JP7814031B2 - Hydrogen fermentation treatment system and hydrogen fermentation treatment method - Google Patents

Description

The present invention relates to a hydrogen fermentation treatment system and a hydrogen fermentation treatment method.

Lignocellulosic biomass is an abundant organic carbon source found on Earth and constitutes the main component of plant cell walls, i.e., plant fiber. It 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. Because it is a persistent organic waste, the decomposition process requires a great deal of energy, cost, and time. This has led to a sluggish expansion of its use as an energy resource.

Conventionally, there is known technology for producing biogas such as hydrogen gas and methane gas by solubilizing organic waste such as food waste and carrying out two-stage hydrogen and methane fermentation (see, for example, Patent Document 1).

Patent Document 1 discloses an anaerobic treatment method that combines anaerobic solubilization, which reduces organic waste from food waste primarily composed of carbohydrate waste or food waste primarily composed of cellulose solids, to smaller molecules through anaerobic solubilization and hydrogen fermentation, followed by a completely mixed methane fermentation process in the latter stage, to recover hydrogen and methane.

JP 2013-13896 A

However, in the anaerobic treatment method described in Patent Document 1, food waste organic waste mainly composed of carbohydrate waste and food waste organic waste mainly composed of cellulose solids are anaerobic solubilized to reduce their molecular weight, and biogas is produced through a two-stage fermentation process involving hydrogen fermentation and methane fermentation. However, in order to anaerobically solubilize lignocellulosic biomass, which is a difficult-to-decompose organic waste, and decompose it into reducing sugars, which are the substrate for hydrogen fermentation, a long decomposition reaction time (hydraulic residence time) is required, necessitating the installation of a large-capacity fermenter. Furthermore, when lignocellulosic biomass with a low moisture content is supplied to the hydrogen fermenter, it must be diluted with water to a concentration that can be transported using a pump, etc., which poses the problem of insufficient dilution in locations with limited available water volume. Furthermore, using tap water for dilution poses the problem of high water costs.

The present invention aims to provide a hydrogen fermentation treatment system and method for efficiently producing biogas such as hydrogen gas by performing hydrogen fermentation using lignocellulosic biomass, a type of persistent organic waste, as a feedstock.

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.

With 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 downstream decomposition/hydrogen fermentation tank.

The hydrogen fermentation treatment system of the present invention may further include a first methane fermentation tank that performs methane fermentation treatment on organic waste, 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.

With the above configuration, a nitrogen source can be provided 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, by supplying a methane fermentation liquid rich in a nitrogen source to the storage tank or the like in advance, lignocellulose decomposition activity can be maintained or improved. Furthermore, when treating organic waste such as sludge generated by biological wastewater treatment methods such as the activated sludge method, 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 a wastewater treatment facility is required for wastewater treatment. However, by using the digested sludge as a nitrogen source for the lignocellulose-degrading microorganisms, facility costs can be reduced.

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.

With 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 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 fermentation tank to produce reducing sugars. Therefore, by supplying a methane fermentation liquid rich in nitrogen source to the storage tank or the like in advance, lignocellulose decomposition activity can be maintained or improved.

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.

With 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 has a separate role from the hydrogen fermenter. This has the advantage of making operation control and management easier.

The hydrogen fermentation treatment system of the present invention may further include a first methane fermentation tank that performs methane fermentation treatment on organic waste, 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.

With 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 fermentation tank to at least one of the storage tank, culture tank, and 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 liquid rich in nitrogen to the storage tank or the like in advance, lignocellulose decomposition activity can be maintained or improved. Furthermore, when treating organic waste such as sludge generated by biological wastewater treatment methods such as the activated sludge method, 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 a wastewater treatment facility is required for wastewater treatment. However, by using the digested sludge as a nitrogen source for the lignocellulose-degrading microorganisms, facility costs can be reduced.

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.

With 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, culture tank, and 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 rich in nitrogen source to the storage tank or the like in advance, lignocellulose decomposition activity can be maintained or improved.

