JP6583388B2 - Sedimentation tank - Google Patents

Description

  The present invention relates to a sedimentation tank for settling and separating sludge, and more particularly to a sedimentation tank in which water to be treated is supplied to the lower part of the precipitation tank via a center well.

  Conventionally, in activated sludge treatment equipment, coagulation sedimentation treatment equipment, etc., sedimentation separation using a solid-liquid separation tank (precipitation tank) is generally used as a means for separating the sludge mixed liquid (coagulation treatment liquid) into treated water and sludge. It has been adopted. In this sedimentation separation, a sludge zone (sludge blanket layer) is formed in the sedimentation tank in order to efficiently remove turbidity and fine SS in the sludge mixture and obtain good treated water. The sludge blanket filtration method is adopted to filter and separate turbidity and fine SS in the sludge mixed liquid by feeding the sludge mixed liquid from the lower part of the sludge zone and passing through the sludge zone through the feed well). Yes.

  As a center well type sedimentation tank, it is known that a plate is provided horizontally facing the lower end of the center well at the center of the tank body, and the flow direction of the outflow water from the center well is changed to the radial direction. (Patent Documents 1 and 2).

  In a coagulating sedimentation apparatus, in order to effectively perform solid-liquid separation in a sedimentation tank to obtain highly purified treated water, it is important to introduce the generated aggregate floc into the sedimentation tank without destroying it. That is, when the aggregated floc is destroyed and refined, its sedimentation property is deteriorated, and it flows out to the treated water side to deteriorate the quality of treated water.

  In Patent Document 3, a cylindrical inflow portion having a diameter larger than that of the center well is formed in the upper portion of the cylindrical center well, and the water to be treated is supplied from the inflow pipe to the tangential direction of the peripheral wall of the inflow portion, A swirl flow along the peripheral wall is formed at the inflow part, and is introduced into the center well as it is to form a flow that descends while swirling in the center well. It is disclosed to prevent and suppress the destruction of the aggregate floc.

JP 2005-66533 A JP 2007-69189 A JP 2017-87090 A

  As in Patent Documents 1 to 3, the treated water that has risen in the settling tank overflows into a trough (overflow weir) provided along the inner peripheral wall of the tank and is taken out. Thus, in the sedimentation tank in which the trough is provided along the inner peripheral wall of the sedimentation tank, when the upward flow LV in the sedimentation tank is high, in the shallow area near the water surface, near the inner peripheral wall of the tank with the trough May become higher than the vicinity of the center well without the trough, and the concentration of SS (suspended substance) in the treated water flowing into the trough may be increased.

  In the precipitation tank in which the water to be treated flows into the tank from the center well, rises in the tank, and flows out of the trough, the present invention can prevent water in the vicinity of the trough even when the rise LV in the tank is high. An object of the present invention is to provide a sedimentation tank in which an increase in flow rate is suppressed and the quality of treated water can be kept good.

  In the sedimentation tank of the present invention, the water to be treated supplied from the center well at the center of the tank body to the lower part of the tank body rises in the tank body and flows out as clear water from the trough at the upper part of the tank body. In the sedimentation tank, the trough includes a first trough along the inner peripheral wall of the tank body, and a second trough disposed between the first trough and the center well. And

  In one aspect of the present invention, the second trough has an annular shape that goes around the center well.

  In one aspect of the present invention, there are provided swirl introduction means for introducing the water to be treated into the center well while swirling, and a plate for changing the flow direction of water against the lower end of the center well. Thus, the upward flow in the tank forms a swirling flow.

  In one aspect of the present invention, the planar view shape of the inner peripheral wall of the tank body is a circle or a regular n-gon (n ≧ 6).

  In the sedimentation tank of the present invention, the trough is provided with a first trough along the upper inner peripheral wall of the tank body and a second trough between the first trough and the center well. Even when the LV is large, an increase in the flow rate of water near the trough is suppressed, and the quality of the treated water can be kept good.

