Abstract
Ultrasound was used for chemical and biological decontamination of water by various types of equipment operating at different frequencies (20 kHz, 40 kHz, 380 kHz, 512 kHz, 850 kHz, 1000 kHz and 1176 kHz). Calorimetric and dosimetric methods were used to study the characteristics of all ultrasonic equipment used in this study. From calorimetric measurements, the 20 kHz probe showed the highest input power of21.35 Watts, but the 850 kHz ultrasonic bath was the most effective in hydrogen peroxide production and in methyl orange decolourisation. The hydrogen peroxide concentration was 15 mg/I and methyl orange was decolourised 81.29% after 2 hour sonication at 850 kHz.
Ultrasound can induce cavitation and produce hydroxyl radicals. As a result ultrasound can be used for decolourisation of chemical dyes and degradation of chlorophenols. Amongst the ultrasonic equipment used in this study, the 850 kHz ultrasonic bath gave the most effective dye decolourisation and 4-chlorophenol degradation. 100 mg/I of 4-chlorophenol was degraded by 19% after sonication for 2 hours using the 850 kHz bath. The major mechanisms of dye decolourisation and chlorophenol degradation are considered to due to oxidation by hydroxyl radicals. For the oxidation of azo dyes, hydroxyl radicals initially attack at the chromophoric azo bonds and the absorbance results showed that the absorbance reduction in the visible region was much higher than the reduction at 254 nm. For chlorophenols, the degradation followed first-order reaction and the rate constants of 2-chlorophenol and 2,4-dichlorophenol were higher than that of 4-chlorophenol. The rate constants of 4- chlorophenol, 2-chlorophenol and 2,4-dichlorophenol were 0.00176, 0.00186, and 0.00225 min-1 respectively.
For disinfection of bacteria, the use of the 20 kHz probe showed the most deactivation and the reduction of cell numbers followed first order behaviour. The reaction rate constants of Enterobacter cloacae, Citrobacter freundii and Enterococcus fecalis were 0.0537, 0.0689 and 0.0166 min-1 respectively. The deactivation of Enterococcus fecalis, gram positive was obviously slower than those of Enterobacter cloacae and Citrobacter freundii which are gram negative. In conclusion from this study, ultrasonic can be used for chemical degradation at 850 kHz and for bacteria inactivation at 20 kHz.
| Date of Award | 2010 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Larysa Paniwnyk (Supervisor) & Timothy Mason (Supervisor) |