JP7485412B2 - Grit basin and sand collection method - Google Patents

Description

The present invention relates to a sedimentation basin in which sand contained in received water settles to the bottom of the basin, and a method for collecting the settled sand.

Some wastewater treatment facilities are provided with a settling basin that receives wastewater such as sewage and rainwater, settles the sand contained in the wastewater on the bottom of the basin or in a groove provided on the bottom of the basin, and then collects the sand deposited on the bottom or in the groove in a sand collection pit to remove it from the wastewater. A known settling basin is equipped with a sand collection means that discharges a fluid from multiple outlets provided near the side wall of the settling basin and causes the sand to flow toward the groove by the fluid after the wastewater in the settling basin is discharged to expose the sand deposited on the bottom to the atmosphere. This groove is made of a long member with a U-shaped or arc-shaped cross section, extends in a direction perpendicular to the width of the basin, and its rear end is connected to the sand collection pit. The groove is also inclined downward toward the sand collection pit, with the sand collection pit side being the deepest. The sand deposited in the groove is transported to the sand collection pit by the flow of the fluid discharged from the tip side of the groove into the groove. During transportation, the flow of the fluid supplied into the groove toward the sand collection pit side is assisted by the inclination of the groove. This makes it easier for the sand in the groove to move toward the sand collection pit. The sand transported to the sand collection pit is discharged outside the sedimentation basin by a sand lifting pump located inside the pit. Examples of sedimentation basins equipped with such grooves and multiple discharge ports provided near the side walls include those described in Patent Documents 1 and 2.

JP 2017-127871 A JP 2018-39007 A

However, when the fluid discharged from the tip of the groove into the groove collides with the sand accumulated in the groove, the fluid and sand may be scattered in the direction of the pond width. If the sand is scattered, it will return to the bottom where it was discharged, reducing the efficiency of sand collection. Not only that, but the flow of the fluid generated by the discharge is weakened by the collision between the fluid and the sand, which also reduces the efficiency of sand collection.

In view of the above circumstances, the present invention aims to provide a settling basin and a method for collecting sand that can efficiently collect sand.

The settling basin of the present invention, which solves the above-mentioned object, is a settling basin in which sand contained in received water settles to the bottom of the basin,
A groove is provided in the bottom of the pond and extends in a predetermined direction;
a first outlet port that discharges a fluid in the predetermined direction into the water stored in the groove;
A bottom surface is provided at the bottom of the pond, formed between the side wall of the settling basin and the groove and connected to the groove;
a second outlet that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall toward the groove;
a cover member that covers a periphery of an imaginary axis extending from the first discharge port in the predetermined direction and has an opening at a lower end portion,
The bottom surface is located above an upper end position of the covering member,
The second discharge port is characterized in that it discharges fluid in a state where the water level is maintained below the upper end position of the covering member.
The groove may be inclined downward at an angle of 0 degrees or more and less than 1 degree toward the predetermined direction .

The sand collection method of the present invention, which achieves the above object, is a method for collecting sand accumulated on a bottom of a settling basin, which allows sand contained in received water to settle, the settling basin having a groove extending in a predetermined direction and a bottom surface formed between a side wall of the settling basin and the groove and connected to the groove, comprising:
an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water stored in the groove;
and an atmospheric discharge step of discharging a fluid from a second discharge port into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall side toward the groove,
the underwater discharge step is a step of discharging a fluid into a space covered by a cover member that has an opening at a lower end portion and covers a periphery of a virtual axis extending from the first discharge port in the predetermined direction,
The atmospheric discharge step is characterized in that it is performed in a state in which the water level is maintained below the upper end position of the covering member, the upper end position of which is located below the bottom surface.

The present invention provides a settling basin and a method for efficiently collecting sand.

1 is a schematic cross-sectional view of a wastewater treatment facility including a grit basin according to one embodiment of the present invention. FIG. 2 is a plan view of a settling basin corresponding to one embodiment of the present invention, viewed from above. 3 is a cross-sectional view of the grit basin shown in FIG. 2 along the line XX. 4A is an enlarged view showing a portion Z in FIG. 3, and FIG. 4B is a schematic perspective view showing a first covering member and an upstream trough first nozzle. 3 is a cross-sectional view of the grit basin shown in FIG. 2 along line AA. FIG. 6 is an enlarged view showing a portion B in FIG. 5 . FIG. 1A is a cross-sectional view illustrating a state in which one pipe having a lap joint is joined to another pipe, and FIG. 1B is a cross-sectional view illustrating a state in which the one pipe having the lap joint is able to rotate freely around its axial direction relative to the other pipe by loosening the bolt. 7A is a cross-sectional view taken along the line CC in FIG. 6, and FIG. 7B is a cross-sectional view similar to FIG. 7A for illustrating the change in the discharge direction by the sand collecting nozzle. This is a diagram of the water supply system in a sewage treatment facility. FIG. 2 is an explanatory diagram showing the water level of the grit basin and the water level sensor. 1 is a flowchart showing the flow of a sand removal operation in a wastewater treatment facility. 6 is a cross-sectional view of a settling basin similar to FIG. 5, showing a case where a sand collecting means is arranged in the upper part of the settling basin and a case where a sand collecting means is arranged near the bottom of the settling basin. FIG. FIG. 4 is a cross-sectional view similar to FIG. 3, showing a modified example of the connection surface. 8A is a diagram showing a first modified example of the supply pipe and the sand collecting nozzle shown in FIG. 8, and FIG. 8B is a diagram showing a second modified example of the supply pipe and the sand collecting nozzle shown in FIG. 8. 6 is a cross-sectional view similar to FIG. 5 showing a variation of the main trough, cover member, and bottom surface. 16 is a cross-sectional view similar to FIG. 8(a) showing the bottom plane near the upstream end of the settling basin and the bottom plane near the sand collection pit in the modified example shown in FIG. 15. 11 is an explanatory diagram similar to FIG. 10 showing an example of detection of the water level when the height of the main trough is increased.

The following describes an embodiment of the present invention with reference to the drawings. A grit basin, which is one embodiment of the present invention, is placed in a wastewater treatment facility and allows sand contained in wastewater such as sewage and rainwater to settle, and then moves the settled sand to a sand collection pit to be removed from the wastewater.

Figure 1 is a schematic cross-sectional view of a wastewater treatment facility including a grit chamber, which corresponds to one embodiment of the present invention.

As shown in Figure 1, the wastewater treatment facility 1 has a grit basin 2, a pump well 3, and a dam device 4. Wastewater such as sewage and rainwater flows into this wastewater treatment facility 1. The wastewater treatment facility 1 receives wastewater from the left side in Figure 1. The received wastewater flows slowly toward the pump well 3 on the right side of the figure in the grit basin 2, causing the sand contained in the wastewater to settle (see the straight arrow in Figure 1). Hereinafter, the upstream side of the flow of the received wastewater will be referred to simply as the upstream side, and the downstream side of the flow of the wastewater will be referred to simply as the downstream side.

A dam device 4 is disposed upstream of the grit basin 2 in the wastewater treatment facility 1. The dam device 4 has an opening wall 41, an inflow gate 42, and a gate drive device 43. The downstream wall surface of the opening wall 41 defines the upstream end of the grit basin 2. An inflow port 411 is opened at the lower end of the opening wall 41. The inflow gate 42 is provided so as to be movable up and down along the upstream wall surface of the opening wall 41. When the inflow gate 42 is in the lower position shown by the solid line in FIG. 1, it blocks the inflow port 411 and blocks the inflow of wastewater upstream of the dam device 4 into the grit basin 2. When the inflow gate 42 is raised to the upper position shown by the two-dot chain line in FIG. 1, it allows the wastewater to flow into the grit basin 2. The gate drive device 43 has a drive mechanism (not shown) inside and moves the inflow gate 42 up and down in response to a command from a control device that controls the dam device 4. This vertical movement allows the inflow gate 42 to be selectively positioned in either the upper or lower position.

The settling basin 2 is equipped with a dust collector 5 located upstream, a sand collection pit 6 located midstream, and a sand lifting pump 61 that transports sand in the sand collection pit 6 out of the basin. A sand lifting pipe 64 is connected to the sand lifting pump 61. Sand sucked up by the sand lifting pump 61 is sent through the sand lifting pipe 64 to a sand separator (not shown) located outside the settling basin 2. The dust collector 5 is used to remove contaminants (seed residue) that are mixed in with the wastewater that flows into the settling basin 2. The configuration of the settling basin 2 will be described in detail later.

A pump well 3 is formed downstream of the grit basin 2 in the wastewater treatment facility 1. The pump well 3 stores wastewater from which sand has been removed by the grit basin 2. The bottom of the pump well 3 is the deepest part of the wastewater treatment facility 1. A lifting pump 31 and a feed water pump 33 are arranged in the pump well 3. The lifting pump 31 moves the wastewater stored in the pump well 3 to the outside of the wastewater treatment facility 1. A lifting pipe 32 is connected to the lifting pump 31. The wastewater sucked by the lifting pump 31 is sent through this lifting pipe 32 to a sedimentation tank (not shown) for the next stage of wastewater treatment. The feed water pump 33 is arranged closer to the bottom of the pump well than the above-mentioned lifting pump 31. A feed water pipe 34 is connected to the feed water pump 33. The wastewater sucked by the feed water pump 33 is sent through this feed water pipe 34 to each nozzle, which will be described later. The wastewater sucked by the water supply pump 33 is referred to as the fluid in the following description.

Figure 2 is a plan view of a grit basin corresponding to one embodiment of the present invention, viewed from above. In Figure 2, the dust collector is indicated by a two-dot chain line rectangle. The flow direction of the wastewater is indicated by a straight arrow.

2, the settling basin 2 is a generally rectangular pond in plan view, with the dust collector 5, the sand collection pit 6, the bottom plane 71, the small trough 72, the connection surface 73, the main trough 8, and the sand collection means 9 between the left side wall Wa and the right side wall Wb. The bottom plane 71 and the small trough 72 correspond to an example of a bottom surface. The main trough 8 corresponds to an example of a groove. Hereinafter, the left side wall Wa and the right side wall Wb may be collectively referred to as the side wall W. A protruding wall 10 for supporting the dust collector 5 is provided in the central portion of the width direction of the pond on the upstream side of the settling basin 2. The sand collection pit 6, the bottom plane 71, the small trough 72, the connection surface 73, and the main trough 8 are each provided in the bottom of the settling basin 2. The bottom plane 71 is formed by the surface of concrete poured into the bottom of the pond. The main trough 8 is composed of an upstream first main trough 815 and an upstream second main trough 816, which extend in the longitudinal direction from near the upstream end of the settling basin 2 and whose rear end is connected to the sand collection pit 6, and a downstream main trough 82, which extends in the longitudinal direction from near the downstream end of the settling basin 2 and whose rear end is connected to the sand collection pit 6. The upstream first main trough 815 corresponds to an example of a first groove, and the upstream second main trough 816 corresponds to an example of a second groove. The settling basin 2 is a so-called low-pressure sand collection type settling basin in which, after the wastewater in the settling basin 2 is drained, a fluid is discharged to the bottom plane 71 and the small trough 72, and the sand that has settled on the bottom plane 71 and the small trough 72 is collected. Hereinafter, the long side direction of the settling basin 2 is referred to as the longitudinal direction, and the short side direction is referred to as the pond width direction. This longitudinal direction is also a perpendicular direction perpendicular to the pond width direction.

A building, piping, etc. (not shown) may be located above the settling basin 2 (the front side of the paper in FIG. 2). A pillar 11 may be formed adjacent to the settling basin 2 to support the building, etc. In the settling basin 2 shown in FIG. 2, the pillar 11 is formed near the left side wall Wa. The part of the left side wall Wa that serves as the base of the pillar 11 has a convex wall portion Wa1 that protrudes toward the center in the width direction of the pond. Conversely, it can be said that the part of the left side wall Wa where the pillar 11 does not exist on the left side wall Wa has a concave wall portion Wa2 that is concave toward the outside in the width direction of the pond. In addition, the part connecting the convex wall portion Wa1 and the concave wall portion Wa2 has an inclined wall portion Wa3 that is inclined with respect to the longitudinal direction and the width direction of the pond. Since there is no pillar 11 near the right side wall Wb, the right side wall Wb is formed in a substantially straight line in a plan view.

The sand collection pit 6 is located slightly downstream of the longitudinal center of the settling basin 2. This sand collection pit 6 is composed of a recess formed in the center of the settling basin 2 in the basin width direction. A sand lifting pump 61 and an agitation nozzle 62 are arranged inside the sand collection pit 6. This sand collection pit 6 is the deepest part of the settling basin 2. This sand collection pit 6 has a rectangular shape in a plan view. Between the side wall W and the sand collection pit 6, there is a sand collection pit slope 6b that slopes gradually to become deeper toward the sand collection pit 6 side located in the center of the basin width direction.

