Grit chamber

Abstract

To provide an inexpensive sand sedimentation pond.SOLUTION: A sand sedimentation pond 2 in which sand contained in received water is settled in a pond bottom part includes a main trough 8 which is provided in the pond bottom part and extends in a predetermined direction, a trough first discharge port 831a for discharging a fluid in a predetermined direction in the water accumulated in the main trough 8, a bottom plane 71 and a small trough 72 which are provided in the pond bottom part, are formed between the side wall of the sand sedimentation pond 2 and the main trough 8, and are connected to the main trough 8, a second discharge port 911 for discharging a fluid for flowing the sand accumulated in the bottom plane 71 and the small trough 72 from the side wall side to the main trough 8, into the air, and a first covering member 13 which covers the periphery of a virtual shaft VL extending in a predetermined direction from the center of the first discharge port 831a, and has an opening 13a in the lower end part, wherein the second discharge port 911 discharges the fluid at a discharge pressure lower than that of the first discharge port 831a.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. [Background technology]

[0002] Some wastewater treatment facilities are provided with a settling basin that receives wastewater such as sewage and rainwater, settles sand contained in the wastewater on the bottom of the basin or in a groove provided in the bottom of the basin, and then collects the sand deposited on the bottom or in the groove in a sand collection pit provided in the bottom of the basin to remove it from the wastewater. For example, Patent Document 1 discloses that a sand removal operation is performed at a predetermined time to collect the deposited sand in the sand collection pit, and the sand is pumped up together with wastewater by a sand lifting pump installed in the sand collection pit, conveyed through a pipe, and sent to a sand separator outside the settling basin. This pipe is composed of a conveying pipe that extends above the settling basin toward a sand separator or the like provided outside the basin, and a sand lifting pipe that extends from the sand lifting pump toward the conveying pipe and is connected to the conveying pipe above the settling basin. A backflow prevention valve is provided in this sand lifting pipe to prevent the wastewater and sand in the pipe from flowing back into the settling basin when the sand lifting pump is not driven. There are two types of backflow prevention valves: one that opens and closes using the driving force of an electric actuator (hereafter referred to as motorized valves), and one that opens and closes automatically depending on the flow of fluid (hereafter referred to as check valves). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-95290 A Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, there is a demand for inexpensive settling basins.

[0005] In view of the above circumstances, an object of the present invention is to provide an inexpensive settling basin. [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 is provided in the bottom of the pond and extends in a predetermined direction; a first outlet that discharges a fluid in the predetermined direction into the water stored in the groove; A bottom surface is provided at the bottom of the pond, formed between the side wall of the settling basin and the groove and connected to the groove; a second outlet that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall toward the groove; a cover member that covers a periphery of a virtual axis extending from a center of the first discharge port in the predetermined direction and has an opening at a lower end portion, The second outlet is characterized in that it ejects fluid at a lower ejection pressure than the first outlet.

[0007] The first discharge port discharges a fluid in a state where the inside of the covering member is filled with water received in the grit basin, The second discharge port may be configured to discharge a fluid after the water received in the grit basin has been drained.

[0008] the first discharge port discharges a fluid at a discharge pressure of 0.05 MPa or more and 0.3 MPa or less, The second discharge port may discharge the fluid at a discharge pressure of not less than 0.0002 MPa and not more than 0.005 MPa. Effect of the Invention

[0009] According to the present invention, an inexpensive grit settling basin can be provided. [Brief description of the drawings]

[0010] [Figure 1]1 is a schematic cross-sectional view of a wastewater treatment facility including a grit basin according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view of a settling basin corresponding to one embodiment of the present invention, viewed from above. [Diagram 3] 3 is a cross-sectional view along the line XX 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. [Diagram 5] 3 is a cross-sectional view of the grit chamber shown in FIG. 2 along line AA. [Figure 6] FIG. 6 is an enlarged view showing a portion B in FIG. 5. [Figure 7] FIG. 1(a) is a cross-sectional view illustrating a state in which one pipe having a lap joint is joined to another pipe, and FIG. 1(b) is a cross-sectional view illustrating a state in which the one pipe having the lap joint is able to rotate freely around its axial direction relative to the other pipe by loosening the bolt. [Figure 8] 7A is a cross-sectional view taken along line CC in FIG. 6, and FIG. 7B is a cross-sectional view similar to FIG. 7A for illustrating a change in the discharge direction by the sand collecting nozzle. [Figure 9] This is a schematic cross-sectional view of four sewage treatment facilities, cut across the sand collection pit in the width direction of the pond and viewed longitudinally. [Figure 10] 1 is a skeleton diagram showing a sand lifting pump, a sand lifting pipe, a transport pipe, and a sand separator. FIG. [Figure 11] 9A is an enlarged view of a portion E in FIG. 9, and FIG. 9B is an enlarged view of FIG. 9A as viewed from the upstream side of the transport direction of the transport pipe. [Figure 12] This is a diagram of the water supply system in a sewage treatment facility. [Figure 13] FIG. 2 is an explanatory diagram showing the water level of the grit basin and the water level sensor. [Figure 14] 1 is a flowchart showing the flow of a sand removal operation in a wastewater treatment facility. [Figure 15]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 16] 4 is a cross-sectional view similar to FIG. 3, showing a modified example of the connection surface. [Figure 17] 8(a) is a diagram showing a first modified example of the supply pipe and the sand collecting nozzle shown in FIG. 8, and FIG. 8(b) is a diagram showing a second modified example of the supply pipe and the sand collecting nozzle shown in FIG. [Figure 18] 6 is a cross-sectional view similar to FIG. 5 showing a modification of the main trough, cover member, and bottom surface. [Figure 19] 19 is a cross-sectional view similar to FIG. 8(a), showing the bottom plane near the upstream end of the settling basin and the bottom plane near the sand collection pit in the modified example shown in FIG. 18. [Figure 20] 14 is an explanatory diagram similar to FIG. 13, showing an example of water level detection when the height of the main trough is increased. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A grit basin according to one embodiment of the present invention is disposed in a wastewater treatment facility, and allows sand contained in wastewater such as sewage and rainwater to settle, and then moves the settled sand to a sand collection pit to be removed from the wastewater.

[0012] 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.

[0013] As shown in FIG. 1, the wastewater treatment facility 1 has a grit basin 2, a pump well 3, and a dam device 4. Wastewater such as sewage and rainwater flows into this wastewater treatment facility 1. Four wastewater treatment facilities 1 of this embodiment are provided in parallel with respect to the flow direction of the wastewater. Since each of the wastewater treatment facilities 1 has the same configuration, one of them will be described first. The wastewater treatment facility 1 receives wastewater from the left side in FIG. 1. The received wastewater slowly flows toward the pump well 3 on the right side of the figure while allowing the sand contained in the wastewater to settle in the grit basin 2 (see the straight arrow shown 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.

[0014] A dam device 4 is disposed upstream of the grit basin 2 in the wastewater treatment facility 1. The dam device 4 has an opening wall 41, an inflow gate 42, and a gate drive device 43. The downstream wall surface of the opening wall 41 defines the upstream end of the grit basin 2. An inflow port 411 is opened at the lower end of the opening wall 41. The inflow gate 42 is provided so as to be movable up and down along the upstream wall surface of the opening wall 41. When the inflow gate 42 is in the lower position shown by the solid line in FIG. 1, it blocks the inflow port 411 and blocks the inflow of wastewater upstream of the dam device 4 into the grit basin 2. When the inflow gate 42 is raised to the upper position shown by the two-dot chain line in FIG. 1, it allows the wastewater to flow into the grit basin 2. The gate drive device 43 has a drive mechanism (not shown) therein and moves the inflow gate 42 up and down in response to a command from a control device that controls the dam device 4. By this vertical movement, the inflow gate 42 is selectively placed at either the upper position or the lower position.

[0015] 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 in 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 passes through the sand lifting pipe 64 and is sent to a sand separator SS (see FIG. 10) located outside the settling basin 2. The dust remover 5 is used to remove contaminants (seed 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.

[0016] A pump well 3 is formed downstream of the grit basin 2 in the wastewater treatment facility 1. The pump well 3 stores wastewater from which sand has been removed by the grit basin 2. The bottom of the pump well 3 is the deepest part of the wastewater treatment facility 1. A lifting pump 31 and a feed pump 33 are arranged in the pump well 3. The lifting pump 31 moves the wastewater stored in the pump well 3 to the outside of the wastewater treatment facility 1. A lifting pipe 32 is connected to the lifting pump 31. The wastewater sucked by the lifting pump 31 is sent through this lifting pipe 32 to a sedimentation tank (not shown) or the like for the next stage of wastewater treatment. The feed pump 33 is arranged closer to the bottom of the pump well than the above-mentioned lifting pump 31. A feed pipe 34 is connected to the feed pump 33. The wastewater sucked by the feed pump 33 is sent through this feed pipe 34 to each nozzle or the like described later. The wastewater sucked by the water supply pump 33 is referred to as a fluid in the following description.

[0017] Fig. 2 is a plan view of a grit basin corresponding to one embodiment of the present invention, seen from above. In Fig. 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.

[0018] As shown in FIG. 2, the settling basin 2 is a pond having a generally rectangular shape in a plan view, and includes a dust remover 5, a sand collecting pit 6, a bottom plane 71, a small trough 72, a connection surface 73, a main trough 8, and a sand collecting means 9 between a left side wall Wa and a right side wall Wb. The bottom plane 71 and the small trough 72 correspond to an example of a bottom surface. The main trough 8 corresponds to an example of a groove. Hereinafter, the left side wall Wa and the right side wall Wb may be collectively referred to as a side wall W. A protruding wall 10 for supporting the dust remover 5 is provided in the center of the width direction of the pond on the upstream side of the settling basin 2. The sand collecting pit 6, the bottom plane 71, the small trough 72, the connection surface 73, and the main trough 8 are each provided in the pond bottom of the settling basin 2. The bottom plane 71 is formed by the surface of concrete poured into the pond bottom. The main trough 8 is composed of an upstream first main trough 815 and an upstream second main trough 816, which extend in the longitudinal direction from the vicinity of the upstream end of the settling basin 2 and whose rear end is connected to the sand collection pit 6, and a downstream main trough 82, which extends in the longitudinal direction from the vicinity of the downstream end of the settling basin 2 and whose rear end is connected to the sand collection pit 6. The upstream first main trough 815 corresponds to an example of a first groove, and the upstream second main trough 816 corresponds to an example of a second groove. The settling basin 2 is a so-called low-pressure sand collection type settling basin, in which a fluid is discharged to the bottom plane 71 and the small trough 72 while the wastewater in the settling basin 2 is drained, and the sand that has settled on the bottom plane 71 and the small trough 72 is collected. Hereinafter, the long side direction of the settling basin 2 is referred to as the longitudinal direction, and the short side direction is referred to as the pond width direction. This longitudinal direction is also a perpendicular direction perpendicular to the pond width direction.

[0019] A building, piping, etc. (not shown) may be arranged above the settling basin 2 (the front side of the paper in FIG. 2). A pillar 11 may be formed adjacent to the settling basin 2 in order to support the building, etc. In the settling basin 2 shown in FIG. 2, the pillar 11 is formed near the left side wall Wa. A part of the left side wall Wa that serves as the base of the pillar 11 is formed with a convex wall portion Wa1 that protrudes toward the center in the width direction of the pond. Conversely, it can be said that a part of the left side wall Wa where the pillar 11 does not exist on the left side wall Wa is formed with a concave wall portion Wa2 that is concave toward the outside in the width direction of the pond. In addition, a part connecting the convex wall portion Wa1 and the concave wall portion Wa2 is formed with an inclined wall portion Wa3 that is inclined with respect to the longitudinal direction and the width direction of the pond. Since the pillar 11 does not exist near the right side wall Wb, the right side wall Wb is formed in a substantially straight line in a plan view.

[0020] The sand collection pit 6 is located slightly downstream of the center in the longitudinal direction 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, there is a sand collection pit slope 6b that slopes gradually to become deeper toward the sand collection pit 6 side located in the center of the basin width direction.

[0021] A total of four stirring nozzles 62 are disposed near each corner of the sand collection pit 6. The stirring nozzles 62 are for stirring the sand collected in the sand collection pit 6. By discharging a fluid from the discharge port 62a of the stirring nozzle 62 while the sand lifting pump 61 is driven, the efficiency of the suction of the sand collected in the sand collection pit 6 by the sand lifting pump 61 can be improved. Two sand collection nozzles 63 for the pit are disposed at each end of the sand collection pit slope 6b in the pond width direction. With the water level of the sand collection basin 2 lowered below a predetermined value, the sand accumulated on the sand collection pit slope 6b can be collected in the sand collection pit 6.

[0022] The bottom plane 71 is composed of a first bottom surface 711 formed between the left side wall Wa and the upstream first main trough 815, a second bottom surface 712 formed between the right side wall Wb and the upstream second main trough 816, a third bottom surface 713 formed between the left side wall Wa and the downstream main trough 82, and a fourth bottom surface 714 formed between the right side wall Wb and the downstream main trough 82. The bottom plane 71 and the small trough 72 are connected to the main trough 8 at the center of the settling basin 2 in the width direction. The bottom plane 71 is inclined downward by about 5 degrees from the side wall W at the outer end in the width direction of the pond toward the main trough 8 so that the end on the side of the main trough 8 is the deepest. On the other hand, the bottom plane 71 is formed horizontally in the longitudinal direction. The small trough 72 is a gutter-shaped trough with a U-shaped cross section, and extends from the vicinity of the side wall W in the width direction of the pond. A plurality of small troughs 72 are arranged at equal intervals in the longitudinal direction. In this embodiment, a total of 56 small troughs 72 are arranged on either side of the main trough 8 in the pond width direction, with 28 on each side. Similar to the bottom plane 71, these small troughs 72 are also inclined downward by about 5 degrees from the side wall W side toward the main trough 8 side so that the part connected to the main trough 8 is located closest to the pond bottom.

