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ABSTRACT: Laboratory experiments and numerical modeling were conducted to evaluate the secondary utilization of eight trace-concentration halogenated solvents in a denitrifying biologically active zone (BAZ) induced by nitrate injection into an acetate fed, porous medium column. Results of column experiments indicated that carbon tetrachloride was removed most completely by the denitrifying BAZ, while bromoform, dibromoethane, tetrachloroethene, trichloroethene, and 1,2-and 1,3-dichlorobenzenes were removed, but to lesser degrees. 1,1,1-trichloroethane removal was slight. Compounds were removed to higher degrees when the BAZ contact time was increased.

The steady-state, one-dimensional solute-transport equation was solved using an iterative finite-difference scheme and by employing a quasi-linearization technique for the biofilm reaction term. The model solved directly for the steady-state profiles of secondary substrates. One set of experimental results was used to obtain best-fit values of kinetic parameters, which were then used to predict the removal at different liquid flow velocities. The model predictions correctly described all experimental trends: removal of the halogenated compounds only in the BAZ, greater removal with increased BAZ contact time, and reduced specific removal rates caused by diffusion limitation in the biofilm.

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