JP2001276868A - Method for treating organic waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating organic waste water which is capable of stably decreasing the amount of excess sludge generated in cleaning the organic waste water by biological treatment by using a wet process medium agitating type mill as a sludge solubilizing method and obtaining a solubilizing effect stable even to the sludge into which impurities, such as fibrous materials, are included in a large amount. SOLUTION: The method for treating organic waste water is characterized in that after the organic waste water (1) is treated in a biological treating vessel (2), the treated liquid is subjected to a solid-liquid separation and the separated water is released as treated water (5). The separated sludge (6) is returned to the biological treating vessel and at this time, part or the whole thereof is treated by a mortar type pulverizing machine (1) and is then solubilized by the wet process medium agitating type mill treatment (12) and is returned to the biological treating vessel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

As a method of biologically reducing excess sludge, a method of treating the sludge by an aerobic digestion method or an anaerobic digestion method is known. However, aerobic digestion and anaerobic digestion require a long residence time of 10 days or more, but have a problem in that the weight loss rate is low, and are hardly used in recent years.

[0004] 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 biological treatment, and converting the solubilized excess sludge into biological wastewater. Many methods have been proposed in which the sludge is returned to the treatment tank and biologically decomposed to reduce the amount of surplus sludge generated. In German Patent Publication No. 403,668, surplus sludge is ground by a wet medium stirring mill or the like. rear,
A method has been proposed in which wastewater is returned to a biological treatment tank and decomposed to reduce the amount of excess sludge generated.

As a method for mechanically crushing sludge, ultrasonic, homogenizer, mixer, mill mortar and the like are known in addition to the wet medium stirring mill.
Among these methods, the millstone-type crusher is configured by a pair of grinding wheels at least one of which rotates, and an impact generated when the object to be processed passes through the opposed gap between the grinding wheels,
Centrifugal force, the principle of grinding the object to be processed by shearing force, but in order to crush microorganisms in the sludge using this mill crusher, it is necessary to make the gap between the whetstone almost zero, Therefore, it takes a long time for the treatment, and the treatment cost increases due to the wear of the grindstone.

[0006] On the other hand, the wet medium stirring mill treatment means that sludge is continuously introduced into a mill chamber filled with a crushing medium (beads), and beads are stirred by rotating a stirring shaft provided with disks and pins at a high speed. Then, the sludge is crushed by the shear frictional force generated between the stirred beads to solubilize the sludge. The wet medium agitation mill treatment is an excellent method for solubilizing sludge in that it is easy to handle and generates little persistent organic matter.

However, when the wet medium stirring mill is used alone, depending on the type of wastewater, impurities such as fibrous materials which cannot be sufficiently crushed by the wet medium stirring mill cannot be treated in the wastewater treatment facility or the like. In recent years, even if there are small amounts of contaminants in the wastewater, there is a method to improve the processing capacity of the biological treatment tank. A wastewater treatment method using a carrier or the like has been developed.In a wastewater treatment plant that performs such treatment, although there is some amount in the sludge, the sludge contains fibers, and these contaminants become beads. There has been a problem that the slits and the screen of the separation part are clogged, and stable operation of the mill becomes impossible.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the amount of excess sludge generated when organic wastewater is subjected to biological treatment and purification is determined by a wet medium as a method for solubilizing sludge. It is an object of the present invention to provide a method for treating organic wastewater that is stably reduced using a stirring mill.

[0009]

Means for Solving the Problems The present inventors have made intensive studies in order to solve such problems, and as a result, sludge generated when biologically treating organic wastewater is treated by a stone mill type pulverizer. By cutting off impurities such as fibrous material contained by the above, and then treated with a wet medium stirring mill,
Even sludge that contains a lot of impurities such as fibrous materials, it is possible to solubilize sludge efficiently and stably. And found that the present invention was achieved.

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. The gist of the present invention is a method for treating organic wastewater, wherein a part or all of the wastewater is treated by a millstone-type pulverizer, solubilized by a wet-medium stirring mill, and returned to a biological treatment tank. is there.

[0011]

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.

[0012] In these wastewaters, although there is a small amount, there are impurities such as fibers which are problematic when treated with a wet-medium stirring mill. It is considered to be natural fibers such as paper and human hair, various synthetic fibers, semi-synthetic fibers, and the like.

