KR20230114927A - Method for anaerobic digestion for high quality bio_methane production - Google Patents

Abstract

The present invention relates to an anaerobic digestion method for manufacturing high quality biomethane. The anaerobic digestion method can include the steps of: preparing a reactor in which an oxidation electrode and a reduction electrode are placed with an ion exchange membrane therebetween; inoculating the reduction electrode with anaerobic microorganisms; supplying biogas including carbon dioxide to the reduction electrode; applying power to the oxidation electrode and the reduction electrode to cultivate anaerobic microorganisms on the surface of the reduction electrode; and converting carbon dioxide into methane using anaerobic microorganisms cultivated on the surface of the reduction electrode.

Description

Anaerobic digestion method for high quality biomethane production {METHOD FOR ANAEROBIC DIGESTION FOR HIGH QUALITY BIO_METHANE PRODUCTION}

The present invention relates to an anaerobic digestion method for producing high-quality biomethane.

In general, organic waste resources that can be used as raw materials for biogasification include food waste, sewage sludge, livestock manure, agricultural and marine waste resources, and the like. Biogas is traditionally a new and renewable energy that can be produced from a simple device configuration and is a driving force for industrial development. It was initially used as thermal energy for heating and cooking, and is now used as electricity and transportation fuel, and recently converted to hydrogen for fuel cells. As such, energy sources that can be used in various fields are being transformed into sources.

As such, commercialization of biogas continues to take place mainly in Europe, and biogas plants that use biogas to produce electricity and transportation fuel are easily accessible throughout Europe. A method for converting biogas into transportation fuel or city gas is called upgrading. Upgrading is to increase the biomethane content, which is to separate carbon dioxide, which contains more than 40% of biogas, but includes a purification process to remove hydrogen sulfide, siloxane, and organic compounds. The process of upgrading is applied in the range of 90 to 97% depending on the place of use.

As for upgrading technology, various technologies such as absorption, adsorption, and membrane separation have been commercialized, and suitable technologies should be applied in consideration of facility capacity and methane purity for production. The absorption method uses the solubility of carbon dioxide. It is a process of absorbing carbon dioxide under a certain pressure condition and degassing by reducing pressure. Since hydrogen sulfide is also removed, the cost of operating facilities for hydrogen sulfide purification in the front end can be reduced. The chemical absorption method uses amine-based solvents and solvents such as methanol and glycol as absorbents. The adsorption method is a method of separation using pressure adsorption and vacuum desorption using zeolite, which is commercially available to a large extent. It uses the difference in gas permeation of carbon dioxide, and has simple facilities and strengths in terms of maintenance. The purpose of such a facility is to increase the methane content in biogas by separating methane from biogas.

Recently, in relation to the carbon neutral policy, technologies for recycling carbon dioxide are being developed in various fields. Among them, the methanation technology of carbon dioxide using bioelectrochemical technology can be converted into methane with low power consumption by using anaerobic microorganisms. It has high technical value.

Bioelectrochemical technology is a technology that uses electron flow to generate hydrogen (H ⁺ ) ions in an oxidation reactor so that carbon dioxide in biogas can be converted into methane, and the generated H ⁺ ions are supplied to a reduction reactor to generate carbon dioxide by anaerobic microorganisms. is converted to methane. Theoretically, 1 mole of methane is produced from 1 mole of carbon dioxide, and this process requires 8 moles of hydrogen (H ⁺ ) ions.

Accordingly, a technology for increasing energy productivity by converting carbon dioxide into methane is required.

Patent Document: Domestic Patent Registration No. 10-1413142 (2014. 06. 23. Registration)

Embodiments of the present invention were invented against the above background, and to provide an anaerobic digestion method for producing high-quality biomethane capable of increasing the methane content of biogas and improving the amount of power generation and extraction hydrogen by utilizing biomethane. .

According to one aspect of the present invention, preparing a reactor in which an oxidation electrode and a reduction electrode are disposed with an ion exchange membrane interposed therebetween; inoculating anaerobic microorganisms on the cathode; supplying biogas containing carbon dioxide to the cathode side; culturing anaerobic microorganisms on the surface of the cathode by applying power to the anode and the cathode; An anaerobic digestion method for producing high-quality biomethane may be provided, including converting carbon dioxide into methane using anaerobic microorganisms cultured on the surface of a cathode.

At this time, the anaerobic digestion method may further include the step of extracting hydrogen from the carbon dioxide-converted methane in a hydrogen extraction facility.

In addition, in the step of extracting hydrogen from methane in a hydrogen extraction facility, carbon dioxide generated as a by-product in the hydrogen extraction facility may be fed back to the reactor.

In the step of culturing anaerobic microorganisms on the surface of the cathode, a biofilm may be formed by culturing anaerobic microorganisms using hydrogen ions of the anode as a reducing agent on the surface of the cathode.

