A stochastic approach to modelling solid transport in settling tanks Dispersion and settling models for suspended solids (SS) in turbulent flow are in the majority of cases Eulerian and deterministic. They simulate SS transport using a convection-diffusion equation. When the diffusion term is supposed not to be zero at the boundary of a settling tank, we show that an alternative(or equivalent) description of the basic convection-diffusion equation for the concentration of suspended solids consists in modelling the particles trajectories as a stochastic diffusion process. This paper has two aims, firstly to present the proposed stochastic approach and secondly to apply this new method to the calculation of a settling tank’s efficiency. (C) 1998 IAWQ. Published by Elsevier Science Ltd. 277–284 37 1 1998 Water Science and Technology G.Chebbo N.Forgues E. Lucas-Aiguier S.Berthebaud