| In the first part of this research, oxidation byproducts of 2-chlorophenol generated during aqueous ozonation were measured under various conditions. The chemical identification was carried out using silylation followed by GC/MS analysis. Byproducts such as aromatic compounds and other carboxylic acids of three- to four-carbons were quantified using HPLC. The overall mass balances were from 75 to 85%. From this study, it was found that the identities of products did not vary noticeably as pH increased from 3 to 9. However, the time-dependent distributions of intermediates and byproducts differed significantly as both pH and ozone dosage varied. From the data of product distributions, oxidation pathways were proposed and fitted to a simplified model. In the second part, a mathematical model describing interactions between ozone and organic contaminants in the vadose zone during in situ ozonation process was developed. Due to the high degree of gas saturation in the vadose region and the lack of bulk liquid, this model treated moisture as a thin film on the surface of soil particle. The Damköhler number was identified to be the most influential parameter controlling the chemical absorption process. Concentration profiles of common soil organic contaminants such as trichloroethylene (TCE), chlorophenols (CPs), pentachlorophenol (PCP) and phenanthrene (PHE) were simulated. Effects of reactivity, volatility, and hydrophobicity of organic compounds on the distributions of ozone and organics inside the film were evaluated. Profile results between a pure numerical computation and an approximation were compared. Furthermore, laboratory column experiments were also conducted to simulate the in situ soil ozonation process in the vadose zone, exemplified by 2-chlorophenol (2CP) and pentachlorophenol (PCP). Experimental data obtained were profiles of residual organic compounds along the column and ozone breakthrough curves. In modeling the profile results, degradation yield factor and gas-liquid interfacial area in the model were obtained empirically. Results indicated that the Stanton number was found to be the major parameter controlling the ozone transport. Finally, the optimal time to adjust the ozone flow rate during the process was obtained by evaluating the changes in the Stanton number. |
