Device and method for producing octanoic acid by semi-artificial photosynthesis coupled with electric field enhancement

Abstract

A device and production method for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production. The present invention aims to solve the problems of existing octanoic acid production processes that rely on harmful chemicals, produce harmful byproducts, or require high-pressure and high-temperature reaction conditions. In the octanoic acid production device, the anode chamber and the cathode chamber are connected by a channel to form an H-type reactor. The anode electrode and the reference electrode are inserted into the anode chamber. The light source illuminates the anode electrode. The cathode electrode is inserted into the cathode chamber. The anode electrode, the reference electrode, and the cathode electrode are all connected to an electrochemical workstation. The cathode electrode is a biological cathode attached with an octanoic acid-producing biofilm. The present invention significantly increases the yield of octanoic acid by applying light and an electric field to the domesticated biological cathode, while also ensuring the stability of the microbial community structure in the reactor. The present invention not only reduces the negative feedback inhibition of the product octanoic acid, but also effectively inhibits the generation of byproducts such as propionic acid and valeric acid, further improving the production efficiency and purity of octanoic acid.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater resource utilization, and in particular relates to a device and a method for producing octanoic acid based on semi-artificial photosynthetic coupled electric field enhancement. Background Art

[0002] Amidst the dire global reliance on fossil fuels and rising greenhouse gas emissions, the need for carbon reduction has become increasingly urgent. Solar energy, an inexhaustible clean energy source, provides enough radiant energy in one hour to match the world's annual energy consumption. Therefore, efficiently converting solar energy into a readily accessible energy form not only opens up a practical path for the chemical industry to achieve a green transformation, but also demonstrates enormous research potential and far-reaching development prospects, fully aligning with the long-term strategy of sustainable development. Natural photosynthesis is a model for efficient solar energy utilization, but it suffers from shortcomings such as narrow spectral absorption and low conversion efficiency. Inorganic semiconductor materials have high light energy utilization rates but are easily compounded. Scientists have developed a semi-artificial photosynthetic system by combining organisms with biocatalytic functions and inorganic semiconductor materials with high-efficiency light capture, aiming to overcome the limitations of natural photosynthesis and achieve more efficient solar energy utilization.

[0003] In recent years, renewable biochemicals have attracted increasing attention as alternatives to various fossil fuel-based products. Microbial carbon chain extension technology has significant potential for producing medium-chain fatty acids (MCFAs), particularly octanoic acid (C8), a high-value-added compound. Octanoic acid is widely used in the food industry as a flavor enhancer and preservative and also exhibits antimicrobial and therapeutic potential in the medical field. In the chemical industry, octanoic acid is also a key raw material for the production of chemical products and surfactants and is recognized as a safe food-grade compound. However, traditional octanoic acid production processes present several challenges, including limited raw material sources, high production costs, environmental impacts, and potential safety risks. Some production techniques may produce harmful byproducts or rely on hazardous chemicals, posing environmental risks. Furthermore, some octanoic acid production methods require specialized equipment under specific conditions, such as high pressure and high temperature, which not only limits production flexibility but also increases economic costs. Therefore, optimizing production processes to minimize environmental impact while reducing costs and improving safety are key to future development in this field.

[0004] Hybrid systems of photocatalytic materials and microorganisms, as an innovative way to simulate natural photosynthesis, show great potential for converting organic solid waste into high-value-added chemical fuels and chemicals. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems that the existing octanoic acid production process relies on harmful chemicals, produces harmful byproducts, or requires high-pressure and high-temperature reaction conditions, and to provide a semi-artificial photosynthetic coupled electric field enhanced octanoic acid production device and production method. By adding light and electric field effects to the domesticated biocathode, the domesticated biocathode is stimulated, thereby significantly increasing the octanoic acid production, while also ensuring the stability of the microbial community structure in the reactor.

