Degradation of polycyclic aromatic hydrocarbons in aqueous solutions by ultrasonic irradiation

The effect of various operating conditions (initial concentration, liquid phase temperature, applied power, ultrasound frequency) and of the presence of matrix components (1-butanol, NaCl and FeSO(4)) on the sonochemical degradation of naphthalene, acenaphthylene and phenanthrene in water has been studied. A horn-type sonicator was used to deliver the ultrasound energy, while immersion sampling solid-phase microextraction (SPME) coupled with GC-MS was employed to follow concentration-time profiles of the chosen PAHs. At the operating conditions in question (initial concentrations of 150, 300 and 450 microg/l, temperatures of 20 and 40 degrees C, applied power of 45, 75 and 150 W and ultrasound frequencies of 24 and 80 kHz), all PAHs were susceptible to sonochemical treatment and, in most cases, complete degradation could be achieved in up to 120 min of treatment. Conversion was found to decrease with increasing initial concentration and temperature and decreasing power and frequency as well as in the presence of an excess of dissolved salts. Addition of 1-butanol, a known hydroxyl radical scavenger, substantially suppressed degradation throughout the course of the reaction, thus highlighting the role of oxidation reactions in PAHs degradation. In contrast, addition of Fe(2+) ions at a low concentration enhanced degradation through a Fenton-like reaction.