Process for treating refractory wastewater by using self-driven electro-fenton reactor

Abstract

This invention relates to a process for treating recalcitrant wastewater using a self-driven electric Fenton reactor, belonging to the field of electrochemical water treatment technology. It includes constructing a continuous-flow self-driven electric Fenton reactor and establishing a recalcitrant wastewater treatment process. This invention uses an iron anode coupled with an air cathode membrane assembly to form a galvanic cell, generating hydrogen peroxide (H2O2) in situ without external power supply. During operation, this invention continuously generates a stable voltage of 20-30 mV, breaking through the limitations of Fe²⁺. + / Fe³ + The limitations of the cycle and the problem of high energy consumption mean that hydrogen peroxide can continuously dissolve ferrous ions (Fe2+) through the iron anode. 2+ After catalysis, it continuously and stably generates hydroxyl radicals (·OH) with strong oxidizing power, which can be used to treat high-concentration, recalcitrant organic wastewater. This invention combines treatment efficiency and economy, and can utilize waste iron slag, bringing a new green and economical technological direction to the treatment of high-concentration, recalcitrant organic wastewater.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical water treatment technology, and relates to a process for treating recalcitrant wastewater using a self-driven electro-Fenton reactor. Background Technology

[0002] The electro-Fenton process is one of the most effective technologies for treating recalcitrant organic wastewater; however, high operating energy consumption and limited iron ion circulation are two major bottlenecks hindering its engineering application. In traditional electro-Fenton processes, external electrical energy is required to drive the oxygen reduction reaction (ORR) at the cathode to generate Fenton's reagent—H₂O₂—in situ. This portion of the energy consumption accounts for approximately 75% of the total system energy consumption. Simultaneously, the Fe³⁺ in the system… + The reduction rate is much lower than that of Fe² + The oxidation rate leads to Fe² + Continued supply shortage or Fe³ + Excessive accumulation inhibits the continuous generation of hydroxyl radicals (·OH), thereby terminating the reaction and affecting the long-term stability during the degradation process.

[0003] The aforementioned problems are particularly prominent in engineering scale-up scenarios. In actual operation, due to the increase in overpotential and the aggravation of ohmic losses, the system's energy consumption increases significantly, and the operating voltage rises accordingly. Furthermore, in existing processes, due to the limited electrode area, oxygen mass transfer is hindered, and the reaction efficiency at the gas-liquid-solid three-phase interface is low, resulting in a low and uneven distribution of H2O2 formation rate, which further limits the overall reaction efficiency and operational stability of the system.

[0004] Therefore, if a Fenton reaction system that requires no external power supply and can operate self-driven is developed, and can overcome the Fe²⁺ ionization problem, it would be highly valuable. + / Fe³ + Cyclic constraints to achieve Fe² + The continuous release of OH and the stable generation of ·OH, along with the engineering scale-up of the cathode, will provide a new technical approach for the treatment of recalcitrant organic wastewater, thus meeting the actual treatment needs of such wastewater. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a process for treating recalcitrant wastewater using a self-driven electric Fenton reactor. This wastewater treatment process can operate self-driven without external power supply and overcomes the limitations of Fe²⁺. + / Fe³ + The cyclic constraint enabled Fe² + The continuous release of and the stable generation of ·OH simultaneously enabled the engineering scale-up of the cathode.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A process for treating recalcitrant wastewater using a self-driven electric Fenton reactor includes the following steps: S1: Constructing a continuous flow self-driven electric Fenton reactor The reactor includes a rectangular reaction tank. An inlet is provided at the bottom of one side wall of the reaction tank, and an outlet is provided at the top of the other side wall of the reaction tank. Multiple membrane modules are provided in the reaction tank, and the multiple membrane modules are arranged sequentially from the side where the inlet is located to the side where the outlet is located. After the wastewater in the reaction tank enters from the inlet, it flows out of the reaction tank from the outlet after passing around each membrane module in sequence. The membrane module includes a rectangular frame, with an air inlet and an air outlet at the top two ends of the frame, respectively. A hose 1 is provided between the air outlet of any membrane module and the air inlet of the membrane module adjacent to it. A hose 2 extending out of the wastewater surface is provided at the air inlet of the membrane module near the water inlet, and a hose 3 extending out of the wastewater surface is provided at the air outlet of the membrane module near the water outlet. An air cathode is provided on each side of the frame, and the space enclosed by the two air cathodes and the frame is a gas chamber; the air cathode is composed of a current collector layer, a catalyst layer and a waterproof layer; Iron anodes are provided between any two adjacent membrane modules in the reaction tank, and between the inner wall of the reaction tank on the outlet side and the membrane module near the inner wall of that side. Each iron anode is provided with a conductive connector between it and the air cathode of the two adjacent membrane modules facing it. The conductive connectors make the iron anode and the air cathode of the membrane module form an anode-cathode short circuit, forming a galvanic cell. S2: Establishing a recalcitrant wastewater treatment process The wastewater treatment process for recalcitrant wastewater includes a stabilization container, metering pump, circulating pump, pH meter, magnetic stirrer, small air pump, dilute sulfuric acid pump, wastewater pump, and reaction tank. The stabilization container has a drain outlet at its bottom. The specific wastewater treatment process is as follows: Before each wastewater treatment cycle begins, a certain amount of wastewater is pumped into the stabilization container. The treatment process then commences. During treatment, wastewater flows from the effluent outlet of the reaction tank into the stabilization container by gravity. H2O2 solution is added to the stabilization container via a metering pump, and the pH level of the wastewater in the stabilization container is continuously monitored using a pH meter. When the wastewater in the stabilization container becomes too alkaline, dilute H2SO4 solution is added via a dilute sulfuric acid pump. Throughout this process, a magnetic stirrer continuously mixes the wastewater in the stabilization container at a speed of 600-1200 rpm. The wastewater in the stabilization container is then pumped back into the reaction tank via a circulation pump through the inlet, thus forming a continuous flow cycle for degradation. The second hose is connected to a small air pump, and the third hose is directly connected to the atmosphere. The small air pump continuously supplies air into the air cathode.

