A screw feeder comprising: - a pipe enclosing a feed screw provided on a rotatory shaft running parallel with the length direction of the pipe , said pipe further comprising a number of dewatering holes ; - a number of anti-rotation bars provided on, and extending along, the inside of said pipe , said anti-rotation bars protruding in a direction towards said feed screw ; - an inlet for receiving a solid-liquid mixture arranged at a first end of said pipe ; and - an outlet arranged at a second end of said pipe for discharging an at least partially dewatered solid from said pipe , wherein said pipe includes at least one longitudinal pipe section having a first peripheral zone provided in the vertically lower area of said longitudinal pipe section and provided with dewatering holes but no anti-rotation bars and a second peripheral zone provided in the vertically upper area of said longitudinal pipe section provided with anti-rotation bars , characterized in that the overall pipe profile of said pipe section is composed of two differently shaped pipe profiles, a first pipe profile (P1) and a second pipe profile (P2), said first pipe profile (P1) defining the shape of the first peripheral zone and is a profile selected from: - a square shaped profile; - a profile having a partly circular cross-section with a squashed end or a circle segment removed; - a partly elliptically shaped profile; and said second pipe profile (P2) defining the shape of the second peripheral zone , where the shape of said first pipe profile (P1) is selected to enable the outer edges of said feed screw to remove material overlying said dewatering holes , and where the shape of said second pipe profile (P2) is selected so as to prohibit any contact between said outer edges of said feed screw and the anti-rotation bars . - a pipe enclosing a feed screw provided on a rotatory shaft running parallel with the length direction of the pipe , said pipe further comprising a number of dewatering holes ; - a number of anti-rotation bars provided on, and extending along, the inside of said pipe , said anti-rotation bars protruding in a direction towards said feed screw ; - an inlet for receiving a solid-liquid mixture arranged at a first end of said pipe ; and - an outlet arranged at a second end of said pipe for discharging an at least partially dewatered solid from said pipe , wherein said pipe includes at least one longitudinal pipe section having a first peripheral zone provided in the vertically lower area of said longitudinal pipe section and provided with dewatering holes but no anti-rotation bars and a second peripheral zone provided in the vertically upper area of said longitudinal pipe section provided with anti-rotation bars , characterized in that the overall pipe profile of said pipe section is composed of two differently shaped pipe profiles, a first pipe profile (P1) and a second pipe profile (P2), said first pipe profile (P1) defining the shape of the first peripheral zone and is a profile selected from: - a square shaped profile; - a profile having a partly circular cross-section with a squashed end or a circle segment removed; - a partly elliptically shaped profile; - a square shaped profile; - a profile having a partly circular cross-section with a squashed end or a circle segment removed; - a partly elliptically shaped profile; and said second pipe profile (P2) defining the shape of the second peripheral zone , where the shape of said first pipe profile (P1) is selected to enable the outer edges of said feed screw to remove material overlying said dewatering holes , and where the shape of said second pipe profile (P2) is selected so as to prohibit any contact between said outer edges of said feed screw and the anti-rotation bars . <EOS>