| Stricter clean water standards are compelling chemical process industries to reduce and eliminate the toxicity of their waste water discharges. Several techniques are widely employed to remove dissolved organic contaminants. These include carbon adsorption, ultraviolet light, and biodegradation. However, several waste water problems require development of innovative techniques. Sonochemistry (chemistry with ultrasound) is a process that uses localized high temperatures and pressures to accelerate chemical reactions such hydroxyl radicals and hydrogen peroxide formation. These agents can then highly degrade organic compounds in aqueous systems. Thus, it offers great potential within the hazardous waste treatment area.; The principal objective of this research was to explore the application of ultrasound to the destruction of toxic aromatic and chlorinated hydrocarbons found in contaminated water and soil. The organic compounds studied were 1,2-dichloroethane, benzene, and toluene. Specifically it was quantified the rates of conversion, assesed the effect of process variables, and determined the enhancement of the action of the wet oxidant hydrogen peroxide in the system. At the end of the study, the effects of changing the reactor temperature and the initial solute concentration were evaluated. The equipment used for the study was an ultrasound generator using a horn mounted transducer and coupled to a flow through cell reactor. This ultrasound generator was calibrated using a calorimetric procedure. The frequency of the sound was constant at 20 kHz. The treatment process was studied by carrying out a statistical factorial design experiment at two levels in four variables. The variables considered in the statistical program included intensity of the sound wave, 30 and 60 watt/cm{dollar}sp2,{dollar} duration of ultrasound application, 1 and 2 hr, initial pH of the problem solution, 7 and 11, and presence of the wet oxidant hydrogen peroxide.; The analysis of results showed reductions of 34, 13, and 22 mg/l for 1,2-dichloroethane, toluene, and benzene respectively. The intensity of the sound and sonication time were found to affect the destruction of the compounds. The higher the intensity and time, the higher the reduction in concentration, as it was expected. The presence of H{dollar}rmsb2Osb2{dollar} enhanced the destruction of 1,2-dichloroethane but not of toluene. For toluene, the initial pH of the solution interacted with the intensity of the sound, thus, both variables have to be evaluated together. In the destruction of benzene with ultrasound, it was found that the initial pH, the sound intensity, and the presence of H{dollar}rmsb2Osb2{dollar} were involved in interactions. The change of the reactor temperature presented an optimum temperature for maximum benzene destruction at a constant sound intensity. Reaction kinetic mechanisms were suggested to explained the results, and could not be probed, since detailed indentification and concentration measurements of the reaction products could not be performed.; The use of ultrasound for the destruction of organic compounds in aqueous solutions could be a very expensive technology. Thus, further research needs to be developed in order to increase the efficiency of the treatment. It was clear throughout this research that ultrasound can destroy very stable organic compounds like benzene, and enhance the oxidation of other compounds like 1,2-dichloroethane. |
