Buoyancy-driven water stop device for water purification plant, water purification plant system, and maintenance method for water purification plant

Abstract

To provide a novel cut-off device which is used in a water purification plant and can be realized by a relatively simple constitution.SOLUTION: The overflow weir 7 is provided in a flow path between the flocculation basin and the sedimentation basin. The water stop plate 12 is rotatably attached to the overflow weir 7. The water cut-off plate 12 is rotated in the buoyancy direction, and closes an upper opening 7a existing between the overflow weir 7 and the roof A to cut off water. The water cut-off plate 12 is rotated in a direction opposite to the buoyancy direction by an external force against the buoyancy, and opens the 7a of the upper opening to pass water. The water stop plate 12 is rotated by moving up and down the guide rod 13. The water stop sheet 15 has flexibility and covers a gap between the overflow weir 7 and the water stop plate 12.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a buoyant water stop device for a water purification plant, a water purification plant system using the same, and a maintenance method for the water purification plant. [Background technology]

[0002] Conventionally, a method for controlling water flow / stoppage using a water cutoff device installed in a wall is known. For example, Patent Document 1 discloses a method for repairing a sedimentation basin in a sewage treatment facility. A sedimentation basin has multiple ponds arranged adjacent to a conduit along the direction of raw water flow in the conduit. When repairing a sedimentation basin, a pair of temporary water cutoff walls is first installed upstream and downstream of the conduit corresponding to the pond to be repaired, thereby closing the water flow in this section of the conduit. Next, water is drained from the conduit between the pair of temporary water cutoff walls and from the pond to be repaired. Then, a connecting pipe installed between the pair of temporary water cutoff walls is opened, and raw water is supplied to another pond located downstream from the pond to be repaired. While this is done, repair work is carried out, including replacing or repairing equipment installed in the pond to be repaired. Water is drained from the pond to be repaired using water cutoff devices installed for each pond on the partition wall separating the conduit from the pond. This water stop device consists of a lower opening at the bottom of the dividing wall and a lift-up inflow door that opens and closes this lower opening. For the pond that is undergoing repair work, the inflow door closes the opening to restrict the inflow of water from the water conduit, while for other ponds, the opening remains open to allow water to flow in from the water conduit. This means that operation only needs to be stopped for the pond that is undergoing repair work, preventing a decline in the operating efficiency of the entire facility.

[0003] Furthermore, Patent Document 2 discloses a buoyancy-type water stop device that prevents water from entering indoor spaces through openings in buildings, underground passages, etc., during floods caused by typhoons or heavy rain. This water stop device is installed on the floor and consists of a main water stop and an auxiliary water stop. The main water stop is positioned so that it intersects with the flow of water. The auxiliary water stop is rotatably attached to the main water stop and rotates upward due to its own buoyancy. In the initial state when there is no water outdoors, the auxiliary water stop is positioned at the bottom, allowing pedestrians to step over it without worrying about the water stop on the floor. On the other hand, when the water outdoors rises, the auxiliary water stop rotates upward due to buoyancy. This increases the water stop height from the initial state, preventing water from entering indoor spaces. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5961489 [Patent Document 2] Japanese Patent Application Publication No. 2023-157496 Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, a water purification plant has a receiving well, a chemical mixing basin, a flocculation basin, a sedimentation basin, and a filtration basin. The sedimentation basin is equipped with treatment devices such as sludge collectors and inclined plate settling devices, which are used while submerged in the sedimentation basin. When inspecting or repairing submerged treatment devices or performing maintenance work such as cleaning the basin, it is necessary to temporarily suspend water treatment and lower the water level in the sedimentation basin by, for example, closing the valve on the inlet pipe that draws raw water from outside into the receiving well. However, because suspending water treatment directly reduces operational efficiency, it is not easy to secure sufficient time for maintenance.

[0006] In this regard, the above-mentioned Patent Document 1 relates to the repair of sedimentation basins in sewage treatment facilities, but is not related to water purification plants because there is no flocculation basin, and the type of water stop device is not buoyant.Furthermore, the above-mentioned Patent Document 2 relates to a buoyant water stop device, but it is installed on the floor surface at the boundary between indoors and outdoors as a flood prevention measure, and is not intended for use in water purification plants.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a novel water stop device that can be used in water purification plants and that can be realized with a relatively simple configuration.