A total of four stirring nozzles 62 are arranged near each corner of the sand collection pit 6. The stirring nozzles 62 are for stirring the sand collected in the sand collection pit 6. By discharging fluid from the discharge port 62a of the stirring nozzle 62 while the sand lifting pump 61 is operating, the efficiency with which the sand collected in the sand collection pit 6 is suctioned by the sand lifting pump 61 can be improved. Two sand collection nozzles 63 for the pit are arranged on each end of the sand collection pit slope 6b in the pond width direction. By discharging fluid from the discharge port 63a of the sand collection nozzle 63 for the pit when the water level of the sand collection basin 2 is lower than a predetermined value, the sand accumulated on the sand collection pit slope 6b can be collected in the sand collection pit 6.

The bottom plane 71 is composed of a first bottom surface 711 formed between the left side wall Wa and the upstream first main trough 815, a second bottom surface 712 formed between the right side wall Wb and the upstream second main trough 816, a third bottom surface 713 formed between the left side wall Wa and the downstream main trough 82, and a fourth bottom surface 714 formed between the right side wall Wb and the downstream main trough 82. The bottom plane 71 and the small trough 72 are connected to the main trough 8 at the center of the pond width direction of the grit basin 2. The bottom plane 71 is inclined downward by about 5 degrees from the side wall W side at the outer end in the pond width direction toward the main trough 8 so that the end on the side of the main trough 8 side is the deepest. On the other hand, the bottom plane 71 is formed horizontally in the longitudinal direction. The small trough 72 is a gutter-shaped with a U-shaped cross section, and extends from the vicinity of the side wall W in the pond width direction. A plurality of small troughs 72 are arranged at equal intervals in the longitudinal direction. In this embodiment, 28 small troughs 72 are arranged on each side of the main trough 8 in the pond width direction, for a total of 56 small troughs 72. Like the bottom plane 71, these small troughs 72 are also inclined downward by about 5 degrees from the side wall W side toward the main trough 8 side so that the part connected to the main trough 8 is located closest to the bottom of the pond.

The upstream first main trough 815, the upstream second main trough 816, and the downstream main trough 82 are grooves formed by a trough forming body that is a stainless steel plate and has a cross section in the shape of a 2/3 circle arc. However, the upstream first main trough 815, the upstream second main trough 816, and the downstream main trough 82 may be formed of concrete integrally with the bottom plane 71. The upstream first main trough 815, the upstream second main trough 816, and the downstream main trough 82 are arranged horizontally over the entire length in the longitudinal direction from near the end of the settling basin to the part connected to the sand collection pit 6.

As shown in FIG. 2, the upstream first main trough 815 is provided on the left side wall Wa side with respect to the center of the pond width direction and extends in the longitudinal direction. The upstream second main trough 816 is provided on the right side wall Wb side with respect to the center of the pond width direction and extends in the longitudinal direction. The upstream first main trough 815 and the upstream second main trough 816 are both 10 m long and have the same shape. The downstream ends of the upstream first main trough 815 and the upstream second main trough 816 are connected to the sand collection pit 6. The upstream end portion of the upstream first main trough 815 (the tip portion of the upstream first main trough 815) is provided with an upstream trough first nozzle 831 having a trough first outlet 831a. The upstream end portion of the upstream second main trough 816 (the tip portion of the upstream second main trough 816) is provided with an upstream trough second nozzle 832 having a trough second outlet 832a. These trough first outlet 831a and trough second outlet 832a correspond to an example of a first outlet. A first cover member 13 is disposed inside the upstream first main trough 815. A second cover member 14 is disposed inside the upstream second main trough 816. The first cover member 13 and the second cover member 14 extend along the upstream first main trough 815 and the upstream second main trough 816, respectively. The total length of the first cover member 13 and the second cover member 14 is approximately the same as the total length of the upstream first main trough 815 and the upstream second main trough 816. As shown in FIG. 2, the first cover member 13 extends from upstream of the trough first outlet 831a to a slightly downstream beyond the part of the upstream first main trough 815 connected to the sand collection pit 6. When wastewater is accumulated in the upstream first main trough 815, the sand accumulated in the upstream first main trough 815 can be moved to the sand collection pit 6 by discharging a fluid from the trough first outlet 831a. The second cover member 14 extends from upstream of the trough second outlet 832a to a slightly downstream position beyond the part of the upstream second main trough 816 connected to the sand collection pit 6. When wastewater is accumulated in the upstream second main trough 816, the sand accumulated in the upstream second main trough 816 can be moved to the sand collection pit 6 by discharging a fluid from the trough second outlet 832a. The movement of sand in the upstream first main trough 815 and the upstream second main trough 816, as well as the first cover member 13 and the second cover member 14, will be described in detail later.

The downstream main trough 82 extends linearly in the longitudinal direction at the center of the width of the settling basin 2. The total length of the downstream main trough 82 is 5 m. The upstream end of the downstream main trough 82 is connected to the sand collection pit 6. A downstream trough nozzle 84 having a trough third outlet 84a is provided at the downstream end of the downstream main trough 82 (the tip portion of the downstream main trough 82). This trough third outlet 84a also corresponds to an example of the first outlet. A third cover member 15 is disposed inside the downstream main trough 82. This third cover member 15 extends along the downstream main trough 82. The total length of the third cover member 15 is approximately the same as the total length of the downstream main trough 82. As shown in FIG. 2, the third cover member 15 extends from downstream of the trough third outlet 84a to a slightly upstream beyond the part of the downstream main trough 82 connected to the sand collection pit 6. When wastewater accumulates in the downstream main trough 82, the sand accumulated in the downstream main trough 82 can be moved to the sand collection pit 6 by discharging fluid from the trough third outlet 84a. The movement of sand in the downstream main trough 82 and the third cover member 15 will be described in detail later.

Between the upstream first main trough 815 and the upstream second main trough 816, a protruding wall 10 for supporting the dust collector 5 is formed in the upstream part of the grit basin 2. This protruding wall 10 is a concrete wall that rises up to the vicinity of the upper end of the grit basin 2. The connection surface 73 is between the upstream first main trough 815 and the upstream second main trough 816, and is arranged in the bottom of the pond downstream of this protruding wall 10. In other words, the connection surface 73 is formed in the part between the upstream first main trough 815 and the upstream second main trough 816 excluding the area where the protruding wall 10 is provided. The connection surface 73 is composed of a ridge portion 731 extending along the longitudinal direction, a first connection surface 732 that connects the ridge portion 731 and the upstream first main trough 815, and a second connection surface 733 that connects the ridge portion 731 and the upstream second main trough 816. The extension direction of the ridge portion 731 does not have to be completely the same as the longitudinal direction, and may be, for example, a direction that is slightly inclined in the pond width direction and in the vertical direction with respect to the longitudinal direction. The ridge portion 731 may also meander slightly in the pond width direction and in the vertical direction. In other words, "extending along the longitudinal direction" is a concept that includes some inclination and meandering.

Figure 3 is a cross-sectional view of the grit basin shown in Figure 2 taken along the line X-X. The dust collector is not shown in Figure 3.

As shown in FIG. 3, the first connection surface 732 is an inclined surface that inclines downward toward the upstream first main trough 815. The second connection surface 733 is an inclined surface that inclines downward toward the upstream second main trough 816. The first connection surface 732 and the second connection surface 733 are made of concrete surfaces. The inclination angle of the first connection surface 732 and the second connection surface 733 is about 45 degrees with respect to the horizontal plane. By inclining the connection surface, the sand that settles on the connection surface 73 can be collected in the upstream first main trough 815 or the upstream second main trough 816 without remaining on the connection surface 73. If the inclination angle of the first connection surface 732 and the second connection surface 733 is 15 degrees or more, most of the sand that settles on the connection surface 73 in the wastewater in the grit basin 2 slides down the connection surface 73 due to its own weight. Moreover, if the inclination angle of the first connection surface 732 and the second connection surface 733 is set to 30 degrees or more, the sand that settles on the connection surface 73 will slide down the connection surface 73 more easily, which is preferable. However, if the inclination angle is too large, the thickness of the concrete that constitutes the connection surface 73 in the pond width direction will be too thin in the vicinity of the ridge line portion 731, and the ridge line portion 731 will be easily damaged. For this reason, it is preferable to set the angle of the ridge line portion 731 formed by the first connection surface 732 and the second connection surface 733 so that the angle of the ridge line portion 731 formed by the first connection surface 732 and the second connection surface 733 is 30 degrees or more. Note that one or both of the first connection surface 732 and the second connection surface 733 do not have to be configured as a single plane, and may be configured as, for example, multiple surfaces with different inclination angles. In this case, the inclination angle of all the multiple surfaces may be 15 degrees or more. Also, one of the first connection surface 732 and the second connection surface 733 may be a vertical surface, and the other may be an inclined surface. However, by making the first connection surface 732 and the second connection surface 733 inclined as in this embodiment, the sand can be distributed and slid down to the upstream first main trough 815 and the upstream second main trough 816, so it is preferable to make each of them inclined. Also, by providing a ridge portion 731 in the center between the upstream first main trough 815 and the upstream second main trough 816 as in this embodiment, the amount of sand that slides down to the upstream first main trough 815 and the upstream second main trough 816 can be made uniform. This prevents a large amount of sand from accumulating in one of the upstream first main trough 815 and the upstream second main trough 816, so that it is possible to prevent the sand from being unable to be transported to the sand collection pit 6 due to the transport resistance of the sand in the upstream first main trough 815 and the upstream second main trough 816.

Figure 4(a) is an enlarged view of the Z portion of Figure 3, and Figure 4(b) is a schematic perspective view showing the first cover member and the upstream trough first nozzle. In Figure 4(a), the left-right direction of the figure is the pond width direction, and the direction perpendicular to the paper surface is the longitudinal direction. Also, in Figure 4(a), hatching representing the cross section of the upstream first main trough and the first cover member is omitted.

Figure 4 (a) shows the upstream first main trough 815, the upstream trough first nozzle 831, and the first cover member 13. The upstream second main trough 816, the upstream trough second nozzle 832, and the second cover member 14, as well as the downstream main trough 82, the downstream trough nozzle 84, and the third cover member 15, have the same shape except for the bottom plane 71 or the connection surface 73 to which they are connected, so their description will be omitted. As described above, the upstream first main trough 815 of this embodiment has a cross-sectional shape of 2/3 of a circle. That is, it has an arc shape with the trough arc center 815c, which is the center in the radial direction, as the center point. However, the cross-sectional shape of the upstream first main trough 815 is not limited to an arc shape, and may be a U-shape, V-shape, or the like. The upstream first main trough 815 has a shape in which the upper part of a cylinder with an inner diameter of 300 mm is cut out, and opens upward over its entire length. Hereinafter, this open portion may be referred to as the first trough opening 815b. The small trough 72 is connected to this first trough opening 815b, and the heightwise position of the first trough opening 815b is the same as the heightwise position of the lower end of the small trough 72. The upper portion 815a of the upstream first main trough 815 above the trough arc center 815c narrows in the pond width direction toward the upper end first trough opening 815b. As a result, even if sand is blown up inside the upstream first main trough 815, the upper portion 815a acts as a return and can return the blown up sand into the upstream first main trough 815.

The first covering member 13 has a cross-sectional shape of a 5/6 circle with an opening 13a at the lower end. In other words, it has an arc shape with the covering arc center 13c, which is the radial center, as the center point. This first covering member 13 is a stainless steel plate material with a plate thickness of 3 mm formed into a cross-sectional arc shape with an inner diameter of 150 mm. The opening 13a is provided over the entire length of the first covering member 13. The first covering member 13 divides the internal space of the upstream first main trough 815. The space inside the first covering member 13 becomes the transport space FS, which is the space covered by the first covering member 13. Since the first covering member 13 has an arc shape with the upper part closed, the sand that has settled toward the upper part of the first covering member 13 in the settling basin 2 easily slides down the outer surface of the upper part of the first covering member 13. The sand that slides down is deposited below the upstream first main trough 815. In addition, the transfer space FS below the cover arc center 13c of the first cover member 13 narrows in the pond width direction toward the lower opening 13a. The first cover member 13 is supported by a support bracket 131 (see FIG. 5) fixed to the concrete poured on the bottom of the settling basin 2 with a chemical anchor (registered trademark). The height position of the upper end of the first cover member 13 is located at approximately the same height as the first trough opening 815b. It is desirable to set the height position of the upper end of the first cover member 13 at approximately the same height as the first trough opening 815b or at a position lower than the first trough opening 815b. By setting it at this position, if water is filled in the upstream first main trough 815, the inside of the first cover member 13 can be filled with water. When the fluid is discharged into the water from the trough first discharge port 831a, a strong flow of fluid can be created inside the first cover member 13 by filling the inside of the first cover member 13 with water. In addition, the opening 13a of the first covering member 13 is disposed below the center 815h in the height direction of the upstream first main trough 815. This arrangement allows the opening 13a of the first covering member 13 to be close to the sand deposited below the upstream first main trough 815, so that the sand deposited in the upstream first main trough 815 can be easily sucked up into the first covering member 13 by the flow of the fluid in the first covering member 13. Since both ends in the extension direction of the first covering member 13 are open, if the water level of the grit basin 2 is higher than the upper end position of the first covering member 13, no air remains in the transport space FS, and the transport space FS is filled with wastewater. In addition, the first covering member 13 of this embodiment has an arc-shaped cross section, but the cross section may be polygonal, or may be a shape in which an arc and a straight portion are connected. However, it is preferable that the cross section of the upper part of the first covering member 13 is an inclined surface that slopes downward toward the width direction of the groove. By making the upper part of the first covering member 13 into an inclined surface, sand that settles on the upper part of the first covering member 13 tends to slide down the upper part, and is therefore more likely to accumulate at the bottom inside the upstream first main trough 815.

