Method for enhancing performance of anaerobic membrane bioreactor by coupling internal electron circulation with external electric field

Abstract

The application relates to the technical field of wastewater biological treatment, in particular to a method for enhancing the performance of an anaerobic membrane bioreactor by coupling internal electron circulation with an external electric field. The method comprises the following steps: preparing a surface conductive flat membrane assembly, the surface conductive flat membrane assembly being formed by alternately coating a stainless steel mesh and a titanium mesh on the surface of a flat membrane unit; constructing an electrochemical anaerobic membrane bioreactor, the surface conductive flat membrane assembly serving as the cathode and the anode of the electrochemical anaerobic membrane bioreactor and being connected to a direct current power supply through wires; preparing a carbonized MIL-53(Fe) microelectric field material, the carbonized MIL-53(Fe) microelectric field material being a powder with a particle size ranging from 1 micrometer to 10 micrometers; dispersing the carbonized MIL-53(Fe) microelectric field material in the form of powder in anaerobic digestion liquid of the electrochemical anaerobic membrane bioreactor; and uniformly mixing the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material by mechanical stirring or anaerobic digestion gas stirring. The method realizes efficient control of membrane pollution of the anaerobic membrane bioreactor and significant enhancement of anaerobic digestion efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater biological treatment, in particular to a method for enhancing the performance of an anaerobic membrane bioreactor by coupling internal electron circulation with external electric field. BACKGROUND

[0002] An anaerobic membrane bioreactor (AnMBR) is a wastewater treatment process that combines anaerobic digestion and membrane filtration technology. It converts biodegradable organic compounds into biogas through hydrolysis and fermentation, hydrogen and acetate production, and methanogenesis. The solid-liquid separation is then achieved by membrane filtration, allowing the wastewater to be recycled as a "carrier of resources and energy". Meanwhile, the selective permeability of the membrane module effectively retains the anaerobic sludge in the reactor, separating the sludge retention time (SRT) and the hydraulic retention time (HRT), and improving the stability of the anaerobic system.

[0003] Despite the advantages of AnMBR, it still has many limitations. Membrane fouling and low anaerobic digestion efficiency are the main limiting factors of AnMBR. To address the problem of low anaerobic digestion efficiency in AnMBR, adding exogenous mediators is an effective method to promote anaerobic digestion performance. Current research usually adds conductive materials to promote the electron transfer rate between anaerobic microorganisms and provide attachment sites for microbial growth. Meanwhile, some studies have found that exogenous mediators with capacitive properties can store excess electrons produced by acid-producing bacteria during anaerobic digestion and slowly release them to methanogens, thereby regulating the metabolic imbalance between acid-producing bacteria and methanogens and effectively alleviating reactor acidification. However, the above materials can only play a "passive" role in regulating electrons between anaerobic microorganisms, and the electron transfer performance is still limited. SUMMARY

[0004] The present application provides a method for enhancing the performance of an anaerobic membrane bioreactor by coupling internal electron circulation with external electric field to solve the above problems.

[0005] In a first aspect, the present application provides a method for enhancing the performance of an anaerobic membrane bioreactor by coupling internal electron circulation with external electric field, which comprises:

[0006] S1, preparing a surface conductive flat sheet membrane module by alternately coating stainless steel mesh and titanium mesh on the surface of a flat sheet membrane unit;

[0007] S2, constructing an electrochemical anaerobic membrane bioreactor, wherein the surface conductive flat sheet membrane module serves as the cathode and anode of the electrochemical anaerobic membrane bioreactor and is connected to a direct current power source through wires;

[0008] S3, preparing the carbonized MIL-53(Fe) microelectric field material, which is a powder with a particle size ranging from 1 to 10 microns;

[0009] S4, dispersing the carbonized MIL-53(Fe) microelectric field material in the form of a powder in the anaerobic digestion liquid of the electrochemical anaerobic membrane bioreactor;

[0010] S5, uniformly mixing the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material by mechanical stirring or anaerobic digestion gas stirring.

[0011] Through the above technical solutions, the microelectric field material is built in the anaerobic membrane bioreactor and coupled with the alternating membrane electric field, achieving efficient control of membrane fouling and significant enhancement of anaerobic digestion efficiency in the anaerobic membrane bioreactor. The problems of membrane fouling and low anaerobic digestion efficiency are simultaneously and efficiently solved, realizing long-term stable operation of the anaerobic membrane bioreactor. By adopting the method of coating metal mesh to construct a new type of efficient surface conductive flat membrane module, and alternately setting it as a cathode and an anode, a more uniform electric field gradient is formed in the interval area of the flat membrane sheet, and the preparation operation is simplified, effectively reducing the cost.

[0012] Optionally, the wire diameter of the stainless steel mesh and the titanium mesh is 0.02-0.03 mm, and the mesh size is 0.2-0.3 mm.

[0013] Through the above technical solutions, it helps to reduce the shielding of the effective filtration area on the membrane surface, thereby maintaining a high membrane flux. At the same time, the fine wire diameter and mesh size can ensure that the metal mesh is closely attached to the surface of the flat membrane unit, forming a uniform conductive layer, thereby producing a more uniform electric field distribution on the membrane surface when the electric field is applied, effectively inhibiting membrane fouling. Secondly, this grid structure provides additional attachment sites for anaerobic microorganisms, promoting the formation and growth of biofilms, which is beneficial to improving the anaerobic digestion efficiency.

[0014] Optionally, the output voltage range of the direct current power supply is 0.4-1.0 V.

[0015] Through the above technical solutions, a stable and uniform alternating electric field is established between the cathode and the anode of the surface conductive flat membrane module. This electric field can effectively prevent the adsorption and accumulation of negatively charged pollutants (such as extracellular polymeric substances EPS) on the membrane surface through electrostatic repulsion, thereby significantly slowing down membrane fouling. At the same time, a moderate electric field strength can also promote interspecies electron transfer (IET) between anaerobic microorganisms, accelerating the degradation of organic matter and the generation of methane, thereby improving the anaerobic digestion efficiency.

[0016] Optionally, the carbonized MIL-53(Fe) micro-electric field material is prepared by pyrolysis of MIL-53(Fe) under a nitrogen atmosphere at 750°C to 900°C.

[0017] The above technical solution endows the carbonized MIL-53(Fe) micro-electric field material with excellent conductivity. At the same time, the pyrolysis under a nitrogen atmosphere can effectively inhibit the oxidation of the material at high temperature, ensure the purity and structural integrity of the carbonization products, and avoid the formation of non-conductive impurities such as amorphous carbon or iron oxide. This makes the carbonized MIL-53(Fe) micro-electric field material not only have good conductivity, but also have micro-electric field effect and charge regulation performance, which can actively induce electron transfer between anaerobic microorganisms and significantly improve the efficiency of anaerobic digestion.

[0018] Optionally, the amount of the carbonized MIL-53(Fe) micro-electric field material added to the electrochemical anaerobic membrane bioreactor is from 0.5 g / L to 2.0 g / L.

[0019] By employing the above technical solutions, a balance is struck between material costs and the improvement in anaerobic digestion performance. This allows the carbonized MIL-53(Fe) micro-electric field material to generate sufficient micro-electric field effects or provide sufficient electron transfer sites while reducing material costs. This effectively promotes electron transfer between anaerobic microorganisms, accelerates the degradation of organic matter and the generation of methane.

[0020] Optionally, the temperature in the electrochemical anaerobic membrane bioreactor is between 20°C and 40°C.

[0021] The above technical solutions ensure the activity and growth of anaerobic microorganisms, thereby achieving efficient organic matter degradation and methane production, and improving reactor stability.

