An experimental device and method for promoting biological gas production based on associated minerals in coal strengthening electron transfer

Abstract

This invention belongs to the field of coal biogasification and anaerobic fermentation technology, and relates to an experimental device and method for promoting biogas production by enhancing electron transfer based on associated minerals in coal. The experimental device includes an enrichment culture reaction vessel integrated within a constant temperature incubator, a sealed top cover, and a stirring device at the bottom; as well as externally integrated auxiliary equipment / instruments, which are connected to the enrichment culture reaction vessel via corresponding circuits or gas lines. The enrichment culture reaction vessel is divided into an upper microbial conductivity acclimation space and a lower biogas production space by a double-layer partition, with valves sandwiched in the double-layer partition to control the communication channel between the two spaces. Associated minerals in coal are placed within the microbial conductivity acclimation space. The experimental method mainly includes packing and inoculation, microbial conductivity acclimation, microbial transfer, anaerobic fermentation, and sample collection and analysis. This integrated device can complete research experiments on microbial conductivity acclimation and biogas production.

Description

Technical Field

[0001] This invention belongs to the field of coal biogasification and anaerobic fermentation technology, specifically relating to an experimental device and method for promoting biogas production based on enhanced electron transfer by associated minerals in coal. Background Technology

[0002] Coal biogas production technology, as an important unconventional natural gas development approach, mainly relies on the degradation and transformation of organic matter in coal by microorganisms.

[0003] Studies have shown that conductive minerals such as pyrite, magnetite, and hematite can act as electron transport mediators, promoting direct electron transfer (DIET) between microorganisms and thus significantly improving methane generation efficiency. Existing research often achieves this effect by adding external conductive minerals or carbon-based electrode materials (see references). [1] Li Xiaoyu, He Huan, Zhang Qian, et al. Effects of pyrite on coal biogas production and microbial community structure [J]. Acta Microbiologica Sinica, 2023, 63(06):2185-2203. DOI:10.13343 / j.cnki.wsxb.20230102. This paper discloses that pyrite can improve the electron transfer efficiency in the coal biogas production process and regulate the microbial community structure, thereby promoting methane production.

[0004] [2] Wang Caiqin. Study on the regulatory mechanism of magnetite on direct interspecific electron transfer (DIET) in anaerobic biological treatment of wastewater [D]. Zhejiang University, 2020. DOI:10.27461 / d.cnki.gzjdx.2020.001807. The study investigated the promoting mechanism of magnetite on DIET in the anaerobic digestion of wastewater, showing that magnetite can enhance the electron transfer capacity between microorganisms and improve the efficiency of anaerobic metabolism.

[0005] [3] Kai Zhang, Hongyu Guo, Norbert Klitzsch, Daping Xia, Zhazha Hu, Xiao Liu, Bin Zhang, Hao Chen. Feasibility assessment of magnetite forenhancing the clean utilization of lignite through anaerobic digestion. International Biodeterioration & Biodegradation 203 (2025) 106122. This paper discloses the feasibility of using magnetite to enhance the anaerobic digestion of lignite, and the results show that magnetite can promote the biodegradation of coal and the generation of methane.

[0006] [4] Kai Zhang, Hongyu Guo, Norbert Klitzsch, Zhazha Hu, Bin Zhang, Hao Chen. Enhanced bio-methanation of coal through direct interspecieselectron transfer mediated by nano-magnetite. Bioprocess and BiosystemsEngineering, 2026. This paper further discloses that nano-magnetite can enhance the bio-methanization process of coal and increase methane yield by mediating direct interspecieselectron transfer.

[0007] Although the above studies have demonstrated the positive role of conductive minerals in promoting electron transfer and enhancing biogas production, the following shortcomings still exist: 1. Reliance on external conductive materials: Existing studies mostly use external magnetite, nanomaterials, or carbon-based electrodes, which not only increases operating costs but may also bring secondary pollution risks; 2. Lack of utilization of naturally associated minerals in coal: Coal itself is rich in conductive minerals such as pyrite, magnetite, and hematite, but existing technologies rarely directly utilize these natural resources for microbial domestication and electron transfer enhancement; 3. Insufficient device integration: Most studies focus on single reactors or external electric field enhancement methods, which carries the risk of contamination by other bacteria during the transfer process, and there is a lack of device designs that integrate microbial conductive domestication with the biogas production process; 4. Limited means of regulating microbial domestication: Existing technologies mainly rely on natural screening for the enrichment of functional microbial communities, and there is a lack of effective structured devices to shorten the domestication cycle.

[0008] Existing technologies are mostly single reactors, lacking devices that integrate the electrical conductivity domestication of microbial communities with the biogas production process. Therefore, it is of great significance to develop an experimental device that utilizes associated minerals in coal to enhance electron transfer and achieve synergistic effects between microbial domestication and biogas production. Summary of the Invention

[0009] The purpose of this invention is to provide an experimental device and method for promoting biogas production by enhancing electron transfer based on associated minerals in coal, in order to solve the problems of single reactor, low electron transfer efficiency, long microbial acclimatization period and low gas production efficiency in the prior art.

[0010] To achieve the above objectives, the present invention provides the following technical solution: An experimental device for promoting biogas production by enhancing electron transfer based on associated minerals in coal includes a constant temperature incubator 1, an enrichment culture reaction vessel 3 and a stirring device 9 located inside the constant temperature incubator 1, and a nitrogen cylinder 11, an electrochemical parameter detector 15, a second gas collection bag 23, a first gas collection bag 20 and a gas analyzer 21 located outside the constant temperature incubator 1. The enrichment culture reaction vessel 3 has a sealed top cover 4, a stirring device 9 at the bottom, and its interior is divided into an upper microbial conductive acclimatization space and a lower biogas production space by a double-layer sealed partition. The horizontally arranged double-layer sealed partition has a central through-hole and a valve device 8. There is also a sensor assembly 5 that is detachably and airtightly connected to the sealed top cover 4. There is also a coal-associated mineral filling assembly 6 that is set in the upper microbial conductive acclimatization space. The nitrogen cylinder 11 is connected to the enrichment culture reaction vessel 3 via a flexible tube through the nitrogen gas penetration interface 10; the electrochemical parameter detector 15 is connected to the sensor assembly 5 located on the enrichment culture reaction vessel 3 via a wiring through the ...

