A method for in-situ electrocleaning of an anaerobic membrane bioreactor

Abstract

This invention relates to a method for in-situ electro-cleaning of an anaerobic membrane bioreactor, wherein the anaerobic membrane bioreactor includes a digester and a membrane tank; the membrane tank includes a working electrode and a counter electrode; the method includes the following steps: applying a pulsed voltage between the working electrode and the counter electrode in the membrane tank to clean the working electrode; the magnitude of the pulsed voltage is 5V-10V. This invention uses pulsed high voltage to clean the anaerobic membrane bioreactor, employing a pulsed (intermittent) method instead of direct current voltage, thus mitigating damage to enzymes, cell structure, and microbial metabolism. It induces a strong electrochemical reaction in the anaerobic membrane bioreactor, achieving efficient in-situ cleaning of the membrane. The process requires no additional chemical dosing or membrane cleaning, nor does it require removing the membrane for separate system cleaning; only the increased high voltage is needed to ensure continuous and uninterrupted system operation, thereby improving work efficiency.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for in-situ electro-cleaning of an anaerobic membrane bioreactor. Background Technology

[0002] Anaerobic membrane bioreactors (AnMBRs) combine anaerobic biological treatment and membrane separation technologies, overcoming the drawbacks of traditional anaerobic reactors such as sludge loss, enhancing the removal of organic pollutants, and enabling the recovery of clean energy (biogas). However, the high cost of membrane modules and membrane fouling are bottlenecks limiting their large-scale deployment.

[0003] Traditional methods for dealing with irreversible fouling primarily involve removing the membrane for intensive chemical cleaning or directly replacing the membrane module. Current research suggests that in-situ membrane cleaning, which involves infrequent offline chemical cleaning, can effectively improve the performance of AnMBRs. In-situ cleaning refers to performing antifouling cleaning of the membrane during operation without removing it from the AnMBR. This method reduces system downtime, ensures a continuous and stable anaerobic process, extends the lifespan of the membrane module, and lowers replacement costs.

[0004] Electrochemical AnMBR has been considered an effective and promising antifouling method. However, applying an electric field often only repels SMPs and EPS to the membrane surface and promotes microbial reduction of EPS concentration, for example, by degrading carbohydrates into monosaccharides and converting proteins into amides. Low voltage has limited effect on EPS, while electrochemical oxidation, with increasing voltage, allows the electrode surface to exhibit redox capabilities. This enables the generated reducing substances to interact with unsaturated bonds and halogenated organic compounds, undergoing hydrogenation reduction, thus reducing their biotoxicity and allowing them to be metabolized. On the other hand, electrochemical oxidation reactions occur near the anode, producing oxygen, chlorine, and other oxidizing compounds (such as ·OH, ClO). - and O 2- These substances can oxidize recalcitrant organic matter. Recent findings suggest that the application of high-voltage electrochemical methods in sludge pretreatment effectively degrades and releases the EPS layer surrounding activated sludge, facilitating further compression and dewatering.

[0005] However, research on the application of high voltage for in-situ cleaning in membrane bioreactors is limited. This is because, while it has the potential to react with EPS (extracellular polymeric substances), high voltage can also adversely affect the microbial community and metabolism. Anaerobic digestion, in particular, is an anaerobic degradation process, and methanogenesis is often strictly anaerobic. When the voltage exceeds 1.0V, the generated oxygen and chlorine will disrupt the anaerobic environment, hindering the metabolism of methanogens and other functional microorganisms. Researchers have found that when the applied voltage exceeds 1.0V, COD removal rates decrease, and microbial metabolism is inhibited. The hydrophobicity of cell membranes is impaired due to the sustained high current density. The secretion of methanogenic enzymes is inactivated under altered redox environments. For example, dehydrogenase activity decreases when voltages exceed 1.0V in AnMBRs. When the voltage exceeds 1.5V, the abundance of specific functional genes is significantly inhibited. Furthermore, when the electrode voltage reaches the redox potential of organic matter, the substrate is consumed and converted into inert or harmful substances, such as haloalkanes. To date, the mechanism by which high voltage damages anaerobic digestion remains unclear, and how to mitigate this damage is a question worthy of further research.

