Two-phase anaerobic digestion system with increased biogas production

Abstract

The present invention relates to a two-phase anaerobic digestion system with increased biogas production. Biochar is applied to an anaerobic digestion system in which an acid fermentation and a methane fermentation are separately performed such that the anaerobic digestion efficiency of organic waste is improved, and thus biogas production can be increased.

Description

Two-phase anaerobic digestion system with increased biogas production

[0001] The present invention relates to a two-phase anaerobic digestion system with increased biogas production, and more specifically, to an anaerobic digestion system and an anaerobic digestion method that can increase both the anaerobic digestion efficiency and biogas production of organic waste by applying biochar to a two-phase anaerobic digestion system in which acid fermentation and methane fermentation are performed separately.

[0002] The present invention was carried out under Project No. 202303-0401 with the support of the Ministry of Climate, Energy and Environment of the Republic of Korea, the research management agency for the said project is the National Water Industry Cluster Project Group, the research project name is "Demand-based Carbon Neutral Water Technology Demonstration Support Project," the research task name is "Demonstration of Biogas Production Increase Technology Using Sewage Sludge-derived Biochar," the lead organization is Choi Lab Co., Ltd., and the research period is May 31, 2023 – December 31, 2025.

[0003] This patent application claims priority to Korean Patent Application No. 10-2024-0199298 filed with the Korean Intellectual Property Office on December 27, 2024, the disclosures of said patent application are incorporated herein by reference.

[0004] Biogas is produced by undergoing an anaerobic digestion process using microorganisms on organic waste such as livestock manure, food waste, and sewage sludge. It consists primarily of methane and carbon dioxide, containing trace amounts of hydrogen sulfide and siloxanes as impurities. Biogas production is attracting global attention as it allows for the disposal of over 65 million tons of organic waste annually without resorting to landfilling or incineration, while simultaneously producing methane gas that can be used as an energy source. In particular, in Korea, following the implementation of the "Act on the Promotion of Production and Utilization of Biogas Using Organic Waste Resources," commonly known as the "Biogas Act," in December 2023, penalties are imposed for failure to meet biogas production targets; consequently, technologies to increase biogas production volume are required to ensure sufficient quantities are generated.

[0005] Accordingly, the inventors confirmed that when the acid fermentation process and the methane fermentation process are separated in the anaerobic digestion process so that the fermented products generated in each fermentation process are treated individually, the digestion efficiency of organic waste is improved, and biogas production can be further increased through the input of biochar during the process.

[0006]

[0007] Accordingly, the objective of the present invention is to provide a two-phase anaerobic digestion system capable of producing biogas by anaerobic digesting organic waste.

[0008] Another objective of the present invention is to provide a method for producing biogas by two-phase anaerobic digestion of organic waste.

[0009] The present invention relates to a two-phase anaerobic digestion system with increased biogas production. Through the anaerobic digestion system of the present invention, acid fermentation and methane fermentation of organic waste are carried out sequentially, thereby increasing the efficiency of biogas production.

[0010] The present invention will be described in more detail below.

[0011]

[0012] One embodiment of the present invention relates to a two-phase anaerobic digestion system comprising: an acid fermentation unit in which acid fermentation of organic waste is performed; and a methane fermentation unit in which methane fermentation of the acid fermentation liquid produced in the acid fermentation unit is performed.

[0013] In the present invention, organic waste refers to waste consisting mainly of organic matter derived from the natural world or from human industrial activities, and may be one or more selected from the group consisting of sludge, livestock manure, food waste, agricultural by-products, forestry by-products, fishery by-products, and microalgae. Examples of agricultural by-products include coffee grounds, oilseed meal, straw, rice husks, etc. Examples of forestry by-products include fallen leaves, tree bark, fruit, weeds, grass, etc. Examples of fishery by-products include seashells, crustacean shells, internal organs, fish scales, fish heads, etc., but are not limited thereto.

[0014] In one embodiment of the present invention, the acid fermentation section or the methane fermentation section may be one in which biochar is introduced during the acid fermentation process or the methane fermentation process.

[0015] In the present invention, biochar refers to an organic carbon mass obtained by carbonizing organic waste by pyrolyzing it in a reducing atmosphere of low oxygen to anaerobic oxygen. For example, biochar can be produced by pyrolyzing one or more organic wastes selected from the group consisting of sludge, livestock manure, food waste, agricultural by-products, forestry by-products, fishery by-products, and microalgae.

[0016] When an appropriate amount of biochar is introduced into the anaerobic digestion process, the biochar can provide minerals, adsorb reaction inhibitors within the anaerobic digester, and immobilize microorganisms. Consequently, the activity of fermenting microorganisms is increased, which reduces the lag phase at the beginning of the anaerobic digestion process and increases the decomposition efficiency of the anaerobic digestion feed and methane production.

