Methane fermentation method, methane fermentation promoter and its manufacturing method

Abstract

To provide a methane fermentation method that can manufacture biogas containing methane with good efficiency from organic waste while using glycerin, and a methane fermentation accelerant which can accelerate methane fermentation.SOLUTION: In a methane fermentation method that inputs organic waste into a methane fermentation system and manufactures biogas containing methane, a methane fermentation accelerant is used in combination with the organic waste, the methane fermentation accelerant contains glycerin, and n-hexane extract is 10,000 mg / kg or less. According to the present invention, the methane fermentation accelerant and a method for manufacture thereof are also provided.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a methane fermentation method in which organic waste is introduced into a methane fermentation system to produce methane-containing biogas, and in particular to a method in which a specific methane fermentation promoter is used in combination with the organic waste. The present invention also relates to the methane fermentation promoter used in the methane fermentation method and a method for producing the same. [Background technology]

[0002] Organic waste such as food waste, sludge from sewage treatment plants, and livestock manure has traditionally been considered biomass resources, and energy has been recovered from them. Methane fermentation is one of the most effective means of recovering energy from these organic wastes.

[0003] From the viewpoint of preventing global warming, development of alternative fuels to conventional fossil fuels that reduce carbon dioxide emissions and lead to resource recycling is underway, and one such fuel that has attracted attention is biodiesel fuel, which is made from vegetable oils, waste cooking oil, etc. The mainstream method for synthesizing biodiesel fuel is a method in which fats and oils from animals and plants, waste cooking oil, etc., and monohydric alcohol are used as raw materials, and an alkaline substance is used as a catalyst to synthesize the fuel through a transesterification reaction (e.g., Non-Patent Document 1). This synthesis reaction also produces a by-product containing glycerin (waste glycerin).

[0004] In addition, methods for industrially producing free fatty acids from fats and oils include high-temperature, high-pressure hydrolysis and enzymatic hydrolysis, all of which involve hydrolyzing fats and oils derived from animals, plants, etc. to liberate fatty acids. Even in such hydrolysis, by-products containing glycerin are produced.

[0005] Glycerin-containing waste contains many impurities such as catalysts and unreacted oils and fats. Therefore, although glycerin itself can be used as a raw material for pharmaceuticals, cosmetics, etc., the above-mentioned glycerin-containing waste must be purified at great expense in order to be used as a raw material for pharmaceuticals, cosmetics, etc., which is not practical. For this reason, glycerin-containing waste has often been disposed of as industrial waste.

[0006] In this situation, a method has been proposed in which glycerin-containing waste such as waste glycerin is mixed with food waste and the like and used as a raw material for the above-mentioned methane fermentation (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-348191 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-279411 [Non-patent literature]

[0008] [Non-Patent Document 1] Journal of the Japan Society of Marine Engineering, 2012, Vol. 47, No. 1, pp. 45-50 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the above-mentioned glycerin-containing waste is known to have an inhibitory effect on methane fermentation, and therefore it has not been possible to add it as a raw material for methane fermentation in a very small amount, which is not sufficient from the viewpoint of effective utilization of the glycerin-containing waste.

[0010] The present invention has been made in consideration of the above problems, and aims to provide a methane fermentation method that can efficiently produce methane-containing biogas from organic waste while utilizing glycerin, and a methane fermentation promoter that can promote methane fermentation. [Means for solving the problem]

[0011] The present inventors have discovered that in methane fermentation using organic waste as a raw material, a specific composition containing glycerin can promote methane fermentation rather than inhibit it, and have thus completed the present invention. Specifically, the present invention is as follows.

[0012] [1] A methane fermentation method in which organic waste is introduced into a methane fermentation system to produce biogas containing methane, A methane fermentation promoter is used in combination with the organic waste, The methane fermentation promoter contains glycerin and has an n-hexane extractable substance content of 10,000 mg / kg or less. A methane fermentation method characterized by: [2] The methane fermentation method according to [1], wherein the glycerin content in the methane fermentation promoter is 600,000 mg / kg or more. [3] COD of the methane fermentation promoter Cr and COD of the organic waste Cr The methane fermentation method according to [1] or [2], wherein the methane fermentation promoter is used in a ratio of 10:1 to 1:10. [4] A method for producing a methane fermentation promoter to be added to a methane fermentation system in combination with organic waste, comprising: a first separation step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating the mixture into a first oil component and a first glycerin-containing liquid; a neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance; a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized first glycerin-containing liquid; A method for producing a methane fermentation promoter, comprising: [5] The method for producing a methane fermentation promoter according to [4], further comprising an alcohol removal step of removing monohydric alcohol after the second separation step. [6] The method for producing a methane fermentation promoter according to [4] or [5], wherein in the first separation step, the mixed liquid of the raw material and the inorganic acid has a pH of 3 or less. [7] The method for producing a methane fermentation promoter according to any one of [4] to [6], wherein in the neutralization step, the first glycerin-containing liquid is neutralized to have a pH of 4 to 8. [8] A methane fermentation promoter for promoting methane fermentation in a methane fermentation method in which organic waste is introduced into a methane fermentation system to produce biogas containing methane, comprising: Contains glycerin and has n-hexane extractables of 10,000 mg / kg or less. Used in combination with the organic waste A methane fermentation promoter characterized by: [9] The methane fermentation promoter according to [8], characterized in that the glycerin content is 600,000 mg / kg or more. [Effects of the Invention]

[0013] According to the methane fermentation method of the present invention, biogas containing methane can be efficiently produced by methane fermentation using organic waste as a raw material. Furthermore, the methane fermentation promoter of the present invention can promote methane fermentation using organic waste as a raw material. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing a flow of a method for producing a methane fermentation promoter according to one embodiment of the present invention. [Figure 2]FIG. 1 is a diagram showing the flow of an esterification step (second esterification step) provided in a preferred embodiment of the present invention. [Figure 3] FIG. 1 is a schematic diagram showing an experimental apparatus used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described. [Methane fermentation method, methane fermentation promoter] A methane fermentation method according to one embodiment of the present invention is a methane fermentation method in which organic waste is introduced into a methane fermentation system to produce biogas containing methane, and a methane fermentation promoter containing glycerin is used in combination with the organic waste.

[0016] (1) Methane fermentation system As used herein, the term "methane fermentation system" refers to an organic mixture in which various anaerobic microorganisms, primarily methanogens (hydrolytic bacteria, acid-producing bacteria, methanogens, etc.), have taken root, and which is capable of decomposing organic matter and carrying out methane fermentation. The methane fermentation system may be obtained by subjecting organic waste such as sewage sludge or animal manure to anaerobically treating to allow the above-mentioned anaerobic microorganisms to settle, or a portion of the methane fermentation system may be collected and used from another methane fermenter that is in stable operation. Such a methane fermentation system contains a certain amount of essential elements for methane fermentation and can cause a methane fermentation reaction by itself, but in a typical methane fermentation method, organic waste, as described below, is also added as a raw material.

[0017] (2) Organic waste In this specification, "organic waste" refers to waste containing organic matter such as organic sludge, livestock manure, food waste, food waste, rice straw, and grass clippings, which is discarded from sewage treatment facilities, sludge recycling centers, sewage treatment facilities, food factory facilities, etc., and which has traditionally been used as a raw material in methane fermentation.

