Wastewater treatment device

Abstract

To provide a wastewater treatment device solving defects of an aerobic microorganism treatment device and effectively activating an organic polymer flocculant to attain cost reduction.SOLUTION: A wastewater treatment device comprises: aerobic microorganism treatment means; flocculation means where an organic polymer flocculant is added to sludge discharged from the aerobic microorganism treatment means to cause flocculation reaction; and solid-liquid separation means where the flocculated sludge flocculated by the flocculation means is successively subjected to dehydration treatment in a gravity dehydration part and a pressure dehydration part. The solid-liquid separation means discharges the flocculated sludge fed to the gravity dehydration part as dehydrated sludge from the pressure dehydration part, and returns desorbed water discharged from the pressure dehydration part to the flocculation means.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a wastewater treatment apparatus in which aerobic microorganism treatment means and solid-liquid separation means for solid-liquid separating sludge discharged from the aerobic microorganism treatment means are combined.

Background Art

[0002] As an apparatus for treating organic wastewater discharged from factories such as food factories, a wastewater treatment apparatus in which an aerobic microorganism treatment apparatus and a solid-liquid separation apparatus are combined is often used.

[0003] FIG. 6 is an explanatory diagram showing the flow of the conventional wastewater treatment apparatus 51. Wastewater is fed into the aeration tank 2, and the organic matter in the wastewater is decomposed by aerobic microorganisms in the aeration tank 2.

[0004] Although not shown in FIG. 6, since wastewater discharged from factories often contains coarse solids, the wastewater is first treated with a screen to remove the coarse solids. Also, since the wastewater discharged from factories is discharged intermittently, in order to enable treatment at a constant flow rate in the wastewater treatment apparatus, the wastewater from which the coarse solids have been removed is usually temporarily stored in an adjustment tank.

[0005] The treated water containing suspended substances composed of organic matter treated in the aeration tank 2 is supplied to the sedimentation tank 3, and the suspended substances are separated as sludge by natural sedimentation action, and the treated water from which the sludge has been separated is discharged from the sedimentation tank 3.

[0006] On the other hand, a part of the sludge separated in the sedimentation tank 3 is returned to the aeration tank 2 as return sludge 5, and the excess sludge 6 is fed to the flocculation tank 7.

[0007] An organic polymer flocculant 8 is added to the flocculation tank 7 as a flocculant and stirred by a stirrer 9, so that the sludge is flocculated into flocculated sludge.

[0008] Although inorganic flocculants may also be used in combination as the flocculants to be used, organic polymer flocculants are used due to the flocculation effect and economic reasons.

[0009] Next, the flocculated sludge is supplied to a screw press type solid-liquid separation device 11 through a supply pipe 10.

[0010] The screw press type solid-liquid separation device 11 has an inlet 12 for flocculated sludge such as a hopper at one end, a discharge section 13 for dewatered sludge at the other end, and inside an outer cylinder 14 made of punched metal or the like, a screw shaft 15 with a larger diameter on the discharge section 13 side and a smaller diameter on the inlet 12 side is rotatably installed. Screw blades 16 are spirally attached to the screw shaft 15, and those disclosed in Patent Document 1 etc. are known.

[0011] As an operation of dewatering the flocculated sludge with the screw press type solid-liquid separation device 11, while feeding the flocculated sludge into the inlet 12, the screw shaft 15 is slowly rotated by a motor 17 via a speed reducer (not shown). By doing so, the flocculated sludge is pushed out in the direction of the discharge section 13 by the screw blades 16.

[0012] In such a process of being pushed out, in the gravity dewatering section A directly below the inlet 12 and near the inlet 12 where the flocculated sludge is not pushed in very densely, the water in the flocculated sludge mainly permeates through the outer cylinder 14 as separated water by a filtration action.

[0013] Subsequently, the flocculated sludge is pushed out in the direction of the discharge port 13 by the screw blades 16. However, in the pressure dewatering section B formed by the outer cylinder 14 and the screw shaft 15, since its volume gradually becomes smaller as it approaches the discharge section 13, the flocculated sludge is gradually squeezed, and the water remaining in the flocculated sludge permeates through the outer cylinder 14 as separated water, and the dewatered sludge with the water removed is discharged from the discharge section 13.

