Method for treating metronidazole pharmaceutical wastewater

Abstract

The application discloses a treatment method of metronidazole pharmaceutical wastewater. The treatment method comprises the following steps: S1, constructing a pulse electro-Fenton reactor: taking inert electrodes and iron electrodes as anodes, taking an air diffusion electrode as a cathode, and taking metronidazole pharmaceutical wastewater as an electrolyte; and S2, operation: alternately electrifying the inert electrodes and the iron electrodes, and continuously electrifying the cathode to form a pulse current. The treatment method adopts the pulse electro-Fenton technology to treat the metronidazole pharmaceutical wastewater, and through cooperation of various conditions, efficient removal of metronidazole in the metronidazole pharmaceutical wastewater can be realized. In addition, the steps S1 and S2 of the treatment method do not need to additionally add ferrous catalyst, and problems that the traditional Fenton oxidation method needs to additionally add ferrous catalyst and generates a large amount of iron sludge are avoided, and the efficiency of the electro-Fenton oxidation method is improved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a method for treating metronidazole pharmaceutical wastewater. Background Technology

[0002] Metronidazole is a typical nitroimidazole antibiotic commonly used to treat various anaerobic bacterial and parasitic infections. It is also used as an additive in poultry and fish feed and is now widely detected in aquatic environments. Metronidazole has a relatively low molecular weight and high solubility in water, easily penetrating the cell membranes of both aerobic and anaerobic microorganisms. Inside the microbial cells, metronidazole is reduced, and the reduction products damage intermediates in microbial DNA. In the ecological environment, metronidazole is an internationally recognized Group 2B carcinogen. Its chemical structure is stable and difficult to biodegrade. Currently used conventional physicochemical methods such as biological treatment, coagulation sedimentation, and activated carbon adsorption are ineffective in removing metronidazole. Therefore, metronidazole easily enters the aquatic environment, is passed up the food chain, and accumulates in organisms, threatening human health. Developing efficient technologies for degrading metronidazole in wastewater is of great significance.

[0003] Generally speaking, pharmaceutical wastewater is characterized by a complex variety and high concentration of organic pollutants, a large amount of recalcitrant substances, and poor biodegradability. In particular, pharmaceutical wastewater containing antibiotics often exhibits biotoxicity due to the high concentration of residual antibiotics, making traditional biological methods ineffective in treating it. How to efficiently treat antibiotic pharmaceutical wastewater is currently a hot topic and a challenge in the field of pharmaceutical wastewater treatment.

[0004] Currently, commonly used methods for treating antibiotic pharmaceutical wastewater are mainly divided into physicochemical methods, biological methods, and advanced oxidation methods. Physicochemical methods utilize the combined effects of physical processes and chemical reactions to treat wastewater. Common physicochemical methods include adsorption, coagulation, flotation, ion exchange, and membrane separation. Simple physicochemical methods cannot decompose and mineralize antibiotics and are prone to causing secondary pollution. Biological methods refer to the process by which microorganisms use pollutants for their own metabolism, degrading and removing pollutants contained in wastewater during their growth and reproduction. The main treatment methods include activated sludge and anaerobic biological treatment. Biological methods have high requirements for influent, requiring the influent to have a certain degree of biodegradability and contain trace elements necessary for microbial growth. They are not suitable for antibiotic pharmaceutical wastewater with high antibiotic concentrations, high toxicity, and poor biodegradability.

[0005] Advanced oxidation processes (AOPs) refer to the generation of highly oxidizing free radicals through reactions under conditions such as catalysts, light irradiation, and ultrasound. These free radicals react with and decompose organic pollutants, ultimately mineralizing them into harmless inorganic substances, thereby achieving the goal of removing pollutants from wastewater. AOPs are mainly divided into traditional Fenton oxidation, Fenton-like oxidation, ozone oxidation, and photocatalytic oxidation. For example, a Chinese patent entitled "A Heterogeneous Fenton-like Co-Cu Catalyst and Its Preparation Method and Application" utilizes a Fenton-like oxidation method to treat metronidazole. AOPs can mineralize antibiotics and oxidize recalcitrant organic matter in pharmaceutical wastewater into harmless small-molecule inorganic substances, showing great application potential in the treatment of antibiotic pharmaceutical wastewater. However, advanced oxidation methods still face limitations in practical applications: for example, traditional Fenton oxidation requires the addition of reagents such as ferrous sulfate, which not only consumes a large amount of reagents but also poses risks to the subsequent treatment of iron sludge; Fenton-like oxidation methods require the development of new catalysts and are costly; photocatalytic oxidation and ozone oxidation methods not only have high requirements for catalyst performance but are also often limited by light conditions and oxygen concentration in actual operation.

