System for producing methane through enhanced anaerobic digestion by coupling biogas backflow with microbial electrolysis cell (MEC) and application of system

Abstract

The invention relates to a system for producing methane through biogas reflux coupling microbial electrolysis cell (MEC) enhanced anaerobic digestion and application. A reactor system comprises an MEC anaerobic digestion system and a biogas reflux system. The MEC anaerobic digestion system is provided with a biological anode plate and a biological cathode plate, electroactive microorganisms attached to the biological anode plate convert organic matters into carbon dioxide and generate electrons, and electroactive microorganisms attached to the biological cathode plate convert carbon dioxide into methane; a secondary biogas separation tank is adopted for biogas separation in the biogas backflow system, carbon dioxide in the biogas is more effectively separated out, and the carbon dioxide intermittently flows back to a biological cathode plate of the MEC anaerobic digestion system after being collected. Compared with the prior art, the anaerobic digestion treatment of the organic solid waste is realized, and the in-situ upgrading of the biogas is also realized; and the separated carbon dioxide reflux can be efficiently methanated, so that the emission of the carbon dioxide is reduced, the in-situ treatment of the carbon dioxide is realized, the intermediate links are reduced, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection and resource recovery, and in particular to a system and application of biogas reflux coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methanogenesis. Background Art

[0002] Anaerobic digestion is widely used in the treatment of organic solid waste because it can more effectively utilize the chemical energy in organic waste. However, the anaerobic digestion system still has shortcomings, such as limited microbial metabolism, insufficient substrate utilization, and poor system stability.

[0003] The anaerobic digestion process and the electrochemical process in the microbial electrolytic cell anaerobic digestion system work together. The electrochemical process provides additional energy driving force for anaerobic digestion, allowing some reaction steps that are difficult to carry out in traditional anaerobic digestion to proceed smoothly. At the same time, the substrates and microbial metabolic activities produced by anaerobic digestion provide a source of electrons and protons for the electrochemical process, maintaining the current and voltage of the electrolytic cell and ensuring the stable operation of the entire system. The microbial community is the core component of the microbial electrolytic cell anaerobic digestion system. These microorganisms form a complex ecological community on the electrode surface or in the liquid environment of the electrolytic cell, and work together to complete the anaerobic digestion process.

[0004] The biogas produced by anaerobic digestion consists of 50%-75% methane and 25%-45% carbon dioxide. Carbon dioxide, as a non-combustible gas, absorbs heat during the combustion process, thereby reducing the combustion efficiency of the biogas, resulting in the need for further processing of the produced biogas before it can be used as fuel.

[0005] Biogas reflow can reintroduce methanogens in biogas into the anaerobic digestion system, where they can participate in the decomposition of substrates and the methane production process again, thus strengthening the methanogenesis reaction. Biogas reflow can also play a stirring role, making the substrates, microorganisms and intermediate products in the anaerobic digester more evenly mixed. The carbon dioxide separated from the biogas can be further methanized, reducing external emissions, achieving in-situ treatment of carbon dioxide, reducing intermediate links and reducing costs. The purity of biogas can be improved, and when it reaches a certain purity, it can be directly used as a clean energy source. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a system and application of biogas reflux coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methane production, which solves the problems of limited microbial metabolism in existing anaerobic digestion systems, insufficient substrate utilization, poor system stability, and high carbon dioxide content in biogas that cannot be used directly as fuel.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] The purpose of the present invention is to protect a system and application of biogas reflow coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methanogenesis.

[0009] The MEC anaerobic digestion system completes the anaerobic digestion treatment of organic solid waste and the methanation of carbon dioxide in the reflowing biogas;

[0010] The biogas reflow system completes the separation, collection and reflow of carbon dioxide in the biogas and the collection of purified methane;

[0011] The bioanode plate of the MEC anaerobic digestion system converts organic matter into carbon dioxide and generates electrons, and the electroactive microorganisms attached to the biocathode plate convert carbon dioxide into methane;

[0012] Furthermore, the secondary biogas separation tank in the biogas reflow system separates and purifies the biogas generated by the biological cathode plate;

[0013] Furthermore, the carbon dioxide collection tank in the biogas reflow system collects the carbon dioxide separated by the secondary biogas separation tank and intermittently reflows it to the biological cathode plate of the MEC anaerobic digestion system through a pump;

[0014] Furthermore, the MEC anaerobic digestion system adds organic solid waste through a feed inlet and discharges anaerobic digestion residues through a discharge outlet;

[0015] Furthermore, the secondary biogas separation tank included in the biogas reflow system contains a carbon dioxide separation mixed matrix membrane, in which the mixed zeolite has a strong affinity for carbon dioxide.

