JP2023018342A - Fuel gas production device and fuel gas production method - Google Patents

Abstract

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

Description

The present invention relates to a fuel gas production device and a fuel gas production method.

Lignocellulosic biomass is an organic carbon source abundantly present on the earth, which constitutes the cell wall of plant cells, that is, the main component of plant fibers. In addition, since lignocellulosic biomass is a persistent organic waste, the decomposition stage requires a great deal of energy, cost and time. Therefore, the actual situation is that the expansion of its use as an energy resource is stagnant.

Conventionally, lignocellulosic biomass is decomposed using rumen microorganisms present in the rumen juice of ruminants to produce volatile fatty acids such as acetic acid, and methane fermentation is performed using volatile fatty acids as substrates. A technique for producing biogas is known (for example, Non-Patent Document 1).

Non-Patent Document 1 discloses a two-phase process in which a methane-producing tank (second reactor) is connected to an acid-producing tank (first reactor) for decomposing cellulose to produce volatile fatty acids. there is Specifically, in the acid production tank, rumen microorganisms work to decompose cellulose to produce volatile fatty acids, and a liquid phase containing a large amount of volatile fatty acids is supplied to the methane production tank using a membrane separator. It is disclosed that methane gas is produced by methane fermentation using volatile fatty acids as substrates.

HubbJ. Gijzen, et al., "High-Rate two-phase process for the anaerobic degradation of cellulose, employing rumen microbes for efficient acid production." microorganisms for an efficient acidogenesis), Biotechnology and Bioengineering, Vol. 31, pp. 418-425 (1988)

However, in the two-phase process described in Non-Patent Document 1, solid-liquid separation is performed for the convenience of adjusting the solid retention time (SRT: Sludge retention time). The solids concentration (TS) should be 1.0% by weight or less. Therefore, a large amount of culture medium and dilution water are required, and as a result, methane production equipment is limited to huge capacity methane fermentation tanks, or UASB and EGSB systems that can handle high loads, and existing methane fermentation There was a problem that even if it was attempted to apply it to a tank, it could not be applied due to insufficient tank capacity. In addition, when the UASB method or EGSB method methane fermentation tank is applied, the suspension containing a lot of suspended solids (high SS concentration) in the acid production tank is not treated, and only the solid-liquid separated membrane filtered water is treated. Therefore, there is a problem that a suspension is discharged out of the system and a large amount of solid waste is generated.

Therefore, the present invention reduces the amount of liquid medium such as artificial medium (artificial saliva) and dilution water used for adjusting the solid concentration (TS) in the treatment liquid in which organic waste is decomposed. It is an object of the present invention to provide a fuel gas production apparatus and a fuel gas production method for producing biomass-derived fuel gas that can reduce the amount of solid waste discharged.

In order to solve the above problems, the fuel gas production apparatus of the present invention is a fuel gas production apparatus for producing biomass-derived fuel gas, comprising a culture tank for culturing rumen microorganisms, and a pretreatment tank for mixing the culture solution of said rumen microorganisms and organic waste, and treating said organic waste to convert it into easily decomposable organic waste and volatile fatty acids; and said pretreatment tank. and a fermenter for fermenting the easily decomposable organic waste and the volatile fatty acid obtained in the interior as substrates.

According to the above configuration, rumen microorganisms (lignocellulose-degrading bacteria) that decompose organic waste can be cultured in the culture tank and stably supplied to the downstream pretreatment tank. Therefore, each time the fuel gas production device is operated, the rumen fluid is collected from the ruminant and transported to the facility where the fuel gas production device is installed. can. In addition, since the pretreatment tank is specialized for the function of treating organic waste and producing easily decomposable organic waste such as partially decomposed organic waste and volatile fatty acids, The amount of organic waste supplied to the pretreatment tank can be set higher than usual. In addition, the pretreatment liquid in the pretreatment tank does not need to undergo solid-liquid separation, and is supplied to the fermentation tank connected downstream. A fermenter of a complete mixing type fermentation (anaerobic digestion) system can be adopted. Unlike the UASB, which processes only the membrane-filtered water of the pretreatment liquid separated into solids and liquids in the upstream pretreatment tank, the fermenter of the complete mixing type fermentation method can also process suspensions. Therefore, the amount of liquid culture medium such as artificial culture medium (artificial saliva) and dilution water used can be reduced. In addition, since fermentation is performed using the easily decomposable organic waste contained in the suspension of the pretreatment liquid as a substrate, the amount of solid waste discharged can be reduced and the production of fuel gas generated can be increased. I can expect it. Furthermore, since the processes performed in each of the culture tank, pretreatment tank, and fermentation tank are clearly defined, operation management and troubleshooting are facilitated.

Moreover, in the fuel gas production apparatus of the present invention, the organic waste may be supplied to the culture tank and the pretreatment tank at a predetermined ratio.

According to the above configuration, organic waste is supplied to the culture tank and the pretreatment tank at a predetermined ratio, so that rumen microorganisms (lignocellulose-degrading bacteria) having high organic waste-decomposing activity are generated in the culture tank. It can be cultured, and in the pretreatment tank, easily decomposable organic waste such as partially decomposed organic waste and volatile fatty acids are efficiently produced.