[0014] Thus, the flocculated sludge is to be dehydrated sequentially by a sludge dehydration section consisting of a gravity dehydration section A and a pressure dehydration section B. The separated water that has passed through the gravity dehydration section A and the pressure dehydration section B is collected by the receiving tank 18 and returned to the aeration tank 2 through the circulation pipe 19.

[0015] In a conventional wastewater treatment apparatus, a contact oxidation apparatus in which aerobic microorganisms are grown on a filler may be used instead of the aeration tank 2, and a rapid sedimentation apparatus or a flotation separation apparatus may be used instead of the sedimentation tank 3 that utilizes natural sedimentation.

[0016] In the conventional wastewater treatment apparatus shown in FIG. 6, the separated water discharged from the gravity dehydration section A is relatively clear, but the separated water discharged from the pressure dehydration section B is quite turbid. In particular, the separated water near the discharge section 13 where the squeezing force acts strongly contains a large amount of fine solids and is quite turbid.

[0017] In addition, the separated water in the receiving tank 18 is turbid because the above-mentioned clear separated water and quite turbid separated water are mixed, and thus it cannot be discharged as it is, so it is returned to the aeration tank 2.

[0018] By the way, the above-mentioned conventional wastewater treatment apparatus has the following problems. That is, there is a risk of various obstacles such as foaming in the aeration tank 2 and sludge floating in the sedimentation tank 3. In addition, when a contact oxidation apparatus is used, there is a risk of obstacles such as deterioration of the quality of the treated water.

[0019] When the cause of these obstacles was investigated, it was found that it was due to the organic polymer flocculant remaining in the turbid separated water returned to the aerobic microorganism treatment apparatus.

[0020] Furthermore, when it was further investigated by what mechanism the organic polymer flocculant remained in the separated water, the following was found.

[0021] As described above, the separated water discharged from the gravity dewatering section A is relatively clear and there is almost no residual organic polymer flocculant. However, in the latter half of the pressure dewatering section B, that is, the part close to the discharge section 13 of the dewatered sludge, since the flocculated sludge is strongly squeezed by the screw blades 16, a considerable amount of fine sludge is contained in the separated water, and the organic polymer flocculant adheres to this fine sludge and exists.

[0022] In addition, the attached organic polymer flocculant still has sufficient flocculation ability. Returning this to the aerobic microorganism treatment device will result in the waste consumption of the organic polymer flocculant, and furthermore, it will increase the BOD load of the aerobic microorganism treatment device by the amount of the organic polymer flocculant.

Prior Art Documents

Patent Documents

[0023]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0024] An object of the present invention is to solve the problems of the aerobic microorganism treatment device in the above-described conventional device, and further to reduce costs by effectively utilizing the organic polymer flocculant.

Means for Solving the Problems

[0025] In order to solve the above problems, the wastewater treatment apparatus according to the present invention comprises aerobic microorganism treatment means, flocculation means for adding an organic polymer flocculant to the sludge discharged from the aerobic microorganism treatment means and causing a flocculation reaction, and solid-liquid separation means for sequentially dehydrating the flocculated sludge flocculated by the flocculation means in a gravity dehydration section and a pressure dehydration section, wherein the solid-liquid separation means discharges the flocculated sludge supplied to the gravity dehydration section as dehydrated sludge from the pressure dehydration section, and is configured to return the separated water discharged from the pressure dehydration section to the flocculation means.

[0026] According to such a wastewater treatment apparatus of the present invention, since the wastewater can be separated into clarified separated water and turbid separated water and discharged, by feeding the clarified separated water with less organic polymer flocculant to the aerobic microorganism treatment means, it is possible to effectively prevent the occurrence of foaming, sludge floating, etc. while suppressing the BOD load of wastewater treatment.

[0027] In the wastewater treatment apparatus of the present invention, it is preferable that the solid-liquid separation means returns the separated water discharged from the gravity dehydration section to the aerobic microorganism treatment means. With such a configuration, the BOD of the separated water discharged from the gravity dehydration section can be further reduced.

[0028] The wastewater treatment apparatus of the present invention is provided with a front-stage receiving tank for receiving the separated water discharged from the gravity dehydration section and a rear-stage receiving tank for receiving the separated water discharged from the pressure dehydration section at a position lower than the front-stage receiving tank, and preferably includes a water volume adjustment mechanism for increasing or decreasing the amount of separated water received by the front-stage receiving tank by adjusting the length of the front-stage receiving tank. By using such a water volume adjustment mechanism to adjust the amount of separated water received by the front-stage receiving tank according to the change in the properties of the sludge discharged from the gravity dehydration section, the turbidity of the separated water can be monitored by transparency, and stable microorganism treatment can be continued even when returned to the aerobic microorganism treatment apparatus. More specifically, by adjusting the transparency of the separated water discharged from the gravity dehydration section to 6 cm or more, stable microorganism treatment can be surely continued.

