Polychlorinated biphenyl sorption to activated carbon and the attenuation caused by sediment

Abstract

Activated carbon (AC) is currently being used to treat polychlorinated biphenyl (PCB) contaminated field sediment. In the presence of sediment, the sorption capacity of AC for PCBs can be reduced. In this study, sorption attenuation of AC is investigated using previously published data from 5 sampling sites where reductions in aqueous concentrations caused by AC amendment have been reported. AC-water partitioning coefficients (KAC_clean_water) were determined at a relevant PCB concentration in clean water using polyoxymethylene (POM) passive samplers. Logarithmic ACwater partitioning coefficient values ranged from 7.39 to 9.59 for trichlorinated to pentachlorinated congeners. These AC-water partitioning coefficients were used in a numerical model to predict expected reductions in aqueous concentrations. Results reveal an overprediction of actual reductions by a median factor ranging from 2.5 to 5.6. To obtain an estimate of AC sorption attenuation, an AC-water partitioning coefficient more representative of sediment conditions (KAC_apparent) was fitted via the model based on the observed reductions in aqueous concentrations. On average, median KAC_apparent values of individual PCB congeners were smaller than KAC_clean_water values by 1.08 log units, or a factor of 12, with corrections ranging from 0.1 to 2.3 log units. The main controls on the reduction in sorption of PCBs to AC are PCB physico-chemical properties and AC amendment variables. Generally AC sorption attenuation increased with PCB hydrophobicity and decreased with increasing AC-sediment contact time and AC dose.