Cleaning structure and coagulation sedimentation tank

Abstract

To provide a cleaning structure for a coagulation sedimentation tank which can prevent an increase in BOD of treated water within the coagulation sedimentation tank for separating suspension solid particles from liquid by sedimentation.SOLUTION: A cleaning structure provided on a coagulation sedimentation tank 1A which includes a circular tank 30, an overflow trough 31 provided on a periphery of the circular tank 30, a spindle structure 33 provided at a center of the circular tank 30, a sludge collection rake 34 which circulates in a circumferential direction of the circular tank 30, a bridge 36 provided on the sludge collection rake 34, and rake arms 37a, 37b which connect the bridge 36 and the sludge collection rake 34. Cleaning structures 2A, 2B include supporting arms 3a, 3b which are protruded on the rake arms 37a, 37b, cleaners 4a, 4b which are provided on the supporting arms 3a, 3b and rub / clean a cleaning surface within the circular tank 30, and holding parts 5a, 5b which are provided between the supporting arms 3a, 3b and the cleaners 4a, 4b and hold the cleaners 4a, 4b slidably along an inclination direction of the cleaning surface.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD

[0001] The present invention relates to a flocculation sedimentation tank capable of suppressing an increase in BOD of treated water stored in the flocculation sedimentation tank that separates suspended solid particles from a liquid by sedimentation, and a cleaning structure provided in this flocculation sedimentation tank.

[0002] First, the structure of a conventionally known flocculation sedimentation tank will be described with reference to Figure 9. Figure 9 is a vertical cross-sectional view of a conventionally known flocculation sedimentation tank. A conventionally known flocculation sedimentation tank 41, for example as shown in Figure 9, includes a circular tank 30 having a circular outer shape when viewed in plan view (not shown), a support shaft structure 33 provided at the center of the circular tank 30, a sludge collection rake 34 that is disposed between the inner side surface 30a of the circular tank 30 and the support shaft structure 33, and collects suspended solid particles (sludge) settled at the bottom of the circular tank 30 while circulating in the circumferential direction of the circular tank 30, and a bridge 36 that is provided on the sludge collection rake 34 and is erected between the outer edge of the circular tank 30 and the top of the support shaft structure 33. Furthermore, in the conventionally known flocculation sedimentation tank 41 as described above, the sludge collection rake 34 is connected to the back side of the bridge 36 via rake arms 37a and 37b. Then, in the flocculation sedimentation tank 41 as shown in Figure 9, when the drive unit 38 provided at the top of the support shaft structure 33 is operated, the traveling unit 39 provided at the end of the bridge 36 travels on the outer edge of the circular tank 30. That is, the bridge 36 circulates in the circumferential direction of the circular tank 30 around the rotation axis Y shown in Figure 9 as the base axis. Then, in conjunction with the circulating motion of the bridge 36, the sludge collection rake 34 connected to the bridge 36 via the rake arms 37a and 37b also circulates on the bottom side of the circular tank 30 around the rotation axis Y as the base axis. In addition, the conventionally known flocculation sedimentation tank 41 is provided with an overflow trough 31 along the outer edge of the circular tank 30, and the overflow liquid 32 overflowing from the circular tank 30 is collected by this overflow trough 31 and discharged to the outside of the circular tank 30.

[0003] In the conventionally known coagulation and sedimentation tank 41 described above, when raw water (treated water) containing suspended solid particles is supplied into the circular tank 30 from the raw water supply pipe 42 provided in the circular tank 30, the suspended solid particles settle in the circular tank 30 and are separated from the treated water. The suspended solid particles separated from the treated water by sedimentation gradually accumulate at the bottom of the circular tank 30. Furthermore, in a conventionally known coagulation and sedimentation tank 41, as described above, the sludge collection rake 34 rotates within the circular tank 30 in conjunction with the rotational movement of the bridge 36. As a result, the sludge collection rake 34 gathers the sludge (suspended solid particles) accumulated at the bottom of the circular tank 30 and discharges it from the very bottom of the circular tank 30 to the outside of the circular tank 30. On the other hand, the treated water from which suspended solid particles (sludge) have settled and been separated is collected in the overflow trough 31 as described above and discharged from the circular tank 30.

[0004] Furthermore, when the conventionally known coagulation and sedimentation tank 41 described above is installed outdoors, algae tend to proliferate in the region P (see Figure 9) near the water surface on the inner surface 30a of the circular tank 30 and in the region Q (see Figure 9) near the water surface of the support shaft structure 33 because sufficient sunlight is obtained there. In this case, the BOD of the treated water stored in the circular tank 30 becomes high, and a problem arises in that when the treated water collected in the overflow trough 31 is discharged into a river or the like, further treatment is required to reduce the BOD of the treated water. Furthermore, in order to address these issues, if an anti-algal agent (such as chlorine) is added to the raw water supplied to the circular tank 30 of the coagulation and sedimentation tank 41, it was necessary to perform other treatments or dilute the treated water (overflow liquid 32) discharged from the circular tank 30 to reduce the concentration of the anti-algal agent before discharging it into a nearby river. More specifically, there were challenges such as the need for additional processes or equipment to perform dechlorination treatment on the treated water (overflow liquid 32), or the need to dilute the treated water (overflow liquid 32) with clean water, resulting in additional costs for the final treatment before discharging the treated water (overflow liquid 32). Another possible solution is to install a roof or similar structure over the coagulation and sedimentation tank 41 to block sunlight, but this also presents the challenge of requiring significant investment in equipment.

[0005] No prior applications with the same problem to be solved as the present invention have been found to date, however, prior applications in related technical fields are known, for example, as shown below.

[0006] Patent Document 1 discloses an invention related to a coagulation reaction tank, which uses a coagulant to dewater sludge and form flocs. Patent Document 1 discloses that the coagulation reaction tank according to the invention is equipped with a wiper for cleaning the surface of a filtration screen provided on the tank wall. Furthermore, page 7 of the specification of Patent Document 1 discloses that the wiper is configured to slide along the surface of the tank wall in conjunction with the rotation of the rotating shaft inside the tank, and that the wiper can be replaced with a brush. Furthermore, considering the invention disclosed in Patent Document 1 as described above, it is conceivable that the inner surface 30a of the circular tank 30 shown in Figure 9 can be cleaned by scrubbing it with a brush.

