JPS60137498A - Anaerobic digesting method of organic waste - Google Patents

Abstract

PURPOSE:To generate stably and efficiently gaseous hydrogen by supplying organic waste consisting essentially of garbage to the first stage, and supplying the organic waste consisting essentially of a slurry from the first stage and a paper component to the second stage. CONSTITUTION:The waste consisting essentially of garbage and the waste consisting essentially of a paper component are respectively crushed, and slurryed in slurrying tanks 1 and 4. The slurry of garbage to be fermented is supplied into a liquefying fermenter 2, and brought into contact with a liquefying ferment fungus. The slurry of the paper component to be fermented is supplied into a gasifying fermenter 5, and brought into contact with a gasifying ferment fungus. The contents of the liquefying fermenter 2 are allowed to stand for 0.3-3.0 day while agitating under anaerobic conditions, and the organic substance is converted into low molecular substances. Gaseous hydrogen and carbon dioxide are simultaneously generated. The amt. of generated gaseous hydrogen can be increased as compared with the existing process wherein various kinds of wastes are not sorted.

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 efficiently generates hydrogen and methane gas by anaerobic digestion.

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. For this reason, in recent years, there has been a growing momentum to not only dispose of the municipal waste generated, but also to recover valuable materials, energy, etc., and to recycle it.

An example of this is a method that aims to recover energy by generating methane gas from municipal waste using anaerobic digestion, which is conventionally used to treat sewage sludge, human waste, livestock manure, and sludge discharged from pulp and paper factories. is taken.

The reaction in which organic matter is broken down by fermentation bacteria and converted into methane gas in anaerobic digestion is divided into two stages. The first stage is a reaction that decomposes organic matter into volatile fatty acids.
This is called liquefaction fermentation, and the second step is a reaction in which the fatty acids produced in the previous step are decomposed to generate methane gas, and is called gasification fermentation. Since these two reactions are carried out by different fermentation bacteria, the optimal reaction conditions are also different. Liquefaction fermentation is carried out under acidic conditions and the bacterial cells multiply rapidly, while gasification fermentation is carried out under alkaline conditions and the bacterial growth is slower than that of liquefaction fermenting bacteria, which 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.
It is difficult to maintain optimal reaction conditions for each reaction, and as a result, bacterial cells cannot grow efficiently and the basic metabolic capacity of bacteria cannot be utilized to the fullest, resulting in poor reaction efficiency and long digestion times. I need.

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 fermentation and gasification fermentation and obtaining optimal conditions for each bacterial cell. There is. In the liquefaction fermentation process in this method, organic matter in slurry waste is decomposed into fatty acids such as acetic acid, propionic acid, and butyric acid by the action of liquefaction fermentation bacteria under acidic conditions. In the next gasification fermentation step, the liquefaction fermentation slurry that has produced fatty 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 hydrogen gas generated 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, it contains easily decomposable components and the kitchen waste, which is a factor in the generation of hydrogen gas, fluctuates. However, the disadvantage is that the concentration of hydrogen gas in the gas generated in the liquefaction fermentation process cannot be stably maintained.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above and to provide an anaerobic digestion method that can stably and efficiently generate hydrogen gas by a two-phase anaerobic digestion method. According to the invention, this is achieved by increasing the amount of fermented bones in the fermentation raw material supplied to the liquefaction fermentation process.

That is, the method for anaerobic digestion of organic waste according to the present invention is as follows:
The organic waste is separated into waste mainly composed of kitchen bones and waste mainly composed of paper, and the organic waste mainly composed of kitchen bones is supplied to the first process, and the second process The process is characterized by anaerobic digestion by supplying the organic waste mainly composed of the slurry and paper obtained from the first process.

In the two-phase anaerobic digestion method, as described above, organic matter is reduced in molecular weight by the action of fermentation bacteria in the liquefaction fermentation process, producing volatile fatty acids and gas. In order to examine changes in the gas composition caused by differences in fermentation raw materials, two fermentation raw materials whose main components were kitchen stubble and paper were subjected to high-temperature liquefaction fermentation for a residence time of 2 days, and the composition of the gas generated from each raw material was investigated. As a result of the measurement, the results shown in Table 1 below were obtained.

Table 1 As shown above, it was found that hydrogen gas and carbon dioxide gas were generated from the fermented raw material whose main component was snail bones, and methane gas and carbon dioxide gas were generated from the fermented raw material whose main component was paper.

Furthermore, the optimum pH for liquefaction fermentation and gasification fermentation of the slurry of the two types of fermentation raw materials was determined based on the amount of volatile fatty acids produced for liquefaction fermentation and the amount of gas generated for gasification fermentation. The results are shown in FIG. 1 for the case where snail bones were used as the raw material, and in FIG. 2 for the case when paper was used as the raw material. Based on these results, the optimum pi for two-phase anaerobic digestion of fermented raw materials mainly composed of chub bones is in the acidic range in liquefaction fermentation, and hydrogen gas is absorbed into this p in parallel with the production of fatty acids.
It is generated in large quantities in the H range, and the optimum pH for gasification fermentation is in the alkaline range. On the other hand, in the case of fermentation raw materials mainly composed of paper, it was found that the optimum pH was in the alkaline range for both liquefaction fermentation and gasification fermentation.

In this way, when carrying out two-phase anaerobic digestion of fermentation raw materials whose main component is paper, hydrogen gas is not generated in liquefaction fermentation, and the optimum p++ for liquefaction and gasification fermentation is alkali. It is rational that the fermentation raw material whose main component is paper is directly supplied to the gasification fermentation process without going through the liquefaction fermentation process. Therefore, by the method of the present invention, waste mainly composed of kitchen waste and waste mainly composed of subdivisions are separated, and only the waste mainly composed of kitchen waste is supplied to the liquefaction fermentation process, and the waste is By supplying waste mainly composed of liquefaction fermentation slurry and paper to the process, hydrogen gas can be efficiently and stably generated in the liquefaction fermentation process and methane gas can be generated in the gasification fermentation process, and the liquefaction fermentation tank The volume of can be reduced.

