Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Up to 80 % of the total energy budget of waste water treatment plants is consumed by the activated sludge process. One idea to improve the efficiency of an aeration tank is to increase the residence time of bubbles within the tank through baffles in the form of plates. Therefore, a detailed study was carried out to obtain an improved understanding of the hydrodynamics and mass transfer process of air bubbles along an inclined plate. For this small-scale investigation, the effects on the bubbly flow in deionized water were observed in a rectangular channel with the help of a high-speed camera and a dissolved oxygen sensor. The target parameters were bubble size distribution, equivalent Sauter mean diameter of the bubbles, bubble rise velocity, residence time, local and global mass transfer coefficient under the variation of wetting behavior of the material (hydrophilic, hydrophobic), roughness profile of the material, inclination angle and length of a plate. The wetting characteristics of these plates were also tested within activated sludge to analyze the influence of a developed biofilm to the surface characteristics of the plates. All plate configuration achieved a clear extension of the residence time whereas only a hydrophilic plate with a low inclination angle and a small length rose the local mass transfer coefficient after the plate contact. Eventually, all results were combined to develop ideas for the application of plates within the activated sludge process.