Method and device for producing medium-chain fatty acid through electric fermentation by using oxide high-entropy ceramic modified electrode

Abstract

The invention relates to a method and a device for producing medium-chain fatty acid through electric fermentation by using an oxide high-entropy ceramic modified electrode. Through the method and the device provided by the invention, the electrode with high electron transfer efficiency, good biocompatibility, low cost and excellent electrochemical characteristics can be obtained, and the production efficiency of medium-chain fatty acid is improved.

Description

Technical Field

[0001] The invention relates to a method and a device for producing medium-chain fatty acids by electric fermentation using oxide high-entropy ceramic modified electrodes, and belongs to the technical fields of environmental engineering and microbial fermentation. Background Art

[0002] Medium-chain fatty acids are straight-chain carboxylic acids with 6 to 12 carbons. Due to their high energy density (3492.4-4798.7 kJ / mol), they have great potential in the fields of edible flavors, medicines, lubricants, antimicrobial agents, food additives and biofuels. The conventional production of medium-chain fatty acids relies on animal fats, vegetable oils or petroleum, which requires a large amount of raw materials and energy input, limiting their production (only meeting 1.2%-1.4% of the market) and economic feasibility (US$3,000-5,000 per ton). The production method is difficult to sustain and urgently needs to be upgraded.

[0003] Recent studies have found that electron transfer plays a key role in the anaerobic metabolism of microorganisms. By regulating the electron transfer in the reaction system, the conversion rate of the fermentation reaction can be effectively improved. Electrofermentation is a new biotechnology field that uses electrochemical means to guide and control the fermentation process. It provides external low electrical power to ensure that microorganisms and electrodes can directly or indirectly transfer electrons. As the electron donor (cathode) and electron acceptor (anode) of microorganisms, the selection of electrode materials plays a vital role in the electrofermentation reaction and the generation of target products. In order to improve the selectivity of the products of the electrofermentation system and the overall current efficiency of the system, it is generally believed that the electrode material should have the characteristics of 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, in order to obtain electrodes with high electron transfer efficiency, good biocompatibility, low cost and excellent electrochemical properties, the preparation of modified carbon felt electrodes has become a research hotspot in the field of electrofermentation.

[0004] Oxide high entropy ceramics have capacitive properties and good biocompatibility, which are conducive to electrode reactions and electron transfer. Modifying carbon-based anodes with oxide high entropy ceramics can increase the surface roughness of the electrode and the specific surface area of ​​the electrode, which can significantly improve the low biocompatibility of traditional carbon-based electrodes and increase the amount of microbial attachment. Moreover, the excellent conductivity of oxide high entropy ceramics to certain metal ions allows them to act as an intermediary for extracellular electron transfer, thereby effectively promoting the extracellular electron transfer of microorganisms. So far, no research has reported the application of oxide high entropy ceramics in the electrofermentation process. Developing a method for producing medium-chain fatty acids by electrofermentation using oxide high entropy ceramic modified electrodes is of great significance to improving the production efficiency of medium-chain fatty acids. Summary of the invention

[0005] Problem that the invention aims to solve

[0006] The present invention aims to provide a method and device 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 properties, and improving the production efficiency of medium-chain fatty acids.

[0007] Solutions for solving problems

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

[0009] Step 1, adding oxide high entropy ceramics, optional activated carbon and optional binder into deionized water, and then performing ultrasonication and shearing to obtain solution A;

[0010] Step 2, on a heating platform, evenly apply the solution A to both sides of the carbon felt electrode to obtain a working electrode;

[0011] Step 3, adding a methane inhibitor, an electron donor and an electron acceptor to the culture medium of the inoculated excess sludge, adjusting the pH of the system to 5-7, and obtaining a cathode solution of the electric fermentation system;

[0012] Step 4, adding potassium ferrocyanide to the phosphate solution to obtain an anode solution of the electric fermentation system;

[0013] Step 5, separating the cathode solution and the anode solution of the electric fermentation system by a proton exchange membrane to obtain an electric fermentation system;

[0014] Step 6: In an anaerobic environment, the cathode solution of the electric fermentation system is cultured with constant temperature stirring until the concentration of medium-chain fatty acids in the cathode solution of the electric fermentation system no longer increases.