[0006] Therefore, studying the feasibility of high voltage in AnMBR and finding a method that can both remove EPS using electrochemical reactions and prevent inhibition of methanogenesis (microbial metabolism) has become an urgent problem to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a method for in-situ electro-cleaning of anaerobic membrane bioreactors. This method employs intermittent or pulsed high voltage, mitigating damage to enzymes, cell structure, and microbial metabolism. The present invention provides a solution (intermittent high voltage) that can initiate strong electrochemical reactions in AnMBRs without inhibiting functional microbial processes. This method not only enables in-situ membrane cleaning but also provides the possibility of introducing other electrochemical reactions in the future development of AnMBRs.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for in-situ electro-cleaning of an anaerobic membrane bioreactor, the anaerobic membrane bioreactor comprising a digester and a membrane tank; the membrane tank comprising a working electrode and a counter electrode; the method comprising the following steps:

[0010] A pulsed voltage is applied between the working electrode and the counter electrode in the membrane tank to clean the working electrode;

[0011] The pulse voltage is between 5V and 10V, for example, it can be 5V, 5.2V, 5.5V, 5.8V, 6V, 6.2V, 6.5V, 6.8V, 7V, 7.5V, 8V, 8.5V, 9V, 9.5V or 10V, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] This invention employs pulsed high voltage for cleaning anaerobic membrane bioreactors (AnMBRs). On one hand, the high voltage significantly improves membrane cleaning efficiency, eliminating the need for additional chemical dosing or membrane cleaning, and avoiding the need to remove the membrane from the system for separate cleaning. Simply increasing the high voltage ensures continuous, uninterrupted system operation, reducing downtime and guaranteeing a continuous and stable anaerobic process. It also extends the membrane module's lifespan, reduces replacement costs, and improves operational efficiency. On the other hand, using pulsed (intermittent) voltage instead of direct current mitigates damage to enzymes, cell structure, and microbial metabolism. The method provided by this invention can achieve highly efficient in-situ membrane cleaning in AnMBRs by initiating strong electrochemical reactions without inhibiting functional microbial processes. It also opens up possibilities for introducing other electrochemical reactions in the future development of AnMBRs.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0014] Preferably, the working cycle ratio of the pulse voltage is 1 / 20 to 1 / 8, for example, it can be 1 / 20, 1 / 18, 1 / 16, 1 / 15, 1 / 14, 1 / 10 or 1 / 8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the frequency of the pulse voltage is 10Hz-2000Hz, for example, it can be 10Hz, 100Hz, 200Hz, 500Hz, 1000Hz, 1500Hz or 2000Hz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, the direction of the pulse voltage is with the working electrode as the anode or the working electrode as the cathode.

[0017] Preferably, the direction of the pulse voltage is such that the working electrode is the cathode.

[0018] Preferably, the material of the working electrode includes any one or a combination of at least two of titanium film, ceramic or metal film. Typical but non-limiting combinations include combinations of titanium film and ceramic, ceramic and metal film, titanium film and metal film, and titanium film, ceramic and metal film.

[0019] Preferably, the pore size of the working electrode is 0.01μm-1μm, for example, it can be 0.01μm, 0.02μm, 0.05μm, 0.1μm, 0.2μm, 0.4μm, 0.5μm, 0.8μm, 0.9μm or 1μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] A schematic diagram of the anaerobic membrane bioreactor device used in this invention is shown below. Figure 1 As shown, the anaerobic membrane bioreactor consists of four identical reactor groups, each sharing a single feed tank 8. Each reactor group includes a 3.0L CSTR digester 1 (150mm inner diameter, 180mm height) and a 0.80L rectangular membrane tank 2 (100mm × 80mm × 120mm). The operating conditions of the digesters are kept consistent across all groups, while the operating conditions of the membrane tanks are adjusted according to experimental requirements. A stirrer 5 in the digester maintains uniform mixing at a speed of 50-100 rpm and is equipped with a pH electrode 6 and a redox potential electrode 7 for real-time monitoring of the reactor's operational stability. A gas bag 9 is connected to the top of the anaerobic membrane bioreactor unit to collect biogas produced by the anaerobic digesters and membrane tanks.

