Abstract
Herein, we present an original report on chlorine activation by ultrasound (US: 600 kHz, 120 W) for intensifying the sonochemical treatment of hazardous organic materials. The coupling of US/chlorine produced synergy via the involvement of reactive chlorine species (RCSs: Cl-center dot, ClO center dot and Cl-2(center dot)-), resulting from the sono-activation of chlorine. The degradation of Allura Red AC (ARAC) textile dye, as a contaminant model, was drastically improved by the US/chlorine process as compared to the separated techniques. A synergy index of 1.74 was obtained by the US/chlorine process for the degradation of ARAC (C-0 = 5 mg.L-1) at pH 5.5 and [chlorine](0) = 250 mM. The synergistic index increased by up to 2.2 when chlorine concentration was 300 mu M. Additionally, the synergetic effect was only obtained at pH 4-6, where HOCl is the sole chlorine species. Additionally, the effect of combining US and chlorine for ARAC degradation was additive for the argon atmosphere, synergistic for air and negative for N-2. An air atmosphere could provide the best synergy as it generates a relatively moderate concentration of reactive species as compared to argon, which marginalizes radical-radical reactions compared to radical-organic ones. Finally, the US/chlorine process was more synergistic for low pollutant concentrations (C-0 <= 10 mg.L-1); the coupling effect was additive for moderate concentrations (C-0 similar to 20-30 mg.L-1) and negative for higher C-0 (>30 mg.L-1). Consequently, the US/chlorine process was efficiently operable under typical water treatment conditions, although complete by-product analysis and toxicity assessment may still be necessary to establish process viability.