Next, the present invention will be described based on the drawings.

FIG. 3 is a flow sheet showing one embodiment of the method of the present invention. Household general kitchen waste and similar industrial waste, which are raw materials for fermentation, are sorted and sorted according to the basic condition of each waste. After crushing the waste mainly composed of kitchen waste and the waste mainly composed of paper, slurry tanks 1 and 4 are respectively processed.
The fermented raw material slurry obtained from kitchen waste is supplied to the liquefaction fermentation tank 2 and brought into contact with liquefaction fermentation bacteria, and
The paper fermentation raw material slurry is supplied to the gasification fermentation tank 5 and brought into contact with gasification fermentation bacteria. Before supplying each slurry, pretreatment for extraction, hydrolysis, etc. of fermentation components may be performed using a rich method.

0.3~ while stirring the inside of the liquefaction fermenter 2 under anaerobic conditions.
3. Hold for 01 minutes. The temperature inside the liquefaction fermenter 2 is 50-6
Optimally, the temperature is 5°C and the pH is 5.0-6°0.

In the liquefaction fermentation tank 2, organic substances are reduced in molecular weight by the action of liquefaction fermentation bacteria and decomposed into volatile fatty acids such as acetic acid and butyric acid. Additionally, hydrogen gas and carbon dioxide gas are generated in parallel with the decomposition of organic matter. According to the method of the present invention, the waste mainly composed of kitchen waste is supplied to the liquefaction fermentation tank 2, so the kitchen waste in the fermentation raw material is reduced compared to the conventional method in which various wastes are fed without being sorted. As the amount increases, the amount of hydrogen gas generated also increases.

The generated gas is stored in the gas boulder 3.

The slurry liquefied in the liquefaction fermentation tank 2 is supplied to the gasification fermentation tank 5 together with the fermentation raw material whose main component is paper.

While stirring the inside of the gasification fermentation tank 5 under anaerobic conditions, the temperature is maintained at 50 to 60"C and the pH is maintained at 7.0 to 8.0.
Leave to stay for 8 days. Under these conditions, the fatty acids in the liquefied slurry are decomposed into methane gas and carbon dioxide gas, and the organic matter in the paper fermentation material is reduced in molecular weight, generating methane gas and carbon dioxide gas.

The generated gas is stored in the gas holder 6. The slurry that has undergone gasification and fermentation is processed separately.

In this manner, according to the present invention, hydrogen gas and methane gas can be generated stably and efficiently, and the volume of the liquefaction fermenter can be further reduced.

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

Example 1 Using a 101-scale experimental apparatus, municipal waste was treated according to the flow sheet shown in FIG. Municipal waste mainly composed of kitchen waste was made into a slurry tank 1 to have a solid concentration of 7 to 9%, heated to a temperature of 60'C, and then supplied to a liquefaction fermentation tank 2. The liquefaction fermentation tank 2 was maintained at a pl+ of 5.5 to 6.0 and a temperature of 60'C for 2 days to carry out liquefaction fermentation. The composition of the gas generated by liquefaction fermentation was analyzed as appropriate, and the results are shown in Table 2.

On the other hand, municipal waste whose main component is paper is brought to a solid concentration of 7 to 9% in a slurry tank 4, heated to 60°C, and then fed into a gasification fermentation tank 5 together with the liquefaction fermentation slurry. , gasification and fermentation.

For comparison, fermentation raw materials mainly composed of kitchen waste and paper were liquefied and fermented under the same conditions as in the liquefaction fermentation process described above (2 days of residence at a temperature of 60'C), and the composition of the gas generated was analyzed. , the results are shown in Table 2.

Table 2 As is clear from the results shown in Table 2, when using fermented raw materials whose main components are kitchen waste, the results are significantly more pronounced than when the fermented raw materials whose main components are kitchen waste and paper are liquefied and fermented. Hydrogen gas can be obtained at high concentrations.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between pll, fatty acid production, and gas generation in liquefaction fermentation and gasification fermentation of organic waste whose main component is kitchen waste, and Figure 2 is a graph showing the relationship between PLL and the amount of fatty acid production and gas generation for organic waste whose main component is paper waste. p in liquefaction fermentation and gasification fermentation of organic waste
FIG. 3 is a graph showing the relationship between ll and the amount of fatty acid produced and the amount of gas produced, and FIG. 3 is a flow sheet of an apparatus for carrying out the method of the present invention. 1.4... Slurry tank, 2... Liquefaction fermentation tank, 5.
...Gasification fermenter, 3,6...gas holder. Patent applicant Director of Institute of Industrial Science and Technology) Hirobe Ida Figure 1? Figure 2 pH (-3 Figure 3 Kokuox.

Claims (1)

[Claims] General household garbage and similar industrial waste are converted into low-molecular organic substances through the action of liquefaction fermentation bacteria, and are further converted into methane gas and carbon dioxide through the first step of converting them into volatile fatty acids and the action of gas fermentation bacteria. In the method of anaerobic digestion with a second step of conversion, organic waste is separated into waste mainly composed of kitchen waste and waste mainly composed of paper, and the kitchen waste is added to the first step. The method is characterized in that anaerobic digestion is carried out by supplying organic waste mainly consisting of organic waste obtained from the first step and supplying organic waste mainly consisting of the slurry and paper obtained from the first step to the second step. A method for anaerobic digestion of organic waste.