[0021] Four working electrodes 3 are arranged inside the membrane tank. Parallel to the titanium membrane electrodes is the counter electrode 4, which is made of graphite plate. A pulsed voltage is applied between the working electrodes and the counter electrode via a power supply 10. During the intervals between the applied pulsed voltages, a 0.6V operating voltage is maintained between the working electrodes and the counter electrode. This low-voltage operation ensures the most basic cleaning conditions for the working electrodes. A pressure sensor 11 is used to monitor changes in transmembrane pressure difference in real time. An effluent peristaltic pump 12 and a sludge circulation peristaltic pump 13 are used to draw effluent from the membrane tank and circulate sludge into the anaerobic tank, respectively.

[0022] The degree of membrane fouling is monitored and assessed in real time by the change in transmembrane pressure (TMP), i.e., pressure sensor 11.

[0023] In this invention, the influent to the digester is simulated aquaculture wastewater. When the membrane is found to be completely fouled and needs to be replaced when the outflow rate is too low to maintain the target hydraulic retention time (HRT), it is considered to be completely fouled.

[0024] Preferably, the stirring speed is 50rpm-100rpm, for example, it can be 50rpm, 55rpm, 60rpm, 65rpm, 70rpm, 75rpm, 80rpm, 85rpm, 90rpm, 95rpm or 100rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0025] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0026] A pulse voltage of 5V-10V with a working cycle ratio of 1 / 20-1 / 12 is applied between the working electrode and the counter electrode in the membrane tank of the in-situ electro-cleaning anaerobic membrane bioreactor to clean the working electrode.

[0027] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] (1) This invention constructs a novel electro-cleaning AnMBR technology, which performs in-situ cleaning and regulates EPS contamination by applying pulsed high voltage to the conductive membrane. This not only improves the membrane cleaning efficiency, but also, due to the high voltage interval, hardly affects the efficiency of microbial degradation of pollutants.

[0030] (2) The method provided by the present invention does not require additional dosing or cleaning of the membrane, is simple to operate, does not require removing the membrane from the system for separate cleaning, only requires increasing the voltage, which can ensure continuous and uninterrupted operation of the system, low energy required for membrane filtration, and no need for frequent membrane replacement, resulting in lower energy consumption and cost. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the anaerobic membrane bioreactor device used in the embodiments of the present invention, wherein 1-digestion tank 1, 2-membrane tank, 3-working electrode, 4-counter electrode, 5-digestion tank agitator, 6-pH electrode, 7-oxidation-reduction potential electrode, 8-feed tank, 9-air bag, 10-power supply, 11-pressure sensor, 12-effluent peristaltic pump, 13-sludge circulation peristaltic pump;

[0032] Figure 2 The transmembrane pressure magnitudes in Examples 1-2 and Comparative Examples 1-2 of this invention;

[0033] Figure 3 The content of EPS (extracellular polymeric substances) and organic matter in the membrane pores in Examples 1-2 and Comparative Examples 1-2 of this invention;

[0034] Figure 4 This refers to the COD removal rate in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0035] Figure 5 This refers to the COD removal rate of the method provided in Comparative Example 3 of this invention;

[0036] Figure 6 This refers to the COD removal rate of the method provided in Comparative Example 4 of this invention. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0038] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0039] A schematic diagram of the experimental apparatus used in this invention is shown below. Figure 1 As shown, the anaerobic membrane bioreactor consists of four identical reactor groups, each sharing a single feed tank. Each reactor group includes a 3.0L CSTR digester (150mm inner diameter, 180mm height) and a 0.80L rectangular membrane tank (100mm×80mm×120mm). The operating conditions of the digesters are kept consistent across all groups, while the operating conditions of the membrane tanks are adjusted according to experimental requirements. The digester agitator maintains uniform mixing at 50-100 rpm and is equipped with pH and redox potential electrodes for real-time monitoring of reactor stability. Four working electrodes are arranged within the membrane tank; the counter electrode, made of graphite plate, is parallel to the titanium membrane electrode.

