JPS621422A - Apparatus for dehydrating sludge - Google Patents

Abstract

PURPOSE:To surely perform the dehydration of sludge, by contacting sludge with a compression belt at a loop angle smaller than the loop angle to the turning means of an endless screening belt. CONSTITUTION:The titled apparatus constituted of a filter zone 10, a suction zone 12 and a pressure zone 14. The preparatorily dried sludge fed from the suction zone 12 by an endless screening belt 18 is compressed on the drive roller 20 of the pressure zone 14 by a compression belt 30 and separated from the above mentioned belt 18 as a paper like sludge cake. At this time, because the loop angle of the compression belt 30 around the drive roller 20 is smaller than that of the screening belt 18 around the same drive roller 20, the paper like band 74 of sludge can be simply separated from two belts. As a result, the dehydration of sludge can be surely performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sewage sludge dewatering device, and particularly to a device that sucks water in sewage sludge through a screening belt and dewaters the sludge.

Traditional methods of naturally dewatering sludge in sludge drying beds have been precluded by a lack of space and labor. Therefore, it is necessary to artificially dehydrate the sludge to the point where it can be scooped up with a hoe and to make it easier to transport.

Various devices have been proposed to achieve this purpose. For example, after using a coagulation accelerator with a relatively high σ, considerable negative pressure is applied to the sludge spread on an endless screening belt from below the screening belt, and the sludge is dehydrated by suction. It is known that the outfit that performs this.

However, in conventional devices of this type, a large amount of P liquid dehydrated from sludge flows into the suction vibrator itself that supplies negative pressure, making it difficult to supply sufficient negative pressure. .

The present invention has been made in view of the above points, and an object thereof is to provide a sludge dewatering device that can reliably dewater sludge.

That is, the sludge dewatering apparatus of the present invention includes an endless screening belt that continuously conveys the sludge lump from the filtration zone to the suction zone and the squeezing zone, and a cough screening belt that suctions the water to be filtered. a suction chamber provided in the suction zone and transverse to the direction of travel of the endless screening belt to distribute the conveyed sludge onto the endless screening belt with a substantially uniform thickness; , sludge dispersion means disposed near the boundary between the V filtration zone and the suction zone, and the J
! [comprising a diverting means provided in the squeezing zone for deflecting an end screening belt, and a squeezing belt provided to press the pre-dried sludge in the suction zone onto the diverting means; The squeezing belt is in contact with the sludge at a smaller loop angle than the loop angle of the & end screening belt relative to the diverting means.

Another feature of the invention comprises the step of artificially dewatering sewage sludge by using an endless screening belt and spreading the sludge on said screening belt, with or without the addition of a coagulation accelerator; Its feature is that the sludge spread out on the screening belt passes continuously through the PVA zone, the suction zone at a slightly lower pressure, and finally the squeezing zone.

By combining dehydration with FA, suction, and compression, it can be done at low cost.
High dehydration effect can be obtained.

Hereinafter, preferred specific examples of the present invention will be explained based on the drawings. The plant as a sludge dewatering device has three consecutive zones: a filtration zone 10, a suction zone 12 and an expression zone 1.
Consists of 4. Sewage sludge 16 is introduced via an agitation device 62 . The stirring device 62 is equipped with a stirring screw drive mechanism and mixes the introduced sludge 16 with a coagulation accelerator 68. It is noteworthy that the amount of coagulation accelerator required in this new plant is significantly less than that required in the conventional plant. The sludge 16 mixed with the coagulation accelerator 68 in the filtration zone 10 is dispersed onto the endless screening belt 18 from the stirring device 62 . In this zone, the screening belt 18 is arranged with a slight upward slope in the direction of travel.

A dispersing device or roller 32 serving as a sludge dispersing means functions to distribute the sewage sludge onto the screening belt 18 in a uniform width and thickness. Due to this equalizing effect, at the same time the screening belt 18 is coated with an even layer of sludge before reaching the suction zone 12. The dispersion device or roller 32 may be an applicator knife 34 transverse to the direction of travel of the screening belt 18 and spaced apart from the belt 18 at a constant distance. The coating knife is No. 1b.
According to the figure, it is arranged perpendicularly to the surface of the screening belt 18. However, it may also be arranged as in FIG. 1C, in which case the lower deformation distribution stage 36 is inclined in the direction of travel of the screening belt 18. It is also possible to use a roller 32 such as the first δ instead of the dispersing knife.

