Continuous fermentation by a highly flocculant strain of the yeast Saccharomyces cerevisiae was carried out in a tower fluidized-bed bioreactor. The synthetic and molasses media with a total sugar concentration of 17% (w/v) were used for fermentation. Different dilution rates were tested. Stable cell densities of 50 kg m-3 (dry weight) were maintained for all dilution rates. The ethanol productivity was increasing linearly with dilution rates up to 15-20 kg m-3 h-1. Aeration of the culture stabilized flocculating activity and viability of yeast and also permitted long-term operation of the bioreactor.
Changes of the main hydrodynamic and oxygen transfer parameters during Aspergillus niger cultivation in an external‐loop air‐lift bioreactor of 200 dm3 operating capacity were investigated. The final average concentrations of biomass and citric acid obtained in batch fermentations were about 17 g 1‐1 and 90 g 1‐1, respectively. Significant influence of the increasing biomass concentration on the rheological properties of the broth and operating parameters was found. Volumetric oxygen transfer coefficient. kLa, was found to be dependent on the apparent viscosity of the broth with an exponent of ‐0.984.
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