JP2011245393A - Structure of settling basin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of a settling basin where two right and left screens are provided, and when the screens are supported by side walls on both sides of the settling basin and a supporting wall erected between the side walls, fundamentally one main trough can be formed on the upstream side without being influenced by the supporting wall, and remaining of earth and sand does not occur when collecting sand, in the settling basin for performing a low pressure sand collecting type sand removing method provided with the screens at the upstream-side end.SOLUTION: The two right and left screens are installed. The screens are supported by the side walls on both sides at the upstream-side end of the settling basin and the supporting wall erected between the side walls, and the main trough on the upstream side is formed in a Y shape. A bifurcated part of the Y shape is formed at a position adjacent to both sides of a downstream part of the supporting wall on the bottom of the settling basin, and a vertical part of the Y shape is formed parallel to the water flow direction of the settling basin so as to communicate to a sand collecting pit.

Description

  The present invention relates to a sand settling basin for precipitating, collecting and removing sediment contained in stored sewage, which is provided with a screen for capturing impurities at an upstream end.

  In sewage treatment facilities, sewage collected by sewage pipes is stored, and sedimentation basins are used to settle sediment from the stored sewage and remove the sediment. In order to remove the dust in advance, a screen for capturing foreign substances (hereinafter simply referred to as a screen) is installed at the upstream end of the sand basin.

  By the way, although the width of the sand basin generally reaches about 4 m, conventionally, a single screen has been installed for the entire width. That is, a screen having the same width as the sand basin was supported by the side walls on both sides of the sand basin.

Japanese Patent No. 3315489

  However, when there is heavy rain, the amount of water flowing into the sand basin and the flow velocity increase considerably, and the resistance by the trapped contaminants may help, and a great deal of pressure may be applied to the screen. Therefore, since the screen supported only at both ends cannot withstand the pressure and may be damaged, a countermeasure has been demanded.

  Therefore, it is proposed to install two screens on the left and right with respect to the entire width of the sand basin, and to support both ends of each screen with side walls on both sides of the sand basin and support walls provided in the center in the width direction of the sand basin.

On the other hand, as a method to collect and remove the sediment deposited in the sedimentation basin, a sand collection pit is formed at the center of the bottom of the sedimentation basin, and the bottom of the sand collection pond is deepest around the sand collection pit. In addition to inclining, the main trough is formed at the bottom of the sand basin between the side walls on both sides of the sand basin so that it crosses the sand pit parallel to the direction of the water flow in the sand basin and the sand pit side is deep. The surface that slopes down from the side walls on both sides of the sand basin to the bottom of the sand collection pit (hereinafter referred to as the sand collection pit slope) is further extended parallel to the bottom of the sand basin in a direction perpendicular to the water flow direction in the sand basin. A large number of small troughs are formed, and each upper end portion of the main trough and the sand collecting pit inclined surface, and an upper end portion of each region in which the bottom surface of the sand basin is divided into a plurality of water flow directions in the sand basin on at least one side of the main trough, , Sand collection pit DOO, the installed nozzles respectively, sediment deposited on the bottom of the settling basin by injecting a low pressure water of less than 3 kg / cm ² from the nozzle while discharging the water settling pond drainage pump (drainage state) The collected sediment is collected in the sand collection pit, and the collected sediment is agitated by the nozzle in the sand collection pit and pumped up with the water by the sand pump installed in the sand collection pit. Patent Document 1 discloses a low-pressure sand collection type sand removal method for transporting to a high pressure.

  Therefore, in a sand basin that implements the low pressure sand collection method sand removal method, if the screen support wall is installed at the center in the width direction of the upstream end of the sand basin, the upstream main trough is placed in the center in the width direction of the sand basin. A new problem arises that it cannot be formed.

  The solution usually conceived for this problem is that, as shown in FIG. 13, the main trough upstream of the sand collecting pit p is linearly formed from the closest positions on the left and right sides of the support wall SW to the sand collecting pit p. It is formed in two parallel main troughs t1a and t1b that extend, and nozzles n1 and n2 are installed at the upper ends of the main troughs, respectively.