Further, in the fuel gas production apparatus of the present invention, the pretreatment liquid containing the easily decomposable organic waste and the volatile fatty acid obtained in the pretreatment tank is supplied to the culture tank. may

According to the above configuration, the pretreatment liquid in the pretreatment tank contains, as a nutrient source for lignocellulose-degrading bacteria, undecomposed or partially decomposed lignocellulose contained in the organic waste, a nitrogen source, and a phosphorus source. Since it contains a substance that becomes Increased productivity.

Moreover, the fuel gas production apparatus of the present invention may further include solid-liquid separation means for performing solid-liquid separation of the culture solution in the culture tank.

According to the above configuration, by providing the solid-liquid separation means in the culture tank, the culture solution in the culture tank is separated from the filtrate containing a high concentration of volatile fatty acids, which is not preferable for the growth and proliferation of lignocellulose-degrading bacteria, and the lignobacterium. It can be separated into a suspension containing suspended matter to which many cellulolytic bacteria are attached. Therefore, the hydraulic retention time (HRT) and the solid retention time (SRT) can be individually controlled, and the filtrate containing a large amount of volatile fatty acids is discharged from the culture tank and suspended. Growth and multiplication of lignocellulose-degrading bacteria contained in the turbid liquid are promoted.

Moreover, in the fuel gas production apparatus of the present invention, easily decomposable organic waste may be supplied to the fermenter.

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

In order to solve the above problems, the fuel gas production method of the present invention is a fuel gas production method for producing a biomass-derived fuel gas, comprising a culturing step of culturing rumen microorganisms, and a pretreatment step of mixing the rumen microorganism culture solution and organic waste, treating the organic waste and converting it into readily degradable organic waste and volatile fatty acids; a fermentation step of performing fermentation using the obtained easily decomposable organic waste and the volatile fatty acid as substrates, and the culture step further includes a solid-liquid separation step of solid-liquid separating the culture solution.

According to the above configuration, in the culturing step, rumen microorganisms (lignocellulose-degrading bacteria) that decompose organic waste can be cultured and stably supplied to the pretreatment tank in which the pretreatment step is performed. Therefore, each time the fuel gas production method is carried out, the rumen fluid is collected from the ruminant and the frequency of transporting it to the facility where the fuel gas production method is carried out is reduced, thereby reducing costs. . In addition, since the pretreatment tank in which the pretreatment process is performed is specialized for functions such as the generation of easily decomposable organic waste such as partial decomposition products of organic waste and the generation of volatile fatty acids, pretreatment The organic waste feed rate to the tank can be set higher than normal. In addition, the pretreatment liquid in the pretreatment tank does not need to undergo solid-liquid separation and is supplied to the downstream fermentation tank. The fermentation process can be carried out using a mixed fermentation (anaerobic digestion) type fermenter. Unlike UASB, etc., which can only process the membrane-filtered water of the pretreatment liquid that has undergone solid-liquid separation, the fermenter of the complete mixing type fermentation method can also process suspensions, so artificial culture medium It is possible to reduce the amount of liquid medium such as (artificial saliva) and dilution water used. In addition, since fermentation is performed using the easily decomposable organic waste contained in the suspension of the pretreatment liquid as a substrate, the amount of solid waste discharged can be reduced and the production of fuel gas generated can be increased. I can expect it. Furthermore, since the culture process, the pretreatment process, and the fermentation process are clearly defined, operation management and troubleshooting are facilitated. In addition, the culture step includes a solid-liquid separation step of solid-liquid separation of the culture solution of rumen microorganisms into a filtrate and a suspension, so that the culture solution in the culture tank is used for the growth and proliferation of lignocellulose-degrading bacteria. The filtrate can be separated into a filtrate containing a large amount of unfavorably high concentrations of volatile fatty acids and a suspension containing a large amount of lignocellulolytic bacteria adhering suspended matter. Therefore, separate control of the hydraulic retention time (HRT) and the solids retention time (SRT) is possible, the filtrate rich in volatile fatty acids is discharged from the culture tank, and the lignocellulose contained in the suspension is degraded. Promotes the growth and proliferation of bacteria.

Moreover, in the fuel gas production method of the present invention, the fermentation process may include at least one of a methane fermentation process and a hydrogen fermentation process.

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

According to the present invention, the amount of liquid medium such as artificial medium (artificial saliva) and dilution water used for adjusting the solids concentration (TS) in the treatment liquid in which organic waste is decomposed is reduced. and reduce solid waste emissions.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the fuel gas manufacturing apparatus which concerns on 1st Embodiment. 1 is a diagram showing a schematic configuration of a culture tank of a fuel gas production apparatus according to a first embodiment; FIG. It is a figure which shows schematic structure of the fuel gas manufacturing apparatus which concerns on 2nd Embodiment. It is a figure which shows schematic structure of the fuel gas manufacturing apparatus which concerns on 3rd Embodiment. It is a figure which shows the conventional fuel gas production apparatus. FIG. 4 is an explanatory diagram of Case 1 in which organic waste is supplied to the fuel gas production apparatus according to the first embodiment; FIG. 3 is an explanatory diagram of Case 2 in which organic waste is supplied to a two-phase fuel gas production apparatus;

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

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

A fuel gas production apparatus 100 shown in FIG. 1 is an apparatus for producing fuel gas such as biomethane gas and biohydrogen using organic waste B as a raw material. The fuel gas production apparatus 100 uses the culture tank 10 for culturing rumen microorganisms and the rumen microorganisms (lignocellulose-degrading bacteria) for treating the organic waste B so that the organic waste B can be easily utilized in the downstream fermentation tank 30. The pretreatment tank 20 that converts (decomposes) into a form (easily decomposable organic waste and volatile fatty acids), and the easily decomposable organic waste and volatile fatty acids that are decomposed products of the organic waste B are used as substrates. It is a three-phase system composed of a fermenter 30 that performs fermentation and produces fuel gas.