[0022] Optionally, the hydraulic retention time in the electrochemical anaerobic membrane bioreactor is 6 to 12 hours.

[0023] The above technical solutions ensure that wastewater has sufficient residence time in the reactor, enabling anaerobic microorganisms to fully degrade organic pollutants, improve effluent quality and methanogenesis efficiency, and avoid unnecessary increases in operating costs.

[0024] Optionally, the flat sheet membrane unit of the surface conductive flat sheet membrane assembly is an organic flat sheet membrane or a ceramic flat sheet membrane.

[0025] The above technical solutions enable the surface conductive flat sheet membrane module to meet the needs of different wastewater treatment scenarios, improve wastewater treatment performance, make the surface conductive flat sheet membrane module easy to maintain and clean, and ensure the service life of the surface conductive flat sheet membrane module.

[0026] Optionally, the electrochemical anaerobic membrane bioreactor is provided with a mechanical stirrer or an anaerobic digestion gas circulating pump; the mechanical stirrer stirs the anaerobic digestion liquid at a rotating speed of 20 rpm to 50 rpm; and the anaerobic digestion gas circulating pump circulates the anaerobic digestion gas at a flow rate of 0.1 L / min to 0.5 L / min to maintain uniform dispersion of the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material.

[0027] Through the above technical solution, uniform dispersion of the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material is ensured, the uniformly dispersed microelectric field material can maximize contact with anaerobic microorganisms, promote electron transfer, improve organic matter degradation efficiency, and through the stirring effect, membrane surface pollution can be effectively reduced, the membrane surface is scoured by shear force, accumulation of pollutants on the membrane holes and the membrane surface is prevented, and thus a higher membrane flux is maintained.

[0028] Optionally, the sludge concentration in the electrochemical anaerobic membrane bioreactor is 6000 mg / L to 12000 mg / L.

[0029] Through the above technical solution, sufficient amount of active microorganisms in the reactor is maintained, thereby realizing efficient organic matter degradation and methane production, and avoiding operation problems caused by excessively high sludge concentration.

[0030] In a second aspect, the application provides a preparation method of the carbonized MIL-53(Fe) microelectric field material, which comprises:

[0031] Terephthalic acid and ferric chloride hexahydrate are added to N-N dimethylformamide (DMF) to configure a solution, and the mass ratio of the terephthalic acid, the ferric chloride hexahydrate and the N-N dimethylformamide (DMF) is in a specific ratio range;

[0032] The solution is transferred to a stainless steel autoclave with a volume of 100 mL and lined with polytetrafluoroethylene, and the autoclave is placed in a constant temperature oven at 160℃ for heating for 6 h;

[0033] The autoclave is taken out of the oven and naturally cooled to 25℃, the reaction solution is transferred to a centrifuge tube, centrifuged at a rotating speed of 8000 rpm for 10 minutes, the supernatant is discarded, 20 mL of anhydrous ethanol is added, ultrasonic dispersion is performed for 5 minutes, the above centrifugation and washing steps are repeated three times, and finally dried in a vacuum oven at 80℃ for 8 hours to obtain a MIL-53(Fe) powder;

[0034] The MIL-53(Fe) powder is placed in a quartz boat of a tube furnace, high-purity nitrogen is passed in at a flow rate of 100 mL / min, heated to 750-900℃ at a heating rate of 5℃ / min, and kept at this temperature for 2 hours, then cooled to 25℃ with the furnace, and taken out to obtain the carbonized MIL-53(Fe) microelectric field material.

[0035] Optionally, the amount of terephthalic acid is 1.328 g, the amount of iron chloride hexahydrate is 2.164 g, and the amount of N-N dimethyl formamide (DMF) is 80 mL.

[0036] Optionally, the solution is heated at 160℃ for 6 h. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0038] Figure 1 A flow chart of a method for enhancing the performance of an anaerobic membrane bioreactor by coupling internal electron circulation with external electric field according to an embodiment of the present application is provided.

[0039] Figure 2 A flow chart of a method for preparing a carbonized MIL-53(Fe) microelectric field material according to an embodiment of the present application is provided.

[0040] Figure 3 A graph of the transmembrane pressure difference of an electrochemical anaerobic membrane bioreactor under different electric field application modes according to an embodiment of the present application is provided.

[0041] Figure 4 A graph of the COD concentration change and methane production change of an anaerobic membrane bioreactor after adding different microelectric field materials according to an embodiment of the present application is provided. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0043] In addition, the term "and / or", used herein, merely describes an associated relationship, which means that there can be three relationships, for example, A and / or B, which means that A exists alone, A and B exist together, and B exists alone. In addition, the character " / " herein, unless otherwise specified, generally represents an "or" relationship between the front and rear associated objects.

[0044] The embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0045] Although AnMBR has many advantages, it still has many limitations. Among them, membrane fouling and low anaerobic digestion efficiency are the main limiting factors of AnMBR. In view of the problem of low anaerobic digestion efficiency of AnMBR, adding exogenous mediators is one of the effective methods to promote anaerobic digestion performance. At present, the research usually adds conductive materials to promote the electron transfer rate between anaerobic microorganisms and provide attachment sites for microbial growth. At the same time, it has been found that exogenous mediators with capacitive properties can store excess electrons produced by acid-producing bacteria during anaerobic digestion and slowly release them to methanogens, thereby regulating the metabolic imbalance between acid-producing bacteria and methanogens, effectively alleviating reactor acidification. However, the above materials can only play a "passive" role in regulating electrons between anaerobic microorganisms, and the electron transfer performance is still limited.

[0046] Based on this, the present application provides a method for enhancing the performance of an anaerobic membrane bioreactor by coupling an internal electron cycle with an external electric field, which realizes efficient control of membrane fouling and significant enhancement of anaerobic digestion efficiency in the anaerobic membrane bioreactor by embedding micro-electric field materials in the anaerobic membrane bioreactor and coupling an alternating membrane electric field. The present application simultaneously and efficiently solves the problems of membrane fouling and low anaerobic digestion efficiency, and realizes long-term stable operation of the anaerobic membrane bioreactor. By adopting the method of coating metal mesh, a new type of high-efficiency surface conductive flat membrane assembly is constructed, and it is alternately set as cathode and anode, forming a more uniform electric field gradient in the interval area of the flat membrane sheet, while simplifying the preparation operation and effectively reducing the cost.

[0047] Figure 1 A flow chart of a method for enhancing the performance of an anaerobic membrane bioreactor by coupling an internal electron cycle with an external electric field is provided for an embodiment of the present application. As shown in the figure, the method comprises: Figure 1

[0048] S1, preparing a surface conductive flat membrane assembly, which is formed by alternately coating stainless steel mesh and titanium mesh on the surface of a flat membrane unit;

[0049] S2, constructing an electrochemical anaerobic membrane bioreactor, the surface conductive flat membrane assembly is used as the cathode and anode of the electrochemical anaerobic membrane bioreactor, and is connected to a direct current power supply through a wire; ​

[0050] S3, preparing carbonized MIL-53(Fe) microelectric field material, the carbonized MIL-53(Fe) microelectric field material is a powder with a particle size ranging from 1 micrometer to 10 micrometers;

[0051] S4, dispersing the carbonized MIL-53(Fe) microelectric field material in the form of a powder in the anaerobic digestion liquid of the electrochemical anaerobic membrane bioreactor;

[0052] S5, uniformly mixing the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material by mechanical stirring or anaerobic digestion gas stirring.

