Linking maximal shear rate and energy dissipation circulation function
in airlift bioreactors
Abstract
Pneumatic reactors are an important class of bioreactors widely used in
biotechnological processes. The growing interest in these reactors is
mainly 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. Several performance parameters are used to
evaluate bioreactors, 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. The difficulty in
estimating the EDCF for pneumatic bioreactors is in defining the volume
of higher energy dissipation. Here, this was achieved employing the
maximal shear rate obtained using computational fluid dynamics
simulations. The estimated volume was validated by comparing pellet
fragmentation in conventional and pneumatic bioreactors, under
conditions that led to similar EDCF values.