Conclusions

The current work presents new insights into stirring and aeration of a pilot-scale multistage Rushton impeller bioreactor. The complementary experimental and simulation analyses indicate that the pre-dispersion of air by the bottom impeller leads to a significantly reduced local gas load at the upper impellers, and thus, to the superior gas utilization efficiency and high power input of the multiple impeller stages. However, the benefits directly depend on the bottom impeller flow regime.
This conclusion is based on several new experimental findings:
The novel two-phase CFD simulation results support the above conclusion and are consistent with the experimental data:
The work provides novel aspects towards at mechanistic understanding of the complex gas dispersion and distribution behavior of multiple Rushton impeller bioreactors, particularly of the individual contribution by each impeller stage. Moreover, this knowledge will open up new opportunities for optimizing their design and operating conditions of bioreactors.