[0023] The first upstream main trough 815, the second upstream main trough 816, and the downstream main trough 82 are grooves formed by a trough forming body, which is a stainless steel plate, 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 be formed of concrete integrally with the bottom plane 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 length in the longitudinal direction from near the end of the settling basin to the part connected to the sand collection pit 6.

[0024] As shown in FIG. 2, the upstream first main trough 815 is provided on the left side wall Wa side with respect to the center in the width direction of the pond, and extends in the longitudinal direction. The upstream second main trough 816 is provided on the right side wall Wb side with respect to the center in the width direction of the pond, and extends in the longitudinal direction. The upstream first main trough 815 and the upstream second main trough 816 both have a total length of 10 m and are the same in shape. The downstream ends of the upstream first main trough 815 and the upstream second main trough 816 are connected to the sand collection pit 6. An upstream trough first nozzle 831 having a trough first outlet 831a is provided at the upstream end portion of the upstream first main trough 815 (the tip portion of the upstream first main trough 815). In addition, 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. In addition, a second cover member 14 is disposed inside the upstream second main trough 816. The first cover member 13 and the second cover member 14 extend along the upstream first main trough 815 and the upstream second main trough 816, respectively. The total length of the first cover member 13 and the second cover member 14 is approximately the same as the total length of the upstream first main trough 815 and the upstream second main trough 816. As shown in FIG. 2, the first cover member 13 extends from upstream of the trough first outlet 831a to a slightly downstream beyond the portion of the upstream first main trough 815 connected to the sand collection pit 6. When wastewater is accumulated in the upstream first main trough 815, the sand accumulated in the upstream first main trough 815 can be moved to the sand collection pit 6 by discharging a fluid from the trough first outlet 831a. In addition, the second cover member 14 extends from upstream of the trough second outlet 832a to a slightly downstream beyond the portion of the upstream second main trough 816 connected to the sand collection pit 6. When wastewater is accumulated in the upstream second main trough 816, the sand accumulated in the upstream second main trough 816 can be moved to the sand collection pit 6 by discharging a fluid from the trough second outlet 832a.The movement of sand 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.

[0025] The downstream main trough 82 extends linearly in the longitudinal direction at the center of the width of the settling basin 2. The total length of the downstream main trough 82 is 5 m. The upstream end of the downstream main trough 82 is connected to the sand collection pit 6. A downstream trough nozzle 84 having a trough third outlet 84a is provided at the downstream end of the downstream main trough 82 (the tip portion of the downstream main trough 82). This trough third outlet 84a also corresponds to an example of the first outlet. A third cover member 15 is disposed inside the downstream main trough 82. This third cover member 15 extends along the downstream main trough 82. The total length of the third cover member 15 is approximately the same as the total length of the downstream main trough 82. As shown in FIG. 2, the third cover member 15 extends from downstream of the trough third outlet 84a to a slightly upstream position beyond the part of the downstream main trough 82 connected to the sand collection pit 6. When wastewater accumulates in the downstream main trough 82, a fluid is discharged from the trough third discharge port 84a, so that the sand accumulated in the downstream main trough 82 can be moved 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.

[0026] Between the upstream first main trough 815 and the upstream second main trough 816, a protruding wall 10 for supporting the dust collector 5 is formed in the upstream portion of the grit basin 2. This protruding wall 10 is a concrete wall that rises up to the vicinity of the upper end of the grit basin 2. The connection surface 73 is between the upstream first main trough 815 and the upstream second main trough 816, and is disposed in the bottom of the pond downstream of this protruding wall 10. That is, the connection surface 73 is formed in a portion between the upstream first main trough 815 and the upstream second main trough 816 excluding the area where the protruding wall 10 is provided. The connection surface 73 is composed of a ridge portion 731 extending along the longitudinal direction, a first connection surface 732 that connects the ridge portion 731 and the upstream first main trough 815, and a second connection surface 733 that connects the ridge portion 731 and the upstream second main trough 816. The extension direction of the ridgeline 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 the up-down direction with respect to the longitudinal direction. Also, the ridgeline portion 731 may meander slightly in the pond width direction and the up-down direction. In other words, "extending along the longitudinal direction" is a concept that includes some inclination and meandering.

[0027] Fig. 3 is a cross-sectional view taken along line XX of the grit basin shown in Fig. 2. In Fig. 3, the dust collector is omitted.

[0028] As shown in FIG. 3, the first connection surface 732 is an inclined surface that is inclined downward toward the upstream first main trough 815. The second connection surface 733 is an inclined surface that is inclined downward toward the upstream second main trough 816. The first connection surface 732 and the second connection surface 733 are made of concrete surfaces. The inclination angle of the first connection surface 732 and the second connection surface 733 is about 45 degrees with respect to the horizontal plane. By inclining the connection surface, sand that settles on the connection surface 73 can be collected in the upstream first main trough 815 or the upstream second main trough 816 without remaining on the connection surface 73. If the inclination angle of the first connection surface 732 and the second connection surface 733 is 15 degrees or more, most of the sand that settles on the connection surface 73 in the wastewater in the grit basin 2 slides down the connection surface 73 due to its own weight. Moreover, if the inclination angle of the first connection surface 732 and the second connection surface 733 is set to 30 degrees or more, the sand that settles on the connection surface 73 will slide down the connection surface 73 more easily, which is preferable. However, if the inclination angle is too large, the thickness of the concrete that constitutes the connection surface 73 in the pond width direction will be too thin in the vicinity of the ridge line portion 731, and the ridge line portion 731 will be easily damaged. For this reason, it is preferable to set the angle of the ridge line portion 731 formed by the first connection surface 732 and the second connection surface 733 so that the angle of the ridge line portion 731 formed by the first connection surface 732 and the second connection surface 733 is 30 degrees or more. Note that one or both of the first connection surface 732 and the second connection surface 733 do not have to be formed of a single plane, and may be formed of multiple surfaces with different inclination angles, for example. In this case, the inclination angle of all the multiple surfaces may be 15 degrees or more. Also, one of the first connection surface 732 and the second connection surface 733 may be a vertical surface, and the other may be an inclined surface. However, by making each of the first connection surface 732 and the second connection surface 733 an inclined surface as in this embodiment, the sand can be distributed and slid down to the upstream first main trough 815 and the upstream second main trough 816, so it is preferable to make each an inclined surface. Also, by providing a ridge portion 731 in the center between the upstream first main trough 815 and the upstream second main trough 816 as in this embodiment, the amount of sand that slides down to the upstream first main trough 815 and the upstream second main trough 816 can be made uniform.This prevents a large amount of sand from accumulating in one of the upstream first main trough 815 and the upstream second main trough 816, thereby preventing the sand from being unable to be transported to the sand collection pit 6 due to the resistance to transport of the sand in the upstream first main trough 815 and the upstream second main trough 816.

[0029] Fig. 4(a) is an enlarged view of the Z portion of Fig. 3, and Fig. 4(b) is a schematic perspective view showing the first cover member and the upstream trough first nozzle. In Fig. 4(a), the left-right direction of the figure is the pond width direction, and the direction perpendicular to the paper surface is the longitudinal direction. In Fig. 4(a), hatching representing the cross section of the upstream first main trough and the first cover member is omitted.

[0030] 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 the same shape except for the bottom plane 71 or the connection surface 73 connected thereto, and therefore the description thereof will be omitted. As described above, the upstream first main trough 815 of this embodiment has a cross-sectional shape of 2 / 3 of a circle. That is, it has an arc shape with the trough arc center 815c, which is the center in the radial direction, as the center point. However, the cross-sectional shape of the upstream first main trough 815 is not limited to an arc shape, and may be a U-shape, a V-shape, or the like. The upstream first main trough 815 has a shape in which the upper part of a cylinder with an inner diameter of 300 mm is cut out, and opens upward over its entire length. Hereinafter, this open portion may be referred to as the first trough opening 815b. The small trough 72 is connected to this first trough opening 815b, and the heightwise position of the first trough opening 815b is the same as the heightwise position of the lower end of the small trough 72. The upper portion 815a of the upstream first main trough 815 above the trough arc center 815c narrows in the pond width direction toward the upper end first trough opening 815b. As a result, even if sand is blown up in the upstream first main trough 815, the upper portion 815a acts as a return and can return the blown up sand into the upstream first main trough 815.

[0031] The first covering member 13 has a cross-sectional shape of a 5 / 6 circle with an opening 13a at the lower end. That is, it has an arc shape with the covering arc center 13c, which is the center in the radial direction, as the center point. This first covering member 13 is a stainless steel plate material with a plate thickness of 3 mm formed into a cross-sectional arc shape with an inner diameter of 150 mm. The opening 13a is provided over the entire length of the first covering member 13. The first covering member 13 divides the internal space of the upstream first main trough 815. The space inside the first covering member 13 becomes the transfer space FS, which is the space covered by the first covering member 13. Since the first covering member 13 has an arc shape with the upper part closed, the sand that has settled toward the upper part of the first covering member 13 in the grit basin 2 easily slides down the outer surface of the upper part of the first covering member 13. The sand that slides down is deposited below the upstream first main trough 815. In addition, the transfer space FS below the cover arc center 13c of the first cover member 13 narrows in the pond width direction toward the lower opening 13a. The first cover member 13 is supported by a support bracket 131 (see FIG. 5) fixed to concrete poured into the bottom of the settling basin 2 with a chemical anchor (registered trademark). The height position of the upper end of the first cover member 13 is located at approximately the same height as the first trough opening 815b. It is desirable to set the height position of the upper end of the first cover member 13 at approximately the same height as the first trough opening 815b or at a position lower than the first trough opening 815b. By setting it at this position, if water is filled in the upstream first main trough 815, the inside of the first cover member 13 can be filled with water. When the fluid is discharged into the water from the trough first discharge port 831a, a strong flow of fluid can be created inside the first cover member 13 by filling the inside of the first cover member 13 with water. Furthermore, the opening 13a of the first covering member 13 is disposed below the center 815h in the height direction of the upstream first main trough 815. This arrangement allows the opening 13a of the first covering member 13 to be closer to the sand accumulated below the upstream first main trough 815, making it easier for the flow of fluid in the first covering member 13 to suck up the sand accumulated in the upstream first main trough 815 into the inside of the first covering member 13.In addition, 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. In addition, the first covering member 13 in this embodiment has an arc-shaped cross section, but the cross section may be polygonal, or may be a shape in which an arc and a straight line are connected. However, it is preferable that the cross section of the upper part of the first covering member 13 is an inclined surface that is inclined downward toward the width direction of the groove. By making the upper part of the first covering member 13 an inclined surface, the sand that has settled in the upper part of the first covering member 13 is more likely to slide down the upper part, and is more likely to accumulate downward in the upstream first main trough 815.

[0032] The trough first outlet 831a is disposed in the transfer space FS in the first cover member 13. The trough first outlet 831a is an elongated hole shape obtained by flattening the tip of a pipe having an inner diameter of 80 mm from above and below. The maximum opening length of the trough first outlet 831a in the pond width direction is 117 mm, and the maximum height in the vertical direction is 18 mm. The trough first outlet 831a may be of other shapes, such as a perfect circle. However, by making the trough first outlet 831a into a flat shape, the fluid can be discharged over a wider range than a perfect circle before being flattened. The discharge flow velocity of the fluid discharged from the trough first outlet 831a is preferably 8 m / sec or more. If it is less than 8 m / sec, the flow velocity may be insufficient, and the sand may not be moved a predetermined distance. In addition, the discharge pressure of the fluid discharged from the trough first outlet 831a is preferably 0.05 MPa or more and 0.3 MPa or less. The center of the trough first outlet 831a coincides with the 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. The axis extending in the flow direction of the fluid discharged from the trough first outlet 831a, starting from the center (cover arc center 13c), becomes the 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 cover member 13 and the discharge direction of the fluid discharged from the trough first outlet 831a do not need to be completely aligned with the longitudinal direction, but by making them aligned, the sand can be transported more efficiently. Even if the discharge direction of the fluid discharged from the trough first outlet 831a and the extension direction of the first cover member 13 are slightly different, the discharged fluid is guided by the first cover member, so the flow direction of the fluid coincides with the extension direction of the first cover member. Therefore, the virtual axis VL in this case becomes the extension direction of the first cover member. However, in this case, the fluid may collide with the first cover member and the flow may be weakened, so it is desirable to make the discharge direction of the fluid discharged from the trough first outlet 831a and the extension direction of the first cover member 13 coincide with each other.The center of the trough first outlet 831a may be located at a position different from the cover arc center 13c, for example, below the cover arc center 13c and above the opening 13a. However, by making the center of the trough first outlet 831a coincide with the cover arc center 13c, the loss of the flow of the fluid discharged from the trough first outlet 831a can be minimized. On the other hand, by making 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 make the center of the trough first outlet 831a between the cover arc center 13c and the opening 13a of the first cover member 13.

