Method and device for the production of medium-chain fatty acids by electrofermentation using oxide high-entropy ceramic modified electrodes

Abstract

This invention relates to a method and apparatus for producing medium-chain fatty acids via electrofermentation using oxide high-entropy ceramic modified electrodes. The method and apparatus of this invention can yield electrodes with high electron transfer efficiency, good biocompatibility, low cost, and excellent electrochemical characteristics, thereby improving the production efficiency of medium-chain fatty acids.

Description

Technical Field

[0001] This invention relates to a method and apparatus for producing medium-chain fatty acids via electrofermentation using oxide high-entropy ceramic modified electrodes, belonging to the fields of environmental engineering and microbial fermentation technology. Background Technology

[0002] Medium-chain fatty acids (MCFAs) are straight-chain carboxylic acids with 6–12 carbon atoms. Due to their high energy density (3492.4–4798.7 kJ / mol), they have enormous potential in fields such as food flavorings, pharmaceuticals, lubricants, antibacterial agents, food additives, and biofuels. Conventional production of MFAs relies on animal fats, vegetable oils, or petroleum, requiring substantial raw material and energy inputs. This limits their output (meeting only 1.2%–1.4% of the market) and economic viability (US$3,000–5,000 per ton), making the production method unsustainable and necessitating upgrades.

[0003] Recent studies have revealed that electron transfer plays a crucial role in microbial anaerobic metabolism, and the conversion rate of fermentation reactions can be effectively improved by regulating electron transfer within the reaction system. Electrofermentation is a novel biotechnology field that uses electrochemical methods to guide and control the fermentation process. It provides low external electrical power to ensure direct or indirect electron transfer between microorganisms and electrodes. As the electron donor (cathode) and electron acceptor (anode) for microorganisms, the selection of electrode materials plays a vital role in the electrofermentation reaction and the formation of target products. To improve the selectivity of products and the overall current efficiency of the electrofermentation system, electrode materials are generally considered to possess characteristics such as biocompatibility, high conductivity, large specific surface area, chemical stability, and low cost. Common electrode materials include carbon-based materials. However, the low mechanical strength and poor plasticity of carbon-based materials limit their application in electrofermentation systems. Therefore, the preparation of modified carbon felt electrodes has become a research hotspot in the field of electrofermentation, aiming to obtain electrodes with high electron transfer efficiency, good biocompatibility, low cost, and excellent electrochemical properties.

[0004] High-entropy oxide ceramics possess capacitive properties and good biocompatibility, which are beneficial for electrode reactions and electron transfer. Modifying carbon-based anodes with high-entropy oxide ceramics can increase the surface roughness and specific surface area of ​​the electrode, significantly improving the low biocompatibility of traditional carbon-based electrodes and increasing microbial adhesion. Furthermore, the excellent conductivity of high-entropy oxide ceramics for certain metal ions allows them to act as mediators for extracellular electron transfer, effectively promoting extracellular electron transfer in microorganisms. To date, no research has reported the application of high-entropy oxide ceramics in electrofermentation processes. Developing a method for producing medium-chain fatty acids via electrofermentation using electrodes modified with high-entropy oxide ceramics is of great significance for improving the production efficiency of medium-chain fatty acids. Summary of the Invention

[0005] The problem the invention aims to solve

[0006] The present invention aims to provide a method and apparatus for producing medium-chain fatty acids by electrofermentation using oxide high-entropy ceramic modified electrodes, thereby obtaining electrodes with high electron transfer efficiency, good biocompatibility, low cost and excellent electrochemical characteristics, and improving the production efficiency of medium-chain fatty acids.

[0007] Solution for solving the problem

[0008] [1] A method for producing medium-chain fatty acids by electrofermentation using an oxide high-entropy ceramic modified electrode, comprising:

[0009] Step 1: Add oxide high-entropy ceramic, optional activated carbon and optional binder to deionized water, then sonicate and shear to obtain solution A;

[0010] Step 2: On the heating stage, uniformly drop solution A onto both sides of the carbon felt electrode to obtain the working electrode;

[0011] Step 3: Add methane inhibitor, electron donor and electron acceptor to the culture medium of the remaining sludge used for inoculation, and adjust the pH of the system to 5-7 to obtain the cathode solution of the electrofermentation system.

