JP2004237246A - Methane fermentation treating apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methane fermentation treating apparatus, in which alkali or acid is less used and cost can be reduced. <P>SOLUTION: A solubilization tub 24 which solubilizes by adding alkali 25 to an object to be treated 22 containing mainly vegetable substance, an acid fermentation tub 29 acid-fermenting by throwing of alkaline solubilizing slurry produced in the solubilization tub 24 and an object 27 to be treated containing mainly an animal substance for mixture, and a methane fermentation tub 10 methane-fermenting an organic acid containing solubilizing slurry produced in the acid-fermentation tub 29 are provided. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a methane fermentation treatment apparatus and a methane fermentation method for solubilizing an organic substance such as organic waste and performing methane fermentation to obtain methane gas.
[0002]
[Prior art]
Methane fermentation has been applied to the treatment of final sedimentation tank sludge and excess activated sludge in the field of sewage and night soil treatment. In recent years, emission of dioxins from refuse incinerators, lack of landfills, global warming due to CO ₂ , etc. have become major problems, and the use of methane fermentation technology has been activated as one of the methods to reduce these environmental impacts. ing. Methane fermentation is a technology that can recover methane gas by fermenting organic waste (garbage, sludge, biomass, etc.), and can recover energy from high-moisture waste that cannot be recovered by burning as it is. .
[0003]
Methane fermentation is roughly divided into a two-stage biochemical reaction of a solubilization process using hydrolytic bacteria and acid-producing bacteria and a methane fermentation process using methanogens. High molecular weight organic compounds such as proteins, carbohydrates, and fats are first degraded to lower fatty acids, amino acids, and saccharides by hydrolytic bacteria or the like. Next, these low molecular organic substances are decomposed by acid-producing bacteria into H ₂ , CO ₂ , and organic acids (acetic acid, butyric acid, propionic acid, pyruvic acid, formic acid, lactic acid, succinic acid, etc.). Methane is produced by the producing bacteria.
[0004]
As described above, the types of the active microorganisms are different between the solubilization step and the methane fermentation step, and the optimum pH value is different from about 4 to 5 for the solubilization step and about 7 to 7.6 for the methane generation step. In addition, bacteria that perform methane fermentation are absolutely anaerobic and cannot grow in an environment where oxygen is present, but many bacteria related to solubilization are aerobic and facultatively anaerobic, and the presence or absence of oxygen and its abundance Optimal bacteria are activated according to the temperature and decompose organic matter. For these reasons, in recent years, a method called a two-phase method in which the solubilization tank and the methane fermentation tank are separated to increase the fermentation efficiency is often used.
[0005]
FIG. 3 shows a flowchart of a methane fermentation system for general waste mainly composed of kitchen waste according to the related art (for example, see Non-Patent Documents 1 and 2).
[0006]
The garbage 1 is put into the solubilization tank 4 and, while being stirred by the stirrer 5, is solubilized mainly by the action of microorganisms present in the waste, and is mixed with an organic acid and a precursor of the organic acid as a raw material for methane fermentation. Organic substances such as higher fatty acids, amino acids, and saccharides.
[0007]
In general, the solubilizing tank 4 is operated in a batch process so as not to discharge the solubilized material. After about 1 to 3 days, the solubilized material is extracted by the pump 9 and temporarily stored in the storage tank 7. The storage tank 7 is not only a buffer for quantitatively supplying the solubilized substance to the subsequent methane fermentation tank 10 but also consumes dissolved oxygen during the storage and makes the solubilized substance suitable for anaerobic methane fermentation. And
[0008]
The solubilized material in the storage tank 7 is quantitatively sent to the methane fermentation tank 10 by the pump 9, and a gas (biogas) G of about 65% methane and about 35% carbon dioxide is converted from the organic acid by the action of methane-producing bacteria. It is generated and sent to gas utilization equipment (not shown) such as a fuel cell. Since biogas contains about several hundred ppm of hydrogen sulfide, it is used as a fuel after desulfurization if necessary, and recovers energy as electricity or hot water.
[0009]
The waste liquid from the methane fermentation tank 10 is withdrawn and sent to the sedimentation tank 13, where it is separated into concentrated sludge concentrated at the bottom and supernatant wastewater. The concentrated sludge is extracted, and a part thereof is returned to the methane fermentation tank 10 via the concentrated sludge return line 18, and is used as seed sludge for methane fermentation.
