Grit basin and sand collection method

Abstract

To provide a sand sedimentation pond which enables efficient collection of sand, and to provide a sand collection method.SOLUTION: A sand sedimentation pond 2 includes: a main trough 8 provided on a pond bottom part and extending in a predetermined direction; a trough first discharge port 831a which discharges fluid in the predetermined direction in water accumulated in the main trough 8; a bottom flat surface 71 which is provided at the pond bottom part, formed between a side wall W of the sand sedimentation pond 2 and the main trough 8, and connected to the main trough 8; a discharge port 911 which discharges fluid for causing sand accumulated on the bottom flat surface 71 from the side wall W side to the main trough 8 into atmospheric air; and a first cover member 13 which covers a periphery of a virtual axis extending from the trough first discharge port 831a in the predetermined direction and has an opening 13a in a lower end portion. The bottom flat surface 71 is located above an upper end position of the first cover member 13.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a settling basin in which sand contained in received water settles to the bottom of the basin, and a sand collection method for collecting the settled sand. [Background technology]

[0002] Some wastewater treatment facilities are equipped with a settling basin that receives wastewater, such as sewage and rainwater, allows the sand contained in the wastewater to settle on the bottom of the basin or in a groove installed in the basin, and then collects the sand accumulated on the bottom or in the groove in a sand collection pit to remove it from the wastewater. Some settling basins are equipped with a sand collection device that discharges wastewater from the basin, exposing the sand accumulated on the bottom to the atmosphere, and then discharges a fluid from multiple outlets installed near the sidewall of the basin to carry the sand toward the groove. The groove is composed of a long member with a U-shaped or arc-shaped cross section, extends perpendicular to the width of the basin, and its rear end is connected to the sand collection pit. The groove slopes downward toward the sand collection pit, with the sand collection pit being the deepest. The sand accumulated in the groove is transported to the sand collection pit by the flow of fluid discharged from the tip of the groove into the groove. During transport, the flow of fluid supplied into the groove toward the sand collection pit is assisted by the slope 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 settling basin by a sand lifting pump located inside the pit. Settling basins equipped with such grooves and multiple discharge ports near the side walls are known, for example, from Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-127871 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-39007 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the fluid discharged into the groove from the tip side collides with the sand accumulated in the groove, the fluid and sand may be scattered in the width direction of the pond. If the sand is scattered, it will return to the bottom where it was discharged, reducing the sand collection efficiency. Moreover, the fluid flow generated by the discharge is weakened by the collision between the fluid and the sand, which also reduces the sand collection efficiency.

[0005] In view of the above circumstances, the present invention aims to provide a settling basin and a sand collection method that can efficiently collect sand. [Means for solving the problem]

[0006] 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 provided in the bottom of the pond and extending in a predetermined direction; a first discharge port that discharges fluid in the predetermined direction into the water accumulated in the groove; a bottom surface 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 the upper end position of the covering member. the law of nature, the first discharge port and the second discharge port alternately discharge fluid, The first outlet is for discharging fluid when the water level is above the upper end position of the cover member. It is characterized by the following.

[0007] In addition, the sand collection method of the present invention that solves the above object includes a settling basin that settles sand contained in received water, the settling basin having a groove extending in a predetermined direction, a cover member having an opening at a lower end portion; A groove is formed between the side wall of the settling basin and the groove and is connected to the groove. Located above the upper end position of the covering memberA sand collection method for collecting sand deposited on the bottom of a pond having a bottom surface, comprising: In the water accumulated in the groove, In the space covered by the covering member an underwater discharge step of discharging the fluid from a first discharge port in the predetermined direction; 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 discharging step and the atmospheric discharging step are alternately performed, The underwater discharge step ,before a first outlet port extending in the predetermined direction and surrounding an imaginary axis; The aforementioned Covering material When the water level is above the upper end position of The method is characterized by being a step of discharging a fluid. [Effects of the Invention]

[0008] According to the present invention, a settling basin and a sand collection method that can efficiently collect sand can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of a wastewater treatment facility including a settling basin according to one embodiment of the present invention. [Figure 2] FIG. 1 is a plan view of a settling basin corresponding to one embodiment of the present invention, viewed from above. [Figure 3] XX cross-sectional view of the settling basin shown in FIG. 2. [Figure 4] FIG. 4(a) is an enlarged view showing a portion Z in FIG. 3, and FIG. 4(b) is a schematic perspective view showing a first covering member and an upstream trough first nozzle. [Figure 5] 3 is a cross-sectional view of the grit basin shown in FIG. 2 along the line AA. [Figure 6] FIG. 6 is an enlarged view showing a portion B in FIG. 5. [Figure 7] (a) is a cross-sectional view illustrating a state in which one pipe provided with a lap joint is joined to another pipe, and (b) is a cross-sectional view illustrating a state in which, by loosening the bolt, the one pipe provided with the lap joint can freely rotate about its axial direction relative to the other pipe. [Figure 8] 6(a) is a cross-sectional view taken along the line CC in FIG. 6, and FIG. 6(b) is a cross-sectional view similar to FIG. 6(a) for explaining the change in the discharge direction by the sand collecting nozzle. [Figure 9] This is a diagram of the water supply system at a sewage treatment facility. [Figure 10] FIG. 2 is an explanatory diagram showing the water level of the settling basin and the water level sensor. [Figure 11] 1 is a flowchart showing the flow of sand removal operations in a wastewater treatment facility. [Figure 12] 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. [Figure 13] 4 is a cross-sectional view similar to FIG. 3, showing a modified example of the connecting surface. [Figure 14] 9(a) is a diagram showing a first modified example of the supply pipe and sand collecting nozzle shown in FIG. 8, and FIG. 9(b) is a diagram showing a second modified example of the supply pipe and sand collecting nozzle shown in FIG. 8. [Figure 15] 6 is a cross-sectional view similar to FIG. 5, showing modifications of the main trough, the cover member, and the bottom surface. [Figure 16] 16 is a cross-sectional view similar to FIG. 8(a), showing the bottom surface near the upstream end of the settling basin and the bottom surface near the sand collecting pit in the modified example shown in FIG. [Figure 17] 11 is an explanatory diagram similar to FIG. 10 showing an example of water level detection when the height of the main trough is increased. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below with reference to the drawings. A grit basin, which is one embodiment of the present invention, is installed in a wastewater treatment facility, where it settles sand contained in wastewater such as sewage and rainwater, and then moves the settled sand to a sand collection pit to remove it from the wastewater.

[0011] FIG. 1 is a schematic cross-sectional view of a wastewater treatment facility including a grit basin according to one embodiment of the present invention.

[0012] As shown in FIG. 1, sewage 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 sewage treatment facility 1. Sewage treatment facility 1 receives wastewater from the left side in FIG. 1. The received wastewater flows slowly toward pump well 3 on the right side of the figure in grit basin 2, allowing the sand contained in the wastewater to settle (see the straight arrow in FIG. 1). Hereinafter, the upstream side of the flow of the received wastewater will be simply referred to as the upstream side, and the downstream side of the flow of the wastewater will be simply referred to as the downstream side.

[0013] A dam device 4 is disposed upstream of the settling basin 2 in the wastewater treatment facility 1. The dam device 4 includes 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 settling basin 2. An inflow port 411 opens at the lower end of the opening wall 41. The inflow gate 42 is vertically movable 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, blocking the flow of wastewater upstream of the dam device 4 into the settling 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 wastewater to flow into the settling basin 2. The gate drive device 43 includes an internal drive mechanism (not shown) and moves the inflow gate 42 up and down in response to commands from a control device that controls the dam device 4. By this vertical movement, the inflow gate 42 is selectively placed in either the upper position or the lower position.

[0014] The settling basin 2 is equipped with a dust remover 5 located upstream, a sand collection pit 6 located midstream, and a sand lifting pump 61 that transports sand from the sand collection pit 6 to the outside of the basin. A sand lifting pipe 64 is connected to the sand lifting pump 61. The sand sucked up by the sand lifting pump 61 is sent through the sand lifting pipe 64 to a sediment separator (not shown) located outside the settling basin 2. The dust remover 5 is used to remove impurities (screen residue) 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.

[0015] A pump well 3 is formed downstream of the settling basin 2 in the sewage treatment facility 1. The pump well 3 stores sewage from which sand has been removed by the settling basin 2. The bottom of the pump well 3 is the deepest part of the sewage treatment facility 1. A lifting pump 31 and a feed pump 33 are disposed in the pump well 3. The lifting pump 31 moves the sewage stored in the pump well 3 outside the sewage treatment facility 1. A lifting pipe 32 is connected to the lifting pump 31. The sewage sucked by the lifting pump 31 is sent through this lifting pipe 32 to a sedimentation basin (not shown) where the next stage of sewage treatment is performed. The feed pump 33 is disposed closer to the bottom of the pump well than the lifting pump 31. A feed pipe 34 is connected to the feed pump 33. The sewage sucked by the feed pump 33 is sent through this feed pipe 34 to each nozzle (described later). The wastewater sucked by the water supply pump 33 will be referred to as a fluid in the following description.

[0016] Figure 2 is a plan view of a settling 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.

[0017] As shown in FIG. 2, the settling basin 2 is a generally rectangular pond in plan view, comprising a dust collector 5, a sand collection pit 6, a bottom surface 71, a small trough 72, a connecting surface 73, a main trough 8, and a sand collection means 9 between a left wall Wa and a right wall Wb. The bottom surface 71 and the small trough 72 are examples of a bottom surface. The main trough 8 is an example of a groove. Hereinafter, the left wall Wa and the right 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 center of the width of the settling basin 2 on the upstream side. The sand collection pit 6, the bottom surface 71, the small trough 72, the connecting surface 73, and the main trough 8 are each provided at the bottom of the settling basin 2. The bottom surface 71 is formed by the surface of concrete poured at 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 longitudinally from near the upstream end of the settling basin 2 and connect at their rear ends to the sand collection pit 6, and a downstream main trough 82, which extends longitudinally from near the downstream end of the settling basin 2 and connects at its rear end 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 draining wastewater from the settling basin 2, fluid is discharged onto the bottom plane 71 and the small troughs 72, and the sand that has settled on the bottom plane 71 and the small troughs 72 is collected. Hereinafter, the long side direction of the settling basin 2 will be referred to as the longitudinal direction, and the short side direction will be referred to as the basin width direction. This longitudinal direction is also the orthogonal direction perpendicular to the basin width direction.

