Sonochemical degradation of PAH in aqueous solution. Part I: Monocomponent PAH solution

The sonolysis of selected monocomponent PAH aqueous solution is studied at 20 and 506 kHz in the μg l−1 range. The highest activity observed at 506 kHz, compared to 20 kHz, is tentatively explained by examination of the physical characteristics of bubbles (size and life-time) as well as by the calculation of the number of bubble at both frequency (5 × 103 bubbles l−1 at 20 kHz and 4.5 × 109 bubbles l−1 at 506 kHz). It is demonstrated that the main mechanism of sonodegradation is the pyrolysis of PAHs in the heart of the cavitation bubbles, and that a possible PAH oxidation by means of HO° appears as a minor way, since gaseous byproducts such as CO, CO2, C2H2 and CH4 have been detected. Correlations have been found by examination of kinetic variations in terms of the physical–chemical properties of PAHs. The rate constants of PAH degradation increase when the water solubility, the vapour pressure and the Henry’s law constant increase.