The biological treatment method in 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 can be 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, a part or all of the returned sludge returned to the biological treatment tank is cut with a millstone type pulverizer to remove impurities such as fibers contained in the sludge, and then the wet medium is stirred. It is solubilized using a mill and returned to the biological treatment tank.

As the grindstone used in the millstone grinder, a material such as silicon carbide, alumina, diamond, and silicon oxide which has been conventionally used in millstone grinders may be used. The shape of the grindstone is not particularly limited. Also, the number of rotations is not particularly limited. In addition, the gap between the whetstones is 0.01 to
2.0 mm is preferable, and 0.02 to 0.5 mm is particularly preferable. If the gap between the grindstones is smaller than 0.01 mm, the friction between the grindstones increases, and in addition to the abrasion of the grindstones, the heat of friction may transform the sludge component into a substance that is hardly biodegradable. Further, if the gap is smaller than 0.01 mm, the processing amount per unit time decreases, which is not desirable in terms of cost. On the other hand, 2.0m
If it is larger than m, undesired impurities such as fine fibers are introduced into a subsequent wet medium stirring mill without being crushed, which is not preferable.

In the sludge treated by the millstone type crusher, impurities such as fibers are cut off, but the microorganisms constituting the sludge are several μm to several tens μm in size. It is difficult to crush. Therefore, in the present invention, the sludge thus treated by the millstone-type pulverizer is treated by a wet-medium stirring mill.

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 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 mill treatment, the bead filling rate is 5% from the solubilizing effect and the 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 decomposable substance, and the quality of the treated water may deteriorate, 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 is usually a double-jacket structure in the mill chamber of a wet media stirring mill,
During this time, it can be easily performed by passing cooling water.

After the completion of the mill treatment, it is desirable to wash the inside of the mill chamber with water in order to easily start the next operation. Tap water, treated water,
It may be performed using raw water 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.

The sludge to be solubilized (to be introduced into a wet medium stirring type mill) may be the treatment liquid itself discharged from the biological treatment tank or the separated sludge after solid-liquid separation. Has a sludge concentration of about 0.1 to 1% by weight, and the sludge concentration of the separated sludge after solid-liquid separation is 0.2 to 2% by weight.
It is desirable to concentrate these sludges using a sludge concentrator since they are as low as about weight%. When 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 introduced, so that the solubilizing device becomes more compact and the processing time becomes longer. Can be greatly reduced, so that operating costs can be significantly reduced. In addition, the concentration treatment may be performed before or after treatment by a millstone crusher. The sludge concentrator is not particularly limited, and examples thereof include a centrifugal concentrator and a flotation concentrator used for normal sludge concentration. The concentration of the sludge after the concentration is not particularly limited as long as it is in a range showing fluidity.

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 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.

Next, an organic wastewater treatment apparatus of the present invention will be described with reference to the drawings. 1 to 3 are schematic flowcharts showing an example of the organic wastewater treatment apparatus of the present invention. In the method for treating organic wastewater of the present invention, a device including a biological treatment tank 2, a solid-liquid separator 4, a stone mill type pulverizer 10, and a wet medium stirring type mill 12 is used.

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 treatment liquid 3 that has been biologically treated is supplied to the millstone crusher 10 to cut off impurities such as fibrous materials. The millstone-type pulverized sludge 11 from which impurities such as fibrous materials have been cut is supplied to a wet-medium-stirring mill 12, where it is solubilized. The millstone-type pulverized sludge 11 solubilized becomes the solubilized sludge 13 and returned sludge 7
At the same time, it is returned to the biological treatment tank 2. Remaining treatment liquid 3
Is sent to a solid-liquid separator 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 return sludge 7, and the sludge concentration in the biological treatment tank 2 is kept almost constant for efficient biological treatment. When it becomes higher, the excess sludge is withdrawn as excess withdrawal sludge 8. In FIG.
Are all sent to the solid-liquid separator 4, and a part of the separated sludge 6 is supplied to the mill crusher 10 and then to the wet medium stirring mill 12. In FIG. 3, after a part of the separated sludge 6 is concentrated in the sludge concentration device 14, the concentrated sludge is supplied to the mill crusher 10, and then supplied to the wet medium stirring mill 12.