[0018] Buildings, piping, and the like (not shown) may be located above the settling basin 2 (the near side of the page in FIG. 2 ). A pillar 11 may be formed adjacent to the settling basin 2 to support the building or the like. In the settling basin 2 shown in FIG. 2 , the pillar 11 is formed near the left wall Wa. The portion of the left wall Wa that serves as the base for the pillar 11 has a convex wall portion Wa1 that protrudes toward the center of the pond width direction. Conversely, the portion of the left wall Wa where the pillar 11 is not present has a concave wall portion Wa2 that is concave toward the outside of the pond width direction. The portion 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 pond width direction. Since there is no pillar 11 near the right wall Wb, the right wall Wb is formed in a substantially linear shape in a plan view.

[0019] The sand collection pit 6 is located slightly downstream of the longitudinal center of the settling basin 2. This sand collection pit 6 is configured as 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 is a sand collection pit slope 6b that gradually becomes deeper toward the sand collection pit 6 side, which is located in the center of the basin width direction.

[0020] A total of four agitation nozzles 62 are arranged near each corner of the sand collection pit 6. These agitation nozzles 62 are used to agitate the sand collected in the sand collection pit 6. By discharging fluid from the discharge port 62a of the agitation 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 pit sand collection nozzles 63 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 pit sand collection nozzle 63 while the water level in the settling basin 2 is kept lower than a predetermined value, the sand accumulated on the sand collection pit slope 6b can be collected into the sand collection pit 6.

[0021] The bottom surface 71 is composed of a first bottom surface 711 formed between the left sidewall Wa and the upstream first main trough 815, a second bottom surface 712 formed between the right sidewall Wb and the upstream second main trough 816, a third bottom surface 713 formed between the left sidewall Wa and the downstream main trough 82, and a fourth bottom surface 714 formed between the right sidewall Wb and the downstream main trough 82. The bottom surface 71 and the small troughs 72 are connected to the main trough 8 at the center of the settling basin 2 in the width direction. The bottom surface 71 slopes downward by approximately 5 degrees from the sidewall W at the outer end of the pond width direction toward the main trough 8, so that the end of the main trough 8 is the deepest. On the other hand, the bottom surface 71 is formed horizontally in the longitudinal direction. The small troughs 72 are gutter-shaped with a U-shaped cross section and extend from the vicinity of the sidewall W in the width direction of the pond. Multiple small troughs 72 are arranged at equal intervals in the longitudinal direction. In this embodiment, a total of 56 small troughs 72 are arranged, 28 on each side of the main trough 8 in the pond width direction. Similar to the bottom plane 71, these small troughs 72 are also inclined downward by approximately 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 pond bottom.

[0022] The first upstream main trough 815, the second upstream main trough 816, and the downstream main trough 82 are grooves formed by trough forming bodies made of stainless steel plates and having a cross section in the shape of a 2 / 3 circle arc. However, the first upstream main trough 815, the second upstream main trough 816, and the downstream main trough 82 may also be formed of concrete integrally with the bottom surface 71. The first upstream main trough 815, the second upstream main trough 816, and the downstream main trough 82 are arranged horizontally over the entire longitudinal length from near the end of the settling basin to the part connected to the sand collection pit 6.

[0023] As shown in FIG. 2, the first upstream main trough 815 is located on the left wall Wa side of the center of the pond width direction and extends in the longitudinal direction. The second upstream main trough 816 is located on the right wall Wb side of the center of the pond width direction and extends in the longitudinal direction. The first upstream main trough 815 and the second upstream main trough 816 both have a total length of 10 m and are identical in shape. The downstream ends of the first upstream main trough 815 and the second upstream main trough 816 are connected to the sand collection pit 6. A first upstream trough nozzle 831 having a first trough outlet 831a is provided at the upstream end portion of the first upstream main trough 815 (the tip portion of the first upstream main trough 815). Furthermore, an upstream trough second nozzle 832 having a trough second outlet 832a is provided at the upstream end portion of the upstream second main trough 816 (the tip portion of the upstream second main trough 816). The trough first outlet 831a and the 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 lengths of the first cover member 13 and the second cover member 14 are approximately the same as the total lengths 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 position slightly downstream, beyond the portion of the upstream first main trough 815 that is connected to the sand collection pit 6. When wastewater has accumulated in the upstream first main trough 815, discharging a fluid from the trough first outlet 831a can move the sand accumulated in the upstream first main trough 815 to the sand collection pit 6. The second cover member 14 extends from upstream of the trough second outlet 832a to a position slightly downstream, beyond the portion of the upstream second main trough 816 that is connected to the sand collection pit 6. When wastewater has accumulated in the upstream second main trough 816, discharging a fluid from the trough second outlet 832a can move the sand accumulated in the upstream second main trough 816 to the sand collection pit 6.The movement of sand within the upstream first main trough 815 and the upstream second main trough 816, as well as the first covering member 13 and the second covering member 14 will be described in detail later.

[0024] 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 third trough outlet 84a is provided at the downstream end of the downstream main trough 82 (the tip portion of the downstream main trough 82). This third trough outlet 84a also corresponds to an example of a 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 third trough outlet 84a to a position slightly upstream beyond the portion of the downstream main trough 82 connected to the sand collection pit 6. When wastewater accumulates in the downstream main trough 82, fluid can be discharged from the trough third discharge port 84a to move the sand accumulated in the downstream main trough 82 to the sand collection pit 6. The movement of sand in the downstream main trough 82 and the third cover member 15 will be described in detail later.

[0025] A protruding wall 10 for supporting the dust collector 5 is formed between the first upstream main trough 815 and the second upstream main trough 816 in the upstream portion of the settling basin 2. This protruding wall 10 is a concrete wall that rises up to near the upper end of the settling basin 2. The connection surface 73 is located between the first upstream main trough 815 and the second upstream main trough 816, and is arranged on the bottom of the basin downstream of this protruding wall 10. In other words, the connection surface 73 is formed in the portion between the first upstream main trough 815 and the second upstream 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 to the first upstream main trough 815, and a second connection surface 733 that connects the ridge portion 731 to the second upstream main trough 816. The extension direction of the ridge line 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 relative to the longitudinal direction. Also, the ridge line portion 731 may 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 slight inclination and meandering.

[0026] Fig. 3 is a cross-sectional view taken along line XX of the settling basin shown in Fig. 2. In Fig. 3, the dust collector is not shown.

[0027] As shown in FIG. 3 , the first connection surface 732 is an inclined surface that slopes downward toward the upstream first main trough 815. The second connection surface 733 is an inclined surface that slopes downward toward the upstream second main trough 816. The first connection surface 732 and the second connection surface 733 are made of concrete. The inclination angle of the first connection surface 732 and the second connection surface 733 is approximately 45 degrees with respect to the horizontal plane. The inclination of the connection surface allows sand that settles on the connection surface 73 to 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. Furthermore, it is preferable to set the inclination angle of the first connecting surface 732 and the second connecting surface 733 at 30 degrees or more, because this makes it easier for sand settling on the connecting surface 73 to slide down the connecting surface 73. However, if the inclination angle is too large, the thickness of the concrete constituting the connecting surface 73 in the width direction of the pond becomes too thin near the ridge line 731, making the ridge line 731 more susceptible to damage. For this reason, it is preferable to set the angle of the ridge line 731 formed by the first connecting surface 732 and the second connecting surface 733 so that the angle is 30 degrees or more. Note that one or both of the first connecting surface 732 and the second connecting surface 733 do not have to be formed by a single plane, but may be formed by multiple surfaces with different inclination angles, for example. In this case, the inclination angle of all multiple surfaces should be 15 degrees or more. Alternatively, one of the first connection surface 732 and the second connection surface 733 may be a vertical surface, and the other an inclined surface. However, by making each of the first connection surface 732 and the second connection surface 733 an inclined surface as in this embodiment, 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 an inclined surface. Furthermore, 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 either the upstream first main trough 815 or the upstream second main trough 816, thereby preventing the sand from being unable to be transported to the sand collection pit 6 due to resistance to transport of the sand within the upstream first main trough 815 and the upstream second main trough 816.

[0028] 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 corresponds to the pond width direction, and the direction perpendicular to the paper surface corresponds to 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.

[0029] FIG. 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 similar shapes except for the connecting bottom plane 71 or the connecting surface 73, and therefore their description is 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 its center point. However, the cross-sectional shape of the upstream first main trough 815 is not limited to an arc shape and may be U-shaped, V-shaped, or the like. The upstream first main trough 815 has a cylindrical shape with an inner diameter of 300 mm, with the upper part cut out, and is open upward along 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 first trough opening 815b at the upper end. As a result, even if sand is blown up inside the upstream first main trough 815, the upper portion 815a acts as a barb, returning the blown up sand into the upstream first main trough 815.

[0030] The first covering member 13 has a 5 / 6 circular cross-sectional shape with an opening 13a at its lower end. That is, it has an arc shape with a covering arc center 13c, which is the radial center, as its center point. This first covering member 13 is made of a 3 mm thick stainless steel plate formed into an arc cross-sectional shape with an inner diameter of 150 mm. The opening 13a is provided along the entire length of the first covering member 13. The first covering member 13 partitions the internal space of the upstream first main trough 815. The space inside the first covering member 13 becomes the transfer space FS, which is the space covered by the first covering member 13. Because the first covering member 13 has an arc shape with a closed upper portion, sand that settles within the settling basin 2 toward the upper portion of the first covering member 13 easily slides down the outer surface of the upper portion of the first covering member 13. The sliding sand accumulates below the upstream first main trough 815. Furthermore, the transfer space FS below the cover arc center 13c of the first covering member 13 narrows in the basin width direction toward the lower opening 13a. The first covering member 13 is supported by support fittings 131 (see FIG. 5) fixed with chemical anchors (registered trademark) to concrete poured into the bottom of the settling basin 2. The height position of the upper end of the first covering member 13 is located at approximately the same height as the first trough opening 815b. The height position of the upper end of the first covering member 13 is preferably located at approximately the same height as the first trough opening 815b or lower than the first trough opening 815b. By positioning the upper end of the first covering member 13 in this manner, the interior of the first covering member 13 can be filled with water by filling the upstream first main trough 815 with water. By filling the interior of the first covering member 13 with water when discharging fluid into water from the trough first outlet 831a, a strong fluid flow can be created inside the first covering member 13. Furthermore, opening 13a of first covering member 13 is disposed below center 815h in the height direction of upstream first main trough 815. This arrangement brings opening 13a of first covering member 13 closer to sand deposited below upstream first main trough 815, making it easier for the flow of fluid inside first covering member 13 to suck up sand deposited in upstream first main trough 815 into the inside of first covering member 13.Since both ends of the first covering member 13 in the extension direction 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 transfer space FS, and the transfer space FS is filled with wastewater. Although the first covering member 13 in this embodiment has an arc-shaped cross-section, the cross-section may be polygonal or may have a shape in which an arc and a straight line are connected. However, it is preferable that the cross-sectional shape of the upper portion of the first covering member 13 be an inclined surface that slopes downward in the width direction of the groove. By making the upper portion of the first covering member 13 an inclined surface, sand that has settled in the upper portion of the first covering member 13 is more likely to slide down the upper portion and accumulate downward in the upstream first main trough 815.

