JP2001340889A - Treating method for organic wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating method for organic wastewater, stably operating a wet medium stirring type mill and not causing the deterioration of treated water quality in the case that the amount of surplus sludge generated at the purification of the organic wastewater by biological treatment is reduced by using the wet medium stirring type mill. SOLUTION: In this treating method for organic wastewater, after treating organic wastewater 1 in a biological treatment tank 2, the treated liquid is subjected to solid-liquid separation 4 and then the separated water is discharged as treated water 5, and the separated sludge 6 is returned to the biological treatment tank 2 after solubilizing a part or all of the sludge by using the wet medium stirring type mill 11. The solubilization treatment is carried out after removing foreign matter, which blocks the passage of the sludge in the wet medium stirring type mill, from the sludge to be solubilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating organic wastewater by biologically treating and purifying organic wastewater, and more particularly to reducing the amount of excess sludge generated in a biological treatment tank. And a method for treating organic wastewater.

[0002]

2. Description of the Related Art Conventionally, raw sludge generated in large quantities from wastewater treatment facilities such as sewage treatment facilities and surplus sludge derived from biological treatment tanks are dewatered and then landfilled or incinerated as industrial waste. However, in recent years, it has become difficult to secure landfill sites, and incineration and disposal of a large amount of excess sludge increases equipment costs and maintenance costs. Therefore, it is required to reduce excess sludge.

[0003] In order to solve these problems, the excess sludge derived from the biological treatment tank is solubilized, thereby improving the biodegradability, increasing the decomposition rate by the biological treatment, and removing the solubilized excess sludge from the biological treatment tank. Many methods have been proposed to reduce the amount of excess sludge generated biologically by using a biological treatment tank after the sludge is ground by a wet medium stirring type mill or the like. A method for reducing the amount of sludge generated by decomposing the sludge has been proposed.

[0004] The wet medium agitation type mill treatment is to continuously introduce sludge into a mill chamber filled with a crushing medium (beads),
A method in which beads are stirred by rotating a stirring shaft equipped with a disk or a pin at high speed, and the sludge is solubilized by the shear friction generated between the stirred beads, and the sludge can be effectively solubilized, It is a method for solubilizing sludge which is excellent in that it is easy to handle and has little generation of hardly biodegradable substances.

[0005]

However, depending on the type of wastewater, a large amount of foreign substances, such as fibrous substances, which cannot be sufficiently crushed by a wet medium stirring mill and cannot be treated in a wastewater treatment facility or the like exist in the sludge. In some cases, even in cases where there is little foreign matter in the wastewater, in recent years, as a method for improving the treatment capacity of the biological treatment tank, wastewater treatment by introducing a fiber carrier made of polyester or the like into the biological treatment tank has been carried out. A method has been developed.In wastewater treatment plants that perform such treatment, sludge contains a small amount of fibrous material, and these foreign substances clog the slits and screen of the bead separation section. Therefore, there was a problem that stable operation of the mill became impossible.

[0006] Therefore, the present inventors, these foreign substances,
As a method of performing wet medium agitation milling after grinding so that it can pass through the gap of the bead separation part of the wet medium agitation type mill, sludge is processed by a mill mill type pulverizer, and then wet medium agitation type milling is performed. A sludge crushing method characterized by this is proposed. (Japanese Patent Application No. 11-13207
No. 0) However, even in this method, when the ground foreign matter is hardly biodegradable, there is a possibility that the quality of the treated water may be reduced.

[0007] The present invention solves the above-mentioned problems, and is intended to reduce the amount of excess sludge generated when biologically treating and purifying organic wastewater using a wet-medium-stirring mill. An object of the present invention is to provide a method for treating organic wastewater, which can stably operate a wet medium stirring mill and does not cause deterioration in treated water quality.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve such problems, and as a result, from the sludge generated when biologically treating organic wastewater, the sludge of a wet-medium stirring mill is used. After removing foreign matter such as fibrous material that blocks the path of the slurry, by milling, even sludge containing a large amount of foreign material such as fibrous material can efficiently and stably solubilize the sludge, The biological treatment of the solubilized sludge again can greatly reduce the amount of excess sludge generated, and can reduce the quality of treated water because it is possible to discharge non-biodegradable foreign substances out of the biological treatment system. They found that they would not invite, and arrived at the present invention.