(Cultivation tank)
In the culture tank 10, rumen microorganisms present in rumen fluid collected from ruminant animals such as cattle are cultured. When a liquid medium M such as an artificial medium (artificial saliva) and organic waste B are supplied to the culture tank 10, rumen microorganisms (lignocellulose-degrading bacteria) proliferate by decomposing and metabolizing the organic waste B. At the same time, decomposition products of organic waste B (easy-to-decompose organic waste such as partial decomposition products of lignocellulose and volatile fatty acids (VFA: Volatile Fatty Acid) such as acetic acid, propionic acid, butyric acid, and valeric acid) produced. In addition, the culture solution of lignocellulose-degrading bacteria in the culture tank 10 is stably supplied to the downstream pretreatment tank 20 .

The culture tank 10 preferably has conditions that simulate the physiological state of the rumen of a ruminant animal such as a cow. Moreover, it is preferable that the hydraulic retention time (HRT) and the solid retention time (SRT) are arbitrarily controlled by the solid-liquid separation means 40 so that the lignocellulose-degrading bacteria grow sufficiently. Since lignocellulose-degrading bacteria grow by adhering to the surface of solids in the culture solution, it is preferable to control the operation so that the SRT is longer than the HRT.

(Pretreatment tank)
A culture solution of lignocellulose-degrading bacteria is supplied from the upstream culture tank 10 to the pretreatment tank 20, and the organic waste B is added and mixed. In the pretreatment tank 20, the organic waste B is decomposed by the action of lignocellulose-degrading bacteria to decompose organic waste B into low-molecular-weight decomposed products (easily decomposable organic waste such as partially decomposed lignocellulose). and volatile fatty acids (VFA: Volatile Fatty Acids) such as acetic acid, propionic acid, butyric acid, and valeric acid are produced. At least one selected from easily decomposable organic waste and volatile fatty acids should be produced in the pretreatment tank 20 . Like the culture tank 10, the pretreatment tank 20 preferably has conditions that simulate the physiological state of the rumen of ruminants such as cattle.

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

(Fermentation tank)
When the pretreatment liquid containing a large amount of easily decomposable organic waste and volatile fatty acids is supplied from the pretreatment tank 20 to the fermentation tank 30, the easily decomposable organic waste and volatile fatty acids are used as substrates (raw materials). Fermentation reaction progresses and fuel gas G is generated. The substrate supplied to the fermentor 30 may contain at least one selected from easily decomposable organic waste and volatile fatty acids. The fermentation reaction performed in the fermentation tank 30 may be methane fermentation that contributes to the generation of biomethane gas, or hydrogen fermentation that contributes to the generation of biohydrogen. For example, hydrogen fermentation is performed as the first stage. It may be hydrogen/methane two-stage fermentation in which methane fermentation is performed as the second stage after the fermentation. Note that the fermentation residue R discharged from the fermentation tank 30 is concentrated and can be used as fertilizer, building materials, and the like.

As described above, according to the fuel gas production apparatus 100 according to the present embodiment, (1) the culture tank 10 for culturing rumen microorganisms, (2) the organic waste B is treated to easily decompose organic waste and volatile (3) a fermenter 30 that performs a fermentation reaction using readily decomposable organic waste and volatile fatty acids as substrates; It has the advantage of being easy to use.

(Solid-liquid separation means)
FIG. 2 is a diagram showing a schematic configuration of the culture tank 10 of the fuel gas production apparatus 100 according to the first embodiment, and a filtration membrane 41 is illustrated as the solid-liquid separation means 40 installed in the culture tank 10. . The solid-liquid separation means 40 separates the culture solution into filtrate and suspension. As shown in FIG. 2, in the culture tank 10, the culture solution is agitated by the stirrer 50, and the suspension containing the filtrate and undecomposed or partially decomposed suspended matter obtained by solid-liquid separation by the filtration membrane 41 is They are sent to the downstream pretreatment tank 20 through the filtrate liquid feeding pipe 11 and the suspension liquid feeding pipe 12, respectively. The hydraulic retention time (HRT) and solids retention time of the culture solution can be adjusted by appropriately adjusting the amount of the filtrate and suspension of the culture solution withdrawn from the culture tank 10 and sent to the pretreatment tank 20 by the pump P. Time (SRT) is controlled separately. Since the filtrate and suspension of the culture solution contain a large number of lignocellulose-degrading bacteria, the organic waste B is efficiently decomposed when supplied to the downstream pretreatment tank 20 . In FIG. 2, a membrane separation method using a filtration membrane 41 is illustrated as the solid-liquid separation means 40, but separation by a gravity sedimentation method or a flotation method (not shown) may also be used. Moreover, when performing a membrane separation method as the solid-liquid separation means 40, as shown in FIG. However, in order to reduce the power of the pump P of the filtrate sending pipe 11 and to reduce the clogging of the filtration membrane 41 by suspended matter, the upper end of the filtration membrane 41 should be lower than the liquid surface of the culture solution. The filtration membrane 41 may be installed so that the inside and outside of the filtration membrane 41 are at the same pressure while being immersed so as to be located above (not shown).

