Desorption of Polychlorinated Biphenyls from Contaminated St. Lawrence River Sediments with Supercritical Fluids

Abstract

Laboratory- and bench-scale polychlorinated biphenyl (PCB) desorption experiments using supercritical fluids are conducted on air-dried, contaminated St. Lawrence River sediments (SLRS) to demonstrate the remediation and scale-up potential of the process. Laboratory-scale desorption experiments reveal that PCB concentrations can be reduced from 2200 ppm to less than 5 ppm in 60 min (99.77% extraction efficiency) when supercritical CO2 with 5 mol % methanol is used at 118 bar and 323 K. Similar or better results are achieved at a bench-scale size of 2 L volume (400 × scale-up) under similar conditions. It is found that the PCB concentration in the sediments can be reduced from 1840 ppm to less than 5 ppm in ∼40 min (>99.73% extraction efficiency). The final PCB concentrations after 60 min of extraction are around 3 ppm, which is comparable with the final PCB concentrations of ∼4 ppm for the laboratory-scale experiments (when the supercritical fluid is CO2/MeOH). These results suggest that the scale-up factors are not significant over this range on the desorption processes of PCBs from real-world SLRS. A two-step linear driving force model is shown to predict well the bench-scale desorption results when using a model obtained independently and the effective diffusion coefficients and mass-transfer coefficients determined from the laboratory-scale information.