The present invention relates to apparatus for separating liquids and solids and is useful, for example, in the treatment of waste water, sludge or industrial effluents or for the separation of fruit juices from pulp.

_*

It is already known to effect the separation of liquids and fluids by means of a cylindrical screen or basket formed by a plurality of co-axial rings which are spaced apart from one another to allow liquid to flow out through the screen while retaining solids or screenings on the inner sides of the rings.. An auger which is co-axial with the rings receives the solids from the rings, e.g. by the use of a rotating comb, and conveys the screenings upwardly from the screen for disposal.

It is an object of the present invention to provide a novel apparatus for separating liquids and solids which is substantially more versatile than such prior art apparatuses.

According to the present invention, there is provided apparatus for separating liquids and solids, comprising an inclined cylindrical separator screen for immersion in a flow of the liquids and solids and for at least partially screening the solids from the liquid, and an auger co-axial with the cylindrical screen and extending upwardly therefrom for conveying the screenings from the cylindrical screen, characterized by a second auger extending co-axially through the first auger and projecting downwardly beyond the cylindrical screen for picking up and removing sedimentary solid material.

The apparatus may have means associated with the first auger for compacting the screenings, means for pelletizing the compacted screenings and means for adding additional material to the screenings conveyed by the first auger.

Preferably, the separator screen is one of a pair of separator screens and in that the first auger receives the screenings from both of the separator screens. The screw conveyor is advantageously an outer one of a pair of co-axial inner and outer screw conveyors in that the outer screw conveyor receives the screenings from the separator screens and the inner screw conveyor projects

SUBSTITUTE SHEET

axially downwardly from the outer screw conveyor for receiving material and conveying the material upwardly through the interior of the outer screw conveyor.

Also according to the present invention, there is provided apparatus for separating liquids and solids, comprising a separator screen for receiving and separating the liquids and solids, a conveyor for feeding the separated solids upwardly from said separator screen and a compactor for compacting the solids, characterized by a cutter device for cutting the compacted solids into pieces.

The cutter preferably comprises cutter blades mounted for rotation with the compactor at an outlet end of the compactor for slicing through compacted material discharged from the compactor. ^■

Further according to the present invention, there is provided apparatus for separating solids and liquids, comprising a separator screen for receiving and separating the liquids and solids, a conveyor for feeding the separated solids upwardly from said separator screen and a compactor for compacting the solids, characterized by a pelletizer for converting the compacted solids into pellets.

The pelletizer preferably comprises a cylindrical housing, an eccentric rotor which is rotatable within the housing, and outlet openings for the extrusion of the compacted solids from the housing by the rotor.

The invention will be more readily apparent from the following description of preferred embodiments thereof given by way of example, with reference to the accompanying drawings, in which: -

Figure 1 shows a view taken in vertical cross-section through a screening apparatus according to a first embodiment of the present invention;

Figure la shows a view taken in cross-section along the line la-la of Figure 1;

Figure lb shows a view taken in cross-section along the line lb- lb of Figure l;

Figure lc shows a line taken in section along the line lc-lc of Figure 1; Figure Id shows a view taken in section along the line Id-Id of Figure lc and showing a portion only of the apparatus shown in Figure lc;

Figure le shows a view corresponding to Figure la but taken in cross-section through a modification of the apparatus of Figure 1;

Figure 2 shows a view in vertical cross-section through a different screening apparatus according to the present invention, in vertical cross section;

Figure 2a shows a view taken in transverse cross-section along the line 2a-2a of Figure 2; Figure 2b shows a view taken in transverse cross-section along the line

2b-2b of Figure 2c;

Figure 2c shows a broken-away view, in longitudinal cross - section, through parts of the apparatus of Figure 2;

Figure 2d shows a view corresponding to Figure to Figure 2a, but of a modification of a pelletizer forming part of the apparatus of Figure 2;

Figure 2e shows a broken-away view of part of the apparatus shown in Figure 2d;

Figure 2f shows a broken-away view taken in cross-section along the line 2f-2f of Figure 2e; Figure 2g shows a broken-away view in end elevation, of an extrusion formed by the apparatus of Figures 2d-2f;

