純鐵粉/鐵砂混合管柱處理地下水中硝酸鹽氮之研究

本研究為以零價鐵處理實場地下水之管柱實驗，並探討避免管柱堵塞因而填入石英砂可能造成之影響。水樣選用台灣地區硝酸鹽氮濃度偏高的南投新街地下水(約30 mg/L)進行實驗。在純鐵粉管柱實驗方面，可以發現零價鐵降解硝酸鹽氮的過程會使pH值上升及ORP下降。當去除效果良好時，pH值在10~11之間，ORP值大約在-200~-300mV，因此pH及ORP可作為零價鐵硝酸鹽氮去除效率好壞之指標。而流通量越大去除效果越差，而當流通量相同時，鐵粉量較多時去除率則增加。因此，當鐵粉量增加而流通量減少時(高水力停留時間)，可達到較高之硝酸鹽氮去除率。實驗中顯示當水力停留時間大於13分鐘時，硝酸鹽氮去除率均可達80%以上。在操作時間方面，在鐵粉使用量方面零價鐵與硝酸鹽氮行氧化還原反應，經XRD及ESCA分析，反應後的零價鐵多以三氧化二鐵（Fe2O3）及四氧化三鐵（Fe3O4）存在，鐵離子濃度甚少約0.2~0.4ppm；硝酸鹽氮方面多轉換為氨氮，亞硝酸鹽氮型式並不穩定最大值僅0.07ppm。在鐵砂混合管柱方面，藉由填入大於鐵粉粒徑之石英砂增加孔隙體積，避免因pH上升時造成之碳酸鈣阻塞，但相對會減少單位體積內鐵粉與水樣接觸面積。在鐵砂混合管柱中， S/V值(比表面積/孔隙體積)及S/Q值(比表面積/流量)為兩重要參數。在相同通量之情況下，純鐵粉管柱S/V值隨著填入的石英砂越多，S/V值會隨之降低，去除效果及單位鐵粉去除硝酸鹽氮量也會降低。S/Q值為單位孔隙體積於單位時間接觸鐵粉表面積，以粒徑212μm鐵粉為例，當S/Q值>7 m2-day/L，鐵粉與水樣才有足夠的反應時間，且去除率可達80﹪以上。若S/Q值<7 m2-day/L，則必須增加鐵粉的填充量(增加表面積)或減少通量(延長水力停留時間)，以達到理想去除效果。反應速率常數計算為一階反應，純鐵粉管柱kobs值在8.23~12.47 hr-1之間，隨著填入的石英砂越多或流通量增加，kobs值會降低，而最佳的單位鐵粉去除量約1.78~2.89 mg-NO3-/g-Fe，僅達理論值的3.25﹪，故可透過鐵粉前處理進行鐵粉再生利用。

關鍵字

零價鐵；管柱；硝酸鹽氮；反應速率常數

並列摘要

The objective of this study was to eliminate nitrate contamination from a groundwater source with 30mg/L NO3--N in Nantou County by zero-valent iron/quartz sand packed columns. In the pure ZVI packed columns, nitrate reduction by ZVI was accompanied by with pH increase and ORP decrease. When nitrate removal was efficient, the pHs were around 10.5 and ORP were around -250 mV. Therefore, both pH and ORP are excellent indicator for nitrate removal. Increasing flux leads to reduce nitrate removal. After the reaction, ZVI was oxidized to Fe2O3 and Fe3O4. The dissolved iron was very few about from 0.2 to 0.4 mg/L, and most of nitrate was converted to the ammonia nitrogen. In the columns mixed with ZVI and quartz sand, the porosity was increased due to stuffing with the quartz sand but the contact area between ZVI and water wasl reduced. S/V is physical factor, representing iron surface per porosity volume. Increase of S/V increases the nitrate removal. S/Q is physical factors, representing iron surface per porosity volume in the operation time. Taking 212μm iron as an example, when S/Q > 7 m2-day/L , nitrate removal rate was over 80%. If S/Q < 7 m2-day/L, columns have to increase the ZVI to fill the quantity. The result also indicated the nitrate removal ratio can be simulated by the pseudo first-order equation. The Kobs of the ZVI columns were from 8.23 to 12.47 hr-1, quartz filling or increases of HRT also reduced the Kobs. Nitrate reduction by ZVI were from 1.78 to 2.89 mg NO/g ZVI. Comparing to the proposed stoichiometry, used ZVI was only 3.25% of the theoretical value. Therefore, the used iron can be reused again by pretreatment of ZVI.

並列關鍵字

Zero-Valent Iron ； Column Test ； Nitrate ； Reaction rate constant

參考文獻

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純鐵粉/鐵砂混合管柱處理地下水中硝酸鹽氮之研究

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