Fuel gas production apparatus and fuel gas production method

Abstract

To provide a fuel gas production device and a fuel gas production method for producing biomass-derived fuel gas that can reduce solid waste emissions, while they are possible to reduce the amount of a liquid medium such as an artificial medium (artificial saliva) and a dilution water to be used for adjusting the total solids (TS) in a treatment liquid in which organic waste is decomposed.SOLUTION: A fuel gas production device comprises: a culture tank 10 for culturing rumen microorganisms; a pretreatment tank 20 in which a rumen microorganism culture solution obtained in the culture tank 10 and an organic waste B are mixed and the organic waste B is treated to be converted into an easily decomposable organic waste and volatile fatty acids; and a fermentation tank 30 for fermentation using the easily decomposable organic waste and the volatile fatty acids obtained in the pretreatment tank 20 as substrates.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fuel gas production apparatus and a fuel gas production method. [Background technology]

[0002] Lignocellulosic biomass is an organic carbon source that is abundant on Earth and constitutes the cell walls of plant cells, i.e., the main component of plant fiber, and has therefore attracted attention as an alternative energy resource to fossil fuels such as petroleum. In addition, since lignocellulosic biomass is a difficult-to-decompose organic waste, the decomposition stage requires a great deal of energy, cost, and time. For this reason, the expansion of its use as an energy resource has been stagnant.

[0003] Conventionally, a technology has been known in which lignocellulosic biomass is decomposed by ruminal microorganisms present in the first stomach fluid (rumen fluid) of ruminants to produce volatile fatty acids such as acetic acid, and then methane fermentation is carried out using the volatile fatty acids as a substrate to produce biogas (e.g., Non-Patent Document 1).

[0004] Non-Patent Document 1 discloses a two-phase process in which a methanogenesis tank (second reactor) is connected to an acidogenesis tank (first reactor) for decomposing cellulose to produce volatile fatty acids. Specifically, it discloses that in the acidogenesis tank, cellulose is decomposed by the action of ruminal microorganisms to produce volatile fatty acids, and a liquid phase rich in volatile fatty acids is supplied to a methanogenesis tank using a membrane separation device, where methane fermentation is carried out using the volatile fatty acids as a substrate to produce methane gas. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Huub J. Gijzen, et al., "High-Rate two-phase process for the anaerobic degradation of cellulose,employing rumen microorganisms for an efficient acidogenesis," Biotechnology and Bioengineering, Vol. 31, pp. 418-425 (1988) Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the two-phase process described in Non-Patent Document 1, solid-liquid separation is performed for the convenience of adjusting the solid retention time (SRT), so the solid concentration (TS) of the treatment liquid in the acid generation tank needs to be 1.0 wt% or less. Therefore, a large amount of medium and dilution water are required, and due to this, methane generation equipment is limited to a methane fermentation tank with a huge capacity or a UASB type or EGSB type that can handle high loads, and even if it is tried to apply it to an existing methane fermentation tank, there is a problem that it cannot be applied because the tank capacity is insufficient. In addition, when a methane fermentation tank of the UASB type or EGSB type is applied, the suspension containing a large amount of suspended solids (high SS concentration) in the acid generation tank is not treated, and only the membrane filtrate separated from the solid-liquid is treated, so there is a problem that the suspension is discharged outside the system and a large amount of solid waste is generated.

[0007] Therefore, the present invention aims to provide a fuel gas production apparatus and a fuel gas production method for producing biomass-derived fuel gas that can reduce the amount of liquid culture medium, such as artificial culture medium (artificial saliva), and dilution water used to adjust the solids concentration (TS) in the treatment liquid in which organic waste is decomposed, and that can reduce the amount of solid waste discharged. [Means for solving the problem]

[0008] In order to solve the above problems, the fuel gas production apparatus of the present invention is a fuel gas production apparatus for producing biomass-derived fuel gas, and includes a culture tank for culturing ruminal microorganisms, a pretreatment tank for mixing the culture solution of the ruminal microorganisms obtained in the culture tank with organic waste and treating the organic waste to convert it into easily degradable organic waste and volatile fatty acids, and a fermentation tank for fermenting the easily degradable organic waste and the volatile fatty acids obtained in the pretreatment tank as substrates.

[0009] According to the above configuration, ruminal microorganisms (lignocellulose-decomposing bacteria) that decompose organic waste can be cultured in the culture tank and stably supplied to the downstream pretreatment tank. Therefore, when operating the fuel gas production apparatus, the frequency of collecting ruminal fluid from ruminants and transporting it to the facility where the fuel gas production apparatus is installed is reduced, thereby reducing costs. In addition, since the pretreatment tank is specialized for treating organic waste and producing easily decomposable organic waste such as partial decomposition products of organic waste and volatile fatty acids, the amount of organic waste supplied to the pretreatment tank can be set higher than usual. Furthermore, since the pretreatment liquid in the pretreatment tank does not need to be separated into solid and liquid and is supplied to the fermentation tank connected downstream, a fermentation tank of a complete mixing type (anaerobic digestion) method that treats solid (slurry-like) waste, which is widely used both domestically and internationally, can be adopted. Unlike UASB, which only treats membrane-filtered water from pretreated liquid that has been separated into solid and liquid in an upstream pretreatment tank, fermentation tanks using the complete mixing fermentation method can also treat suspensions, which reduces the amount of liquid culture medium such as artificial medium (artificial saliva) and dilution water used. In addition, since fermentation is carried out using the easily decomposable organic waste contained in the suspension of the pretreated liquid as a substrate, it is possible to reduce the amount of solid waste discharged and to expect an increase in the production of fuel gas. Furthermore, since the processing carried out in each tank, namely the culture tank, pretreatment tank, and fermentation tank, is clearly defined, operation management and troubleshooting are made easier.

[0010] The fuel gas production apparatus of the present invention may be configured so that the organic waste is supplied to the culture tank and the pretreatment tank at a predetermined ratio.

