Comparison of sulfate and hydroxyl radical based advanced oxidation of phenol

UV-C photo-assisted persulfate (PS), hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) oxidation processes were evaluated and compared for aqueous phenol degradation. The effect of initial oxidant concentration on PS/UV-C, H2O2/UV-C and PMS/UV-C treatment efficiencies was examined on the basis of phenol and total organic carbon (TOC) removals. Complete phenol degradation could be achieved under all examined reaction conditions with apparent phenol degradation rate constants varying between 0.069 ± 0.002 – 0.382 ± 0.003 min−1 accompanied with complete TOC removals (⩾97%) under optimized PS (20 mM), H2O2 (30 mM) and PMS (20 mM) concentrations. Hydroquinone, catechol and benzoquinone were quantified during H2O2/UV-C and PMS/UV-C treatment of phenol verifying a HOHO-dominated oxidation pathway. During PS/UV-C oxidation, the identification of benzoquinone and 3-phenoxyphenol verified the hydroxycyclohexadienyl radical and phenoxyl radical pathways in SO4- mediated phenol oxidation.

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► Phenol was oxidizedvia persulfate, hydrogen peroxide and peroxymonosulfate/UV-C processes.
► Complete phenol and TOC removals were achieved.
► Several oxidation products of phenol were identified via GC/MS and HPLC analyses.
► Dimerization products were evidenced for both studied oxidation processes.
► A hydroxycyclohexadienyl- and phenoxyl radical-initiated degradation pathway was postulated.