JP2002263699A - Digester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digester which is capable of surely digesting organic matters containing a hardly biodegradable material and has high treatment capability. SOLUTION: Filtering means 5 for compartmentalizing the sludge-containing liquid in a chamber 1 is installed between a material-to-be-treated introducing port 3 and a digested sludge discharge port 2 and the organic matter, such as the hardly biodegradable material, which is larger than a prescribed size and takes time to be digested is held in the sludge-containing liquid on the material-to-be-treated introducing port 3 side and is sufficiently digested and is prevented from moving to the digested sludge discharge port 2 side until its size is made smaller than the prescribed size. As a result, the organic matters, such as the hardly biodegradable material, larger than the prescribed size is prevented from being discharged together with the digested sludge while the organic matter is kept undigested in discharging the digested sludge from the digested sludge discharge port 2. The hardly biodegradable material increases its surface area and exhibits a function as a carrier of digesting bacterial as the digestion progresses and therefore the contact efficiency of the organic matters and the digesting bacteria in the sludge-containing liquid is improved and the digestion rate of the organic matter is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digester for digesting organic substances including a substance that is hardly biodegradable.

[0002]

2. Description of the Related Art In agriculture, forestry, and the like, a large amount of woody substances such as rice straw, pruned branches, and bark are discarded. These woody organic wastes are hardly biodegradable, so most of them are incinerated or composted at present. However, with the increasing environmental awareness in recent years, these woody materials are hardly biodegradable. There is a demand for efficient recovery of energy from volatile substances.

As an efficient energy recovery method from organic waste, a digestion treatment method in which methane fermentation of organic waste under anaerobic conditions to recover methane gas as a combustible gas is known. Energy is more efficiently recovered as methane gas from organic waste such as sludge and garbage.

[0004] The methane fermentation is roughly classified into a medium-temperature fermentation in which the temperature in the methane fermentation tank is maintained at around 38 ° C and a high-temperature fermentation in which the temperature in the methane fermentation tank is maintained at around 55 ° C. For medium-temperature fermentation, the amount of organic substances to be fed is often 30 days or more, and for high-temperature fermentation, it is often 15 days or more, and a relatively large apparatus is required. This is because the growth rate of the methanogen is slower than that of a general acid-producing bacterium, and it is necessary to secure an extremely long residence time in order to perform methane fermentation satisfactorily.

Therefore, in recent years, a glass fiber carrier is provided in a methane fermentation tank as a digester capable of efficiently performing methane fermentation and increasing the throughput per volume of the methane fermentation tank. Digestion devices that perform methane fermentation by attaching methanogens have been developed.

[0006]

However, even when sludge, garbage, and the like and a biorefractory substance such as a wood-based substance are put into the digester as described above, for example, the main component of the wood-based substance is The digestion rate of certain cellulose and hemicellulose is much slower than organic waste such as garbage, and especially relatively large woody substances are hardly digested and are discharged from the digester as undigested with digested sludge. There was a problem that would.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a digester capable of reliably digesting an organic substance containing a biodegradable substance and having a high processing capability. .

[0008]

A digestion apparatus according to the present invention is an digestion apparatus for anaerobically digesting organic substances into digested sludge, comprising a tank containing a sludge-containing liquid, and a biodegradable substance. Of sludge in the tank between the inlet for introducing the organic substance containing methane into the tank, the outlet for digesting sludge discharging the digested sludge from the tank, and the inlet for introducing the sludge and the outlet for digesting sludge. A filter installed to partition the liquid and allowing only a substance smaller than a predetermined size to pass therethrough.

According to the digester of the present invention, the organic substance such as a biorefractory substance which is longer than a predetermined size and takes a long time for digestion does not pass through the filtration means without passing through the filtration means. It is retained inside and does not move to the digested sludge outlet side until it is sufficiently digested and smaller than a predetermined size. Thus, when the digested sludge is discharged from the digested sludge outlet, an organic substance such as a biorefractory substance having a predetermined size or more is not discharged together with the digested sludge without being digested.

[0010] In addition, since the biorefractory substance increases in specific surface area as digestion progresses and functions as a carrier for digestive bacteria, the efficiency of contact between organic substances and digestive bacteria in the sludge-containing liquid is improved. The digestion rate of organic substances is improved.

Here, it is preferable to provide a stirring means for sending out the sludge-containing liquid from the digested sludge discharge port side to the treatment object introduction port side through the filtration means and stirring the inside of the tank.

[0012] By this stirring means, a flow is formed in the filtration means from the digested sludge discharge port side to the treatment object introduction port side, and organic substances such as biorefractory substances which are not sufficiently digested are separated from the filtration means by this flow. As a result, the filter is prevented from being completely blocked. In addition, since the sludge-containing liquid in the tank is stirred to make the sludge concentration uniform, digestion is performed more efficiently.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
A preferred embodiment of the digestion apparatus according to the present invention will be described in detail. In the description of the drawings, the same or corresponding elements will be denoted by the same reference characters, without redundant description.

