Abstract: A continuous decantation clarifier, wherein liquid to be clarified flows slowly and homogeneously into the interior of the clarifier, includes a first zone through which the liquid initially passes while the liquid is subjected to homogenization and flocculation, this first zone being penetrated in a substantially vertical descending direction by a second zone where the direction of liquid flow is reversed so that the liquid moves in an ascending vertical direction through flakes and solids in suspension in the liquid. In this latter zone such flakes and solids precipitate toward the bottom of the clarifier. The latter having a third zone wherein liquid commences to flow radially in an outward substantially horizontal direction, across frustoconical surfaces or trays, in which the decantation is concluded, the clarified liquid being collected close to the outer peripheries of the trays.