A method for producing methane based on an iron oxide anaerobic granular sludge microbial electrochemical system

Abstract

The application provides a method for producing methane based on a ferrous oxide anaerobic granular sludge microbial electrochemical system, and belongs to the technical field of microbial electrochemical systems.The application first incubates the anaerobic granular sludge, the ferrous oxide and the culture solution, can directly attach the ferrous oxide to the cells of the anaerobic granular sludge microorganism, effectively solves the characteristics that the ferrous oxide microorganism has poor adhesion, is easy to gather and is unevenly distributed, greatly increases the contact area of the ferrous oxide and the microorganism, and improves the electron transfer efficiency between acid-producing bacteria and methane-producing bacteria in the anaerobic digestion process.The application uses the ferrous oxide anaerobic granular sludge as the electrode of the microbial electrochemical system, solves the limitation that the contact area between the electrode of the microbial electrochemical system and the microorganism is small, and improves the interspecific electron transfer efficiency.The results of the examples show that the method for producing methane based on the ferrous oxide anaerobic granular sludge microbial electrochemical system can obviously improve the methane production.

Description

Technical Field

[0001] This invention relates to the field of microbial electrochemical systems technology, and in particular to a method for producing methane based on an iron oxide anaerobic granular sludge microbial electrochemical system. Background Technology

[0002] Anaerobic digestion can decompose organic waste into clean energy methane, enabling resource utilization. However, the volatile fatty acids produced during anaerobic digestion of organic waste easily accumulate and inhibit the activity of methanogenic bacteria, resulting in poor stability and low digestion efficiency in existing anaerobic digestion systems.

[0003] Microbial electrochemical systems (MECs) can produce methane not only through traditional acetic acid-consuming and hydrogen-consuming methanogenesis pathways, but also through the reduction of CO2 to methane via an externally applied electric field-driven biocathode. Specifically, microorganisms at the anode of the MEC reactor (such as electroactive microorganisms, geobacters) decompose organic matter to produce CO2 and H2. + Electrons are transferred through an external circuit to the cathode to react with CO2 and H2. + The reaction produces CH4. The electrons captured by the CO2 at the cathode of the microbial electrochemical system originate from the electrons generated by the oxidation of organic matter at the anode. Therefore, the microbial electrochemical system can both promote the decomposition of complex organic matter and improve the efficiency of methanogenesis.

[0004] Recent studies have shown that adding iron oxides can replace H2 and formate in anaerobic digestion systems, acting as electron conduits and establishing a stable electron transfer chain between methanogens and acidogens. This allows electrons to be transferred directly from bacteria to methanogens via iron oxides, resulting in direct interspecies electron transfer for methanogenesis. However, iron oxides have poor microbial adhesion; direct addition leads to aggregation and uneven distribution, significantly affecting the contact area between the iron oxide and microorganisms and limiting its application in microbial electrochemical systems. Summary of the Invention

[0005] Therefore, the present invention aims to provide a method for producing methane based on an iron oxide anaerobic granular sludge microbial electrochemical system. The method provided by the present invention can effectively utilize interspecies electron transfer of iron oxides to increase the methane yield of the microbial electrochemical system.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for producing methane based on an iron oxide anaerobic granular sludge microbial electrochemical system, comprising the following steps:

[0008] (1) Mix anaerobic granular sludge, iron oxide and culture medium and incubate to obtain iron oxide anaerobic granular sludge. The culture medium contains inorganic salts, trace elements and organic carbon sources.

[0009] (2) Construct a microbial electrochemical system, the microbial electrochemical system comprising an anode, a cathode, a diaphragm, an anolyte and a catholyte, wherein the anode and / or cathode of the microbial electrochemical system are inoculated with the iron oxide anaerobic granular sludge;

[0010] (3) Apply an external voltage to the microbial electrochemical system for pre-operation;

[0011] (4) Using acetic acid and ethanol in gradient concentration ratios as anode substrates and sodium bicarbonate as cathode substrates, the microbial electrochemical system after pre-running was subjected to microbial domestication to obtain a domesticated microbial electrochemical system.

[0012] (5) Using organic raw materials as anode substrates and sodium bicarbonate as cathode substrates, organic materials are degraded to obtain methane at the anode and cathode.

[0013] Preferably, the inorganic salts in step (1) include NH4HCO3, KH2PO4, NaHCO3 and CaCl2; the trace elements include Ni, Mn, Fe, Zn, B, Mo, Co and Cu; and the organic carbon source includes one or more of formate, acetate and glucose.