The trough first outlet 831a is disposed in the transport space FS in the first cover member 13. The trough first outlet 831a is an elongated hole formed by flattening the tip of a pipe with an inner diameter of 80 mm from above and below. The maximum opening length of the trough first outlet 831a in the pond width direction is 117 mm, and the maximum height in the vertical direction is 18 mm. The trough first outlet 831a may be of other shapes, such as a perfect circle. However, by making the trough first outlet 831a flat, the fluid can be discharged over a wider range than the perfect circle before being crushed. The discharge flow rate of the fluid discharged from the trough first outlet 831a is preferably 8 m/sec or more. If it is less than 8 m/sec, the flow rate may be insufficient and the sand may not be moved a predetermined distance. In addition, the discharge pressure of the fluid discharged from the trough first outlet 831a is preferably 0.05 MPa or more and 0.3 MPa or less. The center of the trough first outlet 831a coincides with the covering arc center 13c. The trough first outlet 831a discharges the fluid in the longitudinal direction, which is the extension direction of the first covering member 13. As shown in FIG. 4B, the first covering member 13 covers the trough first outlet 831a and extends in the fluid discharge direction so as to cover the fluid discharged from the trough first outlet 831a. The axis extending in the flow direction of the fluid discharged from the trough first outlet 831a, starting from the center (covering arc center 13c) of this trough first outlet 831a, becomes the virtual axis VL. In other words, the first covering member 13 extends so as to cover the virtual axis VL extending in the longitudinal direction from the center of the trough first outlet 831a. The extension direction of the first cover member 13 and the discharge direction of the fluid discharged from the trough first outlet 831a do not need to be completely aligned with the longitudinal direction, but by making them aligned, the sand can be transported more efficiently. Even if the discharge direction of the fluid discharged from the trough first outlet 831a and the extension direction of the first cover member 13 are slightly different, the discharged fluid is guided by the first cover member, so the flow direction of the fluid coincides with the extension direction of the first cover member. Therefore, the virtual axis VL in this case becomes the extension direction of the first cover member. However, in this case, the fluid may collide with the first cover member and the flow may be weakened, so it is desirable to match the discharge direction of the fluid discharged from the trough first outlet 831a and the extension direction of the first cover member 13. In addition, the center of the trough first outlet 831a may be located at a position different from the cover arc center 13c, and may be located, for example, below the cover arc center 13c and above the opening 13a. However, by aligning the center of the trough first outlet 831a with the cover arc center 13c, the loss of the flow of the fluid discharged from the trough first outlet 831a can be minimized. On the other hand, by locating the center of the trough first outlet 831a below the cover arc center 13c, the suction force for sucking sand from the opening 13a into the transport space FS can be increased. Therefore, it is desirable to locate the center of the trough first outlet 831a between the cover arc center 13c and the opening 13a of the first cover member 13.

When the fluid is discharged from the trough first outlet 831a into the transport space FS, a flow of the fluid occurs in the transport space FS inside the first cover member 13. A pressure difference occurs between the transport space FS and the outside of the first cover member 13 due to the flow of the fluid. That is, a negative pressure occurs in the transport space FS where the fluid flow occurs. The sand accumulated in the upstream first main trough 815 is sucked into the transport space FS from the opening 13a by the negative pressure, as shown by the curved arrow in FIG. 4(a). In addition, the fluid discharged from the trough first outlet 831a is prevented from diffusing in the radial direction perpendicular to the longitudinal direction by the first cover member 13, so that the flow is maintained in the transport space FS over a long distance. The sucked sand is transported toward the sand collection pit 6 by the flow of the fluid generated in the transport space FS. In this embodiment, the transport space FS is formed by the first cover member 13, so that the flow of the fluid discharged from the trough first outlet 831a can be utilized for transporting sand without impairing it. As a result, the sand accumulated in the upstream first main trough 815 can be efficiently transported toward the sand collection pit 6. As described above, below the covering arc center 13c in the transport space FS, the pond width direction narrows toward the lower opening 13a. By narrowing the pond width direction of the opening 13a, the sand transported in the transport space FS is less likely to leak out of the transport space FS. In addition, since the fluid in the transport space FS is less likely to flow out of the transport space FS, the flow of the fluid can be maintained over a long distance, and the sand can be moved farther. And, it becomes easier to maintain the negative pressure in the transport space FS even at a position away from the trough first discharge port 831a.

As shown in FIG. 2, two dust removers 5 are arranged side by side in the width direction of the pond, sandwiching the protruding wall 10, in the upstream portion of the sedimentation basin 2. In other words, one dust remover 5 is arranged between the left side wall Wa and the protruding wall 10, and one between the right side wall Wb and the protruding wall 10. These two dust removers 5, 5 have the same configuration. The dust removers 5 are intended to remove contaminants (seed residue) mixed in the wastewater that has flowed into the sedimentation basin 2. One dust remover 5 shown in the upper part of FIG. 2 is supported by the left side wall Wa and the protruding wall 10, and the other dust remover 5 shown in the lower part of FIG. 2 is supported by the right side wall Wb and the protruding wall 10. By arranging the two dust removers 5, 5 side by side in the width direction of the pond, the width of each dust remover 5 in the width direction of the pond can be shortened. By shortening the width of the dust collector 5 in the basin width direction, the strength of the dust collector 5 is increased, and damage to the dust collector 5 can be suppressed even if the amount and flow rate of wastewater flowing into the grit basin 2 increases due to heavy rain or other reasons.

Figure 5 is a cross-sectional view of the settling basin shown in Figure 2 taken along the line A-A. In Figure 5, the pillars and sand-lifting pump are omitted, and the shape of the protruding wall is indicated by a two-dot chain line. The direction of sewage flow is indicated by a straight arrow. Note that the water level WL of the settling basin fluctuates depending on the amount of rain and sewage flowing in, but during normal times when the amount of rain and sewage is expected, it is located at a mid-height in the height direction of the settling basin 2, as shown in Figure 5.

As shown in FIG. 5, the dust collector 5 has an endless chain 51, a plurality of rakes 52 attached to the endless chain 51 at intervals, and a filter screen 53. The endless chain 51 is provided in an upright state at an angle on both sides of the width of the grit basin 2, and is wound around a ground-side sprocket 511 and a pond-bottom-side sprocket 512. The upper part of the endless chain 51 and the ground-side sprocket 511 are arranged on the ground part of the grit basin 2. When the water surface WL is in a normal state, if the ground-side sprocket 511 is driven in the rotation direction indicated by the arc-shaped arrow R by a motor (not shown), the endless chain 51 circulates and the rake 52 moves in and out of the water. FIG. 5 shows the water surface WL in a normal state. The protruding wall 10 protrudes above the water surface WL. However, if the protruding wall 10 is formed for a purpose other than supporting the dust collector 5, the protruding wall 10 may be lower than the water surface WL. The filter screen 53 is disposed downstream of the endless chain 51. The filter screen 53 is a structure in which vertically extending bars are arranged at a predetermined interval (for example, 25 mm to 75 mm) in the width direction of the pond, and blocks the passage of contaminants larger than the predetermined interval. The contaminants blocked by the filter screen 53 are scooped up by the rake 52, and the scooped up contaminants are placed on a conveying means such as a belt conveyor (not shown) on the ground side. The bottom sprocket 512 and the lower end of the filter screen 53 are disposed upstream of the bottom plane 71 and the main trough 8. On the other hand, the upper ends of the ground sprocket 511 and the filter screen 53 are located above the bottom plane 71 and the upstream part of the main trough 8. That is, the upper parts of the endless chain 51 and the filter screen 53 overlap the bottom plane 71 and the main trough 8 in the longitudinal direction. Note that FIG. 5 also shows a support bracket 151 that supports the third cover member 15.

The sand collection means 9 has a first nozzle header 9a, a second nozzle header 9b, and a third nozzle header 9c arranged on the left side wall Wa side of the settling basin 2, and a fourth nozzle header 9d, a fifth nozzle header 9e, and a sixth nozzle header 9f arranged on the right side wall Wb side (see FIG. 2). FIG. 5 shows the sand collection means 9 on the left side wall Wa side. The sand collection means 9 on the right side wall Wb side has the same configuration, so the explanation of the sand collection means 9 on the right side wall Wb side is omitted. Each of the first nozzle header 9a, the second nozzle header 9b, and the third nozzle header 9c has 10 sand collection nozzles 91, a supply pipe 92, and a mother pipe 93. The supply pipe 92 is arranged opposite the left side wall Wa and extends in the longitudinal direction. The mother pipe 93 has a single pipe 931 extending above the settling basin 2 and a branch pipe 932 connected to the bottom side end of the single pipe 931. The single pipe 931 and the branch pipe 932 are fixed to the left wall Wa by fixing brackets (not shown).

Figure 6 is an enlarged view of part B in Figure 5. In Figure 6, the flow direction of the wastewater is indicated by a straight arrow. The side wall is also shown in Figure 6. Also, Figure 6 shows one of the six nozzle headers, but the other five nozzle headers have the same configuration as the nozzle header shown in Figure 6.

As shown in FIG. 6, the branch pipe 932 is connected to the single pipe 931 by a flange joint 933. The branch pipe 932 branches into two at the lower side of the part connected to the single pipe 931, and the branched parts extend in the longitudinal direction of the grit basin 2. The supply pipes 92 to which the lap joints 934 are fixed are connected to the tip parts of the branched parts. In this embodiment, three supply pipes 92 are provided for one mother pipe 93: an upstream supply pipe 921 arranged upstream of the branch pipe 932, a downstream supply pipe 923 arranged downstream of the branch pipe 932, and an intermediate supply pipe 922 arranged between the upstream supply pipe 921 and the downstream supply pipe 923. The other ends of the upstream supply pipe 921 and the downstream supply pipe 923, opposite to the one end connected to the branch pipe 932, are closed by lids 97. Both ends of the intermediate supply pipe 922 are connected to the branch pipe 932.

Three sand collection nozzles 91 are fixed at equal intervals to each of the upstream supply pipe 921 and the downstream supply pipe 923. Four sand collection nozzles 91 are fixed at equal intervals to the intermediate supply pipe 922. The total of ten sand collection nozzles 91 are all arranged at equal intervals. The interval between the most downstream sand collection nozzle 91 of the first nozzle header 9a (see FIG. 2) and the most upstream sand collection nozzle 91 of the second nozzle header 9b is also the same as the interval between the ten sand collection nozzles described above. That is, the sand collection nozzles 91 are all arranged at equal intervals in the longitudinal direction of the settling basin 2. The number of sand collection nozzles 91 arranged in each supply pipe 92 may be appropriately determined depending on factors such as the length of the supply pipe 92. An outlet 911 is formed at the tip of each sand collection nozzle 91. This outlet 911 corresponds to an example of a second outlet. Among the discharge ports 911, the discharge ports 911 provided in the first nozzle header 9a (see FIG. 2) and the second nozzle header 9b correspond to an example of a one-side discharge port, and the discharge ports 911 provided in the fourth nozzle header 9d and the fifth nozzle header 9e (see FIG. 2) correspond to an example of a other-side discharge port. By discharging a fluid from the discharge port 911 into the atmosphere in a state in which the water level of the grit basin 2 is lowered below a predetermined value to expose the sand accumulated on the bottom plane 71 and the small trough 72 and the discharge port 911 to the atmosphere, the sand accumulated on the bottom plane 71 and the small trough 72 shown in FIG. 2 and FIG. 5 can be made to flow into the main trough 8. The discharge pressure of the fluid sprayed from one discharge port 911 is, for example, 0.005 MPa, and preferably 0.0002 MPa or more and 0.005 MPa or less. That is, the discharge pressure of the fluid discharged from the discharge port 911 is lower than the discharge pressure of the fluid discharged from the trough first discharge port 831a (0.05 MPa or more and 0.3 MPa or less). This allows for the use of an inexpensive and small water supply pump 33 for supplying the fluid while ensuring a flow rate that allows the sand accumulated on the bottom plane 71 and the small trough 72 to flow into the main trough 8.

