Biogas carbon reduction coupling biogas slurry pollution reduction device and method based on biogas circulation type fermentation

Abstract

The application provides a biogas carbon reduction and biogas slurry pollution reduction device and method based on a biogas circulation type fermentation, and belongs to the technical field of environment and energy. The device comprises an electric fermentation unit, a solid-liquid separation unit, a hydrothermal carbonization unit and a product collection unit. The electric fermentation unit comprises an electric fermentation tank, a cathode chamber, an anode chamber, a cation exchange membrane and a direct current constant voltage power supply. The device couples biological conversion of hydrogen-producing methanogens and electrochemical cathode reduction, circulates biogas to an anaerobic digestion chamber, performs in-situ biogas biological purification, removes ammonia nitrogen and COD in the biogas slurry in the anode chamber while reducing CO2 in the cathode to produce methane, and reasonably utilizes electron transfer and conservation law. The biogas slurry after pollution reduction can be used for irrigation, and can be further purified by absorbing the residual pollutants in the biogas slurry by biogas residue biochar. The biogas residue can be made into hydrothermal carbon and reused for anaerobic digestion or used as an adsorbent, so as to realize comprehensive utilization of the biogas slurry, the biogas residue and the biogas and the purpose of CO2 emission reduction.

Description

Technical Field

[0001] This invention relates to the fields of environmental and energy technology, and in particular to a biogas carbon reduction coupled biogas slurry pollution reduction device and method based on biogas circulating fermentation. Background Technology

[0002] Technologies related to CO2 catalytic reduction are constantly being developed, including photocatalysis, electrocatalysis, and thermochemical reduction. In biogas produced from the anaerobic fermentation of organic waste, methane accounts for 55-65% and CO2 for 35-45%. The biogas slurry after anaerobic fermentation is a high-concentration organic waste liquid with complex composition and poor biodegradability. Conventional biological treatment methods are ineffective. In recent years, electrochemical technology has become a research hotspot for treating recalcitrant and high-concentration organic matter due to its controllable conditions, lack of secondary pollution, and simple equipment.

[0003] There are two methods for biogas bio-purification using externally supplied hydrogen: in-situ and ex-situ. In-situ purification refers to the production and purification of biogas taking place in the same anaerobic reactor. This involves directly introducing H2 into the anaerobic digestion system, allowing it to react with CO2 in the biogas to produce a gas with a high CH4 concentration. In-situ purification is simple to operate, requiring no cultivation of specific microbial strains or the construction of a separate reactor. However, in in-situ purification using externally supplied hydrogen suffers from low H2 mass transfer efficiency due to the low solubility of hydrogen. Furthermore, the non-reacting CH4 gas in the biogas further affects the H2 mass transfer efficiency. Therefore, to truly apply in-situ purification technology to industrial production, further investigation is needed on the impact of irregular external H2 introduction on microbial structure, methane production, and tail gas composition, as well as the reactor's shock resistance, particularly the enhancement of H2 gas-liquid mass transfer.

[0004] Electrocatalytic reduction technology offers controllable and flexible reaction directions and products, and can be synchronized with other reactions, demonstrating promising application prospects. Using the active hydrogen generated during hydrogen electrolysis for in-situ biological purification allows for the immediate generation and consumption of active hydrogen, avoiding the challenges of H2 gas-liquid mass transfer and maximizing in-situ purification efficiency.

[0005] Based on the above background, this invention couples the biotransformation of hydrogen-producing methanogens with electrochemical cathodic reduction in the biogas circulating anaerobic fermentation process to improve the efficiency of CO2 conversion to methane, and simultaneously utilizes anodic oxidation to degrade organic matter in the biogas slurry, reducing ammonia nitrogen and COD content. The reduced-pollution biogas slurry can be used for irrigation, or it can be further purified by adsorbing residual pollutants by biochar in the biogas residue. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a biogas carbon reduction coupled biogas slurry pollution reduction device and method based on biogas circulation fermentation. The device makes reasonable use of the laws of electron transfer and conservation, and can reduce CO2 to produce methane in the cathode chamber while treating biogas slurry in the anode chamber, thereby achieving the purpose of biogas slurry pollution reduction and denitrification, biogas in-situ purification and CO2 emission reduction.

[0007] The device includes an electrofermentation unit, a solid-liquid separation unit, a hydrothermal carbonization unit, and a product collection unit.

[0008] The electro-fermentation unit includes an electro-fermentation tank, a cathode chamber (which also serves as an anaerobic digestion chamber), an anode chamber, a cation exchange membrane, and a DC constant voltage power supply. The solid-liquid separation unit is equipped with a mechanical dehydration device. The hydrothermal carbonization unit is equipped with a hydrothermal reactor. The product collection unit includes a hydrothermal carbon storage tank, a treated liquid storage tank, and a purified biogas storage tank.

