Hydrogen fermentation treatment system and hydrogen fermentation treatment method

Abstract

To provide a hydrogen fermentation treatment system and a hydrogen fermentation treatment method which perform hydrogen fermentation using lignocellulosic biomass, which is refractory organic waste, as raw material, thereby efficiently producing biogas such as hydrogen gas.SOLUTION: A hydrogen fermentation treatment system includes: a storage tank 10 which stores a mixture containing at least one of rumen fluid and rumen microbial culture solution, cultivated in a culture tank 40, as well as lignocellulosic biomass; and a decomposition / hydrogen-fermentation tank 20 which performs decomposition treatment of the mixture supplied from the storage tank 10 and then hydrogen fermentation treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrogen fermentation treatment system and a hydrogen fermentation treatment method. [Background technology]

[0002] Lignocellulosic biomass is an abundant organic carbon source on Earth that 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. Furthermore, lignocellulosic biomass forms a lignocellulose structure in which cellulose is intricately intertwined with polymeric compounds called hemicellulose and lignin, making it a difficult-to-decompose organic waste. Therefore, the decomposition process requires a great deal of energy, cost, and time. Therefore, the expansion of its use as an energy resource has been hindered.

[0003] BACKGROUND ART Conventionally, there is known a technique for producing biogas such as hydrogen gas and methane gas by solubilizing organic waste such as food waste and carrying out two-stage hydrogen-methane fermentation (for example, Patent Document 1).

[0004] Patent Document 1 discloses an anaerobic treatment method that involves a two-stage fermentation process that combines anaerobic solubilization, in which food waste organic waste consisting mainly of carbohydrate waste or food waste organic waste consisting mainly of cellulose solids is anaerobicly solubilized to reduce the molecular weight of the waste, with hydrogen fermentation, followed by a completely mixed methane fermentation process in the latter stage, to recover hydrogen and methane. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-13896 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the anaerobic treatment method described in Patent Document 1, organic waste from food waste, primarily consisting of carbohydrate waste, or organic waste from food waste, primarily consisting of cellulosic solids, is anaerobic-solubilized to lower molecular weight compounds, and biogas is obtained through a two-stage fermentation process involving hydrogen fermentation and methane fermentation. However, to anaerobically solubilize lignocellulosic biomass, a difficult-to-decompose organic waste, and decompose it into reducing sugars, which are the substrate for hydrogen fermentation, requires a long decomposition reaction time (hydraulic residence time), necessitating the installation of a large-capacity fermenter. Furthermore, when lignocellulosic biomass with a low moisture content is fed to a hydrogen fermenter, it must be diluted with water to a concentration that can be transported by pump, etc., which poses a problem in locations with limited available water volume, making sufficient dilution difficult. Furthermore, using tap water for dilution raises the problem of high water costs.

[0007] Therefore, an object of the present invention is to provide a hydrogen fermentation treatment system and a hydrogen fermentation treatment method for efficiently producing biogas such as hydrogen gas by performing hydrogen fermentation using lignocellulosic biomass, which is a difficult-to-decompose organic waste, as a raw material. [Means for solving the problem]

[0008] In order to solve the above problems, the hydrogen fermentation treatment system of the present invention comprises a storage tank for storing a mixed liquid containing at least one of rumen fluid and rumen microbial culture fluid cultured in a culture tank, and lignocellulosic biomass, and a decomposition / hydrogen fermentation tank for performing decomposition treatment and hydrogen fermentation treatment of the mixed liquid supplied from the storage tank.

[0009] According to the above configuration, the decomposition process progresses by mixing lignocellulosic biomass with rumen fluid or rumen microbial culture fluid in the storage tank, making it possible to reduce the hydraulic retention time or tank capacity of the subsequent decomposition / hydrogen fermentation tank.

[0010] Furthermore, the hydrogen fermentation treatment system of the present invention may further include a first methane fermentation tank for subjecting organic waste to methane fermentation treatment, and may be configured to supply the methane fermentation liquid in the first methane fermentation tank to at least one of the storage tank and the culture tank.

[0011] According to the above configuration, a nitrogen source can be supplied to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by supplying the methane fermentation liquid from the first methane fermenter to at least one of the storage tank and the culture tank. The lignocellulose-degrading microorganisms contained in the rumen microorganisms consume nitrogen during the process of decomposing lignocellulose-based biomass in the decomposition / hydrogen fermenter to produce reducing sugars. Therefore, supplying a methane fermentation liquid rich in a nitrogen source to the storage tank or other storage tank in advance can maintain or improve lignocellulose decomposition activity. Furthermore, when treating organic waste, such as sludge generated by biological wastewater treatment methods such as activated sludge, livestock manure, and food waste, in a digester (first methane fermenter), the digested sludge (methane fermentation liquid) is not widely used as liquid fertilizer or compost, so wastewater treatment requires a wastewater treatment facility. However, using the digested sludge as a nitrogen source for the lignocellulose-degrading microorganisms can reduce facility costs.

[0012] Furthermore, the hydrogen fermentation treatment system of the present invention may further include a second methane fermentation tank that performs methane fermentation using the hydrogen fermentation liquid in the decomposition / hydrogen fermentation tank as a raw material, and may be configured to return the methane fermentation liquid in the second methane fermentation tank to at least one of the storage tank and the culture tank.

[0013] According to the above configuration, a nitrogen source can be supplied to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by returning the methane fermentation liquid in the second methane fermenter to at least one of the storage tank and the culture tank. The lignocellulose-degrading microorganisms contained in the rumen microorganisms consume nitrogen in the process of decomposing lignocellulose-based biomass in the decomposition / hydrogen fermenter to produce reducing sugars. Therefore, by supplying a methane fermentation liquid rich in nitrogen source to the storage tank or the like in advance, the lignocellulose decomposition activity can be maintained or improved.

[0014] In order to solve the above problems, the hydrogen fermentation treatment system of the present invention comprises a storage tank for storing a mixed liquid containing at least one of rumen fluid and rumen microbial culture fluid cultured in a culture tank and lignocellulosic biomass, a pretreatment tank for decomposing the mixed liquid supplied from the storage tank, and a hydrogen fermentation tank for hydrogen fermenting the pretreated liquid in the pretreatment tank.

[0015] According to the above configuration, the decomposition process progresses by mixing lignocellulosic biomass with rumen fluid or rumen microbial culture fluid in the storage tank, making it possible to reduce the hydraulic retention time or tank volume of the downstream pretreatment tank and hydrogen fermenter. Furthermore, the pretreatment tank installed downstream of the storage tank is specialized for the function of decomposing lignocellulosic biomass and producing reducing sugars, which serve as a substrate for hydrogen fermentation, and its role is separate from that of the hydrogen fermenter. This has the advantage of making operation control and management easier.

[0016] Furthermore, the hydrogen fermentation treatment system of the present invention may further include a first methane fermentation tank for subjecting organic waste to methane fermentation treatment, and may be configured to supply the methane fermentation liquid in the first methane fermentation tank to at least one of the storage tank, the culture tank, and the pretreatment tank.

