LAUSR

Abstract This study aimed to prove color reduction of dark green Rit dye using nanobubbles (NBs) in comparison with using Al3+ alone and H2O2 alone, and to observe the role of positive NBs, reactive species on decolorization ratio in the processes using NBs alone, ultrasonic NBs, and NBs/H2O2. The color removal processes with Al3+ alone and H2O2 alone were performed using a jar tester while bubbling solutions were injected at a bubble rate of 30% through the bottom of a column reactor containing Rit dye at concentrations of ∼500 and ∼1200 CU. Our experimental results indicated greater color removal for weaker colors. Further, the decolorization rate using NBs systems was more efficient than that using conventional processes. In both dye concentrations, positive ultrasonic NBs (ZPs of +15 mV to +20 mV) and positive NBs/H2O2 (1 mM) systems were found to be effective treatment processes. The color removal mechanisms were owing to the electrostatic attraction between the positive NBs and dye components; furthermore, reactive species such as OH∙, HO2∙, and O2∙ were fundamental in enhancing Rit dye degradation in ultrasonic NB and NBs/H2O2 systems. More than 90% of Rit dye removal was obtained within 30 min and after 60 min in the ultrasonic NB and NBs/H2O2 systems, respectively. Different decolorization times under various NBs presences were attributed to the transfer from the bubbly regime to aggregate regime, and the reaction kinetics of the reactive species and Rit dye components. The NBs processes were confirmed to be reliable evidence for the decolorization of polluted waters.