Suppressing method of methane gas and device thereof, and methane gas suppressant

Abstract

To provide a method of suppressing methane gas and a device thereof, capable of efficiently suppressing methane gas formation without imparting an adverse effect to a stage of methane fermentation.SOLUTION: A suppressing method of a methane gas includes a stage of methane fermentation of organic substance waste water and, as a front stage of the stage of methane fermentation, a stage of addition of active carbon having an average grain diameter (D50) in a range of 0.01-0.5 mm to the organic substance waste water and is characterized by suppressing natural generation of methane gas from organic substances.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for suppressing gas generated in a methane fermentation process, and more particularly to a method and apparatus for methane fermentation treatment in a methane gasification facility or a method and apparatus for treatment in a septic tank. [Background technology]

[0002] The methane fermentation process is a reaction in which, under anaerobic conditions without oxygen, the organic matter contained in organic wastewater, biomass waste, etc. is broken down into methane (CH4) and carbon dioxide (CO2) through the metabolic action of anaerobic bacteria.

[0003] The methane fermentation process has advantages such as reduced environmental impact, energy recovery, residue utilization, resulting in improved economic efficiency, and contribution to global warming countermeasures. Therefore, there has been an increase in methane gasification facilities both in Japan and overseas that aim to recover energy through the methane fermentation process.

[0004] As mentioned above, although the methane fermentation process is a very attractive process, there are various issues that hinder the technological growth of the methane fermentation process, such as the enormous costs associated with the large size of the equipment, the difficulty of stable equipment operation and adjustment, and the resulting lack of cost-effectiveness.

[0005] Currently, in order to overcome the aforementioned issues, methods have been developed to add methane fermentation promoters to fermenters and digesters. These methane fermentation promoters use surfactants and conductive substances.

[0006] Of these, Patent Document 1 (JP 2020-28830) states that nonionic surfactants are more preferable as they have less effect on microorganisms, are easily adsorbed to the interface of suspended solids (SS) in organic waste, and are low-foaming, stable, and less irritating.

[0007] It is also known that adding conductive materials to digesters mediates the electron transfer reaction between microorganisms, which is the rate-limiting step, and increases the efficiency of methane gas production. The conductive materials used here are classified into two types: carbon-based conductive materials (biochar, activated carbon, graphene, carbon cloth, etc.) and iron-based conductive materials (magnetite, iron oxide, hematite, etc.). Patent Document 2 (JP 2020-82044 A) describes a method of promoting methane fermentation by adding powdered activated carbon.

[0008] More specifically, in Patent Document 2, similar to Patent Document 1, a methane gasification facility equipped with a digester for methane fermentation of biomass is introduced, in which a porous material (powdered activated carbon) and phosphoric acid are added to the biomass, and the activated carbon promotes the electro-symbiotic reaction of microorganisms, thereby improving the methane fermentation rate.

[0009] By adding such a promoter, it is possible to stabilize the sludge properties and the generation of digestion gas in the digestion tank, thereby providing an organic waste treatment method and organic waste treatment system that can improve the digestion rate in the digestion tank.

[0010] On the other hand, the opposite of the above is the problem of gases generated from digester gases and septic tanks. For example, in storage tanks for organic raw materials, septic tanks, and rice paddies, an anaerobic atmosphere can be created unintentionally, causing an increase in methane bacteria and the progression of methane fermentation, which can result in the generation of digester gases or their release into the atmosphere, causing an increase in greenhouse gases.

[0011] Therefore, techniques for suppressing the generation of such methane gas have also been proposed. For example, Non-Patent Document 1 describes that when the addition of antibiotics was investigated in order to prevent the use of raw materials by microorganisms other than methane bacteria, the addition of azithromycin increased the activity of methane bacteria and increased the production of methane gas, while conversely, the addition of chloramphenicol decreased the activity of methane bacteria and suppressed the production of methane gas. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2020-28830 [Patent Document 2] Japanese Patent Publication No. 2020-82044 [Non-patent literature]

[0013] [Non-Patent Document 1] Understanding microbial interactions to enhance anaerobic digestion of sewage sludge; Biotechnology Vol. 99 No. 12 (2021) Summary of the Invention [Problem to be solved by the invention]

[0014] In the past, methane fermentation facilities faced the problem of the organic raw material being decomposed by methane bacteria in storage tanks that hold organic materials, such as concentrated sludge from the primary sedimentation tanks of sewage treatment plants, becoming anaerobic, leading to unintended methane fermentation. This resulted in a reduction in the organic material before it entered the methane fermentation facility.

