Abstract
This work deals with the ultrasonic degradation (800
kHz) of crystal violet (CV) under different experimental conditions. The effects of saturating gas (argon, carbon dioxide and air), CV concentration (2.45–1225
μmol
L
−1), pH (3–9) and power (20–80
W) were evaluated. The best performances were obtained at 80
W with argon as a saturating gas. The pH had no significant effect. The influence of several water matrices containing anions (chloride, sulphate and bicarbonate) and cations (Fe
2+) on the sonolytic degradation of CV was also investigated. Significant differences were not observed with the presence of chloride and sulphate. However, at relatively low pollutant concentration (2.45
μmol
L
−1) bicarbonate showed a particular effect: a high bicarbonate concentration (350
mmol
L
−1) produced a detrimental effect, while a low bicarbonate concentration (3
mmol
L
−1) increased the efficiency of the process. The presence of Fe
2+ (1
mmol
L
−1) also increased the CV (49
μmol
L
−1) degradation by 32% after 180
min. Analyses of intermediates by GC–MS led to the identification of several sonochemical by-products:
N,
N-dimethylaminobenzene, 4-(
N,
N-dimethylamino)-4′-(
N′,
N′-dimethylamino)benzophenone, and
N,N,N′,N′-tetramethyl-4,4′-diaminodiphenylmethane. The presence of these aromatic structures showed that the main ultrasonic CV degradation pathway is linked to the reaction with
OH radicals. At the end of the treatment, these early products were converted into biodegradable organic by-products which could be easily treated in a subsequent biological treatment.