Radiation-induced Dechlorination of PCBs and Chlorinated Pesticides and the Destruction of the Hazardous Organic Solvents in Waste Water
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This dissertation presents research on the approach, feasibility and mechanisms of using high energy electrons for the dechlorination of polychlorinated biphenyls (PCBs) in transformer oil, PCBs and chlorinated pesticides in marine sediment, and hazardous organic solvents in waste water. The remediation of the organic contaminants by ionizing radiation is achieved by means of both reduction and oxidation processes. PCBs in transformer oil and in marine sediment can be effectively dechlorinated by reduction, while toxic organic compounds in water are removed by oxidation. The complete conversion of 2,2',6,6'-tetrachlorobiphenyl (PCB 54) in transformer oil to benign products is achieved without degradation of the oil itself. It requires 200 kGy of gamma irradiation of transformer oil containing PCB 54 (0.27 mg/g) to achieve >99% destruction of the PCB. Analysis of samples obtained as a function of dose demonstrates gradual degradation of PCB 54 and successive formation and degradation of trichloro-, dichloro-, and monochlorobiphenyl leading to the environmentally acceptable products, biphenyl and inorganic chloride. The mechanisms and kinetics of reductive degradation, which were obtained by pulse radiolysis studies, are discussed. Radiolysis may be of practical interest because the transformer oil may be re-used following treatment with little or no clean-up. Radiolytic degradation of aqueous suspensions of PCBs in marine sediments in the presence of isopropanol and food grade surfactants was also studied. Additives, such as an alcohol, were necessary to enhance the radiolytic yield and the dechlorination of PCBs. Conditions are demonstrated under which surfactants can be an effective approach for the enhanced remediation of chlorinated compounds in organic-rich environments such as marine sediments. Results presented on the treatment of marine sediment by radiolysis in the presence of additives for the degradation of PCBs advance the chemistry of this costly process, which may prove to be competitive with available alternatives. Also presented are results from an examination and study of the oxidative and reductive effects of electron-beam irradiation on the concentrations of six organic solvents in water. The organic solvents in water were prepared to mimic a pharmaceutical waste stream. Saturation with ozone did not sufficiently lower the unacceptably high dose requirements to meet environmental standards.