Studies on mass transfer characteristics of a modified airlift fermenter

Abstract

An approach to modify external loop airlift bioreactor is presented that examines its performance with respect to mass transfer. There are various designs of airlift fermenter [1]. In the proposed system [2] the riser has been replaced by a tube of irregular geometry, in the form of converging-diverging sections (CDT-ALF), so that better mass transfer may be obtained due to better liquid mixing caused by the bubble flow, pulsation effect and early transition to turbulence. Mass transfer characteristics of the modified airlift fermenter CDT-ALF were studied and compared with those of a conventional one, UT-ALF. Overall volumetric mass transfer coefficient,KLa, was determined by sulfite oxidation method.KLa was determined with respect toUG for differenthi. HigherKLa was always observed in CDT-ALF compared to that in UT-ALF under any operating condition ofhi andUG. If theKLa values are compared in both the systems under their optimum conditions ofhi andUG, CDT-ALF showed 122.5% higher values ofKLa compared to UT-ALF. However, when both the systems were operated at the lowest experimental conditions ofUG, thekLa in CDT-ALF was found to be 170% higher. In UT-ALF while with the decrease ofUG,kLa decreased, in CDT-ALF the reverse was observed i.e. at lowUG,KLa was higher. However with the increase ofhi,KLa decreased in both the systems. To predict volumetric mass transfer coefficientKLa, empirical correlations were developed by dimensional analysis for both the reactors. The correlations were experimentally verified to determine their reliability to predict mass transfer coefficient and the deviation was found within reasonable limit.