[0006] The device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production of the present invention comprises a light source, an H-type reactor, an anode electrode, a reference electrode, a cathode electrode and an ion exchange membrane. The anode chamber and the cathode chamber are connected by a channel to form the H-type reactor. The H-type reactor is an anaerobic environment. The ion exchange membrane is arranged in the channel. The anode electrode and the reference electrode are inserted into the anode chamber. The light source illuminates the anode electrode. The cathode electrode is inserted into the cathode chamber. The anode electrode, the reference electrode and the cathode electrode are all connected to an electrochemical workstation.

[0007] The anode electrode is a photoanode, the cathode electrode is a biological cathode attached with an octanoic acid-producing biofilm, and the H-type reactor is filled with a nutrient solution containing ethanol and acetic acid.

[0008] The method for producing octanoic acid using a device for semi-artificial photosynthetic coupled electric field to enhance octanoic acid production is achieved by the following steps:

[0009] S1. Using soil as the source of functional bacteria, preparing nutrient solution to acclimate and ferment the functional bacteria, and obtaining acclimatized octanoic acid-producing sludge when the fermentation liquid contains octanoic acid;

[0010] S2. Startup of the microbial cathode: An H-type reactor was used to start the cathode electrode. The anode electrode was a titanium ruthenium-iridium electrode, and the cathode electrode was a graphite felt electrode. An Ag / AgCl electrode was inserted into the cathode chamber as a reference electrode. Acclimated octanoic acid-producing sludge was added to the cathode chamber, followed by a nutrient solution. The cathode was started using a three-electrode system at a potential of (-0.5 to -1.0 V) vs. Ag / AgCl. When the cathode current density gradually increased and stabilized, a biocathode with an attached octanoic acid-producing biofilm was obtained.

[0011] S3. Construction of a semi-artificial photosynthetic coupled electric field system: An H-type reactor was used to construct a semi-artificial photosynthetic coupled electric field system. A photoanode and a reference electrode were inserted into the anode chamber, and a biocathode with an octanoic acid-producing biofilm was inserted into the cathode chamber. A potential of (+0.5 to +1.0 V) vs. Ag / AgCl was applied to the photoanode to complete the construction of the semi-artificial photosynthetic coupled electric field system.

[0012] S4. Production of octanoic acid using a semi-artificial photosynthetic coupled electric field system: adding a nutrient solution to the cathode chamber, irradiating the photoanode with a light source, and producing octanoic acid using a three-electrode system at a potential of (+0.5 to +1.0 V) vs. Ag / AgCl, thereby completing a method for enhancing octanoic acid production using a semi-artificial photosynthetic coupled electric field.

[0013] The nutrient solution contains ethanol and acetic acid, the molar ratio of ethanol to acetic acid is controlled to be 4:1-8:1, and the pH value of the nutrient solution is 6.5-7.0.

[0014] In the semi-artificial photosynthetic coupled electric field action system of the present invention, the cathode chamber is responsible for accommodating the successfully started biocathode, and the cathode chamber is added with water containing electron donor ethanol and electron acceptor acetic acid. In order to meet the needs of microbial growth, an appropriate amount of trace elements and vitamins can also be added to the water. The semi-artificial photosynthetic coupled electric field action provides electrons to the biocathode to promote the synthesis of octanoic acid. The light is provided by a photocatalytic reaction LED lamp, and the electric field action is provided by an electrochemical workstation. In addition, the water bath circulation system outside the reactor ensures the suitable temperature (37°C) required for microbial growth. At the same time, the pH value during the reaction process is accurately controlled by graded adjustment, and the entire system is stirred with a magnetic stirrer.

[0015] The device and method for producing octanoic acid by semi-artificial photosynthesis coupled with electric field enhancement of the present invention have the following beneficial effects:

[0016] 1. Efficient conversion and suppression of side reactions: The octanoic acid production method of the present invention significantly promotes the conversion of short-chain fatty acids to octanoic acid in the reactor, while effectively suppressing the formation of by-products such as propionic acid and valeric acid, ensuring that the substrate is mainly used for the production of octanoic acid, thereby significantly improving the yield of octanoic acid.

[0017] 2. Enhancement of direct electron transfer between microorganisms: The octanoic acid production method of the present invention significantly improves the direct electron transfer ability between microorganisms through the action of semi-artificial photosynthetic coupled electric field, providing a more efficient biochemical reaction pathway for the production of octanoic acid.

