (λ=1.5406 Å). Morphological changes on the titanium cathode surface were observed using scanning electron microscopy (SEM, S-4800).

[0057] 3. Ultraviolet-Visible Spectroscopy Analysis The optical behavior of GAT during the degradation of CMPE was investigated using ultraviolet-visible spectroscopy (UV-Vis). The operating conditions for the CMPE process were as follows: initial GAT concentration 100 mg / L, pH 7.8, applied voltage 340 V, and supporting electrolyte 0.05 mol / L KCl. Figure 1 As shown. Specifically, a gatifloxacin solution with an initial concentration of 100 mg·L⁻¹, an initial pH of 7.8, and containing 0.05 mol·L⁻¹ KCl as an auxiliary electrolyte was prepared, placed in an electrolytic reactor, and a voltage of 340 V was applied to both the anode and cathode.

[0058] Figure 1 Figure (a) shows the UV-Vis spectrum of the GAT aqueous solution during a 16-minute treatment cycle. GAT exhibits strong absorption in the 200-400 nm UV-Vis spectrum. The most significant absorption peak appears at 282 nm, corresponding to its visible light absorption characteristics. Changes in this peak intensity can be used to assess the degradation process and determine the degradation efficiency of GAT. Notably, the absorption peak gradually weakens with increasing CMPE treatment time, indicating continuous molecular degradation. After 16 minutes of continuous treatment, the absorbance significantly decreases, indicating that the vast majority of GAT molecules have been effectively decomposed.

[0059] Figure 1 (b) shows the degradation rate calculated based on absorbance at 282 nm. The GAT concentration showed a continuous decreasing trend with increasing treatment time, a phenomenon observed through… Figure 1(a) The UV-Vis spectral data were further validated. Specifically, after 8 minutes and 16 minutes of treatment, the degradation rates reached 72.22% and 90.11%, respectively. The degradation process proceeded rapidly in the initial stage, but slowed down significantly after 6 minutes. Nevertheless, near-complete degradation was achieved at 16 minutes, as evidenced by the near-baseline absorbance in the UV spectrum.

[0060] 4. Effect of initial GAT concentration In this invention, GAT solutions with initial concentrations of 100 mg / L, 200 mg / L, and 300 mg / L were prepared to evaluate their effect on degradation performance. A gatifloxacin solution with an initial pH of 7.8 and containing 0.05 mol·L⁻¹ KCl as an auxiliary electrolyte was prepared, placed in an electrolytic reactor, and a voltage of 340 V was applied to both the anode and cathode.

[0061] The results are as follows Figure 2 As shown in (a), under initial GAT solution concentrations of 200 mg / L and 300 mg / L, the degradation efficiencies after 8 minutes were less than 60% and 40%, respectively. In contrast, 100 mg / L GAT achieved over 90% degradation within 4 minutes and complete removal within 8 minutes. During the CMPE process, •OH and •O2... - The total concentration of active substances remains relatively stable. When the initial concentration of the GAT solution is low, the ratio of active substances to target pollutants is high, which promotes efficient and complete degradation. Conversely, under conditions of high initial GAT solution concentration, the mass of fixed active substances is insufficient to fully react with all pollutant molecules, leading to reduced removal efficiency. Furthermore, the accumulation of intermediate products on the cathode surface can cause electrode fouling, hindering degradation performance.

[0062] A gatifloxacin solution with an initial pH of 7.8 and containing 0.05 mol·L⁻¹ KCl as an auxiliary electrolyte was prepared and placed in an electrolytic reactor, with a voltage of 340 V applied to both the anode and cathode. The results are as follows: Figure 2 As shown in (b), under the conditions of initial GAT solution concentrations of 200 mg / L and 300 mg / L, the first-order kinetic rate constant ( ) increases with increasing initial GAT solution concentration. k app A sharp decrease occurred, within the range of 100 mg / L to 300 mg / L. k app The value is from 0.781 min. -1 It decreased to 0.052 min. -1 This conforms to pseudo-first-order dynamics characteristics.

