The degradation of pentachlorophenol (PCP) in aqueous solution by audible-frequency sonolytic ozonation was studied. The sonolysis of H2O and PCP/H2O solutions and the dissolution and decomposition of ozone under audible-frequency sonication were evaluated as well. The results showed that the ozone dissolution rate and PCP degradation rate were significantly enhanced by sonication in comparison to using mechanical stirring and O-3 bubbling alone. This enhancement is most likely attributed to the strong turbulence induced by sonication. The first-order rate constant of PCP degradation by ozonation with sonication is more than 15 times faster than that with bubbling ozone alone, while the rate constant with mechanical stirring is only four times faster. The influence of the ozone feed rate on PCP degradation and the degradation byproducts were examined as well. In addition, results showed that no H2O2 was generated by sonolysis of water with audible-frequency sonication and no PCP was degraded by sonolysis alone. (c) 2005 Elsevier B.V.