To solve the above problems, the hydrogen fermentation treatment method of the present invention comprises a storage step in which a mixed liquid containing at least one of rumen fluid and rumen microbial culture fluid cultured in a culture tank and lignocellulosic biomass is stored in a storage tank, and a decomposition/hydrogen fermentation step in which the mixed liquid supplied from the storage step is decomposed and hydrogen fermented.

With 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.

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

According to the above configuration, a nitrogen source can be provided to the lignocellulose-degrading microorganisms contained in the rumen microorganisms by supplying the methane fermentation liquid obtained in the first methane fermentation process 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 process to produce reducing sugars by decomposing lignocellulose-based biomass. Therefore, by supplying a methane fermentation liquid rich in a nitrogen source to a storage tank or the like in advance, lignocellulose decomposition activity can be maintained or improved. Furthermore, when treating organic waste such as sludge generated by biological wastewater treatment methods such as the activated sludge method, 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 a wastewater treatment facility is required for wastewater treatment. However, by using the digested sludge as a nitrogen source for the lignocellulose-degrading microorganisms, facility costs can be reduced.

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/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.

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

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; a pretreatment step of decomposing the mixed liquid supplied from the storage step in a pretreatment tank; and a hydrogen fermentation step of subjecting the pretreated liquid obtained in the pretreatment step to hydrogen fermentation in a hydrogen fermentation tank.

With 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 pretreatment tank and hydrogen fermenter. Furthermore, the pretreatment process carried out after the storage process is specialized in the function of decomposing lignocellulosic biomass and producing reducing sugars, which serve as a substrate for hydrogen fermentation, and its role is separate from the hydrogen fermentation process carried out in the subsequent hydrogen fermenter. This has the advantage of making operation control and management easier.

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

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

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 liquor obtained in the hydrogen fermentation process as a raw material, and may be configured to return the methane fermentation liquor obtained in the second methane fermentation process to at least one of the storage tank, the culture tank, and the pretreatment tank.

With 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 process to at least one of the storage tank, culture tank, and 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 process. Therefore, by supplying a methane fermentation liquid rich in nitrogen source to a storage tank or the like in advance, lignocellulose decomposition activity can be maintained or improved.

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, making it possible to reduce the hydraulic retention time or tank volume of downstream hydrogen fermentation tanks, etc.

1 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a first embodiment. FIG. FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a second embodiment. FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a third embodiment. FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a fourth embodiment. FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a fifth embodiment. FIG. 10 is a diagram showing a schematic configuration of a hydrogen fermentation treatment system according to a sixth embodiment.

The following describes in detail the embodiments and drawings relating to the hydrogen fermentation treatment system and 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.

The following describes the hydrogen fermentation treatment system and hydrogen fermentation treatment method according to each embodiment, using Figures 1 to 6.

(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.

(storage tank)
Rumen fluid and lignocellulosic biomass collected from ruminants such as cattle are introduced into the storage tank 10 in FIG. 1( a). Rumen microorganism culture fluid and lignocellulosic biomass cultivated in a culture tank 40 are introduced into the storage tank 10 in FIG. 1( b). Storing a mixture containing at least one of rumen fluid and rumen microorganism culture fluid and lignocellulosic biomass in the storage tank 10 promotes the decomposition of the lignocellulosic biomass, thereby 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 to a solids concentration (TS: Total Solids) of 3.0 to 20.0%. A solids concentration of 3.0% or less 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, if the solids concentration exceeds 20.0%, it may be difficult to pump out the mixed solution. 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, it is no longer necessary 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 may 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 provided with an agitator (not shown) for mixing the mixed solution. In addition, since the solid concentration in the storage tank 10 only needs to be adjusted to fall within the above range, it is not essential to install instruments for temperature control, pH adjustment, etc.

(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 raw material. Specifically, the mixed liquid in the storage tank 10 is supplied to the decomposition/hydrogen fermentation tank 20, where it is maintained at 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 then carried out, followed by hydrogen fermentation by hydrogen-producing bacteria. The resulting hydrogen fermentation-resulting liquid 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, pH 5.5-6.0, preferably pH 5.7.

The decomposition/hydrogen fermenter 20 can be a complete mixing fermentation (anaerobic digestion) type fermenter, which is widely used both domestically and internationally 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, 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 materials, etc.

