WO1992001516A1

WO1992001516A1 - Separator

Info

Publication number: WO1992001516A1
Application number: PCT/SE1991/000499
Authority: WO
Inventors: Richard Bruke
Original assignee: Spirac Engineering Ab
Priority date: 1990-07-19
Filing date: 1991-07-17
Publication date: 1992-02-06
Also published as: SE468158B; AU8237491A; CA2085609A1; SE9002463D0; EP0538370A1; SE9002463L

Abstract

The invention relates to a method and an apparatus for separating and removing, from a liquid, bodies (51) of a density which is less than the density of the liquid. The liquid containing the bodies is supplied to a container whose walls are oriented such that the bodies, on upward flotation to the liquid surface, guide the bodies so that they are concentrated to an area where mechanical devices (26) remove the bodies from the container in association with a first end region (15) thereof. The liquid is removed from the container via an outlet (31) located on a lower level than the lowest level of the upper defining edge of the end region. The apparatus for separation and removal of such bodies includes a container (10) whose defining walls form a storage space, which, in the horizontal plane, is of slight cross-sectional area in that region where the mechanical device (26), as a rule, a conveyor screw, is disposed for removing bodies which have floated up to the liquid surface.

Description

SEPARATOR

The present invention relates to a method and an apparatus for separating bodies or substances from a floating according the preambles to the independent claims.

One none-restrictive example of a field of application for the present invention is the separation of a floating sludge from waste water. As is well known in this art, in the treatment of waste water in a waste water treatment plant, floating sludge is separated in tanks or ponds in that sludge accumulating on the surface of the water is removed by means of mechanical scrapers. It is necessary to take care, in one way or another, of the slurry-like mixture which, in such instance, is generally formed by floating sludge and liquid which accompanies the floating sludge. According to currently applied technology, this mixture is collected in specific containers. In small-scale waste water treatment plants, the containers are used for transport of the mixture of sludge and floating to plants for its destruction and/or landfill deposition. In large-scale waste water treatment plants, the liquid content is reduced prior to transport, by means of a furter flotation step in which the sludge accumulated on the surface of the liquid is transferred by scraping to containers in which the mixture of sludge and liquid transferred to the containers in the scraping operation is transported to plants for destruction and/or landfill deposition.

Most generally, the collected sludge is extremely wet, difficult to handle and noxious, and all concentration and handling of the sludge take place across open surfaces, which entails that there are major difficulties in mastering the ambient problems of smell and other hygienic problems, such as spillage. Thus, the prior art techniques for handling floating sludge suffer from the drawbacks of a poor working and ambient environment in combination with relatively low efficiency and/or low level of utilization of the equipment employed. The present invention obviates the above-outlined drawbacks and problems by means of a method and an apparatus according to the characterizing features as set forth in the characterizing clauses of the independent claims.

According to the present invention, there will be achieved a rational separation of bodies from a liquid of a density which is greater than that of the bodies, for example separation of bodies which form floating sludge on the surface of the waste water. The present invention also encompasses embodiments comprising substantially closed systems in which the above-discussed problems of smell are obviated, without increasing costs as compared with the costs incurred in prior art systems. Furthermore, the present invention affords the possibility of choosing between continuously or intermittently operating systems for separating bodies from a liquid.

Further expedient embodiments of the present invention are disclosed in the appended subclaims.

The present invention will now be described in greater detail hereinbelow, with particular reference to the accompanying Drawings. In the accompanying Drawings:

Fig. 1 is a longitudinal section through a first embodiment of an apparatus according to the invention;

Fig. 2a shows the section A-A in Fig. 1;

Fig. 2b shows the section A-B in Fig. 3;

Fig. 3 is longitudinal section through a second embodiment of the apparatus according to the invention;

Fig. 3a is a detailed section showing the discharge portion of the apparatus for floating sludge; Fig 4. is a longitudinal section through a conveyor included in the apparatus and disposed for receiving and conveying bodies skimmed off from the liquid surface;

Fig. 5 shows the section V-V in Fig. 4; and

Fig. 6 is a cross-section through a third embodiment of the apparatus according to the invention.