[0053] The current anaerobic membrane bioreactor (AnMBR) has the advantages of converting organic matter into biogas and realizing solid-liquid separation in sewage treatment, but still faces problems of membrane fouling and low anaerobic digestion efficiency in practical application. In the prior art, the conductive membrane needs to be provided with a counter electrode as a cathode or anode, it is difficult to form a uniform electric field, and the preparation of the conductive membrane is complex, the cost is high, and the conductivity is poor. In addition, the existing exogenous mediator can only play a "passive" regulation role in electron transfer of anaerobic microorganisms, and the electron transfer efficiency still has room for improvement, and the traditional metal anode has passivation problems. The present application aims to provide a method for coupling an internal microelectric field material to an alternating membrane to strengthen the performance of an anaerobic membrane bioreactor, so as to simultaneously achieve efficient control of membrane fouling and significant strengthening of anaerobic digestion efficiency of the anaerobic membrane bioreactor, thereby realizing long-term stable operation of the anaerobic membrane bioreactor. Based on real-time signal processing and dynamic control theory, the electric field between the membrane and the electrode and the electron transfer function of the microelectric field material are combined to realize precise anaerobic digestion and membrane fouling control. The surface conductive flat membrane assembly is formed by alternately coating stainless steel mesh and titanium mesh, which serves as a cathode and anode of the electrochemical anaerobic membrane bioreactor, and under the action of a direct current power supply, a uniform and effective electric field is formed on the membrane surface. The carbonized MIL-53(Fe) microelectric field material acts as an exogenous mediator and can actively induce electron transfer between anaerobic microorganisms. During operation, first, a surface conductive flat membrane assembly 1 is prepared, then an electrochemical anaerobic membrane bioreactor is constructed and connected to a direct current power supply. Then, carbonized MIL-53(Fe) microelectric field material with a particle size of 1 micrometer to 10 micrometers is prepared, and is dispersed in the form of a powder in the anaerobic digestion liquid, and is uniformly mixed by mechanical stirring or anaerobic digestion gas stirring, thereby strengthening the anaerobic digestion performance and membrane fouling control effect. The components work synergistically to realize stable and efficient operation of the anaerobic membrane bioreactor.

[0054] The application comprises core steps: S1, preparing a surface conductive flat membrane assembly by alternately coating stainless steel mesh and titanium mesh on the surface of a flat membrane unit, which can simultaneously serve as a cathode and an anode, forming a uniform and effective electric field on the membrane surface; S2, constructing an electrochemical anaerobic membrane bioreactor, connecting the surface conductive flat membrane assembly as a cathode and an anode of the electrochemical anaerobic membrane bioreactor to a direct current power supply through wires, which can effectively alleviate membrane fouling through electrostatic repulsion and anode oxidation under the action of an external electric field; S3, preparing carbonized MIL-53(Fe) microelectric field material, which is a powder with a particle size ranging from 1 microns to 10 microns, has excellent conductivity and capacitive properties, and can promote electron transfer between anaerobic microorganisms; S4, dispersing the carbonized MIL-53(Fe) microelectric field material in the form of powder in the anaerobic digestion liquid of the electrochemical anaerobic membrane bioreactor to make it fully contact with anaerobic microorganisms; S5, uniformly mixing the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material by mechanical stirring or anaerobic digestion gas stirring to ensure uniform dispersion of the microelectric field material in the reactor and maximize its role. This stirring method ensures effective contact between the microelectric field material and anaerobic microorganisms, promotes electron transfer, and improves anaerobic digestion efficiency.

[0055] The application realizes efficient control of membrane fouling and significant enhancement of anaerobic digestion efficiency in an anaerobic membrane bioreactor by embedding microelectric field material and coupling an alternating membrane electric field. The application simultaneously and efficiently solves the problems of membrane fouling and low anaerobic digestion efficiency, and realizes long-term stable operation of the anaerobic membrane bioreactor. By adopting the method of coating metal mesh to construct a new type of high-efficiency surface conductive flat membrane assembly, and alternately setting it as a cathode and an anode to form a more uniform electric field gradient in the interval area of the flat membrane sheet, the preparation operation is simplified and the cost is effectively reduced.

[0056] In the above embodiments, the flat sheet membrane unit of the surface conductive flat sheet membrane assembly can be replaced by different materials, such as organic flat sheet membrane or ceramic flat sheet membrane, to adapt to different water quality conditions and treatment requirements. Organic flat sheet membrane has the advantages of lower cost and easy processing, and is suitable for general wastewater treatment; ceramic flat sheet membrane has higher mechanical strength and chemical stability, and is suitable for high-strength or special wastewater treatment. When constructing the electrochemical anaerobic membrane bioreactor, the output voltage range of the direct current power supply can be fine-tuned between 0.4V and 1.0V to optimize the electric field strength, so as to achieve the best membrane fouling control effect and anaerobic digestion efficiency. In the preparation method of the carbonized MIL-53(Fe) micro-electric field material, the pyrolysis temperature of MIL-53(Fe) can be adjusted in a nitrogen atmosphere at 750°C to 900°C. The materials obtained by pyrolysis at different temperatures may differ in particle size distribution, specific surface area and electrical conductivity, thereby affecting the micro-electric field effect and electron transfer efficiency. For example, carbonization at 800°C can obtain the best performance of the micro-electric field material. The dosage of the carbonized MIL-53(Fe) micro-electric field material 2 can be adjusted in the range of 0.5g / L to 2.0g / L to adapt to anaerobic digestion liquid with different sludge concentrations and organic loads, and by optimizing the dosage, the best methane production rate and membrane flux can be achieved. In addition, in step S5, in addition to mechanical stirring or anaerobic digestion gas stirring, other methods such as ultrasonic dispersion and hydraulic circulation can also be used to ensure uniform mixing of the carbonized MIL-53(Fe) micro-electric field material in the anaerobic digestion liquid, and improve the dispersion effect and efficiency. The flow rate of the anaerobic digestion gas stirring and the rotation speed of the mechanical stirring can also be adjusted according to the actual situation of the reactor to adapt to different sludge viscosities and reactor sizes.

[0057] In some embodiments, the wire diameter of the stainless steel mesh and the titanium mesh is 0.02mm to 0.03mm, and the mesh size is 0.2mm to 0.3mm.

[0058] The surface conductive flat sheet membrane assembly is formed by alternately coating stainless steel mesh and titanium mesh, and the wire diameter of the stainless steel mesh and the titanium mesh is 0.02mm to 0.03mm, and the mesh size is 0.2mm to 0.3mm. As the cathode and anode of the electrochemical anaerobic membrane bioreactor, under the action of the direct current power supply, a uniform and effective electric field is formed on the membrane surface. The carbonized MIL-53(Fe) micro-electric field material as an exogenous mediator can actively induce electron transfer between anaerobic microorganisms. During operation, first, the surface conductive flat sheet membrane assembly is prepared, then the electrochemical anaerobic membrane bioreactor 10 is constructed and connected to the direct current power supply. Then, the carbonized MIL-53(Fe) micro-electric field material with a particle size of 1 microns to 10 microns is prepared and dispersed in the anaerobic digestion liquid in powder form, and is uniformly mixed by mechanical stirring or anaerobic digestion gas stirring, thereby strengthening the anaerobic digestion performance and membrane fouling control effect. Through the synergistic effect of each component, stable and efficient operation of the anaerobic membrane bioreactor is achieved.

