Model of Activated Carbon Dose and Sediment-Water Diffusion Fluxes of Hydrophobic Organic Chemicals: Implications for Sediment Remediation

A model correlating the diffusion fluxof a hydrophobicorganic chemical and the activated carbon dose was established tooffer effective governance measures in sediment remediation. Activated carbon (AC) amendment is an effective strategyfor remediatingcontaminated sediment by hydrophobic organic chemicals. Reductionsof porewater chemical concentrations have been used for estimatingrecommended AC dose for effective sediment remediation, but the ACdose may have large uncertainties resulting from site-specific parameters.The present study examined sediment-water diffusion flux asan alternative assessment parameter by correlating diffusion fluxesof organophosphorus flame retardants (OPFRs) and polybrominated diphenylethers (PBDEs) with AC doses. AC at doses of 8-36% substantiallyreduced sediment porewater concentrations and diffusion fluxes ofthe target chemicals. Diffusion fluxes of OPFRs and PBDEs normalizedby their corresponding sediment concentrations significantly correlatedwith total organic carbon contents (r (2) = 0.57-0.93). A model was established to estimate the requiredAC dose for effective sediment amendment from the diffusion flux andsediment concentration of a target chemical. Using contaminated sedimentin a typical e-waste recycling zone, the AC doses (0.1 +/- 1.3-12.8 +/- 0.3%) required to reduce 90% of diffusion fluxes for tri-n-butyl phosphate and BDE-17 were within the recommendedrange (1.9 +/- 3.6-5.6 +/- 8.3%) in lowering porewaterconcentrations by the same magnitude. This finding suggested the feasibilityof the new model in supporting sediment remediation.