[0006] Therefore, it is of great significance to develop a technology that can efficiently degrade metronidazole in pharmaceutical wastewater and overcome the shortcomings of current advanced oxidation methods.

[0007] In addition to containing metronidazole, metronidazole pharmaceutical wastewater also contains a high level of chemical oxygen demand (COD). If a new technology can be developed that efficiently degrades metronidazole while simultaneously reducing COD, it will be more conducive to the widespread application of this technology. Summary of the Invention

[0008] The primary objective of this invention is to overcome the problems of low removal rates or the need to add ferrous sulfate to treat metronidazole pharmaceutical wastewater using advanced oxidation methods, and to provide a method for treating metronidazole pharmaceutical wastewater.

[0009] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0010] A method for treating metronidazole pharmaceutical wastewater includes the following steps:

[0011] S1. Construct a pulsed electric Fenton reactor: using inert and iron electrodes as anodes, air diffusion electrodes as cathodes, and metronidazole pharmaceutical wastewater as electrolyte;

[0012] S2. Operation: Alternately energize the inert electrode and the iron electrode, while continuously energizing the cathode to form a pulsed current;

[0013] In step S2, the ratio of the single energizing time of the inert electrode to the single energizing time of the iron electrode is 6:(1~3); the single energizing time of the inert electrode is 3~12s; the ratio of the current density passing through the inert electrode once to the current density passing through the iron electrode once is (4~6):1; the current density passing through the inert electrode in step S2 is 19~25mA / cm. 2 .

[0014] There are reports on the efficient degradation of organic matter (such as 1,4-dioxane) using pulsed electro-Fenton technology. However, it is uncertain whether pulsed electro-Fenton technology can efficiently degrade any organic matter. This is because the rate constants of the degradation reactions of hydroxyl radicals with different organic matter vary. This leads to a complex competitive relationship between the degradation reaction, the generation of hydroxyl radicals, and the side reactions of hydroxyl radicals with hydrogen peroxide and ferrous ions, making it difficult to predict whether the organic matter can be efficiently removed.

[0015] Through extensive research, the inventors of this invention have discovered that by employing pulsed Fenton technology and controlling the ratio of single-pass energizing time between the inert and iron electrodes, the single-pass energizing time of the inert electrode, the ratio of current density passing through the inert and iron electrodes, and the current density within a specific range, highly efficient removal of metronidazole from metronidazole pharmaceutical wastewater can be achieved. Specifically, the removal rate of metronidazole is at least 70%, and can reach up to 100%. Simultaneously, this treatment method also has a certain removal effect on the chemical oxygen demand (COD) in metronidazole pharmaceutical wastewater.

[0016] Furthermore, steps S1 and S2 of the processing method of the present invention do not require the addition of ferrous catalyst, which avoids the problem of the traditional Fenton oxidation method requiring the addition of ferrous catalyst and generating a large amount of iron sludge, thus improving the efficiency of the electro-Fenton oxidation method.

[0017] Preferably, before constructing the pulsed electric Fenton reactor in step S1, a step of coagulation and sedimentation of metronidazole pharmaceutical wastewater is also included.

[0018] Coagulation and sedimentation treatment removes most of the suspended solids, ensuring the normal operation of subsequent processes.

[0019] More preferably, the coagulant used for coagulation and sedimentation is at least one of inorganic aluminum salts or iron salts.

[0020] More preferably, the dosage of the coagulant is 100-500 mg per liter of metronidazole pharmaceutical wastewater, and more preferably 200-300 mg.

[0021] Preferably, the cathode includes a first cathode and a second cathode, and the electrodes are arranged in the following order: first cathode, iron electrode, inert electrode and second cathode.