[0040] A gas bag is connected to the top of the reactor to collect biogas produced in the anaerobic digester and membrane tank. Influent flows into the reactor by gravity, while effluent is discharged under peristaltic pump control. The system hydraulic retention time (HRT) is set to 7.3 days. Membrane fouling is monitored and assessed in real time by changes in transmembrane pressure (TMP). `influent` represents the influent COD concentration, and `effluent` represents the effluent COD concentration.

[0041] Example 1

[0042] This embodiment provides a method for in-situ electro-cleaning of an anaerobic membrane bioreactor. A schematic diagram of the in-situ electro-cleaning anaerobic membrane bioreactor device is shown below. Figure 1 As shown, the preparation method of the in-situ electro-cleaning anaerobic membrane bioreactor provided in this embodiment includes the following steps:

[0043] A pulse voltage of 6V, with a duty cycle ratio of 1 / 12 and a frequency of 500Hz, is applied between the working electrode and the counter electrode in the membrane tank of the in-situ electro-cleaning anaerobic membrane bioreactor. The direction of the pulse voltage is such that the working electrode is the cathode, and the working electrode is cleaned. This is referred to as cathode cleaning.

[0044] Example 2

[0045] The preparation method of the in-situ electro-cleaning anaerobic membrane bioreactor provided in this embodiment includes the following steps:

[0046] A pulse voltage of 6V, with a duty cycle ratio of 1 / 20 and a frequency of 500Hz is applied between the working electrode and the counter electrode in the membrane tank of the in-situ electro-cleaning anaerobic membrane bioreactor. The direction of the pulse voltage is with the working electrode as the anode, and the working electrode is cleaned. This is called anode cleaning.

[0047] Example 3

[0048] The preparation method of the in-situ electro-cleaning anaerobic membrane bioreactor provided in this embodiment includes the following steps:

[0049] A 10V pulse voltage with a working cycle ratio of 1 / 15 and a frequency of 1500Hz is applied between the working electrode and the counter electrode in the membrane tank of the in-situ electro-cleaning anaerobic membrane bioreactor. The direction of the pulse voltage is with the working electrode as the cathode to clean the working electrode.

[0050] Example 4

[0051] This embodiment provides a method for in-situ electro-cleaning of an anaerobic membrane bioreactor, wherein the pulse voltage is adjusted to 3V, and the rest is the same as in Embodiment 1.

[0052] Example 5

[0053] This embodiment provides a method for in-situ electro-cleaning of an anaerobic membrane bioreactor, wherein the pulse voltage is adjusted to 15V, and the rest is the same as in Embodiment 1.

[0054] Comparative Example 1

[0055] This comparative example provides a method for electro-cleaning an anaerobic membrane bioreactor. The only difference from Example 1 is that no additional pulse voltage is applied between the working electrode and the counter electrode; only a DC operating voltage of 0.6V is used, which is referred to as the pure electric field.

[0056] Comparative Example 2

[0057] This comparative example provides a method for cleaning an anaerobic membrane bioreactor. The only difference from Example 1 is that no additional pulse voltage is applied between the working electrode and the counter electrode, and the DC operating voltage is 0, denoted as AnMBR.

[0058] Comparative Example 3

[0059] This comparative example provides a method for electro-cleaning an anaerobic membrane bioreactor. The only difference from Example 1 is that the cleaning voltage of the membrane is DC 6V, the cleaning frequency is once per hour, and the cleaning time is 5 minutes each time.

[0060] Comparative Example 4

[0061] This comparative example provides a method for electro-cleaning an anaerobic membrane bioreactor. The only difference from Comparative Example 3 is that the cleaning voltage of the membrane is DC 6V, the cleaning frequency is twice per hour, and the cleaning time for each cleaning is 2.5 minutes.