[0033] The fluid is discharged from the trough first discharge port 831a into the transfer space FS, and a flow of the fluid is generated in the transfer space FS inside the first cover member 13. Then, a pressure difference occurs between the transfer space FS and the outside of the first cover member 13 due to the flow of the fluid. That is, a negative pressure is generated in the transfer space FS where the flow of the fluid is generated. The sand deposited in the upstream first main trough 815 is sucked into the transfer space FS from the opening 13a by the negative pressure, as shown by the curved arrow in FIG. 4(a). In addition, the fluid discharged from the trough first discharge port 831a is prevented from diffusing in the radial direction perpendicular to the longitudinal direction by the first cover member 13, so that the flow is maintained in the transfer space FS over a long distance. The sucked sand is transported toward the sand collection pit 6 side by the flow of the fluid generated in the transfer space FS. In this embodiment, the transfer space FS is formed by the first cover member 13, and the flow of the fluid discharged from the trough first discharge port 831a can be utilized for transporting sand without impairing it. As a result, the sand accumulated in the upstream first main trough 815 can be efficiently transported toward the sand collection pit 6. As described above, the area below the cover arc center 13c in the transport space FS narrows in the pond width direction toward the lower opening 13a. By narrowing the pond width of the opening 13a, the sand transported in the transport space FS is less likely to leak out of the transport space FS. In addition, the fluid in the transport space FS is less likely to flow out of the transport space FS, so the flow of the fluid can be maintained for a long distance, and the sand can be moved farther. In addition, the negative pressure in the transport space FS can be easily maintained even at a position away from the trough first discharge port 831a.

[0034] As shown in FIG. 2, two dust removers 5 are arranged side by side in the width direction of the pond, sandwiching the protruding wall 10, in the upstream portion of the settling basin 2. In other words, one dust remover 5 is arranged between the left side wall Wa and the protruding wall 10, and one dust remover 5 is arranged between the right side wall Wb and the protruding wall 10. These two dust removers 5, 5 have the same configuration. The dust removers 5 are intended to remove contaminants (screen residue) mixed in the wastewater that has flowed 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, and the other dust remover 5 shown in the lower part of FIG. 2 is supported by the right side wall Wb and the protruding wall 10. By arranging the two dust removers 5, 5 side by side in the width direction of the pond, the width of each dust remover 5 in the width direction of the pond can be shortened. By shortening the width of the dust collector 5 in the 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.

[0035] Fig. 5 is a cross-sectional view taken along line AA of the settling basin shown in Fig. 2. In Fig. 5, the pillars are omitted, and the shape of the protruding wall is indicated by a two-dot chain line. The direction of the wastewater 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 during normal times when the amount of rain and sewage is expected, as shown in Fig. 5, it is located at a mid-height in the height direction of the settling basin 2.

[0036] As shown in FIG. 5, the dust collector 5 has an endless chain 51, a plurality of rakes 52 attached to the endless chain 51 at intervals, and a filter screen 53. The endless chain 51 is provided in an upright state at an angle on both sides of the width direction of the grit basin 2, and is wound around a ground-side sprocket 511 and a pond bottom-side sprocket 512. The upper part of the endless chain 51 and the ground-side sprocket 511 are disposed on the ground portion of the grit basin 2. When the water surface WL is in a normal state, if the ground-side sprocket 511 is driven in the rotation direction indicated by the arc-shaped arrow R by a motor (not shown), the endless chain 51 circulates and the rake 52 moves in and out of the water. FIG. 5 shows the water surface WL in a normal state. The protruding wall 10 protrudes above the water surface WL. However, when the protruding wall 10 is formed for a purpose other than supporting the dust collector 5, the protruding wall 10 may be lower than the water surface WL. The filter screen 53 is disposed downstream of the endless chain 51. The filter screen 53 is a structure in which vertically extending bars are arranged at a predetermined interval (for example, 25 mm to 75 mm) in the width direction of the pond, and blocks the passage of contaminants larger than the predetermined interval. The contaminants blocked by the filter screen 53 are scooped up by the rake 52, and the scooped up contaminants are placed on a conveying means such as a belt conveyor (not shown) on the ground side. The bottom sprocket 512 and the lower end of the filter screen 53 are disposed upstream of the bottom plane 71 and the main trough 8. On the other hand, the upper ends of the ground sprocket 511 and the filter screen 53 are located above the bottom plane 71 and the upstream part of the main trough 8. That is, the upper parts of the endless chain 51 and the filter screen 53 overlap with the bottom plane 71 and the main trough 8 in the longitudinal direction. Note that FIG. 5 also shows a support bracket 151 that supports the third cover member 15.

[0037] The sand collecting 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 side of the settling basin 2, and a fourth nozzle header 9d, a fifth nozzle header 9e, and a sixth nozzle header 9f arranged on the right side wall Wb side (see FIG. 2). FIG. 5 shows the sand collecting means 9 on the left side wall Wa side. The sand collecting means 9 on the right side wall Wb side has the same configuration, so the description of the sand collecting means 9 on the right side wall Wb side is omitted. Each of the first nozzle header 9a, the second nozzle header 9b, and the third nozzle header 9c includes ten sand collecting 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 in the longitudinal direction. The main pipe 93 includes a single pipe 931 extending above the settling basin 2 and a branch pipe 932 connected to the end of the single pipe 931 on the bottom side of the basin. The single pipe 931 and the branch pipe 932 are fixed to the left side wall Wa by fixing metal fittings (not shown).

[0038] As shown in FIG. 5, one end of a sand lifting pipe 64 is connected to the sand lifting pump 61. The other end of the sand lifting pipe 64 is connected to a transport pipe 66 above the settling basin 2. The sand lifting pipe 64 connects the sand lifting pump 61 and the transport pipe 66. The transport pipe 66 extends in a substantially horizontal direction above the settling basin 2. A check valve 641 and a gate valve 642 are installed in the sand lifting pipe 64. The transport pipe 66 is supported by a suspension stand 67 installed on the ground and extends in the width direction of the pond. The sand lifting pipe 64 and the transport pipe 66 will be described in detail later. The sand lifting pump 61, the sand lifting pipe 64, and the transport pipe 66 correspond to an example of a sand carrying-out facility.

[0039] Figure 6 is an enlarged view of part B in Figure 5. In Figure 6, the flow direction of wastewater is indicated by a straight arrow. A side wall is also shown in Figure 6. Also, Figure 6 shows one of the six nozzle headers, but the other five nozzle headers have the same configuration as the nozzle header shown in Figure 6.

[0040] As shown in FIG. 6, the branch pipe 932 is connected to the single pipe 931 by a flange joint 933. The branch pipe 932 branches into two at the lower side of the part connected to the single pipe 931, and the branched parts extend in the longitudinal direction of the grit basin 2. The supply pipes 92 to which the lap joints 934 are fixed are connected to the tip parts of the branched parts. In this embodiment, three supply pipes 92 are provided for one mother pipe 93: an upstream supply pipe 921 arranged upstream of the branch pipe 932, a downstream supply pipe 923 arranged downstream of the branch pipe 932, and an intermediate supply pipe 922 arranged between the upstream supply pipe 921 and the downstream supply pipe 923. The other end of the upstream supply pipe 921 and the downstream supply pipe 923, opposite to the one end connected to the branch pipe 932, is closed by a lid 97. Both ends of the intermediate supply pipe 922 are connected to the branch pipe 932.

[0041] Three sand collection nozzles 91 are fixed at equal intervals to each of the upstream supply pipe 921 and the downstream supply pipe 923. Four sand collection nozzles 91 are fixed at equal intervals to the intermediate supply pipe 922. The total of ten sand collection nozzles 91 are all arranged at equal intervals. The interval between the most downstream sand collection nozzle 91 of the first nozzle header 9a (see FIG. 2) and the most upstream sand collection nozzle 91 of the second nozzle header 9b is also the same as the interval between the ten sand collection nozzles. That is, the sand collection nozzles 91 are all arranged at equal intervals in the longitudinal direction of the grit basin 2. The number of sand collection nozzles 91 arranged in each supply pipe 92 may be appropriately determined depending on factors such as the length of the supply pipe 92. An outlet 911 is formed at the tip of each sand collection nozzle 91. This outlet 911 corresponds to an example of a second outlet. Among the discharge ports 911, the discharge ports 911 provided in the first nozzle header 9a (see FIG. 2) and the second nozzle header 9b correspond to an example of a one-side discharge port, and the discharge ports 911 provided in the fourth nozzle header 9d and the fifth nozzle header 9e (see FIG. 2) correspond to an example of a other-side discharge port. By discharging a fluid from the discharge port 911 into the atmosphere in a state in which the water level of the grit basin 2 is lowered below a predetermined value to expose the sand accumulated on the bottom plane 71 and the small trough 72 and the discharge port 911 to the atmosphere, the sand accumulated on the bottom plane 71 and the small trough 72 shown in FIG. 2 and FIG. 5 can be made to flow into the main trough 8. The discharge pressure of the fluid sprayed from one discharge port 911 is, for example, 0.005 MPa, and preferably 0.0002 MPa or more and 0.005 MPa or less. That is, the discharge pressure of the fluid discharged from the discharge port 911 is lower than the discharge pressure (0.05 MPa or more and 0.3 MPa or less) of the fluid discharged from the trough first discharge port 831a. This makes it possible to use an inexpensive and small feed water pump 33 for supplying the fluid while ensuring a flow rate that allows the sand accumulated on the bottom plane 71 and the small trough 72 to flow into the main trough 8.

[0042] The distance from the supply pipe 92 to the left side wall Wa is different between the portion facing the convex wall Wa1 and the portion facing the concave wall Wa2. That is, the supply pipe 92 has a first region 92a extending from the left side wall Wa at a first interval in the pond width direction, and a second region 92b extending from the left side wall Wa at a second interval in the pond width direction. In addition, in the settling basin 2 of this embodiment, an inclined wall portion Wa3 is formed in the portion connecting the convex wall portion Wa1 and the concave wall portion Wa2, so that the supply pipe 92 has a third region 92c which is a region connecting the first region and the second region. Each sand collecting nozzle 91 and its discharge port 911 are arranged opposite the left side wall Wa and are fixed to the supply pipe 92 in a line in the longitudinal direction. In the second nozzle header 9b shown in FIG. 6, the upstream supply pipe 921 is arranged opposite the convex wall portion Wa1. That is, the region where the upstream supply pipe 921 is located corresponds to the first region 92a. On the other hand, the region of the intermediate supply pipe 922 where the outlet 911 located in the part closest to the upstream supply pipe 921 is arranged is arranged facing the inclined wall portion Wa3. That is, this region corresponds to the third region 92c. Also, the region of the intermediate supply pipe 922 where three outlets 911 are arranged from the downstream supply pipe 923 side, and the region of the downstream supply pipe 923 where two outlets 911 are arranged from the intermediate supply pipe 922 side are arranged facing the recessed wall portion Wa2. That is, these regions correspond to the second region 92b. Also, the region of the downstream supply pipe 923 where the outlet 911 located in the most downstream side is arranged is arranged facing the inclined wall portion Wa3. That is, this region corresponds to the third region 92c. Between these respective regions, a direction change means using a lap joint 934 is provided.

[0043] 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 one pipe provided with a lap joint can rotate freely about its axial direction relative to the other pipe by loosening a 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 together with a lap joint.

[0044] As shown in FIG. 7(a) and FIG. 7(b), a lap joint 934 is welded to the end of the supply pipe 92. The lap joint 934 is composed of a small diameter portion 934a welded to the supply pipe 92 and a large diameter portion 934b disposed on the branch pipe 932 side. The small diameter portion 934a has an outer diameter equal to that of the supply pipe 92. A free flange 935 is disposed on the outer periphery of the lap joint 934. The free flange 935 is ring-shaped with an inner diameter slightly larger than the outer diameter of the lap joint 934. The free flange 935 has eight free flange through holes 935a evenly spaced in the circumferential direction, into which the bolts 95 are inserted. The free flange 935 is connected to the lap joint 934 so as to be rotatable relative to the lap joint 934 and movable in the axial direction. A fixed flange 9322 is welded to the outer diameter portion of the tip of the branch pipe 932. The fixed flange 9322 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.

[0045] 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 fastened, the lap joint 934 is sandwiched between the fixed flange 9322 and the free flange 935 together with the packing 94, as in the supply pipe 92 shown in FIG. 7(a), so that the supply pipe 92 is fixed to the branch pipe 932. On the other hand, when the bolt 95 is loosened, the supply pipe 92 becomes rotatable about its axial direction relative to the branch pipe 932, as in the supply pipe 92 shown in FIG. 7(b). That is, in this embodiment, the mother pipe 93 (see FIG. 5) and the supply pipe 92 are connected using the lap joint 934 and the free flange 935, so that the supply pipe 92 is configured to be steplessly rotatable about its axial direction relative to the mother pipe 93. Incidentally, even if other loose-fitting flanges such as loose flanges are used instead of the lap joint 934, the supply pipe 92 can be connected to the mother pipe 93 so as to be capable of rotating in a stepless manner.

[0046] As shown in FIG. 6, a lap joint 934 is disposed between the outlet 911 disposed in the first region 92a and the outlet 911 disposed in the third region 92c, and between the outlet 911 disposed in the second region 92b and the outlet 911 disposed in the third region 92c. Therefore, the outlets 911 disposed in the first region 92a, the second region 92b, and the third region 92c are configured to be able to rotate steplessly around the axial direction of the supply pipe 92 independently of each other. With this configuration, the discharge direction of the fluid from the outlet 911 in each region can be set according to the distance from the supply pipe 92 to the left side wall Wa. The lap joint 934 disposed between the outlet 911 disposed in the first region 92a and the outlet 911 disposed in the third region 92c corresponds to an example of a first direction changing means. The lap joint 934 disposed between the outlet 911 disposed in the second region 92b and the outlet 911 disposed in the third region 92c corresponds to an example of a second direction changing means. In addition, in the first region 92a of the supply pipe 92 shown in FIG. 6, the discharge direction of the fluid from the three discharge ports 911 arranged in the first region 92a can be changed collectively, so that the discharge direction in the first region 92a can be easily adjusted. In the second region 92b of the supply pipe 92 shown in FIG. 6, the three discharge ports 911 arranged in the intermediate supply pipe 922 can be changed collectively, and the two discharge ports 911 arranged in the downstream supply pipe 923 can be changed collectively, so that the discharge direction in the second region 92b can be easily adjusted. That is, the lap joint 934 in the case where the discharge directions of the multiple discharge ports 911 can be changed collectively corresponds to an example of a collective direction changing means. Note that, when the longitudinal direction of the third region 92c is short and no discharge port 911 exists in the third region 92c, or when the third region 92c does not exist, the lap joint 934 may be disposed between the first region 92a and the second region 92b.

