Remediation of soil contaminated with lubricating oil by extraction using subcritical water

The remediation of lubricating oil contaminated soil was investigated by extraction using subcritical water. The effects of temperature and time on extraction efficiency were studied by performing eight individual extractions and varying the subcritical water temperature (200, 225, 250, and 275 °C) and extraction time (90, 120, 180, and 240 min) in a dynamic mode. Also, a comparison was carried out of the feasibility of two operational modes, namely, dynamic and static-dynamic mode. Of the 25,088 mg/kg of lubricating oil as the total petroleum hydrocarbon (TPH) concentration in untreated soil, the residual concentration was found to be ∼500 and 235 mg/kg for after 120 min extraction in a lab-scale apparatus and 150 min extraction in a 30-fold scale-up experiment, respectively, at 275 °C in static-dynamic mode. The result of this study showed the significant effect of the static-dynamic mode on extraction efficiency. The time and volume of water needed for the static-dynamic mode were much lower than those needed for the dynamic mode. These results are of practical interest in developing the subcritical water extraction technology for extraction of lubricating oil and, in a broad sense, petroleum hydrocarbons contaminated soil.