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 HO-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.