Kinetics of BTX biodegradation and mineralization in batch and column systems

Flow-through column and liquid batch experiments were performed in the present study in order to evaluate whether the kinetics of biodegradation reactions of organic contaminants for batch conditions were comparable to those measured under solid-to-solution ratios applicable to aquifer or water-saturated soil systems. The biodegradation of benzene, toluene, and xylene was observed under oxic conditions. Steady-state reaction rates were determined for the biodegradation reactions in the flow-through columns and evaluated using a rate law based on the Monod equation for conditions where bacterial growth is negligible. Calculated rate constants (k(1)) for biodegradation, or substrate disappearance, for sole substrate experiments were 1.32 mmol L(-1) h(-1) for benzene, 1.42 mmol L(-1) h(-1) for toluene, and 0.833 mmol L(-1) h(-1) for xylene. Rate constants were determined for batch experiments using a rate law based on the Monod equation that does account for bacterial growth. The maximum specific growth rate, mu(max), was found to be similar between batch and column experiments, indicating that there were no mass-transport limitations in the columns and that the solid-to-solution ratio was not a significant factor affecting kinetic parameters. There is considerable variability in rate constants for BTX biodegradation reported in the literature, up to two orders of magnitude for mu(max). Rate constants from this study were within the range of published values. For the experiments reported here, rates determined for sole carbon sources could be used to predict the reaction rates of BTX mixtures given some adjustment of cell yields and lag times.