Review article

This study focuses on the problem of sludge settling in classic Carrousel type aeration tanks at sewage treatment plants. The ANSYS FLUENT program was used to study the effect of the number of blades in propellers on the movement of activated sludge. The creation of the model involved the use of a standard k -ε model to describe turbulence. The propellers were supposed to be set at three points of the aeration tank, at turns which function simultaneously during the simulation process. The aim of the investigation was to study the velocity distribution in different sections of the aeration tank, and in the general flow, in order to determine the optimal number of propeller blades for a given design of the structure. The results have shown that a double propeller provides faster circulation of water in the aeration tank compared to a single one, which helps to reduce sludge subsidence. Also, the double propeller contributes to a more efficient distribution of the flow velocity at the bottom of the aeration tank, which ensures more efficient operation, eliminating slowing down of the flow in the lower part of the structure.