[0007] Furthermore, in step S1, the bottom of the membrane modules located in the odd-numbered columns is sealed to the bottom surface of the reaction tank, while a gap is provided between the bottom of the membrane modules located in the even-numbered columns and the bottom surface of the reaction tank. The two sides of the membrane modules located in the odd-numbered columns are respectively sealed to the inner walls of the two sides of the reaction tank, and the two sides of the membrane modules located in the even-numbered columns are respectively sealed to the inner walls of the two sides of the reaction tank. The height of the outlet is higher than the height of the top of the membrane modules in the odd-numbered columns, but lower than the height of the top of the membrane modules in the even-numbered columns. The liquid level of the wastewater in the reaction tank is higher than the top of the membrane modules in the odd-numbered columns, but lower than the top of the membrane modules in the even-numbered columns. The bottom of the reaction tank is provided with a slot 1 that is higher than the bottom of the reaction tank, and the inner walls on both sides of the reaction tank are provided with slot 2 that are provided with each membrane module in an even-numbered row. The bottom of the membrane module in the odd-numbered row is inserted into the slot 1 that is directly opposite to its position, and the two ends of the membrane module in the even-numbered row are respectively inserted into the two slot 2 that are directly opposite to its position. The membrane module is bonded and sealed to the inner wall of the reaction tank with waterproof sealant. The bottom height of the slot is set to 3-6cm; each gap is provided with a sludge discharge hole at the bottom of the reaction tank; a horizontal pipe is provided below the reaction tank; the horizontal pipe is connected to each sludge discharge hole; and the horizontal pipe is equipped with a solenoid valve.

[0008] Furthermore, the current collector layer in step S1 is a titanium mesh or a stainless steel mesh, and the waterproof layer in step S1 includes a hydrophobic film layer and a hydrophobic adhesive layer. The hydrophobic film layer is composed of one or more materials selected from PTFE, PVDF, PP, and nylon; the hydrophobic adhesive layer is any one of 60wt% PTFE emulsion, epoxy resin adhesive, and polydimethylsiloxane liquid; the hydrophobic adhesive layer is uniformly applied to the hydrophobic film layer to obtain the waterproof layer.

[0009] Furthermore, the raw material for the hydrophobic adhesive layer is 60wt% PTFE emulsion, and the preparation method of the hydrophobic adhesive layer is as follows: 60wt% PTFE emulsion and Nafion solution are mixed in a volume ratio of 10-15:1 and stirred evenly to obtain the hydrophobic adhesive layer; the thickness of the hydrophobic adhesive layer applied to the hydrophobic film layer is 100-400μm.

[0010] Furthermore, the preparation method of the catalyst layer is as follows: carbon powder and deionized water are mixed at a mass ratio of 1:5-8, and the carbon powder is dispersed evenly by shaking. Then, 60wt% PTFE emulsion is added to the mixture at a mass ratio of carbon powder to 60wt% PTFE emulsion of 1:0.9-1.2. The mixture is stirred thoroughly to form a dough-like mixture. The dough-like mixture is pressed with a mold to obtain the catalyst layer. The carbon powder is one or more of activated carbon powder and carbon black with a particle size of less than 100 mesh.

[0011] Furthermore, the toner contains sodium cellulose powder, and the mass ratio of the toner to sodium cellulose powder is 50-80:3; the thickness of the catalyst layer is 200-500 μm.

[0012] Furthermore, the air cathode is prepared as follows: the waterproof layer, catalyst layer, and current collector layer are stacked and compacted in the order of waterproof layer, current collector layer, and catalyst layer, or in the order of waterproof layer, current collector layer, and catalyst layer. After being pressed in a tablet press at a pressure of 6-12 MPa for 1-3 minutes, it is placed in a precision constant temperature oven and dried at 120-180℃ for 2-4 hours to obtain the air cathode. The side of the waterproof layer coated with the hydrophobic adhesive layer faces the catalyst layer, and the hydrophobic film layer of the waterproof layer faces the air chamber.

[0013] Furthermore, the iron anode is any one of pig iron sheet, cast iron plate, and carbon steel plate, or is made from industrial waste iron slag. The method for preparing the iron anode using industrial waste iron slag is as follows: Take two 30-100 mesh stainless steel meshes, lay the industrial waste iron slag flat on one side of the stainless steel mesh, and then cover the industrial waste iron slag with the other side of the stainless steel mesh. Place the stainless steel mesh containing the industrial waste iron slag under a pressure of 15-25 MPa for 1-3 minutes to obtain the iron anode. The conductive connector is a stainless steel alligator clip with conductive properties. Both sides of the stainless steel mesh of the iron anode are provided with an elongated and bent electrode connection portion one, and both sides of the current collector layer of the membrane module are provided with an elongated and bent electrode connection portion two. The iron anode is clamped together with the electrode connection portion one on the corresponding side by the stainless steel alligator clip to form a short circuit between the anode and cathode, forming a galvanic cell.

[0014] Furthermore, the carbon powder is a mixture of activated carbon powder and carbon black in a ratio of 3-5:1, and the mass ratio of carbon powder to 60wt% PTFE emulsion is 1:1. When preparing the air cathode, a tablet press is used to press and composite the carbon powder under a pressure of 10 MPa, and then the carbon powder is placed in a precision constant temperature oven at 140 ℃ for 180 minutes to dry.

[0015] Furthermore, in step S2, the pH of the wastewater in the stabilization container is maintained at 3-5. When the pH of the wastewater in the stabilization container exceeds 5, a dilute H2SO4 solution is added to it.