[0008] Another object of the present invention is to enable maintenance work on a specific settling basin while suppressing a decrease in the operating efficiency of the water purification plant as a whole. [Means for solving the problem]

[0009] The first invention provides a buoyant water stop device for a water purification plant having a flocculation basin and a sedimentation basin in which a treatment device used in a submerged state is installed. This water stop device has an overflow weir and a water stop plate. The overflow weir is provided in a flow path between the flocculation basin and the sedimentation basin. The water stop plate is rotatably attached to the overflow weir. The water stop plate rotates in the buoyancy direction of the water stop plate, closing an upper opening between the overflow weir and the ceiling to stop water flow. The water stop plate also rotates in the opposite direction to the buoyancy direction, opening the upper opening to allow water to pass through.

[0010] Here, in the first aspect of the invention, a guide rod may be provided. The lower end of this guide rod is rotatably attached to the waterstop and extends upward through the ceiling. The waterstop rotates by raising and lowering the guide rod. In this case, the waterstop may be rotatably attached to the overflow weir via a first connecting member provided on one surface of the waterstop, and the guide rod may be rotatably attached to the waterstop via a second connecting member provided on the other surface opposite to the one surface of the waterstop. Furthermore, it is preferable that the rotation of the waterstop in the buoyancy direction be restricted to a closed state before the waterstop reaches a vertically upward orientation by the waterstop abutting against another member. The other member may be a support member attached to the ceiling. It is preferable that the support member have an inclined portion inclined at a predetermined angle with respect to the ceiling as a portion that abuts against the waterstop.

[0011] In the first aspect of the invention, a side cover attached to the ceiling may be provided. This side cover has a shape that allows it to close an opening formed on the side of the waterstop when in the closed state. A locking mechanism may also be provided to fix the guide rod at a predetermined raised or lowered position. This locking mechanism has a hollow base member and a locking member. The base member is attached to the ceiling and the guide rod is inserted through it. The locking member is inserted through a through hole provided in the base member and a through hole provided in the guide rod. Furthermore, a flexible waterstop sheet may be provided that is attached to the overflow weir and the waterstop and covers the gap between the overflow weir and the waterstop.

[0012] The second invention provides a water purification plant system having a flocculation basin, multiple sedimentation basins, and multiple water cut-off devices. Each of the multiple sedimentation basins is equipped with a treatment device that operates submerged, and water diverted from the flocculation basin into multiple systems flows into each of the basins. The multiple water cut-off devices are provided corresponding to each of the flow paths diverted into the multiple systems, and can be operated independently of each other. The buoyant water cut-off device for water purification plants according to the first invention is used as each of the multiple water cut-off devices.

[0013] The third invention provides a maintenance method for a water purification plant having a flocculation basin, multiple sedimentation basins, and multiple water cut-off devices. Each of the multiple sedimentation basins is equipped with a treatment device that operates submerged, and water diverted from the flocculation basin into multiple systems flows into each of them. The multiple water cut-off devices are provided corresponding to the multiple flow paths diverged into the multiple systems and can be operated independently of each other. The buoyant water cut-off device for a water purification plant according to the first invention is used for each of the multiple sedimentation basins. This maintenance method has the following steps: In the first step, for a sedimentation basin that is the target of maintenance work, water is cut off using the water cut-off device, while water flow is continued through the water cut-off device for the other sedimentation basins. In the second step, maintenance work is performed on the sedimentation basins that have been stopped by the water cut-off device. In the third step, after the maintenance work is completed, water flow is resumed through the water cut-off device for the sedimentation basins that have been stopped by the water cut-off device. [Effects of the Invention]

[0014] According to the first or second invention, a water cut-off device for a water purification plant can be realized with a relatively simple configuration mainly consisting of an overflow weir installed in the flow path between the flocculation basin and the settling basin, and a water stop plate that opens and closes the upper opening between the overflow weir and the ceiling.In particular, according to the second invention, water flow / stopping in each settling basin can be finely controlled.

