Apparatus for clarifying treated waste water in which the waste water is floated and settled in a flotation tank equipped with a rotatable carriage provided with multi-scoop means. The multi-scoop means is rotated as it is passed through the upper strata of the treated waste water for the removal of floated particles or sludge with no appreciable disturbance of the main body of waste water. The multi-scoop carries the floated particles or sludge to a sludge outlet in an efficient manner without clogging by an unique construction self-cleaning in operation.