[0016] The beneficial effects of this invention are as follows: This invention constructs a galvanic cell by coupling an iron anode with an air cathode membrane assembly, enabling in-situ self-driven generation of hydrogen peroxide (H2O2) without the need for external power supply. During operation, this invention continuously generates a stable voltage of 20-30 mV, breaking through the limitations of Fe²⁺. + / Fe³ + The limitations of the cycle and the problem of high energy consumption mean that hydrogen peroxide can continuously dissolve ferrous ions (Fe2+) through the iron anode. 2+ After catalysis, it continuously and stably generates hydroxyl radicals (·OH) with strong oxidizing power, which can be used to treat high-concentration, recalcitrant organic wastewater; This invention differs from traditional methods that rely on Fe³⁺. + Reduced to Fe² + Unlike the closed-loop iron circulation mode, this invention proposes an open-loop iron circulation mechanism that enables Fe²⁺… + The Fe³⁺ produced is continuously supplied by the anode. + It is removed in the form of Fe(OH)3 precipitate, thus effectively avoiding the problem of reduced iron recycling efficiency; This invention also scales up the air cathode into a membrane module and couples it with an inexpensive and highly active industrial-grade iron anode to form a basic degradation unit. By scaling up multiple units in series, a continuous flow degradation reactor is constructed, which can achieve large-scale wastewater treatment, making this invention suitable for practical engineering applications. This invention combines treatment efficiency and economy, and can utilize waste iron slag, bringing a new green and economical technological direction to the treatment of high-concentration, recalcitrant organic wastewater.

[0017] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 The internal structure of the reaction tank in Embodiment 1 of the present invention is shown in the front view. Figure 2 The right view of the frame of Embodiment 1 of the present invention shows the internal structure. Figure 3 This is a schematic diagram of the composition structure of the current collector layer, catalyst layer and waterproof layer of the air cathode (with electrode connection portion two) in Embodiment 1 of the present invention. Figure 4 This is a schematic diagram of the composition structure of an iron anode (with an electrode connection portion) made from industrial waste iron slag in Embodiment 1 of the present invention. Figure 5 This is a schematic diagram of the composition and structure of the recalcitrant wastewater treatment process according to Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the pressing structure of the air cathode in Embodiment 1 of the present invention; Figure 7 This is a schematic diagram of the air cathode film assembly configuration according to Embodiment 1 of the present invention; Figure 8 This is a three-dimensional structural diagram of the iron anode of Embodiment 1 of the present invention; Figure 9 The preparation process of the air cathode in Example 2 of the present invention; Figure 10 An air cathode film assembly prepared according to Example 2 of the present invention; Figure 11 The industrial waste iron slag anode prepared in Example 3 of the present invention; Figure 12 The diagram shows the open-circuit voltage results of the self-driven electric Fenton system prepared in Example 4 of the present invention. Figure 13 The degradation results of pharmaceutical preparation wastewater in Example 5 of the present invention; Figure 14 The degradation results of pharmaceutical concentrated wastewater in Example 5 of the present invention; Figure 15 This is the degradation result of high-salt organic wastewater collected from a food company in Example 6 of the present invention; Figure 16 The contribution rate of H2O2 to COD mineralization during the pharmaceutical preparation water treatment process in Example 7 of the present invention; Figure 17 The volume of H2O2 added to the pharmaceutical concentrated water treatment process in Example 7 of the present invention and its contribution rate to COD mineralization; Figure 18 The contribution rate of H2O2 to COD mineralization in the high-salt pickled mustard tuber wastewater treatment process of this invention in Example 7; Figure 19 This is a schematic diagram of the structure of the iron anode and the membrane assembly connected by a stainless steel alligator clip in Embodiment 1 of the present invention.

[0019] Attached reference numerals: 1. Reaction tank; 2. Inlet; 3. Outlet; 4. Frame; 5. Air inlet; 6. Air outlet; 7. Hose 1; 8. Hose 2; 9. Hose 3; 10. Air cathode; 11. Gas chamber; 12. Current collector layer; 13. Catalytic layer; 14. Waterproof layer; 15. Iron anode; 16. Void; 17. Slot 1; 18. Slot 2; 19. Sludge discharge hole; 20. Solenoid valve; 21. Stabilizing container; 22. Metering pump; 23. Circulation pump; 24. pH meter; 25. Magnetic stirrer; 26. Small air pump; 27. Stainless steel mesh; 28. Industrial waste iron slag; 29. ​​Stainless steel alligator clip; 30. Electrode connection part 1; 31. Electrode connection part 2; 32. Conductive connector; 33. Horizontal pipe; 34. Drain outlet; 35. Dilute sulfuric acid pump; 36. Sewage pump. Detailed Implementation

[0020] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0021] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0022] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0023] Example 1: See attached Figure 1 To be continued Figure 5In this embodiment, a continuous flow self-driven electric Fenton reactor is first constructed. The reactor includes a rectangular reaction tank 1. An inlet 2 is provided at the bottom of one side wall of the reaction tank 1, and an outlet 3 is provided at the top of the other side wall of the reaction tank 1. Multiple membrane modules are provided in the reaction tank 1. The multiple membrane modules are arranged sequentially from the side where the inlet 2 is located to the side where the outlet 3 is located. After the sewage in the reaction tank 1 enters from the inlet 2, it flows out of the reaction tank 1 from the outlet 3 after passing around each membrane module in sequence.

[0024] There are two ways to arrange the membrane modules: left-right flow and up-down flow. In the left-right flow method, the membrane modules are alternately fixed on the inner walls of the left and right sides of the reaction tank 1. One side of the membrane module is fixed, and the other side leaves a water passage between it and the corresponding inner wall of the reaction tank 1. After the sewage enters, it flows left and right in the reactor, and after passing through all the modules, it flows out from the outlet of the reaction tank 1.

