| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 90 === The column experiments were carried out in this study to simulate the operation of zero-valent iron reactive barriers and to investigate the TCE removal efficiency enhanced by applying voltage. The types of electrode, location of electrode, amount of voltage, and inlet velocity were studies to understand the mechanism of iron reactive barriers applied voltage to remove TCE. Finally, the feasibility of long—term operation was also investigated in this study.
Experimental results indicated that 32% of TCE removal efficiency was achieved in the iron reactive barrier. Compare the performance to others system mentioned in the literatures, the TCE removal efficiency was relative low because of the impurity and precipitates on the surface of iron. Consequently, the reactivity of iron surface would be declined. In addition, TCE was accumulated in the column that filled with sand when applying voltage directly and the amount of TCE was not reduced in the system. The TCE removal efficiency was not apparent difference when using graphite, copper and zinc as cathode, respectively. The TCE removal efficiency was different when the electrode located in different ports of column. Meanwhile, results revealed that the removal efficiency of TCE was increased simultaneously when anode located in iron reactive barrier. The two major reasons to explain this phenomenon: (1) H+ resulted from electrolyzing water occurred near the anode could acid wash the iron to enhance the reactivity of iron surface; (2) When the voltage applied, the potential difference would accelerate the electrons of iron to release and induce TCE reduction. Furthermore, as the potential gradient increased, the TCE removal efficiency was increased in the meantime. When potential gradient increased to 1V/cm，TCE removal efficiency in the outlet of column could arise from 32% to 76%. When potential gradient was set in 2V/cm, TCE removal efficiency could reach to 100%. However, results shown the precipitates could cover the iron surface and block the pore of reactive barrier. Therefore, potential gradient of 2V/cm was not suitable for long-term operation. The column inlet velocity increased from 7.5 to 16.6 cm/day would decrease the contact time, but TCE removal efficiency was not decreased in this study. Suppose iron reactive barrier applied voltage could increase iron activity, the contact time would not affect TCE removal efficiency, significantly.
According to the long-term operational analysis, the TCE removal efficiency would increase comply with the time of the voltage applied. At the 7 days operation periods, TCE removal efficiency in the outlet was attained 100%, and in the later 20 days periods, TCE removal could still maintain high efficiency. Thus, zero-valent iron reactive barriers applied voltage demonstrated great potential in the long-term operation when operating in suitable conditions.
Keywords : zero-valent iron reactive barrier, voltage, TCE, reductive dechlorination, electrolyze
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