[0007] Patent Document 2 also discloses an invention with a similar configuration to the invention disclosed in Patent Document 1, under the name "coagulation reaction tank." Therefore, by referring to the invention disclosed in Patent Document 2 as described above, it is considered that the inner surface 30a of the circular tank 30 shown in Figure 9 can be cleaned by scrubbing it with a brush. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Publication No. 61-000811 [Patent Document 2] Publication No. 61-000810 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Considering the inventions disclosed in Patent Documents 1 and 2, it may be possible to suppress algal growth in region P of the circular tank 30 in the coagulation and sedimentation tank 41, but it is not possible to suppress algal growth in region Q. Furthermore, in the conventionally known coagulation and sedimentation tank 41 shown in Figure 9, the circular tank 30 has a maximum water depth of approximately 6 to 10 meters. In addition, in such a coagulation and sedimentation tank 41, the areas P and Q where algae removal is necessary are located within a water depth range of 1 to 3 meters from the water surface. Furthermore, in order to continuously prevent algal growth in regions P and Q of the circular tank 30 of the coagulation and sedimentation tank 41 shown in Figure 9, maintenance such as frequently replacing the cleaning tools used to scrub and clean regions P and Q is necessary. On the other hand, it is not practical to drain the treated water from the circular tank 30 each time for the maintenance of the cleaning equipment.

[0010] The present invention has been made to address the aforementioned conventional circumstances, and its purpose is to provide a cleaning structure that allows for constant scrubbing and cleaning of the 0.5 to 3 m area near the water surface on the inner surface of the circular tank and the 0.5 to 3 m area near the water surface on the outer surface of the support shaft structure of a coagulation and sedimentation tank, and that facilitates the maintenance of the cleaning tools for this purpose, as well as a novel coagulation and sedimentation tank equipped with such a cleaning structure. [Means for solving the problem]

[0011] The first invention for solving the above problems is a cleaning structure provided in a coagulation and sedimentation tank, comprising a circular tank, an overflow trough provided along its outer edge to collect overflow liquid overflowing from the circular tank, a support shaft structure provided in the center of the circular tank, a sludge collection rake provided between the inner surface of the circular tank and the support shaft structure to collect settled sludge while circulating in the circumferential direction of the circular tank, a bridge provided on the sludge collection rake and erected between the outer edge of the circular tank and the support shaft structure, and a rake arm connecting the bridge and the sludge collection rake, characterized in that it comprises a support arm protruding from the rake arm, a cleaning tool provided on the support arm for scrubbing and cleaning the water surface area of ​​the inner surface of the circular tank and the water surface area of ​​the outer surface of the support shaft structure, and a holding part provided between the support arm and the cleaning tool for slidingly holding the cleaning tool along the inclination direction of the cleaning surface that the cleaning tool touches. In the first invention with the above configuration, the circular tank in the coagulation and sedimentation tank has the function of receiving treated water (raw water) containing suspended solid particles and separating the suspended solid particles by sedimentation within the circular tank. The overflow trough has the function of collecting the supernatant liquid (overflow liquid) that has overflowed from the circular tank after the suspended solid particles have been separated by sedimentation and discharging it outside the circular tank. Furthermore, the support shaft structure, which is provided in the center of the circular tank and protruding from the water surface, has the function of supporting the end of the bridge on the support shaft structure side, which is erected between the outer edge of the circular tank and the top of the support shaft structure. The sediment collection rake is positioned directly below the bridge and between the inner surface of the circular tank and the outer surface of the support shaft structure, and is fixed to the back side of the bridge by a rake arm. Then, in conjunction with the circumferential movement of the bridge around the circular tank with the central axis of the support shaft structure as its axis, the sediment collection rake also circumferentially moves around the circular tank with the central axis of the support shaft structure as its axis. As a result, the sludge rake has the function of collecting suspended solid particles (sludge) that have settled at the bottom of the circular tank. Furthermore, in the first invention, the support arm has the function of indirectly attaching the cleaning tool and its holding part to the rake arm while supporting the cleaning tool and its holding part so that the cleaning tool comes into contact with the cleaning surface near the water surface on the inner surface of the circular tank and the cleaning surface near the water surface on the outer surface of the support shaft structure. Then, in conjunction with the circulating motion of the bridge as described above, the rake arm rotates around the central axis of the support shaft structure within the circular tank. As a result, the cleaning tool, indirectly supported by this rake arm, rotates around the circular tank, rubbing against the cleaning surface on the inner side of the circular tank near the water surface, and the cleaning surface on the outer side of the support shaft structure near the water surface, respectively. In other words, the cleaning tools rotate within the circular tank in conjunction with the rotational movement of the bridge and mud-collecting rake, thereby continuously cleaning the cleaning surface near the water level on the inner side of the circular tank, and the cleaning surface near the water level on the outer side of the support shaft structure. Therefore, according to the first invention, the cleaning surface near the water surface on the inner surface of the circular tank and the cleaning surface near the water surface on the outer surface of the support shaft structure can be continuously cleaned when the mud rake is in operation. Furthermore, in the first invention, the cleaning tool is held so as to be slidable along the inclination direction of the cleaning surface that the cleaning tool touches (the water surface area on the inner surface of the circular tank and the water surface area on the outer surface of the support shaft structure), allowing the worker to replace the cleaning tool while standing on the ground outside the outer edge of the circular tank or on the top of the support shaft structure. In other words, in the first invention, when changing cleaning tools, there is no need for an operator to enter the circular tank or to drain the treated water from the circular tank.

[0012] The second invention is the first invention described above, characterized in that the cleaning tool is equipped with a floating structure that allows the cleaning tool to float in treated water stored in a circular tank. The second invention, having the above configuration, has the same function as the first invention described above. Furthermore, in the second invention, the cleaning tool is equipped with a floating structure that allows the cleaning tool to float in the treated water stored in the circular tank, thereby facilitating the removal of the cleaning tool from the holding part by utilizing the buoyancy generated in the cleaning tool itself.

[0013] The third invention is the second invention described above, characterized in that the holding portion is provided with a restricting member on the end of the cleaning tool, which is positioned on the water surface side of the circular tank, which restricts the cleaning tool from sliding in the direction of inclination of the cleaning surface and vertically upward. A third invention configured as described above has the same effects as those of the aforementioned second invention. Further, in the aforementioned third invention, when the cleaning tool having a floating structure is attached to the holding portion installed in the treated water, the regulating member slides in the inclined direction of the cleaning surface and on the vertically upper side due to the buoyancy acting on the cleaning tool itself, and has the effect of preventing the cleaning tool from being disengaged from the holding portion. Therefore, according to the third invention, when the cleaning tool has a floating structure, it has the effect of preventing the cleaning tool from being unintentionally disengaged from the holding portion. Further, in the third invention, the regulating member is disposed on the end portion of the cleaning tool arranged on the water surface side of the circular tank, so that it has the effect of enabling the operation of the regulating member from above the water surface. That is, an operator can perform the operation of the regulating member and the replacement work of the cleaning tool while staying on the ground outside the outer edge of the circular tank or at the top of the support shaft structure.