[0031] The first trough outlet 831a is disposed within the transfer space FS within the first cover member 13. This first trough outlet 831a has a long hole shape formed by flattening the tip of a pipe with an inner diameter of 80 mm from top to bottom. The maximum opening length of the first trough outlet 831a in the pond width direction is 117 mm, and the maximum height in the vertical direction is 18 mm. The first trough outlet 831a may have other shapes, such as a perfect circle. However, by making the first trough outlet 831a flat, the fluid can be discharged over a wider area than with a perfect circle before being flattened. The discharge flow velocity of the fluid discharged from the first trough outlet 831a is preferably 8 m / sec or greater. If the flow velocity is less than 8 m / sec, the sand may not be transported the required distance due to insufficient flow velocity. Furthermore, the discharge pressure of the fluid discharged from the first trough outlet 831a is preferably 0.05 MPa or greater and 0.3 MPa or less. The center of the trough first outlet 831a coincides with the cover arc center 13c. The trough first outlet 831a discharges the fluid in the longitudinal direction, which is the extension direction of the first cover member 13. As shown in FIG. 4(b), the first cover 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. An axis extending from the center of this trough first outlet 831a (cover arc center 13c) as a starting point in the flow direction of the fluid discharged from the trough first outlet 831a becomes a virtual axis VL. In other words, the first cover 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 covering member 13 and the discharge direction of the fluid discharged from the trough first outlet 831a do not need to be perfectly aligned with the longitudinal direction, but aligning them allows for more efficient sand transport. Even if the discharge direction of the fluid discharged from the trough first outlet 831a and the extension direction of the first covering member 13 differ slightly, the discharged fluid is guided by the first covering member, so the flow direction of the fluid coincides with the extension direction of the first covering member. Therefore, the virtual axis VL in this case is the extension direction of the first covering member. However, in this case, the fluid may collide with the first covering member, weakening the flow. Therefore, it is desirable to align the discharge direction of the fluid discharged from the trough first outlet 831a and the extension direction of the first covering member 13.The center of the trough first outlet 831a may be located at a position different from the cover arc center 13c. For example, it may be located 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, loss of the fluid flow 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 transfer 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.

[0032] When the fluid is discharged from the trough first outlet 831a into the transfer space FS, a fluid flow is generated in the transfer space FS inside the first cover member 13. A pressure difference is generated between the transfer space FS and the outside of the first cover member 13 due to the fluid flow. That is, a negative pressure is generated in the transfer space FS where the fluid flow is generated. Sand accumulated in the upstream first main trough 815 is sucked into the transfer space FS through the opening 13a due to the negative pressure, as shown by the curved arrow in FIG. 4(a). Furthermore, the first cover member 13 prevents the fluid discharged from the trough first outlet 831a from diffusing in the radial direction perpendicular to the longitudinal direction, so the flow in the transfer space FS is maintained over a long distance. The sucked sand is transported toward the sand collection pit 6 by the fluid flow generated in the transfer space FS. In this embodiment, the transfer 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, sand accumulated in the upstream first main trough 815 can be efficiently transported toward the sand collection pit 6. As described above, the area below the cover arc center 13c in the transfer space FS narrows in the pond width direction toward the lower opening 13a. By narrowing the pond width of the opening 13a, sand being transported within the transfer space FS is less likely to leak out of the transfer space FS. Furthermore, since the fluid within the transfer space FS is less likely to leak out of the transfer space FS, the flow of the fluid can be maintained over a long distance, allowing sand to be moved further. Furthermore, negative pressure within the transfer space FS can be easily maintained even at a position away from the trough first discharge port 831a.

[0033] As shown in FIG. 2, two dust removers 5 are provided side by side in the width direction of the settling basin 2, with a protruding wall 10 sandwiched between them. In other words, one dust remover 5 is disposed between the left side wall Wa and the protruding wall 10, and one is disposed 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 impurities (screen residue) from the wastewater that flows into the settling 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, while 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 basin, the width of each dust remover 5 in the width direction of the basin can be reduced. By shortening the width of the dust collector 5 in the pond width direction, the strength of the dust collector 5 is increased, and damage to the dust collector 5 can be prevented even if the amount and flow rate of wastewater flowing into the settling basin 2 increases due to heavy rain or other reasons.

[0034] Figure 5 is a cross-sectional view taken along the line AA of the settling basin shown in Figure 2. In Figure 5, the pillars and sand-lifting pumps 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. The water level WL of the settling basin fluctuates depending on the amount of rain and sewage flowing in, but under normal circumstances when the amount of rain and sewage is expected, it is located at a mid-height in the settling basin 2, as shown in Figure 5.

[0035] As shown in Figure 5, the dust collector 5 comprises an endless chain 51, multiple rakes 52 attached at intervals to the endless chain 51, and a filter screen 53. The endless chain 51 is installed diagonally on both sides of the width of the settling basin 2 and is wound around a ground-side sprocket 511 and a bottom-side sprocket 512. The upper portion of the endless chain 51 and the ground-side sprocket 511 are located above the ground of the settling basin 2. When the water level WL is in a normal state, driving the ground-side sprocket 511 in the direction indicated by the arc-shaped arrow R by a motor (not shown) causes the endless chain 51 to circulate, and the rake 52 to move in and out of the water. Figure 5 shows the water level WL in its normal state. The protruding wall 10 protrudes above the water level 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 level WL. The filter screen 53 is located downstream of the endless chain 51. This filter screen 53 is composed of vertically extending bars arranged at predetermined intervals (e.g., 25 mm to 75 mm) across the width 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 then placed on a conveying means such as a belt conveyor (not shown) on the ground. The bottom-side sprocket 512 and the lower ends of the filter screen 53 are located upstream of the bottom plane 71 and the main trough 8. Meanwhile, the upper ends of the ground-side sprocket 511 and the filter screen 53 are located above the bottom plane 71 and the upstream portions of the main trough 8. In other words, the upper portions of the endless chain 51 and the filter screen 53 overlap the bottom plane 71 and the main trough 8 in the longitudinal direction. Figure 5 also shows a support bracket 151 supporting the third cover member 15.

[0036] The sand collection means 9 includes a first nozzle header 9a, a second nozzle header 9b, and a third nozzle header 9c arranged on the left side wall Wa 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 (see FIG. 2). FIG. 5 shows the sand collection means 9 on the left side wall Wa. The sand collection means 9 on the right side wall Wb has a similar configuration, so a description of the sand collection means 9 on the right side wall Wb will be omitted. The first nozzle header 9a, the second nozzle header 9b, and the third nozzle header 9c each include ten sand collection nozzles 91, a supply pipe 92, and a main pipe 93. The supply pipe 92 is arranged opposite the left side wall Wa and extends longitudinally. The main pipe 93 includes 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 side wall Wa by fixing metal fittings (not shown).

[0037] 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. Figure 6 also shows the side wall. Furthermore, 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.

[0038] 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 parts below the part connected to the single pipe 931, and the branched parts each extend in the longitudinal direction of the settling basin 2. Supply pipes 92, to which lap joints 934 are fixed, are connected to the ends of the branched parts. In this embodiment, three supply pipes 92 are provided for one main pipe 93: an upstream supply pipe 921 located upstream of the branch pipe 932, a downstream supply pipe 923 located downstream of the branch pipe 932, and an intermediate supply pipe 922 located between the upstream supply pipe 921 and the downstream supply pipe 923. The ends of the upstream supply pipe 921 and the downstream supply pipe 923, opposite the ends 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.

[0039] 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. These 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. 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 to be arranged on each supply pipe 92 may be determined appropriately 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. Of the outlets 911, the outlets 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 outlet, and the outlets 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 outlet. By lowering the water level of the settling basin 2 below a predetermined value to expose the sand accumulated on the bottom surface 71 and the small trough 72 and the outlets 911 to the atmosphere, and then discharging a fluid from the outlets 911 into the atmosphere, the sand accumulated on the bottom surface 71 and the small trough 72 shown in FIGS. 2 and 5 can be made to flow into the main trough 8. The discharge pressure of the fluid sprayed from one outlet 911 is, for example, 0.005 MPa, and preferably 0.0002 MPa or higher and 0.005 MPa or lower. That is, the discharge pressure of the fluid discharged from the discharge port 911 is lower than the discharge pressure (0.05 MPa or more and 0.3 MPa or less) of the fluid discharged from the trough first discharge port 831a. This ensures a flow rate that can flush the sand accumulated on the bottom plane 71 and the small trough 72 into the main trough 8, while allowing an inexpensive and compact water supply pump 33 to be used for supplying the fluid.

[0040] The distance from the supply pipe 92 to the left side wall Wa differs between the portion facing the convex wall Wa1 and the portion facing the recessed wall Wa2. Specifically, the supply pipe 92 has a first region 92a extending from the left side wall Wa at a first distance in the pond width direction and a second region 92b extending from the left side wall Wa at a second distance in the pond width direction. Furthermore, in the settling basin 2 of this embodiment, an inclined wall Wa3 is formed at the portion connecting the convex wall Wa1 and the recessed wall Wa2. Therefore, the supply pipe 92 has a third region 92c connecting the first and second regions. Each sand collection nozzle 91 and its discharge port 911 is positioned facing the left side wall Wa, aligned longitudinally, and fixed to the supply pipe 92. In the second nozzle header 9b shown in FIG. 6, the upstream supply pipe 921 is positioned facing the convex wall Wa1. That is, the region where the upstream supply pipe 921 is located corresponds to the first region 92a. Meanwhile, the region of the intermediate supply pipe 922 where the outlet 911 closest to the upstream supply pipe 921 is located faces the inclined wall portion Wa3. That is, this region corresponds to the third region 92c. Furthermore, the region of the intermediate supply pipe 922 where three outlets 911 are located from the downstream supply pipe 923 side and the region of the downstream supply pipe 923 where two outlets 911 are located from the intermediate supply pipe 922 side are located face the recessed wall portion Wa2. That is, these regions correspond to the second region 92b. Furthermore, the region of the downstream supply pipe 923 where the outlet 911 located most downstream is located faces the inclined wall portion Wa3. That is, this region corresponds to the third region 92c. A direction change means using a lap joint 934 is provided between these regions.

