GB2306123A

GB2306123A - Scum decanting device

Info

Publication number: GB2306123A
Application number: GB9521081A
Authority: GB
Inventors: Clifford Barton
Original assignee: QPS PLASTICS Ltd
Current assignee: QPS PLASTICS Ltd
Priority date: 1995-10-14
Filing date: 1995-10-14
Publication date: 1997-04-30
Also published as: GB9521081D0

Abstract

A scum decanting device for removing floating scum from a liquid surface comprising a scum discharge means 8, and a relatively movable scum blade (Fig. 14; 19x) with an associated flush bucket (Fig. 14; 15x), where the scum blade is adapted such that it pushes the scum up a scum ramp (Fig. 12; 9x) into said discharge means 8 and the trailing flush bucket flushes the discharge means. A second embodiment of this device is where the scum is collected in a pivotal scum ramp 1 and is pushed into a discharge means 8 by a scum flap (Fig.7; 20) thereafter the a skid 15 associated with said scum flap contacts roller 14 and causes the ramp to pivot whereby the remaining liquid washes the residual scum from the ramp and flushes the discharge means 8.

Description

SCUM DECANTING APPARATUS The invention relates to an apparatus for removing scum and/or floating solids from the surface of a liquid, particularly but not exclusively, a liquid contained in a settlement tank such as a sewage or water purification settlement tank.

It is well known that the settlement of contaminated or unclean liquids in containers or tanks results in the creation of a floating layer of scum. In addition, other floating solids may rise to the surface of such contaminated liquids. It is often desirable to arrange for the removal of scum and/or floating solids and therefore settlement tanks are typically provided with scum removal or decanting devices.

There are currently several types of scum decanting devices on the market, for example, conventional scum decanting units comprising fixed ramps arranged to collect scum from the upper surface of a settled body of liquid are available.

However, the disadvantage of these devices is that they are not provided with a flushing means and so the fixed ramp unit can become undesirably and detrimentally soiled.

An alternative scum decanting device, which is a development of the above decanting device, comprises a fixed ramp with flushing attachments. However, this suffers from the disadvantage of soiling as described above if the flushing device fails to work or if the degree of flushing is inadequate.

A yet further scum decanting device comprises the provision of a valve which is located just below the surface of a liquid, which valve floods when opened by a skid and pivot arrangement, which skid is typically attached to the underside of a half bridge. In this agreement, floating scum enters the valve which remains open for a preset period in order to allow "clean" or carriage water to flush out the valve. The disadvantage of this arrangement is that there is no positive guiding of scum into the valve. Moreover, an excessive amount of carriage water passes through the valve during its operation, which carriage water must eventually be returned to the tank thus creating an unwanted cycling procedure.

In addition, there is a danger with this device that the valve may be blocked open by solids, dead birds etc and thus allow carriage water to continuously pass through the valve. If this happens, for example, over a weekend an unacceptable amount of carriage water can be lost.

An alternative scum decanting device comprises a tube provided with an aperture or slot which tube is adapted to rotate when activated in order to allow scum and carriage water to flow through the aperture or slot to a drain located at a distal end of the tube. The disadvantage of this device is that there is no positive guidance of scum into the tube. In addition, a further disadvantage comprises the significant loss of carriage water that passes through the tube when it is operational.

It can therefore be seen that there is a need to provide a scum decanting device which is adapted so that scum is positively guided into the device and which is arranged to be self cleaning or having a flushing facility and which further, in operation, discharges an acceptable amount of carriage water.

It is therefore an object of the invention to provide a scum decanting device which incorporates the above features.

It is yet a further object of the invention to provide a scum decanting device which is easy to install, maintain and, if required, remove.

It is yet a further object of the invention to provide a scum decanting device made of a number of detachable components so that various components can be removed for the purpose of maintenance, repair or cleaning.

In its broadest aspect the invention concerns the provision of a combined scum ramp and flushing box which is adapted to be pivoted.

According to a first aspect of the invention there is therefore provided a scum decanting device comprising a pivotal scum ramp and associated discharge means which scum ramp in a first pivoted position is arranged so as to allow scum from the surface of a liquid to be collected and in a second pivoted position is arranged so as to tip at least a controlled amount of carriage water into said discharge means.

In a preferred embodiment of the invention said scum decanting device is used with a skimming arm, ideally attached to a half bridge, which skimming arm is arranged to push scum into the scum ramp.

Preferably the lower edge of said skimming arm is adapted to be pivoted so as to push scum up the scum ramp and in turn into the associated discharge means.