[0014] A fourth invention is the invention according to any one of the first to third inventions described above, characterized in that the cleaning tool is fitted into the holding portion, and these fitting portions are wedge-shaped. The fourth invention configured as described above has the same effects as those of any one of the aforementioned first to third inventions. Further, in the aforementioned fourth invention, the cleaning tool is fitted into the holding portion, and the shape of these fitting portions (in particular, the cross-sectional shape perpendicular to the longitudinal direction) is made wedge-shaped, so that it has the effect of enhancing the holding effect of the cleaning tool in the holding portion. In this case, it has the effect of suitably preventing the cleaning tool from being unintentionally disengaged from the holding portion during use of the cleaning tool.

[0015] A coagulation sedimentation tank according to the fifth invention comprises a circular tank, an overflow trough provided along the outer edge thereof for collecting overflow liquid overflowing from the circular tank, a support shaft structure provided at the center of the circular tank, a sludge collection rake disposed between the inner side surface of the circular tank and the support shaft structure for collecting precipitated sludge while circulating in the circumferential direction of the circular tank, a bridge provided on the sludge collection rake and spanning between the outer edge of the circular tank and the support shaft structure, a rake arm connecting the bridge and the sludge collection rake, and the cleaning structure according to any one of the first to fourth inventions described above. The fifth invention having the above configuration specifies the coagulation sedimentation tank provided with the cleaning structure according to any one of the first to fourth inventions described above as a product invention. Therefore, the operation of the fifth invention is the same as the operation of each of the first to fourth inventions described above. Effects of the Invention

[0016] According to the first invention as described above, by operating the sludge collection rake, the cleaning surface near the water surface on the inner side surface of the circular tank and the cleaning surface near the water surface on the outer side surface of the support shaft structure can be continuously cleaned by the cleaning tool. Thereby, the growth of algae on each of the above cleaning surfaces can be suitably suppressed. As a result, an increase in the BOD of the overflow liquid collected in the overflow trough can be suitably suppressed. Therefore, the treatment for discharging the overflow liquid to adjacent rivers or the like can be simplified. Further, according to the first invention, since an increase in the BOD of the overflow liquid discharged from the circular tank as described above can be suitably suppressed, it is not necessary to add an additive such as chlorine to the treated water for the purpose of preventing the growth of algae and the like in the treated water stored in the circular tank. In this case, the cost and labor required for adding the above-mentioned additives and the like to the treated water can be reduced. Furthermore, when an additive such as chlorine is added to the treated water, separate treatment such as lowering the concentration of the additive in the overflow liquid is required when discharging the overflow liquid (separated liquid) obtained after sedimentation and separation of suspended solid particles from the treated water to adjacent rivers or the like. In contrast, according to the first invention, there is no need to perform post-treatment such as reducing the concentration of additives in the overflow liquid, and from this point of view as well, the cost and effort required for treating the treated water can be reduced. Furthermore, in the first invention, even when replacing a cleaning tool in a cleaning structure, and even if the cleaning tool is a long object with a longitudinal length exceeding 0.5 m, it is not necessary for an operator to enter the circular tank or to drain the treated water from the circular tank in order to replace the cleaning tool. In other words, according to the cleaning structure of the first invention, the worker can perform the cleaning tool replacement work while standing on the ground outside the outer edge of the circular tank or on the top of the support shaft structure. As a result, according to the first invention, maintenance such as replacing cleaning tools can be easily performed, making it possible to more effectively prevent the growth of algae on the cleaning surface inside the circular tank.

[0017] The second invention has the same effects as the first invention described above. Furthermore, according to the second invention, since the cleaning tool is equipped with a floating structure, when removing the cleaning tool from the holding part, the buoyancy acting on the cleaning tool itself can be used to efficiently move the cleaning tool towards the water surface of the circular tank. In this case, the replacement of cleaning tools can be performed more easily and efficiently compared to using cleaning tools that do not have a floating structure, i.e., cleaning tools that sink in the treated water.

[0018] The third invention has the same effects as the second invention described above. Furthermore, according to the third invention, even if the cleaning tool has a floating structure and floats in the treated water, the cleaning tool can be securely fixed to the holding part. Furthermore, according to the third invention, a restricting member that restricts the sliding movement of the cleaning tool toward the water surface is disposed on the end of the cleaning tool that is positioned toward the water surface. This allows the operator to easily operate the restricting member when attaching or detaching the cleaning tool from the holder, even while standing on the ground outside the outer edge of the circular tank or on top of the support shaft structure. In this case, the cleaning tool can be replaced easily, safely, and efficiently. Therefore, the third invention provides a cleaning structure that is more convenient than the second invention described above.

[0019] The fourth invention has the same effects as the first to third inventions described above. Furthermore, the fourth invention can effectively prevent the cleaning tool from coming off the holding part. In other words, it effectively prevents the cleaning tool from detaching from the holder due to resistance to the frictional force acting on the cleaning surface during cleaning. Therefore, according to the fourth invention, the reliability of the cleaning structure during use can be improved.

[0020] The fifth invention is a coagulation and sedimentation tank equipped with any of the first to fourth cleaning structures described above, the effect of which is the same as the effect of each of the first to fourth cleaning structures. [Brief explanation of the drawing]

[0021] [Figure 1] This is a vertical cross-sectional view of the coagulation and sedimentation tank according to this embodiment. [Figure 2] This is a side view showing an enlarged view of the main parts of the cleaning structure according to this embodiment. [Figure 3] (a) A partial perspective view of the area around the regulating member located vertically above the cleaning structure according to this embodiment, and (b) A partial perspective view of the cleaning structure with the regulating member in a moved state. [Figure 4] This is a side view showing the cleaning tool in a sliding position in the cleaning structure according to this embodiment. [Figure 5] (a) A partial perspective view showing the relationship between the cleaning tool and the holding part in the cleaning structure according to this embodiment, and (b) A partial perspective view showing the state in which the cleaning tool is slid in the same cleaning structure. [Figure 6] (a) A partial perspective view of the area around a regulating member located vertically above a modified cleaning structure according to this embodiment, and (b) A partial perspective view of the cleaning structure with the regulating member moved. [Figure 7] (a) A partial perspective view showing the relationship between the cleaning tool and the holding part in a modified cleaning structure according to this embodiment, and (b) A partial perspective view showing the state in which the cleaning tool is slid in the same cleaning structure. [Figure 8] This is a vertical cross-sectional view of a coagulation and sedimentation tank according to another modification of this embodiment. [Figure 9] This is a vertical cross-sectional view of a conventionally known coagulation and sedimentation tank. [Modes for carrying out the invention]

[0022] A cleaning structure according to an embodiment of the present invention and a coagulation and sedimentation tank equipped therewith will be described in detail with reference to Figures 1 to 8.