[0022] More preferably, the minimum distance between the first cathode and the iron electrode is 0.5~2cm, the minimum distance between the iron electrode and the inert electrode is 0.1~1cm, and the minimum distance between the inert electrode and the second cathode is 0.5~2cm.

[0023] Inert electrodes commonly used in this field for the electrosynthesis of hydrogen peroxide can be used in this invention.

[0024] Preferably, the inert electrode is a titanium plate, a ruthenium-plated titanium mesh, a platinum electrode, or a graphite electrode.

[0025] Preferably, the iron electrode is a stainless steel mesh, iron sheet, iron mesh, or iron plate.

[0026] Conventional air diffusion electrodes in this field can be used in this invention.

[0027] Preferably, the air diffusion electrode includes a catalyst layer, a stainless steel mesh skeleton, and a diffusion layer, wherein the catalyst layer is carbon black, graphite, or activated carbon; and the diffusion layer is carbon black, graphite, or activated carbon.

[0028] Preferably, the concentration of metronidazole in the metronidazole pharmaceutical wastewater in step S1 is 50~800 mg / L, specifically 50, 100, 200, 400, 600 or 800 mg / L.

[0029] Preferably, the ratio of the single energizing time of the inert electrode to the single energizing time of the iron electrode in step S2 is 6:(1~2).

[0030] Preferably, the single energizing time of the inert electrode in step S2 is 3~6s.

[0031] Preferably, the ratio of the current density passing through the inert electrode once in step S2 to the current density passing through the iron electrode once is (4~4.4):1.

[0032] Preferably, the current density through the inert electrode in step S2 is 20~22 mA / cm². 2 .

[0033] Preferably, the running time in step S2 is 60~90 minutes.

[0034] Preferably, in step S2, the electrolyte is circulated in and out of the pulsed Fenton reactor.

[0035] Preferably, the treatment method further includes step S3. Using metronidazole pharmaceutical wastewater as the anolyte and catholyte, a dual-chamber electric Fenton reactor is constructed; the dual-chamber electric Fenton reactor is operated to generate hydrogen peroxide; then the effluent from the cathode chamber, the effluent from the anode chamber, and the effluent after step S2 are mixed to obtain a mixed solution, and then a ferrous catalyst is added to carry out the Fenton reaction.

[0036] The treatment method of the present invention is further combined with (conventional) electro-Fenton technology, which can more significantly remove chemical oxygen demand (COD) from metronidazole pharmaceutical wastewater. Specifically, the COD removal rate reaches more than 80%, and the COD content in the effluent is less than 50 mg / L. Moreover, compared with conventional electro-Fenton technology, this method requires less ferrous catalyst reagent, reducing reagent usage and the generation of iron sludge.

[0037] Typically, the pH of the mixture is adjusted before adding the ferrous catalyst. The pH is usually adjusted to 2-3, as this pH range is more conducive to the Fenton reaction.

[0038] More preferably, the volume ratio of the water effluent from the cathode chamber, the water effluent from the anode chamber, and the water effluent after step S2 is (1 ~ 5):(1 ~ 2):(1 ~ 2).

[0039] More preferably, the current density of the cathode during operation is 10~30 mA / cm². 2 The running time should be no less than 30 minutes.

[0040] More preferably, the dual-chamber electro-Fenton reactor includes two cathode chambers, an air chamber, two anode chambers, a cathode disposed in the cathode chamber, an anode disposed in the anode chamber, a cation exchange membrane, and a power source.

[0041] More preferably, the anode is an inert electrode; the inert electrode is a titanium plate, a ruthenium-plated titanium mesh, a platinum electrode, or a graphite electrode.

[0042] More preferably, the cathode is an air diffusion electrode; the air diffusion electrode includes a catalyst layer, a stainless steel mesh skeleton and a diffusion layer, wherein the catalyst layer is carbon black, graphite or activated carbon; and the diffusion layer is carbon black, graphite or activated carbon.

[0043] More preferably, in the dual-chamber electric Fenton reactor, the chambers are arranged in the following order: anode chamber, cathode chamber, air chamber, cathode chamber, and anode chamber.

[0044] More preferably, the distance between the cathode and the adjacent cation exchange membrane is 0.3~1.0 cm; the distance between the anode and the adjacent cation exchange membrane is 0.5~2.5 cm; and the distance between the two cathodes is 0.5~2.5 cm.

