A Coupled Thermal Desorption Process for Decontamination of Polycyclic Aromatic Hydrocarbon from Soil: Important Role of the Steam Injection

Thermal desorption (TD) has been widely used for remediation of soils contaminated with volatile/semi-volatile contaminants. There is a need to reduce the temperature of TD technology to minimize energy consumption and soil damage. The effect of low-temperature TD coupled with steam injection (SI) on the remediation of PAH-contaminated soil was investigated in this study. It was shown that the addition of SI to the TD at both 150 and 250 degrees C improved the removal of LPAHs from soil, with better performance at 150 degrees C, especially for LPAHs with boiling points between 295 and 340 degrees C. In contrast, the addition of SI to the TD at both 150 and 250 degrees C reduced the removal of HPAHs from soil, particularly at 250 degrees C. Under TD at 150 degrees C, the removal of LPAHs and HPAHs were further promoted and limited with increasing SI flow rates, respectively. It was noted that the introduction of steam in the low-temperature TD only promoted the removal of LPAHs, and the effect was better with higher steam flow rate. The addition of 4 g/min steam to TD at 150 degrees C could accelerate 259.18% of the removal process of LPAHs, and could improve the removal of LPAHs by 17.88% while reducing the energy consumption by 29.18%. This promotion is likely attributed to the fact that the introduced steam facilitates the release of LPAHs inside the soil matrix through steam replacement, steam distillation, and stripping. In addition, the addition of SI to the TD has little effect on soil physicochemical properties.