Removal of bromoamine acid in dye wastewater by gas-liquid plasma: The role of ozone and hydroxyl radical

As a widely used anthraquinone dye intermediate, bromoamine acid (BAA) exists extensively in dye wastewater. In this study, the gas-liquid discharge non-thermal plasma technology was employed to degrade BAA. Efficient removal was achieved by the system within 15 min treatment. Besides, the effects of input power, working gas flow rate and solution pH value on BAA removal efficiency were investigated. BAA removal rate increased with higher input power and lower pH value, while too high or too low working gas flow rate could lead to the decrease of BAA removal. The existence of BAA caused significant decline of aqueous ozone concentration while enhanced the production of H2O2, indicating that the aqueous ozone participated in BAA degradation. The contributions of main active species were investigated. H2O2 and UV produced by discharges showed little effects on BAA degradation individually, however led to synergistic effect by producing (OH)-O-center dot. Over 60 % removal of BAA was attributed to (OH)-O-center dot oxidation, while direct molecular ozone contributed around 20 % degradation. The second-order rate constants of BAA reacting with ozone and (OH)-O-center dot were determined to be 1.22 x 10(3) M-1 s(-1) and 4.06 x 10(9) M-1 s(-1), respectively. A kinetic model was established to predict BAA degradation. 12 degradation intermediates were detected by HPLC-Q-ToF-MS, GC-MS and HPLC-UV. The degradation was mainly caused by hydroxylation, bond cleavage and addition of (OH)-O-center dot on double bonds.