JPS6034800A - Treatment of organic waste - Google Patents

Abstract

PURPOSE:To recover valuable materials or energy and to contrive reutilization of recovered materials or energy by performing addition and interruption of addition of n-butyric acid in the first stage and adjusting the proportion of n- butyric acid in the formed volatile fatty acid to >=30%. CONSTITUTION:Raw material slurry for fermentation is charged to a liquefaction fermentation tank 2 and org. materials are brought into contact with liquefying fermentation microorganism to decompose to volatile fatty acid such as acetic acid or butyric acid, etc. Gaseous H2, gaseous CO2, or gaseous methane are generated simultaneously with the decomposition of org. materials, and generated gas is stored in a gas holder 4. The compsn. of volatile fatty acid generated in the liquefaction fermentation tank 2 is analyzed, and an amt. of n-butyric acid specified depending on the concn. of the compsn. and concn. of the product is charged. n-butyric acid is charged to the liquefaction fertilization tank from an n-butyric acid tank 3 when the proportion of n-butyric acid is below 30% basing on the amt. of whole volatile fatty acids. By this method, generation of gaseous methane in the liquefaction fertilization tank 2 is retarded and generation of H2 is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating organic waste, and particularly to a method for treating organic waste that stably generates hydrogen gas.

So-called municipal waste, such as general household garbage and similar industrial waste, is disposed of by landfilling or incineration. However, these treatment methods include factors that induce environmental pollution due to secondary pollution such as lack of landfill space, groundwater contamination, and air pollution.

Therefore, in recent years, there has been a growing trend to not only process the municipal waste that is generated, but also to recover and reuse valuable materials, energy, etc. through the development of recycling technology.

For example, energy can be recovered by generating methane gas from municipal waste using anaerobic digestion, which has traditionally been used to treat sewage sludge, human waste, livestock manure, and sludge from pulp and paper factories. It is being

In anaerobic digestion, the reaction in which organic matter is decomposed by fermentation bacteria and converted into methane gas is divided into two stages.

The first stage is a reaction that decomposes organic substances into organic acids, which is called liquefaction fermentation, and the second stage is a reaction that decomposes the organic acids produced in the previous stage to generate methane gas, which is called gasification fermentation. It is. These two reactions are carried out by different fermentation bacteria and have different reaction conditions. Liquefaction fermentation is carried out under acidic conditions, and the bacterial cells multiply at a distance, while gasification fermentation is carried out under alkaline conditions, and the bacterial growth is slower than that of liquefied fermenting bacteria.
It is rate-limiting for anaerobic digestion.

However, in the anaerobic digestion method, which is popular as a method for treating sewage sludge and human waste, these two reactions are carried out in one digestion tank, so it is difficult to maintain the reaction conditions at WkA. The bacterial cells cannot grow efficiently and the basal metabolic capacity of the bacterial cells cannot be utilized to the fullest, resulting in poor reaction efficiency (requires a long digestion period).

Therefore, a two-phase anaerobic digestion method has been developed that aims to improve reaction efficiency and shorten the digestion time by separating the two reactions of liquefaction and gasification and obtaining the optimal conditions for each bacterial cell. . In the liquefaction fermentation process of this method, slurry waste is processed under acidic conditions by the action of liquefaction fermentation bacteria.
Decomposes into organic acids such as acetic acid, propionic acid and butyric acid. In the next step, gasification and fermentation, the liquefied slurry that has produced organic acids is converted into methane gas by the action of gasification fermentation bacteria under alkaline conditions.

Easily degradable components contained in kitchen waste are converted into hydrogen gas and carbon dioxide gas in parallel with the production of volatile fatty acids during the liquefaction fermentation process. The generated hydrogen gas is hygienic and non-polluting, and has a high calorific value, so it can be used as an energy source. However, the quality of municipal waste, which is a raw material for fermentation, changes depending on the living environment and collection location due to seasonal changes.In particular, the amount of kitchen waste that contains highly decomposed components and is a factor in the generation of hydrogen gas fluctuates. The disadvantage is that the gas generation fluctuates, and hydrogen gas cannot be stably supplied.

