Experimental studies of adsorption in bacteria-water-rock systems: Implications for heavy metal transport in the subsurface

Bacteria are ubiquitous in near-surface geologic environments, and bacteria cell walls display a high affinity for metal cations. The adsorption of metals onto bacterial surfaces can affect heavy metal contaminant transport and the effectiveness of bioremediation techniques. Quantitative prediction of the effects of bacterial adsorption on metal mobility requires an accurate knowledge of metal-bacteria and bacteria-mineral interactions. However, the effects of bacterial adsorption on metal transport are poorly understood, and with our current knowledge it is impossible to quantitatively assess the magnitude which bacteria can enhance or retard the mobility of metal contaminants.; The research presented in this dissertation thesis quantitatively describes the effects of bacterial adsorption on metal distribution and transport. Proton and Cd adsorption onto bacteria surfaces is studied for a range of gram-positive and gram-negative bacterial species. The experimental results indicate that a wide range of bacterial species adsorb nearly identical amounts of Cd as a function of pH. Metal adsorption experiments are also conducted with complex bacteria mixtures as functions of pH and bacteria:metal ratio. The adsorption behavior of bacteria mixtures is similar to that of a single bacterial species, and the extent of adsorption can be quantified using a surface complexation model.; Bacterial adsorption onto the mineral surface of corundum is studied as a function of time, pH, ionic strength and bacteria:mineral mass ratio. The data demonstrate that the adsorption of bacteria onto a mineral surface is a completely reversible process, and that the adsorption behavior is governed by the chemical speciation of the bacterial and mineral surfaces. Column and batch experiments are performed with ternary metal-bacteria-mineral systems. The results indicate that a surface complexation model can be applied to successfully quantify the distribution of Cd between the aqueous phase and the bacterial and mineral surfaces, and the model can be used to estimate the distribution of mass in systems not directly studied in the laboratory.; The experimental results underscore the need for a flexible modeling approach to quantify bacterial adsorption reactions. The surface complexation model is proposed as a quantitative means to account for the complex adsorption chemistry in bacteria-water-rock systems.