[0011] According to the above configuration, by supplying organic waste to the culture tank and the pretreatment tank at a predetermined ratio, ruminal microorganisms (lignocellulose-decomposing bacteria) having high organic waste decomposition activity can be cultivated in the culture tank, while the pretreatment tank efficiently produces easily decomposable organic waste such as partial decomposition products of organic waste and volatile fatty acids.

[0012] Moreover, the fuel gas production apparatus of the present invention may be configured to supply a pretreatment liquid containing the easily decomposable organic waste and the volatile fatty acids obtained in the pretreatment tank to the culture tank.

[0013] According to the above configuration, the pretreatment liquid in the pretreatment tank contains undecomposed or partially decomposed lignocellulose contained in the organic waste, as well as substances that serve as nitrogen and phosphorus sources, which serve as nutrient sources for the lignocellulose-decomposing bacteria. Therefore, by supplying the pretreatment liquid to the culture tank, the growth and proliferation of the lignocellulose-decomposing bacteria in the culture tank is further promoted, and further hydrolysis increases the production of volatile fatty acids, etc.

[0014] The fuel gas production apparatus of the present invention may further include a solid-liquid separation means for separating the culture solution into solid and liquid in the culture tank.

[0015] According to the above configuration, by providing a solid-liquid separation means in the culture tank, the culture liquid in the culture tank can be separated into a filtrate containing a high concentration of volatile fatty acids that are unfavorable for the growth and proliferation of lignocellulose-decomposing bacteria, and a suspension containing suspended matter with many lignocellulose-decomposing bacteria attached. Therefore, it becomes possible to individually control the hydraulic retention time (HRT) and the sludge retention time (SRT), and the filtrate containing a large amount of volatile fatty acids is discharged from the culture tank, promoting the growth and proliferation of the lignocellulose-decomposing bacteria contained in the suspension.

[0016] The fuel gas production apparatus of the present invention may be configured so that easily decomposable organic waste is supplied to the fermenter.

[0017] According to the above-mentioned configuration, since the easily decomposable organic waste is supplied to the fermentation tank and not to the pretreatment tank, the pretreatment tank can be made compact, and accordingly, the amount of liquid culture medium such as artificial culture medium (artificial saliva) and dilution water used can be reduced.

[0018] In order to solve the above problems, the fuel gas production method of the present invention is a fuel gas production method for producing biomass-derived fuel gas, and includes a culture process for culturing ruminal microorganisms, a pretreatment process for mixing the culture solution of the ruminal microorganisms obtained in the culture process with organic waste and treating the organic waste to convert it into easily degradable organic waste and volatile fatty acids, and a fermentation process for fermenting the easily degradable organic waste and the volatile fatty acids obtained in the pretreatment process as substrates, and the culture process further includes a solid-liquid separation process for separating the culture solution into solid and liquid.

[0019] According to the above configuration, in the culture step, ruminal microorganisms (lignocellulose-decomposing bacteria) that decompose organic waste can be cultured and stably supplied to the pretreatment tank in which the pretreatment step is carried out. Therefore, when carrying out the fuel gas production method, the frequency of collecting ruminal fluid from ruminants and transporting it to the facility in which the fuel gas production method is carried out is reduced, thereby reducing costs. In addition, since the pretreatment tank in which the pretreatment step is carried out is specialized for the functions of producing easily decomposable organic waste such as partial decomposition products of organic waste and volatile fatty acids, the amount of organic waste supplied to the pretreatment tank can be set higher than usual. Furthermore, since the pretreatment liquid in the pretreatment tank does not need to be separated into solid and liquid and is supplied to the downstream fermentation tank, the fermentation step can be carried out by adopting a fermentation tank of a complete mixing type fermentation (anaerobic digestion) method that treats solid (slurry-like) waste, which is widely used both domestically and overseas. Unlike UASBs and the like, which can only treat membrane-filtered water from solid-liquid separated pretreatment liquid, fermenters using the complete mixing fermentation method can also treat suspensions, which allows for reduced use of liquid media such as artificial media (artificial saliva) and dilution water. In addition, since fermentation is performed using easily decomposable organic waste contained in the suspension of the pretreatment liquid as a substrate, it is possible to reduce the amount of solid waste discharged and to increase the production of fuel gas. Furthermore, since the processes performed in each process, namely the culture process, pretreatment process, and fermentation process, are clearly defined, operation management and troubleshooting are easy. In addition, by providing a solid-liquid separation process that separates the culture solution of ruminal microorganisms into a solid-liquid separation process, the culture solution in the culture tank can be separated into a filtrate containing a high concentration of volatile fatty acids that are unfavorable for the growth and proliferation of lignocellulose-decomposing bacteria, and a suspension containing suspended matter to which many lignocellulose-decomposing bacteria are attached. This enables separate control of hydraulic retention time (HRT) and solid retention time (SRT), and the filtrate containing a large amount of volatile fatty acids is discharged from the culture tank, promoting the growth and proliferation of lignocellulose-decomposing bacteria contained in the suspension.

[0020] In the fuel gas production method of the present invention, the fermentation step may include at least one of a methane fermentation step and a hydrogen fermentation step.

[0021] According to the above configuration, the fermentation process includes at least one of a methane fermentation process and a hydrogen fermentation process, so that methane gas or hydrogen gas that can be used as a fuel gas can be produced according to the purpose. Effect of the Invention

[0022] According to the present invention, it is possible to reduce the amount of liquid medium such as artificial medium (artificial saliva) used to adjust the solids concentration (TS) in the treatment liquid in which organic waste is decomposed, and the amount of dilution water used, and also to reduce the amount of solid waste discharged. [Brief description of the drawings]

[0023] [Figure 1] 1 is a diagram showing a schematic configuration of a fuel gas production apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing a schematic configuration of a culture tank of the fuel gas production apparatus according to the first embodiment. [Diagram 3] FIG. 4 is a diagram showing a schematic configuration of a fuel gas production apparatus according to a second embodiment. [Figure 4] FIG. 11 is a diagram showing a schematic configuration of a fuel gas production apparatus according to a third embodiment. [Diagram 5] FIG. 1 is a diagram showing a conventional fuel gas production apparatus. [Figure 6] FIG. 2 is an explanatory diagram of a first example of supplying organic waste to the fuel gas production apparatus according to the first embodiment. [Figure 7] FIG. 13 is an explanatory diagram of Example 2 in which organic waste is supplied to a two-phase fuel gas production device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The embodiments and drawings relating to the fuel gas production apparatus for producing biomass-derived fuel gas and the fuel gas production method for producing biomass-derived fuel gas according to the present invention will be specifically described below. However, the present invention is not intended to be limited to the configurations shown in the embodiments and drawings described below.