[0018] The properties of the organic waste used in this embodiment are not particularly limited, but for example, COD Cr may be 10,000 mg / kg or more, or even 100,000 mg / kg or more. Here, COD (chemical oxygen demand) is an index that expresses the amount of organic matter in a composition as "oxygen consumption when decomposed by an oxidizing agent," and there are several types depending on the type of oxidizing agent used and reaction conditions. In this embodiment, the COD index is "COD Cr " COD Cr can be measured, for example, in accordance with JIS K0102.

[0019] In addition, when the organic waste used in this embodiment is used alone for methane fermentation, the COD Cr Even if the decomposition rate is low, it can be used suitably. Cr The decomposition rate is the decomposition COD Cr COD of input raw material Cr The value is calculated by dividing by . Cr is methane generation / decomposition COD Cr =0.35nm 3 / kg·COD Cr This is the value calculated from the amount of methane generated. Cr The decomposition rate can be said to be an index that indicates the efficiency of carbon source utilization in methane fermentation. When used alone, COD Cr Organic waste with a low decomposition rate has little value as a raw material for methane fermentation. The residue after the methane fermentation reaction is called digested liquid, which requires wastewater treatment. Cr Using raw materials with low decomposition rates places a heavy burden on wastewater treatment and is costly. In contrast, according to a preferred aspect of the present embodiment, by using the methane fermentation promoter in combination with the above-mentioned methane fermentation promoter, for example, CrThis improves the decomposition rate. As a result, even organic waste, which has traditionally been considered to have little utility value, can be suitably used for methane fermentation. Furthermore, wastewater treatment of the digested liquid becomes easier.

[0020] Furthermore, the organic waste used in this embodiment may have a glycerin content of 100,000 mg / kg or less, or even 10,000 mg / kg or less, or may contain no glycerin at all. This is because organic waste containing a relatively high concentration of glycerin often also contains a high concentration of oil, and this oil may reduce the efficiency of methane fermentation, and because the efficiency of methane fermentation is improved by producing a methane fermentation promoter by the method described below and using it in combination with other organic waste, rather than using the waste as is as a carbon source for methane fermentation.

[0021] (3) Methane fermentation promoter The methane fermentation promoter used in this embodiment contains glycerin. The methane fermentation promoter containing glycerin can promote the methane fermentation reaction by being used in combination with the organic waste described above in methane fermentation.

[0022] Glycerin is a trihydric alcohol with three carbon atoms, and is converted into acetic acid, propionic acid, etc. by anaerobic microorganisms (e.g., acid-producing bacteria) that are established in methane fermentation systems, which then serve as raw materials for methane fermentation reactions by methanogens, etc. In other words, glycerin can be said to be useful as a methane fermentation raw material on its own. However, as shown in the examples below, by using a methane fermentation promoter containing glycerin in combination with organic waste, the methane fermentation reaction is promoted not only when the organic waste is used as a raw material alone, but also when the methane fermentation promoter is used as a raw material alone. The effect of this embodiment is not limited to a specific mechanism of action, but for example, because glycerin is a carbon source that is easily utilized not only by methanogens but also by other anaerobic microorganisms (e.g., hydrolytic bacteria, acid-producing bacteria, etc.) that have settled in the methane fermentation system, it is presumed that not only methanogens but also other anaerobic microorganisms are activated, optimizing the overall balance of the methane fermentation system. Furthermore, optimizing the balance of the methane fermentation system is presumed to enable efficient use of not only glycerin (methane fermentation promoter) but also organic waste in the methane fermentation reaction, thereby promoting the methane fermentation reaction as a whole. However, the methane fermentation promoting effect of this embodiment is not limited to the promoting effect based on such an action mechanism.

[0023] The glycerin content in the methane fermentation promoter is preferably 600,000 mg / kg or more, more preferably 700,000 mg / kg or more, and particularly preferably 900,000 mg / kg or more. The upper limit of the glycerin content in the methane fermentation promoter is not particularly limited and may be, for example, 100% (1,000,000 mg / kg), but such a high purity is not particularly required.

[0024] The methane fermentation promoter used in this embodiment preferably has an n-hexane extractable substance (n-Hex) content of 10,000 mg / kg or less, more preferably 5,000 mg / kg or less, and particularly preferably 2,000 mg / kg or less. n-Hex is a general term for non-volatile substances extracted with n-hexane, an organic solvent, and is used as an indicator of the amount of "oil, etc." in water. n-Hex can be measured by the extraction-gravimetric method in Appendix 4 of Notification No. 64 of the Ministry of the Environment, 1974. The methane fermentation promoter of this embodiment has a low n-Hex value, in other words, oil is removed, thereby improving the efficiency of methane fermentation.

[0025] In addition to the above, the methane fermentation promoter used in this embodiment may have the following properties. COD of the above methane fermentation promoter Cr The COD of the methane fermentation promoter is preferably 730,000 mg / kg or more, more preferably 850,000 mg / kg or more, and particularly preferably 1,100,000 mg / kg or more. Cr There is no particular upper limit to the COD when glycerin is 100%. Cr (1,220,000 mg / kg) is also acceptable, but Cr is not particularly required.

[0026] In this embodiment, the methane fermentation promoter is used in combination with the organic waste described above. Here, the above-mentioned "use in combination" includes not only an embodiment in which the methane fermentation promoter and organic waste are mixed and then introduced into a methane fermentation system, but also an embodiment in which the methane fermentation promoter and organic waste are introduced into the methane fermentation system separately without being mixed. However, when introducing them into the methane fermentation system separately, from the viewpoint of effectively exerting the methane fermentation promotion effect, it is preferable to introduce the methane fermentation promoter and organic waste simultaneously, or to start introducing one of them within a predetermined time (for example, within 24 hours) after the completion of introduction of the other.

[0027] The ratio of the methane fermentation promoter to the organic waste can be adjusted appropriately from the viewpoint of obtaining the methane fermentation promoting effect. For example, Cr and COD of organic waste Cr It is preferable to use the methane fermentation promoter so that the ratio (methane fermentation promoter:organic waste) is 10:1 to 1:10. When the ratio of the methane fermentation promoter to the organic waste used is within the above range, the methane fermentation promotion effect is more effectively exhibited.

[0028] (4) Auxiliary raw materials In this embodiment, in addition to the organic waste and methane fermentation promoter described above, chemical substances containing phosphorus or nitrogen may be used as auxiliary raw materials, such as phosphoric acid, phosphates, ammonia, and ammonium salts, specifically ammonium phosphate, ammonium chloride, ammonium sulfate, phosphoric acid, potassium phosphate, magnesium phosphate, etc. These auxiliary raw materials are input into the methane fermentation system together with the organic waste and methane fermentation promoter described above.

[0029] (5) Methane fermentation reaction In a methane fermentation reaction, a methane fermentation system in which various anaerobic microorganisms, primarily methanogens, are established is typically placed in a methane fermentation tank, which serves as a reaction vessel, and the reaction conditions are maintained under anaerobic conditions. In addition to organic waste as a raw material, auxiliary materials, and other organic matter and essential elements that promote methane fermentation are also added to the methane fermentation system, forming a mixture. It is preferable that the methane fermentation tank be equipped with an agitator so that the methane fermentation system, raw materials, methane-producing bacteria, etc. are uniformly dispersed and the methane fermentation reaction proceeds. The methane fermentation method of this embodiment is characterized in that it uses organic waste that has traditionally been used as a raw material for methane fermentation in combination with the methane fermentation promoter described above. However, other than that, the method can be carried out in the same way as conventional methane fermentation, so that existing methane fermentation equipment, etc. can be used as is.

