Combination with ultrasound and Fe0 in sulfite activation to degrade Tribromophenol: Synergistic performance and mechanism

A novel advanced oxidation process combining low-frequency ultrasound (US) with zero-valent iron (Fe0) and sulfite (S(IV)) has been systematically developed. The combination showed significant synergy and considerable selectivity in the degradation of 2,4,6-tribromophenol (TBP). An 89.6 % removal of TBP was achieved within 30 min using a S(IV) concentration of 0.5 mmol/L and a Fe0 dosage of 0.05 g/L at pH 7.0, accompanied by ultrasonication at 40 kHz in the US/Fe0/S(IV) system. Mechanistic studies have indicated that SO4•− and •OH are the main reactive species in the system, and that •H plays an important role in the conversion of reactive species. The S(IV) activation mode by Fe0 has been found to be divided into homogeneous activation and heterogeneous activation during US. Moreover, US can improve the reactions by promoting mass transfer in the aqueous phase and between the solid and liquid. In the US/Fe0/S(IV) system, TBP degradation is promoted by increases in either US power, Fe0 dosage, or temperature. Too low or too high S(IV) concentration, pH, or dissolved oxygen can have an adverse effect on the reaction. Cations have little influence on the system, except for Cu2+, while anions inhibit the degradation of TBP, except for SO42−. The presence of humic substances (humic acid and fulvic acid) significantly inhibits TBP degradation. Overall, this work provides a new technique for water treatment with high efficiency and application potential.