A system for sludge removal in a circular settling tank having a side wall (106) comprises a rotatable drive ring (130) adapted to be interconnected to a scraper arm provided with scraper blades, wherein the drive ring having a plurality of engagement surfaces (134) A traction assembly (140) is fixedly attached to the side wall and comprises a drive wheel (142). By providing a drive wheel with a plurality of engagement rolls (148) adapted to engage the engagement surfaces of the drive ring during rotation of the drive wheel, the drive ring can be rotated essentially without exerting any radial forces on the drive ring.