[0029] It is preferable that the wastewater treatment apparatus of the present invention is provided with stirring means for stirring the separated water in the latter-stage receiving tank. For example, by providing a nozzle for circulating the separated water in the latter-stage receiving tank with a pump and injecting it into the water to stir the separated water in the latter-stage receiving tank, it is possible to prevent fine sludge from settling at the bottom of the latter-stage receiving tank.

[0030] In the wastewater treatment apparatus of the present invention, as the solid-liquid separation means, it preferably has a sludge dewatering section composed of a gravity dewatering section and a pressure dewatering section, supplies flocculated sludge from the front end of the gravity dewatering section, and sequentially moves the supplied flocculated sludge to the gravity dewatering section and the pressure dewatering section, and a screw press type solid-liquid separation device that discharges dewatered sludge from the rear end of the pressure dewatering section is preferably used. Alternatively, a multi-rotating disk type solid-liquid separation device having a similar configuration can also be suitably used.

Effects of the Invention

[0031] The wastewater treatment apparatus of the present invention can separate and discharge the clarified separated water containing almost no organic polymer flocculant and the turbid separated water containing the organic polymer flocculant from the solid-liquid separation device, and by feeding the separated water containing no organic polymer flocculant to the aerobic microorganism treatment apparatus, it is possible to solve the problems that occurred in conventional apparatuses such as foaming in the aeration tank and floating of sludge in the sedimentation tank. In addition, although the BOD load has been increased by the organic polymer flocculant that was conventionally returned to the aerobic microorganism apparatus, since the organic polymer flocculant is not returned to the aerobic microorganism apparatus, the BOD load is not increased.

[0032] Furthermore, by returning the separated water containing the organic polymer flocculant to the flocculation tank, wasteful consumption of the organic polymer flocculant is also eliminated, which is economically advantageous.

Brief Description of the Drawings

[0033]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0034] Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing an example of an embodiment of the present invention, and parts common to the conventional apparatus shown in FIG. 6 are denoted by the same reference numerals and the description thereof is omitted. The difference between the conventional apparatus and the present invention lies in the structure of the receiving tank at the lower part of the screw press type solid-liquid separation apparatus and the destination of the separated water received in the receiving tank.

[0035] That is, a front receiving tank 20 for receiving separated water discharged from the first half of the sludge dewatering section including the gravity dewatering section A and a rear receiving tank 21 for receiving separated water discharged from the second half of the sludge dewatering section including the pressure dewatering section B are installed at the lower part of the screw press type solid-liquid separation apparatus 11. 19 is a circulation pipe for returning the separated water in the front receiving tank 20 to the aeration tank 2, 22 is a connection pipe for feeding the separated water in the rear receiving tank 21 to the coagulation tank 7, 23 is a pump, 24 is a return pipe to the rear receiving tank 21, and 25 is a nozzle.

[0036] Next, the operation of the wastewater treatment apparatus of the present invention will be described. In the present invention, the separated water discharged from the first half of the sludge dewatering section including the gravity dewatering section A is received by the front receiving tank 20, and the separated water discharged from the second half of the sludge dewatering section including the pressure dewatering section B is received by the rear receiving tank 21.

[0037] The separated water received in the front-stage receiving tank 20 is the mixed water of the separated water in the gravity dewatering section A and the first half of the pressure dewatering section B. However, since the separated water in the gravity dewatering section A is mainly obtained by a filtering action, it is hardly turbid. Also, the separated water in the first half of the pressure dewatering section B is not very turbid because the squeezing force by the screw blades 16 does not strongly act. Therefore, the above-mentioned mixed water Detachment The water is not very turbid.

[0038] On the other hand, the separated water received in the rear-stage receiving tank 21 is discharged from the location where the squeezing force by the screw blades 16 strongly acts. Therefore, it contains a considerable amount of fine sludge and is quite turbid.

