Enhanced degradation performance and mechanisms of decabromodiphenylether in homogeneous system of Fe³⁺ activated dithionite

Brominated flame retardant (BFR) generally could be debrominated and degraded effectively by photolysis with high energy demand and waste production. However, in this study, an innovatively non-photolysis system based on dithionite (DTN) has been established for BFR treatment in water to meet the requirement of low-carbon and sustainable development. Fe³⁺-activated dithionite (DTN), a homogeneous non-photolysis coupled system, was innovatively used for decabromodiphenylether (BDE-209, a frequently detected priority contaminant in several environmental matrices) degradation effectively in 30 min with the simultaneous debromination and mineralization. Based on scavenging experiment and ESR analysis, SO₄^•-, •OH, and SO₃^•- were confirmed to be responsible for BDE-209 removal in Fe³⁺/DTN system. And the contribution rates of SO₄^•-, ·OH, and other species were about 47.5%, 30.8%, and 21.7% for BDE-209 degradation, respectively. Moreover, based on central composite design (CCD) in response surface methodology (RSM), a satisfactory quadratic model with low probabilities (<0.0001) at a confidence level of 95% was established to predict BDE-209 degradation in Fe3+/DTN system (R2 = 0.9691, R2-adj = 0.9413). Furthermore, the predicted BDE-209 degradation efficiency (C/C₀ ≈ 0.11) was achieved with the optimum Fe³⁺ dosage, DTN dosage and initial pH of 81.78 μM, 173.26 μM, and 6.27, respectively. Furthermore, debromination stepwise, hydroxylation, and mineralization were involved for BDE-209 degradation in Fe³⁺/DTN system according to the identified intermediates by gas chromatography–mass spectrometry (GC–MS). And due to the generated mixture including BDE-209 derivates, intermediates and bromide ion, the toxicity effect on Photobacterium phosphoreum growth was increasing in the initial BDE-209 reaction stage and then decreasing to be lower than that of BDE-209 itself. This study has revealed a promising system of DTN activated by Fe³⁺ for BFRs in-situ degradation and detoxification with the synergetic debromination and mineralization.