In the converting of carbon dioxide to methane, a potential difference may be generated between the anode and the cathode so that hydrogen ions are generated at a voltage lower than that of the water decomposition reaction in the reactor.

In addition, the anode may be a platinum felt electrode manufactured by stirring platinum powder (Pt power) and carbon power (Pt power) on graphite felt and coating using polyvinyline fluoride (PVDF). .

In addition, the cathode may provide a porous electrode surface capable of culturing the anaerobic microorganisms.

In addition, the cathode may be a PPY/PDA graphite felt electrode prepared by electrodepositing polypyrrole (PPY) and polydopamine (PDA) on a graphite felt.

In addition, the internal temperature of the reactor satisfies the range of 20 °C to 55 °C, and the anaerobic microorganisms may include fermentation strains capable of activity in the range of 20 °C to 55 °C.

According to the embodiments of the present invention, by using bioelectrochemical technology, the methane content in biogas is increased by 95% or more, and the biogas production is produced without change, so that the amount of power generation and extraction hydrogen can be improved by using biomethane. there is

In addition, according to embodiments of the present invention, produced methane has an effect that hydrogen can be directly produced using a hydrogen extraction facility without separating carbon dioxide, and the amount of extracted hydrogen can be increased.

1 is a block diagram showing an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention.
2 is a flowchart schematically illustrating a process of extracting hydrogen from methane produced by an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention through a hydrogen extraction facility.
Figure 3 extracts hydrogen from methane produced according to the anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention through a hydrogen extraction facility, and carbon dioxide, a by-product generated from the hydrogen extraction facility, is an anaerobic digestion device It is a flow chart schematically showing the feedback process.
4 is a flowchart showing a process in which hydrogen is extracted in a hydrogen extraction facility of an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention.
5 is a block diagram showing an anaerobic digestion apparatus applied to an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention.
6 is a graph showing potential values according to the type of modification of the anode used in the anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention.
7 is a graph showing the potential value according to the type of reforming of the reduction electrode used in the anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention.
8 is a graph showing the methanation reaction rate and current change in carbon dioxide of biogas used in the anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention.

Hereinafter, specific embodiments for implementing the spirit of the present invention will be described in detail with reference to the drawings.

In addition, in the description of the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description will be omitted.

In addition, when a component is referred to as 'connecting', 'supporting', 'connecting', 'supplying', 'transferring', or 'contacting' to another component, it is directly connected to, supported by, or connected to the other component. It may be supplied, delivered, or contacted, but it should be understood that other components may exist in the middle.

Terms used in this specification are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In addition, in this specification, expressions such as upper, lower, side, etc. are described based on the drawings, and it is made clear in advance that they may be expressed differently if the direction of the object is changed. For the same reason, some components in the accompanying drawings are exaggerated, omitted, or schematically illustrated, and the size of each component does not entirely reflect the actual size.

In addition, terms including ordinal numbers, such as first and second, may be used to describe various components, but the components are not limited by these terms. These terms are only used to distinguish one component from another.

As used herein, the meaning of "comprising" specifies specific characteristics, regions, integers, steps, operations, elements, and/or components, and other specific characteristics, regions, integers, steps, operations, elements, elements, and/or groups. does not exclude the presence or addition of

The anaerobic digestion method for producing high-quality biomethane according to the present invention can increase biomethane production by converting carbon dioxide into methane using a bioelectrochemical system (BES or Microbial Electrochemical Synthesis, MES). Here, bioelectrochemical technology can be understood as a technology that can produce electricity and chemical substances such as hydrogen from various biologically degradable organic substances by using a mechanism in which electrically active microorganisms exchange electrons with external electron acceptors.

Hereinafter, a detailed configuration of an anaerobic digestion method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 8.

1 is a block diagram showing an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention, and FIG. 2 is an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention. It is a flowchart schematically showing the process of extracting hydrogen from methane through a hydrogen extraction facility, and FIG. 3 is a hydrogen extraction facility from methane produced according to an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention. It is a flowchart schematically showing the process of extracting hydrogen through and feeding back carbon dioxide, a by-product generated in the hydrogen extraction facility, to an anaerobic digestion device, and FIG. 4 is an anaerobic digestion for producing high-quality biomethane according to an embodiment of the present invention In the hydrogen extraction facility of the method, it is a flow chart showing the process of extracting hydrogen.

