JP3853971B2 - Aerobic digestion method of excess sludge - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for reducing excess sludge discharged from an activated sludge treatment facility for organic wastewater, and more particularly to a method for reducing excess sludge by subjecting it to aerobic digestion. .
[0002]
[Prior art]
Conventionally, surplus sludge generated in large quantities from an activated sludge treatment facility such as a sewage treatment facility has been dehydrated and then disposed of as landfill or incinerated as industrial waste. However, in recent years, it has become difficult to secure landfills, and incineration of a large amount of excess sludge increases equipment costs and maintenance costs, so there is a need to reduce excess sludge.
[0003]
Biological reduction methods for surplus sludge include aerobic digestion and anaerobic digestion, and surplus sludge is crushed by mechanical means and then returned to the biological treatment tank for decomposition. Etc. are known. However, the aerobic digestion method and the anaerobic digestion method have a problem that the weight reduction rate is low while requiring a long residence time of 10 days or more, and have not been used in recent years. As a method for improving the rate of sludge reduction by the aerobic digestion method, Japanese Patent Publication No. 57-19719 discloses that excess sludge is solubilized in a decomposition tank by homogenizer grinding, mixer grinding, etc. A digestion method has been proposed, but in this method, a large amount of new sludge is generated in the aerobic digester from the BOD component generated by solubilizing the sludge, and the newly generated sludge is solubilized. Therefore, aerobic digestion is difficult to proceed and there is a problem that the effect of reducing sludge is not improved so much. Japanese Patent Publication No. 57-24697 proposes a method in which excess sludge is crushed and solubilized by mechanical means, and then returned to a biological treatment tank for wastewater for decomposition to reduce the amount of surplus sludge generated. However, in this method, since the COD component produced by solubilizing sludge is not sufficiently decomposed in the biological treatment tank, the quality of the wastewater-treated water is deteriorated. There are problems such as the need to modify the tank aeration equipment.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for aerobic digestion of surplus sludge that can significantly reduce the amount of surplus discharged sludge economically by an aerobic digestion method without deteriorating the activated sludge treatment water quality of organic wastewater. It is what.
[0005]
[Means for Solving the Problems]
As a result of diligent studies to solve such problems, the present inventors have treated excess sludge generated from a wastewater treatment facility by an aerobic digestion method, and then wet a part or all of the aerobically digested sludge. The present inventors have found that surplus sludge can be greatly reduced by crushing with a medium agitating mill and returning to the aerobic digester.
That is, the present invention introduces surplus sludge discharged from an activated sludge treatment facility of organic wastewater into an aerobic digestion tank and performs aerobic digestion, and then a part or all of the aerobic digested sludge is aerobic digestion. upon lose weight the sludge was returned to the bath, the it is one that returned to aerobic digestion tank part or all of the sludge to be returned after treatment with wet medium stirring mill, in the wet medium stirring mill The gist of the method of aerobic digestion of surplus sludge is characterized in that the amount of sludge to be treated is 1 to 4 times the amount of solids with respect to surplus sludge introduced into the aerobic digester.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
Hereinafter, the sludge generated excessively from the activated sludge treatment facility is referred to as “surplus sludge”, the aerobically digested sludge is referred to as “biologically treated sludge”, and the sludge that has been subjected to the wet medium stirring mill treatment is referred to as “solubilized sludge”.
[0007]
In the present invention, surplus sludge generated by treating activated sludge from organic wastewater such as sewage, food factory wastewater, and chemical factory wastewater is first introduced into an aerobic digestion tank for aerobic digestion.
As the amount of surplus sludge to be introduced, normal conditions for aerobic digestion treatment can be employed. For example, 0.1 to 10 kg of sludge per day may be introduced into 1 m ^{3 of the} aerobic digester.
The surplus sludge to be introduced may be crushed in advance, and the pulverization can be performed by ozone treatment, alkali treatment, heat treatment, etc. in addition to mechanical treatment by a wet medium stirring mill, ultrasonic wave, homogenizer, mixer, etc. .
