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

Abstract

Activated carbon (AC) amendment is an effective strategy for remediating contaminated sediment by hydrophobic organic chemicals. Reductions of porewater chemical concentrations have been used for estimating recommended AC dose for effective sediment remediation, but the AC dose may have large uncertainties resulting from site-specific parameters. The present study examined sediment−water diffusion flux as an alternative assessment parameter by correlating diffusion fluxes of organophosphorus flame retardants (OPFRs) and polybrominated diphenyl ethers (PBDEs) with AC doses. AC at doses of 8−36% substantially reduced sediment porewater concentrations and diffusion fluxes of the target chemicals. Diffusion fluxes of OPFRs and PBDEs normalized by their corresponding sediment concentrations significantly correlated with total organic carbon contents (r 2 = 0.57−0.93). A model was established to estimate the required AC dose for effective sediment amendment from the diffusion flux and sediment concentration of a target chemical. Using contaminated sediment in 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 recommended range (1.9 ± 3.6−5.6 ± 8.3%) in lowering porewater concentrations by the same magnitude. This finding suggested the feasibility of the new model in supporting sediment remediation.