[0017] According to the above configuration, a nitrogen source can be supplied to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by supplying the methane fermentation liquor from the first methane fermenter to at least one of the storage tank, the culture tank, and the pretreatment tank. The lignocellulose-degrading microorganisms contained in the rumen microorganisms consume nitrogen during the process of decomposing lignocellulose-based biomass in the pretreatment tank to produce reducing sugars. Therefore, by supplying a methane fermentation liquor rich in a nitrogen source to the storage tank or the like in advance, the lignocellulose decomposition activity can be maintained or improved. Furthermore, when treating organic waste such as sludge generated by biological wastewater treatment methods such as activated sludge, livestock manure, and food waste in a digester (first methane fermenter), the digested sludge (methane fermentation liquor) is not widely used as liquid fertilizer or compost, and therefore requires a wastewater treatment facility. However, by using the digested sludge as a nitrogen source for the lignocellulose-degrading microorganisms, facility costs can be reduced.

[0018] Furthermore, the hydrogen fermentation treatment system of the present invention may further include a second methane fermentation tank that performs methane fermentation using the hydrogen fermentation liquid in the hydrogen fermentation tank as a raw material, and may be configured to return the methane fermentation liquid in the second methane fermentation tank to at least one of the storage tank, the culture tank, and the pretreatment tank.

[0019] According to the above configuration, a nitrogen source can be supplied to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by returning the methane fermentation liquid in the second methane fermentation tank to at least one of the storage tank, the culture tank, and the pretreatment tank. The lignocellulose-degrading microorganisms contained in the rumen microorganisms consume nitrogen in the process of decomposing lignocellulose-based biomass in the pretreatment tank to produce reducing sugars. Therefore, by supplying a methane fermentation liquid containing a large amount of nitrogen source to the storage tank or the like in advance, the lignocellulose decomposition activity can be maintained or improved.

[0020] In order to solve the above problems, the hydrogen fermentation treatment method of the present invention comprises a storage step of storing a mixed liquid containing at least one of rumen fluid and rumen microbial culture fluid cultured in a culture tank and lignocellulosic biomass in a storage tank, and a decomposition / hydrogen fermentation step of performing decomposition treatment and hydrogen fermentation treatment of the mixed liquid supplied from the storage step.

[0021] According to the above configuration, in the storage process, the decomposition process progresses by mixing lignocellulosic biomass with rumen fluid or rumen microbial culture fluid in the storage tank, making it possible to reduce the hydraulic retention time or tank capacity of the subsequent decomposition / hydrogen fermentation tank.

[0022] Furthermore, the hydrogen fermentation treatment method of the present invention may further include a first methane fermentation step in which organic waste is subjected to methane fermentation treatment, and may be configured to supply the methane fermentation liquid obtained in the first methane fermentation step to at least one of the storage tank and the culture tank.

[0023] According to the above configuration, a nitrogen source can be supplied to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by supplying the methane fermentation liquor obtained in the first methane fermentation step to at least one of the storage tank and the culture tank. The lignocellulose-degrading microorganisms contained in the rumen microorganisms consume nitrogen during the decomposition and hydrogen fermentation step of decomposing lignocellulose-based biomass to produce reducing sugars. Therefore, supplying a methane fermentation liquor rich in a nitrogen source to the storage tank or other storage tank in advance can maintain or improve lignocellulose decomposition activity. Furthermore, when treating organic waste, such as sludge generated by biological wastewater treatment methods such as activated sludge, livestock manure, and food waste, in a digester (first methane fermenter), the digested sludge (methane fermentation liquor) is not widely used as liquid fertilizer or compost, so wastewater treatment requires a wastewater treatment facility. However, using the digested sludge (methane fermentation liquor) as a nitrogen source for the lignocellulose-degrading microorganisms can reduce facility costs.

[0024] Furthermore, the hydrogen fermentation treatment method of the present invention may further include a second methane fermentation process in which methane fermentation is carried out using the hydrogen fermentation liquid obtained in the decomposition and hydrogen fermentation process as a raw material, and may be configured to return the methane fermentation liquid obtained in the second methane fermentation process to at least one of the storage tank and the culture tank.

[0025] According to the above configuration, a nitrogen source can be supplied to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by returning the methane fermentation liquid obtained in the second methane fermentation step to at least one of the storage tank and the culture tank. The lignocellulose-degrading microorganisms contained in the rumen microorganisms consume nitrogen in the process of decomposing lignocellulose-based biomass to produce reducing sugars in the decomposition and hydrogen fermentation step. Therefore, by supplying a methane fermentation liquid containing a large amount of nitrogen source to the storage tank or the like in advance, the lignocellulose decomposition activity can be maintained or improved.

[0026] In order to solve the above problems, the hydrogen fermentation treatment method of the present invention comprises a storage step of storing a mixed liquid containing at least one of rumen fluid and a rumen microorganism culture solution cultured in a culture tank, and lignocellulosic biomass in a storage tank; a pretreatment step of decomposing the mixed liquid supplied from the storage step in a pretreatment tank; and a hydrogen fermentation step of hydrogen fermenting the pretreated liquid obtained in the pretreatment step in a hydrogen fermentation tank.

[0027] According to the above configuration, in the storage process, the decomposition process progresses by mixing the lignocellulosic biomass with rumen fluid or rumen microbial culture solution in the storage tank, making it possible to reduce the hydraulic retention time or tank volume of the subsequent pretreatment tank and hydrogen fermenter. Furthermore, the pretreatment process performed after the storage process is specialized in the function of decomposing the lignocellulosic biomass and producing reducing sugars that serve as a substrate for hydrogen fermentation, and its role is separate from the hydrogen fermentation process performed in the subsequent hydrogen fermenter. This has the advantage of making operation control and management easier.

[0028] Furthermore, the hydrogen fermentation treatment method of the present invention may further include a first methane fermentation step in which organic waste is subjected to methane fermentation treatment, and may be configured to supply the methane fermentation liquid obtained in the first methane fermentation step to at least one of the storage tank, the culture tank, and the pretreatment tank.

[0029] According to the above configuration, a nitrogen source can be supplied to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by supplying the methane fermentation liquor obtained in the first methane fermentation step to at least one of the storage tank, the culture tank, and the pretreatment tank. The lignocellulose-degrading microorganisms contained in the rumen microorganisms consume nitrogen during the process of decomposing lignocellulose-based biomass to produce reducing sugars in the pretreatment step. Therefore, by supplying a methane fermentation liquor rich in a nitrogen source to the storage tank or the like in advance, the lignocellulose decomposition activity can be maintained or improved. Furthermore, when treating organic waste, such as sludge generated by biological wastewater treatment methods such as activated sludge, livestock manure, and food waste, in a digester (first methane fermenter), the digested sludge (methane fermentation liquor) is not widely used as liquid fertilizer or compost, and therefore requires a wastewater treatment facility. However, using the digested sludge (methane fermentation liquor) as a nitrogen source for the lignocellulose-degrading microorganisms can reduce facility costs.

[0030] Furthermore, the hydrogen fermentation treatment method of the present invention may further include a second methane fermentation step in which methane fermentation is carried out using the hydrogen fermentation liquor obtained in the hydrogen fermentation step as a raw material, and may be configured to return the methane fermentation liquor obtained in the second methane fermentation step to at least one of the storage tank, the culture tank, and the pretreatment tank.