[0017] However, when an excessive amount of biochar is added, electron transfer between microorganisms is inhibited, and a large amount of components required for anaerobic digestion are adsorbed onto the biochar, which may actually inhibit the anaerobic digestion reaction and reduce feed decomposition efficiency and methane production.

[0018] Accordingly, the efficiency of the system can be improved by adding an appropriate amount of biochar during the anaerobic digestion of organic waste through the two-phase anaerobic digestion system according to the present invention, and biochar can be added in an amount of 0.5 to 20 g / L, such as 0.5 g / L, 1 g / L, 2 g / L, 5 g / L, 10 g / L, or 20 g / L.

[0019] In one embodiment of the present invention, the system may further include a receiving portion that receives organic waste introduced as a feed for anaerobic digestion.

[0020] In one embodiment of the present invention, the system may further include a pretreatment unit in which pretreatment of organic waste is performed.

[0021] In one embodiment of the present invention, the pretreatment unit may perform one or more operations selected from the group consisting of drying, crushing, composting, microbial decomposition, pyrolysis, sorting, and classification on organic waste.

[0022] In one embodiment of the present invention, the system may further include a carbonization unit in which biochar is produced through the carbonization of organic waste.

[0023] In one embodiment of the present invention, the carbonization part may operate at 300 to 800 ℃.

[0024] In one embodiment of the present invention, the system may further include a collection unit in which biogas generated in an acid fermentation unit or a methane fermentation unit is collected.

[0025] In the present invention, biogas refers to a gas generated when organic matter is decomposed by microorganisms under anaerobic conditions, such as oxygen-free or low-oxygen conditions. It is primarily composed of methane and carbon dioxide, but may also include other gases such as nitrogen, hydrogen, oxygen, hydrogen sulfide, water, and ammonia. At this time, gases other than methane, which can be used as energy sources or materials for chemical synthesis, are treated as impurities in the biogas production process and may be separated from methane during the purification and upgrading process following the capture of biogas. However, considering that gases such as carbon dioxide, nitrogen, hydrogen, and oxygen are also widely utilized in various industrial fields, purification and upgrading operations may be performed on each of these gases as well, thereby converting them into high-purity gas resources.

[0026] In one embodiment of the present invention, the collection unit may perform the compression, storage, purification, or upgrading of biogas.

[0027] In one embodiment of the present invention, the system may further include a byproduct treatment unit in which the anaerobic digestion byproduct generated in the acid fermentation unit or the methane fermentation unit is treated.

[0028] In one embodiment of the present invention, the byproduct processing unit may perform drying, maturation, aging, or crushing operations on the anaerobic digestion byproduct.

[0029] Another aspect of the present invention relates to a two-phase anaerobic digestion method comprising: an acid fermentation step for acid fermenting organic waste; and a methane fermentation step for methane fermenting the acid fermentation liquid obtained from the acid fermentation step.

[0030] In one embodiment of the present invention, the acid fermentation step or the methane fermentation step may involve the additional addition of biochar to organic waste or acid fermentation liquid.

[0031] The present invention relates to a two-phase anaerobic digestion system with increased biogas production. Through the anaerobic digestion system of the present invention, the acid fermentation process and the methane fermentation process of organic waste are performed separately, thereby improving both the anaerobic digestion efficiency and the biogas production efficiency.

[0032] FIG. 1 is a schematic diagram showing the configuration of a two-phase anaerobic digestion system according to one embodiment of the present invention.

[0033] FIG. 2 is a flowchart schematically illustrating a two-phase anaerobic digestion method according to one embodiment of the present invention.

[0034] Figure 3 is a graph showing the total mineral content of six types of biochars prepared with different raw materials according to one embodiment of the present invention.

[0035] Figure 4 is a graph showing the relative biogas production when six types of biochar, each made from different raw materials according to one embodiment of the present invention, are introduced into a methane fermentation tank (AD) or into an acid fermentation tank (Acid).

[0036] Figure 5 is a graph showing the relative methane production when six types of biochar, each prepared from different raw materials according to one embodiment of the present invention, are introduced into a methane fermentation tank (AD) or into an acid fermentation tank (Acid).

[0037] Figure 6 is a graph showing a comparison of relative biogas production over time when biochar produced from sludge according to one embodiment of the present invention is fed into a methane fermentation tank (AD) or into an acid fermentation tank (Acid).

[0038] The present invention will be described in detail below with reference to the accompanying drawings. However, the detailed description disclosed below, together with the accompanying drawings, is intended to describe exemplary embodiments of the present invention and does not represent the only form in which the present invention may be practiced.

[0039] In some cases, known structures may be omitted to avoid obscuring the concept of the invention, and the same components are described using the same reference numerals throughout this specification.

