The presence of human-derived or naturally occumng volatile or nonvolatile toxic organic compounds in drinking water has become a problem of international concern. The presence of some toxic organic compounds in a few parts per billion is enough to render a water supply unpotable because it is haimful to long-term health, even though the water may have no discernible taste and odor. So waste water must be treated. There are several reports about water treatment in early literatures which use the power ultrasound wave to degrade the organic compounds in water. The chemical effects of ultrasound derive from acoustic cavitation. Cavitation is a source of radicals, especially the hydroxy radical, "OH, the veiy strong and nonspecific oxide which escapes out of the bubble and reacts rapidly with compounds in solution. In this paper, degradation effects of ultrasound on pentachlorophenol (PCP) is researched. PCP is treated by low frequency (16 kHz) , high frequency [(800 ±1) kHz], and bi- frequency (combined of 16 kHz and 800 kHz) ultrasound wave, respectively. The results show that the rate of PCP degradation under the same conditions is highest at bi-frequency, lowest at 16 kHz. In the presence of Fenton type reagent the rate of PCP degradation is highest at bi-frequency which is 20.93 times as high as that of the stirring system without ultrasound wave. The ratios are 4.91 and 1.06 at 800 and 16 kHz, respectively. The studies show that the bi- frequency ultrasound is an effective method for pollutants degradation, but it need to make further study.

Key words: PHENOL P, HYDROXY GROUP, FREE RADICAL, DEGRADATION, INDUCTION, ORGANIC POLLUTANTS