Method for promoting microorganisms to reduce carbon dioxide to synthesize multi-carbon fatty acid

Abstract

The invention relates to the technical field of microbial synthesis, and provides a method for promoting microorganisms to reduce carbon dioxide to synthesize multi-carbon fatty acid, which comprises the following steps: in a reactor, inoculating an electroactive carbon chain in a microbial electrosynthesis system to prolong a microbial mixed flora, adding sodium bicarbonate, and aerating by using nitrogen and carbon dioxide to obtain the multi-carbon fatty acid. Applying external voltage to the reactor, and reacting to obtain the multi-carbon fatty acid; the inorganic substrate carbon dioxide is used as a unique carbon source, green electric energy is used as an energy source, conversion of carbon dioxide to fatty acid is promoted, additional organic electron donors or expensive electron mediators do not need to be added, the synthesis process of acetic acid generated by reduction of carbon dioxide to butyric acid and hexanoic acid is remarkably promoted, and the yield of fatty acid is increased. Good application prospects are realized.

Description

Technical Field

[0001] This invention relates to the field of microbial synthesis technology, and in particular to a method for promoting the synthesis of multi-carbon fatty acids by microorganisms from carbon dioxide reduction. Background Technology

[0002] Microbial electrosynthesis is a novel carbon dioxide fixation and resource conversion technology, a coupled system of electrochemistry and biosynthesis. An oxidation reaction occurs at the anode, and the generated electrons are transferred to the cathode under the drive of an external voltage. Electroactive microorganisms at the cathode act as biocatalysts, directly or indirectly acquiring electrons from the electrode surface to absorb and fix carbon dioxide, converting it into high-value-added products. Compared to traditional photoelectric and electrochemical carbon dioxide resource conversion methods, microbial electrosynthesis technology has significant advantages in producing high-energy-density multi-carbon products, while also offering simple system operation, mild reaction conditions, relatively low construction costs, and good operational stability.

[0003] Currently, microbial electrosynthesis technology mainly produces acetic acid and methane through mixed microbial catalysis, achieving coulombic efficiencies approaching 100%. However, the market value of these products is limited. In contrast, the biosynthesis of multi-carbon fatty acids such as butyric acid and hexanoic acid has attracted widespread attention. In conventional anaerobic fermentation reactors, multi-carbon fatty acids can be synthesized via fatty acid biosynthesis (FAB) or reverse β-oxidation (RBO) pathways, extending short-chain carboxylic acids (Cn) to long-chain carboxylic acids (Cn+2) through electron donors. However, this often requires additional carbon sources (such as glucose) and organic electron donors (such as formic acid, ethanol, and lactic acid), significantly increasing operating costs and reducing overall economic efficiency. In microbial electrosynthesis systems, although electrode material modification and the addition of exogenous inorganic electron mediators can promote chain elongation reactions to some extent, electrode preparation and electron mediator preparation are complex and their stability is difficult to maintain. Sodium ions have been found to promote acetic acid and methanogenesis, but this method has not yet been used in the microbial electrosynthesis of multi-carbon fatty acids. In microbial electrosynthesis systems, direct and / or indirect electron transfer occurs between the electroactive biofilm formed on the cathode and the electrode. Whether adding sodium ions to a carbon chain elongation microbial electrosynthesis system is beneficial for enriching electroactive microorganisms, promoting the growth of chain-elongating microorganisms, and enhancing electron transfer between the electrode and functional microorganisms to achieve the production of multi-carbon fatty acids, thereby achieving the dual goals of carbon dioxide emission reduction and high-value utilization, warrants further investigation.

[0004] Therefore, in order to address the high operating costs and other issues of existing methods, a new method for synthesizing multi-carbon fatty acids is needed. Summary of the Invention

[0005] The technical problem this invention aims to solve is that existing methods for the electrosynthesis of multi-carbon fatty acids are costly and complex. To address the shortcomings of existing technologies, this invention provides a method for promoting the synthesis of multi-carbon fatty acids from carbon dioxide by microorganisms. This method involves adding sodium ions to the cathode liquid of a microbial electrosynthesis reactor to promote the enrichment of electroactive microorganisms on the electrodes and the enrichment of chain-elongating microorganisms in the solution, thereby enhancing the electron transfer efficiency of the system and achieving the conversion of carbon dioxide reduction products from acetic acid to butyric acid and hexanoic acid.