  However, when two parallel main troughs t1a and t1b are formed, the following new problem arises. That is, first, since there are two upstream main troughs, the number of nozzles installed in the main trough is increased to two, and the two main nozzles have a conventional main trough. A nozzle having the same discharge amount as the nozzle used in the above is used. Therefore, it is necessary to add a nozzle switching valve. Secondly, the upstream main troughs t1a, t1b and the downstream main troughs t1 are not opposed to each other in the sand collecting pit p and are displaced, so that the three main troughs t1a, t1b, t1 There is a risk that the water mixed with the earth and sand flowing through each of them will pass through the sand collecting pit p and overflow into the area on the opposite side, leaving the earth and sand in that area. Thirdly, there is an island i between the two main troughs t1a and t1b, where the water from the nozzles n1 and n2 does not reach, and there is a risk that the sediment that has settled on the island remains without flowing. Residual earth and sand cause odor generation.

  The present invention has been made in view of the above circumstances, and in a sand basin for carrying out a low pressure sand collection type sand removal method equipped with a screen at an upstream end, the screen is divided into two on the left and right, and each screen is When supported by the side walls on both sides of the sand basin and the support wall erected at the center in the width direction of the upstream end of the sand basin, it is affected by the support wall installed at the center in the width direction of the upstream end of the sand basin Therefore, it is possible to provide a structure of a sand basin that can basically form one main trough at the center in the width direction on the upstream side, and that does not generate residual sediment without being washed away. The first purpose.

  In order to solve the first object, the second object of the present invention is formed so that the upstream main trough is Y-shaped and the bifurcated portions of the Y-shape exist on both sides of the downstream part of the support wall. When the nozzle is installed at the upstream end of the bifurcated portion, the Y-shaped vertical portion is formed to extend to the sand collecting pit at the center in the width direction of the sand basin. It is to prevent excessive water from flowing and not to add an additional nozzle switching valve.

  In order to achieve the above first object, the present invention provides a sand basin for carrying out a low pressure sand collection type sand removal method equipped with a screen at an upstream end, wherein the screen is divided into two sheets on the left and right, and each screen is sanded. The upper main trough is Y-shaped, and the Y-shaped bifurcated portion is downstream of the support wall at the bottom of the sand basin. The Y-shaped vertical portion is formed at a position close to both sides of the side portion, and is formed so as to communicate with the sand collecting pit parallel to the water flow direction of the sand basin.

  In order to achieve the second object described above, the present invention achieves about the discharge amount of the nozzles installed at the upper end of the downstream main trough at the upper end of the Y-shaped bifurcated portion of the upstream main trough. A nozzle having a half discharge amount is installed, and one switching valve for switching the water from the water supply pump to the water-flowing state or the water-stopping state is combined with two nozzles whose discharge amount is about half. .

  According to the present invention, the support walls are erected between the side walls on both sides at the upstream end of the sand basin, thereby increasing the flow rate of sewage on both sides. Since it is supported by the side wall and the support wall, the screen is supported with sufficient strength to withstand the pressure of water flowing between the side wall and the support wall. In addition, the upstream main trough is formed in a Y-shape at the closest position on both sides of the support wall and in the center in the width direction of the sedimentation basin. It is washed away by the trough and collected in the sand collecting pit.

  According to the present invention, the discharge amount of the nozzle installed at the upper end of the Y-shaped bifurcated portion of the upstream main trough is approximately equal to the discharge amount of the nozzle installed at the upper end of the downstream main trough. Since it is a half, the same switching valve as the conventional single main trough switching valve can be used for the upstream main trough, so no additional switching valve is required. Therefore, an increase in cost due to the provision of the support wall is not caused.