[0010]
General waste mainly consists of garbage discharged from homes, restaurants, and prepared food stores, and is a mixture of vegetable waste (vegetables and fruits) and animal waste (meat and fish). Relatively well balanced.
[0011]
FIG. 4 is a diagram showing the elemental composition of various wastes and methane fermentation sludge. As is clear from this figure, vegetable waste has a high carbon (C) content because it is mainly composed of carbohydrates, and animal waste has a high nitrogen (N) content because it is mainly protein. General wastes represented by kitchen wastes (Examples A and B) have a carbon-to-nitrogen ratio (C / N) in the range of 12 to 20 suitable for fermentation because they are already mixed. There are many things inside. In addition, it contains various trace elements necessary for the growth of microorganisms in a well-balanced manner.
[0012]
Fibers contained in vegetables and fruits are softer than fibers of plants and are relatively easily decomposed. On the other hand, in animal waste, high concentrations of ammonia generated by the decomposition of protein and long-chain fatty acids, which are intermediate products of decomposition of fat, inhibit fermentation, but must be mixed with vegetable waste. As a result, the inhibitor is diluted, and the problem hardly occurs. From these facts, general waste is a raw material that is relatively easily solubilized and methane fermented, and can be treated with almost no problem according to the flowchart of FIG.
[0013]
In contrast, industrial waste discharged from food factories, farms, markets, and the like, has an uneven distribution of components depending on the source. For example, vegetable waste, rice husk, straw waste, waste paper, etc. are discharged separately for plants, and dairy products, meat, fish, etc. are discharged separately for animals. When such industrial wastes are separately fermented at the source, a system must be adopted that is adapted to each fermentation characteristic.
[0014]
[Non-patent document 1]
"Methane fermentation of waste [POD version] published by Scientist Co., Ltd. [0015]
[Non-patent document 2]
"Circulation Economic Newspaper" No. 577, issued June 4, 2001.
[Problems to be solved by the invention]
Recently, attempts have been made to collect such industrial wastes of different sources by region and to treat them at one place (eco town planning, etc.). When the different wastes are aggregated and mixed depending on the generation source, and the fermentation is performed using the general waste processing flowchart shown in FIG. 3, there are the following problems.
(1) The nutritional balance such as C / N and trace elements can be improved by mixing various kinds of plant and animal wastes, but depending on the amount of each waste to be carried in, C / N can be obtained by simple mixing. May not be in the proper range.
[0017]
(2) The hard fibrous material of the vegetable waste is hardly solubilized by a normal solubilization operation, so that it is not decomposed in the methane fermentation tank, and the amount of methane fermented sludge discharged increases.
[0018]
(3) In order to improve the above (2), it is possible to add an alkali to the solubilizing tank to destroy the fibrous material. Increase.
[0019]
(4) In order to solubilize the fibrous material by the addition of the alkali in the above (3), the pH value must be extremely high at about 10. However, since the pH value is too high for methane fermentation as it is, it may be necessary to add an acid to lower the pH value. In addition, it is necessary to remove the salt in the final wastewater treatment by the amount of the added chemical.
[0020]
(5) The discharged methane fermentation sludge is composted or incinerated. However, at present, the demand for compost is small, seasonal fluctuations are large, and distribution routes are not established. You can't consume it. Further, since the water content is high, a large amount of fuel is required for incineration. Although it may be burned in incinerators with combustible waste, it is disadvantageous in terms of heat recovery. For these reasons, it is desired to reduce the amount of generated sludge as much as possible.
[0021]
An object of the present invention is to solve such disadvantages of the prior art, and to use an alkali or an acid when treating both an object mainly composed of a plant substance and an object mainly composed of an animal substance. It is an object of the present invention to provide a methane fermentation treatment apparatus and a methane fermentation treatment method, which have a small amount and a small amount of salt to be removed by wastewater treatment, and can reduce costs.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, the first means of the present invention is a solubilization tank that adds an alkali to an object to be treated mainly composed of a plant substance such as a vegetable waste and solubilizes the same,
An alkaline solubilized slurry generated in the solubilization tank, and an acid fermentation tank for mixing and acid-fermenting an object to be processed, which includes, for example, an object to be treated mainly composed of animal substances such as animal waste,
A methane fermentation tank for methane fermentation of the solubilized organic acid-containing slurry produced in the acid fermentation tank.
