Method for obtaining a microbial community suitable for producing methane-containing biogas by methane fermentation of oil-containing biomass resources

Abstract

To provide a method for acquiring microorganism group suitable for producing methane-including biogas by methane fermentation of the biomass resource including an oil content, and to provide a method for producing methane-including biogas by methane fermentation of the oil content-including biomass resource using the microorganism group.SOLUTION: Disclosed is a method for acquiring microorganism group suitable for producing methane-including biogas by methane fermentation of the biomass resource including an oil content. The method includes: a process of adding an oil cake to the biomass resource; a process of cultivating the microorganisms so that the generating amount of biogas by the microorganism group indigenous to the biomass resource under the presence of oil cake is in the range from 300 Nml / g-VS to 1,200 Nml / g-VS; and a process of acquiring microorganism group suitable for producing methane-including biogas by methane fermentation of the biomass resource including the oil content from the biomass resource after cultivation.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for obtaining a microbial community suitable for producing a biogas containing methane by methane fermentation of a biomass resource containing oil, and a method for producing a biogas containing methane by methane fermentation of a biomass resource containing oil using the microbial community. [Background technology]

[0002] In recent years, the amount of waste generated, such as food waste, has been increasing due to population growth and the advancement of lifestyles. Waste is treated using a variety of microorganisms, and methane fermentation, in particular, is a technology that has attracted attention in recent years because it not only reduces the amount of waste but also allows the methane produced to be used as an energy source. However, waste such as food waste often contains a large amount of oil, which can be an inhibitor to the methane fermentation process.

[0003] For example, Patent Document 1 describes that materials with high oil and ammonia concentrations, etc., have a high fermentation load and are therefore difficult to ferment, and adding too much of them is likely to inhibit fermentation, so cow manure, which has a low fermentation load, should be added first, and grease trap sludge, which has a high fermentation load, should be added last. Furthermore, Patent Document 2 describes that when biomass resources with a high oil content, such as coffee grounds, are subjected to methane fermentation, fermentation inhibitors such as higher free fatty acids are produced as the molecules are broken down into smaller molecules, inhibiting methane fermentation. Therefore, the higher free fatty acids are neutralized and removed by centrifugation. Furthermore, Patent Document 3 describes that suspended matter, solid matter, and oil content significantly inhibit methane fermentation treatment, and therefore it is necessary to remove suspended matter, solid matter, and oil content in advance using simple sedimentation treatment equipment, coagulation sedimentation treatment equipment, pressurized flotation treatment equipment, etc.

[0004] Thus, in conventional technology, biomass resources with a high oil content (high fermentation load) were added at the final stage of methane fermentation treatment. Furthermore, when biomass resources with a high oil content are subjected to methane fermentation treatment, higher free fatty acids (fermentation inhibitors) are produced, which are then neutralized. Furthermore, the oil was removed from the biomass resources before the methane fermentation treatment. However, all of these processes are time-consuming, and there has been a demand for a more efficient method for methane fermentation of biomass resources containing oil. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-177372 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-188676 [Patent Document 3] Japanese Patent Application Publication No. 9-290249 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for obtaining a microbial community suitable for producing methane-containing biogas by methane fermentation of an oil-containing biomass resource, and a method for producing methane-containing biogas by methane fermentation of an oil-containing biomass resource using the microbial community. [Means for solving the problem]

[0007] As a result of extensive research to solve the above problems, the present inventors have found that when a predetermined methane fermentation process is carried out using soapstock, a microbial group capable of efficiently carrying out methane fermentation even on biomass resources containing oil can be obtained, and have completed the present invention.

[0008] That is, the present invention relates to the following. [1] A method for obtaining a microbial community suitable for producing methane-containing biogas by methane fermentation of an oil-containing biomass resource, the method comprising the steps of: adding soapstock to the biomass resource; culturing the microbial community indigenous to the biomass resource in the presence of the soapstock so that the amount of biogas produced by the microbial community is in the range of 300 Nml / g-VS to 1200 Nml / g-VS (biogas production rate per organic matter); and obtaining, from the biomass resource after the culturing, a microbial community suitable for producing methane-containing biogas by methane fermentation of the oil-containing biomass resource. [2] The method according to [1], wherein the amount of the soapstock added is 1 to 15 parts by mass per week on average per 100 parts by mass of biomass resources. [3] The method according to [1] or [2], wherein the soapstock is raw soapstock. [4] The method according to any one of [1] to [3], wherein in the culturing step, the culture is carried out for at least 11 to 14 weeks after the addition of the soapstock. [5] A method for producing biogas containing methane, characterized in that a microbial community obtained by the method according to any one of [1] to [4] is added to a biomass resource containing oil, and the resulting mixture is subjected to methane fermentation in a fermenter. [6] The method for producing biogas according to [5], characterized in that the oil-containing biomass resource is added so that the amount of organic matter in the fermentation tank during methane fermentation treatment is maintained at 8 g-VS / L / d or less. [7] The method for producing biogas according to [5] or [6], characterized in that the oil content is 0.01 to 100 parts by mass per 100 parts by mass of the biomass resource containing oil. [8] The method for producing biogas according to any one of [5] to [7], wherein the biomass resource containing oil is soapstock. [9] A method for producing fermented compost using the method for producing biogas according to any one of [5] to [8]. [Effects of the Invention]