[0018] 3. Optimizing the microbial community structure: The present invention adjusts the microbial community structure in the reactor through the action of a semi-artificial photosynthetic coupled electric field, enriches the dominant bacterial communities that are beneficial to acid production, and increases the abundance of acid-producing microorganisms. This is not only beneficial to the production of octanoic acid, but also enhances the stability of the microbial community structure in the reactor and improves its ability to resist shock loads.

[0019] 4. Enhance the activity of carbon chain growth enzymes: The semi-artificial photosynthetic coupled electric field in the present invention can also significantly increase the abundance of related enzymes involved in carbon chain growth reactions in microorganisms to produce octanoic acid, further promoting the production efficiency of octanoic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic structural diagram of the device for semi-artificial photosynthesis coupled with electric field enhanced octanoic acid production according to the present invention;

[0021] Figure 2 is a photocurrent response diagram of the photoelectric coupling system of the present invention;

[0022] Figure 3 Generate product histograms for Example 1 of the present invention and the comparative example;

[0023] Description of reference numerals:

[0024] 1. Light source; 2. Quartz window; 3. H-type reactor; 4. Anode electrode; 5. Electrochemical workstation; 6. Reference electrode (Ag / AgCl electrode); 7. Cathode electrode; 8. Insulation layer; 9. Sampling port; 10. Ion exchange membrane; 11. Water inlet pump; 12. Constant temperature water bath; 13. Magnetic stirrer; 14. Magnetic rotor. DETAILED DESCRIPTION

[0025] Specific embodiment 1: The device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production in this embodiment includes a light source 1, an H-type reactor 3, an anode electrode 4, a reference electrode 6, a cathode electrode 7 and an ion exchange membrane 10. The anode chamber and the cathode chamber are connected by a channel to form an H-type reactor 3. The H-type reactor 3 is an anaerobic environment. The ion exchange membrane 10 is provided in the channel. The anode electrode 4 and the reference electrode 6 are inserted into the anode chamber. The light source 1 illuminates the anode electrode 4. The cathode electrode 7 is inserted into the cathode chamber. The anode electrode 4, the reference electrode 6 and the cathode electrode 7 are all connected to the electrochemical workstation 5.

[0026] The anode electrode 4 is a photoanode, the cathode electrode 7 is a biological cathode attached with an octanoic acid-producing biofilm, and the H-type reactor 3 is filled with a nutrient solution containing ethanol and acetic acid.

[0027] Under light conditions, semiconductor materials can excite photogenerated electrons, which are then used by microorganisms to promote their functional metabolic processes and material synthesis. In order to further improve the photocatalytic efficiency, applying an appropriate electrical bias can promote the effective separation of electrons and holes generated by photoexcitation and reduce their recombination rate. Based on this principle, the present invention proposes an innovative semi-artificial photosynthetic coupled electric field action system, which combines an inorganic photocatalytic anode with an octanoic acid-producing microbial cathode with efficient direct electron transfer capabilities. The system aims to optimize the octanoic acid production process through coupling and explore the positive effect of semi-artificial photosynthetic coupled electric field action on carbon chain growth technology.

[0028] The method of this embodiment not only reduces the negative feedback inhibition of the product octanoic acid, but also successfully inhibits the formation of by-products such as propionic acid and valeric acid, further improving the production efficiency and purity of octanoic acid.

[0029] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the wall of the H-type reactor 3 is a hollow cavity, and warm water at 35-38° C. circulates in the hollow cavity of the wall.

[0030] Specific embodiment three: This embodiment is different from specific embodiment one or two in that a gas storage device is provided on the upper part of the cathode chamber.

[0031] In this embodiment, the gas generated during the reaction is collected and stored by a gas storage device.

[0032] Specific embodiment 4: This embodiment is different from any one of specific embodiments 1 to 3 in that a sampling port 9 is provided on the cathode chamber.

[0033] Specific embodiment 5: This embodiment is different from specific embodiments 1 to 4 in that the reference electrode 6 is an Ag / AgCl electrode.