The distance from the supply pipe 92 to the left side wall Wa is different between the part facing the convex wall Wa1 and the part facing the concave wall Wa2. That is, the supply pipe 92 has a first region 92a extending from the left side wall Wa in the pond width direction at a first interval, and a second region 92b extending from the left side wall Wa in the pond width direction at a second interval. In addition, since the settling basin 2 of this embodiment has an inclined wall portion Wa3 formed in the part connecting the convex wall portion Wa1 and the concave wall portion Wa2, the supply pipe 92 has a third region 92c which is a region connecting the first region and the second region. Each sand collection nozzle 91 and its discharge port 911 are arranged opposite the left side wall Wa and are fixed to the supply pipe 92 in a longitudinal line. In the second nozzle header 9b shown in FIG. 6, the upstream supply pipe 921 is arranged opposite the convex wall portion Wa1. That is, the region where the upstream supply pipe 921 is located corresponds to the first region 92a. On the other hand, the region of the intermediate supply pipe 922 where the outlet 911 located in the part closest to the upstream supply pipe 921 is arranged is arranged opposite the inclined wall portion Wa3. That is, that region corresponds to the third region 92c. Also, the region of the intermediate supply pipe 922 where three outlets 911 are arranged from the downstream supply pipe 923 side, and the region of the downstream supply pipe 923 where two outlets 911 are arranged from the intermediate supply pipe 922 side are arranged opposite the recessed wall portion Wa2. That is, those regions correspond to the second region 92b. Also, the region of the downstream supply pipe 923 where the outlet 911 located in the most downstream side is arranged is arranged opposite the inclined wall portion Wa3. That is, that region corresponds to the third region 92c. Between these respective regions, a direction change means using a lap joint 934 is provided.

Figure 7(a) is a cross-sectional view to explain the state in which one pipe with a lap joint is connected to the other pipe, and Figure 7(b) is a cross-sectional view to explain the state in which the one pipe with a lap joint is able to rotate freely about its axial direction relative to the other pipe by loosening the bolt. In Figure 7, a supply pipe is shown as one pipe and a branch pipe is shown as the other pipe, but the same configuration is used when supply pipes are connected together with a lap joint.

As shown in FIG. 7(a) and FIG. 7(b), a lap joint 934 is welded to the end of the supply pipe 92. The lap joint 934 is composed of a small diameter portion 934a welded to the supply pipe 92 and a large diameter portion 934b arranged on the branch pipe 932 side. The outer diameter of the small diameter portion 934a is formed to be the same as the outer diameter of the supply pipe 92. A free flange 935 is arranged on the outer periphery of the lap joint 934. The free flange 935 is ring-shaped with an inner diameter slightly larger than the outer diameter of the lap joint 934. The free flange 935 has eight free flange through holes 935a evenly spaced in the circumferential direction into which the bolts 95 are inserted. The free flange 935 is connected to the lap joint 934 so as to be rotatable relative to the lap joint 934 and movable in the axial direction. A fixed flange 9322 is welded to the outer diameter portion of the tip of the branch pipe 932. The fixed flange 9322 has eight fixed flange through holes 9322a into which bolts 95 are inserted, similar to the free flange 935. A ring-shaped packing 94 is disposed between the lap joint 934 and the fixed flange 9322. This packing 94 is intended to prevent leakage of fluid passing through the supply pipe 92 and the branch pipe 932 when the supply pipe 92 and the branch pipe 932 are joined.

The bolt 95 is inserted into the fixed flange through hole 9322a of the fixed flange 9322 and the free flange through hole 935a of the free flange 935. When the bolt 95 and the nut 96 are tightened, the supply pipe 92 is fixed to the branch pipe 932 by sandwiching the lap joint 934 together with the packing 94 between the fixed flange 9322 and the free flange 935, as in the supply pipe 92 shown in FIG. 7(a). On the other hand, when the bolt 95 is loosened, the supply pipe 92 becomes rotatable about its axis relative to the branch pipe 932, as in the supply pipe 92 shown in FIG. 7(b). That is, in this embodiment, the mother pipe 93 (see FIG. 5) and the supply pipe 92 are connected using the lap joint 934 and the free flange 935, so that the supply pipe 92 is configured to be infinitely rotatable about its axis relative to the mother pipe 93. In addition, even if other loose flanges such as loose flanges are used instead of the lap joint 934, the supply pipe 92 can be connected to the mother pipe 93 so that it can rotate steplessly.

6, a lap joint 934 is disposed between the outlet 911 disposed in the first region 92a and the outlet 911 disposed in the third region 92c, and between the outlet 911 disposed in the second region 92b and the outlet 911 disposed in the third region 92c. Therefore, the outlets 911 disposed in the first region 92a, the second region 92b, and the third region 92c are configured to be able to rotate steplessly around the axial direction of the supply pipe 92 independently of each other. With this configuration, the discharge direction of the fluid at the outlet 911 in each region can be set according to the distance from the supply pipe 92 to the left side wall Wa. The lap joint 934 disposed between the outlet 911 disposed in the first region 92a and the outlet 911 disposed in the third region 92c corresponds to an example of a first direction change means. The lap joint 934 disposed between the outlet 911 disposed in the second region 92b and the outlet 911 disposed in the third region 92c corresponds to an example of a second direction change means. In addition, in the first region 92a of the supply pipe 92 shown in FIG. 6, the discharge direction of the fluid from the three discharge ports 911 arranged in the first region 92a can be changed collectively, so that the discharge direction in the first region 92a can be easily adjusted. In the second region 92b of the supply pipe 92 shown in FIG. 6, the three discharge ports 911 arranged in the intermediate supply pipe 922 can be changed collectively, and the two discharge ports 911 arranged in the downstream supply pipe 923 can be changed collectively, so that the discharge direction in the second region 92b can be easily adjusted. In other words, the lap joint 934 in the case where the discharge direction of the multiple discharge ports 911 can be changed collectively corresponds to an example of a collective direction changing means. Note that, when the longitudinal direction of the third region 92c is short and there are no discharge ports 911 in the third region 92c, or when the third region 92c does not exist, the lap joint 934 may be arranged between the first region 92a and the second region 92b.

Figure 8(a) is a cross-sectional view taken along line C-C of Figure 6. The side walls and bottom surface are also shown in Figure 8(a).

As described above, the left side wall Wa has a convex wall portion Wa1 and a concave wall portion Wa2. In FIG. 8(a), the convex wall portion Wa1 is shown by a solid line, and the concave wall portion Wa2 is shown by a two-dot chain line. In the discharge port 911 shown by a solid line in FIG. 8(a), the discharge direction of the fluid is directed toward the center of the pond width direction rather than the direction (vertical direction) directly downward from the center of the supply pipe 92. In this discharge port 911, the angle θ at which the fluid is discharged with respect to the bottom plane 71 is about 50 degrees. By setting the angle θ to about 50 degrees, the fluid that has reached the bottom plane 71 can be divided into a direction toward the main trough 8 and a direction toward the convex wall portion Wa1. This angle θ may be any angle at which the discharged fluid is divided into a direction toward the main trough 8 and a direction toward the convex wall portion Wa1, and specifically, may be any angle between 30 degrees and 60 degrees with respect to the bottom plane 71. By setting this angle, when the supply pipe 92 and the left side wall Wa are close to each other as in the convex wall portion Wa1, i.e., in the first region 92a (see FIG. 6), the diverted fluid reaches the sand accumulated on the bottom plane 71 between the supply pipe 92 and the left side wall Wa, and can flush that sand. Also, since the discharge direction of the fluid is directed toward the main trough 8 side in the center of the pond width direction rather than the vertical direction of the supply pipe 92, the momentum of the fluid flowing toward the main trough 8 side is stronger than the momentum of the fluid flowing toward the left side wall Wa side. This fluid momentum allows the sand accumulated on the bottom plane 71 between the supply pipe 92 and the main trough 8 to be efficiently flushed toward the main trough 8.

On the other hand, in the recess wall Wa2 portion shown by the two-dot chain line in FIG. 8(a), the supply pipe 92 and the left side wall Wa are separated. For this reason, in the discharge direction of the discharge port 911 shown by the solid line, even if the discharged fluid is diverted, it does not reach the vicinity of the recess wall Wa2, or even if it does reach, only a very small amount of fluid reaches. If the amount of fluid that reaches the vicinity of the recess wall Wa2 is small, the sand that has accumulated between the supply pipe 92 and the recess wall Wa2 and that is near the recess wall Wa2 cannot be sufficiently flushed away.

In this embodiment, the supply pipe 92 is configured to be rotatable around its axis, so that the discharge direction of the fluid from the sand collection nozzle 91 can be freely changed. In FIG. 8(a), the sand collection nozzle 91 in which the discharge direction of the fluid discharged from the discharge port 911 is adjusted in accordance with the position of the recessed wall portion Wa2 is shown by a two-dot chain line. In the sand collection nozzle 91 shown by the two-dot chain line, the discharge direction of the fluid discharged from the discharge port 911 is directed outward in the pond width direction rather than the direction (vertical direction) directly downward from the center of the supply pipe 92. By adjusting the discharge direction of the fluid discharged from the discharge port 911 according to the distance from the supply pipe 92 to the left side wall Wa, even if the supply pipe 92 and the left side wall Wa are separated as in the second region 92b (see FIG. 6), the sand accumulated near the left side wall Wa can be sufficiently flushed. In this embodiment, the mother pipe 93 and the supply pipe 92 or the supply pipes 92 are connected to each other using a lap joint 934 and a free flange 935, so the connected supply pipe 92 can be rotated steplessly around its axis. Since it can be rotated steplessly, the supply pipe 92 (third region 92c) located opposite the inclined wall portion Wa3 (see FIG. 2) between the convex wall portion Wa1 and the concave wall portion Wa2 can set the fluid discharge direction to the middle direction between the discharge direction of the sand collection nozzle 91 shown by the solid line in FIG. 8(a) and the discharge direction of the sand collection nozzle 91 shown by the two-dot chain line.

In addition, in this embodiment, the parent pipe 93 is provided with a branch pipe 932, so that a total of three supply pipes 92, the upstream supply pipe 921, the intermediate supply pipe 922, and the downstream supply pipe 923, are connected to one parent pipe 93 in line in the longitudinal direction of the grit basin 2. In contrast, if there is no branch pipe 932 and the supply pipe 92 is connected to a single pipe 931, at most two supply pipes 92 can be connected to one parent pipe 93 in the longitudinal direction of the grit basin 2. That is, there are two supply pipes 92, one extending from the tip of the parent pipe 93 to the upstream side of the grit basin 2 and the other extending to the downstream side. The discharge direction of the fluid discharged from the discharge port 911 can be set for each supply pipe 92. Therefore, compared to the case where there is no branch pipe 932, when the branch pipe 932 is provided, the discharge direction of the fluid discharged from the discharge port 911 can be adjusted at many points in the longitudinal direction of the grit basin 2, making it possible to flexibly respond to the shape of the side wall W.

Figure 8(b) is a cross-sectional view similar to Figure 8(a) for explaining the change in discharge direction by the sand collection nozzle. The side walls and bottom plane are also shown in Figure 8(b).

8B, the sand collection nozzle 91 is bent at the middle and is formed in an inverted L-shape when viewed in the longitudinal direction as shown by the solid line. Since it is formed in an inverted L-shape, when the sand collection nozzle 91 shown in the solid line is rotated 180 degrees around the axis L of the attachment part with the supply pipe 92, the discharge direction of the fluid can be changed from the center side in the pond width direction to the outside in the pond width direction as shown by the two-dot chain line. By forming the sand collection nozzle 91 in an inverted L-shape and configuring the connection part between the sand collection nozzle 91 and the supply pipe 92 to be rotatable, it is possible to change the discharge direction of the fluid for each discharge port 911. In other words, the shape of the sand collection nozzle 91 in this embodiment and the configuration in which the sand collection nozzle 91 can rotate with respect to the supply pipe 92 correspond to an example of an individual direction changing means.

Figure 9 is a diagram of the water supply system at a wastewater treatment facility.

9, the water supply pump 33 selectively supplies water from the pump well 3 to the stirring nozzle 62, the pit sand collection nozzle 63, the upstream trough first nozzle 831, the upstream trough second nozzle 832, the downstream trough nozzle 84, and the sand collection means 9. The water supply pipe 34 connected to the water supply pump 33 is provided with a supply switching valve Va for switching whether or not to supply fluid to the above-mentioned nozzles and the sand collection means 9, and a relief switching valve Vb for switching whether or not to return the fluid sucked up by the water supply pump to the pump well 3. The pipeline between the supply switching valve Va and the stirring nozzle 62 is provided with a stirring switching valve Vc for switching whether or not to supply fluid to the stirring nozzle 62. The pipeline between the supply switching valve Va and the pit sand collection nozzle 63 is provided with a pit sand collection switching valve Vd for switching whether or not to supply fluid to the pit sand collection nozzle 63. The pipeline between the supply switching valve Va and the upstream trough first nozzle 831 is provided with an upstream trough first switching valve Ve1 for switching whether or not to supply fluid to the upstream trough first nozzle 831. The pipeline between the supply switching valve Va and the upstream trough second nozzle 832 is provided with an upstream trough second switching valve Ve2 that switches whether or not to supply fluid to the upstream trough second nozzle 832. The pipeline between the supply switching valve Va and the downstream trough nozzle 84 is provided with a downstream trough switching valve Vf that switches whether or not to supply fluid to the downstream trough nozzle 84. In addition, the pipelines between the supply switching valve Va and each nozzle header 9a, 9b, 9c, 9d, 9e, and 9f of the sand collecting means 9 are provided with sand collecting switching valves Vg1, Vg2, Vg3, Vg4, Vg5, and Vg6 that switch whether or not to supply fluid to each nozzle header 9a, 9b, 9c, 9d, 9e, and 9f. These switching valves are composed of solenoid valves, and the opening and closing of the valves is controlled by a control device not shown.

