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ABSTRACT: A methodology involving laboratory-column experiments and computer modeling was utilized to investigate the formation of denitrifying biologically active zones (BAZ's) in a porous medium when a limiting electron acceptor (NO3-) is injected along the flow path. Laboratory experiments conducted in a unique one-dimensional porous-medium column demonstrated the relationship between lateral injection of NO3- and the location and extent of BAZ's when acetate was present as the sole carbon source. The phenomena of BAZ formation and the utilization of limiting and non-limiting substrates were expresed 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 the non- limiting substrate. The predictive ability of the model was verified by successful simulation of particular laboratory experiments using independently determined kinetic parameters for acetate.

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