Extraction of diesel from contaminated soil using subcritical water

In this study, a subcritical water extraction (SCWE) process for the remediation of diesel-contaminated soil was evaluated. The effect of operating parameters, namely extraction temperature (100–200 °C), time (30–60 min), and water flow rate (0.5–1.5 mL/min) were investigated using response surface methodology (RSM) combined with Box-Behnken Design (BBD). Results showed that temperature seems to play a major role in SCWE processes, and the proposed quadratic model was in accordance with the experimental data, with a correlation coefficient R ² = 0.981 and adjusted R ² = 0.947. By predicting the maximum removal efficiency of diesel (~100 %), the optimum extraction conditions were determined to be 200 °C, 60 min and 0.53 mL/min. This predicted value was further verified by 99.8 % removal of diesel from contaminated soil at the predicted optimum condition. The results confirmed that RSM based on the BBD was a compatible method for optimizing the operating conditions of diesel removal from soil. In addition, the results obtained in this study suggest that soil contaminated by diesel can be treated by extraction using pure water without any organic solvent.