In the embodiments of an apparatus 1 according to the invention shown in Figures 1-5, there is disclosed a container 10, 10a with a bounding definition (side walls) lla-d and a closed bottom 12. The container rests on a bottom frame 14. The container is generally of elongate configuration and has, in one preferred embodiment, a substantially rectangular cross-section in the horizontal plane. A first end region 15, and a second end region 16 are opposed to one another and, as a rule, are located along the short walls lid, 11 b, respectively of the container. However, it will be obvious to a person skilled in the art that, in certain embodiments, these end regions are located in association with the longitudinal walls of the container. The container has an upper region 13 which, as a rule, is provided with a roof 19, which, in one preferred embodiment, forms a substantially tight seal of the container.

In the first end region 15 of the container, there is provided at least one outlet 31 for liquid. In the other end region 15 of the container, there is provided at least one inlet 30 for liquid 50 containing bodies 51 which are to be separated from the liquid. Generally, the inlets 30 discharge in the lower region of the container, and moreover at least one inlet is generally disposed at a level which is located more proximal the bottom of the container than half of the level difference betv/een the bottom 12 of the container and the floating sludge discharge opening 24 of the container. Fig. 1 shows one embodiment in which the inlet 30 is substantially vertically oriented and in which the discharge of the inlet is located relatively close to the bottom 12 of the container. Fig 3 shows one embodiment in which the inlet 30 is of a substantially horizontal direction and is located adjacent the bottom 12 of the container. A flow distributor or baffel 34 whose task is to reduce the flow rate of the liquid in the container, is generally disposed adjacent the mouth 39 of the inlet. In one preferred embodiment, the baffel is provided with a substantially planar surface which is turned to face towards the inlet. While the Drawing Figures show embodiments of the container in which the mouth of the inlet is placed in the lower region of the container, it will be obvious to a person skilled in the art that, in certain embodiments, the inlets may be placed considerably higher.

The outlet 31 for liquid is further connected to an upwardly directed outlet channel 33 which, in the embodiment shown on the Drawings, is provided with a recurved portion 35 which forms a spillway overflow 32, whose level determines the level of the liquid surface 53 of the filled container. In the Drawing Figures, the spillway overflow is shown in one embodiment in which it is designed as a damper which is rotary about a shaft 36 and, in this instance, is rotated upwardly or downwardly in the direction of the arrows A. The maximum filling level in the container is hereby adjusted. In the Figures, the damper 32 is shown as having upwardly convex form, the free end 37 of the damper being located inside the defining wall of the downwardly directed portion 38 of the outlet channel. In the region of the damper, the outlet channel is generally designed with a rectangular or quadratic cross-section for facilitating the substantially sealing connection of the damper to the walls of the outlet channel.

In the upper region 13 of the container, there is disposed a first conveyor 20 with a drive end 48 and a discharge end 49. The conveyor includes a conveyor screw 21 with its one end 47 (the drive end) located in the drive end 48 of the conveyor, and its other end 22 (the discharge end) located in the region of the discharge end 49 of the conveyor. In its drive end 47, the conveyor screw 21 is connected, by the intermediary of an anchorage device 44 and a drive shaft 43, to a prime mover 40. In the Drawing Figures, this is shown in one embodiment in which it is composed of a motor 41 and a transmission 42 which connects the motor to the drive shaft 43.

In its discharge end 49, the first conveyor is provided with an outlet 24 which, in the embodiments illustrated in Figs. 1 and 3, is provided with a generally downwardly directed ejector 70, In the region of the discharge end 49, the first converyor is generally provided with a casing 23 which, in the first end region 15 of the container, substantially sealingly connects to the defining wall lid of the container and, in certain embodiments, also to the roof 19 of the container, which thereby also generally forms a roof for the conveyor 20.