As shown in FIGS. 1 to 3, the anaerobic digestion method according to an embodiment of the present invention includes preparing a reactor (S100), inoculating anaerobic microorganisms on a cathode (S200), and biogas Supplying to the cathode side (S300), culturing anaerobic microorganisms (S400), converting carbon dioxide into methane (S500), and extracting hydrogen from a hydrogen extraction facility (S600). can

In the step of preparing the reactor (S100), a reactor of the anaerobic digestion device 10 in which an oxidizing electrode and a reducing electrode are disposed with an ion exchange membrane interposed therebetween is prepared. The oxidation electrode and the reduction electrode may be electrically connected to the power supply. And the internal temperature of the reactor may be maintained in the range of 20 ℃ to 55 ℃.

And in the step of preparing the reactor (S100), the food filtrate, acid fermentation solution, and other wastewater are circulated as a reaction solution in the reactor, so that hydrogen ions are abundantly supplied in the reactor to improve hydrogen production. In this embodiment, the reactor is configured integrally with the anaerobic digestion tank, but depending on the design environment and ambient conditions, the reactor may be manufactured separately from the anaerobic digestion tank in a circular manner.

In addition, in the step of preparing the reactor (S100), the anode is prepared by stirring platinum powder (Pt power) and carbon powder (carbon power) on graphite felt and coating using PVDF (polyvinyline fluoride) It may be a platinum felt electrode. If the anode is made of a platinum felt electrode, it is possible to prevent the potential from becoming unstable due to oxidation of the anode through a water decomposition reaction, and since the potential is lower than that of the graphite felt, methanation power can be reduced.

In addition, in the step of preparing the reactor (S100), the cathode may be a PPY/PDA graphite felt electrode prepared by electrodepositing polypyrrole (PPY) and polydopamine (PDA) on graphite felt. can When polypyrrole (PPY) and polydopamine (PDA) are electrodeposited on graphite felt and applied to the reactor, anaerobic microorganisms form a biofilm on the cathode, allowing them to be cultured at high concentrations, compared to using graphite felt alone. Carbon dioxide can be converted to methane under conditions of low potential difference.

In the step of inoculating the cathode with anaerobic microorganisms (S200), anaerobic microorganisms using carbon dioxide as a substrate may be inoculated on the surface of the cathode. Anaerobic microorganisms may include fermentation strains capable of activity in the range of 20 ° C to 55 ° C.

In the step of supplying the biogas to the cathode side (S300), the biogas containing carbon dioxide in the anaerobic digestion tank 500 is supplied to the cathode side of the anaerobic digestion device 10. At this time, the biogas may undergo a purification and dehumidification process. In this embodiment, biogas (10,000 Nm ³ /d) may include methane (CH ₄ ) 65% and carbon dioxide (CO ₂ ) 35%, as well as H ₂ S, NH ₃ , and silozane.

And in the step of supplying the biogas to the cathode side (S300), in order to effectively supply the biogas containing carbon dioxide to the cathode, a separate stirring device or an internal circulation pump is used to biogas dissolved in the reaction solution. can be supplied to the anaerobic microorganisms of the cathode.

In the step of culturing the anaerobic microorganisms (S400), anaerobic microorganisms may be cultured on the surface of the cathode by applying power to the anode and the cathode. For the cultivation of anaerobic microorganisms, KH ₂ PO ₄ , K ₂ HPO ₄ , NH ₄ Cl, NaHCO ₃ , MgSO ₄ , CaCl ₂ , trace elements, vitamins can be used as a microbial medium, acid fermentation broth or carbon source and mineral ) can be used in place of the medium.

In the step of converting carbon dioxide into methane (S500), high-quality methane can be produced by converting carbon dioxide into methane using anaerobic microorganisms cultured on the surface of the cathode. For example, when 10,000 Nm ³ /d of biogas (including 65% CH ₄ and 35% CO ₂ ) is introduced into the reactor, 356 Nm ³ /h of methane (CH ₄ ) may be produced in the reactor.

In the step of extracting hydrogen from the hydrogen extraction facility (S600), hydrogen may be extracted from methane converted from carbon dioxide in the hydrogen extraction facility 20. For example, when 356 Nm ³ /h of methane (CH ₄ ) is introduced into the hydrogen extraction facility 20 in the reactor of the anaerobic digestion device 10, 791.4 Nm ³ /h of hydrogen can be produced in the hydrogen extraction facility there is.

In more detail, as shown in FIG. 4, in the hydrogen extraction facility, hydrogen may be extracted through a steam methane reforming process (SMR), water gas shift (WGS), and pressure swing adsorption (PSA).

