Influence of sparger on energy dissipation, shear rate, and mass transfer to sea water in a concentric-tube airlift bioreactor

Abstract

Data on volumetric mass-transfer coefficient, K L a L, in a 12 × 10 −3 m 3 airlift bioreactor are reported. Measurements were made in sea water. The superficial gas velocity ranged up to 0.21 m/s. Four cylindrical spargers (60–1000 μm pore size) were tested. In bubbly flow, the sparger pore size strongly influenced the K L a L; the highest K L a L values were obtained with the smallest pore size. In contrast, in the transition and heterogeneous flow regimes, the pore size had little influence on K L a L. The best correlation of the mass transfer data was obtained when both gas holdup and liquid superficial velocity were taken as independent variables. Shear rates were estimated in the different zones of the reactor. The highest values were found in the bottom zone of the reactor and in the gas-liquid separator. The penetration and isotropic turbulence models were used to develop a semi-theoretical equation relating the volumetric mass-transfer coefficient to shear rate; hence providing a better understanding of how the operational variables may be manipulated to attain a moderate shear rate and an appropriate level of mass transfer, two extremely important parameters for the growth of sensible microorganisms as those used in marine biotechnology.