[0063] 5. Effect of initial pH value The initial pH value is crucial for the degradation of pollutants by the CMPE method, as it affects the formation of active substances and the corresponding degradation process. The experimental conditions were set as follows: GAT concentration 100 mg / L, applied voltage 340 V, and KCl concentration 0.05 mol / L. Specifically, a gatifloxacin solution with an initial concentration of 100 mg·L⁻¹ and containing 0.05 mol·L⁻¹ KCl as an auxiliary electrolyte was prepared, placed in the electrolytic reactor, and a voltage of 340 V was applied to both the anode and cathode. Figure 3 As shown.

[0064] Figure 3 (a) illustrates the degradation efficiency of GAT during the CMPE process at different initial pH values ​​(3, 7.8, and 10). Within the first 6 minutes, the GAT degradation efficiency increased with increasing pH, peaking at pH 10. Under alkaline conditions, OH... - Increased concentration increases the probability of hydroxyl radical (•OH) generation, thereby increasing the •OH concentration per unit volume and accelerating degradation. Conversely, high concentrations of H+ under acidic conditions... + It will promote the removal of •OH (as shown in formula (3)), resulting in a decrease in degradation efficiency.

[0065] H⁺+ •OH+e⁻→H2O (3); In the above formula, H⁺ represents hydrogen ions, •OH represents hydroxyl radicals, e⁻ represents high-energy electrons, and H₂O represents water molecules.

[0066] However, after 6 minutes, the degradation efficiency converged to nearly 100% under all pH conditions. This indicates that CMPE exhibits strong pH tolerance for GAT degradation, with efficiency fluctuations of less than 20% across the entire tested pH range. Furthermore, as... Figure 3 As shown in (b), the first-order kinetic rate constant kapp at pH values ​​of 3, 7.8, and 10 is 0.451 min. -1 0.781min -1 and 0.847min -1 .although k app The value increased slightly with pH, ​​but the change was relatively mild, indicating that the effect of pH on GAT degradation was far less significant than that of the initial GAT concentration. A dynamic equilibrium was formed between free radical generation and consumption in the later stages, explaining the decrease in the dependence of degradation efficiency on initial pH. Considering that actual industrial wastewater is usually weakly alkaline and high degradation performance was observed, pH 7.8 was selected as the representative experimental condition.

[0067] 6. The influence of supporting electrolytes During the CMPE process, the supporting electrolyte enhances conductivity and promotes charge transfer. Therefore, this invention uses a 100 mg / L solution at 340 V and pH 7.8 to evaluate the effects of different electrolytes on GAT degradation. Three electrolytes with comparable conductivity (6668 μS / cm) were selected as supporting electrolytes: KCl, K₂SO₄, and KNO₃.

[0068] Figure 4 (a) illustrates the effect of these electrolytes on GAT removal. The results show that when KCl is used as the supporting electrolyte, complete GAT degradation can be achieved within 6 minutes. In contrast, the degradation efficiency is significantly reduced in the presence of K2SO4 and KNO3, with removal rates still below 40% after 12 minutes.

[0069] Figure 4 (b) Displaying KCl, K2SO4, and KNO3 k app The values ​​were 0.781 min. -1 0.030min -1 and 0.036min -1 KCl k app The value was significantly higher than that of the other two electrolytes. These findings indicate that chloride ions (Cl...)... - KNO3 is crucial for enhancing GAT degradation during the CMPE process. Among them, KNO3 performs slightly better than K2SO4.

[0070] During electrochemical oxidation, hydroxyl radicals (•OH) in the solution can react with various anions (Cl-). - NO3 - and SO4 2- The reaction forms secondary reactive substances. Specifically, Cl⁻ can generate highly reactive chlorides (•Cl, Cl₂, HClO, and ClO₂). - This enhances the oxidative attack on organic pollutants. The formation of Cl2 further promotes the formation of hypochlorous acid (HClO) and hypochlorite ions (ClO₂). - The generation of SO42-(as shown in equations (4) to (6)) accelerates GAT degradation through synergistic chemical and catalytic pathways. Conversely, SO42- 2- The introduction of potassium nitrate reduces the availability of direct reactions between hydroxyl radicals and GAT, as these anions preferentially react with •OH. The resulting sulfate-derived radicals have a lower oxidation potential than hydroxyl radicals, thus reducing the overall degradation efficiency. Furthermore, nitrate ions can partially generate •OH under UV irradiation (Equation (7)), while sulfate ions do not have this pathway. Therefore, potassium nitrate performs slightly better than potassium sulfate in promoting GAT degradation.