[0006] To address the aforementioned technical problems, this invention provides a method for promoting the synthesis of multi-carbon fatty acids from carbon dioxide reduction by microorganisms. The method includes: inoculating a mixed microbial community of electroactive carbon chain elongating microorganisms in a microbial electrosynthesis system in a reactor, adding sodium bicarbonate, aerating with nitrogen and carbon dioxide, then applying an external voltage to the reactor, and obtaining multi-carbon fatty acids after the reaction.

[0007] The method provided by this invention involves water oxidation at the anode and carbon dioxide reduction at the cathode of a microbial electrosynthesis reactor under energized conditions. Adding sodium ions to the cathode increases the conductivity of the electrolyte, resulting in the enrichment of more electroactive microorganisms on the cathode and enhancing the electron transfer efficiency between the cathode and the microorganisms. Simultaneously, the addition of sodium ions can create a transmembrane gradient of sodium ions from the extracellular to the intracellular space, promoting the production of more ATP within the cell, thereby accelerating the reduction of carbon dioxide to synthesize butyric acid, hexanoic acid, etc.

[0008] Existing methods are complex: current microbial electrosynthesis systems often rely on high hydrogen partial pressure environments or the provision of additional organic electron donors to promote the synthesis of multi-carbon products. High hydrogen partial pressures not only pose safety hazards and operational risks but also impose stringent requirements on the sealing of the reaction system and the compressive strength of the materials, significantly increasing construction and maintenance costs. Furthermore, while introducing organic electron donors such as ethanol and formic acid can promote reduction reactions to some extent, their high raw material costs limit the economic feasibility of the technology.

[0009] Preferably, the microbial electrosynthesis system includes a cathode chamber, an anode chamber, and a titanium sheet. The cathode chamber and the anode chamber are separated by an ion exchange membrane. The cathode chamber contains a cathode, a reference electrode, and a catholyte, while the anode chamber contains an anode and an anolyte.

[0010] In this invention, the microbial electrosynthesis system employs a dual-chamber H-type reactor. The ion exchange membrane used is a cation exchange membrane, including but not limited to the LE-HoCMGrion001 type ion exchange membrane from Hangzhou Kerui Environmental Energy Technology Co., Ltd.

[0011] Preferably, the cathode is a carbon felt bonded to a titanium sheet that extends outside the reactor.

[0012] In this invention, the carbon felt is connected to the titanium sheet by nylon screws, and the titanium sheet extends outside the reactor as a current collector and is connected to the potentiostat.

[0013] Preferably, the composition of the catholyte is: K₂HPO₄ 0.35 g·L⁻¹ -1 0.25 g·L KH2PO4 -1 NH4Cl 0.25 g·L -1 KCl 0.5 g·L -1 0.15 g·L⁻¹ CaCl₂·2H₂O -1 MgCl2·6H2O 0.6 g·L -1 NaCl 1.2 g·L -1 0.01 g·L yeast extract -1 2-Bromoethylsulfonate sodium 1 g·L -1 L-cysteine ​​0.25 g·L -1 Trace element solution 1 ml·L -1 (The culture medium used was DSMZ-Medium 141 from the German Culture Collection Center. Specifically, 1 L of trace elements included: 1.50 g triacetic acid, 0.10 g CaCl₂·2H₂O, 3.00 g MgSO₄·7H₂O, 0.01 g CuSO₄·5H₂O, 0.50 g MnSO₄·H₂O, 0.01 g H₃BO₃, 1.00 g NaCl, 0.03 g NiCl₂·6H₂O, 0.10 g FeSO₄·7H₂O, 0.40 mg Na₂WO₄·2H₂O, 0.18 g CoSO₄·7H₂O, 0.18 g ZnSO₄·7H₂O, 0.02 g KAl(SO₄)₂·12H₂O, 0.01 g Na₂MoO₄·2H₂O, and 0.30 mg Na₂SeO₃·5H₂O. The triacetic acid was first dissolved and then...) The solution was adjusted to pH 6.5, and then the other salts were dissolved sequentially. After complete dissolution, the pH was adjusted to 7.0 with KOH solution. Vitamin solution 2.5 ml / L -1 (1 L of vitamin solution includes: 2 mg biotin, 10.00 mg pyridoxine hydrochloride, 2 mg folic acid, 5.00 mg para-aminobenzoic acid, 5.00 mg thiamine hydrochloride·2H2O, 5.00 mg D-calcium pantothenate, 5.00 mg riboflavin, 0.10 mg vitamin B12, 5.00 mg niacin, and 5.00 mg lipoic acid) and 0.1 ml·L of tungsten selenate solution. -1 .