It is a longitudinal cross-sectional view of the rainwater treatment facility including a sand basin. It is a schematic plan view which shows the principal part of the range of the XX line of FIG. It is the detailed top view which abbreviate | omitted the water supply pipe | tube of the range of the XX line of FIG. It is a detailed top view similarly including a water supply pipe. FIG. 4 is a sectional view taken along line Y1-Y1 of FIG. FIG. 4 is a sectional view taken along line Y2-Y2 of FIG. FIG. 5 is a sectional view taken along line ZZ in FIG. 4. It is a water supply system diagram. It is a control system figure explaining the control apparatus of a gradual sand apparatus. It is a figure explaining the function of a water level sensor. It is a control flowchart figure of a sand pump control means. It is a control flowchart figure of a switching valve control means. It is a top view which shows the design plan of the upstream main trough.

Next, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a rainwater treatment facility, which has a sand basin 2 and a pump well 3 formed between side walls Wa and Wb (see FIG. 2). The settling basin 2 is connected to an inflow trough 4 from which sewage such as rainwater and sewage is collected from a sewage pipe not shown. A dam device 5 for allowing or preventing the inflow of sewage from the inflow trough 4 to the sand basin 2 is installed at the downstream end of the inflow trough 4. A screen 6 is installed at the upstream end of the screen.

  As shown in FIGS. 2 and 3, the screen 6 includes two screens 6 </ b> A and 6 </ b> B on the left and right sides. , Wb, and is supported by a support wall SW standing at the center in the width direction of the sand basin 2 and side walls Wa or Wb on both sides of the sand basin 2 in the illustrated example.

  As described above, in order to perform low-pressure sand collection, a sand collection pit 7 is formed at the center of the bottom of the sand basin 2, and the bottom surface 2a of the sand basin 2 is inclined so that the periphery of the sand collection pit 7 is deepest. In addition, at the center in the width direction of the bottom of the sand basin, the main troughs 8a1 and 8a2 intersect the sand collection pit 7 upstream and downstream of the sand collection pit 7, and the sand collection pit side is A surface 8b formed so as to be deep and inclined downward from the lower ends of the side walls Wa and Wb to the bottom surface of the sand collecting pit 7 (hereinafter referred to as a sand collecting pit inclined surface) is further formed on the bottom surface of the sand basin. A number of small troughs 8c (not shown in FIG. 2) extending in parallel from the vicinity of Wb to the main troughs 8a1 and 8a2 are formed.

  Of the main troughs 8a1 and 8a2, the main trough 8a2 downstream of the sand collecting pit 7 is straight from the downstream end of the sand basin to the sand collecting pit 7 at the center in the width direction of the bottom of the sand basin. It is formed in a shape. On the other hand, the main trough 8a1 upstream of the sand collecting pit 7 is formed in a Y shape, and the Y-shaped bifurcated portion A is formed in a position close to both side surfaces of the downstream portion of the support wall SW. The Y-shaped vertical portion B is formed in a straight line on the downstream extension line of the support wall SW so as to communicate with the sand collecting pit 7 in the center in the width direction of the bottom of the sand basin in the illustrated example. Thereby, the island i as in the case where two upstream main troughs 8a1 are formed in parallel on both sides of the support wall SW shown in FIG. 13 is not formed.

  In the pump well 3, a drainage pump P <b> 1 described later and a water supply pump P <b> 2 serving also as a pump for discharging stagnant water are installed, and a pumping sand pump P <b> 3 described later is installed in the sand collecting pit 7. F of FIG. 1 is a filter installed at the downstream end of the sand basin 2.

  Nozzles for discharging a predetermined amount of water to the main troughs 8a1, 8a2 and the sand collecting pit inclined surface 8b are installed at the upper ends of the main troughs 8a1, 8a2 and the sand collecting pit inclined surface 8b. A nozzle 9a having a predetermined discharge amount is installed at the upper end portion of the downstream main trough 8a2 as in the prior art, but the upstream main trough 8a1 has a downstream side at both ends of the Y-shaped bifurcated portion A. A nozzle 9a ′ having a discharge amount about half that of the nozzle 9a of the main trough 8a2 is provided.

