Optimizing operation of a single-product, multi-fermentor plant

Fermentation process development, as reported in open literature, typically aims at minimizing the cost price of a fermentation product by maximizing yield on substrate and/or volumetric productivity of a fermentation, given a selected or engineered micro-organism. Large volume biochemicals are produced in dedicated, single-product, multiple fermentor plants. Minimizing the cost price of such fermentation products requires optimization of the integral plant rather than the individual fermentors. Such optimization may lead to design choices beyond the often-used, traditional (extended) fed batch process. One such choice is presented here: the ‘withdrawal fermentation’ concept. Key benefits of this concept are illustrated by means of a simulation study, based on an actual running fermentation plant.

The simulation study highlights potential advantages of this concept, including higher volumetric productivity, smaller number of inoculum fermentations, lower nutrient losses, more constant broth composition for downstream processing, and less labour.

Obviously, the exact numbers presented in this study depend on the case specific kinetic model and parameters, and the operational settings of the fermentor. For new cases, the true operational optimum can easily be found based on an accurate model of the concerning fermentation process.

The ‘withdrawal fermentation’ concept as presented, is only one possible realization out of many thinkable options. The key concept is to create additional residence time for young broth withdrawals at the cost of older broth. Experts can contrive alternative ways to do so. The presented simulation model serves as a powerful tool to quickly compare design alternatives, at little effort and cost.