It is a longitudinal cross-sectional view of the sedimentation tank which concerns on embodiment. It is a top view of the sedimentation tank of FIG. It is a top view of the sedimentation tank concerning another embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. 1 and 2 show a coagulation sedimentation apparatus having a sedimentation tank according to a first embodiment.

  In the sedimentation tank according to this embodiment, the shape of the inner peripheral wall of the tank body 1 in plan view is circular, but it may be a regular polygon (however, a hexagon or more). A center well 2 is installed at the center of the tank body 1. The center well 2 has a cylindrical shape whose upper and lower ends are open, and an upper end 2t of the center well 2 protrudes above the water level WL in the tank body 1. This water level WL is an overflow level of troughs 13 and 15 described later. The upper end 2t has a uniform height over the entire circumference.

  A center well upper 3 having a diameter larger than that of the center well 2 is provided on the center well 2 as a center well upper member. The center well upper 3 is connected to the upper outer peripheral surface of the center well 2, and has a flat bottom surface 3a that expands in the horizontal direction, and a peripheral wall 3b that stands up from the outer peripheral edge of the bottom surface 3a. A portion surrounded by the upper portion of the center well 2, the bottom surface 3 a, and the peripheral wall 3 b is an annular water channel C surrounding the upper outer periphery of the center well 2. The difference (level difference) between the level of the water surface level WL and the level of the upper end 2t of the center well 2 is preferably 0 to 10 cm, particularly preferably 0 to 5 cm.

  An introduction pipe 8 is provided as an introduction member of the water to be treated so that the water to be treated flows into the annular water channel C in the circulation direction. The end portion of the introduction pipe 8 extends along the peripheral wall 3b as shown in FIG. 2, and the water to be treated flows into the annular water channel C along the peripheral wall 3b and swirls in the annular water channel C. The upper end 2t of the center well 2 overflows and flows into the center well 2.

  The diameter of the annular water channel C (the diameter of the inner peripheral surface of the peripheral wall 3b) is preferably about 1.2 to 2.0 times, particularly about 1.4 to 1.8 times the outer diameter of the upper end 2t of the center well 2.

  In this embodiment, the bottom surface 3a is horizontal. The height difference between the upper end 2t and the bottom surface 3a is preferably 5 to 50 cm, particularly preferably 10 to 40 cm.

  A plate 4 commonly referred to as a flat baffle is provided to face the lower end of the center well 2 so that the flow direction of the raw water from the center well 2 is a radial direction. In this embodiment, the plate 4 has a horizontal disk shape. The plate 4 is located below the lower end of the center well 2 by a predetermined distance. The plate 4 and the center well 2 are arranged coaxially.

  A rake shaft 10 to be described later passes through the center of the plate 4, and the plate 4 is supported by the rake shaft 10. However, the plate 4 may be supported by the center well 2 via a support member (not shown).

  The radius of the plate 4 is not less than the radius of the center well 2 and not more than 1.5 times the radius, preferably about 1 to 1.3 times the radius of the center well 2.

  The bottom surface of the tank body 1 has a downward slope toward the center, and a pit 6 for collecting and discharging the settled sludge is provided at the center. Sludge in the pit 6 is discharged out of the tank body 1 through the sludge pipe 7. However, the bottom surface of the tank body 1 may be horizontal.

  A rake device is provided to rotate the rake plate 11 along the bottom surface of the tank body 1. The rake apparatus includes a rake shaft 10 that extends in the vertical direction through an axial center portion of the center well 2, a support arm 12 that extends in a radial direction from the lower portion of the rake shaft 10, and the arm 12. And a drive device (not shown) in which the upper end of the rake shaft 10 is connected.

  The rake plate 11 is disposed in the longitudinal direction and the oblique direction of each arm 12 so as to move the deposit on the bottom surface of the tank body toward the center side of the bottom surface of the tank body when the rake rotates.