  Since the support wall SW is erected between the side walls Wa and Wb on both sides, the flow rate of sewage on both sides of the support wall increases, so that the amount of sediment deposited in the regions B3 and B4 on both sides of the support wall is reduced. Accordingly, the flow rate of the nozzle for supplying water to the Y-shaped bifurcated portion A of the upstream main trough 8a1 is small. Accordingly, the discharge amount of the nozzle 9a 'installed at both ends of the Y-shaped bifurcated portion A can be reduced to half of the discharge amount of the nozzle 9a of the downstream main trough 8a2. That is, a single switching valve having the same performance can be used for the two nozzles 9a 'installed at both ends of the bifurcated portion A of the upstream main trough 8a1.

  In addition, nozzles 9b are installed in areas (B1 to B8) in which the bottom surface of the sand basin is divided into a plurality of sections (eight sections in the illustrated example) on both sides of the main troughs 8a and 8a2. A plurality of nozzles 9b installed in the regions are installed at equal intervals on the nozzle headers NH1 to NH8 installed above the upper end portions of the regions and in positions close to the side walls Wa and Wb. FIG. 7 shows an example in which nozzle headers NH1, NH2,... Formed by attaching a plurality of nozzles 9b to the mother pipe 10 at a predetermined interval are shown. Further, in the sand collecting pit 7, a nozzle 9c for earth and sand agitation is installed. A plurality of nozzles 9c (four in FIGS. 3 and 4) are installed so as to discharge from two directions opposite to the lower part of the sand pump P3 at a position close to the tangential line around the lower part of the sand pump P3. Has been. For simplification of the drawing, the earth and sand stirring nozzle 9c is omitted in FIG. 2, and the sand pump P3 is not shown in FIG.

  Then, as shown in part in FIGS. 4 and 7 and in detail in FIG. 8, the water from the water supply pump P2 of the pump well 3 is supplied to the nozzles 9a, 9a ′, 9b, 9c. (Switching water) and switching valves VG1 and VG2 constituted by solenoid valves for stopping the supply (water stopping), that is, the trough nozzle switching valves Va1 to Va3, and the switching valve for each nozzle header Vb1 to Vb8 and a stirring nozzle switching valve Vc are provided. As the trough nozzle switching valve Va, the nozzle switching valve Va1 of the upstream main trough 8a1 and the nozzle switching valve Va2 of the downstream main trough 8a2 are used. The water supply pipe wp1 connected to the discharge side of the nozzle switching valve Va1 of the upstream main trough 8a1 is branched into two on the way, each of which is the upper end of the Y-shaped bifurcated portion A of the upstream main trough 8a1. It is coupled to two nozzles 9a 'installed in the section.

  As illustrated in FIGS. 3 and 8, when the bottom surface of the sand basin is divided into eight regions, eight nozzle header switching valves Vb (Vb1 to Vb8) are used. A relief circuit wp19 is provided in the pipe line wp0 connecting the feed water pump P2 and the switching valve groups VG1, VG2 via the switching valve Vd, and water from the feed water pump P2 when all the switching valves are closed. Is configured to escape to the sand basin 2.

  As illustrated in FIG. 9, an operation panel 101 having a sand removal start button (not shown) is added to the control device 100 provided in the sand removal device for performing the low pressure sand collecting method, and the drain pump control means PCON1. The feed water pump control means PCON2 and the sand pump control means PCON3 are incorporated, and the switching valve control means VCON is incorporated. As will be described later, the switching valve control means VCON provides a control signal for driving the switching valve groups Va, Vb, Vc, Vd to open (water flow) operation or close (water stoppage) operation in a predetermined order. Give.

