Study of the oxygen transfer in a disposable flexible bioreactor with surface aeration in vibrated medium.

The oxygen mass transfer is a critical design parameter for most bioreactors. It can be described and analyzed by means of the volumetric mass transfer coefficient K(L)a. This coefficient is affected by many factors such as geometrical and operational characteristics of the vessels, type, media composition, rheology and microorganism's morphology and concentration. In this study, we aim to develop and characterize a new culture system based on the surface aeration of a flexible, single-used bioreactor fixed on a vibrating table. In this context, the K(L)a was evaluated using a large domain of operating variables such as vibration frequency of the table, overpressure inside the pouch and viscosity of the liquid. A novel method for K(L)a determination based on the equilibrium state between oxygen uptake rate and oxygen transfer rate of the system at given conditions was also developed using resting cells of baker's fresh yeast with a measured oxygen uptake rate of 21 mg g(-1) h(-1) (at 30 degrees C). The effect of the vibration frequency on the oxygen transfer performance was studied for frequencies ranging from 15 to 30 Hz, and a maximal K(L)a of 80 h(-1) was recorded at 30 Hz. A rheological study of the medium added with carboxymethylcellulose at different concentrations and the effect of the liquid viscosity on K(L)a were determined. Finally, the mixing time of the system was also measured using the pH method.