[0014] Preferably, the reference electrode is a calomel electrode filled with saturated potassium chloride.

[0015] Preferably, the anode is a platinum-plated titanium mesh; the composition of the anolyte is K₂HPO₄ 0.35 g·L⁻¹. -1 0.25 g·L KH2PO4 -1 NH4Cl 0.25 g·L -1 KCl 0.5 g·L -1 0.15 g·L⁻¹ CaCl₂·2H₂O -1 MgCl2·6H2O 0.6 g·L -1 NaCl 1.2 g·L -1 .

[0016] Preferably, the electroactive carbon chain elongation microbial mixed flora includes Clostridium , Bacillus or Oscillibacter At least one of the following: the electroactive carbon chain elongating microbial mixed flora is inoculated on a cathodic liquid culture medium containing sodium 2-bromoethylsulfonate, with a pH of 5.0-5.8, and the inoculation ratio of the electroactive carbon chain elongating microbial mixed flora to the culture medium is 0.05-0.2 by mass to volume.

[0017] Preferably, the concentration of sodium bicarbonate is 0.5~10 g·L. -1 For example, it could be 0.5 g·L -1 1 g·L -1 2g·L -1 3 g·L -1 4 g·L -1 5 g·L -1 6 g·L -1 7 g·L -1 8 g·L -1 9 g·L -1 or 10 g·L -1 The sodium bicarbonate is added to the catholyte. Preferably, the concentration of the sodium bicarbonate is 2.5 g·L⁻¹. -1 .

[0018] In this invention, sodium ions are added to the cathode, and bicarbonate is chosen as the sodium source primarily because of its good biocompatibility and high inhibitory threshold for microorganisms, facilitating safe control over a wide concentration range. Secondly, bicarbonate (HCO3-) - It is converted into gaseous CO2 under the condition that the system pH≈5. -Gaseous CO2 has been shown to be readily immobilized and utilized by microorganisms. Enriching the electrode surface with electroactive microorganisms provides more intracellular reducing power for chain-elongating microorganisms in solution, ensuring sufficient energy to promote the carbon chain elongation reaction. The concentration of added sodium ions is adaptively adjusted according to the composition of the microbial community to avoid inhibiting microbial growth.

[0019] Preferably, the nitrogen and carbon dioxide aeration are carried out sequentially in the catholyte.

[0020] In this invention, nitrogen aeration is performed first to ensure the reaction system reaches sufficient anaerobic conditions, followed by carbon dioxide aeration to ensure the catholyte is saturated with gaseous carbon dioxide, typically for about 30 minutes. Aeration removes oxygen from the solution, ensuring anaerobic conditions and providing sufficient CO2 for microorganisms to convert into multi-carbon products.

[0021] The applied voltage is -0.8 to -1.2V. The applied voltage is generated by a potentiostat.

[0022] In this invention, the non-lethal applied constant potential ensures that the external electron flow of the carbon chain elongation microbial electrosynthesis system reaches the thermodynamic conditions required for the cathode to undergo redox reaction, thereby avoiding insufficient or excessive energy source for microbial carbon dioxide reduction.

[0023] Preferably, the multicarbon fatty acid includes any one or a combination of at least two of acetic acid, butyric acid, or hexanoic acid.

[0024] In this invention, the operation of the microbial electrosynthesis system can be carried out through the following process: A mixed microbial community of carbon-chain elongating microorganisms is inoculated into the cathode solution of the microbial electrosynthesis system, wherein the top three most abundant microorganisms in this community are... Clostridium (42.0%) Oscillibacter (12.2%) or Bacillus At least one of (3.7%), the inoculum ratio of this bacterial group to the culture medium is 10% (m / V), and 2 g / L sodium 2-bromoethylsulfonate is added as an inhibitor of methanogens to prevent the organic acids produced during carbon chain elongation from being utilized by the bacteria as a carbon source. Add 0.5~10 g·L -1 Sodium bicarbonate was used to adjust the initial pH of the culture medium to 5.0–5.8. The catholyte of the bioelectrosynthesis system was deoxygenated by nitrogen aeration (30 min), followed by carbon dioxide aeration for 30 min. A gas collection bag was connected to the cathode chamber, and CO2 with a purity of ≥99% was added. Finally, a non-lethal applied voltage (-0.8 to -1.2V) was applied using a potentiostat. 50% of the catholyte was replaced every 10 days. The reaction apparatus was operated in a constant temperature chamber of 34–37 °C. Catholyte samples were periodically taken from the reactor sampling port for product analysis.