FIG. 1 is a schematic sectional view showing a digestion apparatus 100 according to a first embodiment. Digestion apparatus 100 of the present embodiment
Comprises a tank 1 for storing the sludge-containing liquid, a stirrer (stirring means) 15 for stirring the sludge-containing liquid in the tank 1, and a screen (filtering means) 5 installed horizontally in the tank 1.

The tank 1 has a conical bottom 1a projecting downward.
And a ceiling 1c having a disk and having a downward skirt portion on the outer periphery thereof, and a cylindrical peripheral wall 1b connecting the bottom 1a and the ceiling 1c. The ceiling 1c is provided with an inlet 3 for introducing an organic substance and a methane outlet 4 for discharging gas such as methane generated by digestion. A digested sludge discharge port 2 for discharging generated digested sludge and the like is provided.

The screen 5 is a net having a predetermined mesh width and selectively transmitting a substance smaller than the mesh width.
The sludge-containing liquid in the tank 1 is horizontally installed at the boundary between the bottom 1a and the peripheral wall 1b so as to partition the liquid into the treatment object introduction port 3 and the digestion sludge discharge port 2. This screen 5
The size of the mesh width is set based on the size of an organic substance such as a wood-based substance to be charged, etc., but should be 20 mm or less in order to facilitate the transfer of digested sludge in the subsequent stage of the digester 100. Is preferred.

The agitating device 15 is for agitating the sludge-containing liquid in the tank 1. The agitating device 15 is rotatably supported by the ceiling 1 c side, extends downward, and penetrates through the screen 5. A plurality of agitating blades 13a, 13b, 13 which are installed vertically apart from each other and immersed in a sludge-containing liquid.
c, and a driving device 11 installed on the ceiling 1c to rotate the rotating shaft 12. The lower agitating blade 13a is located between the screen 5 and the digested sludge discharge port 2, and lifts up the sludge-containing liquid on the digested sludge discharge port 2 side to pass through the vicinity of the center of the screen 5 and the periphery thereof. The agitating blades 13b, 13c are used to lift up the sludge-containing liquid in the vicinity of the central axis of the peripheral wall 1b and in the vicinity thereof.

Next, the operation of the digester 100 according to the first embodiment will be described.

First, sludge-containing water containing digestive bacteria such as acid-producing bacteria and methane-fermenting bacteria is charged into the tank 1 of the digester 100 so as to be in a digestible state. Next, the processing object inlet 3
Then, woody materials such as rice straw, pruned branches, bark, and the like, as well as garbage and sludge, are charged into the tank 1 as organic substances. Then, the driving device 11 of the stirring device 15 is driven to drive the stirring blades 13.
The sludge-containing liquid containing an organic substance is stirred by a, 13b, and 13c to digest the organic substance while preventing deposition on the screen 5, while appropriately discharging the digested sludge generated by the digestion from the digested sludge discharge port 2. I do.

At this time, organic substances smaller than the mesh width of the screen 5 and easily digested by acid-producing bacteria or methane-fermenting bacteria in the sludge pass through the screen 5 and circulate in the tank 1 to be further digested. It becomes digested sludge.

On the other hand, an organic substance such as a wood-based substance having a size larger than the mesh width of the screen 5 and requiring a long time for digestion is retained in the sludge-containing liquid on the side of the treatment object introduction port 3 and stirred. Digestion takes place. As a result, the digestion sludge outlet 2
When the digested sludge is extracted from the mash, organic substances such as wood-based substances and the like that are larger than the mesh width of the screen 5 are prevented from being discharged together with the digested sludge without being digested.

As described above, the woody substance held in the sludge-containing liquid on the inlet side of the material to be treated 3 has more irregularities on the surface as the digestion proceeds, and the specific surface area increases. It functions to increase the concentration of digestive bacteria, so the efficiency of contact between organic substances and methane bacteria in the sludge-containing liquid is improved, and the digestion rate of organic substances is increased, and organic substances including wood-based substances Is suitably digested. In particular, in the case of fermentation at high temperatures, in addition to preventing the emission of undigested woody substances, in addition to this woody substance,
In the digestion apparatus disclosed in Japanese Patent No. 2708087, the same effect as the glass fiber carrier installed in the tank is further exhibited, a high load treatment can be performed with a small tank capacity, and decomposition of the woody substance itself is performed. Speed is also increased.

When the organic substance such as a woody substance or the like having a width equal to or larger than the mesh width of the screen 5 is sufficiently digested at the treatment object inlet 3 side and becomes smaller than the mesh width of the screen 5, the organic material penetrates the screen 5 and freely passes through the screen 5. It is further digested while circulating in the tank 1, and is extracted as digested sludge from the digested sludge outlet 2.