[0041] Fig. 7(a) is a cross-sectional view illustrating a state in which one pipe provided with a lap joint is joined to another pipe, and Fig. 7(b) is a cross-sectional view illustrating a state in which the one pipe provided with the lap joint is able to rotate freely about its axial direction relative to the other pipe by loosening the bolt. In Fig. 7, a supply pipe is shown as one pipe and a branch pipe is shown as the other pipe, but the same configuration applies when supply pipes are connected using a lap joint.

[0042] As shown in Figures 7(a) and 7(b), a lap joint 934 is welded to the end of the supply pipe 92. This lap joint 934 is composed of a small-diameter portion 934a welded to the supply pipe 92 and a large-diameter portion 934b located on the branch pipe 932 side. The outer diameter of the small-diameter portion 934a is the same as the outer diameter of the supply pipe 92. A free flange 935 is located on the outer periphery of the lap joint 934. This free flange 935 is ring-shaped, with an inner diameter slightly larger than the outer diameter of the lap joint 934. Eight free flange through-holes 935a, into which bolts 95 are inserted, are formed evenly around the periphery of the free flange 935. The free flange 935 is connected to the lap joint 934 so as to be rotatable and axially movable relative to the lap joint 934. A fixed flange 9322 is welded to the outer diameter portion of the tip of the branch pipe 932. This fixed flange 9322 is formed with 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.

[0043] 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 lap joint 934, together with the packing 94, is sandwiched between the fixed flange 9322 and the free flange 935, as in the supply pipe 92 shown in FIG. 7( a), thereby fixing the supply pipe 92 to the branch pipe 932. 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 main 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 rotatable about its axis relative to the main pipe 93. It should be noted that 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 in a manner that allows it to rotate continuously.

[0044] As shown in FIG. 6 , lap joints 934 are disposed between the outlets 911 in the first region 92a and the outlets 911 in the third region 92c, and between the outlets 911 in the second region 92b and the outlets 911 in the third region 92c. Therefore, the outlets 911 in the first region 92a, the second region 92b, and the third region 92c are configured to be independently and continuously rotatable about the axial direction of the supply pipe 92. This configuration allows the discharge direction of the fluid from the outlets 911 in each region to be set according to the distance from the supply pipe 92 to the left wall Wa. The lap joints 934 disposed between the outlets 911 in the first region 92a and the outlets 911 in the third region 92c are an example of a first direction changer. The lap joints 934 disposed between the outlets 911 in the second region 92b and the outlets 911 in the third region 92c are an example of a second direction changer. 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, making it easy to adjust the discharge direction in the first region 92a. In the second region 92b of the supply pipe 92 shown in FIG. 6, the discharge direction of the fluid from the three discharge ports 911 arranged in the intermediate supply pipe 922 can be changed collectively, and the discharge direction of the fluid from the two discharge ports 911 arranged in the downstream supply pipe 923 can be changed collectively, making it easy to adjust the discharge direction in the second region 92b. In other words, the lap joint 934 configured to change the discharge directions of multiple discharge ports 911 collectively corresponds to an example of a collective direction changing device. Note that if the third region 92c is short in the longitudinal direction and no discharge ports 911 exist in the third region 92c, or if the third region 92c does not exist, the lap joint 934 may be disposed between the first region 92a and the second region 92b.

[0045] Fig. 8(a) is a cross-sectional view taken along CC line in Fig. 6. In Fig. 8(a), the sidewall and bottom plane are also shown.

[0046] 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 indicated by a solid line, and the concave wall portion Wa2 is indicated by a two-dot chain line. The outlet 911, indicated by a solid line in FIG. 8(a), directs the fluid toward the center of the pond width direction rather than directly downward (vertically) from the center of the supply pipe 92. The outlet 911 discharges the fluid at an angle θ of approximately 50 degrees relative to the bottom surface 71. By setting the angle θ to approximately 50 degrees, the fluid that reaches the bottom surface 71 can be diverted into a direction toward the main trough 8 and a direction toward the convex wall portion Wa1. This angle θ may be any angle that diverges the discharged fluid into a direction toward the main trough 8 and a direction toward the convex wall portion Wa1. Specifically, the angle θ may be between 30 degrees and 60 degrees relative to the bottom surface 71. By setting this angle, when the supply pipe 92 and the left side wall Wa are close to each other, as in the case of 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 surface 71 between the supply pipe 92 and the left side wall Wa and flushes away the sand. Also, because the discharge direction of the fluid is directed toward the main trough 8 in the center of the pond width direction rather than perpendicular to the supply pipe 92, the momentum of the fluid flowing toward the main trough 8 is stronger than the momentum of the fluid flowing toward the left side wall Wa. This fluid momentum allows the sand accumulated on the bottom surface 71 between the supply pipe 92 and the main trough 8 to be efficiently flushed toward the main trough 8.

[0047] 8(a) at the recess wall Wa2 indicated by the two-dot chain line, the supply pipe 92 and the left side wall Wa are spaced apart. Therefore, in the discharge direction of the discharge port 911 indicated 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, only a very small amount of fluid reaches it. 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.

[0048] In this embodiment, the supply pipe 92 is configured to be rotatable about its axis, allowing the discharge direction of the fluid from the sand collection nozzle 91 to be freely changed. In FIG. 8(a), the sand collection nozzle 91 in which the discharge direction of the fluid from the discharge port 911 is adjusted according to 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 from the discharge port 911 is directed outward in the pond width direction rather than directly downward (vertically) from the center of the supply pipe 92. By adjusting the discharge direction of the fluid from the discharge port 911 according to the distance from the supply pipe 92 to the left side wall Wa, sand accumulated near the left side wall Wa can be sufficiently flushed away, even if the supply pipe 92 and the left side wall Wa are spaced apart, as in the second region 92b (see FIG. 6). In this embodiment, the main pipe 93 and the supply pipe 92, or the supply pipes 92 themselves, are connected using a lap joint 934 and a free flange 935, so the connected supply pipe 92 can be rotated continuously about its axis. Because of this continuous rotation, the discharge direction of the fluid can be set midway between the discharge direction of the sand collection nozzle 91 shown by the solid line in Figure 8(a) and the discharge direction of the sand collection nozzle 91 shown by the two-dot chain line in the supply pipe 92 (third region 92c) located opposite the inclined wall portion Wa3 (see Figure 2) between the convex wall portion Wa1 and the concave wall portion Wa2.

[0049] Furthermore, in this embodiment, the main pipe 93 is provided with a branch pipe 932. Therefore, a total of three supply pipes 92, including an upstream supply pipe 921, an intermediate supply pipe 922, and a downstream supply pipe 923, are connected to one main pipe 93 in a line in the longitudinal direction of the settling basin 2. In contrast, if the branch pipe 932 is not provided and the supply pipes 92 are connected to a single pipe 931, at most two supply pipes 92 can be connected to one main pipe 93 in the longitudinal direction of the settling basin 2. That is, there are two supply pipes 92: one extending from the tip of the main pipe 93 to the upstream side of the settling 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 a case where the branch pipe 932 is not 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 settling basin 2 when the branch pipe 932 is provided, allowing for more flexible adaptation to the shape of the side wall W.

[0050] Fig. 8(b) is a cross-sectional view similar to Fig. 8(a) for explaining the change in discharge direction by the sand collecting nozzle, in which the side wall and bottom plane are also shown.

[0051] As shown in FIG. 8(b), the sand collection nozzle 91 is bent at its midsection and, as shown by the solid line, is formed into an inverted L-shape when viewed longitudinally. Because of its inverted L-shape, rotating the sand collection nozzle 91 (shown by the solid line) 180 degrees around the axis L of its attachment to the supply pipe 92 changes the fluid discharge direction from the center of the pond width to the outside of the pond width, as shown by the two-dot chain line. By forming the sand collection nozzle 91 into an inverted L-shape and configuring the connection between the sand collection nozzle 91 and the supply pipe 92 to be rotatable, it becomes possible to change the fluid discharge direction for each discharge port 911. In other words, the shape of the sand collection nozzle 91 and the configuration that allows the sand collection nozzle 91 to rotate relative to the supply pipe 92 in this embodiment correspond to an example of an individual direction changing means.

[0052] Figure 9 is a diagram of the water supply system at a sewage treatment facility.

[0053] As shown in FIG. 9 , the water supply pump 33 selectively supplies water from the pump well 3 to the agitation 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 fluid is supplied to the nozzles and the sand collection means 9, and a relief switching valve Vb for switching whether or not fluid pumped up by the water supply pump is returned to the pump well 3. The pipeline between the supply switching valve Va and the agitation nozzle 62 is provided with an agitation switching valve Vc for switching whether or not fluid is supplied to the agitation 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 fluid is supplied to the pit sand collection nozzle 63. A first upstream trough switching valve Ve1, which switches whether or not to supply fluid to the first upstream trough nozzle 831, is provided in the pipeline between the supply switching valve Va and the first upstream trough nozzle 831. A second upstream trough switching valve Ve2, which switches whether or not to supply fluid to the second upstream trough nozzle 832, is provided in the pipeline between the supply switching valve Va and the second upstream trough nozzle 832. A downstream trough switching valve Vf, which switches whether or not to supply fluid to the second downstream trough nozzle 84, is provided in the pipeline between the supply switching valve Va and the nozzle headers 9a, 9b, 9c, 9d, 9e, and 9f of the sand collecting means 9, is provided in each of the pipelines. These switching valves are composed of electromagnetic valves, and the opening and closing of the valves is controlled by a control device (not shown).

[0054] FIG. 10 is an explanatory diagram showing the water level of the grit basin and the water level sensor.

[0055] As shown in Figure 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 (this 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 TLW that is near the upper end position 13b of each covering member 13, 14, 15. It detects and outputs the following signals: L, 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.

[0056] FIG. 11 is a flowchart showing the flow of sand removal operations in a wastewater treatment facility.

