Solid-state fermentation in rotating drum bioreactors: Operating variablesaffect performance through their effects on transport phenomena

Aspergillus oryzae ACM 4996 was grown on an artificial gel-based substrate and on steamed wheat bran during solid-state fermentations in 18.7 L rotati ng drum bioreactors. For gel fermentations fungal growth decreased as rotat ional speed increased, presumably due to increased shear. For wheat bran fe rmentations fungal growth improved under agitated compared to static cultur e conditions, due to superior heat and mass transfer. We conclude that the effects of operational variables on the performance of SSF bioreactors are mediated by their effects on transport phenomena such as mixing, shear, hea t transfer, and mass transfer within the substrate bed. In addition, the su bstrate characteristics affect the need for and the rates of these transpor t processes. Different transport phenomena may be rate limiting with differ ent substrates. This work improves understanding of the effects of bioreact or operation on SSF performance. (C) 1999 John Wiley & Sons, Inc.