[0015] [2] The method according to [1], wherein 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 ultrasound 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.

[0016] [3] The method according to [1] or [2], wherein in step 3, the amount of the residual sludge for inoculation is 5-15% by volume of the cathode solution of the electro-fermentation system; the methane inhibitor is sodium 2-bromoethane sulfonate; the amount of the 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 the methane inhibitor added is 5-20 g / L based on the volume of the cathode solution of the electro-fermentation system; the molar concentration ratio of the electron donor and the electron acceptor added is 1:5-3:2; and the reagent used to adjust the pH is hydrochloric acid and / or sodium hydroxide.

[0017] [4] The method according to [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 anode solution of the electro-fermentation 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] The method according to [1] or [2], wherein the oxide high entropy ceramic has a spinel structure or a perovskite structure; the carbon chain length of the medium-chain fatty acid is C6 to C 12 .

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

[0021] [8] A device for use in the method described in any one of [1] to [7], comprising:

[0022] The cathode unit of the electric fermentation system is used to add a methane inhibitor, an electron donor and an electron acceptor to the culture medium of the inoculated excess sludge, adjust the pH of the system to 5-7, and obtain a cathode solution of the electric fermentation system, wherein the cathode solution is connected to a working electrode and a silver chloride electrode;

[0023] An electric fermentation system anode unit, the electric fermentation system anode unit is used to add potassium ferrocyanide to the phosphate solution to obtain an anode solution of the electric fermentation system, and the anode solution is connected to a titanium sheet electrode;

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

[0025] The working electrode is prepared by adding oxide high entropy ceramics, optional activated carbon and optional binder into deionized water, followed by ultrasonication and shearing to obtain solution A, and then evenly coating the solution A on both sides of the carbon felt electrode on a heating table.

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

[0027]

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

[0028] Effects of the Invention

[0029] The method of the present invention uses an electrode modified with oxide high-entropy ceramics as a carrier for microbial attachment and growth and an electron transfer mediator during the electrofermentation process, effectively enhancing microbial activity, the electron transfer process between microorganisms and between microorganisms and electrodes, and ultimately achieving an improvement in the production efficiency of medium-chain fatty acids.

[0030] In addition, the method of the present invention realizes efficient and high-value resource utilization of substrates, provides a cheap and readily available substrate source option for biological production of medium-chain fatty acids, and reduces the production cost of medium-chain fatty acids.

[0031] In general, the method of the present invention has the advantages of simple operation, low cost and strong stability, which effectively improves the output and yield of medium-chain fatty acids produced by electric fermentation, and has a good market application prospect; compared with the method of producing medium-chain fatty acids by electric fermentation 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 the medium-chain fatty acid product in the carbon chain extension process is increased by 0.6% to 2.9%. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0033] Figure 2 It is a flow chart of the preparation of oxide high entropy ceramics according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0035] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

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

[0037] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0038] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0039] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical 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 to 0.3 g, preferably 0.2 to 0.3 g; the amount of the activated carbon added is 0.1 to 0.3 g, preferably 0.2 to 0.3 g; the binder is polyvinylidene fluoride (PVDF) or perfluorosulfonic acid-polytetrafluoroethylene (Nafion); the amount of the binder added is 0 to 0.5 mL; the amount of the deionized water added is 20 to 40 mL.

[0041] In the step 3, the amount of the inoculated excess sludge is 5-15% by volume of the cathode solution of the electric fermentation system, preferably 7-12% by volume; the culture medium is a 50 mM DSM (Difco Sporulation Medium (Zeye Biological Production) 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 and magnesium acetate; based on the volume of the cathode solution of the electric fermentation system, the amount of the methane inhibitor added is 5-20 g / L, preferably 8-16 g / L; the molar concentration ratio of the electron donor and the electron acceptor added is 1:5-3:2, preferably 1:2.