[0045] More preferably, the air chamber is circulated with air using an air pump, and the air flow rate is 0.5~1.5 L / min.

[0046] More preferably, the molar ratio of ferrous ions in the added ferrous catalyst to hydrogen peroxide in the mixture is 1:(6~8).

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] The treatment method of this invention uses pulsed electric Fenton technology to treat metronidazole pharmaceutical wastewater. By combining various conditions, the efficient removal of metronidazole from the metronidazole pharmaceutical wastewater can be achieved.

[0049] Furthermore, steps S1 and S2 of the processing method of the present invention do not require the addition of ferrous catalyst, which avoids the problem of the traditional Fenton oxidation method requiring the addition of ferrous catalyst and generating a large amount of iron sludge, thus improving the efficiency of the electro-Fenton oxidation method. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the structure of the single-chamber pulsed electric Fenton reactor in Example 1.

[0051] Figure 2 The image shows the removal rate of metronidazole and chemical oxygen demand (COD) over time in the treatment of metronidazole pharmaceutical wastewater using the treatment method described in Example 1.

[0052] Figure 3 Example 2 investigates the metronidazole removal rate-time curve (a) and total iron concentration-time curve (b) under different pulse time ratios.

[0053] Figure 4 Example 2 explores the metronidazole removal rate-time curves under different switching frequency ratios.

[0054] Figure 5 Example 2 explores the metronidazole removal rate-time curves under different current densities.

[0055] Figure 6 Example 2 illustrates the metronidazole removal rate-time curves at different initial metronidazole concentrations.

[0056] Figure 7 This is a schematic diagram of the structure of the dual-chamber electric Fenton reactor in Example 3.

[0057] Figure 8 The chemical oxygen demand (COD) removal rate-time curves are shown for the treatment of metronidazole pharmaceutical wastewater using the methods in Examples 3 and 4, respectively.

[0058] Figure 9Metronidazole removal rate-time curve (a) and chemical oxygen demand removal rate-time curve (b) are provided for the treatment method of metronidazole pharmaceutical wastewater provided in Comparative Example 1. Detailed Implementation

[0059] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0060] Example 1

[0061] This embodiment describes a method for treating metronidazole pharmaceutical wastewater, comprising the following steps:

[0062] 1) Add 300 mg of polyaluminum chloride (PAC) as a coagulant to 1000 mL of metronidazole pharmaceutical wastewater, stir rapidly for 5 min, then let it stand for 60 min to settle, and take the supernatant effluent to complete the pretreatment.

[0063] 2) Construct a single-chamber pulsed electric Fenton reactor: such as Figure 1 As shown, the single-chamber pulsed Fenton reactor includes two cathodes, an inert electrode, an iron electrode, a relay, and a DC power supply; the electrodes are arranged in the following order: cathode, inert electrode, iron electrode, and cathode. The electrolyte is the metronidazole pharmaceutical wastewater after pretreatment in step 1 (metronidazole concentration approximately 200 mg / L, chemical oxygen demand approximately 620 mg / L). From right to left, the distance between the right-hand cathode and the iron electrode is 1.0 cm, the distance between the iron electrode and the inert electrode is 0.5 cm, and the distance between the inert electrode and the left-hand cathode is 1.0 cm.

[0064] The outer frame of the single-chamber pulsed Fenton reactor is primarily constructed of silicone gaskets and plexiglass. Titanium wires connect the electrodes to a DC power supply and a relay, which controls the pulsed energizing of different electrodes (inert and iron electrodes). Both cathodes are air-diffusion electrodes, comprising a catalyst layer and a diffusion layer. Both the catalyst and diffusion layers are made of carbon black, rolled onto a stainless steel mesh to form the air-diffusion electrodes. The two cathodes are located at opposite ends of the reactor, with the diffusion layer facing outwards in direct contact with the air, and the catalyst layer facing inwards in contact with the electrolyte. The inert electrode is a ruthenium-plated titanium mesh. The iron electrode is an iron sheet. The volume of the single-chamber pulsed Fenton reactor is approximately 14 mL, and the effective area (one side) of each electrode is approximately 7 cm². 2 .