[0015] Furthermore, in septic tanks, if the sludge becomes anaerobic for a long period of time due to blower failure or other reasons, methane fermentation by methanogens will progress, and the gas generated by this unexpected methane fermentation will not only be difficult to collect, but will also be released into the atmosphere and become a greenhouse gas that could contribute to global warming. Methane gas in particular is said to contribute 28 times more to global warming than carbon dioxide.

[0016] In view of the above, Patent Document 1 describes a method for promoting methane fermentation in a system for treating organic waste by methane fermentation, in which a nonionic surfactant and a flocculant are added to a digester as methane fermentation promoters, and a portion of the treated digested sludge is returned to a reaction tank. However, this is a phenomenon in which the combined use of a surfactant and a flocculant as additives makes methane fermentation more efficient, and does not describe a method for suppressing methane gas.

[0017] Furthermore, the above-mentioned Patent Document 2 describes that in a methane gasification facility equipped with a digester that processes biomass into methane fermentation, a treatment facility characterized by including an input section for inputting a porous material (such as activated carbon) and phosphoric acid into the biomass, and a treatment method using this treatment facility, it is possible to increase the methane fermentation rate, reduce the size of the treatment facility, and reduce running costs. However, the promotion of methane fermentation by porous materials is a phenomenon that occurs when specific particle shapes are used or when used in combination with phosphoric acid, and does not describe a method for suppressing methane gas using porous materials or a means for solving the problem of releasing methane gas as a greenhouse gas.

[0018] Furthermore, Non-Patent Document 1 states that the addition of chloramphenicol reduces the activity of methanogens and inhibits the production of methane gas. However, inhibition by adding antibiotics is extremely costly and there are concerns about the impact on the downstream methane fermentation tank, making it unrealistic and practical.

[0019] In view of the above problems, an object of the present invention is to find a method for suppressing methane gas production that can efficiently suppress the production of methane gas without adversely affecting the methane fermentation stage. [Means for solving the problem]

[0020] That is, the method for suppressing methane gas according to the present invention includes a step of subjecting organic wastewater to methane fermentation, a step of adding activated carbon to the organic wastewater prior to the methane fermentation step, The activated carbon has an average particle size (D50) in the range of 0.01 to 0.5 mm.

[0021] The step of adding activated carbon to the organic wastewater may be a step of storing the organic wastewater or a step of concentrating the organic wastewater.

[0022] The activated carbon is characterized in that it is biochar.

[0023] The activated carbon is added at a rate of 0.5 to 2.0% by weight with respect to the volume of the organic wastewater.

[0024] The system further comprises a step of methane fermenting organic wastewater, and at least one of the following steps as a step preceding the methane fermentation step: a step of inflowing organic wastewater from the upstream side; a step of anaerobic filtration of the inflowing organic wastewater; a step of contact aerating the anaerobically filtered organic wastewater; and a step of precipitating organic matter in the organic wastewater that has undergone contact aeration; and a step of adding activated carbon to at least one of the step of inflowing organic wastewater, the steps preceding and following the step of inflowing organic wastewater, the anaerobic filtration step, the steps preceding and following the anaerobic filtration step, the contact aeration step, the steps preceding and following the contact aeration step, the precipitating step, and the steps preceding and following the precipitating step, wherein the activated carbon has an average particle size (D50) in the range of 0.01 to 0.5 mm.

[0025] Next, the methane gas suppression device of the present invention comprises a fermentation means for methane fermentation of organic wastewater, a concentrating means for the organic wastewater provided upstream of the fermentation means, and an adding means for adding activated carbon to at least one of the concentrating means, the upstream stage of the concentrating means, and the downstream stage of the concentrating means, wherein the activated carbon has an average particle size (D50) in the range of 0.01 to 0.5 mm.