[0057] The operation of the wastewater treatment facility 1 having the above-described configuration will be described with reference to Figures 1, 2, and 11. When a certain amount of sand has accumulated at the bottom of the settling basin 2, the wastewater treatment facility 1 performs an operation to remove the accumulated sand. This operation can be performed periodically, for example, once a month, or when the total flow rate of wastewater flowing into or out of the settling basin 2 reaches a certain level. In the sand removal operation, the inflow gate 42 of the dam device 4 shown in Figure 1 is first activated to block the inlet 411 and prevent wastewater from flowing into the settling basin 2 (Step S1). Next, the lifting pump 31 is activated to lower the water level in the settling basin 2. When the water level in the pump well 3 drops to a predetermined level, the lifting pump 31 is stopped (Step S2). The water supply pump 33 is then activated for several minutes to discharge fluid from the agitation nozzle 62 shown in Figure 2. After the water supply pump is stopped, the sand lifting pump 61 is activated. When the water level in the settling 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 agitation nozzle 62 shown in FIG. 2. Then, the driving of the sand lifting pump 61 is set to operation mode A, which will be described below (step S3). The sand lifting pump 61 operates in either operation mode A or operation mode B. In operation mode A, the driving is stopped in response to an output from the water level sensor 99 indicating the first low water level TLWL (see FIG. 10), and is automatically 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 positions 13b of the cover members 13, 14, and 15. Therefore, in operation mode A, the cover members 13, 14, and 15, the trough first outlet 831a, the trough second outlet 832a, and the trough third outlet 84a are submerged. In 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 resumed in response to an output indicating the third high water level (HWL) (see FIG. 10). In operation mode B, the water level is maintained below the lower end 72b of the small trough 72. Therefore, the bottom surface 71, the small trough 72, the sand accumulated thereon, and the sand collecting means 9 are exposed to the atmosphere. Meanwhile, the water supply pump 33 shown in FIG. 1 continues to operate until the sand removal operation is completed.When the sand lifting pump 61 is operating, the sand transported to the sand collection pit 6 is carried by the sand lifting pump 61 to a sedimentation separator (not shown) outside the sedimentation basin 2. 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.

[0058] Then, fluid is discharged for a certain period of time from the agitation nozzle 62, the upstream trough first nozzle 831, and the upstream trough second nozzle 832 shown in FIG. 2 to flush 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). Note that in step S4, 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 fluid may be discharged for a certain period of time from the other. When the discharge of fluid from the agitation nozzle 62, the upstream trough first nozzle 831, and the upstream trough second nozzle 832 stops, the sand lifting pump 61 is switched to operation mode B (step S5). Then, when it is detected that the water level is below the third high water level HWL, fluid is discharged from the discharge port 911 (see FIG. 6) provided in the fifth nozzle header 9e. This discharge allows sand accumulated on the bottom plane 71 and the small troughs 72 between the right side wall Wb near the fifth nozzle header 9e and the upstream second main trough 816 to flow into the upstream second main trough 816. After a predetermined time has passed to sufficiently flush the sand, the sand lifting pump 61 is switched to operation mode A while continuing to discharge fluid from the discharge port 911 provided in the fifth nozzle header 9e. Thereafter, when it is detected that the water level is equal to or higher than the first intermediate water level TMWL, the discharge of fluid from the discharge port 911 provided in the fifth nozzle header 9e is stopped (step S6). Then, fluid is discharged from the agitation nozzle 62 and the upstream trough second nozzle 832 for a certain period of time, and the sand that has flowed into the upstream second main trough 816 is sent to the sand collection pit 6 (step S7). After the discharge of fluid from the agitation 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, fluid is discharged from the discharge port 911 provided in the second nozzle header 9b. After a predetermined time has elapsed that allows the sand accumulated on the bottom plane 71 and the small troughs 72 between the left side wall Wa near where the second nozzle header 9b is located and the upstream first main trough 815 to be sufficiently flushed away, the sand lifting pump 61 is switched to operation mode A while continuing to discharge fluid from the discharge port 911 provided in the second nozzle header 9b.Thereafter, when it is detected that the water level is equal to or higher than the first intermediate water level TMWL, the discharge of fluid from the discharge port 911 provided in the second nozzle header 9b is stopped (step S9). In this embodiment, the discharge direction of the discharge ports 911, which are located in the left side wall Wa near 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 depending on the distance from the supply pipe 92 to the left side wall Wa. Therefore, all sand accumulated on the bottom plane 71 and the small troughs 72 between the left side wall Wa near the location of the second nozzle header 9b and the upstream first main trough 815 can be flushed to the upstream first main trough 815. After the discharge of fluid from the discharge port 911 provided in the second nozzle header 9b is stopped, fluid is discharged from the agitation nozzle 62 and the upstream trough first nozzle 831 for a certain period of time, and the sand that has flowed into the upstream first main trough 815 is sent to the sand collection pit 6 (step S10). When the discharge of fluid from the agitation nozzle 62 and the upstream trough second nozzle 832 stops, the sand lifting pump 61 is switched to operation mode B (step S11). Subsequently, similar to the operations of steps S6 to S10 described above, the following operations are performed in order: discharge of fluid from the discharge port 911 provided in the fourth nozzle header 9d and switching to operation mode A after a predetermined time has elapsed (step S12), discharge of fluid from the agitation nozzle 62 and the upstream trough second nozzle 832 (step S13), switching to operation mode B (step S14), discharge of fluid from the discharge port 911 provided in the first nozzle header 9a and switching to operation mode A after a predetermined time has elapsed (step S15), and discharge of fluid from the agitation nozzle 62 and the upstream trough first nozzle 831 (step S16). By these operations, all sand deposited on the pond bottom upstream of the sand collection pit 6 is transported out of the settling basin 2. The order in which fluid is discharged from the nozzle headers 9a, 9b, 9d, and 9e may be any order. However, if the sand accumulated far from the sand collection pit 6 is flushed away first, the sand accumulated closer to the sand collection pit 6 will collapse into the main trough 8 along with the sand being flushed away, causing sand to 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, which are closer to the sand collection pit 6, and then eject fluid from the first nozzle header 9a and the fourth nozzle header 9d, which are farther from the sand collection pit 6.

[0059] After removing the sand accumulated on the upstream side by the above-mentioned operation, fluid is discharged from the agitation nozzle 62 and the downstream trough nozzle 84 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 below the third high water level HWL, fluid is discharged from the outlet 911 provided in the sixth nozzle header 9f. After a predetermined time has elapsed to sufficiently flush the sand accumulated on the bottom plane 71 and the small troughs 72 between the right side wall Wb near the location of the sixth nozzle header 9f and the downstream main trough 82, the sand lifting pump 61 is switched to operation mode A while continuing to discharge fluid from the outlet 911 provided in the sixth nozzle header 9f. Thereafter, when it is detected that the water level is equal to or higher than the first intermediate water level TMWL, the discharge of fluid from the discharge port 911 provided in the sixth nozzle header 9f is stopped (step S19). Then, fluid is discharged from the agitation nozzle 62 and the downstream main trough 82 for a certain period of time, and the sand that has flowed into the downstream main trough 82 is sent to the sand collection pit 6 (step S20). When the discharge of fluid from the agitation nozzle 62 and the downstream main trough 82 is stopped, the sand lifting pump 61 is switched to operation mode B (step S21). Then, similar to the operations of steps S19 and S20 described above, the discharge of fluid from the discharge port 911 provided in the third nozzle header 9c and the switch to operation mode A after a predetermined time has elapsed (step S22), and the discharge of fluid from the agitation nozzle 62 and the downstream trough nozzle 84 (step S23) are performed in this order, and all sand that has accumulated on the pond bottom downstream of the sand collection pit 6 is carried out to the outside of the settling basin 2. Finally, fluid is discharged from the sand collection nozzle 63 for the pit to flush the sand accumulated on the sand collection pit inclined surface 6b into the sand collection pit 6 (step S24). After 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.

[0060] In this sand removal operation, when the sand lifting pump 61 is switched from operating mode A to operating mode B, the supply of fluid to the settling basin 2 is stopped until it is detected that the water level is below the third high water level HWL. This allows the water level to decrease more quickly. To stop the supply of fluid to the settling basin 2, the supply switching valve Va shown in FIG. 9 is closed and the relief switching valve Vb is opened, returning the fluid pumped by the feedwater pump 33 to the pump well 3. This allows the supply of fluid to the settling basin 2 to be stopped while the feedwater pump 33 continues to operate. In the sand removal operation described above, steps S4, S7, S10, S13, S16, S17, S20, and S23 each correspond to an example of a submerged discharge process. Furthermore, steps S6, S9, S12, S15, S19, and S22 each correspond to an example of an atmospheric discharge process. That is, in this embodiment, the process of performing the atmospheric discharge process followed by the submerged discharge process is considered 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 this sand collection process is performed multiple times. Furthermore, the submerged 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 flowing into the main trough 8 during the atmospheric discharge process may be piled on top of the remaining sand, resulting in a large amount of sand accumulating in the main trough 8. Furthermore, during the atmospheric discharge process, the main trough 8 may be filled with sand, and the overflowing sand may remain on the bottom surface 71. In this embodiment, the sand flowing from the bottom surface 71 into the main trough 8 is transported to the sand collection pit 8 as part of one set of sand collection processes, so that no sand remains in the main trough 8. Furthermore, since 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.

[0061] In this embodiment, the sand lifting pump 61 is configured to pump a slightly larger amount of fluid than the feedwater pump 33 during the sand removal operation. Therefore, the sand lifting pump 61 repeatedly stops and restarts during the sand removal operation. However, repeated start-and-stop operation of the sand lifting pump 61 shortens the pump's lifespan due to the inrush current at the start of operation. To address this issue, the pumping capacity of the feedwater pump 33 and the sand lifting pump 61 may be adjusted to be closer to each other to minimize water level changes during the sand removal operation. Furthermore, when the water level sensor 99 detects a drop to the first intermediate water level (TMWL) in operation mode A or the second intermediate water level (MWL) in operation mode B, additional fluid may be discharged from other nozzles in addition to the nozzles currently discharging fluid. Increasing the number of nozzles discharging fluid reduces the load (throttle resistance) on the fluid flow, increasing the amount of fluid pumped by the feedwater pump 33. As a result, more fluid can be supplied to the settling basin 2. This reduces the likelihood of the first low water level (TLWL) or the second low water level (LWL), thereby reducing the number of times the sand lifting pump 61 must be stopped and restarted. The other nozzle is preferably a sand-collecting nozzle 91 attached to the nozzle header scheduled to discharge next. Discharging fluid from the nozzle header scheduled to discharge next allows for preliminary flushing of sand from the bottom surface 71 and small trough 72, thereby further reducing sand residue. The additional fluid discharged may be fluid stored in another facility. Furthermore, instead of stopping the sand lifting pump 61 when the first low water level (TLWL) or the second low water level (LWL) is reached, the system may be configured to supply fluid stored in another facility to the settling basin 2 in addition to the fluid pumped by the feedwater pump 33. In this configuration, the supply of fluid stored in another facility to the settling basin 2 can be stopped when the second high water level (THWL) or the third high water level (HWL) is reached. By reducing the number of times that the sand lifting pump 61 is repeatedly stopped and started, deterioration of the sand lifting pump 61 can be suppressed and its lifespan can be extended.

