Mesh-type zero-valent iron structure, and anaerobic digestion method comprising same

Abstract

An anaerobic digestion tank comprising a mesh-type zero-valent iron structure, according to one embodiment of the present invention, comprises: a mesh-type zero-valent iron structure which is disposed along the inner wall of the digestion tank and which is in contact with or spaced apart from the inner wall of the anaerobic digestion tank; and a magnetite (Fe3O4) film formed on the surface thereof by oxidation, and thus shortcomings such as blocking of a tube due to powder leakage during using powdered magnetite (Fe3O4) can be solved. In addition, in anaerobic digestion comprising a mesh-type zero-valent iron structure, according to one embodiment of the present invention, a mesh-type zero-valent iron structure-magnetite (Fe3O4)-anaerobic microorganism forms a composite, and thus, compared to that of a comparative example not containing the mesh-type zero-valent iron structure, the amount of biogas generated for the same time is significantly increased.

Description

Mesh-type zero-value steel structure and anaerobic digestion process method including the same

[0001] The present invention relates to an anaerobic digestion process, and more particularly, to an anaerobic digestion process using a mesh-type zero-valent iron structure.

[0002] Anaerobic digestion is the process of decomposing waste using microorganisms in an anaerobic (oxygen-free) environment. It primarily treats organic waste resources such as food waste, livestock manure, sewage, and industrial sludge, while simultaneously treating wastewater or waste and producing biogas such as methane (CH4) and carbon dioxide (CO2). This requires a tank capable of housing the microorganisms and allowing the reactions to proceed. Such a tank is called an anaerobic digester.

[0003] Magnetite (Fe3O4) has been reported to play various positive roles in the anaerobic digestion process, but the powder form mainly used has the inconvenience of having to be continuously added because it flows out with the digestate, and it can cause pipe clogging. In addition, Fe3O4 has the disadvantage of being more expensive than simple Fe.

[0004] Among the nanotechnology used in environmental pollution treatment, zero-valent iron (Fe) 0 , ZVI, zero-valent iron) is attracting attention from environmental engineers and scientists as a material with high waste removal efficiency. Zero-valent iron refers to pure iron without oxygen molecules in iron oxide (FeO, Fe2O3, and Fe3O4) that occurs in the steel industry and other natural sources. Zero-valent iron is used to decompose various environmentally hazardous substances by utilizing its strong oxidizing power on the surface.

[0005] Iron (Fe) exists as a zero-type iron 0) causes oxidation and forms a redox couple. This is similar to the corrosion reaction that occurs by spontaneous oxidation due to the tendency of zero-valent metals to lose electrons and exist in the form of cations. In the case of iron, the redox potential according to the following equation 1 is -0.44 V.

[0006] [Formula 1]

[0007] Fe 0 ↔ Fe 2+ + 2e -

[0008] These zero-valent iron (ZVI) can be used as electron donors to purify various environmental pollutants, and common environmental pollutants include trichloroethylene (TCE), nitrates, herbicides, polycyclic aromatic hydrocarbons (PAHs), trichloroacetic acid (TCA), 4-chloroaniline (PCA), chloroform (CF), nitrobenzene (NB), nitrotoluene (NT), dinitrochlorobenzene (DNB), dinitrotoluene, chlorinated methanes, chromium (Cr), lead (Pb), and metalloid arsenic (III and V). It is known to be very effective in a wide variety of transformations and detoxification. It is widely used for the treatment of groundwater and soil contaminated with organic chlorine, heavy metals, pesticides, and dyeing wastewater.

[0009] The present invention was conceived to solve the above-described problem, and aims to provide an anaerobic digestion process method that improves the production rate of biogas by using a mesh-type zero-valent iron structure.

[0010] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0011] In order to solve the above technical problem, one aspect of the present invention is an anaerobic digestion process method including a mesh-type zero-valent iron structure, comprising the steps of: (S01) introducing anaerobic digestion liquid into an anaerobic digestion tank equipped with a mesh-type zero-valent iron structure;

[0012] Step (S02) in which the surface of the above mesh-type ferrous metal structure is oxidized to form a film containing magnetite (Fe3O4); and

[0013] It may include a step (S03) of introducing anaerobic microorganisms into an anaerobic digestion tank equipped with a mesh-type ferrous iron structure having a film formed thereon including the above magnetite (Fe3O4) and culturing them to perform an anaerobic digestion reaction.

[0014] The amount of the mesh-type ferrous sulfide structure may be 0.5 to 65 g per volume (L) of the anaerobic digestion liquid.

[0015] At a point 24 hours after the start of the above-mentioned cultivation, the amount of biogas generated through the above-mentioned anaerobic digestion reaction may be increased by 5 to 60% compared to the amount of biogas generated when an anaerobic digestion tank without a mesh-type zero-valent iron structure is used in the above-mentioned step S01.

