Biodegradation during contaminant transport in porous media: 8. The influence of microbial system variability on transport behavior and parameter determination

Abstract

[1] The impact of microbial system variability on the biodegradation and transport behavior of a model solute, salicylate, was investigated with a series of miscible displacement experiments. Four systems of increasing complexity were employed: a sterilized, well-sorted sand inoculated with a single bacterial isolate, a sterilized soil inoculated with the same isolate, and two soils, each of which contained an indigenous multiple-population community of bacteria. The experiments were conducted in replicate (three or four experiments per set) and with paired controls. The biodegradation and transport behavior of salicylate exhibited a small degree of variability among the replicates for the two inoculated systems and a relatively large degree of variability for the two indigenous systems. The greater variability observed for the two indigenous systems is attributed primarily to greater variability of microbial system properties, such as initial cell density, metabolic status, and community composition. Values for maximum specific growth rate coefficient, mean lag time, and lag time variance were determined by model calibration to the measured breakthrough curves and compared to values obtained from batch experiments. Reasonable correspondence was observed between the two sets of values for both the inoculated and indigenous systems. The maximum specific growth rate coefficient exhibited a relatively small degree of uncertainty for all four systems, whereas greater uncertainty was associated with the lag time mean and variance. The variability in calibrated parameters among each set of replicate experiments was significantly greater than the uncertainty associated with the individual experiment calibrations and the measured input parameters. These results illustrate that variability inherent to natural microbial systems can cause variability in transport behavior even under controlled laboratory conditions and concomitantly enhance the uncertainty of biokinetic parameters obtained from laboratory studies.

Physicochemical Heterogeneity Controls on Uranium Bioreduction Rates at the Field Scale

“…The goal of microbe-mediated bioremediation is to stimulate indigenous bacteria in situ to reduce and immobilize redox sensitive contaminants, such as uranium, by injecting organic carbon into the subsurface (e.g., refs − ). Although the idea has been demonstrated in laboratory systems successfully (e.g., ref ), the ultimate efficacy of bioreduction at the field scale is controlled by many factors, including, for example, bioreduction kinetics, substrates bioavailability, competition between coexisting electron acceptors, and characteristics of contaminated sites (e.g., refs − ).…”

Column transport studies of 3-nitro-1,2,4-triazol-5-one (NTO) in soils

“…If the amount of bacteria remains constant, the NTO transformation rate (m * X) stays the same and the BTC of NTO would attain steady state conditions wherein the effluent concentration of NTO remains constant during continued constant injection. However, depending on extant conditions, significant bacterial growth may cause an increase in the magnitude of NTO transformation, causing NTO effluent concentrations to decrease with time (e.g., Brusseau et al, 1999Brusseau et al, , 2006.…”

Modeling Dehalococcoides sp. Augmented Bioremediation in a Single Fracture System

“…The observed differences in model parameters estimated for the transport and batch model could be due to the heterogeneities present in the fractured system, and/or the elevated PCE and DCE concentrations observed in the fracture experiments compared to the batch experiments that were used to derive the Monod parameters. Several published studies have concluded that batch and column parameters could differ because of pore‐scale variations and other heterogeneities (Jeong‐Hun Park et al 2001; Brusseau et al 2006).…”