[0047] Fig. 8(a) is a cross-sectional view taken along line CC of Fig. 6. In Fig. 8(a), the sidewall and bottom plane are also shown.

[0048] 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. In the discharge port 911 shown by a solid line in FIG. 8(a), the discharge direction of the fluid is directed toward the center of the pond width direction rather than the direction (vertical direction) directly downward from the center of the supply pipe 92. In this discharge port 911, the angle θ1 at which the fluid is discharged with respect to the bottom plane 71 is set to about 50 degrees. By setting the angle θ1 to about 50 degrees, the fluid that has reached the bottom plane 71 can be divided into a direction toward the main trough 8 and a direction toward the convex wall portion Wa1. This angle θ1 may be any angle at which the discharged fluid is divided into a direction toward the main trough 8 and a direction toward the convex wall portion Wa1, and specifically, may be any angle at which the discharged fluid is divided into a direction toward the main trough 8 and a direction toward the convex wall portion Wa1, and may be 30 degrees or more and 60 degrees or less with respect to the bottom plane 71. By setting this angle, when the supply pipe 92 and the left side wall Wa are close to each other as in the convex wall portion Wa1, i.e., in the first region 92a (see FIG. 6), the diverted fluid reaches the sand accumulated on the bottom plane 71 between the supply pipe 92 and the left side wall Wa, and can flush away the sand. Also, since the discharge direction of the fluid is directed toward the main trough 8 in the center of the pond width direction rather than toward the vertical direction of 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 plane 71 between the supply pipe 92 and the main trough 8 to be efficiently flushed toward the main trough 8.

[0049] 8(a) at the recess wall Wa2, the supply pipe 92 is spaced from the left side wall Wa. Therefore, in the discharge direction of the discharge port 911, shown by the solid line, even if the discharged fluid is diverted, it does not reach the vicinity of the recess wall Wa2, or even if it does, 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 is accumulated between the supply pipe 92 and the recess wall Wa2 and that is near the recess wall Wa2 cannot be sufficiently flushed away.

[0050] In this embodiment, the supply pipe 92 is configured to be rotatable about its axis, so that the discharge direction of the fluid from the sand collection nozzle 91 can be freely changed. In FIG. 8(a), the sand collection nozzle 91 in which the discharge direction of the fluid discharged from the discharge port 911 is adjusted 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 discharged from the discharge port 911 is directed outward in the pond width direction rather than the direction (vertical direction) directly downward from the center of the supply pipe 92. By adjusting the discharge direction of the fluid discharged from the discharge port 911 according to the distance from the supply pipe 92 to the left side wall Wa, even if the supply pipe 92 and the left side wall Wa are separated as in the second region 92b (see FIG. 6), the sand accumulated near the left side wall Wa can be sufficiently flushed away. In this embodiment, the mother 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 that the connected supply pipe 92 can be rotated steplessly about its axis. Since it can be rotated steplessly, in the supply pipe 92 (third region 92c) located opposite the inclined wall portion Wa3 (see FIG. 2) between the convex wall portion Wa1 and the concave wall portion Wa2, the discharge direction of the fluid can be set to a direction intermediate between the discharge direction of the sand collecting nozzle 91 shown by the solid line in FIG. 8(a) and the discharge direction of the sand collecting nozzle 91 shown by the two-dot chain line.

[0051] In this embodiment, the parent pipe 93 is provided with a branch pipe 932, so that a total of three supply pipes 92, including the upstream supply pipe 921, the intermediate supply pipe 922, and the downstream supply pipe 923, are connected to one parent pipe 93 in line in the longitudinal direction of the grit basin 2. In contrast, if there is no branch pipe 932 and the supply pipe 92 is connected to the single pipe 931, at most two supply pipes 92 can be connected to one parent pipe 93 in the longitudinal direction of the grit basin 2. That is, there are two supply pipes 92, one extending from the tip of the parent pipe 93 to the upstream side of the grit basin 2 and the other extending to the downstream side. The discharge direction of the fluid discharged from the discharge port 911 can be set for each supply pipe 92. Therefore, compared to the case where there is no branch pipe 932, when the branch pipe 932 is provided, the discharge direction of the fluid discharged from the discharge port 911 can be adjusted at many points in the longitudinal direction of the grit basin 2, so that it is possible to more flexibly respond to the shape of the side wall W.

[0052] Fig. 8(b) is a cross-sectional view similar to Fig. 8(a) for explaining the change in the discharge direction by the sand collecting nozzle, in which the side wall and the bottom plane are also shown.

[0053] As shown in FIG. 8(b), the sand collection nozzle 91 is bent at the middle and is formed in an inverted L-shape when viewed in the longitudinal direction as shown by the solid line. Since the sand collection nozzle 91 shown in the solid line is formed in an inverted L-shape, when the sand collection nozzle 91 shown in the solid line is rotated 180 degrees around the axis L of the attachment part with the supply pipe 92, the discharge direction of the fluid can be changed from the center side in the pond width direction to the outside in the pond width direction as shown by the two-dot chain line. By forming the sand collection nozzle 91 in an inverted L-shape and configuring the connection part between the sand collection nozzle 91 and the supply pipe 92 to be rotatable, it is possible to change the discharge direction of the fluid for each discharge port 911. That is, the shape of the sand collection nozzle 91 in this embodiment and the configuration in which the sand collection nozzle 91 can rotate with respect to the supply pipe 92 correspond to an example of an individual direction changing means.

[0054] Fig. 9 is a schematic cross-sectional view of the four wastewater treatment facilities, cut in the width direction of the pond at the sand collection pit and viewed in the longitudinal direction. Fig. 9 shows the sand collection pit, sand lifting pipe, and transport pipe, but the background is omitted. Fig. 10 is a skeleton diagram showing the sand lifting pump, sand lifting pipe, transport pipe, and sand separator.

[0055] As described above, the wastewater treatment facilities 1 described so far are provided in four in parallel in the direction of the wastewater flow. Therefore, as shown in FIG. 9, four grit basins 2 are also provided in parallel in the width direction of the basin. The sand lifting pump 61 and the sand lifting pipe 64 are provided in each of the grit basins 2. The sand lifting pipe 64 extends from the bottom of the grit basin 2 to above the grit basin 2. The transport pipe 66 is supported by a suspension stand 67 and is hung in a straight line almost horizontally so as to straddle the tops of the three grit basins 2 on the right side in FIG. 9. That is, the transport pipe 66 extends in a direction intersecting with the sand lifting pipe 64. The transport pipe 66 may extend in a direction inclined with respect to the horizontal direction. One end 66a of the transport pipe 66 is composed of a cover that closes the transport pipe 66 and is arranged above the left wall Wa of the leftmost grit basin 2 in FIG. 9. 10, the other end of the transport pipe 66 is connected to a grit separator SS placed on the ground away from the grit basin 2. The sand that passes upward through the sand lifting pipe 64 is sent into the transport pipe 66 and transported inside the transport pipe 66 from the left side to the right side in FIG.

[0056] Fig. 11(a) is an enlarged view of part E in Fig. 9, and Fig. 11(b) is an enlarged view of Fig. 9(a) viewed from the upstream side of the transport direction of the transport pipe. In Fig. 11(a), the left-right direction is the pond width direction, and the direction perpendicular to the paper surface is the longitudinal direction of the settling basin. Also, in Fig. 11(b), the left-right direction of the figure is the longitudinal direction of the settling basin, and the direction perpendicular to the paper surface is the pond width direction. Note that the suspension stand is not shown in Fig. 11.

[0057] As shown in Fig. 11(a) and (b), the sand lifting pipe 64 has a main sand lifting section 64a extending upward from the sand lifting pump 61 beyond the transport pipe 66, a horizontal section 64b whose central axis is oriented horizontally, an inclined section 64c whose central axis is inclined vertically with respect to the horizontal direction, and a first elbow 64e and a second elbow 64f. The first elbow 64e and the second elbow 64f are both identical parts bent at 90 degrees into an L-shape. Here, the 90-degree bent elbow is available on the market as a general-purpose part, so the sand lifting pipe 64 can be constructed inexpensively by adopting the 90-degree bent elbow. The main sand lifting section 64a is provided with a check valve 641 and a gate valve 642. The check valve 641 is a valve that automatically opens due to the flow of sand and wastewater pumped by the sand pump 61 when the sand pump 61 (see FIG. 9) is operating, and automatically closes due to the flow of wastewater returning to the sand pump 61 when the sand pump 61 is stopped. A gate valve 642 is disposed above the check valve 641. This gate valve 642 is a valve that can manually control the flow of sand and wastewater in the main sand lifting section 64a. This gate valve 642 is normally in an open state, allowing the flow of sand and wastewater. When the check valve 641 is removed for inspection of the grit basin 2, the gate valve 642 is switched to a closed state to stop the flow of sand and wastewater, thereby preventing the wastewater above the gate valve 642 from backflowing.

[0058] As shown in FIG. 9, one end of the main sand lifting section 64a is connected to the sand lifting pump 61. The main sand lifting section 64a has a portion extending in the horizontal direction, a portion extending in the vertical direction, and a portion inclined with respect to the vertical direction. However, the main sand lifting section 64a may be inclined with respect to the vertical direction as a whole, or may extend in the vertical direction as a whole. The check valve 641 and the gate valve 642 are disposed at the other end side of the main sand lifting section 64a. As shown in FIG. 11(a) and (b), the other end side of the main sand lifting section 64a from the check valve 641 extends in the vertical direction. The first elbow 64e is welded to the other end of the main sand lifting section 64a, thereby being integrated with the main sand lifting section 64a. The first elbow 64e and the horizontal section 64b are connected with a flange joint. The second elbow 64f is welded to the horizontal section 64b, thereby being integrated with the horizontal section 64b. The second elbow 64f and the inclined portion 64c are connected by a flange joint. As shown in FIG. 11(a), the inclined portion 64c is connected by welding to the upper portion of the conveying pipe 66 in a state inclined upward from the horizontal at an angle of θ2. The upper portion of the conveying pipe 66 here refers to the portion above the central axis 66c of the conveying pipe 66. An opening formed in the portion of the conveying pipe 66 to which the sand lifting pipe 64 is connected becomes the pipe connection portion 66b. This pipe connection portion 66b corresponds to an example of the connection portion of the conveying pipe 66 with the sand lifting pipe 64. The horizontal portion 64b is connected to the first elbow 64e with the angle around the central axis of the horizontal portion 64b adjusted so that the central axis of the flange portion 64f1 of the second elbow 64f coincides with θ2.

[0059] The sand and wastewater pumped up by the sand lifting pump 61 (see FIG. 9) are sent into the transport pipe 66 through the sand lifting pipe 64. The sand and wastewater sent into the transport pipe 66 are transported in the direction of the arrow G shown in FIG. 11(a). When the sand lifting pump 61 is stopped, the check valve 641 closes, and the sand in the main sand lifting section 64a above the check valve 641 falls and accumulates on the check valve 641. However, since the volume of the pipe above the check valve 641 of the main sand lifting section 64a is very small, the amount of sand in the pipe is very small. Therefore, even if the sand accumulates on the check valve 641, it has almost no effect on the opening and closing of the check valve 641. On the other hand, since the pipe connection part 66b of the sand lifting pipe 64 (inclined part 64c) and the transport pipe 66 is located in the upper part of the transport pipe 66, the sand in the transport pipe 66 is unlikely to enter the sand lifting pipe 64. This is because the sand in the conveying pipe 66 is difficult to move to the upper part of the conveying pipe 66 due to its own weight. Even if the sand in the conveying pipe 66 enters the sand lifting pipe 64, the horizontal part 64b, etc. are arranged above the pipe connection part 66b, so that the sand will not climb the inclined part 64c and reach the horizontal part 64b. That is, the sand is blocked by the inclined part 64c, so that the sand that has entered the sand lifting pipe 64 from the conveying pipe 66 is prevented from accumulating on the check valve 641. Therefore, it is possible to reliably prevent a large amount of sand from accumulating on the check valve 641, which would cause the check valve 641 to be unable to open. In this embodiment, an example was shown in which the horizontal part 64b, etc. are arranged above the pipe connection part 66b. However, if there is a part of the sand lifting pipe 64 between the check valve 641 and the conveying pipe 66 that is arranged above the pipe connection part 66b, the above-mentioned effect of blocking the sand can be obtained. Hereinafter, this upper portion may be referred to as the upper portion. Hereinafter, the term "upper portion" refers to the fact that the lowermost portion of the internal space of the sand lifting pipe 64 in the upper portion is located higher than the lowermost portion of the pipe connection portion 66b. However, it is more desirable that the entire internal space of the sand lifting pipe 64 in the upper portion is located higher than the uppermost portion of the pipe connection portion 66b. According to this embodiment, the effect of blocking sand is more reliable.