[0026] The system also includes a fermentation means for methane fermentation of organic wastewater, and at least one of an inflow means, provided upstream of the fermentation means, for introducing the organic wastewater from the upstream side, an anaerobic filtration means for anaerobically filtering the introduced organic wastewater, a contact aeration means for contacting the anaerobically filtered organic wastewater with air, and a precipitation means for precipitating the organic matter in the organic wastewater that has undergone contact aeration, and an addition means for adding activated carbon to any one of the inflow means, the upstream and downstream stages of the inflow means, the anaerobic filtration means, the upstream and downstream stages of the anaerobic filtration means, the contact aeration means, the upstream and downstream stages of the contact aeration means, the precipitation means, and the upstream and downstream stages of the precipitation means, wherein the activated carbon has an average particle size (D50) in the range of 0.01 to 0.5 mm.

[0027] Furthermore, the methane gas inhibitor according to the present invention is characterized by comprising activated carbon having an average particle size (D50) in the range of 0.01 to 0.5 mm, which is added to cause methane fermentation of organic wastewater. [Effects of the Invention]

[0028] The present invention can suppress the spontaneous generation of methane gas from organic wastewater. This leads to avoiding a decrease in organic matter in the subsequent methane fermentation stage, resulting in an efficient increase in industrial methane gas production. At the same time, the unexpected spontaneous generation of methane gas from organic wastewater can be suppressed, which is expected to have an effect in preventing global warming.

[0029] Furthermore, since this method is milder than the method using antibiotics, it has the advantage of having less impact on the downstream methane fermentation tank. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of the method of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing another embodiment of the method of the present invention. [Figure 3]FIG. 3 is a line graph showing the cumulative amount of digestion gas generated when each type of activated carbon was used. [Figure 4] FIG. 4 is a bar graph showing the concentration of hydrogen sulfide generated when biochar (Example 1) and the blank test plot were used. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention was made based on the discovery of a novel property of a specific activated carbon that can suppress methane gas naturally generated by fermentation from organic matter, such as organic wastewater, sludge, human waste / septic tank sludge, livestock manure, food manufacturing residues, agricultural residues, and biomass energy recovery residues, or organic wastewater. That is, by adding the activated carbon of the present invention to organic matter, the amount of methane gas naturally generated from the organic matter can be suppressed.

[0032] By utilizing the above-described properties of activated carbon, for example, in a methane gasification facility, the fermentation stage for generating methane gas can be efficiently and intentionally carried out by fermenting organic matter such as organic wastewater with methane bacteria. In other words, minimizing the loss of organic matter that serves as the substrate for fermentation through methane fermentation before it enters the fermentation stage will lead to efficient methane production thereafter.

[0033] However, in the early stages of the fermentation process, methane gas is spontaneously and unexpectedly produced by the action of methanogens, resulting in a loss of organic matter that should be fermented in the subsequent fermentation stages.

[0034] Therefore, preventing this situation is necessary for industrial production, collection, and utilization of methane gas, and also reduces the uncontrolled release of naturally occurring methane gas into the atmosphere.

[0035] In this regard, in the present invention, a specific activated carbon is added to organic matter such as organic wastewater as a methane fermentation inhibitor to suppress the natural generation of methane gas prior to the methane fermentation stage, thereby suppressing unintended methane fermentation prior to the fermentation stage and reducing the loss of organic matter therein.

[0036] The activated carbon in the present invention can be added at any timing as long as it is added before the stage of methane fermentation of organic matter such as organic wastewater.

[0037] For example, if the present method is designed to have a step of storing organic wastewater before the methane fermentation step, or a step of concentrating the organic wastewater to a TS (semi-solid) concentration suitable for subsequent treatment, the present method may add activated carbon to at least one of the steps of storing the organic wastewater or concentrating the organic wastewater, or may have a means for adding activated carbon before or after these steps.

