Mathematical modeling of sedimentation has attracted considerable attention in the past decades, and nowadays, one of the most popular models of secondary settler in activated Sludge processes is the one proposed by Takacs et al. [1.Takacs. G.G. Patry, D. Nolasco, A dynamic model of the clarification-thickening process,Water Res. 25 (10) (1991) 1263-1271]. This model is based on a discretization in finite Volumes (or layers) of the spatial domain, and in a rather inconsistent way, the number of layers is usually considered as a model parameter chosen so as to fit experimental data. In this study, a simple convection-diffusion partial differential equation (PDE) model is first formulated and solved using a Method of Lines strategy allowing the use of various spatial discretization methods with largely improved accuracy and efficiency. Model parameters are estimated using experimental data collected in batch settling experiments by De Clercq [J. De Clercq, Batch and continuous settling of activated sludge: in-depth monitoring and I D compression modeling, Ph.D. Thesis, Universiteit Gent, Faculteit Ingenieurswetenschappen, Belgium, 20061, showing the good model predictive capability. Finally, the PDE settler model is coupled with a standard ASM1 representation of the activated sludge process, and implemented in a MATLAB dynamic simulator. (C) 2008 Elsevier B.V. All rights reserved.