GB2257376A - Scum collection device - Google Patents

Abstract

A scum collection device for a liquids/solids settlement tank, having a weir edge outlet and a scum board (15) disposed inwardly from and parallel to the weir edge, comprises a catchment net (17) suspended from a travelling bridge (11) above the tank and having an open end dipping into the liquid adjacent the inner side of the scum board (15) and facing the direction of travel of the bridge. A paddle wheel (22) rotates ahead of the open end of the net (17) to direct floating matter into the net. A submerged plate (26) ensures that solids are driven into the net and not beneath it, and a float (20) retains a rear pan of the net adjacent the surface. The device may include a scraper engaging the scum board (15). Bridge (11) may rotate round a circular tank, and a collection device could be provided at each end of a diametral bridge. Or the tank may be rectangular and the bridge moves linearly. Net (17) is mounted on a light frame (18a - 18e) which holds the net mouth open and by which the net is lifted from the main support (18) when full, for emptying or disposal. <IMAGE>

Description

A SCUM COLLECTION DEVICE THIS INVENTION concerns liquids/solids settlement tanks usually, but not necessarily, circular in plan and having a weir edge outlet, and a rotating or traversing bridge above the tank, and usually, but not necessarily a scum board disposed inwardly from and extending parallel to the weir edge.

In apparatus of this kind, there exists a problem in that substantial quantities of scum and other flotsam accumulate against the inner face of the scum board or weir and build up to such an extent that some material inevitably passes beneath the scum board and is discharged over the weir. In addition, the gradual build up of floating matter inside the scum board presents a collection problem for the operators.

An object of the present invention is to provide a collection device which is capable of collecting scum and other flotsam continuously during operation of the tank thus preventing a build up and avoiding contamination the final effluent liquid.

The invention is particularly, though not exclusively, to be applied to primary and secondary settlement tanks in effluent treatment plant in which a rotating or traversing bridge extends across the tank.

According to the present invention, in a liquids/solids settlement tank having a weir edge outlet a travelling bridge above the tank, and usually, but not necessarily a scum board disposed inwardly from and extending parallel to the weir edge, there is provided a scum collection device comprising a catchment net suspended from the bridge and having an open end dipping into the liquid immediately adjacent the inner side of the weir edge or scum board and facing the direction of travel of the bridge, means to retain the open end in an open condition, and a driven paddle ahead of the open end of the net and operable to transfer scum or flotsam into the net for disposal.

Preferably, the device also includes a submerged plate located and adapted to prevent matter being driven beneath the net by the paddle.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: Fig. 1 is a plan view of a circular settlement tank incorporating a scum collection device in accordance with the invention; Fig. 2 is an enlarged view taken in the direction or arrow A in Fig. 1; and Fig. 3 is a perspective view taken generally in the direction of arrow B in Fig. 1.

A typical liquids/solids settlement tank 10 employed as a primary settlement tank in a sewage treatment plant would be 15 metres in diameter and perhaps 4 metres in depth. A radial bridge 11 is rotatably mounted about the centre of the tank and supported on rollers 12 outside its periphery. Paddle blades or other submerged devices are usually suspended from the bridge 11 to assist the settlement process. Solids are collected from the bottom of the tank 10 whilst the liquid outlet is over an annular weir edge 13 into a collection channel 14. A scum board 15 is placed inwardly from, and parallel to, the weir 13, and is typically only a few centimetres in depth with its lower two thirds submerged beneath the surface of the liquid thus to trap scum and other flotsam and prevent it from escaping over the weir edge 13.

In accordance with the invention, to prevent a build up of scum against the board 15 there is provided a device generally indicated at 16 to collect the floating matter.

Referring to Figs. 2 & 3, the device 16 can be seen as consisting of a net 17 suspended by a rigid frame 18 from the bridge 11 closely adjacent the inner surface of scum board 15. The net is supported on a light frame 18a a part 18b of which is preferably attached at 19 so as to be pivotable about a horizontal axis on the frame. A float 20 keeps the net on the surface of the liquid but partially dipping into same at the bottom end of frame 18a.

As can be seen from Fig. 3, the light frame 18a, 18b is removably suspended upon the rigid frame 18 by hooks 18c and pegs 18d. A lifting plate 18e is provided at the top of the light frame whereby it may be removed together with the net 17 from the rigid frame 18.

At the upstream or front end of the rigid frame 18 there may be provided a stainless steel plate (not shown) which, lightly loaded, scrapes against the inner surface of the scum board just ahead of the net.

