The degradation pathways and mineralization of perfluorooctanoic acid (PFOA)

Perfluorooctanoic acid (PFOA) is an anthropogenic contaminant different from most other organic pollutants. Notably, PFOA is water soluble, does not bind well to soil or sediments, and bio-accumulates in serum rather than in fat. PFOA thus enhances the health risks, including endocrine disrupting properties, immunotoxicity and developmental effects etc. In addition, PFOA is extremely resistant to environmental degradation processes and thus persists indefinitely. Reducing treatment technologies such as reverses osmosis, nano-filtration and activated carbon can remove PFOA from water. However, incineration of the concentrated waste is required for complete PFOA destruction. Unlike most other persistent and bioaccumulative organic pollutants, PFOA is oxidatively recalcitrant and resistant to most conventional treatment technologies. The related studies on the exploration and establishment of the effective degradation techniques for PFOA have become the new hotspot to the degradation of organic pollutants in the field of environmental technology. Recently, a number of chemical technologies for PFOA decomposition have been reported. This study briefly classifies the PFOA degradation techniques, including direct photolysis, oxidation, photochemical oxidation, photocatalysis degradation, electrochemical degradation, reducing degradation, high temperature pyrolysis and several coupling technology. Based on the classification, different PFOA degradation techniques are compared in terms of removal efficiency and the defluorination rate. The degradation mechanisms of different techniques are explored and the general laws of PFOA degradation and the inspiration for future techniques are summarized. The latest research progress are introduced. The most promising treatment alternatives to degrade PFOA efficiently, such as sonochemical, electrochemical and photochemical degradation are comprehensively discussed. Transient bubble collapses generate average vapor temperatures near 5000 K and could thermolysis PFOA quickly. Electrochemical decomposition of PFOA in aqueous solution performed well over several anodes, including Ti/SnO2-Sb-Bi, Ti/SnO2-Sb/PbO2 and Ti/SnO2-Sb/MnO2. PFOA molecule tightly configured on the In2O3 surface could be decomposed by photogenerated holes under UV irradiation. Nanostructured In2O3 with greater oxygen vacancy defects shows higher photocatalytic activity to degrade PFOA. Finally, The current problems are discussed and the future trends for the development to degrade PFOA in terms of the harmless treatment are prospected.