Said roller 32, which is likewise arranged at an adjustable spacing with respect to the screening belt, may be of the free-rotating type, or rotate the roller 32 in the direction of travel or in the opposite direction of the screening belt 18! H1)
Said rollers, which may be connected to a JR system, disperse and spread the sludge 16 more completely onto the screening belt 18. Either type of dispersion device is placed proximate the forward end of the filtration zone 10.

In the filtration zone, the screening belt 18 functions as a door cloth. That is, a portion of the moisture content of the sludge 16 falls freely through the screening belt 18 solely due to its own gravity.

Actuation takes place without applying pressure. That is, the screening belt 18 is not sucked from below, and the molecules I! , no pressure is exerted on the sludge except for the pressure exerted by the rolls 32 . However, the above part Wi
The pressure applied by the device is negligible.

Falling moisture is collected in tank 76 and then drained into sump 56 via vibrator 78a.

A tension roll 80 of the screening belt 18 is mounted within the PA zone 10 . Suction zone 1
2 is directly connected to the rear of the filtration zone 1o in the traveling direction. The suction zone 12 essentially consists of a completely closed suction chamber 26. A permeable support member 22 is mounted on top of the suction chamber 26 over which a screening belt 18 slides to transport the sludge cake 16 spread onto the screening belt 18. The support member 22 may be a grid plate or a perforated plate or any other suitable flat transparent plate-like member with openings 24 of some shape. The sludge cake 16 closes the passage of the chamber 26 and the screening belt 18 from above the opening 24 . The elastic seals attached to the cm frame on both sides ensure n i as side guides and seals.

The chamber 26 includes a side opening 52 connected to a suction vibrator 54 in order to establish a light low pressure, for example, about 500 to 2000 xaAQ. The opening 52 is arranged on the side of the chamber 26 at a considerable distance from the holding tank 42 arranged below, so that there is no risk of the suctioned fluid entering the suction opening 52.

The fluid may be collected within the tank. The vibrator 54 is connected to a collection vibrator 85, which is guided to the evacuation trap 84. The discharged moisture is captured by the discharge trap 84 and conveyed to the drain sump 56 via the vibrator 86. A vacuum pump 88 as a suction means, which is schematically illustrated, functions to establish a low pressure and a vibrator 87
connected via. It is preferable to configure the suction means in this way because negative pressure can be supplied more reliably and sludge can be reliably dehydrated by suction.

The water sucked into the chamber 26 from the sludge 16 and collected in the holding tank 42 flows in an inclined direction and flows into the vibrator 43 from the outlet 40. The vibrator 43 extends to the lowest part of the water surface of the drainage basin 56, and low pressure prevails in the chamber 26, so that the P liquid constantly rises in a portion of the vibrator 43, which is formed as a vibrator made of a transparent material, for example. ing. The degree of this increase can then be used as a measure of the underpressure present within chamber 26.

Details of the squeezing zone 14 connected to the rear of the suction zone 12 are shown in the left-hand part of the first electrogram. In the squeezing zone 14, the screening belt 18 rotates along a relatively large diameter impermeable drive row 520.

The sludge 16 pre-dried in the filtration zone 10 and the suction zone 12 is compressed by a compression belt 30 that is conveyed in the advancing direction from the introduction part of the compression zone 14 via a tension roller button roller 28a. The squeezing belt 30 is transparent and is driven along the screening belt 18 via rollers 28 having a total number of 3 g in this example. In this specific example, the roller 28b serving as the central drum controller is fixedly arranged, and the tension roll beating roller 28b
The axis of can be formed as a support and pivot axis of the tension roll 2111a.

For this purpose, the axis of the tension roll 28b supports a length-adjustable extension rod 94, which allows, for example, two opposing screws and the 11
! The length can be adjusted by means of a threaded sleeve. In this way, the distance between the axes of the rollers 28b and 28a is adjusted, and thereby the tension of the squeeze belt 30 is also adjusted, and by adjusting this tension the drive roller 2 as a deflection means is adjusted.
The pressure applied to the sludge cake 16 between the screening belt 18 and the squeeze belt 30 can be adjusted accordingly. Additionally, the axis of the tension roll or O-ra 28a may be loosely fixed at an adjustable angle from the parallel lines of the screening belt 18 in the direction of the arrow, so that the sludge cake 16 is gradually removed. Squeezed gradually] is sent to the second stage.