Close to the bottom of the frame 18 and rotatably supported thereby is a paddle wheel 22 driven by a motor 23 mounted on the frame 18. The paddle wheel 22, which preferably has deflectable blades to avoid damage by any large solid objects, rotates in the direction of arrows 24 whilst the bridge and scum collection device travel in the direction of arrow 25. Since the peripheral speed of the paddle wheel 22 is selected to be between 5:1 and 25:1 in relation to the travelling speed of the bridge, scum or other flotsam collecting in the region of the scum board 15 is transferred rearwardly into the net 17.

A plate 26 fixed to frame 18 is submerged beneath the surface and disposed at an inclined disposition as can be seen in Fig.

2, ensuring that the solids are driven into the net 17 and not beneath the latter.

Preferably, the paddle wheel 22 extends across substantially the entire opening of net 17 which, by the light frame 18a, is held in a generally rectangular configuration.

Emptying and/or disposal of the net 17 is carried out by lifting the light frame 18a, 18b upwardly and rearwardly from the rigid frame 18. As the light frame is lifted the part 18b may pivot downwardly about its pivotal connections 19 so that the net will tend to close and can be dumped in a safe condition at the side of the tank or on the bridge 11.

The frequency of emptying and subsequent disposal of net 17 will be determined by the amount and condition of the solids present, but it is envisaged that a net will remain in operation for approximately one to two weeks before needing replacement. It is not intended that the net shall be reusable in view of the possibility of hazardous substances being collected therein. However, where predominantly harmless deposits such as fat is present, the contents may be emptied and the net re-used.

In cases of severe scum accumulation, and where the bridge extends diametrically right across the tank, a further net and paddle assembly may be provided at the other end of the bridge.

The simple construction of the assembly mounted on the frame 18 will enable the device to be installed easily and rapidly on existing tank bridges. The motor 23 need be of only 20 to 100 watts rating and driven by the existing electrical slip-ring supply on the bridge.

The configuration and operational mode of the paddle, and its driven speed, may be selected to suit the prevailing conditions for optimum transfer of solids into the net. Similarly, the mesh size of the net may be selected to suit the application.

Whilst the apparatus has been described in relation to a circular tank, it may be applied also to a rectangular or other shaped tank with a linearly traversing bridge.

Claims (14)

1. A scum collection device in a liquids/solids settlement tank having a weir edge outlet, a travelling bridge above the tank, and usually, but not necessarily a scum board disposed inwardly from and extending parallel to the weir edge, there is provided a scum collection device comprising a catchment net suspended from the bridge and having an open end dipping into the liquid immediately adjacent the inner side of the weir edge or scum board and facing the direction of travel of the bridge, means to retain the open end in an open condition, and a driven paddle ahead of the open end of the net and operable to transfer scum or flotsam into the net for disposal.

2. A scum collection device according to Claim 1, including a submerged plate located beneath the open end of the catchment net and adapted to prevent matter being driven beneath the paddle.

3. A scum collection device according to Claim 2, wherein the submerged plate is disposed at an inclined angle with its leading edge (in relation to the direction of travel of the bridge) lower than its trailing edge to ensure that solids are driven into the net and not beneath the latter.

4. A scum collection device according to any preceding claim, wherein the paddle is a rotary driven paddle wheel having deflectable blades and a peripheral speed greater than the speed of travel of the bridge.

5. A scum collection device according to Claim 4, wherein the peripheral speed of the driven paddle is selected to be between 5:1 and 25:1 in relation to the travelling speed of the bridge.

6. A scum collection device according to Claim 4 or Claim 5, wherein said paddle wheel extends across substantially the entire open end of the catchment net, the latter being retained in a generally rectangular configuration.

7. A scum collection device according to any preceding claim, wherein said means to retain the open end of the catchment net in an open condition comprises a frame upon which the net is mounted, said frame being suspended from the travelling bridge.

8. A scum collection device according to Claim 7, wherein the frame supporting the catchment net comprises a rigid frame suspended from the travelling bridge and to which is attached a further frame supporting the net so as to be pivotable about a horizontal axis on the rigid frame, and removable therefrom to empty or dispose of the net when filled.

9. A scum collection device according to any preceding claim, including a float associated with a closed end of said net so as to retain a part of the latter near the surface of the liquid.

10. A scum collection device according to any preceding claim, when mounted on a radial travelling bridge above a liquids/solids settlement tank which is circular in plan.

11. A scum collection device according to Claim 9, wherein said travelling bridge extending diametrically across the tank and wherein two such scum collection devices are provided one at each of the two opposed ends of the travelling bridge.

12. A scum collection device according to Claim 1, when mounted on a liquids/solids settlement tank which is rectangular in plan.

13. A scum collection device according to any preceding claim, including a scraping plate to be lightly loaded against the inner surface of the scum board.

14. A scum collection device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.