[0034] Specific embodiment 6: The difference between this embodiment and any one of specific embodiments 1 to 5 is that a magnetic stirring device 13 is respectively provided in the anode chamber and the cathode chamber.

[0035] Specific embodiment seven: This embodiment uses a device for semi-artificial photosynthesis coupled with an electric field to enhance the production of octanoic acid. The method for producing octanoic acid is implemented by the following steps:

[0036] S1. Using soil as the source of functional bacteria, preparing nutrient solution to acclimate and ferment the functional bacteria, and obtaining acclimatized octanoic acid-producing sludge when the fermentation liquid contains octanoic acid;

[0037] S2. Startup of the microbial cathode: An H-type reactor was used to start the cathode electrode. The anode electrode was a titanium ruthenium-iridium electrode, and the cathode electrode was a graphite felt electrode. An Ag / AgCl electrode was inserted into the cathode chamber as a reference electrode. Acclimated octanoic acid-producing sludge was added to the cathode chamber, followed by a nutrient solution. The cathode was started using a three-electrode system at a potential of (-0.5 to -1.0 V) vs. Ag / AgCl. When the cathode current density gradually increased and stabilized, a biocathode with an attached octanoic acid-producing biofilm was obtained.

[0038] S3. Construction of a semi-artificial photosynthetic coupled electric field system: An H-type reactor was used to construct a semi-artificial photosynthetic coupled electric field system. A photoanode and a reference electrode were inserted into the anode chamber, and a biocathode with an octanoic acid-producing biofilm was inserted into the cathode chamber. A potential of (+0.5 to +1.0 V) vs. Ag / AgCl was applied to the photoanode to complete the construction of the semi-artificial photosynthetic coupled electric field system.

[0039] S4. Production of octanoic acid using a semi-artificial photosynthetic coupled electric field system: adding a nutrient solution to the cathode chamber, irradiating the photoanode with a light source, and producing octanoic acid using a three-electrode system at a potential of (+0.5 to +1.0 V) vs. Ag / AgCl, thereby completing a method for enhancing octanoic acid production using a semi-artificial photosynthetic coupled electric field.

[0040] The nutrient solution contains ethanol and acetic acid, the molar ratio of ethanol to acetic acid is controlled to be 4:1-8:1, and the pH value of the nutrient solution is 6.5-7.0.

[0041] Specific embodiment eight: This embodiment differs from specific embodiment seven in that the temperature of the control system during the production of octanoic acid in step S4 is 37°C.

[0042] Specific embodiment 9: This embodiment is different from specific embodiment 7 or 8 in that the concentration of ethanol in the nutrient solution is 7-9 g / L, the concentration of acetic acid is 2-3 g / L, and the nutrient solution also contains trace elements and vitamins.

[0043] The concentrations of trace elements and vitamins in the nutrient solution of this embodiment are both 1 ml / L.

[0044] Specific embodiment 10: The difference between this embodiment and any one of specific embodiments 7 to 9 is that in step S3, both the cathode chamber and the anode chamber are anaerobic environments.

[0045] Example: This example uses a semi-artificial photosynthetic coupled electric field to enhance the production of octanoic acid. The method for producing octanoic acid is implemented by the following steps:

[0046] S1. Using soil as the source of functional bacteria, preparing nutrient solution to domesticate the functional bacteria for anaerobic fermentation. When the fermentation liquid contains a large amount of octanoic acid (the octanoic acid concentration is significantly increased), obtaining domesticated octanoic acid-producing sludge;

[0047] The molar ratio of ethanol to acetic acid in the nutrient solution is 5:1, the concentration of ethanol is 8.625 g / L, the concentration of acetic acid is 2.25 g / L, the concentrations of trace elements and vitamins are 1 ml / L respectively, and the pH value of the nutrient solution is adjusted between 6.5 and 7.0 by sodium bicarbonate (NaHCO3);

[0048] S2. Startup of the microbial cathode: An H-type reactor was used to start the cathode electrode. An ion exchange membrane was installed in the channel. The anode electrode was a titanium ruthenium-iridium electrode. The cathode substrate material was a high-temperature calcined graphite felt electrode. An Ag / AgCl electrode was inserted into the cathode chamber as a reference electrode. Acclimated octanoic acid-producing sludge and nutrient solution were added to the cathode chamber. The mass ratio of inoculated sludge to nutrient solution was 1:5. The cathode was started at a potential of -0.6 V vs. Ag / AgCl using a three-electrode system. When the cathode current density gradually increased and stabilized, a biocathode with an attached octanoic acid-producing biofilm was obtained.