[0059] The present application in the preparation of surface conductive flat sheet membrane module, by the stainless steel mesh and titanium mesh are alternately coated in the flat sheet membrane unit surface, wherein the stainless steel mesh and titanium mesh wire diameter is 0.02mm to 0.03mm, mesh size is 0.2mm to 0.3mm. This specific wire diameter and mesh size design has multiple technical advantages. First, the fine wire diameter (0.02mm to 0.03mm) helps to reduce the effective filtration area of the membrane surface, thereby maintaining a higher membrane flux. At the same time, the fine wire diameter and the appropriate mesh size (0.2mm to 0.3mm) can ensure that the metal mesh is closely attached to the surface of the flat sheet membrane unit, forming a uniform conductive layer, so that a more uniform electric field distribution is generated on the membrane surface when the electric field is applied, effectively inhibiting membrane fouling. Secondly, this grid structure provides additional attachment sites for anaerobic microorganisms, promoting the formation and growth of biofilm, which is beneficial to improve the efficiency of anaerobic digestion. In addition, the alternating use of stainless steel mesh and titanium mesh, combined with their specific wire diameter and mesh size, can optimize the electrochemical performance, the stainless steel mesh provides good conductivity, while the titanium mesh has excellent corrosion resistance, the combination of the two can improve the stability and service life of the surface conductive flat sheet membrane module 1, avoiding the high cost of traditional anode passivation of sacrificial electrode materials. The specific wire diameter and mesh size (0.02mm to 0.03mm wire diameter, 0.2mm to 0.3mm mesh size) ensure the uniformity of the electric field on the membrane surface, significantly reducing the membrane fouling rate.

[0060] In the above embodiments, the wire diameter and mesh size of the stainless steel mesh and titanium mesh can be fine-tuned according to the specific membrane material and processing requirements. For example, for high-concentration wastewater treatment or scenarios requiring higher membrane flux, the mesh size can be appropriately increased to reduce the hydraulic resistance while maintaining sufficient electric field uniformity. For scenarios requiring finer filtration or stronger anti-fouling ability, finer wire diameter and smaller mesh size can be considered, but the impact on membrane flux needs to be balanced. In actual application, the wire diameter and mesh size can be optimized according to the viscosity, suspended solids content and target treatment efficiency of the anaerobic digestion liquid. In addition, in addition to stainless steel mesh and titanium mesh, other metal mesh materials with good conductivity and corrosion resistance, such as nickel mesh or carbon fiber mesh, can also be explored to further optimize the performance of the surface conductive flat sheet membrane module 1. The choice of these alternative materials will affect the cost, life and electrochemical properties of the module, which needs to be evaluated according to the specific application scenario.

[0061] In some embodiments, the output voltage range of the direct current power supply is 0.4V to 1.0V.

[0062] As the cathode and anode of the electrochemical anaerobic membrane bioreactor, they are connected to a direct current power supply with an output voltage range of 0.4V to 1.0V. The MIL-53(Fe) carbonization microelectric field material as an exogenous mediator can actively induce electron transfer between anaerobic microorganisms. During operation, first prepare the surface conductive flat membrane module, then build the electrochemical anaerobic membrane bioreactor and connect the direct current power supply. Then prepare the MIL-53(Fe) carbonization microelectric field material with a particle size of 1-10 microns, and disperse it in the anaerobic digestion liquid in powder form, and mix it uniformly by mechanical stirring or anaerobic digestion gas stirring, thereby strengthening the anaerobic digestion performance and membrane pollution control effect. The components work synergistically to achieve stable and efficient operation of the anaerobic membrane bioreactor.

[0063] In the construction of the electrochemical anaerobic membrane bioreactor, the output voltage range of the direct current power supply is set to 0.4V to 1.0V. The selection of this voltage range is based on the comprehensive consideration of membrane pollution control and anaerobic digestion efficiency optimization. A voltage lower than 0.4V may not be enough to form an effective electric field gradient on the membrane surface, making it difficult to generate enough electrostatic repulsion to effectively inhibit membrane pollution and insufficiently promote microbial electron transfer. While a voltage higher than 1.0V may lead to excessive energy consumption, even trigger hydrolysis side reactions, adversely affect microbial activity, and increase operating costs. Within this 0.4V to 1.0V voltage range, the direct current power supply can ensure the establishment of a stable and uniform alternating electric field between the cathode and anode of the surface conductive flat membrane module. This electric field can effectively prevent the adsorption and accumulation of negatively charged pollutants (such as extracellular polymeric substances EPS) on the membrane surface through electrostatic repulsion, thereby significantly slowing down membrane pollution. At the same time, a moderate electric field strength can also promote interspecies electron transfer (IET) between anaerobic microorganisms, accelerate the degradation of organic matter and the generation of methane, and improve the anaerobic digestion efficiency. The output voltage range of the direct current power supply is 0.4V to 1.0V, which ensures the uniformity and effectiveness of the membrane surface electric field, significantly reducing the membrane pollution rate

[0064] In the above embodiments, the output voltage range of the direct current power supply is 0.4V to 1.0V, which is a preferred range, but in actual applications, it can be fine-tuned according to the specific wastewater quality, organic load, membrane pollution degree and target methane production efficiency. For example, for high-concentration organic wastewater, a slightly higher voltage may be needed to enhance the electric field effect and promote organic matter degradation; while for low-concentration wastewater, a lower voltage can meet the demand, while saving energy consumption. In addition, the application method of the direct current power supply can also be varied, such as using pulsed direct current electric field or periodic reverse electric field to further optimize the membrane pollution control effect and microbial activity. Pulsed electric field can reduce energy consumption by applying electric field intermittently, while taking advantage of the electric field interval to promote the shedding of membrane surface pollutants; periodic reverse electric field can more effectively remove charged pollutants adsorbed on the membrane surface and prevent electrode passivation. These alternative solutions can be adjusted and optimized according to actual operation data and system performance.

[0065] In some embodiments, the carbonized MIL-53(Fe) microelectric field material is prepared by pyrolyzing MIL-53(Fe) powder 21 under a nitrogen atmosphere at 750°C to 900°C.

[0066] In the present application, the preparation method of the carbonized MIL-53(Fe) microelectric field material is crucial, which is obtained by pyrolyzing MIL-53(Fe) powder under a nitrogen atmosphere at 750°C to 900°C. The selection of this preparation condition is based on the optimization of the material's conductivity, microelectric field effect and structural stability. First of all, MIL-53(Fe) is a metal-organic framework material, which contains iron elements in its skeleton. During the high-temperature pyrolysis process, the organic ligand decomposes and carbonizes, and at the same time, the iron element may be converted into a carbonide or nano-iron particle with better conductivity, thereby endowing the material with excellent conductivity. Secondly, pyrolysis under a nitrogen atmosphere can effectively inhibit the oxidation of the material at high temperature, ensuring the purity and structural integrity of the carbonized product, and avoiding the formation of amorphous carbon or iron oxide and other non-conductive impurities. The temperature range of 750°C to 900°C is optimized through experiments. Below 750°C, carbonization may not be complete, and the conductivity is poor; above 900°C, the material structure may collapse, and the specific surface area decreases, thereby affecting its microelectric field effect and microbial adhesion capacity. This preparation method makes the carbonized MIL-53(Fe) microelectric field material not only have good conductivity, but also have microelectric field effect and charge regulation performance, which can actively induce electron transfer between anaerobic microorganisms, significantly improving the anaerobic digestion efficiency.

[0067] The carbonized MIL-53(Fe) micro-electric field material is prepared by pyrolysis of MIL-53(Fe) powder in a nitrogen atmosphere at 750-900°C, ensuring the material's electrical conductivity and micro-electric field effect. By using a metal mesh coating method, the stability of the conductive film is improved, avoiding the high cost of anode passivation of traditional sacrificial electrode materials.