In Fig. 1, the first conveyor 20 is shown in one embodiment in which the casing 23 of the conveyor is of the fundamental configuration of a truncated cone whose top forms the outlet 24. The casing 23 forms, in the region beneath the conveyor screw 21, a path 25 for the screw. In a section at right angles to the axial direction of the conveyor screw, the path is of curved shape (concave towards the conveyor screw) and is, for example, U-shaped or circular, with a smallest radius of curvature slightly exceeding the radius of the conveyor screw. As a result of the shape of the casing, the path 25 rises towards the outlet 24 of the casing from a level beneath the lowest level of the spillway overflow 32 of the apparatus to a level above the spillway overflow of the apparatus. It will be obvious that this orientation of the path is not dependent upon the configuration of the upper region of the casing as long as such configuration permits rotatation of the conveyor screw. In certain embodiments, the path 25 is terminated by a spillway overflow 27 (see Fig. 3a) shown on the drawing in one embodiment in which it includes a substantially horizontal portion 72 which merges into a substantially vertical portion 74 by the intermediary of a transition 73. The spillway overflow is reciprocal in the direction of the double arrow B, whereby the level of the spillway overflow can be adjusted. In Fig. 3a, the spillway overflow is shown as rotary about a shaft 71.

In Fig. 1, the conveyor screw 21 is shown in one embodiment in which, in its discharge end 22, its diameter tapers in a direction towards the outlet 24, the reduction in thread diameter and inclination of the path 25 being adapted to one another so as to achieve the contemplated cooperation with the impeller of the conveyor screw and the path. 6

Fig. 3 shows one embodiment in which the conveyor screw 21 is disposed as inclining, the drive end 47 of the conveyor screw being located at a lower level than the discharge end 22 of the conveyor screw. There will hereby be obtained the contemplated cooperation between an inclined path 25 and the impeller blades of the conveyor screw in its discharge end 22. Also in this embodiment, the path 25 is disposed in a manner corresponding to that described above in connection with Fig. 1. The orientation described in this paragraph of the conveyor screw is often combined with a substantially corresponding outer diameter of the conveyor screw throughout its entire length.

Figs. 4 and 5 show a third embodiment of an apparatus according to the invention. In these Figures, the container 10 and the first conveyor 20 are shown as being disposed in the manner corresponding to that described with particular reference to Fig. 3. A second conveyor 80 is disposed in association with the discharge end 49 of the first conveyor 20 and its conveyor screw 21. The second conveyor is oriented substantially at right angles to the first conveyor and includes a conveyor screw 82 which is at least partly surrounded by a casing 81. The second conveyor 80 is disposed to incline so that its discharge end 83 is located on a higher level than that portion 84 of the conveyor where the first conveyor 20 feeds in floating sludge into the second conveyor. At its lover end 85, the second conveyor is connected, via a chamber 87, and generally a channel 86, to the storage space of the container 10 for liquid. The above-described orientation of the second conveyor entails that the lower end 85 of the second conveyor is located on a lower level than the infeed portion 84 of the second conveyor.

In its lower region, the casing 81 of the second conveyor is provided with drainage openings 88 which place the interior of the second conveyor in communication with the chamber 87 which at least partly surrounds the casing 81. The chamber is formed between the casing 81 and an outer wall 89 disposed outside the casing, and is connected to the storage space of the container 10 for liquid, for example by the channel 86. The Figures also show a receptacle container 75 for floating sludge which has left the second conveyor at its discharge end 83. It is obvious that, in practical applications^' in which it is desired to eliminate problems involving smell, the casing 81 of the second conveyor will wholly surround the conveyor screw 82 of the conveyor, that the connection between the first conveyor and the second conveyor is tight, and that the communication between the discharge end 83 of the second conveyor and the receptacal container 75 is wholly encapsulated.

It will be obvious to a person skilled in the art that, in the embodiment illustrated in Figs. 4 and 5, the conveyor screw 21 of the first conveyor 20 is, in certain practical applications, disposed substantially horizontally, implying that the path 25 is also substantially horizontal. Other practical applications call for the employment, as first conveyor, of that embodiment of the first conveyor which was illustrated and described with reference to Fig. 1, the path 25 having an inclination corresponding to the diameter reduction of the conveyor screw. It will also be obvious to a person skilled in the art that the embodiment shown in Fig. 1 of the first conveyor may be given inclining orientation for amplifying the level difference between the lower region of the part 25 and the upper region of the part 25.

