The mechanical rotating sludge thickener is capable of thickening the sludge up to a concentration of 10{4f1e35c07df61488f28768334a6350a7c20f145341bf5f3233e6477760a58c2c}. The construction is entirely in stainless steel. The sludge is delivered to the external mixer to be conditioned with chemicals and then discharged inside the thickening drum. The drum consists of four zones separated by annular rings, each of which has an adjustable opening to adapt the sludge retention time in accordance with its characteristics.