[0030] In the methane fermentation tank, the mixture is decomposed by anaerobic microorganisms, and as the methane fermentation reaction progresses, biogas containing methane and digested liquid are produced. Specifically, in the methane fermentation tank, biogas, mainly consisting of methane gas produced by methane fermentation, accumulates in the hollow part at the top of the fermentation tank, and digested liquid is stored in the lower part. In this embodiment, either mesophilic fermentation, in which the temperature inside the fermenter is maintained at around 37°C, or thermophilic fermentation, in which the temperature inside the fermenter is maintained at around 55°C, may be used, and it is preferable to carry out methane fermentation while stirring the contents in an anaerobic atmosphere.

[0031] The methane fermentation reaction performed in this embodiment may be a batch type in which the reaction is started after all raw materials are charged into a methane fermentation tank and the generated biogas is appropriately collected, or a continuous type in which the raw materials are continuously charged into the methane fermentation tank and the generated biogas is continuously collected. In methane fermentation, the generated biogas can be easily separated from the digestate and can also be easily collected continuously, so a continuous type can also be preferably used. When methane fermentation is carried out continuously, the COD Cr Load: 2 to 20 kg / m 3 It is preferable to appropriately adjust the input amounts of organic waste and methane fermentation promoter so that the COD in the methane fermentation tank is within the range of 1 / 2 day. Cr Load 5 to 10 kg / m 3 ·Day. COD Cr If too much load is applied, methane fermentation will not proceed smoothly. Cr By adjusting the load in the fermentation tank to the desired range, it becomes easier to maintain the rate of methane fermentation. Cr The load can be adjusted by adjusting the input amount, dilution amount, flow rate, etc. of the organic waste and the methane fermentation raw materials such as the methane fermentation promoter.

[0032] Furthermore, from the viewpoint of efficiently progressing the methane fermentation reaction, it is preferable to adjust the total nitrogen (TN) concentration in the methane fermentation tank to 100 to 10,000 mg / L, and more preferably to 500 to 5,000 mg / L. While the nitrogen components contained in the methane fermentation raw material are used for the synthesis of bacterial cells, ammonia, which is a decomposition product, can inhibit methane fermentation, so it is preferable to adjust the mixing ratio or dilution. By adjusting the TN to be within the above range, methane fermentation proceeds smoothly and the amount of methane produced increases. The TN in the methane fermentation tank can be adjusted by adjusting the amount of organic waste, which is the main raw material, and the amount of auxiliary raw materials, etc., added. Total nitrogen (TN) indicates the total amount of nitrogen compounds contained in the composition, and can be measured in accordance with the "Kjeldahl nitrogen method" in Section 18, Chapter 1, Volume 5 of the Sewage Testing Methods.

[0033] The total phosphorus (TP) in the methane fermentation tank can be adjusted to 100 mg / L or more. The total phosphorus (TP) is the total amount of phosphorus compounds contained in the composition and can be measured in accordance with JIS K0102-46.3.2 "Nitric acid-perchloric acid decomposition method."

[0034] The methane-containing biogas produced in the methane fermentation tank is recovered as appropriate and used as fuel for power generation, etc., and after purification, it can be used for various purposes as high-purity methane gas.

[0035] [Method for producing methane fermentation promoter] The methane fermentation promoter according to the above-described embodiment can be used without any particular limitation as long as it satisfies the above requirements. However, the production method described below is particularly suitable because it allows a methane fermentation promoter that satisfies the above requirements to be produced inexpensively from industrial waste or the like. Specifically, a method for producing a methane fermentation promoter according to one embodiment of the present invention comprises: a first separation step of mixing a raw material containing glycerin and at least one type of fatty acid glycerin ester with an inorganic acid and separating a first oil component and a first glycerin-containing liquid; a neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance; and a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized first glycerin-containing liquid.

[0036] Fig. 1 is a diagram showing the flow of a particularly preferred embodiment of the method for producing a methane fermentation promoter according to this embodiment. Fig. 1 illustrates a method for obtaining a methane fermentation promoter by a first separation step in which an inorganic acid is mixed with a raw material containing a glycerin-containing waste or a fatty acid glycerin ester-containing waste to separate and remove a first oil component, a subsequent neutralization step of the first glycerin-containing liquid, a second separation step in which a second oil component and inorganic salts are separated and removed from the neutralized glycerin-containing liquid, and a subsequent alcohol removal step in which a monohydric alcohol is separated and removed from the second glycerin-containing liquid. The alcohol removal step is an optional step, and the second glycerin-containing liquid may be used as a methane fermentation promoter without going through the alcohol removal step.

[0037] (6) Raw materials for methane fermentation promoters The raw material for the methane fermentation promoter used in this embodiment is not particularly limited as long as it contains at least one of glycerin and fatty acid glycerin esters. An example of a raw material containing glycerin is waste containing glycerin. On the other hand, raw materials containing fatty acid glycerin esters can also be suitably used because glycerin is produced by an acid-catalyzed transesterification reaction or the like in the first separation step described below. Furthermore, when the esterification step (second esterification step) described below is performed, it is preferable to use raw materials containing fatty acid glycerin esters as the raw material for the methane fermentation promoter. In this specification, the term "fatty acid glycerin ester" refers to an ester of a fatty acid and glycerin, and includes triglycerides, diglycerides, and monoglycerides. The glycerin-containing waste and the fatty acid glycerin ester-containing waste will be described in more detail below.

[0038] (6-1) Glycerin-containing waste Examples of the glycerin-containing waste used in this embodiment include waste glycerin produced as a by-product in the production process of biodiesel fuel, glycerin waste liquid produced as a by-product in the production process of free fatty acids, sweet water, and wastewater from washing fatty acid alkyl esters.

[0039] Here, the glycerin waste liquid produced as a by-product in the production process of free fatty acids refers to a waste product produced as a by-product when free fatty acids are produced by hydrolyzing animal and vegetable fats and oils. Methods for producing free fatty acids by hydrolysis include high-temperature, high-pressure decomposition and enzymatic decomposition. The glycerin waste liquid produced as a by-product in such a production process contains, in addition to glycerin, unreacted fats and oils, partially hydrolyzed fats and oils, etc. Sweet water is a by-product produced when fats and oils are saponified (alkaline hydrolysis) to produce fatty acid salts (for example, in the soap manufacturing process), and contains glycerin, water, alkali, etc. The wastewater from washing fatty acid alkyl esters is wastewater generated when reaction products are washed during the production process of fatty acid alkyl esters, including biodiesel fuel. In addition to water, it contains glycerin, which is a by-product of the fatty acid alkyl ester production reaction, as well as unreacted free fatty acids and their salts, monohydric alcohols, etc.