[0009] According to the present invention, a microbial community suitable for producing methane-containing biogas by methane fermentation of biomass resources containing oil can be obtained. By using such a microbial community, methane fermentation can be efficiently carried out even on biomass resources containing oil. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a biogas production device. [Figure 2] FIG. 10 is a graph showing the transition of biogas generation amount from raw soapstock and dried soapstock, which was carried out by sample analysis. [Figure 3] This figure shows various data obtained when series A (raw soapstock), series B (dried soapstock), and series C (simulated waste) were tested continuously from the 1st week to the 14th week. [Figure 4] This figure shows various data obtained when series A (raw soapstock), series B (dried soapstock), and series C (simulated waste) were tested continuously from the 1st week to the 14th week. [Figure 5] This figure shows the trends (from week 1 to week 14) in the input amount of Series A (raw soapstock), dilution water, and biogas generation rate. [Figure 6] This figure shows the trends (from week 1 to week 14) in the input amount of Series B (dried soapstock), dilution water, and biogas generation rate. [Figure 7] This figure shows the trends (from week 1 to week 14) in the input amount of C series (simulated waste), dilution water, and biogas generation rate. [Figure 8] FIG. 1 shows the results of bacterial species involved in lipolysis among the taxonomic groups of OTUs (Operational Taxonomic Units) obtained by data processing of next-generation sequence analysis. [Figure 9] This figure shows the total amount of biogas (NmL / g-VS) obtained per unit of organic matter by methane fermentation using the microbial communities obtained in the continuous test (weeks 1, 9, 11, and 14) using raw soapstock. [Figure 10]This figure shows the total amount of biogas (NmL / g-VS) obtained per unit of organic matter by methane fermentation using the microbial communities obtained in the continuous test (weeks 1, 9, 11, and 14) using dried soapstock. [Figure 11] This figure shows the total biogas volume per organic matter (NmL / g-VS) for weeks 1, 9, 11, and 14 shown in Figures 9 and 10, divided into raw soapstock and dried soapstock. DETAILED DESCRIPTION OF THE INVENTION

[0011] (soil cake) In the present invention, "sothasembly" means raw soapstock, dried soapstock, and a mixture thereof (including intermediates produced in the process of producing dried soapstock from raw soapstock). As will be described later, soapstock is one of biomass resources and contains oil, so it also falls under the category of biomass resources containing oil. In the vegetable oil refining process, phosphoric acid and caustic soda are added to crude vegetable oil and refined by centrifugation or other methods (deacidification process), and after the refined vegetable oil is removed, "raw soapstock" is obtained. "Raw soapstock" is a by-product of the normal vegetable oil refining process, and is highly viscous and paste-like due to its high water and free fatty acid content. This makes it difficult to handle, and in recent years, "dried soapstock" has been developed, in which raw soapstock is neutralized by adding an acid such as sulfuric acid and then further dried. "Dried soapstock" has improved fluidity and is easy to handle. The production of "dried soapstock" is described in detail below.

[0012] First, the raw soapstock, a by-product of the deacidification step in the refining process, is neutralized (to a pH of about 6-8) with an acid such as sulfuric acid, hydrochloric acid, phosphoric acid, or citric acid, and stored in a soapstock tank at about 90°C. The moisture content of the raw soapstock before neutralization is about 50% by mass, and the moisture content of the raw soapstock immediately after the neutralization step is about 40-50% by mass. The neutralized raw soapstock stored in the soapstock tank is transferred by a pump and subjected to a drying step. Drying is preferably performed using, for example, a forced stirring thin-film evaporator (also known as a rotary vane thin-film evaporator) connected to a vacuum generator (vacuum pump, 100 torr). Examples of forced stirring thin-film evaporators include a Luwa evaporator and a high-viscosity thin-film evaporator. A Luer evaporator is a device that efficiently evaporates the material being treated by forcibly stirring it with a rotating (rotor) blade and causing it to fall as a thin film or diffuse onto a heated surface. Kimura Chemical Engineering Co., Ltd. and others offer this type of evaporator in Japan. An example of a high-viscosity thin-film evaporator is the "Exeva" product manufactured by Kobe Environmental Solutions Co., Ltd. Drying conditions include a temperature of approximately 65°C at the evaporator inlet and approximately 125°C at the outlet, with a processing flow rate of approximately 200 to 300 kg / hour. This allows the moisture content after drying to be adjusted to 0.5% by mass or less, preferably 0.2 to 0.3% by mass or less (including 0% by mass).