[0011] Preferably, the valve device 8 is a butterfly valve 801, whose channel port 803 is airtightly connected to the double-layer sealing partition and together forms the connection channel 7; its long handle switch 802 passes through the tank wall and is provided with a hand-held rotating part 804.

[0012] Preferably, the coal-associated mineral filling component 6 includes a mineral filling mesh bag 1 601 and a mineral filling mesh bag 2 602 with the same structure and symmetrical position. The structure of the mineral filling mesh bag is a square plate-shaped mesh bag formed by splicing plastic mesh plates, and the inside is filled with coal-associated mineral filler.

[0013] Furthermore, the coal-associated mineral filling component 6 also includes several limiting angles 603, which are fixed on the upper partition 302 of the double-layer sealing partition, forming a snap-fit ​​area at the four corners of the bottom of the mineral filling mesh plate.

[0014] Preferably, the sealing cover 4 includes a cover body 401, a handle 402, and a sealing ring 403; the cover body 401 is a circular structure with an outer diameter slightly smaller than the inner diameter of the can body 301, and its side wall is fitted with several sealing rings 403; the handle 402 is fixedly connected to the middle of the cover body 401, and the sensor assembly 5 is arranged in front of it.

[0015] Furthermore, the sensor assembly 5 includes a sealing plug 501 and a sensor inserted therein, including but not limited to a pH sensor, an ORP sensor, and a conductivity sensor.

[0016] Preferably, the sealing plug 501 is a rubber sealing plug or a plastic cap structure with a threaded structure.

[0017] Preferably, the nitrogen cylinder 11 is connected to the upper nitrogen connector 14 and the lower nitrogen connector 16 of the enrichment culture reaction vessel 3 via a flexible tube through the nitrogen inlet 10; the upper nitrogen connector 14 is connected to the conductive acclimatization space of the bacterial community, and the lower nitrogen connector 16 is connected to the biogas production space.

[0018] The experimental method using the aforementioned experimental apparatus for enhancing electron transfer and promoting biogas production based on associated minerals in coal includes the following steps: S1, Establish an anaerobic environment: Introduce nitrogen from nitrogen cylinder 11 to replace the oxygen in the system; S2, Filler and Inoculation: Add culture medium, coal-associated mineral filler and methanogenic microbial inoculation solution to the conductive acclimatization space of the microbial community; S3, Constant Temperature Incubation: Start the constant temperature incubator 1 and adjust it through the built-in temperature control touch screen 2 to maintain a suitable incubation temperature; S4, Microbial Conductivity Acclimation: Under the action of associated mineral fillers in coal, conductive bacteria are enriched and the DIET process is enhanced. At the same time, parameter information including but not limited to ORP, pH and conductivity is obtained through electrochemical parameter detector 15 to monitor data acquisition and evaluate the acclimation process. S5, Microbial Transfer: After the methanogenic microbial community has completed its electrical domestication, the domesticated microbial community is allowed to enter the biogas production space layer through the connecting channel 7 by opening the valve device 8. S6, Anaerobic gasification reaction: Anaerobic fermentation is carried out in the biological gasification space layer, and mass transfer is enhanced by stirring device 9; S7, Sample collection and analysis: Gas is collected through gas inlet 13 and liquid samples are collected through liquid inlet 12 for analysis. Gas samples are used to analyze methane production and liquid samples are used to analyze ETS activity. S8, Data Recording: Using computers to record and process monitoring data in real time.

[0019] Specifically, the methods for assessing the domestication process include: (a) ORP parameters are used to determine the anaerobic state and electrical conductivity acclimation degree of the system: When the ORP is higher than -300 mV, it indicates that the system is still in the microbial adaptation stage. At this time, the connection channel 7 should be kept closed. When the ORP is stably lower than -350 mV and lasts for more than 24 hours, it indicates that the electron transfer of the system tends to be stable and the methanogenic bacteria have completed their conductivity acclimatization. At this time, the connection channel 7 should be opened to allow the conductivity-acclimatized bacteria to enter the biogas production stage. (ii) pH parameter is used to determine the degree of acidification of the system and the metabolic stability of the microbial community: When the pH is below 6.5, it indicates that there is too much volatile fatty acid accumulation in the system, which may inhibit the activity of methanogens. In this case, buffer solution should be added to the system to maintain pH stability. When the pH is maintained in the range of 6.8 to 7.5, it indicates that the system is suitable for the stable growth of methanogens. (iii) Electrical conductivity parameters are used to reflect the degree of formation of the mineral's conductive network and its ion migration ability: When the electrical conductivity continues to increase, it indicates that a stable electron transport network is gradually formed between the associated minerals and microbial communities in the coal, which is conducive to the enhancement of the DIET process. If the electrical conductivity changes at a low level, the amount of conductive minerals should be increased or the conductivity acclimation time should be extended.

[0020] The beneficial effects of this invention are: 1. This invention integrates the conductive domestication of microbial communities with the biogas production process; it enhances the extracellular electron transfer process by utilizing associated mineral fillers in coal; it constructs a monitorable electrochemical regulation system to improve process controllability; it improves the electron transfer efficiency and metabolic activity of microorganisms; it effectively increases methane production and gas production rate; it enhances system stability and shortens the microbial domestication cycle; it is closer to the actual coal seam mineral environment and has good engineering application prospects.

[0021] 2. This invention utilizes naturally associated minerals in coal (such as pyrite, magnetite, and hematite) as electron transfer media to provide an attachment interface and an electron transfer "bridge" for microorganisms, shortening the electron transfer path, reducing electron transfer resistance, and reducing costs. It also avoids the introduction of exogenous materials and has better engineering application prospects.

[0022] 3. After the bacterial community has been domesticated to conduct electricity, it can be directly introduced into the biogas production space, maintaining the anaerobic environment and avoiding the contamination of other bacteria, thereby improving the gas production efficiency and stability of the system and facilitating the accuracy of data monitoring and the control of process evaluation during the experiment.

[0023] 4. This invention constructs a monitorable electrochemical regulation system, which uses an electrochemical parameter detector to monitor indicators such as pH, ORP, and conductivity in real time, providing a quantitative regulation method for bacterial community enrichment and system operation. Attached Figure Description

[0024] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1 This is a schematic diagram of the overall structure of the experimental device of the present invention (integrated).

