Mixing time in bioreactors under aerated conditions

Abstract

The major difficulty needing a solution in agitated and aerated bioreactors is closely connected to the optimum hydrodynamics regime in the stirred tank. It is evident that even a simple stirred reactor is geometrically complex and it seems that the mixing time can be one useful criterion for estimation of mixing intensity and therefore the estimation of oxygen profiles and mass transfer coefficients. The mixing time measures are relevant to the length of time for which detectable inhomogeneities last in the extremities of the vessel and can identify the extent of possible concentration gradients in a reactor that should be used as a gradientless unit for bio-kinetic studies. The parameter depends mainly on the mixing system characteristics, the physicochemical properties, the aeration and the rate of cell multiplication. To quantify the influence of some of these factors experiments have been performed using a wide spread laboratory scale stirred dual-impeller bioreactor configuration marketed by “Bioflow”. Experimental data have been obtained for various internal geometries of the reactor under aerated and non-aerated conditions administering real wastewater. A multi-regression analysis method was used to find mathematical correlation relating the influence of the rotation speed and the gas flowrate with the reactor's capacity to mix.