[0025] (First embodiment) Hereinafter, a fuel gas production apparatus 100 and a fuel gas production method according to the first embodiment will be described with reference to Figures 1 and 2. Figure 1 is a diagram showing a schematic configuration of the fuel gas production apparatus 100 according to the first embodiment. Figure 2 is a diagram showing a schematic configuration of a culture tank 10 of the fuel gas production apparatus 100 according to the first embodiment.

[0026] The fuel gas production apparatus 100 shown in Fig. 1 is an apparatus for producing fuel gas such as biomethane gas or biohydrogen using organic waste B as a raw material. The fuel gas production apparatus 100 is a three-phase system consisting of a culture tank 10 for culturing ruminal microorganisms, a pretreatment tank 20 for converting (decomposing) the organic waste B using ruminal microorganisms (lignocellulose-decomposing bacteria) that treat the organic waste B into a form that is easily usable in the downstream fermentation tank 30 (easily decomposable organic waste and volatile fatty acids), and a fermentation tank 30 for fermenting the easily decomposable organic waste and volatile fatty acids, which are decomposition products of the organic waste B, as substrates to produce fuel gas.

[0027] (culture tank) In the culture tank 10, ruminal microorganisms present in ruminal fluid collected from ruminants such as cows are cultured. When a liquid medium M such as an artificial medium (artificial saliva) and organic waste B are supplied to the culture tank 10, the ruminal microorganisms (lignocellulose-decomposing bacteria) proliferate by decomposing and metabolizing the organic waste B, and produce decomposition products of the organic waste B (easily decomposable organic waste such as partial decomposition products of lignocellulose, and volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid). The culture solution of the lignocellulose-decomposing bacteria in the culture tank 10 is steadily supplied to the downstream pretreatment tank 20.

[0028] The conditions in the culture tank 10 are preferably set to simulate the physiological state of the first stomach (rumen) of a ruminant animal such as a cow. In addition, it is preferable that the hydraulic retention time (HRT) and solid retention time (SRT) are arbitrarily controlled by the solid-liquid separation means 40 so that the lignocellulose-decomposing bacteria can grow sufficiently. Since the lignocellulose-decomposing bacteria grow by adhering to the surface of solid matter in the culture solution, it is preferable that the operation is controlled so that the SRT is longer than the HRT.

[0029] (Pretreatment tank) The pretreatment tank 20 is supplied with a culture solution of lignocellulose-decomposing bacteria from the upstream culture tank 10, and furthermore, organic waste B is introduced and mixed. In the pretreatment tank 20, the organic waste B is decomposed by the action of the lignocellulose-decomposing bacteria, and decomposition products of the organic waste B that have been reduced in molecular weight (easily decomposable organic waste such as partial decomposition products of lignocellulose, and volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid) are produced. It is sufficient that at least one selected from easily decomposable organic waste and volatile fatty acids is produced in the pretreatment tank 20. As with the culture tank 10, the pretreatment tank 20 is preferably set to a condition simulating the physiological state of the first stomach (rumen) of a ruminant such as a cow.

[0030] In the fuel gas production apparatus 100, it is preferable to supply organic waste B at a predetermined ratio (for example, 1:10) to the culture tank 10 and the pretreatment tank 20. In the culture tank 10, ruminal microorganisms (lignocellulose-decomposing bacteria) having high decomposition activity for organic waste B can be cultured, and in the pretreatment tank 20, the organic waste B is efficiently treated.

[0031] (Fermentation tank) When the pretreatment liquid containing a large amount of easily decomposable organic waste and volatile fatty acids is supplied from the pretreatment tank 20 to the fermentation tank 30, a fermentation reaction using the easily decomposable organic waste and volatile fatty acids as substrates (raw materials) proceeds, and fuel gas G is produced. The substrate supplied to the fermentation tank 30 may contain at least one selected from easily decomposable organic waste and volatile fatty acids. The fermentation reaction carried out in the fermentation tank 30 may be methane fermentation contributing to the production of biomethane gas, or hydrogen fermentation contributing to the production of biohydrogen. For example, it may be a two-stage hydrogen-methane fermentation in which hydrogen fermentation is carried out as a first stage and then methane fermentation is carried out as a second stage. The fermentation residue R discharged from the fermentation tank 30 is concentrated and can be used as fertilizer, building material, etc.

[0032] As described above, the fuel gas production apparatus 100 of this embodiment has a separate role for each tank: (1) the culture tank 10 for culturing ruminal microorganisms, (2) the pretreatment tank 20 for treating organic waste B to produce easily degradable organic waste and volatile fatty acids, and (3) the fermentation tank 30 for carrying out fermentation reactions using the easily degradable organic waste and volatile fatty acids as substrates. This has the advantage of making it easier to control operation.