[0071] (4); (5); (6); (7); In the above formula, Cl⁻ represents chloride ions, Cl₂ represents chlorine molecules, e⁻ represents electrons, H₂O represents water molecules, HClO represents hypochlorous acid molecules, and H + Represents hydrogen ions, ClO − Represents hypochlorite ion, NO3 − Represents nitrate ions. hν Represents photon energy, NO2 − Represents nitrite ions, OH − • represents hydroxide ions, and •OH represents hydroxyl radicals.

[0072] 7. Effects of applied voltage To investigate the effect of applied voltage on GAT degradation efficiency, this invention selected three voltage levels: 300V, 340V, and 380V. The experimental conditions were set as follows: initial GAT concentration of 100 mg / L, 0.05 mol / L KCl as the supporting electrolyte, and initial pH of 7.8.

[0073] like Figure 5 As shown in (a), the degradation efficiency increases significantly with increasing voltage. In the initial reaction stage, the degradation efficiency shows a rapid growth trend. In particular, after only 2 minutes of treatment, the GAT removal rates under 300V, 340V and 380V conditions reached 51.1%, 71.4% and 85.1%, respectively.

[0074] also, Figure 5 (b) illustrates the degradation kinetics of GAT at different voltages, and all data conform to the pseudo-first-order kinetic model. The first-order kinetic rate constant k is given under conditions of 300V, 340V, and 380V. app 0.546 min respectively -1 0.781min -1 and 0.861min -1 The degradation efficiency was highest at 380V, achieving complete degradation within 6 minutes. However, at 300V, a small amount of GAT remained in the solution after 6 minutes of CMPE treatment. The improved degradation performance at higher voltages can be attributed to enhanced plasma activity: the increased voltage intensifies the vapor-gas film envelope discharge around the titanium cathode. This effect increases the space charge density in the plasma region, thereby promoting the degradation of •OH and •O2. - The formation of key active substances, such as GAT molecules, increases the probability of effective collisions with these species, thereby accelerating the degradation process.

[0075] However, as Figure 5 As shown in (a), the degradation efficiency under all three voltage conditions approached 100% after 6 minutes, and the efficiency differences became negligible. This indicates that increasing the applied voltage no longer provides a significant performance advantage in the later stages of the CMPE process. The fundamental reason is that the plasma discharge stabilizes after 6 minutes, and the generation of active materials under different voltages reaches a dynamic equilibrium. Considering energy consumption, the energy efficiency of GAT degradation within the initial 6 minutes was evaluated. Calculations showed that the energy efficiencies within 6 minutes at 300V, 340V, and 380V were 1.32 g·(kW·h). -1 1.19 g (kW·h) -1 And 1.06 g·(kW·h) -1 .

[0076] The results above suggest that, without affecting degradation performance, a lower voltage setting may be more beneficial for improving energy efficiency.

[0077] 8. COD removal efficiency Chemical oxygen demand (COD) quantifies the amount of oxidant (mg / L) required to oxidize reducible substances in a water sample, and to some extent reflects the degree of mineralization of organic matter by CMPE. The COD of the degraded samples was determined using a digestion system (Sheng Aohua, 6B-12) and a rapid COD analyzer (Sheng Aohua, 6B-200) according to standard methods.

[0078] Figure 6 The results showed a significant correlation between COD and GAT removal efficiency. Figure 5 The trend is consistent—higher voltage improves the removal efficiency of both parameters. After 8 minutes of treatment, the COD removal rates at 300V, 340V, and 380V were 51.1%, 71.4%, and 85.1%, respectively. The results indicate that CMPE treatment possesses strong oxidizing properties and a high capacity for generating active substances.

