Some basic principles for the layout of tower bioreactors

Depending on the bubble-coalescence property of the fermentation medium different aerator types should be used in tower bioreactors. When bubble coalescence is suppressed the use of concentrated gas-dispersion at the tower bottom and for a coalescence-promoting medium distributed gas-dispersion along the tower are recommended. The latter can be realised in multistage towers with stage-separating trays. The aerator efficiency depends on the structure of the turbulence which is produced by the aeration. The smaller the turbulence scale the higher the efficiency of the aerator. By using a loop the bubble-coalescence rate is reduced and the cells are uniformly distributed along the column, but mixing time is increased and volumetric mass-transfer is reduced.