Urban waste water treatment plant, comprising: a tank (1) subdivided in at least two distinct portions (2, 3), said at least two distinct portions (2, 3) comprising at least an accumulation area of the sludge (2) and at least an accumulation area of the liquid phase (3); at least a feeding pipe of the waste water to be treated; at least a recirculation pipe of the liquid phase; at least a discharge pipe of the effluent treated, withdrawn from said at least one area of the liquid phase (3), characterized in that said feeding pipe of the waste water to be treated is configured so that the waste water is inlet on the bottom of said at least one sludge area and in discontinuous mode; inside said at least one sludge area (2) it is provided porous material, contained between two containment planes, configured to allow the filtration of the waste water with removal of the suspended material; said tank (1) is subdivided in said at least two distinct portions by means of one or more vertical partitions (23) lower than the walls of the tank (1), so that the liquid from which the suspended material was removed in said at least one sludge area (2) can overflow from said at least one sludge area (2) to said at least one liquid phase area (3); the bottom of said at least one liquid phase area (3) is connected with the bottom of said at least one sludge area (2) by means of a pipe and pumping means which allow the liquid to recirculate from the bottom of the liquid phase area (3) to the bottom of the sludge area (2).
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