JPH0679720B2 - Methane fermentation method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a methane fermentation method and apparatus capable of suppressing an increase in fatty acid concentration, which is a problem when an organic substrate is subjected to methane fermentation treatment with methane bacteria. Is.

B. Summary of the Invention The present invention is a method for culturing an organic substrate with methane bacteria, in which a fatty acid-decomposing bacteria group, which has a high ability to decompose fatty acids, especially propionic acid, which is an intermediate product of methane fermentation, is cultivated together with the methane bacteria group. By supplementing and supplying the cultured inoculum to the methane fermentation tank, the so-called rancid phenomenon is suppressed and the efficiency of methane fermentation is increased.

C. Conventional Technology In a methane fermentation system, when an appropriate amount of organic substrate is given to an inoculum containing anaerobic microorganisms such as methane bacteria, the concentration of fatty acid, which is an intermediate product of methane fermentation, increases, which causes The pH is lowered and the generation of methane gas is hindered. This phenomenon is called rancidity, which causes the methane fermentation system to lack reliability. Conventionally, when rancidity occurs, a method of refraining from inputting a substrate and recovering gas generation or replacing the inoculum is used.

D. Problems to be Solved by the Invention In the above method, it often takes a long time for the gas generation to be recovered, and there is a problem that the method for replacing the inoculum requires a great deal of labor and cost. .

It is an object of the present invention to provide a methane fermentation method and an apparatus thereof capable of preventing the rancidity phenomenon and recovering the gas generating ability in a short time even when rancidity occurs.

E. Means and Actions for Solving Problems First, the focus of the present invention will be described. Generally, when high load operation is performed in a methane fermentation system or when the fermentation temperature is low, the fatty acid concentration increases. However, regarding the composition ratio of this fatty acid, the composition ratio of propionic acid and acetic acid is high. Of these, acetic acid serves as a direct substrate for methane bacteria, so by mass-culturing the methane bacteria and replenishing them in a fermented tank in a rancid state, methane gas is produced and the concentration of acetic acid decreases.

On the other hand, propionic acid has not received much attention when it is decomposed by conventional microbial treatment. The reason for this is that it is not a direct substrate of methane propionate, but is decomposed by a bacterium that decomposes propionic acid in an anaerobic state as in formula (1): CH ₃ CH ₂ COOH + 2H ₂ O → CH ₃ COOH + CO ₂ + 3H ₂ (1) Moreover, this decomposition reaction is a thermodynamically unfavorable reaction, and the reaction does not proceed unless hydrogen, which is a product, is removed to the outside of the system. There is a small number.

Here, the present inventor cultivates a propionic acid-degrading bacterium and replenishes and supplies it into a methane fermentation tank. In the culturing, methane bacterium is mixed, and hydrogen is consumed by the methane bacterium to generate methane gas. The present invention has been made in view of the point of promoting the decomposition reaction of propionic acid in the culture medium and proliferating the propionic acid-decomposing bacteria.

The method of the present invention comprises inoculating the inoculum having a fatty acid-decomposing bacterium group including a propionic acid-decomposing bacterium group and a methane bacterium group as a main microorganism, and culturing the inoculum by mixing a medium for selective culture of propionic acid-decomposing bacteria, and thereby proliferating. The seed bacteria are replenished and supplied into the methane fermentation tank.

The apparatus of the present invention comprises a medium adjusting tank for adjusting a medium for selective culture of propionic acid-degrading bacteria, a first mixing means for mixing medium components in the tank, and a deoxidizing unit for bubbling the medium for deoxidation. A means for diffusing active gas, an inoculum having a fatty acid-decomposing bacteria group including a propionic acid-decomposing bacteria group and a methane bacteria group as main microorganisms, and an inoculum culture tank containing a medium from the medium adjusting tank, and this inoculum culture Second mixing means for mixing the medium and the inoculum in the tank, a gas holder for accommodating the gas generated in the inoculum culture tank, and a methane fermentation for methane fermentation treatment of an organic substrate with a methane bacteria group. A tank, a medium supply pump provided between the medium adjustment tank and the seed culture tank, and a seed supply pump provided between the seed culture tank and the methane fermentation tank. One in which Ete made.

F. Embodiment FIG. 1 is a block diagram showing an apparatus according to an embodiment of the present invention. Reference numeral 1 is a culture medium adjustment tank, 2 is a mechanical stirrer as a first mixing means, 3 is an inert gas diffusing means, and 4 is a gas cylinder. The tank 1 is for adjusting a culture medium for selective culture of propionic acid-degrading bacteria containing propionic acid and butyric acid, in which the medium components are dissolved and mixed, and the gas cylinder 4 drives the aeration means 3 Bubbling is carried out by the inert gas sent through the medium to deoxidize the medium. As this inert gas, for example, a mixture of nitrogen gas and carbon dioxide gas in a volume ratio of 80:20 is used. The adjustment of the medium will be described after the explanation of the apparatus. In FIG. 1, 5 is a medium supply pump, 6 is a seed culture tank, 7 is a mechanical stirrer as a second mixing means, and 8 is a gas holder. The medium adjusted by the medium adjusting tank is supplied to the seed culture tank 6 via the pump 5, and the medium and the seed are mixed by the mechanical stirrer 7 there. This inoculum is mainly composed of an anaerobic fatty acid-decomposing bacteria group including a propionic acid-decomposing bacteria group and a methane bacteria group. Then, propionic acid and butyric acid in the medium are decomposed by the anaerobic fatty acid decomposing bacteria group and the methane bacteria group, and the methane gas generated by this is stored in the gal holder 8. Hydrogen, which is a product of the decomposition reaction of propionic acid, is removed to the outside of the system by reacting with acetic acid and carbon dioxide that are simultaneously produced by the methane bacteria group. As a result, methane gas is produced, but hydrogen is removed to the outside of the system, so that the propionic acid-decomposing reaction proceeds, and as a result, the growth of the propionic acid-decomposing bacteria is promoted. Moreover, a part of the substrate in the medium serves as a nutrient source for the growth of the fungus. 9 is a seed feed pump, 10 is a methane fermentation tank, and a part of the seed grown in the seed culture tank 6 is intermittently sent to the methane fermentation tank 10 via the seed feed pump 9. Methane fermentation is carried out in the methane fermentation tank 10, and its intermediate product, propionic acid, is decomposed by the propionic acid-decomposing bacteria group and the newly supplemented propionic acid-decomposing bacteria group in the methane fermentation tank 10. It Since the proportion of propionic acid in the fatty acid as an intermediate product is high, decomposition of the fatty acid can prevent the rancidity phenomenon in advance, and even if the rancidity phenomenon occurs, it can be eliminated.