[0015] Furthermore, according to the third invention, by stopping the flow of water into the sedimentation basin that is the target of maintenance work and continuing to allow water to flow through the other sedimentation basins, maintenance work on the sedimentation basins can be carried out while effectively suppressing a decline in the operating efficiency of the entire water purification plant. [Brief explanation of the drawings]

[0016] [Figure 1] Schematic top view of the water purification plant system [Figure 2] Schematic side view of the water purification plant system [Figure 3] Overall configuration of the water stop device [Figure 4] Side view of the main part of the waterproofing device [Figure 5] Side view of the main part of the locking mechanism [Figure 6] An explanatory diagram of the water stop device in the water flow locked state [Figure 7] An explanatory diagram of the water stop device in the water stop locked state DETAILED DESCRIPTION OF THE INVENTION

[0017] FIG. 1 is a schematic top view of a water purification system according to this embodiment. In the figure, arrows indicate the water flow. This water purification system 1 includes, from upstream to downstream, a receiving well 2, a chemical mixing basin 3, a flocculation basin 4, and a settling basin 6. An inlet pipe 2b equipped with a valve 2a is connected to the receiving well 2, and the intake volume and water level of the raw water are adjusted by the opening of this valve 2a. The raw water from the receiving well 2 flows into the adjacent chemical mixing basin 3. In the chemical mixing basin 3, chemicals such as coagulants are added to solidify the impurities in the water, and the water is rapidly mixed. The water from the chemical mixing basin 3 flows into the adjacent flocculation basin 4. The flocculation basin 4 is composed of multiple percolation basins arranged in a matrix. As the water flows in a zigzag pattern, fine impurities in the water grow into clumps, forming flocs. The flocculation basin 4 may be configured not only as a percolation basin but also as a mechanically agitated basin. The water from the flocculation basin 4 flows through the water conveyance space 5 into the settling basin 6. In the settling basin 6, flocs in the water are settled and removed. The water treated in the settling basin 6 flows into a filtration basin (not shown).

[0018] In this embodiment, four settling basins 6A-6D are provided in parallel to one another as the settling basin 6, resulting in four treatment systems. The two settling basins 6A and 6B at the top of the figure are in common communication with the upper water conveying space 5, and share the upstream receiving well 2A, chemical mixing basin 3A, and flocculation basin 4A. The water conveying space 5 is equipped with an overflow weir 7 for directing water to settling basin 6A, and another overflow weir 7 for directing water to settling basin 6B. The settling space 5 is thus divided into three sections: one intermediate tank 5a, a settling tank 5b for settling basin 6A, and a settling tank 5b for settling basin 6B. The two settling tanks 5b are separated from each other by a partition wall. The water flowing through the intermediate tank 5a is divided into two systems, one of which flows into the settling tank 5b for the settling basin 6A via the overflow weir 7 at the top of the figure, and the other system flows into the settling tank 5c for the settling basin 6B via the overflow weir 7 at the bottom of the figure.

[0019] The sedimentation basins 6C and 6D at the bottom of the figure have the same configuration as the two systems of sedimentation basins 6A and 6B described above. These sedimentation basins 6C and 6D are commonly connected to the water conveying space 5 at the bottom of the figure, and share the receiving well 2B, chemical mixing basin 3B, and flocculation basin 4B located upstream of it. The water conveying space 5 at the bottom of the figure has the same configuration as the water conveying space 5 described above.

[0020] FIG. 2 is a schematic side view of the water purification plant system 1. While this figure focuses on one settling basin 6A, the other settling basins 6B-6D have a similar configuration. Water diverted into multiple systems within the water conveyance space 5 flows over an overflow weir 7 and into the settling tank 5b for the settling basin 6A through an upper opening 7a located between the overflow weir 7 and the ceiling A. The water in the settling tank 5b then flows into the settling basin 6A through a straightening wall 8 that separates it from the settling basin 6A. The straightening wall 8 is a partition wall with a slit or multiple holes, and serves to straighten the water flow. The settling basin 6A is equipped with an inclined plate settling device 9 and a sludge scraper 10 (hereinafter, these may be collectively referred to as "treatment devices 9, 10"). The inclined plate settling device 9 is a device that uses multiple inclined plates arranged in the settling basin 6A to increase the settling area and improve settling efficiency, while the sludge collector 10 is a device that scrapes and removes sludge that has settled at the bottom of the basin in one direction. These treatment devices 9 and 10 are installed in each of the settling basins 6A to 6D and are used while submerged in the basin. Here, "submerged" does not only mean that the entire device is completely submerged, but also includes a state where part of the device is exposed above the water surface.

