Laboratory experiments were conducted to study the effect of turbulence on Escherichia coli cells in an oscillating grid reactor under conditions of no oxygen transfer to the liquid phase. Fluid flow was quantified at a submillimeter resolution using a particle image velocimetry measuring technique. The root-mean-square estimates of the velocity gradient tensor components indicated the dominance of shear rate deformation in the fluid surrounding E. coli. The E. coli growth rate, dissolved oxygen (DO), and glucose uptake rates were facilitated by fluid-flow energy dissipation in the turbulent fluid. The Kolmogorov length scale (ηK) and velocity (uK) underlined characteristic scales at which enhanced DO and glucose uptake by E. coli were determined in a turbulent flow in comparison to still-water controls. A first-order power-law relation between the mass transport to the cells and the moving fluid is developed. The combined effects of the enhanced rate of strain at ηK scale and uniform velocity at uK determined the facilitated DO and glucose fluxes to E. coli. The mass transport to the E. coli was modeled by the Sherwood (Sh)-Péclet (Pe) number relationship by Sh = 1 + 1.08 PeuK0.62 where PeuK is the Péclet number defined by the uK velocity scale. The proposed first-order model described experimental data fairly well.
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Acknowledgements Support for this work was provided by the National Center for Earth-surface Dynamics, a Science and Technology Center funded by the Office of Integrative Activities of the National Science Foundation (under agreement Number EAR-0120914).
- E. coli
- Fluid flow
- Mass transfer
- Scale up