Figure 2h shows a view taken in section along the line 2e-2e of Figure 2a; Figure 3 shows a view in vertical cross-section through a screening apparatus according to a third embodiment of the present invention; Figure 3a shows a broken-away view taken in longitudinal cross-section through parts of Figure 3;

Figure 3b shows a view corresponding to that of Figure 3 a but of a modified apparatus;

Figure 3 c shows a view taken in transverse cross-section along the line 3c-3c of Figure 3a;

Figure 4 shows a modification of the screening apparatus of Figure 3; Figure 5 shows a view in side elevation, partly broken-away in longitudinal cross-section, of a further screening apparatus according to the present invention; Figure 6 shows a broken-away view in side elevation of a still further screening apparatus according to the present invention;

Figure 7 shows an end view taken in the direction of arrow A of Figure 6; Figure 8 shows a broken away view in side elevation of a scoop chain

forming part of the apparatus of Figures 6 and 7;

Figure 9 shows a broken-away view in side elevation, and on a larger scale, of parts of the chain of Figure 8;

Figure 10 shows a broken-away view taken in section along the line 10-10 of Figure 9;

Figure 11 shows a view in elevation of a screening element for use in a modified separator screen basket;

Figure 12 shows a part of the screening element being cut from a metal strip; Figure 13 shows a broken-away view in side elevation of a separator screen incorporating screen elements such as that of Figure 11;

Figure 14 shows a side view of a further screening apparatus;

Figure 15 shows an end view of the screening apparatus of Figure 14;

Figure 16 shows a view in perspective of a separating apparatus according to a further embodiment of the invention;

Figure 17 shows a view in side elevation of the apparatus of Figure 16; and

Figure 18 shows a view in side elevation of a separating apparatus according to a still further embodiment of the invention.

Referring firstly to Figures 1 through Id of the accompanying drawings, reference numeral 10 indicates generally a screening apparatus, which comprises a separator section indicated generally by reference numeral 12, a compactor section indicated generally by reference numeral 14 and an output conveyor section indicated generally by reference numeral 16.

The separator section 12 comprises a separator screen or basket indicated generally by reference numeral 18 (see Figure la), which comprises parallel, longitudinally extending screen bars 20 arranged in a generally cylindrically curved array about the periphery of a conveyor auger 22, with the bars 20 spaced laterally apart from one another. A trough indicated generally by reference numeral 24 is upwardly open and has its bottom formed by the screen 18 and serves to receive a mixture of Hquid and solids through the open top thereof.

The liquid can flow outwardly of the separator section 12 through the gaps between the bars 20, but the solids are displaced upwardly along the bars 20 by

rotation of the auger 22.

The compactor section 14 has a compactor auger 26, which forms an extension of the conveyor auger 22 and which serves to compact the separate pieces of solid material advanced from the separator section 12 into a solid mass. The auger 26 rotates within longitudinal, stationery bars 27 (Figure lb), which allow water to escape and prevent, at least to some extent, rotation of the solid material compacted by the auger 26. The bars 27 are mounted on the inner surface of- cylinder 29 enclosing the auger 26. At the upper, outlet end of the compactor section 14, there is provided a cutter device indicated generally by reference numeral 28, by means of which the solid, compacted mass of material is sliced into pieces.

These pieces of solid material then drop from the cutter device 28 into the lower, input end of the conveyor section 16.

A second conveyor auger 30 in the conveyor section 35 then conveys these pieces of the solid material upwardly along the output conveyor section 16 for discharge into a suitable container (not shown). The lower end of the auger includes a shaft 31, which extends through only two turns of the auger 30, the remainder of which has no shaft.

On the compactor section 14, there is mounted an electric drive motor 32, having an output gear 34 which meshes with a ring gear 36. The ring gear 36 is mounted on a shaft 38, which is common to the conveyor auger 22 and the compactor auger 26. More particularly, the ring gear 36 has a hub 40 fixed to the shaft 38. The cutter device 28 comprises four arms 42 connecting the ring gear 36 to the hub 40 and each provided with a cutter blade 44, as shown in Figures lc and Id. The arrangement is such that, as the compacted mass of solid materials is forced through the spaces between the arms 42 by the compactor auger 26, the cutter blades 44 slice this material, which is thus broken into separate pieces. These separate pieces of solid material then drop downwardly to the second conveyor section 16. The auger 30 of the output conveyor section 16 is driven by means of a gear 46, which is mounted on the shaft 31 of the conveyor auger 30 and which meshes with the ring gear 36 so as to be driven thereby.

