Impact of carbon dioxide injection on oxygen dissolution rate during oxygen additions in a bubble column

• Impact of CO2 on dissolution rate under conditions emulating wine fermentations.
• CO2 bubbling increases the volumetric mass transfer coefficient.
• CO2 bubbling reduces oxygen solubility.
• Overall, CO2 bubbling reduces oxygen dissolution rate.

Oxygen additions are common practice during oenological fermentations. Since oxygen dissolution under winemaking conditions is not completely understood, these additions are performed empirically. In particular, the influence of carbon dioxide produced by yeast cells on the oxygen dissolution rate remains unclear. In this paper, we present an oxygen mass balance model that describes the evolution of dissolved oxygen in a laboratory scale carbon dioxide bubbling column emulating wine fermentation hydrodynamic conditions during oxygen additions. The model consists of two partial differential equations for the liquid and gas phases and considers liquid recirculation and mixing. Considering only one fitting parameter, the model can reproduce well the observed dissolved oxygen evolution at different locations in the column. We found that carbon dioxide bubbling has two simultaneous antagonist effects: it enhances the volumetric mass transfer coefficient and decreases the oxygen equilibrium concentration mainly due to the dilution effect in the gas phase. Overall, the latter effect is shown to be more important and explains the reduction of almost 60% of the oxygen dissolution rate for high carbon dioxide bubbling conditions. The model developed here will help to design better oxygen addition systems for oenological fermentations.