[0040] Next, we will explain in some detail about waste glycerin, which is a by-product in the biodiesel fuel manufacturing process. Fatty acid alkyl esters, which are used to make biodiesel fuel, are obtained by adding a monohydric alcohol such as methanol and an alkaline catalyst such as potassium hydroxide to raw oils and fats such as vegetable oil, and then carrying out an ester exchange reaction.

[0041] Examples of raw oils and fats that can be used for biodiesel fuel include vegetable oils such as rapeseed oil, palm oil, olive oil, sunflower oil, soybean oil, rice oil, and hemp oil; fish oil, lard, and animal fats such as beef and pork; and waste cooking oils such as tempura oil. As the monohydric alcohol, methanol, ethanol, 1-propanol, ethylhexanol, etc. can be used, with methanol and ethanol being preferred, and methanol being particularly preferred. As the alkaline catalyst, potassium hydroxide, sodium hydroxide, calcium oxide, etc. can be used, but potassium hydroxide is preferred from the viewpoint of the precipitability and ease of reuse of the salt separated and recovered in this embodiment.

[0042] In the transesterification reaction, fatty acid glycerol esters contained in the raw oil react with monohydric alcohol to produce fatty acid alkyl esters and glycerol. The resulting reaction liquid is separated into a fatty acid alkyl ester phase and a waste glycerol phase. In the production of biodiesel fuel, the resulting fatty acid alkyl ester phase is recovered and washed to produce biodiesel fuel.

[0043] On the other hand, the waste glycerin phase contains a high concentration of glycerin as well as unreacted monohydric alcohol (particularly methanol), unreacted fats and oils (fatty acid glycerin esters), fatty acids and their salts, alkali catalysts, and impurities derived from the raw fats and oils, etc. The waste glycerin may be liquid or solid, but liquid waste glycerin is preferred from the viewpoints of workability, handling, etc. The contents of glycerin, monohydric alcohol, fats and oils, and fatty acids and salts thereof in the waste glycerin are not particularly limited, but typically, based on the total amount of waste glycerin, glycerin accounts for 25% by mass or more and 65% by mass or less, monohydric alcohol for 2% by mass or more and 20% by mass or less, and the total amount of fats and oils, fatty acids and salts thereof for 30% by mass or more and 50% by mass or less.

[0044] Since waste glycerin contains a large amount of alkaline catalyst, the pH is often 9 or higher, and may be 9 to 13 in this embodiment. In the first separation step, from the viewpoint of facilitating the progress of the acid-catalyzed esterification reaction between the unreacted fats and oils contained in the waste glycerin and the monohydric alcohol, the water content in the waste glycerin is preferably 5% by mass or less, and particularly preferably 3% by mass or less. The water content in the waste glycerin can be appropriately adjusted by heating, reducing pressure, using a desiccant, or allowing the waste glycerin to permeate through purified glycerin.

[0045] Glycerin can be used as a raw material for pharmaceuticals, cosmetics, etc., but in order to use the glycerin contained in waste glycerin for such purposes, it must be purified to a high purity, which requires a great deal of cost and energy. Therefore, the utility value of waste glycerin as glycerin is quite low, and it has traditionally been difficult to process. However, according to this embodiment, waste glycerin can be used as the main raw material for the methane fermentation promoter, and the environmental impact can be reduced from the perspective of effectively utilizing waste glycerin, which is an industrial waste. Furthermore, because the methane fermentation promoter produced from such waste glycerin is made from carbon-neutral natural fats and oils, the energy produced by methane fermentation, such as biogas, electricity, and heat, can be classified as renewable energy.

[0046] In this embodiment, from the viewpoint of ease of use in the first separation step described below, it is preferable to use, among the above-mentioned glycerin-containing wastes, at least one of waste glycerin produced as a by-product in the production process of biodiesel fuel and a glycerin waste liquid produced as a by-product in the production process of free fatty acids, and it is particularly preferable to use waste glycerin produced as a by-product in the production process of biodiesel fuel.

[0047] (6-2) Fatty acid glycerin ester-containing waste In this embodiment, waste containing fatty acid glycerin esters can also be used as a raw material for the methane fermentation promoter. In this embodiment, the first separation step using an inorganic acid, the neutralization step, and the second separation step are performed, so that the yield of glycerin can be increased by using a raw material containing fatty acid glycerin esters and performing an acid-catalyzed esterification reaction in the first separation step. Examples of waste containing fatty acid glycerin esters include waste cooking oil, expired oil-containing foods (tempura oil, mayonnaise, dressing, butter, cream, cheese, etc.), animal and vegetable oils, and oils with high acid value (grease trap oil, sewage oil, gutter oil, reclaimed oil from waste liquid treatment, etc.) whose main component is fatty acid glycerin esters; and compositions whose main component is fatty acid salts, such as oil cakes and soap. In this specification, "main component" means the component with the highest content in the composition (however, if the component with the highest content is water, the component with the second highest content), and the content is preferably 40% by mass or more, and more preferably 50% by mass or more.

[0048] Here, the high acid value oil refers to fats and oils with an acid value of 10 mgKOH / g or more, and includes fatty acid glycerol esters, which are the main components of fats and oils, as well as free fatty acids. The acid value may be 20 mgKOH / g or more, or even 50 mgKOH / g or more. The upper limit of the acid value is usually 200 mgKOH / g or less. Sodash is a by-product separated from oils and fats (crude oil) during the deacidification process in the refining of vegetable oils and fats, and contains fatty acid salts, fatty acid glycerin esters, alkali, water, etc.

[0049] In addition, compositions other than those exemplified above can also be used as long as they contain fatty acid glycerin esters. For example, waste glycerin, which is a by-product in the production process of biodiesel fuel and is exemplified as a glycerin-containing waste, contains unreacted fats and oils (i.e., fatty acid glycerin esters), and therefore can also be used as a fatty acid glycerin ester-containing waste.

[0050] (7) First separation step The first separation step is a step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid, and subjecting the mixture to phase separation into a first oil component and a first glycerin-containing liquid. The oil fraction separated in this step includes fatty acid alkyl esters, fatty acid glycerol esters, and free fatty acids.

[0051] When a raw material containing glycerin is used, particularly when waste glycerin is used, in this process, the salts of fatty acids contained in the waste glycerin are converted to free fatty acids by an inorganic acid. Furthermore, the fatty acids and their salts undergo an esterification reaction with unreacted monohydric alcohol contained in the waste glycerin using the inorganic acid as an acid catalyst to produce fatty acid alkyl esters.

[0052] When a waste material containing fatty acid glycerin esters is used as a raw material, a fatty acid alkyl ester and glycerin are produced by a transesterification reaction with a monohydric alcohol. In this case, the monohydric alcohol can be added separately, and for example, the monohydric alcohol recovered in the alcohol separation step described below can be used. Furthermore, by treating the waste material containing fatty acid glycerin esters simultaneously, the unreacted monohydric alcohol contained in the waste glycerin can be utilized. When the first separation step is carried out in the presence of a monohydric alcohol, this step can also be referred to as an acid-catalyzed esterification step. In contrast to the second esterification reaction described below, the first separation step may also be referred to as a "first esterification step."

[0053] Even if the raw material does not contain a monohydric alcohol, the fatty acid glycerin ester generates free fatty acids and glycerin in the presence of an acid in the first separation step. Furthermore, if the raw material contains a fatty acid salt, the fatty acid salt is converted into free fatty acid by the acid, which makes it easier to separate it from glycerin. Therefore, even when the raw material does not contain a monohydric alcohol, this embodiment can be suitably applied.

