Abstract: An arrangement for separation by flocculation of flocculable substances contained in a suspension, as such is used particularly for purifying the backwater of deinking installations for waste paper processing, comprises a container supplied by a conduit with a suspension coming from a reservoir and admixed with flocculating agents and with air. The container contains a rotor with vertical shaft from which two arms extend outwardly at different heights. The suspension to be purified is delivered by the shaft and the upper arm, and by means of the lower situated arm leading the upper arm at an acute angle the purified water is removed. The floated-up flocculated substances are withdrawn from the surface as flotation scum and optionally by means of a conveying device through a scum conduit.