Destruction of Per- and Polyfluoroalkyl Substances (PFAS) with Advanced Reduction Processes (ARPs): A Critical Review

Abstract

Advanced reduction processes (ARPs) have emerged as a promising method for destruction of persistent perand polyfluoroalkyl substances (PFAS) in water due to the generation of short-lived and highly reductive hydrated electrons (e aq − ). This study provides a critical review on the mechanisms and performance of reductive destruction of PFAS with e aq − . Unique properties of e aq − and its generation in different ARP systems, particularly UV/sulfite and UV/iodide, are overviewed. Different degradation mechanisms of PFAS chemicals, such as perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), and others (e.g., short chain perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs), per-and polyfluoro dicarboxylic acids, and fluorotelomer carboxylic acids), are reviewed, discussed, and compared. The degradation pathways of these PFAS chemicals rely heavily upon their head groups. For specific PFAS types, fluoroalkyl chain lengths may also affect their reductive degradation patterns. Degradation and defluorination efficiencies of PFAS are considerably influenced by solution chemistry parameters and operating factors, such as pH, dose of chemical solute (i.e., sulfite or iodide) for e aq − photoproduction, dissolved oxygen, humic acid, nitrate, and temperature. Furthermore, implications of the stateof-the-art knowledge on practical PFAS control actions in water industries are discussed and the priority research needs are identified.

Photochemical Degradation of Short-Chain Chlorinated Paraffins in Aqueous Solution by Hydrated Electrons and Hydroxyl Radicals

“…72,[95][96][97] In this context, e -(aq) have received renewed attention with the report of e -(aq) mediated degradation of the emerging per-and polyfluoroalkyl substances (PFAS). 45,46,52,98,99 The results of this study also imply that e -(aq)generating engineered systems for water treatment would likely be effective for degrading SCCPs, and provides further support to the notion that e -(aq) is a versatile PPRI for degrading persistent organic pollutants.…”

“…In addition, the majority of previous research has focused on engineered systems for water treatment, not environmentally-relevant processes. 40,44,46,[51][52][53][54][55][56] The aim of this study was therefore to determine the reactivity of SCCPs with e -(aq), and compare it to •OH-mediated degradation. This knowledge will provide additional insights into their photochemical fate in surface waters.…”

Reductive Defluorination and Mechanochemical Decomposition of Per- and Polyfluoroalkyl Substances (PFASs): From Present Knowledge to Future Remediation Concepts

“…Advanced reduction processes (ARPs), reductive metals (e.g., zero-valent iron (ZVI)), hydride radicals (H·) and most notably hydrated electrons (E 0 = −2.9 V) have been used to achieve the effective cleavage of C−F bonds in PFASs [ 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 ]. The investigation of PFAS reduction reactions have shown that they are sensitive towards the choice of reagents, their concentrations and reaction times as well as pH value of the solution [ 74 , 75 , 76 ], thus can show variable efficiencies. Hereafter, we give a detailed overview of recent developments of PFAS-degradation based on reductive defluorination.…”

“…Oxidative and photochemical methods were often investigated in several research projects in the past [ 62 , 76 , 87 ]. The photochemical reduction was mainly performed with UV light and free reducing radicals formed from sulphite (SO 3 2- ), but other inorganic and organic compounds were also used.…”

“…Surveying the existing literature concerning PFASs in environmental ambience of the last two decades, it is evident that reported cases of contamination have grown drastically, whereas new insights of PFAS degradation slowly progressed [ 48 ]. Both advanced oxidation and reduction defluorination processes (AOP, ARP) have been developed, utilizing different reaction conditions ranging from basic thermal treatments up to sophisticated photooxidation catalysts [ 62 , 76 ]. Their reaction efficiencies vary from low percentage yields to quantitative decomposition and full mineralization.…”