[0016] The above mesh-type zero-valent iron structure may include any one form selected from a horizontal straight line, a vertical straight line, a diagonal straight line, a wave pattern, a square lattice form intersecting parallel and perpendicular to the lower part of the digester, a rectangular lattice form intersecting diagonally with the lower part of the digester, a form in which square zero-valent iron tiles and square pores are alternately arranged parallel and perpendicular, a form in which square zero-valent iron tiles and square pores are alternately arranged diagonally, a structure in which polygonal tiles are arranged in a polyhedral shape (fullerene structure), a polygonal lattice structure, a circular perforated network structure, and a concentric array structure, or a form in which two or more are mixed.

[0017] The above mesh-type zero-value steel structure is arranged along the inner wall of the anaerobic digestion tank, but may be attached so as to be in contact with the inner wall of the anaerobic digestion tank or installed spaced apart from the inner wall.

[0018] The above anaerobic digestion liquid may be at least one selected from wastewater, waste, by-product, residue, synthetic wastewater, culture medium, and a mixture of two or more thereof containing organic components.

[0019] In order to solve the above technical problem, another aspect of the present invention is an anaerobic digestion tank including a mesh-type zero-valent iron structure,

[0020] An anaerobic digester for receiving anaerobic digestate containing organic acids; and

[0021] It may include a mesh-type zero-valent iron structure arranged along the inner wall of the anaerobic digestion tank, attached so as to be in contact with the inner wall or installed spaced apart from the inner wall, and having a magnetite (Fe3O4) film formed on the surface to provide an attachment site for anaerobic microorganisms.

[0022] The above mesh-type zero-valent iron structure may include any one form selected from a horizontal straight line, a vertical straight line, a diagonal straight line, a wave pattern, a square lattice form intersecting parallel and perpendicular to the lower part of the digester, a rectangular lattice form intersecting diagonally with the lower part of the digester, a form in which square zero-valent iron tiles and square pores are alternately arranged parallel and perpendicular, a form in which square zero-valent iron tiles and square pores are alternately arranged diagonally, a structure in which polygonal tiles are arranged in a polyhedral shape (fullerene structure), a polygonal lattice structure, a circular perforated network structure, and a concentric array structure, or a form in which two or more are mixed.

[0023] The amount of the mesh-type ferrous sulfide structure may be 0.1 to 100 g per volume (L) of the anaerobic digestion liquid.

[0024] The amount of biogas generated through the above anaerobic digestion reaction may be increased by 5 to 60% compared to the amount of biogas generated when using an anaerobic digestion tank without the mesh-type zero-valent iron structure, at a point in time of 24 hours after the start of culturing anaerobic microorganisms.

[0025] An anaerobic digestion tank including a mesh-type zero-valent iron structure according to an example of the present invention is configured such that the mesh-type zero-valent iron structure is disposed along the inner wall of the digester, but is attached or spaced apart from the inner wall of the anaerobic digestion tank so as to be in contact with the inner wall of the anaerobic digestion tank, and includes a magnetite (Fe3O4) film formed by oxidation on the surface thereof, thereby resolving disadvantages such as pipe clogging caused by powder leakage when using powder-type magnetite (Fe3O4). In addition, an anaerobic digestion process including a mesh-type zero-valent iron structure according to an example of the present invention has the effect of significantly increasing the amount of biogas generated in the same period of time compared to a comparative example that does not include a mesh-type zero-valent iron structure, as the mesh-type zero-valent iron structure-magnetite (Fe3O4)-anaerobic microorganism forms a complex.

[0026] The effects of the present invention are not limited to those mentioned above, and also include other effects that are not explicitly mentioned, although they can be clearly understood by those skilled in the art from the description throughout the specification.

[0027] FIG. 1 is a flow chart illustrating an anaerobic digestion process method including a mesh-type zero-valent iron structure according to an example of the present invention.

[0028] Figure 2 is a schematic diagram showing an anaerobic digestion tank having various types of mesh-type ferrous metal structures installed according to an example of the present invention.

[0029] FIG. 3 is a schematic diagram showing a mesh-type ferrous iron structure (a) attached to and (b) spaced apart from the inner wall of the digester in an anaerobic digester according to an example of the present invention, a magnetite (Fe3O4) film formed by oxidation on the surface thereof, and anaerobic microorganisms attached to the surface of the magnetite (Fe3O4) film.

[0030] FIG. 4 is a photograph of a mesh-type steel structure according to an example of the present invention.

[0031] Figure 5 is a graph showing the cumulative methane production rate (%) according to the number of culture days in which an anaerobic digestion process including a mesh-type zero-valent iron structure according to one embodiment of the present invention is applied.

