Oxygen transfer in stirred bioreactors under animal cell culture conditions

Bioreactors designed for animal cell culture may differ significantly in reactor geometry and operating conditions from those used for microbial fermentations. Small impellers, operating at low impeller speeds and low air flow rates, generate only moderate energy dissipation rates so that conventional chemical engineering correlations for oxygen transfer coefficients are usually out of range and unproven in application. A comprehensive oxygen transfer study was conducted in two animal cell bioreactors of 100 litres and 8 in 3 in working volume during the production of recombinant CHO cells using a dynamic method. The results indicated that the correlation of van't Riet(1) for electrolyte solutions predicted the k(L)a data for the smaller bioreactor surprisingly well, though it consistently overestimated k(L)a compared with the actual results obtained in the large scale bioreactor. Additional studies conducted in water indicated that the over-estimation resulted not from the differences in the fluid dynamics between the systems compared, but from differences in the composition of the solutions.