The squeezing takes place between the screening belt 18 and the squeezing belt 30 in the area of the drive roller 20. f Since the drive roller 20 is impermeable, the water remaining in the sludge cake 16 passes through the squeezing belt 30, is collected in the holding tank 90, and is discharged via the vibrator 91 into the drainage sump 56.

Although not necessary, a slotted suction boat 60 may be opened and connected to a suction collection vibrator 85 to assist in this process. Said vibrator is guided from the back into the area of the drive roller 20. It faces the squeezing belt 30. The water sucked in by the suction boat 60 is captured by a simple conventional device (not shown) and then transported to a holding tank 90.

In most cases, a paper band 74 of sludge VB quality is formed from the sludge cake 16 in the pressing zone 14, which can be easily conveyed off via a conveyor belt 75 and subsequently removed from the plant in a suitable manner.

As is clear from the figure, the loop angle of the squeezing belt 30 around the drive roller 20 is smaller than the loop angle of the screening belt 18 around the same drive roller.

The papery band 74 of sludge material therefore simply separates from the two belts.

The press belt 3o returning inside the press zone 14, that is, the press belt between the rollers 28c and 28b, can be cleaned of adhering sludge particles by a suitable cleaning device 73.

In this case, the sludge that has been gradually dewatered in stages has no tendency to enter and adhere to the openings of the press belt 30 and the screening belt 18, and therefore cleaning for the purpose of complete cleaning of the press belt is not necessary. It should be pointed out that the amount of water required for the process is very small and that only occasional washing steps are required.

The cleaning of the screening belt 18 on its way back can also be carried out in a simple manner by means of a freshwater utilization device 77 arranged between the drive roller 20 and a further drum controller 79. Washing water is collected in a small tank and conveyed to a drainage basin 56 via a vibrator 91.

Water necessary for the cleaning process is delivered via the vibrator 50.

Alternatively, a relatively clean P solution may be used.

Finally, the screening belt 18 that has passed the drum controller 79 is guided to the primary tension roller 80, after which the screening belt 18 begins a new circulation necessary for continuous operation.

Incidentally, the suction may be formed in multiple stages, and the low pressure may be gradually increased in each stage in the sludge transport direction. Due to the multi-stage configuration of the suction zone, a high degree of plasticization is achieved in the final suction stage despite the careful suction of the cut and a smooth transfer of the sludge cake to the squeezing zone.

FIG. 2 is an overall view showing another specific example of the present invention. In this example, the same reference numerals as in FIG. 1a, FIG. 11:1, and FIG. 10 are the same members as in the previous example. ell in the same way, detailed explanation of these will be omitted.

The sludge 16 pre-dried by the filtration zone 10 and the suction zone 12 is led to the squeezing zone 14. A pressing belt 30 is rolled over this sludge. This squeeze belt runs in the conveying direction at the entrance to the squeeze zone 14 before the tension roller 28 . The squeeze belt 30 is transparent;
In this example, it is guided through all three rollers 28, 29, 39 and driven by the screening belt 18. In this specific example, the intermediate steering roller 29 is in a fixed state, and the axis of the tension roller 28 is
It may also be configured as a support and pivot point for use. roller 2
The axial distance between 8 and 29 is adjustable, and thereby the tension of the compression belt 30 can be adjusted. By adjusting this tension, the pressing force g1 on the driving roller 20 and the F'3 mud mass 16 between the screening belt 18 and the pressing belt 30 can also be adjusted freely. Furthermore, the axis of the tension roller 28 can be fixed in a position slightly angled from the parallel of the screening belt 18 in the direction of the arrow. This is to slowly compress the sludge mass 16 little by little. Such a configuration is the same as the specific example described above.

In the squeezing zone 14, paper-like bands or crushed sludge material are produced from the sludge mass 16. This can be easily carried away via the screening belt 82 and conveyed in a suitable manner to the zigzag zone 15 formed as the fourth drainage zone.

The zigzag zone 15 consists of a number of rollers 18 whose axes are transverse to the direction of conveyance of the screening belt 18.82 and are mounted horizontally to the screening belt 18.82. The O-roughs 8 are horizontal in the conveying direction and are mounted longitudinally with respect to one another so that the screening belts 18.82 guided between the rollers run in an undulating manner during operation. The screening belt 82 is guided around a deflection roller 84 before and after the zigzag zone. This screening belt 8
It is formed as a 2ml belt.