[0023] [1; Regarding the basic configuration of the present invention] First, with reference to Figure 1, the basic configuration of the cleaning structure according to an embodiment of the present invention (hereinafter simply referred to as "this embodiment") and the coagulation and sedimentation tank equipped therewith will be described. Figure 1 is a vertical cross-sectional view of the coagulation and sedimentation tank according to this embodiment. Note that the same reference numerals are used for parts identical to those shown in Figure 9, and their configurations are not described. The coagulation and sedimentation tank 1A according to this embodiment is equipped with a cleaning structure 2A on the rake arm 37a for cleaning the cleaning surface near the water surface on the inner surface of the circular tank 30, and a cleaning structure 2B on the rake arm 37b for cleaning the cleaning surface near the water surface on the outer surface of the support shaft structure 33, as shown in Figure 9 of the conventionally known coagulation and sedimentation tank 41. As described above, in the coagulation and sedimentation tank 1A according to this embodiment, the configuration other than the cleaning structures 2A and 2B is the same as that of the conventionally known coagulation and sedimentation tank 41 shown in Figure 9. Therefore, the same reference numerals are used here for the same components as those shown in Figure 9.

[0024] First, the mechanism by which the sediment collection rake 34 operates in the coagulation and sedimentation tank 1A according to this embodiment will be explained. The operating mechanism of the sediment collection rake 34 in the coagulation and sedimentation tank 1A according to this embodiment is the same as that of the conventionally known sediment collection rake 34 in the coagulation and sedimentation tank 41 shown in Figure 9, but it will be explained again here as part of the configuration of the present invention. The coagulation and sedimentation tank 1A according to this embodiment includes, for example, a circular tank 30 whose outer shape is circular when viewed from above (not shown), a support shaft structure 33 provided in the center of the circular tank 30, a sludge collection rake 34 provided between the inner surface 30a of the circular tank 30 and the support shaft structure 33, which rotates in the circumferential direction of the circular tank 30 to collect sludge settled at the bottom of the circular tank 30, and a bridge 36 provided on the sludge collection rake 34 and installed between the outer edge of the circular tank 30 and the top of the support shaft structure 33. Furthermore, in the coagulation and sedimentation tank 1A according to this embodiment, a sediment collection rake 34 is connected to the back side of the bridge 36 via rake arms 37a and 37b. In this coagulation and sedimentation tank 1A, when the drive unit 38, which is located at the top of the support shaft structure 33, is activated, the traveling unit 39, which is located at the end (vertically downward) of the bridge 36, travels along the outer edge of the circular tank 30. In other words, the bridge 36 revolves around the circular tank 30 in the circumferential direction with respect to the rotation axis Y shown in Figure 9. Then, in conjunction with the rotation of the bridge 36, the mud-collecting rake 34, which is connected to the back of the bridge 36 via rake arms 37a and 37b, also rotates around the bottom of the circular tank 30 in the circumferential direction of the circular tank 30, with the rotation axis Y as its base. Furthermore, in the coagulation and sedimentation tank 1A according to this embodiment, an overflow trough 31 is provided along the outer edge of the circular tank 30, and the overflow liquid 32 that overflows from the circular tank 30 is collected in this overflow trough 31 and discharged outside the circular tank 30.

[0025] In the coagulation and sedimentation tank 1A according to this embodiment as described above, when raw water (treated water) containing suspended solid particles is supplied from the raw water supply pipe 42 provided in the circular tank 30, the suspended solid particles settle in the circular tank 30 and are separated from the treated water. The suspended solid particles separated from the treated water accumulate at the bottom of the circular tank 30. Then, the suspended solid particles (sludge) accumulated at the bottom of the circular tank 30 are gathered up by the circular motion of the sludge collection rake 34 as described above and discharged from the very bottom of the circular tank 30 to the outside of the circular tank 30. On the other hand, the treated water from which the suspended solid particles (sludge) have settled and been separated is collected in the overflow trough 31 as described above and discharged from the circular tank 30.

[0026] Next, the cleaning structures 2A and 2B provided in the coagulation and sedimentation tank 1A according to this embodiment will be described with reference to Figure 1. The cleaning structure 2A according to this embodiment, as shown in Figure 1 for example, consists of one or more support arms 3a (Figure 1 illustrates the case of two arms) that protrude from the circumferential side of the rake arm 37a toward the inner surface 30a of the circular tank 30, a holding portion 5a provided at the tip of the support arm 3a (on the inner surface 30a side of the circular tank 30), and a cleaning tool 4a that is detachably attached to the holding portion 5a and is provided to contact the cleaning surface (the area indicated by the symbol P in Figure 9) near the water surface of the inner surface 30a of the circular tank 30. Furthermore, the cleaning structure 2B according to this embodiment, as shown in Figure 1 for example, comprises one or more support arms 3b (Figure 1 illustrates the case of two arms) that protrude from the circumferential side of the rake arm 37b toward the outer surface 33a of the support shaft structure 33, a holding portion 5b provided at the tip of the support arm 3b (on the outer surface 33a side of the support shaft structure 33), and a cleaning tool 4b that is detachably attached to the holding portion 5b and is provided to contact the cleaning surface of the outer surface 33a of the support shaft structure 33 near the water surface (the area indicated by the symbol Q in Figure 9). In this embodiment, although cleaning structure 2A and cleaning structure 2B have the same structure in the coagulation and sedimentation tank 1A, their cleaning surfaces are different, so different reference numerals are used for each. Furthermore, in this embodiment, the cleaning tools 4a and 4b in the cleaning structures 2A and 2B are described as brushes, for example, but the cleaning tools 4a and 4b may also be sponges made of hard fibers.

[0027] Furthermore, in the cleaning structure 2A according to this embodiment, the cleaning tool 4a is mounted in the holding portion 5a so as to be slidable along the inclination direction of the cleaning surface near the water surface on the inner surface 30a of the circular tank 30. Furthermore, in the cleaning structure 2B according to this embodiment, the cleaning tool 4b is mounted in the holding portion 5b so as to be slidable along the inclination direction of the cleaning surface near the water surface on the outer surface 33a of the support shaft structure 33. The specific mounting structure of the cleaning tool 4a to the holding part 5a, and the specific mounting structure of the cleaning tool 4b to the holding part 5b, will be described in detail later with reference to the drawings. Furthermore, in the coagulation and sedimentation tank 1A according to this embodiment, the concept of the inner surface 30a of the circular tank 30 includes the side surface of the overflow trough 31. Furthermore, although this embodiment describes the case where the inclination direction of the cleaning surface substantially coincides with the vertical direction, this inclination direction does not necessarily have to coincide with the vertical direction.