  Further, a water level sensor 13 (see FIGS. 9 and 10) installed in the sand collecting pit 7 is electrically connected to the control device 100. As shown in FIG. 10, when the water level in the sand collection pit 7 is higher than a predetermined high water level HWL, and is present in any of the intermediate water level MWL and the low water level LWL, the water level sensor 13 detects a signal higher than the high water level. In addition to outputting an intermediate water level detection signal and a low water level detection signal, when the water level in the sand collecting pit 7 rises to an abnormal water level HHWL set at a position higher than a predetermined high water level HWL, this is detected and abnormal It is configured to output a water level detection signal.

  Then, as will be described later, the sand pump control means PCON3 starts the automatic operation mode of the sand pump P3 by operating the sand removal start button, and then continues until the automatic operation mode is stopped. When the control means VCON switches the trough switching valve Va to the water passing state, the operation of the sand pump P3 is started. Thereafter, the operation of the sand pump P3 is stopped when the low water level detection signal is inputted, Although the operation of starting the sand pump P3 when a detection signal at a high water level or higher is input is the same as in the prior art, in this embodiment, the sand pump P3 is also input when an abnormal water level detection signal is input. It is comprised so that driving | operation may be stopped.

  The water supply pump control means PCON2 starts the water supply pump P2 after the switching valve control means VCON switches the switching valve Vd of the relief circuit 11 to the water supply state by operating the sand removal start button. After the slow sand operation is finished, the water supply pump P2 is stopped after switching the switching valve Vd of the relief circuit wp19 to the water stop state. In this embodiment, when an abnormal water level detection signal is input from the water level sensor 13 Is also configured to stop the water supply pump P2.

  The operation of the above configuration will be described. When the dam device 5 is opened, the sewage flows into the sand basin 2 and further into the pump well 3, and when the water level reaches a predetermined height, the drain pump control means of the control device 100 of the sand removal device. The drain pump P1 provided in the pump well 3 is operated by PCON1, and the water in the pump well 3 is pumped up and transferred to a terminal treatment plant or the like outside the figure.

  During the transfer, earth and sand are precipitated from the sewage mixed with the earth and sand flowing into the sand basin 2 and deposited on the bottom surface 2a of the sand basin. When the accumulation amount reaches a predetermined value, the dam device 5 is closed and the inflow of sewage into the sand basin 2 is prevented. When the water level of the settling basin 2 and the pump well 3 is lowered by drainage by the drainage pump P1 and reaches a predetermined water level (WL in FIG. 1), the drainage pump control means PCON1 stops the operation of the drainage pump P1.

  When it is detected that the water level of the pump well 3 has reached a predetermined water level (WL in FIG. 1), the control device 100 activates the feed water pump control means PCON2, the sand pump control means PCON3, and the switching valve control means VCON.

  As shown in FIG. 11, the sand pump control means PCON3 starts the automatic operation mode of the sand pump P3 (S11), and the water level in the sand collecting pit 7 is set to a predetermined low water level by the detection signal from the water level sensor 13. It is checked whether or not it is LWL (S12). When the water level is low, it is checked whether or not the trough switching valve Va is switched to the water state by the signal from the switching valve control means VCON (S13). Starts the operation of the sand pump P3 (S14).

  Further, as shown in FIG. 12, the switching valve control means VCON first opens the switching valve Vd of the relief circuit wp19 (makes the water flow state), and prepares to drive the water supply pump P2 (step of FIG. 12). S21). Subsequently, after opening the trough switching valve Va and the stirring nozzle switching valve Vc (S22), the switching valve Vd of the relief circuit wp19 is closed (S23), so that the water from the water supply pump P2 is fed from the nozzles 9a 'and 9a. It is discharged to the main troughs 8a1, 8a2 and the sand collecting pit inclined surface 8b.