[0031] According to the above configuration, a nitrogen source can be supplied to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by returning the methane fermentation liquor obtained in the second methane fermentation step to at least one of the storage tank, the culture tank, and the pretreatment tank. The lignocellulose-degrading microorganisms contained in the rumen microorganisms consume nitrogen in the process of decomposing lignocellulose-based biomass to produce reducing sugars in the pretreatment step. Therefore, by supplying a methane fermentation liquor rich in a nitrogen source to the storage tank or the like in advance, the lignocellulose decomposition activity can be maintained or improved. [Effects of the Invention]

[0032] According to the present invention, the decomposition process is advanced by mixing lignocellulosic biomass with rumen fluid or rumen microbial culture fluid in a storage tank, and it becomes possible to reduce the hydraulic retention time or tank volume of downstream hydrogen fermentation tanks, etc. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a second embodiment. [Figure 3] FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a third embodiment. [Figure 4] FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a fourth embodiment. [Figure 5] FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a fifth embodiment. [Figure 6] FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0034] The following describes in detail the embodiments and drawings relating to the hydrogen fermentation treatment system and the hydrogen fermentation treatment method of the present invention. However, the present invention is not intended to be limited to the configurations shown in the embodiments and drawings described below.

[0035] The hydrogen fermentation treatment system and the hydrogen fermentation treatment method according to each embodiment will be described below with reference to FIGS.

[0036] (First embodiment) 1(a) and 1(b) are diagrams showing the schematic configuration of hydrogen fermentation treatment systems 101 and 102 according to a first embodiment. The hydrogen fermentation treatment systems 101 and 102 shown in FIG. 1 are systems that perform hydrogen fermentation treatment using lignocellulosic biomass as a feedstock to produce biohydrogen gas. The hydrogen fermentation treatment systems 101 and 102 shown in FIG. 1 are mainly composed of a storage tank 10 and a decomposition / hydrogen fermentation tank 20. Lignocellulosic biomass is crushed and pulverized as necessary using a crusher 50 or the like and supplied to the storage tank 10.

[0037] (storage tank) Rumen fluid and lignocellulosic biomass collected from ruminants such as cows are introduced into the storage tank 10 in FIG. 1(a). Rumen microbial culture fluid and lignocellulosic biomass cultivated in a culture tank 40 are introduced into the storage tank 10 in FIG. 1(b). By storing a mixture containing at least one of rumen fluid and rumen microbial culture fluid and lignocellulosic biomass in the storage tank 10, the decomposition process of the lignocellulosic biomass progresses, enabling the hydraulic retention time or tank volume of the subsequent decomposition / hydrogen fermentation tank 20 to be reduced. Furthermore, in the storage tank 10, the lignocellulosic biomass is adjusted so that the total solids (TS) is 3.0 to 20.0%. A solids concentration below 3.0% may result in a decrease in the production of reducing sugars, which serve as a substrate for hydrogen fermentation in the subsequent stage. On the other hand, a solids concentration above 20.0% may make it difficult to pump out the mixed liquid. Furthermore, by pre-diluting lignocellulosic biomass with rumen fluid or rumen microbial culture fluid to a solids concentration that can be transported by pump or the like and storing the diluted solution in the storage tank 10, there is no need to add water to the lignocellulosic biomass for dilution. This allows the treatment solution to be adjusted to an appropriate solids concentration, even in facilities with limited available water. Furthermore, since tap water is not required for dilution, water costs can be reduced. Concentration meters used to measure the solids concentration include ultrasonic concentration meters, microwave concentration meters, and near-infrared concentration meters. Alternatively, the solids concentration can be measured manually without using a concentration meter by directly collecting the lignocellulosic biomass, measuring its mass before and after drying, and calculating the solids concentration from the mass difference. The storage tank 10 may be equipped with a mixer (not shown) for mixing the mixed solution. Since the solids concentration in the storage tank 10 only needs to be adjusted to the above-mentioned range, the installation of instruments for temperature control, pH adjustment, etc. is not essential.

[0038] (Decomposition / hydrogen fermentation tank) In the decomposition / hydrogen fermentation tank 20, hydrogen gas is produced using the lignocellulosic biomass in the mixed liquid as a feedstock. Specifically, the mixed liquid in the storage tank 10 is supplied to the decomposition / hydrogen fermentation tank 20. Under conditions of 50–60°C, pH 5.5–6.0, and a hydraulic retention time (HRT) of 24–168 hours, preferably 72 hours, lignocellulose decomposition and reducing sugar production by lignocellulose-decomposing bacteria are carried out, followed by hydrogen fermentation by hydrogen-producing bacteria. The resulting hydrogen fermentation solution contains volatile fatty acids such as acetic acid. In the decomposition / hydrogen fermentation tank 20, the decomposition and hydrogen fermentation of lignocellulosic biomass are carried out in a single tank, thereby reducing equipment costs. The lignocellulose-decomposing bacteria and hydrogen-producing bacteria in the decomposition / hydrogen fermentation tank 20 are contained in rumen fluid or rumen microbial culture solution and are dominant under conditions of 50–60°C, preferably 55°C, and pH 5.5–6.0, preferably pH 5.7.

[0039] The decomposition / hydrogen fermenter 20 can be a complete mixing fermentation (anaerobic digestion) type fermenter, which is widely used in Japan and overseas to treat solid (slurry-like) waste. In other words, the tank used for the decomposition / hydrogen fermenter 20 can be made of the same material, shape, and structure as a general methane fermenter. A complete mixing fermentation type fermenter can also treat suspensions, thereby reducing the amount of liquid medium used, such as dilution water or artificial medium (artificial saliva). The decomposition / hydrogen fermenter 20 may be a steel tank or a concrete tank. The decomposition / hydrogen fermenter 20 may be equipped with an agitator (not shown) to agitate the mixed liquid supplied from the storage tank 10. The post-hydrogen fermentation sludge discharged from the decomposition / hydrogen fermenter 20 is concentrated and can be used as fertilizer, building material, etc.

[0040] As hydrogen fermentation progresses, biohydrogen gas is generated in the decomposition / hydrogen fermentation tank 20. Biohydrogen gas is a gas that is approximately 50% by volume hydrogen gas and approximately 50% by volume carbon dioxide. The generated biohydrogen gas is extracted from the decomposition / hydrogen fermentation tank 20 and used as fuel for heating the decomposition / hydrogen fermentation tank 20 and the culture tank 40, or as fuel for power generation equipment (not shown). In other words, by subjecting lignocellulosic biomass to hydrogen fermentation, the energy contained in the lignocellulosic biomass can be recovered as biohydrogen gas (gas energy).

[0041] The hydrogen fermentation treatment system 102 shown in Figure 1(b) is similar to that shown in Figure 1(a) in that it comprises a storage tank 10, a decomposition / hydrogen fermentation tank 20, and, if necessary, a crusher 50, but differs from that shown in Figure 1(a) in that it further comprises a culture tank 40.

[0042] (culture tank) Rumen microorganisms present in rumen fluid collected from ruminants such as cows are cultivated in the culture tank 40. When a liquid medium such as an artificial medium (artificial saliva) and lignocellulosic biomass are supplied to the culture tank 40, the rumen microorganisms (lignocellulose-degrading bacteria) proliferate by decomposing and metabolizing the lignocellulosic biomass, and produce partially decomposed lignocellulose, reducing sugars (hexoses (six monosaccharides)) such as glucose and fructose, and volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid. The culture fluid of the lignocellulose-degrading bacteria in the culture tank 40 is steadily supplied to the storage tank 10 by continuous or semi-continuous culture.