[0032] FIGS. 6 to 8 are schematic diagrams showing specimens for experiments to confirm the improvement effect of anaerobic digestion by introducing a zero-value iron mesh according to Examples 5 to 8 of the present invention (FIG. 6), a schematic diagram showing the experimental method (FIG. 7), and a schematic diagram showing the experimental sequence (FIG. 8).

[0033] Figures 9 to 12 are results showing cumulative methane production by culture days according to Examples 5 to 8 of the present invention, including experimental values ​​obtained in batch (B) 1 to 4 experiments using three organic acid mixed substrates and Gompertz model fitting results.

[0034] Figures 13 to 15 are results showing the cumulative methane production by culture days according to Examples 5 to 8 of the present invention, including experimental values ​​obtained in the 5th experiment of batch (B) using a single organic acid substrate and Gompertz model fitting results.

[0035] Figures 16 to 17 are tables showing the increase / decrease rate (%) of the maximum methane production rate according to Examples 5 to 8 of the present invention.

[0036] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The advantages and features of the present invention, and methods for achieving them, will become clear with reference to the embodiments described in detail below together with the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

[0037] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise. The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise.

[0038] The terms "comprises" and / or "comprising" as used in the specification do not exclude the presence or addition of one or more other components, steps, operations and / or elements.

[0039]

[0040] Anaerobic digestion tank equipped with mesh-type zero-value steel structure and anaerobic digestion process using the same

[0041] The present invention relates to an anaerobic digestion process using a mesh-type zero-valent iron structure to improve the reaction rate of a biogas production reaction in an anaerobic digestion tank.

[0042] FIG. 1 is a flow chart illustrating an anaerobic digestion process method including a mesh-type zero-valent iron structure according to an example of the present invention.

[0043] Referring to Fig. 1, a step (S01) of first preparing an anaerobic digestion tank equipped with a mesh-type zero-value iron structure and then injecting anaerobic digestion liquid containing organic acid can be performed.

[0044] The term "biogas" used in the present invention refers to a mixed gas of methane (CH4) and carbon dioxide (CO2) produced from biomass through anaerobic digestion. Methane separated from this mixed gas is called biomethane gas, and in one specific example, the biogas of the present invention may refer to methane (CH4).

[0045] The term "anaerobic digestion" used in the present invention means digesting waste organic matter by blocking contact with oxygen and through the action of enzymes secreted by anaerobic microorganisms in wastewater and sewage treatment.

[0046] The anaerobic digestion process largely consists of liquefaction and gasification. In the liquefaction process, enzymes secreted by anaerobic microorganisms hydrolyze organic matter, breaking down carbohydrates into monosaccharides, proteins into amino acids, and fats into fatty acids. In the gasification process, fatty acids generated during the liquefaction process are broken down into methane and carbon dioxide, converting organic matter into inorganic substances. In the present invention, the anaerobic digestion process for generating biogas refers to a process in which organic matter is decomposed without an external electron acceptor and ultimately converted into methane (CH4), the most reduced form of carbon. Specifically, the anaerobic digestion process first involves hydrolysis, in which organic polymers (organic acids), including carbohydrates, proteins, and fats, are broken down by ectoenzymes secreted by microorganisms into soluble substances such as sugars, amino acids, and fatty acids that bacteria can absorb. Acid-producing bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids. Acetic acid production involves converting organic acids into acetic acid along with additional ammonia, hydrogen, and carbon dioxide. Finally, methanogenic archaea convert these products into methane and carbon dioxide.

[0047] The above anaerobic digestion liquid may include at least one selected from wastewater, waste, by-product, residue, synthetic wastewater, culture medium, and mixtures of two or more thereof containing organic components.

[0048] The anaerobic digestion liquid may contain organic acids derived from waste organic matter. The organic acids are carbon sources and serve as substrates fed into the digester, and may include, for example, at least one selected from acetic acid, propionic acid, butyric acid, and mixtures of two or more thereof.

[0049] The above anaerobic digestion tank may use a batch reactor, a semi-continuous reactor, a continuous reactor, etc., and any reactor capable of setting anaerobic conditions may be used without limitation.

[0050] Figure 2 is a schematic diagram showing an anaerobic digestion tank having various types of mesh-type ferrous metal structures installed according to an example of the present invention.

[0051] Referring to FIG. 2, the shape of the mesh-type zero-valent iron structure may include any one shape selected from among (a) horizontal straight lines, (b) vertical straight lines, (c) diagonal straight lines, (d) wave patterns, (e) a square grid that intersects parallel and perpendicular to the bottom of the digester, (f) a rectangular grid that intersects diagonally, (g) a shape in which square zero-valent iron tiles and square pores are alternately arranged parallel and perpendicular, and (h) a shape in which square zero-valent iron tiles and square pores are alternately arranged diagonally, a structure in which polygonal tiles are arranged in a polyhedral shape (e.g., a fullerene structure) (not shown), a polygonal grid structure (not shown), a circular perforated mesh structure (not shown), and a concentric array structure (not shown), or a mixed shape of two or more.

