JP2003093908A - Wet medium stirring mill and crushing method of sludge using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wet medium stirring mill which does not allow a bead separation part in a mill chamber to be clogged even when sludge containing fibrous material such as paper and human hair is treated and performs crushing treatment stably for a long period, and a crushing method of sludge using the same. SOLUTION: This wet medium stirring mill is composed of the mill chamber 2 which has a port for introducing material to be treated and a port for discharging the crushed treated material and is packed with beads 6 and a stirring means 11 which stirs the material 1 to be treated introduced into the mill chamber 2 together with the beads 6 and crushes the same, and is provided with the bead separation part 12 which is formed so as to become narrow in gap width in order to prevent the beads from flowing outside the mill chamber. Therein, it is a feature of this wet medium stirring mill that the gap width (A) of the bead separation part is larger than the particle size of beads.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet medium agitation mill used for crushing sludge containing organic matter generated from a wastewater treatment facility (hereinafter simply referred to as "sludge") and a sludge crushing method using the same. And a method for treating organic wastewater using the same.

[0002]

2. Description of the Related Art Conventionally, sludge such as excess sludge and raw sludge generated in large quantities from wastewater treatment facilities such as sewage treatment facilities has been dehydrated and then disposed of as landfill or incinerated as industrial waste. However, in recent years, it has become difficult to secure a landfill, and if a large amount of sludge is incinerated, the facility cost and maintenance cost increase, so reduction of sludge is required.

As a method of reducing sludge, a method of treating organic matter contained in sludge by biological treatment by anaerobic digestion or aerobic digestion is often used. Further, German Laid-Open Patent No. 4030668 proposes a method of grinding excess sludge by a wet medium agitation mill or the like and then returning the waste sludge to a biological treatment tank for decomposition to reduce the amount of excess sludge generated. ing. The wet medium agitation mill (hereinafter sometimes simply referred to as a mill) treatment involves continuously introducing sludge into a mill chamber filled with crushing media (beads) and rotating a stirring shaft equipped with a disk or pin at high speed. Is a method of stirring the beads by means of shear frictional force generated between the stirred beads. These mills usually use 1/3 of the particle size of the beads as a bead separation unit.
A gap having a certain width that communicates with the inside and outside of the mill is provided, and only the crushed sludge is discharged to the outside of the mill through this gap, and the beads are left in the mill.

[0004]

[Problems to be Solved by the Invention] However, in this way,
The gap width of the bead separation unit attached to the wet medium agitation mill is set narrower than the bead size to prevent the beads from flowing out, so sludge containing fibrous material such as paper or human hair is wet medium agitation mill. When treated with, such fibers remain because they are not easily crushed in the mill, clogging the gaps, slits, screens, etc. in the bead separation part attached to the mill, which makes it impossible to operate the mill stably. there were. INDUSTRIAL APPLICABILITY The present invention uses a wet medium stirring mill capable of stably crushing for a long period of time without blocking the bead separating portion even when treating sludge containing fibrous materials such as paper and human hair, and the same. It is intended to provide a sludge crushing method.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the inventors of the present invention can achieve the above object by making the gap width of the bead separating portion in the mill chamber wider than usual. Surprisingly, they have found that the outflow amount of beads to the outside of the mill chamber can be minimized by adjusting the filling amount of beads and the residence time of sludge in the mill chamber, and arrived at the present invention. It was also found that even if the beads flow out of the mill chamber, they can be stably crushed by collecting and returning them to the mill chamber.

That is, the first aspect of the present invention has a mill chamber having a treatment object introduction port and a crushing treatment physical flow outlet and filled with beads, and the treatment substance introduced into the mill chamber is stirred and crushed together with the beads. In a wet medium agitation mill, which comprises a stirring means, and a bead separating section having a narrow gap width is provided in front of the crushing processing flow outlet in the mill chamber to prevent the beads from flowing out of the mill chamber, A gist of a wet medium stirring mill is that the gap width of the bead separating portion is larger than the particle diameter of the beads.

A second aspect of the present invention has a mill chamber having a treatment object introduction port and a crushing treatment flow outlet, and a mill chamber filled with beads, and the treatment substance introduced into the mill chamber is crushed by stirring together with the beads. It consists of a stirrer and does not have a bead separation part with a narrow gap width to prevent the beads from flowing out of the mill chamber, but has an area for separating the crushed material and the beads by the difference in specific gravity. The subject is a wet medium agitation type mill.