For example, in the steam methane reforming process (SMR) of a hydrogen extraction facility, methane (CH ₄ ) may be reacted with steam to produce carbon monoxide (CO) and hydrogen (H ₂ ). At this time, a strong endothermic reaction occurs, and nickel is mainly used as a catalyst. . Then, steam is injected so that the steam-hydrocarbon ratio is usually 3.0. This is to enhance the main reaction of the hydrogen extraction facility and suppress the side reaction that produces soot. In addition, in order to obtain the heat required for the reaction, the hydrogen extraction facility mainly burns and uses some of the tail gas and feed gas of the downstream PSA. For example, in the inlet condition of the SMR, the temperature may be about 500 to 550 degC and the pressure may be about 10 kg/cm ² g, and in the outlet condition, the temperature is about 800 to 850 degC and the pressure is about 9 kg/cm. It may be ² g. And Steam-Carbon ratio = 3, Catalyst can be Nickel catalyst, and Reaction can be CH4 + H20 + Heat ↔ CO + 3H ₂ (Endothermic reaction).

In addition, in the water gas shift (WGS) of the hydrogen extraction facility, carbon monoxide (CO) generated in the SMR reacts with water (H ₂ O) to produce carbon dioxide (CO ₂ ), and additional hydrogen can be produced. Residual hydrogen may be generated by supplying steam (H ₂ O) to carbon monoxide (CO) generated in the primary reaction. The reaction is divided into a high temperature transition reaction (HTS) reacting in the range of 300 ~ 400degC, and a low temperature transition reaction (LTS) in the range of 200 ~ 250degC. The high-temperature transition reaction mainly uses iron-oxide-based catalysts, and the reaction is fast due to the high temperature, but the carbon monoxide (CO) conversion rate is low. The low-temperature transition reaction mainly uses a Cu-based catalyst, and the reaction is slow, but the carbon monoxide (CO) conversion rate is high. For example, in the inlet condition of WGS, the temperature may be about 350 degC and the pressure may be about 8.5 kg/cm ² g, and in the outlet condition, the temperature may be about 420 degC and the pressure may be about 8.3 kg/cm ² g, and Catalyst is mainly an iron oxide-based catalyst (Fe ₂ O ₃ ), and the reaction may be CO + H ₂ 0 ↔ CO ₂ + H ₂ + Heat (Exothermic reaction).

In addition, in the PSA of the hydrogen extraction facility, hydrogen generated from SMR and WGS can be separated. At this time, carbon dioxide and hydrogen are separated, and the hydrogen concentration is possible up to 99.9999% (generally, only about 99.995% is separated). Hydrogen (H ₂ ) recovery may be about 80 to 85%, and the remaining tail gas after separating hydrogen (H ₂ ) can be generally used as a process for reusing as a heat source for SMR. For example, in the inlet condition of the PSA, the temperature may be about 40 degC and the pressure may be about 8 kg/cm g, and in the outlet condition, the temperature may be about 40 degC and the pressure may be about 7.5 kg/cm ² g, and hydrogen (H ₂ ) Purity is greater than 99.995%, and hydrogen (H ₂ ) Recovery may be in the range of 80 to 85%.

In the step of extracting hydrogen from methane in a hydrogen extraction facility, carbon dioxide generated as a by-product in the hydrogen extraction facility may be fed back to the reactor. For example, when 356 Nm ³ /h of methane (CH ₄ ) is input from the reactor to the hydrogen extraction facility, and 14,196 kg CO ₂ /d of carbon dioxide generated in the hydrogen extraction facility is fed back to the reactor, 312 Nm ³ / methane of h can be additionally produced and put back into the hydrogen extraction facility. The hydrogen extraction facility can additionally produce 693.5.4 Nm ³ /h of hydrogen.

Hereinafter, the configuration and operation of the anaerobic digestion apparatus used in the anaerobic digestion method having the above configuration will be described in detail.

5 is a block diagram showing an anaerobic digestion apparatus applied to an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention, and FIG. 6 is a block diagram for producing high-quality biomethane according to an embodiment of the present invention. It is a graph showing the potential value according to the type of modification of the oxidation electrode used in the anaerobic digestion method, and FIG. 8 is a graph showing a potential value, and FIG. 8 is a graph showing the methanation reaction rate and current change in carbon dioxide of biogas used in an anaerobic digestion method for producing high-quality biomethane according to an embodiment of the present invention.

5 to 8, the anaerobic digestion device 10 according to the present invention includes a reactor 100, an oxidation electrode 210, a reduction electrode 220, a reference electrode 230, an ion exchange membrane 300 , It may include a power supply 400 and an anaerobic digestion tank 500.

Specifically, the reactor 100 may provide a plurality of chambers. For example, the reactor 100 may include a first chamber 110 in which an anode 210 is disposed and a second chamber 120 in which a cathode 220 is disposed. The first chamber 110 may include a first chamber unit 111 disposed on one side of the inside of the reactor 100 and an oxygen exhaust unit 112 provided on an upper portion of the first chamber unit 111 . The oxygen discharge unit 112 may guide and discharge oxygen generated from the anode 210 to the outside.