  A first trough (overflow weir) 13 is provided along the upper part of the inner peripheral wall surface of the tank body 1. An annular second trough 15 that circulates around the center well 2 is provided between the first trough 13 and the center well 2. In this embodiment, the plan view shape of the second trough 15 is circular. The second trough 15 and the first trough 13 are concentric. V-shaped notches (notches) are provided at the upper ends of the troughs 13 and 15 at predetermined intervals. The water in the tank body 1 flows into the troughs 13 and 15 through the V notches. The overflow level to the troughs 13 and 15 is the water level WL in the tank body 1. The water that flows into the trough 15 flows into the trough 13 through the communication channel 14L, and the water that flows into the trough 13 flows out of the tank from the clarified water outlet 14 as treated water. Thus, the trough and the connecting water channel 14L between the troughs reduced the portion extending in the radial direction from the central axis of the tank body 1 so that the upward flow in the tank had a horizontal flow such as a swirling flow. Even in this case, it is possible to reduce the obstruction of the flow.

  The water depth of the tank body 1, that is, the height from the bottom face of the tank body to the water surface level WL is preferably 100 to 400 cm, more preferably 100 to 250 cm.

The diameter (inner diameter) of the tank body 1 is preferably about 1 to 20 m. The width of the troughs 13 and 15 is preferably about 0.1 to 0.5 mm. It is preferable that the V-notches of the troughs 13 and 15 are equally provided at a pitch of 0.3 to 0.8 m. The water area of the water surface region surrounded by the peripheral wall surface of the center well 2 and the inner peripheral wall surface of the second trough 15 is S1, the number of V notches of the second trough 15 in contact with the water surface region is V1, and the second When the water area of the water surface region surrounded by the outer peripheral wall surface of the trough 15 and the inner peripheral wall surface of the first trough 13 is S2, the total number V2 of the V troughs of the second trough 15 and the first trough 13 in contact with the water surface region is V2. It is preferable to design so that the ratio of S1 / S2 and V1 / V2 is approximately the same (for example, approximately 0.8 to 1.2).
The width of the communication channel 14L and the clarified water outlet 14 is preferably about 0.1 to 0.5 m.

  The height of the upper surface of the plate 4 from the bottom surface of the tank body (periphery of the pit 6) is 20 to 150 cm, preferably 25 to 120 cm, particularly 30 to 80 cm.

  The descending flow velocity (LV) in the center well 2 is preferably 10 cm / sec or less, for example, 1 to 6 cm / sec, particularly about 2 to 4 cm / sec.

  The vertical distance of the raw water outlet between the lower end of the center well 2 and the upper surface of the plate 4 is such that the horizontal linear velocity of the raw water flowing out from this raw water outlet is about 1 to 10 cm / sec, particularly about 2 to 6 cm / sec. It is preferable to set to.

  The ascending flow velocity (LV) in the tank body 1 is preferably 1 m / hr or more, for example, 1 to 15 m / hr, particularly about 2 to 8 m / hr.

  In the sedimentation tank configured as described above, the water to be treated is supplied to the annular water channel C in the center well upper 3, swirls in the annular water channel C, overflows the upper end of the center well 2, and flows into the center well 2. Then, it descends in the center well 2 and flows out radially between the lower end of the center well 2 and the plate 4. Thereafter, the water rises in the tank body 1 and flows out into the troughs 13 and 15 due to overflow. The water in the trough 15 flows out to the trough 13 through the connecting water channel 14L, and the water in the trough 13 is discharged from the clarified water outlet 14. Water from the trough 15 may be taken out using piping. This pipe is preferably provided above the water surface. This pipe may be a siphon pipe or a pipe having a pump.

  In this embodiment, the water to be treated gradually flows into the sludge blanket from the raw water outlet between the lower end of the center well 2 and the plate 4 so that the sludge is efficiently settled and separated.

  The sludge settled on the bottom surface of the tank body 1 is scraped up by the rake 6 into the pit 6 and discharged from the mud discharge pipe 7.

  In this embodiment, it is possible to prevent the aggregated floc from being broken due to a locally high flow velocity in the annular water channel C or the center well 2. Further, by reducing the difference in height between the height of the upper end 2t of the center well 2 and the water level in the center well (substantially equal to the water level WL), the aggregated floc is destroyed by the impact of the water to be treated. Therefore, sludge can be separated efficiently.