A third aspect of the invention is a gist of a sludge crushing method characterized in that sludge is crushed by introducing sludge into the wet medium agitation mill described above, and more preferably, After crushing the sludge, the beads that have flowed out together with the crushed sludge are collected by the bead separation and collection device and returned to the mill chamber.

Further, in the fourth invention, after treating the organic wastewater in the biological treatment tank, the treatment liquid is subjected to solid-liquid separation, the separated water is discharged as treated water, and the separated sludge is returned to the biological treatment tank. In this case, the gist is a method for treating organic wastewater, characterized in that a part or all of the sludge is crushed using the above-mentioned wet medium agitation mill and then returned to the biological treatment tank. .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The wet medium agitation type mill of the present invention comprises a mill chamber having a treatment object introduction port and a crushing treatment physical flow outlet, and a bead-filled mill chamber, and a means for stirring the treatment substance and beads in the mill chamber. The width of the gap in the bead separation part is larger than the particle size of the beads packed in the mill chamber, or the crushed material and beads are separated by the difference in specific gravity without providing a bead separation part with a narrow gap width in the mill chamber. There is no particular limitation other than the provision of a region for doing so.

The structure for forming the gap of the bead separating portion in the present invention includes, but is not limited to, a gap, a slit or a screen. For example, in FIG.
Taking the example of the slit type bead separating part shown in FIG. 1, the bead separating part is formed by the shaft of the stirring means and the slit projecting inward from the inner wall of the mill, and the length indicated by A in the figure is the present invention. It corresponds to the gap width.

In the first aspect of the present invention, the gap width of the bead separating portion needs to be larger than the particle diameter of the filled beads, and the larger the gap width, the less the clogging in the gap. Since the outflow of beads increases with increasing, the gap width should be 1.2 to 1000 of the bead size.
It is preferably twice as large, and more preferably 10 to 200 times. Therefore, the gap width of the bead separating part is usually 0.5 m, although it depends on the bead size and the size and amount of the residue.
About m to 300 mm is preferable.

The second aspect of the present invention is to provide an area for separating the crushed material and the beads by the difference in specific gravity, without providing a bead separating portion in which the width of the gap is narrowed by a gap, a slit or a screen. is there. Specifically, when the mill chamber is vertical, it is connected to the mill chamber by providing the crushing physical distribution outlet at the upper part of the region that is stirred by the blades of the stirring means and even when the mill chamber is horizontal. The area corresponds to the area where the crushed material and the beads are separated by the difference in specific gravity. The separation area due to the difference in specific gravity may be provided inside the mill chamber or outside the mill chamber.

The mill chamber in the wet medium agitation mill of the present invention may be oriented vertically or horizontally, but there is a difference in specific gravity between the beads and the material to be crushed. Since it is larger than the crushed object, when a vertical mill is used, beads will be generated at the bottom of the mill chamber due to gravity.
Objects to be crushed will gather on the upper part. Therefore, by providing the crushing treatment physical distribution outlet at the upper portion, the ratio of beads mixed in the crushing-treated product flowing out from the mill chamber can be reduced, so that the amount of beads in the mill chamber can be easily kept constant. When providing a region for separating the crushed product and the beads in the second aspect of the present invention by the difference in specific gravity, it is preferable to use the vertical mill rather than the horizontal mill from this viewpoint.

As the stirring means in the wet medium stirring mill of the present invention, conventionally used stirring devices such as disk type, pin type and pin disk type can be mentioned. The peripheral speed of the disk (pin) tip is 3 to 30 m / sec, especially 5
-20 m / sec is preferable.

The material of the mill chamber and the agitator described above may be stainless steel, ceramics, or the like, but is not particularly limited, but stainless steel or the like causes wear due to contact with beads, and particularly high hardness such as zirconia beads. When beads are used, the wear of the beads increases. Therefore, it is preferable to use a material, such as rubber or polyurethane, that prevents impact or damage due to the collision of beads such as rubber or polyurethane, and it is particularly preferable to use polyurethane. In addition, the material for preventing the impact and the damage due to the collision of the beads may be used as the material of the mill chamber or the stirring device itself, or may be used as the material for lining the surface.