(Second embodiment)
FIG. 3 is a diagram showing a schematic configuration of a fuel gas production device 101 according to the second embodiment. The fuel gas production apparatus 101 according to the second embodiment is the fuel gas production apparatus 100 according to the first embodiment, in which the organic waste B is mixed with the dilution water W and put into the pretreatment tank 20, and A pretreatment liquid supply pipe 21 for supplying the pretreatment liquid obtained in 20 to the culture tank 10 is further provided. Since the pretreatment liquid contains undegraded or partially decomposed lignocellulose and substances that serve as nitrogen sources and phosphorus sources, by supplying it to the culture tank 10, lignocellulose-decomposing bacteria in the culture liquid grow and grow. Growth is promoted further, and further hydrolysis increases the production of volatile fatty acids and easily decomposable organic wastes with low molecular weights.

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

FIG. 5 is a diagram showing a fuel gas production apparatus 200 configured by a conventional two-phase process. In the conventional fuel gas production apparatus 200, the culture of rumen microorganisms and the decomposition of the organic waste B are carried out in a single culture tank and pretreatment tank 220. As shown in FIG. The pretreatment liquid in the culture tank/pretreatment tank 220 is subjected to solid-liquid separation by the filtration membrane 41 (solid-liquid separation means 40 ), and the filtrate is sent to the downstream UASB 230 through the filtrate sending pipe 11 . In the UASB 230, methane fermentation is performed using the volatile fatty acid contained in the filtrate as a substrate.

In order for the solid-liquid separation of the pretreatment liquid in the culture tank/pretreatment tank 220 to be performed without problems, the solid concentration (TS) of the organic waste B supplied to the culture tank/pretreatment tank 220 should be approximately It is necessary to adjust the content to be 1.0% by weight or less. In order to adjust the solids concentration (TS), a large amount of liquid medium M such as artificial medium (artificial saliva) and dilution water W are required. Tanks are limited to UASB and EGSB, which are capable of handling high loads. However, when the SS concentration of the pretreatment liquid supplied from the upstream fermenter/pretreatment tank 220 exceeds 500 mg/L (1000 mg/L in the case of EGSB), the UASB 230 is able to remove the granules present in the methane fermentation tank. UASB 230 is supplied with only the filtrate obtained by solid-liquid separation of the pretreatment liquid by the filtration membrane 41, because it adversely affects the sedimentation of the sludge. Therefore, in the UASB 230, a pretreatment liquid (suspension) containing a large amount of undecomposed suspended matter cannot be treated, and a large amount of solid waste S is discharged.

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

[Organic waste]
Organic waste, which is used as a raw material for fuel gas such as biomethane gas and biohydrogen, includes unused agricultural and forestry waste such as forest thinnings, rice straw, rice husk, bagasse, thatch, and aquatic plants, as well as vegetable scraps, used tea leaves, Examples include lignocellulosic industrial waste such as coffee lees, bean curd refuse, shochu lees, construction waste, used paper/waste paper, and municipal waste, or lignocellulosic biomass such as biomass resource crops such as Erianthus and Giant Miscanthus. . Moreover, paper shredded by a shredder is incinerated because its fibers are broken and it is difficult to recycle, but such shredded paper can also be used as a raw material. Furthermore, one type of the above-mentioned organic waste may be used as a raw material, or a plurality of types may be mixed and used as a raw material.

Lignocellulose, which is the main component of the cell wall of plant cells, is composed of tightly bound hemicellulose, cellulose, and lignin. Rumen fluid present in the rumen of ruminant animals such as cattle contains a large number of rumen microorganisms that produce enzymes that degrade lignocellulose. In the fuel gas production method of the present invention, in the culturing step, rumen microorganisms (lignocellulose-degrading bacteria) that decompose organic waste are cultured, and in the pretreatment step, organic Easily decomposable organic waste, volatile fatty acids, etc. are produced by decomposing waste. In the fermentation process, easily decomposable organic waste, volatile fatty acids, etc. are used as substrates (raw materials) for fermentation reactions. By performing, fuel gas such as biomethane gas and biohydrogen can be efficiently produced. In the fermentation process, under conditions where methanogenic bacteria predominate, methane fermentation is performed and biomethane gas is produced. On the other hand, in the fermentation process, under conditions where hydrogen-producing bacteria predominately exist, hydrogen fermentation is carried out to produce biohydrogen. The fermentation process may be a methane fermentation process or a hydrogen fermentation process depending on the usage and purpose of the fuel gas. Also, a two-stage fermentation of hydrogen/methane fermentation may be performed in which the hydrogen fermentation process is performed as a pre-reaction of the methane fermentation process. In this case, by controlling pH, HRT, etc. in one fermentation tank, methane fermentation may be performed after hydrogen fermentation. Each may be carried out in separate tanks.