[0025] This embodiment uses a top-to-bottom baffle arrangement, which helps to increase the water flow velocity between the membrane modules, thereby enhancing the reaction and mass transfer conditions at the membrane interface. In this embodiment, the bottom of the membrane modules in the odd-numbered rows is sealed to the bottom surface of the reaction tank 1, while a gap 16 is provided between the bottom of the membrane modules in the even-numbered rows and the bottom surface of the reaction tank 1. The two sides of the membrane modules in the odd-numbered rows are sealed to the inner walls of both sides of the reaction tank 1, and the two sides of the membrane modules in the even-numbered rows are also sealed to the inner walls of both sides of the reaction tank 1. The height of the outlet 3 is higher than the top of the membrane modules in the odd-numbered rows but lower than the top of the membrane modules in the even-numbered rows. The wastewater level in the reaction tank 1 is higher than the top of the membrane modules in the odd-numbered rows but lower than the top of the membrane modules in the even-numbered rows.

[0026] At the bottom of reaction tank 1, corresponding to each odd-numbered row of membrane modules, there is a slot 17 higher than the bottom of reaction tank 1. At the inner walls of both sides of reaction tank 1, corresponding to each even-numbered row of membrane modules, there are slots 2 18. Both slots 17 and 2 18 are bonded to the inner walls of reaction tank 1. The bottom of the membrane modules in the odd-numbered rows is inserted into the slot 17 corresponding to their position, and the two ends of the membrane modules in the even-numbered rows are respectively inserted into the two slots 2 18 corresponding to their positions. In this embodiment, each membrane module is sealed to the inner wall of reaction tank 1 using waterproof sealant.

[0027] Each gap 16 has a sludge discharge hole 19 at the bottom of the reaction tank 1. A horizontal pipe 33 is located below the reaction tank 1, and the horizontal pipe 33 is connected to each sludge discharge hole 19. The horizontal pipe 33 is equipped with a solenoid valve 20, and the bottom height of the slot 17 in this embodiment is set to 3-6 cm. The gap 16 formed by the bottom of the even-numbered membrane modules and the bottom of the reaction tank 1 serves as a sedimentation zone for particles in the wastewater and the generated iron sludge. When the wastewater flows up and down between the membrane modules, solid particles are washed and deposited in the sedimentation zone. When the sedimentation reaches a certain level, the sludge can be discharged through the sludge discharge hole 19 by opening the solenoid valve 20.

[0028] The membrane module of this embodiment includes a rectangular frame 4. The top two ends of the frame 4 are respectively provided with an air inlet 5 and an air outlet 6. A hose 7 is provided between the air outlet 6 of any membrane module and the air inlet 5 of the membrane module adjacent to it. The air inlet 5 of the membrane module near the water inlet 2 is provided with a hose 8 extending out of the sewage liquid surface. The air outlet 6 of the membrane module near the water outlet 3 is provided with a hose 9 extending out of the sewage liquid surface. The hoses 7, 8, and 9 are all bonded to the frame 4.

[0029] See attached Figure 7 An air cathode 10 is provided on each side of the frame 4. During assembly, the air cathode 10 is tightly adhered to the internally connected frame 4 with waterproof coating. The space enclosed by the two air cathodes 10 and the frame 4 is the air chamber 11, which is connected to both the air inlet 5 and the air outlet 6.

[0030] See attached Figure 3 The air cathode 10 consists of a current collector layer 12, a catalyst layer 13, and a waterproof layer 14. In this embodiment, the current collector layer 12 is a titanium mesh or stainless steel mesh, which serves as a support and conducts electricity. The air cathode 10 and the frame 4 form an air cathode 10 membrane assembly. The air inlet 5 and the air outlet 6 are used to introduce air, allowing it to diffuse to the surface of the air cathode 10 to undergo an oxygen reduction reaction. This allows the membrane assembly to catalyze the in-situ generation of H2O2 from O2 through the oxygen reduction reaction.

[0031] The waterproof layer 14 in this embodiment includes a hydrophobic film layer and a hydrophobic adhesive layer. The hydrophobic film layer is composed of one or more materials selected from PTFE, PVDF, PP, and nylon, and imparts waterproof performance to the air cathode 10. The hydrophobic adhesive layer is any one of 60wt% PTFE emulsion, epoxy resin adhesive, and polydimethylsiloxane liquid.

[0032] In this embodiment, the preferred raw material for the hydrophobic adhesive layer is 60wt% PTFE emulsion. The preparation method of the hydrophobic adhesive layer is as follows: 60wt% PTFE emulsion and Nafion solution are mixed in a volume ratio of 10-15:1 to make the 60wt% PTFE emulsion into a viscous solution. After stirring, the hydrophobic adhesive layer is obtained.

[0033] The prepared hydrophobic adhesive layer is uniformly applied onto the hydrophobic film layer to obtain the waterproof layer 14. When the raw material of the hydrophobic adhesive layer is 60wt% PTFE emulsion, the thickness of the coating applied onto the hydrophobic film layer is 100-400μm.

[0034] The preparation method of the catalyst layer 13 in this embodiment is as follows: Carbon powder and deionized water are mixed at a mass ratio of 1:5-8. After shaking to disperse the carbon powder evenly, 60wt% PTFE emulsion is added to the evenly dispersed solution at a mass ratio of carbon powder to 60wt% PTFE emulsion of 1:0.9-1.2. The mixture is stirred thoroughly to form a dough-like mixture. The dough-like mixture is pressed using a mold to obtain the catalyst layer 13. The surface of the mold is provided with shallow grooves with a depth of 200-500μm. The thickness of the catalyst layer 13 can be controlled to be 200-500μm through the shallow grooves.

[0035] In this embodiment, the carbon powder material is one or more of activated carbon powder with a particle size of less than 100 mesh, carbon black, and other modified hydrogen peroxide-producing carbon powder catalyst materials. When the carbon powder is a mixture of activated carbon powder and carbon black, the mass ratio of activated carbon powder to carbon black is 3-5:1. Alternatively, sodium cellulose powder can be added to the carbon powder during the preparation of the catalyst layer 13, with a mass ratio of carbon powder to sodium cellulose powder of 50-80:3. After the carbon powder and sodium cellulose powder are mixed evenly, deionized water is added.

