Removal of hexabromocyclododecane using ultrasound-based advanced oxidation process: Kinetics, pathways and influencing factors

In search of a sustainable water treatment process, this work evaluated the effectiveness of an ultrasound-based advanced oxidation process in the elimination of Hexabromocyclododecane (HBCD), a brominated flame retardant known for its toxic effects. Treatments were conducted using a probe-type sonicator of 20 kHz frequency, and the role of reaction parameters was studied subsequently. Under optimum reaction parameters of HBCD initial concentration (200 μM), ultrasound power level (375 W), H2O2 addition (20 ppm), solution temperature (30 °C), as well as pH (3), the highest possible pseudo-first-order degradation rate of k: 0.118 min−1, was obtained. The high-performance liquid chromatography analysis revealed the complete disappearance of HBCD within just 40 min of treatment. HBCD degraded products were detected via gas chromatography-mass spectroscopy analysis, whereas the extent of mineralization was examined by total organic carbon (TOC) analysis, which demonstrated high mineralization efficiency (72% TOC reduction). Moreover, Daphnia Magna bioassay was performed to evaluate the ecotoxicity of HBCD and its degraded products. The outcomes of this study indicated the degradation mechanism of HBCD to be dependent on thermal decomposition at the bubble interfacial region as the dominant pathway along with free radical attack as the successive steps of transformation. Overall, the study has demonstrated the effectiveness of ultrasound-based treatment in the complete elimination of recalcitrant organic pollutants. [Display omitted] •Mineralization of HBCD by sonolysis is effective.•72% of TOC removal was obtained within 40 min of treatment.•A complete removal of HBCD was achieved at optimum parameters.•Six degraded products of HBCD were identified via GC–MS analysis.•Ecotoxicity test indicates a decline in the toxicity with treatment time.