The motor 32 and the gears 34 and 36 are enclosed in a housing indicated generally by reference numeral 50. This housing defines an outlet chute 52 extending 25 downwardly from the cutter device 34 to the inlet end of the output conveyor section 16 for guiding the sliced pieces of solid material to the latter. The gear 46 is enclosed in a separate housing indicated generally by reference numeral 54.

Figure le shows a separator screen or basket indicated generally by reference numeral 18a, which is identical to that shown in Figure la in that the screen 18a is formed by the bars 20 and the trough 24. In addition, however, the screen 18a of Figure le is provided with a microscreen 21 at the interior of the array of bars 20 and between the latter and the auger 22. This microscreen 21 may be made of metal or fabric mesh, perforated sheet metal, woven fabric or woven or mesh plastics material and is useful, in particular, in applications which require relatively small pieces of solid material to be conveyed upwardly by the auger 22 rather than being discharged through the bars 20 with the escaping water.

Turning now to Figures 2 and 2a of the drawings, which show a second screening apparatus indicated generally by reference numeral 100, it can be seen that the screening apparatus 100 has a separator section indicated generally by reference numeral 102, a compactor section indicated generally by reference numeral 104 and an output conveyor section indicated generally by reference numeral 106.

The separator section 102 has a cylindrical screening basket indicated generally by reference numeral 108, which comprises annular screening bars or rings 110 extending coaxially about a first conveyor auger 112, which has a shaft 114, the lower end of which is carried by a support plate 111.

A stationary hopper 107 is provided at the upper end of the screen 108. The hopper 107 has an outlet communicating with an inlet opening 109 in a circular plate 111, which forms the upper end of the screen 108. Through the hopper 107 and the inlet opening 109, substances may be introduced into the interior of the screen 108 of mixing with and treating the waste material in the screen 108.

The cylindrical screening basket 108 has an open lower end, through which a mixture of liquid and solids can enter in the direction indicated by arrows 115. The lower end of the screening basket 108 is carried on a support roller 117, which is rotatably mounted on a support bracket 119. The liquids leave the cylindrical basket 108 through the gaps between the bars 110, while the solids are raised by radially inwardly extending arms 116 (Figure 2a) and dropped into the upwardly-open top of a cylindrically curved trough 118 containing the conveyor auger 112. Bars 119 are interposed between the inner surface of the trough 118 and the periphery of the auger 112 to allow liquid to drain from the solids removed by the auger 112.

These solids are conveyed upwardly by the auger 112 to a compactor auger 120, which forms an extension of the conveyor auger 112. The material compressed by the compactor auger 120 is discharged into a pelletizer indicated generally by reference numeral 121. The pelletizer 121 has an eccentric rotor 122 (Figures 2b and 2c), which with the compactor auger 120 is mounted on the shaft 114, and which forces the compacted material radially outwardly through openings 124 in a cylindrical wall 126, through outwardly convergent frusto-conical openings 123 in a cylindrical wall 125 and through cylindrical extrusion passages 127 in a cylindrical extrusion block 129.

Solid compacted material forced into the pelletizer 121 by the compactor auger 112 is pressed radially outwardly by the eccentric rotor 122 through the openings 123 and is thus extruded as rods from the extrusion passages 127.

Plates 128 rotating about the exterior of the cylindrical extrusion block 129 and within a cylindrical housing 133 break the rods of extruded, compacted solid materials which exit the openings 124, and the broken pieces of rod fall downwardly through an outlet opening 135 in the housing 133 and into the lower, inlet end of the output conveyor section 106. The radial plates 128 extend from plates 131 at right angles to the plates 128, so that plates 128 and 131 together form spaced T-shaped members.

An electric drive motor 130, through an output gear 132 on the shaft of the motor 130, and through a ring gear 134 coaxial with the shaft 114, rotates a gear

136. The ring gear 134 also rotates the plates 128 and 131 and, through a cylindrical housing 137 rotates the screening basket 108.