[0060] In this embodiment, the angle θ2 between the transport pipe 66 and the inclined portion 64c is 45 degrees. By setting θ2 to be greater than 0 degrees and less than 90 degrees, the sand lifting pipe 64 (inclined portion 64c) can be connected to the transport pipe 66 while gradually approaching the transport pipe 66 as it moves toward the transport direction of the transport pipe 66. This has the effect of preventing sand that has been sucked up in another settling basin 2 and transported in the transport pipe 66 from the opposite transport direction side of the pipe connection portion 66b from entering the sand lifting pipe 64. In addition, the sand that moves from the sand lifting pipe 64 to the transport pipe 66 is sent into the transport pipe 66 in a direction close to the transport direction and moves in the transport direction as it is along with the flow of wastewater generated in the transport pipe 66, so that there is also the effect of preventing the sand from returning to the sand lifting pipe 64. These effects prevent a large amount of sand from accumulating on the check valve 641, which makes it impossible for the check valve 641 to open. In addition, the wastewater in the sand lifting pipe 64 is sent into the transport pipe 66 in a direction close to the transport direction of the transport pipe 66, which has the effect of promoting the flow of the wastewater in the transport pipe 66 in the transport direction by the sent wastewater. However, θ2 is preferably between 30 degrees and 60 degrees. If it is less than 30 degrees, it becomes difficult to connect the sand lifting pipe 64 and the transport pipe 66. If it exceeds 60 degrees, the above-mentioned effect is halved.

[0061] Figure 12 is a diagram of the water supply system in a sewage treatment facility.

[0062] As shown in FIG. 12, the water supply pump 33 selectively supplies water from the pump well 3 to the stirring nozzle 62, the sand collection nozzle for the pit 63, the upstream trough first nozzle 831, the upstream trough second nozzle 832, the downstream trough nozzle 84, and the sand collection means 9. The water supply pipe 34 connected to the water supply pump 33 is provided with a supply switching valve Va for switching whether or not to supply fluid to the nozzles and the sand collection means 9, and a relief switching valve Vb for switching whether or not to return the fluid sucked up by the water supply pump to the pump well 3. The pipeline between the supply switching valve Va and the stirring nozzle 62 is provided with a stirring switching valve Vc for switching whether or not to supply fluid to the stirring nozzle 62. The pipeline between the supply switching valve Va and the sand collection nozzle for the pit 63 is provided with a pit sand collection switching valve Vd for switching whether or not to supply fluid to the sand collection nozzle for the pit 63. An upstream trough first switching valve Ve1 is provided in the pipeline between the supply switching valve Va and the upstream trough first nozzle 831, switching whether or not to supply a fluid to the upstream trough first nozzle 831. An upstream trough second switching valve Ve2 is provided in the pipeline between the supply switching valve Va and the upstream trough second nozzle 832, switching whether or not to supply a fluid to the upstream trough second nozzle 832. A downstream trough switching valve Vf is provided in the pipeline between the supply switching valve Va and the downstream trough nozzle 84, switching whether or not to supply a fluid to the downstream trough nozzle 84. In addition, sand collection switching valves Vg1, Vg2, Vg3, Vg4, Vg5, and Vg6 are provided in the pipelines between the supply switching valve Va and the nozzle headers 9a, 9b, 9c, 9d, 9e, and 9f of the sand collection means 9, switching whether or not to supply a fluid to each of the nozzle headers 9a, 9b, 9c, 9d, 9e, and 9f. These changeover valves are constituted by electromagnetic valves, and the opening and closing of the valves is controlled by a control device (not shown).

[0063] FIG. 13 is an explanatory diagram showing the water level of the grit basin and the water level sensor.

[0064] As shown in Fig. 13, 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 which is below the first high water level HHWL and above the upper end positions 13b of each covering member 13, 14, 15 (which is approximately the same position as the upper end 8b of the main trough 8, i.e., the opening of the main trough 8, and is also approximately the same position as the lower end 72b of the small trough 72), and a first low water level TLW which is near the upper end positions 13b of each covering member 13, 14, 15. 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 which is located lower within 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, and outputs the signal.

[0065] FIG. 14 is a flow chart showing the flow of the sand removal operation in the wastewater treatment facility.

[0066] The operation of the wastewater treatment facility 1 having the above-mentioned configuration will be described with reference to FIG. 1, FIG. 2, FIG. 14, etc. At a predetermined time when a certain amount of sand has accumulated on the bottom of the grit basin 2, the wastewater treatment facility 1 performs an operation to remove the accumulated sand. When the predetermined time is reached, the operation to remove sand is performed for all four wastewater treatment facilities 1 one by one in turn. This predetermined time may be periodically, for example, once a month, or may be when the total flow rate of wastewater flowing into or discharged from the grit basin 2 reaches a certain amount. In the sand removal operation, first, the inflow gate 42 of the dam device 4 shown in FIG. 1 is driven to block the inflow port 411, thereby blocking the inflow of wastewater into the grit basin 2 (step S1). Next, the lifting pump 31 is driven to lower the water level of the grit basin 2. When the water level of the pump well 3 has dropped to a predetermined value, the lifting pump 31 is stopped (step S2). Then, the water supply pump 33 is driven for about several minutes to discharge a fluid from the stirring nozzle 62 shown in FIG. 2. After the water supply pump is stopped, the sand lifting pump 61 is driven. At this time, in the past, during the long period between the previous sand removal operation and the current sand removal operation, the sand that had accumulated on the check valve 641 hardened and became almost solid, and the check valve 641 could not be opened. However, in this embodiment, only a very small amount of sand accumulates on the check valve 641, so the check valve 641 does not become unable to open. When the water level of the grit basin 2 drops to the second high water level THWL (see FIG. 13), the water supply pump 33 is driven again to discharge the fluid from the stirring nozzle 62 shown in FIG. 2. Then, the drive of the sand lifting pump 61 is set to the operation mode A described below (step S3). The sand lifting pump 61 operates in either the operation mode A or the operation mode B. In operation mode A, control is automatically executed to stop driving in response to an output from the water level sensor 99 indicating a first low water level TLWL (see FIG. 13), and to resume driving in response to an output indicating a second high water level THWL (see FIG. 13). This operation mode A is a mode in which the water level is maintained above the upper end positions 13b of each of the covering members 13, 14, and 15. Therefore, in operation mode A, each of the covering members 13, 14, and 15, the trough first outlet 831a, the trough second outlet 832a, and the trough third outlet 84a are submerged in water.In the operation mode B, the operation of 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. 13), and the operation is automatically resumed in response to an output indicating the third high water level HWL (see FIG. 13). This operation mode B is a mode in which the water level is maintained below the lower end 72b of the small trough 72. Therefore, the bottom plane 71, the small trough 72, the sand 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 be driven until the sand removal operation is completed. The sand transported to the sand collecting pit 6 is transported to the sand separator SS (see FIG. 10) outside the settling basin 2 by the sand lifting pump 61 while the sand lifting pump 61 is operating. The sand lifting pump 61 repeatedly starts and stops even during this sand removal operation. In this embodiment, a large amount of sand does not accumulate on the check valve 641 during the stoppage, so the check valve 641 does not become unable to open when driving is resumed. 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 FIG. 13), 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.

[0067] Then, the fluid is discharged from the stirring nozzle 62, the upstream trough first nozzle 831, and the upstream trough second nozzle 832 shown in FIG. 2 for a certain period of time to flow the sand accumulated in the upstream first main trough 815 and the upstream second main trough 816 into the sand collecting pit 6 (step S4). In this step S4, the fluid may be discharged from one of the upstream trough first nozzle 831 and the upstream trough second nozzle 832 for a certain period of time, and then the fluid may be discharged from the other for a certain period of time. When the discharge of the fluid from the stirring nozzle 62, the upstream trough first nozzle 831, and the upstream trough second nozzle 832 stops, the sand lifting pump 61 is switched to the operation mode B (step S5). Then, when it is detected that the water level is equal to or lower than the third high water level HWL, the fluid is discharged from the discharge port 911 (see FIG. 6) provided in the fifth nozzle header 9e. This discharge allows the sand deposited on the bottom plane 71 and the small trough 72 between the right side wall Wb near where the fifth nozzle header 9e is located and the upstream second main trough 816 to flow into the upstream second main trough 816. After a predetermined time has elapsed to allow the sand to flow sufficiently, the sand lifting pump 61 is switched to operation mode A while continuing to discharge the fluid from the discharge port 911 provided in the fifth nozzle header 9e. After that, when it is detected that the water level is equal to or higher than the first intermediate water level TMWL, the discharge of the fluid from the discharge port 911 provided in the fifth nozzle header 9e is stopped (step S6). Then, the fluid is discharged from the stirring nozzle 62 and the upstream trough second nozzle 832 for a certain period of time to send the sand that has flowed into the upstream second main trough 816 to the sand collecting pit 6 (step S7). When the discharge of the fluid from the stirring nozzle 62 and the upstream trough second nozzle 832 is stopped, the sand lifting pump 61 is switched to operation mode B (step S8). Then, when it is detected that the water level is equal to or lower than the third high water level HWL, fluid is discharged from the discharge port 911 provided in the second nozzle header 9b. After a predetermined time has elapsed that is sufficient to flush away the sand accumulated on the bottom plane 71 and the small troughs 72 between the left side wall Wa in the vicinity of where the second nozzle header 9b is located and the upstream first main trough 815, 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 the 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 port 911 in the left side wall Wa, which is located 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 according to the distance from the supply pipe 92 to the left side wall Wa. Therefore, all the sand accumulated on the bottom plane 71 and the small trough 72 between the left side wall Wa near where the second nozzle header 9b is disposed and the upstream first main trough 815 can be made to flow to the upstream first main trough 815. After the discharge of the fluid from the discharge port 911 provided in the second nozzle header 9b is stopped, the fluid is discharged from the stirring nozzle 62 and the upstream trough first nozzle 831 for a certain period of time to send the sand that has flowed to the upstream first main trough 815 to the sand collection pit 6 (step S10). When the discharge of the fluid from the stirring nozzle 62 and the upstream trough second nozzle 832 stops, the sand lifting pump 61 is switched to the operation mode B (step S11). Thereafter, similar to the operations of steps S6 to S10 described above, the following operations are performed in order: discharge of the fluid from the discharge port 911 provided in the fourth nozzle header 9d and switching to the operation mode A after a predetermined time has elapsed (step S12), discharge of the fluid from the stirring nozzle 62 and the upstream trough second nozzle 832 (step S13), switching to the operation mode B (step S14), discharge of the fluid from the discharge port 911 provided in the first nozzle header 9a and switching to the operation mode A after a predetermined time has elapsed (step S15), and discharge of the fluid from the stirring nozzle 62 and the upstream trough first nozzle 831 (step S16). By doing so, all the sand deposited on the bottom of the pond upstream of the sand collecting pit 6 is carried out to the outside of the grit basin 2. The order in which the fluid is discharged from each nozzle header 9a, 9b, 9d, and 9e may be any order. However, if the sand that has accumulated farther from the sand collection pit 6 is poured out first, the sand that has accumulated closer to the sand collection pit 6 will collapse into the main trough 8 along with the sand to be poured out, causing sand to accumulate in the main trough, which may make 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.

[0068] After removing the sand accumulated on the upstream side by the above-mentioned operation, the agitation nozzle 62 and the downstream trough nozzle 84 are discharged with fluid 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 the fluid from the agitation nozzle 62 and the downstream trough nozzle 84 is stopped, the sand lifting pump 61 is switched to the operation mode B (step S18). Then, when it is detected that the water level is equal to or lower than the third high water level HWL, the fluid is discharged from the discharge port 911 provided in the sixth nozzle header 9f. When a predetermined time has elapsed to sufficiently flush the sand accumulated on the bottom plane 71 and the small trough 72 between the right side wall Wb near where the sixth nozzle header 9f is located, the sand lifting pump 61 is switched to the operation mode A while continuing to discharge the fluid from the discharge port 911 provided in the sixth nozzle header 9f. After that, when it is detected that the water level is equal to or higher than the first intermediate water level TMWL, the discharge of the fluid from the discharge port 911 provided in the sixth nozzle header 9f is stopped (step S19). Then, the fluid is discharged from the stirring nozzle 62 and the downstream main trough 82 for a certain period of time to send the sand flowing into the downstream main trough 82 to the sand collection pit 6 (step S20). When the discharge of the fluid from the stirring nozzle 62 and the downstream main trough 82 is stopped, the sand lifting pump 61 is switched to the operation mode B (step S21). Then, similar to the operations of steps S19 and S20 described above, the discharge of the fluid from the discharge port 911 provided in the third nozzle header 9c and the switching to the operation mode A after a predetermined time has elapsed (step S22), and the discharge of the fluid from the stirring nozzle 62 and the downstream trough nozzle 84 (step S23) are performed in this order, so that all the sand deposited on the pond bottom downstream of the sand collection pit 6 is carried out to the outside of the grit basin 2. Finally, the sand accumulated on the sand collection pit inclined surface 6b is flushed into the sand collection pit 6 by discharging fluid from the pit sand collection nozzle 63 (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. This series of sand removal operations is carried out for each of the four wastewater treatment facilities 1 in turn.

[0069] In this sand removal operation, when the sand lifting pump 61 is switched from the operation mode A to the operation mode B, the supply of fluid to the grit basin 2 is stopped until it is detected that the water level is equal to or lower than the third high water level HWL. This makes it possible to accelerate the rate at which the water level drops. At this time, in order to stop the supply of fluid to the grit basin 2, the supply switching valve Va shown in FIG. 12 is closed and the relief switching valve Vb is opened, and the fluid pumped up by the feedwater pump 33 is returned to the pump well 3. In this way, the supply of fluid to the grit basin 2 can be stopped while the feedwater pump 33 continues to be driven. In the sand removal operation described above, steps S4, S7, S10, S13, S16, S17, S20, and S23 each correspond to an example of the underwater discharge step. Also, steps S6, S9, S12, S15, S19, and S22 each correspond to an example of the atmospheric discharge step. That is, in this embodiment, the process of performing the underwater discharge process after the atmospheric discharge process is regarded as one set of sand collection processes (combinations of steps S6 and S7, S9 and S10, S12 and S13, S15 and S16, S19 and S20, and S22 and S23), and the sand collection process is performed multiple times. In addition, the underwater discharge process (step S4) is performed before the first sand collection process (steps S6 and S7). If sand remains in the main trough 8 during the atmospheric discharge process, the sand that has been washed into the main trough 8 by the atmospheric discharge process may be piled up on the remaining sand, and a large amount of sand may accumulate in the main trough 8. In addition, there is a risk that the main trough 8 may be filled with sand during the atmospheric discharge process, and the overflowing sand may remain on the bottom plane 71. In this embodiment, the sand washed into the main trough 8 from the bottom plane 71 is transported to the sand collection pit 6 in one set of sand collection processes, so that no sand remains in the main trough 8. In addition, since the underwater discharge process (steps S4 and S17) is performed before the first sand collection process (the combination of steps S6 and S7, and S19 and S20), no sand remains in the main trough 8 even during the first sand collection process.