The second chamber 120 of the reactor 100 includes a second chamber part 121 disposed on the other side of the inside of the reactor 100, and a gas inlet part 122 provided on one side wall of the lower part of the second chamber part 121. ) and a gas discharge unit 123 provided on the upper part of the second chamber unit 121. The second chamber unit 121 may be connected in communication with the first chamber unit 111 of the first chamber 110 with the ion exchange membrane 300 interposed therebetween. The gas inlet 122 is connected between the second chamber 121 and the anaerobic digestion tank 500 of the reactor 100 to deliver the biogas supplied from the anaerobic digestion tank 500 to the second chamber 121 can The gas discharge unit 123 may provide an outlet for discharging the gas generated in the second chamber unit 121 to the outside.

At this time, the installation interval of the ion exchange membrane 300 installed between the first chamber 110 and the second chamber 120 is kept as short as possible. For example, when the reactor 100 is circular, the ion exchange membrane 300 may be installed at a distance within a radius of the reactor 100, and when the reactor 100 is rectangular, the ion exchange membrane 300 is The first chamber 110 and the second chamber 120 may be installed at a distance within 1/2 of the sum of the widths of the installation surfaces. In addition, a physical cleaning method and a chemical cleaning method may be applied to the surfaces of the first chamber 110 and the second chamber 120 in order to minimize membrane contamination due to the adhesion of biological metabolites and sludge. The dissolution of carbon dioxide in the first chamber 110 and the second chamber 120 may be performed using a membrane dissolving method, a pressure mixing method, or a pressure distribution method.

The internal temperature of the reactor 100 may be maintained in the range of 20 °C to 55 °C. To this end, a heater (not shown) may be provided inside the reactor 100 to maintain the internal temperature of the reactor 100 in the range of 20 °C to 55 °C. Since the internal temperature of the reactor 100 is maintained in the range of 20 °C to 55 °C, the anaerobic microorganisms cultured in the reactor 100 may be fermentation strains that can be active in the range of 20 °C to 55 °C. This is because the internal temperature of the reactor 100 should simultaneously examine the temperature conditions for culturing anaerobic microorganisms and the solubility of carbon dioxide according to the temperature.

For example, in the case of operating conditions in which carbon dioxide is directly injected into the reactor 100, the minimum temperature at which methane strains can be cultured while maximizing carbon dioxide solubility is around 20 degrees, but the growth rate of methane strains is quite slow, due to the high solubility of carbon dioxide However, the substrate decomposition rate is not high. Under these conditions, when the temperature increases, the solubility decreases, and the anaerobic microorganisms use carbon dioxide as a substrate to reduce the carbon source, which acts as a disadvantage in that the concentration of the anaerobic microorganisms can be maintained low.

Therefore, anaerobic microorganisms growing in the reactor 100 can be cultured by classifying them into medium temperature (35 to 38 degrees) and high temperature (50 to 55 degrees) conditions. Mesophilic anaerobic microorganisms have a slow substrate decomposition rate, but can be stably cultured. However, high-temperature anaerobic microorganisms have a fast substrate decomposition rate, so they are suitable when a carbon source as a substrate is input with a high load. tends to decrease over time. In addition, when the temperature of the cathode reactor is 38 degrees or more and less than 55 degrees, carbon dioxide is recycled to overcome the low solubility of carbon dioxide, thereby increasing the contact efficiency between carbon dioxide and anaerobic microorganisms, thereby increasing the decomposition rate of carbon dioxide.

On the other hand, in the case of operating conditions in which carbon dioxide is dissolved and then introduced into the reactor 100, carbon dioxide is lowered to 10 degrees or less and injected into the reactor 100 after dissolving carbon dioxide under pressurized conditions in the range of 10 to 20 bar, so anaerobic methanation The strain can be cultured at a high concentration, and the carbon dioxide discharged to the top can be recycled to operate under conditions in which carbon dioxide is stably supplied.

A reaction liquid may be filled in the reactor 100 . For example, the reaction solution may be process water. Of course, it is not limited thereto, and in addition to process water, an acid fermentation solution rich in a reducing agent, an anaerobic digestion dehydration filtrate, or ammonia-containing wastewater may be used as the reaction solution.

The oxidation electrode 210 may be a counter electrode opposite to the reduction electrode 220 . The oxidation electrode 210 may be disposed on one side inside the reactor 100, that is, in the first chamber 110, and electrically connected to the power supply device 400. The oxidation electrode 210 may receive power from the power supply 400 and generate hydrogen ions through electrolysis. In the first chamber 110 where the oxidation electrode 210 is disposed, a reaction as shown in Scheme 1 below may proceed.

[Scheme 1]

2H ₂ O → O ₂ + 4H ⁺ + 4e ^-

The oxidation electrode 210 may be used in the form of a carbon-based sponge (Graphite felt). In addition, as the oxidation electrode 210, a catalyst electrode using platinum or rubidium for accelerating the water decomposition reaction may be used.

