Micro-electric field stimulation coupled anaerobic membrane distillation reactor and method for enhancing methanogenesis thereof

Abstract

The application discloses a micro-electric field stimulation coupled anaerobic membrane distillation reactor and a method for strengthening methane production thereof, and belongs to the technical field of wastewater treatment and resource utilization. The reactor comprises an anaerobic reaction tank body, a micro-electric field stimulation unit, a membrane distillation assembly, a temperature control unit, a water inlet unit, a condensation collection unit, a vacuum pump and a biogas collection unit. The micro-electric field stimulation unit is composed of a composite anode, a carbon brush cathode and an external direct-current power supply, and a micro-electric field of 0.3-0.8 V is applied. The method comprises inoculating anaerobic sludge, adding kitchen waste and / or landfill leachate, starting the membrane distillation at 45-65 DEG C and applying a micro-electric field, increasing the proportion of landfill leachate in stages, collecting biogas and monitoring the methane content. The application promotes interspecies electron transfer by using a low-voltage micro-electric field. When the ratio of kitchen waste to landfill leachate is 1:1, the methane production rate is more than 340 mL / gCOD, which is about 40% higher than that of the control, and the system's impact load resistance and metabolic recovery capacity are enhanced.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource utilization technology, and in particular to a micro-electric field-stimulated coupled anaerobic membrane distillation reactor and a method for enhancing methanogenesis. Background Technology

[0002] Anaerobic membrane distillation bioreactors (AnMDBRs) are promising wastewater treatment and resource recovery technologies that can simultaneously remove pollutants and recover methane. However, when treating complex saline organic wastewater containing high salt, high ammonia nitrogen, and recalcitrant organic matter, traditional anaerobic systems are prone to problems such as inhibited methanogenic bacteria activity, accumulation of volatile fatty acids, and reduced energy recovery efficiency. Although membrane distillation units can achieve high-quality water production through temperature or vapor pressure differences, when coupled with anaerobic systems to treat complex wastewater, substrate toxicity, salt stress, and microbial metabolic imbalances can collectively weaken methane production performance.

[0003] In existing technologies, relying solely on reactor insulation, feedwater adjustment, or the addition of ordinary conductive materials often only improves gas production under limited operating conditions, making it difficult to simultaneously ensure long-term stable operation and metabolic resilience under high-salt conditions. Therefore, there is an urgent need to develop a device and operating method that can directionally enhance electron transfer and improve the activity of key functional bacteria in membrane distillation anaerobic systems, while maintaining a high methane recovery capacity under complex co-digestion substrate conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a micro-electric field-stimulated coupled anaerobic membrane distillation reactor and its method for enhancing methanogenesis, in order to solve the technical defects of existing AnMDBR in the treatment of saline, high ammonia nitrogen organic wastewater, such as inhibited anaerobic microbial metabolic activity, low hydrolysis and acidification efficiency, and hindered interspecies electron transfer, which leads to low methanogenesis efficiency, weak resistance to shock loads, slow recovery of metabolic function after high-load substrate stress, and decreased stability over long periods of operation. The invention aims to achieve efficient degradation of saline organic wastewater, simultaneous water purification and recovery, and methane resource utilization.

[0005] To achieve the above objectives, the present invention provides a micro-electric field-stimulated coupled anaerobic membrane distillation reactor, comprising: Anaerobic reactor; The micro electric field stimulation unit includes a composite anode, a carbon brush cathode, and an external DC power supply. The composite anode and carbon brush cathode are disposed inside the anaerobic reaction vessel and immersed in the liquid phase. The composite anode and carbon brush cathode are electrically connected to the positive and negative terminals of the external DC power supply, respectively, to form a micro electric field of 0.3~0.8V in the liquid phase. Membrane distillation unit, installed on anaerobic reactor, is used to achieve water vapor separation; The temperature control unit includes a circulating water bath heat exchanger located outside the anaerobic reactor and a high-temperature constant temperature bath connected to the circulating water bath heat exchanger, used to control the reaction temperature inside the anaerobic reactor at 45~65℃. The water inlet unit includes a sample bottle and a peristaltic pump. The inlet end of the peristaltic pump is connected to the sample bottle, and the outlet end of the peristaltic pump is sealed and connected to the inlet port provided on the anaerobic reaction vessel. The condensation collection unit includes a condenser tube and a low-temperature constant temperature bath. The air inlet of the condenser tube is connected to the permeate side of the membrane distillation assembly, the liquid outlet of the condenser tube is connected to the water storage bottle, and the circulation interface of the condenser tube is connected to the low-temperature constant temperature bath. A vacuum pump, whose suction end is sealed and connected to the suction port of the water storage bottle, is used to provide a negative pressure environment for membrane distillation. The biogas collection unit includes a gas collection bag, which is sealed and connected to a gas collection port on the anaerobic reactor. The mixing unit includes a magnetic stirrer and a magnetic stir bar. The magnetic stir bar is located inside the anaerobic reactor, and the magnetic stirrer is located at the bottom of the outside of the anaerobic reactor. The magnetic stir bar is used to drive the magnetic stir bar to rotate so as to achieve uniform mixing of materials in the anaerobic reactor.

[0006] Preferably, the composite anode is a metal plate / carbon felt composite structure or a graphite plate / carbon felt composite structure.

[0007] Preferably, the metal sheet is a titanium sheet.