[0070] In this embodiment, when the sand removal operation is being performed, the amount of fluid pumped by the sand lifting pump 61 is set to be slightly greater than the amount of fluid pumped by the feed water pump 33. For this reason, the sand lifting pump 61 is stopped and restarted several times while the sand removal operation is being performed. However, if the sand lifting pump 61 is repeatedly driven and stopped, the pump life will be reduced due to the inrush current at the start of driving. As a countermeasure, the pumping capacity of the feed water pump 33 and the pumping capacity of the sand lifting pump 61 may be made closer to each other to minimize the change in the water level during the sand removal operation. Also, when the water level sensor 99 detects that the water level has dropped to the first intermediate water level TMWL in the operation mode A or the second intermediate water level MWL in the operation mode B, additional fluid may be discharged from other nozzles in addition to the nozzles that are discharging fluid at that time. By increasing the number of nozzles that discharge fluid, the load (throttle resistance) on the flow of the fluid is reduced, so that the fluid pumped by the feed water pump 33 increases, and as a result, more fluid can be supplied to the grit basin 2. This makes it difficult for the water level to reach the first low water level TLWL or the second low water level LWL, so that the number of times the sand lifting pump 61 stops and restarts can be reduced. Here, it is preferable that the other nozzle is a sand collecting nozzle 91 provided in the nozzle header scheduled to discharge next. By discharging fluid from the nozzle header scheduled to discharge next, the sand in the bottom plane 71 and the small trough 72 to be discharged next can be preliminarily discharged, so that the sand residue can be further suppressed. The additional fluid to be discharged may be a fluid stored in another facility. Furthermore, instead of stopping the sand lifting pump 61 even when the water level reaches the first low water level TLWL or the second low water level LWL, the water supply pump 33 may be configured to supply a fluid stored in another facility to the settling basin 2 in addition to the fluid pumped up by the water supply pump 33. In this configuration, the supply of the fluid stored in the other facility to the settling basin 2 may be stopped when the water level reaches the second high water level THWL or the third high water level HWL. By reducing the number of times 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.

[0071] In this embodiment, the discharge port 911 is disposed near the bottom of the settling basin 2. In contrast to this, for example, JP 2011-245391 A proposes a settling basin 2 in which a sand collecting means 9 equipped with a discharge port 911 is disposed in the upper portion of the settling basin 2, and fluid is discharged toward a side wall W so that the fluid flows down the wall surface of the side wall W.

[0072] Fig. 15 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. In Fig. 15, the sand collecting means arranged in the upper part of the settling basin is shown by a two-dot chain line. Furthermore, among the lines showing the piping and side walls, the lines that intersect with the sand collecting means arranged in the upper part of the settling basin are shown with the intersecting portions omitted.

[0073] In FIG. 15, a virtual upper nozzle header 90 is shown in the upper part of the grit basin 2. This upper nozzle header 90 is used instead of the first nozzle header 9a. The dust collector 5 is arranged at an angle at the upstream end of the grit basin 2. The sand collecting means 9 needs to be arranged so as not to interfere with the dust collector 5. Therefore, the upper nozzle header 90 arranged in the upper part of the grit basin 2 is located downstream compared to the case where it is arranged near the bottom of the grit basin 2 as shown in FIG. 15. In other words, the upper nozzle header 90 has to be arranged downstream by a distance S from the first nozzle header 9a. As described above, the upper parts of the endless chain 51 and the filtration screen 53 constituting the dust collector 5 overlap with the bottom plane 71 and the main trough 8 in the longitudinal direction. Therefore, even if a fluid is discharged from the upper nozzle header 90, there will be a part of the bottom plane 71 that the discharged fluid does not reach. If the dust collector 5 and the upper nozzle header 90 are arranged upstream by a distance S from the positions shown in FIG. 5 and FIG. 15, the fluid can reach the most upstream part of the bottom plane 71. However, such an arrangement increases the longitudinal length of the grit basin 2. As a result, the grit basin 2 becomes large, a large amount of land is required for the installation of the grit basin 2, and the grit basin 2 becomes expensive. In the grit basin 2 of this embodiment, the first nozzle header 9a is arranged near the bottom of the grit basin 2, so that the grit basin 2 can be prevented from becoming large and can be provided at a low cost, compared to the case where the upper nozzle header 90 arranged in the upper part of the grit basin 2 is used.

[0074] Next, a description will be given of modified examples of the connection surface 73. In the modified examples described below, the differences from the embodiment shown in Figures 1 to 14 will be mainly described, and components having the same names as those in the embodiment shown in Figures 1 to 14 will be described using the same reference numerals as used above, and duplicated descriptions will be omitted.

[0075] FIG. 16 is a cross-sectional view similar to FIG. 3, showing a modified example of the connection surface.

[0076] In this modified example, the connection surface 73 is different from the example shown in FIG. 3 in that the connection surface 73 is formed as a curved surface. The connection surface 73 is composed of a ridge portion 731 extending along the longitudinal direction, a first connection surface 732, and a second connection surface 733. As shown in FIG. 16, the first connection surface 732 and the second connection surface 733 have a cross-sectional shape of a quarter circle. That is, the connection surface 73 is composed of a semi-cylindrical surface protruding upward as a whole. The ridge portion 731 is composed of the upper end line of the semi-cylindrical shape. In this modified example, as in the example shown in FIG. 3, sand that settles to the connection surface 73 in the wastewater in the grit basin 2 is likely to slide off the connection surface 73 due to its own weight. However, since the inclination angle of the tangent plane of the connection surface 73 becomes gentle near the ridge portion 731, there is a risk that sand will remain in that vicinity. On the other hand, since the thickness of the concrete constituting the connection surface 73 in the pond width direction is thick even in the vicinity of the ridge line portion 731, there is an effect that the ridge line portion 731 is less likely to be damaged. One of the first connection surface 732 and the second connection surface 733 may be formed as a flat surface as in the example shown in Fig. 3, and the other may be formed as a curved surface as in the modified example shown in Fig. 16. Furthermore, one or both of the first connection surface 732 and the second connection surface 733 may be formed as a surface that combines a curved surface and a flat surface.

[0077] Next, a modified example of the sand collecting means 9 will be described.

[0078] FIG. 17(a) is a diagram showing a first modified example of the supply pipe and sand collecting nozzle shown in FIG. 8, and FIG. 17(b) is a diagram showing a second modified example of the supply pipe and sand collecting nozzle shown in FIG.

[0079] This first modified example differs from the example shown in FIG. 8(a) in that the supply pipe 92 does not have a lap joint 934, the supply pipe 92 and the branch pipe 932 are flange-connected, and the sand collecting nozzle 91 is provided with a ball joint 912. In FIG. 17(a), the sand collecting nozzle 91 corresponding to the convex wall portion Wa1 is shown in solid lines, and the sand collecting nozzle 91 corresponding to the concave wall portion Wa2 is shown in two-dot chain lines. In this modified example, a ball joint 912 is provided between the supply pipe 92 and each discharge port 911. This ball joint 912 allows the discharge direction of the fluid to be changed steplessly not only in the rotational direction about the axis of the supply pipe 92, but also in various other directions. Therefore, the discharge direction can be finely adjusted for each discharge port 911. It is also possible to provide a lap joint 934 on the supply pipe 92 and further provide a ball joint 912 on the sand collecting nozzle 91. In this case, the lap joint 934 corresponds to an example of a collective changing means, and the ball joint 912 corresponds to an example of an individual direction changing means.

[0080] 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, the supply pipe 92 and the branch pipe 932 are flange-connected, and a plurality of mounting parts 924 for the sand collection nozzle 91 are formed in the circumferential direction of the supply pipe 92. In FIG. 17(b), the sand collection nozzle 91 corresponding to the convex wall part Wa1 is shown by a solid line, and the sand collection nozzle 91 corresponding to the concave wall part Wa2 is shown by a two-dot chain line. In this modified example, six mounting parts 924 for the sand collection nozzle 91 are formed in the circumferential direction of the supply pipe 92. As a result, after the supply pipe 92 is fixed to the branch pipe 932, the sand collection nozzle 91 can be mounted on any one of the six mounting parts 924. Before the sand collection nozzle 91 is mounted, plug members are attached to all mounting parts 924. When the sand collection nozzle 91 is to be mounted, the plug members are removed before the sand collection nozzle 91 is mounted. Alternatively, a lap joint 934 may be disposed on supply pipe 92, and mounting portion 924 may be formed on supply pipe 92. In this case, lap joint 934 corresponds to an example of a collective changing means, and mounting portion 924 corresponds to an example of an individual direction changing means. Although six mounting portions 924 are formed in the circumferential direction in this modification, the number of mounting portions 924 may be two or more, five or less, or seven or more.

[0081] Next, modified examples of the main trough 8, the covering members 13, 14, and 15, and the bottom plane 71 will be described.

[0082] FIG. 18 is a cross-sectional view similar to FIG. 5 showing a variation of the main trough, cover member, and base planar surface.

[0083] In this modified example, the main trough 8, the cover members 13, 14, 15, and the bottom plane 71 are arranged with an inclination downward toward the sand collection pit 6, which is different from the example shown in FIG. 5. In FIG. 18, the inclination of the main trough 8, the cover members 13, 14, 15, and the bottom plane 71 is exaggerated in order to clearly show the inclination. As shown in FIG. 18, the bottom plane 71 is inclined downward by about 0.5 degrees toward the sand collection pit 6 so that the end of the bottom plane 71 on the side of the sand collection pit 6 is the deepest. In addition, the upstream first main trough 815 and the downstream main trough 82 are also inclined downward by about 0.5 degrees toward the sand collection pit 6, similar to the bottom plane 71, and the part connected to the sand collection pit 6 is the deepest. Furthermore, the first cover member 13 and the third cover member 15 are also inclined downward by about 0.5 degrees toward the sand collection pit 6, and the part connected to the sand collection pit 6 is the deepest. 18, the first upstream main trough 815 and the second cover member 14 are also inclined downward by about 0.5 degrees toward the sand collection pit 6. In this modification, the provision of the cover members 13, 14, and 15 not only increases the sand transport force in the main trough 8, but also assists the flow of the fluid discharged into the cover members 13, 14, and 15 by inclining the main trough 8 and the cover members 13, 14, and 15. This allows the sand accumulated in the main trough 8 to be transported a longer distance. The inclination angle may be set appropriately according to the length of the main trough 8.

[0084] Fig. 19 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 collection pit in the modified example shown in Fig. 18. In Fig. 19, the side walls and the bottom surface are also shown.

[0085] FIG. 19 shows the difference in the height position of the bottom plane 71 when the bottom plane 71 is inclined downward toward the sand collection pit 6 side so that the end on the sand collection pit 6 side is the deepest as shown in FIG. 18. In FIG. 19, the bottom plane 71 near the upstream end of the settling basin 2 is shown by a solid line, and the bottom plane 71 near the sand collection pit 6 is shown by a two-dot chain line. As shown in FIG. 19, in this case, the bottom plane 71 is located at a lower position near the sand collection pit 6 than the bottom plane 71 near the upstream end of the settling basin 2. As shown in the figure, even if a fluid is discharged from the discharge port 911 at the same position, the height position of the bottom plane 71 is different between the upstream end of the settling basin 2 and the vicinity of the sand collection pit 6, so that a difference in distance Y occurs in the point where the discharged fluid reaches the bottom plane 71. In particular, in the settling basin 2 having a long longitudinal length, the distance Y becomes long, and even if the discharge direction is optimal for one of the upstream end of the settling basin 2 and the vicinity of the sand collection pit 6, it may be an inefficient discharge direction for the other. In this embodiment, the direction in which the fluid is discharged from the discharge port 911 can be changed, so that the fluid can be discharged in the optimal direction corresponding to the height of the bottom plane 71 (the distance from the supply pipe 92 to the bottom plane 71).

[0086] Next, a modified example in which the height of the main trough 8 is increased will be described.

[0087] FIG. 20 is an explanatory diagram similar to FIG. 13, showing an example of water level detection when the height of the main trough is increased.

[0088] In the example shown in FIG. 13, each of the cover members 13, 14, 15 was formed at a height exceeding half the height of the main trough 8. The upper end position 13b of each of the cover members 13, 14, 15 was at approximately the same position as the lower end 72b of the small trough 72 (the upper end 8b of the main trough 8). As described above, the operation mode A of the sand lifting pump 61 is a control mode in which each of the cover members 13, 14, 15 is maintained submerged in water, so it is necessary to set the first low water level TLWL above the upper end position 13b of each of the cover members 13, 14, 15. In addition, the operation mode B of the sand lifting pump 61 is a control mode in which the water level is maintained below the lower end 72b of the small trough 72, so it is necessary to set the third high water level HWL below the lower end 72b of the small trough 72. In the example shown in FIG. 13, in order to satisfy the condition that the first low water level TLWL is set above the upper end position 13b and the third high water level HWL is set below the lower end 72b, the third high water level HWL must be set below the first low water level TLWL. As a result, there is no overlap between the water level maintenance ranges in the operation mode A and the operation mode B, and when switching from one mode to the other mode, a waiting time occurs until the water level enters the range of the other mode. As shown in FIG. 20, when the height of the main trough 8 is increased and each of the cover members 13, 14, and 15 is arranged in the lower part of the main trough 8, the upper end position 13b of each of the cover members 13, 14, and 15 is 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. That is, a part of the water level range D1 in the operation mode A and a part of the water level range D2 in the operation mode B can be overlapped, so that the waiting time after the mode switching can be eliminated or reduced.