[0012] Step 4: Add potassium ferrocyanide to the phosphate solution to obtain the anolyte solution of the electrofermentation system;

[0013] Step 5: Separate the cathode solution and anolyte of the electrofermentation system using a proton exchange membrane to obtain the electrofermentation system;

[0014] Step 6: Under anaerobic conditions, the cathode solution of the electrofermentation system is kept at a constant temperature and stirred until the concentration of medium-chain fatty acids in the cathode solution of the electrofermentation system no longer increases.

[0015] [2] According to the method described in [1], in step 1, the amount of oxide high-entropy ceramic added is 0.1-0.3g; the amount of activated carbon added is 0.1-0.3g; the binder is polyvinylidene fluoride (PVDF) or perfluorosulfonic acid-polytetrafluoroethylene; the amount of binder added is 0-0.5mL; the amount of deionized water added is 20-40mL; the time for ultrasonication and shearing is 5-15min and 1-2h, respectively; in step 2, the size of the carbon felt electrode is 2-4cm*4-6cm.

[0016] [3] According to the method described in [1] or [2], wherein, in step 3, the amount of residual sludge for inoculation is 5-15% by volume of the cathode solution of the electrofermentation system; the methane inhibitor is sodium 2-bromoethanesulfonate; the amount of culture medium is 100-200 mL; the culture medium is a 50 mM DSM solution; the electron donor is ethanol or lactic acid; the electron acceptor is acetate or butyric acid; the amount of methane inhibitor added is 5-20 g / L based on the volume of the cathode solution of the electrofermentation system; the molar concentration ratio of the added electron donor and the added electron acceptor is 1:5-3:2; and the reagent used to adjust the pH is hydrochloric acid and / or sodium hydroxide.

[0017] [4] According to the method described in [1] or [2], wherein in step 4, the amount of potassium ferrocyanide added is 15 to 25 g / L based on the volume of the anolyte solution of the electrofermentation system.

[0018] [5] The method according to [1] or [2], wherein the thickness of the proton exchange membrane in step 5 is 12 to 25 μm; the culture temperature in step 6 is 30 to 40 °C; and the stirring speed is 400 to 500 rpm.

[0019] [6] According to the method described in [1] or [2], wherein the oxide high-entropy ceramic has a spinel structure or a perovskite structure; and the carbon chain length of the medium-chain fatty acid is C6 to C6. 12 .

[0020] [7] According to the method described in [1] or [2], wherein the cathode solution of the electrofermentation system is connected to the working electrode and the silver chloride electrode; the anode solution of the electrofermentation system is connected to the titanium sheet electrode; the electrofermentation system provides a constant potential of -1.0V; and the size of the titanium sheet electrode is 2-4cm*4-6cm.

[0021] [8] An apparatus for the method described in any one of [1] to [7], comprising:

[0022] The cathode unit of the electrofermentation system is used to add a methane inhibitor, an electron donor, and an electron acceptor to the culture medium of the residual sludge used for inoculation, adjust the pH of the system to 5-7, and obtain the cathode solution of the electrofermentation system. The cathode solution is connected to the working electrode and the silver chloride electrode.

[0023] An anode unit for an electrofermentation system is used to add potassium ferrocyanide to a phosphate solution to obtain an anode solution for the electrofermentation system, and the anode solution is connected to a titanium electrode.

[0024] An electrofermentation system membrane unit, wherein the electrofermentation system membrane unit is used to separate the electrofermentation system cathode unit and the electrofermentation system anode unit.

[0025] The electrode to be used is prepared by adding oxide high-entropy ceramic, optional activated carbon and optional binder to deionized water, followed by ultrasonication and shearing to obtain solution A, which is then uniformly dripped onto both sides of the carbon felt electrode on a heating stage.

[0026] [9] According to the device described in [8], the membrane unit of the electro-fermentation system is a proton exchange membrane with a thickness of 12 to 25 μm; the cathode unit, the anode unit and the membrane unit of the electro-fermentation system are formed by placing the electro-fermentation reactor on a magnetic stirrer.

