Abstract
Mass transfer is one of the most important factors involved in viscous fermentation processes, like production of pullulan. Impellers play a crucial role in maintaining homogeneity and better mass transfer conditions during the fermentation process. The present study attempted to evaluate the efficiency of impellers with diverse configurations during pullulan fermentation. Initially, the mass transfer coefficients of 10 selected impellers were evaluated in an aqueous system. Among these, three impellers, namely, single helical ribbon, Rushton turbine, and Smith turbine impellers, were found to be more efficient and were further employed in the pullulan fermentation process. The results suggested that the single helical ribbon impeller was able to provide 24% higher pullulan production as compared to the Rushton turbine and Smith turbine impellers. The single helical ribbon was able to maintain the critical demand of dissolved oxygen in fermentation broth. Therefore, it may be commented that the single helical ribbon impeller configuration is suitable for higher production of pullulan during the fermentation process.
Highlights
Pullulan is a neutral, water-soluble exopolysaccharide (EPS) produced by yeast-like fungus Aureobasidium pullulans
The present study showed some important aspects of the effect of impeller types on mass transfer and pullulan production by Aureobasidium pullulans in a stirred tank bioreactor
The mass transfer value increases with an increase in aeration and agitation rates in the case of all types of impellers used in the present work
Summary
Water-soluble exopolysaccharide (EPS) produced by yeast-like fungus Aureobasidium pullulans. The present work was focused on understanding the effect of impeller configuration on mass transfer and pullulan fermentation in a fermenter along with varying aeration and agitation rates. A total of 10 impellers (diameter, 7.5 cm) were employed in the present study, namely, the Rushton turbine (RT), double helical ribbon (DHR), hydrofoil (HDF), three blade segmented (TBS), Rushton turbine 45◦ (RT45), single helical ribbon (SHR), Rushton turbine curved blade (RTCB), pitch blade (PB), Smith turbine (SI), and screw helical ribbon (ScHR) All these impellers were tested initially in a 5 L fermenter with 3.5 L working volume of deionized water for evaluation of mass transfer rate from gas phase to aqueous phase in the fermenter. The average of data points was calculated along with standard deviation
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