Transport and activity of dissimilatory metal-reducing bacteria in porous media for the remediation of heavy metals and chlorinated hydrocarbons

Dissimilatory metal-reducing bacteria (DMRB) are capable of reducing a wide range of metals and the injection of DMRB is considered for the cleanup of contaminated soil and groundwater. The success of such an approach, among other factors, relies upon the bacterial transport through porous media and the contaminant transformation by DMRB.; Long term starvation of Shewanella algae BrY, the model DMRB used in this research, allows for significantly improved transport through quartz sand porous media columns. However, the reasons for the improved transport remain unclear. Changes in cell size, net electrostatic charge, hydrophobicity, buoyant density, and effective diffusion coefficient do not provide a sufficient explanation and this question will have to remain the focus of future research. In addition, it became evident that the employed mathematical model based on the colloid filtration theory is not capable of appropriately describing scale and physiology dependent effects on bacterial transport through porous media. A complete understanding of the processes and factors influencing the porous media transport of starved bacteria is still lacking and will remain as the focus of future research.; The reduction of chromium [Cr(VI)], a compound of significant environmental concern at many Department of Energy, Department of Defense, and Environmental Protection Agency Superfund sites, can be facilitated by DMRB. Starved S. algae BrY cells can be resuscitated into an actively metabolizing state in the presence of ferric iron [Fe(III)], which is abundant in the environment. Active S. algae BrY cells can either directly reduce Cr(VI) or produce surface reactive ferrous iron [Fe(II)]. Fe(II) chemically reduces and precipitates Cr(VI) eliminating it from contaminated water. S. algae BrY cells can also potentially contribute towards the long term reactivity of zero valent iron subsurface barriers. The microbial reduction of Fe(III) allows for the removal or activation of surface associated corrosion products and results in increased transformation rates of carbon tetrachloride, another widespread environmental contaminant.; The results summarized in this dissertation indicate that the injection of starved DMRB is a promising technology for the remediation of subsurface environments contaminated with heavy metals and chlorinated hydrocarbons.