[0021] The water purification system 1 has a distinctive and novel configuration in which it has a buoyancy-type water stop device 11. This water stop device 11 is installed in the flow path between the flocculation basin 4A and the settling basin 6A, which in this embodiment is the water conveying space 5, and includes an overflow weir 7 as a component thereof. In this embodiment, there are four systems corresponding to the settling basins 6A to 6D, and each system is provided with an overflow weir 7, so there are also four water stop devices 11.

[0022] 3 is an overall configuration diagram of the water stop device 11. This water stop device 11 is mainly composed of an overflow weir 7, a water stop plate 12, multiple guide rods 13, multiple locking mechanisms 14, a water stop sheet 15, multiple support members 16, and a pair of side covers 17.

[0023] The waterstop 12 is made of a lightweight material, such as long-fiber-glass reinforced plastic foam, that floats on water. It is rotatably attached to the top of the overflow weir 7 via multiple connecting members 18 (hinges) arranged in the width direction. The waterstop 12 has a shape corresponding to the upper opening 7a between the overflow weir 7 and the ceiling A. In this embodiment, the upper opening 7a extends across the entire width of the overflow weir 7, and the width of the waterstop 12 is accordingly large. However, the shape of the upper opening 7a is not limited to this. For example, the upper opening 7a may be a recess formed by partially recessing the top of the overflow weir 7, which would reduce the width of the waterstop 12. Furthermore, considering factors such as damage during delivery and ease of installation, the waterstop 12 may be constructed as an integrated waterstop 12 by connecting multiple plate-like members that are separated widthwise.

[0024] The guide rods 13 are provided to assist the movement of the waterstop 12, and multiple guide rods 13 are installed at equal intervals across the width of the waterstop 12. The lower end of each guide rod 13 is rotatably attached to the waterstop 12 via a connecting member 19, and extends upward through the ceiling A. The waterstop 12 is rotated by multiple workers manually or by using a drive source such as a motor to raise and lower the multiple guide rods 13 in coordination. Functionally, one guide rod 13 is sufficient, but multiple guide rods 13 are provided to ensure stability of rotation while preventing deformation or damage to the long waterstop 12, which can reach up to 10 meters. A locking mechanism 14 is provided on the upper surface of the ceiling A corresponding to each of the multiple guide rods 13 and fixes the guide rods 13 at a predetermined raised or lowered position.

[0025] The waterstop sheet 15 is a flexible sheet-like member. The lower part of the waterstop sheet 15 is attached to the overflow weir 7, and the upper part is attached to the waterstop plate 12. As a result, the gap between the overflow weir 7 and the waterstop plate 12 is covered by the waterstop sheet 15, minimizing water leakage from this gap. In addition, multiple support members 16 are attached to the ceiling A, arranged at equal intervals in the width direction of the waterstop plate 12. Furthermore, a pair of side covers 17 are attached to the ceiling A so as to be positioned on both sides of the waterstop plate 12.

[0026] FIG. 4 is a side view of a main portion of the waterstop device 11. The connecting member 18 connecting the overflow weir 7 and the waterstop 12 is provided on one side of the waterstop 12, specifically, on the front side facing the upstream side (toward the intermediate tank 5a) of the water overflow weir 7 in the illustrated state. The connecting member 19 connecting the waterstop 12 and the guide rod 13 is provided on the other side of the waterstop 12 (the side opposite the one side), specifically, on the rear side facing the downstream side (toward the settling tank 5b) of the water overflow weir 7 in the illustrated state. As a result, the rotation axis of the waterstop 12 relative to the overflow weir 7 is located on the front side, while the rotation axis of the guide rod 13 relative to the waterstop 12 is located on the rear side. By providing the rotatable connecting member 19 on the rear side rather than the front side, physical interference between the components can be avoided when the waterstop 12 rotates within a predetermined range of motion. Furthermore, a water blocking sheet 15 is provided in front of both the overflow weir 7 and the water blocking plate 12 to prevent water from entering from the intermediate tank 5a side.