[0025] Figure 2 This is a schematic diagram of the enrichment culture reaction vessel in the experimental apparatus of the present invention.

[0026] Figure 3 A top-view diagram showing the enrichment culture vessel with its sealed top cover removed.

[0027] Figure 4 This is a schematic diagram of the upper partition in an enrichment culture reactor.

[0028] Figure 5 This is a schematic diagram of the lower partition in an enrichment culture reactor.

[0029] Figure 6 This is a schematic diagram of the valve device.

[0030] Figure 7 A top-down view of the sealed top cover.

[0031] In the diagram: 1. Constant temperature incubator; 2. Temperature control touch screen; 3. Enrichment culture reaction vessel; 301. Vessel body; 302. Upper partition; 303. Lower partition; 4. Sealed top cover; 401. Cover; 402. Handle; 403. Sealing ring; 5. Sensor assembly; 501. Sealing plug; 502. pH sensor; 503. ORP sensor; 504. Conductivity sensor; 505. Lead wire; 6. Coal-associated mineral filling assembly; 601. Mineral filling mesh plate one; 602. Mineral filling mesh plate two; 603. Limiting angle; 7. Connecting channel 8. Valve device; 801. Butterfly valve; 802. Long handle switch; 803. Channel port; 804. Hand-held rotating part; 9. Stirring device; 901. Magnetic base; 902. Rotor; 10. Nitrogen gas through-box interface; 11. Nitrogen cylinder; 12. Liquid outlet; 13. Gas outlet; 14. Upper nitrogen connector; 15. Electrochemical parameter detector; 16. Lower nitrogen connector; 17. Wiring through-box gland; 18. Power plug; 19. Gas outlet through-box interface; 20. First gas collection bag; 21. Gas analyzer; 22. Exhaust port; 23. Second gas collection bag. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0033] This invention addresses the problem of using a single reactor for both microbial conductivity domestication and biogas production processes. It integrates microbial conductivity domestication and biogas production into a single process, maintaining an anaerobic environment and preventing contamination by other microorganisms. It provides an experimental device for promoting biogas production by enhancing electron transfer based on associated minerals in coal. The specific structure is as follows: Figure 1 As shown: It includes a constant temperature incubator 1, an enrichment culture reaction vessel 3 and a stirring device 9 located inside the constant temperature incubator 1, and a nitrogen cylinder 11, an electrochemical parameter detector 15, a first gas collection bag 20 and a gas analyzer 21 located outside the constant temperature incubator 1; the key equipment is the enrichment culture reaction vessel 3 integrated inside the constant temperature incubator 1. The temperature of the constant temperature incubator 1 is adjusted and displayed by a temperature control touch screen 2, which is a current technology, thereby ensuring that the enrichment culture reaction vessel 3 can carry out strain domestication, reproduction and gas production under constant temperature conditions.

[0034] like Figure 2 As shown, the enrichment culture reaction tank 3 is divided into an upper microbial conductive acclimatization space, a middle interlayer space, and a lower biogas production space by a double-layer partition. A valve device 8 is installed in the middle interlayer, and the valve device 8 is used as a connecting channel 7 when it is open, so that the upper microbial conductive acclimatization space and the lower biogas production space can be connected. This is used to control the intermittent or continuous transfer of acclimatized microorganisms between the two tanks, thereby realizing the coordinated operation of microbial conductive acclimatization and biogas production processes.

[0035] The enrichment culture reaction vessel 3 is made of glass or acrylic, and its main body is a cylindrical vessel 301. The double-layered sealing partitions are an upper partition 302 and a lower partition 303. Figure 4 and Figure 5 As shown, both the upper partition 302 and the lower partition 303 have through holes at their centers to form a connecting channel 7. The valve device 8 is a butterfly valve 801 with a long-handled switch 802. The butterfly valve 801 is set with the central through holes of the upper partition 302 and the lower partition 303 to form the connecting channel 7. At the same time, the valve device 8 is sandwiched between the upper partition 302 and the lower partition 303. The long-handled switch 802 passes through the tank body 301 so that the hand-held rotating part 804 is outside the enrichment culture reaction tank 3. The tank body 301 has through holes at corresponding positions to facilitate the passage of the long-handled switch 802. The through holes are located in the middle air gap and will not affect the airtightness of the upper bacterial conductive acclimatization space and the biogas production space.

[0036] The connection channel 7 is specifically formed as follows: the butterfly valve 801 has a channel port 803, such as... Figure 6 As shown, it protrudes upward to fit into the central through hole of the upper partition 302 and protrudes downward to fit into the central through hole of the lower partition 303. It is then sealed by applying a sealing material (such as silicone sealant) and forming an airtight connection after curing.

[0037] like Figure 2The aforementioned conductive acclimatization space for microorganisms is equipped with mineral-filled mesh bag plate 601 and mineral-filled mesh bag plate 602. Both have the same structure, being open-top mesh bag structures formed by splicing together plastic mesh plates, and the spliced ​​shape is a square thick plate. They are used to contain granular or lumpy coal-associated mineral fillers, such as pyrite, magnetite, or hematite. The associated mineral fillers provide a carrier for microorganisms to attach and accumulate, and promote direct electron transfer (DIET) between microorganisms through their conductive properties. It should be noted that the coal-associated mineral fillers are not used as electrodes, nor are they electrically connected to external circuits.

[0038] The mineral-filled mesh bag 601 and mineral-filled mesh bag 602 are respectively snapped onto the upper partition 302, as shown. Figure 3 and 4 As shown, several limiting angles 603 are fixedly connected to the upper partition 302 to form a locking area. The limiting angles 603 are L-shaped plastic corner structures. Every four limiting angles 603 can restrict the position of a mineral filling mesh bag plate. Specifically, they are positioned at the four corners of the bottom of the mineral filling mesh bag plate according to its size. Because the mineral filling mesh bag plate is a plastic mesh splicing structure with a certain deformation capability, these four limiting angles 603 are slightly tightened inward to lock the bottom of the mineral filling mesh bag plate in it, thus maintaining overall stability after the associated mineral filler in the coal is loaded. The above structure is regarded as the associated mineral filling component 6. Preferably, the mineral filling mesh bag plate one 601 and the mineral filling mesh bag plate two 602 are symmetrically arranged with the axial direction of the connecting channel 7 as the reference, such as Figures 2-4 As shown.

