Re-insight of the degradation of perfluorooctanoic acid (PFOA) through three-dimensional rotating gliding arc plasma

Perfluorooctanoic acid (PFOA), as a pollutant, is widely distribution in the environment. Owing to its stable C-F bond and high toxicity, PFOA seriously threatens ecological and biological health. In this paper, threedimensional (3D) gliding arc plasma discharging in gas-liquid phase is used to degrade PFOA in the artificially polluted water. We obtain that the defluorination rate reaches 50.37 %, the defluorination energy efficiency is 769.37 mg/kWh, and an energy consumption (EE/O) is 44.68 kWh/m3 after 60 min treatment in 3D gliding arc air plasma. Active radical concentrations of & sdot; O 2- , O3, H2O2, NO2- and NO3- in the gaseous and liquid phases varying with the solution pH and conductivity during the degradation process is noticed, and & sdot; O 2- playing the most important role in PFOA defluorination is conformed. Besides, the discharge characteristics are investigated by high-speed camera in whole discharge cycle, and the radical sorts in gaseous plasma are detected by optical emission spectroscopy (OES) for well understanding the degradation mechanism. With liquid chromatograph mass spectrometer (LC-MS) measurement, the intermediate and final products during PFOA degradation are found, and then the degrading pathways are proposed. Furthermore, the toxicity of the intermediates is simulatively analyzed, which demonstrates that the toxicity and bioaccumulation factors of the intermediates are greatly reduced after plasma treatment. Therefore, we believe that gliding arc plasma may be a promising plasma source for green, fast and efficient wastewater treatment.