A review on superior advanced oxidation and photocatalytic degradation techniques for perfluorooctanoic acid (PFOA) elimination from wastewater

Perfluorooctanoic acid (PFOA) has been identified as the most toxic specie of the family of perfluorinated car-boxylic acids (PFCAs). It has been widely distributed and frequently detected in environmental wastewater. The compound's unique features such as inherent stability, rigidity, and resistance to harsh chemical and thermal conditions, due to its multiple and strong C-F bonds have resulted in its resistance to conventional wastewater remediations. Photolysis and bioremediation methods have been proven to be inefficient in their elimination, hence this article presents intensive literature studies and summarized findings reported on the application of advanced oxidation processes (AOPs) and photocatalytic degradation techniques as the best alternatives for the PFOA elimination from wastewater. Techniques of persulfate, photo-Fenton, electrochemical, photo -electrochemical and photocatalytic degradation have been explored and their mechanisms for the degradation and defluorination of the PFOA have been demonstrated. The major advantage of AOPs techniques has been centralized on the generation of active radicals such as sulfate (SO4 center dot-) hydroxyl (center dot OH). While for the photo -catalytic process, photogenerated species (electron (e) and holes (h + vb)) initiated the process. These active radicals and photogenerated species possessed potentiality to attack the PFOA molecule and caused the cleavage of the C-C and C-F bonds, resulting in its efficient degradation. Shorter-chain PFCAs have been identified as the major intermediates detected and the final stage entails its complete mineralization to carbon dioxide (CO2) and fluoride ion (F-). The prospects and challenges associated with the outlined techniques have been highlighted for better understanding of the subject matter for the PFOA elimination from real wastewaters.

Automated summary

This article summarizes the research progress on the formation mechanism of perfluorooctanoic acid (PFOA) in wastewater, the reasons why it cannot be effectively treated by conventional methods, and the application of advanced oxidation processes (AOPs) and photocatalytic degradation techniques for PFOA removal. The study found that the active radicals generated by AOPs and the photogenerated species of the photocatalytic process can effectively attack PFOA molecules, leading to its efficient degradation and the formation of shorter-chain perfluorinated carboxylic acids. Eventually, PFOA is completely mineralized to carbon dioxide and fluoride ion. The prospects and challenges of these techniques are also discussed.