An air diffusion cathode carrying a CoFe2O4-N modified biochar catalyst, a self-driven bioelectric Fenton system, and its applications.

Abstract

The application discloses an air diffusion cathode carrying a CoFe2O4-N modified biochar catalyst, a self-driven bio-electro-Fenton system and application, and belongs to the technical field of wastewater treatment. The air diffusion cathode is provided with an air diffusion layer with water-proof and air-permeable properties on one side of a conductive base, and is provided with a CoFe2O4-N modified biochar catalyst on the other side. The self-driven bio-electro-Fenton system adopts the air diffusion cathode loaded with a high-catalytic-activity heterogeneous iron-based catalyst, realizes self-diffusion supply of oxygen and in-situ generation of hydrogen peroxide, completely gets rid of the dependence on external mechanical aeration and chemical agents, and solves the problems of high energy consumption and high cost of the traditional process. The system is a deep mineralization treatment system with low carbon, low energy consumption and impact resistance, and has important application prospects in wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to an air diffusion cathode carrying a CoFe2O4-N modified biochar catalyst, a self-driven bioelectric Fenton system, and its applications. Background Technology

[0002] Industrial wastewater often contains high concentrations of persistent organic compounds, characterized by high chemical oxygen demand (COD), strong biotoxicity, and poor biodegradability. Some of these persistent organic compounds can remain in the environment for a long time, interfering with the normal function of aquatic ecosystems and being transferred along the food chain through bioaccumulation, ultimately threatening human health.

[0003] Wastewater, while containing pollutants, is also a potential resource carrier. The chemical energy inherent in the high concentration of organic matter in wastewater has a theoretical energy value far exceeding the energy consumed in traditional water treatment processes. Efficient recovery and utilization of this energy holds promise for achieving energy self-sufficiency or even net energy output in the treatment process. The Bio-Electro-Fenton system (BEF) is a process that combines a bioelectrochemical system with Fenton technology. In the BEF system, anolytical electroactive microorganisms consume electrons generated from the organic matter in the wastewater, which are then transferred to the cathode via an external circuit to drive the electro-Fenton reaction and generate hydroxyl radicals that degrade pollutants. The cathode catalytic material directly affects the oxygen reduction reaction and the Fenton reaction process. The electrode material often needs to have high catalytic activity to continuously and stably reduce more oxygen through two electrons to generate hydrogen peroxide, and catalyze the reaction of hydrogen peroxide with Fe. 2+ The reaction produces ·OH, which effectively degrades organic pollutants. Therefore, selecting a suitable cathode catalytic material is crucial. Furthermore, exogenous Fe... 2+ The addition of oxygen and the aeration required for oxygen supply both increase the operating cost of the system.

[0004] For the removal of recalcitrant organic matter, traditional bio-electro-Fenton systems only focus on the cathodic electro-Fenton reaction. While electro-Fenton breaks down large molecules into smaller ones, the mineralization rate is limited, requiring further treatment of the wastewater. It's worth noting that the cathodic electro-Fenton reaction helps improve the biodegradability of wastewater, enabling further deep treatment through biological processes. The anode not only acts as an electron donor for the cathodic reaction, but its microbial activity also contributes to the complete mineralization of organic matter. Therefore, comprehensively utilizing the cathodic electro-Fenton reaction and anode microbial activity to improve the mineralization rate is beneficial for the efficient removal of recalcitrant organic matter. Furthermore, the chemical oxygen demand (COD) and toxicity of actual industrial wastewater often fluctuate dramatically. Existing reactors mostly employ a fixed, integrated chamber design, making it impossible to dynamically adjust the hydraulic retention time (HRT) of the cathode and anode according to changes in influent load. This rigid structure makes the system prone to collapse under high-concentration load shocks and wastes resources under low loads, lacking a synergistic control strategy for in-depth process optimization based on actual water quality. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide an air diffusion cathode carrying a CoFe2O4-N modified biochar catalyst, a self-driven bioelectric Fenton system, and its applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An air diffusion cathode carrying a CoFe2O4-N modified biochar catalyst, wherein the air diffusion cathode has an air diffusion layer with waterproof and breathable properties on one side of a conductive substrate, and the CoFe2O4-N modified biochar catalyst is disposed on the other side.

[0007] Based on the above scheme, the conductive substrate is any one of carbon cloth, titanium mesh and stainless steel mesh; the air diffusion cathode is prepared by rolling, coating or impregnation-drying method.

[0008] Based on the above scheme, the preparation method of the CoFe2O4-N modified biochar catalyst is as follows: (1) Mix ferrous sulfate heptahydrate, cobalt nitrate hexahydrate, urea and seaweed powder in a mass ratio of 1:1:2:1, add to deionized water, and continuously stir at room temperature to complete the impregnation. Then dry the resulting mixture at 80°C and grind it to obtain the precursor powder. (2) The precursor powder obtained in step (1) is heated to 600°C at a heating rate of 10°C / min under a continuous N2 atmosphere and kept at a constant temperature for 2 hours for pyrolysis. (3) After cooling the pyrolysis product of step (2), rinse it with deionized water until the pH of the eluent reaches neutral, dry it under vacuum at 60°C and grind it to obtain the CoFe2O4-N modified biochar catalyst.