[0009] The cathode chamber is equipped with a cathode, a liquid seal feed inlet, a biogas inlet, a perforated gas distribution pipe, a biogas exhaust outlet, and a fermentation residue outlet; the anode chamber is equipped with an anode, a biogas slurry inlet, a perforated liquid distribution pipe, and a treated liquid outlet.

[0010] The bottom of the electro-fermentation tank is equipped with a perforated support plate. The electro-fermentation tank contains a cathode chamber and an anode chamber, which are separated by a cation exchange membrane.

[0011] A biogas inlet is located on one side of the lower part of the electro-fermentation tank. The biogas inlet is connected to a perforated gas distribution pipe inside the electro-fermentation tank. A perforated support plate is installed on the upper part of the perforated gas distribution pipe. A liquid seal feed inlet is located in the cathode chamber. A biogas outlet is located on one side of the upper part of the electro-fermentation tank. A fermentation residue outlet is located at the bottom of the electro-fermentation tank. The fermentation residue outlet is connected to a pipeline and then to a mechanical dehydration device via a water pump. The dehydrated material is sent to a hydrothermal reactor for reaction. The product obtained is sent to a hydrothermal carbon storage tank. The mechanical dehydration device and the hydrothermal reactor are also connected to the biogas slurry inlet via pipelines. Water valves and water pumps are installed on the pipelines.

[0012] The anode chamber has a biogas slurry inlet and a treated liquid outlet. A perforated liquid distribution pipe extends into the bottom of the anode chamber through the biogas slurry inlet. The treated liquid outlet is connected to a treated liquid storage tank via a water valve and a water pump. The cathode chamber is equipped with biogas residue hydrothermal carbon.

[0013] The perforated air distribution pipe has multiple branch pipes evenly distributed on both sides of a main pipe, and air holes are provided on the branch pipes.

[0014] The cathode chamber contains at least two cathodes, the anode chamber contains one anode, the cathodes are arranged around the anode, the wires of each cathode are connected to the negative terminal of the DC constant voltage power supply, and the anode electrode material is a carbon brush, which is connected to the positive terminal of the DC constant voltage power supply through a wire.

[0015] Preferably, the number of cathodes is 4 to 8, and the cathode material is carbon cloth; or the cathode is a thin conductive metal sheet rolled into a cylindrical shape along the edge of the electrofermentation tank, and the cathode material is a thin copper plate.

[0016] The biogas discharged from the biogas outlet enters the purified biogas storage tank through a three-way diverter valve, or enters the biogas inlet through a gas pump. A gas flow meter is installed on the pipeline between the three-way diverter valve and the purified biogas storage tank.

[0017] The diameter of the electrofermentation tank is 10-20 cm; the height is 25-35 cm. The anode chamber is made of CMI-7000 cation exchange membrane. Since the anaerobic fermentation process for producing methane is mainly a reduction process, the volume of the cathode chamber needs to be larger than that of the anode chamber. The cathode chamber occupies 75-85% of the volume of the electrofermentation tank.

[0018] When the device is used, kitchen waste and bacterial bran are mixed as fermentation substrate, digested sludge is inoculated, and biogas residue hydrothermal carbon is added. The mixture is added to the cathode chamber of the electro-fermentation tank and anaerobic fermentation is carried out at a temperature of 50-55℃ until the high-temperature digestion reaction cycle ends.

[0019] Fermentation residue enters the solid-liquid separation unit through the fermentation residue discharge outlet. After being separated by the mechanical dehydration device, the biogas slurry is evenly injected into the bottom of the anode chamber through the biogas slurry inlet and the perforated liquid distribution pipe. The residual liquid after oxidation and pollution reduction is discharged to the treated liquid storage tank through the treated liquid discharge outlet.

[0020] After solid-liquid separation, the biogas residue is subjected to hydrothermal carbonization reaction in a hydrothermal reactor to obtain biogas residue hydrothermal carbon, which is then placed in a hydrothermal carbon storage tank.

[0021] Among them, biogas residue hydrothermal carbon is obtained by mechanically dehydrating the residue after anaerobic fermentation of a mixture of kitchen waste and bacterial bran to obtain solid biogas residue with a moisture content of 70%-90%, which is then placed in a hydrothermal reactor and heated to 180-240℃ at a heating rate of 5℃-7℃ / min, and held at that temperature for 0.5-2h. After the hydrothermal carbonization reaction is completed, it is cooled to room temperature, filtered and dried to obtain the final product.

[0022] A constant current of 1–10 mA is applied between the cathode and anode electrodes, and H in the anode chamber… + It migrates through the cation exchange membrane to the cathode chamber.