[0038] Furthermore, for example, when the present method is assumed to have a configuration in which, in a stage preceding the methane fermentation stage, an organic wastewater is introduced from the upstream side, an anaerobic filtration of the introduced organic wastewater, a contact aeration of the anaerobically filtered organic wastewater, and a precipitating step of the organic matter in the organic wastewater that has undergone contact aeration, the present method may have a step for adding activated carbon in at least one of the stage of introducing organic wastewater, the stages preceding and following the stage of introducing organic wastewater, the anaerobic filtration stage, the stages preceding and following the anaerobic filtration stage, the contact aeration stage, the stages preceding and following the contact aeration stage, the precipitating stage, and the stages preceding and following the precipitating stage.

[0039] 1 and 2 in the embodiment of the present invention, the "previous stage" side can also be referred to as the "upstream" side, while the "next stage" side can be referred to as the "downstream" side.

[0040] The type of activated carbon used in the present invention may be, for example, one or more of powdered activated carbon, formed activated carbon, biochar, or the like. Of these, powdered activated carbon and biochar are preferred.

[0041] In both cases, small particle sizes are particularly preferred. This is to prevent the activated carbon from settling or settling in the tank where it is added. If the activated carbon setstling or settling in the facility tank, the effect of suppressing the generation of methane gas will be reduced. Therefore, small particle sizes are more preferred. This allows the activated carbon to diffuse without settling or settling in the tank, increasing the opportunity for contact with the organic matter that serves as the substrate, and enabling more efficient industrial methane fermentation.

[0042] On the other hand, if the particle size of the activated carbon is too small, dust will fly up when it is handled, which may reduce work efficiency and cause adverse effects on the human body, such as pneumoconiosis.

[0043] From the above viewpoints, the activated carbon used in the present invention preferably has an average particle size (D50) in the range of 0.01 to 0.5 mm, and more preferably has an average particle size (D50) in the range of 0.02 to 0.3 mm.

[0044] The average particle size is measured, for example, according to JIS-K1474 (2014) Activated Carbon Test Method (Particle Size and Particle Size Distribution (Effective Diameter and Uniformity Coefficient)) or using a laser diffraction particle size distribution analyzer (SALD-3000J).

[0045] The activated carbon is preferably 500 ml 2 / g~1200m 2 / g, more preferably 500m 2 / g~900m 2 / g specific surface area.

[0046] Furthermore, the raw material for the activated carbon is not particularly limited, and may be plant-based (coconut shells, charcoal, sawdust, pine, bamboo, hardwood chips, grass peat, cellulose, etc.), coal-based (lignite, brown coal, bituminous coal, anthracite, etc.), or petroleum-based (oil carbon, phenolic resin, rayon, coal pitch, petroleum pitch, etc.), either alone or in combination of two or more.

[0047] From the perspective of preventing global warming, plant-based activated carbon is more preferable than coal- or petroleum-based activated carbon, and among plant-based activated carbon, biochar, which has been attracting attention in recent years, is even more preferable. Biochar is defined as a solid material made by heating biomass at temperatures above 350°C under controlled oxygen concentrations at levels that prevent combustion.

[0048] The activated carbon may be a commercially available product or an unused product (brand new) immediately after production, or may be regenerated activated carbon obtained by activating and regenerating used activated carbon that has been used once or more for water purification, wastewater treatment, sludge treatment, etc., or waste biochips accumulated after being used as fuel, or residues thereof.

[0049] The amount of activated carbon added is preferably in the range of 0.5 to 5.0 weight volume % (w / v%) relative to the volume of the organic matter added, and more preferably in the range of 1.0 to 2.0 weight volume % (w / v%) in consideration of costs, the final amount of sludge to be treated, and fluidity in the tank and piping.

[0050] One embodiment of the method or apparatus of the present invention using activated carbon as described above is, for example, the flow shown in FIG.

[0051] FIG. 1 shows a flow chart of the use of the method or apparatus of the present invention in, for example, a typical methane gasification facility.

[0052] The organic sludge from the primary sedimentation tank is thickened in a gravity thickener to an appropriate TS (saturated solids) concentration. The thickened sludge is then fermented in a methane fermenter (digestion tank), producing methane gas, which is then collected. The sludge can come from the primary sedimentation tank or the final sedimentation tank. A mechanical thickener may also be used instead of a gravity thickener.

