Fluid dynamic conditions and oxygen availability effects on microbial cultures in STBR: An overview

Abstract

Bioprocesses are often carried out in stirred tank bioreactors. Due to the need of mixing, homogenization and interphase transports, cultures are usually agitated by mechanical, hydraulic or pneumatic means. The increasing in agitation decreases mixing time, improves homogeneity, mass and heat transfer rates and, accordingly, the metabolism and the biochemical reaction rates are also influenced. The power input into the system is essentially required in order to increase the mass transfer rate, the oxygen transport rate in aerobic bioprocesses, but also the shear forces are increased and consequently the concentration of some compounds in the liquid phase (oxygen in the aerobic bioprocess) with the corresponding effects on the cellular metabolism and the cellular structures due to fluid dynamics into the bioreactor. Hydrodynamic conditions in STBR are given by the broth characteristic (mainly viscosity), the vessel geometry, including the stirrer and sparger design, and the agitation and gas flow rate. Thus, shear effects would take place, affecting the culture performance, provoking cell damage in some occasions. The primary goal of this work is to describe up to date knowledge on these concepts: fluid dynamic conditions, hydrodynamic stress and oxygen availability influence affecting the microbial processes performance.