| 摘要: | 本研究利用管柱模擬零價鐵反應牆，探討外加電壓提升鐵反應牆去除TCE之成效，藉由電極種類、電極位置、電壓大小及進流流速等不同操作條件，討論零價鐵反應牆外加電壓去除水中TCE之反應機制，最後評估零價鐵反應牆外加電壓長時間操作之可行性。 實驗結果顯示，本研究所建構之鐵反應牆對TCE的去除效果約為32%，此去除率與相關文獻相較並不高，推測是因所使用之鐵純度不高，且有鐵氧化物覆蓋，而降低鐵可參與反應之表面積。插入電極於完全填充石英砂管柱中並施加電壓，直接電解TCE溶液的實驗結果發現，TCE在管柱中有累積的現象，但並無消減的情形，因此藉由電解的方法並無法有效去除TCE。當在鐵反應牆中外加電壓時，使用石墨、銅、鋅等不同陰電極，對於TCE的去除率並無明顯差異。管柱中電極不同擺設位置下，對TCE去除效果有很大的差異，實驗結果顯示，將陽極置於鐵反應牆中，陽極後端的鐵砂因受電解水產生之H+的酸洗作用，及外加電壓所形成之電位差的情況下，加速陽極附近鐵電子釋放能力，進而增加TCE的還原速率，因此，若將陽極置於鐵反應牆前端時，將可增加陽極對鐵反應牆的影響範圍，而提升TCE的去除率。另外，隨著施加的電壓坡降愈高，TCE的去除率愈高，當施加電壓坡昇高至1V/cm時，管柱出流端TCE去除率可由32%提升至76%，而在2V/cm之操作時，TCE去除率可達100%，但實驗過程中發現在2V/cm之操作時，鐵反應牆中容易生成沉澱物，阻塞鐵反應牆的孔隙，因此不利長期操作。當進流流速由7.5cm/day上升至16.6cm/day時，雖然減少TCE與鐵反應牆的接觸時間，但TCE的去除率並未降低，推測是因鐵反應牆外加電壓時，促進鐵表面活性，因此，在本研究所控制之接觸時間，對TCE去除率影響不大。 長時間連續操作下發現，零價鐵反應牆中外加電壓對TCE的去除率會隨通電時間而增加，通電第七天時，管柱出流端TCE可達100%的去除率，隨後20天的操作時間內，一直維持良好的去除效果，因此零價鐵反應牆外加電壓若在適當的操作下，具有良好且穩定的TCE處理能力。 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 |
