Dispersion and settling models for suspended solids (SS) in turbulent
flow are in the majority of cases Eulerian and deterministic. They sim
ulate SS transport using a convection-diffusion equation. When the dif
fusion term is supposed not to be zero at the boundary of a settling t
ank, we show that an alternative(or equivalent) description of the bas
ic convection-diffusion equation for the concentration of suspended so
lids consists in modelling the particles trajectories as a stochastic
diffusion process. This paper has two aims, firstly to present the pro
posed 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.