Abstract: A circular clarifier includes a skimmer assembly mounted on a rotatable arm of the clarifier. The skimmer assembly includes a parallelogram linkage having a pair of end links pivotably connected between upper and lower intermediate links. The skimmer blade is mounted to one of the end links to skim the liquid containing volume of the clarifier. The parallelogram linkage is mounted to the rotating arm by a support assembly at upper and lower pivot connections. These pivot connections are positioned at central portions of the respective intermediate links such that both of the intermediate links extend outwardly on both sides of the respective pivot connection. Either a counterweight or a floatation element is mounted to the parallelogram linkage to bias the linkage for rotation about the pivot connections to position the skimmer blade in an upper position.

Abstract: An intrachannel clarifier for an oxidation ditch includes an enclosure positioned in the flow path of the oxidation ditch. This enclosure defines a perimeter wall which surrounds an internal volume made up of an upper zone, a middle zone and a lower zone. The cross-sectional area of the internal volume increases progressively from the lower zone to the upper zone. A water inlet port introduces waste water from the flow path into the lower zone, a submerged pipe in the upper zone removes clarified water from the upper zone, and sludge is actively removed from the middle zone via a sludge removal manifold disposed in the middle zone to reduce the residence time of sludge in the middle zone while maintaining a filter blanket of sludge in the middle zone.