As hydrogen fermentation progresses, biohydrogen gas is generated in the decomposition/hydrogen fermentation tank 20. Biohydrogen gas is a gas that is approximately 50% hydrogen gas and approximately 50% carbon dioxide by volume. The generated biohydrogen gas is extracted from the decomposition/hydrogen fermentation tank 20 and used as fuel to heat 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).

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

(culture tank)
Rumen microorganisms present in rumen fluid collected from ruminants such as cattle are cultured 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) 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 continuously or semi-continuously cultured to be steadily supplied to the storage tank 10.

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 lignocellulose-degrading bacteria, it is preferable to arbitrarily control the hydraulic retention time (HRT) and solid retention time (SRT) using solid-liquid separation means (not shown). Because lignocellulose-degrading bacteria grow by adhering to the surface of solid matter in the culture solution, it is preferable to control operation so that the SRT is longer than the HRT.

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.

(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 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 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 complete mixing fermentation (anaerobic digestion) type fermenter widely used in Japan and overseas for treating solid (slurry-like) waste. The digester 30 may be a steel tank or a concrete tank. An agitator (not shown) may be attached to the digester 30 to agitate the sewage sludge introduced into it.

The methane fermentation liquid (digested sludge) in the first methane fermentation (digestion) tank 30 contains substances that serve as a nitrogen source. Therefore, 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 liquid, 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, 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 equipment costs.

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

(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 fermentation tank 20. However, it differs from the first embodiment in that a second methane fermentation tank 31 is provided downstream of the decomposition/hydrogen fermentation tank 20, allowing for two-stage hydrogen/methane fermentation.

(Second methane fermentation tank)
The second methane fermenter 31 shown in Figures 3(a) and (b) is a tank in which methane fermentation is performed 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 methane fermentation or thermophilic methane fermentation. In the case of mesophilic fermentation, the treatment is performed 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 performed 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 performed 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 performed at 40 to 60°C, more preferably 50 to 60°C, and even more preferably about 55°C. Furthermore, methane fermentation is performed 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.

The methane fermentation liquid in the second methane fermentation tank 31 contains substances that serve as nitrogen sources. Supplying this to the storage tank 10 or culture tank 40 further promotes the growth and proliferation of lignocellulose-decomposing bacteria in the mixed liquid or culture liquid, 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, 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.

The hydrogen fermentation liquid supplied from the decomposition/hydrogen fermentation tank 20 is subjected to methane fermentation in the second methane fermentation tank 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 fermentation tank 31 and used as fuel for heating the second methane fermentation tank 31, 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 the hydrogen fermentation liquid to methane fermentation, the energy contained in the hydrogen fermentation liquid can be recovered as biomethane gas (gas energy).

(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 fermentation tank 22. The lignocellulosic biomass is crushed and pulverized as necessary using a crusher 50 or the like and supplied to the storage tank 10.

(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 fluid or rumen microbial culture solution. 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.

(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.

As hydrogen fermentation progresses, biohydrogen gas is generated in the hydrogen fermenter 22. Biohydrogen gas is a gas that is approximately 50% hydrogen gas and approximately 50% carbon dioxide by volume. The generated biohydrogen gas is extracted from the hydrogen fermenter 22 and used as fuel for heating the pretreatment tank 21, hydrogen fermenter 22, and 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).

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. Similar to the hydrogen fermentation treatment systems 107 and 108 shown in Fig. 4, the fifth embodiment is primarily 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 first methane fermentation (digestion) tank 30 in a separate system.

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 substances that serve as nitrogen sources. Therefore, supplying this to the storage tank 10, culture tank 40, and 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. Furthermore, 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 equipment costs.

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. Similar to 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 a second methane fermenter 31 is provided downstream of the hydrogen fermenter 22, allowing for two-stage hydrogen and methane fermentation.

The second methane fermentation tank 31 of this embodiment shown in Figures 6(a) and (b) can be a tank similar to the second methane fermentation tank 31 shown in Figures 3(a) and (b), and methane fermentation treatment can be performed under similar conditions. The methane fermentation liquid in the second methane fermentation tank 31 contains a nitrogen source, so supplying it 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, and 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 liquid can be reused as a substrate for hydrogen fermentation or methane fermentation, improving energy recovery efficiency.