[0042] In the method of the present invention, the excess sludge used for inoculation can be commercially available. As a non-limiting example, the excess sludge is taken from a sewage treatment plant in Beijing, and its relevant parameters are shown in Table 1. The excess sludge is used in the following examples and comparative examples.

[0043] Table 1 Residual sludge related parameters

[0044]

[0045] In the method of the present invention, the carbon chain length of the medium-chain fatty acid is C6 to C 12 , preferably C6 to C8. Illustrative 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 Schematic diagram of a device for the method of the present invention, from which it can be seen that the device comprises:

[0047] The cathode unit of the electric fermentation system is used in the step 3, i.e., used to add a methane inhibitor, an electron donor and an electron acceptor to the culture medium of the inoculated excess sludge, adjust the pH of the system to 5-7, and obtain a cathode solution of the electric fermentation system, wherein the cathode solution is connected to the working electrode and the silver chloride electrode;

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

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

[0050] The working electrode is prepared by adding oxide high entropy ceramics, optional activated carbon and optional binder into deionized water, followed by ultrasonication and shearing to obtain solution A, and then evenly coating the solution A on both sides of the carbon felt electrode on a heating table.

[0051] exist Figure 1 In the experiment, the incubation of the cathode solution was carried out at a temperature of 36±0.5°C and a stirring speed of 450 rpm.

[0052] Figure 2 : is a flow chart of the preparation of the oxide high entropy ceramics of the embodiment of the present invention. Figure 2 As shown, the oxide high entropy ceramics are obtained by the following steps.

[0053] According to the molar ratio of Co:Cr:Fe:Mn:Ni being 1:(0.8-1):(0.8-1):(0.8-1):(0.8-1), five kinds of 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 respectively; according to the raw materials:surface active The mass ratio of the surfactant to deionized water is 1: (0.8-0.9): (15-25), and a surfactant, hexadecyltrimethylammonium bromide and deionized water are added to the raw materials, and stirred to obtain a solution I; urea is added to the solution I at a molar ratio of urea to the raw materials of 4-8:1, and the solution is stirred and subjected to hydrothermal treatment; centrifugal separation is performed, the lower precipitate is taken out, dried, and heat-treated at 800-1000° C. for 1-3 hours to obtain an oxide high entropy ceramic powder with a spinel structure or a perovskite structure.

[0054] Example

[0055] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0056] Example 1

[0057] After adding 0.2g of oxide high entropy ceramic to 30mL of deionized water, ultrasonication was performed for 10 minutes and shearing was performed for 2 hours to obtain solution A; on a heating table, the solution A was evenly applied to the front and back sides of the carbon felt electrode, and the electrode was dried to obtain a working electrode. A 250mL double-chamber reaction bottle was used as an electric fermentation reactor, 133mL of culture medium (50mM Difco Sporulation Medium solution (DSM solution), produced by Zeye Biological) was placed in the bottle, 17mL of residual sludge was inoculated, 10.5g / L of sodium 2-bromoethane sulfonate was added as a methane inhibitor, 1.3mL of ethanol and 3.7g of sodium acetate were added as electron donors and electron acceptors, respectively, and the cathode solution of the electric fermentation system was adjusted with hydrochloric acid and sodium hydroxide solution until the pH value of the cathode solution was stabilized within the range of pH = 6 ± 0.1.

[0058] Potassium ferrocyanide is added to the phosphate solution to obtain an anode solution of the electric fermentation system, and the amount of potassium ferrocyanide added is 20 g / L based on the volume of the anode solution of the electric fermentation system. The cathode solution of the electric fermentation system and the anode solution of the electric fermentation system are separated by a proton exchange membrane with a thickness of 25 μm to obtain an electric fermentation system, and a constant potential of -1.0 V is provided. The cathode solution of the electric fermentation system is connected to the working electrode and the silver chloride electrode, and the anode solution of the electric fermentation system is connected to the titanium sheet electrode.