[0043] The conditions in the culture tank 40 are preferably set to simulate the physiological conditions of the rumen of ruminants such as cows. Furthermore, to ensure sufficient proliferation of the lignocellulose-degrading bacteria, the hydraulic retention time (HRT) and solid retention time (SRT) are preferably controlled as desired using a solid-liquid separation means (not shown). Because lignocellulose-degrading bacteria grow by adhering to the surface of solid matter in the culture solution, operation is preferably controlled so that the SRT is longer than the HRT.

[0044] (Second embodiment) 2(a) and 2(b) are diagrams showing the schematic configuration of hydrogen fermentation treatment systems 103 and 104 according to a second embodiment. The hydrogen fermentation treatment systems 103 and 104 shown in Fig. 2 are systems that perform hydrogen fermentation treatment using lignocellulosic biomass as a feedstock to produce biohydrogen gas, and also perform digestion treatment using sewage sludge as a feedstock to produce digestion gas. Like the hydrogen fermentation treatment systems 101 and 102 shown in Fig. 1, the second embodiment is mainly composed of a storage tank 10 and a decomposition / hydrogen fermentation tank 20, but differs from the first embodiment in that it includes a first methane fermentation (digestion) tank 30 in a separate system.

[0045] (First methane fermentation (digestion) tank) The first methane fermentation (digestion) tank 30 shown in Figures 2(a) and 2(b) is a tank for anaerobic fermentation of organic waste, such as sewage sludge. Examples of organic waste fed into the digestion tank 30 include sewage sludge and easily decomposable organic waste, such as livestock manure, sludge, and food waste. The solids concentration (TS: Total Solids) of the raw sludge fed to the digestion tank 30 is preferably, for example, 3.0 to 10.0%. The digestion tank 30 may be operated by either mesophilic methane fermentation or thermophilic methane fermentation. In the case of mesophilic fermentation, the fermentation is carried out for 20 to 30 days, more preferably 23 to 27 days, and even more preferably about 25 days. In the case of thermophilic fermentation, the fermentation 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 a temperature of 20 to 45°C, preferably 30 to 37°C or lower, and even more preferably around 37°C. In the case of thermophilic fermentation, methane fermentation is carried out at a temperature of 40 to 60°C, more preferably 50 to 60°C, and even more preferably around 55°C. Furthermore, methane fermentation is carried out at a pH of 6.5 to 8.5, more preferably 6.8 to 7.6. The digester 30 may be a fermenter of the complete mixing type fermentation (anaerobic digestion) method widely used in Japan and overseas to treat solid (slurry-like) waste. The digester 30 may be a tank made of steel plates or a concrete tank. An agitator (not shown) may be attached to the digester 30 to agitate the sewage sludge introduced into it.

[0046] The methane fermentation liquid (digested sludge) in the first methane fermentation (digestion) tank 30 contains substances that serve as a nitrogen source, so supplying the methane fermentation liquid (digested sludge) to the storage tank 10 or the culture tank 40 further promotes the growth and proliferation of lignocellulose-decomposing bacteria in the mixed liquid or culture solution, and further hydrolysis in the decomposition / hydrogen fermentation tank 20 increases the production of reducing sugars and easily decomposable organic waste with small molecular weights. Furthermore, since digested sludge is not widely used as liquid fertilizer or compost, wastewater treatment requires a wastewater treatment facility; however, using it as a nitrogen source for lignocellulose-decomposing microorganisms can reduce facility costs.

[0047] Digestion gas is generated in the digester tank 30 as a result of the digestion process of the sewage sludge. The digester gas is a gas (biogas) that is approximately 60% by volume methane and approximately 40% by volume carbon dioxide. The generated digester gas is extracted from the digester tank 30 and used as fuel for heating the digester tank 30, the decomposition / hydrogen fermenter 20, and the culture tank 40, or as fuel for power generation equipment (not shown). In other words, by subjecting the sewage sludge to methane fermentation, the energy contained in the sewage sludge can be recovered as digester gas (gas energy).

[0048] (Third embodiment) 3(a) and 3(b) are diagrams showing the schematic configuration of hydrogen fermentation treatment systems 105 and 106 according to a third embodiment. The hydrogen fermentation treatment systems 105 and 106 shown in FIG. 3 are systems that perform hydrogen fermentation and methane fermentation using lignocellulosic biomass as a feedstock to produce biohydrogen gas and biomethane gas. Like the hydrogen fermentation treatment systems 101 and 102 shown in FIG. 1, the third embodiment is mainly composed of a storage tank 10 and a decomposition / hydrogen fermenter 20. However, it differs from the first embodiment in that a second methane fermentation tank 31 is provided downstream of the decomposition / hydrogen fermenter 20, allowing for two-stage hydrogen / methane fermentation.

[0049] (Second methane fermentation tank) The second methane fermenter 31 shown in Figures 3(a) and 3(b) is a tank for performing methane fermentation using volatile fatty acids such as acetic acid contained in the hydrogen fermentation liquid supplied from the upstream decomposition / hydrogen fermenter 20 as a substrate. The second methane fermenter 31 may be operated by either mesophilic or thermophilic methane fermentation. In the case of mesophilic fermentation, the treatment is carried out for 15 to 30 days, more preferably 15 to 25 days, and even more preferably about 20 days. In the case of thermophilic fermentation, the treatment is carried out for 10 to 20 days, more preferably 15 to 20 days, and even more preferably about 15 days. In the case of mesophilic fermentation, methane fermentation is carried out at 20 to 45°C, more preferably 30 to 37°C or lower, and even more preferably about 37°C. In the case of thermophilic fermentation, the treatment is carried out at 40 to 60°C, more preferably 50 to 60°C, and even more preferably about 55°C. Furthermore, methane fermentation is carried out at a pH of 6.5 to 8.5, and more preferably a pH of 6.8 to 7.6. The second methane fermentation tank 31 may be a tank made of steel plate or a tank made of concrete. The second methane fermentation tank 31 may be equipped with an agitator (not shown) to agitate the hydrogen fermentation liquid supplied from the decomposition / hydrogen fermentation tank 20.

[0050] The methane fermentation liquid in the second methane fermentation tank 31 contains a substance that serves as a nitrogen source, so supplying it to the storage tank 10 or the culture tank 40 further promotes the growth and proliferation of lignocellulose-decomposing bacteria in the mixed liquid or culture liquid, and also increases the production of reducing sugars and easily decomposable organic waste with small molecular weights through further hydrolysis in the decomposition / hydrogen fermentation tank 20. Furthermore, the unreacted organic waste contained in the methane fermentation liquid can be reused as a substrate for hydrogen fermentation or methane fermentation, improving energy recovery efficiency.

[0051] The hydrogen fermentation liquid supplied from the decomposition / hydrogen fermenter 20 is subjected to methane fermentation in the second methane fermenter 31, thereby generating biomethane gas. Biomethane gas is a gas (biogas) composed of approximately 60% by volume of methane and approximately 40% by volume of carbon dioxide. The generated biomethane gas is extracted from the second methane fermenter 31 and used as fuel for heating the second methane fermenter 31, the decomposition / hydrogen fermenter 20, and the culture tank 40, or as fuel for power generation equipment (not shown). In other words, by subjecting the hydrogen fermentation liquid to methane fermentation, the energy contained in the hydrogen fermentation liquid can be recovered as biomethane gas (gas energy).