However, a water decomposition reaction should occur smoothly in the oxidizing electrode 210, but the potential may become unstable due to oxidation of the oxidizing electrode 210 during long-term operation. To solve this problem, the oxidation electrode 210 may be modified and used. For example, the anode 210 is a platinum felt coated with graphite felt by stirring platinum powder (Pt power) and carbon powder (carbon power) and using PVDF (polyvinyline fluoride). It can be modified and used as an electrode.

When a conventional graphite felt electrode is used as the anode 210, the total voltage applied to the reactor 100 is 2.9 to 3.1V, whereas a platinum felt electrode is used as the anode 210. At this time, it was confirmed that the total voltage added to the reactor 100 was reduced to a value of 2.5 to 2.7V. Accordingly, it can be expected that the cost of methane production per rube can also be reduced.

The reduction electrode 220 may be a working electrode that converts carbon dioxide into methane by anaerobic microorganisms using carbon dioxide as a substrate. In order to convert carbon dioxide into methane by anaerobic microorganisms, the reduction electrode 220 may use hydrogen ions generated at the oxidation electrode 210 as a reducing agent.

The cathode 220 may be used in the form of a carbon-based sponge (Graphite felt). The cathode 220 may be used in the form of graphite paper, graphite felt brush, or stainless steel mesh.

The cathode 220 may provide a porous electrode surface capable of cultivating anaerobic microorganisms. Since the cathode 220 is provided in the form of a porous mesh, strains such as hydrogentrophic methanogen, a methane-converting microorganism using carbon dioxide as a substrate, and electromethanogen on the surface of the electrode can be cultured at high concentration on the surface of the porous electrode of the cathode 220.

The reduction electrode 220 may be modified and used. For example, the cathode 220 may be modified with a PPY/PDA graphite felt electrode prepared by electrodepositing polypyrrole (PPY) and polydopamine (PDA) on a graphite felt. As a conductive polymer, polypyrrole (PPY) has high conductivity and chemical stability. Polydopamine (PDA) is a polymer that mimics the adhesive protein of mussels, and has properties that adhere well to various surfaces, as well as high biocompatibility and excellent hydrophilicity. When only the graphite felt was applied to the reduction electrode 220, the total voltage of the reactor 100 showed a value of 2.9 to 3.1 V, whereas when the PPY/PDA graphite felt electrode was applied to the reduction electrode 220 , the total voltage of the reactor 100 showed a low value of 2.4 ~ 2.6V.

The cathode 220 may be disposed on the other side of the reactor 100, that is, in the second chamber 120, and electrically connected to the power supply 400. In the second chamber 120 where the reduction electrode 220 is disposed, a reaction as shown in Scheme 2 below may proceed.

[Scheme 2]

CO ₂ + 8H ⁺ + 8e ^- → CH ₄ + 2H ₂ O

CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O

To this end, a biofilm 221 in which anaerobic microorganisms are cultured may be formed on the surface of the cathode 220 . For the cultivation of anaerobic microorganisms, KH ₂ PO ₄ , K ₂ HPO ₄ , NH ₄ Cl, NaHCO ₃ , MgSO ₄ , CaCl ₂ , trace elements, vitamins can be used as a microbial medium, acid fermentation broth or carbon source and mineral ) can be used in place of the medium.

Here, the biofilm 221 may be understood as a culture layer of anaerobic microorganisms cultured to a predetermined thickness in a state in which anaerobic microorganisms are inoculated on the surface of the cathode 220 . Anaerobic microorganisms of the biofilm 221 may generate methane by receiving hydrogen ions from the anode 210 .

In the evaluation of the microbial strain according to the present invention, after confirming that the main methane conversion populations are attached to the electrode, biofilms are formed in the methane conversion bioelectrochemical reactor 100 using a Serum bottle The cathode 220 and the culture solution were separated and cultured. In the case of an experiment using a cerium container, hydrogen (H ₂ ) gas was supplied to supply reducing power.

As a result of the experiment, consumption of carbon dioxide and hydrogen (H ₂ ) gas could be confirmed only in the cerium container into which the reduction electrode 220 on which the biofilm was formed was put. There was no generation or consumption of gas in the CEROM container into which only the liquid phase was input. This indicates that the biofilm 221 attached to the surface of the cathode 220 played a major role in generating methane (CH ₄ ) from carbon dioxide (CO ₂ ).

In addition, it was confirmed that a specific population on the electrode was cultured through subculture of the cerium container, and the methane conversion rate using carbon dioxide increased by setting in the new bioelectrochemical reactor 100. The final methane content was 97%, and the production rate was 2.9L CH ₄ /m ² cat/hour per electrode area. Strain analysis through NGS (next-generation sequencing) analysis is shown in Table 1 below.