[0016] The system for enhancing anaerobic digestion and methanogenesis by biogas reflow coupling with a microbial electrolysis cell (MEC) comprises the following processes:

[0017] The operation process of the MEC anaerobic digestion system: first, the substrate is placed in the reaction tank for a period of time to create an anaerobic environment, then organic solid waste is added through the feed port, and the stirring paddle is turned on;

[0018] Organic solid waste is decomposed into small molecular organic matter and produces protons and electrons under the action of microorganisms on the biological anode plate. The electrons reach the biological cathode plate through the external circuit, and the protons reach the biological cathode plate through the electrolyte and combine with the electrons to produce hydrogen. Methanogens use the electrons at the cathode and the produced hydrogen to reduce carbon dioxide to methane.

[0019] The biogas collection pipe collects the generated biogas and enters the biogas return system.

[0020] Operation process of biogas reflow system: After biogas is collected, it enters the biogas reflow system. The carbon dioxide in the biogas is separated by the first biogas separation tank and enters the carbon dioxide collection tank. The remaining gas enters the second biogas separation tank for further separation. The purified biogas enters the methane collection tank.

[0021] Furthermore, the enriched carbon dioxide is returned to the microbial electrolysis cell to achieve carbon dioxide electromethanation at the anode.

[0022] Furthermore, the system biogas adopts intermittent reflux, and the gas reflux flow rate is controlled not to be higher than 2L / L reactor / min.

[0023] Furthermore, the temperature of the anaerobic digestion reaction zone of the system is 25°C-60°C, and the stirring speed is 60rpm-200rpm.

[0024] Compared with the prior art, the present invention has the following technical advantages:

[0025] 1. The present invention adopts a microbial electrolytic cell anaerobic digestion system to solve the problems of limited microbial metabolism, insufficient substrate utilization, poor system stability, etc. The anaerobic digestion process and the electrochemical process cooperate with each other to enhance the metabolic activity of microorganisms and enhance the compliance of organic solid waste.

[0026] 2. The present invention uses biogas reflow to strengthen the methanogenic reaction and make the substrate, microorganisms and intermediate products in the anaerobic digester more evenly mixed.

[0027] 3. The present invention separates the carbon dioxide in the biogas through a membrane, thereby reducing the carbon dioxide content in the biogas, reducing carbon dioxide emissions, and alleviating the greenhouse effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flow chart of the method for operating the biogas reflow coupled microbial electrolysis cell (MEC) enhanced anaerobic digestion and methanogenesis system.

[0029] Figure 2 It is a schematic diagram of the structure of the biogas reflow coupled microbial electrolysis cell (MEC) enhanced anaerobic digestion and methanogenesis system in the present invention. Specific implementation methods

[0031] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The features such as component models, material names, connection structures, control methods, etc. that are not clearly described in this technical solution are all regarded as common technical features disclosed in the prior art.

[0032] The present embodiment provides a system and application of biogas reflow coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methane production, including a MEC anaerobic digestion system and a biogas reflow system; the MEC anaerobic digestion system and the biogas reflow system are connected via an air pump 8 and a biogas collection pipe 7; the MEC anaerobic digestion system is used for anaerobic digestion of organic solid waste and promoting the conversion of reflowed carbon dioxide into methane, the biogas produced by anaerobic digestion in the microbial electrolysis cell is collected and enters the biogas reflow system, the carbon dioxide in the biogas is separated by a first biogas separation tank 10 and enters a carbon dioxide collection tank 9, the remaining gas enters a second biogas separation tank 11 for further separation, the enriched carbon dioxide is reflowed to the biocathode plate 5 of the MEC anaerobic digestion system to realize carbon dioxide electromethanization, and the biogas reflow system is used to separate carbon dioxide and methane, enrich and reflow carbon dioxide, and collect methane with higher purity.

