Optimization of an Industrial Aerobic Bioreactor Using Combined CFD, Scale-Down, and Experimental Techniques

The dissolution of oxygen into the fermentation medium and the appropriate mass transfer conditions are of crucial importance in designing large-scale aerobic bioreactors. The investigation of mass transfer rates and flow structures in a large-scale process by only using experimental methods is hardly feasible, more likely because of the huge running costs. Also, those investigations by only using simulation approaches would not be accurate. Thus, this study is devoted to the application of a facile hybrid simulation/scale-down/experimental approach to optimize the structure and operation of a 400-L bioreactor used for the diphtheria bacteria culture. Assisted by the Computational Fluid Dynamics (CFD) simulation, the effects of engineering parameters such as the type, agitation rate, and location of the impeller, viscosity as well as the airflow rate and inlet place on the hydrodynamics of large-scale bioreactor were studied. Using the Concaved Blade Disc Turbine (CBDT) impeller located at the 30-cm distance with an agitation rate of 550 rpm as well as the air inlet placed at the bottom with a flow rate of 20 L/min, a superior improvement in air distribution, bubbles size, and kLa value (0.64 s^-1 ) was observed. To verify the simulation results, 15-L bench-scale bioreactors were developed by using a scaled-down (equivalent volumetric power (P/V)) strategy. The CFD simulation results implied that the bench-scale and large-scale bioreactors have comparable hydrodynamic environments. Additionally, the kLa values obtained experimentally were very close to the ones got by the simulation. These results make the CFD-assisted optimized 400-L bioreactor a potential candidate for this bioprocess.