[0059] Before fermentation begins, use nitrogen to blow off the cathode solution of the electric fermentation system and the anode solution of the electric fermentation system for 30 minutes, and then immediately seal the bottle mouth to ensure that the bottle is in an anaerobic environment. The electric fermentation reactor is placed on a magnetic stirrer for cultivation at a temperature of 36.5°C and a stirring rate of 450rpm. During the constant temperature shaking culture process, the liquid in the electric fermentation reactor is sampled every 1-2 days to measure the pH value and medium-chain fatty acid content of the liquid until the concentration of medium-chain fatty acids no longer increases, which is considered to be the end of the fermentation reaction.

[0060] The resulting medium chain fatty acid is caproic acid.

[0061] Comparative Example 1

[0062] A 250 mL double-chamber reaction bottle was used as an electric fermentation reactor, 133 mL of culture medium (50 mM DifcoSporulation Medium solution (DSM solution), produced by Zeye Bio) was placed in the bottle, 17 mL of residual sludge was inoculated, 10.5 g / L of sodium 2-bromoethane sulfonate was added as a methane inhibitor, 1.3 mL of ethanol and 3.7 g of sodium acetate were added as electron donors and electron acceptors, respectively, and the cathode solution of the electric fermentation system was adjusted with hydrochloric acid and sodium hydroxide solutions until the pH value of the cathode solution was stabilized in the range of pH = 6 ± 0.1.

[0063] Potassium ferrocyanide is added to the phosphate solution to obtain an anode solution of the electric fermentation system, and the amount of potassium ferrocyanide added is 20 g / L based on the volume of the anode solution of the electric fermentation system. The cathode solution of the electric fermentation system and the anode solution of the electric fermentation system are separated by a proton exchange membrane with a thickness of 25 μm to obtain an electric fermentation system, and a constant potential of -1.0 V is provided. The cathode solution of the electric fermentation system is connected to an unmodified carbon felt electrode and a silver chloride electrode, and the anode solution of the electric fermentation system is connected to a titanium sheet electrode.

[0064] Before fermentation begins, use nitrogen to blow off the cathode solution of the electric fermentation system and the anode solution of the electric fermentation system for 30 minutes, and then immediately seal the bottle mouth to ensure that the bottle is in an anaerobic environment. The electric fermentation reactor is placed on a magnetic stirrer for cultivation at a temperature of 36.5°C and a stirring rate of 450rpm. During the constant temperature shaking culture process, the liquid in the electric fermentation reactor is sampled every 1-2 days to measure the pH value and medium-chain fatty acid content of the liquid until the concentration of medium-chain fatty acids no longer increases, which is considered to be the end of the fermentation reaction.

[0065] The resulting medium chain fatty acid is caproic acid.

[0066] When the fermentation reaction was carried out to the 19th day, the concentrations of all acids no longer increased, and the reactions of Example 1 and Control Example 1 were all completed. The specific medium-chain fatty acid concentrations, pH values, and electron transfer efficiencies of the carbon chain extension process are shown in Table 2.

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

[0068]

[0069] It can be seen that compared with the production of medium-chain fatty acids by electro-fermentation using carbon felt electrodes modified with non-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 extension process was increased by 0.6%, and the performance of medium-chain fatty acids produced by electro-fermentation was significantly optimized.

[0070] Example 2

[0071] After adding 0.2g of oxide high entropy ceramic and 0.23mL of perfluorosulfonic acid-polytetrafluoroethylene binder (Nafion) to 30mL of deionized water, ultrasonic treatment was performed for 10 minutes and shearing for 2 hours to obtain solution A; on a heating table, the solution A was evenly applied to the front and back sides of the carbon felt electrode, and the electrode was dried to obtain a working electrode. A 250mL double-chamber reaction bottle was used as an electric fermentation reactor, 133mL of culture medium (50mM Difco Sporulation Medium solution (DSM solution), produced by Zeye Biological) was placed in the bottle, 17mL of residual sludge was inoculated, 10.5g / L of sodium 2-bromoethane sulfonate was added as a methane inhibitor, 1.3mL of ethanol and 3.7g of sodium acetate were added as electron donors and electron acceptors, respectively, and the cathode solution of the electric fermentation system was adjusted with hydrochloric acid and sodium hydroxide solution until the pH value of the cathode solution was stabilized within the range of pH=6±0.1.