[0028] [2; Regarding the use of the basic configuration of the present invention] Next, the methods for using the cleaning structures 2A and 2B according to this embodiment will be explained with reference to Figure 1. As mentioned earlier, in the coagulation and sedimentation tank 1A according to this embodiment, the bridge 36 rotates in the circumferential direction of the circular tank 30 with the central axis Y of the support shaft structure 33 as its base axis. Furthermore, in conjunction with the rotational movement of the bridge 36, the sediment collection rake 34, which is connected to the back of the bridge 36 via rake arms 37a and 37b, also rotates in the circumferential direction of the circular tank 30 at the bottom of the circular tank 30. Furthermore, in conjunction with the circumferential movement of the rake arms 37a, 37b and the mud-collecting rake 34, the cleaning tool 4a, which is attached to the rake arm 37a via the support arm 3a and the holding part 5a, rotates around the circular tank 30 in its circumferential direction while rubbing the cleaning surface near the water surface (see area P in Figure 9) of the inner surface 30a of the circular tank 30. In addition, the cleaning tool 4b, which is attached to the rake arm 37b via the support arm 3b and the holding part 5b, rotates around the circular tank 30 in its circumferential direction while rubbing the cleaning surface of the outer surface 33a of the support shaft structure 33 near the water surface (see area Q in Figure 9). In other words, in conjunction with the circulating motion of the bridge 36 and the sediment collection rake 34 in the coagulation sedimentation tank 1A according to this embodiment, the cleaning tool 4a continuously cleans the inner surface 30a of the circular tank 30 near the water surface (see area P in Figure 9), and the cleaning tool 4b continuously cleans the outer surface 33a of the support shaft structure 33 near the water surface (see area Q in Figure 9).

[0029] [3; Regarding the operation and effects of the basic configuration of the present invention] According to the coagulation and sedimentation tank 1A of this embodiment, by providing cleaning structures 2A and 2B as shown in Figure 1, when the sludge collection rake 34 is operated to collect suspended solid particles (sludge) settled at the bottom of the circular tank 30 as described above, the cleaning tool 4a can simultaneously and continuously clean the cleaning surface of the inner surface 30a of the circular tank 30 near the water surface (see area P in Figure 9), and the cleaning tool 4b can simultaneously and continuously clean the cleaning surface of the outer surface 33a of the support shaft structure 33 near the water surface (see area Q in Figure 9). As a result, algae attached to the inner surface 30a of the circular tank 30 near the water surface (see area P in Figure 9) and the outer surface 33a of the support shaft structure 33 near the water surface (see area Q in Figure 9) are scraped off, effectively suppressing the growth of algae in these areas. Furthermore, the algae scraped off by cleaning tools 4a and 4b are discharged into the overflow trough 31 along with the overflow liquid 32. However, since the solid components (algae) are separated and removed downstream, the amount of solid components (algae) remaining in the overflow liquid 32 is minimal. As a result, the rise in BOD of the overflow liquid 32 collected in the overflow trough 31 of the coagulation and sedimentation tank 1A according to this embodiment can be effectively suppressed, thus simplifying the treatment required to discharge the overflow liquid 32 into nearby rivers or the like.

[0030] Furthermore, in the coagulation and sedimentation tank 1A according to this embodiment, the rise in BOD of the overflow liquid 32 overflowing from the circular tank 30 can be effectively suppressed. In other words, because the coagulation and sedimentation tank 1A according to this embodiment is equipped with cleaning structures 2A and 2B, it becomes unnecessary to add additives such as chlorine to the treated water stored in the circular tank 30 in order to prevent algae and other organisms from growing in the treated water. This reduces the cost and effort required to add the aforementioned additives to the treated water supplied to the circular tank 30. Furthermore, when additives such as chlorine are added to the treated water, it is necessary to treat the separated liquid (overflow liquid 32) obtained after the suspended solid particles (sludge) have been settled and removed from the treated water before discharging it into nearby rivers, etc., by reducing the concentration of the additives in the overflow liquid 32. In contrast, with the coagulation and sedimentation tank 1A according to this embodiment, there is no need to perform post-treatment such as reducing the concentration of additives in the overflow liquid 32, and from this point of view as well, the cost and effort required for the final treatment of the treated water can be reduced.

[0031] Furthermore, according to the cleaning structure 2A in the coagulation and sedimentation tank 1A of this embodiment, the cleaning tool 4a can be slid along the inclination direction of the cleaning surface (the inner surface 30a of the circular tank 30 near the water surface) that the cleaning tool 4a is in contact with. Therefore, the worker can perform the cleaning tool 4a replacement work while remaining on the ground 35 outside the outer edge of the circular tank 30. Similarly, according to the cleaning structure 2B in the coagulation and sedimentation tank 1A of this embodiment, the cleaning tool 4b can be slid along the inclination direction of the cleaning surface (the outer surface 33a of the support shaft structure 33 near the water surface) that the cleaning tool 4b is in contact with. Therefore, the operator can perform the cleaning tool 4b replacement work while remaining at the top of the support shaft structure 33. In this case, there is no need for an operator to enter the circular tank 30 or to drain the treated water stored in the circular tank 30 in order to replace the cleaning tool 4a in the cleaning structure 2A or the cleaning tool 4b in the cleaning structure 2B. As a result, with the coagulation and sedimentation tank 1A according to this embodiment, maintenance such as replacing the cleaning tools 4a and 4b can be easily performed, making it possible to more effectively prevent the growth of algae on the cleaning surface (the areas indicated by symbols P and Q in Figure 9, or the areas in contact with cleaning tools 4a and 4b in Figure 1). In other words, in the coagulation and sedimentation tank 1A according to this embodiment, there is no need to drain the treated water from the circular tank 30 for maintenance of the cleaning tools 4a and 4b, and it is only necessary to stop the rotational movement of the sediment collection rake 34 for a short time, so the impact on the treatment of the treated water in the coagulation and sedimentation tank 1A (separation of suspended solid particles) can be kept to the absolute minimum. Thus, in the coagulation and sedimentation tank 1A according to this embodiment, by replacing cleaning tools 4a and 4b in conjunction with, for example, inspection and maintenance of the sediment collection rake 34, it is possible to effectively suppress any disruption to the operation of the coagulation and sedimentation tank 1A.