[0013] A dried soapstock with an adjusted moisture content can also be obtained by immediately mixing, in a static mixer, the undried raw soapstock after neutralization that has been transferred from the soapstock tank without undergoing the drying process with the dried soapstock that has been dried in the drying process. The mixing ratio of the undried raw soapstock after neutralization to the dried soapstock that has been dried in the drying process is preferably, for example, 1:3 to 3:1 by mass. A more preferred ratio is 2:3 to 3:2 by mass, and a 1:1 mass ratio is particularly preferred. The mixing method may be a method of continuously mixing at a temperature of preferably 70 to 90°C, more preferably 70 to 80°C, and most preferably 70 to 75°C at a flow rate of about 100 to 150 kg / hour.

[0014] So far, the dried soapstock that has been subjected to a drying process and the neutralized raw soapstock that has not been subjected to a drying process have been described as examples in which the soapstock is a by-product of the refining process of the same type of vegetable oil. However, the soapstock may be a neutralized raw soapstock that is a by-product of the refining process of a different type of vegetable oil. In terms of handling, dried soapstock is preferable to raw soapstock, but as will be discussed later, raw soapstock is preferable to dried soapstock when acclimatizing microbial communities or producing biogas. Furthermore, because dried soapstock is neutralized, it may be affected by sulfur from the neutralizing salts and chemicals used for neutralization, whereas raw soapstock does not. Another advantage of raw soapstock is that it does not require the use of dangerous chemicals such as sulfuric acid. Furthermore, the pH of raw soapstock is strongly alkaline, which is thought to provide a certain degree of buffering effect even when methane fermentation progresses and organic acids accumulate, potentially preventing rancidity.

[0015] (Biomass resources) The "biomass resource" in the present invention is a fermentation raw material used in methane fermentation treatment, and examples thereof include food waste, food waste, livestock excrement, sludge, plant waste, and soapstock, and one or more of these can be used. In addition, the "oil-containing biomass resource" in the present invention refers to the above-mentioned biomass resource that contains oil. Since soapstock contains oil, it falls under the category of oil-containing biomass resource. Furthermore, in the present invention, a microbial group suitable for producing biogas containing methane by methane fermentation of biomass resources containing oil is obtained, and therefore, it is preferable to use a biomass resource with a high oil content as the biomass resource used as the fermentation substrate. Here, "high in oil" refers to a high oil content extracted by normal hexane extraction or other oil and fat analysis methods. In the field of organic waste treatment, including methane fermentation, the normal hexane extract content (n-Hex) is often used as an indicator of oil content. For example, the n-Hex concentration (n-Hex concentration / amount of organic matter) in the organic matter of a biomass resource is an indicator of the oil concentration contained in the biomass resource, and the higher the oil concentration, the higher this value. Since the higher the oil concentration of a biomass resource, the more difficult methane fermentation becomes, the higher the n-Hex concentration (n-Hex concentration / amount of organic matter) in the organic matter of the biomass resource tends to be. Therefore, from the perspective of stable, continuous operation of the methane fermenter and organic waste treatment device, the n-Hex concentration (n-Hex concentration / amount of organic matter) in the organic matter of the biomass resource in the methane fermenter is preferably 0.4 or less. The soapstock of the present invention can also be an example of a biomass resource with a high oil content. In addition, raw soapstock and dried soapstock are generally samples from which fat cannot be sufficiently extracted unless hydrolyzed, and oil is extracted from these samples using the acid decomposition diethyl ether extraction method. However, in this patent, both the values ​​analyzed by the normal hexane extract analysis method and the values ​​analyzed by the acid decomposition diethyl ether extraction method may be considered as the oil content. Unless otherwise specified, the "oil content" and "oil content" used in the following text are values ​​analyzed using the acid decomposition and diethyl ether extraction method.

[0016] (Methane fermentation process and the microorganisms used in it) The methane fermentation process of the present invention is preferably carried out under controlled conditions in the absence of oxygen. The microorganisms used in the methane fermentation treatment can be the microorganisms indigenous to the biomass resource being used. In the present invention, by performing a predetermined methane fermentation treatment using a biomass resource to which soapstock has been added, the microorganisms indigenous to the biomass resource can be acclimatized to an oil-rich environment, thereby obtaining a microorganism suitable for producing methane-containing biogas by methane fermentation of the oil-containing biomass resource.