[0052] (Fourth embodiment) 4(a) and (b) are diagrams showing the schematic configuration of hydrogen fermentation treatment systems 107 and 108 according to a fourth embodiment. The hydrogen fermentation treatment systems 107 and 108 shown in Fig. 4 are systems that perform hydrogen fermentation treatment using lignocellulosic biomass as a feedstock to produce biohydrogen gas. The hydrogen fermentation treatment systems 107 and 108 shown in Fig. 4 are mainly composed of a storage tank 10, a pretreatment tank 21, and a hydrogen fermenter 22. Lignocellulosic biomass is crushed and pulverized, as necessary, using a crusher 50 or the like, and supplied to the storage tank 10.

[0053] (Pretreatment tank) The pretreatment tank 21 is provided downstream of the storage tank 10. In the pretreatment tank 21, the lignocellulosic biomass contained in the mixed liquid supplied from the storage tank 10 is decomposed to produce reducing sugars, which serve as a substrate for hydrogen fermentation. The pretreated liquid containing a large amount of reducing sugars is supplied to the downstream hydrogen fermenter 22, where hydrogen fermentation is carried out. Furthermore, as shown in FIG. 4, the pretreatment tank 21 may be supplied with rumen liquid or rumen microorganism culture liquid. In the pretreatment tank 21, lignocellulosic biomass is decomposed by the action of lignocellulose-degrading bacteria, producing decomposition products of low-molecular-weight lignocellulosic biomass (easily decomposable organic waste such as partial decomposition products of lignocellulose) and reducing sugars (hexoses (six monosaccharides)) such as glucose and fructose. The pretreatment tank 21 is specialized for the function of decomposing lignocellulosic biomass and producing reducing sugars that serve as substrates for hydrogen fermentation, and its role is separated from that of the downstream hydrogen fermentation tank 22. This has the advantage of making operation control and management easier.

[0054] (hydrogen fermenter) When the pretreated liquid containing a large amount of easily decomposable organic waste and reducing sugars is supplied from the pretreatment tank 21 to the hydrogen fermenter 22, a hydrogen fermentation reaction using the easily decomposable organic waste and reducing sugars as substrates (raw materials) proceeds, producing biohydrogen gas. The substrate supplied to the hydrogen fermenter 22 only needs to contain at least one selected from easily decomposable organic waste and reducing sugars. The post-hydrogen fermentation sludge discharged from the hydrogen fermenter 22 is concentrated and can be used as fertilizer, building material, etc.

[0055] As hydrogen fermentation progresses, biohydrogen gas is generated in the hydrogen fermenter 22. Biohydrogen gas is a gas that is approximately 50% by volume hydrogen gas and approximately 50% by volume carbon dioxide. The generated biohydrogen gas is extracted from the hydrogen fermenter 22 and used as fuel for heating the pretreatment tank 21, the hydrogen fermenter 22, and the culture tank 40, or as fuel for power generation equipment (not shown). In other words, by subjecting lignocellulosic biomass to hydrogen fermentation, the energy contained in the lignocellulosic biomass can be recovered as biohydrogen gas (gas energy).

[0056] (Fifth embodiment) 5(a) and 5(b) are diagrams showing the schematic configuration of hydrogen fermentation treatment systems 109 and 110 according to a fifth embodiment. The hydrogen fermentation treatment systems 109 and 110 shown in Fig. 5 are systems that perform hydrogen fermentation treatment using lignocellulosic biomass as a feedstock to produce biohydrogen gas, and also perform digestion treatment using sewage sludge as a feedstock to produce digestion gas. Like the hydrogen fermentation treatment systems 107 and 108 shown in Fig. 4, the fifth embodiment is mainly composed of a storage tank 10, a pretreatment tank 21, and a hydrogen fermenter 22, but differs from the fourth embodiment in that it includes a first methane fermentation (digestion) tank 30 in a separate system.

[0057] The first methane fermentation (digestion) tank 30 of this embodiment shown in Figures 5(a) and 5(b) can be a tank similar to the digestion tank 30 shown in Figures 2(a) and 2(b), and digestion treatment can be performed under similar conditions. The methane fermentation liquid (digested sludge) in the first methane fermentation (digestion) tank 30 contains a nitrogen source. Supplying this liquid to the storage tank 10, culture tank 40, or pretreatment tank 21 further promotes the growth and proliferation of lignocellulose-degrading bacteria in the mixed liquid, culture liquid, and pretreatment liquid. Further hydrolysis in the pretreatment tank 21 improves the production of reducing sugars and easily decomposable organic waste with low molecular weights. Because digested sludge is not widely used as liquid fertilizer or compost, wastewater treatment requires a wastewater treatment facility. However, using it as a nitrogen source for lignocellulose-decomposing microorganisms can reduce facility costs.

[0058] (Sixth embodiment) 6(a) and 6(b) are diagrams showing the schematic configuration of hydrogen fermentation treatment systems 111 and 112 according to a sixth embodiment. The hydrogen fermentation treatment systems 111 and 112 shown in Fig. 6 are systems that perform hydrogen fermentation and methane fermentation using lignocellulosic biomass as a feedstock to produce biohydrogen gas and biomethane gas. Like the hydrogen fermentation treatment systems 107 and 108 shown in Fig. 4, the sixth embodiment is mainly composed of a storage tank 10, a pretreatment tank 21, and a hydrogen fermenter 22. However, it differs from the fourth embodiment in that it includes a second methane fermenter 31 downstream of the hydrogen fermenter 22, thereby performing two-stage hydrogen and methane fermentation.

[0059] The second methane fermentation tank 31 of this embodiment shown in Figures 6(a) and 6(b) can be a tank similar to the second methane fermentation tank 31 shown in Figures 3(a) and 3(b), and methane fermentation treatment can be performed under similar conditions. The methane fermentation liquor in the second methane fermentation tank 31 contains a nitrogen source. Therefore, supplying the methane fermentation liquor to the storage tank 10, the culture tank 40, and the pretreatment tank 21 further promotes the growth and proliferation of lignocellulose-decomposing bacteria in the mixed liquor, culture liquor, and pretreatment liquor. Further hydrolysis in the pretreatment tank 21 improves the production of reducing sugars and easily decomposable organic waste with small molecular weights. Furthermore, unreacted organic waste contained in the methane fermentation liquor can be reused as a substrate for hydrogen fermentation or methane fermentation, improving energy recovery efficiency.

[0060] Next, the hydrogen fermentation treatment method of the present invention will be described in detail below.

[0061] (lignocellulosic biomass) Lignocellulosic biomass, which can be used as a raw material for biohydrogen gas and biomethane gas, includes unused agricultural and forestry waste such as forest thinnings, rice straw, rice husks, bagasse, thatch, and aquatic plants; lignocellulosic industrial waste such as vegetable scraps, used tea leaves, coffee grounds, soybean pulp, shochu dregs, construction waste, used paper, and municipal solid waste; and biomass resource crops such as Erianthus and Giant Miscanthus. Furthermore, shredded paper is incinerated because its fibers are broken and difficult to recycle, but this shredded paper can also be used as a raw material. Furthermore, the organic waste listed above can be used alone or in combination.

[0062] Lignocellulose, the main component of plant cell walls, is composed of tightly bound hemicellulose, cellulose, and lignin. Rumen fluid in the rumen of ruminants such as cows contains numerous ruminal microorganisms that produce enzymes that break down lignocellulose.