Figure 10 is an explanatory diagram showing the water level of the grit basin and the water level sensor.

As shown in Fig. 10, a water level sensor 99 is disposed in the sand collection pit 6 of the settling basin 2. This water level sensor 99 detects a first high water level HHWL at which the water level of the settling basin 2 is above the bottom plane 71, a second high water level THWL that is below the first high water level HHWL and above the upper end position 13b of each covering member 13, 14, 15 (which is approximately the same position as the upper end 8b of the main trough 8, i.e., the opening of the main trough 8, and is also approximately the same position as the lower end 72b of the small trough 72), and a first low water level TLWL that is near the upper end position 13b of each covering member 13, 14, 15. It detects and outputs the first intermediate water level TMWL between the second high water level THWL and the first low water level TLWL, the third high water level HWL below the upper end 8b of the main trough 8 and above the lower end 8a of the main trough 8, the second low water level LWL below in the sand collection pit 6, the second intermediate water level MWL between the third high water level HWL and the second low water level LWL, and the interlock water level LLWL which is even lower than the second low water level LWL.

Figure 11 is a flowchart showing the procedure for sand removal in a wastewater treatment facility.

The operation of the wastewater treatment facility 1 having the above-mentioned configuration will be described with reference to Figures 1, 2, and 11. At a predetermined time when a certain amount of sand has accumulated on the bottom of the grit basin 2, the wastewater treatment facility 1 performs an operation to remove the accumulated sand. This time may be periodically, for example, once a month, or when the total flow rate of wastewater flowing into or discharged from the grit basin 2 reaches a certain amount. In the sand removal operation, first, the inflow gate 42 of the dam device 4 shown in Figure 1 is driven to block the inflow port 411, thereby blocking the inflow of wastewater into the grit basin 2 (step S1). Next, the lifting pump 31 is driven to lower the water level of the grit basin 2. When the water level of the pump well 3 drops to a predetermined value, the lifting pump 31 is stopped (step S2). Then, the water supply pump 33 is driven for a few minutes to discharge the fluid from the stirring nozzle 62 shown in Figure 2. After the water supply pump is stopped, the sand lifting pump 61 is driven. When the water level of the grit basin 2 drops to the second high water level THWL (see FIG. 10), the water supply pump 33 is driven again to discharge fluid from the stirring nozzle 62 shown in FIG. 2. Then, the driving of the sand lifting pump 61 is set to the operation mode A described below (step S3). The sand lifting pump 61 operates in either the operation mode A or the operation mode B. In the operation mode A, the driving is automatically stopped in response to an output from the water level sensor 99 indicating the first low water level TLWL (see FIG. 10), and the driving is resumed in response to an output indicating the second high water level THWL (see FIG. 10). This operation mode A is a mode in which the water level is maintained above the upper end position 13b of each of the cover members 13, 14, and 15. Therefore, in the operation mode A, the cover members 13, 14, 15, the trough first outlet 831a, the trough second outlet 832a, and the trough third outlet 84a are submerged in water. In the operation mode B, the sand lifting pump 61 is automatically stopped in response to an output from the water level sensor 99 indicating the second low water level LWL (see FIG. 10), and is automatically restarted in response to an output indicating the third high water level HWL (see FIG. 10). This operation mode B is a mode in which the water level is maintained below the lower end 72b of the small trough 72. Therefore, the bottom plane 71, the small trough 72, the sand deposited thereon, and the sand collecting means 9 are exposed to the atmosphere. On the other hand, the water supply pump 33 shown in FIG. 1 continues to be driven until the sand removal operation is completed. The sand transported to the sand collecting pit 6 is transported to a sand separator (not shown) outside the settling basin 2 by the sand lifting pump 61 while the sand lifting pump 61 is operating. If the water level sensor 99 detects that the water level has reached the first high water level HHWL or the interlock water level LLWL (see Figure 10), it is assumed that some kind of abnormality has occurred, so an alert is displayed and the wastewater treatment facility 1 stops the sand removal operation.

After that, the agitation nozzle 62 and the upstream trough first nozzle 831 and the upstream trough second nozzle 832 shown in FIG. 2 are discharged for a certain period of time to flow the sand accumulated in the upstream first main trough 815 and the upstream second main trough 816 into the sand collection pit 6 (step S4). In this step S4, the fluid may be discharged for a certain period of time from one of the upstream trough first nozzle 831 and the upstream trough second nozzle 832, and then the fluid may be discharged for a certain period of time from the other. When the discharge of the fluid from the agitation nozzle 62 and the upstream trough first nozzle 831 and the upstream trough second nozzle 832 stops, the sand lifting pump 61 is switched to the operation mode B (step S5). Then, when it is detected that the water level is equal to or lower than the third high water level HWL, the fluid is discharged from the discharge port 911 (see FIG. 6) provided in the fifth nozzle header 9e. This discharge allows the sand accumulated on the bottom plane 71 and the small trough 72 between the right side wall Wb near where the fifth nozzle header 9e is located and the upstream second main trough 816 to flow into the upstream second main trough 816. After a predetermined time has elapsed to allow the sand to flow sufficiently, the sand lifting pump 61 is switched to operation mode A while continuing to discharge the fluid from the discharge port 911 provided in the fifth nozzle header 9e. After that, when it is detected that the water level is equal to or higher than the first intermediate water level TMWL, the discharge of the fluid from the discharge port 911 provided in the fifth nozzle header 9e is stopped (step S6). Then, the fluid is discharged from the stirring nozzle 62 and the upstream trough second nozzle 832 for a certain period of time to send the sand that has flowed into the upstream second main trough 816 to the sand collection pit 6 (step S7). When the discharge of the fluid from the stirring nozzle 62 and the upstream trough second nozzle 832 is stopped, the sand lifting pump 61 is switched to operation mode B (step S8). Then, when it is detected that the water level is equal to or lower than the third high water level HWL, the fluid is discharged from the outlet 911 provided in the second nozzle header 9b. When a predetermined time has elapsed that allows the sand accumulated on the bottom plane 71 and the small trough 72 between the left side wall Wa in the vicinity of where the second nozzle header 9b is disposed and the upstream first main trough 815 to be sufficiently flushed, the sand lifting pump 61 is switched to the operation mode A while continuing the discharge of the fluid from the outlet 911 provided in the second nozzle header 9b. After that, when it is detected that the water level is equal to or higher than the first intermediate water level TMWL, the discharge of the fluid from the outlet 911 provided in the second nozzle header 9b is stopped (step S9). In this embodiment, the discharge direction of the fluid from the outlet 911 in the left side wall Wa, which is in the vicinity of the recessed wall portion Wa2 and the inclined wall portion Wa3, is adjusted so that a certain amount of fluid reaches the left side wall Wa according to the distance from the supply pipe 92 to the left side wall Wa. Therefore, all the sand accumulated on the bottom plane 71 and the small trough 72 between the left side wall Wa near where the second nozzle header 9b is located and the upstream first main trough 815 can be flowed to the upstream first main trough 815. After the discharge of the fluid from the discharge port 911 provided in the second nozzle header 9b is stopped, the fluid is discharged from the stirring nozzle 62 and the upstream trough first nozzle 831 for a certain period of time to send the sand that has flowed to the upstream first main trough 815 to the sand collection pit 6 (step S10). When the discharge of the fluid from the stirring nozzle 62 and the upstream trough second nozzle 832 is stopped, the sand lifting pump 61 is switched to the operation mode B (step S11). Thereafter, similar to the operations of steps S6 to S10 described above, the fluid is discharged from the discharge port 911 provided in the fourth nozzle header 9d and switched to operation mode A after a predetermined time has elapsed (step S12), the fluid is discharged from the stirring nozzle 62 and the upstream trough second nozzle 832 (step S13), switched to operation mode B (step S14), the fluid is discharged from the discharge port 911 provided in the first nozzle header 9a and switched to operation mode A after a predetermined time has elapsed (step S15), and the fluid is discharged from the stirring nozzle 62 and the upstream trough first nozzle 831 (step S16) in this order, so that all the sand deposited on the bottom of the pond upstream of the sand collection pit 6 is carried out to the outside of the settling basin 2. The order in which the fluid is discharged from each nozzle header 9a, 9b, 9d, and 9e may be any order. However, if the sand that has accumulated farther from the sand collection pit 6 is flushed first, the sand that has accumulated closer to the sand collection pit 6 along with the sand to be flushed may collapse into the main trough 8 and accumulate in the main trough, making it difficult to send the sand in the main trough 8 to the sand collection pit 6. For this reason, it is desirable to eject fluid from the second nozzle header 9b and the fifth nozzle header 9e that are closer to the sand collection pit 6, and then eject fluid from the first nozzle header 9a and the fourth nozzle header 9d that are farther from the sand collection pit 6.

After removing the sand accumulated on the upstream side by the above-mentioned operation, the agitation nozzle 62 and the downstream trough nozzle 84 are discharged for a certain period of time to flush the sand accumulated in the downstream main trough 82 into the sand collection pit 6 (step S17). When the discharge of fluid from the agitation nozzle 62 and the downstream trough nozzle 84 is stopped, the sand lifting pump 61 is switched to operation mode B (step S18). Then, when it is detected that the water level is equal to or lower than the third high water level HWL, the fluid is discharged from the discharge port 911 provided in the sixth nozzle header 9f. When a predetermined time has elapsed that allows the sand accumulated on the bottom plane 71 and the small trough 72 between the right side wall Wb near where the sixth nozzle header 9f is located to the downstream main trough 82 to be sufficiently flushed, the sand lifting pump 61 is switched to operation mode A while continuing to discharge the fluid from the discharge port 911 provided in the sixth nozzle header 9f. After that, when it is detected that the water level is equal to or higher than the first intermediate water level TMWL, the discharge of the fluid from the outlet 911 provided in the sixth nozzle header 9f is stopped (step S19). Then, the fluid is discharged from the stirring nozzle 62 and the downstream main trough 82 for a certain period of time to send the sand flowing into the downstream main trough 82 to the sand collection pit 6 (step S20). When the discharge of the fluid from the stirring nozzle 62 and the downstream main trough 82 is stopped, the sand lifting pump 61 is switched to the operation mode B (step S21). Then, similar to the operations of steps S19 and S20 described above, the discharge of the fluid from the outlet 911 provided in the third nozzle header 9c and the switching to the operation mode A after a predetermined time has elapsed (step S22), and the discharge of the fluid from the stirring nozzle 62 and the downstream trough nozzle 84 (step S23) are performed in this order, so that all the sand deposited on the bottom of the pond downstream of the sand collection pit 6 is carried out to the outside of the sand collection basin 2. Finally, the sand accumulated on the sand collection pit slope 6b is flushed into the sand collection pit 6 by ejecting fluid from the sand collection pit nozzle 63 (step S24). Once all of these operations are completed, the water supply pump 33 is stopped, and after a predetermined time has elapsed, the sand lifting pump 61 is also stopped.

In this sand removal operation, when the sand lifting pump 61 is switched from operation mode A to operation mode B, the supply of fluid to the grit basin 2 is stopped until it is detected that the water level is equal to or lower than the third high water level HWL. This allows the water level to drop faster. At that time, in order to stop the supply of fluid to the grit basin 2, the supply switching valve Va shown in FIG. 9 is closed and the relief switching valve Vb is opened, and the fluid pumped up by the feed water pump 33 is returned to the pump well 3. In this way, the supply of fluid to the grit basin 2 can be stopped while the feed water pump 33 continues to be driven. In the sand removal operation described above, steps S4, S7, S10, S13, S16, S17, S20, and S23 each correspond to an example of the underwater discharge process. Also, steps S6, S9, S12, S15, S19, and S22 each correspond to an example of the atmospheric discharge process. That is, in this embodiment, the process of performing the underwater discharge process after the atmospheric discharge process is regarded as one set of sand collection processes (combinations of steps S6 and S7, S9 and S10, S12 and S13, S15 and S16, S19 and S20, and S22 and S23), and the sand collection process is performed multiple times. In addition, the underwater discharge process (step S4) is performed before the first sand collection process (steps S6 and S7). If sand remains in the main trough 8 during the atmospheric discharge process, the sand that has been washed into the main trough 8 by the atmospheric discharge process may be piled up on the remaining sand, and a large amount of sand may accumulate in the main trough 8. In addition, there is a risk that the main trough 8 may be filled with sand during the atmospheric discharge process, and the overflowing sand may remain on the bottom plane 71. In this embodiment, the sand washed into the main trough 8 from the bottom plane 71 is transported to the sand collection pit 8 in one set of sand collection processes, so that no sand remains in the main trough 8. In addition, because the underwater discharge process (steps S4 and S17) is performed before the first sand collection process (combinations of steps S6 and S7, and S19 and S20), no sand remains in the main trough 8 even during the first sand collection process.