It will be understood by those skilled in the art that in said first position the scum ramp is arranged so as to collect scum from the surface of a liquid. Ideally, collection is undertaken in association with said skimming arm. When in said second position the scum ramp will be tilted so that a controlled amount of carriage water contained in the ramp is poured into the discharge means. Thus in this way carriage water is retained in the scum ramp and is decanted into the discharge means so as to flush same.

It will also be apparent to those skilled in the art that the degree to which carriage water is retained can be determined by the configuration of the scum ramp. Thus, for example, a scum ramp provided with side walls of variable height will pour an amount of carriage water out of the ramp according to the height of said walls.

In a preferred embodiment of the invention there is therefore provided a scum ramp provided with walls on three of its sides for the purpose of retaining scum and carriage water scooped therein and preferably at least said side wall opposite the opening or entrance of the ramp is adapted to be adjustable so that the height of same can be varied.

Preferably said scum ramp is pivoted with respect to said discharge means by way of an articulated member which articulated member, at a first end, is attached to said scum ramp and at a second furthermost end is provided with contact means, ideally in the form of a roller or the like, which contact means is arranged so that, in use, it makes contact with a skid member, ideally, located on the underside of a half bridge.

More preferably still, said skid member is fashioned so as to ensure that contact with said contact means results in predetermined articulation of said articulated member thus resulting in controlled movement of said scum ramp from said first pivoted position to said second pivoted position.

More preferably said skid member comprises a first upwardly angled section, a second substantially horizontally section and a third upwardly angled section.

More preferably said skid member is in the form of a shallow U-shaped member. More preferably still said scum ramp is attached to an upper outermost rim of a discharge means, which discharge means, ideally, comprises a first upper funnel shaped member and a second lower conduit which is arranged to carry scum from a container or settlement tank to a preselected location.

Preferably there is provided means for moving the skid member, with respect to said scum decanting device.

Where the scum decanting device is used in combination with the skimming arm, the skimming arm is arranged foremost of the direction of travel of the relative movement between the scum decanting device and the skid member. In this way, scum is firstly pushed up the scum ramp and into the discharge means, via the skimming arm, before pivoting of the scum ramp takes place.

It will be understood that the scum decanting device of the invention can be used solely with the skimming arm, in which case surface scum will simply be removed from a settlement tank as the skimming arm travels relatively over the scum ramp, or alternatively, the scum decanting device of the invention can be used solely with the skid member, in which case scum and carriage water retained in the scum ramp will be tipped together into the discharge means. However, it is preferred to use the scum decanting device of the invention in combination with both the skimming arm and the skid member. This combined use provides for the positive guidance of scum up the scum ramp and over same into the discharge means and then flushing of the discharge means by pivoting of the scum ramp following interaction between the skid and the articulated member.

Preferably said scum decanting device is fixedly attached to a preselected part of a container or settlement tank and said skid member and/or said skimming arm, attached to the undermost side of a half bridge, are arranged to move over the surface of the liquid in the container or tank, ideally in rotatory fashion.

Alternatively, said skid member and/or said skimming arm are fixedly attached to a preselected part of a container or settlement tank and said scum decanting device is adapted to move within said container or tank. Ideally the open side of the scum ramp travels foremost of the device and, also ideally, said scum ramp interacts firstly with said skimming arm and then with said skid member.

According to a yet further aspect of the invention there is provided a settlement tank comprising at least one scum decanting device in accordance with the invention and at least one skid member and/or at least one skimming arm in accordance with the invention which device and skid member and/or skimming arm are arranged for relative movement.

In a preferred aspect of the invention said skid member and said skimming arm are attached to the underside of a half bridge which is arranged so as to move over the surface of liquid contained in said tank. Ideally, said skimming arm is arranged foremost of said skid member with respect to the direction of travel over said surface.

Preferably said movement is rotatory.

In a yet a further preferred embodiment a plurality of said scum decanting devices are provided within said tank.

More preferably a plurality of skid members and/or skimming arms are provided and preferably a plurality of movable half bridges are provided.

The above problems with the prior art can also be overcome by a further aspect, which aspect, in its broadest sense concerns the provision of a scum/discharge means in conjunction with a relatively movable scum flap and associated flushing bucket.

According to a second aspect of the invention there is provided a scum decanting device for removing scum from a liquid surface, comprising a scum discharge means and a relatively movable scum flap and associated flush bucket whereby firstly the scum flap is adapted to push scum into said discharge means and secondly the flush bucket is adapted to flush said discharge means.