[0023]
According to a second aspect of the present invention, in the first aspect, a pH meter for measuring a pH value in the acid fermentation tank, and adding an alkaline solubilizing slurry to the acid fermentation tank based on the measurement result of the pH meter. Means for adjusting the amount.
[0024]
According to a third means of the present invention, in the first means or the second means, at least one of an alkali addition line and an acid addition line for adding an acid to the acid fermenter is provided. It is a feature.
[0025]
The fourth means of the present invention is characterized in that in the first means, there is provided a sludge return line for returning a part of the sludge generated in the methane fermentation tank to the solubilization tank.
[0026]
According to a fifth aspect of the present invention, in the first aspect, at least one of a pulverizing means of a stirrer, an ultrasonic generating means, and a wet pulverizing pump for pulverizing a solid content in the alkaline solubilized slurry is provided. It is a feature.
[0027]
Sixth means of the present invention is a solubilization step of adding an alkali to a treatment target mainly composed of a plant substance and solubilizing the same,
An acid fermentation step of adding and mixing the generated alkaline solubilized slurry and a substance mainly composed of animal substances to produce an acid,
And a methane fermentation step of fermenting methane from the obtained organic acid-containing solubilized slurry.
[0028]
According to a seventh aspect of the present invention, in the sixth aspect, the pH value of the solubilized slurry in the acid fermentation step is measured, and the alkaline solubilized slurry is supplied to the acid fermentation step based on the measurement result. It is characterized in that the amount is adjusted.
[0029]
According to an eighth aspect of the present invention, in the sixth or seventh aspect, at least one of an alkali addition line and an acid addition line is provided for the acid fermentation step, The pH value of the solubilized slurry is measured, and either one of an alkali and an acid is added based on the measurement result.
[0030]
According to a ninth aspect of the present invention, in the sixth aspect, a part of the sludge generated in the methane fermentation step is returned to the solubilization step.
[0031]
A tenth means of the present invention is the sixth means, wherein the content ratio of carbon and nitrogen of the organic acid-containing solubilized slurry supplied to the methane fermentation step can be maintained within the range of methane fermentation conditions. An object to be treated mainly composed of a plant substance, an object to be treated mainly composed of an animal substance, and adjusting at least one input amount of sludge generated in a methane fermentation step to be returned to the solubilization step. Is what you do.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart of the methane fermentation system according to the first embodiment.
As shown in the figure, a plant waste 22 (for example, vegetable waste, straw, rice hull, waste paper, etc.) is finely crushed by a crusher 23 and then put into an alkali solubilization tank 24 together with water 3. An alkali (for example, NaOH) is added from the alkali addition line 25 so that the pH value becomes about 9 to 12, and the mixture is stirred by the stirrer 5 to break hard fiber and solubilize it. At this time, it is possible to further promote the solubilization by increasing the rotation speed of the stirrer 5 (for example, about 100 to 300 rpm). Further, when the plant waste 22 is dissolved in the alkali solubilization tank 24, the solubility is higher when heated.
[0033]
On the other hand, animal waste 27 (for example, waste milk, fish / meat, livestock dung, etc.) is finely crushed by a crusher 28, then put into an acid fermentation tank 29, and stirred by a stirrer 30. If the target animal waste 27 is only a liquid like waste milk, it does not have to pass through the crusher 28.
[0034]
In the acid fermentation tank 29, the pH value is lowered due to the production of the organic acid. By supplying the alkaline solubilized slurry generated in the alkali solubilization tank 24 by the pump 41, the pH value can be adjusted to a suitable range. it can. At this time, the pH meter 42 is installed in the acid fermentation tank 29, and the measurement signal of the pH meter 42 is transmitted to the control unit 37. From the control unit 37, the pH value falls within the range of 4 to 5 suitable for acid fermentation. Thus, a control signal is sent to the pump 41, which regulates the supply of the alkaline solubilizing slurry.
[0035]
In this manner, in the acid fermentation tank 29, long-chain fatty acid derived from animal waste that inhibits methane fermentation is converted into an organic acid that is a direct substrate of methane fermentation, and at the same time other animal waste derived from animal waste is converted. The organic substances (proteins, amino acids, carbohydrates) and the organic substances (mainly carbohydrates, broken fiber) contained in the added alkaline solubilized slurry are also reduced in molecular weight and converted to organic acids. In addition, by mixing an appropriate amount of the high-carbon content plant waste 22 and the high-nitrogen content animal waste 27, the C / N is adjusted to the range of 12 to 20, and the balance of micronutrients is also improved. You.