[0008]
The treatment conditions for the aerobic digestion treatment are not particularly limited, and the same conditions as those for a normal aerobic digestion treatment can be adopted. For example, the sludge concentration in the aerobic treatment tank is preferably 4 to 50 g / l, The treatment temperature is preferably 5 to 65 ° C., and the oxygen concentration in the treatment tank is preferably 1 to 5 mg / l.
[0009]
Next, the biologically treated sludge thus subjected to the aerobic digestion treatment is separated into the treated water in a solid-liquid separation tank, and then returned to the aerobic digestion tank.
The amount of biologically treated sludge to be returned is not particularly limited, but is preferably 0.5 to 20 times the surplus sludge to be introduced.
[0010]
In the present invention, part or all of the biologically treated sludge to be returned to the aerobic digester is crushed by a wet medium stirring mill and then returned to the aerobic digester.
The wet medium agitation mill processing referred to in the present invention is a method in which sludge is introduced into a mill chamber filled with a crushing medium (beads), and the beads are agitated and agitated by rotating an agitation shaft equipped with a disk and a pin. This refers to crushing sludge by shear friction generated between the beads. The crushed sludge and beads are separated by a slit or screen in the mill, and the crushed sludge is discharged out of the system.
[0011]
The amount of biologically treated sludge to be subjected to wet medium stirring mill treatment is preferably 1 to 4 times the amount of solid matter, particularly 1 to 3 times the amount of solid matter with respect to the excess sludge introduced into the aerobic digester. If the amount of biologically treated sludge to be processed with a wet-medium agitating mill is less than 1 times the amount of solids compared to the excess sludge, the effect of sludge reduction will be reduced. Just doing this will not significantly improve the sludge reduction effect.
[0012]
As biologically treated sludge to be introduced into the mill room, biologically treated sludge after aerobic digestion treatment or separated sludge obtained by solid-liquid separation may be used as it is, but usually the sludge of biologically treated sludge after aerobic digestion treatment is used. Since the concentration is about 0.5 to 1% by weight and the sludge concentration of the separated sludge after solid-liquid separation is as low as about 1 to 2% by weight, it is possible to concentrate these sludges using a sludge concentrator. desirable. Concentrating sludge to increase the sludge concentration and then performing wet media agitation mill treatment reduces the amount of treatment and significantly shortens the treatment time compared to direct introduction of biological treatment sludge. Therefore, the operating cost can be greatly reduced. The concentrating device is not particularly limited, and examples thereof include a centrifugal separator and a flotation concentrator. Although it will not specifically limit if it is the density | concentration which shows fluidity | liquidity as a sludge density | concentration after concentration, It is preferable that it is 7 weight% or less, and 2 to 7 weight% is especially preferable. When the sludge concentration is higher than 7% by weight, the fluidity is almost lost, so that it becomes difficult to crush by the wet medium stirring mill treatment.
[0013]
Examples of the medium for crushing used in the wet medium stirring mill process include beads such as glass and zirconia, and beads having a true specific gravity of 2.0 to 7.0 are preferable. If the true specific gravity is greater than 7.0, the cost for stirring the beads increases, and if it is less than 2.0, the microorganisms cannot be sufficiently disrupted. In addition, if the sludge concentration introduced into the mill chamber is high, the sludge cannot be sufficiently crushed if the true specific gravity is low. If the sludge concentration is high, beads having a true specific gravity of 5.0 to 7.0 should be used. Is desirable.
[0014]
The particle size of the beads for crushing is preferably 0.05 to 2.0 mmφ, particularly preferably 0.05 to 1.0 mmφ. If the particle size of the beads is larger than 2.0 mmφ, the space between the beads will be larger, and it will be difficult to crush microorganisms such as bacteria of several μm to several tens of μm that make up the sludge. It becomes difficult to separate the parts.