[0032] [4; Regarding the detailed structure and optional additional features of the present invention] <4-1; Regarding cleaning tools and retaining parts> Here, with reference to Figures 2 to 5, an example of the specific structure of the cleaning tool 4a and holding part 5a (and the cleaning tool 4b and holding part 5b) in the coagulation and sedimentation tank 1A according to this embodiment will be described. Figure 2 is an enlarged side view showing the main part of the cleaning structure according to this embodiment. Figure 3(a) is a partial perspective view of the area around the regulating member located vertically above the cleaning structure according to this embodiment, and (b) is a partial perspective view of the cleaning structure with the regulating member moved. The same reference numerals are used for parts that are the same as those shown in Figures 1 and 9, and their configurations are not described. As shown in Figures 2 and 3(a), the cleaning structure 2A according to this embodiment consists of a holding part 5a fixed to the tip of the support arm 3a (on the inner surface 30a side of the circular tank 30 in Figure 1) and a cleaning tool 4a, such as a brush 12, which is fitted into a fitting groove 11 formed on the surface of the holding part 5a that faces the inner surface 30a of the circular tank 30 shown in Figure 1 (the left side of the paper in Figure 2).

[0033] Furthermore, the cleaning structure 2A according to this embodiment is equipped with a flat plate-shaped second stopper 7b at the vertically downward end of the holding portion 5a in order to prevent the cleaning tool 4a fitted into the holding portion 5a from sliding vertically downward and falling off. In addition, the cleaning structure 2A according to this embodiment is equipped with a flat plate-shaped first stopper 7a at the vertically upward end of the holding part 5a in order to prevent the cleaning tool 4a fitted into the holding part 5a from unintentionally sliding vertically upward and coming off. Both the first stopper 7a and the second stopper 7b are fixed to the end face of the holding part 5a using fasteners such as bolts 9 (see Figure 2). Furthermore, the first stopper 7a is provided with an elongated hole 8 as a bolt insertion hole for inserting a bolt 9, which is a fastening device. As a result, by loosening the bolt 9, the first stopper 7a can be slid in the direction of the long axis of the elongated hole 8, as shown in Figure 3(b).

[0034] Furthermore, the cleaning tool 4a in the cleaning structure 2A according to this embodiment, for example, the brush 12, is composed of a brush base 14 and brush bristles 13 planted on the brush base 14. In addition, the brush base 14 has a fitting projection 10 on the surface opposite to the side on which the brush bristles 13 are planted, which is fitted into a fitting recess 11 formed in the holding portion 5a.

[0035] Next, with reference to Figures 2 and 3, as well as Figures 4 and 5, the procedure for replacing the cleaning tool 4a (e.g., brush 12) in the cleaning structure 2A according to this embodiment will be described. Figure 4 is a side view showing the cleaning tool in a slid state in the cleaning structure according to this embodiment. Figure 5(a) is a partial perspective view showing the relationship between the cleaning tool and the holding part in the cleaning structure according to this embodiment, and (b) is a partial perspective view showing the cleaning tool in a slid state in the same cleaning structure. The same reference numerals are used for parts that are the same as those shown in Figures 1 to 3 and Figure 9, and their configurations are omitted. In Figure 5, the external shapes of the cleaning tool and the holding part, as well as the first stopper, the second stopper, and their fixing devices are omitted in order to make the operation of the cleaning tool easier to understand. To replace the cleaning tool 4a (e.g., brush 12) of the cleaning structure 2A according to this embodiment, first, as shown in Figures 2 and 3(a), loosen the two bolts 9 (fixing devices) that secure the first stopper 7a to the end face of the holding portion 5a using a tool not shown.

[0036] Next, the first stopper 7a is slid in the direction of the major axis of the elongated hole 8 (the direction indicated by the symbol S in Figure 3(a)), opening the vertically upper end face of the cleaning tool 4a (for example, the brush 12) as shown in Figure 3(b). Then, in the state shown in Figure 3(b), the brush 12 (cleaning tool 4a) can be removed from the holding part 5a by, for example, using a clamping tool (not shown) to clamp the brush base 14 of the brush 12 (cleaning tool 4a) and pulling it out (pulling it up) in the direction of forming the fitting groove 11 (vertically upward in Figure 3(b)), as shown in Figures 4 and 5. In the cleaning structure 2A according to this embodiment, the uppermost vertical position of the brush bristles 13 (cleaning tool 4a) is approximately the same as the water level (not shown, see Figure 1). Therefore, lifting the brush 12 (cleaning tool 4a) vertically upward at the holding part 5a and picking up the brush 12 (cleaning tool 4a) on the ground are substantially equivalent.

[0037] Furthermore, when attaching a new cleaning tool 4a (for example, a brush 12) to the holding part 5a in the cleaning structure 2A according to this embodiment, the reverse of the above procedure can be performed. Furthermore, since the structure of the cleaning structure 2B according to this embodiment is the same as the structure of the cleaning structure 2A, the procedure for replacing the cleaning tool 4b in the cleaning structure 2B is the same as the procedure for replacing the cleaning tool 4a described above.

[0038] In the coagulation and sedimentation tank 1A according to this embodiment, by configuring the cleaning structure 2A (or cleaning structure 2B) as described above, the operator can perform the replacement of the cleaning tool 4a (or cleaning tool 4b) while remaining on the ground 35 (or on the top of the support shaft structure 33). In this case, the cleaning tool 4a (or cleaning tool 4b) can be replaced using conventionally known hand tools, making it easy to perform maintenance on the cleaning structure 2A. Furthermore, because the cleaning structure 2A according to this embodiment has an extremely simple structure, it can be retrofitted to the rake arms 37a and 37b of the conventionally known coagulation and sedimentation tank 41 shown in Figure 9. Moreover, there is no need to add a new drive mechanism or the like to operate the cleaning structures 2A and 2B according to this embodiment. Therefore, by using the cleaning structures 2A and 2B according to this embodiment, the existing coagulation and sedimentation tank 41 can be easily converted into the coagulation and sedimentation tank 1A according to this embodiment.

