OXIDATION-KINETICS OF NATURAL ORGANIC-MATTER BY SONOLYSIS AND OZONE

An advanced oxidation process that combines ultrasound and ozone was studied in terms of its potential to oxidize natural organic matter and to determine whether the approach could extend the application of sonolysis to refractory electrolytes. Sonochemical enhancement of ozone decomposition rates has previously been attributed to ozone pyrolysis in the cavitation bubble or at the bubble interface. In this study, evidence from radical scavenging and dosimetry experiments confirms that ozone decomposition does not significantly occur in bulk solution during sonication. Under conditions of constant ultrasonic irradiation and continuous ozone gas application, total organic carbon (TOC) removal rates were enhanced by ultrasound. After 60 min of ozone and ultrasonic irradiation (55 W, 20 kHz), 91% of the TOC in a 10 mg/l fulvic acid solution was removed and 87% of the original carbon was removed as CO2 (g). With ozone alone, 40% of the TOC was removed and only 28% of the original carbon was mineralized. Direct combustion of volatile intermediates in the cavitation bubble may partially explain the improved mineralization efficiency that was obtained with sonolysis. Hydroxyl radical scavengers, such as carbonate, were found to inhibit TOC removal rates. When the process was applied to a high-color groundwater sample, containing 2.8 mg l(-1) TOC and 35 mg l(-1) bicarbonate, TOC removal was completely inhibited. After pretreatment of the groundwater sample to remove carbonate species, however, 90% of the TOC was removed in 40 min.