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Asadi Zeidabadi, Fatemeh

University of British Columbia

The global spread of over 14,000 per- and poly-fluoroalkyl substances (PFAS) has raised environmental concerns, triggering substantial efforts in developing PFAS treatment technologies. This study focuses on the applications of boron-doped diamond-electrochemical processes for remediation of PFAS-contaminated waters. Perfluorooctanoic acid (PFOA) and its common alternatives, including perfluorobutanoic acid (PFBA), hexafluoropropylene oxide dimer acid (HFPO-DA/GenX), and 6:2 fluorotelomer carboxylic acid (6:2 FTCA) were selected as representative of legacy, emerging, and precursor PFAS. This research offers valuable insights into the impact of key operational and solution parameters on the efficiency of electrochemical systems. Subsequently, the degradability, fluorine recovery, transformation pathway, and contributions from electro-synthesized radicals for the studied PFAS were investigated. The results indicated the significance of chain length and structure, with slower decay rate (min-1) obtained for shorter chains: PFBA (0.008)<GenX (0.013)<PFOA (0.019)<6:2 FTCA (0.031). Along with the main contribution of direct electron transfer (DET) in destruction of the studied PFAS, results indicated important role of SO₄˙ˉ in oxidizing all PFAS, while ˙OH only involved in 6:2 FTCA decomposition. Proposed decomposition pathways suggested that upon DET to the anode and the attack of active species, PFAS could undergo different pathways: (1) functional group cleavage such as -COOˉ in the case of PFCAs and GenX or -CH₂OOˉ for 6:2 FTCA, (2) breakage of etheric bond in GenX, and (3) H-abstraction by the attack of ˙OH to non-fluorinated carbon in 6:2 FTCA. This work is the first to comprehensively investigate the integrated ion-exchange (IX) and electrochemical processes for sustainable PFAS treatment, evaluating system efficiency with various salts ranging from 0.1% to 8%. The findings revealed the potential of alternative salts, such as sulfate and bicarbonate, for superior effectiveness in electrochemical system when compared to the commonly used NaCl. Notably, chloride demonstrated adverse effects, leading to decreased efficiency and the generation of undesirable by-products such as chlorate and perchlorate. The study also investigates the impact of coexisting organic and inorganic constituents on the efficacy of IX/electrochemical process and provides valuable insights into the application of electrochemical process for treating real water samples (e.g., IX brine solution and landfill leachate), enriching water purification methodologies.

Text

2025-04-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87723

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/