In this embodiment, when the sand removal operation is being performed, the amount of fluid pumped by the sand lifting pump 61 is set to be slightly greater than the amount of fluid pumped by the water supply pump 33. For this reason, the sand lifting pump 61 is stopped and restarted several times while the sand removal operation is being performed. However, if the sand lifting pump 61 is repeatedly driven and stopped, the pump life will be reduced due to the inrush current at the start of driving. As a countermeasure, the pumping capacity of the water supply pump 33 and the pumping capacity of the sand lifting pump 61 may be made closer to each other to minimize the change in water level during the sand removal operation. Also, when the water level sensor 99 detects that the water level has dropped to the first intermediate water level TMWL in operation mode A and the second intermediate water level MWL in operation mode B, additional fluid may be discharged from other nozzles in addition to the nozzles that are discharging fluid at that time. By increasing the number of nozzles that discharge fluid, the load (throttling resistance) on the flow of the fluid is reduced, so that the fluid pumped by the water supply pump 33 increases, and as a result, more fluid can be supplied to the grit basin 2. This makes it difficult for the water level to reach the first low water level TLWL or the second low water level LWL, so that the number of times the sand lifting pump 61 stops and restarts can be reduced. Here, it is preferable that the other nozzle is a sand collecting nozzle 91 provided in the nozzle header scheduled to discharge next. By discharging fluid from the nozzle header scheduled to discharge next, the sand in the bottom plane 71 and the small trough 72 to be discharged next can be preliminarily discharged, so that the sand residue can be further suppressed. The additional fluid to be discharged may be a fluid stored in another facility. Furthermore, the sand lifting pump 61 may be configured not to be stopped even when the water level reaches the first low water level TLWL or the second low water level LWL, but to supply the fluid stored in the other facility to the settling basin 2 in addition to the fluid pumped up by the feed water pump 33 instead. In this configuration, the supply of the fluid stored in the other facility to the settling basin 2 may be stopped when the water level reaches the second high water level THWL or the third high water level HWL. By reducing the number of times the sand pump 61 is stopped and started repeatedly, deterioration of the sand pump 61 can be suppressed and its lifespan can be extended.

In this embodiment, the discharge port 911 is located near the bottom of the settling basin 2. In contrast, for example, JP 2011-245391 proposes a settling basin 2 in which a sand collecting means 9 with a discharge port 911 is located in the upper part of the settling basin 2, and fluid is discharged toward the side wall W so that the fluid flows down the surface of the side wall W.

Figure 12 is a cross-sectional view of a sedimentation basin similar to Figure 5, showing a case where a sand collection means is placed in the upper part of the sedimentation basin and a case where a sand collection means is placed near the bottom of the sedimentation basin. In Figure 12, the sand collection means placed in the upper part of the sedimentation basin is shown by a two-dot chain line. Furthermore, of the lines showing the piping and side walls, the lines that intersect with the sand collection means placed in the upper part of the sedimentation basin are shown with the intersecting portions omitted.

In FIG. 12, a virtual upper nozzle header 90 is shown in the upper part of the grit basin 2. This upper nozzle header 90 is used in place of the first nozzle header 9a. A dust collector 5 standing at an angle is arranged at the upstream end of the grit basin 2. The sand collecting means 9 needs to be arranged so as not to interfere with the dust collector 5. Therefore, the upper nozzle header 90 arranged in the upper part of the grit basin 2 is located downstream compared to the case where it is arranged near the bottom of the grit basin 2 as shown in FIG. 12. In other words, the upper nozzle header 90 has to be arranged downstream by a distance S from the first nozzle header 9a. As described above, the upper parts of the endless chain 51 and the filter screen 53 constituting the dust collector 5 overlap with the bottom plane 71 and the main trough 8 in the longitudinal direction. For this reason, even if a fluid is discharged from the upper nozzle header 90, there will be a part of the bottom plane 71 that the discharged fluid does not reach. If the dust collector 5 and the upper nozzle header 90 are arranged upstream by a distance S from the positions shown in FIG. 5 and FIG. 12, the fluid can reach the most upstream part of the bottom plane 71. However, this arrangement increases the longitudinal length of the grit basin 2. As a result, the grit basin 2 becomes larger, a large amount of land is required for the installation of the grit basin 2, and the grit basin 2 becomes expensive. In the grit basin 2 of this embodiment, the first nozzle header 9a is arranged near the bottom of the grit basin 2, so compared to the case where the upper nozzle header 90 arranged in the upper part of the grit basin 2 is used, the grit basin 2 can be prevented from becoming larger and can be provided at a low cost.

Next, modified examples of the connection surface 73 will be described. In the modified examples described below, differences from the embodiment shown in Figures 1 to 11 will be mainly described, and components with the same names as those in the embodiment shown in Figures 1 to 11 will be described using the same reference numerals as used above, and duplicate descriptions will be omitted.

Figure 13 is a cross-sectional view similar to Figure 3, showing a modified example of the connection surface.

In this modified example, the connection surface 73 is formed as a curved surface, which is different from the example shown in FIG. 3. The connection surface 73 is composed of a ridge portion 731 extending along the longitudinal direction, a first connection surface 732, and a second connection surface 733. As shown in FIG. 13, the first connection surface 732 and the second connection surface 733 have a cross-sectional shape of a quarter circle. In other words, the connection surface 73 is composed of a semi-cylindrical surface that protrudes upward as a whole. The ridge portion 731 is composed of the upper end line of the semi-cylindrical shape. In this modified example, as in the example shown in FIG. 3, sand that settles to the connection surface 73 in the wastewater in the grit basin 2 is likely to slide off the connection surface 73 due to its own weight. However, since the inclination angle of the tangent plane of the connection surface 73 becomes gentle near the ridge portion 731, there is a risk that sand will remain in that vicinity. On the other hand, the thickness of the concrete constituting the connection surface 73 in the pond width direction is thick even in the vicinity of the ridge line 731, which has the effect of making the ridge line 731 less likely to be damaged. One of the first connection surface 732 and the second connection surface 733 may be formed flat as in the example shown in Figure 3, and the other may be formed curved as in the modified example shown in Figure 13. Furthermore, one or both of the first connection surface 732 and the second connection surface 733 may be formed as a surface that combines a curved surface and a flat surface.

Next, we will explain modified examples of the sand collection means 9.

Figure 14(a) shows a first modified example of the supply pipe and sand collection nozzle shown in Figure 8, and Figure 14(b) shows a second modified example of the supply pipe and sand collection nozzle shown in Figure 8.

This first modified example differs from the example shown in FIG. 8(a) in that the supply pipe 92 does not have a lap joint 934, the supply pipe 92 and the branch pipe 932 are flange-connected, and the sand collection nozzle 91 is provided with a ball joint 912. In FIG. 14(a), the sand collection nozzle 91 corresponding to the convex wall portion Wa1 is shown in solid lines, and the sand collection nozzle 91 corresponding to the concave wall portion Wa2 is shown in two-dot chain lines. In this modified example, a ball joint 912 is provided between the supply pipe 92 and each discharge port 911. This ball joint 912 allows the discharge direction of the fluid to be changed steplessly not only in the rotational direction around the axis of the supply pipe 92, but also in various other directions. Therefore, it is possible to finely adjust the discharge direction for each discharge port 911. It is also possible to provide a lap joint 934 on the supply pipe 92 and further provide a ball joint 912 on the sand collection nozzle 91. In this case, the lap joint 934 corresponds to an example of a collective change means, and the ball joint 912 corresponds to an example of an individual direction change means.

In the second modified example, the lap joint 934 is not arranged on the supply pipe 92, the supply pipe 92 and the branch pipe 932 are flange-connected, and a plurality of mounting parts 924 of the sand collection nozzle 91 are formed in the circumferential direction of the supply pipe 92, which is different from the example shown in FIG. 8(a). In FIG. 14(b), the sand collection nozzle 91 corresponding to the convex wall part Wa1 is shown in solid lines, and the sand collection nozzle 91 corresponding to the concave wall part Wa2 is shown in two-dot chain lines. In this modified example, six mounting parts 924 of the sand collection nozzle 91 are formed in the circumferential direction of the supply pipe 92. As a result, after the supply pipe 92 is fixed to the branch pipe 932, the sand collection nozzle 91 can be mounted on any one of the six mounting parts 924. Before mounting the sand collection nozzle 91, plug members are attached to all mounting parts 924. When mounting the sand collection nozzle 91, the plug members are removed before mounting the sand collection nozzle 91. Alternatively, a lap joint 934 may be disposed on the supply pipe 92, and the mounting portion 924 may be formed on the supply pipe 92. In this case, the lap joint 934 corresponds to an example of a collective change means, and the mounting portion 924 corresponds to an example of an individual direction change means. In this modification, the mounting portions 924 are formed in six places in the circumferential direction, but the number of mounting portions 924 may be two or more, five or less, or seven or more.

Next, we will explain modified examples of the main trough 8, each cover member 13, 14, 15, and the bottom plane 71.

Figure 15 is a cross-sectional view similar to Figure 5 showing a modified main trough, cover member, and bottom surface.

This modified example differs from the example shown in FIG. 5 in that the main trough 8, the covering members 13, 14, 15, and the bottom plane 71 are arranged with an inclination downward toward the sand collection pit 6. In FIG. 15, the inclination of the main trough 8, the covering members 13, 14, 15, and the bottom plane 71 is exaggerated in order to clearly show the inclination. As shown in FIG. 15, the bottom plane 71 is inclined downward by about 0.5 degrees toward the sand collection pit 6 so that the end on the sand collection pit 6 side is the deepest. In addition, the upstream first main trough 815 and the downstream main trough 82 are also inclined downward by about 0.5 degrees toward the sand collection pit 6, like the bottom plane 71, and the part connected to the sand collection pit 6 is the deepest. Furthermore, the first covering member 13 and the third covering member 15 are also inclined downward by about 0.5 degrees toward the sand collection pit 6, and the part connected to the sand collection pit 6 is the deepest. The upstream first main trough 815 and second cover member 14, not shown in FIG. 15, are also inclined downward by about 0.5 degrees toward the sand collection pit 6. In this modification, the provision of each cover member 13, 14, 15 not only increases the sand transport force in the main trough 8, but also assists the flow of fluid discharged into each cover member 13, 14, 15 by inclining the main trough 8 and each cover member 13, 14, 15. This allows the sand accumulated in the main trough 8 to be transported a longer distance. The inclination angle can be set appropriately according to the length of the main trough 8.

Figure 16 is a cross-sectional view similar to Figure 8(a) showing the bottom surface near the upstream end of the settling basin and the bottom surface near the sand collection pit in the modified example shown in Figure 15. The side walls and bottom surface are also shown in Figure 16.

Figure 16 shows the difference in the height position of the bottom plane 71 when the bottom plane 71 is inclined downward toward the sand collection pit 6 side so that the end on the sand collection pit 6 side is the deepest as shown in Figure 15. In Figure 16, the bottom plane 71 near the upstream end of the settling basin 2 is shown by a solid line, and the bottom plane 71 near the sand collection pit 6 is shown by a two-dot chain line. As shown in Figure 16, in this case, the bottom plane 71 is located at a lower position near the sand collection pit 6 than the bottom plane 71 near the upstream end of the settling basin 2. As shown in the figure, even if a fluid is discharged from the discharge port 911 at the same position, the height position of the bottom plane 71 is different between the upstream end of the settling basin 2 and the vicinity of the sand collection pit 6, so that a difference in distance Y occurs in the point where the discharged fluid reaches the bottom plane 71. In particular, in a settling basin 2 with a long longitudinal length, the distance Y becomes long, and even if the discharge direction is optimal for one of the upstream end of the settling basin 2 and the vicinity of the sand collection pit 6, it may be an inefficient discharge direction for the other. In this embodiment, the direction in which the fluid is discharged from the discharge port 911 can be changed, so the fluid can be discharged in the optimal direction according to the height of the bottom plane 71 (the distance from the supply pipe 92 to the bottom plane 71).

Next, we will explain a modified example in which the height of the main trough 8 is increased.

Figure 17 is an explanatory diagram similar to Figure 10, showing an example of water level detection when the height of the main trough is increased.