[0009] A self-powered bioelectric Fenton system, the system comprising: a cathode reaction system 1 and an anode reaction system 2 stacked vertically; The cathode reaction system 1 includes a cathode housing 1-1, an air diffusion cathode 1-2 disposed on the top of the cathode housing 1-1, and a plurality of parallel perforated plates 1-3 disposed inside the cathode housing 1-1. The air diffusion cathode 1-2 is the aforementioned air diffusion cathode carrying a CoFe2O4-N modified biochar catalyst. The anode reaction system 2 includes an anode box 2-1 and several vertically arranged partitions 2-2; the partitions 2-2 divide the anode box 2-1 into several anode reaction compartments 2-3; the anode reaction compartments 2-3 are filled with a three-dimensional porous conductive material with attached electroactive microorganisms; the three-dimensional porous conductive material with attached electroactive microorganisms is disposed on a current collector 2-4; The cathode reaction system 1 and the anode reaction system 2 are separated by an ion exchange membrane 5; A water pipe 4 is provided between the cathode reaction system 1 and the anode reaction system 2. One end of the water pipe 4 is connected to the bottom of the cathode reaction system 1, and the other end is connected to the bottom of the anode reaction compartment 2-3 through a water distribution head. An external circuit system 6 is provided between the cathode reaction system 1 and the anode reaction system 2. The external circuit system 6 includes a wire 6-1, a resistor 6-2 connected to the wire, and a data acquisition system 6-3. One end of the wire 6-1 is connected to the air diffusion cathode 1-2, and the other end is connected to the current collector 2-4.

[0010] Based on the above scheme, one side of the cathode reaction system 1 is connected to a water inlet pipe, one end of the water inlet pipe is connected to the water inlet tank 3, and the other end is connected to the water outlet. The water outlet extends into the cathode box 1-1 and the outlet of the water outlet is opened at the upper part of the perforated plate 1-3. An overflow weir 2-11 is provided on the top of the anode box 2-1, and the outlet surface of the overflow weir 2-11 is higher than the bottom surface of the ion exchange membrane 5. The water pipe 4 is also connected to a carbon source addition tank 7.

[0011] Based on the above scheme, the partition 2-2 is made of an insulating and corrosion-resistant material; The current collectors 2-4 are titanium mesh, stainless steel mesh, graphite rods, or graphite plates. The three-dimensional porous conductive material is granular activated carbon, graphite felt block, or foamed carbon. The carbon source addition tank 7 contains a pre-prepared mixture of carbon source and trace elements to provide carbon source and trace elements for anodic electroactive microorganisms.

[0012] The above-mentioned self-driven bioelectric Fenton system is applied in wastewater treatment.

[0013] A method for treating wastewater using the aforementioned self-powered bioelectric Fenton system comprises the following steps: S1. Wastewater in the inlet tank 3 is fed into the cathode reaction system 1 through the inlet pipe; the air diffusion cathode 1-2 uses electrons from the anode reaction system 2 to carry out an electro-Fenton reaction on the side coated with CoFe2O4-N modified biochar catalyst. S2. After being treated by the electro-Fenton process of the cathode reaction system 1, the wastewater is injected into the anode reaction system 2 through the water pipe 4. The wastewater flows from bottom to top through the anode reaction compartment 2-3. The anode microorganisms use the organic matter in the cathode effluent to generate electrons. The electrons are transferred to the air diffusion cathode 1-2 through the external circuit system 6. S3. The cations generated in the anode reaction system 2 are driven by the electric field to penetrate the ion exchange membrane 5 and enter the cathode reaction system 1; S4. The wastewater treated by the anode reaction system 2 is continuously pushed upward to the top and discharged through the overflow weir 2-11.

[0014] Based on the above scheme, before the initial wastewater treatment, a micro-ecological step is also included to establish the anode reaction system 2: Wastewater from the inlet tank 3 is fed into the cathode reaction system 1 through the inlet pipe. Under the continuous drive of the pump, the wastewater fills the cathode box 1-1. The carbon source addition tank 7 is started, and the mixture of carbon source and trace elements in it is pumped into the anode reaction system 2 through the water pipe 4. When the data acquisition system 6-3 detects that the output voltage has reached a stable maximum value, it indicates that the electroactive biofilm has matured.

[0015] Based on the above scheme, the regulation mode of the self-driven bioelectric Fenton system is either standard synergistic mode or shock-resistant / high-load mode. The standard collaborative mode is as follows: the volume of the cathode reaction system 1 is the same as that of a single anode reaction compartment 2-3; one anode reaction compartment 2-3 is opened; the hydraulic residence time of the cathode reaction system 1 is kept consistent with the hydraulic residence time of the anode reaction system 2, and the water is gradually increased from slow water intake to the volume of water to be treated; The anti-impact / high-load mode is as follows: when the influent COD is detected to be more than 50% higher than the normal value, the effluent COD removal rate after treatment using the standard collaborative mode is more than 20% lower than the normal value, or the voltage value collected by the external circuit system 6 drops below 0.3V, at least one of the following control operations is executed: a) Simultaneously reduce the opening of the inlet valves of cathode reaction system 1 and anode reaction system 2 to increase the hydraulic residence time; b) Open the additional anode reaction compartments 2-3 in the anode reaction system 2 until all anode reaction compartments 2-3 are open to increase the hydraulic residence time of the anode reaction system; c) Start the carbon source addition tank 7 and inject the carbon source and trace element mixture into the anode reaction system 2.

