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Maximizing Hydrated Electron Concentration in the Advanced Reduction Process Treatment of Per- and Polyfluoroalkyl Substances Under Varying Source Water Matrices
Abstract
Ultraviolet advanced reduction processes (UV-ARP) have received significant attention in recent years for the treatment of recalcitrant contaminants, most notably per- and polyfluoroalkyl substances (PFAS). The effectiveness of UV-ARP contaminant destruction resides in the generation of a powerful reducing species – the hydrated electron (eaq-). This research investigates the factors that influence the available eaq- concentration ([eaq-]) in solution and subsequent contaminant degradation by first presenting results from an extensive literature review on UV-ARP. One major finding of our literature review was the lack of reported photochemical kinetic parameters, namely [eaq-] and eaq- scavenging capacity of a source water. Using a probe compound, we developed the Re,UV method to quantify these key photochemical kinetic parameters for any source water. We discovered that [eaq-] varied significantly throughout a 24 h treatment of perfluorooctane sulfonate, a PFAS known to be recalcitrant in UV-ARP treatment, due to several key eaq- scavengers present in the background source water matrix. One of those eaq- scavengers, dissolved organic matter, was found to both scavenge eaq- well into treatment (≥4 h) and screen UV photons from sensitizer illumination and subsequent eaq- formation. The Re,UV method proved to be useful tool in evaluating contaminant degradation in UV-ARP.
Furthermore, several recent studies have indicated that the most feasible application of UV-ARP for PFAS treatment would be after concentration with membrane technology or ion exchange. While these technologies do concentrate PFAS, the resulting background water matrix will have concentrated eaq- scavengers. We thus decided to deploy our Re,UV method to optimize [eaq-] and subsequent PFAS destruction in a surface water derived reverse osmosis concentrate. We discovered that ultraviolet advanced oxidation processes followed by UV-ARP led to the destruction of all detected PFAS but perfluorobutanesulfonic acid (PFBS) within 24 h in addition to the destruction of ammonium, nitrate, nitrite, and bromate. Furthermore, we observed the conversion of hard-to-treat fluorotelomers to reducible PFAS that were subsequently defluorinated, resulting in a total 90% defluorination at 24 h. Our results indicate that while PFAS can be destroyed in reverse osmosis concentrate by UV-ARP, additional research is needed prior to full scale application of this technology.
Subject
hydrated electronPFAS
PFOS
PFOA
PFBS
PFBA
fluorotelomer
nitrate
UV-ARP
UV-AOP
monochloroacetate
scavenging capacity
dissolved organic matter
reverse osmosis concentrate
electron pulse radiolysis
disinfection byproducts
Citation
Fennell, Benjamin D. (2023). Maximizing Hydrated Electron Concentration in the Advanced Reduction Process Treatment of Per- and Polyfluoroalkyl Substances Under Varying Source Water Matrices. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /200057.