[0027]

[10] The apparatus according to [8] or [9], wherein the oxide high-entropy ceramic is a spinel structure or a perovskite structure; the electro-fermentation system provides a constant potential of -1.0V; the carbon felt electrode has a size of 2-4cm*4-6cm; and the titanium sheet electrode has a size of 2-4cm*4-6cm.

[0028] The effects of the invention

[0029] The method of this invention uses an oxide-modified high-entropy ceramic electrode as a carrier for microbial attachment and growth and an electron transfer medium during electrofermentation, which effectively enhances microbial activity, electron transfer between microorganisms, and electron transfer between microorganisms and electrodes, ultimately improving the production efficiency of medium-chain fatty acids.

[0030] Furthermore, the method of this invention enables efficient and high-value resource utilization of the substrate, providing a cheap and readily available substrate source for the biological production of medium-chain fatty acids, thereby reducing the production cost of medium-chain fatty acids.

[0031] In summary, the method of the present invention has the advantages of simple operation, low cost, and strong stability, which significantly improves the yield and production rate of medium-chain fatty acids in electrofermentation and has good market application prospects. Compared with the method of electrofermentation production of medium-chain fatty acids using unmodified carbon felt electrodes, the concentration of medium-chain fatty acids in the liquid phase product at the end of fermentation in the method of the present invention is increased by 15.2% to 42.0%, and the electron transfer efficiency of medium-chain fatty acid products in the carbon chain elongation process is increased by 0.6% to 2.9%. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of an apparatus used in the method of the present invention.

[0033] Figure 2 This is a flowchart illustrating the preparation process of oxide high-entropy ceramics according to an embodiment of the present invention. Detailed Implementation

[0034] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0035] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0036] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0037] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0038] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0039] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0040] In the method of the present invention, in step 1, the amount of the oxide high-entropy ceramic added is 0.1-0.3g, preferably 0.2-0.3g; the amount of the activated carbon added is 0.1-0.3g, preferably 0.2-0.3g; the binder is polyvinylidene fluoride (PVDF) or perfluorosulfonic acid-polytetrafluoroethylene (Nafion); the amount of the binder added is 0-0.5mL; and the amount of deionized water added is 20-40mL.

[0041] In step 3, the amount of residual sludge used for inoculation is 5-15% by volume of the cathode solution of the electrofermentation system, preferably 7-12% by volume; the culture medium is 50 mM DSM (Difco Sporulation Medium) solution; the electron donor is ethanol or lactic acid; the electron acceptor is acetate or butyric acid, and the acetate can be an alkali metal acetate such as potassium acetate, sodium acetate, or an alkaline earth metal acetate such as calcium acetate, magnesium acetate; based on the volume of the cathode solution of the electrofermentation system, the amount of methane inhibitor added is 5-20 g / L, preferably 8-16 g / L; the molar concentration ratio of the added electron donor and the added electron acceptor is 1:5-3:2, preferably 1:2.

[0042] In the method of this invention, the residual sludge used for inoculation is commercially available. As a non-limiting example, the residual sludge was taken from a wastewater treatment plant in Beijing, and its relevant parameters are shown in Table 1. This residual sludge was used in the embodiments and comparative examples described later.

[0043] Table 1 Relevant parameters of residual sludge

[0044]

[0045] In the method of this invention, the carbon chain length of the medium-chain fatty acid is C6 to C7. 12 Preferably, it is C6 to C8. Exemplary examples of medium-chain fatty acids include, but are not limited to, hexanoic acid, 2-ethylhexanoic acid, heptanoic acid, octanoic acid, 4-methyloctanoic acid, nonanoic acid, 4-methylnonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, and isomers of these acids.

[0046] Figure 1 This is a schematic diagram of an apparatus used in the method of the present invention, which shows that the apparatus includes:

[0047] The cathode unit of the electrofermentation system is used in step 3, that is, to add methane inhibitor, electron donor and electron acceptor to the culture medium of residual sludge for inoculation, adjust the pH of the system to 5-7, and obtain the cathode solution of the electrofermentation system. The cathode solution is connected to the working electrode and the silver chloride electrode.

[0048] An anode unit for an electro-fermentation system is used in step 4, i.e., to add potassium ferrocyanide to the phosphate solution to obtain an anode solution for the electro-fermentation system, wherein the anode solution is connected to a titanium electrode.