The output conveyor section 106 has an output auger 140 having a shaft 142, which is connected to and driven by the gear 136. The shaft 142 extends through only the first two turns of the auger 140, the remainder of which has no shaft.

The drive motor 130 has a second output gear 144, which meshes with and drives a gear 146. The gear 146, in turn, drives the shaft 114 and, therewith, the pelletizer rotor 122, the first conveyor auger 112 and the compactor auger 120 in a direction opposite to the direction of rotation of the screening basket 108.

As can be seen from Figure 2, the inclination of the axis of the shaft 114 is such as to substantially optimise the screening area of the cylindrical screening basket 108, which is immersed in the mixture of liquid and solids to be separated. The angle of inclination of the shaft 142 of the second conveyor auger 140 of the output conveyor 106, however, is disposed at a substantially steeper angle of inclination.

Figures 2d-f show a modification of the pelletizer 121 of Figures 2b and 2c. The pelletizer illustrated in Figures 2d-2f is indicated generally by reference numeral 121a and, instead of the cylindrical walls 125 and 126 and the extrusion block 129 of Figures 2b, has a cylindrical wall 126a formed with outlet slots 124a and a cylindrical extrusion block 129a at the exterior of the wall 126a. The extrusion block 129a is formed with extrusion slots 127a having outwardly convergent inner portions 123a (Figure 2f ). The remainder of each slot 127a is defined by a pair of parallel, generally flat surfaces 130a, which are interrupted by opposed pairs of radial ribs 132a.

Figures 2g shows a broken-away end view of a piece of solid material extruded from one of the slots 127a and indicated generally by reference numeral 132a. The solid material piece 132a has V-shaped indentations 134a which extend longitudinally thereof and are formed by the ribs 132a, and also fissures 136a, which are formed on expansion of the solid material as it leaves the slot 124a. The indentations 134a and the fissures 136a serve to enable moisture to penetrate

into the interior of the extended solid material in order to soften the material and to promote biological action when the material is used for compost.

Referring now to Figures 2h which shows in greater detail components of the basket 108, it will be seen that the basket 108 is formed by rings 150a, 150b and 150c, which are connected together by rods 152 to form the cylindrical basket 108. The rings 150a, 150b and 150c are each formed by flat metal annuli, the rings 150a having the greatest radial dimensions, the rings 150c having the least radial dimensions and the rings 150b having radial dimensions intermediate those of the rings 150a and 150c. Arms 154 are interposed between the rings 150a and 150b. The arms 154 serve as spacers and project radially inwardly, beyond the rings, where they are connected together by a further metal rod 156. Spacers 158, located radially inwardly of the rings 150a, 150b and 150c, are interposed between the arms 154 and are likewise secured by the rod 156. At the radially innermost ends of the arms 154, a longitudinally extending strip-shaped member 159 is mounted at opposite ends thereof on a pair of arms 160 which, in turn, are pivotally mounted on the rod 156 for pivotation about the axis of the latter under the action of a spring 162 interconnecting the strip-shaped member 159 and one of the arms 154. The spring 162 is a tension spring and, thus, biases the strip-shaped member 159 for pivotation in a clockwise direction, as viewed in Figure 2a, about the rod 156.

One of the arms 160 carries a roller 164 which, as the basket 108 rotates, rolls against a fixed guide plate 166 located at the upper end of the basket 108. This guide plate 166 deflects the roller 164 radially inwardly, thus deflecting the strip-shaped member 159 so as to align it with the lengths of the arms 154. In this way, solid material picked up by the arms 154 and the strip-shaped member 159, as the latter travels through the lowermost portions of its path of travel on rotation of the basket 108, is deposited onto the auger 112. The dropping of this solid material from the strip-shaped member 159 and the associated arms 154 into the auger 112 is facilitated by an overhead spray 168.

Figure 2i shows a modification of the basket which in this case comprises single radially wide rings 150d separated by pairs of rings 150e of intermediate

radial width, which in turn are separated by three narrow rings 150f.