[0036]
The slurry after the acid fermentation is extracted by the valve 43 and temporarily stored in the storage tank 7. The storage tank 7 is not only a buffer for quantitatively supplying the solubilized substance to the subsequent methane fermentation tank 10 but also consumes dissolved oxygen during the storage and makes the solubilized substance suitable for anaerobic methane fermentation. And The stored slurry is stirred by the stirrer 8 so as not to settle.
[0037]
The slurry in the storage tank 7 is quantitatively sent to the methane fermentation tank 10 by the pump 9, and by the action of the methane-producing bacteria, a gas (biogas) G of about 65% methane and about 35% carbon dioxide is produced from the organic acid. Generated and sent to the gas holder 11. Since biogas contains about several hundred ppm of hydrogen sulfide, it is used as a fuel after desulfurization if necessary, and recovers energy as electricity or hot water.
[0038]
The waste liquid from the methane fermentation tank 10 is extracted by a pump 12 and sent to a settling tank 13 where it is separated into concentrated sludge 14 concentrated at the bottom and wastewater 15 of supernatant. The concentrated sludge 14 is extracted by a pump 36, and a part of the sludge is returned to the methane fermentation tank 10 through the switching valve 17 via the concentrated sludge return line 18, and is used as seed sludge for methane fermentation. Further, a part of the concentrated sludge 14 is extracted from the sludge extraction line 19 through the switching valve 17, and the wastewater 15 is extracted through the wastewater line 21 by the pump 20.
[0039]
The organic matter load introduced into the methane fermenter 10 needs to be as constant as possible. When the load is lower than the predetermined value, the amount of biogas generated is temporarily reduced, and no major problem occurs. However, when the load is excessive, the organic acid accumulates in the methane fermentation tank 10 and the pH value decreases. However, fermentation may be severely inhibited, leading to a situation requiring a long time for recovery. For this reason, when the amount of waste received is large, it is a good idea to put perishable vegetables and fruits with priority, and keep hard-to-perish wastepaper, sawdust and rice husk as stock.
[0040]
When collecting and treating organic wastes from multiple sources in one place, the type of waste received by the treatment plant is almost constant, but the amount of each waste received is considered to fluctuate depending on the season. The following operation adjustment is required.
[0041]
If the collection amount of the vegetable waste 22 is relatively small and an alkaline slurry sufficient to maintain the pH value of the acid fermentation tank 29 at the optimum range of 4 to 5 cannot be obtained, the alkaline fermentation tank 29 is directly transferred to the acid fermentation tank 29. An alkali (for example, NaOH) is added from the addition line 31. Similarly, when the plant waste 22 is insufficient and the C / N is significantly lower than the optimum range (that is, C is insufficient), the alkali solubilizing tank for the waste paper, sawdust, rice hulls, and the like that have been stocked. 24, and the amount of C is increased. Alternatively, the supply amount of the animal waste 27 may be temporarily reduced.
[0042]
Conversely, when the collection amount of the animal waste 27 is small, the acid fermentation can be continued even if the pH value of the acid fermentation tank 29 slightly exceeds the optimum range of 4 to 5, but when the pH value is greatly increased, The acid (for example, HCl) is directly added to the acid fermentation tank 29 from the acid addition line 44, and is maintained at a neutral level.
[0043]
Specifically, a pump 38 is installed on the alkali addition line 31 and a pump 39 is installed on the acid addition line 44. Based on a measurement signal from the pH meter 42, the control unit 37 sends a pH value suitable for acid fermentation. The control signal is sent to the pump 38 or the pump 39 so as to fall within the range of 4 to 5, whereby the amount of alkali or acid added to the acid fermenter 29 is adjusted.
[0044]
Similarly, when the animal waste 27 runs short and the C / N greatly exceeds the optimum range (that is, N runs short), a part of the concentrated sludge 14 after the completion of the methane fermentation is replaced with the switching valve 45. It is added to the alkali solubilization tank 24 via the return line 46. Since the cells have a fibrous cell wall, the cells can be solubilized by alkali treatment as in the case of the vegetable waste 22, and since the N content is high, the shortage of N can be compensated.
[0045]
Since the properties of industrial waste are relatively constant as compared with general waste of an unspecified number of generation sources, such C / N adjustment is performed in advance as shown in FIG. This is possible by performing an analysis, measuring the weight of each, and adjusting the input amount.