Now be described with respect to adjustment of the medium in said medium adjustment tank 1, first mineral 1 of K ₂ HPO ₄ concentration of K _2H PO ₄ was obtained by dissolving so as to be 6 g / l in water, Table 1 to Table 3 Prepare minerals 2, trace minerals and trace vitamins showing the respective ingredients in advance.

Then, in the culture medium adjustment tank 1, mineral 1, mineral 2, trace mineral are added to the water, and FeSO ₄ · 7H ₂ O, NaHCO ₃ ,
Dissolve resazurin. Next, propionic acid and butyric acid are added, and the pH is adjusted to 7.4 with a KOH solution. After sterilization in an autoclave, the mixture is cooled to room temperature, and while traces of an inert gas are bubbled by an air diffuser 3, trace vitamins, cysteine hydrochloride and sodium sulfide in Table 3 are oversterilized and added. After confirming that the color of resazurin has disappeared and dissolved oxygen has disappeared, the culture medium supply pump 5 supplies the culture medium to the inoculum culture tank 6 while bubbling the inert gas. Here, the medium and the inoculum are kept warm at an appropriate temperature and intermittently stirred by the mechanical stirrer 7. The temperature suitable for culturing is around 30 ° C, but culturing is possible at room temperature. Table 4 shows the composition of medium 1.

As a medium component, butyric acid is not always an indispensable component. For example, in Table 4, 5 ml of propionic acid may be added instead of 2.5 ml each of propionic acid and butyric acid. Since the gas generation rate is high, it is more suitable for culture.

G. Effects of the Invention By culturing the anaerobic fatty acid-decomposing bacteria group and the inoculum that mainly consists of the methane bacteria group, which have been cultivated in a selective culture medium for propionic acid-decomposing bacteria, by culturing them in a mixed manner, and supplementing the methane fermentation tank with the grown inoculum. , Increase the number of anaerobic fatty acid degrading bacteria in methane fermentation tanks, especially propionic acid-degrading bacteria that originally have a low number of bacteria, and enhance the ability to decompose propionic acid, which is difficult to decompose at high load and easily accumulates. You can

At the same time, the number of methane bacteria that produce methane from acetic acid, CO ₂ , and H ₂ , which are the decomposition products of propionic acid (and butyric acid) by anaerobic fatty acid-degrading bacteria, also increases. The ability to gasify such substances becomes higher, the concentration of fatty acids decreases, and the pH rises. Optimum pH for methane bacteria when the pH changes from neutral to weakly alkaline
Next, methane fermentation can be actively carried out.

Therefore, according to the present invention, the efficiency of methane fermentation is improved,
It has the effect of preventing rancidity. It also has the effect of eliminating rancidity in a methane fermentation system where rancidity has already occurred and promptly recovering the gas generating ability.

[Brief description of drawings]

FIG. 1 is a block diagram showing an apparatus according to an embodiment of the present invention. 1 ... medium adjusting tank, 3 ... aeration means, 5 ... medium supply pump, 6 ... inoculum culture tank, 9 ... inoculum supply pump, 10 ... methane fermentation tank.

Claims (2)

[Claims] 1. A method for subjecting an organic substrate to a methane fermentation treatment of an organic substrate in a methane fermentation tank, wherein an inoculum mainly composed of an anaerobic fatty acid-decomposing bacteria group including a propionic acid-decomposing bacteria group and a methane bacteria group, And a medium for selective culture of propionic acid-degrading bacteria, the inoculum is cultivated, and the inoculum grown thereby is supplementarily supplied to the methane fermentation tank. 2. A medium adjusting tank for adjusting a medium for selective culture of propionic acid-degrading bacteria, a first mixing means for mixing medium components in the tank, and a device for deoxidizing the medium by bubbling the medium. Aeration means for active gas, inoculum mainly composed of anaerobic fatty acid-decomposing bacteria group including propionic acid-decomposing bacteria group and methane bacteria group, and a seed culture tank containing a medium from the medium adjusting tank, and Second mixing means for mixing the medium and the inoculum in the inoculum culture tank;
A gas holder for containing gas generated in the seed culture tank, a methane fermentation tank for methane fermentation treatment of an organic substrate with a methane bacteria group, and a medium supply provided between the medium adjustment tank and the seed culture tank A pump,
A methane fermentation apparatus comprising a seed culture feed pump provided between the seed culture tank and the methane fermentation tank.