[0040] Throughout this specification, "%" used to indicate the concentration of a particular substance is (weight / weight)% for solid / solid, (weight / volume)% for solid / liquid, and (volume / volume)% for liquid / liquid, unless otherwise noted.

[0041] Unless otherwise specified, all numbers, values, and / or expressions used herein to denote ingredients, reaction conditions, and the content of ingredients shall be understood to be modified by the term “approximately” in all cases, as these numbers are essentially approximations reflecting the various uncertainties of measurement that occur in obtaining these values ​​among others.

[0042] Additionally, where numerical ranges are disclosed in this specification, such ranges are continuous and, unless otherwise specified, include all values ​​from the minimum value of such range up to the maximum value including the maximum value.

[0043] Furthermore, the term "or" in this specification is intended to mean an implied "or" rather than an exclusive "or." That is, where the combination or use of the configurations is not otherwise specified or is not evident from the context, i.e., where X includes A; X includes B; or X includes both A and B, "X includes A or B" may be applied to either of these cases.

[0044] Furthermore, throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0045]

[0046] FIG. 1 is a schematic diagram showing the configuration of a two-phase anaerobic digestion system according to one embodiment of the present invention.

[0047] Referring to FIG. 1, the two-phase anaerobic digestion system (1000) of the present invention may include an acid fermentation section (1400) and a methane fermentation section (1500). In the acid fermentation section (1400) and the methane fermentation section (1500), fermentation of organic waste is carried out by obligate anaerobic microorganisms or facultative anaerobic microorganisms, and as a result, biogas containing methane and carbon dioxide may be produced.

[0048] In order for anaerobic digestion to take place in the system (1000), raw materials or feed must be introduced into the acid fermentation unit (1400), and in the system according to one embodiment of the present invention, organic waste can be utilized as feed for anaerobic digestion. The introduction of the feed for anaerobic digestion can be done in a batch type or a continuous type, and to increase the digestion efficiency of the feed for anaerobic digestion, the introduced feed can be stirred through a stirrer (not shown) placed at the bottom, side, or top of the acid fermentation unit (1400) or the methane fermentation unit (1500).

[0049] In the acid fermentation section (1400), not only acidogenesis but also hydrolysis and acetogenesis reactions may take place, and for this purpose, the microbial community inside the acid fermentation section (1400) may include all or part of hydrolytic microorganisms, acid-producing microorganisms and acetogenic microorganisms. Hydrolyzing microorganisms may be one or more genera selected from the group consisting of Cellulomonas, Clostridium, Bacillus, Thermomonosporora, Ruminococcus, Bacteroides, Streptomyces, and Microbispora, and acid-producing microorganisms may be Lactobacillus, Escherichia, Staphylococcus, Streptococcus, Pseudomonas, Selenomonas, Sarcina, Desulfobacter, Desulforomonas, and It may be one or more genera selected from the group consisting of Desulfovibrio, and the acetic acid-producing microorganism may be Acetobacterium or Sporomusa, but is not limited thereto.

[0050] Due to the action of various microbial communities inside the acid fermentation unit (1400), organic waste introduced into the acid fermentation unit (1400) can undergo physical and chemical transformation to decompose into gases such as carbon dioxide, hydrogen, nitrogen, ammonia, and hydrogen sulfide, liquids such as fatty acids, volatile fatty acids, aldehydes, alcohols, and acetic acid, or solids such as silicon dioxide, silicates, and siloxanes. Gaseous, liquid, or solid components generated inside the acid fermentation unit (1400) can be introduced into the methane fermentation unit (1500) as a reaction liquid for methane fermentation, or removed from the system (1000) through a separate discharge process as byproducts of the acid fermentation process.

[0051] In the methane fermentation section (1500), a methanogenesis reaction may take place, and in order to concentrate the methanogenesis reaction, the microbial community inside the methane fermentation section (1500) may be composed of methanogenic bacteria. The methanogenic bacteria may be one or more genera selected from the group consisting of Methanobacterium, Methanobrevibacter, Methanococcus, Methanogenium, Methanospillum, Methanomicrobium, Methanosarcina, Methanomassiliicoccus, Methanogranum, and Methanoculeus, but are not limited thereto.

[0052] When the acid fermentation liquid produced in the acid fermentation unit (1400) is introduced into the methane fermentation unit (1500) as a reaction liquid for methane fermentation, acetic acid, carbon dioxide, hydrogen, or ethanol contained in the reaction liquid can be converted into methane through the metabolism of methane-producing bacteria, and gases such as nitrogen, ammonia, and hydrogen sulfide, liquids such as fatty acids and aldehydes, or solids such as silicon dioxide, silicates, and siloxanes that do not undergo metabolism by methane-producing bacteria can be removed from the system (1000) through a separate discharge process as byproducts of the methane fermentation process.