In a preferred embodiment the scum discharge means includes an integral or associated scum ramp which scum ramp receives scum. More preferably still there is a simple geometric relationship between the angle of said scum ramp and the angle of the flush bucket. Ideally the angles of inclination of the scum ramp and bucket side is the same or substantially the same.

In a preferred embodiment said discharge means includes an exit ramp.

In a preferred embodiment at least two adjacent scum discharge means are connected by pipework.

Preferably said scum flap and flush bucket are connected to a skimming arm and ideally said bucket is arranged to trail behind said flap as said arm travels forwardly.

Said trailing arrangement is effected by the provision of an elongate support means having said bucket attached to one end of same. A furthermost end of said support means is attached to a support structure. The elongate support means is of a sufficient length that said bucket can be arranged to trail.

This form of elongate support means may also be provided for said scum flap which can thus equally trail. The relative length of said elongate support means for said scum flap and said bucket may vary.

It will be understood by skilled persons that the scum flap pushes scum up to the ramp, whereas the flush bucket is adapted to drag scum into said discharge means.

Preferably, a skimming board ideally attached to said skimming arm guides scum to said discharge means. Ideally, the skimming board is angled with respect to the vessel side.

In a preferred embodiment said scum flap comprises a plurality of flaps, ideally a leading flap and a trailing flap. Ideally said flaps are made from En-thane material.

Ideally further still said leading flap is shorter than said trailing flap and said leading flap is adapted to hold a blade, ideally said blade is at right angles to said leading flap or is adapted so that said angle is adjustable. Said blade is ideally made form En-thane.

In a further preferred embodiment said plurality of flaps includes at least one sprung scum flap. Ideally the sprung scum flap points in the direction of travel.

As mentioned, in a preferred embodiment said flush bucket is adapted to follow the scum flap, ideally said scum flap and flush bucket are supported on a single structure.

Preferably the flush bucket is adapted to be suspended from said structure, so that said bucket is submerged below the surface of the liquid.

Ideally said bucket is adapted to be suspended by means of wire rope.

An embodiment of the invention will now be described by way of example only with reference to the accompanying figures wherein: Figure 1 shows a side elevation view of a scum decanting device in accordance with the invention.

Figure 2 shows a rear elevation view of the device shown in Figure 1.

Figure 3 shows a front elevation view of the device shown in Figure 1.

Figure 4 shows a plan view of the device shown in Figure 1.

Figures Sa and 5b show the device when in use.

Figure 6 shows a perspective view of a scum ramp/flushing box.

Figure 7 shows a front view of a half bridge and associated skid.

Figure 8 shows an exploded view of a portion of Figure 7.

Figure 9 shows a plan view of a settlement tank; and Figure 10 shows a side sectional view of a settlement tank.

Figure 11 shows a scum discharge means according to one embodiment of the invention.

Figure 12 shows a scum discharge means according to a further embodiment of the invention.

Figure 13 shows a plan view of a settlement tank including an embodiment of the invention.

Figure 14 shows a side sectional view of the scum flap and flush bucket arrangement according to one aspect of the invention.

Figure 15 shows a plan view of the arrangement shown in Figure 14.

Figure 16 shows a cross-sectional view and side sectional view of a scum flap in accordance with one embodiment of the invention.

Figure 17 shows a dual scum discharge means arrangement.

Referring to the figures and firstly to Figure 1 there is shown a pivoting scum ramp and combined flushing box 1 and associated discharge means 2.

The scum ramp 1 is shown in perspective view in Figure 6 and essentially comprises an open sided box having a substantially flat base 3 and three upstanding contiguous wall members 4, 5 and 6. Walls 4, 5 and 6 may be of any preferred height or adapted to be adjustable so that the heights of same can be varied. The reason for this will be explained hereinafter.

If preferred a counter balance 7 may be attached to the underside of scum ramp 1 so as to ensure that, at rest, the open side of scum ramp 1 is held within liquid contained within a settlement tank and so below the surface of said liquid.

Referring briefly to Figures 2, 3 and 4 it can be seen that the discharge means comprises an upper funnel member 8 having an upper rectangular rim 8a which tapers inwardly to form a scum outlet 9.

Scum ramp 1 is attached to a first side of rim 8a by means of a U-shaped bracket 10 which is attached to the underside of base 3. The outermost ends of bracket 10 are pivotably attached to pivot joints 11 which joints 11 are supported by transverse support means 12.