[0062] In this embodiment, the discharge port 911 is located near the bottom of the settling basin 2. In contrast to this, for example, Japanese Patent Application Laid-Open No. 2011-245391 proposes a settling basin 2 in which a sand collecting means 9 equipped with a discharge port 911 is located in the upper part of the settling basin 2, and the fluid is discharged toward the side wall W so that the fluid flows down the surface of the side wall W.

[0063] Fig. 12 is a cross-sectional view of a settling basin similar to Fig. 5, showing a case where a sand collection means is arranged in the upper part of the settling basin and a case where a sand collection means is arranged near the bottom of the settling basin. In Fig. 12, the sand collection means arranged in the upper part of the settling 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 arranged in the upper part of the settling basin are shown with the intersecting portions omitted.

[0064] FIG. 12 shows a virtual upper nozzle header 90 in the upper portion of the settling basin 2. This upper nozzle header 90 is used in place of the first nozzle header 9a. A dust collector 5 is disposed at an angle at the upstream end of the settling basin 2. The sand collection means 9 must be positioned so as not to interfere with the dust collector 5. Therefore, the upper nozzle header 90 disposed in the upper portion of the settling basin 2 is located downstream compared to when it is disposed near the bottom of the settling basin 2, as shown in FIG. 12. In other words, the upper nozzle header 90 must be positioned downstream by a distance S from the first nozzle header 9a. As described above, the upper portions of the endless chain 51 and the filter screen 53 constituting the dust collector 5 overlap the bottom plane 71 and the main trough 8 in the longitudinal direction. Therefore, even when fluid is discharged from the upper nozzle header 90, the discharged fluid does not reach the most upstream portion of the bottom plane 71. If the dust collector 5 and the upper nozzle header 90 are positioned a distance S upstream from the positions shown in FIGS. 5 and 12, the fluid can reach the most upstream portion of the bottom plane 71. However, such a positioning increases the longitudinal length of the settling basin 2. As a result, the settling basin 2 becomes larger, requiring a large amount of land for installation, and the settling basin 2 becomes expensive. In the settling basin 2 of this embodiment, the first nozzle header 9a is positioned near the bottom of the settling basin 2. This has the effect of preventing the settling basin 2 from becoming larger and providing the settling basin 2 at a lower cost than when an upper nozzle header 90 is positioned in the upper part of the settling basin 2.

[0065] Next, we will explain modified examples of the connection surface 73. In the modified examples explained below, we will mainly explain the differences from the embodiment shown in Figures 1 to 11, 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 explanations will be omitted.

[0066] FIG. 13 is a cross-sectional view similar to FIG. 3, showing a modified example of the connection surface.

[0067] This modification differs from the example shown in FIG. 3 in that the connecting surface 73 is formed as a curved surface. The connecting surface 73 is composed of a ridge portion 731 extending along the longitudinal direction, a first connecting surface 732, and a second connecting surface 733. As shown in FIG. 13, the first connecting surface 732 and the second connecting surface 733 have a quarter-circle cross-sectional shape. In other words, the connecting 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 modification, as in the example shown in FIG. 3, sand that settles to the connecting surface 73 in the wastewater in the grit basin 2 easily slides off the connecting surface 73 due to its own weight. However, near the ridge portion 731, the inclination angle of the tangent plane of the connecting surface 73 becomes gentle, which may result in sand remaining in that vicinity. On the other hand, since the thickness of the concrete constituting connecting surface 73 in the pond width direction is thick even in the vicinity of ridge line 731, there is an effect that ridge line 731 is less likely to be damaged. One of first connecting surface 732 and second connecting surface 733 may be formed flat as in the example shown in Fig. 3, and the other may be formed curved as in the modified example shown in Fig. 13. Furthermore, one or both of first connecting surface 732 and second connecting surface 733 may be formed as a surface that combines a curved surface and a flat surface.

[0068] Next, a modified example of the sand collecting means 9 will be described.

[0069] FIG. 14(a) is a diagram showing a first modified example of the supply pipe and sand collecting nozzle shown in FIG. 8, and FIG. 14(b) is a diagram showing a second modified example of the supply pipe and sand collecting nozzle shown in FIG. 8.

[0070] 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, but the supply pipe 92 and the branch pipe 932 are flange-connected, and a ball joint 912 is provided on the sand collection nozzle 91. 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 dashed double-dashed lines. In this modified example, ball joints 912 are provided between the supply pipe 92 and each discharge port 911. These ball joints 912 allow the fluid discharge direction to be continuously changed not only in the rotational direction around the axis of the supply pipe 92 but also in various other directions. This allows for fine adjustment of the discharge direction for each discharge port 911. Alternatively, the supply pipe 92 may have a lap joint 934 and the sand collection nozzle 91 may also have a ball joint 912. In this case, the lap joint 934 corresponds to an example of collective direction changing means, and the ball joint 912 corresponds to an example of individual direction changing means.

[0071] The second modified example differs from the example shown in FIG. 8(a) in that the supply pipe 92 does not have a lap joint 934, but the supply pipe 92 and the branch pipe 932 are flange-connected, and multiple mounting portions 924 for the sand collection nozzle 91 are formed around the supply pipe 92. In FIG. 14(b), the sand collection nozzle 91 corresponding to the convex wall portion Wa1 is indicated by a solid line, and the sand collection nozzle 91 corresponding to the concave wall portion Wa2 is indicated by a two-dot chain line. In this modified example, six mounting portions 924 for the sand collection nozzle 91 are formed around the supply pipe 92. This allows the sand collection nozzle 91 to be mounted to any of the six mounting portions 924 after the supply pipe 92 is fixed to the branch pipe 932. Note that plug members are attached to all mounting portions 924 before the sand collection nozzle 91 is mounted. When mounting the sand collection nozzle 91, the plug members are removed before the sand collection nozzle 91 is mounted. Alternatively, a lap joint 934 may be disposed on the supply pipe 92, and mounting portions 924 may be formed on the supply pipe 92. In this case, the lap joint 934 corresponds to an example of a collective direction changing means, and the mounting portions 924 correspond to an example of an individual direction changing means. In this modification, six mounting portions 924 are formed in the circumferential direction, but the number of mounting portions 924 may be two to five or less, or seven or more.

[0072] Next, modifications of the main trough 8, the cover members 13, 14, 15, and the bottom plane 71 will be described.

[0073] FIG. 15 is a cross-sectional view similar to FIG. 5 showing variations of the main trough, cover member, and bottom surface.

[0074] This modification differs from the example shown in FIG. 5 in that the main trough 8, the cover members 13, 14, and 15, and the bottom surface 71 are arranged at an inclination downward toward the sand collection pit 6. Note that in FIG. 15, the inclination of the main trough 8, the cover members 13, 14, and 15, and the bottom surface 71 are exaggerated to clearly illustrate the inclination. As shown in FIG. 15, the bottom surface 71 is inclined downward by approximately 0.5 degrees in the longitudinal direction toward the sand collection pit 6, so that the end of the bottom surface 71 is deepest toward the sand collection pit 6. Similarly to the bottom surface 71, the upstream first main trough 815 and the downstream main trough 82 are also inclined downward by approximately 0.5 degrees toward the sand collection pit 6, so that the portions connected to the sand collection pit 6 are deepest. Furthermore, the first cover member 13 and the third cover member 15 are also inclined downward by approximately 0.5 degrees toward the sand collection pit 6, so that the portions connected to the sand collection pit 6 are deepest. 15, the first upstream main trough 815 and second cover member 14 are also inclined downward by approximately 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 within 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 angle of inclination can be set appropriately according to the length of the main trough 8.

[0075] 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. Figure 16 also shows the side walls and the bottom surface.

[0076] FIG. 16 shows the difference in the height position of the bottom plane 71 when the bottom plane 71 is tilted downward toward the sand collection pit 6 so that the end of the sand collection pit 6 is the deepest, as shown in FIG. 15 . In FIG. 16 , the bottom plane 71 near the upstream end of the settling basin 2 is indicated by a solid line, and the bottom plane 71 near the sand collection pit 6 is indicated by a two-dot chain line. As shown in FIG. 16 , in this case, the bottom plane 71 near the sand collection pit 6 is lower than the bottom plane 71 near the upstream end of the settling basin 2. As shown in the figure, even if fluid is discharged from the same outlet 911, the height positions of the bottom plane 71 are different between the upstream end of the settling basin 2 and the sand collection pit 6, resulting in a difference in distance Y between the discharged fluid and the bottom plane 71. In particular, for a settling basin 2 with a long longitudinal length, the distance Y becomes long, and an optimal discharge direction either near the upstream end of the settling basin 2 or near the sand collection pit 6 may be inefficient in the other direction. In this embodiment, the direction of fluid ejection from the outlet 911 can be changed, so that the fluid can be ejected in the optimal ejection direction according to the height of the bottom surface 71 (the distance from the supply pipe 92 to the bottom surface 71).

[0077] Next, a modified example in which the height of the main trough 8 is increased will be described.

[0078] FIG. 17 is an explanatory diagram similar to FIG. 10, showing an example of water level detection when the height of the main trough is increased.

[0079] In the example shown in FIG. 10, each of the cover members 13, 14, and 15 was formed to a height exceeding half the height of the main trough 8. The upper end position 13b of each of the cover members 13, 14, and 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, and 15 is kept submerged in water, so the first low water level TLWL must be set above the upper end position 13b of each of the cover members 13, 14, and 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 the third high water level HWL must be set below the lower end 72b of the small trough 72. In the example shown in Figure 10, to satisfy the condition of setting the first low water level TLWL above the upper end position 13b and the third high water level HWL below the lower end 72b, the third high water level HWL must be set below the first low water level TLWL. This eliminates overlap between the water level maintenance ranges in operation mode A and operation mode B, and when switching from one mode to the other, a waiting time occurs until the water level falls within the range of the other mode. As shown in Figure 17, if the height of the main trough 8 is increased and the cover members 13, 14, and 15 are placed below the main trough 8, the upper end positions 13b 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, part of the water level range D1 in operation mode A and part of the water level range D2 in operation mode B can overlap, eliminating or reducing the waiting time after mode switching.