[0033] (solid-liquid separation means) FIG. 2 is a diagram showing a schematic configuration of the culture tank 10 of the fuel gas production apparatus 100 according to the first embodiment, and a filtration membrane 41 is shown as a solid-liquid separation means 40 installed in the culture tank 10. The solid-liquid separation means 40 separates the culture liquid into a filtrate and a suspension. As shown in FIG. 2, in the culture tank 10, the culture liquid is stirred by the stirrer 50, and the filtrate separated into solid and liquid by the filtration membrane 41 and the suspension containing undecomposed or partially decomposed suspended matter are sent to the downstream pretreatment tank 20 through the filtrate sending pipe 11 and the suspension sending pipe 12, respectively. The hydraulic retention time (HRT) and solid retention time (SRT) of the culture liquid are individually controlled by appropriately adjusting the amount of the filtrate and suspension of the culture liquid drawn out from the culture tank 10 and sent to the pretreatment tank 20 by the pump P. Since the filtrate and suspension of the culture liquid contain a large number of lignocellulose-decomposing bacteria, when they are supplied to the downstream pretreatment tank 20, the decomposition of the organic waste B is efficiently performed. In Fig. 2, a membrane separation method using a filtration membrane 41 is illustrated as the solid-liquid separation means 40, but separation by gravity sedimentation separation or flotation separation may also be used (not shown). When a membrane separation method is used as the solid-liquid separation means 40, the filtration membrane 41 may be installed so that the inside of the filtration membrane 41 is under negative pressure with the entire filtration membrane 41 immersed in the culture solution as shown in Fig. 2, but in order to reduce the power of the pump P of the filtrate delivery pipe 11 and reduce clogging of the filtration membrane 41 due to suspended matter, the filtration membrane 41 may be installed so that the inside and outside of the filtration membrane 41 are under equal pressure with the upper end of the filtration membrane 41 immersed above the liquid level of the culture solution (not shown).

[0034] Second embodiment 3 is a diagram showing a schematic configuration of a fuel gas production apparatus 101 according to the second embodiment. The fuel gas production apparatus 101 according to the second embodiment further includes a pretreated liquid supply pipe 21 for mixing organic waste B with dilution water W and feeding the mixture into a pretreatment tank 20, and supplying the pretreated liquid obtained in the pretreatment tank 20 to the culture tank 10, in addition to the fuel gas production apparatus 100 according to the first embodiment. The pretreated liquid contains undecomposed or partially decomposed products of lignocellulose, and substances that serve as nitrogen and phosphorus sources. Therefore, by supplying the pretreated liquid to the culture tank 10, the growth and proliferation of lignocellulose-decomposing bacteria in the culture liquid is further promoted, and further hydrolysis improves the production of volatile fatty acids and easily decomposable organic waste with a small molecular weight.

[0035] Third embodiment FIG. 4 is a diagram showing a schematic configuration 102 of a fuel gas production apparatus according to a third embodiment. The fuel gas production apparatus 102 according to the third embodiment further includes a path for supplying easily decomposable organic waste C to the fermenter in addition to the fuel gas production apparatus 100 according to the first embodiment. Examples of easily decomposable organic waste C include livestock manure, sludge, and food waste. In the fuel gas production apparatus 102 according to the third embodiment, the easily decomposable organic waste C is supplied to the fermenter 30 and not to the pretreatment tank 20, so that the pretreatment tank 20 can be made compact. Accordingly, the amount of liquid medium M such as an artificial medium (artificial saliva) and dilution water W used can be reduced.

[0036] 5 is a diagram showing a fuel gas production apparatus 200 configured with a conventional two-phase process. In the conventional fuel gas production apparatus 200, the cultivation of ruminal microorganisms and the decomposition of organic waste B are carried out in a single culture tank / pretreatment tank 220. The pretreatment liquid in the culture tank / pretreatment tank 220 is separated into solid and liquid by a filtration membrane 41 (solid-liquid separation means 40), and the filtrate is sent to the downstream UASB 230 through a filtrate delivery pipe 11. In the UASB 230, methane fermentation is carried out using volatile fatty acids contained in the filtrate as a substrate.

[0037] In order to perform solid-liquid separation of the pretreated liquid in the culture tank and pretreatment tank 220 without any problems, it is necessary to adjust the solid concentration (TS) of the organic waste B supplied to the culture tank and pretreatment tank 220 to approximately 1.0% by weight or less. Since a large amount of liquid medium M such as an artificial medium (artificial saliva) and dilution water W are required to adjust the solid concentration (TS), the methane fermentation tank connected downstream of the culture tank and pretreatment tank 220 is limited to UASB and EGSB that can handle high loads. However, when the SS concentration of the pretreated liquid supplied from the upstream culture tank and pretreatment tank 220 exceeds 500 mg / L (1000 mg / L in the case of EGSB), it adversely affects the settling of the granular sludge present in the methane fermentation tank. Therefore, only the filtrate obtained by solid-liquid separation of the pretreated liquid by the filtration membrane 41 is supplied to the UASB 230. Therefore, in the UASB 230, the pretreatment liquid (suspension) containing a large amount of undecomposed suspended solids cannot be treated, and a large amount of solid waste S is discharged.

[0038] (Fuel gas production method) The fuel gas production method of the present invention will be described in detail below. The fuel gas in the present invention includes biomethane gas produced by methane fermentation and biohydrogen produced by hydrogen fermentation. Biogas is composed of about 60% methane and about 40% carbon dioxide, and may be used as fuel as it is, or may be used as high-concentration methane gas after removing carbon dioxide.

[0039] [Organic waste] Organic wastes that can be used as raw materials for fuel gases such as biomethane gas and biohydrogen include unused agricultural and forestry waste such as forest thinnings, rice straw, rice husks, bagasse, thatch, and aquatic plants, as well as lignocellulosic industrial waste such as vegetable waste, tea leaves, coffee grounds, soybean pulp, shochu dregs, construction waste, waste paper, waste paper, and urban waste, and lignocellulosic biomass such as biomass resource crops such as Erianthus and Giant Miscanthus. In addition, paper cut into pieces by a shredder is incinerated because the fibers are broken and it is difficult to recycle, but such cut paper can also be used as a raw material. Furthermore, only one type of the organic wastes listed above may be used as a raw material, or multiple types may be mixed together to use as a raw material.