[0039] Furthermore, in the cleaning structures 2A and 2B according to this embodiment, the material and size of the brush base 14 for the brush 12 (cleaning tool 4a, cleaning tool 4b) can be appropriately set. More specifically, the brush base 14 may be formed using a resin or the like with a specific gravity lighter than the treated water stored in the circular tank 30, or a cavity (not shown) may be provided inside the brush base 14, so that the brush 12 (cleaning tool 4a) itself floats in the treated water stored in the circular tank 30. In other words, the brush 12 (cleaning tools 4a and 4b) may be equipped with a floating structure for floating in the treated water stored in the circular tank 30 (optional component). In this case, compared to a case where the cleaning tool 4a (or cleaning tool 4b) does not have the floating structure described above, when replacing the cleaning tool 4a (or cleaning tool 4b) attached to the holding part 5a (or holding part 5b) using the procedure shown in Figures 3 to 5 above, for example, the operation of removing the cleaning tool 4a (or cleaning tool 4b) from the holding part 5a (or holding part 5b) can be easily performed by utilizing buoyancy.

[0040] Furthermore, in the cleaning structures 2A and 2B according to this embodiment, for example, as shown in Figures 5(a) and (b), the cross-sectional shape perpendicular to the longitudinal direction of the fitting projection 10 formed on the brush base 14 of the brush 12 (cleaning tool 4a or cleaning tool 4b), and the cross-sectional shape perpendicular to the longitudinal direction of the holding part 5a (or holding part 5b) may both be "wedge-shaped" (optional component). In this case, the resistance force applied when the brush 12 (cleaning tool 4a or cleaning tool 4b) applies friction to the cleaning surface prevents the cleaning tool 4a (or cleaning tool 4b) from unintentionally detaching from the holding part 5a (or holding part 5b). Therefore, by making the shape of the fitting portion between the cleaning tool 4a and the holding portion 5a in the cleaning structure 2A according to this embodiment a "wedge shape" as shown in Figure 5, for example, and by making the shape of the fitting portion between the cleaning tool 4b and the holding portion 5b in the cleaning structure 2B a "wedge shape" as shown in Figure 5, for example, the strength of the cleaning structures 2A and 2B during use according to this embodiment can be improved.

[0041] <4-2; Modified examples of cleaning tools and retaining parts> The configuration of the cleaning structures 2A and 2B in the coagulation and sedimentation tank 1A according to this embodiment is shown in the previous figure. Other forms are also acceptable, as shown in Figures 2 through 5. Here, with reference to Figures 6 and 7, modified examples of the cleaning structures 2A and 2B in the coagulation and sedimentation tank 1A according to this embodiment will be described. As mentioned above, cleaning structure 2B has the same structure as cleaning structure 2A, so here we will specifically describe modified examples of cleaning structure 2A. Figure 6(a) is a partial perspective view of the area around the regulating member located vertically above the cleaning structure according to a modified example of this embodiment, and (b) is a partial perspective view of the cleaning structure with the regulating member moved. Figure 7(a) is a partial perspective view showing the relationship between the cleaning tool and the holding part in the cleaning structure according to a modified example of this embodiment, and (b) is a partial perspective view showing the cleaning tool in a slid state. The same reference numerals are used for parts that are the same as those shown in Figures 1 to 5 and Figure 9, and their configurations are omitted. In Figure 7, the external shapes of the cleaning tool and the holding part, as well as the first stopper, the second stopper, and their fixing devices are omitted in order to make the operation of the cleaning tool easier to understand.

[0042] More specifically, in the modified cleaning structure 2A', the retaining portion 5a' may have a substantially C-shaped cross-sectional shape perpendicular to its longitudinal direction, as shown in Figures 6(a), (b) and 7(a), (b). More specifically, the outer shape of the hollow portion of the fitting groove 11' formed on the surface of the retaining portion 5a' facing the inner surface 30a of the circular tank 30 (see Figure 1 above) may be substantially rectangular. In conjunction with this, the cross-sectional shape of the brush base 14' of the brush 12' (cleaning tool 4a) fitted into the fitting groove 11' described above may be a rectangular shape, for example, as shown in Figures 6(a), (b) and 7(a), (b) (both are optional components). In this case, the external shape of the holding part 5a' and the brush base 14' can be simplified. In this case, existing steel materials can be reused as the holding part 5a'. Furthermore, it can be expected that the manufacturing cost of the brush 12' (cleaning tool 4a) can be reduced. Furthermore, the methods for using the modified cleaning structure 2A' and the cleaning structure 2B' (not shown) are the same as the method for using cleaning structure 2A, which was explained earlier with reference to Figures 2 to 5; therefore, a detailed explanation is omitted here.

[0043] Furthermore, if the cross-sectional shape perpendicular to the longitudinal direction of the brush base 14' of the brush 12' (cleaning tool 4a, cleaning tool 4b) constituting the modified cleaning structures 2A' and 2B' is rectangular, as shown in Figures 6(a), (b) and 7(a), (b), the brush 12' (cleaning tool 4a, cleaning tool 4b) itself may be configured to float in the treated water stored in the circular tank 30 by constructing a part of the brush base 14' with a float 15 made of a mass of resin or the like that is lighter than the specific gravity of the treated water stored in the circular tank 30, or with a float (not shown) that has a cavity inside (optional component). In this case, there is no need to add a floating structure to the brush base 14' of the brush 12' (cleaning tool 4a, cleaning tool 4b), making it easier to adjust the buoyancy of the brush 12' while maintaining the strength of the brush 12'. As a result, brushes 12' (cleaning tools 4a and 4b) with sufficient strength and buoyancy can be provided at a low cost. In this case, when the brushes 12' (cleaning tools 4a, cleaning tools 4b) are used as consumables, the running costs of the coagulation and sedimentation tank 1A equipped with the modified cleaning structures 2A' and 2B' can be reduced.

[0044] <4-3; Reinforcement structure of support arms> In the coagulation and sedimentation tank 1A according to this embodiment, the cleaning tools 4a and 4b move around the circular tank 30 in the circumferential direction while rubbing their respective cleaning surfaces, so it is expected that a large load will always be applied to the support arms 3a and 3b. Therefore, as shown in Figure 1 above, the connection portion between the rake arm 37a and the support arm 3a, and the connection portion between the rake arm 37b and the support arm 3b may be provided with a reinforcing member 6 made of a right-angled triangular flat plate, or a reinforcing member in the shape of a fire-breathing brace (not shown) (optional component). In this case, damage to the support arms 3a and 3b can be effectively suppressed when the coagulation and sedimentation tank 1A according to this embodiment is in operation, that is, when the cleaning structures 2A and 2B according to this embodiment, or modified cleaning structures 2A' and 2B' thereof, are in use. Note that cleaning structure 2B' is not shown. As a result, the strength and durability of the coagulation and sedimentation tank 1A according to this embodiment can be improved.

