Gas stripping coupled with in-situ oxidation assisted microwave remediation of contaminated soil for efficient removal of polycyclic aromatic hydrocarbons (PAHs)

Abstract

Thermal desorption technology at low temperatures has been extensively researched. However, the challenge remains in maintaining soil ecological function while effectively removing PAHs from contaminated soil using this method. Based on the gas hammer fragmentation concept, this study presents the strategy of gas stripping (steam extraction) coupled with microwave remediation. A multifunctional bluecoke-based modifier (MnO2/KHCO3@BC) was prepared followed by an investigation on the removal effect, soil characteristics and remediation mechanism of MnO2/KHCO3@BC-assisted microwave remediation of pyrene (PAHs model) contaminated soil. The research findings indicate that MnO2/KHCO3@BC is more effective in generating oxygen vacancies, facilitating surface electron transfer, and enhancing the oxidation effect of ROS on pyrene compared to KHCO3@BC and MnO2@BC. Despite having slightly inferior electromagnetic properties to BC, MnO2/KHCO3@BC could achieve a microwave remediation temperature of approximately 300 °C under optimal experimental conditions. MnO2/KHCO3@BC demonstrated remarkable pyrene removal efficiency with a maximum removal rate of 98.34%, making it an ideal candidate for pyrene remediation. Moreover, the remediated soil exhibited a weakly acidic nature, with a significant decrease in particle size and a substantial increase in potassium content. The study also highlighted a novel synergistic mechanism of ''microwave heating - gas stripping - oxidation,'' which can efficiently remove most of the pyrene adsorbed inside and outside of soil particles and degrade it into low-toxic and small-molecule organic matter, CO2, and H2O. Overall, the findings of this study could hold potential significance for upcoming endeavours concerning polluted industrial areas.