[0062] Test Method: The influent to the digester was simulated aquaculture wastewater, containing glucose, sodium acetate, ammonium chloride, potassium dihydrogen phosphate, tryptophan, and trace elements. The design concentrations of the influent were: Chemical Oxygen Demand (COD) 20,000 mg / L, Ammonia Nitrogen 600 mg / L, and Total Phosphorus (TP) 80 mg / L. Raw sludge was used as inoculum from the digester at the Gaobeidian Wastewater Treatment Plant in Beijing. The membrane was considered completely fouled and required replacement when the effluent flow rate was too low to maintain the target hydraulic retention time (HRT).

[0063] The final effect of the cleaning methods in the examples and comparative examples was tested, and the test results are as follows: Figures 2-4 As shown.

[0064] Figure 2 First, the four reactors were interconnected and operated for 30 days to ensure that they had the same sludge concentration and pollution potential in subsequent experiments, thus making the results of subsequent experiments comparable.

[0065] In the examples and comparative examples, the results of the transmembrane pressure magnitude are as follows: Figure 2 As shown, the effect of electrochemical cleaning on membrane fouling mitigation is demonstrated. The results show that anodic cleaning (Example 2) and cathodic cleaning (Example 1) are both superior to comparative examples 1-2 in terms of membrane fouling control, with Example 1 showing the lowest cleaning TMP.

[0066] By applying pulsed voltage, the average TMP of anodic and cathodic electrocleaning decreased to 14.7 kPa and 10.2 kPa, respectively, which are 54.1% and 69.7% lower than those of pure electric field cleaning. This demonstrates that high-voltage electrochemical cleaning significantly improves membrane fouling mitigation, and this effect does not diminish with changing cleaning frequency. Specifically, the TMP of anodic and cathodic electrocleaning decreased by 45% and 64%, respectively. It is hypothesized that when higher voltages are applied, electrochemical reactions occurring at the membrane-electrode surface can effectively transform pollutants, such as converting extracellular polymeric substances (EPS) into forms with lower fouling potential or directly degrading them, thereby significantly improving the membrane's antifouling ability. This mechanism may involve electrochemical redox reactions, which disrupt the EPS structure and reduce its adsorption capacity on the membrane surface by generating reactive oxygen species (such as hydroxyl radicals ·OH) or through direct electron transfer. Studies have shown that electrochemical oxidation can effectively degrade organic components such as proteins and polysaccharides in EPS, thereby reducing membrane fouling formation. In addition, electrochemical reactions may also reduce the adhesion of pollutants by altering the surface charge characteristics of EPS and weakening its interaction with the membrane material.

[0067] Figure 3 The levels of EPS (extracellular polymeric substances) and organic matter within the membrane pores of four reactors were measured using TOF-SIMS. Green represents protein-like substances, and yellow represents total organic carbon content. The AnMBR membrane pores were filled with organic matter, while the spatial concentration of organic matter was significantly reduced in a pure electric field compared to AnMBR. This indicates that the electrostatic repulsion repels EPS, reducing its entry and deposition in the membrane pores. The organic matter content in the membrane pores after cathodic electrochemical cleaning was significantly lower than in the other three reactors, indicating that cathodic electrochemical cleaning effectively reduced the amount of EPS residue in the membrane pores.

[0068] Figure 4 The COD (Chemical Oxygen Demand) removal rate was demonstrated. The COD removal rate reflects the wastewater treatment facility's ability to remove organic matter from wastewater; it is an important indicator of wastewater treatment effectiveness. Generally, the higher the COD removal rate after treatment, the better the wastewater treatment effect. The inhibitory effect of electrochemical cleaning on anaerobic digestion was mitigated by increasing the cleaning frequency. Initially, four reactors were connected together and adapted to sludge under the same conditions to maintain the initial state of each reactor. Once the COD removal rate reached over 90% and biogas production stabilized, the four reactors were disconnected and operated under different conditions.

[0069] Figure 5 and Figure 6 The figures show the COD removal rate curves of the methods provided in Comparative Examples 3 and 4 of this invention, respectively. The comparison shows that, under the premise of keeping the total cleaning time constant, the COD removal rate will increase with the increase of cleaning frequency.

