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標題: 外加碳源對EDTA生物分解之影響
The effect of additional carbon sources on the microbial degradation of EDTA
作者: 林君翰
關鍵字: 醋酸鈉;EDTA;乙二胺;共代謝;NADH
出版社: 環境工程學系
EDTA為一種人工合成的螯合劑,能與金屬離子形成穩定的化合物。由於其化合物具有高穩定性,因此EDTA被廣泛應用於各種行業,諸如纖維染整業、清潔劑製造業、金屬工業…化妝品業等等。雖然EDTA在環境中不具毒性,但它的難分解特性使得無法以傳統的生物處理及物化處理方法去除。此外,EDTA的存在會使土壤及河川底泥中的重金屬再度溶解於水中,而直接影響人體健康或經由植物的累積再由食物鏈傳輸到人體中。因此如何有效且妥善處理含有EDTA之廢水成為刻不容緩之事。本研究的目的即在探討不同的環境因子以及外加碳源對Pseudomonas aeruginosa分解EDTA之影響,盼能提昇EDTA之去除率。此外,以不同的醋酸利用菌進行實驗,並探討NADH對於EDTA分解之影響。
本研究利用16S rRNA序列菌種鑑定的方法進行鑑定,確定菌株An1之菌名為Pseudomonas aeruginosa。由實驗結果顯示,P. aeruginosa之最佳生長溫度為30℃,在此溫度下之比生長速率為0.0744hr-1。P. aeruginosa 所能忍受的pH範圍相當廣泛,在不同起始的pH下皆能生長良好,其中在pH 5時EDTA去除率最差(44.3%),而在pH 9時EDTA去除率最佳(58.1%),顯示EDTA在鹼性條件下的去除效果較好。P. aeruginosa 於含鈣離子之磷酸鹽緩衝溶液與不含鈣離子之磷酸鹽緩衝溶液中,對FeEDTA的去除率沒有太大的差別。換句話說,影響EDTA分解之酵素不需要鈣離子作為輔助因子。P. aeruginosa 在有添加氯化銨的磷酸鹽緩衝溶液中,對於FeEDTA的去除率是沒有添加氯化銨的一倍以上。顯示P. aeruginosa無法以EDTA為唯一氮源,須額外添加易分解氮源以利菌株生長,而EDTA的去除率才有明顯增加的現象。

EDTA is a chelating agent from the group of aminopolycarboxylic acids with the ability to form stable, water-soluble complexes with most metal ions. Because of high stability of its complexes, EDTA is employed for various industrial and domestic applications, e.g. cleaners, metal processing etc. EDTA exhibits no environmental toxicity, but it is a recalcitrant organic compound that cannot be removed by conventional biological and physical-chemical methods of wastewater treatment. Moreover, EDTA has some undesirable environmental consequences such as the remobilization of radionuclides and heavy metals from soils and sediments. The mobilized radionuclides and toxic heavy metals can cause direct health problems or can be accumulated by plants and then transferred to human beings through the food chain. Therefore, it becomes a great urgency to treat the wastewaters containing EDTA efficiently. To raise the treatment efficiency, the environmental factors and the additional carbon sources affecting the degradation of EDTA by Pseudomonas aeruginosa were studied. Besides, the degradation of EDTA by different pure cultures that utilize sodium acetate as substrate was tested, and the effect of NADH on EDTA degradation was also investigated.
The strain An1 was identified as Pseudomonas aeruginosa by the method of 16S rRNA sequencing. The temperature and pH optima for EDTA oxidation were 30℃ and 9, respectively. The addition of CaCl2 to the phosphate buffer was no help of the removal of EDTA, suggesting that the enzyme does not require calcium for its activity. The removal ability of EDTA by Pseudomonas aeruginosa grown with NH4Cl and EDTA as the nitrogen sources was about one-fold higher than with EDTA as the sole nitrogen source. It indicated that Pseudomonas aeruginosa could not be grown with EDTA as the sole nitrogen source and the degradation of EDTA was stimulated by the addition of NH4Cl.
In the aspect of carbon source addition, the degradation of EDTA was stimulated by the addition of either sodium acetate or ethylenediamine. However, additional nitrilotriacetic acid and sodium lactate did not influence EDTA degradation. Since the strain grown with EDTA as the sole carbon source could not degrade EDTA and could only metabolize EDTA by adding biodegradable carbon sources, the mechanism of EDTA degradation must be co-metabolism. In addition, EDTA could be cometabolized by all the sodium acetate-utilizing microorganisms in the presence of sodium acetate, but could not be completely mineralized. The removal ability of EDTA by strain MDC-3 was the best (56.1%) and that by strain TDM-3 was the worst (33.1%).
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