[0079] GAT degradation at different voltages (see) Figure 5 ) and COD removal (see Figure 6 The results showed that degradation progressed more rapidly in the initial stages (especially the first 2 minutes). Therefore, the average current efficiency (ACE) was evaluated at the 2-minute mark (see [link to citation]). Figure 7The ACE value steadily increases with the applied voltage: 0.168 at 300V, 0.614 at 340V, and further climbs to 1.050 at 380V. The highest ACE value is observed at 380V, indicating that this voltage offers superior current utilization in practical applications. It is noteworthy that the ACE value decreases as the degradation efficiency stabilizes after 6 minutes. Furthermore, excessively high input power may lead to energy waste and increased temperature. Overall, an applied voltage of 340V is considered ideal for this invention, achieving a balance between performance and energy efficiency.

[0080] 9. Active substance capture experiment Oxidation of active substances is considered the main pathway for CMPE-mediated pollutant degradation. This invention uses methanol (MeOH), benzoquinone (BQ), and ammonium oxalate (AO) as •OH and •O2. - and h + The capture agent was used to conduct active substance capture experiments to elucidate its role in the CMPE process. Furthermore, all reagents were at a concentration of 2 mM. Specifically, a gatifloxacin solution with an initial concentration of 100 mg·L⁻¹, an initial pH of 7.8, and containing 0.05 mol·L⁻¹ KCl as an auxiliary electrolyte was prepared, and 2 mM of MeOH, BQ, and AO were added respectively. The solution was placed in an electrolytic reactor, and a voltage of 340 V was applied to both the anode and cathode.

[0081] Figure 8 The results showed that after 6 minutes of adding methanol, benzoquinone, and ammonium oxalate, the GAT degradation efficiency decreased by 6.96%, 32.76%, and 14.63%, respectively. These results indicate that all three species participate in the GAT oxidation process. Specifically, •OH is mainly generated through high-energy electron radiation splitting of water (Equation 8), and secondarily through conversion by •O2 and h⁺ (Equations 9 and 10). Due to its extremely short lifetime in aqueous solution (on the order of nanoseconds), its reactivity is limited to the region near the titanium cathode, thus reducing the probability of bulk reaction with methanol. In contrast, •O2 has a longer lifetime (about 1 second) and a greater diffusion distance, contributing significantly to the overall inhibition effect. The capture experiment provides supporting qualitative evidence for the involvement of the •OH, •O2⁻, and h⁺-related oxidation pathways in MOX oxidation. Furthermore, the interconversion between active substances further complicates the reaction pathway. In addition to the aforementioned free radicals, species such as O3, H2O2, high-energy electrons, and UV-induced photolysis may also participate in the degradation of GAT in CMPE.

[0082] (8); (9); (10); In the above formula, H2O represents a water molecule, •OH represents a hydroxyl radical, and H+ Represents hydrogen ions, e⁻ represents electrons, •O₂⁻ represents superoxide radicals, OH⁻ represents ... − Represents hydroxide ions. h ⁺ represents a hole.

[0083] 10. Degradation pathway of GAT by CMPE To further investigate the oxidation mechanism and identify the intermediates generated during GAT degradation, the solution was analyzed by liquid chromatography-mass spectrometry after CMPE treatment for 4 minutes.

[0084] The degradation samples after CMPE treatment for 4 min were analyzed by liquid chromatography-mass spectrometry (LC-MS, OTOF-QII). The mobile phase was prepared by mixing 0.1% (v / v) aqueous phosphoric acid (adjusted to pH 3.8 with triethylamine) and acetonitrile at a ratio of 80:20 (v / v), with a flow rate of 1.0 mL / min. The detection wavelength was set to 291 nm, and the total run time was 20 min.