When it is required to clean or service the apparatus shown in Figure 2, the entire apparatus may be pivoted upwardly, in a clockwise direction as viewed in Figure 2, about a pivotal support indicated generally by reference numeral 160. Figure 3 shows a separator apparatus indicated .generally by reference numeral 200, which has a separator section indicated generally by reference numeral 202, a compactor section indicated generally by reference numeral 204 and an output conveyor section indicated generally by reference numeral 206. The separator section 202 has a cylindrical separator basket, indicated generally by reference numeral 208, which is similar to the separator basket 108 of Figure 2 and which, therefore, will not be described in further detail. A shaft 210 is provided with a first conveyor auger 212, within the separator section 202 and a compactor auger 214, which forms an extension of the first conveyor auger 212. A cutting device 216 which is similar to the cutting device 28 of Figure 1, is fixed to the compactor auger 214 at the upper, outer end thereof for slicing the compacted solids into pieces which drop into the second conveyor 244.

An electric drive motor 218 has an output gear 220 which meshes with and rotates a ring gear 222. The ring gear 222 is fixedly connected to a sleeve 224, which is rotatably mounted in bearings 226. Four annular members 228 (Figure 3A) are provided within the sleeve 224 and are fixedly connected by welding to the latter and, also, to the outer periphery of the compactor auger 214 for imparting drive to the latter and, thus, to the shaft 210 and the first conveyor auger 212.

Through meshing gears 230 and 232, and through a pinion 234 which meshes with an internally toothed ring gear 236 at the lower, input end of the screenings basket 208, the latter is rotated about an upwardly open trough 238 containing the first conveyor auger 212. In this way, the solid material picked up by the rotating screening basket is deposited into the first conveyor auger 212 in the same manner as that described above in connection with the embodiment of Figure 2. Longitudinal metal strips 239 are spaced around the auger 212 and 214.

The ring gear 222 meshes with a further gear 240 on the lower end of a shaft 242 of a second conveyor auger 244, within the output conveyor section 206,

for rotating the second conveyor auger 244 and, thus, removing in an upward direction the cut pieces of solid material dropping from the cutting device 216. The slot 242 extends through only the first two turns of the auger 244.

As will be apparent from Figure 3, the angle of inclination of the second conveyor auger, which in this case is the auger 244, is once again substantially greater than that of the first conveyor auger.

The arrangement shown in Figure 36 may be modified by replacing the four annular members 228 by a single helical member 250, which is fixed, by welding, to the periphery of the auger 214 and to the inner surface of the sleeve 224.

The entire apparatus of Figure 3 can be pivoted upwardly in a clockwise direction as viewed in Figure 3, about a support pivot indicated generally by reference numeral 252, for cleaning and/or servicing of the apparatus.

Figure 4 shows a further separator device 35 indicated generally by reference numeral 300. The separator device 300 has a separator section 302 and a compactor section 304, which are similar to the separator section 202 and the compactor section 204 of Figure 3 and which, therefore, are not described in further detail.

In this embodiment, however, the output of the compactor is not provided with a cutting device for cutting the compacted solid material, nor a pelletizer device such as that of Figure 2 for pelletizing the solid material. Instead, the compactor auger, which in this embodiment is indicated by reference numeral 306 and which is mounted on an auger shaft 308, is extended as a conveyor auger 310.

The shaft 308 is connected through a universal joint 311 to a further auger shaft 312, which extends upwardly at an inclination greater than that of the shaft

308 and which is provided with a second or output conveyor auger 314. The auger 314 terminates in a radial plate 316, which serves to retain the solid material which has been forced beyond the plate 316. The solid material is at least partly prevented from rotating by means of a plurality of stationary metal strips 318, which are spaced around the augers 310 and 314.

Figure 5 shows a separator apparatus which is designed to separate solid materials floating in a liquid in a channel and, in addition, to pick up settlings, i.e.

sediment such as sand, mud and sludge, and other objects such as stones and gravel from the bottom of the channel.

The apparatus shown in Figure 5 is indicated generally by reference numeral 500, and has at its lower end an auger indicated generally by reference numeral 502 for removing the settlings from a recess 504 formed in the bottom of a channel containing a liquid 506, in which waste material floats.