[0052] The above mesh-type zero-valent iron structure is arranged along the inner wall of the anaerobic digester, but may be attached so as to be in contact with the inner wall of the anaerobic digester or installed at a distance therefrom. It may be more preferable for the mesh-type zero-valent iron structure to be installed at a certain distance from the inner wall of the anaerobic digester so as to react with a greater surface area with the anaerobic digestate.

[0053] The amount of the mesh-type zero-valent iron added may be 0.1 to 100 g per volume (L) of the anaerobic digestate, and for example, 0.5 to 65 g. Specifically, the amount of the mesh-type zero-valent iron added may be 2 to 30 g per volume (L) of the anaerobic digestate, and more specifically, 2.5 to 21 g. When the amount of mesh-type zero-valent iron added is within the above range, the direct interspecies electron transfer (DIET) mechanism is performed, so that the anaerobic digestion reaction is performed smoothly and the rate of biogas generation can be fast. On the other hand, if the amount of mesh-type zero-valent iron input is less than the above range, the amount of biogas generated may be too small, and if an excessive amount of mesh-type zero-valent iron is input exceeding the above range, the appropriate oxidation-reduction potential range in the anaerobic digestion process is exceeded, creating a more excessive reducing atmosphere. This change in reducing atmosphere may randomly react with various organic substances and CO2, depleting substances that serve as electron donors and electron acceptors of methanogens. In addition, the pH and hydrogen ion (H) changes in the excessive mesh-type zero-valent iron atmosphere + ) and hydrogen molecules (H2) concentrations can inhibit microbial activity, and in addition, zero-valent iron can react with water to produce H2O2 or OH radicals, which are reactive oxygen species, and thus can have a toxic effect on microorganisms including bacteria and methanogens. In one specific example, the amount of the mesh-type zero-valent iron may be 3.9 to 15.5 g per volume (L) of the anaerobic digestion liquid, but is not limited thereto.

[0054]

[0055] Next, a step (S02) can be performed in which the surface of the mesh-type ferrous metal structure is oxidized to form a magnetite (Fe3O4) film.

[0056] FIG. 3 is a schematic diagram showing a mesh-type ferrous iron structure (a) attached to and (b) spaced apart from the inner wall of the digester in an anaerobic digester according to an example of the present invention, a magnetite (Fe3O4) film formed by oxidation on the surface thereof, and anaerobic microorganisms attached to the surface of the magnetite (Fe3O4) film.

[0057] Referring to Fig. 3, the mesh-type zero-valent iron structure may be attached so as to be in contact with (a) the inner wall of the anaerobic digester, or (b) installed spaced apart from it. The surface of the mesh-type zero-valent iron structure immersed in the anaerobic digester liquid naturally forms magnetite (Fe3O4) on the surface of the structure over time, and this may be formed in the form of a film. When iron is exposed to air, hematite (Fe2O3) is formed, but under anaerobic conditions lacking oxygen, magnetite (Fe3O4), which is a reduced form, may be formed more predominantly.

[0058] Magnetite (Fe3O4) is one of the most well-known conductors that causes direct interspecies electron transfer (DIET) in anaerobic digestion, and can have positive effects such as increasing the rate of organic acid removal, increasing the rate of methane production, and increasing the stability of the digester against organic acids or salts. Generally, magnetite (Fe3O4) is mainly used in the anaerobic digestion process in powder form. However, the powder form has the disadvantage of having to be continuously added because it flows out with the digestate, and it can cause pipe clogging, and it is more expensive than iron. When the mesh-type zero-valent iron structure is attached to the inner wall of the anaerobic digester and used, magnetite (Fe3O4) is naturally formed on its surface, which can solve the disadvantages of using it in powder form. However, the time required for surface Fe to be converted into magnetite (Fe3O4) may vary depending on the environmental conditions of the anaerobic digester, such as temperature, pH, and microbial activity.

[0059]

[0060] Thereafter, a step (S03) of introducing anaerobic microorganisms into an anaerobic digestion tank equipped with a mesh-type ferrous iron structure on which the magnetite (Fe3O4) film is formed and culturing the anaerobic digestion reaction can be performed.

[0061] Anaerobic microorganisms can be attached to the attachment sites provided on the surface of the magnetite (Fe3O4) film formed on the surface of the above mesh-type ferromagnetic structure. The magnetite (Fe3O4) film, which provides attachment sites for anaerobic microorganisms, can create a state in which direct interspecies electron transfer (DIET) can occur.