[0015]
Among the conditions of the wet medium stirring mill treatment, the bead filling rate is preferably 50 to 100%, particularly 70 to 90% from the crushing effect and power consumption, and the disk (pin) tip peripheral speed is preferably 3 to 30 m / Seconds, in particular 5 to 20 m / second, are preferred. The direction of the mill chamber may be either a vertical type or a horizontal type, and examples of the stirring device for stirring the crushing medium include a disk type, a pin type, and a pin disk type.
[0016]
The sludge residence time in the wet medium agitation mill treatment is appropriately set depending on the sludge concentration to be introduced, the crushing medium to be used, etc., and is not particularly limited, but is usually preferably 20 seconds to 20 minutes, particularly 30. Second to 10 minutes are preferred. If the residence time is shorter than 20 seconds, there is a possibility that the sludge is not sufficiently crushed, and even if it is longer than 20 minutes, only the power consumption increases and the crushing effect is not improved so much.
[0017]
The treatment temperature is preferably 60 ° C. or less, and particularly preferably 4 to 40 ° C. When the treatment temperature is higher than 60 ° C., a part of the sludge component is thermally denatured to become a hardly decomposable substance, which is not preferable because the quality of the treated water may be deteriorated. Usually, since the temperature of the sludge crushed by the mill treatment rises by about 10 to 30 ° C. compared to the sludge before the treatment, it is preferable to cool with cooling water when the temperature is high as in summer. Cooling can be easily performed by passing cooling water between the mill chambers of the wet-medium agitating mill, since it normally has a double jacket structure.
[0018]
The example of the outline of the process of the aerobic digestion method of the excess sludge of the present invention as described above is as shown in FIG. 1, FIG. 2, and FIG.
In FIG. 1, surplus sludge 1 discharged from an activated sludge treatment facility for organic wastewater such as sewage, food factory wastewater, and chemical factory wastewater is introduced into an aerobic digester 2 and subjected to aerobic digestion. In the aerobic digestion tank 2, the sludge concentration is maintained almost constant in order to efficiently perform the aerobic digestion treatment, and when the sludge concentration becomes high, it is extracted as the extracted sludge 3. Part of the biologically treated sludge 4 after aerobic digestion is sent to a wet medium stirring mill 5, and the rest is separated into separated water 7 and separated sludge 8 in a solid-liquid separation tank 6. The biologically treated sludge 4 sent to the wet medium agitating mill 5 is treated by the wet medium agitating mill 5 to become a solubilized sludge 9, which is returned to the aerobic digester 2 together with most of the separated sludge 8. In FIG. 2, the biological treatment sludge 4 is all sent to the solid-liquid separation tank 6, and a part of the separated sludge 8 is transferred to the wet medium stirring mill 5. In FIG. 3, a part of the separated sludge 8 is concentrated in the sludge concentrating device 10 and then transferred to the wet medium stirring mill 5.
[0019]
In the present invention, surplus sludge generated from a wastewater treatment facility is treated by an aerobic digestion method, and sludge newly generated in an aerobic digester is crushed and solubilized by a wet medium agitation mill, and further By aerobic digestion in the aerobic digester, surplus sludge is decomposed into carbon dioxide and water, and a significant reduction in surplus sludge is realized. As a result, the life of the sludge landfill can be extended, and the sludge incineration facility can be significantly reduced in scale. In addition, separation of wastewater treatment and sludge treatment does not cause water quality deterioration of wastewater treatment facilities, and when used in existing facilities, it is not necessary to modify aeration equipment for biological treatment tanks. It is economical because excess sludge can be reduced.
[0020]
【Example】
Next, the present invention will be specifically described with reference to examples.
Examples 1-3, Comparative Example 1
According to the treatment flow shown in FIG. 1, the aerobic digestion process of the excess sludge 1 (solid substance concentration 5g / L) generated in the sewage treatment facility was performed.