[0070] In Example 1, under pulsed voltage, the COD concentration of the effluent from cathodic electrochemical cleaning was basically the same as that of AnMBR and pure electric field, and the COD removal rate increased by 19% compared with that using DC power supply (Comparative Example 3).

[0071] Table 1

[0072]

[0073]

[0074] The test results show that:

[0075] (1) As can be seen from Examples 1-3, the present invention uses pulsed high voltage to clean the anaerobic membrane bioreactor. The pulsed (intermittent) voltage instead of DC voltage reduces the damage to enzymes, cell structure and microbial metabolism. It triggers a strong electrochemical reaction in AnMBR to achieve efficient in-situ cleaning of the membrane. No additional drugs or membrane cleaning are required during the process, and the membrane does not need to be removed from the system for separate cleaning. Only the high voltage needs to be increased to ensure continuous and uninterrupted operation of the system, which improves work efficiency and achieves the dual effect of efficient cleaning without damaging microorganisms.

[0076] (2) By comparing Example 1 with Example 4-5, it can be seen that by further optimizing the range of pulse voltage, the present invention can achieve better cleaning effect while saving energy. When the pulse voltage is too small, it cannot meet the cleaning effect. If the pulse voltage is too large, it will not only fail to enhance the cleaning effect but also waste energy.

[0077] (3) As can be seen from Examples 1, 1, and 2, the electrochemical cleaning method with applied high voltage can significantly improve the mitigation of membrane fouling. As can be seen from Examples 1, 3, and 4, the improvement in mitigation of membrane fouling by the electrochemical cleaning method with applied high voltage does not disappear with changes in cleaning frequency. This is because high voltage significantly alters the composition of archaea and bacterial communities, and also affects metabolic pathways in the anaerobic digestion process by inhibiting the growth of acetic acid-producing methanogens and certain propionate-producing bacteria.

[0078] In summary, this invention employs pulsed high voltage for in-situ electro-cleaning of anaerobic membrane bioreactors. On one hand, the high voltage significantly improves membrane cleaning efficiency, eliminating the need for additional chemical dosing or membrane cleaning, and avoiding the need to remove the membrane for separate system cleaning. Simply increasing the high voltage ensures continuous, uninterrupted system operation, reducing downtime and guaranteeing a continuous and stable anaerobic process. Simultaneously, it extends the membrane module's lifespan, reduces replacement costs, and improves operational efficiency. On the other hand, using pulsed (intermittent) voltage instead of direct current mitigates damage to enzymes, cell structure, and microbial metabolism. The method provided by this invention can achieve highly efficient in-situ membrane cleaning in AnMBRs by initiating strong electrochemical reactions without inhibiting functional microbial processes, and also opens up possibilities for introducing other electrochemical reactions in the future development of AnMBRs.

[0079] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for in-situ electro-cleaning of an anaerobic membrane bioreactor, characterized in that, The anaerobic membrane bioreactor includes a digester and a membrane tank; the membrane tank includes a working electrode and a counter electrode. The method includes the following steps: A pulsed voltage is applied between the working electrode and the counter electrode in the membrane tank to clean the working electrode; The magnitude of the pulse voltage is 5V-10V; the duty cycle ratio of the pulse voltage is 1 / 20-1 / 8. The frequency of the pulse voltage is 10Hz-2000Hz.

2. The method according to claim 1, characterized in that, The direction of the pulse voltage is either with the working electrode as the anode or the working electrode as the cathode.

3. The method according to claim 1, characterized in that, The direction of the pulse voltage is with the working electrode as the cathode.

4. The method according to claim 1, characterized in that, The working electrode is made of any one or a combination of two of ceramic or metal films.

5. The method according to claim 1, characterized in that, The working electrode has a pore size of 0.01μm-1μm.

6. The method according to claim 1, characterized in that, The material of the counter electrode includes a graphite plate.

7. The method according to claim 1, characterized in that, The digester and the membrane tank are connected by a peristaltic pump.

8. The method according to claim 1, characterized in that, The digester includes a stirrer, a pH electrode, and a redox potential electrode.

9. The method according to claim 8, characterized in that, The stirring speed is 50rpm-100rpm.

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