JP2002361291A - Anaerobic digesting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sedimentation property and dehydration property of sludge in a solid-liquid separation process of the sludge subjected to anaerobic digestion and to efficiently treat in an anaerobic digesting apparatus to reduce the volume of raw water containing an organic waste liquid by anaerobic treatment. SOLUTION: The raw sludge is subjected to anaerobic digestion in an anaerobic digestion tank 1 and the digested sludge is concentrated by a centrifugal separator 4. The separated sludge is returned to the anaerobic digestion tank 1, while the separated water is discharged to the outside of the system. A part of the digested sludge is solubilized in an ozone reaction tank 3 and then returned to the anaerobic digestion tank 1. A part of the raw sludge is bypassed the anaerobic digestion tank 1 and mixed with the digested sludge, and the mixed sludge is concentrated by the centrifugal separator 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anaerobic digester, and particularly to anaerobic digestion of raw water containing organic wastewater such as organic sludge, night soil, sludge from the first sedimentation basin, excess sludge, livestock manure, food wastewater and the like. TECHNICAL FIELD The present invention relates to an anaerobic digester that reduces the volume of anaerobic digestion sludge generated by anaerobic digestion and improves the sedimentation and dehydration properties of the generated anaerobic digestion sludge.

[0002]

2. Description of the Related Art In a method of aerobically biologically treating an organic wastewater in the presence of activated sludge, a large amount of hardly dewaterable surplus sludge is generated. Also, a method of anaerobically treating in the presence of anaerobic sludge generates a large amount of excess sludge. In order to reduce the volume of such excess sludge, a method of digesting excess sludge aerobically or anaerobically has been used. Among them, in aerobic digestion, excess sludge is simply aerated and digested in a digestion tank, the aerated sludge is separated into solid and liquid, and the separated sludge is returned to the digestion tank. In anaerobic digestion, excess sludge is put into a digestion tank and digested by the action of anaerobic bacteria.

[0003] Such a digestion method digests by utilizing the action of aerobic or anaerobic organisms. However, since excess sludge itself is biologically stable through biological treatment, sludge is reduced. There is a limit to the volume of waste sludge, usually 35
Only ５０50% volume reduction.

In order to improve such a point, as shown in FIG. 2, raw sludge such as surplus sludge is supplied to the anaerobic digestion tank 1 from a raw mud supply path 11 and the anaerobic digestion tank 1 performs anaerobic digestion. Then, the digested sludge is sent to the solid-liquid separation means 2 through the sludge transfer path 12 to be separated into solid and liquid, and the separated water is discharged out of the system from the treated water discharge path 13 to return the separated sludge (condensed sludge) to the sludge. In the method of circulating the digested sludge from the passage 14 to the anaerobic digestion tank 1, the ozone reaction tank 3 is provided, a part of the digested sludge is fed to the ozone reaction tank 3 from the sludge extraction passage 15, and the digested sludge is converted into ozone by the ozone reaction tank 3. A method has been proposed in which after treatment and solubilization, the solution is returned to the anaerobic digestion tank 1 from the solubilized liquid return path 16 (Japanese Patent Application Laid-Open No. 8-299999).
No.). With this method, most of the viable bacteria in the sludge are killed by ozone treatment of the digested sludge, and the sludge is reformed to be easily biodegradable. Therefore, this sludge must be returned to the anaerobic digestion tank. Thereby, the sludge can be further decomposed to significantly reduce the volume of sludge. In this method, the amount of excess sludge generated can be reduced to zero by treating the sludge with a larger amount than the growing sludge with ozone.

By returning the separated sludge separated and concentrated by the solid-liquid separation means 2 to the anaerobic digestion tank 1 for circulating treatment, the reaction efficiency and the operation efficiency of the apparatus can be improved, and the treatment efficiency can be increased. it can.

[0006]

In carrying out the method shown in FIG. 2, in order to increase the treatment efficiency, the solid-liquid separation means 2 efficiently separates the digested sludge into solid and liquid, and is highly concentrated. It is necessary to return high concentration sludge to the anaerobic digestion tank 1. However, digested sludge flowing out of the anaerobic digestion tank 1 contains a large amount of anionic polymer which is an intermediate product of decomposition by digestion, and has poor sedimentation and dehydration properties. For this reason, the solid-liquid separation property in the solid-liquid separation means 2 is poor, and it is difficult to obtain high-concentration sludge. In addition, when a cationic organic polymer flocculant (cationic polymer) is added to improve the dehydration efficiency, there is a problem that the required addition amount becomes extremely large.