[0072] Potassium ferrocyanide is added to the phosphate solution to obtain an anode solution of the electric fermentation system, and the amount of potassium ferrocyanide added is 20 g / L based on the volume of the anode solution of the electric fermentation system. The cathode solution of the electric fermentation system and the anode solution of the electric fermentation system are separated by a proton exchange membrane with a thickness of 25 μm to obtain an electric fermentation system, and a constant potential of -1.0 V is provided. The cathode solution of the electric fermentation system is connected to the working electrode and the silver chloride electrode, and the anode solution of the electric fermentation system is connected to the titanium sheet electrode.

[0073] Before fermentation begins, use nitrogen to blow off the cathode solution of the electric fermentation system and the anode solution of the electric fermentation system for 30 minutes, and then immediately seal the bottle mouth to ensure that the bottle is in an anaerobic environment. The electric fermentation reactor is placed on a magnetic stirrer for cultivation at a temperature of 36.5°C and a stirring rate of 450rpm. During the constant temperature shaking culture process, the liquid in the electric fermentation reactor is sampled every 1-2 days to measure the pH value and medium-chain fatty acid content of the liquid until the concentration of medium-chain fatty acids no longer increases, which is considered to be the end of the fermentation reaction.

[0074] The resulting medium chain fatty acid is caproic acid.

[0075] When the fermentation reaction was carried out to the 19th day, the concentrations of all acids no longer increased, and the reactions of Example 2 and Control Example 1 were all completed. The specific medium-chain fatty acid concentrations, pH values, and electron transfer efficiencies of the carbon chain extension process are shown in Table 3.

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

[0077]

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

[0079] Example 3

[0080] 0.2g of oxide high entropy ceramic, 0.2g of activated carbon and 0.46mL of perfluorosulfonic acid-polytetrafluoroethylene binder (Nafion) were added to 30mL of deionized water, and then ultrasonicated for 10 minutes and sheared for 2 hours to obtain solution A; on a heating table, the solution A was evenly dripped on both sides of the carbon felt electrode, and the electrode was dried to obtain a working electrode. A 250mL double-chamber reaction bottle was used as an electric fermentation reactor, 133mL of culture medium (50mM Difco Sporulation Medium solution (DSM solution), produced by Zeye Biological) was placed in the bottle, 17mL of residual sludge was inoculated, 10.5g / L of sodium 2-bromoethane sulfonate was added as a methane inhibitor, 1.3mL of ethanol and 3.7g of sodium acetate were added as electron donors and electron acceptors, respectively, and then hydrochloric acid and sodium hydroxide solutions were used to adjust the cathode solution of the electric fermentation system until the pH value of the cathode solution was stabilized within the range of pH=6±0.1.

[0081] Potassium ferrocyanide is added to the phosphate solution to obtain an anode solution of the electric fermentation system, and the amount of potassium ferrocyanide added is 20 g / L based on the volume of the anode solution of the electric fermentation system. The cathode solution of the electric fermentation system and the anode solution of the electric fermentation system are separated by a proton exchange membrane with a thickness of 25 μm to obtain an electric fermentation system, and a constant potential of -1.0 V is provided. The cathode solution of the electric fermentation system is connected to the working electrode and the silver chloride electrode, and the anode solution of the electric fermentation system is connected to the titanium sheet electrode.

