Apparatus for clarifying a sludge-containing effluent

Abstract

Apparatus for clarifying a sludge-containing effluent, comprising a clarification basin (2), at least one arm (7) able to move over the upper surface of the liquid in the basin; at least one trough (8) supported by the arm so that it can be immersed over part of its height in the liquid of the basin, suction tubes (T1, T2) held relative to the trough, each tube comprising at the top a vertically adjustable sleeve (B1, B2) opening into the trough, and a means of removing sludge from the trough; the sleeve (B1, B2) of at least one suction tube (T1, T2) is free to slide vertically relative to the mobile arm (7) supporting the trough, and to the tube (T1, T2) and a reserve of buoyancy necessary and sufficient for keeping the overspill end (E1, E2) of the sleeve in the trough (8) continuously out of the water is installed on the sleeve (B1, B2) so that the overspill level of the sleeve adjusts automatically in relation to the level (16) of liquid and sludge in the trough.

Claims

1. An apparatus for clarifying a sludge-containing effluent, comprising: a clarification basin for clarification by settling of sludge that is deposited on the bottom of the basin while clarified water is evacuated at the upper level of the basin; at least one arm able to move above the upper level of the liquid in the basin to sweep all the surface of the liquid; at least one trough supported by the arm, so that it is immersed over part of its height in the liquid in the basin; suction tubes held relative to the trough, extending downwardly toward the bottom of the basin, each suction tube including at the top a vertically adjustable sleeve opening into the trough at a level lower than the level of the liquid in the basin, the downwardly extending tubes enabling delivery into the trough of liquid and sludge coming from the bottom of the basin, and means for evacuation of sludge from the trough, wherein the sleeve of at least one suction tube is free to slide vertically relative to the mobile arm supporting the trough and to the tube and in that the sleeve has a reserve of buoyancy necessary and sufficient for keeping the overspill end of the sleeve in the trough continuously out of the water so that the overspill level of the sleeve adapts automatically relative to the level of the liquid and sludge in the trough.

2. The apparatus as claimed in claim 1, wherein each suction tube is equipped with a sleeve free to slide vertically relative to the mobile arm and to the tube and in that each sleeve has a reserve of buoyancy necessary and sufficient for keeping the overspill end of the sleeve in the trough continuously out of the water.

3. The apparatus as claimed in claim 1, wherein each sleeve is made from a material the density of which is higher than that of the liquid in the trough and that to provide the reserve of buoyancy the sleeve includes a floating device that is immersed in the liquid in the trough and that holds the upper edge of the sleeve at a constant distance above the liquid level in the trough.

4. The apparatus as claimed in claim 3, wherein the sleeves and the suction tubes are made of polyvinyl chloride.

5. The apparatus as claimed in claim 3, wherein the floating device consists of a float that surrounds the corresponding sleeve.

6. The apparatus as claimed in claim 5, wherein the float has the shape of a ring or a torus.

7. The apparatus as claimed in claim 5, wherein each float is made of expanded polystyrene.

8. The apparatus as claimed in claim 3, wherein the floating device is adjustably mounted on the sleeve so that its position is adjustable in the heightwise direction.

9. The apparatus as claimed in claim 3, wherein the various floating devices equipping the sleeves of the same clarifier differ in terms of size and/or the density of the materials so that the positions of the overspill ends of each of the sleeves can vary from one tube to another and thus enable individual adjustment of the aspiration capacity of each suction tube.

10. The apparatus as claimed in claim 1, further comprising a vertical guide device for the movement of each sleeve free to slide vertically relative to the mobile support arm.

11. The apparatus as claimed in claim 10, wherein each sleeve is made from a material the apparent density of which is less than that of the liquid in the trough and the basin and is equipped with an adjustable ballast weighing on the guide device for the adjustment of the position of the upper overspill end of the sleeve in the trough.