[0053] In the flow chart of Figure 1, the activated carbon of the present invention is preferably added to a location where the sludge creates an anaerobic environment and there is a risk of spontaneous generation of methane gas. That is, the activated carbon of the present invention is preferably added to at least one of the following locations: (A) upstream of the gravity thickener, (B) upstream of the mechanical thickener, (D) upstream of the mechanical thickener, (E) upstream of the methane fermenter, and (C and F) upstream of the methane fermenter.

[0054] FIG. 2 shows a flow chart of the method or apparatus of the present invention when used in a general septic tank.

[0055] The organic wastewater is filtered through the wastewater inlet (G) in two anaerobic filter bed tanks (H and I), and the filtered wastewater is further purified by contacting with air in the contact aeration tank (J). The purified wastewater is then treated in the settling tank (K) to settle suspended solids in the wastewater, and is then treated as treated water.

[0056] In the flow chart of Figure 2, the activated carbon of the present invention is preferably added to a location where the wastewater creates an anaerobic environment and there is a concern about the spontaneous generation of methane gas. That is, the activated carbon of the present invention is preferably added to at least one of the wastewater inflow location, the anaerobic filter bed tank, the contact aeration tank, and the sedimentation tank. The contact aeration tank is an aerobic environment due to aeration, but the subsequent sedimentation tank K can become an anaerobic environment, so it can be a location where the activated carbon used in the present invention is added.

[0057] Examples of sites where the method of the present invention can be used include methane fermentation tanks or septic tanks in methane gasification facilities, as well as rice paddy soil and cow stomachs. [Example]

[0058] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0059] [Test Example 1] Biochar with various particle shapes was prepared and the optimal particle size range was investigated. A teaspoonful of biochar was intentionally spilled in a fume hood to investigate whether dust was generated. The possibility of pneumoconiosis was considered based on the knowledge that dust particles with a particle size of 0.005 mm or less are more likely to cause pneumoconiosis. Furthermore, 150 mg of biochar was added to mixed raw sludge (a mixture of excess sludge and raw sludge) and visually observed to assess whether it accumulated at the bottom of the sludge after standing overnight.

[0060] The results are shown in Table 1 below.

[0061] The smaller the particle size, the more likely it is that dust will be stirred up, which could lead to the risk of pneumoconiosis, while the larger the particle size, the more likely it is to accumulate in sludge, and it is thought that when large amounts are added to storage tanks or septic tanks, problems such as pipe blockages may occur.The same tendency was observed with powdered activated carbon, rather than biochar.

[0062] From the above results, it was considered that the particle size of the biochar and activated carbon according to this example is preferably in the range of 0.01 to 0.5 mm, and more preferably in the range of 0.02 to 0.3 mm.

[0063] [Table 1]

[0064] [Test Example 2] In a simple methane fermentation test, the inhibition of methane fermentation (the effect of suppressing digestion gas) when biochar (Example 1) and powdered activated carbon (Example 2) were added was confirmed.

[0065] A 1 L glass bottle was filled with 300 ml of digested sludge containing methanogens as a culture medium, and 10 g of mixed raw sludge (a mixture of excess sludge and raw sludge) was added as a substrate, and biochar or powdered activated carbon was added as a methane fermentation inhibitor at a concentration of 0.5 to 2.0 weight / volume % (w / v%) relative to the digested sludge. The mixture was then cultured with shaking in a constant temperature bath at 30°C.

[0066] On the other hand, as a comparative example, granular activated carbon was added, and a methane fermentation test was carried out under the same conditions as above, and the cumulative amount of digestion gas generated was confirmed.

[0067] A blank test was conducted without adding biochar or activated carbon.

[0068] The physical properties of each activated carbon used in Test Example 2 are as follows, and are also shown in Table 2.

[0069] The biochar (Example 1) was made from waste biochips (by-products) discharged from a gasification furnace for the purpose of wood biomass power generation. The average particle size was approximately 0.03 mm, the iodine adsorption capacity was approximately 600 mg / g, and the specific surface area was 500 m. 3 / g, pore volume is 0.5 cm 2 / g and an average pore diameter of about 35 Å.