[0014] Preferably, in the mixture of anaerobic granular sludge, iron oxide and culture medium in step (1), the concentration of the anaerobic granular sludge is 4~12 gVS / L;

[0015] The concentration of the iron oxide is 40-80 mmol / L.

[0016] Preferably, in step (2), the anolyte comprises phosphate buffer, trace elements and organic acid salts; the catholyte comprises phosphate buffer, trace elements and sodium bicarbonate.

[0017] Preferably, in the anolyte, the organic acid salt is one or more of sodium acetate and sodium propionate, and the concentration of the organic acid salt is 500~1000 mg / L;

[0018] The concentration of sodium bicarbonate in the cathode electrolyte is 500~1000 mg / L.

[0019] Preferably, in step (2), the inoculum amount of iron oxide anaerobic granular sludge is 15~30 gVS / L.

[0020] Preferably, in step (3), the applied voltage for pre-running is 0.6~1.0V, the operating temperature is 30~40℃, and the hydraulic residence time for a single pre-running cycle is 2~4 days; the pre-running cycle is 3~4 cycles.

[0021] Preferably, the temperature for microbial domestication in step (4) is 30~40℃, the water retention time for a single microbial domestication cycle is 2~4 days, and the cycle of microbial domestication is 3~4 cycles.

[0022] Preferably, in step (4), the mass ratio of acetic acid to ethanol is 2:1, 1:1, and 1:2.

[0023] Preferably, in step (5), the organic raw material is one or more of glucose, cellulose and protein; the concentration of the organic raw material is 1000~6000 mg / L.

[0024] This invention provides a method for producing methane based on an iron oxide anaerobic granular sludge microbial electrochemical system, comprising the following steps: (1) mixing anaerobic granular sludge, iron oxide and culture medium, and incubating to obtain iron oxide anaerobic granular sludge, wherein the culture medium comprises inorganic salts, trace elements and organic carbon sources; (2) constructing a microbial electrochemical system, wherein the iron oxide anaerobic granular sludge is inoculated at the anode and / or cathode of the microbial electrochemical system; (3) applying an external voltage to the microbial electrochemical system for pre-running; (4) using acetic acid and ethanol in gradient concentration ratios as anode substrates and sodium bicarbonate as cathode substrates to acclimate the microbial electrochemical system after pre-running to obtain an acclimatized microbial electrochemical system; (5) using organic raw materials as anode substrates and sodium bicarbonate as cathode substrates to degrade organic matter and obtain methane at the anode and cathode. This invention first incubates anaerobic granular sludge, iron oxides, and a culture medium, allowing the iron oxides to directly attach to the microbial cells of the anaerobic granules. This effectively solves the problems of poor microbial adhesion, easy aggregation, and uneven distribution of iron oxides, greatly increasing the contact area between iron oxides and microorganisms and improving the electron transfer efficiency between acid-producing and methanogenic bacteria during anaerobic digestion. This invention uses iron oxide-based anaerobic granular sludge as the electrode in a microbial electrochemical system, overcoming the limitation of small contact area between the electrode and microorganisms and improving interspecies electron transfer efficiency. The results of the examples show that the method for producing methane based on an iron oxide-based anaerobic granular sludge microbial electrochemical system provided by this invention can significantly increase methane production. Compared with using ordinary anaerobic granular sludge as the electrode, this invention can increase methane production by 11.76% to 29.59%, significantly increasing the application of microbial electrochemical systems in the anaerobic digestion of organic matter for methanogenesis.

[0025] Meanwhile, the method provided by this invention is simple to operate and easy to implement for industrial production. Attached Figure Description

[0026] Figure 1 The loading of Fe in granular sludge containing iron oxides at different incubation times;

[0027] Figure 2 Scanning electron microscope image of anaerobic granular sludge;

[0028] Figure 3 Scanning electron microscope image of iron oxide anaerobic granular sludge;

[0029] Figure 4 The methane yields for Examples 1-2 and Comparative Example 1 are given. Detailed Implementation

[0030] This invention provides a method for producing methane based on an iron oxide anaerobic granular sludge microbial electrochemical system, comprising the following steps:

[0031] (1) Mix anaerobic granular sludge, iron oxide and culture medium and incubate to obtain iron oxide anaerobic granular sludge. The culture medium contains inorganic salts, trace elements and organic carbon sources.