[0039] The inventors of the present invention coagulated the sludge discharged from the aerobic microorganism treatment apparatus with an organic polymer coagulant, and when dehydrating the coagulated sludge with a conventional screw press type solid-liquid separation apparatus, the transparency and flow rate of the separated water at various locations from the inlet of the coagulated sludge to the discharge section of the dehydrated sludge were measured by experiments.

[0040] That is, the section from the inlet of the coagulated sludge to the discharge section of the dehydrated sludge was partitioned into six equal intervals. The portion closest to the inlet was designated as the 1st section, the adjacent one as the 2nd section, and then the 3rd, 4th, 5th, and 6th sections toward the discharge section of the dehydrated sludge. As a result of measuring the transparency and flow rate of each section, the results were as shown in Table 1.

[0041]

Table 1

[0042] As is clear from Table 1, it can be seen that the separated water close to the sludge discharge section is quite turbid.

[0043] The inventors of the present invention returned various separated waters with different transparencies to the aerobic microorganism treatment apparatus and confirmed the influence by experiments. As a result, it was confirmed that if the separated water has a transparency of 6 cm or more, no problem occurs even if this is returned to the aerobic microorganism treatment apparatus.

[0044] According to these experimental results, in the present invention, the relatively clear desorbed water received in the front-stage receiving tank 20 is returned to the aeration tank 2 through the circulation pipe 19, and the considerably turbid desorbed water received in the rear-stage receiving tank 21 is returned to the coagulation tank 7 through the connection pipe 22 via the pump 23.

[0045] In addition, in order to prevent fine sludge from settling at the bottom of the rear-stage receiving tank 21, the desorbed water in the rear-stage receiving tank 21 is returned by the return pipe 24 and sprayed from the nozzle 25 in the water in the rear-stage receiving tank 21, so as to stir the desorbed water in the rear-stage receiving tank 21.

[0046] In FIG. 1, the desorbed water in the rear-stage receiving tank 21 is returned to the coagulation tank 7 by the pump 23, the connection pipe 22, etc. However, the coagulation tank 7 can also be installed below the screw press type solid-liquid separation device 11. In this case, the pump 23, the connection pipe 22, and the return pipe 24 are not required, and the desorbed water in the rear-stage receiving tank 21 can be returned to the coagulation tank 11 by natural fall. However, even in this case, in order to prevent fine sludge from settling at the bottom of the rear-stage receiving tank 21, it is preferable to install some stirring means to stir the desorbed water in the rear-stage receiving tank 21.

[0047] FIG. 2 is an explanatory view of the front-stage receiving tank 20 seen from above, and the front-stage receiving tank 20 can be provided with a water volume adjustment mechanism as described below. That is, the front-stage receiving tank 20 is composed of an outer fixed part 26 and an inner movable part 27, and by making the movable part 27 movable in the vertical direction, the area for receiving the desorbed water can be changed. By adjusting the vertical length of the front-stage receiving tank 20 in this way, the water volume of the desorbed water received in the front-stage receiving tank 20 can be increased or decreased.

[0048] According to the change in the properties of the sludge discharged from the sedimentation tank 3, the transparency of the desorbed water flowing in the circulation pipe 19 for returning to the aeration tank 2 can be adjusted by using the above-mentioned water volume adjustment mechanism, and based on the above-mentioned experimental results, the transparency of the desorbed water flowing in the circulation pipe 19 can be adjusted to 6 cm or less.

[0049] By installing the front receiving tank 20 above the rear receiving tank 21, it is possible to make the rear receiving tank 21 receive the separated water that could not be received when the movable part 27 was moved.

[0050] As described above, the separated water in the front receiving tank 20 is quite clear and contains almost no organic polymer flocculant, so there is no problem at all even if it is returned to the aeration tank 2. In some cases, it is also possible to discharge it directly without returning it to the aeration tank 2.

[0051] Next, the solid-liquid separation device used in the present invention will be described. In FIG. 1, a screw press type solid-liquid separation device is used as a solid-liquid separation device having a sludge dewatering part composed of a gravity dewatering part and a pressure dewatering part, supplying flocculated sludge from the front end part of the gravity dewatering part, sequentially moving the supplied flocculated sludge to the gravity dewatering part and the pressure dewatering part, and discharging dewatered sludge from the rear end part of the pressure dewatering part. However, as such a type of solid-liquid separation device, a multi-rotating disk type solid-liquid separation device can also be used.