After the sludge mass passes through the pressure strip zone 14 and falls onto the screening belt 82, the sludge mass is conveyed between the two screening belts 18 and 82, and then conveyed in a wave-like manner between the guide rollers 78. be done. At this time, the sludge mass is sufficiently compressed and sheared by compressive stress and shear stress. This results in a further considerable drainage of the sludge mass. It is also possible to run screening belts at different speeds to increase this crushing effect. It is also possible to set a part of zone 15 to a negative pressure state.

The water removed in the zigzag zone 15 is directly transferred to the receiving water W.
176. Since this receiving water tank is an integrated component of the entire device, the entire device enclosed by the casing 86 can be installed as a tight structural unit anywhere in any desired location. After passing through the zigzag zone 15, the sludge mass 16 floats up from the turning row 584 and onto the conveying belt 88 at i/1. d is done. The drained sludge mass is carried away in a very good manner by means of this conveying belt.

Because the degree of shear stress is adjustable, the guide rollers 78, particularly the upper rollers, are mounted movably transversely to the conveying direction. In particular, the zigzag zone may be divided into two separate steps.

In this case, the longitudinal offset of the roller in the first step is smaller than in the second step. This results in greater shear stress in the second step than in the first step. At the end of each step, the rollers may overlap directly, so that the sludge mass is compressed again by compressive stress due to the shear stress.

Finally, the screening belt 18 is attached to the tension roller 8
0, and behind this roller 80 the screening belt 18 begins a new circulation. This circulation is necessary for continuous operation.

Incidentally, in order to make the overall structural dimensions of the sludge dewatering device as short as possible even with the addition of the fourth drainage zone, it is possible to install the fourth drainage zone below the suction zone.

As described above, in the present invention, the pre-dried sludge conveyed from the suction zone by the endless screening belt is compressed by the compression belt on the drive roller of the compression zone, so that the sludge becomes a paper-like sludge cake and becomes endless. Leave the screening belt. In this case, the loop angle of the squeezing belt around the drive roller is smaller than the loop angle of the endless screening belt around the same TIAwJ roller, so that the paper band of sludge can be easily separated from the two belts.

Some examples of embodiments of the invention are listed below.

1. Device according to claim 1, characterized in that: (1) the squeezing zone is arranged in the area of the guide roller of the screening belt;

(2) The screening belt passing through the FIA zone picks up and passes freely through the transit zone in the form of P cloth, moves over the suction chamber covered by the support member in the suction zone, and passes at least two times in the squeezing zone. Device according to any one of claims 1 and 2 and the preceding paragraph, characterized in that it is subjected to the pressure of an endless squeezing belt guided by two rollers.

(3) The screening belt is guided over an impermeable surface in the squeezing zone (
1), <2), and the device according to any one of the above items.

(4) The device according to claim 1 or 2, characterized in that in the filtration zone the dewatering is carried out without negative pressure, and in the subsequent suction zone it is carried out at a slightly lower pressure.

(5) The RF device according to any one of claims (1) and (2) and each of the above items, characterized in that the final stage of the compression zone runs in a vertical direction.

(6) The device according to any one of claims (1) and (2) and each of the above items, characterized in that the compression belt spaced apart from the screening belt moves straight ahead by a certain distance.

(7) A fourth drainage zone is provided behind the squeezing zone, in which shear stress is applied to the sludge mass formed in the squeezing zone. The device according to scope (2).

(8), the preceding item (7), characterized in that the sludge mass is compressed in accordance with the progression of a certain shear stress inside the fourth drainage zone;
The device described in.

(9) The apparatus according to any one of (7) and (8) above, wherein the sludge mass is transported by performing wave-like motion in the transport direction.

(10) The device according to claim (1) or (2), characterized in that in the filtration zone, the screening belt is arranged with a slight upward slope in the direction of travel.

(11) A special FF M characterized in that the dispersion knife is arranged at a distance from the screening belt.
The device according to claim (1) or (2).

(12), the previous item (11) characterized in that the dispersion knife is arranged perpendicularly to the surface of the screening belt.
).

(13) Kl! according to the previous item (12), characterized in that the dispersion knife is inclined in the advancing direction of the screening belt! .

