Degradation of the flame retardant triphenyl phosphate by ferrous ion-activated hydrogen peroxide and persulfate: Kinetics, pathways, and mechanisms

Abstract

The efficacies of ferrous ion-activated hydrogen peroxide (Fe2+/H2O2, Fenton) and persulfate (Fe2+/S2O82−, Fe2+/PS) processes for degrading triphenyl phosphate (TPhP) in aqueous solutions were systemically investigated and compared. Both Fenton and Fe2+/PS processes can effectively degrade TPhP in water. A fast TPhP degradation was achieved in 5 min by Fenton oxidation, while TPhP was gradually degraded with prolonging reaction time via Fe2+/PS oxidation. The effects of operating parameters, including oxidant and Fe2+ dosage, pH, and water constitutes, on TPhP degradation were systemically evaluated. TPhP removal was increased as the oxidant and Fe2+ dosage increase, while TPhP degradation was not greatly changed under the examined pH (4.0–9.0). Water constitutes, humic acid, and anions (Cl− and NO3−) did not obviously influence TPhP degradation for both processes. However, HCO3− significantly inhibited TPhP oxidation, and the inhibition was inversely related to HCO3− concentrations. Radical quenching experiments and electron paramagnetic resonance spectrometry revealed that HO was the dominant radical in Fenton process whereas SO4− played a dominant role in Fe2+/PS process for TPhP degradation. Moreover, TPhP removal in various natural water matrices was examined to better understand the feasibility of AOPs on the elimination of TPhP from natural waters. The lower removal of TPhP indicates that both of high oxidant dosage and/or long reaction time were required to achieve high removal efficiency and high mineralization. Furthermore, TPhP degradation products were identified through LC-MS/MS technology. Similar products were observed in both oxidation processes, and the degradation pathways mainly involved hydroxylation and phenoxy bond cleavage. The results of this study indicates that it is technically feasible for applying HO and SO4− based AOPs to treat TPhP contamination in water/wastewater.