Hydrodynamic characteristics and mixing behaviour of Sclerotium glucanicum culture fluids in an airlift reactor with an internal loop used for scleroglucan production

The filamentous fungus, Sclerotium glucanicum NRRL 3006, was cultivated in a 0.008 m³ airlift bioreactor with internal recirculation loop (ARL-IL) for production of the biopolymer, scleroglucan. The rheological behaviour of the culture fluid was characterised by measurement of the fluid consistency coefficient (K) and the flow behaviour index (n). Based on these measurements, the culture fluid changed from a low viscosity Newtonian system early in the process, to a viscous non-Newtonian (pseudoplastic) system. In addition, reactor hydrodynamics and mixing behaviour were characterised by measurement of whole mean gas hold-up (ɛ _g), liquid re-circulation velocity (U _ld) and mixing time (t _m). Under identical process conditions, the effects of the viscosity of the culture fluid and air flow rate on ɛ _g, U _ld and t _m were examined and empirical correlations for ɛ _g, U _ld and t _m with both superficial velocity U _g and consistency coefficient K were obtained and expressed separately. The correlations obtained are likely to describe the behaviour of real fungal culture fluids more accurately than previous correlations based on Newtonian or simulated non-Newtonian systems. Journal of Industrial Microbiology & Biotechnology (2001) 27, 208–214. Received 05 June 2000/ Accepted in revised form 18 March 2001