[0016] Advantages of the technical solution of this invention This invention's self-driven bioelectric Fenton system utilizes an air diffusion cathode loaded with a highly catalytically active heterogeneous iron-based catalyst to achieve self-diffusion oxygen supply and in-situ hydrogen peroxide generation, completely eliminating reliance on external mechanical aeration and chemical reagents, thus solving the problems of high energy consumption and high cost associated with traditional processes. Breaking through the structural limitations of existing reactors, it innovatively recycles the water degraded by the cathode reaction system to the anode electrogenic microorganisms for use, generating electrons to supply the cathode Fenton circuit, achieving self-drive for the entire system. In its design, the anode chamber features a vertical multi-chamber partitioning, and valve control enables dynamic allocation and process optimization of the anode and cathode hydraulic retention times based on the influent COD concentration, allowing the two reaction systems to efficiently synergize at optimal hydraulic retention times. Internal water circulation is achieved through gravity, while the efficient coupling of strong oxidation pretreatment at the cathode and deep biological degradation at the anode achieves energy self-sufficiency, ultimately forming a low-carbon, low-energy, and shock-resistant deep mineralization treatment system for complex organic wastewater, demonstrating significant application prospects in wastewater treatment. Attached Figure Description

[0017] Figure 1 SEM images of the cathode electrode material; Figure 2 TEM and EDS images of the cathode electrode material; Figure 3 XRD images of the cathode material; Figure 4 The COD removal efficiency of a CoFe2O4-N modified biochar catalyst air cathode bioelectric Fenton system at different times; Figure 5 Schematic diagram of a self-driven bioelectric Fenton system; Figure 6 Results of treating wastewater with initial COD of approximately 400 mg / L and 600 mg / L using the standard co-processing mode; Figure 7 A graph showing the results of treating wastewater with an initial COD of approximately 2000 mg / L; Figure 8 A graph showing the results of treating wastewater with an initial COD of approximately 2500 mg / L; Figure 9 The figure shows the results of treating wastewater with an initial COD of approximately 2500 mg / L by controlling the addition of carbon sources. Detailed Implementation

[0018] The terminology used in this invention, unless otherwise specified, generally has the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and are not intended to limit the scope of the invention in any way.

[0019] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the experimental materials, reagents, and chemicals used in the following embodiments can be obtained through general channels.

[0020] The seaweed powder in the following examples was obtained from seaweed grown on Jinshatan Beach in Qingdao City, Shandong Province. After being washed in deionized water, it was dried in an oven at 80°C for 2 hours, ground into powder, and passed through a 200-mesh sieve for later use.

[0021] Example 1

[0022] An air diffusion cathode carrying a CoFe2O4-N modified biochar catalyst, wherein the cathode is based on carbon cloth, titanium mesh or stainless steel mesh, and an air diffusion layer with waterproof and breathable properties is provided on one side of the substrate, and the CoFe2O4-N modified biochar catalyst is provided on the other side.

[0023] Preparation of biochar materials by impregnation pyrolysis: (1) Ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt nitrate hexahydrate (CoNO3·6H2O), urea (CH4N2O) and seaweed powder were mixed in a mass ratio of 1:1:2:1 and added to 100mL of deionized water. The mixture was stirred continuously at room temperature for 24h to complete the impregnation. The resulting mixture was then placed in an oven at 80℃ for drying and ground to obtain the precursor powder.

[0024] (2) Place the precursor powder obtained in step (1) into an alumina crucible, transfer it into a tube furnace, and heat it to 600°C at a heating rate of 10°C / min under a continuous N2 atmosphere, and keep it at a constant temperature for 2 hours.

[0025] (3) After cooling the pyrolysis product of step (2), rinse it with deionized water until the pH of the eluent reaches neutral. Then dry and grind it in a vacuum drying oven at 60°C to obtain the CoFe2O4-N modified biochar catalyst (Fe / Co / N / EC).

[0026] Taking carbon cloth as an example, an air diffusion cathode is prepared by coating method, and the specific method is as follows: (1) The cut carbon cloth was soaked in acetone (analytical grade) for 2 hours, washed with deionized water, and dried in a forced-air drying oven at 120°C for 2 hours. Then it was soaked in a 30% polytetrafluoroethylene (PTFE) solution for 1 hour, air-dried, and then placed in a muffle furnace and calcined at 340°C for 25 minutes. After cooling, the carbon cloth was rinsed with deionized water until the rinsing solution was neutral, and then dried in an oven for later use. Subsequently, a 60% PTFE solution was repeatedly brushed onto one side of the carbon cloth, and it was sintered in a muffle furnace at 370°C for 25 minutes. The brushing was repeated 4 times to form an air diffusion layer with both waterproof and breathable properties.

[0027] (2) A 60% PTFE solution was used as a binder and mixed with the prepared CoFe2O4-N modified biochar at a mass ratio of 1:1. After continuous mechanical stirring and ultrasonic homogenization, a uniform slurry was obtained, which was then coated onto the side of the carbon cloth prepared in step (1) that did not have an air diffusion layer. The coated electrode was dried at room temperature for 24 hours to finally obtain a shaped air diffusion cathode supported on the CoFe2O4-N modified biochar catalyst.

[0028] The air diffusion cathode of the CoFe2O4-N modified biochar catalyst prepared by the above method was characterized. Scanning electron microscopy and transmission electron microscopy results showed that the nanoparticles were uniformly embedded and dispersed in the carbon matrix, forming a highly developed spherical nanoparticle cluster structure. Figure 1 High-resolution transmission electron microscopy (HRTEM) revealed lattice fringes with a spacing of 0.473 nm, corresponding to the (111) crystal plane of CoFe₂O₄. EDS elemental mapping confirmed that Co, Fe, N, C, and O elements were uniformly distributed in the catalyst. Figure 2 The X-ray diffraction pattern shows obvious characteristic peaks of the CoFe2O4 spinel phase and the Fe2O3 phase. Figure 3 ).

[0029] The air diffusion cathode of the above-mentioned CoFe2O4-N modified biochar catalyst was assembled into the cathode of a bioelectric Fenton system for treating wastewater with an initial chemical oxygen demand (COD) of 600 mg / L. The results are as follows: Figure 4 As shown, when one compartment is opened at the anode and the hydraulic residence time of both the cathode and anode is controlled at 48 h, the system can achieve a COD removal efficiency of 95%. This result demonstrates that the prepared cathode material possesses excellent catalytic activity and efficient organic matter degradation capability.