[0032] (2) Construct a microbial electrochemical system, the microbial electrochemical system comprising an anode, a cathode, a diaphragm, an anolyte and a catholyte, wherein the anode and / or cathode of the microbial electrochemical system are inoculated with the iron oxide anaerobic granular sludge;

[0033] (3) Apply an external voltage to the microbial electrochemical system for pre-operation;

[0034] (4) Using acetic acid and ethanol in gradient concentration ratios as anode substrates and sodium bicarbonate as cathode substrates, the microbial electrochemical system after pre-running was subjected to microbial domestication to obtain a domesticated microbial electrochemical system.

[0035] (5) Using organic raw materials as anode substrates and sodium bicarbonate as cathode substrates, organic materials are degraded to obtain methane at the anode and cathode.

[0036] This invention involves mixing anaerobic granular sludge, iron oxides, and a culture medium, followed by incubation to obtain iron oxide-based anaerobic granular sludge. In this invention, the anaerobic granular sludge originates from flocculent sludge generated from organic wastewater treatment, preferably containing starch, alcohol, papermaking, or citric acid. In this invention, the concentration of the anaerobic granular sludge in the mixture of anaerobic granular sludge, iron oxides, and the culture medium is preferably 4–12 gVS / L, more preferably 6–10 gVS / L.

[0037] In this invention, the iron oxide is preferably a hydrated iron oxide. The iron oxide is preferably FeOOH, Fe2O3, or Fe3O4. The concentration of the iron oxide is preferably 40-80 mmol / L, more preferably 50-60 mmol / L.

[0038] In this invention, the culture medium comprises inorganic salts, trace elements, and an organic carbon source. Preferably, the inorganic salts include NH4HCO3, KH2PO4, NaHCO3, and CaCl2. The concentration of NH4HCO3 is preferably 450-500 mg / L, more preferably 460-480 mg / L; the concentration of KH2PO4 is preferably 60-80 mg / L, more preferably 70 mg / L; the concentration of NaHCO3 is preferably 500-1000 mg / L, more preferably 600-800 mg / L; and the concentration of CaCl2 is preferably 6-8 mg / L, more preferably 7 mg / L.

[0039] In this invention, the trace elements preferably include Ni, Mn, Fe, Zn, B, Mo, Co, and Cu. Preferably, the compounds containing the trace elements in this invention are NiCl2, MnCl2, FeCl2, ZnCl2, H3BO3, Na2MoO4, CoCl2, and CuSO4. In this invention, the preferred concentrations of the trace elements are: NiCl2 = 450~500 μg / L, more preferably 460~480 μg / L; MnCl2 = 450~500 μg / L, more preferably 460~480 μg / L; FeCl2 = 450~500 μg / L, more preferably 460~480 μg / L; ZnCl2 = 80~100 μg / L, more preferably 90 μg / L; H3BO3 = 80~100 μg / L, more preferably 90 μg / L; Na2MoO4 = 40~60 μg / L, more preferably 50 μg / L; CoCl2 = 40~60 μg / L, more preferably 50 μg / L; and CuSO4 = 5~7 μg / L, more preferably 6 μg / L.

[0040] In this invention, the organic carbon source preferably includes one or more of formate, acetate, and glucose. In this invention, the formate is preferably sodium formate, and the acetate is preferably sodium acetate. In this invention, the concentration of the organic carbon source is preferably 2000-4000 mg / L, more preferably 2500-3500 mg / L.

[0041] The present invention does not have any special requirements for the mixing method; any mixing method known to those skilled in the art can be used, such as stirring.

[0042] In this invention, the incubation is preferably carried out in a constant temperature shaker. The incubation temperature is preferably 30-40°C, more preferably 35°C; the incubation time is preferably 1-5 days, more preferably 2-4 days.

[0043] In this invention, iron oxides possess excellent electrical conductivity. They not only effectively promote direct interspecies electron transfer between acid-producing and methanogenic bacteria in anaerobic granular sludge, but also supplement the extracellular secretion of OmcS cytochromes by microorganisms, constructing direct interspecies electron transfer channels between microorganisms and improving the methanogenic efficiency of anaerobic digestion of organic matter. During the incubation process, iron oxides directly adhere to the microbial cells of the anaerobic granules, effectively overcoming the shortcomings of poor microbial adhesion, easy aggregation, and uneven distribution of iron oxides. This significantly increases the contact area between iron oxides and microorganisms, thereby improving the electron transfer efficiency between acid-producing and methanogenic bacteria during anaerobic digestion.