[0007] The present invention solves the above-mentioned conventional problems, and anaerobic-treats raw water containing organic wastewater such as organic sludge, night soil, sewage first sedimentation tank sludge, excess sludge, livestock manure, food wastewater, and the like. Provided is an anaerobic digester capable of improving the sedimentation and dewatering properties of sludge in a solid-liquid separation step of anaerobic digested sludge and performing an efficient treatment in the anaerobic digester which is reduced in volume. The purpose is to:

[0008]

An anaerobic digester according to the present invention comprises: an anaerobic digester; raw water supply means for supplying raw water containing organic wastewater to the anaerobic digester; An anaerobic digester comprising: a solid-liquid separation unit for solid-liquid separation of the effluent from the digestion tank; and a sludge return unit for returning sludge separated by the solid-liquid separation unit to the anaerobic digestion tank. A bypass unit that bypasses the anaerobic digestion tank and joins the effluent of the anaerobic digestion tank to feed the solid-liquid separation unit.

In the present invention, a part of raw water (hereinafter sometimes referred to as “raw mud”) is bypassed to the anaerobic digestion tank,
Mixing with the effluent of the anaerobic digestion tank (hereinafter sometimes referred to as “digestion sludge”) and separating the mixed sludge by solid-liquid separation means enables efficient solid-liquid separation. Become. The details of the mechanism by which the sedimentation and dewatering properties of the sludge are improved by mixing the raw mud are not clear, but the dilution effect of mixing the raw sludge and the fiber content in the raw mud It is presumed to form a water channel during dehydration.

The anaerobic digester of the present invention further comprises a solubilizing means for solubilizing a part of the effluent of the anaerobic digestion tank, and the solubilized solution from the solubilizing means is returned to the anaerobic digestion tank. It is preferable to include a means for returning the solubilized solution, and a means for adding an organic polymer flocculant (polymer) to the effluent of the anaerobic digestion tank.

In the present invention, it is preferable to use a centrifuge as the solid-liquid separation means.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the anaerobic digester of the present invention. In FIG. 1, members having the same functions as those shown in FIG. 2 are denoted by the same reference numerals.
Reference numeral 4 denotes a centrifugal separator, reference numeral 17 denotes a raw mud bypass which mixes the raw sludge into the digested sludge in the sludge transfer passage 12 by bypassing the anaerobic digestion tank 1, and reference numeral 18 denotes a digested sludge in the sludge transfer passage 12. This is a pipe for injecting the polymer.

The raw mud is first introduced into the anaerobic digestion tank 1 from the raw mud supply path 11 and subjected to methane fermentation. At this time, part of the raw mud is supplied from the raw mud bypass path 17 to the anaerobic digestion tank. 1 and is fed to the subsequent sludge return path 12.

In the anaerobic digestion tank 1, the raw sludge is mixed with a concentrated sludge returned from a centrifugal separator 4 described below and a solubilized liquid returned from the ozone reaction tank 3, and mixed with methane under stirring by a stirrer or the like. A fermentation process is performed. By this methane fermentation treatment, organic matter in the sludge is decomposed by acid-producing bacteria and methane-producing bacteria. The digestion gas containing methane gas generated by this methane fermentation is discharged out of the system from a gas extraction path (not shown).

From the anaerobic digestion tank 1, a sludge transfer path 1
A part of the digested sludge is taken out through 2 and mixed with the raw mud from the raw mud bypass 17, and after the polymer is added from the pipe 18, it is sent to the centrifugal separator 4 and concentrated. The concentrated sludge from the centrifugal separator 4 is returned to the anaerobic digestion tank 1 from the sludge return line 14. A part of this concentrated sludge is discharged out of the system as a surplus sludge from a surplus sludge discharge passage (not shown) as necessary. The separated water of the centrifugal separator 4 is discharged out of the system through a treated water discharge passage 13 and is treated by an arbitrary method such as activated sludge treatment.

A part of the digested sludge in the sludge transfer passage 12 is shown in FIG.
In the same manner as in the conventional method shown in FIG. 1, the water is fed to the ozone reaction tank 3 through the sludge extraction path 15 and solubilized by ozone treatment. The solubilized liquid in the ozone reaction tank 3 is returned to the anaerobic digestion tank 1 through the solubilized liquid return path 16.

As described above, by solubilizing digested sludge subjected to methane fermentation and performing methane fermentation again, the amount of excess sludge discharged outside the system can be significantly reduced.

