JP2002166298A - Atmospheric flotation thickening facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct flotation thickening of polluting particulate matter with inexpensive facility cost by controlling increase of the manufacturing cost of a floating separation tank put to use. SOLUTION: Using an atmospheric flotation thickening facility 10 comprising a preliminary thickening device 12 which dehydrates sludge mixed with bubbles and coagulant, and a floating separation tank 13 which conducts flotation thickening of polluting particulate matter included in the dehydrated sludge by the preliminary thickening device 12, the sludge is dehydrated and thereafter the flotation thickening of the polluting particulate matter is conducted included in the dehydrated sludge by means of the floating separation tank 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a normal pressure flotation concentrator.

[0002]

2. Description of the Related Art In order to finally dispose of sludge generated during water treatment or dredging in a safe state, it is generally required as an intermediate process to concentrate and dewater the treated liquid containing the sludge, and further, if necessary. Sludge treatment such as drying (incineration) is performed to separate and remove polluted particles.
The concentrated and dewatered sludge is disposed of, such as landfill or dumping, or sintered, laid on the road surface and reused.

[0003] Concentration of a processing solution can be performed by a screening method using a back screen, a rotating screen, or the like,
When the density of polluted particles suspended in the treatment liquid (water) is higher than the density of water, sedimentation separation using sedimentation using density difference, centrifugal concentration by centrifugal force, and It is carried out by various means such as flotation method which floats and separates polluted particles in a gravitational field.However, in particular, concentration of processing liquid by flotation method is suitable for mass processing, so for example, production of meat products and dairy products It is widely used for wastewater treatment in industries such as vegetable oil and fat manufacturing, petroleum refining, and steelmaking.

The flotation method comprises: (i) a natural flotation method in which, when the density of polluted particles is lower than that of water, the particles are floated under normal pressure by utilizing only the buoyancy which acts naturally in the flotation tank; When the density of water is approximately equal to or greater than water, a large amount of air is sent into the processing solution in the flotation tank at normal pressure to generate fine bubbles, and then fine bubbles adhere to the polluted particles by stirring. Atmospheric pressure flotation method such as forced flotation method to reduce the apparent density of polluted particles by floating, or (ii) Saturate the air in the flotation tank under normal pressure or pressure and then reduce the pressure to reduce the air. By precipitating,
A bubble precipitation type flotation method in which pollutants are brought into contact with air bubbles, or a vacuum that saturates the air in a flotation tank at normal pressure and then reduces the pressure in a closed tank to precipitate dissolved air to generate fine bubbles. Pressurized flotation method, such as pressurized flotation method, in which the treatment liquid in the flotation tank is pressurized to dissolve air to a saturated state and then returned to normal pressure to precipitate dissolved air and generate fine bubbles It is roughly divided into the separation method.

Among these flotation methods, the normal pressure flotation method has been widely used so far, because the cost of processing equipment can be greatly reduced, especially since a pressure adjusting mechanism of the flotation tank is not required. .

FIG. 4 is an explanatory view schematically showing a situation in which floating particles contained in excess sludge generated in a sewage treatment plant are floated and concentrated using a normal pressure flotation method. As shown in FIG. 1, in the normal pressure flotation concentrator 1, surplus sludge having a concentration of polluting particles of usually about 0.5 to 0.8%, bubbles and a flocculant are supplied to a mixing tank 2 and mixed sufficiently. The processing liquid is supplied to the bottom of the flotation tank 4 via the pipe 3.

In the flotation / separation tank 4, fine particles adhere to the contaminant particles in the supplied processing solution, and the apparent density of the contaminant particles is reduced. A floss zone 6 in which the material 5 is floated and concentrated is formed. The concentration of the contaminant particles forming the floss zone 6 usually reaches about 4%.

[0008] The floating material in the floss zone 6 is
Is carried out of the flotation tank 4 by a scraper (not shown) provided at the upper part of the system. On the other hand, the separation liquid 7 located below the floss zone 6 is discharged out of the system via a discharge pipe 8 provided near the bottom of the floating separation tank 4.

[0009]

However, in the conventional normal pressure flotation and concentration apparatus 1 shown in FIG. 4, the concentration of the polluted particles contained in the sludge supplied to the flotation tank 4 via the pipe 3 is reduced. It depends on the source and cannot be controlled.