[0063] (Rumen microorganisms) Rumen microorganisms are anaerobic bacteria present in ruminal fluid, a digestive fluid found in the rumen of ruminants. Ruminants include cattle, sheep, goats, deer, camels, and llamas. For example, the rumen of an adult cow has a volume of 150 to 200 liters, and the ruminal fluid is home to numerous lignocellulose-degrading bacteria, hemicellulose-degrading bacteria, lignin-degrading bacteria, starch-degrading bacteria, methanogens, and hydrogen-producing bacteria. Lignocellulose-degrading bacteria can produce enzymes such as cellulases that break down lignocellulose (fiber). Therefore, when ruminants ingest fiber such as grass, lignocellulose-degrading bacteria break down the lignocellulose into reducing sugars (hexoses, six monosaccharides) such as oligosaccharides, glucose, and fructose. As the decomposition progresses, volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid are produced, which serve as an energy source for ruminants. Hydrogen-producing bacteria produce acetic acid and hydrogen using the reducing sugars, propionic acid, butyric acid, and valeric acid produced by lignocellulose-degrading bacteria as substrates. Methanogenic bacteria produce methane using acetic acid or hydrogen and carbon dioxide produced by lignocellulose-degrading bacteria or hydrogen-producing bacteria as substrates.

[0064] (Rumen microbial culture medium) In the culture vessel 40 for culturing rumen microorganisms, a culture solution of rumen microorganisms (lignocellulose-degrading bacteria) with high lignocellulose-degrading activity can be obtained. In culturing rumen microorganisms, for example, the number of at least one species of lignocellulose-degrading bacteria present in the culture solution, Fibrobacter succinogenes, Ruminococcus albus, and Prevotella ruminicola, can be 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 culture medium to obtain a culture solution of rumen microorganisms (lignocellulose-degrading bacteria) with high lignocellulose-degrading activity. The number of these bacteria can be quantified, but is preferably determined by quantitative PCR, which can rapidly and accurately measure the number of specific bacteria. When quantifying the number of lignocellulose-degrading bacteria using quantitative PCR, genomic DNA is extracted from the culture medium and purified. Ruminal microbial culture medium can be cultured in large quantities and subcultured, so the culture medium with an adjusted bacterial population can be used for lignocellulose degradation as needed.

[0065] The culture medium for rumen microorganisms may be a natural medium whose base material is derived from natural products, or a synthetic medium whose nutrients necessary for the growth of rumen microorganisms are all composed of chemicals. It is particularly preferable for the medium to contain a nitrogen source such as ammonium salt, a phosphorus source such as phosphate, and a carbon source such as cellulose or hemicellulose, which are useful nutrients for rumen microorganisms. It is also preferable to add a buffer to the medium to mitigate pH changes and increases in osmotic pressure. Ruminant saliva has a high buffering capacity, so it is preferable to use a liquid medium such as an artificial medium (artificial saliva) that mimics this. Examples of buffers include sodium chloride, sodium bicarbonate, phosphate, and potassium chloride. The pH of the medium is adjusted to 6.0 to 7.5, preferably 6.5 to 7.0, by adding an acid or alkali as needed. It is preferable to use tap water or groundwater for the water used in the medium. The ammonium nitrogen concentration of the medium is controlled by adding water to 50 to 2,000 mg / L, preferably 60 to 500 mg / L.

[0066] To create an anaerobic environment in the culture tank 40 similar to that in the rumen, the oxidation-reduction potential (ORP) of the culture solution is adjusted to -100 mV or less, preferably -200 mV or less, and even more preferably approximately -250 mV. Because rumen microorganisms (lignocellulose-degrading bacteria) are anaerobic, if the ORP exceeds a predetermined value (approaching an aerobic state), measures may be taken, 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 cause facultative anaerobic bacteria to consume oxygen. Alternatively, rumen microorganisms may be cultured in a closed system under a nitrogen or carbon dioxide atmosphere.

[0067] When culturing rumen microorganisms in the fermentor 40, it is important that the solid retention time (SRT) is longer than the hydraulic retention time (HRT). Lignocellulose-degrading bacteria grow by adhering to the surface of solids, and if the SRT is short, they are discharged from the system along with the solids. On the other hand, an HRT longer than necessary can lead to negative effects 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 to 36 hours, preferably 10 to 24 hours, and the SRT to 24 hours or more, preferably 48 to 168 hours, and more preferably 72 to 168 hours. The temperature of the reaction system for culturing rumen microorganisms is controlled using a temperature sensor or the like to maintain a temperature of 35 to 42°C, more preferably 37 to 40°C. The lignocellulose-based biomass introduced into the fermentor 40 is adjusted so that the solid concentration (TS) in the culture solution is 1.0 to 20.0%, more preferably 3.0 to 10.0%. If the solid concentration (TS) is 1.0% or less, the growth and proliferation of lignocellulose-decomposing bacteria may not be promoted, whereas if it exceeds 20.0%, solid-liquid separation of the culture solution may not be performed properly.

[0068] (Storage process) In the storage step, a mixture of lignocellulosic biomass and at least one of rumen fluid and rumen microbial culture fluid is stored in storage tank 10. Storing the mixture in storage tank 10 promotes the decomposition of the lignocellulosic biomass, enabling the hydraulic retention time or capacity of the subsequent decomposition / hydrogen fermentation tank 20, pretreatment tank 21, and hydrogen fermentation tank 22 to be reduced. Furthermore, in the storage step, the solids concentration of the mixture is adjusted to 3.0 to 20.0%. If the solids concentration (TS) is 3.0% or less, there is a risk of reduced production of reducing sugars, which serve as a substrate for hydrogen fermentation in the subsequent step. On the other hand, if the solids concentration exceeds 20.0%, there is a risk of it being difficult to pump out the mixture. Furthermore, by pre-diluting the lignocellulosic biomass with rumen fluid or rumen microbial culture fluid to a solids concentration that can be transported by pump or the like and storing the diluted solution in the storage tank 10, there is no need to add water to the lignocellulosic biomass for dilution. This allows the treated solution to be adjusted to an appropriate solids concentration even in facilities with limited available water. Furthermore, since there is no need to use tap water for dilution, water costs can be reduced. The storage step may be performed statically or with stirring, but stirring is preferred for more appropriate adjustment of the solids concentration of the mixed solution. The mixed solution with the adjusted solids concentration is supplied to the decomposition / hydrogen fermentation tank 20 or the pretreatment tank 21. In the storage step, it is sufficient to adjust the solids concentration to within the above-mentioned range; therefore, temperature control or pH adjustment within the storage tank 10 is not required. The method of mixing lignocellulosic biomass with at least one of rumen fluid and rumen microbial culture solution is not particularly limited, but at least one of rumen fluid and rumen microbial culture solution may be supplied to the storage tank 10, or may be supplied to a path that supplies lignocellulosic biomass to the storage tank 10. Also, at least one of rumen fluid and rumen microbial culture solution may be supplied from the gas phase within the storage tank 10, or from the bottom, or may be sprayed onto the lignocellulosic biomass in a shower-like manner. When at least one of rumen fluid and rumen microbial culture solution is supplied to the storage tank 10 from the gas phase or the bottom, the device configuration can be simplified.Furthermore, when at least one of the rumen fluid and the rumen microbial culture solution is supplied to the pathway for supplying the lignocellulose biomass to the storage tank 10 or when it is sprayed onto the lignocellulose biomass in a shower-like manner, the lignocellulose biomass and at least one of the rumen fluid and the rumen microbial culture solution can be uniformly mixed with the lignocellulose biomass.