[0039] Another upper nitrogen connector 14 penetrates the tank body 301 for airtightness. Its position and height are level with the top plane of the mineral filling mesh plate 601 and the mineral filling mesh plate 602, so as to jointly restrict the position of the sealing cover 4. The upper nitrogen connector 14 is connected to the nitrogen cylinder 11 through a hose. The hose passes through the constant temperature incubator 1 in the following way: the nitrogen incubator interface 10 is set in an airtight manner to allow the hose to pass through, so as to introduce nitrogen into the conductive acclimatization space of the bacterial community.

[0040] At the same height as the upper nitrogen connector 14, an airtight vent 22 is provided on the other side of the tank. The vent 22 is connected to a second gas collection bag 23 via a hose through a gas intake port 19. A one-way valve is installed at the outlet of the second gas collection bag 23, primarily for gas venting. If the second gas collection bag 23 inflates, venting is required. If gas analysis is needed, the second gas collection bag 23 can be connected to a gas analyzer 21 via a hose. Figure 1 This connection method is not shown in the image.

[0041] like Figure 1 and Figure 2The enrichment culture reaction vessel 3 is provided with a sealing top cover 4, which includes a cover body 401, a handle 402, and a sealing ring 403. Figure 2 As shown, the cover 401 is circular, with its outer diameter slightly smaller than the inner diameter of the can 301, and several sealing rings 403 are fitted on its side wall. Figure 2 The top, middle, and bottom sections are displayed in the middle section. When the sealing cover 4 is closed on the tank body 301, it is squeezed and deformed to achieve a seal. A handle 402 is fixedly connected to the top surface of the cover 401 to facilitate pulling the cover 401 out of the tank body 301. The closed position of the cover 401 stops at the top of the mineral filling mesh plate 1 601 and the mineral filling mesh plate 2 602.

[0042] Furthermore, a sensor assembly 5 is provided on the sealed top cover 4, such that the probes of all sensors extend into the bacterial conductive acclimation space. If there is culture medium in the bacterial conductive acclimation space, the probes of all sensors extend into the culture medium. The sensor assembly 5 includes a sealing plug 501, a pH sensor 502, an ORP sensor 503, a conductivity sensor 504, and corresponding leads 505 inserted into the sealing plug. Figure 5 As shown, the specific configuration is as follows: a through hole is reserved on the lower partition 303 and the size is adapted to the sealing plug 501, so that the sealing plug 501 can seal and block the reserved through hole; the sealing plug 501 is made of rubber and has a reserved small hole for inserting sensor probes for tight connection of pH sensor 502, ORP sensor 503 and conductivity sensor 504 respectively, which can also ensure good airtightness of sealing plug 501 after connection.

[0043] The leads 505 of the pH sensor 502, ORP sensor 503, and conductivity sensor 504 extend through the wiring gland 17 on the side wall of the constant temperature incubator to the outside of the incubator and are connected to the electrochemical parameter detector 15. The wiring gland 17 also allows the power cord of the stirring device 9 to pass through, and the end of the power cord is a power plug 18, which supplies power to the stirring device 9 after being connected to a power source.

[0044] The analog signals collected by the electrochemical parameter detector 15 are amplified and converted from analog to digital, then connected to a computer via USB, RS-232, or Ethernet interface to achieve real-time monitoring, recording, and analysis of electrochemical parameters. This further connection to the computer allows for real-time acquisition and recording of environmental parameter changes during the microbial community domestication process, characterizing the evolution of microbial electron transfer activity. This monitoring system does not apply external voltage or current to the system, nor does it involve electrical connections to the mineral packing layer.

[0045] like Figure 1As shown, the enrichment culture reactor 3 is equipped with a stirring device 9 at the bottom. The stirring device 9 is preferably a high-power magnetic rotor stirrer, comprising a magnetic base 901 and a magnetic base 902. The rotor 902 is located within the biogas production space of the enrichment culture reactor 3, and the entire enrichment culture reactor 3 rests on the magnetic base 901. The stirring device 9 is used to enhance mass transfer within the system and ensure sufficient contact between the substrate and microorganisms, thereby improving the efficiency of anaerobic fermentation.

[0046] The tank 301 in the biogas production space is equipped with a lower nitrogen connector 16, a liquid outlet 12, and a gas outlet 13, all of which are airtight connectors that penetrate the tank 301, but their installation methods are different: The lower nitrogen connector 16 is positioned adjacent to the lower partition 303, serving as a location limit for the lower partition 303 and also at the highest point of the biogas production space. This prevents backflow of the culture medium from affecting nitrogen flow. The lower nitrogen connector 16 connects to the nitrogen cylinder 11 in the same way as the upper nitrogen connector 14 connects to the nitrogen cylinder 11. Alternatively, the hose can pass directly through the nitrogen gas inlet 10 to connect to the nitrogen cylinder 11, or the hose connecting to the nitrogen cylinder 11 can pass through the nitrogen gas inlet 10 and connect to a T-junction, branching into two gas paths that connect to the upper nitrogen connector 14 and the lower nitrogen connector 16 respectively. Supplying gas via a nitrogen cylinder is a current technology; the specific locations and configurations of instruments and valves involved in gas path control will not be detailed here.

[0047] The liquid sampling port 12 is located at the bottom of the tank 301, and a liquid valve is added to control the liquid flow. The valve is opened when sampling and closed when sampling is not required.

[0048] The gas intake port 13 is positioned at a height lower than or equal to the lower nitrogen connector 16, but higher than the lowest point of the sensor probe (the principle is to position it above the culture medium surface). It connects to the first gas collection bag 20 via a flexible hose through the gas intake port 19 for collecting biological gases. Gas can be released as needed based on the expansion of the first gas collection bag 20. The first gas collection bag 20 is connected to a gas analyzer 21 via a flexible hose for analyzing gas conditions. Installing valves as control nodes in the gas path is a conventional technique; their location and installation methods are not detailed here.

