Abstract: The potential of hexachlorobenzen(HCB),one of POPs,decomposition by ultrasonic irradiation and its combination with other AOPs(advanced chemical oxidation processes) and surfactant addition was evaluated.Comparing the ultrasonic irradiation alone with the combination with the UV(ultraviolet) light irradiation,the degradation ratios were almost the same,40.0% and 39.7%,respectively.On the other hand,the degradation ratio increased to 49.4% when combining with photocatalysis possibly attributed to the promotion of the cavitation due to the addition of TiO₂ particles.When the surfactant concentration was increased to 0.1%,the degradation ratio increased to 49.2%.It seemed that the added surfactant could contribute to desorbing HCB from the sediment surface and increasing the effective reaction surface area.The degradation ratio of HCB under the dual-frequency ultrasonic irradiation was higher than that under the mono-frequency ultrasonic irradiation.After 1 h ultrasonic irradiation,the degradation ratio was 57.5% for the dual-frequency ultrasound of 20/176 kHz combination,whereas 3.67% and 41.0% for 20 and 176 kHz ultrasound,respectively.