That is, according to the present invention, when the organic wastewater is treated in the biological treatment tank, the treatment liquid is separated into solid and liquid, the separated water is discharged as treated water, and the separated sludge is returned to the biological treatment tank. In a method for treating organic wastewater in which part or all of it is solubilized using a wet-medium stirring mill and then returned, foreign matter that blocks the path of the sludge of the wet-medium stirring mill from the sludge to be solubilized The gist of the present invention is a method for treating organic wastewater, which comprises the steps of:

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The organic wastewater targeted by the present invention is not particularly limited as long as it is a wastewater containing organic matter treated by a normal biological treatment method, and domestic wastewater, human waste, industrial wastewater such as pulp manufacturing wastewater. And the like. Naturally, organic sludge may be used.

[0011] Although there is a small amount of these organic wastewaters, foreign substances that may block the passage of the sludge of the wet medium stirring mill during treatment with the wet medium stirring mill are fiber-shaped. And those in the form of particles, such as plastic, stone, metal, paper,
Human hair and the like are conceivable, which are generally biodegradable.

The biological treatment method of the present invention is not particularly limited as long as the biological treatment is performed on such organic wastewater, and the organic wastewater is treated in an aeration tank in the presence of activated sludge. Aerobic treatment for aeration and anaerobic treatment are mentioned, and these treatments are performed alone or in combination. Naturally, a case where a fiber carrier or the like is charged into these biological treatment tanks may be used.

As a method for solid-liquid separation of the treatment liquid discharged from the biological treatment tank, separation by a membrane or separation by a sedimentation tank can be mentioned. The separated water after solid-liquid separation is discharged as treated water. In addition, the separated sludge is partially withdrawn as surplus sludge as necessary, and most of the separated sludge is returned to the biological treatment tank as returned sludge.

In the present invention, foreign matter that blocks the passage of the sludge in the wet medium stirring mill is removed. The removal of foreign substances contained in the sludge may be performed before the wet-medium-stirring mill treatment, and is performed on wastewater in addition to sludge and separated sludge in the biological treatment tank.

In the present invention, the means used for removing foreign matter is not particularly limited as long as the foreign matter to be removed can be removed, but it is possible to employ a filtration method using an inclined type or a drum type screen, or a method using gravity such as sedimentation. And methods utilizing centrifugal force such as a centrifuge and a cyclone. These methods can be used alone, in series, or in parallel.

In the case where a screen is used for removing foreign matter, the shape, size, material, filtration rate and the like are appropriately set depending on the ratio and properties of the foreign matter to be introduced, and are not particularly limited. Since the gap between the bead separation portions is the narrowest portion in the sludge path, it is desirable that the opening of the screen be equal to or less than the gap width of the bead separation portion.

Next, the sludge from which a part or all of the returned sludge returned to the biological treatment tank is removed is solubilized using a wet medium stirring mill, and then returned to the biological treatment tank. The sludge to be solubilized may be the treatment liquid itself discharged from the biological treatment tank or the separated sludge after solid-liquid separation, but the sludge concentration of the treatment liquid is usually about 0.1 to 1% by weight. In addition, since the sludge concentration of the separated sludge after solid-liquid separation is as low as about 0.2 to 2% by weight, it is desirable to concentrate these sludges using a sludge concentration device. If the sludge is concentrated to increase the sludge concentration and then solubilized with a wet medium agitated mill, the amount of processing is reduced compared to the case where the processing liquid is directly processed, so the solubilizing device becomes compact,
Further, since the processing time can be greatly reduced, the operating cost can be significantly reduced.

As the amount of sludge to be solubilized, the amount of solid matter of the sludge multiplied by the assimilation of the BOD of the wastewater and a part of the sludge solubilized by the wet medium agitation type mill treatment are converted into sludge again in the biological treatment step. Therefore, it is sufficient to appropriately set the target reduction rate in consideration of the growth amount.