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

(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. Paper shredded by a shredder is incinerated because its fibers are broken and difficult to recycle, but such shredded paper can also be used as a raw material. Furthermore, only one type of the above-listed organic waste may be used as a raw material, or multiple types may be mixed together.

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

(Rumen microorganisms)
Rumen microorganisms are anaerobic bacteria present in ruminal fluid, a digestive fluid present 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 L, 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 the lignocellulose-degrading bacteria as substrates. Methanogenic bacteria produce methane using acetic acid or hydrogen and carbon dioxide produced by the lignocellulose-degrading bacteria or hydrogen-producing bacteria as substrates.

(Rumen microbial culture solution)
A culture solution of rumen microorganisms (lignocellulose-degrading bacteria) with high lignocellulose decomposition activity can be obtained in the culture tank 40 for culturing rumen microorganisms. In culturing rumen microorganisms, for example, the quantity of at least one of three types of lignocellulose-decomposing bacteria, 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 medium, thereby obtaining a culture solution of rumen microorganisms (lignocellulose-decomposing bacteria) with high lignocellulose decomposition activity. The quantification of the number of bacteria of these bacteria is not particularly limited, but is preferably carried out by quantitative PCR, which can rapidly and accurately measure the number of bacteria of specific bacteria. When quantifying the number of bacteria of lignocellulose-degrading bacteria using quantitative PCR, genomic DNA extracted from the culture solution and purified is used. Since the culture solution of rumen microorganisms can be cultured in large quantities or subcultured, the culture solution of rumen microorganisms with an adjusted number of bacteria can be used for lignocellulose decomposition as needed.

The culture medium used for culturing 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 salts, 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.

To create an anaerobic environment within the culture tank 40 similar to that within the rumen, the oxidation-reduction potential (ORP) of the culture solution is adjusted to -100 mV or less, more 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 reducing substances 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. Rumen microorganisms may also be cultured in a closed system under a nitrogen or carbon dioxide atmosphere.

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 will be discharged from the system along with the solids. On the other hand, if the HRT is longer than necessary, negative factors such as a decrease in pH due to the produced volatile fatty acids (VFAs) and inhibition of microbial growth can occur. Specifically, the HRT should be 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. Furthermore, the temperature of the reaction system for culturing rumen microorganisms is controlled using a temperature sensor or other device to maintain a temperature of 35 to 42°C, more preferably 37 to 40°C. The lignocellulose biomass introduced into the culture tank 40 is adjusted so that the solids concentration (TS) in the culture solution is 1.0 to 20.0%, and more preferably 3.0 to 10.0%. If the solids concentration (TS) is 1.0% or less, there is a risk that the growth and proliferation of lignocellulose-degrading bacteria will not be promoted. On the other hand, if it exceeds 20.0%, there is a risk that solid-liquid separation of the culture solution will not occur properly.

(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, making it possible to reduce the hydraulic retention time or the capacity of the subsequent decomposition/hydrogen fermentation tank 20, pretreatment tank 21, and hydrogen fermentation tank 22. 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 a decrease in the 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 treatment 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 to more appropriately adjust 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, so temperature control or pH adjustment within the storage tank 10 is not required. The method for mixing lignocellulosic biomass with at least one of rumen fluid and rumen microbial culture solution is not particularly limited. 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 for supplying lignocellulosic biomass to the storage tank 10. Furthermore, 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. Supplying at least one of rumen fluid and rumen microbial culture solution to the storage tank 10 from the gas phase or the bottom can simplify the device configuration. Supplying at least one of rumen fluid and rumen microbial culture solution to a path for supplying lignocellulosic biomass to the storage tank 10 or spraying it onto the lignocellulosic biomass in a shower-like manner allows the lignocellulosic biomass, at least one of rumen fluid and rumen microbial culture solution, and the lignocellulosic biomass to be uniformly mixed.

(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.

