Abstract: In one embodiment, the present invention relates to a method for thickening sludge carried along in waste water, wherein the waste water is subjected to a pretreatment reinforcing the flocculation and is subsequently introduced in the direction of gravity into a bath so as to separate the sludge from the water, in which the sludge particles descend under the action of gravity and are removed in the lower portion of the bath characterized in that the waste water, upon its introduction into the bath, is flowed against a baffle, by which the flow of the waste water in the bath is deflected.