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 and a second pipe profile, said first pipe profile 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 defining the shape of the second peripheral zone, where the shape of said first pipe profile 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 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 and a second pipe profile, said first pipe profile 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 defining the shape of the second peripheral zone, where the shape of said first pipe profile 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 is selected so as to prohibit any contact between said outer edges of said feed screw and the anti-rotation bars.