[0069] (Pretreatment (decomposition) process) In the pretreatment process, the lignocellulose contained in lignocellulosic biomass is partially decomposed by lignin-degrading enzymes produced by lignocellulose-degrading bacteria, loosening the rigid structure of the lignocellulose. The lignocellulose is then decomposed into cellulose and hemicellulose by endoglucanases, exoglucanases, xylanases, etc., respectively, and converted into reducing sugars (hexoses (six monosaccharides)) such as glucose and fructose.

[0070] To achieve anaerobic conditions during the pretreatment process, the oxidation-reduction potential (ORP) of the pretreatment solution is adjusted to -100 mV or less, preferably -200 mV or less, and even more preferably approximately -250 mV. Because rumen microorganisms (lignocellulose-degrading bacteria) are anaerobic, if the ORP exceeds a predetermined value (approaching 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 through the action of facultative anaerobic bacteria, may be taken. The pretreatment process may also be performed in a closed system under a nitrogen or carbon dioxide atmosphere.

[0071] In the pretreatment step, pretreatment (hydrolysis and reducing sugar production) is carried out in a completely mixed system. The temperature of the reaction system in the pretreatment step is controlled using a temperature sensor or the like to maintain it at 50 to 60°C, preferably about 55°C. Keeping the temperature at 50 to 60°C reduces bacterial activity, suppressing the reaction in which reducing sugars are further decomposed into organic acids. The pH of the mixed liquid is adjusted to 5.5 to 6.0, preferably 5.7. The hydraulic residence time is 4 to 36 hours, more preferably about 24 hours. The reaction in the pretreatment step may be carried out statically or with stirring; however, stirring is preferred to speed up the progress of the pretreatment step.

[0072] The pretreatment process is specialized in the decomposition of lignocellulosic biomass to produce reducing sugars, which serve as the substrate for hydrogen fermentation, and its role is separate from that of the hydrogen fermentation process, which has the advantage of making operation control and management easier.

[0073] (Hydrogen fermentation process) The hydrogen fermentation process is carried out under anaerobic conditions, just like the pretreatment process using lignocellulose-degrading bacteria. In the fermentation process, reducing sugars (hexoses (six monosaccharides)) such as glucose and fructose produced in the pretreatment process are used as substrates for hydrogen fermentation. As the hydrogen fermentation reaction progresses, the reducing sugars are broken down to produce pyruvic acid and other compounds, and as the reaction progresses further, volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid are produced. In addition, biohydrogen gas and carbon dioxide are produced in an approximately 1:1 ratio during the metabolic process, and organic acids such as acetic acid, as well as hydrogen and carbon dioxide, are also produced.

[0074] Hydrogen fermentation is carried out at 50 to 60°C, preferably about 55°C, at a pH of 5.5 to 6.0, preferably about 5.7, and with a hydraulic retention time of 24 to 168 hours, preferably about 120 hours.

[0075] (Decomposition and hydrogen fermentation process) The decomposition and hydrogen fermentation process is a process in which the above-mentioned pretreatment (decomposition) process and hydrogen fermentation process are carried out in a single tank (decomposition and hydrogen fermentation tank 20). The decomposition and hydrogen fermentation process is carried out at 50 to 60°C, preferably around 55°C. The decomposition and hydrogen fermentation process is also carried out at a pH of 5.5 to 6.0, preferably around 5.7. The hydraulic retention time is 24 to 168 hours, more preferably around 72 hours. Because the decomposition and hydrogen fermentation process involves the decomposition and hydrogen fermentation of lignocellulosic biomass in a single tank, it is possible to reduce equipment costs.

[0076] (First methane fermentation (sludge digestion) process) In the first methane fermentation (sludge digestion) step in the second and fifth embodiments, a methane fermentation (digestion) process is carried out using sewage sludge as a raw material. The first methane fermentation (sludge digestion) step is carried out under anaerobic conditions, similar to the hydrogen fermentation step. The digestion gas produced in the first methane fermentation (sludge digestion) step is composed of 60-70% by volume of methane, 30-40% by volume of carbon dioxide, and trace amounts of nitrogen, oxygen, hydrogen sulfide, water, and the like. The digestion gas is composed of approximately 60% by volume of methane and approximately 40% by volume of carbon dioxide, and may be used as fuel as is, or may be used as high-concentration methane gas after removing the carbon dioxide.

[0077] The digestion treatment of sewage sludge (organic waste) may be either wet methane fermentation or dry methane fermentation. It may also be either mesophilic methane fermentation or thermophilic methane fermentation. Mesophilic fermentation is carried out for 20 to 30 days, more preferably 23 to 27 days, and even more preferably about 25 days. Thermophilic fermentation is carried out for 10 to 20 days, more preferably 13 to 17 days, and even more preferably about 15 days. Mesophilic methane fermentation is carried out at 20 to 45°C, more preferably 30 to 37°C or lower, and even more preferably about 37°C. Thermophilic fermentation is carried out at 40 to 60°C, more preferably 50 to 60°C, and even more preferably about 55°C. Methane fermentation is carried out at a pH of 6.5 to 8.5, and more preferably 6.8 to 7.6.

[0078] (Second methane fermentation process) In the second methane fermentation step in the third and sixth embodiments, methane fermentation is carried out using volatile fatty acids such as acetic acid contained in the hydrogen fermentation liquor, hydrogen, and carbon dioxide as substrates. The second methane fermentation step is carried out under anaerobic conditions, similar to the hydrogen fermentation step. The biogas produced in the second methane fermentation step is composed of 60 to 70% by volume of methane, 30 to 40% by volume of carbon dioxide, and trace amounts of nitrogen, oxygen, hydrogen sulfide, water, and the like. Biomethane gas is composed of approximately 60% by volume of methane and approximately 40% by volume of carbon dioxide, and may be used as fuel as is, or may be used as high-concentration methane gas after removing the carbon dioxide.

[0079] The second methane fermentation step may be either wet methane fermentation or dry methane fermentation. It may also be either mesophilic methane fermentation or thermophilic methane fermentation. In the case of mesophilic fermentation, the treatment is carried out for 15 to 30 days, more preferably 15 to 25 days, and even more preferably about 20 days. In the case of thermophilic fermentation, the treatment is carried out for 10 to 20 days, more preferably 15 to 20 days, and even more preferably about 15 days. In the case of mesophilic fermentation, methane fermentation is carried out at 20 to 45°C, more preferably 30 to 37°C or lower, and even more preferably about 37°C. In the case of thermophilic fermentation, it is carried out at 40 to 60°C, more preferably 50 to 60°C, and even more preferably about 55°C. Furthermore, methane fermentation is carried out at a pH of 6.5 to 8.5, and more preferably a pH of 6.8 to 7.6.

[0080] The methane fermentation liquid obtained in the first methane fermentation step and the second methane fermentation step contains a large amount of nitrogen source. The lignocellulose-decomposing microorganisms contained in the rumen microorganisms consume nitrogen in the process of decomposing lignocellulose-based biomass to produce reducing sugars in the decomposition / hydrogen fermentation tank 20 or the pretreatment tank 21. Therefore, by supplying the methane fermentation liquid in advance to the storage tank 10, the culture tank 40, or the pretreatment tank 21, the lignocellulose decomposition activity in the decomposition / hydrogen fermentation tank 20 or the pretreatment tank 21 can be maintained or improved. Furthermore, since there is no need to add a separate nitrogen source, costs can be reduced.

