Abstract: 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.

Abstract: 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.

Abstract: Improved skimmer apparatus for use in dissolved air floatation basins employed in water purification and waste water treatment plants is provided. The invention includes centrally positioned, longitudinal guide rails affixed to the basin and two or more interconnected reciprocating carriages, each carriage having a skimmer blade affixed thereto, the carriages being moveably mounted on the rails. At the effluent end of the basin is an upwardly shaped ramp, and the carriage nearest in proximity to the ramp has a ramp profile duplicating mechanism pivotally mounted to it.