Adsorption of polychlorinated biphenyls to activated carbon: Equilibrium isotherms and a preliminary assessment of the effect of dissolved organic matter and biofilm loadings

Abstract

Sequestration of polychlorinated biphenyls (PCBs) by activated carbon (AC) has been proposed as a remediation strategy for PCB-contaminated sediments. However, published PCB–AC adsorption isotherm data are sparse and, while sediment-derived dissolved organic matter (DOM) and biofilms are likely to be present in sediments, the impacts of these loadings have not been quantified. Batch laboratory experiments were undertaken to obtain equilibrium adsorption capacities, q e, for 9 PCBs on virgin AC, DOM-loaded AC, and biofilm-covered AC. Isotherm data fit the Freundlich isotherm equation (average R 2=0.94, n=27) over the range of aqueous concentrations studied (∼0.1–1000 ng/L). Planarity effects were evident at low aqueous concentrations only (0.1–10 ng/L), where q e of three PCBs of similar hydrophobicity decreased with an increasing number of ortho-chlorines, indicating steric hindrances attenuated adsorption. The values of q e for DOM- and biofilm-loaded ACs were approximately one order of magnitude smaller than those on virgin AC when normalized by the available AC surface area, indicating that PCB adsorption likely occurred on specific regions of the AC structure. Nevertheless, virgin and loaded ACs used in this study had sufficiently high PCB adsorption capacities to warrant further study as an in-situ remediation alternative for PCB-contaminated sediments.