Abstract: The invention relates to a solid bowl centrifuge with a horizontal elongated, hollow, rotatable, solid-wall bowl (2) with an inlet and an outlet and a rotatable screw conveyor with a shaft (6) and helical screw (7) rotatable mounted inside said bowl and extending substantially the full length thereof. It is mainly characterized in that on the shaft there are mounted a number of truncated conical discs (24), whereby the discs are directly surrounded by the helical screw. With such design the decanter capacity can be increased and the polymer consumption reduced. Further power consumption can be reduced by obtaining the same performances as the traditional decanter at lower rotational speed (lower g-force).