[0025] The method of this invention has the following beneficial effects: (1) This invention differs from the synthesis of organic acids by using organic matter as a carbon source for microorganisms in an anaerobic fermentation bioreactor. Instead, it uses inorganic substrate carbon dioxide as the sole carbon source and green electrical energy as the energy source to promote the conversion of carbon dioxide into fatty acids.

[0026] (2) Unlike other microbial electrosynthesis systems, this invention does not require the addition of additional organic electron donors or expensive electron mediators, and significantly promotes the synthesis of butyric acid and hexanoic acid from acetic acid generated by carbon dioxide reduction.

[0027] (3) In this invention, the synthesis yield of the product is greatly improved by the addition of sodium ions. The maximum production concentrations of butyric acid and hexanoic acid are increased by 3.5 times and 2.8 times respectively compared with the control group, which has good application prospects and value. Attached Figure Description

[0028] Figure 1 This is the microbial electrosynthesis system and reaction principle diagram provided in Embodiment 1 of the present invention; Figure 2 The graph shows the changes in the concentration of acetic acid during synthesis under the conditions of adding sodium bicarbonate and not adding sodium bicarbonate in Examples 1 to 3. Figure 3 The graph shows the changes in the concentration of butyric acid during synthesis under the conditions of adding sodium bicarbonate and not adding sodium bicarbonate in Examples 1 to 3. Figure 4 The graph shows the changes in the concentration of hexanoic acid during synthesis under the conditions of adding sodium bicarbonate and not adding sodium bicarbonate in Examples 1 to 3. Figure 5 The output current density graphs for Examples 1 to 3 are shown under the conditions of adding sodium bicarbonate and not adding sodium bicarbonate. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the following embodiments of the present invention, the instruments and methods for testing the products are as follows: The testing instrument is an Agilent GC-7890B high-performance gas chromatograph, the chromatographic column is an Agilent 19095N-123, the injection volume is 1 μL, the temperature program is 40℃ for 0 min, 70℃ for 10℃ / min for 2 min, and 230℃ for 20℃ / min for 2 min, the FID detector temperature is 300℃, and the flow rate is 10 mL / min. The peak times for acetic acid, butyric acid, and hexanoic acid are 9.17 min, 10.36 min, and 11.6 min, respectively. The sample is acidified with formic acid at a volume ratio of 1:19, filtered through a 0.45 μm aqueous membrane, placed in a gas chromatograph, and then injected using an autosampler to determine the concentration of organic acids.

[0031] Example 1 This embodiment provides a method for promoting the synthesis of multi-carbon fatty acids from microbial reduction of carbon dioxide. (1) With a final concentration of 2.5 g·L -1 Sodium bicarbonate was added to the cathode medium of the electroactive carbon chain elongation mixed inoculum, and the medium without sodium bicarbonate was used as a control under the same conditions. (2) Construct a microbial electrosynthesis system, specifically as follows: Figure 1 The diagram shows: 1-anode chamber; 2-platinum-plated titanium mesh; 3-cation exchange membrane; 4-cathode carbon felt; 5-cathode biofilm; 6-sampling port; 7-chain elongating microorganisms in the cathode electrolyte; 8-cathode chamber; 9-gas collection bag; 10-potentiostat. The anode and cathode chambers each have an effective volume of 125 mL, separated by a cation exchange membrane. The anode is a platinum-plated titanium mesh, and the cathode is a carbon felt (4 cm × 4 cm). The cathode reference electrode is a calomel electrode. The cathode electrolyte is: K₂HPO₄ 0.35 g·L⁻¹. -1 0.25 g·L KH2PO4 -1 NH4Cl 0.25 g·L -1 KCl 0.5 g·L -1 0.15 g·L⁻¹ CaCl₂·2H₂O -1 MgCl2·6H2O·0.6 g·L -1 NaCl 1.2 g·L -1 Yeast extract 0.01 g·L -1 2-Bromoethylsulfonate sodium 1 g·L -1 L-cysteine ​​0.25 g·L -1 1 ml·L of trace element solution -1 Vitamin solution 2.5 ml / L -1 , and 0.1 ml·L tungsenosyl solution -1The initial pH of the culture medium was adjusted to 5.5. The anolyte was 0.35 g·L⁻¹ K₂HPO₄. -1 0.25 g·L KH2PO4 -1 NH4Cl 0.25 g·L -1 KCl 0.5 g·L -1 0.15 g·L⁻¹ CaCl₂·2H₂O -1 MgCl2·6H2O 0.6 g·L -1 NaCl 1.2 g·L -1 Adjust the initial pH to 7.0; (3) Aerate the catholyte with high-purity nitrogen for 30 minutes to ensure that the reaction system reaches sufficient anaerobic conditions. Then aerate the catholyte with high-purity carbon dioxide for 30 minutes to ensure that the gaseous carbon dioxide in the catholyte is saturated. Provide 100 mL of carbon dioxide gas to the cathode for microbial reduction. (4) The mixed culture of carbon chain elongation microorganisms cultured at 37°C was inoculated into the cathode chamber, and an external voltage of -0.8V was applied to the reactor using a potentiostat. The reactor was then placed in a constant temperature chamber at 37°C for operation.