[0023] The biogas produced in the cathode chamber is circulated into the lower biogas inlet through the upper biogas outlet, a three-way diverter valve, and an air pump. It is then evenly distributed throughout the cathode chamber via a perforated gas distribution pipe. CO2 in the biogas reacts with active hydrogen produced at the cathode to form methane under the action of hydrogenotrophic methanogens. H₂, which migrates from the anode chamber... +It participates in the biochemical conversion reaction; it monitors the methane concentration in biogas in real time, and when the methane concentration in biogas reaches more than 90%, the biogas enters the biogas storage tank through the three-way diversion valve and the gas flow meter.

[0024] Hydrothermal char from biogas residue is formed into blocks of a specific shape and mechanical strength. These blocks serve as both biological carriers and cathode conductors, filling the cathode chamber. Hydrogen-producing methanogens are pre-immobilized and attached to the hydrothermal char carrier. As circulating biogas bubbles pass through the hydrothermal char layer, the biogas flow rate decreases, which facilitates the dissolution and adsorption of more CO2 from the biogas onto the hydrothermal char. This CO2 is then utilized by the hydrogen-producing methanogens and converted into methane, ultimately achieving the goal of purifying the biogas.

[0025] The technical principle of this invention is as follows:

[0026] (1) Cathode chamber reaction: The mixed substrate of kitchen waste and bacterial bran undergoes anaerobic digestion in the cathode chamber, and biogas circulation results in in-situ biogas biological purification. There are three main mechanisms.

[0027] a) Direct interspecies electron transfer pathway: Some methanogenic bacteria can directly utilize electrons to convert CO2 into CH4.

[0028] CO2 + 8H + +8e - →CH4+2H2O

[0029] b) Bioelectrochemical-assisted hydrogen production + hydromethanation: The cathode produces hydrogen gas, which hydromethanogenic bacteria use in situ to convert CO2 into CH4.

[0030] CO2 + 4H2 → CH4 + 2H2O

[0031] c) Electrochemical alkali production + CO2 alkali absorption: Due to the partial restriction on the migration of hydrogen ions from the anode chamber through the cation exchange membrane to the cathode chamber, the cathode chamber is weakly alkaline and can absorb some CO2 in situ.

[0032] (2) Anode chamber reaction: The biogas slurry after mechanical dehydration undergoes an oxidation reaction in the anode chamber:

[0033] OH - -e - →·OH or 2H₂O-2e - →2·OH+2H + ;

[0034] C a H b O c N d +·OH→C w H x O y N z+CO2+H2O+NH3

[0035] Ammonia nitrogen can undergo both direct and indirect electrochemical oxidation. Direct electrochemical oxidation refers to the oxidation of ammonia (NH4+) adsorbed on the surface of a carbon brush electrode. 3,ads It directly loses electrons and captures hydroxide ions (OH-) in the solution. - The dehydrogenation step is achieved; the final N atoms are coupled together and converted into N2.

[0036] NH 3,ads +OH - -e - →NH 2,ads +H2O;

[0037] NH 2,ads +OH - -e - →NH ads +H2O;

[0038] NH ads +OH - -e - →N ads +H2O;

[0039] N ads +N ads →N2

[0040] Indirect electrochemical oxidation removes hydroxyl radicals generated during the electrochemical reaction. These radicals can be oxidized by water or OH groups. - Produced during anodic oxidation, it is a very strong oxidizing agent with high electronegativity and hydrophilicity. It attacks the adsorbed and activated NH3, converting it into N2.

[0041] 2NH 3,ads +6·OH→N2+6H2O

[0042] Food waste contains high levels of salt, and its chloride ions are oxidized on the electrode surface to form ·Cl free radicals (·Cl is formed more easily than ·OH), resulting in the following reaction:

[0043] 2NH 3,ads +6·Cl→N2+6HCl

[0044] Ammonia nitrogen in the anode chamber can also migrate through the cation membrane to the cathode chamber in the form of ammonium ions, neutralizing the acidic substances produced in the anaerobic digestion chamber and alleviating the acid inhibition problem.

[0045] The beneficial effects of the above-described technical solution of the present invention are as follows:

[0046] (1) The device of the present invention makes reasonable use of the laws of electron transfer and conservation. While the anode degrades organic pollutants in the biogas slurry, CO2 in the biogas is reduced to methane by the cathode. At the same time, it achieves the purpose of reducing pollutants in the biogas slurry and increasing the methane content and calorific value of the biogas to replace natural gas.

[0047] (2) The present invention combines anaerobic digestion and biogas biological purification in situ to form an integrated device that serves as both a cathode chamber and an anaerobic digestion reaction chamber. The reaction uses constant current electrolysis and the reaction rate is controllable.