[0082] Before fermentation begins, use nitrogen to blow off the cathode solution of the electric fermentation system and the anode solution of the electric fermentation system for 30 minutes, and then immediately seal the bottle mouth to ensure that the bottle is in an anaerobic environment. The electric fermentation reactor is placed on a magnetic stirrer for cultivation at a temperature of 36.5°C and a stirring rate of 450rpm. During the constant temperature shaking culture process, the liquid in the electric fermentation reactor is sampled every 1-2 days to measure the pH value and medium-chain fatty acid content of the liquid until the concentration of medium-chain fatty acids no longer increases, which is considered to be the end of the fermentation reaction.

[0083] The resulting medium chain fatty acids are caproic acid and caprylic acid.

[0084] Comparative Example 2

[0085] 0.2g of activated carbon and 0.23mL of perfluorosulfonic acid-polytetrafluoroethylene binder (Nafion) were added to 30mL of deionized water, and then ultrasonicated for 10 minutes and sheared for 2 hours to obtain solution A; on a heating table, the solution A was evenly dripped on both sides of the carbon felt electrode, and the electrode was dried to obtain a working electrode. A 250mL double-chamber reaction bottle was used as an electric fermentation reactor, 133mL of culture medium (50mM Difco Sporulation Medium solution (DSM solution), produced by Zeye Biological) was placed in the bottle, 17mL of residual sludge was inoculated, 10.5g / L of sodium 2-bromoethane sulfonate was added as a methane inhibitor, 1.3mL of ethanol and 3.7g of sodium acetate were added as electron donors and electron acceptors, respectively, and then hydrochloric acid and sodium hydroxide solutions were used to adjust the cathode solution of the electric fermentation system until the pH value of the cathode solution was stabilized within the range of pH=6±0.1.

[0086] Potassium ferrocyanide is added to the phosphate solution to obtain an anode solution of the electric fermentation system, and the amount of potassium ferrocyanide added is 20 g / L based on the volume of the anode solution of the electric fermentation system. The cathode solution of the electric fermentation system and the anode solution of the electric fermentation system are separated by a proton exchange membrane with a thickness of 25 μm to obtain an electric fermentation system, and a constant potential of -1.0 V is provided. The cathode solution of the electric fermentation system is connected to the working electrode and the silver chloride electrode, and the anode solution of the electric fermentation system is connected to the titanium sheet electrode.

[0087] Before fermentation begins, use nitrogen to blow off the cathode solution of the electric fermentation system and the anode solution of the electric fermentation system for 30 minutes, and then immediately seal the bottle mouth to ensure that the bottle is in an anaerobic environment. The electric fermentation reactor is placed on a magnetic stirrer for cultivation at a temperature of 36.5°C and a stirring rate of 450rpm. During the constant temperature shaking culture process, the liquid in the electric fermentation reactor is sampled every 1-2 days to measure the pH value and medium-chain fatty acid content of the liquid until the concentration of medium-chain fatty acids no longer increases, which is considered to be the end of the fermentation reaction.

[0088] The resulting medium chain fatty acid is caproic acid.

[0089] When the fermentation reaction was carried out to the 19th day, the concentrations of all acids no longer increased, and the reactions of Example 3 and Control Example 2 were all completed. The specific medium-chain fatty acid concentrations, pH values, and electron transfer efficiencies of the carbon chain extension process are shown in Table 4.

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

[0091]

[0092] It can be seen that compared with the production of medium-chain fatty acids by electro-fermentation using carbon felt electrodes modified with non-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 extension process was increased by 2.9%, and the performance of medium-chain fatty acids produced by electro-fermentation was significantly optimized.

[0093] It can be seen from the above embodiments that the use of oxide high entropy ceramic modified carbon felt electrodes can effectively increase the concentration of medium-chain fatty acids produced by electro-fermentation; compared with the original method of producing medium-chain fatty acids by electro-fermentation using unmodified carbon felt electrodes, 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 the electron transfer efficiency of the medium-chain fatty acid product during carbon chain extension is increased by 0.6% to 2.9%, which significantly improves the production efficiency of medium-chain fatty acids.