[0036] See attached Figure 6 After preparing the materials for pressing the air cathode 10, the air cathode 10 is pressed using the following method: The waterproof layer 14, catalyst layer 13, and current collector layer 12 are stacked and compacted in the order of waterproof layer 14, current collector layer 13, and catalyst layer 12, or in the order of waterproof layer 14, current collector layer 12, and catalyst layer 13. The mixture is then placed in a tablet press and pressed at 6-12 MPa for 1-3 minutes, followed by drying in a precision constant temperature oven at 120-180℃ for 2-4 hours to obtain the air cathode 10. The side of the waterproof layer 14 coated with a hydrophobic adhesive layer faces the catalyst layer 13, and the hydrophobic film layer of the waterproof layer 14 faces the gas chamber 11. The waterproof layer 14 is close to the gas chamber 11, while the catalyst layer 13 and current collector layer 12 face the wastewater.

[0037] In this embodiment, iron anodes 15 are provided between any two adjacent membrane modules in the reaction tank 1, and between the inner wall of the reaction tank 1 on the side of the outlet 3 and the membrane module near that inner wall. Each iron anode 15 is connected to the air cathode 10 of the two adjacent membrane modules facing it via a conductive connector 32. The conductive connector 32 forms an anode-cathode short circuit between the iron anode 15 and the air cathode 10 of the membrane module, forming a galvanic cell. The multiple iron anodes and air cathodes in the reaction tank 1 are thus connected in series to form a complete galvanic cell. When there is no membrane module on one side of an iron anode 15, the iron anode 15 is only connected to the membrane module on the other side via the conductive connector 32.

[0038] In this embodiment, the iron anode 15 can be any one of pig iron sheet, cast iron plate, and carbon steel plate, or it can be composed of industrial waste iron slag 28 and stainless steel mesh 27. See the appendix for details. Figure 4 and attached Figure 8 The role of iron anode 15 in this device is to release Fe²⁺ through anodic dissolution during the reaction process. + This provides an iron source for the reaction in this device.

[0039] When the iron anode 15 is composed of industrial waste iron slag 28 and stainless steel mesh 27, the preparation method is as follows: Take two 30-100 mesh stainless steel meshes 27, lay the industrial waste iron slag 28 flat on one side of the stainless steel mesh 27, and then cover the industrial waste iron slag 28 with the other side of the stainless steel mesh 27. Place the stainless steel mesh 27 containing the industrial waste iron slag 28 under a pressure of 15-25 MPa and press for 1-3 minutes to obtain the iron anode 15.

[0040] See attached Figure 19 When the iron anode 15 is composed of industrial waste iron slag 28 and stainless steel mesh 27, the conductive connector 32 can be a stainless steel alligator clip 29 with conductive properties. Both sides of the stainless steel mesh 27 of the iron anode 15 are provided with elongated and bent electrode connection portions 30. Both sides of the current collector layers 12 of the membrane module are provided with elongated and bent electrode connection portions 31. The iron anode 15 uses the stainless steel alligator clips 29 to clamp the electrode connection portions 30 and 31 together, forming a short circuit between the anode and cathode, thus creating a galvanic cell. The bending of the electrode connection portions 30 and 31 facilitates clamping them together with the stainless steel alligator clips 29.

[0041] Next, a recalcitrant wastewater treatment process production line was built, see attached. Figure 5 The production line is equipped with a stabilization container 21, a metering pump 22, a circulation pump 23, a pH meter 24, a magnetic stirrer 25, a small air pump 26, a dilute sulfuric acid pump 35, a sewage pump 36, and a reaction tank 1. The bottom of the stabilization container 21 is equipped with a drain outlet 34. The specific sewage treatment process is as follows: Before each wastewater treatment cycle begins, a certain amount of wastewater (the amount of wastewater depends on the actual capacity of the device to process at one time) is pumped into the stabilization container 21 by wastewater pump 36. Then, the treatment process begins. During treatment, the wastewater flows out of the outlet 3 of the reaction tank 1 and into the stabilization container 21 by gravity. H2O2 solution is added to the stabilization container 21 by metering pump 22. The H2O2 solution helps maintain the Fe content in the system. 2+ The concentration and pH value of the system are adjusted to maintain a stable reaction. During the treatment process, a pH meter is used to continuously monitor the pH of the wastewater in the stabilization container 21. When the wastewater in the stabilization container 21 becomes too alkaline, dilute H2SO4 solution is added via a dilute sulfuric acid pump 35. In the above process, a magnetic stirrer 25 is used to continuously mix the wastewater in the stabilization container 21 at a speed of 600-1200 rpm. The wastewater in the stabilization container 21 is then pumped back to the reaction tank 1 via a circulation pump 23 through the inlet 2, thus forming a continuous flow circulation degradation. Hose 28 is connected to a small air pump 26, and hose 39 is directly connected to the atmosphere. The small air pump 26 continuously supplies air to the air cathode 10. Sludge deposited in the reaction tank 1 is cleaned as needed. During the above operation, the pH of the wastewater in the stabilization container 21 needs to be maintained at 3-5. When the pH of the wastewater in the stabilization container 21 exceeds 5, dilute H2SO4 solution is added to maintain the pH at 3-5.

[0042] The above treatment is carried out in cycles (the amount of sewage treated in each cycle is fixed). After each cycle is completed, the water is discharged through the drain outlet 34, and sludge is discharged at regular intervals.

[0043] Example 2: This embodiment discloses a method for preparing an electro-Fenton air cathode assembly for catalytic H2O2 production, see attached figure. Figure 9 The details are as follows: Step 1. Preparation of the catalyst layer: The carbon powder (in this embodiment, the carbon powder is a mixture of activated carbon powder and carbon black in a ratio of 3-5:1) is mixed with water and 60wt% polytetrafluoroethylene emulsion (PTFE) in mass ratios of 1:5 and 1:1, respectively, and then ultrasonically vibrated to make it uniformly dispersed; and then it is thoroughly stirred with a glass rod to form a clay-like material for later use.