[0049] The above describes an experimental device for enhancing electron transfer and promoting biogas production based on associated minerals in coal. The assembly steps during design and installation are as follows: First, the existing cylindrical glass jar in the laboratory or a purchased cylindrical acrylic jar will be used as the main body of the enrichment culture reaction vessel 3. Considering the ease of drilling, the following operation will be carried out using a cylindrical acrylic jar. First, according to the size of the channel port 803, holes will be drilled at the center of the upper partition 302 and the lower partition 303 (also made of acrylic material). Then, the butterfly valve 801 will be clamped between the upper partition 302 and the lower partition 303 to determine the height of the interlayer space. According to the height value, the preset positions of the upper partition 302 and the lower partition 303 will be marked in the middle of the cylindrical acrylic jar.

[0050] Second, based on the height of the interlayer space, a through hole is made in the tank wall for the long-handled switch 802 to pass through; adjacent to the preset position of the lower partition 303, a through hole is made in the lower tank wall for the lower nitrogen connector 16 and the gas inlet 13 to pass through, and a corresponding airtight connector / interface is installed; then, a through hole is made in the tank wall at the bottom position for the liquid inlet 12 to be installed, and a corresponding liquid valve is installed; then, based on the size of the mineral filling mesh plate and the thickness of the sealing cover 4, the positions of the upper nitrogen connector 14 and the exhaust port 22 are estimated, and a through hole is made for the airtight connector / interface to pass through, but the airtight connector / interface is not installed for the time being.

[0051] Third, place rotor 902 into the tank, and then... Figure 5 The lower partition 303 shown is placed horizontally on the lower nitrogen connector 16 to separate the tank body, and then sealed with glass glue (silicone sealant). If the lower nitrogen connector 16 and the gas inlet 13 are at the same horizontal position and are set opposite each other, it makes it easier to determine the position of the lower partition 303. Then, place the butterfly valve 801, remove the long handle switch 802 of the hand-held rotating part 804, pass it through the preset through hole, and then place the channel port 803 at the center through hole of the lower partition 303. Apply glass glue (silicone sealant) to seal the connection, and then install the hand-held rotating part 804 on the outside of the tank body.

[0052] Fourth, the limiting angle 603 is pre-fixed (preferably bonded) to the upper partition 302 according to the size of the mineral-filled mesh plate, such as... Figure 4 The upper partition 302 is placed on the butterfly valve 801. The channel port 803 is pre-fitted with a sealing ring or pre-applied with glass glue. The upper partition 302 is pressed tightly against the channel port 803 to achieve an airtight connection. Then, the upper partition 302 is sealed to the inner wall of the tank with glass glue (silicone sealant). The mineral filling mesh plate 1 601 and the mineral filling mesh plate 2 602 are snapped together at the positions defined by the limiting angle 603. The mineral filling mesh plate 1 601 and the mineral filling mesh plate 2 602 are then filled with associated minerals in the coal to form the associated mineral filling component 6. The upper nitrogen connector 14 and the exhaust port 22 are installed. The sealing cover 4 is inserted to complete the assembly of the enrichment culture reaction tank 3.

[0053] Fifth, after connecting the pH sensor 502, ORP sensor 503, and conductivity sensor 504 to the sealing plug 501, a through hole is made in the sealing cover 4 according to the size of the sealing plug 501, and the sealing plug 501 with the sensor is inserted into this through hole, thus completing the connection between the sensor assembly 5 and the sealing cover 4. Figure 7 As shown.

[0054] Alternatively, a plastic cap structure (with a threaded structure) from a three-electrode electrolytic cell can be selected as the sealing plug 501. In this case, a threaded through hole is made on the sealing cap 4, so that the sealing plug 501 is fixedly connected to this threaded hole. Here, a rubber sealing plug is preferred for safety reasons. The plug-type plug can be pushed open when the gas pressure is too high, thus acting as a safety valve.

[0055] Sixth, open the door of the constant temperature incubator 1 and place the assembled enrichment culture reaction vessel 3 into the constant temperature incubator 1, specifically on the magnetic base 901. The constant temperature incubator 1 has been modified beforehand, with a nitrogen gas inlet 10, a wiring gland 17, and a gas outlet inlet 19 installed on the wall. Pass the gas supply hose connected to the nitrogen cylinder 11 through the nitrogen gas inlet 10 into the constant temperature incubator 1, and connect the upper nitrogen connector 14 and the lower nitrogen connector 16 via a T-junction. Place the magnetic base... The power cord of 901 passes through the cable tray 17 and is connected to the power plug 18 outside the enclosure. At the same time, the lead wire 505 also passes through the cable tray 17 and is electrically connected to the electrochemical parameter detector 15 outside the enclosure. The hose passes through the gas intake interface 19, with one end connected to the gas intake port 13 and the other end connected to the gas analyzer 21 through the first gas collection bag 20. The other hose passes through the gas intake interface 19, with one end connected to the exhaust port 22 and the other end connected to the second gas collection bag 23.

[0056] Among them, the nitrogen gas through-box interface 10 and the gas intake through-box interface 19 are both conventional airtight interfaces, including stainless steel through-wall connectors, double-end threaded locking structures, high-temperature resistant silicone sealing rings, and gas duct clamp fixing components, etc.

[0057] The stirring device 9 of this invention uses a high-power magnetic rotor stirrer, eliminating the need to consider bottom airtightness. If a bottom-entry blade stirrer is to be used, a hole is made in the center of the bottom of the tank in the first step, and the bottom-entry blade stirrer is installed first, ensuring airtightness at the bottom of the tank. A base is provided to accommodate the motor to stabilize the entire tank. This technique is not currently used due to airtightness issues.

[0058] Before using the above devices, an anaerobic environment is first established with nitrogen. Then, the electrical equipment (stirring device 9, electrochemical parameter detector 15, and gas analyzer 21) is powered on. During operation, the microorganisms first come into full contact with the associated mineral packing material in the coal in the conductive acclimation space of the microbial community, so as to achieve the enrichment and functional enhancement of conductive bacteria. Then, by opening the valve device 8, the acclimated microbial community enters the biogas production space layer through the box connection channel 7 to carry out efficient anaerobic fermentation reaction, thereby realizing the coordinated operation of microbial community acclimation and gas production process.