[0044] After obtaining the iron oxide anaerobic granular sludge, this invention constructs a microbial electrochemical system, which includes an anode, a cathode, a diaphragm, an anolyte, and a catholyte. The anode and / or cathode of the microbial electrochemical system are inoculated with the iron oxide anaerobic granular sludge. In this invention, the anode of the microbial electrochemical system is preferably graphite, and the graphite is preferably graphite felt.

[0045] In this invention, the membrane of the microbial electrochemical system is preferably a proton exchange membrane. In this invention, the membrane separates the microbial electrochemical system into an anode chamber and a cathode chamber; the anode chamber contains an anolyte, and the cathode chamber contains a catholyte. In this invention, the anolyte of the microbial electrochemical system comprises phosphate buffer, trace elements, and organic acid salts; the catholyte comprises phosphate buffer, trace elements, and sodium bicarbonate.

[0046] In this invention, the phosphate buffer solution in the anolyte preferably comprises Na₂HPO₄, NaH₂PO₄, NH₄Cl, and KCl. Preferably, the concentrations of Na₂HPO₄ and NaH₂PO₄ are 4.09 g / L, 2.54 g / L, 0.31 g / L, and 0.13 g / L, respectively.

[0047] In this invention, the types and concentrations of the trace elements are preferably the same as those of the trace elements in the culture medium in step (1), and will not be repeated here.

[0048] In this invention, the organic acid salt is sodium acetate and / or sodium propionate, and the concentration of the organic acid salt is preferably 500-1000 mg / L, more preferably 600-800 mg / L.

[0049] In this invention, the types and concentrations of the phosphate buffer and trace elements in the cathode electrolyte are the same as those in the phosphate buffer and trace elements in the anolyte, and will not be repeated here.

[0050] In this invention, the concentration of sodium bicarbonate is preferably 500-1000 mg / L, more preferably 800-1000 mg / L.

[0051] In this invention, the content of the iron oxide anaerobic granular sludge is preferably 15~30 gVS / L, more preferably 20~25 gVS / L.

[0052] In this invention, when the anode or cathode of the microbial electrochemical system is not inoculated with iron oxide anaerobic granular sludge, it is preferable to inoculate ordinary anaerobic granular sludge onto the electrode that is not inoculated with iron oxide anaerobic granular sludge. In this invention, the content of the ordinary anaerobic granular sludge is preferably 15-30 gVS / L, more preferably 20-25 gVS / L.

[0053] This invention applies an external voltage to the microbial electrochemical system for pre-operation. In this invention, the applied voltage for pre-operation is preferably 0.6~1.0V, more preferably 0.8~0.9V; the operating temperature is preferably 30~40℃, more preferably 35℃; the hydraulic residence time for a single pre-operation cycle is preferably 2~4 days, more preferably 3 days; and the pre-operation cycle is preferably 3~4 cycles. In this invention, the purpose of the pre-operation is to start up the microbial electrochemical reaction system.

[0054] Following the pre-run, the present invention uses acetic acid and ethanol in gradient concentration ratios as the anode substrate and sodium bicarbonate as the cathode substrate to acclimate the pre-run microbial electrochemical system, thereby obtaining an acclimatized microbial electrochemical system. In this invention, the preferred gradient concentration ratios of acetic acid and ethanol are 2:1, 1:1, and 1:2 by mass. Specifically, the preferred concentrations of the gradient concentration ratios of acetic acid and ethanol are: 1000 mg / L:500 mg / L, 500 mg / L:500 mg / L, and 500 mg / L:1000 mg / L.

[0055] In this invention, the concentration of sodium bicarbonate is preferably 500-1000 mg / L, more preferably 800-1000 mg / L.

[0056] In this invention, the preferred temperature for microbial acclimatization is 30-40°C, more preferably 35°C; the preferred hydraulic retention time for a single microbial acclimatization cycle is 2-4 days, more preferably 3 days; and the preferred number of microbial acclimatization cycles is 3-4 cycles. Through this microbial acclimatization, this invention can enrich electroactive microorganisms in iron oxide anaerobic granular sludge.

[0057] After the microorganisms are domesticated, the present invention uses organic raw materials as anode substrates and sodium bicarbonate as cathode substrates to degrade organic matter and obtain methane at the anode and cathode.