[0068] In the above embodiments, the preparation method of the carbonized MIL-53(Fe) micro-electric field material can be varied and optimized. For example, in addition to a nitrogen atmosphere, pyrolysis carbonization can also be carried out in an inert gas (such as argon) atmosphere to further control the morphology and composition of the carbonized product. The heating rate and isothermal time of pyrolysis can also be adjusted to affect the crystallinity, pore structure and electrical conductivity of the material. For example, a faster heating rate or longer isothermal time can result in different degrees of carbonization and material properties. In addition, in addition to MIL-53(Fe) powder, other metal organic frameworks (MOFs) can also be explored as precursors, such as MOFs based on other transition metals (such as Co, Ni) or different organic ligands, which can form carbon-based materials with different micro-electric field effects and electron transfer capabilities after pyrolysis. Other dopants (such as sulfur, phosphorus) can also be introduced during the pyrolysis process to further improve the electrical conductivity and catalytic activity of the material.

[0069] In some embodiments, the dosage of the carbonized MIL-53(Fe) micro-electric field material 2 in the electrochemical anaerobic membrane bioreactor 10 is 0.5-2.0 g / L.

[0070] In the present application, the dosage of the carbonized MIL-53(Fe) micro-electric field material in the electrochemical anaerobic membrane bioreactor is set to 0.5-2.0 g / L. This dosage range has been optimized through experiments, aiming to balance the material cost and the performance improvement effect of anaerobic digestion. A dosage lower than 0.5 g / L may result in a too low concentration of the micro-electric field material in the anaerobic digestion liquid, which cannot form sufficient micro-electric field effects or provide enough electron transfer sites, thus not significantly improving the anaerobic digestion efficiency. A dosage higher than 2.0 g / L may further improve the performance, but will significantly increase the material cost, and a too high concentration may cause the material to agglomerate, affecting its dispersibility and effectiveness, and even increasing the viscosity of the anaerobic digestion liquid, adversely affecting stirring and membrane filtration. Within this 0.5-2.0 g / L dosage range, the carbonized MIL-53(Fe) micro-electric field material can fully exert its micro-electric field effect and charge regulation performance, effectively promoting electron transfer between anaerobic microorganisms, accelerating the degradation of organic matter and the generation of methane.

[0071] In the above embodiments, the dosage of the carbonized MIL-53(Fe) microelectric field material can be dynamically adjusted according to the actual operating conditions of the anaerobic membrane bioreactor. For example, during the start-up phase or when treating high-concentration organic wastewater, the dosage can be appropriately increased to quickly establish microbial activity and enhance degradation efficiency; while in the stable operation phase or when treating low-concentration wastewater, the dosage can be appropriately reduced to save costs. In addition, in addition to directly adding in powder form, it can also be explored to immobilize the carbonized MIL-53(Fe) microelectric field material on certain carriers, or to prepare it into granular, film-like or other forms, in order to improve its dispersibility, recoverability and long-term stability in the anaerobic digestion liquid. This immobilization or modification method can further optimize the utilization efficiency of the material and reduce loss.

[0072] In some embodiments, the temperature in the electrochemical anaerobic membrane bioreactor 10 is 20°C to 40°C.

[0073] In the present application, the temperature in the electrochemical anaerobic membrane bioreactor is set to 20°C to 40°C. This temperature range is the suitable temperature interval for anaerobic microorganisms, especially methanogens, to carry out efficient anaerobic digestion activities. Below 20°C, the metabolic activity of anaerobic microorganisms will be significantly reduced, resulting in a decrease in organic matter degradation rate and methane production, thereby affecting the efficiency of anaerobic digestion. While above 40°C, although certain thermophilic bacteria may exhibit higher activity, the activity of most mesophilic anaerobic microorganisms will be inhibited, and even lead to microbial inactivation, thereby disrupting the stability of the reactor. Therefore, controlling the temperature to 20°C to 40°C, especially in the mesophilic temperature range (30°C-37°C), can maximize the activity and growth of anaerobic microorganisms, thereby achieving efficient organic matter degradation and methane production.

[0074] In the above embodiments, the operating temperature of the electrochemical anaerobic membrane bioreactor can be adjusted according to the actual application scenario and climate conditions. For example, in cold regions, additional heating measures may be needed to maintain a temperature above 20°C; while in warm regions, cooling measures may be needed to avoid excessive temperature. In addition, it can also be explored to carry out staged operation within different temperature intervals, for example, using a higher temperature in the early start-up phase to accelerate microbial proliferation, and then adjusting to a lower temperature in the stable operation phase to save energy. In addition to constant temperature control, temperature gradient or periodic temperature fluctuation strategies can also be considered to adapt to the response of different anaerobic microbial communities to temperature, thereby optimizing the efficiency and stability of anaerobic digestion.

[0075] In some embodiments, the hydraulic retention time in the electrochemical anaerobic membrane bioreactor 10 is 6h to 12h.

[0076] In the present invention, the hydraulic retention time (HRT) in the electrochemical anaerobic membrane bioreactor is set to 6-12 hours. HRT is one of the key parameters that affect the efficiency of anaerobic digestion and the stability of the reactor. A shorter HRT (e.g. less than 6 hours) can result in insufficient residence time of wastewater in the reactor, and the organic matter cannot be fully degraded, thereby reducing the water quality and methane production efficiency. While a longer HRT (e.g. more than 12 hours) may improve the removal rate of organic matter, it will significantly increase the volume and operating cost of the reactor, reduce the treatment efficiency, and may cause a decrease in microbial activity. Therefore, controlling the HRT to be 6-12 hours can ensure that the wastewater has sufficient residence time in the reactor, allowing anaerobic microorganisms to fully degrade organic pollutants, while avoiding unnecessary increases in operating costs.

[0077] In the above embodiments, the setting of the hydraulic retention time (HRT) can be dynamically adjusted according to the influent water quality (such as COD concentration, biodegradability), the target effluent water quality, and the actual operating conditions of the reactor. For example, for high-concentration organic wastewater, the HRT may need to be appropriately extended to ensure sufficient degradation; while for low-concentration wastewater, the HRT can be shortened to improve the treatment efficiency. In addition, a hierarchical HRT strategy can also be adopted, i.e. different HRTs are set in different reactor units to optimize the performance of the entire treatment system. In addition to constant HRT, variable HRT strategies can also be explored, i.e. automatically adjusting the influent flow rate according to real-time monitoring data (such as effluent COD, methane production) to achieve more precise operation control.

[0078] In some embodiments, the flat sheet membrane unit of the surface conductive flat sheet membrane module is an organic flat sheet membrane or a ceramic flat sheet membrane.

[0079] In the present invention, the flat sheet membrane unit of the surface conductive flat sheet membrane module can be selected as an organic flat sheet membrane or a ceramic flat sheet membrane. This selection provides technical flexibility and adaptability, which can meet the needs of different wastewater treatment scenarios. Organic flat sheet membranes, such as polyvinylidene fluoride (PVDF), polyether sulfone (PES), etc., have the advantages of relatively low cost, moderate mechanical strength, easy processing and installation. They perform well in treating municipal sewage and general industrial wastewater, and are easy to maintain through physical or chemical cleaning. Ceramic flat sheet membranes are known for their excellent chemical stability, high temperature resistance, corrosion resistance, high mechanical strength, and longer service life. Ceramic membranes can withstand more severe operating conditions, such as high-concentration organic matter, strong acid or alkali, or wastewater containing abrasive particles, and have longer cleaning cycles and stronger anti-pollution ability.

