Degradation of the nonionic surfactant Triton^™ X-45 with HO and SO4- - Based advanced oxidation processes

In the present study the nonionic surfactant Triton^™ X-45 (TX-45), an octylphenol polyethoxylate, was treated by persulfate (S2O82-)/UV-C process involving the intermediacy of sulfate radicals and the relatively well-known hydrogen peroxide (H₂O₂)/UV-C process. TX-45 removal occurred rapidly via both advanced oxidation processes. Complete oxidation was also achieved under the studied reaction conditions, however required extended treatment periods (>30min) and high oxidant concentrations (≥2.5mM). Several degradation products could be qualified via GC-MS and HPLC analyses. Inspection of the identified degradation products indicated that the reaction mechanism of TX-45 was a combination of various pathways; (i) progressive shortening of the exhoxylate chain leading to relatively short-chain TX-45 and ultimately octylphenol, (ii) ω-carboxylation of the terminal alcoholic groups yielding octylphenol ethoxy carboxylates (OPECs) and (iii) central fission of the ethoxy chain resulting in the formation of polyethylene glycols (PEGs). Continued oxidation of the primary degradation products resulted in mono- and di-carboxylated PEGs. Degradation products bearing a smaller number of ethylene oxide units (≤3) were generated during H₂O₂/UV-C treatment, whereas OPECs was only detected during S2O82-/UV-C treatment of TX-45. Acetic and succinic acids were quantitatively identified during S2O82-/UV-C treatment, whereas oxalic and fumaric acids were additionaly detected during H₂O₂/UV-C oxidation. Product identification suggested similar reaction pathways for the treatment of TX-45 by SO4-- and HO-driven oxidation processes.