| Abstract
| - The sorption kinetics and concentration of polychlorinatedbiphenyls (PCBs) in historically polluted sediment ismodeled to assess a remediation strategy based on insitu PCB sequestration by mixing with activated carbon (AC).We extend our evaluation of a model based on intraparticlediffusion by including a biomimetic semipermeablemembrane device (SPMD) and a first-order degradationrate for the aqueous phase. The model predictionsare compared with the previously reported experimentalPCB concentrations in the bulk water phase and in SPMDs.The simulated scenarios comprise a marine and afreshwater sediment, four PCB congeners, two AC grainsizes, four doses of AC, and comparison with laboratoryexperiments for up to 540 days of AC amendment slowlymixed with sediment. The model qualitatively reproduces theobserved shifts in the PCB distribution during repartitioningafter AC amendment but systematically overestimatesthe overall effect of the treatment in reducing aqueousand SPMD concentrations of PCBs by a factor of 2−6. Forour AC application in sediment, competitive sorption ofthe various solutes apparently requires a reduction by afactor of 16 of the literature values for the AC−waterpartitioning coefficient measured in pure aqueous systems.With this correction, model results and measurementsagree within a factor of 3. We also discuss the impact ofthe nonlinearity of the AC sorption isotherm and first-order degradation in the aqueous phase. Regular mixingof the sediment accelerates the benefit of the proposedamendment substantially. But according to our scenario,after AC amendment is homogeneously mixed into thesediment and then left undisturbed, aqueous PCBconcentrations tend toward the same reduction afterapproximately 5 or more years.
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