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 microbi al properties but also by physicochemical properties. The purpose of this w ork is to systematically evaluate the impact of coupled physicochemical fac tors (residence time, substrate concentration, and electron-acceptor concen tration) on the biodegradation of contaminants during transport in porous m edia. A suite of miscible-displacement experiments was conducted with diffe rent residence times and initial contaminant concentrations, using a petrol eum-contaminated aquifer material and benzoate as a model compound. The res ults were evaluated using a framework developed from a mathematical analysi s of the nondimensional parameters that control biodegradation during trans port. The results show that the type of transport behavior observed is depe ndent upon system conditions and is predictable using the controlling-param eter approach. For benzoate, which is a relatively labile compound, transpo rt was measurably influenced by biomass growth under most conditions tested , albeit to different extents. The exceptions occurred when either the subs trate or oxygen (electron acceptor) concentrations were limiting,The result s obtained from this study should improve our understanding of the coupled influence of residence time, substrate concentration, and microbial propert ies-on the biodegradation of contaminants during transport in the subsurfac e.