Bacterial interactions and transport in unsaturated porous media

The convection-dispersion transport model, which can well define solute transport, has been introduced to describe bacterial transport. Due to different interaction natures within the porous media, bacterial transport in the subsurface, especially in the vadose zone is a complex scenario. When transported in the vadose zone, bacteria may be captured on the media surface, at the air–water interface, or at the media–air–water three-phase interface depending upon the predominant interactions of concerned bacteria within the pore system. In this study, transport of Echerichia coli, Pseudomonas fluorescens and Bacillus subtilis in silica sand under water unsaturated conditions was investigated using column experiments. Bacterial interactions within the system were characterized based on bacterial and media surface thermodynamic properties, which were determined independently by means of contact angle measurements. These calculated interactions provided solid evidence of the bacterial retention mechanisms in the pore system, which served as the bases for suitable assumptions of bacterial transport modeling. The micro-scale interaction investigations helped eliminate uncertainties arising with bacterial transport modeling.