[0008] Preferably, the membrane distillation module uses a hydrophobic polyvinylidene fluoride flat sheet membrane with an effective membrane area of ​​100 cm². 2 The membrane pore size is 0.2~0.22μm.

[0009] The present invention also provides a method for enhancing methanogenesis using a micro-electric field-coupled anaerobic membrane distillation reactor, comprising the following steps: S1. Inoculate the anaerobic reactor with anaerobic activated sludge and introduce nitrogen into the reactor to replace the air inside the reactor, thus establishing a strict anaerobic environment. S2. Start the temperature control unit to control the reaction temperature inside the tank at 45~65℃, and at the same time start the low temperature constant temperature bath in the condensation collection unit to pre-cool the condenser tube. S3. Add saline organic wastewater into the tank through the water inlet unit, start the stirring unit to mix the materials in the tank evenly; at the same time, start the micro electric field stimulation unit to apply a continuous micro electric field of 0.3~0.8V to the liquid phase through an external DC power supply. S4. Under the stimulation of a micro electric field, saline organic wastewater undergoes anaerobic digestion to produce methanogens. The vacuum pump is started, and driven by the vapor pressure difference across the membrane, water vapor passes through the membrane distillation module and enters the pre-cooled condenser tube. After condensation, it becomes liquid water and is collected in the effluent storage bottle. S5. Biogas produced by anaerobic digestion is continuously collected through a biogas collection unit, and the methane content is monitored.

[0010] Preferably, in step S3, the saline organic wastewater includes kitchen wastewater and / or landfill leachate.

[0011] Preferably, a phased water intake method is adopted to change the mixing ratio of kitchen wastewater and landfill leachate, gradually increasing the mass proportion of landfill leachate in the influent, and gradually reducing the mass ratio of kitchen wastewater to landfill leachate from 3:1 to 0:1.

[0012] Preferably, the mass ratio of kitchen wastewater to landfill leachate is 3:1 to 1:3.

[0013] Preferably, step S5 further includes monitoring the COD of the effluent from the reactor, the concentration of volatile fatty acids, and methanogenic metabolic indicators, and adjusting the influent load or micro-electric field voltage based on the monitoring results.

[0014] Preferably, metabolic indicators include one or more of α-glucosidase activity, protease activity, coenzyme F420 activity, and electron transport system activity.

[0015] Therefore, the micro-electric field-stimulated coupled anaerobic membrane distillation reactor and its method for enhancing methanogenesis provided by the present invention have the following beneficial effects: (1) This invention integrates low-voltage micro electric field stimulation with anaerobic membrane distillation process for the first time, and uses electric field to promote direct interspecies electron transfer between methanogens and electroactive bacteria, breaking through the bottleneck of methanogenic metabolism under high salt environment, and improving gas production efficiency and methane recovery capacity. (2) Under the condition that the mass ratio of kitchen wastewater to landfill leachate is 1:1, the methane yield can exceed 340 mL / gCOD, which is about 40% higher than the control without electricity, and the quality of the produced water is stable. (3) The composite anode provides high specific surface area and biocompatibility, while the carbon brush cathode enriches the methanogenic biofilm. Together, they form a highly efficient micro electric field region with low energy consumption and no significant water electrolysis side reaction. At the same time, micro electric field stimulation can enhance the activity of α-glucosidase, protease, coenzyme F420 and electron transport system, thereby strengthening the hydrolysis of organic matter and methanogenic metabolism. (4) The phased gradient water intake combined with the micro electric field enhances the system’s tolerance to high salt and high ammonia nitrogen shocks and allows it to quickly restore metabolic function after the stress is relieved, which is beneficial for long-term continuous operation.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the structure of a micro-electric field-stimulated coupled anaerobic membrane distillation reactor according to the present invention; Figure label: 1. Sample inlet bottle; 2. Peristaltic pump; 3. Anaerobic reaction vessel; 4. Magnetic stirrer; 5. Valve; 6. Gas collection bag; 7. High-temperature thermostat; 8. Low-temperature thermostat; 9. Water storage bottle; 10. Vacuum gauge; 11. Vacuum pump; Figure 2 The graph shows the effect of different anaerobic membrane distillation reactors of this invention on biogas production and methane yield; (a) is the biogas production curve of the control group (AnMDBR) over time; (b) is the biogas production curve of the titanium plate-carbon felt composite anode experimental group (TIC-AnEMDBR) over time; (c) is the biogas production curve of the graphite plate-carbon felt composite anode experimental group (CC-AnEMDBR) over time; and (d) is a bar chart comparing the methane yield of the three reactors at different operating stages (stages I to VI). Figure 3 The diagram shows the effects of different anaerobic membrane distillation reactors of the present invention on the activities of key enzymes, coenzyme F420, and electron transport system; where (a) is a comparison diagram of changes in α-glucosidase activity; (b) is a comparison diagram of changes in protease activity; (c) is a comparison diagram of changes in coenzyme F420 activity; and (d) is a comparison diagram of changes in INT-electron transport system (ETSA) activity. Figure 4 The diagram shows the effects of different anaerobic membrane distillation reactors of the present invention on the microbial community structure in the mixed liquid and electrode biofilm; where (a) is the result of bacterial community structure analysis and (b) is the result of archaea community structure analysis. Detailed Implementation

[0018] The present invention provides a micro-electric field stimulation coupled anaerobic membrane distillation reactor, including an inlet unit, an anaerobic reaction tank, a micro-electric field stimulation unit, a temperature control unit, a membrane distillation assembly, a condensation and collection unit, a vacuum pump, a biogas collection unit, and a stirring unit.