[0058] In this invention, the organic raw material is preferably one or more of glucose, cellulose and protein; the concentration of the organic raw material is preferably 1000~6000 mg / L, more preferably 2000~5000 mg / L.

[0059] In this invention, the degradation of organic matter is carried out under anaerobic conditions. Preferably, nitrogen gas is used to purge and remove oxygen from the microbial electrochemical system. The temperature for the degradation of organic matter is preferably 30-40 °C, more preferably 35 °C.

[0060] The following detailed description of the method for producing methane based on an iron oxide anaerobic granular sludge microbial electrochemical system provided by the present invention, with reference to specific embodiments, is not intended to limit the scope of protection of the present invention. Example

[0061] The trace element solution was prepared according to the following composition: NiCl2·6H2O=500 mg / L, MnCl2·4H2O=500 mg / L, FeCl2·4H2O=500 mg / L, ZnCl2·7H2O=100 mg / L, H3BO3=100 mg / L, Na2MoO4·2H2O=50 mg / L, COCl2·6H2O=50 mg / L, CuSO4·5H2O=5 mg / L.

[0062] The culture medium was prepared according to the following composition: NH4HCO3 (460 mg / L), KH2PO4 (70 mg / L), NaHCO3 (1000 mg / L), CaCl2 (7.5 mg / L), glucose (2500 mg / L), sodium acetate (20 mM), and 1 mL / L trace element solution.

[0063] The method for producing methane based on an iron oxide-based anaerobic granular sludge microbial electrochemical system is as follows:

[0064] (1) Cultivation of iron oxide anaerobic granular sludge:

[0065] Anaerobic granular sludge (denoted as AnGSs) from a citric acid wastewater treatment plant was washed with phosphate buffer and placed in a 500 mL glucose bottle to achieve a sludge concentration of 6 g VS / L. Carbon source glucose, electron donor sodium acetate, hydrated iron oxide, and inorganic salt culture medium were added. The hydrated iron oxide concentration was 60 mM, the Fe to sludge mixed liquor biomass concentration ratio was 1:1, the effective reactor volume was 300 mL, and the reactor pH was adjusted to 7. The mixture was then cultured in a constant temperature shaker at 35℃ for 1–5 days to obtain iron oxide granular sludge (denoted as Fe-AnGSs).

[0066] Fe loading in granular sludge of iron oxide at different culture times is as follows: Figure 1 As shown. By Figure 1 It can be seen that the Fe loading is the highest when the culture time is 3 days.

[0067] The scanning electron microscope (SEM) image of the anaerobic granular sludge is shown below. Figure 2 As shown in the image, the scanning electron microscope (SEM) image of the iron oxide anaerobic granular sludge is as follows. Figure 3 As shown. By Figure 2 , 3 It can be seen that, compared with the plate-like structure on the surface of ordinary granular sludge, the surface of Fe-AnGSs is mostly spherical and stalk-like, indicating that iron oxides are loaded into the granular sludge.

[0068] (2) Construction of microbial electrochemical systems:

[0069] The microbial electrochemical system employs a dual-chamber microbial electrolyzer (MEC) with an effective volume of 200 mL. The anode is graphite felt, and the cathode is the iron oxide anaerobic granular sludge cultured for 3 days, added at a concentration of 20 g VS / L. The anode is inoculated with anaerobic granular sludge at a concentration of 20 g VS / L. The two chambers are separated by a proton exchange membrane. The anode chamber is supplemented with phosphate buffer, trace elements, and sodium acetate at a concentration of 500 mg / L, while the cathode chamber is supplemented with phosphate buffer, trace elements, and sodium bicarbonate at a concentration of 1000 mg / L. The applied voltage is set to 0.6–1.0 V, the reaction temperature to 35 °C, and the hydraulic retention time to 4 days for reactor startup.

[0070] (3) Domestication of microorganisms through direct interspecific electron transfer:

[0071] After the reactor was started and stabilized, the anode was acclimatized with acetic acid and ethanol at a ratio of 2:1 (1000 mg / L:500 mg / L), 1:1 (500 mg / L:500 mg / L), and 1:2 (500 mg / L:1000 mg / L), respectively, and the cathode was acclimatized with sodium bicarbonate (1000 mg / L) for direct interspecies electron transfer. The acclimatization temperature was 35℃, the hydraulic retention time was 4 days, and the number of operation cycles was 3.