The conveyor screw 21 or 82, respectively, of the first conveyor and/or the second conveyor consists, in certain embodiments, of a free-floating spiral thread 26 while, in other embodiments, it is formed of a spiral thread with a mechanical shaft 29 (cf. Fig. 2b). The spiral thread is either fixed to the mechanical shaft or rotary in relation thereto. In those practical applications (cf. Fig. 2a) in which the conveyor screw consists of a floating spiral thread, at least one support 45 is generally provided, for example designed as a carrier rail which supports the conveyor thread. Generally, the carrier rail turns to present a concave cylindrical surface towards the spiral thread. As a rule, the carrier rail is disposed in a vertical plane in the region of the geometric axis of the spiral thread. This arrangement is adapted to such factors as the composition and consistency of the liquid, the concentration of bodies in the liquid, the properties of such bodies, the speed of rotation of the conveyor screw, etc. Fig. 6 shows a cross-section corresponding to the cross-section A-A in Fig. 1, in which the inlet to the container has been omitted from the Figure and the container is provided with two opposing, mutually inclining longitudinal walls, 60,61. In the upper region 62 of the container, there are disposed two conveyor screws 63, each one of which being of a design and disposition corresponding to that described above for the conveyor screws in the embodiments described in the foregoing. Thus, each one of the conveyor screws cooperates with a path 25 corresponding to those described above. The conveyor screws 63 are disposed to rotate in opposing directions. The direction of rotation of each respective conveyor screw is, in such instance, selected such that the thread of the screw, when this is located most proximal each respective inclining wall, is displaced downwardly.

It will also be apparent from Figures 2a, 2b and 6 that the cross sectional area of the container 10 in the storage space of the container for liquid is, in a horizontal section, at its smallest in that region of the container where the liquid surface is located in a completely filled container. This is achieved in that at least one 11a of the defining walls of the container inclines towards the opposing wall. The defining walls I1a-d of the container thereby form a storage space which, in the horizontal plane in the region of the container for the liquid surface 53 in a filled container, is of smaller cross-sectional surface area than the mean value of the cross-sectional areas in the horizontal plane through the storage space of the container in the region of the container beneath the region of the liquid surface.

In the Figures, the apparatus is shown with the container filled with liquid. The liquid includes matter or bodies 51 which are of a density slightly less than the density of the liquid. As a result, these bodies rise towards the surface 53 of the liquid. The bodies there form a stratum or layer 52, hereinafter generally designated a layer of floating sludge.

When the apparatus according to the present invention is put into practice, liquid 50 containing the bodies 51 is supplied via the inlet 30. The bottom 12 of the container or the flow distributor 34 impede the rate of flow of the incoming liquid so that the bodies of a density less than the density of the liquid are displaced upwardly towards the surface of the liquid. In such instance, the bodies are guided (concentrated) to a surface whose size is less than the mean value of the horizontal cross section through the storage space of the container beneath the area of the container for the liquid surface in a filled container. On the surface of the liquid, the bodies form the stratum or layer 52 of floating sludge. The conveyor screw 21 is rotated by the prime mover 40, in which instance the bodies in the layer of floating sludge are displaced towards and through the outlet 24 of the conveyor. In those embodiments in which the spillway overflow 32 of the outlet channel 33 is on a lower level than the highest level of the path 25, it is only by the rotation of each respective conveyor screw that bodies in the area of the path will be displaced therealong. In certain practical applications, the prime mover 40 provides an intermittent rotation of the conveyor screw, while in other embodiments, the conveyor screw is rotated continuously. The choice of continuous or intermittent rotation of the conveyor screw is made int. al. in view of that speed at which the bodies are accumulated on the surface of the liquid, the speed of rotation which is employed for the screw and the conveyance or transport capacity possessed by the screw. Intermittent or continuous supply to the container of liquid containing bodies is also selected int. al. in view of the time consumed for displacement of the bodies to the surface of the liquid and the maximum permitted quantity of bodies in the liquid when it leaves the container through the outlet 31.

The level of the surface of the liquid 53 in the container and thereby also the level of the layer of floating sludge may be adapted to relevant operational conditions by adjustment of the level difference between the spillway overflow 27 of the path 25 and the spillway overflow 32 of the outlet channel. The choice of angle of inclination of the path 25 may also be adapted to the relevant operational situation (the composition of the sludge, the proportion of matter or bodies, the mechanical properties of such bodies, etc).