12. The apparatus as claimed in claim 10, wherein the guide device includes a flat part having a shape similar to the shape of a ladder, the lower portion of which is forceps-shaped with two branches that engage in diametrically opposite holes at the upper end of the sleeve, the vertical plane of the part being oriented at a right angle to the radial direction of the arm and the trough, guide plates fixed to the arm including a slot through which the part passes vertically and which guides it.

13. The apparatus as claimed in claim 12, wherein the slot is equipped with a shoe made from a material having a low coefficient of friction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Apart from the features explained above, the invention consists in a certain number of other features described more explicitly hereinafter with reference to the appended drawings, which are in no way limiting on the invention. In these drawings:

(2) FIG. 1 is a partial diagrammatic vertical section of clarification apparatus in accordance with the invention, the mobile arm not being represented.

(3) FIG. 2 is a perspective view, with parts removed, of a trough with four sleeves below a mobile arm of clarification apparatus in accordance with the invention.

(4) FIG. 3 shows in elevation a sleeve provided with its float and vertical guide means.

(5) FIG. 4 is an exploded view in elevation of the elements from FIG. 3, and

(6) FIG. 5 is a diagrammatic perspective view from above of part of the trough and the sleeves of clarification apparatus in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) Referring to FIG. 1 of the drawings, there can be seen apparatus A for clarifying effluent 1 which in the embodiment represented arrives via a pipe in the lower part of the apparatus A, which includes a clarification basin 2. The basin 2 is generally circular and its diameter is at least 20 m for the kind of clarifier to which the invention more particularly relates. Only half of the basin 2 is represented in FIG. 1, the other half being symmetrical with respect to the vertical geometrical axis Y-Y of the circular basin.

(8) Sludge is deposited on the bottom of the basin to form a layer 3 and clarified water 4 is evacuated at the upper level of the apparatus over an overspill weir 5 and is collected in a gully 6 to be recovered by means that are not represented. In accordance with the FIG. 1 embodiment, the bottom 2p of the basin 2 has a more or less pronounced slope or is horizontal.

(9) The apparatus A includes at least one mobile arm 7 that can be seen in FIG. 2 but is not represented in FIG. 1. The arm 7 extends radially from the central area of the basin 2 where it is supported and driven in rotation by a central or peripheral motor (not represented). The radially outermost end of the arm 7 is supported by a support leg, not represented, provided in its lower part with a rolling member resting on a rolling track 2b integral with the cylindrical wall of the basin 2, optionally projecting radially outward. The arm 7 constitutes a turning bridge, represented diagrammatically, which enables sweeping of all the surface of the liquid in the basin 2 by a 360° rotation. The arm 7 is designed to allow an operator to move safely on the arm to carry out the necessary adjustments of the apparatus.

(10) Although clarification basins are generally circular, the invention applies equally to rectangular basins surmounted by an arm mobile in translation along one dimension of the basin, notably the length.

(11) At least one trough 8 is supported by the arm 7, for example with the aid of tie-rods that are not represented, so that it is immersed over a portion of its height in the liquid in the basin 2. The trough 8 has a substantially rectangular cross section open at the top and closed on all its other sides. In FIG. 2, a longitudinal wall of the trough is opened up to expose the interior of the trough. The upper edge 8b of the wall of the trough is above the upper level 4a of the clarified water, that is to say above the upper level of the liquid in the basin 2.

(12) The bottom 8c of the trough is substantially horizontal from the radially outermost end to a well 8d provided at the radially innermost end of the trough 8. A vertical branch 9a of a siphon 9 dips into the well 8d and the other vertical branch 9b of the siphon constitutes a mobile hydraulic seal. A vertical pipe 10 is connected to the hydraulic seal for the evacuation of sludge taken up from the bottom of the well 8d via the siphon 9. The maximum motive head because of the difference in liquid level for the evacuation of sludge in the pipe 10 is equal to the head difference between the upper level 4a of the clarified water in the basin and the outlet level of the suction tubes above the level in the trough.