[0030] Taking carbon cloth as an example, the air cathode is prepared by impregnation and drying method, and the steps are as follows: Carbon cloth pretreatment: Soak the cut carbon cloth in acetone to remove surface impurities and oil stains, wash with deionized water and dry in a drying oven.

[0031] The pretreated carbon cloth is completely immersed in a 30% PTFE emulsion for a period of time to allow for full absorption. After natural air drying, the carbon cloth is calcined in a muffle furnace at 340 ℃~370 ℃ for 25 min. This process solidifies the PTFE within the carbon cloth fibers, giving the substrate excellent hydrophobic properties. To achieve the ideal unidirectional air permeability and water-blocking effect, this "impregnation-drying-sintering" process can be repeated multiple times.

[0032] The CoFe2O4-N modified biochar catalyst was added to a volatile solvent (such as a mixture of deionized water and ethanol) containing a small amount of PTFE emulsion (or binder such as Nafion). After continuous mechanical stirring and ultrasonic homogenization, a uniformly dispersed catalyst suspension was formed.

[0033] The carbon cloth with the diffusion layer (i.e., the side without air diffusion properties, or the side with weaker air permeability) is slowly attached or pulled into the catalyst slurry, controlling the immersion depth so that the slurry adheres only to the other side of the conductive substrate. The impregnated electrode is then placed in an oven (e.g., dried at room temperature for 24 h or vacuum dried at 60 °C) to allow the solvent to evaporate completely. As the solvent dries, the catalyst particles are firmly anchored to the substrate by the binder, ultimately yielding a shaped air diffusion cathode carrying a CoFe2O4-N modified biochar catalyst.

[0034] When using titanium mesh or stainless steel mesh as the substrate, an air diffusion cathode is prepared by a roll pressing method. One side of the substrate is rolled with an air diffusion layer containing carbon black powder, and the other side is rolled with a catalytic layer using CoFe2O4-N modified biochar as the catalyst. The specific preparation steps are as follows: Conductive carbon black powder was dispersed in anhydrous ethanol (the amount added depends on the area of ​​the cathode stainless steel or titanium mesh, for example, 4 g of carbon black and 80 mL of anhydrous ethanol for an 8 cm × 16 cm cathode). The dispersion was ultrasonically stirred for 20 min at a constant temperature of 30°C. Then, a 60 wt% polytetrafluoroethylene (PTFE, density 1.5 g / mL) solution was added dropwise (6 g of PTFE was added for every 4 g of carbon black, with a carbon black to PTFE mass ratio of 2:3). Ultrasonic stirring was continued for 10 min, followed by stirring at 60–80°C until the solvent partially evaporated, forming a dough-like mass with certain extensibility and elasticity. The mass was fed into a roller press and repeatedly rolled by adjusting the roller spacing to produce a uniform (0.3–0.6 mm) and smooth air diffusion layer film.

[0035] The prepared air diffusion layer film is laid flat on one side of a titanium or stainless steel mesh, and then pressed firmly into the metal mesh using a roller press with mechanical pressure. Afterwards, it is placed in a muffle furnace and calcined at 340 °C for 25 min, then air-dried naturally.

[0036] The prepared CoFe2O4-N modified biochar catalyst powder was ultrasonically dispersed in anhydrous ethanol at 30℃ for 10 min (the amount added is 6 g of catalyst and 80 mL of anhydrous ethanol for an 8 cm × 16 cm cathode). Then, PTFE solution (0.7 mL of 60 wt% PTFE) was added dropwise, and ultrasonic stirring was continued for another 10 min. The mixture was then stirred at 60~80 ℃ until a dough-like colloid was formed. The colloid was then pressed into a uniformly thick catalytic film using a roller press.

[0037] The catalyst layer film is laid flat on the other side of a titanium or stainless steel mesh and then pressed onto it using a roller press. This yields an air diffusion cathode loaded with CoFe2O4-N modified biochar catalyst, using a titanium or stainless steel mesh as the conductive substrate.

[0038] Example 2

[0039] like Figure 5 As shown, the present invention also provides a self-driven bioelectric Fenton system, the system comprising: a cathode reaction system 1 and an anode reaction system 2 stacked vertically; The cathode reaction system 1 includes a cathode housing 1-1, an air diffusion cathode 1-2 disposed on the top of the cathode housing 1-1, and a plurality of parallel perforated plates 1-3 disposed inside the cathode housing 1-1; the perforated plate 1-3 is a flat plate with a plurality of through holes.

[0040] The water inlet pipe is connected to the cathode reaction system 1. One end of the water inlet pipe is connected to the water inlet tank 3, and the other end is connected to the water outlet. The water outlet extends into the cathode box 1-1 and the outlet of the water outlet is located at the top of the perforated plate 1-3. An anode reaction system 2 is located at the bottom. The anode reaction system 2 includes an anode box 2-1 and several partitions 2-2 disposed within the anode box 2-1. The anode box 2-1 is divided into several anode reaction compartments 2-3 by the partitions 2-2. The anode reaction compartments 2-3 are filled with a three-dimensional porous conductive material with attached electroactive microorganisms. The three-dimensional porous conductive material with attached electroactive microorganisms is disposed on a current collector 2-4.

[0041] Specifically, the current collectors 2-4 can be titanium mesh, stainless steel mesh, graphite rods, or graphite plates.

[0042] As a preferred embodiment, the anode housing 2-1 is made entirely of insulating material or has insulating material laid on its inner wall.