[0044] Step 2-3. Pressing and Drying: Spread the mixed slurry from Step 1 evenly in a mold with a thickness of 0.3 mm, and press it to form the catalyst layer; finally, stack the stainless steel mesh, catalyst layer and PTFE waterproof membrane in sequence, press them together using a tablet press at a pressure of 10 MPa, and then dry them in a precision constant temperature oven at 140 ℃ for 180 minutes to obtain the air cathode.

[0045] See attached Figure 10 In this embodiment, a glass frame is used, and the dimensions of a single membrane module are 160cm × 110cm, with an effective cathode area of ​​120cm².

[0046] Example 3: This embodiment discloses a method for preparing an electro-Fenton anode from industrial-grade waste iron slag. The specific method is as follows: A certain amount of industrial waste iron slag is evenly spread on a flat 3 cm × 5 cm stainless steel mesh substrate; then, another stainless steel mesh of the same specification is placed on top of the waste iron slag to form a "sandwich" structure. The assembly is placed on a tablet press and mechanically pressed at a pressure of 20 MPa to tightly bond the iron slag and stainless steel mesh, forming a dense and stable composite anode material. The iron anode prepared in this embodiment is shown in the attached figure. Figure 11 As shown.

[0047] Example 4: In this embodiment, the air cathode and iron anode prepared in Examples 2 and 3 are coupled together and placed in a reaction cell prepared in accordance with the method of Example 1 (the reaction cell contains a mixed solution of 150 mL Na2SO4 and 20 mg / L simulated pollutant 2,4-DCP) to simulate the electro-Fenton system reaction process, and the open-circuit voltage between the anode and cathode is measured using an electrochemical workstation.

[0048] The results are attached. Figure 12 As shown, the results indicate that the self-driven electric Fenton system prepared in this embodiment can stably output a voltage of 20-30 mV.

[0049] Example 5: This embodiment uses the self-driven electric Fenton system from Example 4 to conduct a degradation experiment on pharmaceutical wastewater.

[0050] In this embodiment, pharmaceutical blending water and pharmaceutical concentrate water were collected from the blending section and production section of a pharmaceutical factory's wastewater treatment plant, respectively. (The following text appears to be a separate, unrelated sentence: "Using...") Figure 5The wastewater treatment process shown degrades the aforementioned wastewater, with a treatment volume of 1.8 L per cycle. During operation, wastewater is pumped into the reaction tank through the inlet using a circulation pump, circulates, and then flows out through the outlet into an external stabilization container. It is then pumped back into the reactor by the circulation pump, and this cycle repeats. Specifically, the initial pH of the wastewater is adjusted to 3-5 (the pH of pharmaceutical preparation wastewater and concentration wastewater are both within this range, so no adjustment is needed). Wastewater in the stabilization container is pumped into the reactor at a rate of 110 r / min by the circulation pump, resulting in a flow rate of approximately 390 mL / min. Wastewater in the reaction tank flows into the stabilization container by gravity at a flow rate of approximately 410 mL / min. At the start of the reaction, a metering pump continuously injects a 10% hydrogen peroxide solution at a rate of 0.1 rpm into the stabilization container (the reaction time is 2 hours; the amount of hydrogen peroxide solution used after the reaction is completed can be determined by weighing). Samples are taken from the stabilization container at specific times during operation for analysis. After sampling, the pH of the solution in the stabilization container is adjusted back to 5 using a dilute H2SO4 solution. If the pH is less than 5, no adjustment is made. Because of the added H2O2 solution, the process operating environment is automatically regulated, so manual pH adjustment is usually unnecessary. Only in rare cases is a small amount of dilute H2SO4 solution added, usually just a few drops, which can be disregarded.

[0051] In this embodiment, the pharmaceutical preparation wastewater was first treated for degradation for 2 hours, and the results are shown in the appendix. Figure 13 As can be seen, the COD of the wastewater decreased from the initial 4370 mg / L to 2740 mg / L, while the BOD / COD ratio increased from 0.48 to 0.60. This increase in the ratio indicates that the biodegradability of the wastewater has been significantly improved, confirming the effectiveness of the process of the present invention in treating recalcitrant organic wastewater.

[0052] To verify the operational stability of the present invention, three parallel degradation experiments were conducted on pharmaceutical concentrated wastewater in this embodiment.

[0053] The results are attached. Figure 14 As can be seen from the three experiments, the initial COD of the wastewater was approximately 5000 mg / L, which was stably reduced to around 2600 mg / L after 2 hours of treatment. No significant deactivation of the degradation effect was observed, and the slope of the COD curve did not approach zero in the later stages of the reaction, indicating that ·OH was continuously generated and the oxidation reaction was effectively maintained. The BOD / COD ratio increased from 0.41 to over 0.55, indicating that this embodiment not only effectively degraded COD but also significantly improved the biodegradability of the wastewater, creating favorable conditions for subsequent biological treatment. In addition to removing organic matter, this embodiment can also simultaneously remove multiple pollutants. As shown in Table 1, when treating concentrated pharmaceutical wastewater, nitrates and total phosphorus were completely removed, and the ammonia nitrogen concentration decreased by 34.24 mg / L.

[0054] Table 1. Changes in indicators before and after treatment of pharmaceutical concentrate water

[0055] Example 6: This embodiment uses high-salt organic wastewater collected from a food company, and employs [a specific method / approach]. Figure 5 The wastewater treatment process shown was used to degrade the aforementioned wastewater. Because this wastewater exhibits typical characteristics of high ionic strength and high pollutant load, this embodiment aims to further evaluate the in-situ degradation performance of the electro-Fenton reactor and treatment process of the present invention in actual wastewater treatment.

