Ultrasound has been found to be an attractive advanced oxidation technology for the degradation of hazardous organic compounds in water. The ultrasonic degradation of methylene blue as a model hazardous organic compound was carried out in the absence and presence of dimethyl sulfoxide (DMSO) as a radical scavenger for various frequencies and temperatures, and the effects of DMSO addition on the degradation rate constant estimated by assuming first-order kinetics were investigated. The degradation of methylene blue mainly proceeds via oxidation reaction with hydroxyl radicals, but also proceeds via a direct pyrolysis reaction. Also, the apparent degradation rate constant increased with increasing temperature both in the absence and presence of DMSO. The effects of degradation mechanism of activation energy was investigated, and the activation energy of hydroxyl degradation was higher than that of pyrolysis.