[0027] The clockwise rotation of the waterstop 12 is restricted by the waterstop 12 abutting against another component, so that the waterstop 12 faces diagonally upward just before reaching a vertically upward orientation. In this embodiment, the waterstop 12 rotates up to a rotation angle of approximately 135 degrees from a vertically downward orientation. The other component that abuts the waterstop 12 may be the ceiling A itself, but in this embodiment, that role is played by a support member 16 attached to the ceiling A. The support member 16 has an inclined portion 16a that extends at a predetermined angle relative to the underside of the ceiling A as the portion that abuts the waterstop 12. The reason for providing the support member 16 is that the height of the ceiling A that the waterstop 12 abuts against may vary depending on the location, and the support member 16 absorbs this error.

[0028] The side covers 17 are provided to close the openings formed on the sides of the waterstop 12 when the waterstop 12 is stopped just before reaching the vertically upward position, and have a shape that corresponds to this opening. In addition, elastic materials such as rubber are attached to both sides of the waterstop 12 to seal any small gaps between the waterstop 12 and the side covers 17.

[0029] FIG. 5 is a side view of a main portion of the locking mechanism 14. The locking mechanism 14 is provided to fix the rotational position of the waterstop 12 and includes a hollow base member 20 and a locking member 21. The base member 20 has a generally cylindrical shape with flanges formed on the top and bottom. The base member 20 is attached to the upper surface of the ceiling A, and a guide rod 13 that penetrates the ceiling A from top to bottom is inserted through the base member 20. A through-hole 20a that passes laterally through the interior of the locking member 20 is provided in the side of the locking member 20. In addition, two through-holes 13a and 13b that pass laterally through the interior of the guide rod 13 are provided in the side of the guide rod 13. These through-holes 13a and 13b are provided at different positions in the height direction of the guide rod 13, and the lower through-hole 13a is used when stopping water, and the upper through-hole 13b is used when allowing water to pass through. The locking member 21 may be, for example, a set bolt, which is inserted through the through hole 20a on the base member 20 side and either the upper or lower through hole 13a, 13b on the guide rod 13 side.

[0030] Figure 6 is an explanatory diagram of the water stop device 11 in a water flow locked state. When water is flowing (when the downstream sedimentation basin 6 is operating), the water stop plate 12 faces downward, and the upper opening 7a is open. The guide rod 13 is also lowered, and is locked in the state shown in the figure by the locking member 21 inserted into the upper through-hole 13b. When water is flowing, water is allowed to flow into the sedimentation basin 6 located downstream of the water stop device 11, and treatment in this sedimentation basin 6 continues.

[0031] FIG. 7 is an explanatory diagram of the water stop device 11 in the water stop locked state. When water flow is stopped (when the downstream sedimentation basin 6 is not operating), the water stop plate 12 faces diagonally upward, and the upper opening 7a is closed. The guide rod 13 is raised and locked in the state shown in the figure by the locking member 21 inserted into the lower through-hole 13a. When water flow is stopped, the inflow of water into the sedimentation basin 6 located downstream of the water stop device 11 is restricted, and the water level in the sedimentation basin 6 drops, exposing the treatment devices 9 and 10 that were submerged in the sedimentation basin 6. Note that the drop in the water level in the sedimentation basin 6 is caused by the outflow exceeding the inflow into the sedimentation basin 6. Therefore, it is not necessary to completely shut off the inflow into the sedimentation basin 6; a certain amount of inflow (leakage) does not hinder operation.

[0032] Next, we will explain the maintenance procedures, such as inspecting / repairing the treatment equipment installed in the sedimentation basin 6A shown in Figure 1 and cleaning the inside of the basin, for example. Note that for sedimentation basins 6B to 6D that are not subject to maintenance, water continues to flow through them (water flow locked state) without shutting off the water with the water stop device 11, even during maintenance of sedimentation basin 6A, in order to prevent a decrease in the operating efficiency of the entire water purification plant.