As a method for supplying sludge to the mill, a sludge supply pump may be used.
There is no particular limitation as long as it can discharge sludge, and a vortex pump, a vortex mixed flow pump, a mixed flow pump,
Examples include an axial flow pump, a screw pump, a single screw pump, a plunger pump, and a tube pump.

Examples of the crushing medium (beads) used in the wet medium stirring mill treatment include beads such as glass, alumina and zirconia, and a true specific gravity of 2.0 to 7.0.
0 beads are preferred. When the true specific gravity is less than 2.0, it becomes difficult to crush microorganisms sufficiently, and even when the true specific gravity is more than 7.0, there is almost no improvement in the effect of solubilizing sludge, and the power required for stirring increases. It is not preferable.

The particle size of the crushing medium is 0.05
~ 2.0mmφ is preferred, especially 0.25-1.0mm
φ is preferred. If the particle diameter of the beads is larger than 2.0 mmφ, the voids between the beads become large, so that it becomes difficult to solubilize microorganisms such as bacteria of several μm to several tens μm that constitute the sludge, which is not preferable. On the other hand, if the particle diameter of the beads is smaller than 0.05 mmφ, it is necessary to narrow the gap such as the screen of the bead separating section, and it is difficult to separate the beads at the bead separating section.

Among the conditions of the wet medium stirring type mill treatment, the filling rate of beads is set at 5 from the solubilizing effect and power consumption.
0 to 100%, particularly preferably 70 to 90%, and the peripheral speed of the tip of the disc (pin) is 3 to 30 m / sec, particularly 5 to 30 m / sec.
20 m / sec is preferred. Also, as the orientation of the mill room,
Any of a vertical type and a horizontal type may be used, and examples of a stirring device for stirring the crushing medium include a disk type, a pin type, and a pin disk type.

The residence time of the sludge in the wet medium stirring mill treatment is appropriately set depending on the concentration of the sludge to be introduced, the crushing medium to be used, and the like, and is not particularly limited, but is usually 20 seconds to 20 minutes. Preferred, especially 3
0 seconds to 10 minutes is preferred. If the residence time is shorter than 20 seconds, the sludge may not be sufficiently solubilized, and if the residence time is longer than 20 minutes, the power consumption only increases,
The solubilizing effect does not improve much.

The processing temperature is preferably 60 ° C. or lower, particularly preferably 4 to 40 ° C. Processing temperature is 60 ° C
If it is higher, a part of the sludge component is thermally denatured to become a hardly biodegradable substance, and the quality of the treated water may be deteriorated, which is not preferable. Usually, the temperature of the sludge solubilized by the mill treatment rises by about 10 to 30 ° C. as compared with the sludge before the treatment, and therefore, when the temperature is high as in summer, it is preferable to cool the sludge using cooling water. Cooling can be easily performed by passing cooling water during the cooling, since the mill chamber of the wet medium stirring type mill usually has a double jacket structure.

After the completion of the mill treatment, it is desirable to wash the inside of the mill chamber with water in order to facilitate the next operation start-up. Tap water, treated water,
It may be performed using wastewater or the like. The amount and time of water to be washed may be set as appropriate, but it is preferable to wash until the sludge concentration of the washing water becomes 1% by weight or less. The sludge solubilized in this way has improved biodegradability, and can be returned to the biological treatment tank and biologically degraded to reduce the amount of sludge generated.

Next, the method for treating organic wastewater of the present invention will be described with reference to the drawings. The method for treating organic wastewater of the present invention comprises a biological treatment step, a solid-liquid separation step, a foreign matter removal step, and a sludge solubilization step.