[0054] In this embodiment, since the first separation step is performed in the presence of an inorganic acid, a variety of raw materials can be simultaneously treated. Furthermore, by performing the first separation step, waste materials containing glycerin and fatty acid glycerin esters, such as waste glycerin, waste cooking oil, and high acid value oil, can be effectively utilized, which can also contribute to reducing the environmental load. In particular, high acid value oils have a high acid value of 10 mg KOH / g or more, making them difficult to use as a raw material for the above-mentioned alkali-catalyzed transesterification reaction. However, in the first separation step, which can be called an acid-catalyzed esterification reaction, high acid value oils can also be used as a suitable raw material.

[0055] When waste glycerin or waste containing fatty acid glycerin esters is used as a raw material for the methane fermentation promoter, the fatty acid alkyl esters and free fatty acids produced in the first separation step are transferred to an oil phase consisting of the first oil component, and can be separated from the first glycerin-containing liquid. When the oil phase is recovered, the resulting first oil component (fatty acid alkyl esters, free fatty acids, etc.) can be subjected to a further esterification reaction (the esterification step described below) and ultimately used as a raw material for biodiesel fuel, etc. On the other hand, the first glycerin-containing liquid is acidified by adding an inorganic acid. The first glycerin-containing liquid may contain inorganic salts formed from the inorganic acid and the alkali contained in the glycerin-containing waste. Some of the inorganic salts may be precipitated, i.e., the first glycerin-containing liquid may contain an acidic glycerin phase and precipitated inorganic salts.

[0056] The raw material that can be used in the first separation step preferably has a moisture content of 10% by mass or less, and more preferably 5% by mass or less. By using a raw material with a low moisture content (for example, waste glycerin with a low moisture content), it becomes easy to reduce the moisture content of the reaction solution described below. The moisture content of the raw material can be appropriately adjusted by heating, reducing pressure, using a desiccant, or passing the raw material through purified glycerin.

[0057] Examples of inorganic acids used in the first separation step include concentrated sulfuric acid, phosphoric acid, concentrated nitric acid, and hydrogen chloride. Concentrated sulfuric acid and phosphoric acid, which have low water contents, are preferred, and concentrated sulfuric acid is particularly preferred.

[0058] In the first separation step, the pH of the mixture (reaction liquid) of the raw material and the inorganic acid is preferably adjusted to 3 or less, and particularly preferably to 1 or less. The pH of the reaction liquid can be adjusted by the amount of the inorganic acid added. The water content of the reaction solution is preferably 10% by mass or less, and particularly preferably 0.5% by mass or less. The water content of the reaction solution can be appropriately adjusted by adjusting the water content and amount of each raw material added, using a desiccant in the reaction solution, etc. By setting the pH and water content of the reaction liquid within the above ranges, the efficiency of the acid-catalyzed esterification reaction can be increased, and the first oil component and the first glycerin-containing liquid (containing an acidic glycerin phase and inorganic salts) can be separated well.

[0059] The temperature of the reaction solution in the first separation step can be 30 to 64°C, or even 50 to 60°C. The reaction time can be 0.5 hours or more, or even 4 hours or more, or even 8 hours or more. It is preferable to stir the reaction solution during this time. There is no particular upper limit to the reaction time, but it can be, for example, within 20 hours, or even within 12 hours. After the reaction (or stirring) is completed, the mixture is allowed to stand for 0.2 to 12 hours, whereby a first oil fraction containing fatty acid alkyl esters and unreacted fats and oils is separated from a first glycerin-containing liquid containing an acidic glycerin phase and inorganic salts. The first oil fraction can be used to produce fatty acid alkyl esters by further subjecting it to an acid-catalyzed esterification reaction. Meanwhile, the first glycerin-containing liquid is subjected to the subsequent neutralization step.

[0060] (8) Neutralization process The neutralization step is a step of neutralizing the first glycerin-containing liquid obtained in the first separation step with an alkaline substance. As such an alkaline substance, hydroxides such as potassium hydroxide and sodium hydroxide can be used.

[0061] Furthermore, a substance containing glycerin can be used as the alkaline substance. Examples of such glycerin-containing alkaline substances include the waste glycerin and other by-products of alkali-catalyzed transesterification of fats and oils. These substances can not only neutralize acidic glycerin but also increase the yield of glycerin, making the use of glycerin-containing alkaline substances preferable from this perspective. Such glycerin-containing alkaline substances may contain fatty acid salts or fatty acid glycerin esters. The glycerin content of the glycerin-containing alkaline substance is preferably 25% by mass or more, particularly preferably 50% by mass or more. The upper limit is not particularly limited, but may be, for example, 99% by mass or less, or 90% by mass or less. The glycerin-containing alkaline substance preferably has a pH of 9 or higher, and particularly preferably 9 to 13.

[0062] Furthermore, the alkaline substance may be a composition containing a fatty acid salt as a main component, such as soapstock or alkaline soap.

[0063] In the neutralization step, the glycerin-containing liquid is preferably neutralized to a pH of 4 to 8, more preferably 4.5 to 7.5, and particularly preferably 5 to 7.5. Neutralizing the glycerin-containing liquid so that its pH falls within this range facilitates separation of oil and precipitation of inorganic salts in the subsequent second separation step. The pH of the glycerin-containing liquid can be appropriately adjusted by controlling the amount of alkaline substance added.

[0064] In the neutralization step, it is preferable to add the alkaline substance to the acidic glycerin-containing liquid while stirring it so that the liquid pH changes from acidic to near-neutral. As mentioned above, a substance containing a fatty acid salt may be used as the alkaline substance used for neutralization, and by using the above-mentioned addition order, the fatty acid salt is converted to free fatty acid by the acid. The free fatty acid migrates to the oil phase that separates from the glycerin-containing liquid, and is less likely to redissolve in the glycerin-containing liquid even if the pH of the glycerin-containing liquid increases. This makes separation in the subsequent second separation step even easier. In addition to the above-mentioned substances whose main components are fatty acid salts, fatty acid salts are also included in by-products of alkali-catalyzed transesterification and alkaline hydrolysis of fats and oils.

[0065] The first glycerin-containing liquid obtained in the first separation step is neutralized by the alkaline substance, and the neutralized glycerin-containing liquid is then subjected to the subsequent second separation step.

[0066] (9) Second separation step The second separation step is a step of separating the second oil component and precipitated inorganic salts from the neutralized glycerin-containing liquid obtained in the neutralization step to obtain a second glycerin-containing liquid.

[0067] The second oil component to be separated includes not only the fats and oils and fatty acids that were not separated in the first separation step and remained in the first glycerin-containing liquid, but also fats and oils and free fatty acids derived from the alkaline substance added in the neutralization step.

[0068] The inorganic salt separated in the second separation step is a salt of an inorganic acid (e.g., concentrated sulfuric acid) added in the first separation step and an alkali (e.g., potassium, sodium), preferably potassium sulfate. The alkali is contained in the raw material (e.g., waste glycerin) added in the first separation step or the alkaline substance added in the neutralization step, and the inorganic salt is precipitated in the first separation step or the neutralization step.

