Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/5562
標題: 促進厭氧生物處理四氯乙烯代謝方式之探討
作者: 王有盛
Wang, yu-sheng
關鍵字: 四氯乙烯
甲烷菌
脫氯作用
氧化還原電位
出版社: 環境工程學系
摘要: 本實驗的目的在於探討厭氧混合族群中,菌液濃度的減少造成批次實驗中四氯乙烯總降解量提高的可能原因,並於低菌量的批次實驗條件下,觀察添加甲烷化抑制劑(BES)與不同的電子接受者(如:亞硫酸鹽),及改變厭氧條件下的氧化還原電位(ORP),對於還原性脫氯作用及甲烷化作用的影響,以釐清甲烷菌於本實驗室混合系統中所扮演的角色及其對脫氯作用的影響,並探討四氯乙烯厭氧還原性脫氯之中間代謝物的脫氯情形。 實驗結果顯示甲烷菌並非系統中主要的脫氯族群,但其本身為具優勢的基質競爭者,可快速將批次實驗所提供的醋酸鈉轉化為甲烷,造成系統中碳源或電子供給者缺乏,而脫氯作用也在醋酸鈉被耗盡時呈現明顯遲緩的現象。亞硫酸鹽的試驗中,添加與未添加亞硫酸鹽的實驗組其兩者脫氯現象的差異並不顯著,因此亞硫酸鹽的存在並未如文獻中指出會對四氯乙烯厭氧脫氯作用造成抑制。不同濃度營養鹽及缺乏單一營養鹽的實驗結果顯示,四氯乙烯的總降解量隨著營養鹽濃度降低而減少,其中又以CoCl2的缺乏對脫氯作用的影響最明顯,因此營養鹽不足即可能造成脫氯成效不佳。由不同的氧化還原電位的實驗中得知,初始氧化還原電位為 —300 mV (實測為-250 mV)時,系統約只有50%的四氯乙烯總降解量,而總降解量隨著氧化還原電位降低而增加,當氧化還原電位低於 —350 mV 時,系統具有最高的四氯乙烯總降解量,但甲烷的生成並沒有受到氧化還原電位改變而有明顯的變化。由中間代謝物的脫氯現象中發現,本實驗室混合族群對於四氯乙烯及三氯乙烯具有脫氯能力,但對於順-二氯乙烯、氯乙烯及乙烯則幾乎不具有脫氯的能力,因此系統完全脫氯的比例並不高。
The objective of this study is trying to find out the probable reasons why the overall tetrachloroethylene (PCE) dechlorination increases with a decrease in biomass in anaerobic mixed cultures in the batch reactors. And then, We try to discuss the dechlorination of PCE in different environmental conditions, such as the addition of inhibitors. When biomass is diluted to 5% (v/v) by micronutritions, the effect of addition of 2-bromoethanesulfonate(BES),an methanogen inhibitor, and sulfite on the reductive dechlorination of PCE and the activity of methanogens in the batch experiments are investigated. The dechlorination and methanogenesis effects in the different redox potential by varying the dose of reductant Na2S are alse studied. Finally, we investigate the dechlorination of trichloroethylene (TCE), cis- dichloroethene (cis-DCE), and vinyl chloride(VC) , the intermediates of PCE reductive dechlorination, in the conditions that could be used to effectively dechlorinate PCE in our study. The results indicated that methanogens were not the major dechlorinator in our culture, but they could rapidly utilite acetate to form mehtane. Because the excellent competition of acetate for methanogens, the lack of substrate decreased the dechlorination of PCE in high biomass conditions. Additions of BES and sulfite block the formation of methane, but the reductive dechlorination of PCE was not affected. A decrease in the trace metal significantly affect the dechlorination. There is almost no dechlorination, when the concerntration of CoCl2 decreased to 0.5 mg/L. In the experiment of various initial redox potentials under anaerobie condition, PCE could nearly be completely dechlorinated when the redox potential was below —350 mV. In addition, we found that lower chlorinated ethenes, cis-DCE and VC, could not be dechlorinated in our system in the conditions we adopt to dechlorinate PCE and TCE.
URI: http://hdl.handle.net/11455/5562
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