[0080] In addition to organic flat sheet membranes and ceramic flat sheet membranes, other types of flat sheet membrane materials can be explored as the base of the surface conductive flat sheet membrane module in the above embodiments. For example, new composite membranes or nanofiber membranes can be considered, which may have higher porosity, smaller pore size, or more excellent surface hydrophilicity or hydrophobicity, thereby further improving membrane flux and anti-fouling performance. In addition, when coating the metal mesh, different coating methods such as spraying, dipping or electrodeposition can also be tried to optimize the bonding strength and conductivity uniformity of the metal mesh and the membrane surface. For specific application scenarios, according to the characteristics of the wastewater, membranes with specific functional coatings, such as antibacterial or self-cleaning membranes, can be selected to further enhance the performance and stability of the anaerobic membrane bioreactor.

[0081] In some embodiments, the electrochemical anaerobic membrane bioreactor is provided with a mechanical stirrer or an anaerobic digestion gas circulation pump; the mechanical stirrer stirs the anaerobic digestion liquid at a speed of 20 rpm to 50 rpm; the anaerobic digestion gas circulation pump circulates the anaerobic digestion gas at a flow rate of 0.1 L / min to 0.5 L / min to maintain uniform dispersion of the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material.

[0082] In the present application, the electrochemical anaerobic membrane bioreactor is provided with a mechanical stirrer or an anaerobic digestion gas circulation pump to ensure uniform dispersion of the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material. This stirring mechanism is the key to the efficient operation of the anaerobic membrane bioreactor. First, the uniformly dispersed microelectric field material can maximize contact with anaerobic microorganisms, promote electron transfer, and improve organic matter degradation efficiency. Second, the stirring action can effectively reduce membrane surface pollution, and through the shearing force to flush the membrane surface, prevent the accumulation of pollutants in the membrane pores and membrane surface, thereby maintaining a high membrane flux. The mechanical stirrer stirs the anaerobic digestion liquid at a speed of 20 rpm to 50 rpm, which can ensure sufficient mixing while avoiding excessive shearing damage to microbial flocs and membranes. The anaerobic digestion gas circulation pump circulates the anaerobic digestion gas at a flow rate of 0.1 L / min to 0.5 L / min, which forms a disturbance to the anaerobic digestion liquid through the rising movement of the gas bubbles, and also achieves uniform mixing and membrane surface flushing.

[0083] In the above embodiments, in addition to the mechanical stirrer and anaerobic digestion gas circulation pump, other stirring or mixing methods can also be explored to adapt to anaerobic membrane bioreactors of different scales and configurations. For example, a jet stirrer, magnetic stirrer or ultrasonic dispersion device can be used to achieve a more efficient or gentler mixing effect. The rotation speed of the mechanical stirrer (20 rpm to 50 rpm) and the flow rate of the anaerobic digestion gas circulation pump (0.1 L / min to 0.5 L / min) can be dynamically adjusted according to the viscosity of the anaerobic digestion liquid, the sludge concentration and the degree of membrane fouling. For example, at the initial stage of membrane fouling or under high organic load, the stirring intensity can be appropriately increased to enhance the scouring effect on the membrane surface and the mass transfer efficiency. In addition, intermittent stirring or pulse stirring can also be used to save energy and optimize the mixing effect.

[0084] In some embodiments, the sludge concentration in the electrochemical anaerobic membrane bioreactor 10 is 6000 mg / L to 12000 mg / L.

[0085] In the present application, the sludge concentration in the electrochemical anaerobic membrane bioreactor is set to 6000 mg / L to 12000 mg / L. The sludge concentration is one of the key indicators of the operating efficiency of the anaerobic membrane bioreactor, and directly affects the organic matter removal rate and the amount of methane produced. A lower sludge concentration (e.g. less than 6000 mg / L) can result in insufficient number of active microorganisms in the reactor, which cannot effectively degrade high-concentration organic matter, thereby reducing the treatment efficiency and the quality of the effluent. On the other hand, a too high sludge concentration (e.g. more than 12000 mg / L) can increase the viscosity of the anaerobic digestion liquid, increase the mass transfer resistance, affect the stirring effect and membrane flux, and even exacerbate membrane fouling. Therefore, by controlling the sludge concentration to be 6000 mg / L to 12000 mg / L, it is possible to ensure that there is sufficient amount of active microorganisms in the reactor, thereby achieving efficient organic matter degradation and methane production, while avoiding the problems caused by too high sludge concentration.

[0086] In the above embodiments, the sludge concentration of the electrochemical anaerobic membrane bioreactor can be dynamically adjusted according to the influent water quality, organic load and target treatment efficiency. For example, when treating high-concentration organic wastewater or requiring rapid start-up, the sludge concentration can be appropriately increased to enhance the degradation capacity; while in the stable operation stage or when treating low-concentration wastewater, a lower sludge concentration can be maintained to save operating costs. In addition, the sludge concentration and activity in the reactor can be precisely controlled and optimized by means of sludge backflow, addition of external sludge or cultivation of specific microbial communities. The sludge concentration can be monitored by online sensors or periodic sampling analysis to ensure that it is maintained within the optimal operating range.

[0087] Figure 2A flow chart of a preparation method of carbonized MIL-53(Fe) microelectric field material is provided for an embodiment of the present application. The preparation method includes two main stages: synthesis of MIL-53(Fe) powder and pyrolytic carbonization of MIL-53(Fe) powder.

[0088] In the MIL-53(Fe) powder synthesis stage, terephthalic acid and ferric chloride hexahydrate are first added to N-N dimethylformamide (DMF) in a specific ratio to configure a solution. This ratio is critical to the formation of the MIL-53(Fe) crystal structure. Then, the solution is transferred to a 100 mL volume stainless steel autoclave lined with polytetrafluoroethylene, and heated in a constant temperature oven at 160℃ for 6 hours. The autoclave and polytetrafluoroethylene lining ensure that the reaction is carried out in a closed, high temperature and high pressure environment, which is conducive to the growth of MIL-53(Fe) crystals. After heating is completed, natural cooling to 25℃ is performed, and unreacted substances and impurities are removed through repeated steps of centrifugation, anhydrous ethanol washing and ultrasonic dispersion, and finally dried in a vacuum oven at 80℃ for 8 hours to obtain pure MIL-53(Fe) powder.

[0089] In the MIL-53(Fe) powder pyrolytic carbonization stage, the MIL-53(Fe) powder is placed in a quartz boat of a tube furnace, high-purity nitrogen gas is introduced at a flow rate of 100 mL / min, and heating is performed at a heating rate of 5℃ / min to 750℃ to 900℃, and held at this temperature for 2 hours. The nitrogen atmosphere ensures that the carbonization process is carried out in an inert environment to prevent oxidation; precise control of the heating rate and holding temperature ensures that the MIL-53(Fe) framework can be fully carbonized and form carbonized MIL-53(Fe) microelectric field material with excellent electrical conductivity and microelectric field effect. Finally, the furnace is cooled to 25℃, and the target product is obtained by removal.

[0090] In the above embodiments, the preparation method of carbonized MIL-53(Fe) microelectric field material can be modified and optimized in various ways. For example, the mass ratio of terephthalic acid, ferric chloride hexahydrate and N-N dimethylformamide (DMF) can be fine-tuned to optimize the yield and crystal morphology of the MIL-53(Fe) powder. The temperature and time of the hydrothermal synthesis can also be adjusted according to actual needs, for example, to shorten the reaction time to improve production efficiency, or to adjust the temperature to control the crystal size. The washing solvent for the MIL-53(Fe) powder can also be tried using other organic solvents (such as methanol, acetone) or water in addition to anhydrous ethanol to optimize the washing effect and cost. In the pyrolytic carbonization stage, the nitrogen flow rate, heating rate and holding time can also be optimized to precisely control the carbonization degree and pore structure of the material. For example, a faster heating rate can result in smaller grain size, while a longer holding time can result in higher carbonization degree. In addition, in addition to the tube furnace, a muffle furnace or other types of pyrolysis equipment can also be used for carbonization.