[0062] The above anaerobic microorganisms can be added as an inoculum at a concentration within the range of 0.5 to 3 g VS / L. The VS is an abbreviation for volatile solids, i.e., the content of volatile solids (g). The content of volatile solids is determined by first drying the anaerobic microorganism sample at 105°C, then burning it at 660°C to carbonize it, and then subtracting the mass after carbonization from the dried mass and dividing it by the initial sample volume, thereby obtaining the anaerobic microorganism inoculum concentration in units of g VS / L.

[0063] The amount of biogas generated through the above anaerobic digestion reaction can increase by 5 to 60% compared to the amount of biogas generated when using an anaerobic digestion tank without the mesh-type zero-valent iron structure (comparative example described below) 24 hours after starting the cultivation of anaerobic microorganisms.

[0064]

[0065] Below, specific experimental examples of the present invention will be examined.

[0066]

[0067] Examples 1 to 4: Anaerobic digestion process including mesh-type zero-valent iron structures

[0068] A mesh-type zero-valent iron structure was installed on the inner wall of the anaerobic digestion tank. The amount of the mesh-type zero-valent iron structure added was 0.97 g (Example 1), 3.9 g (Example 2), 15.5 g (Example 3), and 62 g (Example 4) per volume (L) of anaerobic digestion liquid, and the mixture was cultured.

[0069] FIG. 4 is a photograph of a mesh-type steel structure according to an example of the present invention.

[0070] Referring to Figure 4, the mesh-type zero-valent iron structure used is a plate-shaped structure in which wire-type zero-valent iron is formed in a mesh shape, and its thickness is 0.5 mm, and 30 ppi (pores per inch) is per unit centimeter area (1 cm 2) was used with approximately 11x11 pores.

[0071] Next, organic acids as carbon sources (substrates) such as acetic acid, propionic acid, and butyric acid were mixed in a mass ratio of 1:1:1 based on COD (chemical oxygen demand). The organic acid concentration was 3 g / L based on the volume of the anaerobic digester and fed into the anaerobic digester. Anaerobic microorganisms (inoculants) were fed at 1.5 g VS / L. Afterwards, culture was performed under mesophilic conditions of 35°C to generate biogas. At this time, the volume of the anaerobic digester was 100 mL / bottle, and the experiment was repeated three times for each example.

[0072]

[0073] Comparative example: Anaerobic digestion process without mesh-type zero-valent iron structure

[0074] The anaerobic digestion process was performed using the same method as in Examples 1 to 4, except that the mesh-type zero-valent iron structure was not installed on the inner wall of the anaerobic digestion tank.

[0075]

[0076] FIG. 5 is a graph showing the increase / decrease rate (%) of cumulative methane production compared to a comparative example according to the number of days of cultivation in which an anaerobic digestion process including a mesh-type zero-valent iron structure according to one embodiment of the present invention was applied.

[0077] Referring to Figure 5, the cumulative methane production amount according to the number of days of cultivation from the 2nd day (indicated as Day 2) 24 hours after the start of cultivation to the 10th day when biogas (methane) production ended was calculated, and the increase / decrease rate (%) compared to the cumulative methane production amount of the comparative example that did not use the mesh-type zero-valent iron structure is indicated. When the input amount of the mesh-type zero-valent iron structure was 15.5 g (Example 3, indicated as Fe0 Mesh 15.5 g / L), the cumulative methane production amount was the highest on the 2nd day, showing an increase rate of 52.6% compared to the control group. Furthermore, the increase rates were 20.3% on the 3rd day, 18.6% on the 4th day, 17.2% on the 5th day, 10.6% on the 6th day, 8.1% on the 7th day, 6.1% on the 8th day, 4.5% on the 9th day, and 3.3% on the 10th day.

[0078] In addition, when the amount of mesh-type zero-valent iron structure input was 3.9 g (Example 2, expressed as Fe0 Mesh 3.9 g / L), the highest cumulative methane production was also observed on the 2nd day, 24 hours after the start of cultivation, showing an increase rate of 27.2% compared to the control group. Furthermore, the increase rates were 14.9% on the 3rd day, 17.7% on the 4th day, 16.4% on the 5th day, 10.6% on the 6th day, 8.7% on the 7th day, 6.0% on the 8th day, 4.2% on the 9th day, and 3.7% on the 10th day.

[0079] On the other hand, when the amount of mesh-type ferrous iron structure injected was 0.97 g (Example 2, expressed as Fe0 Mesh 0.97 g / L) and 62 g (Example 4, expressed as Fe0 Mesh 62 g / L), the cumulative methane production rate was shown to decrease except for the second day.

[0080] If the results are organized into a table, they can be displayed as in Table 1 below.