Further, the digested sludge from the anaerobic digester 1 is extracted and concentrated by the centrifugal separator 4, and the concentrated sludge is removed from the anaerobic digester 1.
By returning the sludge to the sludge and concentrating the sludge, the reaction efficiency of the solubilization treatment and the operation efficiency of the apparatus can be increased, and the treatment efficiency can be improved. In addition, in this concentration, by adding a cationic polymer, the cohesiveness of sludge can be increased, and the concentration efficiency can be increased.

According to the present invention, in concentrating the digested sludge, by mixing the raw sludge, the sedimentation and dewatering properties of the sludge are improved, the required amount of polymer added is reduced, and the centrifugal separator 4 is removed. The solid content of the separated sludge can be increased.

The apparatus shown in FIG. 1 is an example of an embodiment of the anaerobic digester of the present invention, and the present invention is not limited to the illustrated apparatus.

For example, in FIG. 1, an ozone reaction tank is employed as a means for solubilizing digested sludge. However, a solubilizing means using an oxidizing agent having a strong oxidizing power such as hydrogen peroxide, other physical treatment, and chemical treatment Or thermal treatment.
In addition, a centrifugal separator is used as a solid-liquid separating means for digested sludge, but other solid-liquid separating means such as a sedimentation tank and a membrane separator can be used. However, it is preferable to use a centrifugal separator in terms of sludge concentration efficiency.

In FIG. 1, the digested sludge from the anaerobic digestion tank 1 is solubilized in the ozone reaction tank 3 and returned to the anaerobic digestion tank 1. A solubilization treatment may be performed to return to the anaerobic digestion tank 1.

The solubilized solution is supplied to the raw mud supply path 11.
In addition to returning to the anaerobic digestion tank 1, it may be directly returned to the anaerobic digestion tank 1. The sludge to be solubilized may be directly extracted from the anaerobic digestion tank 1.

Further, a part of the raw mud is transferred to the digestion sludge transfer path 12.
In addition, the raw mud may be directly introduced into the centrifugal separator 4 as shown in FIG.

In the present invention, the ratio of raw mud which bypasses the anaerobic digestion tank 1 and is separated into solid and liquid together with digested sludge is appropriately determined in accordance with the properties of the raw sludge, operating conditions of the apparatus, required concentration characteristics and the like. However, in the normal case, it is 1/2
It is preferable to fractionate １／1/1 and perform solid-liquid separation together with digested sludge. If the amount of the raw sludge is too small, the effect of improving the sludge concentration efficiency according to the present invention cannot be sufficiently obtained,
If the amount is too large, the amount of raw mud that bypasses the anaerobic digestion tank increases, and the power required for solid-liquid separation increases. In this case, the amount of the polymer added is 0.1 to 0.1% of the sum of the digested sludge and the raw sludge (the amount of sludge introduced into the centrifuge 4).
It is preferably about 0.4% by weight.

In this way, the sludge which is concentrated by mixing the raw sludge with the digested sludge and separating it into solid and liquid and returned to the anaerobic digestion tank 1 returns the concentrated sludge when the solid content concentration is too low. In this case, the effect of improving the treatment efficiency cannot be sufficiently obtained, and if it is too high, the sludge is difficult to disperse in the digestion tank.
It is preferable to set the degree. Therefore, in order to obtain such concentrated sludge of solid content concentration, a separated water return path 19 is provided in the treated water discharge path 13 for taking out the separated water from the centrifuge 4 as necessary, and a part of the separated water is provided. May be fed to the sludge return path 14 to adjust the concentration of the concentrated sludge.

The amount of digested sludge fed to the ozone reaction tank 3 for solubilization is preferably about 20 to 80% of the amount of digested sludge withdrawn from the anaerobic digestion tank 1.

Such an anaerobic digester of the present invention comprises organic sludge, night soil, sewage first settling tank sludge, and excess sludge (the activated sludge of the sewage first settled in the first settling tank is subjected to activated sludge treatment.
It is suitable for the treatment of sludge in a sedimentation basin that separates this into sludge and treated water), livestock manure, food wastewater, etc., or a mixture of these mixed sludge, and efficiently reduces the volume of sludge with high treatment efficiency. Can be performed.

