Bioprocessing of exopolysaccharides (EPS): CFD optimization of bioreactor conditions

Abstract Computational fluid dynamic (CFD) simulation based on standard “ k-e ” RANS (Reynolds-averaged Navier-Stokes) model and Euler-Euler model of two-phase gas-liquid flow have been employed to aid experimentation in elucidating the performance conditions in a stirred bioreactor for exopolysaccharide (EPS) production. The study is focused on the effect of viscosity; the effect of 10 2 -fold consistency rise is studied. Psychrophilic yeast Sporobolomyces salmonicolor AL 1 supplied from Antarctic soil was the prototype biomass in the model media and glucomannan was the biopolymer produced. In order to be able to generalize, reference data for EPS bacterial strain producers were also used for extrapolation. Being important for cells' microenvironment, bioreactor local characteristics are considered: substrate distribution and oxygen mass transfer have been addressed, as related to velocity and kinetic energy dissipation specific for EPS production. In single impeller case, the substrate-depleted dead zones are found to exceed 30% by transfer area and mass transfer coefficient K L a is found to decrease twice compared to starting condition. Optimization is foreseen and demonstrated by variation of mixing intensity and retrofitting of impeller design.