[0052] FIG. 3 is an explanatory view showing an example of a multi-rotating disk type solid-liquid separation device that can be used in the present invention. In the multi-rotating disk type solid-liquid separation device 28 shown in FIG. 3, a rotating shaft 31 with a number of circular rotating disks 30 fitted therein is pivotally supported side by side from the upstream side to the downstream side within a housing 29. The lower rotating disk group 32 is arranged from one corner to the other corner within the housing 29, while the upper rotating disk group 33 is arranged only between the central part and the downstream side.

[0053] In both the rotating disk groups 32 and 33, the adjacent rotating disks 30 are in contact with each other in a meshing manner. The rotating directions of the rotating disks 30 in each rotating disk group are the same, but the rotating direction of the rotating disks 30 in the lower rotating disk group 32 is opposite to that of the rotating disks 30 in the upper rotating disk group 33.

[0054] Below the housing 29 is the subsequent receiving tank 21 for the separated water, and above the subsequent receiving tank 21, a preceding receiving tank 20 for the separated water is installed. Pipes, pumps, etc. attached to the preceding receiving tank 20 and the subsequent receiving tank 21 are the same as those in FIG. 1, so the description thereof is omitted.

[0055] In the multi-rotary disk type solid-liquid separation device 28, the operation of dewatering the flocculated sludge is performed by supplying the flocculated sludge from the supply pipe 10 while rotating each rotary disk 30. The supplied flocculated sludge stays above the rotary disk group 32, and the separated water falls downward from the gaps between the rotary disks 30. While placing the flocculated sludge on the upper part of each rotary disk 30, the flocculated sludge is moved from the upstream side to the downstream side of each rotary disk 30, and sequential dewatering is also performed during this process.

[0056] The flocculated sludge formed from the central part of the lower rotary disk group 32 to the upper part of each downstream rotary disk 30 is squeezed by the rotary disks 30 of the upper rotary disk group 33, and finally, the dewatered sludge is discharged from the discharge part 13.

[0057] In FIG. 3, the part mainly dehydrated by the filtering action of only the rotary disk group 32 is the gravity dewatering part, and the part dehydrated by the squeezing by the rotary disk group 32 and the rotary disk group 33 is the pressure dewatering part.

[0058] The separated water discharged from the gravity dewatering part and the first half of the pressure dewatering part is clear. The separated water in this part is received by the preceding receiving tank 20, and the separated water turbid due to containing other fine sludge is received by the subsequent receiving tank 21. Other operations are the same as those in FIG. 1, so the description thereof is omitted.

[0059] FIG. 4 is an explanatory diagram showing another example of the multi-rotary disk type solid-liquid separation device that can be used in the present invention. In the multi-rotary disk type solid-liquid separation device 34 shown in FIG. 4, rotating shafts 37 with a large number of elliptical rotary disks 36 fitted therein are arranged side by side from the upstream side to the downstream side in a housing 35 and are rotatably supported, and fixing members 38 are horizontally provided above each rotating shaft.

[0060] FIG. 5 is an enlarged perspective view of the main part of the multi-rotary disk type solid-liquid separator 34 shown in FIG. 4. A rotary disk 36 is arranged between four fixing members 38, and each rotary disk 36 is fitted to a rotary shaft 37 via a spacer ring 39. The rotation directions of the rotary disks 36 are the same, and adjacent rotary disks 36 are rotatably arranged without contacting each other.

[0061] The upper part of the housing 35 is a pressure plate 40 inclined from the upstream side to the downstream side. A pressure mechanism 41 is attached to the downstream side of the pressure plate 40. By vertically moving the pressure plate 40 with the pressure mechanism 41 using the pressure plate support shaft 42 as a fulcrum, the gap between the tip of the fixing member 38 and the tip of the pressure plate 40 can be adjusted, and this gap serves as the discharge part 13 for dewatered sludge. An air cylinder or the like is used as the pressure mechanism 41.

[0062] The lower part of the housing 35 is the subsequent receiving tank 21 for separated water. An upstream receiving tank 20 for separated water is installed above the subsequent receiving tank 21. Since the pipes, pumps, etc. attached to the upstream receiving tank 20 and the subsequent receiving tank 21 are the same as those in FIG. 1, the description is omitted.