[0065] 3) Operation of a single-chamber pulsed Fenton reactor: The electrolyte is circulated with water, the circulation pump flow rate is set to 10 mL / min, and the electrolyte volume is 100 mL; the pulse energizing time ratio of the inert electrode to the iron electrode is 6:1, the single energizing time of the inert electrode is 6 s, and the current density applied to the inert electrode and the iron electrode is 20 mA / cm². 2 and 5 mA / cm 2 Run for 60 minutes.

[0066] like Figure 2 As shown, after treatment using the method described in this embodiment, the removal rate of metronidazole in the metronidazole pharmaceutical wastewater can reach 98.9%, achieving a highly efficient removal effect. Furthermore, the removal rate of chemical oxygen demand (COD) is approximately 55%.

[0067] Example 2: Investigation of Operating Conditions of Pulsed Electrical Fenton

[0068] This embodiment investigates the effects of pulse-time ratio, switching frequency, current density, and initial metronidazole concentration on the removal efficiency of metronidazole from pharmaceutical wastewater using a single-compartment pulsed electro-Fenton method. To avoid interference from other substances in actual pharmaceutical wastewater, this embodiment uses a self-made simulated metronidazole wastewater: metronidazole was dissolved in a 0.1 mol / L sodium sulfate solution to prepare simulated metronidazole wastewater with initial concentrations of 400, 200, and 50 mg / L, respectively.

[0069] 2.1 Pulse Time Ratio

[0070] The initial concentration of the simulated metronidazole wastewater was 200 mg / L. The pulse energizing time ratios of the inert electrode and the iron electrode were set to 6:9, 6:7, 6:5, 6:3, 6:2, 6:1.5, and 6:1, respectively. The running time was 90 min, and other conditions were the same as in steps 2) and 3) of Example 1. The metronidazole removal efficiency and the amount of iron sludge generated within 90 min were compared, and the results are as follows: Figure 3 As shown. From Figure 3 It can be seen that when the pulse time ratio is 6:(1~3), the metronidazole removal rate reaches a high level, while the amount of iron sludge generated is also low; further controlling the pulse time ratio to 6:(1~2) results in an even higher metronidazole removal rate and even less iron sludge generation. If the pulse time ratio is not properly adjusted (e.g., 6:5), the metronidazole removal rate will be poor.

[0071] 2.2 Switching Frequency

[0072] The initial concentration of the simulated metronidazole wastewater was 200 mg / L. The single-pass energizing times for the inert electrode were set to 12 s, 6 s, 3 s, 1.2 s, and 0.6 s (correspondingly, the single-pass energizing times for the iron electrode were 2 s, 1 s, 0.5 s, 0.2 s, and 0.1 s; other conditions were the same as in steps 2) and 3) of Example 1). The metronidazole removal efficiency within 60 min was compared, and the results are as follows: Figure 4 As shown. From Figure 4 It can be seen that when the pulse time ratio is 6:1, the metronidazole removal rate reaches a relatively high level when the single energizing time of the inert electrode is 3-12 seconds; further adjustment to 3-6 seconds results in an even higher metronidazole removal rate. If the single energizing time of the inert electrode is inappropriate, such as 0.6 seconds, the metronidazole removal rate will be low.

[0073] 2.3 Current density

[0074] The initial concentration of the simulated metronidazole wastewater used was 200 mg / L, and the current densities applied to the inert electrodes were set to 15, 20, and 25 mA / cm². 2 The running time was 90 min, and other conditions were the same as steps 2) and 3) of Example 1 (equivalent to current density ratios of 3:1, 4:1, and 5:1 for the inert and iron electrodes). The metronidazole removal efficiency was compared within 90 min, and the results are as follows: Figure 5 As shown. From Figure 5 It can be seen that when the current density of the inert electrode is 20~25 mA / cm² 2 At a current density ratio of 4~5:1 (equivalent to an inert electrode to an iron electrode), the metronidazole removal rate reached a relatively high level; further adjustment to 20~22 mA / cm² was achieved. 2 Metronidazole removal rate is higher. However, if the current density of the inert electrode is not properly controlled, such as 15 mA / cm², the removal rate will be higher. 2 If the removal rate of metronidazole is poor, then the removal rate of metronidazole will be poor.