(13) The pipe 10 is connected to a sludge take-up ditch 11. The ditch 11 is divided into two compartments 12, 13 by a partition 12a forming an overspill weir. The sludge arrives in the compartment 12 and the pump 14 is in the other compartment 13 into which the sludge overspills. The pump 14 constitutes means for evacuation of the sludge to an aeration basin that is not represented. The flow rate of the pump 14 is regulated. The feed pipe 1 for effluent to be treated is connected to a cylindrical vertical part 1a around the pipe 10.

(14) Suction tubes T1, T2 are secured to the underside of the trough 8 and extend downwardly toward the bottom of the basin 2 so that their lower end enters the bed 3 of sludge. The tubes T1, T2 are at different radial distances from the geometrical axis Y-Y and there is a sufficient number of them to ensure satisfactory evacuation of the deposited sludge. In accordance with the embodiment represented in FIG. 1, for simplicity, only two tubes T1, T2 have been represented, but the number of tubes may be greater than this and as high as 20 or more. The tubes T1, T2 may be fixed under the bottom 8c of the trough, which includes orifices in line with the tubes T1, T2.

(15) Each tube T1, T2 includes in its upper part a sleeve B1, B2 that opens into the trough 8 at a level 15 lower than the level 4a of the liquid in the basin. The difference between the liquid level 4a in the clarifier and the level 15 at which sludge overspills into the trough at the outlet from the sleeves provides the motive force for suction and extraction of the sludge from the bottom of the clarifier 2. The sleeves B1, B2 are of cylindrical tubular shape and are engaged inside the tubes T1, T2.

(16) In accordance with the invention, for at least one suction tube, and preferably for each suction tube, the sleeve B1, B2 is free to slide vertically relative to the associated tube and the mobile arm 7. The vertical sliding movement between the sleeve B1, B2 and the associated tube T1, T2 is almost completely sealed by means of appropriate seals.

(17) Each sleeve B1, B2 has a reserve of buoyancy necessary and sufficient to maintain the upper, overspill end E1, E2 of the sleeve continuously above the water in the trough. The overspill level of the sleeve is automatically adjusted relative to the level 16 of the liquid and the sludge in the trough 8.

(18) To provide this reserve of buoyancy, the sleeve B1, B2 is advantageously provided with a floating device consisting of a float F1, F2 that is immersed in the liquid in the trough 8 and maintains the upper edge of the sleeve at a constant distance above the level 16 of liquid in the trough. As can be seen in FIGS. 2 to 4, the floats can have a ring or torus shape to surround the corresponding sleeve B1, B2.

(19) Each float is mounted on the sleeve so as to be adjustable in the vertical direction, in particular by screwing it relative to said sleeve, by means of a helicoidal open clamping ring J fastened to the sleeve (FIG. 4) so that its position is easily adjustable in the heightwise direction.

(20) The floats F1, F2 may be made from expanded polystyrene or some other material of lower density than the liquid in the trough 8. With such a float, the corresponding sleeve may be made from a material the density of which is higher than that of the liquid in the trough. The sleeves B1, B2 and the tubes T1, T2 are advantageously made of polyvinyl chloride (PVC).

(21) Alternatively, each sleeve may be produced with an apparent density lower than that of the liquid in the trough and the basin, in which case the reserve of buoyancy is inherent to the sleeve itself. For the adjustment of the position of the upper overspill end of the sleeve in the trough, there is then provided an adjustable ballast acting on the sleeve to weigh on the mobile guidance system, notably a guide rod. In accordance with this variant the inherent density of the material of the sleeve may be either less than that of the liquid or greater than the latter, in which case closed voids are provided in the material to reduce the apparent density.

(22) The various floating devices, or floats F1, F2, equipping the suction tubes T1, T2 of the same clarifier may differ in terms of size and/or the density of the material used so that the overspill ends E1, E2 of each of the sleeves can vary from one tube to another and therefore allow individual adjustment of the aspiration capacity of each suction tube.