In the embodiment of the apparatus according to the invention shown in Figs. 4 and 5, the first conveyor 20 feeds the bodies direct into the second conveyor 80. The thread spiral 82 of the second conveyor is rotated about its axis and thereby displaces the received bodies towards the discharge end 83 of the second conveyor and out therethrough, the bodies departing from the apparatus. Fig. 4 shows one example of a receptacle device 75 for discharged matter or bodies, but it will be obvious to a person skilled in the art that such discharge may be effected to any optional device suited for receiving such matter or bodies, for example a closed container, a subsequent conveyor, etc.

In the lower region 85 of the second conveyor 80, liquid 50 is accumulated which is supplied to the second conveyor 80 from the first conveyor 20. The surface 53a of the liquid is located on a level corresponding to the level of the liquid surface 53 in the container. The space in the lower end 85 of the conveyor forms a communication vessel, via the channel 86, with the storage space of the container 10. Any possible liquid supplied via the first conveyor to the second conveyor entails that liquid from the lower region of the second conveyor runs via the channel 86 to the container 10. The described interconnection of the lower region of the second conveyor with the storage space of the container 10, for example by means of a recycle channel 86, also makes possible the employment of an embodiment in which the path 25 of the first conveyor 20 is of such orientation or is located on such a level, for example in the region of or lower than the surface of the liquid, that liquid passes via the path 25 to the second conveyor 80. In other words, the path 25 is, in the discharge end 49 of the first conveyor, given such orientation in certain practical applications that it impedes or prevents liquid passage to the second conveyor 80, while, in other practical applications, the path is designed so as to permit the passage of liquid.

In certain embodiments, the second conveyor screw 82 includes at least one cleaner device 90 which is disposed in association with the outer edge region of the spiral thread of the conveyor screw and projects substantially radially outwards therefrom. The cleaner device consists, for example, of a scraper panel of plastic material, a brush (ideally a spiral brush), etc. The cleaning device accompanies the spiral in its rotation and, in such instance, abuts against the casing 81 of the second conveyor 80 for cleaning of the drainage openings 88 when the device passes them. It will hereby be ensured that the drainage openings and, thereby, the communication between the lower inner space of the conveyor 80 and the inner space of the container 10 is kept open.

In certain practical applications, use is made of at least one partition wall 18 (shown by broken lines in Fig. 1) with an upper bounding definition 17. In certain embodiments, the partition or wall 18 is disposed for displacement in the horizontal direction in order to be placed in a position adapted to the relevant operational situation. There are also embodiments in which the vertical extent of the partition (and thereby also the level of the upper bounding definition 17) is adjustable. In other embodiments, the partition is fixedly placed in the container. The partition entails that all liquid supplied to the container is forced to pass over the upper definition 17 of the partition before liquid reaches the outlet 31 of the container. This will achieve an upwardly-directed flow, which contributes to displacing the matter or bodies towards the surface of the liquid and thereby hastens accumulation of bodies at the liquid surface. Since the flow area of the downward liquid current is, once the liquid has passed the partition 18, considerably greater than the area of the inlet and outlet, respectively, of the container, the flow rate of the downwardly directed liquid flow will be so low that bodies carried in the liquid do not accompany the liquid in its downwardly directed movement - or accompany the liquid to but a very slight degree. It will be obvious that the flow area and, thereby, the rate of flow of the liquid once it has passed the upper definition 17 of the partition 18 is, in certain practical applications, adjusted by means of the above-disclosed displacement of the partition and/or its upper definition. Such a displacement, combined where applicable with a regulation of the incoming flow volume, is employed int. al. to make possible continuous throughflow and separation of bodies from the liquid in the container.

In the foregoing description, the first conveyor 20 has been disclosed as including at least one conveyor screw, but it will be obvious to a person skilled in this art that, in certain practical applications, the conveyor is designed as a scraper which is displaced by drive means between a starting postition adjacent the second end region 16 of the container to the first end region 15 of the container and out through the outlet 24 of the conveyor. Thereafter, the scraper returns to the starting position. On displacement towards the outlet 24, the scraper is at least partly immersed through the liquid surface, whereby bodies 51 in the region of the liquid surface are entrained by the scraper on its displacement. On return to the starting position, the scraper is raised from the liquid.