[0046]
In addition, even though it is vegetable waste, bread crumbs and rice cooked with a low fiber content can be directly introduced into the acid fermentation tank 29 without being treated in the alkali solubilization tank 24. Use can be reduced.
[0047]
According to the present embodiment, the solubilization of vegetable waste and the promotion of organic acid generation can be achieved with a minimum amount of added chemicals, and since the nutritional balance can be adjusted, the efficiency of methane fermentation is improved, and the amount of biogas generated is reduced. It is possible to increase and reduce the amount of discharged sludge. In addition, by converting most of the organic matter to organic acids that are easily fermented by methane, methane fermentation can be sped up and the apparatus can be made compact.
[0048]
FIG. 2 is a flowchart of the methane fermentation system according to the second embodiment of the present invention.
By providing a strong crushing means in the alkali solubilization tank 24, the solubilization rate can be improved, the amount of biogas generated can be increased, and the amount of discharged sludge can be reduced. Since the cell wall of the plant is softened by the alkali, the solid content can be atomized by strengthening the crushing. Actually, a method in which the stirring blade of the stirrer 5 is shaped like a cutter, ultrasonic waves are applied to the alkali solubilizing slurry by attaching ultrasonic wave generating means to the alkali solubilizing tank 24, or a wet crushing pump is used. is there.
[0049]
This embodiment shows an example in which a wet crush pump 47 is used. During the solubilization operation, the wet crushing pump 47 is operated continuously or intermittently to circulate and mix the solubilized liquid through the circulation line 48 while crushing the solubilized slurry. Then, the valve 49 is switched as necessary, and the solubilized slurry is supplied to the acid fermentation tank 29.
[0050]
Normally, for a raw material containing a large amount of solids, the methane fermentation tank 10 is often of a complete mixing type provided with a sludge return line 18 as shown in FIG. In the complete mixing type, clogging in the tank is not a problem, but it is difficult to maintain the bacterial concentration in the tank because the same amount of sludge as the supplied raw material is withdrawn. Concentration and return are required.
[0051]
On the other hand, if the solid content can be atomized as in the present embodiment, the problem of clogging is reduced, so that a fixed bed or UASB capable of maintaining cells at a high concentration in the methane fermentation tank 33 can be used, and the fermentation efficiency can be further improved. It is possible to increase the processing amount.
[0052]
UASB (Upflow Anaerobic Sludge Blanket: Anaerobic Upflow Sludge Blanket Method) is a solution for preparing and treating a cell aggregate (Granule) under conditions such that coagulation of anaerobic sludge is favorably maintained. Is supplied from the bottom of the tank and floated. A baffle for separating gas, sludge and liquid is provided in the middle of the tank, and the liquid is discharged from the upper part of the tank. Since methane bacteria can be highly concentrated, the treatment efficiency is high and the HRT (Hydraulic Retention Time: hydraulic retention time) can be reduced.
[0053]
In these methods, it is not necessary to constantly pull out sludge, but if bacteria grow too much in the tank, it will cause blockage, so that excess sludge is sometimes pulled out from the sludge extraction line 19. Since the extracted sludge is already in a concentrated state, it can be returned to the alkali solubilization tank 24 as it is through the switching valve 45 and the return line 46 to be used as a fermentation raw material, and excess sludge is reduced. In the figure, reference numeral 34 denotes a wastewater line from which wastewater containing little bacterial cells.
[0054]
In FIG. 2, a control system centering on the control unit 37 is not shown because the drawing is complicated.
[0055]
【The invention's effect】
According to the present invention, the following effects can be obtained.
(1). The amount of alkali and acid used is minimized, and the amount of salts to be removed in wastewater treatment is reduced, so that costs can be reduced. To explain this in more detail, when various kinds of wastes are mixed and alkali-treated, the amount of alkali chemicals required increases because there are many objects to be alkali-treated. If only the plant system is alkali-treated, the amount of the alkali drug and the amount of the acid added when the need for subsequent pH adjustment arises can be reduced.
[0056]
Further, in order to continue the acid fermentation, it is necessary to adjust the pH by adding an alkali. However, by adding a plant-based alkali treatment product, an external alkali agent is unnecessary or can be reduced. Further, as described above, by reducing the amount of the alkali agent and the acid, the amount of salts in the treatment liquid is also reduced.
[0057]
(2). The amount of biogas recovered can be increased by solubilizing and acid fermenting individually or mixed according to the type of the object to be treated.