[0019] The anaerobic reactor is a glass fermentation tank. The top cover of the fermentation tank has at least seven standardized sealing interfaces: a liquid inlet, a membrane distillation module installation port, a sampling port, a gas collection port, a reserved salt discharge port, an anode electrode interface, and a cathode electrode interface. Each interface is equipped with a seal to ensure a strictly anaerobic sealed environment for the reactor. The sampling port is used for offline or online sampling and detection of materials within the anaerobic reactor; the reserved salt discharge port is used to drain accumulated salts from the anaerobic reactor.

[0020] The micro-electric field stimulation module is the core enhancement unit of the system, located in the liquid-phase reaction zone of the anaerobic reactor. It includes a composite anode, a carbon brush cathode, and an external DC power supply. Both the composite anode and the carbon brush cathode are completely immersed in the liquid-phase reaction system of the anaerobic reactor. The electrode wires of the composite anode exit the anaerobic reactor through a sealed anode electrode interface, while the electrode wires of the carbon brush cathode exit the anaerobic reactor through a sealed cathode electrode interface. These two wires are connected to the positive and negative terminals of the external DC power supply, respectively, to generate a stable micro-electric field of 0.3~0.8V, preferably 0.6V, within the liquid-phase zone of the reactor. The composite anode is a metal plate / carbon felt composite structure or a graphite plate / carbon felt composite structure; the metal plate is preferably a titanium plate.

[0021] The membrane distillation module is sealed and installed at the installation port of the membrane distillation module. Its reflux side is immersed in the liquid phase system of the anaerobic reactor, while the permeate side is sealed and connected to the condenser tube of the condensation collection unit via a gas supply line with a control valve. The condensation collection unit includes a condenser tube, a cryogenic bath, and an effluent storage bottle, used to condense and liquefy the water vapor output from the permeate side of the membrane distillation module and collect the permeate. The suction end of the vacuum pump is sealed and connected to the suction port of the effluent storage bottle to provide a negative pressure driving environment for membrane distillation. The discharged water vapor passes through the condenser tube and condenses into liquid water under the control of the cryogenic bath, and is finally collected in the effluent storage bottle. The membrane distillation module uses a hydrophobic polyvinylidene fluoride (PVDF) flat sheet membrane with an effective membrane area of ​​100 cm². 2 The average pore size of the membrane is 0.2~0.22 μm.

[0022] The inlet unit includes a sample bottle and a peristaltic pump. The outlet of the sample bottle is sealed and connected to the inlet of the peristaltic pump through a delivery pipeline. The outlet of the peristaltic pump is sealed and connected to the inlet of the anaerobic reactor through a pipeline with a control valve. This unit is used to quantitatively and stably deliver saline organic wastewater to be treated into the anaerobic reactor.

[0023] The temperature control unit includes a high-temperature constant temperature bath and a matching circulating water bath heat exchanger. The heat exchanger is externally connected to the anaerobic reactor. The circulating water interface of the high-temperature constant temperature bath is sealed and connected to the inlet and outlet of the heat exchanger through an insulated pipeline, forming a closed-loop constant temperature water bath circulation circuit. The reaction temperature inside the anaerobic reactor is precisely and stably controlled by the heat exchange method of the external circulating water bath. The temperature control range is 45~65℃, preferably 55℃.

[0024] The biogas collection unit includes a gas collection bag, which is sealed and connected to the gas collection port of the anaerobic reactor through a pipeline with a control valve, for leak-free collection of methane-containing biogas produced by anaerobic fermentation.

[0025] The mixing unit includes a magnetic stirrer and a magnetic stir bar. The magnetic stir bar is located inside the anaerobic reactor, while the magnetic stirrer is located outside the bottom of the anaerobic reactor. The magnetic stir bar is used to drive the magnetic stir bar to rotate so as to achieve uniform mixing of materials inside the anaerobic reactor.

[0026] The present invention also provides a method for enhancing methanogenesis based on the above-mentioned micro-electric field stimulation coupled anaerobic membrane distillation reactor, comprising the following steps: S1. Inoculate the anaerobic reactor with anaerobic activated sludge and introduce nitrogen into the reactor to replace the air inside. It is preferable to purge for 30 minutes to establish and maintain a strictly anaerobic environment inside the anaerobic reactor.

[0027] S2. Start the temperature control unit to control the reaction temperature inside the tank at 45~65℃, and at the same time start the low temperature constant temperature bath in the condensation collection unit to pre-cool the condenser tube.

[0028] S3. The saline organic wastewater to be treated is continuously added to the anaerobic reaction tank through the peristaltic pump of the water inlet unit. The addition of saline organic wastewater to the tank and the start of the stirring unit make the materials in the tank uniformly mixed. At the same time, the micro electric field stimulation unit is started to apply a continuous micro electric field of 0.3~0.8V to the liquid phase through an external DC power supply.

[0029] The saline organic wastewater includes kitchen wastewater and / or landfill leachate. A staged influent approach is adopted to alter the mixing ratio of the two types of wastewater, gradually increasing the mass proportion of landfill leachate in the influent, while gradually decreasing the mass ratio of kitchen wastewater to landfill leachate from 3:1 to 0:1. Preferably, the mass ratio of kitchen wastewater to landfill leachate is 3:1 to 1:3.