The above detailed description has referred to but a limited number of embodiments of the present invention, but it will be readily perceived by a person skilled in the art that the present invention encompasses a large number of embodiments within the spirit and scope of the appended Claims.

Claims

1. A method of separating and removing, from a liquid, bodies (51) which are of a density which is less than the density of the liquid, and in which the liquid containing the bodies is, for separation of the bodies from liquid, supplied to a container (10) in order to be displaced, in a container, towards the surface of the liquid, c h a r a c t e r z e d i n t h a t the bodies (51) in the liquid (50) are, on floating to the surface of the liquid, guided (concentrated) by the walls of the container to a surface whose size is less than the mean value of the horizontal cross section through the storage space of the container under the area of the container for the liquid surface in a filled container; that bodies accumulated in association with the liquid surface are, by mechanical devices (20), removed from the container in association with a first end region (15) thereof; and that the liquid (50) is removed from the container (10) via an outlet (31) located on a lower level than the lowest level of the defining edge of the end region.

2. The method as claimed in Claim 1, c h a r a c t e r i z e d i n t h a t the bodies are removed from the liquid surface by means of mechanical scraper devices.

3. The method as claimed in Claim 1, c h a r a c t e r i z e d i n t h a t the bodies are removed from the liquid surface by means of at least one conveyor (20) including a conveyor screw (21) which is rotated in order, in its discharge end, to remove said bodies accumulated on the liquid surface.

4. The method as claimed in anyone of Claims 1-3, c h a r a c t e r ¬ i z e d i n t h a t the liquid containing the bodies is supplied to the container (10) via at least one inlet (30) disposed in a second end region (16) opposing the first end region (15); and that the liquid is removed from the container via at least one outlet (31) disposed in association with the first end region, and preferably via an outlet (31) located on a lower level than a discharge opening (24) disposed in the discharge end (22) of the screw.

5. The method as claimed in anyone of Claims 1-4, c h a r a c t e r i z e d i n t h a t the liquid is removed via a spillway overflow (32) and/or that the sludge is removed via a spillway overflow (27).

6. The method as claimed in anyone of Claims 1-5, c h a r a c t e r i z e d i n t h a t an adaptation is effected between, on the one hand, the level difference between the outlet (31) for liquid and the discharge opening (24) for sludge and, on the other hand, the speed of rotation of the screw (21, 46a, 46b) relating the viscosity of the liquid and the composition of the sludge; and/or that the layer (52) is defined by the walls (11a-d, 60, 61) of the container to an extent adapted to that surface which is accommodated by the conveyor or conveyors (20, 46a, 46b), respectively.

7. An apparatus for separating and removing, from a liquid, bodies of a density which is less than the density of the liquid, comprising a container (10) with a sealed bottom (12) connecting to a bounding definition (lla-d) disposed in the circumferential direction of the container, and in which the container is provided with an inlet (30) and an outlet (31) for the liquid, c h a r a c t e r i z e d n t h a t one of the defining walls (11a-d) of the container (10) forms a storage space which, in the horizontal plane in the region of the liquid surface (53) of the container in a filled container is of lesser cross-sectional area than the mean value of the cross-sectional areas in the horizontal plane through the storage space of the container in that region of the container located beneath the region of the container for liquid surface; and that at least one mechanical device (26) is provided for removing, from the storage space of the container, bodies (51) floated up to the liquid surface.

8. The apparatus as claimed in Claim 7, c h a r a c t e r i z e d i n t h a t said mechanical devices consist of a scraper disposed in the upper region (13) of the container and displaceable in the region of the liquid surface, or of a conveyor (20) which includes at least one conveyor screw (21) and displays a discharge end (22), the scraper or conveyor screw, respectively, being disposed to displace bodies (51) accumulated on the liquid surface towards a discharge end (22) for the purposes of removing said bodies from the liquid surface.