[0075] 2.4 Initial concentration of metronidazole

[0076] The initial concentrations of the simulated metronidazole wastewater used were 400, 200, and 50 mg / L. The running time was until a high removal rate of metronidazole was achieved, and other conditions were the same as in steps 2) and 3) of Example 1. The results are as follows: Figure 6 As shown. From Figure 6 It can be seen that the simulated metronidazole artificial wastewater with different shock loads (different initial concentrations) has a good treatment effect, and the treatment efficiency increases as the metronidazole concentration decreases, while the treatment time also decreases.

[0077] Example 3

[0078] This embodiment describes a method for treating metronidazole pharmaceutical wastewater. Based on Embodiment 1, this embodiment further includes steps 4) to 6):

[0079] 4) Construct a dual-chamber electro-Fenton reactor: such as Figure 7 As shown, the dual-chamber Fenton reactor includes two cathode chambers, an air chamber, two anode chambers, two cathodes in the cathode chambers, two anodes in the anode chambers, a cation exchange membrane, and a DC power supply. The chambers are arranged in the following order: anode chamber, cathode chamber, air chamber, cathode chamber, and anode chamber. The catholyte in the cathode chambers and the anolyte in the anode chambers are both metronidazole pharmaceutical wastewater after pretreatment in step 1). The distance between the cathode and the adjacent cation exchange membrane is 0.5 cm. The distance between the anode and the adjacent cation exchange membrane is 0.5 cm. The distance between the two cathodes is 0.5 cm.

[0080] The outer frame of the cathode and air chambers in the dual-chamber Fenton reactor is primarily made of silicone gaskets, while the anode chamber is a glass container. Titanium wires connect the electrodes to the DC power supply. The cation exchange membrane is a commercially available polyethylene heterogeneous ion exchange membrane. The cathode composition is the same as that of the single-chamber pulsed Fenton reactor. The anode is a ruthenium-plated titanium mesh. Each cathode chamber has a volume of approximately 70 mL. The effective area of ​​each cathode is 70 cm². 2 Each anode chamber has a volume of approximately 300 mL, and the effective area of ​​each anode is 36 cm². 2 .

[0081] 5) Operation: A peristaltic pump is used to circulate the catholyte at a flow rate of 10 mL / min, with a catholyte volume of 100 mL. An air pump is used to ventilate the air chamber at an air flow rate of 0.5 L / min. The anolyte volume is 300 mL. The applied current density to each cathode is 20 mA / cm². 2 The running time is 30 minutes. This step is to generate hydrogen peroxide in the cathode chamber for use in the subsequent Fenton reaction.

[0082] 6) Fenton treatment: The effluent from the cathode chamber after 30 minutes of operation in step 5), the effluent from the anode chamber, and the effluent from 60 minutes of operation in step 3) are mixed in a 1:1:1 ratio. After mixing, the pH is adjusted to approximately 2.50 using hydrochloric acid to obtain a mixed solution. Ferrous sulfate is then added to the mixed solution, with a molar ratio of ferrous ions in ferrous sulfate to hydrogen peroxide in the mixed solution of 1:8, to initiate the Fenton reaction for 30 minutes.

[0083] Example 4

[0084] This embodiment describes a method for treating metronidazole pharmaceutical wastewater, which differs from Embodiment 3 in that:

[0085] In step 6), the effluent from the cathode chamber after running for 30 minutes in step 5), the effluent from the anode chamber, and the effluent from running for 60 minutes in step 3 are mixed in a ratio of 2:1:1.

[0086] Examples 3 and 4, in addition to effectively removing metronidazole, also effectively removed chemical oxygen demand (COD). Specifically, the COD removal rate during the Fenton treatment in step 6) is as follows: Figure 8 As shown. From Figure 8 It can be seen that 85% and 89% of the chemical oxygen demand (COD) were removed under the two different mixing ratios, and the COD content in the effluent was below 30 mg / L. Among these, Figure 8 The process of calculating the removal rate is as follows: Divide the remaining chemical oxygen demand in the system at a certain time point in step 6) by the total chemical oxygen demand of the metronidazole pharmaceutical wastewater after the pretreatment in step 1) of the whole treatment method to obtain the chemical oxygen demand non-removal rate. Then subtract the chemical oxygen demand non-removal rate from 1 to get the result.