  In the above embodiment, the second trough 15 has an annular shape in plan view, but may be a polygonal annular shape. FIG. 3 shows a settling tank 1 in which the trough 15 has an octagonal ring shape. Instead of the octagon, a hexagon or the like may be used. In order to make the distance from the center well 2 as uniform as possible, and when the upward flow in the tank body 1 forms a swirling flow, a hexagon or more polygons are used so as not to hinder the swirling. In particular, a regular polygon is preferable. In addition, a polygonal trough can be manufactured by connecting a straight short trough (a trough having a length of one side of a polygon).

  In the above-described embodiment, the first and second troughs 13 and 15 are provided as troughs, and the trough arrangement is double-circular in plan view. These troughs may be provided to provide a triple or more multi-circular trough arrangement.

For double troughs,
Distance (radius) R1 from the tank body axis of the inner peripheral wall surface of the first trough 13;
Width (width in the tank body radial direction) d2 of the second trough 15, distance (radius) R2 from the tank body axis of the inner peripheral wall surface,
Radius r of center well 2,
Then, it is preferable to design so that (R1-d2-R2) and (R2-r) are approximately the same (for example, the ratio is approximately 0.8 to 1.2).

On the other hand, in the case of the Mie trough,
Distance (radius) R1 from the tank body axis of the inner peripheral wall surface of the first trough 13;
Width (width in the tank body radial direction) d2 of the second trough 15, distance (radius) R2 from the tank body axis of the inner peripheral wall surface,
The width of the third trough (width in the tank body radial direction) d3, the distance (radius) R3 (R2> R3) from the tank body axis of the inner peripheral wall surface,
Radius r of center well 2,
Then, it is possible to design so that (R1-d2-R2), (R2-d3-R3), and (R3-r) are approximately the same (for example, the ratio of each is approximately 0.8 to 1.2). preferable.

  In the above embodiment, the upper end portion of the center well 2 rises above the bottom surface 3a of the center well upper 3, but the upper end of the center well 2 may be flush with the bottom surface 3a. If it does in this way, the to-be-processed water swirling within the annular water channel C will flow into the center well 2 while maintaining the swirling flow, and will flow out into the tank body 1 while swirling from the lower end of the center well 2. And in the tank body 1, water rises while turning.

  In the above embodiment, the plate 4 is horizontal, but at least the vicinity of the center may be an inclined surface of less than 15 ° in the radial direction. However, at least the outer peripheral portion is preferably horizontal.

  In the above embodiment, the introduction pipe 8 is provided as the introduction member, but a bowl-shaped water channel may be provided as the introduction member.

  In the above embodiment, the center well 2 has the same diameter from the upper end to the lower end, but the lower part may have a large diameter. In this case, a tapered shape having a larger diameter at the lower end may be used.

1 tank body 2 center well 2t upper end 3 center well upper 3a bottom surface 3b peripheral wall 4 plate 6 pit 8 introduction pipe 10 rake shaft 13, 15 trough

Claims (2)

In the settling tank in which the water to be treated supplied from the center well at the center of the tank body to the lower part of the tank body rises in the tank body and flows out as clear water from the trough at the upper part of the tank body,
As the trough, a settling tank comprising a first trough along the inner peripheral wall of the tank body, and a second trough disposed between the first trough and the center well,
The second trough has an annular shape that circulates around the center well, and the second trough is provided with V notches at the inner peripheral upper end and the outer peripheral upper end,
A connecting water channel connecting the first trough and the second trough is provided in a radial direction;
Between the inner peripheral wall of the tank body and the center well, it does not comprise a portion extending in the radial direction except for the connecting water channel,
There are provided swirl introducing means for introducing the water to be treated into the center well in a swirling direction, and a plate for changing the flow direction of the water against the lower end of the center well. A settling tank characterized in that the upward flow of the water forms a swirling flow.   The sedimentation tank according to claim 1, wherein the shape of the inner peripheral wall of the tank body in a plan view is a circle or a regular polygon.

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