[0080] The present invention is not limited to the above-described embodiments and modifications, and various modifications can be made within the scope of the claims. For example, in this embodiment, the present invention is applied to the grit basin 2 of a sewage treatment facility 1 into which sewage and rainwater flow. However, the present invention can also be applied to a grit basin of a stormwater treatment facility into which only rainwater flows. Furthermore, in this embodiment, sand accumulated on the bottom surface 71 and small trough 72 upstream of the sand collection pit 6 is flushed out, followed by sand accumulated on the bottom surface 71 and small trough 72 downstream of the sand collection pit 6. However, sand accumulated on the bottom surface 71 and small trough 72 downstream of the sand collection pit 6 may be flushed out first. Furthermore, in this embodiment, the dust collector 5 and protruding wall 10 are disposed at the upstream end of the grit basin 2, but the dust collector 5 and protruding wall 10 may also 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 settling basin 2, two downstream main troughs 82 are provided, one on the left wall Wa side and one on the right wall Wb side of the protruding wall 10. The ridge portion, the first connecting surface, and the second connecting surface are formed between the two downstream main troughs 82, excluding the area where the protruding wall 10 is provided. In this embodiment, each of the main troughs 8 is provided at the end (tip) opposite the sand collection pit 6 with one outlet for discharging fluid into the transfer space FS. However, additional nozzles with outlets may be provided at intermediate positions in the extension direction of each of the cover members 13, 14, and 15. In particular, when the length of each of the cover members 13, 14, and 15 in the extension direction is long or the fluid discharge pressure is low, it is desirable to add a nozzle at an intermediate position or the like. In this embodiment, the fluid is discharged into the transfer space FS with the cover members 13, 14, and 15 completely submerged in water. However, if a portion of each cover member 13, 14, and 15 is submerged in water, the fluid may be discharged while the atmosphere remains in the transfer space FS. In this embodiment, the fluid is discharged while the first trough outlet 831a, the second trough outlet 832a, or the third trough outlet 84a is completely submerged in water. However, the fluid may be discharged while a portion of each outlet 831a, 832a, and 84a is submerged in water and the remaining portion 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 desirable to discharge fluid from the trough first outlet 831a, trough second outlet 832a, and trough third outlet 84a while the cover members 13, 14, and 15 and the trough first outlet 831a, trough second outlet 832a, and trough third outlet 84a are completely submerged in water.

[0081] According to this embodiment or its modified example, sand can be efficiently collected. Furthermore, sand accumulated on the bottom surface 71, the small trough 72, and the connecting surface 73 can be washed away by the fluid without remaining behind. Furthermore, a straight supply pipe 92 can be used even in a settling basin whose left side wall Wa or right side wall Wb is not formed in a straight line, allowing for the provision of an inexpensive settling basin 2. Furthermore, even if the shape of the side wall W is unknown when designing the settling basin 2 or when constructing the supply pipe 92, the discharge direction can be adjusted during construction of the settling basin 2, allowing for flexible adaptation to settling basins 2 of various shapes. Furthermore, sand that settles on the connecting surface 73 slides down the first connecting surface 732 or the second connecting surface 733 and is deposited in the upstream first main trough 815 or the upstream second main trough 816. Therefore, sand does not remain between the upstream first main trough 815 and the upstream second main trough 816. Furthermore, in this embodiment, the inclination angles of the first bottom surface 711 and the second bottom surface 712 are set to a gentle inclination angle (approximately 5 degrees) that allows the accumulated sand to be washed away by the fluid discharged from the discharge port 911. This makes it possible to create the settling basin 2 without digging deeply into the ground. On the other hand, by making the connecting surface 73 at a steeper angle than the first bottom surface 711 and the second bottom surface 712, even though the fluid discharged from the discharge port 911 is configured not to reach the connecting surface 73, the sand that has settled on the connecting surface 73 can be deposited in the upstream first main trough 815 or the upstream second main trough 816.

[0082] Furthermore, many settling basins 2 have longitudinal lengths of 20 meters or more. In conventional settling basins 2, the main trough 8 is inclined downward, for example, by 1 degree toward the sand collection pit 6. Therefore, the end (rear end) of the main trough 8 on the sand collection pit 6 side is located at a depth proportional to the length of the settling basin 2, relative to the depth at which the pond-side end (front end) of the main trough 8 is located. Furthermore, because 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 settling basin 2 is long, the main trough 8 and the bottom plane 71 on the sand collection pit 6 side are located at a deeper position than when the longitudinal length of the settling basin 2 is short. When constructing the settling basin 2, the ground is excavated below the deepest point of the settling basin 2, and then the settling basin 2 is formed with concrete. If the main trough 8 and bottom plane 71 are inclined, the sand collection pit 6 is located deeper than if it were not inclined, which requires digging deeper into the ground, making the excavation work more time-consuming. Furthermore, when forming the bottom plane 71 from the excavated position with concrete, the concrete must be gradually thickened from the sand collection pit 6 toward the end of the settling basin to create the slope of the bottom plane 71, resulting in the use of a large amount of concrete. These factors result in the high cost of the settling basin 2. In this embodiment, the covering members 13, 14, and 15 are provided to improve sand collection efficiency, allowing the sand in the main trough 8 to be transported to the sand collection pit 6 even if the inclination angle of the main trough 8 and bottom plane 71 is gentle. This inclination angle is preferably between 0 degrees and less than 1 degree, and more preferably between 0 degrees and 0.5 degrees. A gentle inclination angle eliminates the need to dig deeper into the ground and reduces the amount of concrete used, allowing the settling basin 2 to be constructed inexpensively.

[0083] The following inventive concept can also be extracted from the settling basin of this embodiment.

[0084] In a settling basin where sand contained in the received water settles, A groove provided in the bottom of the pond below the side wall and extending in a predetermined direction; a bottom surface provided at the bottom of the pond and connected to the groove; a plurality of discharge ports that discharge 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 those that discharge fluid toward the center of the pond width direction relative to the axis of the supply pipe in which the discharge outlet is installed, and those that discharge fluid toward the outside of the pond width direction relative to the axis of the supply pipe.

[0085] Furthermore, the following inventive concept can be extracted from the settling basin of this embodiment.

[0086] In a settling basin where sand contained in the received water settles, A groove provided in the bottom of the pond below the side wall and extending 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 toward the groove, A settling basin characterized in that the direction of fluid discharged from the discharge port is changeable.

[0087] In this settling basin, a supply pipe provided with the discharge port; a header pipe for supplying a fluid to the supply pipe; The supply pipe may be rotatable relative to the mother pipe around the axial direction of the supply pipe.

[0088] In addition, in the settling basin, The supply pipe may have a plurality of outlets.

[0089] 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 means of a ball joint disposed between the supply pipe and the discharge port.

[0090] In addition, in the settling basin, a supply pipe provided with the discharge port in a detachable manner; The supply pipe may have a plurality of attachment portions, to which the discharge ports are attached, in the circumferential direction of the supply pipe.

[0091] Furthermore, the following inventive concept can be extracted from the settling basin of this embodiment.

[0092] In a settling basin where sand contained in the received water settles, A groove provided in the bottom of the pond below the side wall and extending 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 toward the groove; a supply pipe that is disposed closer to the center in the pond width direction than the side wall, and in which the plurality of discharge ports are aligned in the predetermined direction; the supply pipe has a first region extending from the side wall in the pond width direction at a first interval, and a second region extending from the side wall in the pond width direction at a second interval, A settling 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.

[0093] The first region may have a single or multiple outlets. When the first region has a multiple outlets, it is preferable that the discharge direction of the fluid from those outlets can be changed collectively. The second region may have a single or multiple outlets. When the second region has a multiple outlets, it is preferable that the discharge direction of the fluid from those outlets can be changed collectively. Here, "changeable collectively" is realized, for example, by the first region portion and the second region portion of the supply pipe being rotated separately around the axial direction of the supply pipe. In addition, the supply pipe may have rotatable portions at both ends of the first region, and may have rotatable portions at both ends of the second region. The supply pipe may be a straight pipe or a pipe with a slightly curved portion.

[0094] 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 the fluid, separately from the ejection port provided in the first region and the ejection port provided in the second region.

[0095] The third region may be an inclined region in which the distance to the sidewall changes gradually in the extension direction, or may be a region in which the distance changes stepwise.

[0096] Furthermore, the number of outlets provided in the third region may be one or more. When the third region has a plurality of outlets, 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 portions in the first region and the second region.

[0097] Furthermore, the following inventive concept can be extracted from the settling basin of this embodiment.

[0098] In a settling basin where sand contained in the received water settles, A groove provided in the bottom of the pond below the side wall and extending 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 discharging 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 that protrudes toward the center in the pond width direction and extends in the predetermined direction, and a concave wall portion that is concave toward the outside in the pond width direction and extends in the predetermined direction, the discharge ports are disposed opposite the convex wall portion and the concave wall portion, A sedimentation basin characterized by being equipped with a direction change means that can change the discharge direction of a fluid discharged from an outlet arranged opposite the recessed wall portion to a different direction from the discharge direction of a fluid discharged from an outlet arranged opposite the convex wall portion.

[0099] Furthermore, the following inventive concept can be extracted from the settling basin of this embodiment.

[0100] In a settling basin where sand contained in the received water settles, A groove provided in the bottom of the pond below the side wall and extending 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 toward the groove; The side wall has a convex wall portion that protrudes toward the center in the pond width direction and extends in the predetermined direction, and a concave wall portion that is concave toward the outside in the pond width direction and extends 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 sedimentation basin characterized in that the supply pipe is provided with a direction change 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.

[0101] 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 is provided with a first direction change means, between a discharge port arranged opposite to the convex wall portion and a discharge port arranged opposite to the inclined wall portion, capable of changing a discharge direction of the fluid discharged from the discharge port; The nozzle may be provided with a second direction change means between the plurality of outlets arranged opposite the recessed wall portion and the outlets arranged opposite the inclined wall portion, which is capable of changing the direction of discharge of fluid discharged from the outlets.

[0102] In addition, the following inventive concept can be extracted from the settling basin of this embodiment.

[0103] In a settling basin where sand contained in the received water settles, A groove provided in the bottom of the pond below the side wall and extending in a predetermined direction; a bottom surface provided at the bottom of the pond and connected to the groove; a plurality of discharge ports that discharge 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 fluids ejected from at least two of the plurality of ejection ports; A settling basin characterized by being equipped with an individual direction changing means that can change the discharge direction of the fluid discharged from the discharge outlet for each discharge outlet.

[0104] Furthermore, the following inventive concept can be extracted from the settling basin of this embodiment.