[Rumen microorganisms]
Rumen microbes are anaerobic bacteria present in the ruminal fluid, the digestive fluid present in the rumen of ruminants. Ruminants include cattle, sheep, goats, deer, camels, llamas, and the like. For example, the rumen of an adult cow has a capacity of 150 to 200 L, and many lignocellulose-degrading bacteria, hemicellulose-degrading bacteria, lignin-degrading bacteria, starch-degrading bacteria, methanogenic bacteria, and hydrogen-producing bacteria live in the rumen fluid. are doing. Lignocellulolytic bacteria can produce enzymes such as cellulases that degrade lignocellulose (fiber). Therefore, when fiber such as grass is ingested by ruminant animals, lignocellulose-degrading bacteria decompose lignocellulose, and volatile fatty acids such as acetic acid, propionic acid, butyric acid, and valeric acid, which serve as an energy source for ruminants. (VFA: Volatile Fatty Acid) is produced. Hydrogen-producing bacteria produce acetic acid and hydrogen using substrates such as propionic acid, butyric acid, and valeric acid produced by lignocellulose-degrading bacteria. In addition, methanogenic bacteria produce methane using acetic acid or hydrogen and carbon dioxide produced by lignocellulose-degrading bacteria or hydrogen-producing bacteria as substrates.

(Culturing process)
In the culture step, rumen microorganisms with high lignocellulolytic activity (lignocellulolytic bacteria) are cultured. In the culture step, for example, the abundance of at least one of three types of lignocellulose-degrading bacteria, Fibrobacter succinogenes, Ruminococcus albus, and Prevotella ruminicola, is used as an index. , temperature, oxidation-reduction potential (ORP), hydraulic retention time (HRT) or solids retention time (SRT), and ammonium nitrogen concentration in the culture medium to achieve high lignocellulolytic activity. It is possible to obtain a culture solution of rumen microorganisms (lignocellulose-degrading bacteria) having Although quantification of the number of these bacteria is not particularly limited, it is preferably carried out by a quantitative PCR method, which enables rapid and accurate measurement of the number of specific bacteria. When quantitative PCR is used to quantify the number of lignocellulose-degrading bacteria, genomic DNA extracted from the culture medium and purified is used. Since the rumen microorganism culture solution can be cultured in large quantities or subcultured, the rumen microorganism culture solution with the adjusted number of bacteria can be used for lignocellulose decomposition as needed. can.

As the medium used for the culture solution of rumen microorganisms, a natural medium in which the base material of the medium is derived from natural products may be used, and various nutrients necessary for the growth of rumen microorganisms are all composed of chemicals. A medium may be used. In particular, it preferably contains a nitrogen source such as an ammonium salt, a phosphorus source such as a phosphate, and a carbon source such as cellulose and hemicellulose, which are useful nutrients for rumen microorganisms. In addition, the pretreatment solution contains undegraded or partially decomposed lignocellulose contained in organic waste, as well as nitrogen and phosphorus sources, as nutrients for lignocellulose-degrading bacteria. As shown in 3, a pretreatment liquid may be supplied to the culture medium. In addition, when volatile fatty acids (VFA) such as acetic acid are produced in the pretreatment step following the culturing step, the pH in the pretreatment solution decreases and the osmotic pressure increases, resulting in the production of lignocellulose. It is preferable to add a buffering agent to the medium in order to moderate the change in pH and the increase in osmotic pressure, since the abundance and function of the degrading bacteria are changed. As the buffering agent, since the saliva of ruminants has a high buffering capacity, it is preferable to use a liquid medium such as an artificial medium (artificial saliva) that imitates saliva. Buffers include sodium chloride, sodium bicarbonate, phosphate, potassium chloride, and the like. The pH of the medium is adjusted to 6.0 to 7.5, more preferably 6.5 to 7.0 by adding an acid or an alkali, if necessary. Moreover, it is preferable to use tap water or underground water as the water used for the culture medium. Further, the ammonium nitrogen concentration in the medium is controlled by adding water so as to be 50 to 2,000 mg/L, more preferably 60 to 500 mg/L.

The oxidation-reduction potential (ORP) of the culture solution is adjusted to -100 mv or less, more preferably -200 mv or less, and still more preferably about -250 mv so that the culture process is in an anaerobic state like the rumen environment. Since rumen microorganisms (lignocellulose-degrading bacteria) are anaerobic bacteria, if the ORP is higher than a predetermined level (when approaching an aerobic state), inject an inert gas such as nitrogen gas or carbon dioxide gas. , Reducing substances such as cysteine, L-ascorbic acid, sodium sulfide, ascorbic acid, methionine, thioglycol, and DTT are introduced, or organic substances are introduced to consume oxygen by the action of facultative anaerobes. may be applied. Alternatively, the culturing step may be performed in a closed system under a nitrogen or carbon dioxide atmosphere.

Cultivation of ruminal microorganisms in the fermenter 10 is critical for solids retention time (SRT) to be greater than hydraulic retention time (HRT). That is, lignocellulose-degrading bacteria adhere to the surface of solids and proliferate, so if the SRT is short, they are discharged out of the system together with the solids. On the other hand, an excessively long HRT causes negative factors such as a decrease in pH and inhibition of microbial growth due to the produced volatile fatty acids (VFA). Specifically, HRT is adjusted to 8 hours to 36 hours, preferably 10 hours to 24 hours, and SRT is adjusted to 24 hours or more, preferably 48 hours to 168 hours, more preferably 72 hours to 168 hours. In addition, the temperature of the reaction system in the culture step is controlled to 35 to 42°C, more preferably 37 to 40°C, using a temperature sensor or the like. The solid matter concentration (TS) in the culture solution of the organic waste B introduced into the culture tank 10 is 0.1 to 1.5% by weight, more preferably 0.5 to 1.0% by weight. Adjust so that If the solid concentration (TS) is 0.1% by weight or less, the growth and proliferation of lignocellulose-degrading bacteria may not be promoted. On the other hand, if it exceeds 1.5% by weight, there is a risk that solid-liquid separation of the culture solution will not be performed properly.