[0081] Day 2Day 3Day 4Day 5Day 6Day 7Day 8Day 9Day 10Comparative Example0.0%0.0%0.0%0.0%0.0%0.0%0.0%0.0%0.0%Example 16.9%-1.3%-0.2%2.9%0.7%0.2%0.3%-0.1%-1.1%Example 227.2%14.9%17.7%16.4%10.6%8.7%6.0%4.2%3.7%Example 352.6%20.3%18.6%17.2%10.6%8.1%6.1%4.5%3.3%Example 431.9%-9.1%-13.7%-17.5%-22.1%-26.5%-28.7%-27.6%-27.3%

[0082]

[0083]

[0084] Examples 5 to 8: Confirmation of the improvement effect of anaerobic digestion by introducing zero-value iron mesh.

[0085] FIGS. 6 to 8 are schematic diagrams showing specimens for experiments to confirm the improvement effect of anaerobic digestion by introducing a zero-value iron mesh according to Examples 5 to 8 of the present invention (FIG. 6), a schematic diagram showing the experimental method (FIG. 7), and a schematic diagram showing the experimental sequence (FIG. 8).

[0086] Referring to FIGS. 6 to 8, a lattice-type mesh-type zero-valent iron (ZVI) structure was installed inside the anaerobic digester, and the effects of introducing various concentrations of ZVI mesh on the biogas production rate and methane production amount in the anaerobic digestion process were evaluated. In this experiment, the amount of ZVI mesh introduced was set differently, and the substrate conditions were changed to analyze the changes in microbial activity and methane production rate in the reactor. The experiment was performed in a reactor with a capacity of 250 mL, and the working volume was set to 100 mL. A lattice-type mesh-type zero-valent iron mesh (ZM) was introduced inside the anaerobic digester, and the introduction amount was adjusted to four concentrations: 0.9 g / L (Example 5), 3.8 g / L (Example 6), 15.5 g / L (Example 7), and 62.0 g / L (Example 8). The zero-valent iron mesh used was 30 pores per inch (ppi), 0.5 mm thick, and 2x2 cm in size, and no zero-valent iron mesh was used in the negative control group (Blank, BL).

[0087] Cultivation was conducted at 35 ℃, and a serial batch process was applied to partially recycle the microorganisms and medium in the reactor. The batch was terminated when the daily biogas production was less than 0.5% of the total cumulative biogas production, and the culture was maintained by removing 14% of the effective volume as a supernatant and adding the same volume of new medium. The medium composition was referenced from a previous study (Joonyeob Lee et al., Bioresource Technology, 2019), and for the substrate (carbon source), acetic acid, propionic acid, and butyric acid were mixed in a ratio of 1:1:1 based on COD in batches B1 to B4 and added at a concentration of 3 g COD / L. In batch B5, each organic acid was added alone to compare the methane production rate by substrate.

[0088]

[0089] The reason acetic acid, propionic acid, and butyric acid were used as substrates in this experiment is because short-chain fatty acids (SCFAs) are major intermediate metabolites produced during the decomposition of organic matter. In particular, acetic acid, propionic acid, and butyric acid are the most commonly found organic acids in actual anaerobic digesters and play an important role in the anaerobic digestion process. Generally, high molecular weight organic compounds such as starch or protein must undergo bacterial hydrolysis to be converted into a form usable by microorganisms, but SCFAs can be immediately utilized as metabolic substrates by methanogens. Therefore, in this experiment, SCFAs were used directly as substrates to more directly evaluate the effect of zero-valent iron mesh (ZM) on the methane production process in the anaerobic digestion process.

[0090]

[0091] Figures 9 to 12 are results showing cumulative methane production by culture days according to Examples 5 to 8 of the present invention, including experimental values ​​obtained in batch (B) 1 to 4 experiments using three organic acid mixed substrates and Gompertz model fitting results.

[0092] Referring to Figures 9 to 12, changes in cumulative methane production are confirmed as the amount of zero-valent iron mesh (ZVI mesh, ZM) added increases. Under ZM conditions of 0.9 g / L (Example 5) and 3.8 g / L (Example 6), cumulative methane production tended to gradually increase as cultivation progressed, and in particular, the methane production rate remained stable as the batch progressed.

[0093] On the other hand, under the condition of ZM 15.5 g / L (Example 7), a temporary decrease in the methane production rate was observed in the initial cultivation stage, but a gradual recovery trend was observed as the cultivation period increased. Under the condition of ZM 62.0 g / L (Example 8), a significant decrease in the methane production rate was observed in the initial cultivation days (B2, B3), but the cumulative methane production showed a tendency to increase again in the latter half of the cultivation period (B4).

