Abstract

SOLER, Andrea  and  BUITRAGO H, Gustavo. Evaluating oxygen transfer in a Lactococcus lactis cultures using an external aeration fermentation system (EAFS). Rev. colomb. biotecnol [online]. 2010, vol.12, n.2, pp.124-138. ISSN 0123-3475.

In aerobic fermentations, oxygen as terminal electron acceptor in respiration process, is commonly a limiting due to factors like its low solubility in aqueous solutions, bioreactors’ geometric factors and operating characteristics, liquid media properties, oxygen concentration in gas supply, microorganisms’ characteristics, environmental culture conditions, power supply by agitation system, etc. Oxygen limitation is present in cultures using the IBUN 34.1 Lactococcus lactis strain where oxygen availability is low some minutes after the exponential phase starts. A high transfer rate oxygen supply system was thus designed to overcome such limitations; it consisted of an external aeration fermentation system (EAFS) which was compared in this work with a conventional agitated tank fermenter equipped with two Rushton turbines and internal diffuser aeration flute mechanism. This paper evaluates the EAFS; some operational variables were selected and studied as well as their effect on oxygen transfer. Our results showed that agitation and culture medium flow through the aerator (called external recirculation flow) were the variables having the main effect on overall volumetric mass transfer coefficient (k_La). The highest k_La value in the conventional bioreactor having internal aeration was 40.68 k_La (h^-1), while the EAFS reached 90 (h^-1).

Keywords : Bioreactor; k_La; oxygen transfer; aerobic fermentation; gas-liquid mass transfer.

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