[0058]
(3). The discharge amount of methane fermentation sludge can be reduced by the above (2), and the final treatment amount to be composted and incinerated is reduced.
[0059]
(4). The speed of methane fermentation can be increased, and the apparatus can be made more compact.
[Brief description of the drawings]
FIG. 1 is a flowchart of a methane fermentation system according to a first embodiment of the present invention.
FIG. 2 is a flowchart of a methane fermentation system according to a second embodiment of the present invention.
FIG. 3 is a flowchart of a conventional methane fermentation system for general waste.
FIG. 4 is a diagram showing the elemental composition of various wastes and methane fermentation sludge.
[Explanation of symbols]
1: General waste, 2: Crusher, 3: Water, 4: Solubilization tank, 5: Stirrer, 6: Valve, 7: Storage tank, 8: Stirrer, 9: Pump, 10: Methane fermentation tank, 11: Gas holder, 12: Pump, 13: Sludge settling tank, 14: Condensed sludge, 15: Wastewater, 16: Pump, 17: Switching valve, 18: Sludge return line, 19: Sludge extraction line, 20: Pump, 21: Wastewater line , 22: vegetable waste, 23: crusher, 24: alkali solubilization tank, 25: alkali addition line, 26: N addition line, 27: animal waste, 28: crusher, 29: acid fermentation tank , 30: stirrer, 31: alkali addition line, 32: C addition line, 33: methane fermentation tank, 34: wastewater line, 35: valve, 36: pump, 37: control unit, 38: pump, 39: pump, 41: pump, 42: pH meter, 43 Valve, 44: acid addition line, 45: switching valve, 46: sludge return line, 47: wet pulverizer 48: circulation line, 49: switching valve, G: Biogas

Claims (10)

A solubilization tank that adds an alkali to a treatment target mainly composed of a plant substance and solubilizes the same;
An acid fermentation tank in which an alkaline solubilized slurry generated in the solubilization tank and an object to be processed mainly composed of animal substances are charged, mixed and acid fermented, and
A methane fermentation tank for methane fermenting the solubilized organic acid-containing slurry produced in the acid fermentation tank. 2. The methane fermentation treatment apparatus according to claim 1, wherein a pH meter for measuring a pH value in the acid fermentation tank and an amount of the alkaline solubilized slurry added to the acid fermentation tank are adjusted based on a measurement result of the pH meter. And a methane fermentation treatment apparatus. 3. The methane fermentation treatment apparatus according to claim 1, wherein the methane fermentation tank has at least one of an alkali addition line for adding an alkali and an acid addition line for adding an acid to the acid fermentation tank. Processing equipment. The methane fermentation apparatus according to claim 1, further comprising a sludge return line for returning a part of the sludge generated in the methane fermentation tank to the solubilization tank. 2. The methane fermentation apparatus according to claim 1, further comprising at least one of a stirrer, an ultrasonic generator, and a wet pulverizer for pulverizing a solid content in the alkaline solubilized slurry. apparatus. A solubilization step of adding an alkali to a substance to be treated mainly composed of a plant substance to solubilize the substance,
An acid fermentation step of adding and mixing the generated alkaline solubilized slurry and a substance mainly composed of animal substances to produce an acid,
A methane fermentation step of fermenting methane from the obtained organic acid-containing solubilized slurry. 7. The methane fermentation treatment method according to claim 6, wherein a pH value of the solubilized slurry in the acid fermentation step is measured, and a supply amount of the alkaline solubilized slurry to the acid fermentation step is adjusted based on the measurement result. A methane fermentation treatment method comprising: The methane fermentation treatment method according to claim 6 or 7, wherein at least one of an alkali addition line and an acid addition line is provided for the acid fermentation step, and the pH of the solubilized slurry during the acid fermentation step is adjusted. A methane fermentation treatment method comprising measuring a value and adding one of an alkali and an acid based on the measurement result. 7. The methane fermentation treatment method according to claim 6, wherein a part of the sludge generated in the methane fermentation step is returned to the solubilization step. The methane fermentation treatment method according to claim 6, wherein the content of carbon and nitrogen in the organic acid-containing solubilized slurry to be supplied to the methane fermentation step is maintained within the range of the methane fermentation conditions. A methane fermentation process comprising adjusting at least one input amount of an object to be processed, an object to be processed mainly composed of an animal substance, and sludge generated in a methane fermentation step returned to the solubilization step. Method.

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