[0053] The acid fermentation liquid produced in the acid fermentation unit (1400) can be supplied to the methane fermentation unit (1500) continuously or intermittently, and the amount of acid fermentation liquid supplied to the methane fermentation unit can be adjusted so that the acid fermentation liquid supplied to the methane fermentation unit and the reaction liquid for methane fermentation remaining in the methane fermentation unit maintain a predetermined volume ratio. For example, the volume ratio of the acid fermentation liquid supplied to the methane fermentation unit and the reaction liquid for methane fermentation remaining in the methane fermentation unit can be adjusted to 10:1, 5:1, 1:1, 1:3, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, or 1:50, and more specifically, the volume ratio of the acid fermentation liquid and the reaction liquid for methane fermentation can be 1:30, but is not limited thereto.

[0054] The operating environment of the acid fermentation unit (1400) and the methane fermentation unit (1500) can be adjusted according to the characteristics of the microbial community included in each component, for example, the acid fermentation unit (1400) and the methane fermentation unit (1500) can be operated at a temperature of 20 to 50°C, and the acid fermentation unit (1400) can be operated under aerobic conditions where an appropriate amount of oxygen is present, while the methane fermentation unit (1500) can be operated under low oxygen to anaerobic conditions and ultimately under anaerobic conditions. Meanwhile, to increase the efficiency of organic waste decomposition and digestion of the system (1000), biochar can be introduced into the acid fermentation unit (1400) or the methane fermentation unit (1500). When biochar is introduced, the decomposition and digestion of the feed for anaerobic digestion are promoted by supplying minerals through biochar, adsorbing acid fermentation or methane fermentation inhibitors, and immobilizing fermentation microorganisms, and as a result, the biogas production of the system (1000) can be increased. At this time, biochar can be introduced at a ratio of 0.5 to 20 g per 1 L of volume of the reaction liquid for acid fermentation inside the acid fermentation section (1400) or the reaction liquid for methane fermentation inside the methane fermentation section (1500). At this time, considering that the anaerobic digestion feed, which consists of organic waste, is first introduced into the acid fermentation unit (1400) and then subsequently introduced into the methane fermentation unit (1500) after undergoing the acid fermentation process, the biochar can promote the biodegradation and acid fermentation of the feed by introducing it into the acid fermentation unit (1400), or both the acid fermentation unit (1400) and the methane fermentation unit (1500).

[0055] The system (1000) of the present invention may further include a receiving section (1300). The receiving section (1300) may receive organic waste that is fed as feed for anaerobic digestion, and a predetermined weight of feed may be supplied from the receiving section (1300) to the acid fermentation section (1400) in accordance with the operating environment of the acid fermentation section (1400). Accordingly, when the system (1000) is further equipped with a receiving section (1300), the organic waste to the system (1000) may be controlled by comprehensively considering the state of the fermentation microorganisms, such as the activity of the fermentation microorganisms inside the acid fermentation section (1400), the composition of the fermentation microorganisms, and environmental conditions for the proliferation of the fermentation microorganisms, as well as the remaining amount of feed for anaerobic digestion.

[0056] The system (1000) of the present invention may further include a pretreatment unit (1100). In the pretreatment unit (1100), pretreatment of organic waste may be performed, for example, after drying, crushing, sorting, and classification of organic waste is performed first, a second process of composting or decomposition through aerobic microorganisms at a temperature of 20 to 50°C or a pyrolysis process at a temperature of 100°C or higher may be performed on the dried, crushed, sorted, or classified organic waste, but is not limited thereto.

[0057] The system (1000) of the present invention may further include a carbonization unit (1200). In the carbonization unit (1200), organic waste may be converted into biochar through pyrolysis and gasification processes. As carbonization raw materials for the carbonization unit (1200), one or more organic wastes selected from the group consisting of sludge, livestock manure, food waste, agricultural by-products, forestry by-products, fishery by-products, and microalgae may be introduced, and organic waste that has undergone drying, crushing, and sorting through the pretreatment unit (1100) may be introduced into the carbonization unit (1200).

[0058] In order to obtain biochar from organic waste introduced into the carbonization unit (1200), heating may be performed for 1 to 5 hours at a temperature of 300 to 800 °C in a low-oxygen to anaerobic atmosphere. At this time, the physicochemical properties of the biochar can be controlled by controlling the carbonization temperature and carbonization time of the organic waste. For example, if the organic waste is carbonized at 550 °C for about 1 hour, the pH of the biochar may be 8 to 9, and if it is carbonized at 550 °C for about 2 hours, the pH of the biochar may be 10 to 11. Therefore, by controlling the carbonization conditions of the carbonization unit (1200), biochar suitable for the reaction environment of the acid fermentation unit (1400) or methane fermentation unit (1500) where anaerobic digestion takes place can be obtained.