[0048] (3) The anode chamber is made of CMI-7000 cation exchange membrane, and the H generated in the anode chamber... + or NH4 + Migrating through the cation membrane to the cathode chamber, where H + It participates in the bioreduction reaction of CO2, while NH4 + It can neutralize the acidic substances produced in the anaerobic digestion chamber, alleviating acid inhibition problems. Because the two electrode chambers are completely separated, it facilitates the collection of methane at the cathode;

[0049] (4) Based on the traditional two-electrode reaction cell, this invention fills the cathode chamber with biogas residue hydrothermal carbon, so that the hydrothermal carbon can serve as both a biological carrier and a conductor. Since the particle surface of the biogas residue hydrothermal carbon has the same electrical properties as the electrode in the cathode chamber, the cathode surface area that can serve as a reaction site is increased, which can improve the electrolysis efficiency by about 3 times;

[0050] (5) The active hydrogen produced during the electrolytic hydrogen production process can be generated and consumed immediately, avoiding the difficulty of H2 gas-liquid mass transfer, which helps to improve the activity of anaerobic methanogens and maximize the efficiency of anaerobic digestion, thereby achieving increased methane and in-situ purification of biogas.

[0051] (6) The biogas residue after mechanical dehydration of anaerobic digestion residue is converted into biogas residue hydrothermal char through hydrothermal reaction and reused in the anaerobic reaction chamber. This can increase the residence time of the returned biogas in the reaction chamber and increase the efficiency of CO2 in biogas combining with hydrogen to convert into methane. Biogas residue biochar can also be used as an adsorbent to adsorb residual pollutants in biogas slurry and wastewater reduction residue, thereby achieving the comprehensive utilization of biogas slurry, biogas residue and biogas and the purpose of CO2 emission reduction. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulation fermentation of the present invention.

[0053] Figure 2 This is a top view of the anode distribution inside the electro-fermentation unit of the biogas carbon reduction coupled biogas slurry pollution reduction device based on biogas circulating fermentation of the present invention.

[0054] Figure 3This is a top view of the cathode distribution inside the electro-fermentation unit of the biogas carbon reduction coupled biogas slurry pollution reduction device based on biogas circulating fermentation of the present invention.

[0055] Figure 4 This is a schematic diagram of the perforated gas distribution pipe structure in the biogas carbon reduction and biogas slurry pollution reduction device based on biogas circulation fermentation of the present invention.

[0056] Wherein: 1-Electro-fermentation tank; 2-Cathode chamber; 3-Anode chamber; 4-Cation exchange membrane; 5-Cathode; 6-Liquid seal feed inlet; 7-Biogas inlet; 8-Perforated gas distribution pipe; 9-Biogas outlet; 10-Fermentation residue outlet; 11-Anode; 12-Biogas slurry inlet; 13-Perforated liquid distribution pipe; 14-Treatment liquid outlet; 15-DC constant voltage power supply; 16-Mechanical dehydration device; 17-Hydrothermal reactor; 18-Hydrothermal charcoal storage tank; 19-Treatment liquid storage tank; 20-Purified biogas storage tank; 21-Three-way diverter valve; 22-Gas flow meter; 23-Gas pump; 24-Water valve; 25-Water pump; 26-Hydrothermal charcoal for biogas residue; 27-Perforated support plate; 28-Anode conductor; 29-Cathode conductor; 30-Branch pipe; 31-Gas hole. Detailed Implementation

[0057] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0058] This invention provides a biogas carbon reduction coupled with biogas slurry pollution reduction device and method based on biogas circulation fermentation.

[0059] like Figure 1 As shown, the device includes an electrofermentation unit, a solid-liquid separation unit, a hydrothermal carbonization unit, and a product collection unit.

[0060] The electro-fermentation unit includes an electro-fermentation tank 1, a cathode chamber 2, an anode chamber 3, a cation exchange membrane 4, and a DC constant voltage power supply 15. The solid-liquid separation unit is equipped with a mechanical dehydration device 16. The hydrothermal carbonization unit is equipped with a hydrothermal reactor 17. The product collection unit includes a hydrothermal carbon storage tank 18, a treated liquid storage tank 19, and a purified biogas storage tank 20.

[0061] The cathode chamber 2 is equipped with a cathode 5, a liquid seal feed inlet 6, a biogas inlet 7, a perforated gas distribution pipe 8, a biogas exhaust outlet 9, and a fermentation residue outlet 10; the anode chamber 3 is equipped with an anode 11, a biogas slurry inlet 12, a perforated liquid distribution pipe 13, and a treated liquid outlet 14.

[0062] A perforated support plate 27 is provided at the bottom of the electro-fermentation tank 1. A cathode chamber 2 and an anode chamber 3 are provided inside the electro-fermentation tank 1. The cathode chamber 2 and the anode chamber 3 are separated by a cation exchange membrane 4.

