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 FeII/FeIII cycle. A four-phase conceptual process of NAP degradation was established. The instantaneous degradation stage (IDS), in which FeII and PAA instantaneous react within 1 s, resulted in the degradation of similar to 20% of NAP. The rapid degradation stage (RDS), in which the regenerated FeII rapidly activates PAA to produce the hydroxyl radicals (center dot OH) and organic radicals including CH3C(O)O center dot, CH3C(O)OO center dot, CH3OO center dot and center dot CH3 (defined as R-C center dot) without being scavenged by the FeII/FeIII-EDDS complexes, contributed to the degradation of similar to 55% of NAP. The slow degradation stage (SDS), during which FeII/FeIII-EDDS complexes started competing for radicals, and resulted in the degradation of similar to 15% of NAP. The continuous degradation stage (CDS), in which hydrogen peroxide (H2O2) was the only oxidant because PAA was exhausted, corresponded to the degradation of another similar to 10% of NAP. The effect of water matrices including Cl-/Br-, HCO3-/CO32-, and humic acid (HA) was evaluated: Br-, HCO3-/CO32-, 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 FeII dosage and neutral conditions, demonstrating the great potential of the FEUP process for practical applications.