[0017] (Biogas) The biogas obtained by the present invention is a gas obtained by adding the above-mentioned soapstock to a biomass resource and performing a methane fermentation treatment using a microbial community contained in the biomass resource in the presence of the soapstock.The biogas can also be obtained by adding a microbial community suitable for producing a methane-containing biogas by methane fermentation of an oil-containing biomass resource through the methane fermentation treatment (acclimation) to a new biomass resource and then performing a methane fermentation treatment with the microbial community. The obtained biogas mainly contains methane gas, but also contains carbon dioxide, ammonia, hydrogen sulfide, etc. In the present invention, this is referred to as "methane-containing biogas."

[0018] (Method for obtaining a microbial community suitable for producing methane-containing biogas by methane fermentation of biomass resources containing oil) The "method for obtaining a microbial community suitable for producing biogas containing methane by methane fermentation of biomass resources containing oil" of the present invention includes the steps of adding soapstock to biomass resources, culturing the microbial community indigenous to the biomass resources in the presence of the soapstock so that the amount of biogas produced by the microbial community is in the range of 300 Nml / g-VS to 1200 Nml / g-VS (biogas production rate per organic matter), and obtaining, from the biomass resources after the culturing, a microbial community suitable for producing biogas containing methane by methane fermentation of the biomass resources containing oil.

[0019] (addition process) In the adding step, the soapstock is added to the biomass resource to increase the oil content of the biomass resource. This adding step is optional, as long as the culture is performed so that the amount of biogas generated in the culturing step described below is within a certain range. Preferably, the soapstock is added continuously every week. That is, it is preferable to continuously add 1 to 15 parts by mass of soapstock per 100 parts by mass of biomass resource every week on average. More preferably, 5 to 10 parts by mass of soapstock are added every week on average, and even more preferably, 6 to 9 parts by mass of soapstock are added every week on average. In this way, by adjusting the amount of soapstock added to the biomass resource to a constant value every week on average, the amount of soapstock contained in the biomass resource gradually increases, and as a result, a microbial community suitable for methane fermentation of the oil-containing biomass resource to produce biogas containing methane can be obtained. Next, regarding the gradual increase in the amount of soapstock contained in this biomass resource, for example, based on the data in Figure 3, the proportion of soapstock in the biomass resource increases from 3.88% (at the start) to 17.25% (at week 14). This corresponds to an average weekly increase of 0.96% per week. In other words, the proportion of soapstock in the biomass resource increases by 0.5% to 1.5% by mass per week, preferably 0.7% to 1.2% by mass per week, and more preferably 0.8% to 1.0% by mass per week, through this addition process. This places a fermentation load on the microbial community native to the biomass resource due to the increased oil content, and allows the microbial community to acclimate to a microbial community capable of adequate methane fermentation even in the presence of oil. The addition method may be any, and it is preferable to stir the biomass resource after adding the soapstock to the biomass resource so as to make the mixture as uniform as possible. Therefore, this addition step may optionally include a stirring step. This is because if the soapstock is present locally, the free fatty acids will be high in that area, which may cause fermentation inhibition.

[0020] (Culture process) In the culturing step, the biomass resource to which the soapstock has been added is cultured as described above so that the amount of biogas generated by the microorganisms indigenous to the biomass resource ranges from 300 Nml / g-VS to 1200 Nml / g-VS (biogas generation rate per organic matter). More preferably, the biomass resource is cultured so that the amount of biogas generated ranges from 400 Nml / g-VS to 1100 Nml / g-VS (biogas generation rate per organic matter). Even more preferably, the biomass resource is cultured so that the amount of biogas generated ranges from 500 Nml / g-VS to 1000 Nml / g-VS (biogas generation rate per organic matter). An important aspect of the present invention is that the amount of biogas generated by the microorganisms is within a certain range. In order to keep the amount of biogas generated within a certain range, the temperature, pH, water content, organic matter content (VS), etc., during the cultivation process are adjusted. Those skilled in the art can easily adjust these parameters. Furthermore, the amount of soapstock added in the aforementioned addition process can also be adjusted as described above to keep the amount of biogas generated within a certain range. Specific examples of this include the amount of soapstock added or the rate at which the soapstock increases.