The apparatus 500 also has a cylindrical screen indicated generally by reference numeral 508, an outer auger indicated generally by reference numeral 510, which is coaxial with and extends around the auger 502, an inlet indicated generally by reference numeral 512, a compactor and pelletizer unit indicated generally by reference numeral 514 and two outlet conveyors indicated generally by reference numerals 516 and 518. The inlet 512 has a funnel 519 through which substances may be introduced into the outer auger 510 for conditioning the solids conveyed by the latter. The screen 508 is constructed similarly to the screen 108 of Figure 2 and, therefore, will not be described in greater detail. However, the screen 508 is provided with a heater element 520, which is wound in a helical fashion around the periphery of the cylindrical screen 508 and serves to heat the latter and the waste material within the screen 508. The mixture of liquid and floating solid material travelling along the channel 506 enters the lower end of the screen 508, in the manner described above, and the solid material is then removed from the liquid and deposited into the outer auger 510, which extends through the screen 508 and upwardly therefrom to the compactor and pelletizer unit 514. At the opening 512, additional substances can, if 20 required, be added to the solid material being conveyed upwardly by the outer conveyor 510, for the purpose of treating the solid material before it is compacted.

The inner conveyor 502 extends through the compactor and pelletizer unit 514 and is connected, through a universal joint (not shown) in a manner similar to that described above with reference to Figure 4, to an outlet auger (not shown) in the outlet conveyor 518.

The compactor and pelletizer unit 514 is similar to that shown in Figure

UB

2 and, therefore, will not be described in greater detail.

The outlet conveyor 516, which corresponds to the conveyor 106 of

Figure 2, serves to convey upwardly the pellets produced by the compacting and pelletizing unit 514. The outlet conveyors 516 and 518 have an inclination substantially greater than the inclination of the inner and outer augers 502 and

510, so as to save space.

Figures 6 through 10 show a different type of apparatus for picking up sediment from the bottom of a channel in front of a separator screen. More particularly, in Figure 6 there is shown a duct, indicated generally by reference numeral 600, which may, for example, be a concrete trough, defining a channel for flow of waste water or sewage in the direction of arrow A.

A separator screen, indicated generally by reference numeral 604, forms part of a separating apparatus such as those described above with reference to Figures 1 to 4, and a sediment pick-up mechanism indicated generally by reference numeral 606 is provided upstream from the separator screen 604.

The sediment pick-up mechanism, as shown in Figure 7, comprises a rectangular front portion 608, formed with an opening 610 through which the waste water can flow to the screen 604. The front portion 608 is spaced upstream from a rear portion 612, which likewise has an opening (not shown) through which the waste water can flow to the screen 604.

The front and rear portions 608 and 612 are formed of sheet metal. The rear portion 612 extends downwardly to the bottom of the channel defined by the duct 600, whereas the bottom of the front portion 608 is formed with a horizontally elongate opening 613, through which sediment, indicated generally by reference numeral 614, can travel along the bottom of the duct 600 into the space between the front and rear portions 608 and 612. A drive chain indicated generally by reference numeral 616 in Figure 8 is provided for driving scoops, one of which is indicated by reference numeral 618, and plates 620 along the bottom of the duct 600 between the front and rear portion 608 and 612 so as to pick up the sediment, which is then deposited from the scoops 618 through a funnel 622 into an outlet duct 624.

Alternatively, the sediment picked up by the bucket 618 may be deposited

into laterally offset outlet ducts, shown in broken lines in Figure 7 and indicated by reference numerals 626 and 628, or may be carried laterally for discharge into any suitable container, for example a truck 629, also shown in broken lines in Figure 7. The drive chain 616 is illustrated in greater detail in Figures 9 and 10, and travels along a track formed by a pair of L-section metal channels 630 and 632. The drive chain comprises links 634 and 636, connected by pins 638, which extend through ball bearings 640 between the plates 634. The pins 638 project laterally into connecting members 642 which, in turn, carry the plates 620, as shown in Figures 9 and 10, and the scoops 618.

The cylindrical screens described above and illustrated in Figures 1 to 6 of the drawings are formed by a plurality of ring-shaped or annular members.

Referring now to Figures 11 through 13, reference numeral 700 indicates generally a screen element which may advantageously be employed instead of the annular screen bars of the separator sections of Figures 1 through 5.