[0087] Comparative Example 1

[0088] This comparative example provides a method for treating metronidazole pharmaceutical wastewater, including the following steps:

[0089] 1) Pre-treat the metronidazole pharmaceutical wastewater according to step 1) of Example 3.

[0090] 2) Construct a dual-chamber electric Fenton reactor according to step 4) of Example 3.

[0091] 3) Run the dual-chamber electric Fenton reactor according to step 5 of Example 3.

[0092] 4) Fenton Treatment: The effluent from the cathode chamber and the effluent from the anode chamber after 30 minutes of operation in step 3) of this comparative example, along with the pretreated metronidazole pharmaceutical wastewater from step 1), were mixed in ratios of 3:1:1, 4:1:1, 5:1:1, 6:1:1, and 5:1:3 to obtain a mixed solution with a pH of 2-3. Ferrous sulfate was then added, with a molar ratio of ferrous ions in the ferrous sulfate solution to hydrogen peroxide in the mixed solution of 1:2, to conduct a Fenton reaction. The removal efficiency of metronidazole and chemical oxygen demand was tested within 60 minutes.

[0093] The results are as follows Figure 9 As shown. From Figure 9It can be seen that, compared with Example 1, this comparative example can also remove metronidazole well, but this comparative example requires the external addition of ferrous sulfate, which consumes a large amount of iron and produces a large amount of iron sludge. Compared with Examples 3 and 4, the amount of Fenton's reagent used in step 4) of this comparative example is more (the amount of hydrogen peroxide and ferrous catalyst added in Comparative Example 1 is more, while the amount of ferrous catalyst used in Examples 3 and 4 is reduced by about 70% compared with Comparative Example 1), but the removal of chemical oxygen demand is about 57-60%, which is significantly lower; compared with Examples 3 and 4, the chemical oxygen demand in the effluent of this comparative example is still about 248 mg / L, which is significantly higher.

[0094] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for treating metronidazole pharmaceutical wastewater, characterized by, It comprises the following steps: S1. Constructing a pulse electro-Fenton reactor: taking inert electrode and iron electrode as anode, taking air diffusion electrode as cathode, and taking metronidazole pharmaceutical wastewater as electrolyte; S2. Running: alternately electrifying inert electrode and iron electrode, continuously electrifying cathode to form pulse current; The ratio of the single energizing time of the inert electrode to the single energizing time of the iron electrode in step S2 is 6:(1-3); the single energizing time of the inert electrode is 3-12 s; the ratio of the current density of single pass through the inert electrode to the current density of single pass through the iron electrode is (4-5):1; the current density of step S2 through the inert electrode is 19-25 mA / cm 2 ; S3. Taking metronidazole pharmaceutical wastewater as anode liquid and cathode liquid to construct a double-chamber electro-Fenton reactor; running the double-chamber electro-Fenton reactor to produce hydrogen peroxide, then mixing the cathode chamber effluent, anode chamber effluent and effluent after running of step S2 to obtain a mixed liquid, and adding ferrous catalyst to perform Fenton reaction; The volume ratio of the cathode chamber effluent, anode chamber effluent and effluent after running of step S2 is (1-2):1:

1.

2. The process according to claim 1, characterized in that, Before step S1, the metronidazole pharmaceutical wastewater is subjected to a coagulation and sedimentation step.

3. The method of claim 1, wherein, The cathode of step S1 comprises a first cathode and a second cathode; the electrodes of the pulse electro-Fenton reactor are arranged in the order of first cathode, iron electrode, inert electrode and second cathode.

4. The process of claim 3 wherein, The minimum distance between the first cathode and iron electrode is 0.5-2 cm, the minimum distance between the iron electrode and inert electrode is 0.1-1 cm, and the minimum distance between the inert electrode and second cathode is 0.5-2 cm.

5. The method of claim 1 wherein, The concentration of metronidazole in the metronidazole pharmaceutical wastewater of step S1 is 50-800 mg / L.

6. The process of claim 1 wherein, Step S2 is performed at a current density of 20 to 22 mA / cm 2 .

7. The method of claim 1 wherein, The running time of step S2 is 60-90 min.

8. The method of claim 1 wherein, The current density of the cathode when the double-chamber electro-Fenton reactor is running is 10-30 mA / cm 2 , and the running time is not less than 30 min.

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