Abstract. Intermediate-scale experiments (meter-long, two-dimensional flow cell) were performed with aerobic biodegradation of benzoate substrate in physically heterogeneous (bimodal inclusive) media. Clastic heterogeneities were represented in a quasi-twodimensional field, with low-conductivity inclusions embedded in a high-conductivity sandy matrix. The two media had similar pore-scale dispersivities but the conductivity ratio (•1:50) incurred macrodispersive spreading in the longitudinal direction. The highconductivity sand was uniformly inoculated with Pseudomonas cepacia sp., and a pulse input of substrate and chloride ion tracer were evaluated. Degradation and growth were oxygen-limited under nonlinear dual-Monod kinetics and controlled by spatial and temporal variations in nutrient flux. The low-conductivity inclusions created regions of slow transport that prolonged the dual availability of both oxygen and substrate, which in turn enhanced microbial growth in these regions. Bacterial detachment was significant, and the fivefold increase in biomass due to growth was entirely accounted for in the aqueous effluent which displayed a complicated nonlinear breakthrough curve. Highresolution deterministic modeling was applied to simulate the intermediate-scale experiment, with parameters of the relevant constitutive relations calibrated independently through batch and small-scale column experiments. Parameter fitting to match flow cell data was avoided. This approach was taken in order both to test the predictive modeling capability as it would necessarily be used in a field application and to avoid the a priori assumption that all relevant processes were adequately represented in the respective constitutive theories. Analyses of the fit between the independently calibrated model and the flow cell data were then used to isolate processes for further experimental study. This iterative experimental/modeling approach identified processes that contributed (surprisingly) to biodegradation in heterogeneous media and yet are not currently incorporated in most mathematical models: (1) buoyancy effects associated with very small solution density variations, amplified in heterogeneous media, and (2) dynamic biological processes associated with growth, namely, endogenous respiration, cell division partitioning to the aqueous phase, and active adhesion/detachment that are strongly coupled to the transport of dissolved nutrients or microorganisms.

No abstract

ErrataSince this report was written, RAFT has undergone a lot of changes so that this report does not any longer reflect the current status of RAFT. An updated report is expected to be placed on WWW in the neas future. Please send an e-mail to if you want to be notified when the report becomes available on WWW. a,chilakapati@pnl.gov SummaryThis report documents the use of the simulator RAFT for the ReActive Flow and Transport of groundwater contaminants. RAFT can be used as a predictive tool in the design and analysis of laboratory and field experiments or it can be used for the estimation of model/process parameters from experiments. RAFT simulates the reactive transport of groundwater contaminants in one-, two-, or three-dimensions and it can model user specified source/sink configurations and arbitrary injection strategies. A suite of solvers for transport, reactions and regression are employed so that a combination of numerical methods best suited for a problem can be chosen. User specified coupled equilibrium and kinetic reaction systems can be incorporated into RAFT. RAFT is integrated with a symbolic computational language MAPLE, to automate code generation for arbitrary reaction systems.RAFT is expected to be used as a simulator for engineering design for field experiments in groundwater remediation including bioremediation, reactive barriers and redox manipulation. As an integrated tool with both the predictive ability and the ability to analyze experimental data, RAFT can help in the development of remediation technologies, from laboratory to field.

No abstract

No abstract

Abstract. Multisolute reactive transport was investigated in chemically heterogeneous systems to determine the influence of the shapes of the reactive heterogeneities (iron oxide inclusions) by comparison of two-dimensional heterogeneous experiments with spatially averaged models that had differing inclusion characterization. Eleven reactions were considered in this system, starting with adsorption of the initial solute (conEDTA) to Fe oxides, followed by two competing surface reactions: oxidation forming conIEDTA and Fe dissolution forming FenIEDTA and Co 2+. Spatial moments of the eight mobile species were compared between data and models. One spatially averaged model (homogeneous equivalent), which incorporated inclusion mass only, significantly under predicted oxidation (up to 74%), the influence of reaction kinetics, and species retardation. In contrast, the ensemble average model (incorporating inclusion mass and length) well predicted speciation, retardation, and skewness. This large difference in prediction between two spatially averaging models was caused by the lack of incorporation of contact time of solutes with iron oxides in the homogeneous equivalent model and the importance of the contact time with the differing timescales of reactions. Experimental and modeling results also showed that the uncertainty in prediction of specific species increased as the inclusions varied from more ideal (fixed-length) to more natural (variable-length) shape of inclusions.