An object of the present invention is to provide a method for anaerobic digestion of organic waste, which eliminates the drawbacks of the prior art and can efficiently produce hydrogen gas by a two-phase anaerobic digestion method. This objective is achieved according to the invention by regulating the concentration of n-butyric acid in the liquefaction fermenter.

That is, in the method of the present invention, n-butyric acid is added and stopped during the liquefaction process using a two-phase anaerobic digestion method, and the proportion of n-butyric acid in the volatile fatty acids produced is adjusted to 30% or more. It is characterized by

In the two-phase anaerobic digestion method, as mentioned above, organic matter is reduced to lower molecular weight by the action of fermentation bacteria in the liquefaction fermentation process and decomposed into volatile lower fatty acids. Figure 1 shows the result of high-temperature liquefaction fermentation using daily collected municipal waste as fermentation raw material for two days of residence. Among the volatile fatty acids, acetic acid and n-butyric acid account for the majority, and propionic acid and iso-valeric acid are also produced. Next, comparing the fatty acid composition and the generated gas composition, when n-butyric acid is less than 30%, methane gas and carbon dioxide gas are generated, and when n-butyric acid is over 30%, hydrogen gas and carbon dioxide gas are generated. Occur. From this, it was found that there is a correlation between the composition of gas generated and the composition of fatty acids produced.

Therefore, when n-butyric acid produced in the liquefaction fermentation process is less than 30% of the total fatty acids, if n-butyric acid is injected into the liquefaction fermentation tank to adjust the fatty acid composition, hydrogen gas can be stably generated. can.

Next, the present invention will be explained in detail based on the drawings.

FIG. 2 is a flow sheet showing an embodiment of the method of the present invention. The raw materials for fermentation, such as general household garbage and industrial waste, are sorted and sorted according to the nature of each type of waste, and after crushing the organic waste, which mainly consists of kitchen waste and paper, the slurry is made into slurry tank 1. to slurry. The obtained fermentation raw material slurry is put into the liquefaction fermentation tank 2 and comes into contact with the liquefaction fermentation bacteria. Pretreatment for extraction, hydrolysis, etc. of fermentation components may be performed before charging. The slurry is then held under anaerobic conditions with stirring for 0.5 to 3 days. The temperature inside the liquefaction fermenter 2 is 5
It is optimal that the temperature is 0 to 65°C and the pH is 5.0 to 6.0. In the liquefaction fermentation tank 2, organic matter is decomposed into volatile fatty acids such as acetic acid and butyric acid by the action of liquefaction fermentation bacteria. Also,
Hydrogen gas, carbon dioxide gas, or methane gas is generated in parallel with the decomposition of organic matter.

The generated gas is stored in the gas holder 4. The composition of volatile fatty acids produced in the liquefaction fermentation tank 2 is analyzed, and n-butyric acid is injected according to its concentration. When the proportion occupied by n-butyric acid becomes lower than 30% of the total volatile fatty acids, n-butyric acid is injected from the n-butyric acid tank 3 into the liquefaction fermentation tank 2. The upper limit of the proportion of n-butyric acid is not definitive, but even if it is added in excess of 50%, the generation of hydrogen gas will not increase accordingly, so from the point of view of saving the amount of added chemicals, it should be set at 50%.
There is no need to exceed %. That is, it is preferable that n-butyric acid accounts for 30 to 50% of the total volatile fatty acids.

In this way, in the liquefaction fermenter, n-
Expressing the proportion of butyric acid, i.e. n-butyric acid and other fatty acids,
In particular, by maintaining the balance with acetic acid, even if the fermentation raw material changes, the generation of methane gas in the liquefaction fermenter can be suppressed and the generation of hydrogen gas can be stabilized without having to adjust the fermentation raw material.