[0069] On the other hand, the glycerin-containing liquid contains, in addition to glycerin, monohydric alcohol derived from waste glycerin, water, etc. Oils and inorganic salts have low solubility in such a glycerin-containing liquid, so they are separated from the glycerin-containing liquid.

[0070] In this second separation step, the neutralized raw material is allowed to stand for about 3 to 12 hours, and then the upper liquid (oil) and lower liquid (glycerin-containing liquid) are separately recovered to obtain the lower liquid, which is a glycerin-containing liquid. However, it is preferable to increase the separation speed by centrifugation or the like. In such centrifugation, a three-phase separation centrifuge capable of separating the upper liquid (i.e., oil), the lower liquid (i.e., glycerin-containing liquid), and solids (i.e., inorganic salts) can be suitably used. Furthermore, when a large amount of inorganic salts precipitates, it is preferable to first separate a certain amount of inorganic salts using a centrifuge capable of solid-liquid separation, such as a decanter-type centrifuge, and then further separate the liquid phase using a three-phase separation centrifuge.

[0071] The second oil fraction obtained in the second separation step can be used to produce fatty acid alkyl esters, for example, by combining it with the first oil fraction separated in the first separation step and subjecting it to a further acid-catalyzed esterification reaction (the esterification step described below). Specifically, the second oil fraction obtained in the second separation step can be used as a raw material for producing fatty acid methyl esters (FAME), which are used as biodiesel fuel. That is, methanol and a catalyst are added to this oil fraction to cause a methyl esterification reaction. Furthermore, the inorganic salts can be used as raw materials for inorganic fertilizers, etc., after undergoing a washing process, for example. On the other hand, the second glycerin-containing liquid obtained as described above can be used as a methane fermentation promoter as it is, but when monohydric alcohol derived from raw materials, etc. is to be removed, it may be further subjected to an alcohol removal step. Furthermore, subjecting the second glycerin-containing liquid to an alcohol removal step may be preferable from the viewpoints of improving the efficiency of methane fermentation, workability, and avoiding the need to handle the second glycerin-containing liquid as a hazardous material. On the other hand, from the viewpoint of reducing the operating costs required for alcohol removal or when the presence of a monohydric alcohol in the second glycerin-containing liquid is not a problem (for example, when the raw material does not contain a monohydric alcohol and the second glycerin-containing liquid does not contain a monohydric alcohol), the second glycerin-containing liquid may be used as it is as a methane fermentation promoter without being subjected to the alcohol removal step.

[0072] (10) Alcohol removal process The alcohol removal step is a step of removing monohydric alcohol (such as methanol) from the second glycerin-containing liquid obtained in the second separation step, and is an optional step that is carried out as needed. The second glycerin-containing liquid may contain a monohydric alcohol derived from the waste glycerin and remaining in the first separation step (acid-catalyzed esterification reaction). Although the monohydric alcohol can be used as a methane fermentation promoter even if it remains, removing it can improve the efficiency of promoting methane fermentation.

[0073] In the step of separating and removing the monohydric alcohol, a vacuum distillation method, a gas-liquid contact method, a membrane separation method, or the like can be used. In vacuum distillation, a glycerin-containing liquid is heated (for example, to about 60°C) to evaporate a monohydric alcohol such as methanol, and then the pressure is reduced to separate the monohydric alcohol. The separated monohydric alcohol can be recovered by cooling. The gas-liquid contact method is a method in which a glycerin-containing liquid is brought into contact with a gas phase in the form of fine droplets, and a monohydric alcohol having a low boiling point is transferred to the gas phase and separated. Specifically, a spray drying method or the like can be suitably employed. Membrane separation is a method that uses a membrane that preferentially allows monohydric alcohols to permeate. Incidentally, the monohydric alcohol such as methanol recovered by distilling the second glycerin-containing liquid can be actively used in the production of biodiesel fuel.

[0074] The second glycerin-containing liquid may further contain water. Such water does not interfere with the methane fermentation promoting effect and may remain in the methane fermentation promoter, but in methods such as reduced pressure distillation and gas-liquid contact, the water can be removed because it transfers to the gas phase together with the monohydric alcohol. Further, before or after the alcohol separation step for separating the monohydric alcohol, a further purification treatment may be carried out using an ion exchange method or activated clay, diatomaceous earth, carbon, zeolite, or the like.

[0075] The monohydric alcohol separated in this step can be reused as a raw material for alkali-catalyzed transesterification or acid-catalyzed esterification, either directly or after purification by redistillation or the like, if necessary, or as a washing liquid for the inorganic salts separated in the second separation step.

[0076] The glycerin produced by the method according to this embodiment has high purity and can be suitably used for the methane fermentation promoter according to the above-described embodiment. According to this production method, by carrying out the first separation step, neutralization step, and second separation step described above, it is possible to obtain purified glycerin that can be used for a methane fermentation promoter, even though industrial waste such as waste glycerin can be used as a raw material, and the method is relatively simple.

[0077] The second glycerin-containing liquid obtained by the above method can be used as a methane fermentation accelerator, as described below, as well as for a variety of other applications, such as a stripper for asphalt-containing compositions or cement-containing compositions, a denitrifier used as an organic carbon source in biological nitrification denitrification treatments, and an industrial raw material (e.g., a raw material for fatty acid glycerin esters). Furthermore, by further subjecting the liquid to a process such as distillation, it can also be used in applications requiring even higher purity (e.g., cosmetics, food and beverages, pharmaceuticals, etc.).

[0078] (11) Esterification step In the first and second separation steps described above, first and second oil fractions are recovered from the separated oil phase, respectively. These can be recycled and supplied as raw materials for the production of fatty acid alkyl esters using an alkali catalyst method. However, because their purity is not necessarily high, using them as raw materials as is can make it difficult to efficiently produce fatty acid alkyl esters. Furthermore, the first and / or second oil fractions contain oils and fats with high acid values, such as free fatty acids. The first oil fraction, in particular, is an acidic oil because it was separated in the first separation step (first esterification step), which can also be considered an esterification reaction using an acid catalyst. Therefore, it is even more difficult to use the first and second oil fractions directly as raw materials for the production of fatty acid alkyl esters using an alkali catalyst.

[0079] However, if a method other than the alkali catalyst method is used, it is possible to produce fatty acid alkyl esters even from oils and fats with a high acid value. Therefore, in this embodiment, it is preferable to include an esterification step in which fatty acid alkyl esters are produced by a method other than the alkali catalyst method. In contrast to the first separation step (first esterification step) described above, this step may be referred to as a "second esterification step."

[0080] In the second esterification step, it is preferable to use the first oil fraction separated in the first separation step and / or the second oil fraction separated in the second separation step as raw materials. As other raw materials, the same raw materials (high acid value oil, etc.) as those in the acid reaction step (first esterification step) can be used.

[0081] By using these as raw materials, industrial waste can be recycled more efficiently in the production of the methane fermentation promoter described above. These raw materials can also be suitably used as long as they are produced by a method other than the alkali catalyst method.

[0082] In the second esterification step, it is preferable to use the monohydric alcohol separated in the alcohol separation step as a raw material, which enables more efficient recycling of industrial waste in the production of the methane fermentation promoter.