[0059] Meanwhile, subsequent formulation can be performed on the biochar obtained from the carbonization section (1200). For example, the biochar can be formulated into a powder, granule, or pellet shape, and more specifically, into a cylindrical pellet shape with a diameter of 0.3 to 3 cm and a height of 0.3 to 3 cm. In the formulation process of the biochar, biodegradable biopolymers such as alginate, carrageenan, chitosan, carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), and hydroxypropyl methylcellulose (HPMC) may be added to increase the viscosity and binding strength between biochar particles, and a cationic, anionic, or neutral curing agent may be further added to match the charge characteristics of the biopolymer.

[0060] The system (1000) of the present invention may further include a collection unit (1600). In the collection unit (1600), biogas generated in an acid fermentation unit (1400) or a methane fermentation unit (1500) may be collected. When biogas is collected, it may be compressed and stored as a high-pressure gas for convenience in gas transport and storage. Before or after the compressed storage, the biogas may undergo filtration and adsorption processes to purify and improve the quality of the biogas.

[0061] The system (1000) of the present invention may further include a byproduct treatment unit (1700). In the byproduct treatment unit (1700), anaerobic digestion byproducts generated in the acid fermentation unit (1400) or the methane fermentation unit (1500) may be treated. When the anaerobic digestion byproducts are treated, the byproducts, which are in the form of sludge and mixed with solid residue or liquid filtrate, may be dried, composted, or aged, and then crushed to a predetermined particle size to be converted into solid organic waste. Accordingly, the anaerobic digestion byproducts generated in the system (1000) of the present invention may be recycled again as feed for anaerobic digestion of the system (1000) or as carbonization raw material for biochar production in the carbonization unit (1200).

[0062] The system (1000) of the present invention may further include a control unit (not shown) capable of controlling the operation of the system.

[0063] The control unit can be connected to each component of the system (1000) via wired or wireless connection to control the operation of individual components. For example, the control unit can analyze the characteristics of organic waste supplied to the system (1000) and, based on the analysis results, control the pretreatment unit (1100) to ensure that a pretreatment operation suitable for the organic waste is performed. Alternatively, the control unit can analyze the characteristics of the organic waste supplied to the system (1000) or the organic waste that has undergone pretreatment in the pretreatment unit (1100), and, by collecting the analysis results and internal operating environment information of the acid fermentation unit (1400) or the methane fermentation unit (1500), control the carbonization unit (1200) so that biochar production is carried out under appropriate carbonization conditions in the carbonization unit (1200). Furthermore, the control unit can analyze the characteristics of the anaerobic digestion feed supplied to the system (1000) or the anaerobic digestion feed that has undergone pretreatment in the pretreatment unit (1100), and, based on the analysis results and the acid fermentation unit The control unit can control the receiving unit (1400) by collecting internal operating environment information of the (1400) so that feed for anaerobic digestion is properly fed from the receiving unit (1300) to the acid fermentation unit (1400), and the control unit can control the acid fermentation unit (1400) so that reaction liquid for methane fermentation is properly fed from the acid fermentation unit (1400) to the methane fermentation unit (1500) by collecting the analysis results and internal operating environment information of the methane fermentation unit (1500), and the control unit can control the operation of the collection unit (1600) and the byproduct treatment unit (1700) by analyzing the internal operating environment information of the acid fermentation unit (1400) or the methane fermentation unit (1500) and calculating the amount of biogas to be collected at a specific time and the amount of anaerobic digestion byproduct to be treated at a specific time based on the analysis results.

[0064] Control of the system (1000) through the control unit can be based on operational data generated and collected during the operation of the system and information data pre-input before the operation of the system, and the control unit can derive conditions for optimal operation of the system (1000) by comprehensively machine learning operational data and information data including the pretreatment characteristics of organic waste, the manufacturing characteristics of biochar, the anaerobic digestion characteristics of the feed for anaerobic digestion, and the characteristics of biogas and by-products generated from anaerobic digestion through a separate learning module (not shown), and can control the operation of each component of the system (1000) accordingly. At this time, the operation data and information data may include internal operating environment information including the internal temperature, internal humidity, internal pressure, feed weight, feed distribution, feed fluidity of the acid fermentation unit (1400), the internal temperature, internal humidity, internal pressure, reaction liquid weight, reaction liquid fluidity of the methane fermentation unit (1500), as well as information regarding the composition, degree of impurity inclusion, degree of drying, size and weight of organic waste, raw materials of biochar, degree of carbonization, pH, formulation, size and weight, composition, density, temperature, pressure, composition, shape, degree of drying, size and weight of by-products, but are not limited thereto.