[0043] The three-dimensional conductive material is a conductive medium with high specific surface area and good biocompatibility, preferably granular activated carbon, graphite felt blocks, or foamed carbon. In terms of filling layout, the three-dimensional conductive material is uniformly filled inside each compartment, with its filling volume typically accounting for 70% to 80% of the effective volume of the compartment. This ensures the continuity of the electron conduction network while maintaining the appropriate porosity required for the upward flow of water. During system operation, this three-dimensional conductive material provides a large attachment area for microorganisms. Electroactive microorganisms attach and colonize extensively on its surface and in the pores, forming an active biofilm. Electrons generated by the degradation of organic matter by electroactive bacteria are first transferred to the highly conductive three-dimensional conductive material, and then conducted to the external circuit through the current collector in close contact with the three-dimensional conductive material, thereby significantly improving the system's power generation efficiency and volumetric load.

[0044] The partition 2-2 is made of insulating and corrosion-resistant polyvinyl chloride material, which physically isolates each anode area; each compartment is equipped with a three-dimensional porous conductive material on which electroactive microorganisms attach.

[0045] A water pipe 4 is provided between the cathode reaction system 1 and the anode reaction system 2. One end of the water pipe 4 is connected to the bottom of the cathode reaction system 1, and the other end is connected to several water distribution heads. Each water distribution head extends into the bottom of the anode reaction compartment 2-3. Its function is to inject the cathode effluent into each anode reaction compartment 2-3 of the anode reaction system.

[0046] An ion exchange membrane 5 is provided between the cathode box 1-1 and the anode box 2-1 to separate the cathode reaction system 1 and the anode reaction system 2.

[0047] An external circuit system 6 is provided between the cathode reaction system 1 and the anode reaction system 2. The external circuit system 6 includes a wire 6-1, a resistor 6-2 connected to the wire, and a data acquisition system 6-3. One end of the wire 6-1 is connected to the air diffusion cathode 1-2, and the other end is connected to the current collector 2-4. Specifically, the current collectors 2-4 in each anode reaction compartment 2-3 are electrically connected to each other and connected to the wire 6-1 of the external circuit system 6.

[0048] In the embodiments of the present invention, the data acquisition system 6-3 used is the DAQM-4202C data acquisition card of Xi'an Zhouzheng Electronic Technology Co., Ltd.

[0049] Specifically, The resistor 6-2 (1000Ω external resistance) not only serves as an external electrical load of the system to regulate the electron transfer rate and maintain a stable potential difference between the anode and cathode to promote the growth of electrogenic microorganisms at the anode and the occurrence of the electro-Fenton reaction at the cathode; at the same time, this resistor serves as a data acquisition node for the system's operating status, and the voltage changes across its terminals are monitored in real time by the external data acquisition system 6-3, thereby enabling online assessment of the electrochemical activity of microorganisms and the load fluctuations of wastewater treatment.

[0050] An overflow weir 2-11 is provided on the top of the anode box 2-1, and the outlet surface of the overflow weir 2-11 is higher than the bottom surface of the ion exchange membrane 5. The water pipe 4 is also connected to a carbon source addition tank 7.

[0051] Before use, a mixture of carbon source and trace elements is prepared and stored in the carbon source addition tank. This liquid is mainly composed of a 5%~10% sodium acetate solution and a certain proportion of concentrated trace element solution.

[0052] The composition and content of the concentrated trace element solution (based on 1L of pure water) are as follows: 1.5g of nitric acid, 3.0g of MgSO4·7H2O, 0.5g of MnSO4·H2O, 1.0g of NaCl, 0.1g of FeSO4·7H2O, 0.1g of CoCl2·6H2O, 0.1g of CaCl2, 0.1g of ZnCl2, 0.13g of CuSO4·5H2O, 0.01g of H3BO3, 0.025g of Na2MoO4·2H2O, and 0.024g of NiCl2·6H2O.

[0053] The method for preparing the mixture in the carbon source addition tank 7 is as follows: (1) First, add 1.5g of aminotriacetic acid (NTA) to about 800mL of ultrapure water, and add an appropriate amount of KOH or NaOH solution to adjust the pH to about 6.5 so that it is completely dissolved. Then, under continuous magnetic stirring, weigh the remaining metal salts and slowly add them to the solution. Add the next one after the previous one is completely dissolved. Finally, use ultrapure water to make up to 1L and store it in the dark for later use.

[0054] (2) Weigh 50g~100g of sodium acetate trihydrate and add it to the water tank to be prepared. Add tap water or deionized water and stir to dissolve. Then, mix according to the ratio of 10mL of the above concentrated trace element solution per liter of sodium acetate solution. After stirring evenly, it can be used as a supplementary carbon source and nutrient solution for the anode reaction system and stored in the carbon source addition tank for later use.

[0055] The air diffusion cathode 1-2 has an air diffusion layer with both waterproof and breathable properties coated on one side of the conductive substrate (the side away from the anode reaction system 2), and a CoFe2O4-N modified biochar catalyst coated on the other side (the side closer to the anode reaction system 2).

[0056] The conductive substrate is any one of carbon cloth, titanium mesh, and stainless steel mesh. The main methods for preparing air diffusion cathodes 1-2 include rolling, coating, and impregnation-drying.

[0057] The method for preparing the air diffusion cathode used here is the same as in Example 1.

[0058] During operation, the sewage entering from the outlet passes through the perforated plate 1-3 for horizontal cross-sectional uniform flow. Utilizing its porous gaps, the water flow is further evenly dispersed to form a stable flow, ensuring that the sewage comes into full contact with the catalytic layer of the air diffusion cathode 1-2 at the top without any dead corners.