[0029]

Next, the present invention will be described specifically with reference to examples. Comparative Example 1 As a system that does not include the sludge solubilization step 9 in the treatment flow shown in FIG. 1, a 10-L biological treatment tank 2 was used, and 50 L of domestic wastewater 1 was supplied per day. The water temperature of the biological treatment tank 2 was set at 25 ° C., the dissolved oxygen concentration was set at 2.5 mg / L, and the sludge was appropriately withdrawn so as to have a sludge concentration of 5 g / L as surplus sludge 8. The treatment liquid 3 treated in the biological treatment tank 2 is solid-liquid separated in the sedimentation tank 4, the separated water is discharged out of the system as treated water 5, and the separated sludge 6 is returned to the biological treatment tank 2 as return 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 12. Wet media stirring mill 1
2 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 / s, 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 path of the wet medium stirring mill 12 was blocked by contaminants, and further operation was not possible.

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 millstone type pulverizer 10. The stone mill type pulverizer 10 is manufactured by Masuko Sangyo Co., Ltd. (MKCA6-3 type),
Using a grindstone made of silicon carbide and having a diameter of 150 mm, the treatment was performed under the conditions of a grindstone rotation speed of 1,800 rpm and a grindstone gap of 0.02 mm. Next, the millstone-type pulverized sludge 11 was supplied to a wet medium stirring type mill 12. Wet medium stirring mill 12
Is manufactured by WAB (DYNO-MILL Type KDL)
Zirconia beads (manufactured by Nikkato) with a filling rate of 85% and a peripheral speed of the disk tip of 6.8 m.
/ S, slit gap 0.15 mm, residence time 2 minutes, temperature 19 ± 1 ° C.
3 was returned to the biological treatment tank 2.

The amount of solubilized sludge in Example 1 was determined by the amount of excess sludge (3.1 g / ml) generated in the system without sludge solubilization (Comparative Example 1).
The amount of the solid matter was set to 2.7 times (8.4 g / day) the amount of the solubilized sludge 13 and the same amount of the solubilized sludge 13 was added every day. It should be noted that the stone mill type pulverizer treatment and the wet medium agitation type mill treatment are performed once a week for one week,
Each L was performed, but no blockage of the path of the wet medium stirring mill occurred.

FIG. 4 is a graph showing the reduction effect of the present invention. The vertical axis represents the value obtained when the sludge concentration in the biological treatment tank is constant.
It shows the amount of accumulated excess sludge generated during the five-day treatment. FIG.
Therefore, in Comparative Example 1, 109 g of surplus sludge was generated, whereas in Example 1, the amount of generation was 3.3 g (97% reduction).
It can be seen that the amount of sludge discharged out of the system is greatly reduced by solubilizing a part of the biologically treated sludge by solubilizing the sludge and returning it to the biological treatment tank.

[0034]

According to the present invention, the sludge generated when the organic wastewater is biologically treated and purified is treated by a millstone-type pulverizer, crushed by a wet medium stirring type mill, solubilized, and By treating in the treatment process, the sludge is decomposed into carbon dioxide gas and water, etc., and a large reduction in excess sludge is realized. Further, the method for solubilizing sludge according to the present invention can obtain a stable solubilizing effect even on sludge containing a large amount of impurities such as fibrous substances. 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 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.

FIG. 4 is a diagram showing the effect on the amount of sludge generated in the treatment of organic wastewater by the sludge solubilization treatment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic wastewater 2 Biological treatment tank 3 Treatment liquid 4 Solid-liquid separation apparatus 5 Treatment water 6 Separation sludge 7 Return sludge 8 Excessive extraction sludge 9 Sludge solubilization process 10 Stone mill type grinding machine 11 Stone mill type grinding treatment sludge 12 Wet medium stirring type Mill 13 Solubilized sludge 14 Sludge thickener 15 Thickened 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. Alternatively, a method for treating organic wastewater, wherein the whole is treated by a millstone-type pulverizer, solubilized by a wet-medium-stirring mill, and returned to a biological treatment tank.