Linking maximal shear rate and energy dissipation/circulation function in airlift bioreactors
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The interest in pneumatic bioreactors is related to their good mass transfer capacity, as well as lower operating costs, due to the simple mechanical structure. Knowledge of the transport phenomena and hydrodynamics of bioreactors is important to enable definition of the best bioreactor model and operating conditions for a specific bioprocess, with the imposed shear being one of the most difficult to quantify. For stirred tanks, the fragmentation of microorganisms has been well correlated with a hydrodynamic parameter called the “energy dissipation/circulation function” (EDCF). However, there have been no estimates of the EDCF for pneumatic bioreactors. The present work proposes a methodology to estimate the EDCF for different pneumatic bioreactors and operating conditions using two approaches: Computational Fluid Dynamics and, comparison of pellet fragmentation in conventional and pneumatic bioreactors. First, the volume of higher energy dissipation was estimated in 5 L pneumatic bioreactors, exhibiting values ranging from 57.9 to 106.5 cm³. Subsequently, EDCF values were estimated, ranging from 0.71 to 9.1 kW·m−3·s−1 for pneumatic bioreactors. Finally, these values were validated by pellet fragmentation assays in stirred tank and pneumatic bioreactors under conditions of similar fragmentation, that resulted in similar EDCF values.