The paper presents the results of a study carried out using the computer program ZB1 simulating the flocculation of suspended solids. A description of the program is followed by an analysis of the effect of colloidal particle size and settling rate on sol destabilization. It was demonstrated that the tested program is consistent with the classical theories of particle motion and destabilization of colloidal systems. It was also found that the value of the diffusion coefficient increased along with an increase in the particle diameter S, regardless of the settling rate Q. An increase in the particle diameter caused an increase in the diffusion coefficient and allowed to shorten the duration of the destabilization process. (C) 2009 Elsevier B.V. All rights reserved.