Transient product spectrum during batch Acetone-Butanol-Ethanol fermentation is known to evolve in response to pH-dependent Clostridium acetobutylicum metabolic variations. Although previous works have evidenced the coexistence of distinct cell subpopulations, this culture heterogeneity has been neglected in ABE modeling to date. Here, a dynamic model for ABE fermentation based on bacterial population dynamics was developed under the hypothesis of the existence of a specific solventogenic phenotype. By proposing a simplified metabolic network, the metabolic switches are described, triggered by the partial conversion of acid vegetative cells into solventogenic and sporulating subpopulations. The proposed model succeeds in adequately describing the evolution of all extracellular metabolites in a batch culture both at free and controlled pH. Since the model is controlled by cell population dynamics with no time dependent variable it can be directly applied to alternative flow (e.g. continuous) regimes allowing for its application to a broader range of operating conditions.

The reindustrialization of Acetone-Butanol-Ethanol (ABE) fermentation is hampered by its significant production cost, linked to high product inhibition and low product yield. ABE fermentation can be significantly enhanced by integrating in situ liquid-liquid extraction. In this study, hybrid simulations using Excel® and ASPEN Plus® based on experimental data were performed to quantify the energy requirements and economic improvement of the overall ABE extractive fermentation process. Four scenarios, based on two different organic solvents (2-butyl-1-octanol, 2B1O, and a vegetable oil, VO) applied in batch or fed-batch operation, were compared with the conventional process. Total energy demand decreased in all extractive configurations and the greatest energy savings (61%) were reached with the VO-based fed-batch operation. However, the highest profit increase was achieved with 2B1O in fed-batch mode, reducing the minimum butanol selling price by 29% over the base case, along with 34% savings in raw materials and 80% wastewater reduction.