Overall volumetric oxygen transfer coefficient in an aerated bench-top stirred fermenter in aqueous dispersions of sodium alginate.

The dynamic gassing-out method was used to assess the effect of stirrer speed, air flow rate and alginate concentration on the overall volumetric oxygen mass transfer coefficient (K(L)a) in a bench-top stirred fermenter equipped with two Rushton-type turbines. As the alginate concentration in the medium was increased from 0 to 2% (w/v), the liquid film time constant (tau(F)) increased from approx. 30 to 300% of the electrode time constant (tau(E)), clearly showing that the liquid-probe diffusion film affected the oxygen-electrode response. By accounting for delayed probe response, liquid film time constant and gas residence time, the corrected values of K(L)a were empirically correlated with the above independent variables as converted into gassed power input and aeration number per unit liquid volume and the effective liquid/water shear viscosity ratio. Despite an average error of 19%, such a correlation might be useful to adjust the oxygen transfer in bench-top stirred reactors during viscous aerobic fermentations.