Novel FeII/EDDS/UV/PAA advanced oxidation process: Mechanisms and applications for naproxen degradation at neutral pH and low FeII dosage

The application of the integrated Fe II /EDDS/UV/PAA (FEUP) process (EDDS = ethylenediamine- N,N’ -disuccinic acid; PAA = peracetic acid) as a novel advanced oxidation process (AOP) for the degradation of a model contaminant, namely, naproxen (NAP), at neutral pH was investigated. The enhanced NAP degradation in this system at pH 7 was primarily attributable to the continuous activation of PAA via the UV-assisted Fe II /Fe III cycle. A four-phase conceptual process of NAP degradation was established. The instantaneous degradation stage (IDS), in which Fe II and PAA instantaneous react within 1 s, resulted in the degradation of ~ 20% of NAP. The rapid degradation stage (RDS), in which the regenerated Fe II rapidly activates PAA to produce the hydroxyl radicals (•OH) and organic radicals including CH 3 C(O)O•, CH 3 C(O)OO•, CH 3 OO• and •CH 3 (defined as R-C•) without being scavenged by the Fe II /Fe III -EDDS complexes, contributed to the degradation of ~ 55% of NAP. The slow degradation stage (SDS), during which Fe II /Fe III -EDDS complexes started competing for radicals, and resulted in the degradation of ~ 15% of NAP. The continuous degradation stage (CDS), in which hydrogen peroxide (H 2 O 2 ) was the only oxidant because PAA was exhausted, corresponded to the degradation of another ~ 10% of NAP. The effect of water matrices including Cl - /Br - , HCO 3 – /CO 3 2– , and humic acid (HA) was evaluated: Br - , HCO 3 – /CO 3 2– , and HA exhibited an inhibiting effect on NAP degradation, while Cl - showed no influence on NAP degradation in the FEUP process. A superior degradation performance was achieved under a low Fe II dosage and neutral conditions, demonstrating the great potential of the FEUP process for practical applications.