Modeling microbial processes in porous media

The incorporation of microbial processes into reactive transport models has generally proceeded along two separate lines of investigation: (1) transpo rt of bacteria as inert colloids in porous media, and (2) the biodegradatio n of dissolved contaminants by a stationary phase of bacteria. Research ove r the last decade has indicated that these processes are closely linked. Th is linkage may occur when a change in metabolic activity alters the attachm ent/detachment rates of bacteria to surfaces, either promoting or retarding bacterial transport in a groundwater-contaminant plume. Changes in metabol ic activity, in turn, are controlled by the time of exposure of the microbe s to electron acceptors/donor and other components affecting activity. Simi larly, metabolic activity can affect the reversibility of attachment, depen ding on the residence time of active microbes. Thus, improvements in quanti tative analysis of active subsurface biota necessitate direct linkages betw een substrate availability, metabolic activity, growth, and attachment/deta chment rates. This linkage requires both a detailed understanding of the bi ological processes and robust quantitative representations of these process es that can be rested experimentally. This paper presents an overview of cu rrent approaches used to represent physicochemical and biological processes in porous media, along with new conceptual approaches that link metabolic activity with partitioning of the microorganism between the aqueous and sol id phases.