[0049] The electrofermentation system membrane unit is used in step 5, specifically to separate the electrofermentation system cathode unit and the electrofermentation system anode unit.

[0050] The electrode to be used is prepared by adding oxide high-entropy ceramic, optional activated carbon and optional binder to deionized water, followed by ultrasonication and shearing to obtain solution A, which is then uniformly dripped onto both sides of the carbon felt electrode on a heating stage.

[0051] exist Figure 1 The cathodic solution was cultured at a temperature of 36±0.5℃ and a stirring speed of 450rpm.

[0052] Figure 2 This is a flowchart illustrating the preparation process of high-entropy oxide ceramics according to an embodiment of the present invention. Figure 2 As shown, oxide high-entropy ceramics are obtained through the following steps.

[0053] According to the molar ratio of Co:Cr:Fe:Mn:Ni of 1:(0.8~1):(0.8~1):(0.8~1):(0.8~1), five metal nitrates of Co, Cr, Fe, Mn and Ni, namely Co(NO3)2·6H2O, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Mn(NO3)2·6H2O and Ni(NO3)2·6H2O, were weighed as raw materials; according to the raw materials: surface active The mass ratio of surfactant to deionized water is 1:(0.8-0.9):(15-25). Hexadecyltrimethylammonium bromide and deionized water are added to the raw materials, and the mixture is stirred to obtain solution I. Urea is added to solution I at a molar ratio of urea to the raw materials of 4-8:1. The mixture is stirred and subjected to hydrothermal treatment. The mixture is then centrifuged, the lower precipitate is collected, dried, and heat-treated at 800-1000℃ for 1-3 hours to obtain high-entropy oxide ceramic powder with a spinel or perovskite structure.

[0054] Example

[0055] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0056] Example 1

[0057] 0.2 g of oxide high-entropy ceramic was added to 30 mL of deionized water, followed by sonication for 10 minutes and shearing for 2 hours to obtain solution A. Solution A was uniformly dripped onto both sides of a carbon felt electrode on a heating stage, and the electrode was dried to obtain the working electrode. A 250 mL double-chamber reaction flask was used as the electrofermentation reactor. 133 mL of culture medium (50 mM Difco Sporulation Medium solution (DSM solution, produced by Zeye Biotechnology) was placed in the flask, and 17 mL of residual sludge was inoculated. 10.5 g / L of sodium 2-bromoethanesulfonate was added as a methane inhibitor, and 1.3 mL of ethanol and 3.7 g of sodium acetate were added as electron donor and electron acceptor, respectively. The cathode solution of the electrofermentation system was then adjusted with hydrochloric acid and sodium hydroxide solution until the pH value of the cathode solution stabilized within the range of pH = 6 ± 0.1.

[0058] Potassium ferrocyanide was added to a phosphate solution to obtain the anolyte of the electroferrofermentation system. The amount of potassium ferrocyanide added was 20 g / L, based on the volume of the anolyte. The cathodic and anolyte solutions of the electroferrofermentation system were separated by a 25 μm thick proton exchange membrane to obtain the electroferrofermentation system, which provided a constant potential of -1.0 V. The cathodic solution of the electroferrofermentation system was connected to the working electrode and the silver chloride electrode, and the anolyte solution was connected to a titanium electrode.

[0059] Before fermentation began, the cathode and anolyte solutions of the electroferrofer system were purged with nitrogen for 30 minutes, and then the bottle was immediately sealed to ensure an anaerobic environment. The electroferrofer reactor was placed on a magnetic stirrer and incubated at 36.5℃ and a stirring rate of 450 rpm. During the isothermal shaking incubation, samples of the liquid in the electroferrofer reactor were taken every 1-2 days to determine the pH value and medium-chain fatty acid content. The fermentation reaction was considered complete when the concentration of medium-chain fatty acids no longer increased.

[0060] The medium-chain fatty acid obtained is hexanoic acid.

