When municipal as well as industrial waste water or process water is treated, generally a sludge is formed. In many cases reduction of the moisture content (increase of dry content) of this sludge is desired before the sludge is deposited, transported o - applied to further use.

Dewatering can be effected, for example, in a chamber filter press, whereby a higher dry content and thereby a substantial reduction of the sludge volume is obtained.

Unfortunately, however, when us-ing the chamber filter press for the treatment of waste sludge, a relatively large amount of manual work is required for removing the compressed dry sludge cakes, which have been formed between the filter-cloth coated filter plates in the chamber filter press. The present invention, therefore, has the object to facilitate the utiliz¬ ation of a chamber filter press in connection with the dewater*; ing of waste sludge, and particularly to facilitate the remov¬ al of the sludge cakes from the filter plates and clothes .

This object is achieved according to the invention, in that between a filter cloth covering the plate and the plate one or more membranes are provided, which cover only a part of the total filter plate surface, and which by supply of a medium under pressure can be expanded from the compressed position assumed at the pressing so as to extend or bulge the filter cloth so that the contact surface between the cloth and the filter cake decreases, and thereby also the adherence of the filter cake on the cloth decreases, so that the filter cake due to gravity detaches from the cloth and plate.

The membranes preferably can have the form of hoses, and the expansion is effected by compressed air.

In order to ensure the emptying of the chamber filter press (dropping of the sludge cakes), within the scope of the in¬ vention rubber membranes can alternatingly be filled with air and emptied. The pulsating motion to which the filter clothes thereby are subjected, causes vibrations of the sludge cake, which thereby loosens.

It is to be observed that the invention implies the possibili of separating several (possibly all) filter plates from each other at the same time, whereby the time required for emptyin is reduced substantially. The mechanism for moving the plates besides, can be simple because it can be based on compressed air. The movable parts even can be restricted to be only the plates , and the membrane motion is utilized for separating th plates .

The invention is described in greater detail in the following by way of an embodiment, with reference"to the accompanying drawings, in which

Fig. 1 is a schematic lateral view of some filter plates in a chamber filter press,

Fig . 2 is a front view of a filter plate,

Fig . 3 is a lateral sectional view in greater detail,

Fig . 4 is a sectional view of two filter plates and an intermediate filter cake, and

Fig . 5 shows a complementary separation device.

The chamber filter press shown in Fig. 1 schematically compri es a stand 11, in which a plurality of f-ilter plates 1 are flexibly suspended. When the spaces between the filter plates have been filled with sludge, the filter plate package is com pressed for pressing out the water by means of a hydraulic piston 12 and an intermediate plate 13.

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As appears from Figs. 2 - 4, each filter plate 1 includes on each side cupped recesses 2 so that only a wide edge remains which extends all about. Each filter plate 1 is coated on both sides with filter cloth 3, which is stretched so loosely that it can be pressed into the cupped recess 2 in the filter plate 1. The filter cloth is attached to the filter plate along the edge extending all about and to the centre of the recess 2. In the filter plate drain passageways are arranged, which are shown schematically in the form of a tap at 4.

In each recess 2 in the respective filter plate two (or more) soft rubber hoses 5 are provided, one on each side of the central attachment point of the filter cloth. The rubber hoses 5 are connected to sealed air passageways 15, which extend through the edges of the filter plate 1 out to compressed air connections (not shown). The hoses 5 are closed at their opposite ends. ......

When after a completed pressing cycle the respective filter cakes are to be released from the filter plates, the rubber hoses 5, which are completely compressed, are filled with compressed air via the air passageways 15, so that the hoses expand and stretch the filter cloth outward from the filter plate, as shown in Fig. 4. Hereby the possible contact surface between the completely pressed filter cake and the filter cloth decreases, and the filter cake, therefore, easily can drop down from the filter plate. In Fig. 4 is shown just when the filter cake has been released from the adjacent filter plates. Due to the rubber hoses 5 being sealed at their free ends, compressed air cannot leak out and, respectively, press water cannot enter. It is, however, also imaginable that the two hoses are united to one hose.

It can, of course, be imagined within the scope of the invent¬ ion tha the membranes have designs other than rubber hoses,

and also the pressure medium may be another one than air.

As an alternative to the "opening" or separation of the filte plates as described above, a wheel 9 can be used which is located above the filter plates and upon rotation moves one plate at a time, in that a recess 10 in the wheel hooks on a pin attached to _. the respective filter plate. The distance, through which each plate is moved, is determined by the wheel diameter. The wheel is fixed in vertical direction and moves horizontally when a plate is being moved, whereby the plate next ^' in turn is moved at the next wheel rotation. This com¬ plementary opening mechanism is particularly motivated when the filter press has great length, because then the force from the membranes may not be sufficient for the distribut¬ ion of the filter plates .

From Fig. 5 appears in detail how the filter plates are flex¬ ibly suspended on horizontal, horizontally movable pins 7 via strips or the like 8.