[0049] S3. Construction of semi-artificial photosynthetic coupled electric field system: A semi-artificial photosynthetic coupled electric field system was constructed using an H-type reactor. A titanium dioxide nanowire photoanode and a reference electrode were inserted into the anode chamber, and a biocathode with an octanoic acid-producing biofilm was inserted into the cathode chamber. A potential of +0.6 V vs. Ag / AgCl was applied to the photoanode. Figure 2 It can be seen that when illuminated, the titanium dioxide nanowire photoanode has a significant current response, indicating that the titanium dioxide nanowire photoanode can provide electrons for the microbial cathode, completing the construction of a semi-artificial photosynthetic coupled electric field system;

[0050] S4. Production of octanoic acid using a semi-artificial photosynthetic coupled electric field system: Nutrient solution is added to the cathode chamber, a light source illuminates the anode electrode, and a three-electrode system is used to produce octanoic acid at a potential of +0.6V vs. Ag / AgCl. Simultaneously, the pH is stepwise controlled during the operation of the reactor. In the first stage, the pH is set at 5.5-6.5. After the octanoic acid production begins to increase, the pH is set to 6.5-7. The generated octanoic acid can be conveniently sampled and tested from the sampling port, thereby completing the method for enhancing the production of octanoic acid using a semi-artificial photosynthetic coupled electric field.

[0051] The nutrient solution contains ethanol and acetic acid, and the molar ratio of ethanol to acetic acid is 5:1.

[0052] The device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production described in this embodiment includes a light source 1, an H-type reactor 3, an anode electrode 4, a reference electrode 6, a cathode electrode 7 and an ion exchange membrane 10. The anode chamber and the cathode chamber are connected by a channel to form the H-type reactor 3. The anode chamber and the cathode chamber are respectively provided with a magnetic rotor 14, which is driven to rotate by a magnetic stirring device 13. A quartz window 2 is provided on the anode chamber. The wall of the H-type reactor 3 is a hollow cavity. Warm water at 35 to 38° C. circulates in the hollow cavity of the wall. Covered with an insulation layer 8, the warm water circulating in the hollow cavity comes from a constant temperature water bath 12 and is driven by a water inlet pump 11 to form a circulating water circuit. The H-type reactor 3 is an anaerobic environment, and an ion exchange membrane 10 is provided in the channel. The anode electrode 4 and the reference electrode 6 are inserted into the anode chamber, the light source 1 illuminates the anode electrode 4, and the cathode electrode 7 is inserted into the cathode chamber. The anode electrode 4, the reference electrode 6 and the cathode electrode 7 are all connected to the electrochemical workstation 5; the anode electrode 4 is a photoanode, and the cathode electrode 7 is a biological cathode attached with an octanoic acid-producing biofilm.

[0053] The preparation process of the titanium dioxide nanowire photoanode described in this embodiment is as follows:

[0054] Fluorine-doped tin oxide (FTO) glass was used as the substrate for the growth of titanium dioxide nanowire arrays. The FTO glass was first pretreated with ultrasonic cleaning using acetone and ethanol (volume ratio of 2:1). The pretreated FTO glass was then placed in a 100 mL polytetrafluoroethylene-lined autoclave, with the conductive surface facing downward. A precursor solution consisting of 1 mL of tetrabutyl titanate, 30 mL of 37% HCl, and 30 mL of deionized water was then added. The autoclave was then heated at 150°C for 5 hours for a hydrothermal reaction, forming a white titanium dioxide film on the FTO glass surface. After the reaction, the sample was removed, rinsed with deionized water, and then air-dried. Finally, the sample was annealed in air at 550°C for 3 hours to enhance the crystallinity of the titanium dioxide nanowires.