(Solid-liquid separation step)
In the culturing step, the solid-liquid separation of the culture solution of rumen microorganisms in the culture tank 10 may be performed by the filtration membrane 41 shown in FIG. good (not shown). In the culture tank 10 shown in FIG. 2, a filtrate liquid feeding pipe 11 and a suspension liquid feeding pipe 12 are installed, respectively. When discharging a liquid phase (suspension) with a high concentration out of the tank, discharge the culture solution while stirring it, and when discharging a liquid phase with a low SS concentration out of the tank, stop stirring and let it stand for a while. There may be only one liquid feeding pipe because the liquid can be discharged by

(Pretreatment step)
In the pretreatment process, lignocellulose contained in organic waste is partially degraded by lignin-degrading enzymes produced by lignocellulose-degrading bacteria. By glucanase, xylanase, or the like, they are decomposed into cellulose and hemicellulose, respectively, and converted into hexoses (hexamonosaccharides) such as glucose. Furthermore, pyruvic acid and the like are produced from hexoses (six monosaccharides) such as glucose, and volatile fatty acids (VFA) such as acetic acid, propionic acid, butyric acid, and valeric acid are produced as the reaction progresses. Hydrogen and carbon dioxide are also produced during the metabolic process. In the pretreatment process, lignocellulose does not need to be decomposed and metabolized to hexose (six monosaccharide) or volatile fatty acid (VFA), and difficult-to-decompose lignocellulose can be easily used in the downstream fermentation process. Degradation to the extent of oligosaccharides is sufficient. In the pretreatment step, the organic waste B supplied to the pretreatment tank 20 has a solid concentration (TS) of 1.0 to 10.5% by weight, more preferably 0.5 to 10.0% by weight. Adjust so that If the solids concentration (TS) is 1.0% by weight or less, the production of easily decomposable organic wastes, volatile fatty acids, etc., which serve as substrates for fermentation, may decrease. On the other hand, if it exceeds 10.5% by weight, it may become difficult to pump out the pretreatment liquid.

In order to make the pretreatment step anaerobic like the environment in the rumen of ruminants, the oxidation-reduction potential (ORP) of the pretreatment solution is -100 mv or less, more preferably -200 mv or less, and still more preferably -250 mv. Adjust to some extent. Since rumen microorganisms (lignocellulose-degrading bacteria) are anaerobic bacteria, when the ORP is higher than a predetermined level (when approaching an aerobic state), an inert gas such as nitrogen gas or carbon dioxide gas is injected, cysteine , L-ascorbic acid, sodium sulfide, ascorbic acid, methionine, thioglycol, DTT, or other reducing substances, or organic substances are introduced to consume oxygen by the action of facultative anaerobes. The pretreatment step may be performed in a closed system under nitrogen or carbon dioxide atmosphere.

In the pretreatment step, since HRT and SRT are individually controlled in the upstream culture step, there is no need to individually control HRT and SRT, and pretreatment (hydrolysis, acid generation) is performed. That is, since the pretreatment liquid in the pretreatment bath 20 in which the pretreatment process is performed is not separated into the filtrate and the suspension, HRT and SRT are the same. Both HRT and SRT of the pretreatment solution are preferably 4 to 36 hours. The temperature of the reaction system in the pretreatment step is controlled using a temperature sensor or the like so as to be 35 to 42°C, more preferably 37 to 40°C. The reaction in the pretreatment step may be carried out with standing still or with stirring, but is preferably carried out with stirring in order to speed up the progress of the pretreatment step.

(Fermentation process)
In the fermentation process, fuel gas is generated using easily decomposable organic wastes, volatile fatty acids, etc. generated in the pretreatment process as substrates. Here, the fuel gas includes biogas containing biomethane gas produced by methane fermentation as a main component, and biohydrogen produced by hydrogen fermentation. In the fermentation process, whether to perform methane fermentation or hydrogen fermentation can be adjusted by controlling the temperature and pH within the fermentation tank 30 . For example, when the temperature in the fermentation tank 30 is around 37° C. (or 55° C.) and the pH is 7.0 to 8.0, methanogenic bacteria predominately exist, so methane fermentation is mainly performed. On the other hand, when the temperature in the fermentation tank 30 is around 55° C. and the pH is 4.0 to 5.0, hydrogen-producing bacteria are predominantly present, so hydrogen fermentation is mainly performed. These fermentation processes may be performed independently, but two-step fermentation may be performed like a hydrogen-methane fermentation process. The methane fermentation process and the hydrogen fermentation process are described below.

(Methane fermentation process)
In the methane fermentation process, methane fermentation is performed using volatile fatty acids such as acetic acid, hydrogen, and carbon dioxide as substrates. A methane fermentation process is performed under anaerobic conditions like a pretreatment process. The biogas produced in the methane fermentation process contains 60 to 70% methane, 30 to 40% carbon dioxide, and trace amounts of nitrogen, oxygen, hydrogen sulfide, and water.