[0021] In the culture step, the culture is preferably carried out for 1 to 14 weeks, more preferably 9 to 14 weeks, and even more preferably 11 to 14 weeks. However, the culture period is not limited to this. As will be described later, by culturing for 11 to 14 weeks, the amount of biogas generated reaches its upper limit, and it is believed that a sufficient effect has been obtained to acclimate the microbial population. Furthermore, the culture conditions are preferably medium-temperature fermentation, for example, at a temperature of 37°C (30 to 45°C). However, high-temperature fermentation, in which fermentation is performed at a temperature of 45 to 55°C, is also acceptable. In addition, the present invention employs a wet fermentation method in which dilution water is appropriately added to maintain a moisture content of 80 to 99% (more preferably, 90 to 98%, and even more preferably, 95 to 97%). However, dry fermentation, in which a moisture content of approximately 65 to 80% is also acceptable. The method to be adopted is selected in consideration of the moisture content, organic matter amount, nitrogen amount, and other factors in the biomass resource. The medium-temperature wet fermentation method is a widely used technology, and is considered to be a condition under which relatively stable operation can be performed.

[0022] (Step of obtaining a microbial community) In the step of obtaining a microbial population, a microbial population suitable for producing methane-containing biogas by methane fermentation of an oil-containing biomass resource is obtained from the biomass resource after the cultivation. Because the cultivation step transforms the microbial population originally indigenous to the biomass resource into a microbial flora suitable for fermenting an oil-containing biomass resource, by collecting a portion of the biomass resource after the cultivation step, a microbial population suitable for producing methane-containing biogas by methane fermentation of an oil-containing biomass resource can be obtained. Here, "obtaining a microbial population" does not mean isolating the microbial population from a biomass resource (isolation is practically impossible), but rather means obtaining a biomass resource containing habituated microbial populations obtained through the culture process described above. In other words, the "microbial population" referred to here is equivalent to a "biomass resource containing habituated microbial populations." In other words, "obtaining a microbial population" means collecting the required amount of biomass resource containing habituated microbial populations after the culture process. Any collection method can be used, and examples include scraping with a spatula.

[0023] (Biogas production method) The method for producing biogas of the present invention is characterized by adding the above-mentioned microorganisms (i.e., a biomass resource containing acclimated microorganisms) to a biomass resource and subjecting the biomass resource to methane fermentation. The biomass resource preferably contains a large amount of oil. "High in oil" has the same definition as above. Furthermore, in order to utilize the generated biogas, the biogas production method of the present invention may optionally include a step of recovering the biogas. Any recovery method may be used. For example, a method of recovering biogas may include providing a gas-solid-liquid separator above the fermentation reaction section of the fermenter to separate and recover treated water, generated biogas, etc. Furthermore, the separated and recovered biogas may be desulfurized using a desulfurization device, if necessary, and stored in a gas holder. The produced biogas can be used as fuel for power generation or boilers, either directly or after being made into a gas with an increased methane gas concentration. Known methods can be used to increase the methane gas concentration. For example, one method for increasing the methane gas concentration is to wash the biogas with water and selectively separate the methane by utilizing the difference in solubility in water. This method can concentrate methane gas to 97% or more.

[0024] The amount of oil-containing biomass resource added is adjusted to maintain the organic matter at 8 g-VS / L / d or less. More preferably, it is added to maintain the organic matter at 5 g-VS / L / d or less, and even more preferably, it is added to maintain the organic matter at 3 g-VS / L / d or less. Adding it in this manner allows for efficient production of biogas. The amount of organic matter in the oil-containing biomass resource that serves as the fermentation substrate can also be adjusted by adding dilution water. Here, the unit (g-VS / L / d) refers to the amount of organic matter processed per day.

[0025] Because the microbial consortium obtained by the present invention is suitable for fermenting biomass resources containing oil, the oil content is preferably 0.01 to 100 parts by mass, more preferably 0.05 to 90 parts by mass, and even more preferably 0.1 to 80 parts by mass, per 100 parts by mass of the biomass resource containing oil. Note that "100 parts by mass of oil" means that the biomass resource is oil itself. As the above-mentioned biomass resource containing oil, soapstock is preferably used. Furthermore, raw soapstock is more preferably used as the oil-containing biomass resource. In the present invention, it is preferable to add soapstock as the oil-containing biomass resource and perform methane fermentation treatment using the microbial community of the present invention, which is suitable for fermenting biomass resources containing oil.

[0026] (Manufacturing method of fermented compost) When the method for producing methane-containing biogas of the present invention is carried out, in addition to biogas, a digestate is also obtained, which is a wet product rich in organic matter and called digestate. The resulting fermentation residue can be dehydrated and dried to produce fermented compost, which can be effectively used as fertilizer.

[0027] Next, the effects of the present invention will be specifically explained using examples, but the present invention is not limited to these examples. [Example]

[0028] (sample) The raw soapstock used was raw soapstock generated in the refining process (deacidification treatment) in the production of vegetable oils and fats at Nisshin Oillio Group, Ltd. The dried soapstock used was the raw soapstock neutralized and dried as described above. Furthermore, as a biomass resource, simulated waste made by Biogas Lab Co., Ltd., which was made by crushing and mixing several types of items (cabbage, apples, rice, meat, dog food, etc.), was used, simulating urban waste.