  The discharge amount of the nozzle 9a 'is about half of the discharge amount of the nozzle 9a, but only the sediment from one region flows into one of the Y-shaped bifurcated portion A of the upstream main trough 8a1. The amount of water is sufficient to eliminate water. Moreover, since about half of the water discharged from the Y-shaped bifurcated portion A merges with the Y-shaped vertical portion B, the amount of water is substantially equal to the amount of water in the downstream main trough 8a2. Therefore, the speed of the earth and sand flowing into the sand collecting pit 7 from the upstream main trough 8a1 and the speed of the earth and sand flowing into the sand collecting pit 7 from the downstream main trough 8a2 are almost equal to each other, and the flow velocity is remarkably large. Therefore, the sand collection efficiency is stable over time, so that it is possible to prevent an uneven load from being applied to the sand pump P3.

  In a preferred embodiment, the switching valve control means VCON switches the trough switching valve Va to the water passing state and simultaneously switches the stirring nozzle switching valve Vc to the water passing state. As described above, at the same time, the sand pump control means PCON3 is configured to start the operation of the sand pump P3.

  Water from the water supply pump P2 is discharged from the nozzles 9a 'and 9a of the main troughs 8a1 and 8a2 and the sand collecting pit inclined surface 8b by passing through the trough switching valve Va, and these troughs 8a1 and 8a2, and the sand collecting pit inclined surface. The earth and sand deposited in 8b is washed away with water and then towards the sand collecting pit 7. Further, since water is discharged from the agitation nozzle 9c of the sand collection pit by passing water through the agitation nozzle switching valve Vc, a small amount of soil and water already existing in the sand collection pit are agitated and fluidized. Therefore, after that, the earth and sand flowing into the sand collecting pit from the trough merge with the stirring earth and sand and are fluidized in the same manner. On the other hand, since the sand pump P3 starts operation almost simultaneously with the water discharged from the stirring nozzle 9c, the sewage mixed with the earth and sand to be stirred in the sand collecting pit is pumped up and passes through the sand set separator 11 to the sewage settling basin 12. It is transferred to.

  Since the discharge amount of the sand pump P3 is set to be larger than the discharge amount of the water supply pump P2, the water level in the sand collecting pit 7 will eventually drop. When the water level sensor 13 detects that the water level has reached a predetermined intermediate water level (Y in S24), the switching valve control means VCON is based on the intermediate water level detection signal from the water level sensor 13 in the first region B1. In order to open the nozzle header switching valve Vb1 (S25), water is sprayed from each nozzle of the nozzle header, and the sediment accumulated in the first region B1 is flowed toward the main troughs 8a1 and 8a2, and further collected. It flows into the sand pit 7. In this way, the sewage mixed with the earth and sand collected and stirred in the sand collecting pit 7 temporarily rises in water surface, but since it is pumped up by the sand pump P3 and transferred to the sewage settling basin 12, it will eventually drop. To do.

  When the water level sensor 13 detects that the water surface has again reached the predetermined intermediate water level (Y in S26), the switching valve control means VCON closes the nozzle header switching valve Vb1 in the first region B1. In order to open the nozzle header switching valve Vb2 in the second region B2 (S27), water is sprayed from each nozzle of the nozzle header, and the earth and sand accumulated in the second region B2 flows toward the main trough 8a. And then flows into the sand collecting pit 7.

  Accordingly, as in the case of the first region B1, the water surface in the sand collecting pit 7 temporarily rises but then declines, so when the water surface reaches a predetermined intermediate water level (Y in S28). The switching valve control means VCON closes the nozzle header switching valve Vb2 in the second region B2 and opens the nozzle header switching valve Vb3 in the next third region B3 (S29). Water is jetted from.

  Therefore, as in the previous case, the water level in the sand collecting pit 7 temporarily rises but then drops, so when the water level reaches a predetermined intermediate water level (Y in S210), the switching valve The control means VCON closes the nozzle header switching valve Vb3 in the third region B3 and opens the nozzle header switching valve Vb4 in the fourth region B4 (S211), so that water is injected from each nozzle of the nozzle header. .