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

[0095] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for producing medium-chain fatty acids by electrofermentation using oxide high-entropy ceramic modified electrodes, characterized in that: include: Step 1, adding oxide high entropy ceramics, optional activated carbon and optional binder into deionized water, and then performing ultrasonication and shearing to obtain solution A; Step 2, on a heating platform, evenly apply the solution A to both sides of the carbon felt electrode to obtain a working electrode; Step 3, adding a methane inhibitor, an electron donor and an electron acceptor to the culture medium of the inoculated excess sludge, adjusting the pH of the system to 5-7, and obtaining a cathode solution of the electric fermentation system; Step 4, adding potassium ferrocyanide to the phosphate solution to obtain an anode solution of the electric fermentation system; Step 5, separating the cathode solution and the anode solution of the electric fermentation system by a proton exchange membrane to obtain an electric fermentation system; Step 6: In an anaerobic environment, the cathode solution of the electric fermentation system is cultured with constant temperature stirring until the concentration of medium-chain fatty acids in the cathode solution of the electric fermentation system no longer increases.

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

3. The method according to claim 1 or 2, characterized in that: In the step 3, the amount of the residual sludge for inoculation is 5-15 volume % of the cathode solution of the electric fermentation system; the methane inhibitor is sodium 2-bromoethane sulfonate; the amount of the 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; based on the volume of the cathode solution of the electric fermentation system, the added amount of the methane inhibitor is 5-20 g / L; the molar concentration ratio of the added amount of the electron donor and the electron acceptor is 1:5-3:2; the reagent used to adjust the pH is hydrochloric acid and / or sodium hydroxide.

4. The method according to claim 1 or 2, characterized in that: In the step 4, the amount of potassium ferrocyanide added is 15-25 g / L based on the volume of the anode solution of the electric fermentation system.

5. The method according to claim 1 or 2, 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.

6. The method according to claim 1 or 2, characterized in that: The oxide high entropy ceramic is a spinel structure or a perovskite structure; the carbon chain length of the medium-chain fatty acid is C6 to C 12 .

7. The method according to claim 1 or 2, characterized in that: The cathode solution of the electric fermentation system is connected to the working electrode and the silver chloride electrode; the anode solution of the electric fermentation system is connected to the titanium sheet electrode; the electric fermentation system provides a constant potential of -1.0V; the size of the titanium sheet electrode is 2-4cm*4-6cm.

8. A device for the method according to any one of claims 1 to 7, characterized in that: include: The cathode unit of the electric fermentation system is used to add a methane inhibitor, an electron donor and an electron acceptor to the culture medium of the inoculated excess sludge, adjust the pH of the system to 5-7, and obtain a cathode solution of the electric fermentation system, wherein the cathode solution is connected to a working electrode and a silver chloride electrode; An electric fermentation system anode unit, the electric fermentation system anode unit is used to add potassium ferrocyanide to the phosphate solution to obtain an anode solution of the electric fermentation system, and the anode solution is connected to a titanium sheet electrode; An electric fermentation system membrane unit, wherein the electric fermentation system membrane unit is used to separate the electric fermentation system cathode unit and the electric fermentation system anode unit, The working electrode is prepared by adding oxide high entropy ceramics, optional activated carbon and optional binder into deionized water, followed by ultrasonication and shearing to obtain solution A, and then evenly coating the solution A on both sides of the carbon felt electrode on a heating table.

9. The device according to claim 8, characterized in that The electric fermentation system membrane unit is a proton exchange membrane with a thickness of 12 to 25 μm; the electric fermentation system cathode unit, the electric fermentation system anode unit and the electric fermentation system membrane unit are formed by placing the electric fermentation reactor on a magnetic stirrer.

10. The device according to claim 8 or 9, characterized in that The oxide high entropy ceramic is a spinel structure or a perovskite structure; the electric fermentation system provides a constant potential of -1.0V; the size of the carbon felt electrode is 2-4cm*4-6cm; the size of the titanium sheet electrode is 2-4cm*4-6cm.

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