When the concentration of the polluted particles contained in the sludge supplied to the flotation tank 4 is low, the amount of the processing liquid supplied to the flotation tank 4 is inevitably increased when the load of the polluted particles (dry amount) is the same. And the residence time of the processing liquid in the flotation tank 4 is shortened. For this reason, the floating time of the floating material 5 cannot be sufficiently secured, and the floating-concentrating function of the floating separation tank 4 for polluting particles is reduced.

In order to prevent such a decrease in the flying floating concentrating function of the separation tank 4, the volume of the flotation tank 4, must in particular sufficiently ensure the height h _1. For this reason, not only does the manufacturing cost of the flotation tank 4 significantly increase, but also the height of the building in which the normal pressure flotation / concentration device is installed needs to be increased, which significantly reduces the processing cost merit of the normal pressure flotation / concentration device. Resulting in.

Here, an object of the present invention is to suppress the increase in the manufacturing cost of the flotation tank used, suppress the construction cost of the building to be installed, and carry out the flotation and concentration of polluting particles at a low construction cost. It is an object of the present invention to provide a normal pressure flotation and concentration device.

[0013]

In the conventional flotation tank 4 shown in FIG. 4, a residence time of about 0.5 to 1 hour is secured with respect to the amount of sludge. Therefore, the present inventor has repeatedly studied and removed a part of the water contained in the processing liquid in the stage immediately before being supplied to the flotation / separation tank 4 to reduce the water content of the processing liquid. Has been found to be able to substantially reduce the amount of the processing liquid to be supplied to the flotation tank 4. For example, the concentration of the pollutant particles is increased from 0.5 to 0.8% to 1.0%.
The amount of processing liquid to be supplied to the flotation separation tank 4 is reduced to about 1/2 by slightly concentrating the processing liquid in the stage immediately before being supplied to the flotation separation tank 4 to about 1.5%. can do. For this reason, if the residence time of the processing liquid in the flotation tank 4 is set to be approximately the same as the conventional _one , the capacity of the flotation tank 4, particularly the height h ₁ , can be reduced to half.

The present inventor has further studied and found that a pre-concentrator is provided between the mixing tank 2 and the flotation tank 4 for easily and lightly concentrating the water contained in the sludge. However, it has been found that by reducing the amount of the processing liquid to be supplied to the flotation tank 4, it is possible to both reduce the size of the flotation tank 4 and thereby reduce the manufacturing cost.

The present invention is characterized by comprising a pre-concentrator for slightly condensing sludge, and a flotation tank for flotation and concentration of polluted particles contained in sludge lightly condensed by the pre-concentrator. This is a normal pressure flotation concentrator.

In the preconcentrator used in the present invention, a plurality of fixed members and a plurality of movable members are provided in parallel, and both of the plurality of fixed members and the plurality of movable members are directed in the direction in which these members are provided. A sludge circulation hole through which sludge flows is provided,
A plurality of movable members are arranged so as to be movable in a direction orthogonal to the direction in which the plurality of fixed members and the plurality of movable members are arranged in parallel.

As a similar device to the preconcentrator according to the present invention, there is known a complicated dewatering device for dewatering the sludge heavily by pressing the sludge while transporting the sludge by a screw, for example (trade name). Tsurumi multi-plate outer shell type screw dehydrator TMS type ", manufactured by Tsurumi Seisakusho Co., Ltd.). However, such a device using a screw is expensive, and it is difficult to increase its size. In the pre-concentrator used in the present invention, since it is only necessary to lightly condense the sludge having a low concentration of pollutant particles, it is possible to lightly remove water from the sludge flowing by the head difference or the pressure of the sludge transfer pump without using a screw, By using such a pre-concentrator,
The present inventor has found that it is possible to sufficiently reduce the size of the flotation tank 4 and the resulting reduction in manufacturing costs, and further, the reduction in building construction costs.

The preconcentrator may be arranged in the middle of a pipe connecting a mixing device for mixing bubbles and a flocculant into the sludge and a flotation tank for floating the polluted particles contained in the sludge. It may be arranged in the middle of a pipeline for supplying sludge to the mixing device.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of a normal pressure flotation and concentration apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the following description, the sludge to be treated is
The case of excess sludge generated in a sewage treatment plant is taken as an example, but it goes without saying that the application of the present invention is not limited to such excess sludge.