[0094] These results suggest that a temporary decrease in microbial activity may occur during the initial cultivation process when high-concentration ZM is added. However, over time, as the microbial community within the anaerobic digester adjusts, cumulative methane production tends to recover. In particular, iron oxides such as magnetite (Fe3O4) formed on the ZM surface promote direct interspecies electron transfer (DIET), which can enhance the methane production efficiency of the anaerobic digestion process in the long term.

[0095]

[0096] Figures 13 to 15 are results showing the cumulative methane production by culture days according to Examples 5 to 8 of the present invention, including experimental values ​​obtained in the 5th experiment of batch (B) using a single organic acid substrate and Gompertz model fitting results.

[0097] Referring to Figures 13 to 15, the methane production rate and cumulative methane production by substrate were found to vary depending on the amount of zero-valent iron mesh (ZVI mesh, ZM) input. In the butyric acid substrate (Figure 13), the cumulative methane production tended to increase at all ZM concentrations, and in particular, the highest increase rate was recorded under the conditions of ZM 15.5 g / L (Example 11) and 62.0 g / L (Example 12).

[0098] Although a relatively low increase rate was observed in the propionic acid substrate (Fig. 14), a steady increase in cumulative methane production was observed at concentrations of ZM 3.8 g / L (Example 10) or higher. In particular, a significant increase in the methane production rate was observed at ZM 15.5 g / L (Example 11) or higher.

[0099] On the other hand, in the acetic acid substrate (Fig. 15), the cumulative methane production tended to decrease under the condition of ZM 3.8 g / L (Example 10), suggesting that ZM may have different effects on the direct acetic acid decomposition pathway under specific conditions. However, the methane production tended to increase at ZM 0.9 g / L (Example 9) and 15.5 g / L or higher (Examples 11 and 12).

[0100] These results suggest that ZM may have different effects on the anaerobic digestion process depending on the type of substrate, and in particular, it can be interpreted that ZM enhances methane production efficiency by promoting direct interspecies electron transfer (DIET) in butyric and propionic acid substrates.

[0101]

[0102] Figures 16 to 17 are tables showing the increase / decrease rate (%) of the maximum methane production rate according to Examples 5 to 8 of the present invention.

[0103] Referring to Figures 16 and 17, it was confirmed that the maximum methane production rate tended to change differently depending on the substrate according to the introduction of zero-valent iron mesh (ZVI mesh, ZM). In the mixed organic acid substrates (B1 to B4), Rm showed a tendency to gradually increase as the batch progressed under the conditions of ZM 0.9 g / L (Example 5) and 3.8 g / L (Example 6). On the other hand, under the condition of ZM 15.5 g / L (Example 7), it decreased by -29.5% in the initial batch (B2), but gradually recovered in B3 (-9.0%) and B4 (-4.8%) thereafter. Under the condition of ZM 62.0 g / L (Example 8), a strong inhibitory effect was observed in the beginning (B2, -43.0%; B3, -37.4%), but thereafter, it showed a tendency to recover to +6.4% in B4.

[0104] In the single organic acid substrate (B5), the highest increase rate was observed in the butyric acid substrate, especially at ZM 15.5 g / L (Example 7) and 62.0 g / L (Example 8), showing increases of +27.2% and +21.0%, respectively. A constant increase was also observed in the propionic acid substrate, and an increase rate of +6.2% to +29.6% was observed at ZM 3.8 g / L (Example 6) or higher. On the other hand, in the acetic acid substrate, an inhibitory effect was observed in which Rm decreased by -11.7% at ZM 3.8 g / L (Example 6), but an increasing trend was observed at ZM 0.9 g / L (Example 5) and 15.5 g / L or higher (Examples 7 and 8).

[0105] These results suggest that ZM may exert different effects on anaerobic digestion depending on the type of substrate. In particular, ZM is thought to increase the methane production rate by promoting direct interspecies electron transfer (DIET) in butyric and propionic acid substrates. On the other hand, an inhibitory effect was observed at a certain concentration in acetic acid substrate, but a tendency to increase again under high concentration conditions was observed, indicating that chemical modifications and reactivity on the ZM surface may change over time.

[0106]

[0107] In summary, the present invention confirmed that the effects of zero-valent iron mesh (ZM) addition on the methane production rate and efficiency in the anaerobic digestion process varied depending on the substrate type and ZM concentration. In particular, the methane production rate tended to increase when low-concentration ZM (0.9 g / L, 3.8 g / L) was added, and a temporary inhibitory effect was observed in the initial cultivation stage at high concentrations of ZM (15.5 g / L, 62.0 g / L), but the effect recovered over time. These results suggest that the formation of iron oxides such as magnetite (Fe3O4) on the ZM surface likely promotes direct interspecies electron transfer (DIET), thereby modulating the electron transfer activity of the microbial community. In addition, the analysis results by substrate confirmed that butyric acid and propionic acid substrates had the greatest methane production rate-enhancing effects, implying that ZM can maximize the electron transfer-promoting effect in the reaction with specific organic acids. Therefore, the present invention can provide an important technological foundation that can contribute to optimizing the anaerobic digestion process and improving biogas production by utilizing a zero-valent iron mesh-based catalyst system.