[0033] First, the worker removes the locking member 21 inserted into the upper through-hole 13b of the guide rod 13 of the water stop device 11 for the sedimentation basin 6A to be maintained, thereby releasing the water flow lock state. Next, the worker raises the lowered guide rod 13 while rotating the downward-facing water stop plate 12 in the buoyancy direction (clockwise). This closes the open upper opening 7a, stopping the water flow, and the water level in the sedimentation basin 6A begins to gradually drop. Next, the worker raises the guide rod 13 to the height shown in Figure 7, and then inserts the locking member 21 into the lower through-hole 13a to lock this state. After confirming that the water level in the sedimentation basin 6A has sufficiently dropped (drained), the worker begins the necessary maintenance work on the sedimentation basin 6A.

[0034] When maintenance work on the sedimentation basin 6A is completed, the worker removes the locking member 21 inserted into the lower through-hole 13a of the water stop device 11 for the sedimentation basin 6A to release the water stop lock state. Next, while pushing down the raised guide rod 13, the worker rotates the water stop plate 12, which was facing diagonally upward, in the opposite direction (counterclockwise) to the buoyancy direction by using an external force (artificial force or driving force from a driving source) that resists buoyancy. This opens the closed upper opening 7a, restarting water flow and gradually increasing the water level in the sedimentation basin 6A. Then, after pushing down the guide rod 13 to the height shown in Figure 6, the worker inserts the locking member 21 into the upper through-hole 13b to lock this state. This completes the series of maintenance work on the sedimentation basin 6A.

[0035] Thus, according to this embodiment, a water stop device 11 for a water purification plant can be realized with a relatively simple configuration mainly consisting of the overflow weir 7 and the water stop plate 12 attached thereto. Furthermore, installation of the water stop device 11 in a water purification plant can be achieved by relatively simple construction mainly consisting of installing the water stop plate 12 on the overflow weir 7, and does not require large-scale construction, which has the advantages of being easy to install and low-cost.

[0036] Furthermore, according to this embodiment, a guide rod 13 is provided that extends upward through the ceiling A, and the waterstop plate 12 is rotated by raising and lowering the guide rod 13, making it possible to easily switch the waterstop device 1 between water passing and water stopping. In particular, the worker raising and lowering the guide rod 13 can be assisted by the buoyancy of the waterstop plate 12, and can rotate the waterstop plate 12 in the buoyancy direction without any strain. Note that if a waterstop sheet 15 is used as part of the waterstop device 11, assistance from the buoyancy of the waterstop sheet 15 can also be obtained.

[0037] Furthermore, according to this embodiment, the rotation of the waterstop 12 in the buoyancy direction is restricted to a state in which the waterstop 12 faces diagonally upward just before facing vertically upward by abutting against another member (the support member 16 or the ceiling A). This reduces the load on the waterstop 12 resulting from the water pressure on the intermediate tank 5a side compared to when the waterstop 12 faces vertically upward.

[0038] Furthermore, according to this embodiment, the water purification plant system 1 includes multiple water stop devices 1 corresponding to each of the multiple branched flow paths, allowing for precise control of water flow through each settling basin 6. This is particularly effective when water is stopped only for a settling basin 6 undergoing maintenance while allowing water to continue to flow through the other settling basins 6. This effectively prevents a decrease in the overall operating efficiency of the water purification plant system 1, even during maintenance. As a comparative example, consider the configuration shown in FIG. 1 , where water flow is stopped by closing the valve 2a on the inlet pipe 2b connected to the receiving well 2A. In this case, all settling basins 6A and 6B downstream of the receiving well 2A are simultaneously stopped, significantly reducing the operating efficiency of the entire water purification plant. In contrast, controlling water flow through each settling basin with multiple water stop devices 11 allows for precise control of water flow through each settling basin, such as stopping water flow through only the settling basin 6A and allowing water to flow through the settling basin 6B. This reduces the decrease in operating efficiency by half compared to the comparative example. [Explanation of symbols]

