In situ bioreclamation of contaminated groundwater

This report summarizes the results of a research project aimed at developing a better mechanistic understanding of the phenomena controlling in situ biological activity. A methodology involving laboratory-column experiments and computer modeling was utilized to investigate the formation of biologically active zones (BAZs) when a limiting electron acceptor (NO_3-) is injected along the flow path and the secondary utilization of trace-level pollutants contained in the water flowing through the BAZ. Laboratory experiments conducted in a unique one-dimensional porous-medium column demonstrated the relationship between lateral injection of NO_3- and the location and extent of BAZs when acetate was present as the sole carbon source. BAZs established and sustained by acetate and NO_3- were able to degrade trace-level halogenated compounds. The fundamental phenomena of BAZ formation and the utilization of limiting, nonlimiting, and secondary substrates were expressed quantitatively in a computer model that coupled principles of one-dimensional solute transport and steady-state-biofilm kinetics. A new, highly efficient solution algorithm was developed to solve directly for the steady-state profiles of the limiting substrate and biofilm mass, as well as for non-limiting and secondary substrates. The predictive ability of the model was verified by successful simulation of the laboratory experiments using independently determined kinetic parameters.