[0063] A biogas inlet 7 is opened on one side of the lower part of the electric fermentation tank 1. The biogas inlet 7 is connected to the perforated gas distribution pipe 8 inside the electric fermentation tank 1. The perforated support plate 27 is set on the upper part of the perforated gas distribution pipe 8. The liquid seal feed inlet 6 is set in the cathode chamber 2. A biogas outlet 9 is opened on one side of the upper part of the electric fermentation tank 1. A fermentation residue outlet 10 is opened at the bottom of the electric fermentation tank 1. The fermentation residue outlet 10 is connected to the mechanical dehydration device 16 through the pipeline via the water pump 25. The dehydrated material is sent to the hydrothermal reactor 17. The product obtained from the reaction is sent to the hydrothermal carbon storage tank 18. The mechanical dehydration device 16 and the hydrothermal reactor 17 are also connected to the biogas liquid inlet 12 through the pipeline. A water valve and a water pump are installed on the pipeline.

[0064] Above the anode chamber 3, there is a biogas slurry inlet 12 and a treated liquid outlet 14. A perforated liquid distribution pipe 13 extends into the bottom of the anode chamber 3 through the biogas slurry inlet 12. The treated liquid outlet 14 is connected to the treated liquid storage tank 19 via a water valve 14 and a water pump 25. Biogas residue hydrothermal carbon 26 is placed in the cathode chamber 2.

[0065] like Figure 2 and Figure 3 As shown, at least two cathodes 5 are provided in the cathode chamber 2, and one anode 11 is provided in the anode chamber 3. The cathodes 5 are arranged around the anode 11. The cathode wires 29 of each cathode 5 are connected and then connected to the negative terminal of the DC constant voltage power supply 15. The electrode material of the anode 11 is a carbon brush, which is connected to the positive terminal of the DC constant voltage power supply 15 through the anode wire 28.

[0066] Preferably, the number of cathodes 5 is 4 to 8, and the cathode 5 is made of carbon cloth; or the cathode 5 is made of a conductive metal sheet rolled into a cylindrical shape along the edge of the electrofermentation tank, and the cathode 5 is made of thin copper plate.

[0067] The biogas discharged from biogas outlet 9 enters the purified biogas storage tank 20 through the three-way diverter valve 21, or enters the biogas inlet 7 through the gas pump 23. A gas flow meter 22 is installed on the pipeline between the three-way diverter valve 21 and the purified biogas storage tank 20.

[0068] The electro-fermentation tank 1 has a diameter of 10-20 cm and a height of 25-35 cm. The anode chamber 3 is made of CMI-7000 cation exchange membrane 4. The cathode chamber occupies 75-85% of the volume of the electro-fermentation tank 1.

[0069] like Figure 4 As shown, the perforated air distribution pipe 8 consists of a main pipe and multiple branch pipes 30 evenly arranged on both sides. Air holes 31 are evenly arranged on the branch pipes 30, and the number of branch pipes is not less than 3.

[0070] When the device is used, kitchen waste and bacterial bran are mixed as fermentation substrate, digested sludge is inoculated, and biogas residue hydrothermal carbon 26 is added. The mixture is added to the cathode chamber 2 of the electro-fermentation tank 1 and anaerobic fermentation is carried out at a temperature of 50-55℃ until the high-temperature digestion reaction cycle ends.

[0071] Fermentation residue enters the solid-liquid separation unit through fermentation residue outlet 10. After being separated by mechanical dehydration device 16, the biogas slurry is evenly injected into the bottom of anode chamber 3 through biogas slurry inlet 12 and perforated liquid distribution pipe 13. The residual liquid after oxidation and pollution reduction is discharged to the treated liquid storage tank 19 through treated liquid outlet 14.

[0072] After solid-liquid separation, the biogas residue is subjected to hydrothermal carbonization reaction in hydrothermal reactor 17 to obtain biogas residue hydrothermal carbon, which is then placed in hydrothermal carbon storage tank 18.

[0073] The aforementioned hydrothermal biogas residue is obtained by mechanically dehydrating the residue after anaerobic fermentation of a mixture of kitchen waste and inoculum residue to obtain solid biogas residue with a moisture content of 70%-90%. This residue is then placed in a hydrothermal reactor and heated to 180-240°C at a rate of 5-7°C / min, held at this temperature for 0.5-2 hours, and after the hydrothermal carbonization reaction is complete, cooled to room temperature, filtered, and dried. The hydrothermal biogas residue is then formed into blocks, serving as a biological carrier and cathode conductor, and filled into the cathode chamber. Hydrogen-producing methanogens are pre-immobilized and attached to the hydrothermal biogas residue carrier.

[0074] During fermentation, a constant current of 1–10 mA is applied between the cathode and anode electrodes. The H₂ in the anode chamber 3… + It migrates through cation exchange membrane 4 to cathode chamber 2.