[0072] (4) Microbial electrochemical system for the production of methane from organic matter:

[0073] Glucose was added at the anode to simulate the anaerobic digestion process of organic wastewater in the MEC system at a concentration of 2000 mg / L, along with phosphate buffer and trace elements. After purging the reactor with nitrogen, the anaerobic digestion experiment was conducted at 35°C. The gases produced at the anode and cathode were collected, and the methane content was measured. Simultaneously, the amount of methane produced by direct interspecies electron transfer was calculated using the external circuit current. Example

[0074] This embodiment is basically the same as embodiment 1, except that in step (2), the anode of the microbial electrolysis cell (MEC) is graphite felt + iron oxide anaerobic granular sludge, and the cathode is ordinary anaerobic granular sludge.

[0075] The difference from Example 1 is that the cathode is ordinary anaerobic granular sludge, and the anode is graphite felt + ordinary anaerobic granular sludge.

[0076] The methane yields of Examples 1-2 and Comparative Example 1 are shown in Table 1. Figure 4 As shown.

[0077] Table 1. Methane production in Examples 1-2 and Comparative Example 1

[0078] Test Project Anode methane production (mL) Cathode methane production (mL) Methane production (mL) from direct interspecies electron transfer Comparative Example 1 66.43 17.09 5.61 Example 1 66.62 19.50 7.25 Example 2 75.51 17.65 7.27

[0079] It can be seen that, compared with ordinary anaerobic granular sludge as the cathode, when iron oxide anaerobic granular sludge is used as the cathode, the cumulative methane production at the cathode increases by 14.10%, and the methane production through direct interspecies electron transfer increases by 29.23%; when iron oxide anaerobic granular sludge is used as the anode, the cumulative methane production at the anode increases by 13.67%, and the methane production through direct interspecies electron transfer increases by 29.59%.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing methane based on a ferric oxide anaerobic granular sludge microbial electrochemical system, comprising the following steps: (1) mixing anaerobic granular sludge, ferric oxide and culture solution, and incubating to obtain ferric oxide anaerobic granular sludge, wherein the culture solution comprises inorganic salts, trace elements and organic carbon sources; (2) constructing a microbial electrochemical system, wherein the microbial electrochemical system comprises an anode, a cathode, a diaphragm, an anode electrolyte and a cathode electrolyte, the anode and / or the cathode of the microbial electrochemical system is inoculated with the ferric oxide anaerobic granular sludge to serve as an electrode; the inoculation amount of the ferric oxide anaerobic granular sludge is 15-30 gVS / L; the anode electrolyte comprises phosphate buffer, trace elements and organic acid salt, the organic acid salt is sodium acetate and / or sodium propionate, and the concentration of the organic acid salt is 500-1000 mg / L; the cathode electrolyte comprises phosphate buffer, trace elements and sodium bicarbonate, and the concentration of the sodium bicarbonate is 500-1000 mg / L; (3) applying an external voltage to the microbial electrochemical system for pre-operation; the external voltage for pre-operation is 0.6-1.0 V, the operation temperature is 30-40℃, the hydraulic retention time of a single pre-operation cycle is 2-4 days, and the pre-operation cycle is 3-4 cycles; (4) using gradient concentration ratios of acetic acid and ethanol as anode substrates and sodium bicarbonate as a cathode substrate to perform microbial domestication on the pre-operated microbial electrochemical system to obtain a domesticated microbial electrochemical system; the mass ratio of the gradient concentration ratios of acetic acid and ethanol is 2:1, 1:1 and 1:2; the temperature for microbial domestication is 30-40℃, the hydraulic retention time of a single microbial domestication cycle is 2-4 days, and the microbial domestication cycle is 3-4 cycles; (5) using organic material as an anode substrate and sodium bicarbonate as a cathode substrate to perform organic matter degradation and obtain methane at the anode and the cathode; the organic material is one or more of glucose, cellulose and protein; and the concentration of the organic material is 1000-6000 mg / L.

2. The method of claim 1, wherein, The inorganic salts in step (1) comprise NH4HCO3, KH2PO4, NaHCO3 and CaCl2; the trace elements comprise Ni, Mn, Fe, Zn, B, Mo, Co and Cu; and the organic carbon sources comprise one or more of formate, acetate and glucose.

3. The method according to claim 1 or 2, characterized in that, The concentration of the anaerobic granular sludge in the mixture of the anaerobic granular sludge, the ferric oxide and the culture solution in step (1) is 4-12 gVS / L; The concentration of the ferric oxide is 40-80 mmol / L.

Images