[Table 1]

The anaerobic microorganism used in this embodiment may include a methane producing species mainly suspended in the reactor 100 and an acetate producing species mainly attached to the reduction electrode 220 . Methane producing species may include Methanobacterium movens, Methanobacterium petrolearium, Methanobacterium subterraneum, Methanobrevibacter arboriphilus, Methanothrix soehngenii. Acetate producing species may include Proteiniphilum acetatigenes, Proteiniphilum saccharofermentans, Acetivibrio alkalicellulosi, and Soehngenia saccharolytica.

Meanwhile, the reference electrode 230 may be provided in the second chamber 120 . The reference electrode 230 is an electrode that is a reference for a potential for generating a potential, and may be positioned adjacent to the working electrode, the reduction electrode 220 . For example, the reference electrode 230 may be an Ag/AgCl electrode.

The ion exchange membrane 300 may be installed between the first chamber 110 in which the oxidation electrode 210 is disposed and the second chamber 120 in which the reduction electrode 220 is disposed. The ion exchange membrane 300 may transfer hydrogen ions (H ⁺ ) generated in the first chamber 110 by the anode 210 to the second chamber 120 where the cathode 220 is disposed. In this embodiment, a cation exchange membrane (proton exchange membrane (PME)) is used as the ion exchange membrane 300, but in addition to the cation exchange membrane, the ion exchange membrane 300 may be made of a cation separator, a nonwoven fabric, a ceramic separator, an ion exchange separator, or the like. there is.

The power supply 400 may supply power to the anode 210 and the cathode 220 . When the power supply 400 supplies power to the oxidation electrode 210 and the reduction electrode 220 through an electric circuit, reduction potential or reduction current may be applied to the reduction electrode 220, and the oxidation electrode 210 The electrons (e ⁻ ) generated in may move to the reduction electrode 220.

Further, the power supply device 400 may generate a potential difference between the oxidizing electrode 210 and the reducing electrode 220 so that hydrogen ions are generated at a voltage lower than that of the water decomposition reaction in the reactor 100 . For example, the potential applied to the reactor 100 using a potentiometer may be 1.0V (vs. Ag/AgCl).

At this time, a device called Potentiostat may be used to control the power supply to generate hydrogen (H ⁺ ) ions at a voltage lower than that of the water decomposition reaction. Theoretically, for hydrogen gas generation through water decomposition reaction, E total = Ecathode - Eanode: -0.83V - (0.40V) = -1.23V (25 degrees, pH = 0, standard condition) voltage should be applied. If a carbon-based electrode is used, there is a disadvantage in that a voltage higher than the theoretical voltage must be applied due to the overpotential of the electrode. In the experimental method used in the present invention, the hydrogen generation reaction was confirmed using a GC equipment, and hydrogen gas generation was confirmed when applied over -1.1V (vs.Ag/AgCl), so below that, -1.0V ( When vs.Ag/AgCl) voltage was applied, hydrogen peak was not confirmed on GC (Gas chromatography), and when voltage lower than -1.0V was applied, carbon dioxide (CO ₂ ) was used to remove methane (CH ₄ ) It was confirmed that the conversion rate was significantly slowed down. When carbon-based electrode is used, the suggested range is based on cathode (-0.8 _~ -1.0V vs. Ag/AgCl, when using carbon-based electrode). Methane (CH ₄ ) conversion is performed by using an electrode with high conductivity, such as platinum, based on cathode (-0.5 ~ -0.8 V vs. Ag/AgCl), and methane is supplied with H+ and electrons without generating hydrogen (g). Conversion is possible.

When hydrogen ions (H ⁺ ) generated at a voltage lower than that of the water decomposition reaction are supplied to the reduction electrode 220 using the potential difference between the oxidation electrode 210 and the reduction electrode 220, the reduction electrode 220 side to anaerobic microorganisms Carbon dioxide can be converted into methane as a substrate. In particular, since hydrogen ions neutralize pH while being converted into bicarbonate, carbonate, etc. when carbon dioxide is dissolved, hydrogen ions can play an important role in maintaining the activity of anaerobic microorganisms.

For example, in the case of the second chamber 120, which is a reduction chamber containing anaerobic microorganisms, the pH range for methanogen growth is between 6.5 and 8.2 pH, and as a result of the experiment, it is also in the range of 6.5 to 8.2 pH It was confirmed that the In order to maintain an appropriate pH, potassium monohydrogen phosphate (K ₂ HPO ₄ ) and potassium dihydrogen phosphate (KH ₂ PO ₄ ) may be used to maintain the appropriate pH, but when carbon dioxide is dissolved, the bicarbonate effect The pH can be maintained between 7.8 and 8.2.

