title: One-dimensional modelling of the secondary clarifier-factors affecting simulation in the clarification zone and the assessment of the thickening flow dependence.
abstract: This paper presents a one-dimensional (1-D) model of the secondary settling tank (SST), and the drive for model development is discussed using steady-state simulation results generated with a 2-D computational fluid dynamics (CFD) model. Concentration profiles measured in a flat-bottom circular (fbSST) that is equipped with suction-lift sludge removal, served for CFD model validation. We investigate the factors that may deteriorate the 1-D simulation performance of clarifier models, which incorporate dispersion both in terms of the effluent sludge concentration and in terms of the sludge blanket height. Furthermore, dispersion-models can account for the effect of clarifier flow conditions on thickening performance. However, correlations, found in the literature, are shown to have limited efficiency under the wide flow boundary conditions examined in this study. Optimisation of the 1-D clarifier model structure is proposed by using an overflow dependent dispersion coefficient and including a feed flow dependent reduction factor in the downward convective velocity term. Results obtained show improved simulation performance in the clarification zone and allow for an efficient flow-dependency formulation of the thickening performance.
authors.affiliation: Veolia Environnement Research and Development Center, Chemin de la Digue, B.P. 76, 78603 Maisons-Laffitte, France. benedek.plosz@niva.no
authors.forename: Benedek Gy
authors.initials: BG
authors.lastname: Plósz
authors.forename: Michael
authors.initials: M
authors.lastname: Weiss
authors.forename: Cyril
authors.initials: C
authors.lastname: Printemps
authors.forename: Karim
authors.initials: K
authors.lastname: Essemiani
authors.forename: Jens
authors.initials: J
authors.lastname: Meinhold
mesh_terms: D003198:Computer Simulation; D008962:Models, Theoretical; D012212:Rheology; D012722:Sewage; D014865:Waste Disposal, Fluid
chemical_list: D012722:Sewage