[0056] In this embodiment, the treatment volume for each wastewater treatment is 1.8 L, and the operating method is consistent with that of the pharmaceutical wastewater in Example 5. Degradation results are shown in the appendix. Figure 15 As can be seen, during the continuous operation for 6 hours, the COD concentration of the wastewater decreased from the initial 42,000 mg / L to about 25,000 mg / L, and the average degradation rate reached 38 mg / (L·min), which verifies the good degradation ability of the system of the present invention in terms of high efficiency and speed.

[0057] Example 7: This embodiment needs to explain that, in the processes involved in Examples 1 to 6, the main degradation factor is H2O2 generated by the air cathode through the oxygen reduction reaction (ORR). Since the ORR reaction involves both 4-electron and 2-electron pathways, the 4-electron pathway generates H2O, while the 2-electron pathway generates Fenton's reagent H2O2. The 4-electron pathway causes the accumulation of ferrous iron and an increase in the pH of the reaction system. Furthermore, an unstable reaction environment can lead to a gradual weakening or even termination of the reaction, affecting degradation. Therefore, it is necessary to add H2O2 externally to adjust the reaction pathway, ensuring that the ORR proceeds primarily via the 2-electron pathway, thereby mitigating the adverse effects of the 4-electron pathway and allowing the reaction to proceed stably and continuously.

[0058] In summary, the main function of adding H2O2 in this embodiment is to regulate the system, not to provide reactants. To verify that the primary degradation factor in this embodiment is H2O2 generated by the oxygen reduction reaction at the air cathode, this embodiment verified the COD mineralization contribution rate of H2O2 from different sources in actual wastewater degradation experiments, as detailed below: The contribution ratio EF (%) of added H2O2 to the total COD mineralization rate is calculated using formula 1-3: (1) in, The number of electrons transferred (mmol) during the reduction of added H2O2 to H2O. The total number of electrons (mmol) equivalent to the complete degradation of COD is calculated using the following formula: (2) (3) Δ in the formula (g) and ΔC （COD） (mg / L) represents the mass of H2O2 consumed and the difference in COD concentration before and after degradation, respectively, and V is the volume of the treated wastewater (L).

[0059] The H2O2 dosage for each experiment is shown in the table below, and the contribution rate of H2O2 to COD mineralization in the pharmaceutical water treatment process is shown in the appendix. Figure 16 The volume of H2O2 added during the pharmaceutical concentrated water treatment process and its contribution to COD mineralization are shown in the appendix. Figure 17 The contribution rate of H2O2 to COD mineralization during the treatment of high-salt pickled mustard tuber wastewater is shown in the appendix. Figure 18 The results show that the main degradation effect in this invention is H2O2 generated by the oxygen reduction reaction of the air cathode.

[0060]

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A process for treating recalcitrant wastewater using a self-driven electric Fenton reactor, characterized in that, Includes the following steps: S1: Constructing a continuous flow self-driven electric Fenton reactor The reactor includes a rectangular reaction tank (1). An inlet (2) is provided at the bottom of one side wall of the reaction tank (1), and an outlet (3) is provided at the top of the other side wall of the reaction tank (1). Multiple membrane modules are provided in the reaction tank (1). The multiple membrane modules are arranged sequentially from the side where the inlet (2) is located to the side where the outlet (3) is located. After the sewage in the reaction tank (1) enters from the inlet (2), it flows out of the reaction tank (1) from the outlet (3) after passing around each membrane module in sequence. The membrane module includes a rectangular frame (4), with an air inlet (5) and an air outlet (6) respectively at the top two ends of the frame (4). A hose (7) is provided between the air outlet (6) of any membrane module and the air inlet (5) of the membrane module adjacent to it. The air inlet (5) of the membrane module near the water inlet (2) is provided with a hose (8) extending out of the sewage liquid surface. The air outlet (6) of the membrane module near the water outlet (3) is provided with a hose (9) extending out of the sewage liquid surface. An air cathode (10) is provided on both sides of the frame (4), and the space enclosed by the two air cathodes (10) and the frame (4) is an air chamber (11); the air cathode (10) is composed of a current collector layer (12), a catalyst layer (13) and a waterproof layer (14); Iron anodes (15) are provided between any two adjacent membrane modules in the reaction tank (1) and between the inner wall of the reaction tank (1) on the side of the outlet (3) and the membrane module near the inner wall of that side. Each iron anode (15) is provided with a conductive connector (32) between it and the air cathode (10) of the two adjacent membrane modules facing it. The conductive connector (32) makes the iron anode (15) and the air cathode (10) of the membrane module form a short circuit between the anode and cathode, forming a galvanic cell. S2: Establishing a recalcitrant wastewater treatment process The wastewater treatment process includes a stabilization container (21), a metering pump (22), a circulation pump (23), a pH meter (24), a magnetic stirrer (25), a small air pump (26), a dilute sulfuric acid pump (35), a wastewater pump (36), and a reaction tank (1). The stabilization container (21) has a drain outlet (34) at its bottom. The specific wastewater treatment process is as follows: Before each wastewater treatment cycle begins, a certain amount of wastewater is pumped into the stabilization container (21) by a wastewater pump (36). Then, the treatment process begins. During treatment, wastewater flows out of the outlet (3) of the reaction tank (1) and into the stabilization container (21) by gravity. H2O2 solution is added to the stabilization container (21) by a metering pump (22), and the pH of the wastewater in the stabilization container (21) is continuously monitored using a pH meter. When the wastewater in the stabilization container (21) becomes too alkaline, dilute H2SO4 solution is added to it by a dilute sulfuric acid pump (35). During the above process, a magnetic stirrer (25) is used at a speed of 600-1200... The wastewater in the stabilization container (21) is continuously mixed at a speed of rpm. The wastewater in the stabilization container (21) is pumped back to the reaction tank (1) through the inlet (2) by the circulation pump (23), thereby forming a continuous flow circulation degradation. The second hose (8) is connected to the small air pump (26), and the third hose (9) is directly connected to the atmosphere. The small air pump (26) continuously inputs air into the air cathode (10).