[0039] 1. Water purification system 2(2A,2B) Water landing well 3(3A,3B) Chemical mixing pond 4(4A,4B) Flocculation pond 5 Water conduction space 5a Intermediate tank 5b Sedimentation tank 6(6A~6D) Sedimentation pond 7 Overflow weir 7a Upper opening 8 Rectification wall 9 Inclined Plate Sedimentation Device 10 Sludge collector 11 Water stop device 12 Waterstop 13 Guide rod 14 Locking mechanism 15 Waterproof sheet 16 Support member 17 Side cover 18,19 Connecting members 20 Base member 21 Locking member

Claims

1. A buoyant water cut-off device for a water purification plant having a flocculation basin and a sedimentation basin in which a treatment device used in a submerged state is installed, an overflow weir provided in a flow path between the flocculation basin and the sedimentation basin; a waterstop rotatably attached to the overflow weir, A buoyant water stop device for a water purification plant, characterized in that the water stop rotates in the buoyancy direction of the water stop, closing the upper opening between the overflow weir and the ceiling to stop water, and rotates in the opposite direction to the buoyancy direction to open the upper opening to allow water to pass through.

2. The water stop further includes a guide rod whose lower end is rotatably attached to the water stop and which extends upward through the ceiling, 2. The buoyancy type water stop device for a water purification plant according to claim 1, wherein the water stop plate rotates by raising and lowering the guide rod.

3. the waterstop is rotatably attached to the overflow weir via a first connecting member provided on one surface of the waterstop, A buoyant-type water stop device for a water purification plant as described in claim 2, characterized in that the guide rod is rotatably attached to the water stop plate via a second connecting member provided on the other surface opposite to the one surface of the water stop plate.

4. A buoyancy-type water stop device for a water purification plant as described in claim 3, characterized in that the rotation of the water stop plate in the buoyancy direction is restricted to a closed state just before the water stop plate reaches a vertically upward position by the water stop plate abutting against another member.

5. the other member is a support member attached to the ceiling, A buoyant water stop device for a water purification plant as described in claim 4, characterized in that the support member has an inclined portion that is inclined at a predetermined angle relative to the ceiling as a portion that abuts against the water stop plate.

6. Further, a side cover attached to the ceiling is provided. A buoyant water stop device for a water purification plant as described in claim 4, characterized in that the side cover has a shape that can close an opening formed on the side of the water stop plate when in the closed state.

7. a locking mechanism for fixing the guide rod at a predetermined elevation position; The locking mechanism is a hollow base member attached to the ceiling and through which the guide rod is inserted; a locking member inserted into a through hole provided in the base member and a through hole provided in the guide rod; 3. The buoyancy type water stop device for a water purification plant according to claim 2, further comprising:

8. A buoyant water stop device for a water purification plant as described in claim 1, further comprising a flexible water stop sheet attached to the overflow weir and the water stop plate and covering the gap between the overflow weir and the water stop plate.

9. In the water purification system, a flocculation pond; a plurality of sedimentation basins, each of which is equipped with a treatment device that is used in a submerged state, and into which water diverted from the flocculation basin into a plurality of systems flows; a plurality of water stop devices that are provided corresponding to the flow paths branched into the plurality of systems and that can be operated independently of each other; A water purification plant system, wherein each of the plurality of water stop devices is a buoyancy type water stop device for the water purification plant according to any one of claims 1 to 8.

10. 9. A maintenance method for a water purification plant, comprising: a flocculation basin, a treatment device used in a submerged state, a plurality of sedimentation basins into which water diverted from the flocculation basin into a plurality of systems flows; and a plurality of water stop devices provided corresponding to the diverted flow paths into the plurality of systems and operable independently of each other, wherein each of the plurality of water stop devices is a buoyant type water stop device for a water purification plant as defined in any one of claims 1 to 8, a first step of stopping water flow using the water stop device for a sedimentation basin that is a target for maintenance work among the plurality of sedimentation basins, and continuing water flow using the water stop device for the other sedimentation basins; a second step of performing maintenance work on the sedimentation basin whose water has been stopped by the water stopping device; a third step of restarting water flow through the sedimentation basin, which has been stopped by the water stop device, when the maintenance work is completed; A maintenance method for a water purification plant, comprising:

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