[0030] S4. Under the stimulation of a micro electric field, saline organic wastewater undergoes anaerobic digestion to produce methane. The vacuum pump is started, and driven by the vapor pressure difference across the membrane, water vapor passes through the membrane distillation module and enters the pre-cooled condenser tube. After condensation, it becomes liquid water and is collected in the effluent storage bottle.

[0031] S5. Biogas produced by anaerobic digestion is continuously collected through the biogas collection unit, and methane content, effluent COD, liquid phase volatile fatty acid concentration, and methanogenic metabolic indicators are monitored regularly. Metabolic indicators include one or more of α-glucosidase activity, protease activity, coenzyme F420 activity, and electron transport system activity. The influent load or micro-electric field voltage is adjusted according to the monitoring results to maintain the long-term stable methanogenic operation of the system.

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0033] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0034] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0035] Unless otherwise specified, the materials, reagents, instruments, and equipment used in this invention are all materials, reagents, instruments, and equipment routinely used by those skilled in the art, and the testing standards all use national or international standards commonly used in the field, without further explanation.

[0036] Example 1: Construction and operation of a micro-electric field-coupled anaerobic membrane distillation reactor This embodiment constructs as follows: Figure 1 The diagram illustrates a micro-electric field-stimulated coupled anaerobic membrane distillation reactor. The reactor uses a 3000 mL glass fermenter as the anaerobic reaction vessel 3. The top cover of the vessel is equipped with an inlet, a membrane module mounting port, a gas collection port, a sampling port, a reserved salt discharge port, an anode electrode interface, and a cathode electrode interface. The vessel is placed on a magnetic stirrer 4, with the magnetic stir bar located inside the vessel. The stirring speed is 1000 r / min. An effective area of ​​100 cm² is used. 2A hydrophobic polyvinylidene fluoride (PVDF) flat sheet membrane with a pore size of 0.2 μm is used as the membrane distillation module. The membrane module is sealed and installed at the membrane module installation port, with its reflux side immersed in the liquid phase and its permeate side sealed and connected to the condenser tube via valve 5. The high-temperature constant temperature bath 7 is connected to the circulating water bath heat exchanger outside the tank through an insulated pipeline, forming a closed-loop water bath circulation to control the reaction temperature inside the tank at 55℃. The low-temperature constant temperature bath 8 is connected to the circulation interface of the condenser tube, allowing the condenser tube to be pre-cooled.

[0037] This embodiment provides two alternative electrode implementation schemes: in the TIC-AnEMDBR system, the composite anode is composed of a titanium plate and carbon felt; in the CC-AnEMDBR system, the composite anode is composed of a graphite plate and carbon felt. Both systems use carbon brushes made of bundled carbon fiber bundles as cathodes. The anode and cathode are arranged in parallel with a spacing of 20 mm and are completely immersed in the liquid phase. The anode wire passes through the sealed anode electrode interface, and the cathode wire passes through the sealed cathode electrode interface, respectively, and is electrically connected to the positive and negative terminals of an external DC power supply. The DC power supply output voltage is set to 0.6 V. The sample bottle 1 contains wastewater to be treated, and is sealed and connected to the tank inlet through a peristaltic pump 2 and a delivery pipeline, continuously supplying water according to the set hydraulic load.

[0038] The vacuum pump 11 has its suction end sealed to the suction port of the water storage bottle 9, and a vacuum gauge 10 is installed on the suction line. Water vapor passes through the membrane module and enters the condenser tube, where it condenses into liquid water under the cooling of the cryogenic bath 8 and is collected in the water storage bottle 9. The gas collection bag 6 is sealed to the gas collection port of the tank through a pipeline and is used to collect the biogas produced by anaerobic digestion.

[0039] Example 2: A method for enhancing methanogenesis using a micro-electric field-coupled anaerobic membrane distillation reactor. This embodiment provides a method for enhancing methanogenesis based on the aforementioned micro-electric field stimulation coupled anaerobic membrane distillation reactor. The reactor operates as follows: before startup, anaerobic activated sludge inoculation, influent preparation, and sealing and airtightness testing of the entire system pipeline are completed. Nitrogen gas is introduced for 30 minutes to establish a strictly anaerobic environment. The high-temperature constant temperature bath 7 is started to raise the temperature inside the tank to 55°C, while the low-temperature constant temperature bath 8 is started to pre-cool the condenser tube. The magnetic stirrer 4 is started to stir at 1000 r / min, and the peristaltic pump 2 is started to continuously deliver the influent from the sample bottle 1 to the anaerobic reaction tank 3 according to the set hydraulic load. The micro-electric field stimulation unit is turned on, and the output voltage is adjusted to 0.6 V. After the temperature inside the tank stabilizes and stable water vapor is generated, the vacuum pump 11 is started. Driven by the vapor pressure difference across the membrane, the water vapor passes through the hydrophobic membrane and enters the condenser tube, where it is collected in the effluent storage bottle 9 after condensation. Biogas is simultaneously collected in the gas bag.

[0040] Performance verification: Three parallel tests were set up: control group (no electric field, AnMDBR), test group 1 (titanium plate-carbon felt composite anode, TIC-AnEMDBR), and test group 2 (graphite plate-carbon felt composite anode, CC-AnEMDBR). A constant voltage of 0.6V was applied to the two test groups, while no voltage was applied to the control group. All other operating conditions were exactly the same.

[0041] (1) Verify the methanogenesis enhancement effect of the micro-electric field-coupled anaerobic membrane distillation reactor and the reactor's operational stability under complex salt substrate stress.