[0089] The present invention is not limited to the above-mentioned embodiment and modified examples, and various modifications can be made within the scope of the claims. For example, in this embodiment, the present invention is used in the grit basin 2 of the wastewater treatment facility 1 into which sewage and rainwater flow, but it can also be applied to the grit basin of a rainwater treatment facility into which only rainwater flows. In this embodiment, the sand accumulated on the bottom plane 71 and the small trough 72 on the upstream side of the sand collection pit 6 is poured, and then the sand accumulated on the bottom plane 71 and the small trough 72 on the downstream side of the sand collection pit 6 is poured. However, the sand accumulated on the bottom plane 71 and the small trough 72 on the downstream side may be poured first. In this embodiment, the dust remover 5 and the protruding wall 10 are disposed at the upstream end of the grit basin 2, but the dust remover 5 and the protruding wall 10 may be disposed at the downstream end of the grit basin 2. When the dust remover 5 and the protruding wall 10 are disposed at the downstream end of the grit basin 2, two downstream main troughs 82 are provided and disposed on the left side wall Wa side and the right side wall Wb side of the protruding wall 10, respectively. Then, the ridge portion, the first connection surface, and the second connection surface are formed between the two downstream main troughs 82, except for the area where the protruding wall 10 is provided. In addition, in this embodiment, one discharge port for discharging the fluid into the transfer space FS is provided at the end (tip portion) of the main trough 8 opposite to the sand collection pit 6, but a nozzle having a discharge port may be additionally provided at the intermediate position or the like in the extension direction of each of the cover members 13, 14, 15. In particular, when the length of each of the cover members 13, 14, 15 in the extension direction is long or the discharge pressure of the fluid is low, it is desirable to add a nozzle at the intermediate position or the like. In the present embodiment, the fluid is discharged into the transfer space FS in a state where each of the cover members 13, 14, and 15 is completely submerged in water, but if a part of each of the cover members 13, 14, and 15 is submerged in water, the fluid may be discharged in a state where the atmosphere remains in the transfer space FS. In the present embodiment, the fluid is discharged in a state where the trough first outlet 831a, the trough second outlet 832a, and the trough third outlet 84a are completely submerged in water, but the fluid may be discharged in a state where the outlets 831a, 832a, and 84a are partially submerged in water and the remaining parts are exposed to the atmosphere. However, in these cases, loss occurs in the flow of the discharged fluid, especially at the interface between the atmosphere and water.Therefore, it is preferable to discharge the fluid from the outlets 831a, 832a, 84a while the cover members 13, 14, 15 and the trough first outlet 831a, trough second outlet 832a, and trough third outlet 84a are completely submerged in water.

[0090] In addition, in the present embodiment, four sewage treatment facilities 1 are provided in parallel, but the number of sewage treatment facilities 1 may be one or any number. In addition, in the present embodiment, the so-called low-pressure sand collection type of sand collection system in which sand is collected while the sewage in the sand collection basin 2 is drained is described, but the present embodiment can also be applied to a high-pressure sand collection type of sand collection system in which sand is collected while the sewage is stored. Furthermore, in the present embodiment, the check valve 641 that opens and closes depending on the flow of the fluid sucked up by the sand lifting pump 61 is described as an example of a backflow prevention valve, but an electric valve that opens and closes depending on the driving force of an electric actuator may be used. In addition, the sand lifting pipe 64 is connected to the upper part of the conveying pipe 66, but the sand lifting pipe 64 may be connected to the side of the conveying pipe 66 or to the lower part. Furthermore, the sand lifting pipe 64 is connected to the conveying pipe 66 while gradually approaching the conveying pipe 66 as it moves toward the conveying direction of the conveying pipe 66, but the sand lifting pipe 64 may also be connected to the conveying pipe 66 from a perpendicular direction so that the sand lifting pipe 64 and the conveying pipe 66 form a T-shape.

[0091] According to this embodiment or its modified example, the occurrence of defects in the grit basin 2 can be suppressed. In addition, sand can be efficiently collected. In addition, sand accumulated on the bottom plane 71, the small trough 72, and the connection surface 73 can be washed away by the fluid without remaining thereon. In addition, the straight supply pipe 92 can be used even in a grit basin in which the left side wall Wa or the right side wall Wb is not formed in a straight line, so that the grit basin 2 can be provided at low cost. In addition, even if the shape of the side wall W is unknown when designing the grit basin 2 or when creating the supply pipe 92, the discharge direction can be adjusted when constructing the grit basin 2, so that it is possible to flexibly accommodate various shapes of grit basins 2. Furthermore, the sand that has settled on the connection surface 73 slides down the first connection surface 732 or the second connection surface 733 and is accumulated in the upstream first main trough 815 or the upstream second main trough 816, so that no sand remains between the upstream first main trough 815 and the upstream second main trough 816. In this embodiment, the inclination angle of the first bottom surface 711 and the second bottom surface 712 is set to a gentle inclination angle (about 5 degrees) that allows the accumulated sand to be washed away by the fluid discharged from the discharge port 911. This makes it possible to create the settling basin 2 without digging deeply into the ground. On the other hand, by making the connection surface 73 at a steeper angle than the first bottom surface 711 and the second bottom surface 712, the sand that has settled on the connection surface 73 can be deposited in the upstream first main trough 815 or the upstream second main trough 816, despite the configuration in which the fluid discharged from the discharge port 911 does not reach the connection surface 73.

[0092] Moreover, many of the settling basins 2 have a longitudinal length of 20 meters or more. In the conventional settling basin 2, the main trough 8 is inclined downward toward the sand collection pit 6 by, for example, 1 degree. Therefore, the end (rear end) of the main trough 8 on the side of the pond edge is located at a deeper position proportional to the length of the settling basin 2, compared to the depth position at which the end (front end) of the main trough 8 on the side of the pond edge is located. Moreover, since the bottom plane 71 is formed at the same inclination angle as the main trough 8, the bottom plane 71 is also located at a deeper position on the side of the sand collection pit 6. When the longitudinal length of the settling basin 2 is long, the main trough 8 and the part of the bottom plane 71 on the side of the sand collection pit 6 are located at a deeper position compared to when the longitudinal length of the settling basin 2 is short. When constructing the settling basin 2, the ground is excavated below the deepest position of the settling basin 2, and then the settling basin 2 is formed with concrete. If the main trough 8 and the bottom plane 71 are inclined, the sand collection pit 6 is placed at a deeper position than if they were not inclined, so the ground needs to be dug deep, and the excavation work is time-consuming. In addition, when forming the bottom plane 71 with concrete from the dug position, it is necessary to gradually thicken the concrete from the sand collection pit 6 side toward the end of the sand collection basin in order to incline the bottom plane 71, and a large amount of concrete is used. This causes a problem that the sand collection basin 2 becomes expensive. In this embodiment, the covering members 13, 14, and 15 are provided to increase the sand collection efficiency, so that the sand in the main trough 8 can be transported to the sand collection pit 6 even if the inclination angle of the main trough 8 and the bottom plane 71 is made gentle. This inclination angle is preferably 0 degrees or more and less than 1 degree, and more preferably 0 degrees or more and 0.5 degrees or less. By making the inclination angle gentle, it is not necessary to dig deep into the ground, and the amount of concrete used is small, so the sand collection basin 2 can be made inexpensively.

[0093] The following inventive concept can also be extracted from the settling basin of this embodiment.

[0094] In a settling basin where sand contained in the received water settles, A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction; A bottom surface provided at the bottom of the pond and connected to the groove; a plurality of outlets for discharging a fluid for causing the sand that has settled on the bottom surface to flow from the side wall toward the groove; a supply pipe provided with the discharge port, A settling basin characterized in that the multiple discharge outlets include one that discharges fluid toward the center of the pond width direction relative to the axis of the supply pipe in which the discharge outlet is provided, and one that discharges fluid toward the outside of the pond width direction relative to the axis of the supply pipe.

[0095] In addition, the following inventive concept can be extracted from the settling basin of this embodiment.

[0096] In a settling basin where sand contained in the received water settles, A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction; A bottom surface provided at the bottom of the pond and connected to the groove; a discharge port that discharges a fluid for causing the sand that has settled on the bottom surface to flow from the side wall side toward the groove, A settling basin characterized in that the direction of the fluid discharged from the discharge port is changeable.

[0097] In this settling basin, A supply pipe provided with the discharge port; a mother pipe for supplying a fluid to the supply pipe; The supply pipe may be rotatable relative to the mother pipe about an axial direction of the supply pipe.

[0098] In addition, in the settling basin, The supply pipe may have a plurality of outlets.

[0099] Furthermore, in the settling basin, a supply pipe provided with the discharge port, The discharge port may be capable of changing the discharge direction of the fluid by a ball joint disposed between the supply pipe and the discharge port.

[0100] In addition, in the settling basin, The discharge port has a supply pipe detachably provided therein, The supply pipe may have a plurality of mounting portions, to which the discharge ports are attached, in a circumferential direction of the supply pipe.

[0101] In addition, the following inventive concept can be extracted from the settling basin of this embodiment.

[0102] In a settling basin where sand contained in the received water settles, A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction; A bottom surface provided at the bottom of the pond and connected to the groove; a discharge port that discharges a fluid for causing the sand that has settled on the bottom surface to flow from the side wall toward the groove; a supply pipe that is disposed closer to the center in the pond width direction than the side wall and has a plurality of the discharge ports aligned in the predetermined direction; The supply pipe has a first region extending from the side wall in a pond width direction at a first interval, and a second region extending from the side wall in a pond width direction at a second interval, A sedimentation basin characterized in that the discharge direction of the fluid from the discharge outlet arranged in the first area and the discharge outlet arranged in the second area can be changed independently of each other.

[0103] The number of outlets provided in the first region may be multiple or may be one. When the number of outlets provided in the first region is multiple, it is preferable that the discharge direction of the fluid from those outlets can be changed collectively. The number of outlets provided in the second region may be multiple or may be one. When the number of outlets provided in the second region is multiple, it is preferable that the discharge direction of the fluid from those outlets can be changed collectively. The term "changeable collectively" as used herein means that, for example, the first region part and the second region part of the supply pipe rotate separately around the axial direction of the supply pipe. In addition, the supply pipe may have a rotatable portion at both ends of the first region, and a rotatable portion at both ends of the second region. The supply pipe may be a straight pipe, or a pipe with a slightly bent portion.

[0104] 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.

[0105] The third region may be an inclined region in which the distance between the third region and the sidewall changes gradually in the extension direction, or may be a region in which the distance changes stepwise.

[0106] Also, the number of outlets provided in the third region may be multiple or may be one. When the number of outlets provided in the third region is multiple, 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 third region of the supply pipe about the axial direction of the supply pipe separately from the portion of the first region and the portion of the second region.

[0107] In addition, the following inventive concept can be extracted from the settling basin of this embodiment.

[0108] In a settling basin where sand contained in the received water settles, A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction; A bottom surface provided at the bottom of the pond and connected to the groove; a plurality of discharge ports disposed opposite the side wall and configured to discharge a fluid for causing the sand that has settled on the bottom surface to flow from the side wall toward the groove; The side wall has a convex wall portion protruding toward the center in the pond width direction and extending in the predetermined direction, and a concave wall portion concave toward the outside in the pond width direction and extending in the predetermined direction, the discharge port is disposed opposite the convex wall portion and the concave wall portion, A sedimentation basin characterized by being equipped with a direction changing means capable of changing the discharge direction of a fluid discharged from an outlet arranged opposite the concave wall portion to a different direction from the discharge direction of a fluid discharged from an outlet arranged opposite the convex wall portion.

[0109] Furthermore, the following inventive concept can be extracted from the settling basin of this embodiment.

[0110] In a settling basin where sand contained in the received water settles, A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction; A bottom surface provided at the bottom of the pond and connected to the groove; A supply pipe disposed opposite the side wall and extending in the predetermined direction; a plurality of discharge ports disposed in the supply pipe for discharging a fluid for causing the sand that has settled on the bottom surface to flow from the side wall side toward the groove; The side wall has a convex wall portion protruding toward the center in the pond width direction and extending in the predetermined direction, and a concave wall portion concave toward the outside in the pond width direction and extending in the predetermined direction, the discharge ports are disposed at positions facing the convex wall portion and at positions facing the concave wall portion, A settling basin characterized in that the supply pipe is provided with a direction changing means between an outlet located opposite the convex wall portion and an outlet located opposite the concave wall portion, which is capable of changing the discharge direction of the fluid discharged from the outlet.

[0111] In addition, in this settling basin, The side wall has an inclined wall portion formed between the convex wall portion and the concave wall portion and extending in a direction inclined with respect to the predetermined direction and the pond width direction, The discharge port is also disposed at a position facing the inclined wall portion, the supply pipe includes a first direction changing means between a discharge port arranged opposite to the convex wall portion and a discharge port arranged opposite to the inclined wall portion, the first direction changing means being capable of changing a discharge direction of a fluid discharged from the discharge port, The nozzle may be provided with a second direction changing means between the plurality of outlets arranged opposite the recessed wall portion and the outlets arranged opposite the inclined wall portion, the second direction changing means being capable of changing the discharge direction of the fluid discharged from the outlets.