In FIG. 1, organic wastewater 1 such as domestic wastewater, human waste, industrial wastewater such as pulp manufacturing wastewater is supplied to a biological treatment tank 2 for biological treatment. A part of the biologically treated treatment liquid 3 is supplied to a foreign matter removing device 9 to remove foreign matter such as fibers. The foreign matter removal sludge 10 from which foreign matter such as fibers has been removed is supplied to a wet medium stirring type mill 11 and subjected to a solubilization treatment. Solubilized sludge removal treatment sludge 1
0 is solubilized sludge 12 and is returned to the biological treatment tank 2 together with the returned sludge 7. The remaining treatment liquid 3 is sent to a solid-liquid separation device 4 where it is separated into treated water 5 and separated sludge 6. Most of the separated sludge 6 is returned to the biological treatment tank 2 as sludge 7.
When the sludge concentration in the biological treatment tank 2 is maintained substantially constant for efficient biological treatment and the sludge concentration in the biological treatment tank 2 increases, the excess sludge is withdrawn as surplus withdrawn sludge 8. In FIG. 2, all the processing liquid 3 is sent to a solid-liquid separation device 4, and after a part of the separated sludge 6 is supplied to a foreign matter removing device 9, it is supplied to a wet medium stirring mill 11. In FIG. 3, after a part of the separated sludge 6 is supplied to the foreign matter removing device 9, the separated sludge is concentrated in the sludge concentration device 13 and then supplied to the wet medium stirring mill 11.

[0028]

The present invention will be described below in more detail with reference to examples. Comparative Examples 1 to 3 and Example 1 Comparative Example 1 As a system that does not include the foreign matter removing device 9 and the wet medium stirring mill 11 in the processing flow shown in FIG. Was supplied at 50 L per day. The water temperature of the biological treatment tank 2 is 25 ° C., and the dissolved oxygen concentration is 2.
The sludge was appropriately extracted as excess sludge 8 so that the sludge concentration was 5 mg / L and the sludge concentration was 5 g / L. The treatment liquid 3 treated in the biological treatment tank 2 is solid-liquid separated in the sedimentation tank 4,
The separated water was discharged out of the system as treated water 5, and the separated sludge 6 was returned to the biological treatment tank 2 as returned sludge 7.

Comparative Example 2 After completion of the test for 35 days, the biologically treated sludge of Comparative Example 1 was supplied to a wet medium stirring mill 11. Wet media stirring mill 1
1 is manufactured by WAB (DYNO-MILL Type KD
L type), filled with 0.5% zirconia beads (manufactured by Nikkato Corporation) at a filling rate of 85%, and a disk tip peripheral speed of 6.8.
The treatment was performed under the conditions of m / sec, a slit gap of 0.15 mm, a residence time of 2 minutes, and a temperature of 19 ± 1 ° C. As a result, when 8 L of the sludge was passed, the passage of the sludge of the wet medium stirring mill 11 was blocked by foreign matter, and further operation was not possible.

COMPARATIVE EXAMPLE 3 In the treatment flow shown in FIG. 1, a 10-liter biological treatment tank 2 was used as a system for crushing foreign matter and returning it to the biological treatment tank instead of not including the foreign matter removal device 9, and using domestic wastewater 1 Was supplied at 50 L per day. The water temperature of the biological treatment tank 2 is 25 ° C., the dissolved oxygen concentration is 2.5 mg / L, and the sludge concentration is 5 g / L.
The sludge was extracted as surplus withdrawn sludge 8 as appropriate. A part of the sludge in the biological treatment tank 2 was supplied to the wet-medium stirring mill 11 after the sludge was ground to below the slit gap of the wet-medium stirring mill using a crusher. As a pulverizer, a stone mill type pulverizer (MKCA6-3 manufactured by Masuko Sangyo Co., Ltd.)
Mold)), using a grinding wheel made of silicon carbide having a diameter of 150 mm, a grinding wheel rotation speed of 1,800 rpm, and a grinding wheel gap of 0.02.
The treatment was performed under the condition of mm. Next, the pulverized sludge was supplied to a wet medium stirring mill 11. Wet media stirring mill 1
1 is manufactured by WAB (DYNO-MILL Type KD
L type), filled with 0.5% zirconia beads (manufactured by Nikkato Corporation) at a filling rate of 85%, and a disk tip peripheral speed of 6.8.
m / sec, a slit gap of 0.15 mm, a residence time of 2 minutes, and a temperature of 19 ± 1 ° C.
Was returned to the biological treatment tank 2.

