|Ph.D Thesis||Department of Civil and Environmental Engineering|
|Supervisor:||Prof. Emeritus Narkis Nava|
In this research ultrasound irradiation was employed in order to degrade trihalomethanes, THMs, compounds: CHCl3, CHBrCl2, CHBr2Cl, CHBr3, and CHI3. The effect of temperature, pH, ultrasonic intensity, power density, solute concentration, solvent, and solution composition, on the rates and removal efficiencies of the organic compounds, as a sole component and as a mixture in the aqueous solution were investigated. Batch experiments were conducted at an ultrasonic frequency of 20 kHz. It was found that the THMs compounds studied were sonochemically degraded. The first-order degradation rate constants and the sonolysis efficiencies followed the decreasing order of: CHCl3 > CHBrCl2 > CHBr2Cl > CHBr3 > CHI3. Up to 100% of CHCl3 was removed, while only 60% of CHI3 was sonodegraded, within 180 minutes. Correlation was found between the THMs vapor pressure and the sonolysis kinetics and efficiency. The aqueous solution pH and its inorganic composition had no significant effect on the ultrasonic reaction. Nevertheless, an increase of the solution temperature, acoustic intensity and power density resulted in faster reaction rates. Pyrolysis was the main degradation mechanism of the CHCl3, CHBrCl2, CHBr2Cl, and CHBr3. While, the idoform was sonodegraded mainly by free radicals oxidation. A total of 48% mineralization was achieved, at the end of 180 minutes sonication of a mixture of the THMs.
Hydrogen peroxide, nitrate, chloride, bromide, iodide and iodate ions were identified and quantified as the THMs sonication by-products. The results of this research proved that ultrasonic irradiation can be applied as an efficient destructive method for THMs removal from polluted groundwaters. The sonochemical destruction can be achieved at ambient conditions, without the addition of chemicals to the treated water, and through avoidance of additional processes such as combustion.