Oxygen Mass Transfer Coefficient and Power Consumption in a Conventional Stirred-Tank Bioreactor Using Different Impellers in a Non-Newtonian Fluid: An Experimental Approach

In this study, we investigated the power consumption and volumetric mass transfer characteristics in an un-baffled stirred-tank bioreactor using a non-Newtonian fluid and different impellers. The impellers studied were a Rushton turbine impeller, a paddle impeller, a marine impeller, a segmented impeller, and, an elephant ear impeller. Studies were performed over a wide range of agitation speeds (0–2000 rpm) and aeration (0.1–0.3 vvm). The effects of superficial gas velocity, impeller speed, power input, and liquid viscosity were studied as significant factors for KLa and power input estimation. The Rushton turbine impeller was found to be the most efficient in achieving higher KLa (0.015 min-1) even at lower agitation and aeration rates compared to other impellers. The trend of KLa was found to be similar for axial flow generating impellers. Correlations were derived for all the impellers at different superficial gas velocities (Vg) and gassed power per volume (Pg/V), and a correlation coefficient R2>0.99 was achieved in all the cases. The power drawn by the impellers was tested, and maximum power consumption was observed using the Ruston impeller (198.04W), followed by the paddle impeller (152.3W). However, under aerated conditions, the power consumption was lowered by 25–35% in all the cases. The power input ratio (Pg/Po) was found to be in the range of 0.35–0.61 for all the impellers studied. The power number (Np) was estimated and the results were found to be comparable with earlier studies. Thus, the present study gives more insight into the performance of different impellers and will be helpful in process development.