Exploring the impact of proteins and surfactant on oxygen mass transfer in gas-liquid bioreactors: An experimental investigation

This study investigates the impact of whey protein concentrate, sodium caseinate, and Tween 20 on gas-liquid mass transfer in a stirred-tank reactor operating at low Reynolds numbers and low volumetric gas flow rates, typical of the hydrodynamic conditions observed in anaerobic systems. These compounds, prevalent in biological media, significantly impact the physico-chemical properties of the liquid phase, which in turn affects mass transfer efficiency. The study examines the effect of these compounds on the liquid-side mass transfer coefficient ($k_{\text{L}}$) and gas-liquid interfacial area under conditions of low agitation Reynolds numbers and superficial gas velocities. The results indicate that proteins and surfactants increase gas hold-up, thereby increasing the gas-liquid interfacial area. Compared to an air-water system, proteins caused a rise in the interfacial area ranging from 2 to 20 times, while Tween 20 surpassed 100 times. This enhancement is attributed to Tween 20's rapid adsorption dynamics. However, both proteins and surfactants adsorb at the gas-liquid interface, which impedes oxygen diffusion and introduces additional resistance to mass transfer, consequently reducing $k_{\text{L}}$. Proteins resulted in a reduction in $k_{\text{L}}$ ranging from 26 to 92%, while Tween 20 showed a reduction of 80 to 90% compared to the air-water system. These results provide some of the first quantitative data on the impact of proteins on gas-liquid mass transfer and represent an initial step towards accounting for the impact of proteins in the control of biological and biochemical processes involving these macromolecules.