[0091] In some embodiments, the amount of terephthalic acid is 1.328 g, the amount of iron chloride hexahydrate is 2.164 g, and the amount of N,N-dimethylformamide (DMF) is 80 mL.

[0092] In the present invention, the amounts of key components in the preparation method of carbonized MIL-53(Fe) microelectric field material are precisely defined: the amount of terephthalic acid is 1.328 g, the amount of iron chloride hexahydrate is 2.164 g, and the amount of N,N-dimethylformamide (DMF) is 80 mL. These precise ratios are the basis for the successful synthesis of MIL-53(Fe) powder and the achievement of ideal crystal structure and yield. Terephthalic acid serves as the organic ligand, iron chloride hexahydrate provides the metal center, and DMF acts as the solvent and reaction medium. Under hydrothermal synthesis conditions (160°C, 6h), these components form MIL-53(Fe) crystals with regular pore structure through self-assembly. Precise control of the amounts of each component ensures the optimal stoichiometric ratio between reactants, maximizing the yield of MIL-53(Fe) and ensuring the purity and crystallinity of the product. Any deviation from these ratios may result in decreased yield, irregular crystal morphology, or the production of byproducts, which in turn affect the conductivity and microelectric field effect of the subsequent carbonized MIL-53(Fe) microelectric field material 2.

[0093] In the above embodiments, the amounts of terephthalic acid, iron chloride hexahydrate, and N,N-dimethylformamide (DMF) can be adjusted according to the target yield, crystal size, and morphology. For example, while maintaining a specific molar ratio, the amounts of all components can be increased or decreased proportionally to prepare larger or smaller batches of MIL-53(Fe) powder. In addition, besides DMF, other solvents such as water, ethanol, or other organic amines can be explored as reaction media, which may affect the crystallization process of MIL-53(Fe) and the morphology of the final product. In industrial production, to improve efficiency and reduce costs, further process optimization can be performed on these parameters, such as using a continuous flow reactor instead of an autoclave for the synthesis of MIL-53(Fe).

[0094] In some embodiments, the solution is heated at 160°C for 6h.

[0095] In the present application, the MIL-53(Fe) powder synthesis step in the preparation method of the carbonized MIL-53(Fe) microelectric field material, the solution is heated in a constant temperature oven at 160°C for 6h. This temperature and time parameter is a key control condition for the hydrothermal synthesis of MIL-53(Fe) crystals. The temperature of 160°C can provide sufficient energy to promote the dissolution and reaction of terephthalic acid and iron chloride hexahydrate in DMF solvent, and accelerate the nucleation and growth of MIL-53(Fe) crystals. Heating for 6h ensures that the reaction has sufficient time to proceed completely, thereby obtaining MIL-53(Fe) powder with high yield and high crystallinity. If the heating temperature is too low or the heating time is too short, the reaction may not be complete, the product may contain more impurities or have poor crystallinity, which may affect the performance of the subsequent carbonized product. On the contrary, if the temperature is too high or the time is too long, the crystals may grow excessively, the morphology may be irregular, and even decomposition may occur, which is also not conducive to the obtainment of the target product. Therefore, the combination of 160°C and 6h is optimized to ensure the effective synthesis of MIL-53(Fe) and provide high-quality precursors for the subsequent pyrolysis and carbonization steps.

[0096] In the above embodiments, the heating temperature and time during the synthesis of MIL-53(Fe) powder can be fine-tuned according to specific needs. For example, to obtain MIL-53(Fe) crystals with different sizes or morphologies, the heating temperature can be adjusted appropriately or the heating time can be extended / shortened. In some cases, to speed up the reaction process, short-time heating at a temperature slightly higher than 160°C can be tried, but this may need to be balanced in terms of product purity and crystallinity. In addition, the heating method of hydrothermal synthesis can also be varied, for example, microwave heating or electromagnetic heating can be used to achieve faster and more uniform heating, thereby improving the synthesis efficiency.

[0097] Figure 3 The transmembrane pressure difference variation diagram of the electrochemical anaerobic membrane bioreactor under different electric field application modes provided by an embodiment of the present application, and the variation comparison diagram of the membrane electrode after the operation cycle ends, the processing process described in the embodiment includes the following steps:

[0098] (1) The simulated wastewater with COD of 600mg / L is introduced into the electrochemical anaerobic membrane bioreactor, the reactor temperature is controlled at 37°C, the sludge concentration of the reactor is 8000mg / L, and the hydraulic retention time is maintained at 10h.

[0099] (2) Set up four groups of control reactors respectively, hollow flat ceramic membrane modules without coated electrode mesh are placed in reactor R1, no direct current power is connected; surface conductive flat membrane modules coated with stainless steel mesh are placed in reactor R2, and the negative pole of direct current power is connected (i.e. only the conductive membrane is used as the cathode); surface conductive flat membranes coated with titanium mesh and surface conductive flat membranes coated with stainless steel mesh are alternately placed in reactor R3, and the positive pole and the negative pole of direct current power are connected respectively (i.e. the conductive membrane is alternately used as the anode and the cathode); the surface conductive flat membrane modules coated with titanium mesh are connected to the positive pole of direct current power in reactor R4 (i.e. only the conductive membrane is used as the anode).

[0100] (3) The four groups of reactors are started at the same time, and the voltage is adjusted to 0.8 V.

[0101] (4) The four groups of reactors are continuously operated for 35 days, and the changes of transmembrane pressure difference of different reactors are continuously monitored, and the morphological changes of membrane electrodes before and after reaction are recorded.

[0102] Experimental results:

[0103] 1. As shown in Figure 3 a, under the condition of constant flux operation, the change of transmembrane pressure difference (TMP) with time reflects the membrane fouling characteristics of anaerobic membrane bioreactor. Obviously, in the reactor R3 where the conductive membrane alternately acts as the anode and the cathode, the fouling degree of the two groups of membranes is significantly lower than that of the control reactor R1. At the same time, in the reactor R2 where the conductive membrane only acts as the cathode, the membrane fouling is lighter than that of the control reactor R1, but the degree of reduction is significantly lower than that of R3. In the reactor R4 where the conductive membrane only acts as the anode, the membrane fouling is heavier than R1 in the early stage, which is consistent with the theory of anode electrostatic attraction, but as time goes on, it can be observed that the fouling degree has a rising trend in the later stage of membrane filtration, which may be due to the anodic oxidation on the surface of the anode, which can gradually oxidize the fouling layer, thereby slowing down the membrane fouling. Overall, the membrane fouling rate in the R3 reactor where the conductive membrane coated with metal mesh alternately acts as the anode and the cathode is significantly lower than that in the R2 and R4 reactors where the conductive membrane only acts as the cathode or the anode.

[0104] 2. As shown in Figure 3 b, after the end of the entire experimental period, the metal mesh coated on the surface of the conductive membrane basically has no change and loss, which proves that the conductive membrane prepared by this method has excellent stability compared with traditional sacrificial electrode materials.

[0105] Therefore, the above results show that in the electrochemical anaerobic membrane bioreactor where the surface conductive membrane coated with metal mesh alternately acts as the anode and the cathode, a good and stable electric field is formed, and the membrane fouling problem is effectively alleviated, and this method is helpful for the stable operation of the anaerobic membrane bioreactor.