[0042] A phased mixing scheme was adopted during water intake to simulate the stress process of the system on saline substrates of varying complexity. Kitchen wastewater and landfill leachate were mixed at different mass ratios (the physicochemical properties of the kitchen wastewater and landfill leachate used in this invention are shown in Table 1). The operation period lasted 97 days and was divided into six phases. Phase I was the acclimatization phase, used to acclimate the anaerobic bacteria and start up the system, verifying the basic operational stability of the system under micro-electric field conditions. Phases II and III successively introduced a high proportion of kitchen wastewater influent and a co-digestion condition of kitchen wastewater and landfill leachate in equal proportions, to investigate the enhancing effect of micro-electric field stimulation on the system's methane recovery performance under medium salinity and complex organic substrate conditions. Phases IV and V further increased the proportion of landfill leachate in the influent until 100% landfill leachate was used as the influent, to investigate the system's operational stability and shock load resistance under combined stress conditions of high salinity, high ammonia nitrogen, and recalcitrant organic matter. Phase VI returned to the 1:1 co-digestion condition of kitchen wastewater and landfill leachate, to verify the system's metabolic function recovery ability after high load stress. Specific ratios are shown in Table 2.

[0043] Table 1: Physicochemical properties of landfill leachate and kitchen wastewater

[0044] Table 2: Operation Stages and Influent Composition

[0045] The verification results are as follows Figure 2 As shown in Table 3.

[0046] Table 3: Key Results of Biogas Production and Methane Proportion at Each Stage

[0047] Depend on Figure 2As shown in Table 3, during Phase I (acclimation period), the average daily gas production of the AnMDBR group (without micro-electric field), the TIC-AnEMDBR experimental group, and the CC-AnEMDBR experimental group were 1.93 L / d, 2.16 L / d, and 2.10 L / d, respectively, and the average methane volume percentages were 83.71%, 81.70%, and 82.52%, respectively. This result confirms that the micro-electric field stimulation module described in this invention does not inhibit the activity of anaerobic functional bacteria during operation. The system can maintain microbial activity and methane metabolism stability comparable to conventional anaerobic systems and has good operational compatibility. When the system operated in stages II to III, with the influent being complex organic substrates with moderate salinity, the overall average daily gas production of the three systems was 1.29 L / d, 2.03 L / d, and 1.88 L / d, respectively, and the average methane volume percentages were 90.54%, 82.21%, and 89.54%, respectively. The experimental results confirmed that the micro-electric field stimulation described in this invention can significantly improve the gas production efficiency of the system under complex organic substrate conditions. Further comparison of methane yield showed that when the influent was co-digested with kitchen wastewater and landfill leachate at a mass ratio of 1:1, the methane yield of both AnEMDBR experimental systems exceeded 340 mL / gCOD, an increase of about 40% compared to the control group without electricity. This result indicates that under the enhanced effect of the micro-electric field, easily degradable organic matter and complex, difficult-to-degrade substrates in the influent can produce a synergistic methanogenic effect, significantly improving the system's methane recovery efficiency and organic matter degradation performance. When the system operates in stages IV to V, the proportion of landfill leachate in the influent further increases. Under the combined stress conditions of high salt, high ammonia nitrogen, and recalcitrant organic matter, the two electrochemical test systems with applied micro-electric fields still maintain a significantly higher average daily gas production than the control group. This indicates that the micro-electric field stimulation described in this invention has a good buffering effect on the environmental stress caused by high-salt complex substrates and can effectively improve the system's resistance to shock loads. However, under the long-term stress condition of 100% landfill leachate, the daily gas production and methane volume ratio of the three systems all show a certain degree of decrease. This indicates that the micro-electric field enhancement effect does not completely eliminate the biotoxicity of the substrate, but can significantly improve the system's tolerance, operational stability, and stress resistance under complex and harsh conditions. When the system reaches stage VI and returns to the co-digestion condition of kitchen wastewater and landfill leachate in a 1:1 ratio, the gas production performance and methane yield of the two experimental systems with applied micro-electric fields can recover to a certain extent. However, the recovery rate of the control group is significantly lower than that of the experimental group, which further verifies that the micro-electric field stimulation module described in this invention can effectively improve the metabolic recovery ability of the system after high load impact and has better long-term operational stability.

[0048] (2) Verify the activity of key enzymes and electron transport system in the micro-electric field-coupled anaerobic membrane distillation reactor.

[0049] During long-term operation, the activities of key metabolic enzymes of microorganisms within the reactor were systematically monitored. Monitoring indicators included α-glucosidase, protease, methanogenic coenzyme F420, and INT-electron transport system (ETSA) activity. Specifically, the activity levels of α-glucosidase and protease were used to characterize the system's ability to hydrolyze and acidify complex organic substrates; the activity level of coenzyme F420 was used to characterize the metabolic activity of methanogenic archaea; and the activity level of ETSA was used to characterize the overall electron transport efficiency and energy metabolism intensity of the microorganisms. Results are as follows: Figure 3 As shown.