[0029] (Sample analysis method) The pH, moisture content, and loss on ignition (organic matter or VS) of the raw and dried soapstock were measured according to the sewage test method, CODcr (chemical oxygen demand) according to the fertilizer test method, and carbon and nitrogen according to the enzyme circulation method. Ammonia nitrogen was calculated according to JIS K0102. The analytical values ​​of the raw soapstock and dried soapstock used are shown in Table 1.

[0030] [Table 1]

[0031] The pH of the raw soapstock was high at 11.3, while that of the dried soapstock was 7.8. The moisture content of the raw soapstock was 43% and 17.9%, respectively, which was lower than that of the raw soapstock. The loss on ignition, which indicates the amount of organic matter, was similar for the raw soapstock and dried soapstock at 80.7% and 82.9%, respectively. The CODcr was 1,300,000 mg / kg for the raw soapstock and 1,600,000 mg / kg for the dried soapstock, a higher value for the raw soapstock considering its higher moisture content. The nitrogen content of the solids was very low at 0.2% and 0.4%, respectively for the raw soapstock and dried soapstock. The ammonia nitrogen content was very low, less than 50 mg / kg for the raw soapstock and 29 mg / kg for the dried soapstock. The carbon content per solid matter was higher in raw soapstock (62.4%) and dried soapstock (59.7%). These results indicate that soapstock is a useful substrate for methane fermentation.

[0032] (Biogas production) In the equipment shown in Figure 1, biogas was produced by methane fermentation using biomass resources to which soapstock was added. Specifically, 3,500 g of seed sludge acclimated with Biogas Lab's simulated waste, 25 g each of raw soapstock and dried soapstock were fed into a 3.5 L fermentation tank through the raw material inlet, and methane fermentation treatment was carried out at 37°C ± 0.5°C while constantly stirring with a stirrer. The fermentation treatment was continued until it was confirmed that the rate of biogas production had slowed down and that biogas production had almost ceased. Table 2 shows the final amount of biogas generated at the end of the test. Figure 2 shows the cumulative amount of biogas generated. The cumulative amount of biogas generated is the cumulative value obtained by subtracting the amount of gas generated from Biogas Lab's seed sludge under no load (i.e., when no soapstock is added) from the amount of gas generated during biogas production.

[0033] [Table 2]

[0034] The measurement results of the methane concentration in the biogas generated in the test are shown in Table 3. To measure the methane concentration, the entire amount of biogas generated from the start to the end of the test was collected in aluminum bags and analyzed by TCD gas chromatography after the fermentation process was completed.

[0035] [Table 3]

[0036] These results confirmed that biogas can be generated by methane fermentation of biomass resources with added soapstock. Raw soapstock and dried soapstock were highly degradable raw materials for biogas generation. Furthermore, because soapstock has a low nitrogen content, ammonia inhibition is unlikely to occur. With raw soapstock and dried soapstock, no gas generation was observed within one week of addition, and the gas generation rate remained lower than with a no-load blank. The possible reason for this is that the seed sludge was not sufficiently acclimatized to the oil.

