Measurement and Modelling of 3-Dimensional Multi Phase Flow in Wastewater Treatment Plant Process- and Sedimentation Tanks.

The hydrodynamic and biological processes of wastewater treatment plant process tanks are investigated. The research includes laboratorial and numerical analysis of the hydrodynamics in a bubble plume generated by an air diffuser, commonly used for aeration of process tanks at wastewater treatment plants. The impact on the flow field, due to the presence of mixing impellers is also investigated both in the laboratory and by numerical modelling. Experiments regarding sludge rheology and settling velocity is conducted on sludge samples, and characteristic hydrodynamic properties of the sludge particles is determined. The results and experiences drawn from the laboratory experiments are transferred to the modelling of full scale process tanks on wastewater treatment plants. The numerical model is substantiated by measurement data from full scale wastewater treatment plant process tanks. The final model of the process tanks is based on an Eulerian-Eulerian multiphase scheme applied to the Navier-Stokes equations in 3 dimensions. In the final model, interfacial force interaction between the continuous water phase and the dispersed bubble and sludge particle phase are included. The hydrodynamic multiphase model is coupled with different models for the biological processes in the process tanks, in order to be able to model both oxygen and nutrient concentrations in the tank. An analysis of the results dependency upon the models mesh size is conducted in order to assure mesh independent results. (Jesper Laursen, Michael R. Rasmussen)