Flocculation is a complicated and delicate stage since several parameters intervene and react with each other. The study of these flocculation parameters was the subject matter of various works. A view of literature shows that floc strength depends on its dimensions, structure, and age. However. flocculation constants K-A and K-B depend on the settling time, coagulant dosing and initial particle concentration. The aim of this present work is to visualize the effect of the dispersed particle's nature on floc strength and the evolution of kinetic constants K-A and K-B. In order to show the effect of a particle's nature. we studied six various synthetic suspended particles, namely: kaolin, often used by the authors; dam's mud; vegetal peat; mineralised secondary sludge, and two mixtures of mud and peat. The study comes out with: The breakup of floc is more significant when the organic matter rate is important. As the content of organic matter increases, the optimal disturbance power decreases. The interaction between mineral and organic matters is shown: it appears that an addition of mineral matter decreases the breakup constant K-B. The suspensions which contain less than 25% of organic matter behave like mineral suspensions with high effectiveness of turbidity elimination, low coagulant consumption, low residual coagulant, and the formed floc is strong. The flocculation of suspensions which contain 50% or more of organic matter exhibits excessive coagulant with poor elimination of turbidity, and the formed floc is fragile. (C) 2009 Elsevier B.V. All rights reserved.