In the example shown in FIG. 10, each of the cover members 13, 14, 15 was formed at a height exceeding half the height of the main trough 8. The upper end position 13b of each of the cover members 13, 14, 15 was approximately the same position as the lower end 72b of the small trough 72 (the upper end 8b of the main trough 8). As described above, the operation mode A of the sand lifting pump 61 is a control mode in which each of the cover members 13, 14, 15 is maintained submerged in water, so it is necessary to set the first low water level TLWL above the upper end position 13b of each of the cover members 13, 14, 15. In addition, the operation mode B of the sand lifting pump 61 is a control mode in which the water level is maintained below the lower end 72b of the small trough 72, so it is necessary to set the third high water level HWL below the lower end 72b of the small trough 72. In the example shown in Fig. 10, in order to satisfy the condition that the first low water level TLWL is set above the upper end position 13b and the third high water level HWL is set below the lower end 72b, the third high water level HWL must be set below the first low water level TLWL. As a result, the water level maintenance ranges in the operation modes A and B do not overlap, and when switching from one mode to the other mode, a waiting time occurs until the water level enters the range of the other mode. As shown in Fig. 17, when the height of the main trough 8 is increased and each of the cover members 13, 14, and 15 is arranged in the lower part of the main trough 8, the upper end positions 13b of each of the cover members 13, 14, and 15 are located below the lower end 72b of the small trough 72. Therefore, even if the above condition is satisfied, the third high water level HWL can be set above the first low water level TLWL. In other words, a portion of the water level range D1 in operation mode A and a portion of the water level range D2 in operation mode B can be made to overlap, eliminating or reducing the waiting time after switching modes.

The present invention is not limited to the above-mentioned embodiment and modified examples, and various modifications can be made within the scope of the claims. For example, in this embodiment, the present invention is used in the grit basin 2 of the sewage treatment facility 1 into which sewage and rainwater flow, but it can also be applied to the grit basin of a rainwater treatment facility into which only rainwater flows. In this embodiment, the sand accumulated on the bottom plane 71 and small trough 72 upstream of the sand collection pit 6 is poured, and then the sand accumulated on the bottom plane 71 and small trough 72 downstream of the sand collection pit 6 is poured, but the sand accumulated on the bottom plane 71 and small trough 72 downstream may be poured first. In this embodiment, the dust remover 5 and the protruding wall 10 are disposed at the upstream end of the grit basin 2, but the dust remover 5 and the protruding wall 10 may be disposed at the downstream end of the grit basin 2. When the dust collector 5 and the protruding wall 10 are disposed at the downstream end of the grit basin 2, two downstream main troughs 82 are provided and disposed on the left side wall Wa side and the right side wall Wb side of the protruding wall 10, respectively. Then, the ridge portion, the first connection surface, and the second connection surface are formed between the two downstream main troughs 82, except for the area where the protruding wall 10 is provided. In addition, in this embodiment, one outlet for discharging the fluid into the transport space FS is provided at the end (tip portion) of the main trough 8 opposite to the sand collection pit 6, but a nozzle having an outlet may be additionally provided at the intermediate position or the like in the extension direction of each of the cover members 13, 14, 15. In particular, when the length of each of the cover members 13, 14, 15 in the extension direction is long or the discharge pressure of the fluid is low, it is desirable to add a nozzle at the intermediate position or the like. In this embodiment, the fluid is discharged into the transport space FS when each of the cover members 13, 14, and 15 is completely submerged in water, but if a part of each of the cover members 13, 14, and 15 is submerged in water, the fluid may be discharged in a state where the atmosphere remains in the transport space FS. In this embodiment, the fluid is discharged in a state where the trough first outlet 831a, the trough second outlet 832a, and the trough third outlet 84a are completely submerged in water, but the fluid may be discharged in a state where a part of the outlets 831a, 832a, and 84a is submerged in water and the remaining part is exposed to the atmosphere. However, in these cases, loss occurs in the flow of the discharged fluid, especially at the interface between the atmosphere and water. Therefore, it is preferable to discharge the fluid from the outlets 831a, 832a, and 84a when each of the cover members 13, 14, and 15 and the trough first outlet 831a, the trough second outlet 832a, and the trough third outlet 84a are completely submerged in water.

According to this embodiment or its modified example, sand can be efficiently collected. In addition, sand accumulated on the bottom plane 71, the small trough 72, and the connection surface 73 can be washed away by the fluid without remaining. In addition, even in a settling basin in which the left side wall Wa or the right side wall Wb is not formed in a straight line, the straight supply pipe 92 can be used, so that the settling basin 2 can be provided at low cost. In addition, even if the shape of the side wall W is unknown when designing the settling basin 2 or when creating the supply pipe 92, the discharge direction can be adjusted when constructing the settling basin 2, so that it can flexibly accommodate settling basins 2 of various shapes. Furthermore, the sand that has settled on the connection surface 73 slides down the first connection surface 732 or the second connection surface 733 and is deposited in the upstream first main trough 815 or the upstream second main trough 816, so that no sand remains between the upstream first main trough 815 and the upstream second main trough 816. In this embodiment, the inclination angle of the first bottom surface 711 and the second bottom surface 712 is a gentle inclination angle (about 5 degrees) that allows the accumulated sand to be washed away by the fluid discharged from the discharge port 911. This allows the settling basin 2 to be created without digging deep into the ground. On the other hand, by making the connection surface 73 at a steeper angle than the first bottom surface 711 and the second bottom surface 712, the sand that has settled on the connection surface 73 can be deposited in the upstream first main trough 815 or the upstream second main trough 816, even though the fluid discharged from the discharge port 911 does not reach the connection surface 73.

In addition, many of the sedimentation basins 2 have a longitudinal length of 20 meters or more. In conventional sedimentation basins 2, the main trough 8 is inclined downward toward the sand collection pit 6 by, for example, 1 degree. For this reason, the end (rear end) of the main trough 8 on the side of the pond edge is located at a deeper position proportional to the length of the sedimentation basin 2 compared to the depth position at which the end (front end) of the main trough 8 is located. In addition, since the bottom plane 71 is formed at the same inclination angle as the main trough 8, the bottom plane 71 is also located at a deeper position on the sand collection pit 6 side. When the longitudinal length of the sedimentation basin 2 is long, the main trough 8 and the sand collection pit 6 side part of the bottom plane 71 are located at a deeper position compared to when the longitudinal length of the sedimentation basin 2 is short. When constructing the sedimentation basin 2, the ground is excavated below the deepest position of the sedimentation basin 2, and then the sedimentation basin 2 is formed with concrete. If the main trough 8 and the bottom plane 71 are inclined, the sand collection pit 6 is placed at a deeper position than if they were not inclined, so the ground needs to be dug deep, and the excavation work is time-consuming. In addition, when forming the bottom plane 71 with concrete from the dug position, it is necessary to gradually thicken the concrete from the sand collection pit 6 side toward the end of the sand collection basin in order to incline the bottom plane 71, and a large amount of concrete is used. This causes a problem that the sand collection basin 2 becomes expensive. In this embodiment, the covering members 13, 14, and 15 are provided to increase the sand collection efficiency, so that the sand in the main trough 8 can be transported to the sand collection pit 6 even if the inclination angle of the main trough 8 and the bottom plane 71 is made gentle. This inclination angle is preferably 0 degrees or more and less than 1 degree, and more preferably 0 degrees or more and 0.5 degrees or less. By making the inclination angle gentle, it is not necessary to dig deep into the ground, and the amount of concrete used is small, so the sand collection basin 2 can be made inexpensively.

The following inventive concepts can also be extracted from the settling tank of this embodiment:

In a settling basin where sand contained in the received water settles,
A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction;
A bottom surface provided at the bottom of the pond and connected to the groove;
a plurality of outlets for discharging a fluid for causing the sand that has settled on the bottom surface to flow from the side wall toward the groove;
a supply pipe provided with the discharge port,
A sedimentation basin characterized in that the multiple discharge outlets include one that discharges fluid toward the center of the pond width direction relative to the axis of the supply pipe in which the discharge outlet is provided, and one that discharges fluid toward the outside of the pond width direction relative to the axis of the supply pipe.

In addition, the following inventive concepts can be extracted from the settling tank of this embodiment.

In a settling basin where sand contained in the received water settles,
A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction;
A bottom surface provided at the bottom of the pond and connected to the groove;
a discharge port that discharges a fluid for causing the sand that has settled on the bottom surface to flow from the side wall side toward the groove,
A settling basin characterized in that the direction of the fluid discharged from the discharge port is changeable.

In this settling basin,
A supply pipe provided with the discharge port;
a mother pipe for supplying a fluid to the supply pipe;
The supply pipe may be rotatable relative to the mother pipe about an axial direction of the supply pipe.

In addition, in the settling basin,
The supply pipe may have a plurality of outlets.

Furthermore, in the settling basin,
a supply pipe provided with the discharge port,
The discharge port may be capable of changing the discharge direction of the fluid by a ball joint disposed between the supply pipe and the discharge port.

In addition, in the settling basin,
The discharge port has a supply pipe detachably provided therein,
The supply pipe may have a plurality of mounting portions, to which the discharge ports are attached, in a circumferential direction of the supply pipe.

In addition, the following inventive concepts can be extracted from the settling tank of this embodiment.

In a settling basin where sand contained in the received water settles,
A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction;
A bottom surface provided at the bottom of the pond and connected to the groove;
a discharge port that discharges a fluid for causing the sand that has settled on the bottom surface to flow from the side wall side toward the groove; and a supply pipe that is disposed closer to the center in the pond width direction than the side wall and in which a plurality of the discharge ports are arranged in the predetermined direction,
The supply pipe has a first region extending from the side wall in a pond width direction at a first interval, and a second region extending from the side wall in a pond width direction at a second interval,
A sedimentation basin characterized in that the discharge direction of the fluid from the discharge outlet arranged in the first area and the discharge outlet arranged in the second area can be changed independently of each other.

The number of outlets provided in the first region may be multiple or may be one. When the number of outlets provided in the first region is multiple, it is preferable that the discharge direction of the fluid from these outlets can be changed collectively. The number of outlets provided in the second region may also be multiple or may be one. When the number of outlets provided in the second region is multiple, it is preferable that the discharge direction of the fluid from these outlets can be changed collectively. The term "changeable collectively" as used herein means, for example, that the first region part and the second region part of the supply tube rotate separately around the axial direction of the supply tube. In addition, the supply tube may have rotatable parts at both ends of the first region, and rotatable parts at both ends of the second region. The supply tube may be a straight tube, or may have a slightly curved part.

the supply pipe is provided with a third region connecting the first region and the second region,
The ejection port provided in the third region may be capable of changing the ejection direction of a fluid, separately from the ejection port provided in the first region and the ejection port provided in the second region.

The third region may be an inclined region in which the distance to the side wall changes gradually in the extension direction, or may be a region in which the distance changes stepwise.

The number of outlets provided in the third region may be multiple or may be one. When there are multiple outlets provided in the third region, it is preferable that the discharge direction of the fluid from these outlets can be changed collectively. Here, "changeable collectively" is realized, for example, by rotating the portion of the supply pipe in the third region around the axial direction of the supply pipe separately from the portion of the first region and the portion of the second region.

In addition, the following inventive concepts can be extracted from the settling tank of this embodiment.

In a settling basin where sand contained in the received water settles,
A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction;
A bottom surface provided at the bottom of the pond and connected to the groove;
a plurality of discharge ports disposed opposite the side wall and configured to discharge a fluid for causing the sand that has settled on the bottom surface to flow from the side wall toward the groove;
The side wall has a convex wall portion protruding toward the center in the pond width direction and extending in the predetermined direction, and a concave wall portion concave toward the outside in the pond width direction and extending in the predetermined direction,
the discharge port is disposed opposite the convex wall portion and the concave wall portion,
A sedimentation basin characterized by being equipped with a direction changing means capable of changing the discharge direction of a fluid discharged from an outlet arranged opposite the concave wall portion to a different direction from the discharge direction of a fluid discharged from an outlet arranged opposite the convex wall portion.

Furthermore, the following inventive concepts can be extracted from the settling tank of this embodiment:

In a settling basin where sand contained in the received water settles,
A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction;
A bottom surface provided at the bottom of the pond and connected to the groove;
A supply pipe disposed opposite the side wall and extending in the predetermined direction;
a plurality of discharge ports disposed in the supply pipe for discharging a fluid for causing the sand that has settled on the bottom surface to flow from the side wall side toward the groove;
The side wall has a convex wall portion protruding toward the center in the pond width direction and extending in the predetermined direction, and a concave wall portion concave toward the outside in the pond width direction and extending in the predetermined direction,
the discharge ports are disposed at positions facing the convex wall portion and at positions facing the concave wall portion,
A settling basin characterized in that the supply pipe is provided with a direction changing means between an outlet located opposite the convex wall portion and an outlet located opposite the concave wall portion, which is capable of changing the discharge direction of the fluid discharged from the outlet.

In addition, in this settling basin,
The side wall has an inclined wall portion formed between the convex wall portion and the concave wall portion and extending in a direction inclined with respect to the predetermined direction and the pond width direction,
The discharge port is also disposed at a position facing the inclined wall portion,
the supply pipe includes a first direction changing means between a discharge port arranged opposite to the convex wall portion and a discharge port arranged opposite to the inclined wall portion, the first direction changing means being capable of changing a discharge direction of a fluid discharged from the discharge port,
A second direction changing means may be provided between the multiple outlets arranged opposite the recessed wall portion and the outlets arranged opposite the inclined wall portion, the second direction changing means being capable of changing the discharge direction of the fluid discharged from the outlets.

