PNNL

Abstract

A multi-scale approach was designed to investigate deposition of flagellated and non-flagellated strains of Azotobacter vinelandii in porous media. In a radial stagnation point flow cell (RSPF), the deposition rate of the flagellated strain (DJ77) on quartz was higher than that of the non-flagellated (Fla-) strain. In contrast, deposition of the Fla- strain exceeded that of DJ77 in two-dimensional silicon microfluidic models (micromodels) and in columns packed with glass beads. Direct cell counts in micromodel experiments showed decreasing values of clean collector removal efficiencies over time, suggesting that approaching cells were blocked from deposition by cells already attached to the collector surface. Column breakthrough curves for both strains also showed a decrease in deposition rates with time. Modeling results showed that blocking becomes effective for DJ77 strain at lower ionic strengths (1mM and 10mM), while for Fla- strain blocking was similar at all ionic strengths. In later stages of micromodel experiments, a ripening effect was also observed, where cells preferentially attached to already attached cells. Ripening happened earlier with the Fla- strain, which suggested that flagella interfered with ripening. Different mechanisms dominate at different stages of bacteria transport in porous media.