[0059] The microorganisms involved in this invention originate from coal seam mine water discharged during coal seam mining. This water is naturally rich in various anaerobic microorganisms, including methanogenic archaea, fermentative bacteria, and synthetic trophic bacteria. Associated mineral fillers in coal can effectively promote the enrichment of conductive bacteria and methanogenic archaea, enhancing direct extracellular electron transfer (DIET) between microorganisms, thereby shortening the microbial community cultivation cycle and significantly improving biogas production efficiency. The main genera include, but are not limited to, *Methanothrix*, *Methanosarcina*, *Methanobacterium*, *Methanoculleus*, *Lentimicrobium*, *Fermentimonas*, *Sphaerochaeta*, *Proteiniphilum*, *Aminobacterium*, and *Desulfolutivibrio*. Those skilled in the art can repeatedly obtain microbial communities with similar functions by collecting coal seam mine water and conducting anaerobic cultivation in the device of this invention.

[0060] Associated minerals in coal originate from the crushed raw ore of the target coal seam (such as pyrite, magnetite, and clay minerals). They possess good electrical conductivity and a large specific surface area, serving as a medium for microbial attachment and electron transfer. During the process of acclimation of the microbial community to electrical conductivity, these minerals can promote the enrichment of conductive bacteria and methanogenic archaea, enhance direct extracellular electron transfer (DIET), thereby significantly shortening the microbial community cultivation cycle and improving biogas production efficiency.

[0061] Based on the above device, the present invention provides an experimental method for promoting biogas production by enhancing electron transfer based on associated minerals in coal. The process mainly includes two core steps: the microbial community conductivity acclimatization stage and the biogas production stage. By enhancing the extracellular electron transfer capacity of microorganisms through the associated mineral filler layer in coal, the biogas production efficiency is improved.

[0062] (a) Microbial community electrical conductivity acclimatization stage 1. Equipment preparation Check that the connection channel 7 between the microbial conductive acclimatization space and the biogas production space in the enrichment culture reaction tank 3 is unobstructed and leak-free, and then ensure that the channel valve controller 8 is in the closed state.

[0063] Adjust the enrichment culture reaction vessel 3 to be stably placed on the magnetic base 901, and check that the rotor 902 is operating well in the biogas production space.

[0064] Check the airtightness of the sealing cover 4, upper nitrogen connector 14, lower nitrogen connector 16, liquid inlet 12, gas inlet 13, exhaust port 22, and sensor assembly 5 to ensure that the system is in a sealed state.

[0065] Place the entire enrichment culture reaction vessel 3 inside the constant temperature incubator 1, and set the appropriate culture temperature (usually 35 ℃) through the temperature control touch screen 2.

[0066] 2. Addition of substrate and bacterial source The mineral-filled mesh plate 1 and mineral-filled mesh plate 2 are pre-filled with associated minerals in the coal to form a filler layer, which is used to promote microbial attachment and electron transfer.

[0067] Open the sealed top cover 4, and add culture medium, coal mine water, or inoculum containing methanogenic microorganisms into the conductive acclimatization space. The liquid level must not exceed the height of the upper nitrogen connector 14 and the exhaust port 22.

[0068] 3. Establishment of an anaerobic environment By introducing high-purity nitrogen from nitrogen cylinder 11, the system is purged multiple times to remove oxygen and establish a stable anaerobic environment. During this process, sensor assembly 5 remains closed and sealed.

[0069] 4. Online monitoring of electrochemical parameters A pH sensor, an ORP sensor, and a conductivity sensor were inserted into the liquid within the bacterial community's conductive acclimatization space.

[0070] Each sensor is electrically connected to the electrochemical parameter detector 15 via leads. The detector is then connected to a computer via a USB, RS-232, or Ethernet interface to achieve real-time data acquisition and recording.

[0071] Specifically, the electrochemical parameter detector 15 is used to monitor the system's ORP, pH, and conductivity parameters in real time. A pressure sensor can also be added (to acquire pressure parameters). In the sensor assembly 5, the electrochemical parameter detector 15 can be connected to a computer, allowing for real-time recording, analysis, and dynamic control of the monitoring data to determine the enrichment level of the microbial community and the improvement in its electron transfer capacity. Among these: (1) ORP is used to determine the anaerobic state and electrical conductivity acclimation degree of the system: When the ORP is higher than -300 mV, it indicates that the system is still in the microbial adaptation stage, and at this time, the connection channel 7 should be kept closed. When the ORP is stably lower than -350 mV and lasts for more than 24 hours, it indicates that the electron transfer of the system tends to be stable and the methanogenic microbial community has completed its conductivity acclimatization. At this time, the connection channel 7 should be opened to allow the conductivity-acclimatized microbial community to enter the biogas production stage.

[0072] (2) pH is used to determine the degree of acidification of the system and the metabolic stability of the microbial community: When the pH is below 6.5, it indicates that there is too much volatile fatty acid accumulation in the system, which may inhibit the activity of methanogens. In this case, buffer solution should be added to the system to maintain pH stability. When the pH is maintained in the range of 6.8 to 7.5, it indicates that the system is suitable for the stable growth of methanogens.

[0073] (3) Electrical conductivity is used to reflect the degree of formation of the conductive network in minerals and their ion migration ability: When the electrical conductivity continues to increase, it indicates that a stable electron transport network is gradually formed between the associated minerals and microbial communities in the coal, which is conducive to the enhancement of the DIET process. If the electrical conductivity changes at a low level, the amount of conductive minerals should be increased or the conductivity acclimation time should be extended.

[0074] (4) Pressure parameters are used to maintain the safe operation of the system: When the internal pressure exceeds the set threshold, exhaust is performed through the exhaust port 22.

[0075] 5. Conductivity Acclimation Process Static culture under constant temperature conditions promotes the attachment of microorganisms to the associated mineral packing material and the formation of biofilm.

[0076] Conductive minerals can act as electron mediators, promoting direct extracellular electron transfer (DIET), thereby accelerating the enrichment of methanogens, significantly shortening the acclimatization period, and improving the activity of the bacterial community.

