Degradation kinetic of phthalate esters and the formation of brominated byproducts in heat-activated persulfate system

Abstract

The degradation kinetics of two phthalate esters (PAEs) (i.e., diethyl phthalate (DEP) and dibutyl phthalate (DBP)) in heat-activated persulfate (PS) system were studied and followed pseudo-first-order kinetics. Results demonstrated that both sulfate radical (SO4-·) and hydroxyl radical (HO) were responsible for degrading DEP and DBP. The pseudo-first-order rate constant (kobs) enhanced remarkably as reaction temperature and PS dosages increased, while it decreased as the initial PAEs concentrations increased. Lower pH values promoted the degradation over the pH range chosen here (5.0–8.0). Natural organic matter (NOM) and HCO3- showed inhibitory effects on PAEs degradation by quenching SO4-· and HO. At any pH value studied here, Cl− enhanced PAEs degradation at lower concentrations while it suppressed degradation as Cl− concentration further increased. The coexisting Br− hindered the degradation of PAEs mainly by suppressing SO4-·. Significant formation of dibromoacetonitrile (DBAN) and bromoform (TBM) was verified with Br− and NOM in the degradation system, while only TBM was detected without NOM. Bromate was also detected in the Br− containing degradation system. Generally, NOM facilitated the formation of brominated disinfection byproducts (Br-DBPs), while it suppressed the generation of bromate. Additionally, it is noteworthy that the degradation efficiency of DBP was higher than that of DEP probably owing to the longer alkyl side chain of DBP. The DBP degradation system was observed to form slightly more Br-DBPs than DEP, while bromate had an opposite trend. Besides, the potential initial degradation pathways of DEP and DBP were discussed by the computational analysis.