FIG. 1 is an explanatory view schematically showing a schematic configuration of a normal pressure flotation enrichment apparatus 10 of the present embodiment. As shown in FIG.
, A preconcentrator 12 and a flotation tank 13. Hereinafter, these components of the normal pressure flotation enrichment device 10 will be sequentially described.

[Mixing tank 11] The mixing tank 11 mixes the sludge to be treated with bubbles generated by a bubble generator (not shown) and a coagulant supplied by a coagulant adding device (not shown). And a mixing apparatus for producing the processing liquid 14.

The excess sludge treated in the present embodiment usually contains polluted particles at a concentration of about 0.5 to 0.8%. Further, in the present embodiment, as the coagulant,
Organic polymer coagulant and inorganic coagulant iron (III) chloride
Although a compound obtained by combining the above is used, it is also possible to use an organic polymer-based flocculant alone.

The processing liquid 14 obtained by the mixing tank 11 is
The water is supplied to a pre-concentration device 12 disposed below the mixing tank 11 through a pipe 15 provided at the bottom 11a of the mixing tank 11 due to a head difference.

The mixing tank 11 in the present embodiment is a well-known and commonly used mixing tank of this type.
Further description regarding 1 will be omitted. In the present embodiment, the mixing tank 11 is configured as described above.

[Preconcentrator 12] The processing liquid 14 is supplied to the pipe 1
5, the water is supplied to the inflow portion 31 of the pre-concentrator 12 disposed below the mixing tank 11 by a head difference. FIG.
FIG. 2 is a perspective view showing a configuration example of the preconcentrator 12 in a partially omitted and simplified manner and in a transparent state. Less than,
The preconcentrator 12 of the present embodiment will be described with reference to FIGS.

As shown in FIG. 1, the preconcentrator 12 is disposed between the mixing tank 11 described above and a flotation tank 13 described later, connected to both of them. 1 and 2
As shown in FIG. 1, the pre-concentrator 12 has disk-shaped base members 16a and 16b arranged to face each other. Between the base members 16a and 16b, there are fixed members 17a, 17b and 17c in the form of round bars, and the base members 16a and 16c.
Round shafts l, m and n arranged between 16b
And rotating bodies 18a, 18b and 18c in the form of round bars each having

The fixed members 17a to 17c are
a and 16b are fixedly arranged by appropriate means such as fastening or screwing. On the other hand, as shown in the enlarged view at the lower right in FIG. 1, all of the rotating bodies 18a to 18c have their respective rotation axes l to n eccentric. The rotating shafts 1 to n are connected to the base member 16 via bearings (not shown) embedded in the base members 16a and 16b, respectively.
a and 16b are rotatably arranged. For this reason, the rotating bodies 18a to 18
When rotating c, the rotating bodies 18a to 18c are
An eccentric rotation is performed for n.

As shown in FIGS. 1 and 2, toothed pulleys 19a to 19c are attached to one ends of rotating bodies 18a to 18c penetrating the base member 16a, respectively. A toothed belt 20 is stretched over the pulleys 19a to 19c. As a result, the toothed pulleys 19a to 19c rotate synchronously, so that the rotation axes l to n
Also rotate synchronously. For this reason, the rotating bodies 18a to 18c
In synchronization with each other, eccentric rotational movements are performed with the rotation axes l to n as the rotation centers.

On the other hand, as shown in FIGS. 1 and 2, a pulley 21 is mounted on the other end of the rotating body 18b penetrating the base member 16b. A belt 23 is wound around the pulley 21 and the pulley 22 mounted on the drive motor 24.

For this reason, when the drive motor 24 is started, the driving force is transmitted to the rotating body 18b via the pulleys 22 and 21, thereby rotating the rotating body synchronously by the toothed pulleys 19a to 19c and the toothed belt 20. 18a ~
18c is driven to rotate eccentrically with respect to the rotation axes l to n.

Further, in the present embodiment, the fixed body 17a
A large number of fixing rings 25 as fixing members are fixed side by side in the extending direction of the fixed bodies 17a to 17c. As shown in the upper left drawing of FIG. 2, through holes 25a to 25c through which the fixing bodies 17a to 17c respectively penetrate are formed at the corners of the fixing rings 25, and the through holes 25a to 25c are formed. Fixed bodies 17a to 17c
Penetrates, a number of fixing rings 25 are juxtaposed and fixedly arranged in the extending direction of the fixing bodies 17a to 17c.

