NOVELTY - Screw feeder (1) comprises: a screw tube (10) extending in a longitudinal direction, which includes an inlet opening (30) of the organic substances in the region of a first screw tube end (11) and an outlet opening for organic substances in region of a second screw tube end; a screw conveyor (20) arranged in screw tube and extending in longitudinal direction, which is rotatably mounted and set into rotation by a worm drive; a fermenter port for directly connecting outlet opening with biogas fermenter under gas pressure; and a material section in a region between inlet- and outlet openings.    USE - The screw feeder is useful for introducing organic substances into a biogas fermenter under gas pressure.    ADVANTAGE - The screw feeder: achieves improved delivery of the organic solids; and ensures good sealing of the biogas tank, thus it prevents leakage of solids, liquids or gases through the feeder.    DETAILED DESCRIPTION - Screw feeder (1) comprises: a screw tube (10) extending in a longitudinal direction, which includes an inlet opening (30) of the organic substances in the region of a first screw tube end (11) and an outlet opening for the organic substances in the region of a second screw tube end; a screw conveyor (20) arranged in the screw tube and extending in the longitudinal direction, which is rotatably mounted and set into rotation by a worm drive; a fermenter port for directly connecting the outlet opening with the biogas fermenter under gas pressure; and a material section in a region between the inlet- and outlet openings for the compression of the organic substances to reduce a gas passage through the screw conveyor. The material section comprises an extension region, in which the passage cross-section widens between the screw conveyor and the screw tube in the conveying direction and exhibits a constricting portion arranged in the extension region in the conveying direction, in which the passage cross-section reduces between the screw conveyor and the screw tube in the conveying direction. A separation portion comprising many openings in the screw tube and a fluid collection device outside the worm tube is arranged in a conveying direction before the material section. A rinsing liquid feed opening is provided at the second screw tube end in the conveying direction after the material section for supplying a rinsing liquid into the passage cross section between the screw tube and the screw conveyor. At least one screw blade is provided in the region of the second screw tube end, which is detachably attached to the screw conveyor. An INDEPENDENT CLAIM is also included for a biogas plant comprising a gas-tight sealable fermenter containing a solid feed port of a gas discharge port, and a screw conveyor, where the outlet opening is directly connected to the solid feed port or a feed line projecting under fermenter pressure, conveying direction is expanded before the reduction, optional separation of liquid is carried out from the organic material by many radial openings in the screw conveyor prior to compression, and optional flushing of liquid is carried out after compression.    DESCRIPTION OF DRAWING(S) - The figure shows a vertical longitudinal sectional side view of a screw feeder.    Screw feeder (1)    Screw tube (10)    First screw tube end (11)    Screw conveyor (20)    Inlet opening (30)