At this time, the liquid in the tank 1 flows from the inlet 3 to the digested sludge outlet 2 along with the discharge, and the undecomposed woody substance at the inlet 3 is removed. Although an attempt is made to accumulate on the surface of the screen 5, an upward flow is formed at the center of the screen by the stirrer 15, and undecomposed wood-based material is separated from the surface of the screen 5.
The entire blockage of the screen is prevented. In addition, since the sludge concentration of the sludge-containing liquid in the tank 1 is made uniform, digestion is performed more efficiently.

As described above, the digestion apparatus 100 of the present embodiment is
By installing the screen 5, an organic substance such as a wood-based substance, which is longer than a predetermined size and takes a long time to digest, is retained in the sludge-containing liquid on the side of the treatment object introduction port 3, and is discharged from the digested sludge discharge port 2. It is prevented from being discharged together with digested sludge without being digested, and the digestion rate of organic substances is improved because the wood-based substance is used as a carrier for digestive bacteria as it is digested. Therefore, it is possible to provide the digestion apparatus 100 capable of reliably digesting organic substances including wood-based substances and having high processing capability.

Next, a digestion apparatus 200 according to a second embodiment will be described with reference to FIG. The digester 200 of the present embodiment is different from the digester 100 of the first embodiment in that the sludge-containing liquid discharged from the digested sludge discharge port 2 is replaced with a stirrer 15 having stirring blades 13a to 13c. 1 and is provided with a stirring device (stirring means) 25 for stirring the sludge-containing liquid by sending it toward the screen 5 from the digested sludge discharge port 2 side. This stirrer 25 is described in detail
A pump 21 for sucking the sludge-containing liquid on the digested sludge discharge port 2 side through the line L1 and sending it again to the digested sludge discharge port 2 side in the tank 1 via the line L2; And a sprinkling nozzle 20 for uniformly discharging the water toward the screen 5 on the digested sludge discharge port 2 side in the tank 1.

It is needless to say that the same effect as in the first embodiment can be obtained even with this configuration.

The digestion apparatus according to the present invention is not limited to the above-described embodiment, but can take various modifications.

For example, in the above embodiment, the screen 5 which is a net is used as the filtering means. However, the present invention is not limited to this. For example, a lattice, a punching plate, or the like may be used.

Further, in the above embodiment, the screen 5 is provided horizontally, but is not limited to this. For example, the screen 5 may be installed vertically. In this case, for example, a treatment object introduction port may be provided on one side of the tank partitioned by the screen, and a digested sludge discharge port may be provided on the other side.

In the above-described embodiment, the digested sludge outlet 2 is provided to the screen 5 by the stirring devices 15 and 25.
The flow is formed from the side to the treatment object inlet 3 side, but is not limited to this. If the filtration area of the screen 5 is sufficiently large and the likelihood of blocking of the screen 5 is low, this is not provided. No problem.

In the above embodiment, a wood-based substance such as rice straw is used as the biodegradable substance. However, the present invention is not limited to this, and other biodegradable substances such as paper may be used.

[0033]

As described above, the digestion apparatus according to the present invention is provided with the filtering means, and the organic substance such as the biologically hardly decomposable substance which is longer than a predetermined size and which is difficult to digest is covered by the filtering means. It is kept in the sludge-containing liquid on the treated material inlet side, and is not moved to the digested sludge outlet side until it is sufficiently digested and smaller than a predetermined size. Accordingly, when the digested sludge is discharged from the digested sludge discharge port, organic substances such as a biorefractory substance having a predetermined size or more are not discharged without digestion together with the digested sludge. In addition, since the biodegradable substance increases in specific surface area as digestion progresses and functions as a carrier for digestive bacteria, the contact efficiency between the organic substance and digestive bacteria in the sludge-containing liquid is improved, and Digestion speed is improved.

[0034] Thus, it is possible to provide a digester capable of surely digesting organic substances including biodegradable substances and having a high processing ability.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of a digestion apparatus of the present invention.

FIG. 2 is a schematic sectional view showing a second embodiment of the digestion apparatus of the present invention.

[Explanation of symbols]

1 ... tank, 2 ... digestion sludge outlet, 3 ... inlet for treated material, 5
... screen (filtration means), 15, 25 ... stirring device (stirring device), 100, 200 ... digestion device.

Claims (2)

[Claims] 1. A digestion apparatus for anaerobically digesting an organic substance into digested sludge, comprising: a tank for storing a sludge-containing liquid; and a container for introducing an organic substance containing a biodegradable substance into the tank. A treated material inlet, a digested sludge outlet for discharging the digested sludge from the inside of the tank, and a sludge-containing liquid in the tank between the treated object inlet and the digested sludge outlet. A filter installed to allow only a substance smaller than a predetermined size to pass therethrough. 2. A stirring means for sending out the sludge-containing liquid from the digested sludge discharge port side to the treatment object introduction port side via the filtration means and stirring the inside of the tank, The digestion device according to claim 1.