[0083] Methods that can be used in the second esterification step are methods other than the alkali catalyst method, and more specifically, examples include the acid catalyst method, acid-alkali catalyst method, biocatalyst method, ion exchange resin method, supercritical method, subcritical method, and solid catalyst method. These methods can carry out transesterification with monohydric alcohols such as methanol even for waste cooking oils or fats with a high acid value, or even for fats or oils containing unreacted free fatty acids.

[0084] In the second esterification step, glycerin is by-produced together with an oil containing fatty acid alkyl esters. The oil obtained in the second esterification step and the glycerin-containing liquid can be phase-separated by standing, centrifugation, or the like. The fatty acid alkyl esters are recovered from the separated oil, and can be used as biodiesel fuel, etc. Meanwhile, the by-produced glycerin can be supplied to the neutralization step, for example, together with the first glycerin-containing liquid obtained in the first separation step (first esterification step). In this configuration, the glycerin by-produced in the second esterification step can also be made into part of the methane fermentation promoter through the neutralization step, second separation step, etc., and can be recycled more efficiently.

[0085] As the second esterification step, it is particularly preferable to employ an acid catalyst method among the methods other than the above-mentioned alkali catalyst method. As shown in Figure 2, when an acid catalyst method is used in the second esterification step, the first oil component and / or the second oil component are used as raw materials. As other raw materials, the monohydric alcohol recovered in the alcohol removal step can be used, and further, the same raw materials (high acid value oil, etc.) as those in the first separation step (first esterification step) can also be used. The reaction liquid obtained in the second esterification step is separated into an oil fraction containing fatty acid alkyl esters and a glycerin-containing liquid containing by-product glycerin, an acid catalyst and its salts, etc. The obtained oil fraction and glycerin-containing liquid are both acidic, and the acidic glycerin-containing liquid can be supplied to the neutralization step or the like.

[0086] On the other hand, oils containing fatty acid alkyl esters are preferably neutralized and dehydrated. A preferred example of a neutralization and dehydration method is a method using waste glycerin, a by-product of biodiesel fuel production. Specifically, waste glycerin, a by-product of biodiesel fuel production, is dealcoholized and stored in a tank or the like. The oil to be neutralized is then introduced into the bottom of the tank and brought into contact with the waste glycerin. This neutralizes the acidic oil with the alkali of the waste glycerin, and the water and monohydric alcohol contained in the oil are absorbed into the waste glycerin liquid. The oil introduced from the bottom overflows from the top due to the difference in specific gravity, allowing for easy recovery. This method allows for simultaneous neutralization, dehydration, and dealcoholization, allowing for the easy production of high-quality oils. The waste glycerin liquid that has absorbed the water and monohydric alcohol can be supplied to the neutralization process described above and, after a second separation process, can be used as part of the methane fermentation promoter.

[0087] In the second esterification step, preferred examples of methods other than the acid catalyst method include a biocatalytic method, a supercritical method, and a subcritical method. The biocatalytic method uses lipases or phospholipases with catalytic activity for esterification to promote transesterification. The biocatalytic method has the advantage that it can promote transesterification even with high-acid-value oils and fats, while producing few by-products, despite its mild reaction conditions. The supercritical and subcritical methods are methods that change the phase state of the material from a gas-liquid two-phase to a liquid-liquid two-phase, and then further to a single phase by lowering the dielectric constant, by adjusting the temperature and pressure to change the raw material into a supercritical or subcritical state, thereby converting a reaction system that originally required the use of a catalyst into a catalyst-free system and promoting hydrolysis.

[0088] By carrying out such a second esterification step, industrial waste can be recycled more efficiently. The obtained fatty acid alkyl ester can be shipped as biodiesel fuel, bioheavy oil, etc., or energy can be recovered by applying it to power generation, etc. That is, the method may further include a power generation step in which power is generated using the fatty acid alkyl ester obtained in the second esterification step.

[0089] The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention. [Example]

[0090] The present invention will be explained in more detail below by showing production examples, test examples, etc., but the present invention is not limited to the following examples in any way.

[0091] [Production example] Production of methane fermentation promoter (Waste glycerin preparation) Biodiesel fuel was produced by transesterification of waste cooking oil with methanol using an alkaline catalyst method with potassium hydroxide as a catalyst. The by-products produced during this process, including glycerin, were recovered as waste glycerin.

[0092] To this waste glycerin, 20 g of zeolite was added per 1 kg of waste glycerin to remove moisture. The waste glycerin to which zeolite had been added was passed through a 250 mesh filter to remove the zeolite and solid impurities. The composition and physical properties of the waste glycerin thus obtained as a raw material (hereinafter referred to as "raw material waste glycerin") are shown in Table 1.

[0093] [Table 1]

[0094] (First Separation Step) 500 kg of raw material waste glycerin and 300 kg of high acid value oil (150 mg KOH / g) were placed in a 1,000 L (liter) reactor equipped with heating and cooling functions and heated to 55°C while stirring (120 rpm). Under this condition, 32 L of concentrated sulfuric acid was added to the reactor over 15 minutes. Care was taken during the addition of concentrated sulfuric acid to ensure that the temperature of the mixture in the reactor did not exceed 65°C. The pH of the reaction solution after the entire amount of concentrated sulfuric acid was added was 1. After the addition of concentrated sulfuric acid was completed, stirring was continued for 240 minutes. The mixture was then allowed to stand for 10 hours, allowing it to separate into an oil phase (first oil) and an acidic glycerin phase (first glycerin-containing solution), and the first glycerin-containing solution (acidic glycerin phase, including precipitated potassium sulfate) was recovered. By repeating the above procedure, 5,000 kg of a first glycerin-containing solution was obtained.

[0095] (neutralization process) 5,000 kg of the first glycerin-containing liquid and 5,000 kg of waste glycerin were charged into a 15,000 L reaction tank with stirring. The pH was 7.1. Stirring was continued for another 4 hours, and then the mixture was allowed to stand for 24 hours.

[0096] (Second Separation Step) The neutralized glycerin was centrifuged at 5,500 rpm for 180 minutes in a decanter centrifuge (product name: Z18H-V, manufactured by Tanabe Wiltec Co., Ltd.), and the precipitated potassium sulfate was separated and collected. The liquid phase was further centrifuged at 8,000 rpm for 180 minutes in a three-phase separation centrifuge (manufactured by Alfa Laval), and the second oil, second glycerin-containing liquid, and potassium sulfate were separated and collected.

[0097] (Alcohol removal process) The second glycerin-containing liquid obtained in the second separation step was distilled batchwise for 10 minutes at a distillation temperature of 110°C using a vacuum distillation apparatus to separate and remove methanol and water. The resulting glycerin-containing liquid contained 870,000 mg / kg of glycerin and was used as a methane fermentation promoter.

[0098] [Test example] Methane fermentation test A methane fermentation test was carried out using the methane fermentation promoter obtained in the production example and organic waste as follows. The organic waste used was dehydrated swine manure sludge obtained from a pig farm and excess dehydrated sludge obtained from a human waste treatment facility. These were mixed in the ratios shown in Table 1 to prepare the test material for methane fermentation. The mixing ratios and properties of the test material are shown in Table 2.

