Gas hold-up and gas-liquid mass transfer in three-phase stirred tank bioreactors with simulated non-Newtonian fermentation broths

Gas hold-up and gas-liquid mass transfer characteristics have been studied in three-phase stirred tank bioreactors. Effects of the non-Newtonian flow behavior of fermentation broths on gas hold-up and oxygen mass transfer were examined. Measurements were carried out in a 0.2m i.d. stirred tank bioreactor. The aqueous solutions of carboxymethyl cellulose (CMC) were used to study the effect of non-Newtonian flow behavior. In the CMC solutions, the solids loading caused the increase in gas hold-up unlike the results in water. The volumetric mass transfer coefficients were found to decrease due to the presence of solid particles in water, On the other hand, solids loading led to higher mass transfer rates in non-Newtonian media. A semitheoretical model for volumetric mass transfer coefficient based on a combination of Higbie's penetration theory and Kolmogoroff's theory of isotropic turbulence agreed with the experimental data both for Newtonian and non-Newtonian media reasonably well.