DE29810474U1 - Sludge thickening device - Google Patents

Description

Device for thickening sludge

The invention relates to a device for thickening sludge, sediments from water bodies or the like, in particular excess sewage sludge in sewage treatment plants.

It is known that thickening takes place during sewage sludge treatment. This is done either statically or with the help of machines. In static thickening, gravity is used to allow the solid particles, which have a higher density than water, to settle on the bottom of a settling tank. The thickened sludge is removed using sludge pumps or scrapers. In static thickening, a continuous thickening process has also become known, in which the sludge to be concentrated is continuously fed into a tank.

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Patent Attorneys · European Patent Attorneys - Authorized Representatives before the European Patent Office
Authorised representatives at the Office for Harmonisation in the Internal Market

Lawyer: admitted to the Hamburg courts

Deutsche Bank AG Hamburg, No. 05 28497 (bank code 200 700 00) · Postbank Hamburg, No. 28 42 206 (bank code 200 100 20)
Dresdner Bank AG Hamburg, No. 933 60 35 (bank code 200 800 00)

which is equipped with sludge blades and floating sludge removers. Static thickening has the disadvantage that the achievable solids contents vary greatly. This is due to the different operating systems and the sludge properties. With the help of special machines for sewage sludge thickening, a higher concentration can be achieved in a shorter time. When these are used, additional flocculation or flocculation aids are used which reduce or eliminate the water binding forces. Machines which use the natural gravitational field to thicken the sludge include sieve reactors, screw presses and belt thickeners. In the sieve reactor, the sludge to be concentrated is fed into the interior of a drum container which is covered with a sieve fabric on the outside. With the help of a built-in screw spiral, the sludge is transported through the drum as the drum rotates slowly. The thickened sludge is discharged at the other end of the drum. The filtrate runs through the filter fabric into a collecting tray. In the screw press, the sludge conditioned in the flocculation reactor passes through the free overflow into the screw press in a way that protects the flocs. The subsequent filtration unit consists of a fixed cylindrical slotted screen drum with an internal screw spiral for the sludge transport. In a belt thickener, the thin sludge is evenly distributed on a rotating belt filter or sieve belt and thickened by the effect of gravity.

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Machines for sludge concentration using the artificial gravitational field have also become known, especially centrifuges. Depending on the drum speed, the difference in speed between the screw and the drum and the sludge throughput per 2' unit, considerable thickening and throughput rates can be achieved.

The known mechanical devices for sludge concentration require a considerable amount of space, technology and costs, which are often not feasible for small or medium-sized sewage treatment plants. This also includes the energy required to operate them.

The invention is therefore based on the object of creating a device for thickening sludge, sediment from water bodies or the like, in particular for excess sewage sludge in sewage treatment plants, which makes it possible to achieve a high concentration of the sludge by utilizing gravity while achieving a sufficient throughput. In particular, the expenditure on equipment and energy for this should be minimal.

This object is solved by the features of claim 1.

The device according to the invention also provides a mixing device for sludge and flocculation or flocculation aids. Furthermore, this

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The flocculated sludge is fed into the sludge separator at the top of the sludge separator, which is arranged at an incline, and the concentrated sludge (thick sludge) flows out at the bottom. The filtrate (water) is collected below the sludge separator and drained away. Particularly when the slits of the separator run in the direction of the incline, a simple arrangement of this kind can achieve sufficient concentration of the thin sludge with sufficient throughput. The water separation is particularly effective when the slits run in the direction of the incline. The cost of such a device is extremely low. Flocculation reactors, in which flocculation aids such as polyelectrolytes are mixed with thin sludge, are well known and not very complex. It goes without saying that a wide variety of known apparatus can be used to mix thin sludge and flocculation agents or flocculation aids, in which the mixing process takes place with the aid of a mixer, nozzles, in countercurrent, or the like. Flocculation of the sludge prevents solids from passing through the gaps. The gradient causes the flakes to slide down to the outlet of the slotted screen. At this point, for example, excess sludge from municipal sewage treatment plants has a concentration of 3 to 6%. It goes without saying that the gradient and the gap width can be adjusted depending on the nature of the thin sludge produced. The bars of the slotted screen can be adjustable and set in the desired positions, e.g. using threaded rods on which the screen bars can be slidably arranged.

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It has been shown that the inclination of the screen is preferably in the range of 40 to 50°, preferably in the range of 45°. The use of the device according to the invention is particularly advantageous when a screw pump is present. This is the case in many installed sewage treatment plants. In this case, it is only necessary to arrange the device for mixing with flocculation or flocculation aids after the screw pump, which is then followed by the slotted screen with gradient as described.

It will be necessary to clean the slotted screen from time to time. Water can be used for this, for example filtrate water, process water or waste water from the secondary clarification, which is sprayed onto the slotted screen from above using a suitable nozzle arrangement. The nozzle arrangement can be arranged on a traverse that can be moved along the gradient. Alternatively, a nozzle arrangement can be attached to a swivel arm in order to cover the entire surface of the slotted screen.

Fixed nozzles can also be installed in a suitable arrangement, preferably as slotted nozzles, above the slotted screen. However, the flushing water consumption is higher than with movable nozzles.

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Embodiments of the invention are explained in more detail below with reference to drawings.

Fig. 1 shows schematically a device according to the invention.

Fig. 2 shows a plan view of the slotted screen of the device according to Fig.

Fig. 3 shows a section through the slotted screen according to Fig. 2 along the line 3-3.