[0061] Compare with Example 1

[0062] A 250 mL double-chamber reaction flask was used as the electrofermentation reactor. 133 mL of culture medium (50 mM DifcoSporulation Medium solution (DSM solution, produced by Zeye Biotechnology) was placed in the flask, and 17 mL of residual sludge was inoculated. 10.5 g / L of sodium 2-bromoethanesulfonate was added as a methane inhibitor, and 1.3 mL of ethanol and 3.7 g of sodium acetate were added as electron donor and electron acceptor, respectively. The cathode solution of the electrofermentation system was then adjusted with hydrochloric acid and sodium hydroxide solution until the pH value of the cathode solution stabilized within the range of pH = 6 ± 0.1.

[0063] Potassium ferrocyanide was added to a phosphate solution to obtain the anolyte of the electroferrofermentation system, with an addition amount of 20 g / L based on the volume of the anolyte. The catholyte and anolyte of the electroferrofermentation system were separated by a 25 μm thick proton exchange membrane to obtain the electroferrofermentation system, which provided a constant potential of -1.0 V. The catholyte of the electroferrofermentation system was connected to an unmodified carbon felt electrode and a silver chloride electrode, while the anolyte was connected to a titanium sheet electrode.

[0064] Before fermentation began, the cathode and anolyte solutions of the electroferrofer system were purged with nitrogen for 30 minutes, and then the bottle was immediately sealed to ensure an anaerobic environment. The electroferrofer reactor was placed on a magnetic stirrer and incubated at 36.5℃ and a stirring rate of 450 rpm. During the isothermal shaking incubation, samples of the liquid in the electroferrofer reactor were taken every 1-2 days to determine the pH value and medium-chain fatty acid content. The fermentation reaction was considered complete when the concentration of medium-chain fatty acids no longer increased.

[0065] The medium-chain fatty acid obtained is hexanoic acid.

[0066] When the fermentation reaction proceeded to day 19, the concentrations of all acids stopped increasing, and the reactions of Example 1 and Control Example 1 were completed. The specific medium-chain fatty acid concentrations, pH values, and electron transfer efficiency during the carbon chain elongation process are shown in Table 2.

[0067] Table 2. Index data of medium-chain fatty acids produced by electrofermentation in Example 1 and Control Example 1.

[0068]

[0069] As can be seen, compared with the electrofermentation production of medium-chain fatty acids using carbon felt electrodes modified with unutilized oxide high-entropy ceramics (Control Example 1), the concentration of medium-chain fatty acids in Example 1 was increased by 15.2%, the electron transfer efficiency of medium-chain fatty acids in the carbon chain elongation process was increased by 0.6%, and the performance of medium-chain fatty acids produced by electrofermentation was significantly optimized.

[0070] Example 2

[0071] 0.2 g of oxide high-entropy ceramic and 0.23 mL of perfluorosulfonic acid-polytetrafluoroethylene binder (Nafion) were added to 30 mL of deionized water, followed by sonication for 10 minutes and shearing for 2 hours to obtain solution A. Solution A was uniformly dripped onto both sides of a carbon felt electrode on a heating stage, and the electrode was dried to obtain the working electrode. A 250 mL double-chamber reaction flask was used as the electrofermentation reactor. 133 mL of culture medium (50 mM Difco Sporulation Medium solution (DSM solution, produced by Zeye Biotechnology) was placed in the flask, and 17 mL of residual sludge was inoculated. 10.5 g / L of sodium 2-bromoethanesulfonate was added as a methane inhibitor, and 1.3 mL of ethanol and 3.7 g of sodium acetate were added as electron donor and electron acceptor, respectively. The cathode solution of the electrofermentation system was then adjusted with hydrochloric acid and sodium hydroxide solution until the pH value of the cathode solution stabilized within the range of pH = 6 ± 0.1.

[0072] Potassium ferrocyanide was added to a phosphate solution to obtain the anolyte of the electroferrofermentation system. The amount of potassium ferrocyanide added was 20 g / L, based on the volume of the anolyte. The cathodic and anolyte solutions of the electroferrofermentation system were separated by a 25 μm thick proton exchange membrane to obtain the electroferrofermentation system, which provided a constant potential of -1.0 V. The cathodic solution of the electroferrofermentation system was connected to the working electrode and the silver chloride electrode, and the anolyte solution was connected to a titanium electrode.