[0033] The MEC anaerobic digestion system has a bioanode plate 4 and a biocathode plate 5. The bioanode plate 4 provides electrons and protons by oxidizing organic matter. The biocathode plate 5 is close to the biogas reflow system. After carbon dioxide enters the biocathode plate 5, carbon dioxide is methanated, thereby increasing methane production and achieving efficient methanation of hydrolysis acidification products and reflow gas.

[0034] The biogas reflux system includes a secondary biogas separation tank, a methane collection tank 13 and a carbon dioxide collection tank 9; the secondary biogas separation tank can achieve a more efficient separation effect, so that the methane purity in the separated biogas is higher; the carbon dioxide collection tank 9 is to avoid the low concentration of carbon dioxide in the biogas separation tank, and the enriched carbon dioxide can be better refluxed to the biological cathode plate 5 of the MEC anaerobic digestion system through the air pump 8; the methane collection tank 13 is used to store methane with higher purity. The secondary biogas separation tank contains a carbon dioxide separation mixed matrix membrane 12, which contains zeolite that is carbon dioxide-friendly, so that more carbon dioxide can pass through the membrane and enter the enricher, thereby achieving efficient separation of carbon dioxide and methane in biogas.

[0035] The MEC anaerobic digestion system and the biogas return system are connected via an air pump 8 and a biogas collection pipe 7. The biogas collection pipe 7 is used to collect the biogas generated by the MEC anaerobic digestion system and transmit it to the biogas return system; the air pump 8 is used to return the carbon dioxide collected by the carbon dioxide collection tank 9 to the MEC anaerobic digestion system.

[0036] The MEC anaerobic digestion system also includes a stirring paddle 3 and a stirring motor 1 for driving the stirring paddle to rotate; a feed port 2 for adding organic solid waste and a discharge port 6 for discharging residues after anaerobic digestion. The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. Example

[0037] In this example, a system of enhanced anaerobic digestion and methanogenesis by biogas reflow coupled with a microbial electrolysis cell (MEC) was used to treat food waste, wherein the effective volume of the microbial electrolysis cell was 2 L. The food waste was taken from the swill bucket of a university cafeteria, and the substrate was broken into smaller particles of less than 5 mm using a kitchen blender. The solid content (TS) was measured to be 14.50.8%, and the volatile matter ratio (VS / TS) was 95.40.6%.

[0038] The above-mentioned system of using biogas reflow coupled with microbial electrolysis cell (MEC) to enhance anaerobic digestion and methane production to treat food waste operates as follows:

[0039] First, 1900 mL of inoculum sludge from a mesophilic anaerobic digester was added to the microbial electrolysis cell. Nitrogen was introduced into the reactor for 10 minutes to create an anaerobic environment.

[0040] Subsequently, 100 mL of food waste was added into the microbial electrolysis cell through the injection port 2.

[0041] Subsequently, the stirring motor 1 of the microbial electrolysis cell is turned on, and the stirring motor 1 drives the stirring paddle 3 to mix the biogas slurry in the microbial electrolysis cell; the electrochemically active microorganisms on the biological anode plate 4 of the microbial electrolysis cell use the food waste as a substrate to provide protons and electrons through an oxidation reaction, and produce carbon dioxide, and the electrons circulate through the external circuit, and the protons reach the biological cathode plate 5 from the biological anode plate 4, and hydrogen is produced at the cathode, and the methanogens use the protons to convert the carbon dioxide into methane.

[0042] Subsequently, the generated biogas enters the first biogas separation tank 10 through the biogas collection pipe 7, wherein the volume of the biogas separation tank is 1L, and the carbon dioxide passes through the carbon dioxide separation mixed matrix membrane 12 to complete the first carbon dioxide separation; the remaining gas enters the second biogas separation tank 11 to complete the second separation.

