JPS5845918B2 - Anaerobic digestion method for organic waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating organic waste, and more particularly to an anaerobic treatment method for efficiently decomposing, digesting, and gasifying organic waste containing cellulose.

In recent years, anaerobic digestion has been gaining importance due to the growing need for processing organic waste and for energy production.

Anaerobic digestion is especially suitable for kitchen waste in municipal waste that contains a lot of water. Conventionally, kitchen waste is mixed with water or sewage sludge to form a slurry, and then anaerobic fermentation (so-called methane fermentation) is performed. However, kitchen waste in municipal waste also contains a considerable amount of paper, etc., so 1) the paper in the raw material swells and the viscosity of the slurry increases, making stirring and pumping difficult. , 11) In the anaerobic fermentation treatment, the cellulose content is hardly decomposed;

In order to eliminate these drawbacks of the conventional technology, to saccharify paper and other cellulose content, to facilitate transport of the raw material slurry, to increase the amount of methane gas generated, and to reduce the amount of digested sludge, the following methods were developed: 1) adding acid to the raw material slurry; 11) Adding cellulase or cellulase culture solution to the raw material slurry to pre-decompose cellulose into sugars have been proposed, but both methods require decomposition and saccharification of cellulose. This method requires a reaction tank and a heat source for heating the reaction.

By the way, the reaction of anaerobic digestion is firstly an anaerobic liquefaction reaction in which the organic matter in the material to be treated is reduced to lower molecular weight by the action of anaerobic liquefying bacteria and becomes lower fatty acids, and then these lower fatty acids are converted into lower fatty acids by gasifying bacteria. The two reactions, consisting of the gasification reaction that is converted to methane and A stepwise method is known.

However, this method does not solve the above-mentioned drawbacks caused by cellulose in kitchen waste.

The present inventors have discovered that cellulase can decompose undecomposed cellulose even during an anaerobic liquefaction reaction in which the physiological activity of anaerobic liquefaction bacteria is being expressed, leading to the present invention.

That is, the present invention provides a method for treating organic waste containing cellulose by an anaerobic digestion method, which consists of separately performing at least a liquefaction step and a gasification step, in which the liquefaction step is performed in the presence of cellulase. This method of treating organic waste is characterized by eliminating the drawbacks of the conventional technology associated with the treatment of cellulose-containing organic waste, increasing the amount of recovered methane gas generated and reducing the amount of digested sludge, and further improving the cellulose content. The aim is to make it possible to apply anaerobic digestion to large amounts of organic waste.

The present invention will be explained in detail below.

Examples of organic waste to be treated in the present invention include conventional surplus activated sludge, kitchen waste, livestock excrement, waste liquid from fermentation factories and food processing factories, cellulose-containing waste liquid from paper and pulp factories, and urban waste. Fibers in garbage and agricultural waste are removed.

These raw materials are subjected to physical treatment such as pulverization or chemical treatment using acids, alkalis, etc., as necessary, to form a slurry, and then sent to an anaerobic liquefaction tank.

Among them, it is preferable that the ClN ratio of the raw material is in the range of 10 to 20, as in the conventional anaerobic digestion method.

Cellulases that should be present in the anaerobic liquefaction process include reprinted cellulase preparations, as well as cellulases produced by cellulase-producing bacteria belonging to the genus Trichoderma, Aspergillus, Irpex, Fusarium, Pseudomonas, Ruminococcus, Bacillus, etc. In the form of 11 cultures of those producing bacteria, or culture filtrates,
It can also be used in the form of a culture extract.

The anaerobic liquefaction reaction is performed under anaerobic conditions by allowing liquefaction bacteria and cellulase to act on the raw material slurry.

The temperature and pH at this time are 30-60℃ and 4-6, respectively.
It can be selected appropriately depending on the waste to be treated, the liquefaction bacteria used, and the cellulase used.

In order to maintain a predetermined pH during the liquefaction reaction, it is desirable to use a neutralizing agent such as caustic soda, soda carbonate, slaked lime, or calcium carbonate.

Since the liquefaction reaction is completed within a few days, the slurry after the liquefaction reaction or the liquid portion when solid-liquid separation is performed is led to the gasification step.

For the gasification reaction, a conventional two-stage anaerobic digestion gasification process can be applied.

These steps are usually performed continuously.

According to the method of the present invention, it is now possible to apply anaerobic digestion to wastes with a high cellulose content, for which it was difficult to apply anaerobic digestion in the past. Problems with stirring and transportation have been solved.
This will greatly improve waste treatment, such as reducing residual sludge and improving methane gas yield.

The present invention will be specifically described below by way of examples.

Example: Preparation of raw materials for treatment: A mixture consisting of 3 parts of sewage sludge generated during sewage treatment, 1 part of a category mainly containing organic components in municipal waste, 1 part of pulp lees from a pulp mill, and 5 parts of water was mixed into a blender. The slurry mixed and pulverized was used as the raw material for treatment.

The properties of the slurry are shown in Table 1.

Preparation of cellulase: Trichoderma viride ATCO26
921 was used as a cellulose source by drying the fiber content in municipal waste and pulverizing it in a ball mill, as reported in "Journal of the Fermentation Engineering Society," No. 5.
A culture cultured at 28° C. for 6 days according to the method described in Vol. 4, p. 267, 1976 was used as it was as a cellulase.

Liquefaction reaction: 7.5 liters of the above raw material slurry was charged into a 1M glass jar fermenter, and heated at 50°C under anaerobic conditions.
After maintaining the pH at 4.8 (using caustic soda as a pH adjuster) for 2 days, the raw material slurry was continuously introduced at a rate of 211 days, and at the same time the culture of Trichoderma viride was added to 500 m71! /day.

The fermentation tank was gently stirred at 120 rpm, and the gas generated was led to a gas storage tank.

Gasification reaction: Fill a 301-volume glass jar fermenter with the raw material slurry 151, and heat at 50° under anaerobic conditions.
C, pH was maintained at 7.5 (hydrochloric acid was used as a pH adjuster) and stirred gently at 120 r.

After one week, the treated slaty IJ-2 from the liquefaction process
, 511 days were supplied to the gasification fermenter and continuous operation started.

The generated gas was led to the gas storage tank, and the gasified slurry was led to the receiving tank.

The gas yield when continuous operation reached a stable state (usually took 20 days or more after starting continuous operation) was 9.7.
! M (standard state conversion)/l (treated slurry), and the methane content in the gas was 61vol%.

The dry solids content in the treated slurry was 0.9% by weight.

Comparative example: For comparison, the liquefaction reaction was performed and the raw material slurry was used instead of 500 rrIl/day of culture as cellulase! J
When anaerobic treatment was carried out using -500 yd/day and the other operations were exactly the same, the gas yield was 7.60 liters (converted to standard conditions)/liter (treated slurry), and the methane content in the gas was The rate was 62vo1%.

i! The dry solid content in the treated slurry was 1.3% by weight.

From the above results, it is clear that the presence of cellulase in the liquefaction process can improve the gas yield and reduce the residue after treatment.

Due to the presence of cellulase during the liquefaction reaction, the fibrous material disappeared quickly, and the fluidity of the slurry was significantly lower than when cellulase was not used.

Claims (1)

[Claims] 1. Regarding the method for anaerobic digestion of organic waste, which includes the steps of liquefying organic waste containing cellulosic materials and other solids using a group of anaerobic liquefaction bacteria, and gasifying the obtained liquid, the method described above The anaerobic digestion method described above is characterized in that organic waste is liquefied in the coexistence of anaerobic liquefying bacteria and cellulase.