The screen element 700 comprises a metal strip 701 which is formed in a meander or serpentine shape having a plurality of radially inwardly open concavities or loop-shaped formations 702 alternating with radially outwardly open concavities or loop-shaped formations 703. Annular radially outwardly extending projections 705 in the interiors of the formations 703 define circular openings 706, the projections 705 being formed in one piece with the strip 701.

As illustrated in Figure 12, the screen element 700 is cut in one 'piece from a metal strip 708, with slots 709 having convergent opposite sides 710 extending into the openings 706 from the opposite sides of the strip 701.

After the strip 701 has cut from the strip 710, the opposite ends of the strip

701 are drawn together and welded together to form the endless screen element

700 extending symmetrically about a central point P as shown in Figure 11. This deformation of the strip 701 causes the opposite sides 710 of the slots 709 to be drawn together into abutment with one another, thus closing the slots 709.

A plurality of such screen elements, indicated by reference numerals 712 in Figure 13, are then secured together by connecting or securing rods, one of

which is shown in Figure 13 and indicated by reference numeral 714, to form a separating screen. Spacers 716 are provided on the securing rods for maintaining drainage gaps or spacings between the separating elements 712.

By forming the separating elements in the endless meander or serpentine shape shown in Figure 11, the separator screen or section is provide with an internal peripheral length which is much greater than that of a separating screen having substantially the same diameter but formed of annular screen elements or bars.

Thus, the separator screen formed by the screen elements 712 has a substantially larger effective area than a cylindrical screen of the same diameter, resulting in a substantially more efficient utilization of space.

Figures 14 and 15 show a modification of the apparatus of Figure 6, in which the sediment pick-up mechanism 606 of Figure 6 has been omitted and has been replaced by an auger 650 for removing sediment, for example sand, from the bottom of the duct 600. The auger 650 extends forwardly, i.e. upstream, of the separator screen 604. In this case, the bottom of the duct 600 is formed with a recess 652 for receiving a lower end 654 of the auger 650.

The inclination of the auger 650 is such that the axes of the auger 650 and the cylindrical separator screen 604 are parallel to one another, the auger 650 being almost level with the top of the separator screen 604 and extending between the separator screen 604 and a side wall 654 of the concrete duct 600.

The auger 650, as viewed in Figure 15, is located at the lefthand side of the separator screen 604, but may alternatively be provided at the opposite side of the separator screen 604, as shown in broken lines in Figure 15 and indicated by reference numeral 650a.

The auger 650a is also parallel to the axis of the separator screen 604. Furthermore, the augers 650 and 650a may be replaced by a different auger, which is shown in broken lines in Figure 14 and indicated by reference numeral 650b, and which has a substantially steeper inclination than the augers 650 and 650a.

In the embodiments of the invention illustrated in Figures 15 and 16, two cylindrical separator screens 712 A and 712B are provided at opposite

sides of a double screw conveyor indicated generally by reference numeral 740.

The double screw conveyor 740 comprises an outer screw conveyor indicated generally by reference numeral 741 and formed by a cylindrical sleeve

742 and by a screw 744 on the sleeve 742, and an inner screw conveyor indicated generally by reference numeral 745 and comprising a shaft 746 provided with a screw 748.

The double screw conveyor 740 is provided in a cylindrical casing 750 formed with an opening 752 through which screenings can be deposited by the separator devices 12A and 12B into the outer screw conveyor 741, i.e. between the casing 750 and the sleeve 742.

The inner screw conveyor 745 projects axially downwardly beyond the outer screw conveyor 741 and through a tube 749 for picking up sand and other grit form the bottom of a waste water channel and for conveying the sand or other grit upwardly for discharge from the upper end of the double screw conveyor 740.

The embodiment of Figure 16 is similar to that of Figure 17 except that there is in addition provided a microscreen, indicated generally by reference numeral 754, which is provided between the opposite ends of the screw conveyors and which serves to screen, for example, solid material from a slurry into an inlet hopper 756 opening into the outer conveyor.

Figure 17 shows a compact, combined separator screen, pelletizer, microscreen and sediment auger apparatus, indicated generally by reference numeral 1000, according to a further embodiment of the invention.

