Screw extruder

A screw extruder comprising a screw shaft rotationally mounted in oppositely located frames and having a conically widening diameter between an inlet port for crude liquid and a discharge port for dehydrated material, and on which screw shaft at least one screw blade extending at a substantially constant pitch is disposed, wherein a filter screen cylindrically surrounding the screw shaft and including a plurality of filter openings is further arranged within the frames, wherein a cleaning device with a plurality of cleaning nozzles for the filter screen and a funnel-shaped filtrate trough disposed below the filter screen are additionally arranged on the outer side of the filter screen, wherein the screw shaft is configured to be cylindrical in the region of the inlet port for crude liquid, to conically widen in the direction towards the discharge port in a central region of the screw extruder, and to be cylindrical in the region of the discharge port, and that the filtrate trough disposed below the filter screen is configured to comprise at least two chambers, or two mutually separated portions, which two chambers are each provided with a drain for filtrate, that the first chamber of the at least two chambers in a region of the inlet port has a longitudinal extension corresponding to at least the length of the cylindrically configured portion of the screw shaft in the region of the inlet port for crude liquid, and that the drain of the first chamber in the region of the inlet port is connected, via a return line for filtrate, to the cleaning device for the filter screen to recirculate the filtrate.