[0075] The biogas produced in cathode chamber 2 is circulated into the lower biogas inlet 7 through the upper biogas outlet 9, three-way diverter valve 21, and air pump 23, and is evenly distributed in cathode chamber 2 through perforated gas distribution pipe 8. The CO2 in the biogas and the active hydrogen produced at the cathode are converted into methane by hydrogenotrophic methanogens. H2, which migrates from the anode chamber... + It participates in the biochemical conversion reaction; it monitors the methane concentration in biogas in real time, and when the methane concentration in biogas reaches more than 90%, the biogas enters the biogas storage tank 20 through the three-way diversion valve 21 and the gas flow meter 22.

[0076] The following description, in conjunction with specific embodiments, illustrates this point.

[0077] Example 1

[0078] The method for reducing carbon emissions from biogas and coupling it with biogas slurry pollution reduction based on biogas recycling fermentation mainly includes the following steps:

[0079] (1) Start-up stage: Digested sludge is inoculated into a substrate with a VS ratio of 7:3 for kitchen waste and bacterial bran, so that the VS ratio of digested sludge to substrate is 1:1 to 2:1. This mixture is added to cathode chamber 2 through liquid-sealed inlet 6, and nitrogen is introduced to maintain the system under anaerobic conditions. Anaerobic fermentation is carried out at a temperature of 50 to 55°C until the high-temperature digestion reaction cycle ends. The fermentation residue enters the solid-liquid separation unit through fermentation residue outlet 10;

[0080] (2) The fermentation residue is separated by mechanical dehydration device 16 to obtain biogas slurry, which is evenly injected into the bottom of anode chamber 3 through biogas slurry inlet 12 and perforated liquid distribution pipe 13. The liquid after oxidation and pollution reduction treatment is discharged to the treated liquid storage tank 19 through upper treatment liquid outlet 14. The biogas residue after solid-liquid separation is subjected to hydrothermal carbonization reaction in hydrothermal reactor 17 to obtain biogas residue hydrothermal carbon 26, which is placed in hydrothermal carbon storage tank 18.

[0081] (3) The biogas residue with a water content of about 80% after solid-liquid separation is placed in the hydrothermal reactor 17 in the hydrothermal carbonization unit and heated to 180-240℃ at a heating rate of 5℃~7℃ / min. After holding at this temperature for 0.5~2h, it is cooled to room temperature, filtered and dried to obtain biogas residue hydrothermal carbon 26, which is then sent to the hydrothermal carbon storage tank 18. The hydrothermal carbon yield is 51-85%. The hydrothermal residue can be injected into the anode chamber together with the biogas slurry for treatment.

[0082] (4) Start the DC constant voltage power supply 15 and apply a constant current of 1-10mA between the two electrodes;

[0083] (5) The mixture of biogas slurry and hydrothermal residue undergoes an oxidation reaction in the anode chamber 3, degrading macromolecular organic matter into small molecule organic acids and removing ammonia nitrogen and COD; the residue after anodizing and pollution reduction is discharged from the liquid outlet 14 to the treated liquid storage tank 19, which can be used for irrigation, or can be further purified by adsorbing residual pollutants by biogas residue biochar.

[0084] Example 2

[0085] The difference between this embodiment and Embodiment 1 is that the biogas produced by the anaerobic digestion of the mixed substrate of kitchen waste and inoculum is circulated into the lower biogas inlet 7 through the upper biogas outlet 9 of the cathode chamber, the three-way diversion valve 21, and the air pump 23, and is evenly distributed in the cathode chamber 2 through the perforated gas distribution pipe 8. During the continuous operation of anaerobic fermentation in the biogas circulation period, the CO2 in the biogas and the active hydrogen produced at the cathode are converted into methane by hydrogenotrophic methanogens. H2 passing through the anode chamber... + It also participates in the biochemical conversion reaction; it monitors the methane concentration in biogas in real time, and when the methane concentration in biogas reaches more than 90%, it can enter the purified biogas storage tank 20 through the three-way diversion valve 21 and the gas flow meter 22.

[0086] Example 3

[0087] The difference between this embodiment and Embodiment 1 is that the biogas residue hydrothermal carbon 26 is made into blocks with a certain shape and mechanical strength, and is used as a biological carrier (also serving as a cathode conductor) to fill the cathode chamber 2. Hydrogen-producing methanogens are pre-immobilized and attached to these hydrothermal carbon carriers. When the circulating biogas bubbles pass through the hydrothermal carbon layer, the biogas flow rate decreases, which is conducive to the dissolution and adsorption of more CO2 in the biogas onto the hydrothermal carbon, so that it can be utilized by the hydrogen-producing methanogens and converted into methane.

