零價鐵流體化床降解EDTA之研究

Fluidized Zero Valent Iron Bed for EDTA Degradation

林益君(Yi-Jiun Lin)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境規劃與管理研究所/碩士(2007年)

摘要

EDTA為一種四羧基類、廣泛被運用於工業製程與廢水處理之螯合劑。有效降解廢水中之EDTA，可避免EDTA造成對環境之危害性與金屬離子排放而超出放流水標準。零價鐵已證明可有效降解EDTA，其降解途徑為有氧氣存在時，零價鐵與氧氣反應產生氫氧自由基，此時EDTA之降解循氧化途徑，並且使用零價鐵流體化床程序更可增加零價鐵與EDTA之傳輸而提升去除效率。
本研究利用零價鐵(粒徑≦212μm) 流體化程序利用自行配置之EDTA，在固定進流水EDTA之濃度下(50mg/L)，於不同pH値(1.5、2、3、4)、不同之水力停留時間(5、10、15分鐘)、不同零價鐵劑量(0.5、1、2克)及曝氣條件下，探討EDTA降解效率與反應機制。研究結果顯示出當未曝氣下，利用零價鐵降解EDTA未曝氣時，進流水之pH值越低、水力停留時間越長與零價鐵加藥量越高時，可增加EDTA降解效率，進流水pH值 ≦ 2、水力停留時間 ≧ 30分鐘與零價鐵加藥量 ≧ 0.5克時，可達到80 % 以上之EDTA降解效率；在相同水質條件與零價鐵加藥量下增加曝氣時，曝入空氣可增加水樣溶氧量，因而提升零價鐵降解EDTA之效率，水樣之溶氧量為6.8 mg/L時，EDTA降解效率為82%，而曝入氮氣時，水樣中之溶氧量降低為0.5 mg/L，EDTA降解效率僅50 %。
反應速率常數之評估本流體化床研究為假一階反應，反應速率常數會隨著近流水pH值、水力停留時間降低與零價鐵加藥量、水樣溶氧量增加而增加，而水樣中溶氧量增加時，反應數率常數會大幅增加，水樣中溶氧量為6.8 mg/L，反應速率常數為27.79 hr-1，隨著水樣中溶氧量之減少反應速率常數隨著降低。在零價鐵使用效率上，當未曝氣時EDTA進流水pH越低、水力停留時間延長與增加零價鐵加藥量時，單位零價鐵劑量對於EDTA降解量越高，最高可達18.31 mg EDTA / g ZVI；經過曝氣出流水溶氧量為6.8 mg/L時，進流水pH值為 2、水力停留時間為10分鐘與零價鐵加藥量0.5克，單位鐵粉去除量為19.01 mg EDTA / g Fe。 EDTA於未曝氣與曝氣下經過零價鐵降解後，分析結果推估其反應機制為零價鐵與水樣中溶氧反應後產生氫氧自由基進而將EDTA氧化，所生成之副產物包含了二氧化碳、NH4+與低分子量之有機酸－丙酸。

關鍵字

EDTA ； 零價鐵 ； 流體化床 ； 溶氧量

並列摘要

Ethylenediaminetetraacetic acid (EDTA) is a chelating agent that has been extensively used to enhance the solubilization of heavy metal during the production process in the industry, resulting in high chelating agent and heavy metal in the wastewater. The presence of chelating agent reduces the metal ion precipitation, and the release of chelating agent contributes to serious environmental problems. Recently, zero valent iron (ZVI) has been extensively used to remove organic pollutants, and is suitable for treatment of chelating agents. The fluidized ZVI can be effectively degraded as well.
In this study , the synthetic water samples containing 50 EDTA mg/L were treated at various pH, retention time and ZVI grains (＜212μm) dosage that carried out in or without aeration and aeration system. The EDTA degradation efficiency 80% over when the pH is smaller than 2, retention time is greater than 30 minutes, and ZVI dosage is greater than 0.5g in without aeration system. The EDTA degradation efficiency is 82 % when pH is 2, retention time is 10 minutes, and ZVI of 0.5 g in air of aeration system.
The kinetic mechanism of EDTA degradation is pseudo-first order rate constant, kobs, was enhanced with increased ZVI dosage, DO of water sample (dissolved oxygen concentration) and decreased pH. The greatest kobs was 27.79 hr-1 when DO of 6.8 mg/L is in aeration system. The largest amount of EDTA degraded per gram of ZVI oxidized is calculated as 18.31 mg EDTA / g ZVI in without aeration system of this study.
The mechanism by which procedure of this reaction is hypothesized to involve reactive oxygen intermediates. Many Fe2+ complexes can react with O2 which leads to the production of OH radical to oxidize EDTA. Finally, the analysis of the degraded products shows CO2 , NH4+, and propionic acid.

並列關鍵字

EDTA ； Zero valent iron ； Fluidized bed ； DO

參考文獻

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