Biodegradation during contaminant transport in porous media. 2. The influence of physicochemical factors

The biodegradation of contaminants in the subsurface has become a topic of great interest. In systems wherein biodegradation is coupled with transport, the magnitude and rate of biodegradation is influenced not only by microbial properties but also by physicochemical properties. The purpose of this work is to systematically evaluate the impact of coupled physicochemical factors (residence time, substrate concentration, and electron-acceptor concentration) on the biodegradation of contaminants during transport in porous media. A suite of miscible-displacement experiments was conducted with different residence times and initial contaminant concentrations, using a petroleum-contaminated aquifer material and benzoate as a model compound. The results were evaluated using a framework developed from a mathematical analysis of the nondimensional parameters that control biodegradation during transport. The results show that the type of transport behavior observed is dependent upon system conditions and is predictable using the controlling- parameter approach. For benzoate, which is a relatively labile compound, transport was measurably influenced by biomass growth under most conditions tested, albeit to different extents. The exceptions occurred when either the substrate or oxygen (electron acceptor) concentrations were limiting. The results obtained from this study should improve our understanding of the coupled influence of residence time, substrate concentration, and microbial properties on the biodegradation of contaminants during transport in the subsurface.