| The radical chemistry involved in aqueous advanced oxidation processes is investigated in three steps. In the first step, the parent compound destruction and the effect of water chemistry and reactor design on the performance of UV/H2O2 process examined. For the second step, the chemistry of byproducts formation and destruction is investigated for trichloroethylene (TCE) destruction using UV photolysis and UV/H2O2. For the third step, the initial work on generating reaction pathways using computer software is examined.; Based on a virgin model previously developed in this research group, a software, namely AdOx(TM), is debugged and commercialized to help engineers determine key parameters including the influence of water chemistry and operational parameters on reactor performance. A dye study analysis tool and a rate constant database were added into the previous kinetic model to facilitate the use of the software.; The research on the trichloroethylene (TCE) provides insight on radical reaction networks that are involved in the photolysis and advanced oxidation process. Dichloroacetic acid (DCA), monochloroacetic acid (MCA), oxalic acid and formic acid are detected in both processes as byproducts. Several aldehydes and carboxylic acids, such as dichloroacetaldehyde, formaldehyde, glyoxylic acid, are only detected in the photolysis process. TCE and the byproducts degrade much faster in the UV/H2O2 reactor than in the photolysis reactor. The formation and degradation mechanisms of these byproducts are examined. Four pathways are proposed for the photolysis of TCE in the UV only system and they produce CCl=C·(Cl) radical, HC≡CCl, ClC≡CCl and ClCH(OH)-CHCl2 respectively.; Kinetic models are developed for the simulation of the byproducts fate. The models consider the multiple-wavelength irradiation of the UV lamp, the UV interference by the main byproducts and the kinetics for TCE and all byproducts. The results for all byproducts agree with the experimental measurements. In the UV process, quantum yields for the four photolysis pathways of TCE (involving CCl=C·(Cl) radical, HC≡CCl, ClC≡CCl and ClCH(OH)CHCl2) are determined to be 0.13, 0.035, 0.084 and 0.2 respectively. Quantum yields and/or rate constants for the byproducts photolysis are also determined. In the UV/H2O2 system, analysis of the byproducts shows that only one of the four TCE photolysis pathways is significant. The important pathway is the homolytic splitting of Cl · from TCE that finally leads to the formation of MCA. (Abstract shortened by UMI.)... |