[0088] Example 4

[0089] The difference between this embodiment and Embodiment 1 is that the biogas produced by the anaerobic digestion of the mixed substrate of kitchen waste and inoculum is circulated into the lower biogas inlet 7 through the upper biogas outlet 9 of the cathode chamber, the three-way diversion valve 21, and the air pump 23, and is evenly distributed in the cathode chamber 2 through the perforated gas distribution pipe 8. During the continuous operation of anaerobic fermentation in the biogas circulation period, the CO2 in the biogas and the active hydrogen produced at the cathode are converted into methane by hydrogenotrophic methanogens. H2 passing through the anode chamber... + It also participates in the biochemical conversion reaction; it monitors the methane concentration in biogas in real time, and when the methane concentration in biogas reaches more than 90%, it can enter the biogas storage tank 20 through the three-way diversion valve 21 and the gas flow meter 22.

[0090] The biogas residue hydrothermal carbon 26 is made into blocks with a certain shape and mechanical strength, and is used as a biological carrier (also serving as a cathode conductor) to fill the cathode chamber 2. Hydrogen-producing methanogens are pre-immobilized and attached to these hydrothermal carbon carriers. When the circulating biogas bubbles pass through the hydrothermal carbon layer, the biogas flow rate decreases, which is conducive to the dissolution and adsorption of more CO2 in the biogas onto the hydrothermal carbon, so that it can be utilized by the hydrogen-producing methanogens and converted into methane, ultimately achieving the purpose of purifying biogas.

[0091] The following specific experiments illustrate the effectiveness of the device and method of the present invention.

[0092] The electro-fermentation unit used in the experiment had a volume of approximately 6L. The anode was a carbon brush, and the anode chamber was made of CMI-7000 cation exchange membrane (Membranes International Inc.). Eight cathodes, made of carbon cloth, were arranged around the anode, and the cathode chamber occupied 80% of the reactor volume.

[0093] Weigh out 57.8g of dry kitchen waste and 11.5g of dry mushroom substrate, making the ratio of kitchen waste to mushroom substrate 7:3 (based on VS). Inoculate with biogas digester sludge acclimated at 50-55℃, making the VS ratio of digested sludge to substrate 2:1. Add this mixture to the cathode chamber, apply a constant current of 4mA across the electrodes, and perform anaerobic fermentation at 55℃. Periodically pump in a mixture of biogas slurry and hydrothermal residue to replenish the water consumed in the anode chamber.

[0094] During the continuous operation of the electrofermentation, the biogas purification and biogas slurry treatment effects were investigated with and without circulating biogas and with and without the addition of biogas residue hydrothermal char. As shown in Table 1, regardless of whether the biogas was circulated or with the addition of biogas residue hydrothermal char, the ammonia nitrogen removal rate in the biogas slurry in the anode chamber was 30%–40%, and the COD removal rate was 70%–78%. The biofilm attached to the cathode surface contained more electroactive microorganisms (Firmicutes, Geobacter, Pseudomonas, etc.) and hydrogen-producing methanogens (Methanoculleus, etc.) as well as other anaerobic digesting microorganisms. The methane content in the biogas produced in the cathode chamber of the biogas circulation group was significantly higher than that in the non-circulating biogas group, and the addition of biogas residue hydrothermal char further increased the methane content. This indicates that the device and method described in this invention have achieved excellent in-situ biogas purification effects.

[0095] Table 1. Effects of biogas recycling and the addition of biogas residue hydrothermal char on methane content in biogas and pollution reduction in biogas slurry.

[0096]

[0097] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulating fermentation, characterized in that, It includes an electrofermentation unit, a solid-liquid separation unit, a hydrothermal carbonization unit, and a product collection unit. The electro-fermentation unit includes an electro-fermentation tank, a cathode chamber, an anode chamber, a cation exchange membrane, and a DC constant voltage power supply. The solid-liquid separation unit is equipped with a mechanical dehydration device. The hydrothermal carbonization unit is equipped with a hydrothermal reaction vessel. The product collection unit includes a hydrothermal carbon storage tank, a treated liquid storage tank, and a purified biogas storage tank. The cathode chamber is equipped with a cathode, a liquid seal feed inlet, a biogas inlet, a perforated gas distribution pipe, a biogas exhaust outlet, and a fermentation residue outlet; the anode chamber is equipped with an anode, a biogas slurry inlet, a perforated liquid distribution pipe, and a treated liquid outlet. The bottom of the electro-fermentation tank is equipped with a perforated support plate. The electro-fermentation tank contains a cathode chamber and an anode chamber, which are separated by a cation exchange membrane. A biogas inlet is located on one side of the lower part of the electro-fermentation tank. The biogas inlet is connected to a perforated gas distribution pipe inside the electro-fermentation tank. A perforated support plate is installed on the upper part of the perforated gas distribution pipe. A liquid seal feed inlet is located in the cathode chamber. A biogas outlet is located on one side of the upper part of the electro-fermentation tank. A fermentation residue outlet is located at the bottom of the electro-fermentation tank. The fermentation residue outlet is connected to a pipeline and then to a mechanical dehydration device via a water pump. The dehydrated material is sent to a hydrothermal reactor. The reaction product is sent to a hydrothermal carbon storage tank. The mechanical dehydration device and the hydrothermal reactor are also connected to the biogas slurry inlet via pipelines. Water valves and water pumps are installed on the pipelines. The anode chamber has a biogas slurry inlet and a treated liquid outlet. A perforated liquid distribution pipe extends into the bottom of the anode chamber through the biogas slurry inlet. The treated liquid outlet is connected to a treated liquid storage tank via a water valve and a water pump. Biogas residue hydrothermal carbon is placed in the cathode chamber. The perforated air distribution pipe has multiple branch pipes evenly arranged on both sides of a main pipe, and air holes are provided on the branch pipes. The anode chamber is made of CMI-7000 cation exchange membrane; the cathode chamber occupies 75-85% of the volume of the electrofermentation tank. A constant current of 1–10 mA is applied between the cathode and anode electrodes, and H in the anode chamber… + They migrate through the cation exchange membrane to the cathode chamber; The cathode chamber is provided with no less than two cathodes, the anode chamber is provided with one anode, the cathodes are arranged around the anode, the wires of each cathode are connected and connected to the negative terminal of the DC constant voltage power supply, the anode electrode material is a carbon brush, and it is connected to the positive terminal of the DC constant voltage power supply through a wire.

