mixer 20 for optimisation of the flocculation effect and from there passes on to a strainer belt 22 for the preliminary dewatering operation disposed in a feed hopper 24 which is arranged downstream of the strainer belt 22 of a high pressure belt press 28 is a mixing device 26 in the form of a cell type wheel in which the slurry which has been subjected to preliminary dewatering is mixed with dry material which is recycled in a dry material line 52 of a dry material container indicated at 46 the feed hopper serves as a buffer container for the high pressure pressing operation which in the selected embodiment operates in a cyclic fashion in this case the lowest point of the feed hopper 24 comprises the upper run of an upper filter belt of the high pressure belt press 28 which moves forwardly in the cyclic procedure with adjustable residence times approximately by a respective pressing chamber length a to a first pressing station which is in the form of a variable wedge zone between an upper filter belt and a lower filter belt which permits a precisely adjustable layer thickness at its discharge end and which in addition expels further liquid the layer of slurry which has been subjected to preliminary dewatering is conveyed between the two filter belts in the cyclic procedure into a first pressing chamber in which the slurry is pressed between the two filter belts by perforated pressure plates applied.