[0037] (Continuous testing to obtain beneficial microbial populations) A 14-week continuous test was conducted to identify a microbial community suitable for producing methane-containing biogas by methane fermentation of oil-containing biomass resources. The continuous test was conducted in the same manner as in the biogas production test described above, except that soapstock was continuously added. The test conditions are shown in Figure 3. The values ​​shown in Figure 3 are weekly average values. The specific details of the test were as follows: For Series A (raw soapstock), Series B (dried soapstock), and Series C (simulated garbage), (simulated garbage + raw soapstock), (simulated garbage + dried soapstock), and (simulated garbage only) were added in the amounts shown in Figure 3, respectively. In addition, dilution water was added in the amount shown in Figure 3 to maintain a constant solids concentration (TS) in the fermenter. When biomass resources and dilution water were added, the amount of fermentation residue shown in Figure 3 was withdrawn from the fermenter to maintain a constant fermenter volume. In addition, for both Series A and B, the biomass resources added at one time, i.e., (simulated waste + raw soapstock) and (simulated waste + dried soapstock), were adjusted to a constant solids concentration (TS) of approximately 20% and organic matter content (VS) of approximately 95%. Similarly, the oil content per organic matter content in the biomass resources added was set to 23–26%. As the amount of biomass resources added gradually increased, the amount of organic matter added per fermentation volume (volume load) increased, as shown in Figure 3. In this way, the addition of soapstock gradually increased the oil content in the fermenter tank, creating an oil load. The temperature in Series A, B, and C was maintained at 37°C ± 0.5°C, and the pH in the fermenter was maintained at 7.7 ± 0.3. The biogas, including methane, generated during fermentation was measured over time using a flow meter. Data up to 14 weeks of continuous testing for Series A (raw soapstock), Series B (dried soapstock), and Series C (simulated waste) are shown in Figures 3 and 4. The following terms in Figures 3 and 4 are defined as follows: "Raw material" in Figures 3 and 4 means the input biomass resource. The values ​​shown in Figures 3 and 4 are weekly average values. Tank capacity (kg): Amount of fermented sludge to be cultivated. Raw material input amount (g / d): The amount of raw material (simulated waste + raw soapstock or simulated waste + dried soapstock or simulated waste only) input into the fermentation tank. Sodash volume (g / d): The amount of raw or dried soapstock to be added. Amount of simulated waste (g / d) The amount of simulated waste to be put in. Dilution water (g / d): The amount of distilled water added to the fermenter. Total input amount (g / d) - The total amount of raw material and dilution water added to the fermentation tank. Withdrawal volume (g / d): The amount of fermented sludge withdrawn from the fermentation tank. Raw material TS (%): Amount of solids in the raw material. When the moisture content is W (%), Raw material TS (%) = 100 - W (%). Raw material VS (%-TS) - Inside the tank, this shows the percentage of organic matter (VS) in the raw material solids (raw material TS). TS (%) in the tank: Amount of solids in the fermentation tank. When the moisture content is W (%), raw material TS (%) = 100 - W (%). VS in the tank (%-TS) - Indicates the percentage of organic matter (VS) in the solid matter (TS in the tank) in the fermentation tank Retention period (days): The time that the input raw materials and dilution water remain in the fermentation tank (retention period = volume of fermentation tank / total input amount). Volumetric load (g-VS / L / d): The amount of organic matter added per volume. Gas generation rate (Nml / d) - The total amount of biogas generated from the fermentation tank. Unit consumption (Nml / d): The amount of biogas generated per unit of input raw material (wet weight). Unit consumption (Nml / g-VS / d) - The amount of biogas generated per amount of organic matter (VS) in the input solid raw material (raw material TS). Ammonia nitrogen (mg / kg) Amount of ammonia nitrogen in the fermenter (the fermented sludge withdrawn from the fermenter was analyzed). 5 to 7 show the amounts of biomass resources input, the amounts of dilution water input, and the resulting biogas generation rate per organic matter in the biomass resources (Nml / g-VS) for Series A (raw soapstock), Series B (dried soapstock), and Series C (simulated waste).

[0038] After 12 weeks had passed since the start of the test, the biogas production rate did not fluctuate significantly even when the oil load was increased, indicating that both series A and B were being cultivated smoothly.

[0039] As shown in Figures 5 to 7, the biogas generation rate per unit volume ranged from 300 Nml / g-VS to 1200 Nml / g-VS from week 1 to week 14 for both series A (raw soapstock) and series B (dried soapstock). Cultivating the microorganisms to generate a stable, constant amount of biogas is useful for obtaining a microbial community suitable for producing methane-containing biogas through methane fermentation of oil-containing biomass resources. By culturing the microorganisms while gradually increasing the oil content rather than rapidly increasing it, the amount of biogas generated does not decrease and remains within a certain range, activating the eubacteria that contribute to the decomposition of organic matter (especially oil decomposition).

[0040] Next-generation sequencing data were processed for the continuous test described above. The taxonomic groups of OTUs (Operational Taxonomic Units) were determined by comparison with MiDAS 4.8.1, a database specialized for bacterial information detected in activated sludge and digested sludge. Taxonomic groups were also determined using the Silva database. Major bacterial species were defined as OTUs detected at a rate of 2% or higher in any sample. Thirty OTUs were extracted. The time course of the bacterial species involved in lipolysis (from week 1 to week 15) is summarized in Figure 8. The data analysis was performed using the software QIIME2, R (version 4.0.3), and R studio (version 1.4.1103). As can be seen in Figure 8, the detection rate of bacterial species related to fat decomposition was higher in Series A (raw soapstock) and Series B (dried soapstock) than in Series C (simulated waste). This confirms that continuous cultivation while increasing the oil load from the soapstock allows for the production of microbial communities suitable for producing biogas containing methane through methane fermentation of biomass resources containing oil.