[0070] As the powdered activated carbon (Example 2), powdered activated carbon for water treatment, Evadia 5LPD (wood-based), manufactured by Suing Co., Ltd., was used. The average particle size was approximately 0.02 mm, the iodine adsorption capacity was approximately 900 mg / g, and the specific surface area was 900 m 3 / g, pore volume is 0.5m 2 / g and an average pore diameter of about 22 Å.

[0071] As a granular activated carbon (comparison example), Evadia LG-10S (wood-based), a granular activated carbon for water treatment manufactured by Suing Co., Ltd., was used. The average particle size was approximately 1.3 mm, the iodine adsorption capacity was approximately 1,200 mg / g, and the specific surface area was 1,200 m. 3 / g, pore volume is 0.5m 2 / g and an average pore diameter of about 17 Å.

[0072] [Table 2]

[0073] The amount of digestion gas (including methane, carbon dioxide, etc.) generated in the methane fermentation test was measured over time, and the cumulative amount obtained was used to confirm the digestion gas suppression effects of Example 1, Example 2, Comparative Example, and the blank test. The results are shown in the line graph in Figure 3.

[0074] In FIG. 3, the vertical axis indicates the cumulative amount of gas generated (ml), and the horizontal axis indicates the number of days that have passed (days).

[0075] The results in Figure 3 confirmed that in the test areas where biochar (Example 1) and powdered activated carbon (Example 2) were added, the cumulative amount of digestion gas generated decreased by approximately 30 to 100% as the amount added increased, compared to the mixed cultivation + digestion (blank test area).

[0076] The reduction in the cumulative amount of gas generated by biochar (Example 1) and powdered activated carbon (Example 2) is thought to be due to their small particle size, which increased the opportunity for contact with the organic matter that serves as the substrate, resulting in the adsorption of more organic matter.

[0077] On the other hand, in the test area where granular activated carbon (comparison example) was added, it was confirmed that the cumulative amount of gas generated was only reduced by 2 to 5% compared to the mixed cultivation + digestion (blank test area).

[0078] Furthermore, when the glass bottles were observed after the test, it was confirmed that a larger amount of granular activated carbon (comparison example) settled at the bottom of the glass bottle compared to biochar (example 1) and powdered activated carbon (example 2).

[0079] From the above results and confirmation, it is believed that the granular activated carbon used (comparison example) has a larger specific surface area value and is superior to biochar (Example 1) and powdered activated carbon (Example 2) (Table 2), but it settles to the bottom of the glass bottle, reducing the opportunity for contact with the organic matter that serves as the substrate, thereby reducing the gas suppression effect.

[0080] [Test Example 3] In Test Example 3, biochar (Example 1) or powdered activated carbon (Example 2) was added to sludge, and the effect of suppressing odorous substances generated from the sludge was confirmed.

[0081] First, 100 mL of concentrated sludge as an odor source and biochar (Example 1) as a gas suppressant were added to a 1 L sealed container so that the concentration was 0.1 to 0.5 w / v% relative to the concentrated sludge. After thorough mixing, 600 mL of air was added to prepare the test sample.

[0082] A blank test was prepared without adding biochar (Example 1). Note that the biochar (Example 1) used was the same as that used in Test Example 2 above.

[0083] The prepared test sample was stored at 30°C, and the concentration (ppm) of hydrogen sulfide, one of the odorous substances, was measured 24 hours after the addition. The test results are shown in the bar graph in Figure 4.

[0084] In FIG. 4, the vertical axis indicates the concentration of hydrogen sulfide generated, and the horizontal axis indicates the elapsed time (24 hours after addition).

[0085] From the results in Figure 4, the hydrogen sulfide concentration after 24 hours was 500 ppm in the blank test area, 150 ppm with the addition of 0.1 w / v% biochar (Example 1), and 40 ppm with the addition of 0.5 w / v% biochar (Example 1), confirming that the use of biochar (Example 1) suppressed the generation of hydrogen sulfide by 70 to 90%.