Fig. 4 shows a modification of the slotted screen according to Fig.

Fig. 5 shows a modification of the slotted screen according to Fig.

Fig. 6 shows a plan view of the slotted screen according to Fig. 1 with a cleaning device.

Fig. 7 shows a view of the illustration according to Fig. 6 in the direction of arrow. Fig. 8 shows another embodiment for cleaning a slotted sieve.

Fig. 9 shows schematically another embodiment of a device according to the invention.

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In Fig. 1, a sieve reactor 10 is indicated with a rotor 12 within a column-like housing 14. A mixture of thin sludge 18 and flocculation aid, which is fed from a container 20, is fed to the housing 14 at the bottom right at 16. The thin sludge comes, for example, from a secondary settling tank of a sewage treatment plant. The thin sludge is flocculated in the reactor 10 and is applied to the upper end of a slotted sieve 24 via an upper outlet 22. The thin sludge is expediently discharged evenly across the width of the slotted sieve. The filtrate is collected in a pan 26 and returns to the inlet of the sewage treatment plant via an outlet 28. The concentrated or thick sludge enters a container 30 and can be withdrawn from there via a closure 32 and a pump (not shown) for further treatment, stacking and later removal or concentration.

In Fig. 2 it can be seen that the slotted screen 24 has gaps 34 running in the direction of the gradient (see also Fig. 3). The distance and width of the gaps 34 depend on the thin sludge fed in. The gradient of the slotted screen 24 can also be adjusted accordingly.

In Fig. 4, a slotted screen 24a is indicated with a trough 26a, to which a brake flap 25 is hinged. As can be seen, this can be arranged at a smaller angle to the horizontal and thus develop a kind of slipping deceleration. The

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25 can be pivoted and locked into desired angular positions in order to achieve a different deceleration effect depending on the prevailing operating conditions.

Fig. 5 shows a modification of a slotted screen, a so-called curved screen 24b, in which the slots also run in the direction of the gradient. The curved screen can be pivoted in order to change the inclination and thus the filtering effect.

In Fig. 6 and 7 a top view of the slotted screen according to Fig. 1 is shown and it can be seen that guide rails 36, 38 are arranged on both sides of the screen 24, along which a cross-member-like carriage 40 can be moved in the direction of the double arrow 42. Several nozzles 42 are arranged adjacent to the beam 40, which spray water over the entire width of the screen 24. By moving the nozzles 42 along the rails 36, 38, the entire surface of the slotted screen 24 can be cleaned.

Fig. 8 shows a slotted screen 24c corresponding to the slotted screen 24 according to Fig. 1 and 2. A row of nozzles is arranged on a cross member 44, with a swivel arm 46 swiveling the cross member 44 about a horizontal axis of rotation 48 in the direction of the double arrow 50 in order to clean the screen 24c. The drive for this is not shown, nor is the drive for the beam 40 according to Fig. 6.

In Fig. 9, a secondary settling tank outlet 52 is indicated, where a screw pump 54 conveys thin sludge to a mixing section. A rotor 58 in the tank 56 is driven by a motor 60 in order to mix flocculation aid supplied via a line 62 with the thin sludge. The flocculated sludge is fed via an overflow 64 onto a slotted screen 24d, comparable to that of the device according to Fig. 1.

If necessary, a rotor can be dispensed with if a sufficiently long mixing section is available.

Claims (8)

1. Device for thickening sludge, sediments from bodies of water or the like, in particular excess sewage sludge in sewage treatment plants, with a mixing device ( 10 , 56 ) in which sludge and flocculation agents or flocculation aids are mixed and a slotted screen ( 24 , 24 a, 24 b, 24 , 24 c, 24 d) arranged downstream of the outlet of the mixing device ( 10 , 56 ) and arranged with a gradient, wherein the flocculated sludge is fed to the upper end of the slotted screen, the concentrated sludge (thick sludge) is discharged at the lower end and the filtrate is collected below the slotted screen. 2. Device according to claim 1, characterized in that the gaps ( 28 ) of the sieve ( 24 ) run in the direction of the gradient. 3. Device according to claim 1, characterized in that the gap width and/or the inclination of the sieve are preselectable or variable. 4. Device according to claims 1 to 3, characterized in that a column-like flocculation reactor ( 10 ) is provided with an inlet ( 16 ) and an outlet ( 22 ) at the upper end and a mixing rotor ( 12 ) having a series of axially spaced blades, the outlet ( 22 ) being located above the edge of the sieve ( 24 ). 5. Device according to one of claims 1 to 4, characterized in that, in the presence of a screw pump ( 54 ) for conveying the thin sludge up from a basin ( 52 ) or the like, a flocculation reactor or a mixing device ( 56 ) is arranged at the upper end of the screw pump, at the outlet of which the sieve ( 24 d) is connected. 6. Device according to one of claims 1 to 5, characterized in that a rinsing device ( 40 , 42 ; 44 ) is arranged above the sieve ( 24 , 24c ). 7. Device according to claim 6, characterized in that the flushing device ( 44 ) has a pivoting arm ( 46 ) which is pivotably mounted about a horizontal axis ( 48 ), at the lower end of which a nozzle arrangement is attached. 8. Device according to claim 7, characterized in that a row of rinsing nozzles ( 42 ) is arranged on a cross member ( 40 ), which can be moved along a guide ( 36 , 38 ) above the sieve ( 24 ) in the direction of inclination of the sieve ( 24 ).