[0041] (Biogas production) After the continuous test described above, the biomass resources (including the acclimatized microbial population) were used to measure their biogas production potential. Specifically, a batch methane fermentation experiment using a 100 ml plastic syringe was conducted to measure the biogas production potential of the microbial population suited to producing methane-containing biogas through methane fermentation of the oil-containing biomass resources. 30 ml of the biomass resources (from weeks 1, 9, 11, and 14) from the continuous test described above were sampled, and 0.1 g each of raw soapstock and dried soapstock was added to each sample for measurement (experimental group). (Assuming that the organic matter content of the soapstock is approximately 70-80%, adding 0.1g to 30ml is equivalent to 0.1 x 70-80% / 30.1ml = 2.33-2.66g-VS / L. Since no organic matter was added during the treatment, for example, over 52 days, the calculation is 2.33-2.66 / 52 ≒ 0.05g-VS / L / d.) On the other hand, 0.1 g each of raw soapstock and dried soapstock was added to 30 ml of seed sludge that had been acclimatized for a long period of time using simulated waste from Biogas Lab, and measurements were taken (control area). After the air was expelled from the syringes in both the experimental and control groups, they were cultured for 52 days in a thermostatic shaker at 37±0.5°C. In this experiment, the plunger was pushed up by the generation of biogas in the syringe, and the amount of biogas produced was measured using the scale on the syringe. The results for the microbial communities continuously cultured on raw soapstock and dried soapstock are shown in Figures 9 and 10, respectively. The results for the total biogas production rate per organic matter are also shown in Figure 11.

[0042] As is clear from Figures 9 to 11, the microbial communities (biomass resources containing acclimated microbial communities) from the 1st, 9th, 11th, and 14th week continuous tests were used to perform methane fermentation of oil-containing biomass resources (raw soapstock and dried soapstock) and produce methane-containing biogas. For both raw soapstock and dried soapstock, the highest biogas generation rate per organic matter was achieved when the microbial communities continuously cultured up to week 11 were used. On the other hand, the microbial communities continuously cultured up to week 14 achieved a lower biogas generation rate per organic matter than the microbial communities continuously cultured up to week 11. This suggests that continuous culture for approximately 11 weeks may produce microbial communities suitable for producing methane-containing biogas through methane fermentation of oil-containing biomass resources. However, this invention does not exclude continuous culture for 11 weeks or longer. Longer culture periods beyond 11 weeks may result in more acclimated microbial communities.

[0043] Furthermore, Figure 11 shows that when biogas containing methane was produced using biomass resources from the continuous tests conducted in weeks 1, 9, 11, and 14, more biogas was generated when raw soapstock was used than when dried soapstock was used. This suggests that the use of raw soapstock may produce a microbial community that is more suitable for producing biogas containing methane through methane fermentation of biomass resources containing oil than the use of dried soapstock. [Industrial Applicability]

[0044] The biogas obtained by the present invention can be used in the energy field to generate electricity or as fuel. Since soapstock is a by-product of vegetable oil production, using it as a biomass resource will also contribute to carbon neutrality. Furthermore, the fermentation residue (biomass resource) obtained by the present invention can be used as fermented compost.

Claims

1. A method for obtaining a microbial population suitable for producing a methane-containing biogas by methane fermentation of an oil-containing biomass resource, the method comprising the steps of: adding soapstock to the biomass resource; culturing the microbial population indigenous to the biomass resource in the presence of the soapstock so that the amount of biogas produced by the microbial population is in the range of 300 Nml / g-VS to 1200 Nml / g-VS (biogas production rate per organic matter); and obtaining, from the biomass resource after the culturing, a microbial population suitable for producing a methane-containing biogas by methane fermentation of the oil-containing biomass resource.

2. 2. The method according to claim 1, wherein the amount of the soapstock added is 1 to 15 parts by mass per week on average per 100 parts by mass of biomass resources.

3. 3. The method according to claim 1 or 2, characterized in that the soapstock is raw soapstock.

4. 4. The method according to claim 1, wherein the culturing step comprises culturing for at least 11 to 14 weeks after adding the soapstock.

5. A method for producing biogas containing methane, comprising adding a microbial community obtained by the method according to any one of claims 1 to 4 to a biomass resource containing oil, and subjecting the resulting mixture to methane fermentation in a fermenter.

6. The method for producing biogas according to claim 5, wherein the oil-containing biomass resource is added so that the amount of organic matter in the fermentation tank during methane fermentation treatment is maintained at 8 g-VS / L / d or less.

7. The method for producing biogas according to claim 5 or 6, wherein the oil content is 0.01 to 100 parts by mass per 100 parts by mass of the biomass resource containing oil.

8. 8. The method for producing biogas according to claim 5, wherein the biomass resource containing oil is soapstock.

9. A method for producing fermented compost, using the method for producing biogas according to any one of claims 5 to 8.

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