The methane fermentation may be wet methane fermentation or dry methane fermentation. Also, medium-temperature methane fermentation or high-temperature methane fermentation may be used. In the case of intermediate temperature fermentation, it is carried out for 20 to 30 days, more preferably 23 to 27 days, more preferably about 25 days. will be Methane fermentation is performed at 20 to 40°C, more preferably 30 to 37°C or less, more preferably about 37°C in the case of mesophilic fermentation, and 40 to 60°C, more preferably 50 to 55°C in the case of high temperature fermentation. , and more preferably at about 55°C. Also, the methane fermentation is carried out at pH 6.8-7.6, more preferably pH 7.0-8.0.

(Hydrogen fermentation process)
In the hydrogen fermentation step, hydrogen fermentation is performed using volatile fatty acids such as propionic acid, butyric acid, and valeric acid as substrates. The hydrogen fermentation step is performed under anaerobic conditions, as is the pretreatment step with lignocellulose-degrading bacteria. In the hydrogen fermentation process, biohydrogen and carbon dioxide are produced at a ratio of about 1:1, and organic acids such as acetic acid are produced.

Hydrogen fermentation is carried out at 30-60°C, more preferably 50-60°C, even more preferably 55°C. Also, the hydrogen fermentation is carried out at pH 4.0-6.5, more preferably pH 4.0-5.0.

In the hydrogen fermentation process, acetic acid, hydrogen, and carbon dioxide are produced as substrates for methane fermentation. Therefore, it is good also as two-step fermentation of hydrogen-methane fermentation which performs a methane fermentation process after a hydrogen fermentation process. Hydrogen-producing bacteria proliferate faster than methanogenic bacteria, so even if the HRT in the tank is set to 2 to 3 hours, the cells can be retained. In the case of two-step fermentation of hydrogen/methane fermentation, hydrogen fermentation takes 1 to 2 days and methane fermentation takes 7 to 10 days. Furthermore, in the case of two-step fermentation of hydrogen/methane fermentation, part of the methane fermentation liquid discharged from the methane fermentation process may be returned to the hydrogen fermentation process. In the hydrogen fermentation process, the pH drops due to the production of volatile organic acids, so there is a risk that the activity of hydrogen-producing bacteria will decrease and the amount of hydrogen generated will decrease. In addition, it is possible to neutralize the lowered pH or prevent the pH from lowering, thereby suppressing the decrease in the activity of hydrogen-producing bacteria and maintaining the amount of hydrogen generation.

(example)
Examples of treating the lignocellulosic waste discharged from the food factory A by the three-phase process and the two-phase process are discussed below. As a fermenter, UASB shall not be used, but an existing fully mixed methane fermenter for solid biomass shall be used.

<Conditions for consideration>
・Amount of organic waste discharged: 2.2 tons per day (2.2t-DW/d) as dry weight
・Capacity of existing methane fermentation tank: 200 m ³
・ Planned HRT for the existing methane fermentation tank: 10 days ・ Biomass solid concentration (TS) in the culture tank (both culture tank and pretreatment tank): about 1.1% by weight
・ Solid concentration (TS) of biomass in pretreatment tank: about 10.0% by weight
・HRT for fermenter or fermenter/pretreatment tank: about 14 hours ・SRT for fermenter or fermenter/pretreatment tank: about 62 hours

The SRT of the culture tank or the culture tank and pretreatment tank is defined as the amount of liquid medium such as artificial medium (artificial saliva) supplied per day (m ³ /d) or dilution water (m 3 /d), and the discharge of filtrate per day. It can be calculated by the following formula (Equation 1), where fV is the amount (m ³ /d) and FV is the tank volume (m ³ ) of the culture tank. Note that the following equation (Equation 1) is based on Huub J. et al. Gijzen et al., ``Continuous cultivation of rumen microorganisms, a system with possible application to the anaerbic degradation of lignocellulosic waste. , Vol 25, pp 155-162 (1986).

The HRT of a methane fermenter is the value obtained by dividing the tank volume (m ³ ) of the methane fermenter by the amount (m ³ /d) of liquid medium such as artificial medium (artificial saliva) or dilution water supplied per day (m 3 /d). Become.

(Case 1)
FIG. 6 is an explanatory diagram of Case 1 in which organic waste is supplied to the fuel gas production apparatus according to the first embodiment. In Case 1, a three-phase process comprising a culture tank 10, a pretreatment tank 20, and a methane fermentation tank 30 was examined.
Of the 2.2 t-DW/d of lignocellulosic biomass discharged from food factory A, 0.22 t-DW/d is used as a substrate (medium component) for culturing rumen microorganisms in a culture tank. In the culture tank, the supply amount (dV) of liquid medium such as artificial medium (artificial saliva) or dilution water is 20 m ³ /d so that solid-liquid separation is sufficiently performed, and the solid concentration (TS ) is 1.1% by weight. Also, in the culture tank, for example, SRT is 64 hours, HRT is about 11 hours, and the filtrate discharge (fV) is 17 m ³ /d so that the rumen microorganisms can grow sufficiently. According to the formula, the tank volume (FV) of the culture tank is 8 m ³ . The operation of the culture tank is controlled so that the pH is approximately 6.9, the oxidation-reduction potential (ORP) is -250 mV or less, and the temperature is 39°C.
Of the 2.2 t-DW/d of lignocellulosic biomass discharged from food factory A, the remaining 1.98 t-DW/d of 0.22 t-DW/d that was put into the culture tank was supplied to the pretreatment tank. , with 17 m ³ /d of filtrate and 3 m ³ /d of suspension discharged from the fermenter. The optimal value for HRT in the pretreatment tank (same as SRT because it is a complete mixing type) differs depending on the type of organic waste to be treated. ³ pretreatment baths can be used. (When HRT is set to 6 hours, a pretreatment tank having a tank volume of 5 m ³ can be used, and when HRT is set to 24 hours, a tank volume of 20 m ³ can be used). As with the culture tank, the pretreatment tank is operated and controlled such that the pH is approximately 6.9, the oxidation-reduction potential (ORP) is -250 mV or less, and the temperature is 39°C.
20 m ³ /d of the pretreatment liquid treated in the pretreatment tank is supplied to the methane fermentation tank (tank volume 200 m ³ ). The HRT in the methane fermentation tank shall be the value obtained by dividing the volume of the methane fermentation tank, 200 m ³ , by the daily supply rate of 20 m ³ /d (dV) of liquid medium such as artificial medium (artificial saliva) or dilution water. , 10 days [200 (m ³ )/20 (m ³ /d)]. Since it is the same number of days as the planned HRT of 10 days for the existing methane fermenter, it is clear that sufficient HRT can be secured for the methane fermenter in Case 1 to perform its function.

