Enhancement of ultrasonic and ultraviolet irradiation with chemical oxidants

Citation

Weavers, Linda K. (1998) Enhancement of ultrasonic and ultraviolet irradiation with chemical oxidants. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/WPCP-PA50. https://resolver.caltech.edu/CaltechETD:etd-02052008-100328

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The combination of ultrasound and ozone was used to study the degradation of nitrobenzene, 4-nitrophenol, 4-chlorophenol, cyclohexene, and pentachlorophenol in aqueous solutions. Using ultrasonic frequencies of 20 and 500 kHz revealed apparent enhancement at 20 kHz and antagonism at 500 kHz for the combined system although the first-order degradation rate constants in the absence of 03 (ozone) was typically a factor of 10 larger at 500 kHz. A comparison of the first-order degradation rate constants for nitrobenzene, 4-nitrophenol, and 4-chlorophenol by sonication, ozonation, and the combination of sonication and ozonation revealed that the observed enhancement upon the combination of ultrasound and ozone is mainly the result of thermolytic decomposition of ozone in a collapsing cavitation bubble. A continuous flow reactor closed to the atmosphere, open to the atmosphere, and open to the atmosphere with gas bubbling was used to probe the effects of ultrasound on [...] mass transfer. Enhanced mass transfer of [...] appeared to be the result of rapid decomposition of [...] in a cavitation bubble. The degradation of pentachlorophenol and observation of intermediates showed OH attack of the aromatic ring. A chemical kinetic model was developed to gain insight into the formation of radicals in various bubbles at 20 and 500 kHz with and without [...] present. The model revealed [...] pyrolysis slightly before the end of collapse followed rapid free- radical formation in the last nanoseconds due to [...] and [...] decomposition. In addition, a new advanced oxidation process, photoactivated periodate, was developed to investigate the decomposition of triethanolamine, its associated chemical oxygen demand, and the oxidation of an industrial wastewater. The optimal [...] for COD degradation was determined to be pH 7.6 due to the combined effects of pH on the speciation of TEA and [...]. Increasing the [...] ratio increased the degradation rate up to an apparent saturation value. Irradiation with a 1000 W Hg(Xe) lamp increased the pseudo first-order degradation rate constant of COD by a factor of 5.5 for synthetic TEA solutions and 2.3 for the industrial wastewater as compared to irradiation with a 1000 W Xe lamp.

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