[0073] Before fermentation began, the cathode and anolyte solutions of the electroferrofer system were purged with nitrogen for 30 minutes, and then the bottle was immediately sealed to ensure an anaerobic environment. The electroferrofer reactor was placed on a magnetic stirrer and incubated at 36.5℃ and a stirring rate of 450 rpm. During the isothermal shaking incubation, samples of the liquid in the electroferrofer reactor were taken every 1-2 days to determine the pH value and medium-chain fatty acid content. The fermentation reaction was considered complete when the concentration of medium-chain fatty acids no longer increased.

[0074] The medium-chain fatty acid obtained is hexanoic acid.

[0075] When the fermentation reaction proceeded to day 19, the concentrations of all acids stopped increasing, and the reactions of Example 2 and Control Example 1 were completed. The specific medium-chain fatty acid concentrations, pH values, and electron transfer efficiency during the carbon chain elongation process are shown in Table 3.

[0076] Table 3. Index data of medium-chain fatty acids produced by electrofermentation in Example 2 and Control Example 1.

[0077]

[0078] As can be seen, compared with the electrofermentation production of medium-chain fatty acids using carbon felt electrodes modified with unutilized oxide high-entropy ceramics (Control Example 1), the concentration of medium-chain fatty acids in Example 2 was increased by 39.1%, the electron transfer efficiency of medium-chain fatty acids in the carbon chain elongation process was increased by 1.7%, and the performance of medium-chain fatty acids produced by electrofermentation was significantly optimized.

[0079] Example 3

[0080] Add 0.2 g of oxide high-entropy ceramic, 0.2 g of activated carbon, and 0.46 mL of perfluorosulfonic acid-polytetrafluoroethylene binder (Nafion) to 30 mL of deionized water, followed by sonication for 10 minutes and shearing for 2 hours to obtain solution A. Apply solution A evenly to both sides of a carbon felt electrode on a heating stage, then dry the electrode to obtain the working electrode. Use a 250 mL double-chamber reaction flask as an electrofermentation reactor. Place 133 mL of culture medium (50 mM Difco Sporulation Medium solution (DSM solution, produced by Zeye Biotechnology) into the flask, inoculate with 17 mL of residual sludge, add 10.5 g / L of sodium 2-bromoethanesulfonate as a methane inhibitor, and add 1.3 mL of ethanol and 3.7 g of sodium acetate as electron donor and electron acceptor, respectively. Adjust the cathode solution of the electrofermentation system with hydrochloric acid and sodium hydroxide solution until the pH value of the cathode solution stabilizes within the range of pH = 6 ± 0.1.

[0081] Potassium ferrocyanide was added to a phosphate solution to obtain the anolyte of the electroferrofermentation system. The amount of potassium ferrocyanide added was 20 g / L, based on the volume of the anolyte. The cathodic and anolyte solutions of the electroferrofermentation system were separated by a 25 μm thick proton exchange membrane to obtain the electroferrofermentation system, which provided a constant potential of -1.0 V. The cathodic solution of the electroferrofermentation system was connected to the working electrode and the silver chloride electrode, and the anolyte solution was connected to a titanium electrode.

[0082] Before fermentation began, the cathode and anolyte solutions of the electroferrofer system were purged with nitrogen for 30 minutes, and then the bottle was immediately sealed to ensure an anaerobic environment. The electroferrofer reactor was placed on a magnetic stirrer and incubated at 36.5℃ and a stirring rate of 450 rpm. During the isothermal shaking incubation, samples of the liquid in the electroferrofer reactor were taken every 1-2 days to determine the pH value and medium-chain fatty acid content. The fermentation reaction was considered complete when the concentration of medium-chain fatty acids no longer increased.

[0083] The medium-chain fatty acids obtained are hexanoic acid and octanoic acid.

