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

Data on volumetric mass-transfer coefficient. K-L alpha L, in a 12 X 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 sparg ers (60-1000 mu m 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 obt ained with the smallest pore size. Ln contrast, in the transition and heter ogeneous flow regimes, the pore size had little influence on K,a,. The best correlation of the mass transfer data was obtained when both gas holdup an d liquid superficial velocity were taken as independent variables. Shear ra tes were estimated in the different zones of the reactor. The highest value s were found in the bottom zone of the reactor and in the gas-liquid separa tor. The penetration and isotropic turbulence models were used to develop a semi-theoretical equation relating the volumetric mass-transfer coefficien t to shear rate; hence providing a better understanding of how the operatio nal variables may be manipulated to attain a moderate shear rate and an app ropriate level of mass transfer, two extremely important parameters for the growth of sensible microorganisms as those used in marine biotechnology. ( C) 1999 Elsevier Science Inc. All rights reserved.