[0085] Based on LC-MS spectrum Figure 9 This invention identifies nine core intermediates and proposes three degradation pathways accordingly, such as... Figure 10 As shown. In pathway I, the free radical first attacks GAT, leading to partial cleavage of the piperazine ring to generate P1 (m / z=350). P1 undergoes side-chain oxidative dealkylation and defluorination to give P2 (m / z=291). In pathway II, the degradation of GAT begins with the demethylation of the piperazine ring, forming intermediate P3 (m / z=361). Subsequently, piperidine ring cleavage and fluorine atom hydroxyl substitution occur, generating product P2 (m / z=291). As a common intermediate for both pathways, P2 then loses the cyclopropyl group and carboxyl group from the nitrogen atom of the benzene ring, forming P4 (m / z=207). In pathway III, GAT undergoes N-cyclopropyl fragment cleavage to form P5 (m / z=336). This molecule then undergoes piperidine ring cleavage and decarboxylation to generate P6 (m / z=265). Subsequently, the alkyl group on the nitrogen atom of the P6 molecule is removed, and the fluorine atom is replaced by a hydroxyl group, generating P4 (m / z=207). P4 continues to degrade, with its benzene ring successively losing hydroxyl and amino groups to form P7 (m / z=176). P7 eventually decomposes into smaller organic molecules P8 (m / z=123) and P9 (m / z=85). The final mineralization reaction of these intermediates produces CO2, H2O, and NO. x And various other byproducts. In addition, the high temperature and pressure in the plasma region may trigger local carbonization reactions, leading to the formation of carbonaceous particles.

[0086] The above results indicate that under optimal conditions (100 mg·L⁻¹), -1 GAT, 340V, pH=7.8, 0.5mol·L -1KCl) and CMPE can achieve near-complete removal of gatifloxacin from aqueous solutions within 8 minutes. The mechanism of rapid GAT degradation by CMPE can be attributed to the synergistic mechanism of discharge plasma and electrochemical action: First, during the CMPE degradation process, as the voltage increases, water near the surface of the titanium cathode evaporates due to Joule heating, releasing a large number of bubbles and forming a continuous gas film layer around the titanium cathode. Subsequently, when the voltage continues to rise and tends to stabilize, the gas film breaks down, triggering plasma micro-arc discharge, thereby forming a plasma sheath layer on the cathode surface. Ultraviolet radiation, shock waves, and ultrasonic cavitation effects are generated during the discharge process. Simultaneously, the collision between high-energy particles and liquid molecules promotes the generation of •OH and •O2. - Active substances such as H2O2 and O3 are present. Under the synergistic effect of physical effects such as ultraviolet radiation and shock waves and active chemical substances, antibiotic organic compounds are rapidly degraded.

[0087] It is worth noting that, such as Figure 12 As shown, unlike the common understanding that "anodic oxide film dominates surface reactions" in traditional electrolysis / electrochemical oxidation processes, this invention has also observed the formation of a TiO2 oxide film on the cathode surface in previous studies, and this has been supported by XRD analysis. The basic principle is inferred to be that oxygen-containing free radicals such as ·OH decompose due to collisions in the plasma region, generating O free particles (•OH+). e *→O+•H+ e O combines with Ti particles on the substrate surface that are excited into active particles due to heating, forming oxides (e.g., Ti* + 2O → TiO2). The formation of the oxide film on the cathode surface during CMPD suggests that, under the micro-arc environment of the cathode, the surface oxide layer may not be a mere byproduct, but could potentially act as an active site participating in the discharge process and pollutant conversion. Combined with the discussion in the literature regarding the potential surface catalytic effect of TiO2 films under strong ultraviolet irradiation, it can be inferred that this oxide film may play a role in the generation of active substances, the enhancement of interfacial reactions, or pathway selectivity.

[0088] Recent researchers have explored various methods for the degradation and analysis of gatifloxacin. For example, using a blue TiO2 nanorod array sensitized with gold nanoparticles for photocatalytic degradation achieved a GAT removal efficiency of 95.0% with a reaction rate constant of 0.020 min⁻¹. -1 Its performance was significantly lower than that of the CMPE technology explored in this study (0.546 min at 300V, 340V, and 380V respectively). -1 0.781min -1 and 0.861min -1Wang et al. reported that the MnS / FeAl-MOF / ARM photoelectrocatalytic system exhibits excellent photocatalytic and electrocatalytic performance. Under optimized reaction conditions, a 50 mg / L concentration of GAT (300 mL) achieved a removal rate of 88.4% within 30 minutes. Furthermore, the researchers found that adding ferrate (Fe(VI)) to water under optimal conditions (pH 8.00, Fe(VI) to GAT molar ratio 30:1, 25°C) resulted in a GAT degradation rate of 96.72% within 30 minutes. Compared to these advanced oxidation processes (AOPs), the CMPE system achieves complete GAT degradation in just 8 minutes, demonstrating superior degradation efficiency (see [link to article]). Figure 6 In terms of energy efficiency, the energy consumption range of the electric Fenton process is 1.58 to 5.6 kWh·m³. -3 Ozone treatment, under optimal conditions, yields approximately 0.53 kWh. 3 Studies have shown that the CMPE system has a highly efficient degradation capacity for GAT, with energy efficiency varying from 1.06 to 1.32 g·(kW·h)⁻ over 6 minutes as a function of voltage. -1 Therefore, future applications need to strike a balance between rapid degradation and sustainable energy consumption.

