CFD modelling of sludge sedimentation in secondary clarifiers

M Weiss, Benedek Plosz, K Essemiani, J Meinhold

Research output: Chapter in Book/Report/Conference proceedingChapter

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Abstract

We present a CFD model that predicts the sedimentation of activated sludge in a full-scale circular secondary clarifier that is equipped with a suction-lift sludge removal system. The axisymmetric single-phase model is developed using the general-purpose CFD solver FLUENT 6, which uses the finite-volume method. A convection-diffusion equation, which is extended to incorporate the sedimentation of sludge flocs in the field of gravity, governs the mass transfer in the clarifier. The standard k-ε turbulence model is used to compute the turbulent motion, and our CFD model accounts for buoyancy flow and non-Newtonian flow behaviour of the mixed liquor. The activated sludge rheology was measured for varying sludge concentrations and temperatures. These measurements show that at shear rates typical of the flow in secondary clarifiers, the relationship between shear stress and shear rate follows the Casson law. The sludge settling velocity was measured as a function of the concentration, and we have used the double-exponential settling velocity function to describe its dependence on the concentration. The CFD model is validated using measured concentration profiles
Original languageEnglish
Title of host publicationAdvances in Fluid Mechanics VI
EditorsM. Rahman, C. A. Brebbia
PublisherWIT Press
Pages509–519
ISBN (Print)9781845641634
DOIs
Publication statusPublished - 2006

Publication series

NameWIT Transactions on Engineering Sciences
Volume52

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Weiss, M., Plosz, B., Essemiani, K., & Meinhold, J. (2006). CFD modelling of sludge sedimentation in secondary clarifiers. In M. Rahman, & C. A. Brebbia (Eds.), Advances in Fluid Mechanics VI (pp. 509–519). (WIT Transactions on Engineering Sciences ; Vol. 52). WIT Press. https://doi.org/10.2495/AFM06050