[0043] Subsequently, the separated carbon dioxide enters the carbon dioxide collection tank 9, where the volume of the carbon dioxide collection tank is 2L. After carbon dioxide is enriched, it flows back to the vicinity of the biological cathode plate of the microbial electrolysis cell through the air pump 8, and carbon dioxide electromethanization is completed at the biological cathode plate 5; the biogas after separation and purification is upgraded in situ and enters the methane collection tank 13.

[0044] Among them, the biogas return adopts an intermittent cycle, which is turned on every 35 minutes and lasts for 20 minutes.

[0045] Through the operation of this embodiment, the methane production in the anaerobic digestion process increased by 110%, the methane content increased by 82%, and the organic load rate was able to operate stably under the condition of 6gVS / L / day.

[0046] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A system and application of biogas reflow coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methanogenesis, characterized in that: Includes MEC anaerobic digestion system and biogas return system; The MEC anaerobic digestion system completes the anaerobic digestion treatment of organic solid waste and the methanation of carbon dioxide in the reflowing biogas; The biogas reflow system completes the separation, collection and reflow of carbon dioxide in the biogas and the collection of purified methane; The bioanode plate (4) of the MEC anaerobic digestion system converts organic matter into carbon dioxide and generates electrons, and the electroactive microorganisms attached to the biocathode plate (5) convert carbon dioxide into methane; The secondary biogas separation tank (10) (11) in the biogas recirculation system separates and purifies the biogas generated by the biological cathode plate (5); The carbon dioxide collection tank (9) in the biogas reflow system collects the carbon dioxide separated in the secondary biogas separation tank, and intermittently reflows it to the biological cathode plate (5) of the MEC anaerobic digestion system through an air pump (8); The MEC anaerobic digestion system adds organic solid waste through a feed inlet (2) and discharges anaerobic digestion residues through a discharge outlet (6).

2. The system and application of biogas reflow coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methanogenesis according to claim 1, characterized in that: A large number of electroactive microorganisms are attached to the bio-electrodes of the MEC anaerobic digestion system, which can enhance the performance and stability of anaerobic digestion.

3. The system and application of biogas reflow coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methanogenesis according to claim 1, characterized in that: The biogas reflow system comprises a secondary biogas separation tank which contains a carbon dioxide separation mixed matrix membrane (12), wherein the mixed zeolite has a strong carbon dioxide affinity.

4. A system and application of biogas reflow coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methanogenesis as claimed in any one of claims 1 to 3, characterized in that: The process includes: The operation process of the MEC anaerobic digestion system is as follows: first, the substrate is placed in the reaction tank for a period of time to create an anaerobic environment, then organic solid waste is added through the feed port (2), and the stirring paddle (3) is turned on; Organic solid waste is decomposed into small molecular organic matter and produces protons and electrons under the action of microorganisms on the biological anode plate (4). The electrons reach the biological cathode plate (5) through an external circuit. The protons reach the biological cathode plate (5) through an electrolyte and combine with the electrons to produce hydrogen. Methanogens use the electrons at the cathode and the produced hydrogen to reduce carbon dioxide to methane. The biogas collecting pipe (7) collects the generated biogas and enters the biogas return system. The operation process of the biogas reflow system: after the biogas is collected, it enters the biogas reflow system, the carbon dioxide in the biogas is separated by the first biogas separation tank (10) and enters the carbon dioxide collection tank (9), the remaining gas enters the second biogas separation tank (11) for further separation, and the purified biogas enters the methane collection tank (13). The enriched carbon dioxide is returned to the bioanode plate (5) of the MEC anaerobic digestion system to realize carbon dioxide electromethanization.

5. The system and application of biogas reflow coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methanogenesis according to claim 1, characterized in that: The biogas is refluxed intermittently, and the gas reflux flow rate is controlled not to be higher than 2L / L reactor / min.

6. The system and application of biogas reflow coupled microbial electrolysis cell (MEC) to enhance anaerobic digestion and methanogenesis according to claim 1, characterized in that: The temperature of the anaerobic digestion reaction zone is 25°C-60°C, and the stirring speed is 60rpm-200rpm.

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