(378b) Numerical Simulation of Dynamics of Microbes in NASA's Rotating Wall Vessel

Gravity, being one of the most dominant forces on Earth, can negatively influence microbial growth in suspended media, as it causes sedimentation. This settling impedes cell growth, creating mass-transfer limitation and reduced substrate utilization. Space-flight experiments have shown enhanced growth, but they are expensive. As an alternative, NASA developed a rotating-wall vessel (RWV), which counteracts the effects of gravity on the microbes here on Earth. Growth of microbes in RWVs have been investigated both numerically and experimentally, but most of these investigations utilized large spherical particles in the presence of inertia forces, which complicates the explanation of the growth. Furthermore, the dynamics of the cells are typically expressed independently from their initial positions, which is generally not the case.

In this investigation, we present simulation results based on a Stokesian dynamics code that we have developed to describe the dynamics of microbes in a RWV. Blocks of spheres are used to build the wall, and the interactions between the suspended particles and the wall are approximated by the summations of interactions between suspended particles and the constituent spheres of wall. We have shown that the orbits that are formed are based on a simple dimensionless number, and they are dependent on the initial position of the cells. Also, three-dimensional models will be presented to further investigate the dynamics of the cells in the axial direction of the RWV when rotated.