[0084] Compare with Example 2

[0085] Add 0.2g of activated carbon and 0.23mL of perfluorosulfonic acid-polytetrafluoroethylene binder (Nafion) to 30mL of deionized water, then sonicate for 10 minutes and shear for 2 hours to obtain solution A. Apply solution A evenly to both sides of a carbon felt electrode on a heating stage, then dry the electrode to obtain the working electrode. Use a 250mL two-chamber reaction flask as the electrofermentation reactor. Place 133mL of culture medium (50mM Difco Sporulation Medium solution (DSM solution, produced by Zeye Biotechnology) into the flask, inoculate with 17mL of residual sludge, add 10.5g / L of sodium 2-bromoethanesulfonate as a methane inhibitor, and add 1.3mL of ethanol and 3.7g of sodium acetate as electron donor and electron acceptor, respectively. Adjust the cathode solution of the electrofermentation system with hydrochloric acid and sodium hydroxide solution until the pH value of the cathode solution stabilizes within the range of pH = 6 ± 0.1.

[0086] Potassium ferrocyanide was added to a phosphate solution to obtain the anolyte of the electroferrofermentation system. The amount of potassium ferrocyanide added was 20 g / L, based on the volume of the anolyte. The cathodic and anolyte solutions of the electroferrofermentation system were separated by a 25 μm thick proton exchange membrane to obtain the electroferrofermentation system, which provided a constant potential of -1.0 V. The cathodic solution of the electroferrofermentation system was connected to the working electrode and the silver chloride electrode, and the anolyte solution was connected to a titanium electrode.

[0087] Before fermentation began, the cathode and anolyte solutions of the electroferrofer system were purged with nitrogen for 30 minutes, and then the bottle was immediately sealed to ensure an anaerobic environment. The electroferrofer reactor was placed on a magnetic stirrer and incubated at 36.5℃ and a stirring rate of 450 rpm. During the isothermal shaking incubation, samples of the liquid in the electroferrofer reactor were taken every 1-2 days to determine the pH value and medium-chain fatty acid content. The fermentation reaction was considered complete when the concentration of medium-chain fatty acids no longer increased.

[0088] The medium-chain fatty acid obtained is hexanoic acid.

[0089] When the fermentation reaction proceeded to day 19, the concentrations of all acids stopped increasing, and the reactions of Example 3 and Control Example 2 were completed. The specific medium-chain fatty acid concentrations, pH values, and electron transfer efficiency during the carbon chain elongation process are shown in Table 4.

[0090] Table 4. Index data of medium-chain fatty acids produced by electrofermentation in Example 3 and Control Example 2.

[0091]

[0092] As can be seen, compared with the electrofermentation production of medium-chain fatty acids using carbon felt electrodes modified with unutilized oxide high-entropy ceramics (Control Example 2), the concentration of medium-chain fatty acids in Example 3 was increased by 42.0%, the electron transfer efficiency of medium-chain fatty acids in the carbon chain elongation process was increased by 2.9%, and the performance of medium-chain fatty acids produced by electrofermentation was significantly optimized.

[0093] As can be seen from the above embodiments, the use of oxide high-entropy ceramic modified carbon felt electrode can effectively increase the concentration of medium-chain fatty acids produced by electrofermentation. Compared with the original method of electrofermentation to produce medium-chain fatty acids using unmodified carbon felt electrode, the method of the present invention increases the concentration of medium-chain fatty acids in the liquid phase product at the end of fermentation by 15.2% to 42.0%, and increases the electron transfer efficiency of medium-chain fatty acid product during carbon chain elongation by 0.6% to 2.9%, significantly improving the production efficiency of medium-chain fatty acids.

[0094] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0095] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for producing medium-chain fatty acids via electrofermentation using an oxide high-entropy ceramic modified electrode, characterized in that, include: Step 1: Add high-entropy oxide ceramic to deionized water and then sonicate and shear to obtain solution A; in the high-entropy oxide ceramic, the molar ratio of Co∶Cr∶Fe∶Mn∶Ni is 1∶(0.8~1)∶(0.8~1)∶(0.8~1)∶(0.8~1); Step 2: On the heating stage, uniformly drop solution A onto both sides of the carbon felt electrode to obtain the working electrode; Step 3: Add methane inhibitor, electron donor and electron acceptor to the culture medium of the remaining sludge used for inoculation, and adjust the pH of the system to 5-7 to obtain the cathode solution of the electrofermentation system. Step 4: Add potassium ferrocyanide to the phosphate solution to obtain the anolyte solution of the electrofermentation system; Step 5: Separate the cathode solution and anolyte of the electrofermentation system using a proton exchange membrane to obtain the electrofermentation system; Step 6: Under anaerobic conditions, the cathode solution of the electrofermentation system is kept at a constant temperature and stirred until the concentration of medium-chain fatty acids in the cathode solution of the electrofermentation system no longer increases.