[0059] The electroactive microorganisms were derived from mixed sludge bacteria from the anaerobic process section of a municipal wastewater treatment plant. After prior enrichment and culture, the dominant genera included *Geobacterium* and *Shewanella*. During inoculation, the initial bacterial concentration in the anodic reaction system 2 was controlled at 1500–3000 mg VSS / L. To ensure the electroactive microorganisms firmly adhered to the three-dimensional conductive material and formed an electroactive biofilm, a multi-cycle circulating liquid exchange method was used to drive growth. The specific steps are as follows: (1) Mix the bacterial solution of the above concentration with the nutrient solution containing basic carbon source and trace elements and inject it into the anode reaction system 2 to completely immerse the three-dimensional conductive material. Keep the external circuit system 6 connected under anaerobic conditions. Inject 0.05-0.1M Na2SO4 / K2SO4 solution or 0.05-0.5M H2SO4 or 0.1M phosphate buffer solution into the cathode.

[0060] (2) The output voltage of the closed loop is monitored in real time by the data acquisition system 6-3. When the system voltage reaches its peak as the microorganisms consume organic matter and then drops to below 50mV, it indicates that the substrate has been basically exhausted, and this is marked as the end of one power generation cycle. At this time, the waste liquid in the anode reaction compartment 2-3 is emptied and an equal volume of fresh nutrient solution is added. At the same time, the cathode reaction system 1 is also replaced with fresh cathode liquid, and the next cycle begins.

[0061] (3) Repeat the above process, and through multiple washing, eliminate the non-electroactive bacteria in the suspension state, and promote the enrichment and colonization of electroactive microorganisms on the rough surface of carbon fiber. When the highest output voltage of the system remains consistent and without significant fluctuations for three or more consecutive cycles, it indicates that the electroactive microorganisms have successfully grown on the three-dimensional conductive material and formed a mature and stable anodic biofilm.

[0062] Description of the operation process of the system of this invention: Before the system treats actual wastewater for the first time, the micro-ecology of the anode must be established.

[0063] First, the wastewater stored in the inlet tank 3 is pumped to the cathode reaction system 1. Under the continuous drive of the pump, the wastewater fills the cathode housing 1-1. The water flow forms a lateral flow on the side of the air diffusion cathode 1-2 coated with CoFe2O4-N modified biochar catalyst, thereby effectively overcoming the short-circuiting caused by gravity and achieving full and dead-angle-free contact between the water and the catalytic sites.

[0064] The carbon source addition tank 7 is started, and the readily degradable liquid carbon source is pumped into the anode reaction system 2 through the water pipe 4. Electroactive microorganisms utilize the readily degradable carbon source to grow rapidly and attach to the three-dimensional conductive material to form a mature electroactive biofilm. When the data acquisition system 6-3 detects that the output voltage has reached a stable maximum value, it indicates that the anode has a continuous and stable electron output capability. At this time, electrons are conducted in large quantities to the air diffusion cathode 1-2 through the external circuit system 6; hydrogen peroxide is generated in situ and catalyzes the production of high concentrations of hydroxyl radicals, which mineralize or degrade the recalcitrant organic matter in the wastewater into small molecules.

[0065] After the biological culture in the anode reaction system 2 matures, the wastewater to be treated is injected into the cathode reaction system 1. Through continuous flow and valve control, the effluent from the cathode is continuously injected into the anode, and the wastewater flows continuously from the cathode to the anode through the water pipe under the action of gravity.

[0066] After completing the cathodic electro-Fenton pretreatment, the wastewater flows out from the side of the cathodic reaction system into the water guide pipe 4. Driven by gravity, it is evenly injected into each anode reaction compartment 2-3 of the anode reaction system 2 through the water distribution head at the bottom. The wastewater flows from bottom to top through the anode reaction compartments 2-3. The anode microorganisms use the small molecule organic matter in the cathodic effluent as a carbon source, and the generated electrons are directionally transferred to the air diffusion cathode 1-2 above through the external circuit system 6, thus forming a complete current loop.

[0067] Simultaneously, cations generated in the anolyte, driven by the electric field, penetrate upwards through the ion exchange membrane 5 and enter the cathode reaction system 1 to maintain the charge balance of the entire device. Wastewater, after deep treatment in the anolyte zone, continues to flow upwards to the top of the anolyte reaction system. Finally, the treated purified water is discharged through the overflow port 2-11 at the top of the anolyte reaction system.

[0068] Furthermore, the influent flow rate of the cathode reaction system can be controlled by valves to regulate the hydraulic residence time of the cathode. Similarly, the number of openings and the flow rate into the anode reaction chambers 2-3 can be controlled by valves to regulate the residence time of the anode reaction system 2. By adjusting the electron supply requirements of the cathode reaction system 1 and the anode reaction system 2, the outlet head and distribution head can be controlled to achieve electron supply to the cathode electro-Fenton, and the intermediate small molecule products after electro-Fenton degradation can ensure the growth of electrogenic microorganisms at the anode.

[0069] The operation method of the system of this invention: This invention regulates operation based on wastewater quality and operational conditions. The specific operation method is as follows: (1) Standard Collaboration Mode In this invention, the volume of the cathode reaction system is the same as the volume of a single reaction compartment in the anodic reaction system, and the anodic reaction system consists of 3-5 reaction compartments. Under normal conditions, the electrons generated by the domesticated anodic electroactive microorganisms using organic matter in the water can fully supply the needs of the cathode for generating hydroxyl radicals. The corresponding compartments in the cathode inlet water distributor and the anode water distributor are opened with the same valve opening degree, ensuring consistent hydraulic retention time throughout the entire process. The influent volume is gradually increased from a slow start to the volume of water to be treated, ensuring that the COD removal rate of the system reaches the ideal requirement. This mode is suitable for actual wastewater with COD below 600 mg / L.

