Remediation of PAHs contaminated soil by extraction using subcritical water

The remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil has been investigated by extraction using continuous flowing subcritical water. Water temperature ranging from 100 to 300 °C, extraction time ranging from 15 to 60 min, and flow rate ranging from 0.5 to 2.0 mL/min were investigated to determine their effect on the removal efficiencies of target PAHs. More than 95% extraction of the phenanthrene, fluoranthene, and pyrene from contaminated soil was observed at 300 °C for 30 min and 250 °C for 60 min at a constant pressure of 100 bar. However, naphthalene was almost completely extracted only at a comparatively low temperature of 150 °C and extraction time of up to 30 min and a pressure of 100 bar. The subcritical water flow rate of 0.5 mL/min was recommendable in this study. The extraction efficiency of PAHs was extremely dependent on water temperature, since the dielectric constant (polarity) of water could be dramatically lowered by raising the water temperature. These results suggest that soils contaminated by persistent organic chemicals such as PAHs can be easily remediated by extraction using pure water under a high temperature without any modification.