[0050] Depend on Figure 3 As shown in (a) and (b) of this invention, in the two electrochemical systems, TIC-AnEMDBR and CC-AnEMDBR, the activities of α-glucosidase and protease were significantly higher than those in the AnMDBR control group without a micro-electric field. This result indicates that the micro-electric field stimulation used in this invention can effectively enhance the hydrolytic acidification capacity of microorganisms in the reactor, promote the degradation of complex organic substances such as polysaccharides and proteins, and convert them into volatile fatty acids such as acetic acid and propionic acid, providing sufficient substrates for the subsequent methanogenesis process. At the same time, the increasing trend of the above-mentioned hydrolytic enzyme activity matches the changing trend of extracellular polymeric substances (EPS) concentration in the reactor. Under the combined stress environment of micro-electric field stimulation, thermal environment and landfill leachate, the content of proteins and polysaccharides secreted by microorganisms under stress increases, and the activity and expression level of related hydrolytic enzymes are simultaneously upregulated, further enhancing the system's ability to degrade complex organic substrates.

[0051] Coenzyme F420 is an electron carrier unique to methanogenic archaea. It can accept electrons to form reduced F420H2, providing the core reducing power for anaerobic methanogenesis and is a key indicator of the metabolic activity of methanogens. For example... Figure 3 As shown in (c), the coenzyme F420 activity of both electrochemical systems was higher than that of the control group throughout the entire operating cycle, reaching its peak in the middle of the system operation, i.e., stage III-IV. This indicates that the micro-electric field stimulation of the present invention can simultaneously enhance the metabolic activity of methanogens while strengthening the hydrolysis and acidification function of microorganisms, achieving synergistic enhancement of the entire metabolic process of hydrolysis, acid production, and methanogenesis. However, when the system influent was switched to stage V, which consisted of 100% landfill leachate, the coenzyme F420 activity of all experimental systems decreased by about 50%, indicating that the combined stress of high salt, high ammonia nitrogen, and toxic and recalcitrant organic matter has a significant inhibitory effect on the physiological function of methanogens. To assess the overall energy metabolism intensity of the microorganisms, the ETSA activity of the INT-electron transport system was simultaneously detected in this embodiment. Figure 3As shown in (d), the ETSA activity of the two electrochemical systems was consistently higher than that of the control group throughout the entire operating cycle. This indicates that the micro electric field applied by the present invention can effectively enhance the transmembrane proton dynamics and overall energy metabolism level of microorganisms, providing sufficient energy support for the entire chain of anaerobic respiration processes such as hydrolysis, acid production, and methanogenesis, and further ensuring the operating efficiency of the system under complex working conditions.

[0052] To examine the recoverability of the system function, in stage VI, the system influent ratio was adjusted back to a co-digestion condition of 50% kitchen wastewater and 50% landfill leachate to reduce the inhibitory effect of recalcitrant toxic substrates on microorganisms. The experimental results showed that the coenzyme F420 activity and ETSA activity of both electrochemical systems significantly rebounded in this stage, and the corresponding methane yield was also effectively restored. In contrast, the enzyme activity recovery rate and degree of the control group were significantly lower than those of the electrochemical system, indicating that the micro-electric field stimulation system of the present invention has stronger metabolic resilience and functional recovery ability after environmental stress is relieved.

[0053] In summary, the micro-electric field stimulation employed in this invention, during the treatment of high-salt organic wastewater in an electro-enhanced anaerobic membrane distillation bioreactor system, can enhance the functional expression activity of key hydrolytic enzymes and methanogenic coenzymes, thereby increasing the electron transfer efficiency of microorganisms and optimizing the metabolic network of anaerobic microorganisms. This effectively improves the system's organic matter degradation efficiency and methane recovery efficiency, while significantly enhancing the system's resistance to shock loads, operational stability, and functional recovery ability under the combined stress of high salt, high ammonia nitrogen, and recalcitrant organic matter, demonstrating excellent long-term operational performance.

[0054] (3) The mechanism of microbial community structure regulation in the micro-electric field-coupled anaerobic membrane distillation reactor was analyzed and verified.

[0055] To elucidate the effects of micro-electric field stimulation on bacterial communities and their hydrolysis and acidification functions in anaerobic membrane distillation reactors, the bacterial community composition within each reactor system was analyzed, and the results are as follows: Figure 4As shown in (a) of the figure, after long-term acclimatization, the control group reactor formed a community structure at the genus level dominated by *Sclerotium spp.* (13.58%-55.63%), *Bacillus fecalith* (6.15%-54.31%), *Acetobacter* (1.75%-7.21%), *Pseudomonas* (0.08%-7.05%), and *Alternaria* (1.00%-6.09%). After long-term acclimatization with landfill leachate, *Sclerotium spp.* became the dominant genus in the system, accounting for more than 50%. In the TIC-AnEMDBR system, the bacterial community in the mixed liquor was dominated by *S. spp.* (9.97%-47.78%), *Bacillus fecalith* (1.74%-65.21%), *Acetobacter* (5.42%-9.81%), *Pseudomonas* (0.09%-6.79%), and *Alternaria* (0.46%-3.44%). The results showed that a high proportion of landfill leachate influent significantly inhibited the growth of *Bacillus fecalith*, reducing its abundance from 65.21% to 1.74%, while the proportion of *S. spp.* increased from 9.97% to 47.48%. When the influent is mainly composed of easily degradable substrates, the anode biofilm is mainly enriched with *Sclerotinia spp.*, *Femtothecinus*, *Acetobacter*, syntrophic acetic acid oxidizing bacteria, and *Pseudomonas*, with *Femtothecinus* accounting for about 50%. However, after long-term acclimation with 100% landfill leachate, the proportion of *Sclerotinia spp.* in the mixed liquor exceeds 47%, and *Sclerotinia spp.*, *Acetobacter*, and syntrophic acetic acid oxidizing bacteria show significant enrichment on the anode biofilm, while the proportion of *Femtothecinus* drops to 1.40%. This change in community structure is not conducive to the interspecies metabolic cooperation of subsequent methanogenic bacteria and is an important reason for the decrease in the stability of methanogenesis in the electrochemical system under this extreme condition. In the CC-AnEMDBR system, with the increase of the proportion of landfill leachate in the influent, the proportion of *Sclerotium spp.* in the mixed liquor increased from 12.65% to 33.40%, while the proportion of *Femtothecinus* spp. decreased sharply from 50.64% to 0.69%, and the proportion of unclassified bacteria was about 30%, further confirming that the high-salt and high-ammonia nitrogen environment has a significant inhibitory effect on *Femtothecinus* spp. When the system treats easily degradable substrates, *Sclerotium spp.* and *Femtothecinus* spp. are mainly enriched on the anode biofilm, with the latter accounting for more than 30%. After long-term acclimation with 100% landfill leachate, the proportion of *Sclerotium spp.* in the mixed liquor exceeded 30%, while the proportion of *Femtothecinus* spp. on the anode surface dropped to below 1%, corresponding to a significant decrease in system operating efficiency. This indicates that the abundance of *Femtothecinus* spp. is closely related to the system's hydrolysis and acidification function and overall operational stability. Micro-electric field stimulation can significantly enrich this functional bacteria under easily degradable substrate conditions, enhancing the system's hydrolysis and acidification capacity.

