Radical chemistry of diethyl phthalate oxidation via UV/peroxymonosulfate process: Roles of primary and secondary radicals

The UV/peroxymonosulfate (PMS) process forms hydroxyl radicals (OH) and sulfate radicals (SO4−) to degrade micro-pollutants. Both these two radicals can be converted to secondary radicals (e.g. Cl2−, CO3− and Cl) by effects of water matrix components. By using laser flash photolysis, the second-order rate constants for reactions of three PAEs with OH, SO4−, Cl2−, Cl and CO3− were determined as (3.5–4.4) × 109, (4.9–5.6) × 108, (1.1–1.3) × 107, (1.8–2.0) × 1010 and <1 × 106 M−1s−1, respectively. Then diethyl phthalate (DEP) was selected as the target compound to investigate the radical chemistry of its degradation during the 254 nm UV/PMS process. Multiple effects of water matrix components in DEP degradation were investigated. Alkaline condition, chloride, bicarbonate and natural organic matter (NOM) inhibited DEP degradation while their effects were radical specific. SO4− could better withstand the negative effect of alkaline condition, bicarbonate and NOM than OH, while OH was less affected by chloride than SO4−. Cl accounted for 12% of DEP degradation in the presence of 1 mM chloride. Cl2−, CO3− and 1O2 hardly contributed to DEP oxidation but they might be involved in the further oxidation of transformation intermediates. Transient-state intermediates and steady-state products were identified by time-resolved spectroscopy and GC-MS, respectively, from which the degradation pathways of DEP in different water matrices were proposed.