[0040] Lignocellulose, the main component of the cell wall of plant cells, is composed of hemicellulose, cellulose, and lignin tightly bound together. Rumen fluid present in the first stomach (rumen) of ruminants such as cows contains a large number of ruminal microorganisms that produce enzymes that decompose lignocellulose. In the method for producing fuel gas in the present invention, in the culture step, ruminal microorganisms (lignocellulose-decomposing bacteria) that decompose organic waste are cultured, in the pretreatment step, the organic waste is decomposed using the action of the lignocellulose-decomposing bacteria to produce easily decomposable organic waste, volatile fatty acids, etc., and in the fermentation step, a fermentation reaction is carried out using the easily decomposable organic waste, volatile fatty acids, etc. as fermentation substrates (raw materials), thereby making it possible to efficiently produce fuel gas such as biomethane gas and biohydrogen. In the fermentation step, if the conditions are such that methane-producing bacteria are predominantly present, methane fermentation is carried out and biomethane gas is produced. On the other hand, in the fermentation step, if the conditions are such that hydrogen-producing bacteria are predominantly present, hydrogen fermentation is carried out and biohydrogen is produced. Depending on the use and purpose of the fuel gas, the fermentation process may be a methane fermentation process or a hydrogen fermentation process. In addition, a two-stage fermentation of hydrogen and methane fermentation may be performed in which a hydrogen fermentation process is performed as a pre-reaction of the methane fermentation process. In this case, hydrogen fermentation may be performed in one fermentation tank by controlling pH, HRT, etc., and then methane fermentation may be performed in a separate tank. Alternatively, a hydrogen fermentation tank and a methane fermentation tank may be used separately, and hydrogen fermentation and methane fermentation may be performed in separate tanks.

[0041] [Rumen microorganisms] Rumen microorganisms are anaerobic bacteria that exist in the ruminal fluid, which is a digestive fluid present in the first stomach (rumen) of ruminants. Ruminants include cows, sheep, goats, deer, camels, llamas, etc. For example, the first stomach of an adult cow has a volume of 150 to 200 L, and many lignocellulose-decomposing bacteria, hemicellulose-decomposing bacteria, lignin-decomposing bacteria, starch-decomposing bacteria, methanogens, hydrogen-producing bacteria, etc. live in the ruminal fluid. Lignocellulose-decomposing bacteria can produce enzymes such as cellulase that decompose lignocellulose (fibrous material). Therefore, when ruminants ingest fibrous material such as grass, the lignocellulose-decomposing bacteria decompose the lignocellulose, producing volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid, which serve as an energy source for ruminants. Hydrogen-producing bacteria produce acetic acid and hydrogen using substrates such as propionic acid, butyric acid, and valeric acid produced by lignocellulose-decomposing bacteria.Methanogenic bacteria produce methane using substrates such as acetic acid or hydrogen and carbon dioxide produced by lignocellulose-decomposing or hydrogen-producing bacteria.

[0042] (Culture process) In the culturing step, ruminal microorganisms (lignocellulose-decomposing bacteria) having high lignocellulose decomposition activity are cultured. In the culturing step, for example, the number of at least one of three types of lignocellulose decomposing bacteria, Fibrobacter succinogenes, Ruminococcus albus, and Prevotella ruminicola, present is used as an indicator to adjust the temperature, oxidation-reduction potential (ORP), hydraulic retention time (HRT) or solid retention time (SRT), and ammonium nitrogen concentration of the medium, thereby obtaining a culture solution of ruminal microorganisms (lignocellulose decomposing bacteria) having high lignocellulose decomposition activity. The number of bacteria of these bacteria is not particularly limited, but is preferably determined by a quantitative PCR method, which can rapidly and accurately measure the number of bacteria of a specific bacteria. When quantifying the number of lignocellulose-degrading bacteria using quantitative PCR, genomic DNA is extracted from the culture solution and purified. Since the culture solution of ruminal microorganisms can be cultured in large quantities and subcultured, the culture solution of ruminal microorganisms with an adjusted bacterial count can be used for lignocellulose decomposition as needed.

[0043] As a medium for use in the culture solution for ruminal microorganisms, a natural medium whose base material is derived from natural products may be used, or a synthetic medium in which all of the various nutrients necessary for the growth of ruminal microorganisms are composed of chemicals may be used. In particular, it is preferable that the medium contains a carbon source such as cellulose or hemicellulose, in addition to a nitrogen source such as ammonium salt, which is a nutrient source useful for ruminal microorganisms, a phosphorus source such as phosphate, and the like. In addition, since the pretreatment liquid contains undecomposed or partially decomposed products of lignocellulose contained in organic waste, and substances that serve as nitrogen and phosphorus sources, as a nutrient source for lignocellulose-decomposing bacteria, the pretreatment liquid may be supplied to the culture solution as shown in FIG. 3. In addition, when volatile fatty acids (VFAs) such as acetic acid are produced in the pretreatment step following the culture step, the pH of the pretreatment liquid decreases and the osmotic pressure increases, which changes the quantity and function of the lignocellulose-decomposing bacteria. Therefore, it is preferable to add a buffering agent to the medium in order to mitigate the change in pH and the increase in osmotic pressure. As a buffering agent, it is preferable to use a liquid medium such as an artificial medium (artificial saliva) that imitates the saliva of ruminants, which has a high buffering capacity. Examples of the buffer include sodium chloride, sodium bicarbonate, phosphate, and potassium chloride. The pH of the medium is adjusted to 6.0 to 7.5, more preferably 6.5 to 7.0, by adding an acid or alkali as necessary. The water used for the medium is preferably tap water or groundwater. The ammonium nitrogen concentration of the medium is controlled by adding water to be 50 to 2,000 mg / L, more preferably 60 to 500 mg / L.

[0044] In order to make the culture process anaerobic like the environment in the rumen, the oxidation-reduction potential (ORP) of the culture solution is adjusted to -100mv or less, more preferably -200mv or less, and even more preferably about -250mv. Since ruminal microorganisms (lignocellulose-decomposing bacteria) are anaerobic bacteria, when the ORP becomes higher than a predetermined value (when the ORP approaches an aerobic state), treatments such as injecting an inert gas such as nitrogen gas or carbon dioxide gas, introducing reducing substances such as cysteine, L-ascorbic acid, sodium sulfide, ascorbic acid, methionine, thioglycol, and DTT, or introducing organic matter to consume oxygen by the action of facultative anaerobic bacteria may be performed. The culture process may also be performed in a closed system under a nitrogen or carbon dioxide atmosphere.

