HYDRODYNAMICS OF NON-NEWTONIAN LIQUIDS IN EXTERNAL-LOOP AIRLIFT BIOREACTORS PART 2 - STUDY OF THE LIQUID CIRCULATION VELOCITY

In order to obtain further information on the behaviour and optimal de sign of external-circulation-loop airlift bioreactors, the liquid circ ulating velocity was studied using highly viscous pseudoplastic soluti ons of starch and antibiotic biosynthesis liquids of Penicillium chrys ogenum, Streptomyces griseus, Streptomyces erythreus, Bacillus licheni formis and Cephalosporium acremonium. Measurements of liquid circulati on velocity were made in laboratory and pilot plant external-loop airl ift bioreactors, under various conditions concerning gas flow rate, ri ser liquid height at constant downcomer height, A(D)/A(R) ratio, using the impulse-response technique. It has been found that these paramete rs had a significant effect on liquid circulation velocity together wi th the apparent viscosity and dry weight of the solid phase in the bio synthesis liquids. For the tested liquids, the superficial liquid velo city in the riser section of an external-loop airlift bioreactor may b e described by the following equation: nu(SLR) = c nu (A(D)/A(R))(b)(H -s/H-D)(c)(eta(ap)/eta(w))C-d(s)e, where the exponents and the constan t c take different values depending on the liquid phase properties and flow regime.