[0065] FIG. 2 is a flowchart schematically illustrating a two-phase anaerobic digestion method according to one embodiment of the present invention.

[0066] Referring to FIG. 2, the two-phase anaerobic digestion method (S1000) of the present invention comprises the input of a feed containing organic waste (S1), an acid fermentation step of the feed (S200), a methane fermentation step of the acid fermentation liquid (S300), and a capture step (S400) for capturing gas produced by acid fermentation or methane fermentation, through which biogas (S2) can be obtained.

[0067] The acid fermentation step (S200) or the methane fermentation step (S300) can be carried out under low oxygen to anaerobic conditions of 20 to 50 ℃, and the reaction temperature and oxygen conditions can be controlled according to the characteristics of the microorganisms used for acid fermentation or methane fermentation.

[0068] Anaerobic digestion in the acid fermentation stage (S200) or methane fermentation stage (S300) can be performed in batch, continuous, or continuous batch, and the feed or reaction liquid can be stirred in all or part of the acid fermentation stage (S200) or methane fermentation stage (S300) to increase the fermentation efficiency in each stage.

[0069] In the acid fermentation stage (S200) or the methane fermentation stage (S300), biochar may be additionally added to improve the decomposition and digestion efficiency of organic waste. If the contact time between the reactants and microorganisms and the biochar needs to be maintained for a long period during the anaerobic digestion process, biochar may be added in the acid fermentation stage (S200); conversely, if the contact time of biochar does not need to be maintained for a long period, biochar may be added in the methane fermentation stage (S300). If the contact time of biochar needs to be maintained for the longest possible period, biochar may be added in both the acid fermentation stage (S200) and the methane fermentation stage (S300). The amount of biochar added can be appropriately adjusted within the range of 0.5 to 20 g / L.

[0070] Since the gas captured in the capture step (S400) contains not only methane and carbon dioxide but also impurities such as water vapor, hydrogen sulfide, nitrogen, and ammonia, a purification process may be additionally performed to increase the purity of the biogas. The purification process is performed based on the principles of gas filtration and adsorption to achieve high purity of the biogas, such as methane and carbon dioxide, and the purified biogas or unpurified biogas may be compressed and stored under high pressure for convenience in transportation and storage.

[0071] The biogas production method (S1000) of the present invention may further include a pretreatment step (S101) in which a pretreatment operation is performed on organic waste constituting the feed for anaerobic digestion prior to the acid fermentation step (S200).

[0072] In the pretreatment step (S101), drying, crushing, sorting, or classification of the waste may be performed to improve the suitability of the organic waste input, and composting and decomposition using aerobic microorganisms or pyrolysis through high-temperature heating may be performed to improve digestion efficiency, but is not limited thereto.

[0073] The biogas production method (S1000) of the present invention may further include a carbonization step (S102) for obtaining biochar to be fed into an anaerobic digestion step (S200) from organic waste. In the carbonization step (S102), one or more organic wastes selected from the group consisting of sludge, livestock manure, food waste, agricultural by-products, forestry by-products, fishery by-products, and microalgae may be converted into biochar by heating and pyrolyzing them at a temperature of 300 to 800°C for 1 to 5 hours in a low-oxygen to anaerobic atmosphere.

[0074] The biogas production method (S1000) of the present invention may further include a byproduct treatment step (S401) for treating anaerobic digestion byproducts generated along with gas in an acid fermentation step (S200) or a methane fermentation step (S300). In the byproduct treatment step (S401), a mixture in the form of sludge containing liquid or solid byproducts generated during the anaerobic digestion process may be dried, composted, aged, or crushed to be converted into organic waste.

[0075]

[0076] The present invention will be explained in more detail below through the following examples. However, these examples are merely illustrative of the invention, and the scope of the invention is not limited by these examples.

[0077]

[0078] Example 1. Preparation of Biochar

[0079] Biochar was manufactured for use in the anaerobic digestion process of organic waste.

[0080] Specifically, fallen leaves, microalgae, coffee grounds, rice husks, grass, and sewage sludge were obtained from sewage treatment plants, municipal waste treatment plants, municipal solid waste treatment plants, and farms. Each raw material was dried and then crushed to a particle size of 10 mm or less. Each crushed raw material was fed into a pyrolysis reactor and pyrolyzed at 550°C for 2 hours while injecting nitrogen gas. Afterward, the materials were washed with distilled water to remove impurities and subsequently dried at 105°C for 24 hours to produce a total of 6 types of biochar.

[0081] Each of the six types of biochar produced was named as follows:

[0082] Leaf Biochar: M-BC

[0083] Microalgae Biochar: SP-BC

[0084] Coffee Grounds Biochar: CF-BC

[0085] Rice Husk Biochar: RH-BC

[0086] Grass Biochar: KB-BC

[0087] Sludge Biochar: Slu-BC.