(Case 2)
FIG. 7 is an explanatory diagram of Case 2 when lignocellulosic biomass is supplied to a two-phase fuel gas production apparatus. In Case 2, a two-phase process comprising a culture tank/pretreatment tank 320 and a methane fermentation tank 30 was examined.
The 2.2 t-DW/d lignocellulosic biomass discharged from the food factory has a solid concentration (TS) of is 1.1% by weight in the culture tank/pretreatment tank, 200 m ³ of liquid medium such as artificial medium (artificial saliva) should be supplied to the culture tank/pretreatment tank per day. become. That is, 200 m ³ of treated water is supplied to the subsequent methane fermentation tank through the culture tank and pretreatment tank. The HRT in the methane fermentation tank shall be the value obtained by dividing the volume of the methane fermentation tank, 200 m ³ , by the daily supply rate of liquid medium such as artificial medium (artificial saliva) or dilution water, 200 m ³ /d (dV). , one day is [200 (m ³ )/200 (m ³ /d)]. Since this is significantly shorter than the planned HRT of 10 days for the existing methane fermenter, it is clear that sufficient HRT for the methane fermenter in Case 2 to fulfill its function cannot be secured.

As described above, by adopting a three-phase process consisting of a culture tank for rumen microorganisms, a pretreatment tank specialized for hydrolysis and acid generation of organic waste, and a methane fermentation tank, Since the concentration of organic waste treated in the pretreatment tank can be increased, the amount of pretreatment liquid supplied to the methane fermentation tank can be reduced, and the existing complete mixing type methane fermentation tank can function. It was found that sufficient HRT can be secured to fulfill

The fuel gas production apparatus and fuel gas production method of the present invention include industrial waste such as municipal waste such as waste paper and waste paper, lignocellulosic industrial waste such as food waste, agricultural and forestry waste, and construction waste. It can be used for the purpose of decomposing organic waste and using the decomposed product as a raw material to generate fuel gas such as methane or hydrogen.

10: Culture tank 11: Filtrate feed pipe 12: Suspension liquid feed pipe 20: Pretreatment tank 21: Pretreatment liquid supply pipe 30: Fermentation tank 40: Solid-liquid separation means 41: Filter membrane 50: Stirrer 100 , 101, 102: Fuel gas production device B: Organic waste C: Easily decomposable organic waste G: Fuel gas M: Liquid medium such as artificial medium (artificial saliva) W: Dilution water S: Solid waste Material T: Treated water P: Pump R: Fermentation residue

Claims (7)

A fuel gas production apparatus for producing biomass-derived fuel gas,
a culture tank for culturing rumen microorganisms;
A pretreatment tank in which the culture solution of the rumen microorganisms obtained in the culture tank is mixed with organic waste, and the organic waste is treated and converted into easily decomposable organic waste and volatile fatty acids. and,
A fuel gas production apparatus, comprising: a fermenter for fermenting the easily decomposable organic waste and the volatile fatty acid obtained in the pretreatment tank as substrates. 2. The fuel gas production apparatus according to claim 1, wherein said organic waste is supplied to said culture tank and said pretreatment tank at a predetermined ratio. 3. A pretreatment liquid containing the easily decomposable organic waste and the volatile fatty acid obtained in the pretreatment tank is supplied to the culture tank. The fuel gas production device according to 1. The fuel gas production apparatus according to any one of claims 1 to 3, further comprising solid-liquid separation means for solid-liquid separation of the culture solution in the culture tank. The fuel gas production apparatus according to any one of claims 1 to 4, characterized in that it is configured to supply easily decomposable organic waste to the fermenter. A fuel gas production method for producing biomass-derived fuel gas, comprising:
a culturing step of culturing rumen microorganisms;
a pretreatment step of mixing the culture solution of the rumen microorganisms obtained in the culturing step with organic waste, and treating the organic waste to convert it into easily decomposable organic waste and volatile fatty acids; ,
a fermentation step of performing fermentation using the easily decomposable organic waste and the volatile fatty acid obtained in the pretreatment step as substrates;
The fuel gas production method, wherein the culturing step further includes a solid-liquid separation step of solid-liquid separating the culture solution. 7. The fuel gas production method according to claim 6, wherein the fermentation process includes at least one of a methane fermentation process and a hydrogen fermentation process.

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