To achieve anaerobic conditions during the pretreatment process, the oxidation-reduction potential (ORP) of the pretreatment liquid is adjusted to -100 mV or less, more preferably -200 mV or less, and even more preferably around -250 mV. Because rumen microorganisms (lignocellulose-degrading bacteria) are anaerobic, if the ORP exceeds a predetermined level (approaching an aerobic state), measures such as injecting an inert gas such as nitrogen gas or carbon dioxide gas, adding reducing substances 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, can be taken. The pretreatment process can also be carried out in a closed system under a nitrogen or carbon dioxide atmosphere.

The pretreatment process (hydrolysis and production of reducing sugars) is carried out in a completely mixed system. The temperature of the reaction system in the pretreatment process is controlled using a temperature sensor or other device to maintain it at 50-60°C, preferably around 55°C. Keeping the temperature at 50-60°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 5.5-6.0, preferably 5.7. The hydraulic residence time is 4-36 hours, more preferably around 24 hours. The reaction in the pretreatment process can be carried out statically or with stirring, but stirring is preferred to speed up the progress of the pretreatment process.

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

(Hydrogen fermentation process)
The hydrogen fermentation process is carried out under anaerobic conditions, similar to 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. Furthermore, 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.

Hydrogen fermentation is carried out at a temperature of 50-60°C, preferably around 55°C. Hydrogen fermentation is also carried out at a pH of 5.5-6.0, preferably around 5.7. The hydraulic retention time is 24-168 hours, preferably around 120 hours.

(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, more preferably at about 55°C. The decomposition and hydrogen fermentation process is also carried out at a pH of 5.5 to 6.0, more preferably at about 5.7. The hydraulic retention time is 24 to 168 hours, more preferably about 72 hours. Because the decomposition and hydrogen fermentation process involves the decomposition treatment and hydrogen fermentation treatment of lignocellulosic biomass in a single tank, it is possible to reduce equipment costs.

(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 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. 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.

Sewage sludge (organic waste) can be digested using either wet methane fermentation or dry methane fermentation. It can also be either mesophilic 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.

(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.

The second methane fermentation step may be either wet methane fermentation or dry methane fermentation. It may also be 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, 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.

The methane fermentation liquid obtained in the first and second methane fermentation processes contains a large amount of nitrogen source. 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/hydrogen fermentation tank 20 or pretreatment tank 21. Therefore, by supplying the methane fermentation liquid to the storage tank 10, culture tank 40, or pretreatment tank 21 in advance, the lignocellulose decomposition activity in the decomposition/hydrogen fermentation tank 20 or pretreatment tank 21 can be maintained or improved. Furthermore, since there is no need to add a separate nitrogen source, costs can be reduced.

The present invention is not limited to the above-described embodiments. It is possible to combine the various components of the above-described embodiments as appropriate, and to make various modifications to the above-described embodiments. For example, the above-described embodiments can be modified as follows:

In the above embodiment, an example was described in which a crusher 50 was provided to crush and pulverize lignocellulosic biomass, but the crusher 50 is not required.

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 were described. However, 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.

In the above embodiment, an example was described in which lignocellulosic biomass was supplied to the storage tank 10 and the culture tank 40, but lignocellulosic biomass may also be supplied directly to the pretreatment tank 21. By supplying lignocellulosic biomass directly to the pretreatment tank 21, the production volume 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 3.0 to 20.0%, more preferably 5.0 to 10.0%.

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

In the above embodiment, an example was described in which the hydrogen fermentation liquid was supplied to the second methane fermentation tank 31, but the hydrogen fermentation liquid may also 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 liquid contains volatile fatty acids that serve as a substrate for methane fermentation, the energy contained in the hydrogen fermentation liquid can be recovered as methane gas (gas energy).

The hydrogen fermentation treatment system and method of the present invention can be used to decompose organic waste, including industrial waste such as municipal waste, including used paper and waste paper, and lignocellulosic industrial waste, including 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.

10: Storage tank 20: Decomposition/hydrogen fermentation tank 21: Pretreatment tank 22: Hydrogen fermentation tank 30: First methane fermentation (digestion) tank 31: Second methane fermentation tank 40: Culture tanks 101-112: Hydrogen fermentation treatment system

Claims (12)

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: 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. 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. 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: 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. 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. 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: 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. 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. 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: 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. 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.