The apparatus 1000 is contained in a tank 1002, which is supported on a foundation 1004 by means of jacks 1006. By adjustment of the jacks 1006, the bottom of the tank 1002 can be tilted so as to be downwardly inclined to the right, as viewed in Figure 15.

An upwardly open inlet 1008 is provided at one end of the tank 1002 for receiving a flow of waste water containing sludge and sediment, e.g. stones and/or sand, mixed with a liquid.

A sediment removal auger 1010 has one end located in the inlet 1008 and is upwardly inclined from that end. The auger 1010 serves to remove

sediment from the bottom of the inlet. Lighter material, for example paper, which can float in the liquid, and sludge are kept above the bottom of the inlet 1010 by means of an annular air duct 1012, to which compressed air is supplied. The compressed air is discharged from the annular duct 1012 in directions inclined upwardly and inwardly with respect to the annular duct 1012 by spaced air discharge nozzles 1014 at the inner side of the annular duct 1012. The thus- suspended material floats into the tank 1002 and enters a cylindrical separator screen or basket 1016, which is similar to the screen 308 of Figure 11 and is co¬ axial with the auger 1010. Instead of employing compressed air to keep the floating material in suspension, a pump or other type of agitation may be employed for that purpose.

The separator screen 1016 removes paper and other floating material from the liquid and the thus-removed material is deposited, through a hopper 1018, into an auger 1019, which extends co-axially around the auger 1010 and is driven in a manner analogous to the driving of the auger 410 of Figures 12

- 12C.

The auger 1019 has a compactor section 1017, immediately following the hopper 1018, at which the pitch of the auger is reduced in order to compact and at least partially dewater the material conveyed by the auger 1019. This has the advantage that the addition of material subsequently into the auger 1019, beyond the compactor section 1017 at a location where the pitch of the auger 1019 is increased, is facilitated and also travel of such additional material downwardly along the auger 1019 is counteracted. The liquid itself, with entrained fine solid material and sludge, passes radially outwardly from the screen into the interior of a cylindrical microscreen 1020, which is also co-axial with the auger 1010.

The microscreen 1020 is formed of a plurality of endless serpentine screen elements 1021, which are spaced apart from one another by a spacing of e.g. 20 cm. The screen elements 1021 are covered, at the interior of the thus- formed cage or basket, by a metal screen 1023.

Water sprinkler or compressed air nozzles (not shown) may be

provided above the microscreen 1020 to assist in removal of sludge from the interior surface of the screen 1023.

The microscreen 1020 removes the sludge and fine solid material from the liquid and deposits them through a hopper 1022 into the auger 1019. Additional material may also be deposited into the auger 1019 through the hopper 1022 in order to facilitate disposal of such additional material and/or to condition the material already in the auger 1019.. For example, microsludge or biologically treated sludge may in this way be added to the auger 1019. The sediment conveyed by the auger 1010 is transferred from the upper end of the latter to the lower end of a further auger 1024, which is upwardly inclined at an angle greater than that of the auger 1010. The upper end of the auger 1024 may, for example, discharge this material into a suitable container, truck or the like (not shown) for transport to a disposal site. The material conveyed by the auger 1019 is fed by the auger 1019 into a compactor 1025 and a pelletizer 1026 which form this material into pellets.

The thus-formed pellets drop into the lower end of an auger 1028, which is parallel to the auger 1024 and which deposits the pellets into a suitable container (not shown), e.g. for transportation. The augers 1010 and 1019, the separator screen 1016 and the microscreen 1020 are all rotated about their common axis by a drive motor 1030, acting through transmission gearing 1032, and for cleaning and other servicing can be pivoted upwardly about a pivot 1034, for example by use of a hoist indicated generally by reference numeral 1031. In a modified embodiment of the invention, which is not illustrated in the drawings, the separator screen 1016 and the microscreen 1020 are driven by separate drive motors. This has the advantage that the separator screen 1016 and the microscreen 1020 can be driven at different speeds and/or at different times. The liquid which passes through the microscreen 1020 leaves the tank 1002 through an outlet pipe 1036, the tank 1002 being provided near its bottom with another outlet pipe 1038 through which the tank 1002 may be

drained, when required.