[0063] In the operation of dewatering the flocculated sludge in the multi-rotary disk type solid-liquid separator 34, while rotating each rotary disk 36, the flocculated sludge is supplied from the supply pipe 10. The supplied flocculated sludge stays on the upper part of each rotary disk 36, and the separated water falls downward from the gaps between the rotary disks 36. While placing the flocculated sludge on the upper part of the rotary disk 36, the flocculated sludge is moved from the upstream side to the downstream side of each rotary disk 36, and sequential dewatering is also performed during this process.

[0064] The flocculated sludge formed from the central part of the lower rotary disk 36 to the upper part of the downstream rotary disk 36 is squeezed by the pressure plate 40, and finally the dewatered sludge is discharged from the discharge part 13.

[0065] In Fig. 4, the portion mainly dehydrated by the filtering action of only the rotary disk 36 is the gravity dehydration section, and the portion dehydrated by the pressing between the rotary disk 36 and the pressing plate 40 is the pressure dehydration section. The separated water discharged from the gravity dehydration section and the first half of the pressure dehydration section is clear. The separated water in this part is received by the front-stage receiving tank 20, and the separated water turbid due to containing other fine sludge is received by the rear-stage receiving tank 21. Since other operations are the same as those in Fig. 1, the description is omitted.

Industrial Applicability

[0066] The wastewater treatment apparatus of the present invention can be widely used as an apparatus for treating organic wastewater discharged from factories such as food factories.

Explanation of Reference Numerals

[0067] 1, 51 Wastewater treatment apparatus 2 Aeration tank 3 Sedimentation tank 5 Return sludge 6 Sludge 7 Coagulation tank 8 Organic polymer coagulant 9 Stirrer 10 Supply pipe 11 Screw press type solid-liquid separation device 12 Inlet 13 Discharge part 14 Outer cylinder 15 Screw barrel 16 Screw blade 17 Motor 18 Receiving tank 19 Circulation pipe 20 Front-stage receiving tank 21 Rear-stage receiving tank 22 Connection pipe 23 Pump 24 Return pipe 25 Nozzle 26 Fixed part 27 Movable part 28, 34 Multi-rotary disk type solid-liquid separation device 29, 35 Housing 30, 36 Rotary disk 31, 37 Rotation shaft 32 and 33 Rotary Disk Groups 38 Fixed Member 39 Spacer Ring 40 Pressing Plate 41 Pressing Mechanism 42 Pressing Plate Support Shaft A Gravity Dewatering Section B Pressing Dewatering Section

Claims

1. A wastewater treatment apparatus comprising an aerobic microorganism treatment means, a coagulation means for adding an organic polymer coagulant to the sludge discharged from the aerobic microorganism treatment means and causing a coagulation reaction, and a solid-liquid separation means for sequentially dehydrating the coagulated sludge coagulated by the coagulation means in a gravity dewatering section and a pressure dewatering section, wherein the solid-liquid separation means sequentially moves the coagulated sludge supplied to the front end of the gravity dewatering section to the gravity dewatering section and the pressure dewatering section, discharges it as dehydrated sludge from the rear end of the pressure dewatering section, and returns the separated water discharged from a part of the gravity dewatering section and the pressure dewatering section to the aerobic microorganism treatment means or discharges it as it is without returning it, and is configured to return the separated water discharged from the remaining part of the pressure dewatering section to the coagulation means. A wastewater treatment apparatus characterized by this.

2. A front-stage receiving tank for receiving the separated water discharged from a part of the gravity dewatering section and the pressure dewatering section, and a rear-stage receiving tank for receiving the separated water discharged from the remaining part of the pressure dewatering section at a position lower than the front-stage receiving tank are installed, and a water volume adjustment mechanism for increasing or decreasing the amount of separated water received by the front-stage receiving tank by adjusting the length of the front-stage receiving tank is provided. The wastewater treatment apparatus according to claim 1.

3. The wastewater treatment apparatus according to claim 2, wherein the transparency of the separated water discharged from a part of the gravity dewatering section and the pressure dewatering section is adjusted to 6 cm or more using the water volume adjustment mechanism.

4. The wastewater treatment apparatus according to any one of claims 1 to 3, further comprising stirring means for stirring the separated water in the rear-stage receiving tank.

5. The wastewater treatment apparatus according to any one of claims 1 to 4, wherein the solid-liquid separation means is a screw press type solid-liquid separation device.

6. The wastewater treatment apparatus according to any one of claims 1 to 4, wherein the solid-liquid separation means is a multi-rotating disk type solid-liquid separation device.

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