HYDRODYNAMIC PERFORMANCE OF A 3-PHASE AIRLIFT BIOREACTOR WITH AN ENLARGED DEGASSING ZONE

The hydrodynamics of biotechnological processes is complex. So far, fe w studies were made with bioreactors of the airlift type with an enlar ged degassing zone. In this work, the influence of solids loading, sol ids specific gravity and draught tube dimensions on mixing and circula tion times and critical air flow rate for an internal loop airlift bio reactor with an enlarged sedimentation/degassing zone is studied. The results indicate that the critical air flow rate as well as the mixing time increase with an increase in solids loading in the bioreactor. C irculation time presents a maximum for a solids load between 5 and 10% (v/v). It is also shown that small variations in solids specific grav ity, for values close to that of the liquid, have a significant influe nce on the critical air flow rate and on the mixing time. An optimal ( minimal) value for the circulation time and for the critical air flow rate was obtained for a riser to down comer diameter ratio of 0.46. Th e minimum mixing time was obtained for a riser to down comer height ra tio of 0.80.