The beads used in the present invention include beads of glass, alumina, zirconia and the like, preferably beads having a true specific gravity of 2.0 to 7.0. If the true specific gravity is less than 2.0, it will be difficult to crush the microorganisms sufficiently, and if the true specific gravity is more than 7.0, there will be almost no improvement in the sludge crushing effect, and the power required for stirring will increase. Not preferable. Further, in order to easily keep the amount of beads in the mill chamber constant, the true specific gravity is 5.0 to 7.0.
The beads are particularly preferable.

The particle size of the beads is 0.05 to 2.0.
mmφ is preferable, and 0.25 to 1.0 mmφ is particularly preferable. When the particle size of the beads is larger than 2.0 mmφ, the voids between the beads become large, which makes it difficult to crush microorganisms such as bacteria of several μm to several tens μm that compose the sludge, which is not preferable. The particle size of the beads is 0.05 mm
If it is smaller than φ, the beads are likely to flow out of the mill chamber, and it becomes difficult to keep the amount of beads in the mill chamber constant, which is not preferable.

The bead filling rate in the mill chamber is not particularly limited, but is preferably 30 to 95%, particularly preferably 50 to 95%. When the filling rate is lower than 30%, the crushing effect becomes low, which is not preferable. Further, if the filling rate is 95% or more, the beads are likely to flow out of the mill chamber, and it becomes difficult to easily keep the amount of beads in the mill chamber constant, which is not preferable.

Next, the sludge crushing method of the present invention will be described. The sludge to be treated in the present invention is not particularly limited as long as it is a sludge containing an organic matter, and as such sludge, wastewater such as sewage, food factory wastewater, pulp factory wastewater, activated sludge treatment In addition to raw sludge and surplus sludge generated when treating in biological wastewater treatment facilities such as facilities, or anaerobic digestion sludge generated when anaerobically digesting these, mixed sludge and concentrated sludge, etc. Can be mentioned. In these sludges, although present in a small amount, there are fibers that are problematic in the wet medium agitation mill treatment. These fibers are used for natural fibers such as paper and human hair and various types of fibers. It is considered to be synthetic fiber, semi-synthetic fiber and the like.

The sludge crushing method of the present invention introduces such sludge into the wet medium agitating mill of the first and second inventions and crushes it. The retention time of sludge is appropriately set depending on the concentration of sludge to be introduced, the crushing medium used, etc., and is not particularly limited, but usually 2
0 second to 20 minutes are preferable, and 30 seconds to 10 minutes are particularly preferable. If the residence time is shorter than 20 seconds, the sludge may not be sufficiently crushed, and the beads tend to flow out of the mill chamber, making it difficult to keep the amount of beads in the mill chamber constant. Not preferable. Moreover, even if it is longer than 20 minutes, the power consumption is increased, and the crushing effect is not so improved.

The treatment temperature is preferably 60 ° C. or lower, and more preferably 4 to 40 ° C. Processing temperature is 60 ℃
If it is higher, a part of the sludge component is heat-denatured to become a hardly decomposable substance, which may deteriorate the water quality of the treated water, which is not preferable. Usually, the temperature of the sludge crushed by the mill treatment rises by about 10 to 30 ° C. as compared with the untreated sludge, so that it is preferable to cool with cooling water when the temperature is high such as in the summer. Since the mill chamber usually has a double jacket structure, cooling can be easily performed by passing cooling water between them.

After the mill treatment, it is desirable to wash the inside of the mill with water so that the next operation can be started easily. As the water to be washed, treated water, raw water, tap water or the like may be used. The amount and time of washing water may be set appropriately, but the sludge concentration of the washing water is 1% by weight.
It is preferable to wash until the following.

In the sludge crushing method of the present invention, since the gap width of the beer separation section of the wet medium stirring mill used for crushing is larger than the bead particle size, some of the beads may flow out. In order to suppress the outflow of beads and keep the amount of beads in the mill chamber constant at a preferable value, it is preferable that the true specific gravity of the beads is large and the particle size is large as described above, and the filling rate of the beads is low. . Further, it is preferable that the residence time is long. However, when the beads are not completely separated in the mill chamber and a part is discharged together with the crushed product, a means for separating and collecting the beads from the crushed product that has flown out and returning the collected beads to the mill chamber. It is preferable to provide means.

The means for separating and recovering the beads from the crushed product is not particularly limited as long as it is a bead separating / collecting device capable of separating and collecting the beads and the crushed product, and gravity separation or centrifugation. By separating the beads and the crushed material and collecting the beads, by separating the beads and the crushed material with a slit or screen, and collecting the beads, or by a combination of these. And so on. At this time, in the case of a gap, a slit, a screen, or the like, it is preferable to make the gap smaller than the particle diameter of the beads. As an example, FIG. 4 shows a bead separation / collection device using the gravity separation tank 9.
Shown in. A baffle plate 10 is provided inside.

