(66d) E. Coli Deposition and Transport in Porous Media: Influence of Solution Chemistry and Bacterial Surface Polymers

The influence of solution ionic strength and electrolyte valence on the cell deposition of two E. coli strains has been investigated in well-controlled packed-bed column experiments using D21g and XL1-Blue, a mutant strain and wild-type respectively. The cells were also characterized under a range of solution chemistry conditions for the viability, size, electrophoretic mobility, hydrophobicity, surface charge density, and extracellular polymeric substances (EPS) composition. Results have shown the cell deposition rate and amount of retention in the column increased with ionic strength (IS) for both E. coli strains, as predicted by traditional DLVO theory. The deposition rate of D21g was found to be greater than that of XL1-Blue, a trend which cannot be explained by cell hydrophobicity, size, or viability. However, the cell mobility corresponds with the deposition trends, as the more negatively charged XL1-blue deposited the least suggesting that electrostatic interactions were the dominating mechanism. Additional experiments with D21g cells found the valence played an important role on the deposition kinetics, with the deposition rate in the presence of a divalent electrolyte (CaCl₂) being substantially greater than in a monovalent electrolyte (KCl). These results were also consistent with the measured mobility of the D21g cells in the two types of electrolyte solutions. Notably, at high ionic strength conditions when no energy barrier to deposition is predicted, the deposition rates were different for D21g cells in mono- and divalent electrolytes suggesting that non-DLVO type interactions are involved and influencing cell deposition kinetics. Further characterization of the cell surface charge density and EPS composition of D21g and XL1-Blue has provided additional evidence of a complex combination of DLVO and non-DLVO type interactions occurring. These proposed mechanisms and the implications in cell transport in aquatic environments will be discussed.