[0045] In culturing ruminal microorganisms in the culture tank 10, it is important that the solid retention time (SRT) is longer than the hydraulic retention time (HRT). That is, since lignocellulose decomposing bacteria grow by adhering to the surface of solids, if the SRT is short, they are discharged out of the system together with the solids. On the other hand, if the HRT is longer than necessary, it will cause negative factors such as a decrease in pH due to the produced volatile fatty acids (VFAs) and inhibition of microbial growth. Specifically, the HRT is adjusted to 8 hours to 36 hours, preferably 10 hours to 24 hours, and the SRT is adjusted to 24 hours or more, preferably 48 hours to 168 hours, and more preferably 72 hours to 168 hours. In addition, the temperature of the reaction system in the culture step is controlled to 35 to 42°C, more preferably 37 to 40°C, using a temperature sensor or the like. The organic waste B to be introduced into the culture tank 10 is adjusted so that the solid concentration (TS) in the culture solution is 0.1 to 1.5% by weight, more preferably 0.5 to 1.0% by weight. If the solid concentration (TS) is 0.1% by weight or less, there is a risk that the growth and proliferation of lignocellulose-decomposing bacteria will not be promoted, whereas if it exceeds 1.5% by weight, there is a risk that solid-liquid separation of the culture solution will not be performed properly.

[0046] (solid-liquid separation process) In the culture step, solid-liquid separation of the culture solution of ruminal microorganisms in the culture tank 10 may be performed by a filtration membrane 41 shown in Fig. 2, or may be performed by gravity sedimentation or flotation concentration (not shown). The culture tank 10 shown in Fig. 2 is provided with a filtrate delivery pipe 11 and a suspension delivery pipe 12, but when performing solid-liquid separation by gravity sedimentation or flotation separation, the liquid phase (suspension) with a high SS concentration can be discharged from the tank while stirring the culture solution, and the liquid phase with a low SS concentration can be discharged from the tank by stopping stirring and leaving it to stand for a while. Therefore, only one delivery pipe may be used.

[0047] (Pretreatment process) In the pretreatment process, the lignocellulose contained in the organic waste is partially decomposed by lignin-decomposing enzymes produced by lignocellulose-decomposing bacteria, loosening the strong structure of the lignocellulose, and then decomposed into cellulose and hemicellulose by endoglucanases, exoglucanases, xylanases, etc., respectively, and converted into hexoses (six monosaccharides) such as glucose. Furthermore, pyruvic acid and the like are produced from hexoses (six monosaccharides) such as glucose, and as the reaction proceeds further, volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid are produced. Hydrogen and carbon dioxide are also produced during the metabolic process. In the pretreatment process, it is not necessary for lignocellulose to be decomposed and metabolized to hexoses (six monosaccharides) and volatile fatty acids (VFAs). It is sufficient for the refractory lignocellulose to be decomposed to a form that is easily utilized in the downstream fermentation process, for example, to the oligosaccharide level. In the pretreatment step, the solid matter concentration (TS) of the organic waste B supplied to the pretreatment tank 20 is adjusted to 1.0 to 10.5% by weight, more preferably 0.5 to 10.0% by weight. If the solid matter concentration (TS) is 1.0% by weight or less, there is a risk of a decrease in the production of easily decomposable organic waste and volatile fatty acids, which serve as substrates for fermentation. On the other hand, if it exceeds 10.5% by weight, there is a risk of it becoming difficult to discharge the pretreatment liquid by pump.

[0048] In order to make the pretreatment process anaerobic like the environment in the rumen of a ruminant, the oxidation-reduction potential (ORP) of the pretreatment liquid is adjusted to -100mv or less, more preferably -200mv or less, and even more preferably about -250mv. Since ruminal microorganisms (lignocellulose-decomposing bacteria) are anaerobic bacteria, when the ORP becomes higher than a predetermined value (when it approaches an aerobic state), measures such as injecting an inert gas such as nitrogen gas or carbon dioxide gas, adding a reducing substance such as cysteine, L-ascorbic acid, sodium sulfide, ascorbic acid, methionine, thioglycol, or DTT, or adding organic matter to consume oxygen by the action of facultative anaerobic bacteria, may be taken. The pretreatment process may be carried out in a closed system under a nitrogen or carbon dioxide atmosphere.

[0049] In the pretreatment step, since the HRT and SRT are individually controlled in the upstream culture step, there is no need to individually control the HRT and SRT, and the pretreatment (hydrolysis, acid production) is performed in a completely mixed system. In other words, the pretreatment liquid in the pretreatment tank 20 where the pretreatment step is performed is not separated into a filtrate and a suspension, so that the HRT and SRT are the same. It is preferable that both the HRT and SRT of the pretreatment liquid are 4 to 36 hours. In addition, the temperature of the reaction system in the pretreatment step is controlled to 35 to 42°C, more preferably 37 to 40°C, using a temperature sensor or the like. The reaction in the pretreatment step may be performed statically or with stirring, but it is preferable to perform the reaction with stirring in order to speed up the progress of the pretreatment step.

[0050] (Fermentation process) In the fermentation step, fuel gas is produced using the easily decomposable organic waste and volatile fatty acids produced in the pretreatment step as substrates. Here, examples of fuel gas include biogas, the main component of which is biomethane gas produced by methane fermentation, and biohydrogen produced by hydrogen fermentation. Whether methane fermentation or hydrogen fermentation is carried out in the fermentation step can be adjusted by controlling the temperature and pH in the fermentation tank 30. For example, when the temperature in the fermentation tank 30 is about 37°C (or 55°C) and the pH is 7.0 to 8.0, methane fermentation is mainly carried out because methanogens are predominant. On the other hand, when the temperature in the fermentation tank 30 is about 55°C and the pH is 4.0 to 5.0, hydrogen fermentation is mainly carried out because hydrogen fermentation is predominant. These fermentation steps may be carried out alone, or two-stage fermentation may be carried out, such as a hydrogen-methane fermentation step. The methane fermentation step and the hydrogen fermentation step will be described below.

