Peracetic acid-based UVA photo-Fenton reaction: Dominant role of high-valent iron species toward efficient selective degradation of emerging micropollutants

The activation of peracetic acid (PAA) by using Fe2+ has been used to degrade emerging micropollutants in water, the slow cycle of Fe3+/Fe2+ however limits the process efficiency, and debates on the dominant reactive species are still ongoing. This study investigated Fe2+-catalyzed PAA under ultraviolet-A (UVA) irradiation toward the degradation of five representative micropollutants (carbamazepine, diclofenac, naproxen, sulfamethoxazole and trimethoprim). The results showed that PAA was efficiently catalyzed by trace Fe2+ (≤ 10 μM) with the synergy of UVA, resulting in more efficient naproxen degradation than that by inorganic peroxides (H2O2/persulfates)-based photo-Fenton processes. Notably, high-valent iron (IV)-oxo complex (FeIVO2+) was identified as the primary reactive species in Fe2+/PAA/UVA process, whereas the generation of organic radicals and hydroxyl radical were quite minimal. As such, remarkable selectivity toward the degradation of multiple micropollutants were observed, which resulted in much faster degradation rates of naproxen and diclofenac than those of carbamazepine, sulfamethoxazole and trimethoprim. Moreover, the critical operating parameters were optimized based on the degradation kinetics of naproxen, and the application potential has been revealed by the efficient naproxen degradation in actual water samples. The findings highlight that the introduction of UVA in the Fe2+/PAA system not only solves the problem of the slow rate of Fe2+ regeneration, but also greatly decreases the iron sludge production by using trace Fe2+, making it attractive for practical application.