[0077] (II) Transfer of acclimatization culture 1. Connecting box Once the electrochemical parameters indicate that the bacterial community has completed enrichment, ensure that the liquid intake port 12 is closed, and open the valve device 8 to form the connection channel 7; transfer the acclimated bacterial solution from the upper bacterial community conductive acclimation space to the lower biological gas production space. At this time, the liquid level will not exceed the height of the lower nitrogen connector 16 and the gas intake port 13.

[0078] 2. Prevent pollution Keep the system sealed during the transfer process. If necessary, positive pressure can be maintained with nitrogen to prevent outside air from entering.

[0079] (III) Biogas Production Stage 1. Substrate addition Before enriching the microbial community, organic substrates to be degraded, such as coal, straw, or other organic waste, are added to the biogas production space. After acclimatization, these substrates are injected into the biogas production tank and mixed with the organic substrates to be degraded.

[0080] Start the gas-generating stirring device 9 to ensure full contact between the substrate and the acclimatization bacterial solution, thereby improving mass transfer efficiency.

[0081] 2. Anaerobic fermentation Under the control of the constant temperature incubator 1, a suitable temperature is maintained, and microorganisms accelerate the degradation of organic matter and promote the generation of gases such as methane through enhanced electron transfer capabilities.

[0082] 3. Gas Collection The generated biogas is discharged through the gas intake port 13 and connected to a gas collection bag or gas analyzer for component analysis and gas production measurement.

[0083] Sampling at gas intake 13 primarily analyzes methane production to evaluate coal bioconversion efficiency and electrical conductivity acclimation effects. This invention uses timed gas sampling, gas chromatography analysis, and cumulative gas production volume calculation to obtain the methane volume fraction and cumulative methane production. By comparing changes in methane yield at different stages, the electrical conductivity acclimation effect, the mineral's ability to promote electron transfer, and the stability of microbial metabolism can be evaluated.

[0084] 4. Liquid and Residue Treatment After fermentation is complete, the fermentation broth is collected through the liquid collection port 12 or the residue is discharged for subsequent analysis or processing.

[0085] Sampling at port 12 is primarily used to analyze the activity of the ETS (Electron Transport System) in the fermentation broth, reflecting the electron transport capacity and metabolic activity of the microorganisms. Higher ETS activity indicates more active electron transport in the microbial respiratory chain, stronger metabolic capacity of the microbial community, and higher methane metabolism efficiency. If ETS activity decreases, nutrient solution should be added appropriately or culture conditions adjusted to improve microbial community activity.

[0086] Example An experimental device based on the enhancement of electron transfer in coal associated minerals to promote biogas production was used to study the influence of coal associated minerals on the conductivity of microbial communities and their effects on biogas production performance.

[0087] 1. Experimental materials Inoculum: Anaerobic microbial flora taken from coal seam mine water.

[0088] Culture medium: conventional anaerobic methanogenic medium, pH 7.0±0.1.

[0089] Mineral filler: A mixture of pyrite, magnetite and clay minerals with a particle size of 5-10 mm.

[0090] Control group: No mineral filler added.

[0091] Experimental group: The amount of mineral filler was 10% of the effective volume of the conductive acclimatization space for the microbial community.

[0092] 2. Operating conditions Incubation temperature: 37 ℃; Anaerobic environment: High-purity nitrogen gas is introduced for 10 min; Stirring speed: 120 rpm; Monitoring parameters: ORP, pH, conductivity, ETS activity, and methane production; Microbial community analysis: 16S rRNA high-throughput sequencing.

[0093] 3. Microbial acclimatization effect The system's ORP (Operating Rate) stabilizing below -350 mV was used as the criterion for successful acclimatization. Comparison between the experimental and control groups showed that associated conductive minerals in coal significantly shortened the acclimatization period and improved system startup efficiency. The acclimatization time was reduced from 28 days to 21 days.

[0094] 4. Gas production performance After the microbial community was domesticated, it was transferred to a biogas production chamber for anaerobic fermentation. The results of the experimental group and the control group were as follows: the cumulative methane production increased by a maximum of 40.4%, and the maximum gas production rate increased by 3.3%.

[0095] 5. Changes in electrochemical parameters Electron transfer characteristics were monitored using an electrochemical parameter detector. By comparing the experimental group with the control group, the results showed that the activity of the electrochemical electron transfer system (ETS activity) increased by a maximum of 29.4%, the conductivity was improved, the electrochemical capacitance was enhanced, and the abundance of conductive bacteria such as Methanothrix increased by a maximum of 33.4% compared with the control group, indicating enhanced electron transfer activity.

[0096] 6. Conclusion In summary, the device of the present invention has the following significant technical effects: The acclimatization period of the microbial community was shortened from 28 days to 21 days; the cumulative methane production increased by approximately 40.4%; the maximum gas production rate increased by approximately 3.3%; ETS activity increased by 29.4%, and electron transport capacity was significantly enhanced; the abundance of the conductive methanogen Methanothrix increased by 33.4%.

[0097] The above experimental results fully verify the feasibility of the present invention and its significant advantages in promoting DIET and improving biogas production efficiency.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0099] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0100] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0101] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" and "second" may explicitly or implicitly include one or more features.

[0102] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, it can be a fixed connection or a movable connection, a detachable connection or a non-detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection or a connection that allows communication between the two components; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components, an indirect connection, or an interaction between two components.

Claims

1. An experimental device for promoting biogas production by enhancing electron transfer based on associated minerals in coal, characterized in that, It includes a constant temperature incubator (1), an enrichment culture reaction vessel (3) and a stirring device (9) located inside the constant temperature incubator (1), and a nitrogen cylinder (11), an electrochemical parameter detector (15), a second gas collection bag (23), a first gas collection bag (20) and a gas analyzer (21) located outside the constant temperature incubator (1). The enrichment culture reaction tank (3) has a sealed top cover (4), and a stirring device (9) is installed at the bottom. The interior is divided into an upper microbial conductive acclimatization space and a lower biological gas production space by a double-layer sealed partition. The horizontally arranged double-layer sealed partition is centrally connected and clamped with a valve device (8). There is also a sensor assembly (5) that is detachably and airtightly connected to the sealed top cover (4). There is also a coal-associated mineral filling assembly (6) installed in the upper microbial conductive acclimatization space. The nitrogen cylinder (11) is connected to the enrichment culture reaction vessel (3) via a flexible tube through the nitrogen gas penetration interface (10); the electrochemical parameter detector (15) is connected to the sensor assembly (5) located on the enrichment culture reaction vessel (3) via a wire through the wire penetration interface (17); the power cord of the stirring device (9) is also connected to the power plug (18) via the wire penetration interface (17); one end of the first gas collection bag (20) is connected to the gas intake port (13) of the biological gas generation space via a flexible tube through the gas intake interface (19), and the other end is connected to the gas analyzer (21) via a flexible tube; the second gas collection bag (23) is connected to the exhaust port (22) of the bacterial community conductive acclimatization space via a flexible tube through the gas intake interface (19); the bottom side wall of the enrichment culture reaction vessel (3) is also provided with a liquid intake port (12) with a valve.