The applied pH range proposed in the present invention is 6.5 to 8.2 pH range in the reducing solution, and anaerobic microorganisms can be grown and cultured. When the pH is higher than 8.2 pH, the conversion rate of methane (CH ₄ ) using carbon dioxide (CO ₂ ) may be significantly reduced. In the case of the first chamber 110, which is an oxidation chamber (Anode chamber), the pH is reduced to the 2-3 pH range due to the water decomposition reaction, and under the condition that hydrogen ions are enriched, carbon dioxide corresponding to the same molar mass is dissolved and supplied It must be dissolved for methanation by bioreaction to occur.

The anaerobic digestion tank 500 may supply biogas containing carbon dioxide to the reduction electrode 220 side. At this time, the biogas of the anaerobic digestion tank 500 is supplied to the reactor 100 through a hydrogen sulfide adsorber, so that hydrogen sulfide (H ₂ S) contained in the biogas can be removed. The anaerobic digestion tank 500 may supply methane and carbon dioxide generated by decomposing organic matter remaining in the treated water to the reactor 100. In this embodiment, biogas may consist of 65% methane (CH ₄ ) and 35% carbon dioxide (CO ₂ ).

For example, the anaerobic digester 500 injects biogas (CH ₄ 65%, CO ₂ 35%) into the reactor 100 for 20 minutes (40ml/min), complete gas replacement of the headspace in the reactor And, it can be operated in a batch type by connecting a syringe from the outside of the reactor 100.

Although the embodiments of the present invention have been described as specific embodiments, this is merely an example, and the present invention is not limited thereto, and should be construed as having the widest scope according to the basic ideas disclosed herein. A person skilled in the art may implement a pattern of a shape not indicated by combining/substituting the disclosed embodiments, but this also does not deviate from the scope of the present invention. In addition, those skilled in the art can easily change or modify the disclosed embodiments based on this specification, and it is clear that such changes or modifications also fall within the scope of the present invention.

10: anaerobic digestion device
100: reactor 110: first chamber
111: first chamber unit 112: gas inlet unit
113: gas discharge unit 120: second chamber
121: second chamber unit 122: oxygen discharge unit
210: oxidation electrode 220: reduction electrode
230: reference electrode 300: ion exchange membrane
400: power supply 500: anaerobic digester

Claims (9)

Preparing a reactor in which an anode and a cathode are disposed with an ion exchange membrane interposed therebetween;
inoculating anaerobic microorganisms on the cathode;
supplying biogas containing carbon dioxide to the cathode side;
culturing anaerobic microorganisms on the surface of the cathode by applying power to the anode and the cathode;
Containing the step of converting carbon dioxide into methane using anaerobic microorganisms cultured on the surface of the cathode,
Anaerobic digestion method for high-quality biomethane production. According to claim 1,
Further comprising the step of extracting hydrogen from carbon dioxide converted methane in a hydrogen extraction facility,
Anaerobic digestion method for high-quality biomethane production. According to claim 2,
The step of extracting hydrogen from methane in a hydrogen extraction facility,
Feeding back the carbon dioxide generated as a by-product in the hydrogen extraction facility to the reactor,
Anaerobic digestion method for high-quality biomethane production. According to claim 1,
The step of culturing anaerobic microorganisms on the surface of the cathode,
Forming a biofilm by culturing anaerobic microorganisms using hydrogen ions of the anode as a reducing agent on the surface of the cathode,
Anaerobic digestion method for high-quality biomethane production. According to claim 1,
The step of converting the carbon dioxide to methane,
Generating a potential difference between the oxidizing electrode and the reducing electrode so that hydrogen ions are generated at a voltage lower than the water decomposition reaction in the reactor,
Anaerobic digestion method for high-quality biomethane production. According to claim 1,
The anode is
A platinum felt electrode prepared by stirring platinum powder (Pt power) and carbon powder (Pt power) and carbon power in a graphite felt and coating using polyvinyline fluoride (PVDF),
Anaerobic digestion method for high-quality biomethane production. According to claim 1,
The reduction electrode is
Providing a porous electrode surface on which the anaerobic microorganisms can be cultured,
Anaerobic digestion method for high-quality biomethane production. According to claim 1,
The reduction electrode is
A PPY/PDA graphite felt electrode prepared by electrodepositing polypyrrole (PPY) and polydopamine (PDA) on graphite felt,
Anaerobic digestion method for high-quality biomethane production. According to claim 1,
The internal temperature of the reactor is
Satisfies the range of 20 ℃ to 55 ℃,
The anaerobic microorganisms
Including a fermentation strain capable of activity in the range of 20 ℃ to 55 ℃,
Anaerobic digestion method for high-quality biomethane production.