[0088]

[0089] Example 2. Measurement of mineral content of biochar

[0090] The total mineral content of the six types of biochar prepared in Example 1 was measured.

[0091] Specifically, the total mineral content of the biochar was quantitatively and qualitatively analyzed using inductively coupled plasma emission spectrometry (ICP-OES) for various minerals, and the analyzed minerals included nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), and silicon (Si). The total mineral content per biochar was calculated by summing the measurements of each mineral, and the results are shown in Figure 3 and Table 1 below.

[0092] Fallen leaves, biochar microalgae, biochar coffee grounds, biochar rice husks, biochar grass, biochar sludge, total biochar mineral content (%) 5.76 14.6 24.45 15.0 96.70 20.85

[0093] As a result of measuring mineral content, it was found that the mineral content of biochar produced from microalgae, rice husks, and sludge was relatively high, whereas the mineral content of biochar produced from fallen leaves, coffee grounds, and grass was relatively low.

[0094] Example 3. Measurement of Biogas Production Volume

[0095] 3-1. Measurement of Biogas Production Volume with Biochar Addition

[0096] In a two-phase anaerobic digestion process in which acid fermentation and methane fermentation of organic waste are separated and carried out sequentially, the amount of biogas produced was compared and measured when the biochar prepared according to Example 1 was added to the acid fermentation tank and when it was added to the methane fermentation tank.

[0097] Specifically, organic waste consisting of food waste, livestock manure, and sewage sludge was fed into a two-phase anaerobic digester as an anaerobic digestion feed to carry out anaerobic digestion. The feed was initially fed into an acid fermentation tank for acid fermentation, after which the acid fermentation liquid produced in the acid fermentation tank was subsequently fed into a methane fermentation tank for methane fermentation. The ratio of acid fermentation liquid fed into the methane fermentation tank was controlled to 1 (acid fermentation liquid) : 30 (methane fermentation reaction liquid) (v / v). The feeding of the acid fermentation liquid into the methane fermentation tank was carried out in batches to accommodate biogas capture and the treatment of fermentation byproducts. Anaerobic digestion was conducted for a total of 9 days, and the temperatures of both the acid fermentation tank and the methane fermentation tank were maintained at 35°C until the completion of anaerobic digestion.

[0098] The relative biogas production in the control group (w / o) in which no biochar was added during the anaerobic digestion process and the experimental group in which biochar was added to the methane fermentation tank (AD) or the acid fermentation tank (Acid) was measured and shown in Figure 4 and Table 2 below, and the relative methane production in the control group and the experimental group was measured and shown in Figure 5 and Table 3 below.

[0099] Relative Biogas Production (%) by Input Location of 6 Types of Biochar Control Group: Fallen Leaves Biochar, Microalgae Biochar, Coffee Grounds Biochar, Rice Husk Biochar, Grass Biochar, Sludge Biochar Methane Fermentation Tank Input 100 77.9 93.0 77.0 67.0 68.7 102.6 Acid Fermentation Tank Input 100 110.7 116.6 95.0 96.0 101.9 123.5

[0100] Relative Methane Production (%) by Input Location of 6 Types of Biochar Control Group: Fallen Leaves, Biochar, Microalgae, Biochar, Coffee Grounds, Biochar, Rice Husk, Biochar, Grass, Biochar, Sludge Methane Fermentation Tank Input: 100 53.2 111.0 7 4.3 5 1.5 6 4.3 115.5 Acid Fermentation Tank Input: 100 114.9 126.4 89.7 86.1 105.5 133.6

[0101] As a result of measuring biogas and methane production, it was found that for all types of biochar, biogas and methane production increased when biochar was fed into an acid fermentation tank compared to when it was fed into a methane fermentation tank, and that biogas or methane production varied depending on the type of biochar fed into the anaerobic digester. Sludge biochar (Slu-BC) produced the highest increase in biochar and methane production, and microalgae biochar (SP-BC) and leaf litter biochar (M-BC) were also confirmed to have excellent increase effects. Grass biochar (KB-BC), coffee grounds biochar (CF-BC), and rice husk biochar (RH-BC) did not show a significant increase in biogas or methane production compared to other biochars.

[0102] At this time, considering that the mineral content of sludge biochar and microalgae biochar was measured to be high in the mineral content measurement results for each biochar performed in Example 2, it was considered that the mineral content contained in the biochar would have a significant influence on increasing biogas production through the addition of biochar during anaerobic digestion. However, judging from the fact that the effect of increasing biogas production was not significant in the case of rice husk biochar despite its high mineral content, it was considered that there would also be an influence based on the physical properties or surface characteristics of each type of biochar in addition to the mineral content.