[0055] The final octanoic acid concentration in this example is 1189-1323 mg / L, and the concentrations of propionic acid and valeric acid in the competitive reaction for octanoic acid production in the reactor are 120-233 mg / L and 150-295 mg / L, respectively.

[0056] Comparative Example: The method for producing octanoic acid under a single electric field system in this embodiment is implemented according to the following steps:

[0057] S1. Using soil as the source of functional bacteria, preparing nutrient solution to acclimate and ferment the functional bacteria, and obtaining acclimatized octanoic acid-producing sludge when the fermentation liquid contains a large amount of octanoic acid;

[0058] The molar ratio of ethanol to acetic acid in the nutrient solution is 5:1, the concentration of ethanol is 8.625 g / L, the concentration of acetic acid is 2.25 g / L, the concentration of trace elements and vitamins is 1 ml / L, and the pH value of the nutrient solution is adjusted between 6.5 and 7.0 by sodium bicarbonate (NaHCO3);

[0059] S2. Startup of the microbial cathode: An H-type reactor was used to start the cathode electrode. An ion exchange membrane was installed in the channel. The anode electrode was a titanium ruthenium-iridium electrode. The cathode substrate material was a high-temperature calcined graphite felt electrode. An Ag / AgCl electrode was inserted into the cathode chamber as a reference electrode. Acclimated octanoic acid-producing sludge and nutrient solution were added to the cathode chamber. The cathode was started at a potential of -0.6 V vs. Ag / AgCl using a three-electrode system. When the cathode current density gradually increased and stabilized, a biocathode with an attached octanoic acid-producing biofilm was obtained.

[0060] S3. Construction of a single electric field action system and octanoic acid production: An H-type dual-chamber reactor was used to construct a single electric field action system. A titanium dioxide nanowire photoanode synthesized by a hydrothermal method was added to the anode chamber, but no light was applied. A +0.6Vvs.Ag / AgCl potential was applied to the anode. The cathode chamber was responsible for accommodating the successfully started biocathode, and a nutrient solution containing electron donor ethanol and electron acceptor acetic acid (molar ratio of 5:1) was added to the cathode chamber. At the same time, the pH was stepwise controlled during the operation of the reactor. In the first stage, the pH was set at 5.5-6.5. After the octanoic acid production began to increase, the pH was set to 6.5-7. The generated octanoic acid could be conveniently sampled and tested from the sampling port. After the reaction stabilized, the final octanoic acid concentration was 687-864mg / L. The concentrations of propionic acid and valeric acid, the competing reactions for octanoic acid production in the reactor, were 460-523mg / L and 390-457mg / L, respectively.

[0061] Therefore, the present invention achieves a significant increase in octanoic acid production by coupling semi-artificial photosynthesis with electric field action. Compared with using an electric field alone, the photoanode provides electrons to the microbial cathode under light, effectively supplementing the electron demand during anaerobic fermentation. This coupling strategy not only enhances the stability of the microbial community in the reactor, but also effectively avoids the production of by-products such as propionic acid and valeric acid by reducing the negative feedback inhibition of octanoic acid, thereby further optimizing the production efficiency and purity of octanoic acid. In summary, the device and method of the present invention not only significantly improve the yield of octanoic acid, but also ensure the long-term stability of the microbial community structure, thereby achieving a simultaneous improvement in production efficiency and product quality.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A device for semi-artificial photosynthesis coupled with electric field to enhance the production of octanoic acid, characterized in that The semi-artificial photosynthetic coupled electric field enhanced octanoic acid production device comprises a light source (1), an H-type reactor (3), an anode electrode (4), a reference electrode (6), a cathode electrode (7) and an ion exchange membrane (10). The anode chamber and the cathode chamber are connected by a channel to form the H-type reactor (3). The H-type reactor (3) is an anaerobic environment. The ion exchange membrane (10) is arranged in the channel. The anode electrode (4) and the reference electrode (6) are inserted into the anode chamber. The light source (1) illuminates the anode electrode (4). The cathode electrode (7) is inserted into the cathode chamber. The anode electrode (4), the reference electrode (6) and the cathode electrode (7) are all connected to the electrochemical workstation (5). The anode electrode (4) is a photoanode, and the cathode electrode (7) is a biocathode attached to an octanoic acid-producing biofilm. The preparation process of the biocathode attached to an octanoic acid-producing biofilm is as follows: acclimated octanoic acid-producing sludge is added to the cathode chamber, and then a nutrient solution is added. The cathode is started at a potential of (−0.5~−1.0 V) vs. Ag / AgCl using a three-electrode system. When the cathode current density gradually increases and tends to be stable, a biocathode attached to an octanoic acid-producing biofilm is obtained. The H-type reactor (3) is filled with a nutrient solution containing ethanol and acetic acid.