In the case of an ordinary wet-medium agitation type mill, there is a gap separating the beads from the material to be crushed, a bead separating part having a narrow gap formed by a slit or a screen, and the like. It is necessary to disassemble the mill and open the mill chamber for the maintenance of the parts, which requires a great deal of labor, but in the wet medium agitation type mill of the present invention, the bead separation / collection device should be installed outside the mill chamber. Therefore, even if the bead separation / collection device is blocked, its cleaning and replacement are very easy.

Further, in the method of the present invention, a plurality of such bead separating and collecting apparatuses may be combined in parallel or in series depending on the purpose. In particular, when a plurality of devices are combined in parallel, it is possible to incorporate a cleaning process for the device periodically while continuously performing the crushing process.

The means for returning the collected beads to the mill chamber is not particularly limited, and may be a mono pump,
A tube pump, a conveyor, an air lift pump, etc. are mentioned. The beads may be returned to the mill chamber alone or may be introduced into the mill chamber in a state where the beads and the object to be treated are mixed.

Further, the beads and the crushed sludge can be further separated by washing the collected beads with water. The water used here is not particularly limited as long as it is water normally used in a wastewater treatment facility and the like, and examples thereof include treated water, raw water, overflow water in a sedimentation basin, desorption water, tap water, and tap water. To be

When the beads are returned, the beads may be returned alone, or the beads may be mixed with the sludge before crushing and sent at the same time.

The sludge crushed by the method of the present invention is
Since the biodegradability is improved, it can be sent to a biological treatment tank such as an aerobic biological treatment tank or an anaerobic biological treatment tank and easily biodegraded.

Next, a method for treating organic wastewater using such a wet medium agitating mill will be described. The organic wastewater to be the subject of the present invention is not particularly limited as long as it is a wastewater containing an organic matter treated by a normal biological treatment method, and sewage, night soil, food factory wastewater, pulp factory wastewater, etc. Can be mentioned. The biological treatment method in the present invention is not particularly limited as long as it performs biological treatment for such organic wastewater,
Examples of the aerobic treatment include aeration of organic wastewater in the presence of activated sludge in an aeration tank, and anaerobic treatment.

As a method for solid-liquid separation of the treatment liquid discharged from the biological treatment tank, there are a membrane separation and a precipitation tank separation. The separated water after solid-liquid separation is discharged as treated water. In addition, a part of the separated sludge is drawn out as excess sludge, and most of it is returned to the biological treatment tank as return sludge.

In the present invention, a part or all of the sludge returned to the biological treatment tank is crushed and then returned to the biological treatment tank. The sludge to be crushed may be the treatment liquid itself discharged from the biological treatment tank or the separated sludge after solid-liquid separation, but usually the sludge concentration of the treatment liquid is 0.1.
Since it is about 1% by mass and the sludge concentration of the separated sludge after solid-liquid separation is as low as about 0.2-2% by mass, it is desirable that these sludges are concentrated by using a sludge concentrating device.
If the sludge is concentrated to increase the sludge concentration and then crushed, the crusher becomes more compact and the processing time can be greatly shortened, as compared with the case where the treated liquid is directly treated. Therefore, the operating cost can be significantly reduced. However, as the sludge concentration increases, the viscosity of the sludge increases, and the sludge easily flows out of the mill room.
In order to easily keep the amount of beads in the mill chamber constant, the sludge concentration is preferably 5% by mass or less, more preferably 3% by weight or less.

The amount of sludge to be crushed depends on the BOD of the wastewater.
The solid amount of sludge that grows due to assimilation and a part of the sludge that has been crushed will become sludge again in the biological treatment process, so if you set it appropriately to achieve the target reduction rate in consideration of the amount of growth. Good.

The sludge thus crushed has improved biodegradability, and can be returned to the biological treatment tank and biodegraded to reduce the amount of sludge generated.

Next, the sludge crushing method of the present invention will be described with reference to the drawings. 1 to 3 are views showing the outline of the steps of the sludge crushing method of the present invention. In the method shown in FIG. 1, sludge 1 is supplied to a mill chamber 2 and crushed. After the treatment, when the beads that cannot be separated in the mill chamber are included, the crushed sludge 3 is separated by the bead separation / collection device 4 into the crushed sludge 5 in which the beads have been collected and the beads 6. The beads 6 are returned to the mill chamber 2. Needless to say, the bead separating / collecting device 4 may not be provided when beads can be separated in the mill chamber depending on the operating conditions of the mill.