That is, 1 L of surplus sludge 1 (solid matter concentration 5 g / L) of a sewage treatment facility was supplied to a 10 L aerobic digester 2 per day. The water temperature of the aerobic digester 2 was 25 ° C., the amount of aerated air was 0.7 to 0.8 L / min, and the sludge was appropriately extracted so that the sludge concentration was 4 to 5 g / L (extracted sludge 3). A part of the biologically treated sludge 4 digested in the aerobic digestion tank 2 was sent to the wet medium agitation mill 5, solubilized by the wet medium agitation mill, and returned to the aerobic digester 2. The remaining bioactive sludge 4 was subjected to solid-liquid separation in a sedimentation tank (solid-liquid separation tank 6), the separated water 7 was discharged out of the system, and the separated sludge 8 was returned to the aerobic digestion tank 2. The amount of biologically treated sludge 4 to be treated with a wet medium agitating mill is the amount of solid matter (5 g / day: Example 1) that is 1 times the amount of (surplus) sludge treated amount (15 g / day: Example 2). ) 4 times the amount of solids (20 g / day, Example 3), and compared with a system (Comparative Example 1) in which all biologically treated sludge 4 was returned without wet media stirring milling. Wet medium stirring mill treatment uses DYNO-MILL KDL (manufactured by Bachofen, Switzerland) as a wet medium stirring mill, and 0.6 mmφ glass beads (manufactured by Silibeads, true specific gravity 2.5) as a crushing medium. Processing was performed at a bead filling rate of 85%, a disk tip peripheral speed of 8.5 m / sec, a residence time of 2 minutes, and a processing temperature of 10 ± 2 ° C.
The result is shown in FIG.
[0021]
FIG. 4 is a diagram showing the influence of sludge reduction by aerobic digestion treatment of wet medium stirring mill treatment, and the vertical axis shows the ratio of sludge discharge outside the system to the total surplus supply sludge weight.
From FIG. 4, when the biologically treated sludge is returned without being subjected to the wet-medium agitating mill treatment (Comparative Example 1), only 28% of the sludge is reduced, whereas part of the biologically treated sludge is wet. 49% (Example 1), 65% (Example 2) and 64% (Example 3) are reduced by media stirring mill treatment, respectively, and a part of biologically treated sludge is wet media stirring mill It turns out that the amount of sludge discharged | emitted out of the system can be reduced significantly by returning to an aerobic digester after processing and solubilizing.
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the excess sludge discharged | emitted can be reduced significantly by an aerobic digestion method economically, without deteriorating the activated sludge process water quality of organic wastewater.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing an example of an outline of steps of an aerobic digestion method of excess sludge according to the present invention.
FIG. 2 is a diagram showing another example of the outline of the process of the aerobic digestion method of excess sludge according to the present invention.
FIG. 3 is a diagram showing another example of the outline of the process of the aerobic digestion method of excess sludge according to the present invention.
FIG. 4 is a diagram showing the influence of wet medium stirring mill treatment on sludge reduction by aerobic digestion treatment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Surplus sludge 2 Aerobic digestion tank 3 Pull-out sludge 4 Biological treatment sludge 5 Wet medium stirring mill 6 Solid-liquid separation tank 7 Separation water 8 Separation sludge 9 Solubilization sludge 10 Sludge concentrator

Claims (1)

After surplus sludge discharged from the activated sludge treatment facility of organic wastewater is introduced into the aerobic digestion tank and subjected to aerobic digestion, a part or all of the aerobic digested sludge is returned to the aerobic digestion tank and sludge is recovered. When the amount of sludge to be returned is treated with a wet medium stirring mill after part or all of the returned sludge is returned to the aerobic digester, the amount of sludge to be treated with the wet medium stirring mill is A method for aerobic digestion of surplus sludge, wherein the amount of solids is 1 to 4 times the amount of surplus sludge introduced into the aerobic digester.

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