[0112] In addition, the following inventive concept can be extracted from the settling basin of this embodiment.

[0113] In a settling basin where sand contained in the received water settles, A groove is provided in a bottom portion of the pond that is lower than the side wall and extends in a predetermined direction; A bottom surface provided at the bottom of the pond and connected to the groove; a plurality of outlets for discharging a fluid for causing the sand that has settled on the bottom surface to flow from the side wall toward the groove; a collective direction changing means capable of collectively changing the discharge direction of fluid discharged from at least two of the plurality of discharge ports; A settling basin characterized by being equipped with an individual direction changing means capable of changing the discharge direction of the fluid discharged from the discharge outlet for each discharge outlet.

[0114] In addition, the following inventive concept can be extracted from the settling basin of this embodiment.

[0115] In a settling basin, water is allowed to flow downward in a direction perpendicular to the width of the basin between one side wall and the other side wall that constitute the end faces in the width direction of the basin, and sand contained in the water is allowed to settle. A first groove and a second groove are provided in the bottom of the pond, spaced apart in the pond width direction and extending in the perpendicular direction, a protruding wall formed between the first groove and the second groove and protruding upward from the bottom of the pond; A sedimentation basin characterized in that a ridge portion extending along the perpendicular direction, a first connection surface connecting the ridge portion and the first groove, and a second connection surface connecting the ridge portion and the second groove are formed in the portion of the bottom of the basin excluding the area between the first groove and the second groove in which the protruding wall is provided.

[0116] the first connection surface is an inclined surface that is inclined downward from the ridge portion toward the first groove, The second connection surface may be an inclined surface that is inclined downward from the ridge portion toward the second groove.

[0117] The first groove is provided on the one side wall side, The second groove is provided on the other side wall side, a first bottom surface formed between the one side wall and the first groove and inclined downward toward the first groove; a second bottom surface formed between the other side wall and the second groove and inclined downward toward the second groove; The inclination angle of each of the first connection surface and the second connection surface may be steeper than the inclination angle of the first bottom surface and the second bottom surface.

[0118] 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 second bottom surface may have 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.

[0119] The apparatus may further 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.

[0120] In addition, the following inventive concept can be extracted from the settling basin of this embodiment.

[0121] In a settling basin, water is allowed to flow downward in a direction perpendicular to the width of the basin between one side wall and the other side wall that constitute the end faces in the width direction of the basin, and sand contained in the water is allowed to settle. A first groove and a second groove are provided in the bottom of the pond, spaced apart in the pond width direction and extending in the perpendicular direction, A sand collection pit provided at the bottom of the pond, to which the first groove is connected and to which the second groove is connected; a protruding wall formed between the first groove and the second groove and protruding upward from the bottom of the pond; A sedimentation basin characterized in that a ridge portion extending along the perpendicular direction, a first connection surface connecting the ridge portion and the first groove, and a second connection surface connecting the ridge portion and the second groove are formed in the portion of the bottom of the basin between the first groove and the second groove and between the sand collection pit and the protruding wall.

[0122] In addition, the following inventive concept can be extracted from the settling basin of this embodiment.

[0123] In a settling basin where sand contained in the received water settles to the bottom of the basin, A groove is provided in the bottom of the pond and extends in a predetermined direction; a first outlet that discharges a fluid in the predetermined direction into the water stored in the groove; A bottom surface provided at the bottom of the pond and connected to the groove; a second 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 sedimentation basin characterized by being equipped with a covering member that covers the periphery of an imaginary axis extending from the center of the first discharge outlet toward the specified direction and has an opening at its lower end.

[0124] In this settling basin, the opening of the cover member may be positioned below the center of the groove in the height direction.

[0125] Furthermore, the following inventive concept can be extracted from the sand collecting method shown in this embodiment.

[0126] A method for collecting sand accumulated on a bottom of a settling basin having a groove extending in a predetermined direction and a bottom surface connected to the groove, the method comprising the steps of: an underwater discharge step of discharging a fluid from a first discharge port in the predetermined direction into the water stored in the groove; and an atmospheric discharge step of discharging a fluid from a second discharge port into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall side toward the groove, A sand collecting method characterized in that the underwater discharge process is a process of discharging a fluid into a space covered by a covering member that has an opening at a lower end portion and covers the periphery of a virtual axis extending from the center of the first discharge port toward the specified direction.

[0127] The underwater discharge step is a step performed in a state where a water level is maintained above the covering member, The discharge into the atmosphere step may be a step performed in a state where a water level is maintained below the bottom surface.

[0128] The process of performing the atmospheric discharging step followed by the underwater discharging step is regarded as one set of sand collecting processes, and the sand collecting process may be performed a plurality of times.

[0129] The underwater discharge step may be carried out before the sand collecting process is carried out a plurality of times.

[0130] In addition, 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.

[0131] The embodiment of the present invention has been described above, and problems thereof will be summarized below.

[0132] When sand removal is not being performed, the sand pump is stopped. Also, during sand removal work, the sand pump may be temporarily stopped to adjust the water level in the grit basin. When the sand pump is stopped, the backflow prevention valve is closed. When the sand pump is stopped and the backflow prevention valve is closed, the flow of sewage in the sand lift pipe stops, and the sand between the backflow prevention valve and the conveying pipe falls and accumulates on the backflow prevention valve. If it is only the sand in the sand lift pipe, it is not a significant amount. However, if more sand in the conveying pipe gets into the sand lift pipe, a large amount of sand may accumulate on the backflow prevention valve. With both motorized valves and check valves, if too much sand accumulates on the valve, the weight of the sand may cause a problem in which the valve cannot be opened. In other words, with motorized valves, if the sand accumulated on the valve becomes heavier than the driving force of the valve by the electric actuator, the valve cannot be opened. In addition, with a check valve, if the sand accumulated on the valve becomes heavier than the force with which the sand pump can pump up the wastewater, the valve will not be able to open. When this malfunction occurs, it requires a lot of effort to disassemble and clean the backflow prevention valve or to remove the entire sand lift pipe and remove the sand inside the pipe. In addition, if the electric actuator or sand lift pump continues to operate after the valve has become stuck, there is a risk that the electric actuator or sand lift pump will overheat and be damaged.

[0133] Therefore, it is desirable to provide a sand transport facility that is less susceptible to malfunctions.

[0134] The sand discharge equipment, which is designed to be less likely to cause malfunctions, is a sand discharge equipment installed in a settling basin where sand contained in received water settles, A pump to suck up the settled sand; a sand lifting pipe connected to the pump through which sand sucked by the pump passes upward; A conveying pipe extending in a direction intersecting with the sand lifting pipe and conveying the sand that has passed through the sand lifting pipe, The sand lifting pipe is characterized in that it is provided with a backflow prevention valve to prevent backflow from the conveying pipe to the pump, and has a portion between the backflow prevention valve and the conveying pipe that is positioned above the connection portion of the conveying pipe with the sand lifting pipe.

[0135] Here, the transport pipe may extend across a plurality of the settling basins, and the sand lifting pipes arranged in each of the plurality of settling basins may be connected to the transport pipe. The transport pipe may be provided above the settling basin, and the pump may be arranged at the bottom of the settling basin. The sand lifting pipe may extend from the bottom of the settling basin toward the transport pipe above the settling basin. In addition, the sand lifting pipe may have a portion extending vertically, and may further have a portion extending horizontally. In this case, the vertically extending portion and the horizontally extending portion may be connected by an L-shaped pipe.

[0136] According to this sand discharge facility, even if sand in the transport pipe gets into the sand raising pipe for some reason, the sand is blocked just before the sand raising pipe reaches the part located above the transport pipe, so that it is possible to prevent the backflow prevention valve from accumulating. Therefore, it is possible to prevent the backflow prevention valve from becoming unable to open due to accumulated sand.

[0137] In addition, in this sand transport equipment, the sand lifting pipe may be connected to an upper portion of the transport pipe.

[0138] According to this aspect, the sand in the conveying pipe tends to gather at the lower part of the conveying pipe due to its own weight and is difficult to move to the upper part, so that the sand in the conveying pipe can be prevented from entering the sand lifting pipe. This makes it possible to more reliably prevent the sand from accumulating on the backflow prevention valve.

[0139] Furthermore, in this sand transport equipment, the connection side portion of the sand lifting pipe with the transporting pipe may be positioned at an incline relative to the transporting pipe so as to gradually approach the transporting pipe as it proceeds toward the transporting direction of the transporting pipe.

[0140] In this way, sand being transported through the transport pipe from the upstream side of the connection between the sand lifting pipe and the transport pipe will not enter the sand lifting pipe unless it moves against the transport direction, so the sand is prevented from entering the sand lifting pipe. Also, sand moving from the sand lifting pipe into the transport pipe is sent toward the transport direction and moves downstream along with the flow of sewage in the transport pipe, so that the sand is prevented from returning to the sand lifting pipe. Furthermore, because the sewage in the sand lifting pipe is sent in the transport direction in the transport pipe, the flow of sewage in the transport pipe can be supported by the sent sewage.

[0141] The settling basin described above is a settling basin in which sand contained in the received water settles to the bottom of the basin. A groove is provided in the bottom of the pond and extends in a predetermined direction; a first outlet that discharges a fluid in the predetermined direction into the water stored in the groove; a cover member that covers a periphery of a virtual axis extending from a center of the first discharge port in the predetermined direction and has an opening at a lower end portion, The covering member may be disposed so that a height position of an upper end of the covering member is equal to or lower than a height position of an opening of the groove.

[0142] In addition, in this settling basin, the first discharge outlet may be one in which the center of the first discharge outlet is disposed between the center of the covering member and the opening of the covering member.

[0143] In addition, the above-described settling basin is a settling basin in which sand contained in the received water settles to the bottom of the basin, A groove is provided in the bottom of the pond and extends in a predetermined direction; a first outlet that discharges a fluid in the predetermined direction into the water stored in the groove; A bottom surface is provided at the bottom of the pond, formed between the side wall of the settling basin and the groove and connected to the groove; a second outlet that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall toward the groove; a cover member that covers a periphery of a virtual axis extending from a center of the first discharge port in the predetermined direction and has an opening at a lower end portion, the covering member is disposed such that a height position of an upper end of the covering member is equal to or lower than a height position of an opening of the groove, The first outlet may be configured to outlet fluid in a state in which a water level is maintained above an upper end of the cover member.

[0144] In addition, the settling basin is provided with a sand pump for pumping up water together with sand, The sand lifting pump may be configured to stop and restart driving so that the water level falls within a predetermined range while the first discharge port is discharging the fluid.

[0145] Meanwhile, a settling basin having a high capacity for collecting settled sand is desired.

[0146] The settling basin described above is a settling basin in which sand contained in the received water settles to the bottom of the basin. A groove is provided in the bottom of the pond and extends in a predetermined direction; a first outlet that discharges a fluid in the predetermined direction into the water stored in the groove; A bottom surface is provided at the bottom of the pond, formed between the side wall of the settling basin and the groove and connected to the groove; a second outlet that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall toward the groove; a cover member that covers a periphery of a virtual axis extending from a center of the first outlet toward the predetermined direction and has an opening at a lower end portion; It is equipped with a sand pump that pumps up water along with sand, the covering member is disposed such that a height position of an upper end of the covering member is equal to or lower than a height position of an opening of the groove, the first outlet is configured to outlet a fluid in a state where a water level is maintained above an upper end of the cover member; The sand-lifting pump is characterized in that, while the first outlet is discharging fluid, it stops and resumes driving so that the water level is within a first predetermined range, and, while the second outlet is discharging fluid, it stops and resumes driving so that the water level is within a second predetermined range that partially overlaps with the first predetermined range.

[0147] The settling basin described above is a settling basin in which sand contained in the received water settles to the bottom of the basin. A groove is provided in the bottom of the pond and extends in a predetermined direction; a first outlet that discharges a fluid in the predetermined direction into the water stored in the groove; A bottom surface is provided at the bottom of the pond, formed between the side wall of the settling basin and the groove and connected to the groove; a second outlet that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall toward the groove; a cover member that covers a periphery of a virtual axis extending from a center of the first outlet toward the predetermined direction and has an opening at a lower end portion; a pump that selectively supplies a fluid to the first outlet and the second outlet; The second outlet is characterized in that it ejects fluid at a lower ejection pressure than the first outlet. [Explanation of symbols]

[0148] 2. Grit chamber 61 Sand lifting pump 64 Sand pumping pipe 64c Slope 66 Conveyor Pipe 66b Pipe connection part 641 Check valve

Claims

1. In a settling basin where sand contained in the received water settles to the bottom of the basin, A groove is provided in the bottom of the pond and extends in a predetermined direction; a first outlet port that discharges a fluid in the predetermined direction into the water stored in the groove; A bottom surface is provided at the bottom of the pond, formed between the side wall of the settling basin and the groove and connected to the groove; a second outlet that discharges a fluid into the atmosphere to cause the sand accumulated on the bottom surface to flow from the side wall toward the groove; a cover member that covers a periphery of an imaginary axis extending from a center of the first discharge port in the predetermined direction and has an opening at a lower end portion, A settling basin characterized in that the second discharge outlet discharges fluid at a lower discharge pressure than the first discharge outlet.

2. The first discharge port discharges a fluid in a state where the inside of the covering member is filled with water received in the grit basin, 2. A settling basin according to claim 1, wherein the second discharge outlet discharges fluid after the water received in the settling basin has been drained.

3. the first discharge port discharges a fluid at a discharge pressure of 0.05 MPa or more and 0.3 MPa or less, 3. A settling basin according to claim 1 or 2, characterized in that the second discharge port discharges fluid at a discharge pressure of 0.0002 MPa or more and 0.005 MPa or less.

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