The method shown in FIG. 2 is different from the method shown in FIG. 1 in that two bead separating / collecting devices 4 are connected in series to separate and collect the beads.
The method is particularly effective when a gravity separator or a centrifugal separator is used. The method shown in FIG. 3 is different from the method shown in FIG. 1 in that two bead separation / collection devices 4 are connected in parallel to separate and collect beads.
The bead separation / collection device 4 is alternately washed with the washing water 7. Such a method is particularly effective when a slit or a screen is used as the bead separation / collection device 4. The cleaning waste water 8 may be discharged as it is, or may be returned to the mill chamber 2 again.

Next, FIG. 6 is a diagram showing the outline of the steps of the method for treating organic wastewater according to the present invention. In FIG. 6, sewage,
Organic wastewater 13 such as human waste, food factory wastewater, pulp factory wastewater, etc. is supplied to a biological treatment tank 14 and biologically treated. The biological treated sludge 15 is sent to the solid-liquid separation device 16 and treated water 1
7 and separated sludge 18. Most of the separated sludge 18 is returned to the biological treatment tank 14 as return sludge 20, and the sludge concentration of the biological treatment tank 14 is kept substantially constant for efficient biological treatment. When the temperature rises, the excess sludge is extracted as the excess extraction sludge 19. A part of the separated sludge 18 is supplied to the mill chamber 2 and crushed. After the treatment, when the beads that cannot be separated in the mill chamber are included, the crushed sludge 3 is separated by the bead separation / collection device 4 into the crushed sludge 5 in which the beads have been collected and the beads 6. The beads 6 are returned to the mill chamber 2. Needless to say, the bead separating / collecting device 4 may not be provided when beads can be separated in the mill chamber depending on the operating conditions of the mill. The crushed sludge 3 or the crushed sludge 5 from which the beads have been collected is returned to the biological treatment tank 14 together with the returned sludge 20.

[0040]

EXAMPLES Next, the present invention will be specifically described by way of examples. Example 1 A wet medium agitation mill having a gap width of 70 mm was used by adjusting the position of the gap separator in the gap type bead separation unit attached to the wet medium agitation mill (Ashizawa's PM12.5RL type). The excess sludge (sludge concentration: 1% by weight) generated in the sewage treatment facility was introduced into a wet medium agitation mill, and
5 mmφ zirconia beads (manufactured by Nikkato Co., Ltd.) were used, and the bead packing ratio to the mill chamber volume was 30, 50, 7
0%, disk tip peripheral speed 13 m / sec, residence time 0.
Crushing treatment was carried out for 5 minutes, 1 minute, 1.5 minutes and 2 minutes. Since the mill chamber of the mill used is vertical, the filling rate of the beads is the ratio of the height from the bottom of the mill chamber to the height of the mill chamber. When beads were mixed in the crushed sludge discharged from the mill, the crushed sludge was introduced into a gravity separation type bead separation / collection device, the beads were sedimented and collected, and returned to the mill by a pump. The crushed sludge was poured out from the upper part of the gravity separation tank. Table 1 shows the presence / absence of beads flowing out of the mill under each condition.

[0041]

[Table 1]

From Table 1, when the filling rate of beads is low,
No outflow of beads was observed even with a short residence time, but it was necessary to lengthen the residence time in order to prevent the outflow of beads when the filling rate was high. However, by such a method of returning the beads to the mill, the sludge crushing treatment could be stably operated for 1 day continuously in any case.

Example 2 Using the same wet-medium agitating mill used in Example 1, excess sludge generated in a sewage treatment facility (sludge concentration: 1
If the beads are mixed in the crushed sludge discharged from the mill, the crushed sludge is introduced into a bead separation / collection device having a separation area of 600 cm ² and a screen gap width of 0.15 mm. The crushed sludge was poured out from the gap of the screen, and the beads separated by the screen were collected and returned to the mill by a pump. By such a method, in any case, the sludge crushing treatment could be stably operated for one continuous day.

