Flocculation process based on water soluble polymers as flocculating agents is still intensively researched nowadays, despite the introduction of these materials about fifty years ago. Dual polymer flocculation or application of new, more sophisticated macromolecules is proposed as a new approach. Simultaneously, more detailed mathematical models of flocculation are developed. The employment of polymer degradation model in population balance equations (PBE) is proposed in the paper. The suspension of chalk in distilled water was flocculated using three types of ultrasonically conditioned commercial flocculants. The experiments were performed using an apparatus for on-line determination of particle size distribution (PSD). The obtained results were compared with simulations using the Class Method. It was proved that the kinetic constant in the aggregation kernel can be described by a function similar to the one showing a change of mean molecular weight of polymer with sonication time. (C) 2011 Elsevier B.V. All rights reserved.