9. The apparatus as claimed in Claim 8, c h a r a c t e r i z e d i n t a t the container (10) is provided with a spillway overflow (32) for liquid, and with a spillway overflow (27) for floating sludge; and that the spillway overflow for liquid is located on a lower level than the spillway overflow for floating sludge; and that the spillway overflow (32) for liquid and/or the spillway overflow (27) are preferably provided with means for adjusting the level of each respective spillway overflow.

10. The apparatus as claimed in anyone of Claims 7-9, c h a r a c t e r i z e d i n t h a t the conveyor screw (21) is disposed as a spiral thread in the absence of a mechanical central shaft; or that the conveyor screw (21) is disposed as a spiral thread surrounding a mechanical centre shaft.

11. The apparatus as claimed in Claims 7-10, c h a r a c t e r i z e d i n t h a t the first end region (15) and the second end region (16) are located in conjunction with opposing walls (lib, lid) of the definition (lla-d) of the container.

12. The apparatus as claimed in anyone of claims 7-11, c h a r a c t e r i z e d i n t h a t the conveyor (20) is, in association with the discharge end (22) of the conveyor screw, provided with a casing (23) connecting to the bounding definition of the container and at least partly surrounding the conveyor screw, and is terminated by an outlet (24); and that the casing forms, at least in the region beneath the conveyor screw, a path (25) which, in section at right angles to the axial direction of the conveyor screw, is concave in configuration.

13. The apparatus as claimed in Claim 12, c h a r a c t e r i z e d n t h a t the path (25) rises towards the outlet (24) of the casing from a level beneath the lowest lewel of the outlet (31) of the apparatus for liquid to a level above the lowest level of the outlet of the apparatus for liquid.

14. The apparatus as claimed in Claim 13, c h a r a c t e r i z e d i n t h a t the conveyor (20, 46a, 46b) is of an inclination substantially corresponding to the inclination of the path (25); or that the radius of the conveyor screw (21) in the region of the path (25) tapers in a direction towards the outlet (24) of the casing.

15. The apparatus as claimed in anyone of Claims 7-14 c h a r a t e r i z e d i n t h a t two (11a, 11c) of the defining walls (11a-d) of the container are disposed substantially parallel with the axial direction of the conveyor screw (21); and that at least one (11a) of said walls (11a, lie) inclines towards the conveyor screw and, with its upper region (17) is located at a minimum distance from the opposing wall (lie) which exceeds the diameter of the conveyor screw (21).

16. The apparatus as claimed in Claim 15, c h a r a c t e r i z e d i n t h a t the conveyor screw (21) is disposed, on rotation for transport of floating sludge towards the discharge end (22), to displace the spiral thread (26) downwardly when this is located most proximal the upper region (17) of the inclining definition (Ha).

17. The apparatus as claimed in anyone of Claims 7-16 c h a r a c t e r i z e d i n t h a t two or more screws (46a, 46b) are disposed in parallel with one another; that mutually adjacent screws (46a, 46b) are disposed to rotate in opposite directions; and that the distance between mutually adjacent screws (46a, 46b) preferably amounts to at least a fourth of the radius of each respective screw.

18. The apparatus as claimed in anyone of Claims 7-17, c h a r a c t e r i z e d i n t h a t a second screw conveyor (80) including a conveyor screw (82) with no mechanical shaft is provided, the geometric axial direction of the screw thread being located in a vertical plane oriented substantially at right angles to a vertical plane in the geometric axial direction of the axial direction of the first conveyor screw (21); that the geometric axis of the first conveyor screw is directed towards the conveyor screw (82) of the second conveyor; and that the first conveyor (20) is, with its discharge portion, connected to the infeed portion (84) of the second conveyor (80).

19. The apparatus as claimed in Claim 18, c h a r a c t e r i z e d i n t h a t the second conveyor (80) is disposed to be obliquely inclined; that in its lower end (85), the interior space of the conveyor is connected to the storage space for liquid of the container (10); that drainage openings (88) are preferably provided at least in the lower end (85) of the second conveyor (80), via which the interior space of the second conveyor is in communication with the conduit (86); and that the second conveyor screw (82) is, in the region of the drainage openings (88), preferably provided with at least one cleaning device (90), for example a spiral brush which is fixedly secured to the thread of the conveyor screw and projects out therefrom in a radial direction.