| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 101 === Hexachlorobenzene (HCB) was widely used in agriculture as pesticides. Some of the important characteristics of HCB include low water solubility, bioaccumulation. It is easy to adsorb and difficult to remove from soil. In this study, pyrolysis with static system and dynamic system are applied to treat HCB-contaminated soil, the impact of nanoscale iron on HCB removal will also be evaluated. The results display the HCB removal efficiencies achieved with the static system with temperature varying from 250 to 300, 350oC and 400oC at 60 min without nZVI are 18%, 42%, 74% and 96%, respectively. It displays the benefit of HCB removal at a higher temperature. However, the removal efficiency does not change much as the treatment time is extended from 30 to 60 min. The HCB removal efficiencies achieved with temperature varying from 250 to 300, 350oC and 400oC at 60 min with 5%-nZVI are 34%, 42%, 67% and 97%, respectively. The HCB removal efficiency increases at 250oC if compared with the case without nZVI but decreases at 350oC. It displays that nZVI has different effects on HCB removal at different temperatures. The results obtained with the dynamic system indicate that HCB removal efficiencies achieved with temperature varying from 250 to 300, 350 and 400oC at 60 min without nZVI are 22%, 53%, 66 and 87%, respectively. In the presence of 5%-nZVI, the HCB removal efficiencies achieved are 36%, 51%, 65 and 87%, respectively. These trends are similar to that observed in static system. The results obtained from both static system and dynamic system indicate that CBs are generated when nZVI is added. CBs are generated significantly at 350oC but decreased at 400oC. It indicates that the destruction efficiency is increased significantly at 400oC. Possible reasons of CB generated are that nZVI release electrons and generate other iron-containing compounds, like FeCl2 or FeCl3. Precursors exist in soil may react with chloride to form chlorobenzenes through the catalysis of these iron-containing compounds. PCDD/Fs are generated significantly at 350oC and form higher chlorinated congeners. 2,3,7,8-TeCDD, 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDF are the main species contributing to toxicity. On the other hand, formation of PCDD/Fs is not significant for the system operating at 400oC. It indicates that pyrolysis of HCB-contaminated soil also generates PCDD/Fs even oxygen is not provided to the system.
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