[0056] To elucidate the regulatory effect of micro-electric field stimulation on the methanogenic archaea community in anaerobic membrane distillation reactors, the archaea composition within each reactor system was analyzed simultaneously, and the results are as follows: Figure 4As shown in (b) of the figure, after long-term acclimatization, the control group reactor formed a community structure at the genus level dominated by *Methanobacterium* (23.80%-84.91%), *Methanobacterium* (10.76%-60.06%), *Methanococcus* (2.29%-5.77%), and candidate methylmethanogens (0.63%-11.85%). When a high proportion of landfill leachate was added to the influent, *Methanobacterium* became the absolutely dominant genus in the system, accounting for more than 80%. In the TIC-AnEMDBR system, the mixed-liquid archaeal community was dominated by *Methanobacter* (47.19%-81.33%), *Methanobacter* (9.43%-44.54%), and *Methanocytococcus* (0.66%-3.17%), consistent with the control group. A high proportion of landfill leachate influent also inhibited the growth of *Methanobacter* and *Methanocytococcus*, leading to a shift in the archaeal community towards a single dominant *Methanobacter* species. When the influent substrate consisted mainly of readily degradable components, the electrode biofilm was primarily enriched with *Methanobacter*, *Methanobacter*, and *Methanocytococcus*, with a significant increase in the abundance of *Methanocytococcus*. The abundance of methanogenic bacteria increased from 6.41% to 14.88% on the anode biofilm and from 14.34% to 26.39% on the cathode biofilm. This genus is a common facultative nutrient methanogen that can produce methanogens using acetic acid or CO2. It can also receive electrons from electroactive bacteria to reduce CO2 and produce methanogens via direct interspecies electron transfer (DIET). The increased abundance indicates that the micro-electric field stimulation of this invention can effectively promote the efficiency of interspecies electron transfer within the system. Methanobacterium can directly receive electrons from the electrode and reduce carbon dioxide to produce methanogens through redox proteins on its outer membrane that are in contact with the electrode, further confirming the enhancing effect of the micro-electric field of this invention on the methanogenesis process. In the CC-AnEMDBR system, with the increase of the proportion of landfill leachate in the influent, the proportion of *Methanobacterium* in the mixed liquor increased from 37.64% to 83.97%, while the proportion of *Methanobacterium* decreased from 46.16% to 7.62%, and the proportion of *Methanococcus methanans* decreased from 9.33% to 0.39%. This result confirms that *Methanobacterium* and *Methanococcus methanans* are more sensitive to high-salt and high-ammonia nitrogen environments. When the system treats easily degradable substrates, the electrode biofilm showed a significant enrichment effect on specific electroactive microbial species. The proportion of *Methanobacterium* on the anode increased from 17.23% to 41.17%, and the proportion of *Methanococcus methanans* on the cathode increased significantly from 10.33% to 47.00%. *Methanococcus methanans* can participate in DIET or directly obtain electrons from the electrode and is the core electroactive methanogen.After the system was acclimatized to 100% landfill leachate for a long period and fully adapted to this extreme substrate environment, the proportion of *Methanobacterium* in the mixture exceeded 80%, and its proportion on the anode and cathode biofilms reached approximately 97%, while the proportion of *Methanobacterium* and *Methanococcus* on the electrodes decreased to approximately 1%. This result further indicates that the extreme substrate environment stress of high-salt and high-ammonia nitrogen landfill leachate leads to the inactivation of key electroactive methanogenic archaea in the system, interfering with the interspecies electron transfer efficiency of microorganisms, and ultimately causing the methane metabolism of the AnMDBR system to be hindered. The micro-electric field stimulation of the present invention can significantly enrich electroactive functional bacteria under normal operating conditions without extreme stress, thereby enhancing the metabolic efficiency of the system.

