Defluorination of per-fluorinated compound (PFC) by microwave discharge plasma in liquid: A green and efficient water treatment technology

Abstract

Per-fluorinated compound (PFC) is a kind of persistent and refractory organic pollutants with high concerns in recent years. Perfluorooctane sulphonate (PFOS) and Perfluorooctanoic acid (PFOA) are the most typical per-fluorinated compounds in the water environment. In this work, a new treatment method-microwave discharge plasma in liquid (MDPL) is used to study the defluorination of PFOA and PFOS. The effects of initial concentration of pollutants, microwave input power, distance between electrode and liquid according to the characteristics of pollutants on the defluorination rate are studied. The results show that the defluorination of PFOA and PFOS by MDPL is excellent, with the defluorination of 58.4% and 26.8%. Because MDPL has high mass transfer efficiency and the discharge process is accompanied by the production of ultraviolet light and reactive species. Adding Fe2+ to synergistic degradation, the defluorination of PFOA is 82.9%, PFOS is 52.6%. The defluorination increased by 24.5% and 25.8%, the synergistic factor reached 2.18 and 2.37. Reactive species experiments confirms that eaq- is the key reactive species that initiates the decomposition of PFOA and PFOS. In addition, the characteristics of intermediates and free radicals in the process of defluorination are discussed. Reactive species experiments confirms that eaq- is the key reactive species that initiates the decomposition of PFOA and PFOS. Finally, the decomposition mechanism of PFOA and PFOS are analyzed and the degradation pathway of the reaction processes is given. This work proves that MDPL is efficient for the defluorination of PFOA and PFOS, which also provides a new insight for the treatment of PFC pollution.