| Summary: | 碩士 === 崑山科技大學 === 環境工程研究所 === 104 === In this study, the field groundwater samples contaminated with vinyl chloride (VC) were taken for batch tests under electrolyzing at a constant potential 1.2 V, 1.5 V, 2.0 V, 2.5 V or 3.0 V. Oxygen evolution and hydrogen evolution have a similar effect of air stripping to vaporize VC during water electrolysis, and the breakdown of VC may occur through the attack of the electrochemically generated radicals and strong oxidants at the same time. The generation of radicals and strong oxidants can be triggered by the control of electrolyzing potentials, and thus electrolyzing stripping experiments and electrolyzing oxidation experiments were conducted for differentiate the mechanisms of VC removals. Electrolyzing stripping experiments showed that the efficiencies of VC removal were 33.6% and 63.9% after electrolyzing 3 hours at a constant potential 1.2 V and 1.5 V, respectively. Stripping removal mechanism of VC followed the pseudo first order reaction kinetics based on the linear relationship of ln(C0/C) vs. time. At the end of electrolyzing stripping experiments, the stable level of chloride ions, the rise on pH and the upturn on ORP did not implicate the remarkable signal of redox reactions. Electrolyzing oxidation experiments showed that the efficiencies of VC removal were 69.6%, 78.6% and 100% after electrolyzing 3 hours at a constant potential 2.0 V, 2.5 V and 3.0 V, respectively. Oxidation removal mechanism of VC also followed the pseudo first order reaction kinetics based on the linear relationship of ln(C0/C) vs. time. The decreased level of chloride ions might result from the transform of chloride to hypochlorite, and the drops on pH and ORP were in accordance with the symbols of dechlorination reactions. When electrolyzing field groundwater samples, the precipitation of metal oxides on the electrode surface were observed during experiments. The cleanup of electrode deposits can improve current efficiency and thus upgrade VC removal efficiency. Comparatively, the efficiencies of VC removal were improved to 74.8%, 86.2% and 100% after electrolyzing 3 hours at a constant potential 2.0 V, 2.5 V and 3.0 V due to the cleanup of electrode deposits. Vinyl chloride can be completely mineralized and completely dechlorinated when electrolyzing 3 hours at a constant potential 3.0 V. Based on carbon mass balance calculation, carbon distributions are 1.7% as VC in volatile phase and 98.3% as CO2 in gaseous phase. Based on chlorine mass balance calculation, chlorine distributions are 1.7% as VC in volatile phase, 92.0% as chloride ions in aqueous phase and 6.3% round-off errors.
|
|---|