[0045] Furthermore, although not specifically shown in the figures, similar reinforcing members may also be added to the connection between the support arm 3a and the holding part 5a (or holding part 5a'), and to the connection between the support arm 3b and the holding part 5b (or holding part 5b', not shown) for the same reasons (optional component). In this case, damage to the holding portion 5a provided at the tip of the support arm 3a and the holding portion 5b (or holding portion 5b') provided at the tip of the support arm 3b can be effectively suppressed when the coagulation and sedimentation tank 1A according to this embodiment is in operation. In this case as well, the strength and durability of the coagulation and sedimentation tank 1A according to this embodiment can be improved.

[0046] [5; Regarding variations of the circular tank] Finally, with reference to Figure 8, we will describe another modification of the coagulation and sedimentation tank according to this embodiment. Figure 8 is a vertical cross-sectional view of a coagulation and sedimentation tank according to another modification of this embodiment. Note that the same reference numerals are used for parts identical to those shown in Figures 1 to 7 and Figure 9, and their configurations are not described. In the coagulation and sedimentation tank 1A according to this embodiment shown in Figure 1, the overflow trough 31 is provided to protrude toward the support shaft structure 33. However, this overflow trough 31 may also be provided to protrude toward the ground 35 (into the ground 40) outside the outer edge of the circular tank 30, as in the coagulation and sedimentation tank 1B according to another modification shown in Figure 8. Furthermore, even when the overflow trough 31 in the circular tank 30 is in the form shown in Figure 8, the same effect as shown in [3] above can be achieved by providing the cleaning structures 2A and 2B as shown in Figure 1, or by providing the cleaning structures 2A' and 2B' as shown in <4-3> above.

[0047] [6; Others] In the cleaning structures 2A and 2B (or cleaning structures 2A' and 2B') provided in the coagulation and sedimentation tanks 1A and 1B according to this embodiment, the length of the cleaning tools 4a and 4b (or cleaning tools 4a' and 4b') from the water surface to the water depth (the length of the brush stand 14 and brush stand 14' in the longitudinal direction) is not particularly limited, but is assumed to be about 0.5 to 3 m.

[0048] Furthermore, if the cleaning structures 2A and 2B (or cleaning structures 2A' and 2B') according to this embodiment are equipped with a floating structure, and the restriction on the sliding of the cleaning tools 4a and 4b (or cleaning tools 4a' and 4b') by the first stopper 7a is released, the cleaning tools 4a and 4b (or cleaning tools 4a' and 4b') will automatically move toward the water surface due to the buoyancy acting on them. Therefore, when workers replace cleaning tools 4a, 4b (or cleaning tools 4a', 4b'), they do not need to actively operate clamping devices or the like to lift the cleaning tools 4a, 4b (or cleaning tools 4a', 4b') above the water surface of the circular tank 30. In other words, the cleaning tools 4a, 4b (or cleaning tools 4a', 4b') according to this embodiment do not necessarily have to be provided as a single long body, but may be composed of multiple divided bodies (optional components). Furthermore, when the cleaning tools 4a, 4b (or cleaning tools 4a', 4b') according to this embodiment are composed of multiple divided parts, the manufacturing cost can be reduced compared to when the cleaning tools 4a, 4b (or cleaning tools 4a', 4b') are provided as a single long body. As a result, the running costs of the coagulation and sedimentation tanks 1A and 1B according to this embodiment can be reduced. [Industrial applicability]

[0049] As described above, the present invention relates to a coagulation-sedimentation tank that can suppress the rise in BOD of treated water in a coagulation-sedimentation tank that separates suspended solid particles from a liquid by sedimentation, and a cleaning structure provided in this coagulation-sedimentation tank, and is applicable in the technical field related to wastewater treatment. [Explanation of Symbols]

[0050] 1A, 1B…Coagulation and sedimentation tank 2A, 2A', 2B, 2B'…Cleaning structure 3a, 3b…Support arm 4a, 4a', 4b, 4b'…Cleaning tool 5a, 5a', 5b, 5b'…Holding part 6…Reinforcement material 7a…First stopper 7b…Second stopper 8…Slotted hole 9…Bolt 10…Matching projection 11, 11'…Matching recess 12, 12'…Brush 13…Brush bristles 14, 14'…Brush stand 15…Float 30…Circular tank 30a…Inner surface 31…Overflow trough 32…Overflow liquid 33…Support shaft structure 33a…Outer surface 34…Sludge collection rake 35…Ground 36…Bridge 37a, 37b…Rake arm 38…Drive unit 39…Traveling unit 40…Underground 41... Coagulation and sedimentation tank 42... Raw water supply pipe

Claims

1. A cleaning structure provided in a coagulation and sedimentation tank comprising a circular tank, an overflow trough provided along its outer edge to collect overflow liquid overflowing from the circular tank, a support shaft structure provided in the center of the circular tank, a sludge collection rake provided between the inner surface of the circular tank and the support shaft structure to collect settled sludge while circumferentially moving around the circular tank, a bridge provided on the sludge collection rake and erected between the outer edge of the circular tank and the support shaft structure, and a rake arm connecting the bridge and the sludge collection rake, A support arm is provided protruding from the aforementioned rake arm, A cleaning tool provided on the support arm for scrubbing and cleaning the water-level portion of the inner surface of the circular tank and the water-level portion of the outer surface of the support shaft structure, A cleaning structure characterized by comprising a holding part provided between the support arm and the cleaning tool, which slidably holds the cleaning tool along the inclined direction of the cleaning surface that the cleaning tool touches.

2. The cleaning structure according to claim 1, characterized in that the cleaning tool is provided with a floating structure that allows the cleaning tool to float in the treated water stored in the circular tank.

3. The cleaning structure according to claim 2, characterized in that the holding portion is provided with a restricting member on the end of the cleaning tool disposed on the water surface side, which restricts the cleaning tool from sliding in the inclined direction and vertically upward.

4. The cleaning tool is fitted into the holding part, The cleaning structure according to any one of claims 1 to 3, characterized in that these fitting parts are wedge-shaped.

5. A circular tank, An overflow trough is provided along its outer edge to collect the overflow liquid that spills out of the circular tank, A support shaft structure is provided in the center of the aforementioned circular tank, A sludge collection rake is provided between the inner surface of the circular tank and the support shaft structure and rotates in the circumferential direction of the circular tank to collect the settled sludge, A bridge provided on the aforementioned mud-collecting rake and erected between the outer edge of the circular tank and the support shaft structure, A rake arm connecting the bridge and the mud-collecting rake, A coagulation and sedimentation tank characterized by having a cleaning structure according to claim 1 or claim 2.

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