[0099] Regarding methane fermentation promoters and organic waste, pH and COD Cr The concentrations of TN, TP, n-Hex extracts, and glycerin were measured. For mixed test materials, the concentrations were calculated from the mixing ratio. COD (Chemical Oxygen Demand) is an index that expresses the amount of organic matter in a composition as "oxygen consumption when decomposed by an oxidizing agent," and there are several types depending on the type of oxidizing agent used and reaction conditions. In this embodiment, the COD index is "COD Cr " can be used preferably. "COD" which uses potassium permanganate as an oxidizing agent Mn This is because the capture rate is low relative to the actual amount of organic matter. Cr was measured in accordance with JIS K0102-20.2 "Absorbance method." Next, TN (total nitrogen) indicates the total amount of nitrogen compounds contained in the composition, and was measured in accordance with the "Kjeldahl nitrogen method" in Section 18-1 of Chapter 1 of Volume 5 of the Sewage Testing Methods. TP (total phosphorus) indicates the total amount of phosphorus compounds contained in the composition, and was measured in accordance with JIS K0102-46.3.2 "nitric acid-perchloric acid decomposition method." n-Hex (n-hexane extractable substances) was measured using the extraction-gravimetric method as described in Appendix 4 of Notification No. 64 of the Ministry of the Environment in 1974. n-Hex is a general term for non-volatile substances extracted with n-hexane, an organic solvent, and is used as an indicator of the amount of "oil, etc." in a composition. Here, oil, etc. includes animal and vegetable oils and fats, fatty acids, fatty acid esters, fatty acid derivatives such as phospholipids, wax, grease, and petroleum hydrocarbons. The glycerin concentration was measured by liquid chromatography.

[0100] [Table 2]

[0101] Next, a methane fermentation experiment was conducted on the above test materials using the methane fermentation apparatus shown in Figure 3 as described below, and the amount of biogas generated from each sample was measured. The test was completed 26 days after the start of the test (feeding of raw materials).

[0102] The methane fermentation apparatus used in the examples will be described with reference to Figure 3. The methane fermentation apparatus 1 has a fermenter 2, a stirrer 4, a heating / stirrer rotator 6, a thermometer 8, a raw material inlet 10, a drain 12, and a gas outlet 14. The fermenter 2 is a sealed cylindrical tank made of stainless steel with a capacity of 3.5 L. A gas tube 16 is attached to the gas outlet 14 of the fermenter 2, and this gas tube 16 is connected to a gas flow meter 18 (positive displacement flow meter). The flow meter 18 has a built-in data logging device, which allows the amount of biogas generated to be monitored and recorded continuously for 24 hours. Furthermore, an aluminum gas bag 22 for collecting the generated biogas is connected to the flow meter 18 via another gas tube 20.

[0103] First, 3.5 L of sludge acclimatized with food waste containing nitrogen and phosphorus was added as seed sludge to the fermentation tank 2. The properties of the seed sludge were TS: 3.5%, COD Cr : 34,000 mg / L, TN: 5,100 mg / L, TP: 510 mg / L. Next, the test material was charged into fermenter 2 in the amount shown in Table 3 while the inside of the fermenter was heated to 37°C. The atmosphere inside fermenter 2 was purged with nitrogen, and the inside temperature was maintained at 37°C ± 0.5°C while the stirrer 4 was constantly operated to continuously stir the inside of fermenter 2. The amount of gas generated was measured using flow meter 18, and the total amount of gas was collected using gas pack 22 connected to the flow meter. The amount of gas generated was continuously recorded by a data logger attached to flow meter 18. Furthermore, the methane concentration of the biogas stored in the gas bag 22 was measured by gas chromatography.

[0104] The results are shown in Table 3. The methane generation amount (unit: n-mL) in Table 3 is calculated by multiplying the volume of biogas generated by the methane concentration, and then converting it to the standard conditions (0°C, 1 atm, 0% humidity).The amount of biogas generated was calculated by subtracting the amount of biogas generated (5,500 n-mL) measured in the blank (seed sludge only), and the converted amount of methane is shown in Table 3. In addition, the methane generation rate (nm 3 / t) is the volume of methane generated (unit: m 3 ) is converted to the standard condition (0℃, 1atm, humidity 0%) and used as the methane generation amount (unit: nm 3 ), which is the value obtained by dividing it by the raw material mass (unit: t). Cr (g) is methane generation / decomposition COD Cr =0.35nm 3 / kg·COD Cr COD was calculated from the amount of methane generated. Cr The decomposition rate is the COD of the input material. Cr (g) Decomposition COD Cr It was calculated by dividing by .

[0105] [Table 3]

[0106] As shown in Table 3, Sample 2, which is a mixture of dehydrated swine manure sludge and a methane fermentation promoter, has a methane generation rate of 268 nm-m 3 / t, and the predicted methane generation rate calculated from the mixing ratio is 217n-m 3 / t, it was confirmed that methane fermentation was significantly promoted. Furthermore, Sample 2 had a significantly higher COD than the organic waste alone and the methane fermentation promoter alone. Cr The decomposition rate was significantly high. Cr Since the decomposition rate exceeded 100%, it is believed that methane fermentation was carried out using the carbon source in the seed sludge in addition to the input raw material. In addition, sample 3, which is a mixture of dehydrated swine manure sludge and excess dehydrated sludge with a methane fermentation promoter, has a methane generation rate of 198 nm-m 3 / t, and the predicted methane generation rate calculated from the mixing ratio is 173n-m 3 / t, it was confirmed that methane fermentation was also significantly promoted in this methane fermentation raw material. Cr The decomposition rate was high.

Claims

1. A methane fermentation method for producing biogas containing methane by feeding organic waste as a raw material into a methane fermentation system, The organic waste as the raw material does not include sludge constituting the methane fermentation system, A methane fermentation promoter is used in combination with the organic waste as the raw material, The methane fermentation promoter contains glycerin and has an n-hexane extractable substance content of 10,000 mg / kg or less; The COD of the methane fermentation promoter Ｃｒ and the COD of the organic waste Ｃｒ The methane fermentation promoter is used so that the ratio of A methane fermentation method characterized by:

2. 2. The methane fermentation method according to claim 1, wherein the methane fermentation promoter has a glycerin content of 600,000 mg / kg or more.

3. COD in the methane fermentation tank where methane fermentation takes place Ｃｒ Load: 2 to 20 kg / m 3 3. The methane fermentation method according to claim 1, wherein the input amounts of the organic waste and the methane fermentation promoter are adjusted so that the input amount falls within a range of 1 / day.

4. A method for producing a methane fermentation promoter used in the methane fermentation method according to any one of claims 1 to 3, a first separation step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating the mixture into a first oil component and a first glycerin-containing liquid; a neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance; a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized first glycerin-containing liquid; A method for producing a methane fermentation promoter, comprising:

5. The method for producing a methane fermentation promoter according to claim 4, further comprising an alcohol removal step of removing monohydric alcohol after the second separation step.

6. 6. The method for producing a methane fermentation promoter according to claim 4, wherein in the first separation step, the mixed liquid of the raw material and the inorganic acid has a pH of 3 or less.

7. The method for producing a methane fermentation promoter according to any one of claims 4 to 6, wherein the first glycerin-containing liquid is neutralized to have a pH of 4 to 8 in the neutralization step.

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