Model-based evaluation of cell retention by crossflow ultrafiltration during fed-batch fermentations with Escherichia coli

Fermentations with cell retention by membrane technology offer a means to increase fermentation productivity. In these systems, fermentation and membrane filtration interact with each other, and consequently, these two operations should be evaluated simultaneously. In this work we performed glucose-limited fermentations with Escherichia coli using an ultrafiltration membrane for cell retention. Models were derived to evaluate both fermentation and membrane performance. Concerning the fermentation, a model derived from fermentations without cell retention could describe the system with cell retention properly. This model had correctly assumed that the cell retention system would not affect the fermentation performance. The membrane performance, on the other hand, was well described in short-term experiments, but the long-term effects could not be predicted and the calculated cake mass and particle diameter were unrealistic. Further evaluation of the model and experimental results suggest that other fouling sources besides the bacterial cells - such as medium components and/or intracellular products released to the medium due to cell lysis - might play a more important role in flux decline.