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Chemical Geology
Vol. xx, No. xx, 2007; Pages: 1-11

Appropriateness of equilibrium assumptions for determining metal distribution and transport in bacteria-bearing porous media*

Benjamin F. Turner*, Jeremy B. Fein

Pennsylvania State University DuBois, DuBois, PA 15801, United States.


The fate and transport of strongly-sorbed contaminants in aquifers is tied to the mobility of the surfaces to which they are adsorbed. Mobile particulates, including mineral colloids, natural organic matter, ormicrobes, can enhance themobility of contaminants thatwould otherwise be adsorbed to stationary surfaces. In this study, we compare numerical transport simulations of systems involving dissolved metals and microbial suspensions with previously published experimental results. The transport simulations utilize a finite difference solute transport scheme, a colloid attachment term, and a Newton–Raphson chemical speciation solver assuming thermodynamic equilibrium in the metal distribution between solution, mobile surfaces, and stationary surfaces. While model predictions of metal breakthrough are of mixed quality, adjustment of model equilibrium constants is adequate to provide accurate fits to observed breakthrough curves. Therefore, the idealized behaviors apparent in experimental breakthrough curves indicate metal transport under equilibrium sorption conditions, and hence the assumption of chemical equilibrium used in the model is appropriate. Since flow rates in the column experiments are fast compared to most flow rates in aquifers, we conclude that the kinetics of metal redistribution are fast enough that an assumption of chemical equilibrium would be appropriate for modeling coupled solute–colloid transport in pore environments where water flow is controlled by advective transport under water velocity conditions typical for most aquifers.

Keywords:Metals, Bacteria, Aquifer, Cadmium, Transport; Equilibrium,clays,organic particulates,microbes,bacterial suspension,microbes and metals.

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