Chemical Process Engineering, University of Oulu, P.O. Box 4300, Oulu FIN-90014, Finland.
Department of Biochemistry and Biocenter, University of Oulu, Oulu FIN-99020, Finland.
Water Res. 2021 Oct 15;205:117676. doi: 10.1016/j.watres.2021.117676. Epub 2021 Sep 22.
Hydrated electrons (eE= -2.9 V) generated by advanced reduction processes (ARPs) have been proved to be a promising approach to eliminate various per- and polyfluoroalkyl substances (PFASs) in water. In this study, the decomposition of perfluorooctanoic acid (PFOA) in a complex water matrix by e generated from the UV/sulfite process was investigated. The effect of pH (9-12) and co-existing compounds (chloride, nitrate, phosphate, carbonate and humic acid) on PFOA degradation efficiency was studied. In addition, the intermediates and possible degradation pathways were analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS). The results showed that the concentration of PFOA was below the detection limit (10 μg/L) after 1 h (conditions: C 10 mg/L, initial pH = 10, sulfite 10 mM) while 89% defluorination was achieved after 24 h. Using a higher initial pH (pH = 12) greatly enhanced the PFOA degradation as 100% degradation and 98% defluorination were achieved after 24 h. The presence of carbonate (> 5 mM), nitrate (> 2 mM) and humic acid (> 25 mg/L) showed a significant negative effect on PFOA degradation via a UV blocking effect or quenching of hydrated electrons while the presence of chloride and phosphate had a smaller effect on PFOA degradation. Even at extremely high concentrations of chloride (1.709 M, pH = 11.25), the defluorination ratio reached 97% after 24 h of reaction time. During the process, short-chain perfluorinated carboxylic acids (PFCAs, C < 7) and hydrogen substituted compounds were detected, which implies that chain-shortening and H/F change reactions had occurred. Moreover, this confirmed the generation of sulfonated and unsaturated intermediates during the process, which disclosed valuable new mechanistic insights into PFOA degradation.
水合电子（eE=-2.9V）是通过先进的还原过程（ARPs）产生的，已被证明是消除水中各种全氟和多氟烷基物质（PFASs）的一种很有前途的方法。在本研究中，研究了由 UV/亚硫酸盐过程产生的 e 还原水中全氟辛酸（PFOA）的情况。考察了 pH 值（9-12）和共存化合物（氯离子、硝酸盐、磷酸盐、碳酸盐和腐殖酸）对 PFOA 降解效率的影响。此外，通过超高效液相色谱-串联质谱（UPLC-MS）分析了中间产物和可能的降解途径。结果表明，在 1 小时（条件：C10mg/L，初始 pH=10，亚硫酸盐 10mM）后，PFOA 的浓度低于检测限（10μg/L），而在 24 小时后达到 89%的除氟率。使用较高的初始 pH 值（pH=12）可极大地增强 PFOA 的降解效果，在 24 小时后可达到 100%的降解率和 98%的除氟率。当存在碳酸盐（>5mM）、硝酸盐（>2mM）和腐殖酸（>25mg/L）时，由于紫外线阻断作用或水合电子的猝灭，对 PFOA 的降解会产生明显的负面影响，而氯离子和磷酸盐的存在对 PFOA 的降解影响较小。即使在氯离子浓度极高的情况下（1.709M，pH=11.25），反应 24 小时后除氟率仍达到 97%。在此过程中，检测到短链全氟羧酸（PFCAs，C<7）和氢取代化合物，这意味着发生了链缩短和 H/F 取代反应。此外，这证实了在该过程中生成了磺化和不饱和中间产物，这为 PFOA 降解提供了有价值的新机制见解。