(23) As shown in FIGS. 2 to 4, each sleeve such as B1 is equipped with a vertical guide device 17 adapted to retain the sleeve B1 along its vertical geometrical axis of movement within the suction tube T1 fixed relative to the trough 8 and the arm 7.

(24) In accordance with the embodiment of FIGS. 2 to 4, the guide device 17 includes a flat part 18 similar to a ladder, the lower portion 19 of which is forceps-shaped with two branches that engage in diametrically opposite holes at the top end of the sleeve B1. The upper end 20 of the part 18 is of closed semicircular shape to constitute a handle facilitating grasping of the part 18 for vertical movement. The vertical plane of the part 18 is oriented at a right angle relative to the radial direction of the arm 7 and the trough 8. Guide plates 21 (FIGS. 2 and 5) fixed under the arms 7 include a slot 22 orthogonal to the radial direction. The part 18 passes vertically through this slot 22, which guides it. The slot 22 is advantageously equipped with a shoe 23 made from a material with a low coefficient of friction, notably polytetrafluoroethylene (PTFE), making it possible to limit the risk of abrasion and to render the device long-lasting. The shoes 23 may be made from any material identified for its properties of low friction and mechanical strength.

(25) This being the case, the adjustment and the operation of clarifying apparatus in accordance with the invention are as follows.

(26) For any flow rate of effluent to be treated arriving via the pipe 1 and to which there corresponds a level 16 in the trough 8 and a bed 3 of sludge, the operator adjusts the position of the sleeves B1, B2 by adjusting the position of the floats F1, F2. For each sleeve, this adjustment is effected so that the upper overspill end E1, E2 of the sleeve is at an appropriate level, lower than the level 4a, of course, to ensure a satisfactory flow rate of evacuation of the sludge via the corresponding tube T1, T2.

(27) When this adjustment has been carried out, a variation in the height of the level 16 leads to a corresponding variation in the height of the upper ends E1, E2, which therefore remain at a constant distance above the level 16, so that there is no other adjustment to be carried out when the level in the trough 8 varies.

(28) In accordance with the invention, the overspill level of the suction tubes and the sleeves therefore depends on the level of sludge in the trough 8 and consequently becomes intrinsically linked to the flow rate of evacuation of sludge from the trough. As a result of this the flow rate of evacuation of sludge from the trough 8, already controlled and/or being easily controllable in real time according to the real requirements of the station, enables optimum control in real time of the flow rate of extraction of sludge from the clarifier with no automation additional to that already existing and without human intervention.

(29) Moreover, the present invention advantageously eliminates all risk of totally immersing the suction tubes T1, T2 and the sleeves B1, B2 the overspill end of which remains above the level 16 of liquid in the trough 8 by virtue of their buoyancy.

(30) In contrast to this, in a conventional clarifier not using the invention, the sleeves would be fixed relative to the arm 7. When an adjustment of the position of the upper end has been carried out, this position relative to the arm 7 and to the bottom of the trough 8 remains fixed. If the level 16 of liquid in the trough varies, the distance between the overspill end of the sleeve and the liquid level in the trough varies, whereas in accordance with the invention this distance remains constant and enables self-regulation of the level 16 of liquid in the trough 8. In fact, in accordance with the invention, if the level 16 falls, the overspill end of the sleeve also falls, which increases the motive hydraulic head and increases the flow rate of sludge aspirated via the suction tube T1, T2 to cause the liquid level in the trough 8 to rise. Conversely, if the level in the trough 8 rises, the overspill end of the sleeves also rises, which reduces the motive hydraulic force.

(31) The means proposed by the invention are: simple, rugged, of relatively low cost to purchase, very easy to fit to an existing clarifier.

(32) They do not necessitate any modification of civil engineering structures and/or plant that would impact on the warranties of the structures. They do not lead to additional maintenance costs. They require little if any modification of existing automatic control and regulation systems in treatment stations.