Bracket 10 may be releasably attached to pivot joints 11 so that scum ramp 1 can be detached for the purpose of repair or so that a different size scum ramp can be substituted.

At least one pivot joint 11 is further connected to an articulated arm member 13 which has on its outermost end a roller 14.

In use, when the device is at rest, member 13 is positioned so that scum ramp 1 is pivoted in a first position where the open side of scum ramp 1 rests just beneath the surface of liquid within a settlement tank. This arrangement is shown in Figure 5a.

Interaction with, and so relative movement of, an associated skid results in contact between roller 14 and the underside of a skid 15. This brings about a change in articulation of member 13 and thus the raising of scum ramp 1 to a position above water level, and also to a position where the open side of scum ramp 1 is uppermost and the rear wall member 5 of scum ramp 1 is lowermost. Thus in this tilted position carriage water and any surface scum on liquid retained in scum ramp 1 is made to flow over rear wall member 5 and thus into discharge means 8.

It will be apparent that the height of wall members 4, 5 and 6 will determine the amount of carriage water made to flow into discharge means 8. The higher the wall members 4, 5 and 6 then the more carriage water will be retained in scum ramp 1.

Figure 7 shows an embodiment of a half bridge 16 and associated skid 17 and skimming arm 19.

The half bridge 16 has attached to the undermost side thereof, via downwardly depending support members 18, a skid 17. Skid 17 takes the form of a relatively shallow U-shaped cross-sectional member, thus it comprises a first upwardly projecting section, a second substantially horizontal section and a third upwardly projecting section. It follows, from the arrangement shown in the accompanying figures, that relative movement of skid 17 with respect to the scum decanting device will result in roller 14, via articulated member 13, moving scum ramp 1 upwardly to the afore described second pivoted position so that carriage water and any scum can be decanted from same for a period equal to the length of time it takes roller 14 to pass along the substantially horizontal section of skid 17.

Thereafter roller 14 will travel along the upwardly projecting section of skid 17 and as a result of this scum ramp 1 will return to its original position.

Figure 8 shows an exploded view of a part of half bridge 16. It can be seen that a skimmer arm 19 is fixedly attached to half bridge 16. Attachment is executed using conventional means and therefore is not illustrated. Skimmer arm 19 is provided with a lower pivotal scum flap 20. Skimmer arm 19 is provided foremost of skid 17 so that, in use, skimmer arm 19 firstly interacts with scum ramp 1 and then secondly skid 17 interacts with articulated member 13 attached to scum ramp 1.

In use, skimmer arm 19 travelling foremost of skid 17 pushed scum up scum ramp 1 using flexible scum flap 20. At the uppermost part of scum ramp 1 pivotal scum flap 20 pushes scum over scum ramp 1 and into discharge means 2.

Once this has taken place interaction between skid 17 and articulated member 13 takes place so as to pivot scum ramp 1 in a raised tilted position thus allowing for carriage water and any remaining scum in scum ramp 1 to be tipped into discharge means 2. This results in discharge means 2 being flushed clean.

In Figure 9 there is shown a plan view of a settlement tank which comprises two outer concentric scum boards 21 and inwardly thereof there is located one scum decanting device in accordance with the invention. A half bridge 16 spans the tank from the centre of same to the outer of same. Half bridge 16 is adapted for rotatory movement, so that half board 16 is made to rotate over the surface of the tank.

Figure 10 shows a side sectional view of a settlement tank. To the upper right hand side is shown a scum decanting device in accordance with the invention.

The device is fixedly attached to the inner uppermost side of the tank. Inwardly thereof and in the centre of the tank there is shown a diffuser drum or stilling box which is suspended about a central support column. On the uppermost end of the support column there is provided a V-notched weir.

Towards the left hand side of Figure 10 a scum board is illustrated, and rearwardly thereof a lauder channel for the extraction of clean water.

The arrangement shown in Figure 10 illustrates the location of the scum decanting device of the invention when in use.

It will apparent from the afore description that the device of the invention when in operation results in the positive guidance of scum up scum ramp 1 by skimming arm 19 and then the discharge or decanting of carriage water and any remaining scum from scum ramp 1 in a controlled manner so that the minimum amount of carriage water is lost from the system. In addition, it will also be apparent that the scum decanting device of the invention is provided with flushing means in that discharge means 2 is continuously flushed when in use as scum ramp 1 is raised to a decanting position and carriage water is poured from same.

Figures 1 to 10 depict embodiments of a device which overcome the problems associated with the prior art. Figures 11 to 17 describe further embodiments which have also been devised to overcome the problems associated with the prior art.

