Aeration in tower fermenters containing microorganisms.

Aerobic tower fermenters have been used both for the production of microbial biomass and for their metabolites. Aeration in these fermenters differs from that of conventional stirred tank fermenters in that it also accomplishes the agitation. A bioengineering study was made of an aerobic tower fermenter used for the growth of the filamentous fungus, Aspergillus niger. Since it was obvious that no single parameter or measurement can determine the effect of aeration in this system, four main features were considered: (a) the aeration itself particularly in terms of bubble size, mixing, and flow patterns (coupled with the effect of scale); (b) the mass transfer of oxygen into media both with and without the microorganism and the effect of fermenter design; (c) the mass transfer of oxygen into the microorganism during growth; and (d) the interaction of the aeration and the microorganism in its various morphological forms. Comparison of the growth in the tower and in the stirred fermenter showed little overall differences in biomass yield, concentration or generation time for the same aeration and fermentation conditions. However, specific differences due to the aeration gave the tower the additional advantages of lower energy requirements and the possibility of simpler fermenter constructionmore » but also the greater biological advantage of allowing the development of morphology of the microorganism and the possibility of its control.« less