[0032] Under the same conditions, a culture medium without added sodium bicarbonate was used as a control.

[0033] Example 2 The difference between this embodiment and Embodiment 1 is that only the applied voltage is adjusted to -1V. Under the same conditions, a culture medium without added sodium bicarbonate is used as a control.

[0034] Example 3 The difference between this embodiment and Embodiment 1 is that only the applied voltage is adjusted to -1.2V. Under the same conditions, a culture medium without added sodium bicarbonate is used as a control.

[0035] In a microbial electrosynthesis reactor for carbon chain elongation, the production of medium-chain fatty acids mainly involves two processes: first, carbon dioxide is converted into acetic acid via the Wood-Ljungdahl pathway; then, the microorganisms using acetic acid as a substrate generate butyric acid via a fatty acid synthesis pathway, and finally, butyric acid is used as a substrate to synthesize hexanoic acid. Therefore, the production of medium-chain fatty acids in a microbial electrosynthesis reactor includes the accumulation and reconsumption of acetic acid, as well as the accumulation of butyric and hexanoic acids.

[0036] Figure 2 2.5 g·L⁻¹ was added or not added at different potentials in Examples 1 to 3. -1 The concentration change of acetic acid under sodium ion conditions. The results showed that microorganisms can utilize cathode electrons to reduce carbon dioxide and synthesize acetic acid, with the maximum acetic acid concentration at a potential of -1.0 V and the addition of 2.5 g·L⁻¹. -1Obtained under sodium ion conditions, yielding a concentration of 1.6 g·L⁻¹. -1 Furthermore, the addition of sodium ions promoted the conversion of acetic acid. The potential at -1.0V without the addition of sodium ions decreased by 52.6%.

[0037] Figure 3 2.5 g·L was added or not added in Examples 1 to 3. -1 The concentration change of butyric acid under sodium ion conditions. The results showed that microorganisms can utilize cathode electrons to reduce carbon dioxide and synthesize acetic acid, which then undergoes a chain elongation reaction to synthesize butyric acid. The cumulative concentration of butyric acid increased after the addition of sodium ions. The maximum butyric acid concentration was also observed at a potential of -1.0 V, with the addition of 2.5 g·L⁻¹. -1 Obtained under sodium ion conditions, yielding 0.54 g·L⁻¹. -1 Compared to the blank group with a potential of -1.0V and no sodium ions added, it was 3.9 times higher.

[0038] Figure 4 2.5 g·L was added or not added in Examples 1 to 3. -1 The concentration change of hexanoic acid under sodium bicarbonate conditions. The results showed that microorganisms can utilize cathode electrons to reduce carbon dioxide and synthesize acetic acid, which then undergoes a chain elongation reaction to synthesize hexanoic acid. The cumulative concentration of hexanoic acid increased upon the addition of sodium ions. The maximum hexanoic acid concentration was also observed at a potential of -1.0 V, with the addition of 2.5 g·L⁻¹. -1 Obtained under sodium ion conditions, yielding 0.19 g·L⁻¹. -1 Compared to the blank group with a potential of -1.0V and no sodium ions added, it was 2.8 times higher.

[0039] Figure 5 Examples one through three involve adding or not adding 2.5 g·L. -1 Current density output under sodium bicarbonate conditions.

[0040] Experimental results show that, at an applied electrode potential of -1.0 V, adding 2.5 g·L -1 Under sodium bicarbonate conditions, the production of butyric acid and hexanoic acid is optimal.

