A mechanistic model for gas-liquid mass transfer prediction in a rocking disposable bioreactor.

Rocking disposable bioreactors are a newer approach to smaller-scale cell growth that use a cyclic rocking motion to induce mixing and oxygen transfer from the headspace gas into the liquid. Compared with traditional stirred-tank and pneumatic bioreactors, rocking bioreactors operate in a very different physical mode and in this study the oxygen transfer pathways are reassessed to develop a fundamental mass transfer (kL a) model that is compared with experimental data. The model combines two mechanisms, namely surface aeration and oxygenation via a breaking wave with air entrainment, borrowing concepts from ocean wave models. Experimental data for k L a across the range of possible operating conditions (rocking speed, angle, and liquid volume) confirms the validity of the modeling approach, with most predictions falling within ±20% of the experimental values. At low speeds (up to 20 rpm) the surface aeration mechanism is shown to be dominant with a k L a of around 3.5 hr-1 , while at high speeds (40 rpm) and angles the breaking wave mechanism contributes up to 91% of the overall k L a (65 hr-1 ). This model provides an improved fundamental basis for understanding gas-liquid mass transfer for the operation, scale-up, and potential design improvements for rocking bioreactors.