2. The experimental apparatus for promoting biogas production based on enhanced electron transfer by associated minerals in coal as described in claim 1, characterized in that, The valve device (8) is a butterfly valve (801), whose channel port (803) is airtightly connected to the double-layer sealing partition and together forms a connection channel (7); its long handle switch (802) passes through the tank wall and is provided with a hand-held rotating part (804).

3. The experimental apparatus for promoting biogas production based on enhanced electron transfer by associated minerals in coal as described in claim 1, characterized in that, The coal-associated mineral filling component (6) includes a mineral filling mesh bag plate one (601) and a mineral filling mesh bag plate two (602) with the same structure and symmetrical position. The structure of the mineral filling mesh bag plate is a square plate-shaped mesh bag formed by splicing plastic mesh plates, and the inside is filled with coal-associated mineral filler.

4. The experimental apparatus for promoting biogas production based on enhanced electron transfer by associated minerals in coal as described in claim 2, characterized in that, The coal-associated mineral filling component (6) also includes several limiting angles (603), which are fixed on the upper partition (302) of the double-layer sealing partition, forming a snap-fit ​​area at the four corners of the bottom of the mineral filling mesh plate.

5. The experimental apparatus for promoting biogas production based on enhanced electron transfer by associated minerals in coal as described in claim 1, characterized in that, The sealing cover (4) includes a cover body (401), a handle (402), and a sealing ring (403); the cover body (401) is a circular structure with an outer diameter slightly smaller than the inner diameter of the tank body 301, and its side wall is fitted with several sealing rings (403); the handle (402) is fixedly connected to the middle of the cover body (401), and the sensor assembly (5) is arranged in front of it.

6. An experimental apparatus for promoting biogas production based on enhanced electron transfer by associated minerals in coal, as described in claim 1 or 5, characterized in that, The sensor assembly (5) includes a sealing plug (501) and a sensor inserted therein, including but not limited to a pH sensor, an ORP sensor, and a conductivity sensor.

7. The experimental apparatus for promoting biogas production based on enhanced electron transfer by associated minerals in coal as described in claim 6, characterized in that, The sealing plug (501) is a rubber sealing plug or a plastic cap structure with a threaded structure.

8. The experimental apparatus for promoting biogas production based on enhanced electron transfer by associated minerals in coal as described in claim 1, characterized in that, The nitrogen cylinder (11) is connected to the upper nitrogen connector (14) and lower nitrogen connector (16) of the enrichment culture reaction vessel (3) via a flexible tube through the nitrogen inlet (10); the upper nitrogen connector (14) is connected to the conductive acclimatization space of the microbial community, and the lower nitrogen connector (16) is connected to the biological gas production space.

9. An experimental method using the experimental apparatus for enhancing electron transfer and promoting biogas production based on associated minerals in coal, as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1, Establish an anaerobic environment: Introduce nitrogen from nitrogen cylinder (11) to replace oxygen in the system; S2, Filler and Inoculation: Add culture medium, coal-associated mineral filler and methanogenic microbial inoculation solution to the conductive acclimatization space of the microbial community; S3, constant temperature incubation: start the constant temperature incubator (1) to maintain a suitable incubation temperature; S4, Microbial Conductivity Acclimation: Under the action of associated mineral fillers in coal, conductive bacteria are enriched and the DIET process is enhanced. At the same time, parameter information including but not limited to ORP, pH and conductivity is obtained through an electrochemical parameter detector (15) to monitor data collection and evaluate the acclimation process. S5, Microbial transfer: After the methanogenic microbial community has completed its electrical domestication, the domesticated microbial community is allowed to enter the biogas production space layer through the connecting channel 7 by opening the valve device (8). S6, Anaerobic gasification reaction: Anaerobic fermentation is carried out in the biogas generation space layer, and mass transfer is enhanced by stirring device (9); S7, Sample collection and analysis: Gas is collected through the gas inlet (13), and liquid samples are collected through the liquid inlet (12) for analysis. Gas samples are used to analyze methane production, and liquid samples are used to analyze ETS activity. S8, Data Recording: Using computers to record and process monitoring data in real time.

10. The experimental method according to claim 9, characterized in that, The methods for assessing the domestication process include: (a) ORP parameters are used to determine the anaerobic state and electrical conductivity acclimation degree of the system: When the ORP is higher than -300 mV, it indicates that the system is still in the microbial adaptation stage. At this time, the connection channel (7) is kept closed. When the ORP is stable below -350 mV and lasts for more than 24 hours, it indicates that the electron transfer of the system tends to be stable and the methanogenic bacteria have completed the conductivity acclimatization. At this time, the connection channel (7) is opened to allow the conductivity acclimatized bacteria to enter the biogas production stage. (ii) pH parameter is used to determine the degree of acidification of the system and the metabolic stability of the microbial community: When the pH is below 6.5, it indicates that there is too much volatile fatty acid accumulation in the system, which may inhibit the activity of methanogens. In this case, buffer solution should be added to the system to maintain pH stability. When the pH is maintained in the range of 6.8 to 7.5, it indicates that the system is suitable for the stable growth of methanogens. (iii) Electrical conductivity parameters are used to reflect the degree of formation of the mineral's conductive network and its ion migration ability: When the electrical conductivity continues to increase, it indicates that a stable electron transport network is gradually formed between the associated minerals and microbial communities in the coal, which is conducive to the enhancement of the DIET process. If the electrical conductivity changes at a low level, the amount of conductive minerals should be increased or the conductivity acclimation time should be extended.

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