In the present embodiment, the rotating members 18a to 18a
A large number of movable rings 26 as movable members are supported side by side in the extending direction of the fixed bodies 17a to 17c by 18c. As shown in the upper left drawing of FIG. 2, the outer peripheral surfaces of the fixed bodies 17a to 17c abut against the end faces of the movable rings 26, so that a large number of movable rings 26 face the extending direction of the rotating bodies 18a to 18c. It is supported side by side. Therefore, when the rotating bodies 18a to 18c perform the eccentric rotation driving with respect to the rotation axes l to n by activating the drive motor 24, the movable rings 26 are synchronized with the extension of the fixed bodies 17a to 17c. It is driven to rotate while drawing an eccentric circular trajectory in a plane perpendicular to the installation direction.

Further, in this embodiment, as shown in FIGS. 1 and 2, each fixed ring 25 and each movable ring 26
Are arranged alternately in the direction in which the fixed bodies 17a to 17c extend and with a predetermined gap therebetween. Note that, unlike the present embodiment, the fixed rings 25 and the movable rings 26 do not necessarily need to be alternately arranged one by one. For example, the arrangement of the fixed ring 25 and each movable ring 26 may be changed as appropriate. The gap between the adjacent rings does not become a resistance during the operation of the movable ring 26 and may be appropriately set on condition that a desired degree of drainage described later can be ensured.

In FIG. 1, three fixed rings 25 and three movable rings 26 are shown, and the others are omitted, in order to avoid complicating the drawing and to facilitate understanding of the structure.

A sludge flow hole 27 as a through hole is provided at a substantially central portion of each fixing ring 25, and a sludge flow hole 28 as a through hole is provided in each movable ring 26. The base member 16a is also provided with a sludge circulation hole 29 which is a through hole, and the base member 16b is also provided with a sludge circulation hole 30 which is a through hole. Further, a hollow inflow portion 31 communicating with the sludge circulation hole 29 is provided on the outer surface of the base member 16a, and the pipe 15 is connected to the inflow portion 31. Also, the base member 1
A hollow discharge portion 32 communicating with the sludge circulation hole 30 is provided on the outer surface of 6b, and a pipe 36 described later is connected to the discharge portion 32.

For this reason, a large number of sludge flow holes 2 provided in each fixed ring 25 and each movable ring 26 are provided.
The sludge flow holes 33 through which the treatment liquid containing sludge flows due to the head difference are formed by the sludge flow holes 29 and 30 provided in the base members 16a and 16b, respectively.

Each movable ring 26 has a fixed body 17a to 17c.
When the eccentric drive is performed by drawing an eccentric circular trajectory in a plane perpendicular to the extending direction of the movable ring 26, the processing liquid 14 containing the sludge flowing through the Part, ie, the end face of the sludge flow hole 28, is pressed slightly. Thus, only a part of the water contained in the processing liquid 14 is squeezed out, and the contaminant particles contained in the processing liquid 14 remain in the processing liquid without being squeezed out.

A part of the water squeezed out of the processing liquid 14 falls downward through a gap formed between each fixed ring 25 and each movable ring 26 and is disposed below the pre-concentrator 12. The water falls into the drain pan 35 and is discharged out of the system.

Further, since each movable ring 26 is driven eccentrically, clogging between each fixed ring 25 and each movable ring 26 is prevented. In this way, a slight concentration of the processing liquid containing sludge is performed.

On the other hand, the processing liquid 14 containing the sludge that has been slightly concentrated is supplied to the flotation tank 13 through the pipe 36. Thus, in the present embodiment, the base member 16
a and 16b, fixed bodies 17a to 17c and rotating bodies 18a to 18c, fixed rings 25 fixedly supported by fixed bodies 17a to 17c, and rotating bodies 18a to 18c.
The sludge enrichment section 34 is formed by each movable ring 26 movably supported by 18c.

As described above, in the present embodiment, the use of the pre-concentrator 12 allows a slight concentration process to be performed on the processing liquid immediately before being supplied to the flotation tank 13. Therefore, a part of the process of concentrating the polluted particles contained in the processing liquid to be supplied to the flotation tank 13 described later can be performed in advance by the pre-concentrator 12. For this reason, according to the present embodiment, the load of concentration flotation by the flotation / separation tank 13 can be reduced, and the capability of concentration flotation can be relatively enhanced.