Referring to Figure 11, there is shown a scum discharge means 8x in accordance with one embodiment of the invention. Scum discharge means 8x is adapted to discharge scum in a horizontal direction. In Figure 12 there is shown a scum discharge means 8y adapted to discharge scum vertically from the base. In addition, Figure 12 shows a scum ramp 9x and an exit ramp 10x. From the side sectional view of discharge means 8y it can be seen that scum ramp 9x comprises two angular portions. A first portion is defined by an outer part of ramp 9x which is inclined upwardly at a first angle, which angle is substantially similar to the angle of the flush bucket. A second portion is defined by an inner part of ramp 9x whose angle is less steep than the first angle and is adapted so that as a flush bucket travels upwardly of same it is tipped and its contents discharge into the discharge means.

Referring to Figure 13, many of the features described previously are illustrated, but in addition, there is shown a plan view of settlement tank lix, showing half bridge 12x, skimming board 13x, discharge means 8y and scum flap 14x (flush bucket 1 5x is not shown). Figure 13 demonstrates operation of the invention at intervals in a clockwise direction.

Referring to Figure 14 there is shown a plan view of flush bucket 15x which is attached to bridge 12x using suspension wires 16x. In addition there is shown a trailing scum flap 17x, leading scum flap 18x and attached to the lower part thereof blade 19x. Figure 15 shows a side sectional view of Figure 14. There is shown an angled skimming board 20x and half bridge 12x.

Said scum flap and/or said blade may be provided with sides so as to contain the scum as it is guided towards the scum box.

In use blade 19x travels forwardly and pushes scum up the scum ramp 9x of discharge means. It will be appreciated that the flush bucket follows the blade 19x. The bucket 15x is angled so that the sides are ideally the same angle as scum ramp 9x. Bucket 15x travels up scum ramp 9x and towards the top of same it is tipped forwardly so as to empty its contents into the discharge means.

Said scum flap 18x may also be adapted to trail in the same manner as the flush bucket but it would trail forwardly of said flush bucket.

Referring to Figure 16 there is shown a cross-sectional view and a side-sectional view of sprung scum flap 21x.

It will be apparent that the height of the scum discharge means in a settling tank will only be limited by the height of the half bridge.

In some applications scum can be collected at a plurality of predetermined positions from the centre of the tank, preferably in a concentric arrangement of aligned and/or staggered discharge means. In such an application one or more skimming boards may be operatively coupled to same. In such an application, scum discharge means may be connected as shown in Figure 17.

The device of the invention thus provides for an improved decanting of scum from the surface of liquid, ideally liquid located in the settlement tank.

Claims

1. A scum decanting device for removing scum from a liquid surface in a vessel, comprising a scum discharge means and a relatively movable scum flap and associated flush bucket whereby firstly the scum flap is adapted to push scum into said discharge means and secondly the flush bucket is adapted to flush said discharge means.

2. A scum decanting device according to claim 1 wherein the scum discharge means includes an integral or associated scum ramp, which scum ramp is adapted to receive scum.

3. A scum decanting device according to claims 1 and 2 wherein there is a simple geometric relationship between the angle of said scum ramp and a side of the flush bucket.

4. A scum decanting device according to claim 3 wherein the angles of inclination of the scum ramp and flush bucket are the same or substantially the same.

5. A scum decanting device according to claims 1 to 4 wherein said discharge means includes an exit ramp.

6. A scum decanting device according to claims 1 to 5 wherein said device includes two adjacent scum discharge means connected by pipework.

7. A scum decanting device according to claims 1 to 6 wherein said scum flap and said flush bucket are connected to a skimming arm.

8. A scum decanting device according to claim 7 wherein said bucket is arranged to trail behind said flap as said arm travels forwardly.

9. A scum decanting device according to claims 1 to 8 wherein a skimming board is provided to guide scum into said discharge means.

10. A scum decanting device according to claim 9 wherein said skimming board is attached to said skimming arm.

11. A scum decanting device according to claims 7 to 10 wherein the skimming arm is angled with respect to a side of the vessel.

12. A scum decanting device according to claims 1 to 11 wherein said scum flap comprises a plurality of flaps.

13. A scum decanting device according to claim 12 wherein said scum flap comprises a leading flap and at least one trailing flap.

14. A scum decanting device according to claims 1 to 13 wherein said flaps are made from En-thane material.

15. A scum decanting device according to claims 13 and 14 wherein said leading flap is shorter than said trailing flap(s) and said leading flap is adapted to hold a blade.

