A device for separating solids from waste water comprising: - a support frame provided with at least an inlet mouth, arrangeable internally of a collecting tank of fluids containing a solid fraction dispersed in a liquid fraction, a first outlet mouth of the liquid fraction when separated from the fluid and a second outlet mouth of at least a part of the solid fraction when separated from the fluid, - a first filter screen associated to the support frame so as to intercept the fluid which flows from the inlet mouth to the first outlet mouth and configured such as to retain and accumulate a part of the solid fraction at least at a first surface of the first filter screen, - at least an Archimedes screw associated rotatably to the support frame and provided with a first portion able to transport the solid fraction accumulated by the first filter screen towards the second outlet mouth, - a second filter screen associated to the support frame so as to intercept the fluid flowing from the inlet mouth to the first outlet mouth, located upstream of the first filter screen in an advancement direction of the fluid from the inlet mouth to the first outlet mouth and configured so as to retain and accumulate a part of the solid fraction at least at a second surface of the second filter screen, the Archimedes screw comprising a second portion able to transport the solid fraction accumulated from the second filter screen towards the second outlet mouth, characterised in that the second filter screen exhibits a substantially truncoconical shape, with an external diameter and an internal diameter larger than the external diameter of the Archimedes screw, and is inserted on the second portion of the Archimedes screw with a concavity facing towards the free end of the Archimedes screw located at the inlet mouth. - a support frame provided with at least an inlet mouth, arrangeable internally of a collecting tank of fluids containing a solid fraction dispersed in a liquid fraction, a first outlet mouth of the liquid fraction when separated from the fluid and a second outlet mouth of at least a part of the solid fraction when separated from the fluid, - a first filter screen associated to the support frame so as to intercept the fluid which flows from the inlet mouth to the first outlet mouth and configured such as to retain and accumulate a part of the solid fraction at least at a first surface of the first filter screen, - at least an Archimedes screw associated rotatably to the support frame and provided with a first portion able to transport the solid fraction accumulated by the first filter screen towards the second outlet mouth, - a second filter screen associated to the support frame so as to intercept the fluid flowing from the inlet mouth to the first outlet mouth, located upstream of the first filter screen in an advancement direction of the fluid from the inlet mouth to the first outlet mouth and configured so as to retain and accumulate a part of the solid fraction at least at a second surface of the second filter screen, the Archimedes screw comprising a second portion able to transport the solid fraction accumulated from the second filter screen towards the second outlet mouth,