2. The device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production according to claim 1, characterized in that The wall of the H-type reactor (3) is a hollow cavity, and warm water at 35-38° C. circulates in the hollow cavity of the wall.

3. The device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production according to claim 1, characterized in that A gas storage device is provided at the upper part of the cathode chamber.

4. The device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production according to claim 1, characterized in that A sampling port (9) is provided on the cathode chamber.

5. The device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production according to claim 1, characterized in that The reference electrode (6) is an Ag / AgCl electrode.

6. The device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production according to claim 1, characterized in that A magnetic stirring device (13) is provided in the anode chamber and the cathode chamber respectively.

7. A method for producing octanoic acid using the device for semi-artificial photosynthetic coupled electric field enhanced octanoic acid production as claimed in claim 1, characterized in that The method for producing octanoic acid is achieved by following the steps: S1. Using soil as the source of functional bacteria, preparing nutrient solution to acclimate and ferment the functional bacteria, and obtaining acclimatized octanoic acid-producing sludge when the fermentation liquid contains octanoic acid; S2. Startup of the microbial cathode: An H-type reactor was used to start the cathode electrode. The anode electrode was a titanium ruthenium-iridium electrode, and the cathode electrode was a graphite felt electrode. An Ag / AgCl electrode was inserted into the cathode chamber as a reference electrode. Acclimated octanoic acid-producing sludge and nutrient solution were added to the cathode chamber. The cathode was started using a three-electrode system at a potential of (−0.5 to −1.0 V) vs. Ag / AgCl. When the cathode current density gradually increased and stabilized, a biocathode with an attached octanoic acid-producing biofilm was obtained. S3. Construction of a semi-artificial photosynthetic coupled electric field system: An H-type reactor was used to construct a semi-artificial photosynthetic coupled electric field system. A photoanode and a reference electrode were inserted into the anode chamber, and a biocathode with an octanoic acid-producing biofilm was inserted into the cathode chamber. A potential of (+0.5–+1.0 V) vs. Ag / AgCl was applied to the photoanode to complete the construction of the semi-artificial photosynthetic coupled electric field system. S4. Production of octanoic acid using a semi-artificial photosynthetic coupled electric field system: Nutrient solution is added to the cathode chamber, a light source illuminates the photoanode, and octanoic acid is produced using a three-electrode system at a potential of (+0.5 to +1.0 V) vs. Ag / AgCl, completing a method for semi-artificial photosynthetic coupled electric field-enhanced octanoic acid production. The nutrient solution contains ethanol and acetic acid, the molar ratio of ethanol to acetic acid is controlled to be 4:1-8:1, and the pH value of the nutrient solution is 6.5-7.

0.

8. The method for producing octanoic acid according to claim 7, wherein During the production of octanoic acid in step S4, the temperature of the system is controlled to be 37°C.

9. The method for producing octanoic acid according to claim 7, wherein The concentration of ethanol in the nutrient solution is 7-9 g / L, the concentration of acetic acid is 2-3 g / L, and the nutrient solution also contains trace elements and vitamins.

10. The method for producing octanoic acid according to claim 7, characterized in that In step S3, both the cathode chamber and the anode chamber are anaerobic environments.

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