Example 1 According to the processing flow shown in FIG. 1, 50 L of domestic wastewater 1 was supplied per day using a 10 L biological treatment tank 2. The water temperature of the biological treatment tank 2 is 25 ° C., and the dissolved oxygen concentration is 2.
The sludge was appropriately extracted as excess sludge 8 so that the sludge concentration was 5 mg / L and the sludge concentration was 5 g / L. The treatment liquid 3 treated in the biological treatment tank 2 is solid-liquid separated in the sedimentation tank 4,
The separated water was discharged out of the system as treated water 5, and the separated sludge 6 was returned to the biological treatment tank 2 as returned sludge 7. Biological treatment tank 2
A part of the sludge was supplied to the sieve 9. The screen 9 used was a screen having an opening of 0.15 mm. Next, the sludge 10 subjected to the foreign matter removal passing through the sieve was supplied to a wet medium stirring mill 11. The wet medium stirring mill 11 is provided with a WA
Using a B company (DYNO-MILL Type KDL type), 0.5% zirconia beads (manufactured by Nikkato) are filled at a filling rate of 85%, the disk tip peripheral speed is 6.8 m / sec,
Slit gap 0.15mm, residence time 2min, temperature 19 ±
The treatment was carried out under the condition of 1 ° C. to solubilize, and the solubilized sludge 12 was returned to the biological treatment tank 2.

The amount of solubilized sludge in Comparative Example 3 and Example 1 was 2.7 times the solid content (8. 7) of the excess sludge (3.1 g / day) generated in the system without sludge solubilization (Comparative Example 1). 4g /
), And the same amount of solubilized sludge was added while being withdrawn from the biological treatment tank every day. In addition, the foreign matter treatment and the wet medium stirring mill treatment in Comparative Example 3 and Example 1 were performed once a week for one week, 12 L each, but the passage of the sludge of the wet medium stirring mill was blocked. Did not happen.

Table 1 is a table showing the reduction effect and the treatment performance of the present invention. When the sludge concentration in the biological treatment tank is kept constant, the accumulated surplus sludge generated in the treatment for 35 days is shown in Comparative Example 1.
In Example 1, while 109 g of excess sludge was generated,
, The amount generated is reduced to 2.2 g (98% reduction), and a part of the biologically treated sludge is solubilized by sludge solubilization and returned to the biological treatment tank. It can be seen that the amount of discharged sludge is greatly reduced. Further, regarding the treated water quality, the treated water quality of Example 1 was almost the same as that of Comparative Example 1 and was lower than that of Comparative Example 3 in which the foreign matter was pulverized and returned to the biological treatment tank. It can be seen that the effect on treated water quality is minor.

[0034]

[Table 1]

[0035]

According to the present invention, the sludge generated when organic wastewater is biologically treated and purified is crushed and solubilized by a wet medium stirring mill, and further treated in a biological treatment step. Is decomposed into carbon dioxide and water, etc., and a large reduction in excess sludge is realized. Further, in the present invention,
A wet medium stirring mill can obtain a stable solubilizing effect even on sludge containing a large amount of foreign matter such as fiber, and there is almost no deterioration in treated water quality.
Therefore, according to the present invention, excess sludge generated by biological treatment of organic wastewater can be economically and stably reduced. For this reason, the sludge landfill cost can be reduced, and the facility of the process such as sludge incineration can be simplified and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic flow chart showing an example of a method for treating organic wastewater of the present invention.

FIG. 2 is a schematic flow chart showing another example of the method for treating organic wastewater of the present invention.

FIG. 3 is a schematic flow chart showing another example of the method for treating organic wastewater of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Organic wastewater 2 Biological treatment tank 3 Treatment liquid 4 Solid-liquid separation device 5 Treatment water 6 Separated sludge 7 Return sludge 8 Excessive withdrawal sludge 9 Foreign matter removal device 10 Foreign matter removal treatment sludge 11 Wet medium stirring mill 12 Solubilized sludge 13 Sludge Concentrator 14 Concentrated sludge

Claims (1)

[Claims] 1. After treating an organic wastewater in a biological treatment tank, the treated liquid is separated into solid and liquid, and the separated water is discharged as treated water. When the separated sludge is returned to the biological treatment tank, a part of the separated sludge is used. Or, in a method of treating organic wastewater in which all is solubilized by using a wet medium stirring mill and returned, in the sludge to be solubilized, foreign substances that block the passage of the sludge of the wet medium stirring mill were removed. And a solubilization treatment.