[0070] (2) Shock-resistant / High-load mode: When a sudden increase in influent COD is detected (e.g., COD of influent increases by more than 50% compared to the normal 600 mg / L), a significant decrease in effluent COD (e.g., a decrease of more than 20% compared to the normal COD removal rate of 85%), or a significant decrease in voltage displayed by the voltage data acquisition system (e.g., voltage drops from the normal 0.5V to below 0.3V), it indicates that the cathode COD removal rate cannot guarantee the growth of anode organisms, thus affecting electricity generation and ultimately impacting the COD removal rate of the anode effluent. In this case, the opening of the cathode influent distributor and the anode distributor should be reduced simultaneously to increase the hydraulic retention time. By increasing the hydraulic retention time, the COD in the water is fully reduced within the cathode reaction system using electro-Fenton degradation, and the degraded organic matter can then be used by the electroactive microorganisms at the anode.

[0071] When COD suddenly increases, COD significantly decreases, or the voltage data acquisition system shows a significant voltage drop, and the above methods are ineffective, the valve of the second reaction compartment can be opened until all compartments are open. This increases the hydraulic residence time of the anodic reaction system by adjusting the number of compartments.

[0072] If the above situation still cannot be resolved, start the carbon source addition tank and slowly inject the organic carbon in the tank into the anode reaction system to enhance the activity of the anode electrogenic microorganisms. This will improve the overall COD removal rate of the system.

[0073] Example 3

[0074] The standard co-operation mode of the anode and cathode of this bioelectric Fenton system was used to treat wastewater with initial CODs of approximately 600 mg / L and 400 mg / L. The overall flow rate was controlled by adjusting the inlet valve of the cathode distributor, while simultaneously opening the inlet valve of one compartment in the anode distributor, ensuring that the hydraulic retention times of both the anode and cathode systems were the same (24 hours). Results are as follows... Figure 6 As shown, after co-processing by this system, the total COD removal rate of high-concentration wastewater with an initial COD of 600 mg / L can reach 87.32%, while the removal rate of wastewater with an initial COD of 400 mg / L can reach 92.37%.

[0075] Example 4

[0076] For wastewater with an initial COD of around 2000 mg / L, using the above-mentioned single-compartment control method results in a decrease in system treatment efficiency, with the total COD removal rate only reaching 81.32%. By simultaneously opening the inlet valve of the second compartment of the anode distributor, the effective working volume of the anode is further increased, extending the hydraulic retention time of the anode reaction system to 36 hours. At this point, the hydraulic retention time of the cathode reaction system is 18 hours, and the total COD removal rate can reach 93.29%. Figure 7 ).

[0077] Example 5

[0078] When the system encounters wastewater with an initial COD of approximately 2500 mg / L, the system's output voltage will significantly decrease. To cope with high load conditions, all compartments of the anode distributor are opened, further extending the anode hydraulic retention time to 48 hours, while the hydraulic retention time of the cathode reaction system is 16 hours. The COD removal efficiency can increase from 84.17% to 95.63%. Figure 8 ).

[0079] Example 6

[0080] When the system faced recalcitrant wastewater with an initial COD of approximately 2500 mg / L, and the treatment effect declined after a period of continuous operation, even with all three compartments of the anodic reaction system fully activated and the anode hydraulic retention time maintained at 48 hours, the system's decontamination capacity remained limited, with the total COD removal rate stagnating at around 76.37%. This was because the high concentration of recalcitrant organic matter resulted in a lack of readily available "electron donors" for the anode electrochemical microorganisms, inhibiting their bioelectrochemical activity. Further co-metabolic regulation was implemented by initiating a carbon source addition tank. Pre-prepared auxiliary carbon source was slowly injected into the anode water supply pipeline via valves and metering pumps, while maintaining the original system hydraulic parameters. Test results showed that, through the synergistic regulation of readily degradable carbon source, the electrochemical activity of the anode microorganisms was rapidly restored, effectively feeding back into the cathode's electro-Fenton reaction, and the system's total COD removal efficiency significantly increased to 91.65%. Figure 9 ).

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A self-powered bioelectric Fenton system, characterized in that, The system includes: a cathode reaction system (1) and an anode reaction system (2) stacked on top of each other. The cathode reaction system (1) includes a cathode box (1-1), an air diffusion cathode (1-2) disposed on the top of the cathode box (1-1), and several parallel perforated plates (1-3) disposed inside the cathode box (1-1). The air diffusion cathode (1-2) has an air diffusion layer with waterproof and breathable properties on one side of a conductive substrate, and a CoFe2O4-N modified biochar catalyst on the other side. The anode reaction system (2) includes an anode box (2-1) and several vertically arranged partitions (2-2); the partitions (2-2) divide the anode box (2-1) into several anode reaction compartments (2-3); the anode reaction compartments (2-3) are filled with a three-dimensional porous conductive material with attached electroactive microorganisms; the three-dimensional porous conductive material with attached electroactive microorganisms is disposed on a current collector (2-4); The cathode reaction system (1) and the anode reaction system (2) are separated by an ion exchange membrane (5); A water pipe (4) is provided between the cathode reaction system (1) and the anode reaction system (2). One end of the water pipe (4) is connected to the bottom of the cathode reaction system (1), and the other end is connected to the bottom of the anode reaction compartment (2-3) through a water distribution head. An external circuit system (6) is provided between the cathode reaction system (1) and the anode reaction system (2). The external circuit system (6) includes a wire (6-1), a resistor (6-2) connected to the wire, and a data acquisition system (6-3). One end of the wire (6-1) is connected to the air diffusion cathode (1-2), and the other end is connected to the current collector (2-4). The cathode reaction system (1) is connected to a water inlet pipe on one side. One end of the water inlet pipe is connected to the water inlet tank (3), and the other end is connected to the water outlet. The water outlet extends into the cathode box (1-1), and the outlet of the water outlet is located at the top of the perforated plate (1-3). An overflow weir (2-11) is provided on the top of the anode box (2-1), and the outlet surface of the overflow weir (2-11) is higher than the bottom surface of the ion exchange membrane (5). The cathode reaction system (1) has the same volume as the individual anode reaction compartments (2-3); The influent flow rate of the cathode reaction system (1) is controlled by valves to regulate the hydraulic residence time of the cathode; the number of openings and the flow rate into the anode reaction compartments (2-3) are controlled by valves to regulate the residence time of the anode reaction system (2).