2. The process according to claim 1, characterized in that, In step S1, the bottom of the membrane module located in the odd-numbered column is sealed to the bottom surface of the reaction tank (1), and a gap (16) is provided between the bottom of the membrane module located in the even-numbered column and the bottom surface of the reaction tank (1). The two sides of the membrane module located in the odd-numbered column are sealed to the inner walls of the two sides of the reaction tank (1), and the two sides of the membrane module located in the even-numbered column are sealed to the inner walls of the two sides of the reaction tank (1). The height of the outlet (3) is higher than the height of the top of the membrane module in the odd-numbered column and lower than the height of the top of the membrane module in the even-numbered column. The liquid level of the sewage in the reaction tank (1) is higher than the top of the membrane module in the odd-numbered column and lower than the top of the membrane module in the even-numbered column. The bottom of the reaction tank (1) is provided with a slot 1 (17) higher than the bottom of the reaction tank (1) at the position directly opposite to each odd-numbered column membrane assembly. The inner walls on both sides of the reaction tank (1) are provided with a slot 2 (18) directly opposite to each even-numbered column membrane assembly. The bottom of the membrane assembly located in the odd-numbered column is inserted into the slot 1 (17) directly opposite to its position, and the two ends of the membrane assembly located in the even-numbered column are respectively inserted into the two slots 2 (18) directly opposite to its position. The membrane assembly and the inner wall of the reaction tank (1) are bonded and sealed with waterproof sealant. The bottom height of the card slot (17) is set to 3-6cm; each of the gaps (16) is provided with a sludge discharge hole (19) at the bottom of the reaction tank (1); a horizontal pipe (33) is provided below the reaction tank (1); the horizontal pipe (33) is connected to each sludge discharge hole (19); and the horizontal pipe (33) is provided with a solenoid valve (20).

3. The process according to claim 1, characterized in that, The current collector layer in step S1 is a titanium mesh or a stainless steel mesh. The waterproof layer in step S1 includes a hydrophobic film layer and a hydrophobic adhesive layer. The hydrophobic film layer is composed of one or more materials selected from PTFE, PVDF, PP, and nylon. The hydrophobic adhesive layer is any one of 60wt% PTFE emulsion, epoxy resin adhesive, and polydimethylsiloxane liquid. The hydrophobic adhesive layer is uniformly applied to the hydrophobic film layer to obtain the waterproof layer.

4. The process according to claim 3, characterized in that, The raw material for the hydrophobic adhesive layer is 60wt% PTFE emulsion. The preparation method of the hydrophobic adhesive layer is as follows: 60wt% PTFE emulsion and Nafion solution are mixed in a volume ratio of 10-15:1 and stirred until homogeneous to obtain the hydrophobic adhesive layer; the thickness of the hydrophobic adhesive layer applied to the hydrophobic film layer is 100-400μm.

5. The process according to claim 4, characterized in that, The preparation method of the catalyst layer is as follows: carbon powder and deionized water are mixed in a mass ratio of 1:5-8. After shaking to disperse the carbon powder evenly, 60wt% PTFE emulsion is added to it in a mass ratio of carbon powder to 60wt% PTFE emulsion of 1:0.9-1.

2. The mixture is stirred evenly to form a dough-like mixture. The dough-like mixture is pressed with a mold to obtain the catalyst layer. The carbon powder is one or more of activated carbon powder and carbon black with a particle size of less than 100 mesh.

6. The process according to claim 5, characterized in that, The carbon powder contains sodium cellulose powder, and the mass ratio of carbon powder to sodium cellulose powder is 50-80:3; the thickness of the catalyst layer is 200-500 μm.

7. The process according to claim 6, characterized in that, The air cathode is prepared as follows: the waterproof layer, catalyst layer, and current collector layer are stacked and compacted in the order of waterproof layer, current collector layer, and catalyst layer, or in the order of waterproof layer, current collector layer, and catalyst layer. After pressing in a tablet press at 6-12 MPa for 1-3 minutes, it is placed in a precision constant temperature oven and dried at 120-180℃ for 2-4 hours to obtain the air cathode. The side of the waterproof layer coated with the hydrophobic adhesive layer faces the catalyst layer, and the hydrophobic film layer of the waterproof layer faces the air chamber.

8. The process according to claim 1, characterized in that, The iron anode is any one of pig iron sheet, cast iron plate, and carbon steel plate, or is made from industrial waste iron slag. The method for preparing the iron anode using industrial waste iron slag is as follows: Take two 30-100 mesh stainless steel meshes (27), lay the industrial waste iron slag (28) flat on one side of the stainless steel mesh (27), and then cover the industrial waste iron slag (28) with the other side of the stainless steel mesh (27). Place the stainless steel mesh (27) wrapped with the industrial waste iron slag (28) at 15-25 degrees Celsius. Pressed under MPa pressure for 1-3 minutes, an iron anode (15) is obtained; the conductive connector (32) is a stainless steel alligator clip (29) with conductive properties. The stainless steel mesh (27) on both sides of the iron anode (15) is provided with an elongated and bent electrode connection part one (30). The current collector layer (12) on both sides of the membrane module is provided with an elongated and bent electrode connection part two (31). The iron anode (15) clamps the electrode connection part one (30) with the corresponding electrode connection part two (31) by the stainless steel alligator clip (29) to form a short circuit between the anode and cathode, forming a galvanic cell.

9. The process according to claim 7, characterized in that, The carbon powder is a mixture of activated carbon powder and carbon black in a ratio of 3-5:1, and the mass ratio of carbon powder to 60wt% PTFE emulsion is 1:

1. When preparing the air cathode, a tablet press is used to press and composite the carbon powder under a pressure of 10MPa, and then the carbon powder is placed in a precision constant temperature oven at 140℃ for 180 minutes to dry.

10. The process according to claim 1, characterized in that, In step S2, the pH of the wastewater in the stabilization container is maintained at 3-5. When the pH of the wastewater in the stabilization container exceeds 5, a dilute H2SO4 solution is added to it.

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