The liquefied and fermented slurry is put into the gasification fermenter 5,
Contact with gasifying fermentation bacteria. Inside the gasification fermentation tank 5, the slurry is maintained at a temperature of 50 to 65° C. and pl+7.0 to 8.0 while stirring under anaerobic conditions, and is retained therein for 5 to 8 days. When the liquefied fermentation slurry is brought into contact with gasifying fermentation bacteria under these conditions, the fatty acids in the liquefied fermented slurry are decomposed into methane gas and carbon dioxide gas. The generated gas is stored in gas holder 6.
is stored in

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

Example 10 Using an experimental apparatus on the scale of IV, municipal waste was treated according to the flow sheet shown in FIG. Municipal waste mainly composed of kitchen waste and paper is slurried in tank 1 to a solids concentration of 7~
After adjusting the concentration to 9% and heating it to 60°C, it was put into the liquefaction fermenter 2. The slurry is liquefied in the fermenter 2 at pH 5.2 to 5.6.
The mixture was maintained at a temperature of 60'C for 2 days for liquefaction and fermentation. The composition of the volatile fatty acids produced in the liquefaction fermentation tank 2 was analyzed as appropriate, and the proportion of each fatty acid constituting the volatile fatty acids was determined. Then, when the proportion of n-butyric acid became lower than 30% of the total volatile fatty acids, n-butyric acid was injected from the n-butyric acid tank 3 into the liquefaction fermentation tank 2, and when it exceeded 50%, the injection was stopped. We also analyzed the composition of gases generated in parallel with fatty acid production.

The change in the proportion of fatty acid composition and the change in the gas composition generated when the concentration of n-butyric acid in the liquefaction fermenter 2 is adjusted are shown in the third table.
As shown in the figure. The municipal waste used as the fermentation raw material used in this experiment was the same sample used to obtain the results shown in Figure 1. This is the case when the concentration of

As is clear from Figure 3, by adjusting the proportion of n-butyric acid to 30 to 50% of the total volatile fatty acids,
The gas generated from the liquefaction fermenter 2 could be converted into hydrogen gas and carbon dioxide gas, and hydrogen gas generation could be stabilized.

When the liquefied slurry was then put into the gasification tank 5 and gasified under anaerobic conditions, the fatty acids in the liquefied fermentation slurry were
It was successfully decomposed into methane gas and carbon dioxide gas.

[Brief explanation of drawings]

FIG. 1 is a diagram of oral changes in the composition of volatile fatty acids and the composition of gas generated in the liquefaction fermentation process when the concentration of n-butyric acid is not adjusted, and FIG. 2 is a flow sheet showing one embodiment of the method of the present invention. FIG. 3 is a diagram showing the changes over time in the composition of volatile fatty acids and the composition of gas generated in the liquefaction fermentation process in an example of the present invention in which the concentration of monobutyric acid was adjusted. 1... Slurry tank, 2... Liquefaction fermentation tank, 3...
n-butyric acid tank, 5... gasification fermentation tank. Patent applicant Hitachi Plant Construction Co., Ltd.

Claims (2)

[Claims] (1) After sorting and sorting household general kitchen waste and similar industrial waste according to their basic condition and turning the organic waste mainly composed of kitchen waste and paper into a slurry, the organic matter is removed by the action of liquefaction fermentation bacteria. It consists of a first step in which it is reduced in molecular weight and converted into volatile fatty acids, and a second step in which the volatile fatty acids in the slurry obtained from the first step are further converted into methane gas and carbon dioxide gas by the action of gas-fermenting bacteria. When treating organic waste by anaerobic digestion, the proportion of n-butyric acid in the volatile fatty acids produced is adjusted to 30% or more by adding and stopping the addition of n-butyric acid in the first step. A method for treating organic waste characterized by the following. (2) The proportion of n-butyric acid in fatty acids is 30-50%
The processing method according to claim 1, characterized in that the treatment method is adjusted to: