A turbulent mass diffusivity model for the simulation of the biodegradation of toluene in an internal loop airlift reactor

In this study, a three-dimensional computational fluid dynamics model is established in Ansys Fluent to describe the biodegradation of toluene in an internal loop airlift reactor (IALR). The Euler-Euler approach is used with the standard k-ε method to predict the hydrodynamics of the reactor, and the population balance model is used to describe the bubble size distribution in the reactor. The recently developed concentration variance c2¯ and its dissipation rate εc formulations are adopted to close the turbulent mass transfer differential equations, so that the turbulent mass diffusivity can be determined without using empirical methods. There is a good agreement between the simulated dissolved oxygen concentrations obtained by the proposed model and the experimental data reported in the literature. As the predicted turbulent mass diffusivity is found to be unevenly distributed and the calculated turbulent Schmidt number Sct is not a constant but varies, it may not be appropriate to use a constant Sct or an experimentally determined dispersion coefficient. In addition, the maximal shear stress is found in the top region of the IALR and the liquid flow are very uniform in the riser and downcomer.