(619k) Multi-Objective Optimization of Integrated Aspen Plus Unsteady-State Batch and Fed-Batch Fermentation and in Situ Gas Stripping Simulations

Authors: 
Darkwah, K., University of Kentucky
Knutson, B. L., University of Kentucky
Seay, J., University of Kentucky
The batch Acetone-Butanol-Ethanol (ABE) fermentation process produces low final ABE concentrations, yields and productivity as a result of substrate and product inhibition to the microorganisms. Approaches to reduce product toxicity to the microorganisms include integrated fermentation and in situ product recovery techniques, such as gas stripping, adsorption, pervaporation, etc. Fed-batch fermentation reduces substrate inhibition by supplying substrate as it is consumed to keep the substrate concentration in the reactor below the inhibitory levels to the microorganisms.

Process simulation can predict the most informative experiments to conduct for process design, control and optimization. Previous Aspen Plus simulations and analyses of the ABE fermentation represented the batch and fed-batch processes with steady-state stoichiometric reactors with fixed product yields relative to key inputs, such as substrate (glucose) concentration. These steady-state representations of the batch and fed-batch fermentation processes are inadequate as these processes are inherently unsteady-state; the fermentation environment changes due time-dependent concentrations of cells, substrate, intermediates and products. This simulation approach results in Aspen Plus steady-state simulations that decouple the ABE fermentation kinetics from the fermentation environment and may not be representative of the integrated batch and fed-batch ABE fermentation and in situgas stripping. The operating conditions of the fermentation must be directly linked to the fermentation kinetics in order to optimize productivity and control product profiles in the fermentation process.

To this end, this study will use a multi-objective optimization strategy to maximize the ABE productivity, yield and concentration by manipulating the operation conditions of integrated batch and fed-batch fermentations and in situ gas stripping processes. The integrated batch and fed-batch ABE fermentation process will be simulated as unsteady-state processes using a Fortran user kinetics subroutine linked to the batch reactor (RBatch) in Aspen Plus. This research can serve as a basis to evaluate the economic viability and technical feasibility of bioprocesses as a decision-support tool for researchers, investors and policy makers in the long run.