Coagulation/flocculation apparatus for the treatment of a hydraulic flow of any type of liquid, upstream of a physical separation element, in particular upstream of a flotation unit, or of a filtration unit, in particular a membrane filtration unit, which apparatus comprises at least one coagulator with injection of coagulant, followed by a flocculator, which are successively passed through by the hydraulic flow, in which apparatus: the coagulator comprises a reactor (1) for injection of coagulant under high energy, followed by a low-energy coagulation reactor (2); an intermediate high-energy element (3) is placed between the coagulation reactor (2) and the flocculator (4); and the flocculator is a static flocculator of piston type (4) having the same width as the physical separation element (5) located downstream.