Note that, unlike the present embodiment, the pre-concentrator 12 is provided with a mixed layer 1 in which bubbles and a coagulant are mixed into sludge.
1 may be disposed in the middle of a pipeline for supplying sludge, for example, at a position A in FIG. Pre-concentrator 12 at position A
Are connected, the same effect as in the present embodiment can be obtained.

In the present embodiment, the preconcentrator 12 is configured as described above. [Flotation tank 13] As shown in FIG.
The pipe 36 is connected to the discharge part 32 of the. The pipe 36 is disposed so as to communicate with the inside of the flotation tank 13 via the vicinity of the bottom of the flotation tank 13. For this reason, the processing liquid that has been slightly concentrated by the preconcentrator 12 is supplied to the flotation tank 13.

In the flotation / separation tank 13, fine bubbles are attached to the contaminated particles in the supplied processing solution to reduce the apparent density of the contaminated particles. A floss zone 38 in which the floating substance 37 is concentrated by floating is formed. The concentration of the contaminant particles forming the floss zone 38 is usually about 4%.

The floating material in the floss zone 38 is carried out of the flotation tank 13 by a scraper (not shown) provided above the flotation tank 13. On the other hand, the separated liquid 39 located at the lower part of the floss zone 38 is discharged out of the system via the discharge pipe 40.

As described above, in the present embodiment, the mixing tank 11
Before the processing liquid is supplied to the flotation tank 13 due to the head difference, the processing liquid contained in the sludge is slightly dewatered to reduce the water content. Can be reduced. For example, the sludge having a concentration of polluting particles of 0.5 to 0.8% is dewatered using the preconcentrator 12 so that the concentration of the polluting particles is 1.0 to 1.5%, and is supplied to the flotation tank 13. The amount of processing solution can be reduced to about half. For this reason, according to the present embodiment, while maintaining the sludge residence time in the flotation tank 13 the same as the sludge residence time in the conventional flotation tank 4, the capacity of the flotation tank 13, particularly its height, is maintained. the h _2, can be reduced to approximately half the height h ₁ of a conventional flotation tank 4 shown by FIG.

As described above, in the present embodiment, the flotation tank 13 performs the flotation and concentration of the polluted particles contained in the sludge dewatered by the pre-concentrator 12. In the present embodiment, the flotation tank 13 is configured as described above.

The normal pressure flotation / concentration apparatus 1 according to the present embodiment including the mixing tank 11, the preconcentration apparatus 12, and the flotation / separation tank 13
0 is configured as described above. Next, a situation in which flotation separation of polluted particles contained in excess sludge is performed using the normal pressure flotation / concentration apparatus 10 will be described.

In this embodiment, a treatment liquid obtained by mixing sludge, air bubbles, and a flocculant is supplied to a pre-concentration device 12 using a head difference by using a mixing tank 11. And the pre-concentrator 1
After performing a mild dehydration treatment of the treatment liquid in Step 2, the floating separation tank 13 is used to float and concentrate polluted particles contained in the sludge that has been slightly dehydrated.

As a result, the processing liquid supplied to the flotation tank 13 can be reduced by the preconcentrator 12, so that the size of the flotation tank 13 can be reduced, and the cost of the flotation tank 13 can be reduced.

When the concentration of sludge supplied to the normal pressure flotation / concentration apparatus fluctuates extremely, a pipe may be provided to bypass the preconcentration apparatus. As described above, as a device similar to the pre-concentrator used in the present invention, for example, a screw is inserted and inserted into a portion corresponding to the sludge circulation hole 33 in the present embodiment. There is known an expensive and complicated dewatering apparatus that dewaters sludge heavily by pressing sludge while transporting the sludge by applying external force to the sludge. However, this dehydrator is not used in combination with the flotation tank 13 as in the present embodiment, but performs dehydration of sludge sufficiently by using the dehydrator alone. On the other hand, the pre-concentrator 12 of the present embodiment can sufficiently reduce the size of the flotation tank 13 by simply squeezing a part of the water from the treatment liquid 14 without using such a screw. In addition, the manufacturing cost is reduced accordingly.

