The application of air-lift fermenters to the cultivation of filamentous fungi

Summary An investigation of the performance of air-lift fermenters showed that the value of the oxygen mass transfer coefficient (K_La) increased with both the aeration rate and vessel size. Although some change in the liquid circulation pattern occurred with increasing superficial gas velocity, there was no transition from bubbly to slug flow over the range of superficial gas velocities studied. Increases in broth viscosity caused an increase in gas hold up and a reduction in the values for K_La, although this reduction was not as great as that observed in mechanically agitated fermenters. Under conditions of aeration and agitation which gave comparable K_La values similar biomass yields of Aspergillus oryzae were obtained in 7.25 l and 100 l air-lift fermenters, and in a 3.5 l mechanically agitated fermenter.