Enhanced oxidative degradation of decabromodiphenyl ether in soil by coupling Fenton-persulfate processes: Insights into degradation products and reaction mechanisms

Decabromodiphenyl ether (BDE-209) has extreme hydrophobicity, which results in its significant accumulation in soil, sediments and other solid materials. In this work, an oxidation method coupling Fenton with persulfate (PS) was proposed for the effective degradation of BDE-209 adsorbed on solid surfaces. After adding 0.1 M PS to the Fenton system at 1.0 h, the removal rate of BDE-209 was significantly increased from 62.2% to 94.0%. The degradation of BDE-209 in various soil samples was also investigated by the coupling Fenton-PS method. Removal efficiency of 73.4–95.8% was obtained, suggesting that this coupling method was feasible in real application. According to the radical scavenging experiments, •OH dominated the overall reaction of BDE-209 in the coupling system. Meanwhile, the enhanced removal was attributed to the generation of SO4•- from the catalytic decomposition of PS. The calculated energy barriers for SO4•- attacking on the carbons were smaller than •OH initiated reactions, which further confirmed that SO4•- plays a role in the accelerated removal of BDE-209. The initial attack of BDE-209 by SO4•- generated the SO4•- adducts, which may undergo debromination or CO bond cleavage reaction together with subsequent hydroxyl substitution to form the primary product OH-Nona-BDEs and pentabromophenol. Under the successive attack of radicals, these primary products were further transformed into lower-brominated hydroxylation products and bromophenols via direct debromination and hydroxyl substitution reaction. This work provides an economical and effective method for treating BDE-209 contaminated soils and samples.