[0030]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 Sludge load 0.2 kg using peptone and yeast extract as substrates
Excess sludge (hereinafter, referred to as “synthetic wastewater sludge”) when the activated sludge treatment was performed at −BOD / kg-SS · d was used as raw sludge, and the sludge was treated by the anaerobic digester in FIG. [Raw properties] TS: 25 g / L TVS: 23 g / L COD _Cr : 30 g / L

50% of the raw mud flowing in was mixed with digested sludge from the anaerobic digester 1 by bypassing the anaerobic digester 1 and concentrated by a centrifuge. Anaerobic digestion tank (capacity 1m
Loading of ^{3) 1.5kg-COD / m 3 · d} , the water temperature is 35 ° C.. 25 L / d of 50 L / d of digested sludge withdrawn from anaerobic digestion tank 1
Feeding feeds were returned to anaerobic digestion tank 1 after ozone treatment with ozone injection rate _0.04g-O 3 / _g-SS in. The remainder of the digested sludge is mixed with the raw sludge, and a polymer (40:60 of acrylamide and quaternary methyl chloride of dimethylaminoethyl acrylate) is mixed with the amount of the mixed sludge.
(Molar ratio) copolymer) in the amount shown in Table 1 and solid-liquid separation in a centrifuge 4 at 2500 G.

The concentrated sludge concentrated by the centrifugal separator 4 is returned to the anaerobic digestion tank 1 and separated water (desorbed liquid) 50 L / d.
Was discharged out of the system.

In addition, once a week, 1 L
Was extracted from the return path of the concentrated sludge.

In this treatment, the solids concentration of the concentrated sludge concentrated by the centrifuge 4 and the SS concentration of the desorbed liquid are shown in Table 1.
As shown in FIG.

Example 2 A treatment was performed in the same manner as in Example 1 except that sewage sludge having the following properties was used as raw mud. [Raw properties] TS: 25 g / L TVS: 20 g / L COD _Cr : 28 g / L At this time, the polymer addition amount, the solid content concentration of the concentrated sludge, and the SS concentration of the desorbed liquid were as shown in Table 1. .

Comparative Examples 1 and 2 In Examples 1 and 2, treatment was carried out in the same manner as in Examples 1 and 2, except that part of the raw mud was not mixed with the digested sludge but was entirely introduced into the anaerobic digestion tank 1. And the solids concentration of the concentrated sludge and the SS concentration of the desorbed liquid were examined. The results are shown in Table 1.

Further, the amount of polymer added was increased, and the amount of polymer required to obtain concentrated sludge having the same solid content concentration as in Examples 1 and 2 was investigated. The results are shown in Table 1. In addition,
In this case, in Examples 1 and 2 and Comparative Examples 1 and 2,
No significant difference was found in sludge volume reduction efficiency, separated water (treated water) water quality, and the like.

[0039]

[Table 1]

From Table 1, it can be seen that, according to the present invention, the concentration efficiency of digested sludge can be increased to perform an efficient sludge volume reduction treatment.

[0041]

As described in detail above, according to the anaerobic digester of the present invention, organic effluent such as organic sludge, night soil, sewage first sedimentation tank sludge, surplus sludge, livestock manure, food wastewater and the like are included. In an anaerobic digester that reduces the volume of raw water by anaerobic treatment, the sedimentation and dehydration properties of the sludge in the solid-liquid separation process of anaerobic digested sludge are improved, and thus the cationic properties used for solid-liquid separation are improved. After reducing the required amount of the polymer, the highly concentrated sludge can be returned to the anaerobic digestion step for efficient treatment.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of an anaerobic digester of the present invention.

FIG. 2 is a system diagram showing a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anaerobic digestion tank 2 Solid-liquid separation means 3 Ozone reaction tank 4 Centrifuge

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D040 AA25 AA27 AA31 4D059 AA01 AA04 AA05 BA12 BC02 BE31 BE38 BE42 BE57 CA28 DA43 DA44

Claims (4)

[Claims] An anaerobic digestion tank, raw water feeding means for feeding raw water containing organic wastewater to the anaerobic digestion tank, and solid-liquid separation for solid-liquid separation of the effluent of the anaerobic digestion tank Means, and a sludge return means for returning the sludge separated by the solid-liquid separation means to the anaerobic digestion tank, wherein the anaerobic digestion device bypasses a part of the raw water through the anaerobic digestion tank. An anaerobic digester, comprising: a bypass unit that joins an effluent of an anaerobic digestion tank and feeds the combined liquid to the solid-liquid separation unit. 2. The solubilizing means according to claim 1, wherein a part of the effluent of said anaerobic digestion tank is solubilized, and the solubilization liquid of said solubilizing means is returned to said anaerobic digestion tank. An anaerobic digester comprising a liquid returning means. 3. An anaerobic digester according to claim 1, wherein said solid-liquid separation means is a centrifuge. 4. The anaerobic digester according to claim 1, further comprising a means for adding an organic polymer flocculant to the effluent of the anaerobic digester.