16. A scum decanting device according to claim 15 wherein said blade is fixed at right angles to said leading flap.

17. A scum decanting device according to claim 15 wherein the angle of said blade is adjustable.

18. A scum decanting device according to claims 15 to 17 wherein said blade is ideally made from En-thane.

19. A scum decanting device according to claims 12 to 18 wherein said plurality of flaps includes at least one sprung scum flap.

20. A scum decanting device according to claim 19 wherein said sprung scum flap points in the direction of travel.

21. A scum decanting device according to claims 1 to 20 wherein said flush bucket is adapted to follow the scum flap.

22. A scum decanting device according to claims 1 to 21 wherein said scum flap and flush bucket are supported on a single structure.

23. A scum decanting device according to claim 22 wherein the flush bucket is adapted to be suspended from said structure so that said bucket is at least partially submerged below the surface of the liquid.

24. A scum decanting device according to claims 1 to 23 wherein said bucket is suspended by means of a rope.

25. A scum decanting device comprising a pivotal scum ramp and associated discharge means, which scum ramp in a first pivoted position is arranged so as to allow scum from the surface of a liquid to be collected and in a second pivoted position is arranged so as to tip at least a controlled amount of carriage water into said discharge means.

26. A scum decanting device according to claim 25 which includes a skimming arm arranged to push scum into the scum ramp.

27. A scum decanting device according to claim 26 wherein the skimming arm is attached to a half-bridge.

28. A scum decanting device according to claims 26 and 27 wherein the lower edge of said skimming arm is adapted to be pivoted so as to push scum up the scum ramp and in turn into the associated discharge means.

29. A scum decanting device according to claims 25 to 28 wherein said scum ramp is provided with walls on three of its sides for the purpose of retaining scum and carriage water scooped therein.

30. A scum decanting device according to claim 29 wherein at least said side wall opposite the opening or entrance of the ramp is adapted to be adjustable so that the height of same can be varied.

31. A scum decanting device according to claims 25 to 30 wherein said scum ramp is pivoted with respect to said discharge means by way of an articulated member, which articulated member at a first end, is attached to said scum ramp and at a second furthermost end is provided with a contact means, which means is arranged so that in use it makes contact with a skid member.

32. A scum decanting means according to claim 31 wherein said contact means is in the form of a roller or the like.

33. A scum decanting device according to claims 31 and 32 wherein said skid member is located on the underside of a half-bridge.

34. A scum decanting device according to claims 31 to 33 wherein said skid member is fashioned so as to ensure that contact with said contact means results in predetermined articulation of said articulated member, thus resulting in controlled movement of said scum ramp from said first pivoted position to said second pivoted position.

35. A scum decanting means according to claims 31 to 34 wherein said skid member comprises a first upwardly angled section, a second substantially horizontal section and a third upwardly angled section.

36. A scum decanting means according to claims 31 to 35 wherein said skid member is in the form of a shallow U-shaped member.

37. A scum decanting device according to claims 25 to 36 wherein said scum ramp is attached to an upper outermost rim of said discharge means.

38. A scum decanting device according to claims 25 to 37 wherein said discharge means comprises a first upper funnel-shaped member and a second lower conduit which is arranged to carry scum from a container or settlement tank to a preselected location.

39. A scum decanting device according to claims 31 to 38 wherein there is provided a means for moving the skid member with respect to said scum decanting device.

40. A scum decanting device according to claims 25 to 39 wherein a skid member is also attached to said half-bridge and said scum decanting device is fixedly attached to a preselected part of a container or tank and said skimming arm and said skid member are attached to the underside of said half-bridge and arranged to move over the surface of a liquid in said container or tank.

41. A scum decanting device according to claim 40 whereby said skid member and said skimming arm are arranged to move in a rotary fashion over the surface of the liquid.

42. A scum decanting device according to claims 25 to 39 wherein said skid member and said skimming arm are fixedly attached to a preselected part of a container or settlement tank and said scum decanting device is adapted to move within said container or tank.

43. A scum decanting device according to claim 42 in which the open side of the scum ramp travels foremost of the device and said scum ramp interacts firstly with said skimming arm and then with said skid member.

44. A settlement tank comprising at least one scum decanting device according to claims 25-43.

45. A settlement tank according to claim 44 wherein said tank contains a plurality of scum decanting devices.

46. A scum decanting device as herein described with reference to the figures.

47. A settlement tank as herein described with reference to the figures.