Enhanced sonolytic mineralization of basic red 29 in water by integrated ultrasound/Fe2+/TiO2 treatment

Advanced oxidation processes (AOPs), based on hydroxyl radical ((OH)-O-center dot) induced oxidation, have been widely investigated to develop novel and green technologies for wastewater treatment. In this work, the degradation and mineralization of Basic Red 29 (BR29), a cationic azo dye, by ultrasound (US) at 300 kHz and 80 W was investigated. Even if ultrasound eliminated BR29 (30 mg L-1) in 1 h, a low degree of mineralization (similar to 10 %) was obtained due to the hydrophilic character of the byproducts formed during the sono-oxidative process. To overcome this weakness, an innovative technique integrating ultrasound/Fe2+/TiO2 was used and was found to be more effective for the degradation and mineralization of the dye. The amount of each catalyst was optimized for the three systems US/TiO2, US/Fe2+ and US/Fe2+/TiO2. The degradation rate of BR29 with US/Fe2+ and US/Fe2+/TiO2 treatments was, respectively, 2 and 2.34 times higher than that obtained with US alone. Correspondingly, the mineralization degree increased from 5 % with ultrasound alone to 10 % with US/TiO2, 35 % with US/Fe2+ and 64 % with US/Fe2+/TiO2 after 30 min of treatment and from 10 % with US to 13, 51, and 81 % with, respectively, US/TiO2, US/Fe-2+,Fe- and US/Fe2+/TiO2 processes after 1 h of treatment. These results showed a synergy of 1.41 at 30 min and 1.29 at 1 h between US/Fe2+ and US/TiO2 processes toward the mineralization of BR29. The mechanism of the beneficial effect of the US/Fe2+/TiO2 integrating treatment was clarified and discussed.