(14), Claim characterized in that the roller is arranged at an opening distance from the screening belt (
The device according to 1) or (2).

(15) The device according to item (14), wherein the roller is of a freely rotating type.

(16), the preceding clause (14), characterized in that the roller can be driven in a direction opposite to the advancing direction of the screening belt;
The device described in.

(17) The device according to item (14), wherein the roller can be driven in the same direction as the screening belt.

(18) Claim (1) characterized in that the suction means includes a suction pump, and the connecting pipe line of the pump opens from part 11 above the holding tank to the suction titonba.
Or the device described in (2).

(19), Claim (1) characterized in that the suction chamber is divided into several chambers with a lower pressure increasing in the direction of travel of the screening belt.
, (2) or the arrangement described in the preceding section (18).

(20), the suction chamber communicates with a water tank via a conduit, said conduit being immersed in said tank, thereby measuring the pressure in the suction chamber VAli! Claim (1) characterized in that it is formed as: (
2) or the device described in the preceding section (18).

(21) Device according to any of the preceding claims, characterized in that the impermeable surface is the surface area of the drive roller for the screening belt of the squeezing zone.

(22) The device according to item (21), wherein the pressing belt presses a screening belt conveyed by an m-movement roller.

(23) A device according to any one of claims 1 and 2 and the preceding clause, characterized in that the squeezing belt can be moved by a screening belt without a self-driving mechanism.

(24), the pressure in the squeezing zone can be adjusted by changing the tension of the squeezing belt. i! Device according to any one of the preceding claims, characterized in that it is flexible.

(25) The company according to any one of claims (1) and (2) and the preceding paragraph, characterized in that the opening angle of the pressing belt with respect to the screening belt is adjustable.

(26) A feature characterized in that a device is formed to freely adjust the tension or opening angle of the compression belt.
5).

(27) The device according to any one of claims (1) and (2) and the preceding paragraph, characterized in that the residual moisture squeezed out of the squeezing belt is suctioned by one or several suction devices. .

(28) A device according to any of the preceding claims, characterized in that the squeezing belt is spaced from the drive roller according to a smaller loop angle than the screening belt.

(30) The apparatus according to the preceding item (28), characterized in that the loop angle is adjustable.

(31) HliS according to claim 1, (2) or any of the preceding paragraphs, characterized in that the final guide roller of the squeezing belt has a diameter essentially smaller than the drive roller of the screening belt. ! .

(32) The device according to claim (1) or (2), having the following features.

(a) An endless screening belt is conveyed freely in the filtration zone as a P cloth, moves in the suction zone above a suction chamber covered with a support member, and in the squeeze zone is an endless squeezing belt supported by at least two rollers. (aa) Dewatering in the 1' filtration zone is carried out without using low pressure. (ab) The screening belt in the filtration zone is arranged with a slight upward slope in the direction of travel. (aC) A device disposed in a direction transverse to the direction of movement of the screening belt in the filtration zone spreads the sewage sludge onto the screening belt with a uniform thickness and width; (ae) said i+a is a dispersion means arranged vertically or obliquely, said i+a being a row wheel arranged at a distance from the screening belt and freely rotating in the direction of travel of the screening belt or in the opposite direction; , (bb) Dewatering of the suction zone is carried out at a very low pressure, (
b) The suction chamber comprises a holding tank inclined towards the outlet and a support member arranged above. ! (bd) The suction chamber consists of several closed chambers, provided with side seals for sewage sludge conveyed by the screening belt through the support member, and furthermore the suction chamber has a low pressure device connected to the suction VAI. subdivided into chambers, the low pressure in each partial chamber increasing towards the direction of travel of the screening belt, (be) a suction device
(bf) The suction chamber communicates with the drainage sump via a vibrator, and the connecting pipe is opened from the upper side of the holding tank into the suction chamber. (CC) the squeezing zone is arranged in the area of the guide roller of the screening belt; (cd) the screening belt of the squeezing zone is impermeable; (ce) the impermeable surface is the surface area of the roller that drives the screening belt of the squeezing zone; (cf) the squeezing belt presses against the screening belt conveyed by the drive roller; obtain. Furthermore, the squeezing zone is movable by the screening belt without having any self-layer VJ machine side, and is constructed so that the tension of the (CO) squeezing belt and the opening angle of the screening belt can be changed at will. (ch) The residual water squeezed out from the compression belt is sucked by 1 g or several suction means, (ci) A screening belt that runs vertically at the final stage of the compression zone. (cj) the press belt is spaced apart from the drive roller according to an adjustable loop angle that is smaller than the loop angle of the screening belt; (ck) the final guide roller of the press belt; has an essentially smaller diameter than the drive roller of the screening belt, (33) in the fourth drainage zone an additional screening belt is guided between the rollers around the screening belt and at least one end roller. The device according to the preceding item (7), (8) or (9), characterized in that:

(34) The device according to item (30), characterized in that the upper roller and/or the lower roller are movable in a direction above adjacent rollers across the conveying direction.

(35) The device according to any one of (33) and (34), characterized in that at least two of the rollers are movable.

(36) The device according to item (35), characterized in that the rollers are mounted so as to press against each other at the ends of each roller block.

(31) Claim (1) characterized in that the fourth drainage zone is located below the suction zone.

(2) and the device according to any one of the preceding sections (33) to (36).

(38), any one of claims (1) and (2) and the preceding paragraphs (33) to (37), characterized in that the integrated reception tank accommodates the water removed in all four drainage zones. 'IAaW as described in Crab.

(39), the water removed in the fourth drainage zone is directly
and the moisture removed in the filtration and suction zone flows into the receiving tank via a conduit (paragraph 38).
Vt direct as described in.

(40) The device according to Pis item (38), wherein the drain port of the receiving tank is mounted at a high position so that a constant water level is maintained in the tank.

(41), the conduit carrying the water removed in the suction zone extends into the water of the receiving tank, and the il pipe conducting the water removed in the F' passage leads above the water level of the receiving tank. Vt1° (42) as described in any of the preceding paragraphs (33) to (40), the entire device is transportable and can be installed anywhere [1j (1), (2) and the preceding paragraph. ¥AI described in any of (33) to (41)! !
.

[Brief explanation of drawings]

FIG. 1a is a schematic explanatory diagram of the device of the present invention, FIGS. 1b and 10 are explanatory diagrams each showing a modification of the filtration zone, and FIG. 2 is a book with a different configuration from FIG. 1'a. FIG. 2 is a schematic explanatory diagram of the invention device. 10...Filtration zone, 12...Suction zone, 14...Compression zone, 16...
Sludge, sludge cake, 18... Screening belt, 20... Roller, 22... Support member, 24... Opening, 26...・Suction chamber, 28...Roller, 30...
Thickness belt, 32...Roller, 34...
- Application knife, 36-... Dispersion means, 40...
...outlet, 42...tank, 52...
...Opening, 56...Drainage basin, 60...-
・Boat, 62... Stirring device, 68...
・Coagulation accelerator, 73...Cleaning device, 74...
... Paper band, 75 ... Conveyor belt,
76...tank, 77...freshwater utilization device, 79...drum controller, 80...
...Tension roller, 84...Trap,
88... Vacuum pump, 90... Tank, 94... Rod. Procedural amendment form) July 1st, 1986, 2, Title of the invention: Sludge dewatering system d 3, Relationship to the M-correction case Patent applicant name: Kubota Iron Works Co., Ltd. 4, Agent: Shinjuku, Tokyo Shinjuku 1-1-14
No. Yamada Building 5, date of amendment 1B order June 4, 1986
Day (1) Appropriate drawings drawn clearly in black should be supplemented as shown in the attached sheet. (No change in content) (2) Supplement the power of attorney as shown in the attached document. (The attachment to Patent Application No. 69978M of 1985 filed on the same date is incorporated herein by reference.)

Claims (1)

[Claims] an endless screening belt that continuously transports the sludge mass from the filtration zone to the squeezing zone via the suction zone; and a suction chamber provided in the suction zone to suck the water filtered through the screening belt; In order to disperse the conveyed sludge onto the endless screening belt with a substantially uniform thickness, the belt is transverse to the traveling direction of the endless screening belt and is disposed near the boundary between the filtration zone and the suction zone. sludge dispersion means provided in the squeezing zone for deflecting the endless screening belt; and a squeezing belt provided for pressing the sludge pre-dried in the suction zone onto the diverting means. The device comprises: the squeezing belt contacting the sludge at a loop angle smaller than the loop angle of the endless screening belt relative to the diverting means.