[0041] The experimental conditions and procedures were set the same as in Example 2, except that the concentration of sodium bicarbonate added was set at five gradients: 0 g / L, 0.5 g / L, 2.5 g / L, 7 g / L, and 10 g / L. The maximum production concentrations and currents of acetic acid, butyric acid, and hexanoic acid are shown in Table 1.

[0042] Table 1 As shown in Table 1, the highest yield was obtained when the sodium bicarbonate concentration was 2.5 g / L.

[0043] Comparative Example 1 The difference between this comparative example and Example 1 is that sodium bicarbonate is replaced with sodium nitrate. Under the same operating conditions, the concentration of the main product is: acetic acid 1106.2 mg·L⁻¹. -1 Butyric acid 54.6 mg·L -1 Hexanoic acid 11.9 mg·L -1 The concentrations of all products were lower than in Example 1. This indicates that the introduction of nitrate competes with the reduction of CO2 for electrons. This is because the introduction of nitrate enriches nitrate-reducing bacteria, which reduce it to N2O or N2 through denitrification. This process consumes electrons that would otherwise be used to reduce CO2, thus leading to a decrease in product concentration.

[0044] 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for promoting the synthesis of multi-carbon fatty acids from carbon dioxide reduction by microorganisms, characterized in that: The method includes: inoculating a mixed microbial community of electroactive carbon chain elongating microorganisms in a microbial electrosynthesis system in a reactor, adding sodium bicarbonate, aerating with nitrogen and carbon dioxide, then applying an external voltage to the reactor, and obtaining multi-carbon fatty acids after the reaction.

2. The method according to claim 1, characterized in that: The microbial electrosynthesis system includes a cathode chamber, an anode chamber, and a titanium sheet. The cathode chamber and the anode chamber are separated by an ion exchange membrane. The cathode chamber contains a cathode, a reference electrode, and a catholyte, while the anode chamber contains an anode and an anolyte.

3. The method according to claim 2, characterized in that: The cathode is a carbon felt bonded to a titanium sheet that extends outside the reactor.

4. The method according to claim 2, characterized in that: The composition of the catholyte is: K₂HPO₄ 0.35 g·L⁻¹ -1 KH2PO4 0.25 g·L -1 NH4Cl 0.25 g·L -1 KCl 0.5 g·L -1 0.15 g·L⁻¹ CaCl₂·2H₂O -1 MgCl2·6H2O 0.6 g·L -1 NaCl 1.2 g·L -1 0.01 g·L yeast extract -1 2-Bromoethylsulfonate sodium 1 g·L -1 L-cysteine ​​0.25 g·L -1 Trace element solution 1 ml·L -1 Vitamin solution 2.5 ml / L -1 and 0.1 ml·L tungsenosyl solution -1 .

5. The method according to claim 2, characterized in that: The reference electrode is a calomel electrode filled with saturated potassium chloride.

6. The method according to claim 2, characterized in that: The anode is a platinum-plated titanium mesh; the composition of the anolyte is K₂HPO₄ 0.35 g·L⁻¹. -1 KH2PO4 0.25 g·L -1 NH4Cl 0.25 g·L -1 KCl 0.5 g·L -1 0.15 g·L⁻¹ CaCl₂·2H₂O -1 MgCl2·6H2O 0.6 g·L -1 NaCl 1.2 g·L -1 .

7. The method according to claim 1, characterized in that: The electroactive carbon chain elongating microbial mixed flora includes Clostridium , Bacillus or Oscillibacter At least one of the following: the electroactive carbon chain elongating microbial mixed flora is inoculated on a cathodic liquid culture medium containing sodium 2-bromoethylsulfonate, with a pH of 5.0-5.8, and the inoculation ratio of the electroactive carbon chain elongating microbial mixed flora to the culture medium is 0.05-0.2 by mass to volume.

8. The method according to claim 1, characterized in that: The concentration of sodium bicarbonate is 0.5~10 g·L. -1 The sodium bicarbonate is added to the catholyte; Preferably, the concentration of sodium bicarbonate is 2.5 g·L. -1 .

9. The method according to claim 1, characterized in that: The nitrogen and carbon dioxide aeration is carried out sequentially in the catholy solution; The applied voltage is -0.8 to -1.2V.

10. The method according to claim 1, characterized in that: The multicarbon fatty acids include any one or a combination of at least two of acetic acid, butyric acid, or hexanoic acid.

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