Mesocosm Studies on the Efficacy of Bioamended Activated Carbon for Treating PCB-Impacted Sediment

This report describes results of a bench-scale treatability study to evaluate the efficacy of bioaugmentation with bioamended activated carbon (AC) for in situ treatment of polychlorinated biphenyl (PCB) impacted sediments. To this end, the ability of PCB transforming microorganisms to degrade and reduce the overall concentration of PCBs in sediment was determined in 2 L recirculating mesocosms designed to simulate conditions in Abraham's Creek in Quantico, Virginia. Ten sediment mesocosms were tested for the effects of AC alone, AC with slow release electron donor (cellulose) and different concentrations and combinations of PCB dehalogenating and degrading microorganisms added as bioamendments. A 78% reduction of total PCBs was observed using a cell titer of 5 × 10⁵ Dehalobium chlorocoercia and Paraburkholderia xenovorans cells g^-1 sediment with 1.5% AC as a delivery system. Levels of both higher and lower chlorinated congeners were reduced throughout the sediment column indicating that both anaerobic reductive dechlorination and aerobic degradation occurred concurrently. Porewater concentrations of all PCB homologues were reduced 94-97% for bioaugmented treatments. Toxicity associated with coplanar PCBs was reduced by 90% after treatment based on toxic equivalency of dioxin-like congeners. These results suggest that an in situ treatment employing the simultaneous application of anaerobic and aerobic microorganisms on AC could be an effective, environmentally sustainable strategy to reduce PCB levels in contaminated sediment.