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Kinetic modeling of batch culture and operation of multi-stage continuous ethanol production with cell recycle using Zymomonas mobilis
Abstract
The present study compared the experimental inhibitory effects of added and produced ethanol on Zymomonas mobilis from a mathematical point of view. A parabolic relationship was used to express the kinetics of ethanol inhibition on Zymomonas mobilis. The exponent n in parabolic model is less than one for inhibition exerted by added ethanol and is larger than one by produced ethanol. The added ethanol exhibits a smaller inhibitory effect than the produced ethanol. The inhibitory effect of ethanol on the biomass yield is correlated to a mathematical equation. The predictions of cell concentration using the model derived from inhibition kinetic analysis of added ethanol deviate from experimental results. The higher the ethanol level, the larger the deviation will be. However, the model developed from inhibition kinetic analysis of produced ethanol will predict the cell, glucose and ethanol profile of batch experiments with Zymomonas mobilis over a range of substrate concentration from 20 to 160 g/L. The continuous culture studies revealed oscillations in cell concentration, glucose consumption and ethanol production. The oscillatory phenomenon can be attributed to the dynamic response of Zymomonas mobilis to ethanol inhibition. The current experiments suggest that the lower biomass yield of Zymomonas mobilis may not be an advantage for its use in ethanol production. This study indicates that it is not feasible to continuously produce ethanol by Zymomonas mobilis using conventional methods if a higher ethanol concentration is required. The three stage continuous system with cell recycle was used to solve the oscillation problem encountered in conventional continuous fermentation. The total fermentation time required for complete conversion of 16% glucose to ethanol is only 6 hr in the three stage cell recycle system versus 19 hr in the batch system. The 16% glucose was not completely converted to ethanol in a conventional continuous system. The overall volumetric productivity in this preliminary study is 12.99 g/L-h with a final ethanol concentration of 77.8 g/L for the continuous three stage cell recycle system versus 4.34 g/L-h with a final ethanol concentration of 66.3 g/L for the conventional continuous system. Further study on this system is needed.
Subject Area
Chemical engineering
Recommended Citation
Zhou, Kang Ping, "Kinetic modeling of batch culture and operation of multi-stage continuous ethanol production with cell recycle using Zymomonas mobilis" (1993). ETD collection for University of Nebraska-Lincoln. AAI9416008.
https://digitalcommons.unl.edu/dissertations/AAI9416008