[0106] Figure 4COD concentration and methane production of anaerobic membrane bioreactor after adding different micro-electric field materials provided by an embodiment of the application, the treatment process described in the embodiment includes the following steps:

[0107] (1) The simulated wastewater with COD of 600, 1300, 2000 mg / L was introduced into the anaerobic membrane bioreactor, the reactor temperature was controlled at 37℃, the sludge concentration of the reactor was 8000 mg / L, and the hydraulic retention time was maintained at 10 h.

[0108] (2) The preparation of carbonized precursor (MIL-53 (Fe)) was carried out according to the material preparation method described in the content of the application. Then it was carbonized at temperatures of 500, 800, 1050℃ respectively to obtain three different micro-electric field materials, and their effects on the performance of the anaerobic membrane bioreactor were tested.

[0109] (3) Four groups of control reactors were set up, no micro-electric field material was added in reactor R1; the micro-electric field material CMIL-500 carbonized at 500℃ was added in reactor R2; the micro-electric field material CMIL-800 carbonized at 800℃ was added in reactor R3; the micro-electric field material CMIL-1050 carbonized at 1050℃ was added in reactor R4.

[0110] (3) The addition amount of micro-electric field material in the four groups of reactors was 1 g / L.

[0111] (4) The four groups of reactors were continuously operated for 90 days, and the COD concentration change and methane production of different reactors were continuously monitored.

[0112] Experimental results:

[0113] 1、As shown in Figure 4 a, the COD concentration of the control reactor R1 was always higher than that of the reactors with added micro-electric field materials, and when the organic load increased, the difference was gradually enlarged. When the influent COD concentration increased to 2000 mg / L, the effluent COD concentration of the control reactor R1 was 1.8, 2.3 and 1.9 times that of reactors R2, R3 and R4 respectively, proving that the addition of different micro-electric field materials can improve the hydrolysis degree of organic matter. Among them, the COD removal rate of the reactor with added CMIL-800 can reach 96.9%, which is significantly higher than that of the reactors with added other materials. It is proved that too low carbonization temperature cannot form a good micro-electric field, and too high temperature will also destroy the effect of micro-electric field. While the appropriate carbonization temperature (800℃) can form a good micro-electric field material, which can effectively improve the performance of the anaerobic membrane bioreactor.

[0114] 2、As shown in Figure 4As shown in b, methane production gradually increased with increasing organic substrate concentration. By day 91 of reactor operation, the final net methane production of the four reactor groups were 226.3, 256.6, 332.8, and 285.8 mL / g COD, respectively. In contrast, the addition of CMIL-800 effectively improved the net methane production of the anaerobic membrane bioreactor, demonstrating that micro-electric field materials can promote electron transfer between anaerobic microorganisms. Furthermore, CMIL-800 carbonized at 800℃ can more effectively regulate the metabolic imbalance between acetogenic and methanogenic bacteria, thereby effectively improving the anaerobic digestion performance of the reactor.

[0115] 3. In addition, after the operating cycle ended, the anaerobic membrane bioreactor was shut down for 6 months and then restarted, and its COD concentration and methanogenesis performance were evaluated. Figure 4 As shown, the reactor with added CMIL-800 recovered rapidly, exhibiting excellent COD removal rates and a net methane yield exceeding 290 mL / g COD after only 10 days of operation. Conversely, even after 22 days of acclimatization, the performance of all other reactors was essentially lost. These results demonstrate that CMIL-800 carbonized at 800℃ can significantly stabilize the performance of anaerobic microorganisms and rapidly activate their metabolic functions after a prolonged dormancy period.

[0116] Therefore, the above results indicate that the micro-electric field material carbonized at a suitable temperature effectively promotes the anaerobic digestion performance of the anaerobic membrane bioreactor. Furthermore, this micro-electric field material possesses sufficient stability to maintain its promoting effect on anaerobic digestion performance over a long period.

[0117] Finally, it should be noted that the above embodiments are merely illustrative examples of the present invention and should not be considered as limitations on the method. The scope of protection of the present invention should be defined as the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for enhancing the performance of an anaerobic membrane bioreactor by internal electron circulation coupled with an external electric field, characterized in that, Comprising: S1, preparing a surface conductive flat sheet membrane module by alternately wrapping stainless steel mesh and titanium mesh on the surface of a flat sheet membrane unit; S2, constructing an electrochemical anaerobic membrane bioreactor, the surface conductive flat sheet membrane module as the cathode and anode of the electrochemical anaerobic membrane bioreactor, connected to a direct current power supply through wires; S3, preparing carbonized MIL-53(Fe) microelectric field material, which is a powder with a particle size range of 1-10 microns; S4, dispersing the carbonized MIL-53(Fe) microelectric field material in the form of powder in the anaerobic digestion liquid of the electrochemical anaerobic membrane bioreactor; S5, uniformly mixing the anaerobic digestion liquid and the carbonized MIL-53(Fe) microelectric field material by mechanical stirring or anaerobic digestion gas stirring; The dosage of the carbonized MIL-53(Fe) microelectric field material in the electrochemical anaerobic membrane bioreactor is 0.5-2.0 g / L; The carbonized MIL-53(Fe) microelectric field material is prepared by the following method: Terephthalic acid and ferric chloride hexahydrate are added to N-N dimethylformamide (DMF) to prepare a solution, the amount of terephthalic acid is 1.328 g, the amount of ferric chloride hexahydrate is 2.164 g, and the amount of N-N dimethylformamide (DMF) is 80 mL; The solution is transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, which is placed in a constant temperature oven at 160℃ for heating for 6 h; The autoclave is taken out of the oven and naturally cooled to 25℃, the reaction solution is transferred to a centrifuge tube, centrifuged at 8000 rpm for 10 min, the supernatant is discarded, 20 mL of anhydrous ethanol is added, ultrasonic dispersion is carried out for 5 min, the above centrifugation and washing steps are repeated three times, and finally dried in a vacuum oven at 80℃ for 8 h to obtain MIL-53(Fe) powder; The MIL-53(Fe) powder is placed in a quartz boat of a tube furnace, high-purity nitrogen gas is introduced at a flow rate of 100 mL / min, heated to 750-900℃ at a heating rate of 5℃ / min, and kept at this temperature for 2 h, then cooled to 25℃ with the furnace, and taken out to obtain the carbonized MIL-53(Fe) microelectric field material.

2. The method of claim 1, wherein, The wire diameter of the stainless steel mesh and titanium mesh is 0.02-0.03 mm, and the mesh size is 0.2-0.3 mm.

3. The method of claim 1, wherein, The output voltage of the direct current power supply ranges from 0.4 V to 1.0 V.

4. The method of claim 1, wherein, The temperature in the electrochemical anaerobic membrane bioreactor is 20-40℃.

5. The method of claim 1, wherein, The hydraulic retention time in the electrochemical anaerobic membrane bioreactor is 6-12 h.

6. The method of claim 1, wherein, The flat sheet membrane unit of the surface conductive flat sheet membrane module is an organic flat sheet membrane or a ceramic flat sheet membrane.

7. The method of claim 1, wherein, The electrochemical anaerobic membrane bioreactor is provided with a mechanical stirrer or an anaerobic digestion gas circulating pump; The mechanical stirrer stirs the anaerobic digestion liquid at a speed of 20-50 rpm; The anaerobic digestion gas circulation pump circulates anaerobic digestion gas at a flow rate of 0.1 L / min to 0.5 L / min to maintain uniform dispersion of the anaerobic digestion liquid and the carbonated MIL-53(Fe) microelectric field material.

8. The method of claim 1, wherein, The sludge concentration in the electrochemical anaerobic membrane bioreactor is 6000 mg / L to 12000 mg / L.

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