[0089] Compared to traditional advanced oxidation processes, CMPE offers the following advantages: no secondary pollution from catalysts (superior to photocatalysis), lower capital costs than ozone treatment, and less stringent pH control requirements (superior to the Fenton process). Furthermore, the cathode discharge mechanism avoids the electrode corrosion and wear common in anode-dominated NTP systems. Therefore, CMPE shows great potential in treating high-concentration medical wastewater. Future research should focus on three key aspects: discharge stability, energy efficiency, and byproduct toxicity. The findings will determine the ecological compatibility and practical application value of CMPE.

[0090] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. To avoid redundancy, this invention describes preferred embodiments.

[0091] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments, all of which fall within the scope of the invention.

Claims

1. A method for degrading gatifloxacin in wastewater based on cathode micro-arc plasma electrolysis technology, characterized in that, Includes the following steps: Wastewater is placed in an electrolysis reactor with a titanium rod as the cathode and a platinum sheet as the anode. A pulsed DC voltage of 320V~360V and a frequency of 140Hz~160Hz is applied to form a gas film on the surface of the cathode and trigger plasma discharge. The active substances generated by the discharge degrade gatifloxacin in the wastewater. The treatment time is 8 minutes~12 minutes. The wastewater includes wastewater containing gatifloxacin.

2. The method according to claim 1, characterized in that, The initial concentration of the wastewater containing gatifloxacin was 50 mg·L⁻¹. -1 ~150mg·L -1 .

3. The method according to claim 2, characterized in that, The initial pH of the wastewater containing gatifloxacin is 7-9.

4. The method according to claim 1, characterized in that, The electrolytic reactor contains an auxiliary electrolyte with a concentration of 0.04 mol·L⁻¹. -1 ~0.06 mol·L -1 .

5. The method according to claim 4, characterized in that, The auxiliary electrolyte is KCl.

6. The method according to claim 1, characterized in that, The titanium rod is cylindrical, with a length of 40mm to 60mm and a diameter of 4mm to 6mm; the platinum sheet is rectangular, with a length of 40mm to 60mm and a width of 20mm to 30mm.

7. The method according to claim 1, characterized in that, The cathode is first polished and rinsed with 500-1500 grit sandpaper before use.

8. The method according to claim 1, characterized in that, The distance between the cathode and the anode is 15mm to 25mm.

9. The method according to any one of claims 1 to 8, characterized in that, The wastewater also includes wastewater containing fluoroquinolone antibiotics.

10. An apparatus for implementing the method of claim 1, characterized in that, Including the electrolysis reactor (3); The electrolytic reactor (3) is provided with a cathode (4) and an anode (5), which are arranged opposite to each other; the cathode (4) and the anode (5) are connected to a pulse power supply (1), which is used to apply a pulsed DC voltage to form a gas film on the surface of the cathode (4) and trigger plasma discharge; The electrolysis reactor (3) is also movably equipped with a circulating cooling device (6) and a condensing device (7). The circulating cooling device (6) and the condensing device (7) are connected to each other. The circulating cooling device (6) is used to remove the heat generated during the plasma discharge process to control the reaction temperature. The condensing device (7) is used to condense and recover the gaseous products generated during the plasma discharge process. The electrolysis reactor (3) is connected to an OES emission spectrometer (2), which is used to monitor the emission spectrum during the plasma discharge process in real time.

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