2. The method according to claim 1, characterized in that, Step 1 also includes the step of adding activated carbon and / or binder to deionized water.

3. The method according to claim 2, characterized in that, In step 1, the amount of the oxide high-entropy ceramic added is 0.1–0.3 g; the amount of the activated carbon added is 0.1–0.3 g; the binder is polyvinylidene fluoride (PVDF) or perfluorosulfonic acid-polytetrafluoroethylene; the amount of the binder added is 0–0.5 mL; the amount of deionized water added is 20–40 mL; the ultrasonic and shearing times are 5–15 min and 1–2 h, respectively; in step 2, the size of the carbon felt electrode is 2–4 cm * 4–6 cm.

4. The method according to any one of claims 1 to 3, characterized in that, In step 3, the amount of residual sludge used for inoculation is 5-15% by volume of the cathode solution of the electrofermentation system; the methane inhibitor is sodium 2-bromoethanesulfonate; the amount of culture medium is 100-200 mL; the culture medium is a 50 mM DSM solution; the electron donor is ethanol or lactic acid; the electron acceptor is acetate or butyric acid; the amount of methane inhibitor added is 5-20 g / L based on the volume of the cathode solution of the electrofermentation system; the molar concentration ratio of the added electron donor and the added electron acceptor is 1:5-3:2; the reagent used to adjust the pH is hydrochloric acid and / or sodium hydroxide.

5. The method according to any one of claims 1 to 3, characterized in that, In step 4, the amount of potassium ferrocyanide added is 15-25 g / L, based on the volume of the anolyte solution in the electrofermentation system.

6. The method according to any one of claims 1 to 3, characterized in that, The thickness of the proton exchange membrane in step 5 is 12–25 μm; the culture temperature in step 6 is 30–40 °C; and the stirring speed is 400–500 rpm.

7. The method according to any one of claims 1 to 3, characterized in that, The oxide high-entropy ceramic has a spinel structure; the carbon chain length of the medium-chain fatty acid is C6~C6. 12 .

8. The method according to any one of claims 1 to 3, characterized in that, The cathode solution of the electrofermentation system is connected to the working electrode and the silver chloride electrode; the anolyte solution of the electrofermentation system is connected to the titanium sheet electrode; the electrofermentation system provides a constant potential of -1.0V; the size of the titanium sheet electrode is 2-4cm * 4-6cm.

9. An apparatus for use in the method according to any one of claims 1 to 8, characterized in that, include: The cathode unit of the electrofermentation system is used to add a methane inhibitor, an electron donor, and an electron acceptor to the culture medium of the residual sludge used for inoculation, adjust the pH of the system to 5-7, and obtain the cathode solution of the electrofermentation system. The cathode solution is connected to the working electrode and the silver chloride electrode. An anode unit for an electrofermentation system is provided, wherein potassium ferrocyanide is added to a phosphate solution to obtain an anode solution for the electrofermentation system, and the anode solution is connected to a titanium electrode. An electrofermentation system membrane unit, wherein the electrofermentation system membrane unit is used to separate the electrofermentation system cathode unit and the electrofermentation system anode unit. The electrode to be used is prepared by adding oxide high-entropy ceramic, optional activated carbon and optional binder to deionized water, followed by ultrasonication and shearing to obtain solution A, which is then uniformly dripped onto both sides of the carbon felt electrode on a heating stage.

10. The apparatus according to claim 9, characterized in that, The membrane unit of the electrofermentation system is a proton exchange membrane with a thickness of 12-25 μm; the cathode unit, anode unit, and membrane unit of the electrofermentation system are formed by placing the electrofermentation reactor on a magnetic stirrer.

11. The apparatus according to claim 9 or 10, characterized in that, The oxide high-entropy ceramic has a spinel structure; the electrofermentation system provides a constant potential of -1.0V; the carbon felt electrode has a size of 2-4cm * 4-6cm; and the titanium sheet electrode has a size of 2-4cm * 4-6cm.

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