Microwave heating:A new high efficiency and low energy-consumption option for removing PFOA and PFOS from soil

Per- and polyfluoroalkyl substances (PFASs) are synthetic organic chemicals that are frequently detected in soil. Thermal treatment is an effective technique for removing PFASs from soil. However, the application of thermal treatment is a challenge because of the high energy consumption. Microwave heating (MWH) is proposed as an innovative thermal method for eliminating PFASs from soil. In this study, the removal efficiency, energy consumption and decomposition products were systematically investigated and compared with those of traditional electrical heating (EH). The results demonstrated that under optimal parameters (10 % moisture content, N₂ condition, and resistance time of 30 min), MWH could effectively remove more PFASs from soil. Specifically, the removal efficiencies of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) increased by 78.05 % and 24.82 %, respectively, at 200 °C and 300 °C via MWH. When the removal efficiency of PFASs reached over 95 %, the energy consumption of MWH was 74.33 %-76.19 % lower than that of EH. Decomposition mechanism of PFASs primarily included C-C and C-S bond cleavage and β-elimination defluorination. Additionally, MWH treated soil may be more effective in preserving soil fertility. This study provides new insights into efficient and energy-saving options for removing PFASs from soil.