[0051] (Methane fermentation process) In the methane fermentation process, methane fermentation is carried out using volatile fatty acids such as acetic acid, hydrogen, and carbon dioxide as substrates. As with the pretreatment process, the methane fermentation process is carried out under anaerobic conditions. The composition of the biogas produced in the methane fermentation process is 60-70% methane, 30-40% carbon dioxide, and other trace amounts of nitrogen, oxygen, hydrogen sulfide, water, etc.

[0052] Methane fermentation may be either wet methane fermentation or dry methane fermentation. In addition, either mesophilic methane fermentation or high-temperature methane fermentation may be used. In the case of mesophilic fermentation, it is carried out for 20 to 30 days, more preferably 23 to 27 days, and even more preferably about 25 days, and in the case of high-temperature fermentation, it is carried out for 10 to 20 days, more preferably 13 to 17 days, and even more preferably about 15 days. In the case of mesophilic fermentation, methane fermentation is carried out at 20 to 40°C, more preferably 30 to 37°C or less, and even more preferably about 37°C, and in the case of high-temperature fermentation, it is carried out at 40 to 60°C, more preferably 50 to 55°C, and even more preferably about 55°C. In addition, methane fermentation is carried out at pH 6.8 to 7.6, and more preferably pH 7.0 to 8.0.

[0053] (Hydrogen fermentation process) In the hydrogen fermentation process, hydrogen fermentation is carried out using volatile fatty acids such as propionic acid, butyric acid, and valeric acid as substrates. The hydrogen fermentation process is carried out under anaerobic conditions, similar to the pretreatment process using lignocellulose-decomposing bacteria. In the hydrogen fermentation process, biohydrogen and carbon dioxide are produced in a ratio of approximately 1:1, and organic acids such as acetic acid are produced.

[0054] Hydrogen fermentation is carried out at 30 to 60° C., more preferably 50 to 60° C., and even more preferably 55° C. In addition, hydrogen fermentation is carried out at a pH of 4.0 to 6.5, and more preferably a pH of 4.0 to 5.0.

[0055] In the hydrogen fermentation process, acetic acid, hydrogen, and carbon dioxide, which are substrates for methane fermentation, are produced. Therefore, a two-stage fermentation of hydrogen and methane fermentation may be performed after the hydrogen fermentation process. Since hydrogen-producing bacteria grow faster than methane-producing bacteria, the bacteria can be retained even if the HRT in the tank is 2 to 3 hours. In the case of two-stage fermentation of hydrogen and methane fermentation, hydrogen fermentation takes 1 to 2 days and methane fermentation takes 7 to 10 days, which is shorter than the case of methane fermentation alone. Furthermore, in the case of two-stage fermentation of hydrogen and methane fermentation, a part of the methane fermentation liquid discharged from the methane fermentation process may be returned to the hydrogen fermentation process. In the hydrogen fermentation process, the pH decreases due to the production of volatile organic acids, which may decrease the activity of the hydrogen-producing bacteria and reduce the amount of hydrogen generated. However, by returning the methane fermentation liquid to the hydrogen fermentation process, the decreased pH can be neutralized or the decrease in pH can be prevented, making it possible to suppress the decrease in activity of the hydrogen-producing bacteria and maintain the amount of hydrogen generated.

[0056] (Case Study) Below, we consider cases where lignocellulosic waste discharged from food factory A is treated using a three-phase process and a two-phase process. As the fermentation tank, a UASB is not used, but an existing complete mixing type methane fermentation tank for solid biomass is used.

[0057] <Conditions for consideration> Organic waste output: 2.2 tons of dry weight per day (2.2t-DW / d) -Volume of existing methane fermentation tank: 200m 3 - Planned HRT for existing methane fermentation tank: 10 days Solid concentration (TS) of biomass in the culture tank (culture tank and pretreatment tank): Approximately 1.1% by weight Solid concentration (TS) of biomass in the pretreatment tank: Approximately 10.0% by weight - HRT of culture tank or culture tank / pretreatment tank: approx. 14 hours - SRT of culture tank or culture tank / pretreatment tank: Approx. 62 hours

[0058] The SRT of the culture tank or culture tank / pretreatment tank is the amount of liquid culture medium such as artificial medium (artificial saliva) or dilution water supplied per day (m 3 / d) is taken as dV, and the amount of filtrate discharged per day (m 3 / d) is fV, and the tank volume of the culture tank (m 3 ) as FV, ​​and the calculation can be made using the following formula (1). The following formula (1) was taken from "Continuous cultivation of rumen microorganisms, a system with possible application to the anaerbic degradation of lignocellulosic waste materials" by Huub J. Gijzen and 3 others, Vol. 25, pp. 155-162 (1986).

[0059]

number

[0060] The HRT of a methane fermentation tank is calculated by the tank volume (m 3 ) is calculated by dividing the daily supply of liquid medium (artificial saliva) or dilution water (m 3 / d) The value is divided by dV.