[0086] The odorous substance suppression effect in Test Example 3 above is thought to be due to the fact that biochar (Example 1) inhibits the substrate that is the source of odor, adsorption of the generated hydrogen sulfide, or the growth of sulfate-reducing bacteria in a microanaerobic environment.

[0087] From the above results, the activated carbon of this example is extremely useful as a methane fermentation inhibitor. Therefore, by using it in a methanation facility, it is expected that it will enable efficient industrial production of methane gas while suppressing unintended production of methane gas, thereby reducing adverse effects on the global environment. [Explanation of symbols]

[0088] A: Pre-stage of gravity thickener B: Gravity concentration tank C: Pre-stage of methane fermentation tank (post-stage of gravity thickener) D: Pre-stage of mechanical thickener E: Mechanical concentrator F: Pre-stage of methane fermentation tank (post-stage of mechanical concentrator) G: Sewage inflow point H: Anaerobic filter bed tank (before solids removal) I: Anaerobic filter bed tank (after solids removal) J: Contact aeration tank K: Sedimentation tank

Claims

1. A step of subjecting organic wastewater to methane fermentation; As a preliminary step of the methane fermentation step, a step of adding activated carbon having an average particle size (D50) in the range of 0.01 to 0.5 mm to the organic wastewater; and A method for suppressing methane gas, characterized by suppressing the natural generation of methane gas from the organic matter.

2. The step of adding activated carbon to the organic wastewater includes: Storing organic wastewater or concentrating organic wastewater 2. The method for suppressing methane gas according to claim 1, wherein:

3. The method for suppressing methane gas according to claim 1 or 2, characterized in that the activated carbon is biochar.

4. 3. The method for suppressing methane gas according to claim 1, wherein the activated carbon is added at a rate of 0.5 to 2.0% by weight of the organic wastewater.

5. A method for suppressing natural generation of methane gas from organic wastewater, comprising: A step of subjecting the organic wastewater to methane fermentation; As a stage preceding the methane fermentation stage, the system has at least one of a stage of introducing organic wastewater from the upstream side, a stage of anaerobic filtration of the introduced organic wastewater, a stage of contact aeration of the anaerobically filtered organic wastewater, and a stage of precipitating organic matter in the organic wastewater that has been contact aerated, and a stage of adding activated carbon to at least one of the stage of introducing organic wastewater, the stage before and the stage after the stage of introducing organic wastewater, the anaerobic filtration stage, the stage before and the stage after the anaerobic filtration stage, the contact aeration stage, the stage before and the stage after the contact aeration stage, the precipitating stage, and the stage before and the stage after the precipitating stage; and A method for suppressing methane gas, characterized in that the activated carbon has an average particle size (D50) in the range of 0.01 to 0.5 mm.

6. a fermentation means for performing methane fermentation on the organic wastewater; A concentrating means for the organic wastewater is provided upstream of the fermentation means; adding means for adding activated carbon having an average particle size (D50) in the range of 0.01 to 0.5 mm to at least one of the concentrating means, a stage preceding the concentrating means, and a stage following the concentrating means; and A methane gas suppression device characterized by suppressing the natural generation of methane gas from the organic wastewater.

7. a fermentation means for performing methane fermentation on the organic wastewater; The system has at least one of an inflow means provided upstream of the fermentation means for inflowing organic wastewater from the upstream side, an anaerobic filtration means for anaerobically filtering the inflowing organic wastewater, a contact aeration means for contacting the anaerobically filtered organic wastewater with air, and a precipitation means for precipitating organic matter in the organic wastewater that has been contact aerated, and adding means for adding activated carbon to any one of the inflow means, the upstream and downstream stages of the inflow means, the anaerobic filtration means, the upstream and downstream stages of the anaerobic filtration means, the contact aeration means, the upstream and downstream stages of the contact aeration means, the precipitation means, and the upstream and downstream stages of the precipitation means, A methane gas suppression treatment device, characterized in that the activated carbon has an average particle size (D50) in the range of 0.01 to 0.5 mm.

8. A methane gas inhibitor comprising activated carbon having an average particle size (D50) in the range of 0.01 to 0.5 mm, which is added to cause methane fermentation of organic wastewater.

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