In addition, the following inventive concepts can be extracted from the settling tank of this embodiment:

In a settling basin where sand contained in the received water settles,
A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction;
A bottom surface provided at the bottom of the pond and connected to the groove;
a plurality of outlets for discharging a fluid for causing the sand that has settled on the bottom surface to flow from the side wall toward the groove;
a collective direction changing means capable of collectively changing the ejection direction of fluid ejected from at least two of the plurality of ejection ports;
A settling basin characterized by being equipped with an individual direction changing means capable of changing the discharge direction of the fluid discharged from the discharge outlet for each discharge outlet.

In addition, the following inventive concepts can be extracted from the settling tank of this embodiment.

In a settling basin, water is allowed to flow downward in a direction perpendicular to the width of the basin between one side wall and the other side wall that constitute the end faces in the width direction of the basin, and sand contained in the water is allowed to settle.
A first groove and a second groove are provided on the bottom of the pond, spaced apart in the pond width direction, and extending in the perpendicular direction;
a protruding wall formed between the first groove and the second groove and protruding upward from the bottom of the pond;
A sedimentation basin characterized in that a ridge portion extending along the perpendicular direction, a first connection surface connecting the ridge portion and the first groove, and a second connection surface connecting the ridge portion and the second groove are formed in the portion of the bottom of the basin excluding the area between the first groove and the second groove in which the protruding wall is provided.

the first connection surface is an inclined surface that is inclined downward from the ridge portion toward the first groove,
The second connection surface may be an inclined surface that slopes downward from the ridge portion toward the second groove.

The first groove is provided on the one side wall side,
The second groove is provided on the other side wall side,
a first bottom surface formed between the one side wall and the first groove and inclined downward toward the first groove;
a second bottom surface formed between the other side wall and the second groove and inclined downward toward the second groove;
The inclination angle of each of the first connection surface and the second connection surface may be steeper than the inclination angle of the first bottom surface and the second bottom surface.

a one-side discharge port that discharges a fluid for causing the sand that has settled on the first bottom surface to flow from the one side wall side toward the first groove;
The sand trap may further include an other-side discharge port that discharges a fluid for causing the sand that has settled on the second bottom surface to flow from the other side wall side toward the second groove.

The system may also be provided with two dust removers disposed between the one side wall and the protruding wall, and between the other side wall and the protruding wall, respectively, for removing impurities contained in the received water.

In addition, the following inventive concepts can be extracted from the settling tank of this embodiment.

In a settling basin, water is allowed to flow downward in a direction perpendicular to the width of the basin between one side wall and the other side wall that constitute the end faces in the width direction of the basin, and sand contained in the water is allowed to settle.
A first groove and a second groove are provided on the bottom of the pond, spaced apart in the pond width direction, and extending in the perpendicular direction;
A sand collection pit provided at the bottom of the pond, to which the first groove is connected and to which the second groove is connected;
a protruding wall formed between the first groove and the second groove and protruding upward from the bottom of the pond;
A settling basin characterized in that a ridge portion extending along the perpendicular direction, a first connection surface connecting the ridge portion and the first groove, and a second connection surface connecting the ridge portion and the second groove are formed in the portion of the bottom of the basin between the first groove and the second groove and between the sand collection pit and the protruding wall.

The settling basin described above is a settling basin in which sand contained in the received water settles to the bottom of the basin.
A groove is provided in the bottom of the pond and extends in a predetermined direction;
a first outlet port that discharges a fluid in the predetermined direction into the water stored in the groove;
A bottom surface provided at the bottom of the pond and connected to the groove;
a second discharge port that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from a side wall of the settling basin toward the groove;
The nozzle may further include a cover member that covers a periphery of an imaginary axis extending from a center of the first outlet in the predetermined direction and has an opening at a lower end portion.

In this settling basin, the opening of the cover member may be positioned below the center of the groove in the height direction.

According to this embodiment, the opening of the cover member and the sand accumulated below the groove are close to each other, making it easier to suck up the sand accumulated in the groove into the cover member.

The above-described sand collection method is a method for collecting sand accumulated on the bottom of a settling basin having a groove extending in a predetermined direction and a bottom surface connected to the groove, in which sand contained in received water is allowed to settle on the bottom of the basin, the method comprising the steps of:
an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water stored in the groove;
and an atmospheric discharge step of discharging a fluid from a second discharge port into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall side toward the groove,
The underwater discharge process may be characterized in that it is a process of discharging fluid into a space covered by a covering member having an opening at a lower end portion and covering a periphery of a virtual axis extending from the center of the first discharge port toward the specified direction.

In the sand collecting method, the underwater discharge step is performed in a state where a water level is maintained above the covering member,
The discharge into the atmosphere step may be a step performed in a state where a water level is maintained below the bottom surface.

In the underwater discharge process, the fluid is discharged from the first discharge port into the water while the cover member is filled with fluid, so there is little loss of discharge pressure and a strong fluid flow can be created inside the cover member. In addition, in the atmospheric discharge process, the sand accumulated on the bottom surface is exposed to the atmosphere, so even if the discharge pressure of the fluid discharged from the second discharge port is weak, the sand accumulated on the bottom surface can be flushed away.

In addition, in this sand collection method, the process of performing the atmospheric discharge process followed by the underwater discharge process may be regarded as one set of sand collection processes, and the sand collection process may be performed multiple times.

If the sand that was flushed into the groove by the atmospheric discharge step remains in the groove, the sand that was flushed into the groove by the next atmospheric discharge step may be piled on top of the remaining sand, resulting in a large amount of sand accumulating in the groove. If a large amount of sand accumulates, the sand may become an obstacle, making it difficult to transport the sand in the groove in the underwater discharge step. In addition, even if sand is tried to be flushed into the groove by the next atmospheric discharge step, the groove may be filled with sand, and the overflowing sand may remain on the bottom. In this sand collection method, the process of flushing into the groove by the atmospheric discharge step and the process of transporting the sand in the groove by the underwater discharge step are treated as a set of sand collection processes, so that the sand that was flushed into the groove in the previous sand collection process does not remain in the groove during the next sand collection process. As a result, in the atmospheric discharge step in the next sand collection process, the sand can be flushed toward the groove from which the sand has been removed, preventing the sand from overflowing from the groove. In addition, in the underwater discharge step in the next sand collection process, it is possible to prevent the large amount of sand that has accumulated in the groove from making it difficult to transport the sand in the groove.

Furthermore, in this sand collection method, the underwater discharge process may be carried out before carrying out the sand collection process multiple times.

By transporting the sand that has settled in the grooves using the underwater discharge process before the first sand collection process, the sand can be directed toward the grooves from which it has been removed during the atmospheric discharge process in the first sand collection process, preventing the sand from overflowing from the grooves. In addition, the underwater discharge process in the first sand collection process can prevent a situation in which the large amount of sand that has accumulated in the grooves makes it difficult to transport the sand in the grooves.

The settling basin described above is a settling basin in which sand contained in the received water settles to the bottom of the basin.
A groove is provided in the bottom of the pond and extends in a predetermined direction;
a first outlet port that discharges a fluid in the predetermined direction into the water stored in the groove;
A bottom surface provided at the bottom of the pond and connected to the groove;
a second discharge port that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall of the settling basin toward the groove;
a cover member that covers a periphery of an imaginary axis extending from a center of the first discharge port in the predetermined direction and has an opening at a lower end portion,
the bottom surface has a bottom plane formed between the side wall and the groove,
The groove and the bottom plane are characterized in that they are horizontal toward the predetermined direction or inclined downward toward the predetermined direction at an angle of less than 1 degree.

Here, the covering member may have an inclined surface in the upper portion thereof that slopes downward in the width direction of the groove. This inclined surface may be formed of a flat surface or a curved surface. If the inclined surface is formed of a curved surface, it is preferable that the curved surface has a curved shape with an upward convex shape. The covering member may also be cylindrical in shape with an opening at the lower end.

In this settling basin, the fluid discharged in a predetermined direction from the first outlet is prevented from diffusing in a radial direction perpendicular to the predetermined direction by the covering member, creating a strong fluid flow within the covering member. This flow creates a pressure difference between the inside and outside of the covering member, and the sand accumulated in the groove is sucked into the covering member through an opening at the bottom end of the covering member. The sucked-in sand is then transported by the flow of fluid within the covering member. In other words, the flow of the fluid discharged from the first outlet can be effectively used for transport, so the sand accumulated in the groove can be efficiently transported.

In this settling basin, the bottom plane is located above the upper end position of the cover member,
The second outlet may be configured to outlet the fluid in a state where the water level is maintained below an upper end position of the covering member.

The above-described sand collection method is a method for collecting sand that has accumulated on a bottom of a settling basin, the bottom of which has a groove extending in a predetermined direction and inclined horizontally toward the predetermined direction or downwardly toward the predetermined direction at an angle of less than 1 degree, and a bottom surface connected to the groove and having a bottom plane that is horizontally toward the predetermined direction or inclined downwardly toward the predetermined direction at an angle of less than 1 degree, the method comprising:
an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water stored in the groove;
and an atmospheric discharge step of discharging a fluid from a second discharge port into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall side toward the groove,
The underwater discharge process is characterized in that it is a process of discharging fluid into a space covered by a covering member that has an opening at a lower end portion and covers the periphery of a virtual axis extending from the center of the first discharge port toward the specified direction.

The underwater ejection process may be a process performed in a state where the covering member is filled with a fluid, or may be a process performed in a state where air remains inside the covering member. The underwater ejection process may also be a process performed in a state where the first ejection port is completely submerged in water, or may be a process performed in a state where a portion of the first ejection port is submerged in water and the remaining portion is exposed to the air.

According to this sand collection method, the fluid discharged in a predetermined direction from the first discharge port in the underwater discharge process creates a strong fluid flow within the covering member, sucking the sand accumulated in the groove into the inside of the covering member and transporting it in a predetermined direction, so that the sand can be efficiently transported and collected. In addition, the fluid discharged into the atmosphere from the second discharge port in the atmospheric discharge process does not encounter water resistance, so the sand accumulated on the bottom surface can be efficiently flushed away.

In addition, in this sand collection method, the atmospheric discharge process may be a process carried out in a state where the water level is maintained further below the upper end position of the covering member, the upper end position of which is located below the bottom plane.
The above-described sand collection method is a method for collecting sand accumulated on a bottom of a settling basin, which allows sand contained in received water to settle on a bottom of the basin having a groove extending in a predetermined direction and a bottom surface formed between a side wall of the settling basin and the groove and connected to the groove, comprising:
an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water stored in the groove;
and an atmospheric discharge step of discharging a fluid from a second discharge port into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall side toward the groove,
the underwater discharge step is a step of discharging a fluid into a space covered by a cover member that has an opening at a lower end portion and covers a periphery of a virtual axis extending from the first discharge port in the predetermined direction,
The atmospheric discharge step may be characterized in that it is performed in a state in which the water level is maintained below an upper end position of the covering member, the upper end position of which is located below the bottom surface.

Note that even if a component is included only in the description of the embodiment or each of the variations described above, that component may be applied to the embodiment or other variations.

2 Grit basin 8 Main trough 13 First cover member 13a Opening 14 Second cover member 15 Third cover member 84a Trough third outlet 71 Bottom surface 831a Trough first outlet 832a Trough second outlet 911 Outlet Side wall W

Claims (3)

In a settling basin where sand contained in the received water settles to the bottom of the basin,
A groove is provided in the bottom of the pond and extends in a predetermined direction;
a first outlet port that discharges a fluid in the predetermined direction into the water stored in the groove;
A bottom surface is provided at the bottom of the pond, formed between the side wall of the settling basin and the groove and connected to the groove;
a second outlet that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall toward the groove;
a cover member that covers a periphery of an imaginary axis extending from the first discharge port in the predetermined direction and has an opening at a lower end portion,
The bottom surface is located above an upper end position of the covering member,
A settling basin characterized in that the second discharge outlet discharges fluid while the water level is maintained below the upper end position of the covering member. 2. The settling basin according to claim 1 , wherein the groove is inclined downward at an angle of 0 degrees or more and less than 1 degree toward the specified direction. A method for collecting sand deposited on a bottom of a settling basin that allows sand contained in received water to settle, the settling basin having a groove extending in a predetermined direction and a bottom surface formed between a side wall of the settling basin and the groove and connected to the groove, comprising:
an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water stored in the groove;
and an atmospheric discharge step of discharging a fluid from a second discharge port into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall side toward the groove,
the underwater discharge step is a step of discharging a fluid into a space covered by a cover member that has an opening at a lower end portion and covers a periphery of a virtual axis extending from the first discharge port in the predetermined direction,
A sand collecting method characterized in that the atmospheric discharge process is carried out in a state where the water level is maintained further below the upper end position of the covering member, the upper end position of which is located below the bottom surface.

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