  Therefore, as in the previous case, the water level in the sand collecting pit 7 temporarily rises but then drops, so that when the water level reaches a predetermined intermediate water level (Y in S212), the switching valve The control means VCON determines that the water discharge to the fourth region B4, that is, the last region has ended, opens the relief valve switching valve Vd, and closes the nozzle header switching valve Vb4 in the fourth region B4. To complete a series of switching valve controls. Also, the feed water pump control means PCON2 stops the operation of the feed water pump P2.

  On the other hand, the sand pump control means PCON3 always monitors the detection state of the water level sensor 13 from the start of operation of the sand pump P3 (S15), and the water level in the sand collecting pit 7 does not decrease to the low water level LWL. Continues the operation of the sand pump P3 until it drops to the low water level LWL (S16). However, closing the nozzle header switching valve Vb4 in the fourth region B4 causes the water level in the sand collecting pit 7 to drop to the low water level LWL (when S15 is Y), so the operation of the sand pump P3 is stopped. (S17). Thereafter, the sand pump control means PCON3 checks whether or not the control of the switching valve is completed (S18), and if not completed, the process returns to step S16, but recognizes the completion of the switching valve control (Y in S18). After that, the automatic operation mode of the sand pump P3 is canceled (S19).

As described above, when starting the automatic operation mode, the sand pump P3 is automatically activated when the water level in the sand collection pit is above a predetermined high water level HWL in order to maintain the sand collection pit 7 in a drained state. The operation is automatically started, and the operation is automatically stopped when the water level drops to a predetermined low water level LWL. In the present embodiment, when the water level in the sand collecting pit is lowered to the intermediate water level MWL between the predetermined high water level HWL and the predetermined low water level LWL, the nozzle header switching valve in the preceding region is closed, Since the switching valve for the nozzle header in the rear area is opened, the water surface in the sand collecting pit during the switching operation of these switching valves is the water injection by the closing operation of the nozzle header switching valve in the previous area. The intermediate water level MWL, which is a temporal reference for the switching operation of the switching valve, varies depending on the stop, pumping of the sand pump, and the start of water injection by the opening operation of the nozzle header switching valve in the subsequent order. If the water level in the sand collection pit is set to a height position that does not drop to the predetermined low water level LWL during the switching operation, from the start of sand collection to the end of sand collection / slow sand from the entire area of the sand basin, Operation of the sand pump P3 It can not locked.
The intermediate water level MWL serving as a temporal reference for the switching operation of the switching valve can be calculated from the discharge amount of the water supply pump P2, the cross-sectional area of the sand collecting pond, the discharge amount of the sand pump P3, and the like.

1 Rainwater treatment facility 2 Settling basin 2a Bottom of settling basin SW Support wall
6 screens (screens for capturing foreign substances)
7 Sand collecting pit 8a1 Upstream main trough Bifurcated portion of upstream main trough b Upstream main trough vertical portion 8a2 Downstream main trough 8b Sand collecting pit inclined surface 8c Small trough 9a, 9a ', 9b, 9c Nozzle NH1-NH4 Nozzle header P1 Drainage pump P2 Water supply pump P3 Sand pump

Claims (2)

  In a sand basin that implements a low pressure sand collection type sand removal method with a screen at the upstream end, the screen is divided into two pieces on the left and right, and each screen is erected between the side walls on both sides at the upstream end of the sand basin. The upper main trough is Y-shaped, and the Y-shaped bifurcated portion is formed at a position close to both sides of the downstream portion of the support wall at the bottom of the sand basin; and A sand basin characterized in that the Y-shaped vertical portion is formed so as to communicate with a sand collecting pit parallel to the water flow direction of the sand basin.   At each upper end of the Y-shaped bifurcated portion of the upstream main trough, a nozzle having a discharge amount approximately half of the discharge amount of the nozzle installed at the upper end of the downstream main trough is installed, and the discharge amount 2. The sand basin according to claim 1, wherein one switching valve for switching the water from the water supply pump to a water-flowing state or a water-stopping state is coupled to about two nozzles.

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