Theory and simulation of self-cycling fermentation: A population balance approach

Self-cycling fermentation (SCF) is a technique in which sequential batch fermentations are performed using a computerized feedback control scheme. In this method, half of the reactor volume is periodically removed and replaced by fresh medium. This results in very stable and repeatable growth cycles and synchronized cell cultures.;In this work, two segregated microbial population balance models are developed and used to simulate SCF. Cell age and cell mass distribution models are both used to study the behavior of microorganisms in various systems. One example is the study of autonomous oscillations and partial synchronization in cultures of Saccharomyces cerevisiae. However, when the cell age and cell mass models are compared for the modeling of cell synchrony in SCF, two contrasting population profiles arise from the simulations.;The SCF technique with its existing data can be used as a powerful tool to test and validate models of microbial systems. When used to simulate SCF, the cell age model was able to predict cell synchrony, however, the cell number profile obtained was remarkably different than that observed in experiments. The cell mass model, as proposed by Eakman et al. was able to capture the dissolved oxygen concentration, the limiting substrate concentration, and the biomass concentration, but was not able to describe the cell number profile or the feature of cell synchrony. By introducing a feedback mechanism between the critical division mass and the limiting substrate, cell synchrony was achieved and the experimental cell profile was captured.