2. The biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulating fermentation according to claim 1, characterized in that, The number of cathodes is 4 to 8, and the cathode material is carbon cloth; or the cathode is a thin conductive metal sheet rolled into a cylindrical shape along the edge of the electrofermentation tank, and the cathode material is a thin copper plate.

3. The biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulating fermentation according to claim 1, characterized in that, The biogas discharged from the biogas outlet enters the purified biogas storage tank through a three-way diverter valve, or enters the biogas inlet through a gas pump. A gas flow meter is installed on the pipeline between the three-way diverter valve and the purified biogas storage tank.

4. The biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulating fermentation according to claim 1, characterized in that, The diameter of the electro-fermentation tank is 10-20cm; the height is 25-35cm.

5. The application method of the biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulating fermentation according to claim 1, characterized in that, Kitchen waste and bacterial bran are mixed as fermentation substrate, digested sludge is inoculated, and biogas residue hydrothermal char is added. The mixture is added to the cathode chamber of the electro-fermentation tank and anaerobic fermentation is carried out at a temperature of 50-55℃ until the high-temperature digestion reaction cycle ends. Fermentation residue enters the solid-liquid separation unit through the fermentation residue discharge outlet. After being separated by the mechanical dehydration device, the biogas slurry is evenly injected into the bottom of the anode chamber through the biogas slurry inlet and the perforated liquid distribution pipe. The residual liquid after oxidation and pollution reduction is discharged to the treated liquid storage tank through the treated liquid discharge outlet. After solid-liquid separation, the biogas residue is subjected to hydrothermal carbonization reaction in a hydrothermal reactor to obtain biogas residue hydrothermal carbon, which is then placed in a hydrothermal carbon storage tank.

6. The application method of the biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulating fermentation according to claim 5, characterized in that, The biogas residue hydrothermal carbon is obtained by mechanically dehydrating the residue after anaerobic fermentation of a mixture of kitchen waste and inoculum residue to obtain solid biogas residue with a moisture content of 70%-90%, placing it in a hydrothermal reactor, heating it to 180-240℃ at a heating rate of 5℃-7℃ / min, holding it at that temperature for 0.5-2h, cooling it to room temperature after the hydrothermal carbonization reaction is completed, filtering it and drying it.

7. The application method of the biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulating fermentation according to claim 5, characterized in that, The biogas produced in the cathode chamber is circulated into the lower biogas inlet through the upper biogas outlet, a three-way diverter valve, and an air pump. It is then evenly distributed throughout the cathode chamber via a perforated gas distribution pipe. CO2 in the biogas reacts with active hydrogen produced at the cathode to form methane under the action of hydrogenotrophic methanogens. H₂, which migrates from the anode chamber... + It participates in the biochemical conversion reaction; it monitors the methane concentration in biogas in real time, and when the methane concentration in biogas reaches more than 90%, the biogas enters the biogas storage tank through the three-way diversion valve and the gas flow meter.

8. The application method of the biogas carbon reduction coupled with biogas slurry pollution reduction device based on biogas circulating fermentation according to claim 6, characterized in that, The biogas residue hydrothermal carbon is made into blocks, which serve as biological carriers and cathode conductors, and are filled into the cathode chamber. Hydrogen-loving methanogens are pre-immobilized and attached to the biogas residue hydrothermal carbon carrier.

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