Pressure-assisted ozonation of PCB and PAH contaminated sediments

Sediment contamination by recalcitrant organics such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) is prevalent and of a great concern. Remediation efforts are hampered by the hydrophobic nature of the contaminants that limits their availability as well as by the sediment matrix that limits their exposure to treatment agents. Using contaminated sediment samples from the Passaic River, St. Louis River, Waukegan Harbor, and Wells National Estuarine Research Reserve, this research demonstrated a new ozonation technique that incorporates rapid, successive cycles of pressurization (690 kPa) and depressurization, enabling more effective treatment than conventional ozonation would. Conventional ozonation reached maximum 60% and 40% removal of PAHs from the Passaic River (40 mg kg−1 initially) and St. Louis River sediment (520 mg kg−1 initially), respectively, in 1 h; however, removals ceased despite prolonged treatment for 2 h. The pressure-assisted technique removed 96% of PAHs from both river sediments within 1 h; it completely removed both PAHs (16 mg kg−1 initially) and PCBs (5.1 mg kg−1 initially) from the Waukegan Harbor sediment in 0.5 h. The heightened treatment is explained by soil aggregate fracturing upon pressure cycles that exposes the contaminants as well as by the confluence of hydrophobic contaminants and O3 at the gas–liquid interface in the presence of microbubbles. The technique is expected to accelerate O3 treatment of a wide range of organic contaminants, and it may provide treatment to dredged and stored contaminated sediment.