Abstract
This study aims to build a computational fluid dynamics (CFD) model that can be used to predict fluid flow pattern and to analyse the mixing process in a full-scale OD. CFD is a widely used numerical tool for analysing, modelling and simulating fluid flow patterns in wastewater treatment processes. In this study, a three-dimensional (3D) computational geometry was used, and the Eulerian-Eulerian multiphase flow model was built. Pure water was considered as the continuous phase, whereas air was modelled as the dispersed phase. The Shear Stress Transport (SST) turbulence model was specified which predicts turbulence eddies in free stream and wall-bounded region with high accuracy. The momentum source term approach and the transient rotor-stator approach were implemented for the modelling of the submersible agitators. The hydrodynamic analysis was successfully performed for four different scenarios. In order to prevent the incorrect positioning of the submerged agitators, thrust analysis was also done. The results show that the minimum required water velocity was reached to maintain the solid particles suspended in the liquid media and adequate mixing was determined.
Highlights
Biological wastewater treatment is the main and integral part of wastewater treatment plants (WWTPs) in order to remove biodegradable organic wastes and suspended solids
Each of flowmakers modelled as a cylinder and thrust value was taken in momentum source term calculations as illustrated in Equation (2)
The computation speed increased to a great extent with this model
Summary
Biological wastewater treatment is the main and integral part of wastewater treatment plants (WWTPs) in order to remove biodegradable organic wastes and suspended solids. An oxidation ditch (OD) is a modified activated sludge process with the advantage of minimizing mixing limitations and maximizing aeration efficiency in comparison with large bioreactors applications [1]. The geometrical shape of ODs contributes to the development of fluid flow pattern throughout the tank. Oblong shaped tanks are industrially preferred since they help the circulation of fluid flow with relatively high velocity. In terms of energy consumption in a WWTP, aeration can account for up to 70% of overall energy expenditure [2]. From this point of view, optimizing aeration processes or equipment upgrades are required to minimize operating costs and to provide a highly efficient treatment in WWTPs [3]. Fine bubble diffusers are more energy-efficient aeration system compared to surface aerators [4]
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