[0081] The present invention is not limited to the above-described embodiment. The configurations of the above-described embodiment can be appropriately combined, and various modifications can be made to the above-described embodiment. For example, the above-described embodiment can be modified as follows.

[0082] In the above embodiment, an example was described in which the crusher 50 for crushing and pulverizing the lignocellulose biomass was provided, but the crusher 50 is not essential.

[0083] In the above embodiments, hydrogen fermentation treatment systems 101, 102, 107, 108, hydrogen fermentation treatment systems 103, 104, 109, 110 equipped with a first methane fermentation (digestion) tank 30, and hydrogen fermentation treatment systems 105, 106, 111, 112 equipped with a second methane fermentation tank 31 and performing two-stage hydrogen and methane fermentation have been described, but a hydrogen fermentation treatment system equipped with a first methane fermentation (digestion) tank 30 and a second methane fermentation tank 31 may also be used.

[0084] In the above embodiment, an example has been described in which lignocellulose biomass is supplied to the storage tank 10 and the culture tank 40, but lignocellulose biomass may also be supplied directly to the pretreatment tank 21. By directly supplying lignocellulose biomass to the pretreatment tank 21, the production amount of reducing sugars and easily decomposable organic waste with a small molecular weight can be further improved. In this case, the solids concentration (TS) of the pretreatment liquid in the pretreatment tank 21 is adjusted to be 3.0 to 20.0%, more preferably 5.0 to 10.0%.

[0085] In the above embodiment, an example has been described in which the methane fermentation liquor is supplied to the culture tank 40, but the pretreated liquor obtained in the pretreatment tank 21 may also be supplied to the culture tank 40. The pretreated liquor contains undecomposed or partially decomposed lignocellulose, as well as substances that serve as nitrogen and phosphorus sources. Therefore, by supplying the pretreated liquor to the culture tank 40, the growth and proliferation of lignocellulose-decomposing bacteria in the culture liquor is further promoted, and further hydrolysis improves the production of reducing sugars and easily decomposable organic waste with a small molecular weight.

[0086] In the above embodiment, an example has been described in which the hydrogen fermentation liquor is supplied to the second methane fermentation tank 31, but the hydrogen fermentation liquor may be mixed with organic waste such as sewage sludge and supplied to the first methane fermentation (digestion) tank 30, regardless of whether the second methane fermentation tank 31 is present. Because the hydrogen fermentation liquor contains volatile fatty acids that serve as a substrate for methane fermentation, the energy contained in the hydrogen fermentation liquor can be recovered as methane gas (gas energy). [Industrial Applicability]

[0087] The hydrogen fermentation treatment system and hydrogen fermentation treatment method of the present invention can be used to decompose organic waste, including industrial waste such as urban garbage (e.g., used paper and waste paper), and lignocellulosic industrial waste such as food waste, agricultural and forestry waste, and construction waste, and to produce biohydrogen gas or biomethane gas using the decomposed product as a raw material. [Explanation of symbols]

[0088] 10: Reservoir 20: Decomposition and hydrogen fermentation tank 21: Pre-treatment tank 22: Hydrogen fermenter 30: First methane fermentation (digestion) tank 31: Second methane fermentation tank 40:Culture tank 101-112: Hydrogen fermentation treatment system

Claims

1. a storage tank for storing a mixed liquid containing at least one of rumen fluid and a rumen microbial culture solution cultured in a culture tank and lignocellulosic biomass; a decomposition / hydrogen fermentation tank that performs decomposition treatment and hydrogen fermentation treatment on the mixed liquid supplied from the storage tank; A hydrogen fermentation treatment system comprising:

2. The system further includes a first methane fermentation tank for subjecting organic waste to methane fermentation treatment; 2. The hydrogen fermentation treatment system according to claim 1, wherein the methane fermentation liquid in the first methane fermentation tank is supplied to at least one of the storage tank and the culture tank.

3. Further provided is a second methane fermentation tank for performing methane fermentation using the hydrogen fermentation liquid in the decomposition / hydrogen fermentation tank as a raw material, 3. The hydrogen fermentation treatment system according to claim 1, wherein the methane fermentation liquid in the second methane fermentation tank is returned to at least one of the storage tank and the culture tank.

4. a storage tank for storing a mixed liquid containing at least one of rumen fluid and a rumen microbial culture solution cultured in a culture tank and lignocellulosic biomass; a pretreatment tank for decomposing the mixed liquid supplied from the storage tank; a hydrogen fermentation tank for subjecting the pretreated liquid in the pretreatment tank to hydrogen fermentation; A hydrogen fermentation treatment system comprising:

5. The system further includes a first methane fermentation tank for subjecting organic waste to methane fermentation treatment; 5. The hydrogen fermentation treatment system according to claim 4, wherein the methane fermentation liquid in the first methane fermentation tank is supplied to at least one of the storage tank, the culture tank, and the pretreatment tank.

6. Further provided is a second methane fermentation tank for performing methane fermentation using the hydrogen fermentation liquid in the hydrogen fermentation tank as a raw material, 6. The hydrogen fermentation treatment system according to claim 4, wherein the methane fermentation liquid in the second methane fermentation tank is returned to at least one of the storage tank, the culture tank, and the pretreatment tank.

7. a storage step of storing a mixed liquid containing at least one of rumen fluid and a rumen microorganism culture solution cultured in a culture tank and lignocellulosic biomass in a storage tank; a decomposition / hydrogen fermentation process in which the mixed liquid supplied from the storage process is decomposed and subjected to hydrogen fermentation; A hydrogen fermentation treatment method comprising:

8. The method further includes a first methane fermentation step of subjecting organic waste to methane fermentation treatment, 8. The hydrogen fermentation treatment method according to claim 7, wherein the methane fermentation liquid obtained in the first methane fermentation step is supplied to at least one of the storage tank and the culture tank.

9. The hydrogen fermentation liquid obtained in the decomposition / hydrogen fermentation step is used as a raw material for methane fermentation.

9. The hydrogen fermentation treatment method according to claim 7, wherein the methane fermentation liquid obtained in the second methane fermentation step is returned to at least one of the storage tank and the culture tank.

10. a storage step of storing a mixed liquid containing at least one of rumen fluid and a rumen microorganism culture solution cultured in a culture tank and lignocellulosic biomass in a storage tank; a pretreatment step of decomposing the mixed liquid supplied from the storage step in a pretreatment tank; a hydrogen fermentation step in which the pretreated liquid obtained in the pretreatment step is subjected to hydrogen fermentation in a hydrogen fermenter; A hydrogen fermentation treatment method comprising:

11. The method further includes a first methane fermentation step of subjecting organic waste to methane fermentation treatment, 11. The hydrogen fermentation treatment method according to claim 10, wherein the methane fermentation liquid obtained in the first methane fermentation step is supplied to at least one of the storage tank, the culture tank, and the pretreatment tank.

12. The hydrogen fermentation process further includes a second methane fermentation process in which methane fermentation is performed using the hydrogen fermentation liquid obtained in the hydrogen fermentation process as a raw material.

12. The hydrogen fermentation treatment method according to claim 10, wherein the methane fermentation liquid obtained in the second methane fermentation step is returned to at least one of the storage tank, the culture tank, and the pretreatment tank.

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