[0061] (Case 1) 6 is an explanatory diagram of Case 1 in which organic waste is supplied to the fuel gas production apparatus according to the first embodiment. In Case 1, a three-phase process consisting of a culture tank 10, a pretreatment tank 20, and a methane fermentation tank 30 was considered. Of the 2.2t-DW / d of lignocellulosic biomass discharged from food factory A, 0.22t-DW / d is used as a substrate (culture medium component) for culturing ruminal microorganisms in a culture tank. In the culture tank, the supply volume (dV) of liquid culture medium such as artificial medium (artificial saliva) or dilution water is set at 20m3 so that solid-liquid separation is sufficiently performed. 3 The culture medium is set to a solid concentration (TS) of 1.1% by weight. In order to allow the ruminal microorganisms to grow sufficiently in the culture tank, the SRT is set to 64 hours, the HRT to about 11 hours, and the filtrate discharge rate (fV) to 17m 3 / d, the tank volume (FV) of the culture tank is 8m according to the above formula 1. 3 The culture tank is controlled to maintain a pH of approximately 6.9, an oxidation-reduction potential (ORP) of -250 mV or less, and a temperature of 39°C. Of the 2.2t-DW / d of lignocellulosic biomass discharged from food factory A, 0.22t-DW / d was fed to the culture tank, and the remaining 1.98t-DW / d was fed to the pretreatment tank. The filtrate discharged from the culture tank was 17m 3 / d and suspension 3m 3 The optimal HRT of the pretreatment tank (same as SRT because it is a complete mixing type) varies depending on the type of organic waste being treated. As shown in Figure 6, if the HRT is 12 hours, and the tank volume is 10 m 3 (When the HRT is 6 hours, the tank volume is 5m 3 If the HRT is 24 hours, the tank volume is 20 m 3 (A pretreatment tank of this type can be used.) The pretreatment tank, like the culture tank, should be controlled to maintain a pH of approximately 6.9, an oxidation-reduction potential (ORP) of -250 mV or less, and a temperature of 39°C. 20m of pre-treated liquid being treated in the pre-treatment tank 3 / d is a methane fermentation tank (tank volume 200m 3 The HRT in the methane fermentation tank is 200 m 3 The daily supply of artificial medium (artificial saliva) or other liquid medium or diluted water is 20 m 3 / d(dV), the value is 10 days [200(m 3 ) / 20(m 3 Since this is the same as the planned HRT of 10 days for the existing methane fermentation tank, it is clear that the methane fermentation tank in Case 1 can secure a sufficient HRT to function.

[0062] (Case 2) 7 is an explanatory diagram of Case 2 in which lignocellulosic biomass is supplied to a two-phase fuel gas production device. In Case 2, a two-phase process consisting of a culture tank / pretreatment tank 320 and a methane fermentation tank 30 was considered. The 2.2 t-DW / d of lignocellulosic biomass discharged from the food factory is fed into the culture / pretreatment tank at a solids concentration (TS) of 1.1% by weight to facilitate solid-liquid separation using membrane filtration in the culture / pretreatment tank. The total solids concentration is 200 m3 / day. 3 In other words, 200m of artificial medium (artificial saliva) or other liquid medium is supplied to the culture tank / pretreatment tank. 3 The treated water is fed to the downstream methane fermentation tank through the culture tank / pretreatment tank. The HRT in the methane fermentation tank is 200 m3. 3 The daily supply of artificial medium (artificial saliva) or other liquid medium or diluted water is 200 m 3 / d(dV), the value is calculated as [200(m 3 ) / 200(m 3 Since this is significantly shorter than the planned HRT of 10 days for the existing methane fermentation tank, it is clear that the methane fermentation tank in Case 2 cannot ensure a sufficient HRT to function properly.

[0063] As described above, by adopting a three-phase process consisting of a culture tank for ruminal microbial communities, a pretreatment tank specialized in the functions of hydrolysis and acid production of organic waste, and a methane fermentation tank, it is possible to increase the concentration of organic waste treated in the pretreatment tank, which in turn reduces the amount of pretreatment liquid supplied to the methane fermentation tank, and it has become clear that a sufficient HRT can be secured to enable the existing complete mixing type methane fermentation tank to function. [Industrial Applicability]

[0064] The fuel gas production apparatus and fuel gas production method of the present invention can be used in applications where organic waste including industrial waste such as urban garbage, including waste paper and other waste materials, and lignocellulosic industrial waste, including food waste, agricultural and forestry waste, and construction waste, is decomposed and used as a raw material to generate fuel gas such as methane or hydrogen. [Explanation of symbols]

[0065] 10:Culture tank 11: Filtrate delivery pipe 12: Suspension delivery pipe 20: Pre-treatment tank 21: Pre-treatment liquid supply pipe 30: Fermentation tank 40: Solid-liquid separation means 41: Filtration membrane 50: Mixer 100, 101, 102: Fuel gas production equipment B: Organic waste C: Easily decomposable organic waste G: Fuel gas M: Liquid medium such as artificial medium (artificial saliva) W: Diluted water S: Solid waste T: Treated water P: Pump R: Fermentation residue

Claims

1. A fuel gas production apparatus for producing a fuel gas derived from biomass, A culture tank for culturing ruminal microorganisms; A pretreatment tank in which the culture solution of the rumen microorganisms obtained in the culture tank is mixed with organic waste and the organic waste is treated to convert it into easily decomposable organic waste and volatile fatty acids; a fermenter for performing fermentation using the easily decomposable organic waste and the volatile fatty acids obtained in the pretreatment tank as substrates; Equipped with The culture tank is provided with a solid-liquid separation means for separating the culture solution into a filtrate and a suspension, a filtrate delivery pipe for supplying the filtrate to the pretreatment tank, and a suspension delivery pipe for supplying the suspension to the pretreatment tank.

2. 2. The fuel gas production device according to claim 1, wherein the organic waste is supplied to the culture tank and the pretreatment tank at a predetermined ratio.

3. 3. The fuel gas production apparatus according to claim 1, wherein a pretreatment liquid containing the easily decomposable organic waste and the volatile fatty acids obtained in the pretreatment tank is supplied to the culture tank.

4. 4. The fuel gas production device according to claim 1, wherein the device is configured to supply easily decomposable organic waste to the fermenter.

5. A method for producing a fuel gas derived from biomass, comprising: A culturing step of culturing ruminal microorganisms; A pretreatment process in which the culture solution of the rumen microorganism obtained in the culture process is mixed with organic waste, and the organic waste is treated to convert it into easily decomposable organic waste and volatile fatty acids; a fermentation step in which the easily decomposable organic waste obtained in the pretreatment step and the volatile fatty acids are fermented as substrates; Equipped with The culture step further includes a solid-liquid separation step of separating the culture solution into a filtrate and a suspension, A fuel gas production method comprising: a filtrate delivery step of supplying the filtrate to the pretreatment step; and a suspension delivery step of supplying the suspension to the pretreatment step.

6. 6. The method for producing fuel gas according to claim 5, wherein the fermentation process includes at least one of a methane fermentation process and a hydrogen fermentation process.

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