Effects of nonionic surfactants on bacterial transport through porous media

The introduction of surfactants to groundwater has the potential to significantly enhance the transport of bacteria through porous media. This enhanced transport may be beneficial, such as facilitating the introduction of acclimated bacteria during bioaugmentation or reducing biofouling at an injection well. It may also be harmful if surfactants found in common consumer goods enhance the transport of pathogenic bacteria from waste streams and septic systems into potable aquifers. In order to predict the effects of surfactants on bacterial transport, it must first be understood how surfactants affect both bacterial cell surface properties and bacterial transport through porous media.; This thesis is a first step at systematically quantifying the effects of surfactants on bacterial cell surface properties and bacterial transport. Through experimentation, it was shown that nonionic surfactants affect the cell surface properties through changes in the cell surface hydrophobicity and the electric double layer surrounding bacterial cells. The magnitude of these effects was shown to be a function of the structure and concentration of the surfactant.; Column experiments showed that nonionic surfactants can significantly affect bacterial transport through aquifer sand, with the effect a function of the solution ionic strength and the surfactant polyoxyethylene chain length. It was also demonstrated that this effect can occur at concentrations well below the critical micelle concentration, and is related to the surfactant adsorption isotherm. While no dependency was found between the bacteria] transport though sand columns and cell surface hydrophobicity, a dependency was found with changes to the electric double layer due to the presence of surfactants. Theoretical analysis suggests that the nonionic surfactants displace counter ions, which results in expansion of the electric double layer about the bacteria. This expanded double layer increases the repulsive electrostatic potential between the bacteria and the sand grains, with a resultant increase in bacterial transport.; Finally, application of the colloid filtration theory indicates that the presence of surfactants can significantly increase the travel distance of bacteria. The effect is more pronounced at lower ionic strengths, and is thus very important when considering the transport of bacteria through potable groundwater aquifers.