2. The self-driven bioelectric Fenton system according to claim 1, characterized in that, The water pipe (4) is also connected to a carbon source addition tank (7).

3. The self-driven bioelectric Fenton system according to claim 1, characterized in that, The partition (2-2) is made of an insulating and corrosion-resistant material; The current collector (2-4) is a titanium mesh, stainless steel mesh, graphite rod, or graphite plate; The three-dimensional porous conductive material is granular activated carbon, graphite felt block, or foamed carbon. The carbon source addition tank (7) contains a pre-prepared mixture of carbon source and trace elements to provide carbon source and trace elements for anodic electroactive microorganisms.

4. The self-driven bioelectric Fenton system according to claim 1, characterized in that, The conductive substrate is any one of carbon cloth, titanium mesh, and stainless steel mesh. The air diffusion cathode is prepared by rolling, coating or impregnation-drying.

5. The self-driven bioelectric Fenton system according to claim 1, characterized in that, The preparation method of the CoFe2O4-N modified biochar catalyst is as follows: (1) Mix ferrous sulfate heptahydrate, cobalt nitrate hexahydrate, urea and seaweed powder in a mass ratio of 1:1:2:1, add to deionized water, and continuously stir at room temperature to complete the impregnation. Then dry the resulting mixture at 80°C and grind it to obtain the precursor powder. (2) The precursor powder obtained in step (1) is heated to 600°C at a heating rate of 10°C / min under a continuous N2 atmosphere and kept at a constant temperature for 2 hours for pyrolysis. (3) After cooling the pyrolysis product of step (2), rinse it with deionized water until the pH of the eluent reaches neutral, dry it under vacuum at 60°C and grind it to obtain the CoFe2O4-N modified biochar catalyst.

6. The application of the self-driven bioelectric Fenton system according to any one of claims 1 to 5 in wastewater treatment.

7. A method for treating wastewater, characterized in that, The specific steps of using the self-driven bioelectric Fenton system according to any one of claims 1 to 5 are as follows: S1. Wastewater in the inlet tank (3) is fed into the cathode reaction system (1) through the inlet pipe; the air diffusion cathode (1-2) uses electrons from the anode reaction system (2) to carry out an electro-Fenton reaction on the side coated with CoFe2O4-N modified biochar catalyst; S2. After being treated by the cathode reaction system (1) by electro-Fenton, the wastewater is injected into the anode reaction system (2) through the water pipe (4). The wastewater flows from bottom to top through the anode reaction compartment (2-3). The anode microorganisms use the organic matter in the cathode effluent to generate electrons. The electrons are transferred to the air diffusion cathode (1-2) through the external circuit system (6). S3. The cations generated in the anode reaction system (2) are driven by the electric field to penetrate the ion exchange membrane (5) and enter the cathode reaction system (1). S4. The wastewater treated by the anode reaction system (2) is continuously pushed upward to the top and discharged through the overflow weir (2-11).

8. The method for treating wastewater according to claim 7, characterized in that, Before the initial wastewater treatment, a microecological step is also included in establishing the anodic reaction system (2): Wastewater from the inlet tank (3) is fed into the cathode reaction system (1) through the inlet pipe. Under the continuous drive of the pump, the wastewater fills the cathode box (1-1). The carbon source addition tank (7) is started, and the carbon source and trace element mixture in it is pumped into the anode reaction system (2) through the water pipe (4). When the data acquisition system (6-3) detects that the output voltage has reached a stable maximum value, it indicates that the electroactive biofilm has matured.

9. The method for treating wastewater according to claim 7, characterized in that, The regulation mode of the self-driven bioelectric Fenton system is either the standard synergistic mode or the shock-resistant / high-load mode. The standard collaborative mode is as follows: the volume of the cathode reaction system (1) is the same as that of a single anode reaction compartment (2-3); one anode reaction compartment (2-3) is opened; the hydraulic residence time of the cathode reaction system (1) is kept consistent with that of the anode reaction system (2), and the water is gradually increased from slow water intake to the volume of water to be treated; The anti-impact / high-load mode is as follows: when the influent COD is detected to be more than 50% higher than the normal value, the effluent COD removal rate after treatment using the standard collaborative mode is more than 20% lower than the normal value, or the voltage value collected by the external circuit system (6) drops below 0.3V, at least one of the following control operations is performed: a) Simultaneously reduce the opening of the inlet valves of the cathode reaction system (1) and the anode reaction system (2) to increase the hydraulic residence time; b) Open the additional anode reaction compartments (2-3) in the anode reaction system (2) until all anode reaction compartments (2-3) are open to increase the hydraulic residence time of the anode reaction system; c) Start the carbon source addition tank (7) and inject the carbon source and trace element mixture into the anode reaction system (2).

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