[0057] In summary, this embodiment elucidates the enhancement mechanism of micro-electric field stimulation at the microbial community level. Specifically, the micro-electric field can directionally enrich hydrolytic acidifying bacteria and electroactive methanogenic bacteria, optimize the community structure of anaerobic bacteria and archaea, and improve the system's hydrolytic acidification efficiency and interspecies electron transfer capacity, thereby enhancing methanogenic efficiency. At the same time, it clarifies the performance boundaries of the system under extreme high-salt and high-ammonia nitrogen stress conditions, providing complete microbiological theoretical support for the engineering application of the system.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. 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 still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for enhancing methanogenesis in a micro-electric field stimulation coupled anaerobic membrane distillation reactor, characterized in that, This is achieved using a micro-electric field-coupled anaerobic membrane distillation reactor, which includes: Anaerobic reactor; The micro-electric field stimulation unit includes a composite anode, a carbon brush cathode, and an external DC power supply. The composite anode and carbon brush cathode are disposed inside the anaerobic reactor and immersed in the liquid phase. The composite anode and carbon brush cathode are electrically connected to the positive and negative terminals of the external DC power supply, respectively, to form a micro-electric field of 0.3~0.8V in the liquid phase. The composite anode is a metal plate / carbon felt composite structure or a graphite plate / carbon felt composite structure. Membrane distillation unit, installed on the anaerobic reactor, is used to achieve water vapor separation; The temperature control unit includes a circulating water bath heat exchanger located outside the anaerobic reactor and a high-temperature constant temperature bath connected to the circulating water bath heat exchanger, used to control the reaction temperature inside the anaerobic reactor at 45~65℃. The water inlet unit includes a sample bottle and a peristaltic pump. The inlet end of the peristaltic pump is connected to the sample bottle, and the outlet end of the peristaltic pump is sealed and connected to the inlet port provided on the anaerobic reaction vessel. The condensation collection unit includes a condenser tube and a low-temperature constant temperature bath. The air inlet of the condenser tube is connected to the permeate side of the membrane distillation assembly, the liquid outlet of the condenser tube is connected to the water storage bottle, and the circulation interface of the condenser tube is connected to the low-temperature constant temperature bath. A vacuum pump, whose suction end is sealed and connected to the suction port of the water storage bottle, is used to provide a negative pressure environment for membrane distillation. The biogas collection unit includes a gas collection bag, which is sealed and connected to a gas collection port on the anaerobic reactor. The mixing unit includes a magnetic stirrer and a magnetic stir bar. The magnetic stir bar is located inside the anaerobic reaction vessel, and the magnetic stirrer is located at the bottom outside the anaerobic reaction vessel. The magnetic stir bar is used to drive the magnetic stir bar to rotate so as to achieve uniform mixing of materials in the anaerobic reaction vessel. The above-mentioned method for enhancing methanogenesis includes the following steps: S1. Inoculate the anaerobic reactor with anaerobic activated sludge and introduce nitrogen into the reactor to replace the air inside the reactor, thus establishing a strict anaerobic environment. S2. Start the temperature control unit to control the reaction temperature inside the tank at 45~65℃, and at the same time start the low temperature constant temperature bath in the condensation collection unit to pre-cool the condenser tube. S3. Add saline organic wastewater into the tank through the water inlet unit, start the stirring unit to mix the materials in the tank evenly; at the same time, start the micro electric field stimulation unit to apply a continuous micro electric field of 0.3~0.8V to the liquid phase through an external DC power supply; wherein, the saline organic wastewater includes kitchen wastewater and / or landfill leachate; S4. Under the stimulation of a micro electric field, saline organic wastewater undergoes anaerobic digestion to produce methanogens. The vacuum pump is started, and driven by the vapor pressure difference across the membrane, water vapor passes through the membrane distillation module and enters the pre-cooled condenser tube. After condensation, it becomes liquid water and is collected in the effluent storage bottle. S5. Biogas produced by anaerobic digestion is continuously collected through a biogas collection unit, and the methane content is monitored.

2. The method of enhancing methanogenesis in a micro-electrical field stimulation coupled anaerobic membrane distillation reactor according to claim 1, characterized in that, The metal sheet is made of titanium.

3. The method of enhancing methanogenesis in a micro-electrical current stimulation coupled anaerobic membrane distillation reactor according to claim 1, characterized in that, The membrane distillation assembly adopts a hydrophobic polyvinylidene fluoride flat membrane, and the effective membrane area is 100 cm 2 , and the membrane pore size is 0.2-0.22 μm.

4. The method of enhancing methanogenesis in a micro-electrical current stimulation coupled anaerobic membrane distillation reactor according to claim 1, characterized in that, The mixing ratio of kitchen wastewater and landfill leachate was changed by adopting a phased water intake method, gradually increasing the mass proportion of landfill leachate in the influent, and gradually reducing the mass ratio of kitchen wastewater to landfill leachate from 3:1 to 0:

1.

5. The method of enhancing methanogenesis in a micro-electrical current stimulation coupled anaerobic membrane distillation reactor according to claim 4, characterized in that, The mass ratio of kitchen wastewater to landfill leachate is 3:1 to 1:

3.

6. The method of enhancing methanogenesis in a micro-electrical current stimulation coupled anaerobic membrane distillation reactor according to claim 1, wherein, Step S5 also includes monitoring the COD of the effluent from the reactor, the concentration of volatile fatty acids, and methanogenic metabolic indicators, and adjusting the influent load or micro-electric field voltage based on the monitoring results.

7. The method for enhancing methanogenesis in a micro-electric field-coupled anaerobic membrane distillation reactor according to claim 6, characterized in that, Metabolic indicators include one or more of the following: α-glucosidase activity, protease activity, coenzyme F420 activity, and electron transport system activity.

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