[0105] In a settling basin, water is received between one side wall and the other side wall that form the end faces in the width direction of the basin, and the water flows down in a direction perpendicular to the width direction of the basin, thereby allowing sand contained in the water to settle. a first groove and a second groove provided at 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 reservoir; A sedimentation basin characterized in that a ridge portion extending along the perpendicular direction, a first connection surface connecting the ridge portion to the first groove, and a second connection surface connecting the ridge portion to the second groove are formed in the part of the bottom of the basin between the first groove and the second groove, excluding the area where the protruding wall is provided.

[0106] the first connection surface is an inclined surface that is inclined downward from the ridge line portion toward the first groove, The second connection surface may be an inclined surface that slopes downward from the ridge line portion toward the second groove.

[0107] 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 connecting surface and the second connecting surface may be steeper than the inclination angle of the first bottom surface and the second bottom surface.

[0108] a one-side outlet 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.

[0109] The apparatus may include 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.

[0110] Furthermore, the following inventive concept can be extracted from the settling basin of this embodiment.

[0111] In a settling basin, water is received between one side wall and the other side wall that form the end faces in the width direction of the basin, and the water flows down in a direction perpendicular to the width direction of the basin, thereby allowing sand contained in the water to settle. a first groove and a second groove provided at 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 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 reservoir; A sedimentation basin characterized in that a ridge portion extending along the perpendicular direction, a first connection surface connecting the ridge portion to the first groove, and a second connection surface connecting the ridge portion to 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.

[0112] 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 provided in the bottom of the pond and extending in a predetermined direction; a first discharge port that discharges fluid in the predetermined direction into the water accumulated in the groove; a bottom surface provided at the bottom of the pond 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 of the settling basin toward the groove; The nozzle may further include a cover member that covers the periphery of an imaginary axis extending from the center of the first outlet toward the predetermined direction and has an opening at a lower end portion.

[0113] In this settling basin, the opening of the cover member may be positioned below the center of the groove in the height direction.

[0114] According to this aspect, the opening of the covering member and the sand accumulated below the groove are close to each other, so that the sand accumulated in the groove can be easily sucked up into the covering member.

[0115] The sand collection method described above is a method for collecting sand deposited on the bottom of a settling basin that has a groove extending in a predetermined direction and a bottom surface connected to the groove, and in which sand contained in received water is allowed to settle on the bottom of the basin, an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water accumulated 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 ejection process may be characterized in that it is a process of ejecting fluid into a space covered by a covering member that has an opening at a lower end portion and covers the periphery of an imaginary axis extending from the center of the first ejection port toward the predetermined direction.

[0116] In this sand collecting method, the underwater discharge step is performed in a state where the water level is maintained above the covering member, The atmospheric discharge step may be a step performed in a state where the water level is maintained below the bottom surface.

[0117] In the underwater discharge step, the fluid is discharged into the water from the first discharge port 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 step, 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 washed away.

[0118] In this sand collecting method, the process of performing the atmospheric discharging step followed by the submerged discharging step may be regarded as one set of sand collecting processes, and the sand collecting process may be performed multiple times.

[0119] If sand released into the groove during the atmospheric discharge step remains in the groove, sand released into the groove during 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, it may obstruct the transport of sand in the groove during the submerged discharge step. Furthermore, even if sand is attempted to be released into the groove during the next atmospheric discharge step, the groove may become filled with sand, resulting in the overflowing sand remaining at the bottom. This sand collection method combines the atmospheric discharge step of releasing sand into the groove and the submerged discharge step of transporting sand within the groove. Therefore, sand released into the groove during the previous sand collection step does not remain in the groove during the next sand collection step. This allows the sand to flow toward the groove from which sand was removed during the atmospheric discharge step, preventing sand from overflowing from the groove. Furthermore, the submerged discharge step during the next sand collection step prevents the large amount of sand accumulated in the groove from making it difficult to transport the sand in the groove.

[0120] Furthermore, in this sand collecting method, the underwater discharge step may be carried out before the sand collecting process is carried out a plurality of times.

[0121] By transporting the sand that has settled in the grooves by the underwater discharge step before the first sand collection process, the sand can be directed toward the grooves from which the sand has been removed in the atmospheric discharge step of the first sand collection process, preventing the sand from overflowing from the grooves. Also, the underwater discharge step of the first sand collection process can prevent the sand in the grooves from becoming difficult to transport due to a large amount of sand that has accumulated in the grooves.

[0122] 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 provided in the bottom of the pond and extending in a predetermined direction; a first discharge port that discharges fluid in the predetermined direction into the water accumulated in the groove; a bottom surface provided at the bottom of the pond 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 of the settling basin toward the groove; a cover member that covers a periphery of an imaginary axis extending from the 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.

[0123] 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 as a flat surface or a curved surface. If the inclined surface is formed as a curved surface, it is preferable that the curved surface has a curved shape with an upward convexity. Furthermore, the covering member may be cylindrical with an opening at the lower end.

[0124] 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 cover member, creating a strong fluid flow within the cover member. This flow creates a pressure difference between the inside and outside of the cover member, and the sand accumulated in the groove is sucked into the cover member through an opening at the bottom end of the cover member. The sucked-in sand is then transported by the fluid flow within the cover 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.

[0125] 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 discharge the fluid while the water level is maintained below the upper end position of the cover member.

[0126] The sand collection method described above is a method for collecting sand that has accumulated on the bottom of a settling basin, which allows sand contained in received water to settle on the bottom of the basin, and which has a groove that extends in a predetermined direction and is horizontal toward the predetermined direction or inclined downward toward the predetermined direction at an angle of less than 1 degree, and a bottom surface that has a bottom plane that is horizontal toward the predetermined direction or inclined downward toward the predetermined direction at an angle of less than 1 degree and is connected to the groove, an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water accumulated 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 ejection process is characterized in that it is a process of ejecting a fluid into a space covered by a covering member that has an opening at the lower end portion and covers the periphery of a virtual axis extending from the center of the first ejection port toward the specified direction.

[0127] Here, the underwater discharge step may be a step performed with the covering member filled with fluid, or may be a step performed with air remaining inside the covering member. Also, the underwater discharge step may be a step performed with the first discharge port completely submerged in water, or may be a step performed with part of the first discharge port submerged in water and the remaining part exposed to the air.

[0128] According to this sand collection method, the fluid discharged in a predetermined direction from the first discharge port in the underwater discharge step creates a strong fluid current within the cover member, sucking the sand accumulated in the groove into the cover member and transporting it in the predetermined direction, thereby efficiently transporting and collecting the sand. Furthermore, the fluid discharged into the atmosphere from the second discharge port in the atmospheric discharge step does not encounter water resistance, so it can efficiently flush away the sand accumulated on the bottom surface.

[0129] In this sand collecting method, the discharge step into the atmosphere is performed by discharging the sand from the bottom surface of the sand collector. The step may be performed in a state where the water level is maintained below the upper end position of the covering member positioned toward the upper end of the covering member.

[0130] The sand collection method described above is a method for collecting sand deposited on the bottom of a settling basin, which allows sand contained in received water to settle on the bottom, the bottom having a groove extending in a predetermined direction and a bottom surface formed between the side wall of the settling basin and the groove and connected to the groove, and an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water accumulated 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 the fluid into a space covered by a cover member that has an opening at a lower end portion and covers a periphery of an imaginary axis extending from the first discharge port in the predetermined direction, The atmospheric discharge step may be a step performed in a state where 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.

[0131] 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 provided in the bottom of the pond and extending in a predetermined direction; a first discharge port that discharges fluid in the predetermined direction into the water accumulated in the groove; a bottom surface 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 the upper end position of the covering member, The second discharge port is characterized in that it discharges the fluid in a state where the water level is maintained below the upper end position of the covering member.

[0132] The groove may be inclined downward at an angle of 0 degrees or more and less than 1 degree toward the predetermined direction.

[0133] The sand collection method described above is a method for collecting sand deposited on the bottom of a settling basin that settles sand contained in received water, the settling basin having a groove extending in a predetermined direction and a bottom surface formed between the side wall of the settling basin and the groove and connected to the groove, an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water accumulated 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 the fluid into a space covered by a cover member that has an opening at a lower end portion and covers a periphery of an imaginary axis extending from the first discharge port in the predetermined direction, The atmospheric discharge step is characterized in that it is a step carried out in a state where 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 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 provided in the bottom of the pond and extending in a predetermined direction; a first discharge port that discharges fluid in the predetermined direction into the water accumulated in the groove; a bottom surface 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 characterized in that it is positioned above the upper end position of the covering member. The sand collection method described above is a method for collecting sand deposited on the bottom of a settling basin that settles sand contained in received water, the settling basin having a groove extending in a predetermined direction and a bottom surface formed between the side wall of the settling basin and the groove and connected to the groove, an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water accumulated 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 ejection process is characterized in that it is a process of ejecting a fluid into a space covered by a covering member that has an opening at the lower end portion and covers the periphery of an imaginary axis extending from the first ejection port in the predetermined direction.

[0134] Note that even if a constituent element is included only in the description of the embodiment or each of the modified examples described above, that constituent element may be applied to the embodiment or other modified examples. [Explanation of symbols]

[0135] 2. Settling pond 8 Main Trough 13 First covering member 13a aperture 14 Second covering member 15 Third covering member 84a Trough third outlet 71 Bottom plane 831a Trough No. 1 outlet 832a Trough No. 2 Outlet 911 Discharge port Side wall W

Claims

1. In a settling basin where sand contained in the received water settles to the bottom of the basin, A groove provided in the bottom of the pond and extending in a predetermined direction; a first discharge port that discharges fluid in the predetermined direction into the water accumulated in the groove; a bottom surface 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 the upper end position of the covering member, the first discharge port and the second discharge port alternately discharge fluid, A settling basin characterized in that the first discharge outlet discharges fluid when the water level is above the upper end position of the cover member.

2. A method for collecting sand deposited on the bottom of a settling basin that settles sand contained in received water, the settling basin having a groove extending in a predetermined direction, a cover member having an opening at its lower end, and a bottom surface formed between the side wall of the settling basin and the groove, connected to the groove, and positioned above the upper end position of the cover member, an underwater discharge step of discharging fluid from a first discharge port in the predetermined direction into a space covered by the cover member in the water accumulated in the groove; 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 discharging step and the atmospheric discharging step are alternately performed, A sand collecting method characterized in that the underwater discharge process is a process of discharging fluid when the water level is above the upper end position of the covering member that covers the periphery of an imaginary axis extending from the first discharge outlet in the predetermined direction.

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