[0103] Meanwhile, although sludge biochar and microalgae biochar produced the most superior effects in increasing biogas and methane production, it was confirmed that changes in production volume depending on the biochar input location were more pronounced in leaf biochar, rice husk biochar, and grass biochar. These results were attributed to the physical characteristics of the leaf biochar, rice husk biochar, and grass biochar input into the acid fermentation tank promoting the activity of aerobic microorganisms present in the tank.

[0104] Therefore, it is believed that the physical properties of biochar act in combination to promote the activity of microorganisms in the acid fermentation tank, thereby promoting the production of secondary metabolites, and that the metabolites containing volatile fatty acids from the acid fermentation liquid are introduced into the methane fermentation tank, contributing to the promotion of the growth of microorganisms related to methane fermentation.

[0105]

[0106] 3-2. Measurement of Hourly Biogas Production with Biochar Addition

[0107] Using the sludge biochar that was confirmed to have the highest effect of increasing biogas production among the biochars prepared according to Example 1, when the sludge biochar was introduced into a methane fermentation tank or an acid fermentation tank, the relative biogas production in the anaerobic digester over the duration of anaerobic digestion was measured compared to the control group (w / o) in which no biochar was introduced, and the results are shown in Figure 6 and Table 4 below.

[0108] Relative biogas production by anaerobic digestion duration upon sludge biochar input Elapsed 0 days Elapsed 1 day Elapsed 3 days Elapsed 6 days Elapsed 9 days Elapsed Input into methane fermentation tank: 0 - 6.7 2.1 4.6 2.6 Input into acid fermentation tank: 0 9.5 11.9 18.8 23.5

[0109] Measurement results showed that when biochar was introduced into the methane fermentation tank, the biogas production efficiency dropped significantly in the early stages of anaerobic digestion and did not show a significant increase in biogas production thereafter. On the other hand, when sludge biochar was introduced into the acid fermentation tank, the biogas production continued to increase throughout the entire anaerobic digestion period, confirming that it can produce a superior increase in biogas production compared to when biochar is introduced into the methane fermentation tank.

[0110] The present invention relates to a two-phase anaerobic digestion system with increased biogas production, and more specifically, to an anaerobic digestion system and an anaerobic digestion method that can increase both the anaerobic digestion efficiency and biogas production of organic waste by applying biochar to a two-phase anaerobic digestion system in which acid fermentation and methane fermentation are performed separately.

Claims

1. An acid fermentation section in which acid fermentation of organic waste takes place; and A methane fermentation section in which methane fermentation of the acid fermentation liquid generated in the above acid fermentation section takes place; A two-phase anaerobic digestion system including 2. A two-phase anaerobic digestion system according to claim 1, wherein the acid fermentation unit or the methane fermentation unit is a system in which biochar is introduced during the acid fermentation process or the methane fermentation process.

3. In paragraph 1, the above system is, A receiving section for receiving organic waste input as a feed for anaerobic digestion; A two-phase anaerobic digestion system that further includes 4. In paragraph 1, the above system is, A pretreatment unit where organic waste pretreatment takes place; A two-phase anaerobic digestion system that further includes 5. A two-phase anaerobic digestion system according to paragraph 4, wherein the pretreatment unit performs one or more operations selected from the group consisting of drying, crushing, composting, microbial decomposition, pyrolysis, sorting, and classification on organic waste.

6. In paragraph 1, the above system is, A carbonization section where biochar is produced through the carbonization of organic waste; A two-phase anaerobic digestion system that further includes 7. A two-phase anaerobic digestion system according to claim 6, wherein the carbonization part operates at 300 to 800 ℃.

8. In paragraph 1, the above system is, A collection unit in which biogas generated in the above acid fermentation unit or the above methane fermentation unit is collected; A two-phase anaerobic digestion system that further includes 9. A two-phase anaerobic digestion system according to claim 8, wherein the collection unit performs the compression, storage, purification, or upgrading of biogas.

10. In paragraph 1, the above system is, A byproduct treatment unit in which anaerobic digestion byproducts generated in the above acid fermentation unit or the above methane fermentation unit are treated; A two-phase anaerobic digestion system that further includes 11. A two-phase anaerobic digestion system according to claim 10, wherein the byproduct treatment unit performs drying, composting, maturation, or crushing operations on the anaerobic digestion byproduct.

12. An acid fermentation step for acid fermenting organic waste; and A methane fermentation step for methane fermenting the acid fermentation liquid obtained in the above acid fermentation step; A two-phase anaerobic digestion method comprising 13. A two-phase anaerobic digestion method according to claim 12, wherein the acid fermentation step or the methane fermentation step involves the additional addition of biochar to organic waste or acid fermentation liquid.

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