Design and Optimisation of Final Clarifier Performance with Cfd Modelling

A Computational Fluid Dynamics (CFD) prediction procedure for computing the internal hydrodynamic behaviour of final clarifiers is presented. Calculations are carried out and presented for comparison with experimental measurements of point velocities in a shallow circular clarifier in operation at a UK waste water treatment works. The calculations compare favourably with the data and the model has subsequently been used for many design studies. A separate study is described where CFD predictions are used to investigate the influence of introducing energy dissipating influents (EDI), varying the stilling well diameter, adding Stamford baffles at the side wall or placing an influent floor baffle (McKinney baffle) below the stilling well. From the study it is possible to determine the sizes and combinations of internal baffling likely to give the best clarification performance across a range of operating conditions. The success of the optimum design is judged by the depth of the settling sludge bed and the magnitude of the effluent suspended solids (ESS) for the state points considered.