Modeling of the Aeration System of a Sequencing Batch Reactor

The use of modern methods and modelling and simulation tools in the design of bioreactors allows for the analysis of flow phenomena in a short period of time without the need of physical model preparation, and thus for the optimization of existing solutions. The article presents simulations of the aeration process in the bioreactor of SBR type realized by means of computational fluid dynamics (CFD) and ANSYS 12.1 software. The subject of the analysis was a diffuser of own design. For the preparation of geometry representing the analyzed design the Design Modeler 12.1 module was used and the discretization of the continuous domain was carried out with the ANSYS Meshing 12.1 tool. For model calculations the ANSYS Fluent 6.3 solver was used. On the basis of the results obtained from the conducted simulations it is possible to predict the parameters which will increase efficiency and effectiveness without the need to build real set of prototype models of aeration systems. The results obtained indicate that an increase in aeration velocity results in a decrease in the minimum Y-axis velocity for both the mixture and air. The observed differences are caused by the shape of the geometric model and the velocity of the air outlet through the openings, which affects the hydraulic process in the chamber. These processes affect, both, the amount of oxygen dissolved in the bioreactor and the behavior of the suspension in volume. The turbulence intensity during the aeration process is concerned mainly are in the range from 3.9 to 8.7 % and are comparable with the average values of turbulence degree obtained by other researchers. The air bubble diameter range are 0.3 to 4.5 mm, in the case of aeration velocity 5.68 cm/s, a significant part of the chamber were air bubbles with a diameter of 2.6 to 3.9 mm, i.e. they were not limit values.