As described above, according to the present embodiment, it is possible to reduce the amount of the processing liquid before entering the flotation / separation tank 13, thereby reducing the capacity of the flotation / separation tank 13 and the manufacturing cost. We can work together.

Further, according to the present embodiment, the concentration of the polluted particles contained in the excess sludge to be treated immediately before the flotation tank 13 is stabilized, so that the operation control of the entire normal pressure flotation / concentration apparatus 10 is ensured. You can do it too.

For this reason, the normal pressure flotation enrichment apparatus 10 of the present embodiment can be extremely suitably used for treating excess sludge generated in a sewage treatment plant requiring a large amount of treatment.

[0055]

Next, the present invention will be described more specifically with reference to examples. Using the normal pressure flotation and concentration apparatus 10 shown in FIGS. 1 and 2, the degree of dehydration by the pre-concentration apparatus 12 was variously changed, and the sludge was floated and concentrated. In addition, the concentration of the polluted particles in the excess sludge contained in the treatment liquid when the pre-concentrator 12 was not operated was 5000 ppm. The results are shown graphically in FIG.

As shown in the graph of FIG.
The sludge concentration (concentration of polluted particles) when the amount of water equivalent to 20% of the treatment liquid was removed by Step 2 increased to 6250 ppm. Also, needless to say, the volume of the processing liquid supplied to the flotation tank 13 in this case was reduced to 80%.

For this reason, the residence time of the processing liquid in the flotation tank 13 is 6 hours, which is the residence time of the conventional flotation tank 4.
It was extended from 0 minutes to 72 minutes, and it was possible to increase the concentration of sludge.

Therefore, by keeping the residence time at the conventional value of 60 minutes, the capacity of the flotation / separation tank 13, that is, its height h ₂ could be reduced accordingly.
For this reason, the manufacturing cost of the flotation tank 13 could be significantly reduced.

[0059]

As described above in detail, according to the present invention, it is possible to suppress the increase in the manufacturing cost of the flotation tank used, and thereby to carry out the flotation and concentration of the polluted particles at a low processing equipment cost. It has become possible to provide a pressure flotation concentrator.

Therefore, according to the present invention, sludge requiring large-scale treatment, such as surplus sludge generated in a sewage treatment plant, can fully enjoy the treatment cost merit inherent in the normal pressure flotation method. However, it can be performed reliably and at low cost.

The significance of the present invention having such effects is remarkable.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram schematically showing a schematic configuration of a normal-pressure flotation concentrator according to an embodiment.

FIG. 2 is a perspective view showing a part of a configuration example of a pre-concentrator in the normal-pressure flotation concentrator according to the embodiment, partially omitted and simplified.

FIG. 3 is a graph showing the results of Examples.

FIG. 4 is an explanatory diagram schematically showing a situation in which floating particles contained in excess sludge generated in a sewage treatment plant are floated and concentrated by a normal pressure flotation method.

[Explanation of symbols]

 Reference Signs List 10 Atmospheric pressure flotation / concentration device 11 Mixing tank 12 Preconcentration device 13 Flotation / separation tank 14 Treatment liquid 34 Sludge concentration section

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 11/14 C02F 11/14 A

Claims (4)

[Claims] Atmospheric pressure flotation and concentration comprising a preconcentration device for lightly concentrating sludge in the middle of a pipeline for supplying sludge to a flotation tank for flotation and concentration of polluted particles contained in sludge. apparatus. 2. The normal pressure flotation / concentration apparatus according to claim 1, wherein the pre-concentration apparatus is disposed in the middle of a conveying path for feeding sludge from a mixing apparatus for mixing bubbles and a flocculant into the sludge to a flotation / separation tank. . 3. The normal pressure flotation and concentration device according to claim 1, wherein the preconcentration device is disposed upstream of a mixing device for mixing bubbles and a flocculant into sludge. 4. The pre-concentration device, wherein a plurality of fixed members and a plurality of movable members are alternately provided side by side with a slight gap therebetween, and both of the plurality of fixed members and the plurality of movable members are provided with: 2. A pre-concentrator which is provided with a sludge flow hole through which sludge flows in these juxtaposition directions, and wherein the plurality of movable members are movably arranged in a direction orthogonal to the juxtaposition direction. An atmospheric flotation concentrator according to any one of claims 1 to 3.