Comparative Example 1 Except that the excess sludge (sludge concentration: 1% by weight) generated in the sewage treatment facility was set to 0.5 mm, which is the same as the particle size of the beads, in the slit type bead separation unit attached to the mill. The crushing treatment was carried out by using a wet medium stirring type mill similar to that in Example 1. As the crushing conditions, the packing rate was 70%, which had a higher crushing effect than the other packing rates in the examples, and the retention time was 0.5 minutes when the beads flowed out of the mill chamber and 2 minutes when the beads did not flow out. As a result, in any case, the route of the wet medium agitation mill was blocked about 8 hours after the start of operation, and the mill could not be operated any further.

Next, regarding the soluble COD of the crushed sludge of Comparative Example 1 and Examples 1 and 2, the results under the condition that the beads flowed out and the condition under which the beads did not flow are shown in comparison with FIG. As shown in FIG. 7, there was almost no difference between the two regardless of whether or not the beads flowed out. Therefore, since the sludge crushed by the mill of the present invention has improved biodegradability similarly to a normal mill, by sending the crushed sludge to a biological treatment tank, the sludge reduction by biological treatment can be reduced. Can be efficiently converted.

[0046]

According to the wet medium stirring type mill of the present invention,
Conventionally, it is possible to stably crush sludge containing fibrous material which has been difficult to crush. In addition, since the sludge thus crushed has improved biodegradability, it is possible to efficiently reduce the amount of sludge by biological treatment.

[Brief description of drawings]

FIG. 1 is a schematic process drawing showing an example of a sludge crushing method of the present invention.

FIG. 2 is a schematic process drawing showing another example of the sludge crushing method of the present invention.

FIG. 3 is a schematic process drawing showing another example of the sludge crushing method of the present invention.

FIG. 4 is a schematic view of a bead separating and collecting apparatus using gravity separation.

FIG. 5 is a schematic view showing an example of a wet medium stirring type mill of the present invention.

FIG. 6 is a schematic process diagram showing an example of a method for treating organic wastewater according to the present invention.

FIG. 7 is a diagram showing the concentration of soluble COD under various crushing conditions.

[Explanation of symbols]

1 sludge 2 mill room 3 crushed sludge 4 Bead separation and collection device 5 Crushed sludge from which beads were collected 6 Return beads 7 wash water 8 Wash drain 9 Gravity separation tank 10 baffle 11 stirring discs 12 slits 13 Organic wastewater 14 Biological treatment tank 15 Biological sludge 16 Solid-liquid separator 17 Treated water 18 Separation sludge 19 Surplus drawn sludge 20 Return sludge

Continued front page    (72) Inventor Kazuhiro Korekawa             Unitika Stock, 4-1 Hinakitamachi, Okazaki City, Aichi Prefecture             Inside the Okazaki factory F-term (reference) 4D028 BD11                 4D059 AA03 AA05 BK11 CA28                 4D063 FF14 FF21 FF35 GA10 GC05                       GC14 GC16 GD27

Claims (5)

[Claims] 1. A mill chamber having a treatment object introduction port and a crushing flow outlet, and comprising a mill chamber filled with beads and a stirring means for stirring and crushing the treatment substance introduced into the mill chamber together with the beads. In the wet media agitating mill, the gap width of the bead separation part is provided in front of the crushing processing distribution outlet in the room, and the bead separation part is formed with a narrow gap width to prevent the beads from flowing out of the mill room. Is larger than the particle size of the beads. 2. A bead containing a mill chamber having a treatment object introduction port and a crushing treatment flow outlet, and a stirring means for stirring and crushing the treatment substance introduced into the mill chamber together with the beads. Wet medium agitation method characterized by not providing a bead separating part with a narrow gap width to prevent the outflow of the beads to the outside of the mill chamber, but providing a region for separating the crushed material and the beads by the difference in specific gravity. mill. 3. A sludge crushing method, which comprises introducing sludge into the wet medium agitating mill according to claim 1 and crushing the sludge. 4. The sludge is introduced into the wet medium agitation mill according to claim 1 or 2, and the sludge is crushed. Then, the beads flowing out together with the crushed sludge are collected by a bead separation / collection device and returned to the mill chamber. A method for crushing sludge, which is characterized in that 5. After treating the organic wastewater in the biological treatment tank, the treated liquid is subjected to solid-liquid separation, the separated water is discharged as treated water, and the separated sludge is partially returned when returned to the biological treatment tank. Alternatively, a method for treating organic wastewater is characterized in that sludge is crushed using the wet medium agitation type mill according to claim 1 or 2 and then returned to the biological treatment tank.