植物生長所需要的氮肥，往往因為施用過多而殘留在植物上或是經由土壤滲入至地下水中，造成地下水的污染。土壤及地下水中硝酸鹽可藉由脫硝反應將硝酸鹽氮還原為亞硝酸鹽及一氧化二氮等中間產物，最終還原為氮氣。
本研究以零價金屬具有低原料成本、反應迅速，減少操作成本及可將硝酸鹽氮轉換成其他物質等優點來還原去除水中硝酸鹽。本研究使用自行合成奈米級零價鐵及外購之商用微米級零價鐵(100mesh)，以1：9(重量比)比例混合石英砂來填充管柱，並控制不同流量，不同起始pH值及硝酸鹽初始濃度來探討零價鐵還原處理硝酸鹽氮之有效利用壽命。同時，本研究也以調整pH值，添加Fe2+、HCl酸洗液及硼氫化鈉來測試零價鐵再生的可能性。
研究結果發現以微米鐵還原硝酸鹽的研究中發現，進流溶液起始pH值控制為2.5時較未控制(6.05-6.17)時之還原效率為佳，且氮之平衡可達100%。在各種零價鐵再生方式的探討中，以添加強還原劑硼氫化鈉之效果最好，尤其在進流溶液pH值未控制(約9.78)的條件下，硝酸鹽的還原去除效率最佳且隨著硼氫化鈉添加量增加而增加。一開始未控制進流溶液pH值的管柱，以調降進流溶液pH值來再生反應過後之零價鐵時，對硝酸鹽之還原有較佳的效果。此外，在本研究中也嘗試添加Fe2+及HCl進行管柱內零價鐵的再生，結果發現並沒有明顯的效果。
在不同流量的條件下，可發現奈米鐵填充管柱內單位重量之鐵粉可還原處理硝酸鹽的重量差異並不大；且研究結果發現奈米級零價鐵具高還原效率之有效利用壽命在低流量時比高流量時為長，但奈米級零價鐵單位處理量並沒有受到流量之變化影響。 Nitrogen, an essential nutrient for plants, maybe pollutes the groundwater via the transportation from soil with overdosing fertilizer. Nitrate remaining in soil and groundwater could be reduced to form nitrite and N2O, and finally nitrogen gas.
The aim of this study is to observe the reduction of aqueous nitrate by using zero-valent metals, which has some strength of low cost and prompt reaction.
Results of column tests indicate the reduction of nitrate by microscale zero-valent iron could be more efficient under the initial condition of controlled pH (2.5) than uncontrolled pH (6.05-6.17).
Results also reveal that the addition of sodium borohydride is an effective regeneration method for activating the used and oxidized iron particles, especially under the condition of uncontrolled pH (near 9.78). However, the addition of ferrous ion and h ydrochloric acid could not be efficient for the regeneration of irons.
The specific reduction of nitrate by nanoscale zero-valent iron was found little difference under different inflow flux. The available operation time with high reduction efficiency in iron-packed column was found longer in high inflow flux than low flux.