[0108]

[0109] Although embodiments of the present invention have been described with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

Claims

1. Step (S01) of injecting anaerobic digestion liquid into an anaerobic digestion tank equipped with a mesh-type zero-value steel structure; Step (S02) in which the surface of the above mesh-type ferrous metal structure is oxidized to form a film containing magnetite (Fe3O4); and An anaerobic digestion process method including a mesh-type zero-valent iron structure, comprising a step (S03) of introducing anaerobic microorganisms into an anaerobic digestion tank equipped with a mesh-type zero-valent iron structure having a film formed thereon including the magnetite (Fe3O4) and culturing the same to perform an anaerobic digestion reaction.

2. In paragraph 1, An anaerobic digestion process method including a mesh-type zero-valent iron structure, wherein the amount of the mesh-type zero-valent iron structure input is 0.1 to 100 g per volume (L) of the anaerobic digestion liquid.

3. In paragraph 1, An anaerobic digestion process method including a mesh-type zero-valent iron structure, wherein the amount of biogas generated through the anaerobic digestion reaction at a point in time of 24 hours after the start of the above-mentioned cultivation is increased by 5 to 60% compared to the amount of biogas generated when an anaerobic digestion tank without a mesh-type zero-valent iron structure is used in the above-mentioned step S01.

4. In paragraph 1, An anaerobic digestion process method including a mesh-type zero-valent iron structure, wherein the mesh-type zero-valent iron structure includes one or more of a horizontal straight line, a vertical straight line, a diagonal straight line, a wave pattern, a square lattice shape intersecting parallel and perpendicular to the lower part of the digester, a rectangular lattice shape intersecting diagonally with the lower part of the digester, a shape in which square zero-valent iron tiles and square pores are alternately arranged parallel and perpendicular, a shape in which square zero-valent iron tiles and square pores are alternately arranged diagonally, a structure in which polygonal tiles are arranged in a polyhedral shape (fullerene structure), a polygonal lattice structure, a circular perforated mesh structure, and a concentric array structure, or a shape in which two or more are mixed.

5. In paragraph 1, An anaerobic digestion process method including a mesh-type zero-valent iron structure, wherein the mesh-type zero-valent iron structure is arranged along the inner wall of the anaerobic digestion tank, but is attached so as to be in contact with the inner wall of the anaerobic digestion tank or installed spaced apart from the inner wall.

6. In paragraph 1, An anaerobic digestion process method including a mesh-type zero-valent iron structure, wherein the anaerobic digestion liquid is at least one selected from wastewater, waste, by-product, residue, synthetic wastewater, culture medium, and mixtures of two or more thereof containing organic components.

7. An anaerobic digester for receiving anaerobic digestate containing organic acids; and A mesh-type zero-valent iron structure arranged along the inner wall of the anaerobic digestion tank, attached so as to be in contact with the inner wall or installed spaced apart from the inner wall, and having a magnetite (Fe3O4) film formed on the surface to provide an attachment site for anaerobic microorganisms; An anaerobic digester comprising a mesh-type ferrous metal structure, comprising:

8. In paragraph 7, An anaerobic digester comprising a mesh-type zero-valent iron structure, wherein the mesh-type zero-valent iron structure includes one or more of a horizontal straight line, a vertical straight line, a diagonal straight line, a wave pattern, a square lattice shape intersecting parallel and perpendicular to the lower part of the digester, a rectangular lattice shape intersecting diagonally with the lower part of the digester, a shape in which square zero-valent iron tiles and square pores are alternately arranged parallel and perpendicular, a shape in which square zero-valent iron tiles and square pores are alternately arranged diagonally, a structure in which polygonal tiles are arranged in a polyhedral shape (fullerene structure), a polygonal lattice structure, a circular perforated mesh structure, and a concentric array structure, or a shape in which two or more are mixed.

9. In paragraph 7, An anaerobic digestion tank including a mesh-type zero-valent iron structure, wherein the amount of the mesh-type zero-valent iron structure input is 0.1 to 100 g per volume (L) of the anaerobic digestion liquid.

10. In paragraph 7, An anaerobic digestion tank including a mesh-type zero-valent iron structure, wherein the amount of biogas generated through the above anaerobic digestion reaction is increased by 5 to 60% compared to the amount of biogas generated when using an anaerobic digestion tank without the mesh-type zero-valent iron structure, 24 hours after the start of culturing anaerobic microorganisms.

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