Hydrodynamics, mass transfer and cell growth characteristics in a novel microbubble stirred bioreactor employing sintered porous metal plate impeller as gas sparger

Stirred tank bioreactors are one of the most widely used bio-fermentation systems at both the laboratory and factory scale for the production of high value bioproducts. However, conventional systems suffer from irreconcilable contradictions to ensure adequate volumetric oxygen mass transfer rates (k(L)a) the necessary operating conditions to increase the energy consumption and the shear conditions. Adaptation of systems that incorporate microbubbles (MBs) generated by microporous sparger are advantageous for high viscosity and low shear stress bio-fermentation systems due to their superior k(L)a's, high gas-liquid interfacial area to volume ratios, high gas holdup, and slow coalescence rates. Herein, we describe the development of a novel microbubble-based stirred tank bioreactor (MSTBR) using a sintered porous metal plate impeller as gas sparger that produces MBs in both Newtonian and non-Newtonian fluids. The MSTBR showed increased k(L)a and improved the gas holdup by forming an abundance of MBs, while avoiding the high shear stress and reducing the mixing energy consumption that are typically caused by utilization of Rushton turbine impellers. To validate the robustness of the MSTBR, arachidonic acid (ARA)-rich oil was produced from the shear-sensitive, high oxygen consuming filamentous fungus Mortierella alpine. The total ARA content produced using the MSTBR system was found to be 2.82 times that of the control bioreactor. Taken together, our data indicates that the new MSTBR bio-fermentation system can be broadly utilized in applications requiring elevated oxygen levels, shear-sensitive microorganisms, and high viscosity medium during the bio-fermentation process. (C) 2018 Elsevier Ltd. All rights reserved.