en Water quality and wastewater treatment and reuse Original articles <div style="text-align: justify;"><span style="font-size:11pt"><span style="line-height:115%"><span style="font-family:&quot;Calibri&quot;,sans-serif"><b><i><span lang="EN" style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,serif">Introduction:</span></span></span></i></b><span lang="EN" style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,serif"> Perfluorooctanoic acid (PFOA) is a persistent and toxic contaminant that requires effective degradation and defluorination strategies. Although several UV-based advanced oxidation and reduction processes have been investigated, direct comparisons under identical conditions are limited. In this study, we compared the degradation efficiency, mechanisms, and defluorination potential of three UV-based systems: UV/persulfate (UV/PDS), UV/peroxymonosulfate (UV/PMS), and UV/sulfite (UV/SS).</span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="line-height:115%"><span style="font-family:&quot;Calibri&quot;,sans-serif"><b><i><span lang="EN" style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,serif">Materials and Methods:</span></span></span></i></b><span lang="EN" style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,serif"> PFOA degradation experiments were conducted under 254 nm UV irradiation with an initial PFOA concentration of 0.24 mM and oxidant/reductant dosages of 1.0 mM. Reaction kinetics, transformation products, and fluoride generation were analyzed using LC‑MS/MS and ion chromatography over a 6‑hour treatment period.</span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="line-height:115%"><span style="font-family:&quot;Calibri&quot;,sans-serif"><b><i><span lang="EN" style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,serif">Results:</span></span></span></i></b><span lang="EN" style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,serif"> Direct UV photolysis was ineffective, achieving only 4% removal. Among the tested systems, UV/SS exhibited the highest performance, achieving 47% PFOA removal, compared with 24% and 31% for UV/PDS and UV/PMS, respectively. UV/PDS and UV/PMS primarily proceeded through oxidative radical pathways (sulfate and hydroxyl radicals), resulting in chain shortening and accumulation of shorter-chain perfluorinated carboxylic acids (PFHpA, PFHxA, PFPeA, PFBA, and TFA). In contrast, UV/SS operated through reductive pathways mediated by hydrated electrons, promoting sequential C&ndash;F bond cleavage and enhanced defluorination.</span></span></span></span></span></span><br> <span style="font-family:Times New Roman;"><b><i><span lang="EN" style="font-size:10.0pt"><span style="line-height:107%">Conclusion:</span></span></i></b><span lang="EN" style="font-size:10.0pt"><span style="line-height:107%"> The UV/SS process demonstrated the greatest potential for PFOA pretreatment due to its ability to achieve true defluorination, whereas oxidative systems mainly transformed PFOA into persistent short-chain intermediates.</span></span></span></div> PFOA, Advanced oxidation processes (AOPs), Ultraviolet/Sulfite, Defluorination, Water remediation, Perfluorinated compounds. 3032 3050 http://jehsd.ssu.ac.ir/browse.php?a_code=A-10-1310-1&slc_lang=en&sid=1 Ali Behnami ali.behnami64@gmail.com 0000-0001-9113-2102 No Department of Environmental Health Engineering, Iran University of Medical Sciences, Tehran, Iran Mojtaba Pourakbar ppourakbar@hotmail.com 0000-0002-8211-9640 No Department of Environmental Health Engineering, Maragheh University of Medical Sciences, Maragheh, Iran Khaled Zoroufchi Benis kh.benis@gmail.com 0000-0003-3532-6839 No Department of Process Engineering and Applied Science, Dalhousie University, Halifax, NS, Canada Mahdi Farzadkia mahdifarzadkia@gmail.com 0000-0001-7795-9461 No Department of Environmental Health Engineering, Iran University of Medical Sciences, Tehran, Iran Roshanak Rezaei Kalantari rezaei.r@iums.ac.ir 0000-0002-8071-9028 No Department of Environmental Health Engineering, Iran University of Medical Sciences, Tehran, Iran Mojtaba Yeganeh mybb123@yahoo.com 0000-0002-6790-670X No Department of Environmental Health Engineering, Iran University of Medical Sciences, Tehran, Iran Ali Esrafili a_esrafily@yahoo.com 0000-0002-2612-6977 No Department of Environmental Health Engineering, Iran University of Medical Sciences, Tehran, Iran Mitra Gholami gholamim@iums.ac.ir 0000-0003-3094-9893 Yes Department of Environmental Health Engineering, Iran University of Medical Sciences, Tehran, Iran