JP6601475B2 - 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 mixture by passing the sludge mixture 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. Yes (Patent Document 1).

  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 2, a cylindrical inflow portion having a diameter larger than that of the center well is formed on 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 in the inflow part, and it is introduced into the center well as it is to form a flow that descends while swirling in the center well, thereby preventing the occurrence of drift when introducing the water to be treated. In addition, it is disclosed that the destruction of the aggregate floc is suppressed.

  However, there is a concern that the flow velocity introduced into the center well tends to be non-uniform between the vicinity of the introduction portion of the water to be treated and the distant place in the inflow portion. When the flow velocity is locally high, the aggregated flocs are likely to be broken locally.

JP 2005-66533 A JP 2017-87090 A

  An object of this invention is to provide the sedimentation tank which can introduce in-process water into a center well uniformly.

  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 becomes clear water from the overflow part at the upper part of the tank body. In the sedimentation tank that flows out, a center well upper member that forms an annular water channel surrounding the upper outer periphery of the center well is provided, and the center well upper member has a bottom surface that extends in the expanding direction from the center well. A peripheral wall standing up from the outer peripheral edge of the bottom surface, and water to be treated is introduced into the annular water channel by the introduction member in a circumferential direction along the peripheral wall, overflowing the upper end of the center well and It flows into the center well.

  In one aspect of the present invention, the upper end of the center well has a uniform height over the entire circumference.

  In one aspect of the present invention, a difference between the level of the overflow portion and the level of the upper end of the center well is 0 to 20 cm.

  In one aspect of the present invention, the bottom surface of the annular water channel is horizontal and is positioned lower than the upper end of the center well.

  In one aspect of the present invention, the bottom surface of the annular water channel is an inclined surface in which at least the center well side becomes lower toward the outer periphery.

  In one aspect of the present invention, the angle of the inclined surface with respect to the horizontal plane is 5 to 60 °.

  In one aspect of the present invention, a plate is provided for changing the direction of water flow against the lower end of the center well.

  In the settling tank of the present invention, the water to be treated that flows into the annular channel in the circulation direction overflows the upper end of the center well and uniformly flows into the center well while forming a swirling flow in the annular channel. For this reason, it is possible to prevent the aggregated floc from being broken due to a locally increased flow velocity in the annular water channel or the center well. In addition, by preventing the difference in height between the height of the upper end of the center well and the water level in the center well as much as possible, the destruction of the aggregated floc due to the impact of falling on the water surface in the center well of the overflowed treated water is prevented. Sludge can be separated efficiently.

It is a longitudinal cross-sectional view of the sedimentation tank which concerns on embodiment. It is a top view of the center well vicinity of the sedimentation tank of FIG. It is a longitudinal cross-sectional view of the center well vicinity of the sedimentation tank which concerns on another embodiment. It is a longitudinal cross-sectional view of the center well vicinity of the sedimentation tank which concerns on another embodiment. It is a top view of the center well vicinity 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 tank body 1 is circular, and the 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 an overflow weir 13 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 20 cm, more preferably 0 to 10 cm, and 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, 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.

  An overflow weir 13 as an overflow portion is provided along the upper part of the inner peripheral wall surface of the tank body 1. The level of the upper end of the overflow weir 13 is the water level WL in the tank body 1.

  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 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, overflows the overflow weir 13, and is discharged from the clarified water outlet 14.

  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-described embodiment, the bottom surface 3a of the center well upper 3 is horizontal, but in the second embodiment shown in FIG. 3, the bottom surface 3a is an inclined surface having a downward slope toward the outer periphery. In the third embodiment shown in FIG. 4, the inner peripheral side of the bottom surface 3a, that is, the center well 2 side is an inclined surface having a downward slope toward the outer periphery. The inclination angle θ of the inclined surface with respect to the horizontal plane is preferably about 5 to 60 °.

  3 and 4, the bottom surface 3 a is continuous with the upper end 2 t of the center well 2. However, it may be slightly lower than the upper end of the center well 2.

  Other configurations of the second and third embodiments are the same as those of the first embodiment, and the same reference numerals denote the same parts. Also in these embodiments, the same effects as in the first embodiment can be obtained.

  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 said embodiment, although the tank 1 is made into the cylindrical shape, a square shape (square or more polygonal shape) may be sufficient. Moreover, the bottom face of the tank body 1 may be 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 FIGS. 1 and 2, the introduction pipe 8 is bent in the middle so that the end portion is along the peripheral wall 3 b of the center well upper 3, and the end portion is installed so as to be located below the water surface of the annular water channel C. However, in order to prevent the water flow inhibition in the introduction pipe 8 and the water flow inhibition of the swirl flow in the annular water channel C, the water flow port 8 flows along the peripheral wall of the center well upper 3 as shown in FIG. It is preferable to provide '.

  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 overflow weir

Claims (6)

The treated water supplied to the lower part of the tank body from the center well with the upper end opened at the center of the tank body rises in the tank body and flows out as clear water from the overflow part at the upper part of the tank body. In the settling tank
A center well upper member forming an annular water channel surrounding the upper outer periphery of the center well is provided;
The center well upper member has a bottom surface extending in the expanding direction from the center well, and a peripheral wall rising from an outer peripheral edge of the bottom surface,
The water to be treated is introduced into the annular water channel by the introduction pipe in the circumferential direction along the peripheral wall, forms a swirling flow in the annular water channel, overflows the upper end of the center well, and flows into the center well. A settling tank,
The introduction pipe is arranged so that the water to be treated is directly supplied to the annular water channel in a downward flow from above,
The diameter of the annular channel is 1.2 to 2.0 times the outer diameter of the upper end of the center well,
The height difference between the bottom surface of the annular water channel and the upper end of the center well is 5 to 50 cm,
A sedimentation tank, wherein a difference in height between the upper edge of the center well and the level of the overflow portion is 0 to 20 cm.   2. The sedimentation tank according to claim 1, wherein the upper end of the center well has a uniform height over the entire circumference. The sedimentation tank according to claim 1 or 2 , wherein the bottom surface of the annular water channel is horizontal and is positioned lower than the upper end of the center well. In the sedimentation tank in which the water to be treated supplied from the center well in the center of the tank body to the lower part of the tank body rises in the tank body and flows out as clarified water from the overflow part at the upper part of the tank body,
A center well upper member forming an annular water channel surrounding the upper outer periphery of the center well is provided;
The center well upper member has a bottom surface extending in the expanding direction from the center well, and a peripheral wall rising from an outer peripheral edge of the bottom surface,
A settling tank in which the water to be treated is introduced into the annular water channel by the introduction member in the circumferential direction along the peripheral wall, overflows the upper end of the center well and flows into the center well,
The sedimentation tank, wherein the bottom surface of the annular water channel is an inclined surface having at least the center well side becoming lower toward the outer periphery. In Claim 4 , the angle with respect to the horizontal surface of the said inclined surface is 5-60 degrees, The sedimentation tank characterized by the above-mentioned. The sedimentation tank according to any one of claims 1 to 5 , wherein a plate for changing a flow direction of water is provided opposite to a lower end of the center well.

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