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標題: | 氮系消毒副產物於天然水體間之生成機制 The formation mechanism of nitrogenous disinfection byproducts from natural waters |
作者: | Yi-Hsueh Chuang 莊易學 |
指導教授: | 童心欣 |
關鍵字: | 氯胺,消毒副產物,生成動力,鹵乙腈,鹵化硝基甲烷,N-亞硝基二甲基胺, chloramines,disinfection byproduct,formation kinetic,haloacetonitriles,halonitromethanes,N-nitrosodimethylamine, |
出版年 : | 2013 |
學位: | 博士 |
摘要: | 含氮消毒副產物鹵乙腈(HAN)、鹵化硝基甲烷(HNM)與亞硝基二甲基胺(NDMA)具有高毒性。目前對於該類氮系消毒副產物及其前驅物質的研究較少,增加控制其生成的困難度。模式物質研究雖指出胺基酸與二甲基胺為HAN與NDMA之可能前質,然而自然水體天然有機物成分複雜,對於消毒副產物生成之關係仍有待進一步探討。以胺基酸為模式物質的研究指出於氯胺存在下,含鹵氮系消毒副產物之生成機制可為協同去碳酸基路徑 (concerted decarboxylation, 同時脫除HCl及CO2)或氯胺-醛基路徑 (chloramine-aldehyde pathway)。協同去碳酸基與氯胺-醛基路徑中,消毒副產物之氮源分別來自於有機氮與氯胺。然而天然有機物與氯胺反應之主要機制仍不清楚。此外,氯胺-醛基反應途徑常伴隨著天然有機物氧化時其關鍵醛基中間產物的產生,因此其反應速率與協同去碳酸基途徑有所不同;而目前為止卻無實驗證據加以論證。
目前工程手段常以臭氧-生物活性碳濾床進行水處理,但臭氧程序會因此增加了HNM的生成潛勢。有關HNM濃度增加的原因目前為止並無實驗上的證據加以說明。因此,本研究試圖以天然水體之有機物為調查對象,進一步釐清消毒副產物生成的機制。本研究針對不同含氮量之原水進行鹵乙腈、三鹵硝基甲烷與亞硝基二甲基胺生成之機制探討。實驗結果發現,二鹵乙腈於添加氯胺下之生成與三鹵甲烷及二鹵乙酸在微酸性(pH 6.0)、中性(pH 7.2)與弱鹼性(pH8.5)環境下皆存在良好的相關性。不同親疏水性與不同官能基的有機物類群並不影響此相關性,顯示該類消毒副產物前質並無酸鹼性官能基參與。生成動力曲線更進一步證實二鹵乙腈的生成與有機碳氮比(DON/DOC)比例無關。該結果支持了環境水樣中鹵乙腈與三鹵甲烷及鹵乙酸前質有共通性的論點。本實驗結果可用β-二羰基(β-dicarbonyl moieties)生成消毒副產物之模式解釋。氮源追蹤試驗結果發現天然有機物與氯胺對NDMA生成各貢獻了相同量的氮原子,得以解釋使用氯胺會造成NDMA生成濃度增加的原因。 本研究亦探討不同有機物類群中兩類氮系消毒副產物前驅物質的生成動力情形。結果發現二鹵乙腈與三鹵硝基甲烷生成時,氯胺貢獻其氮源的前驅物質在被氯胺轉換成消毒副產物的過程與氯胺暴露量(chloramine exposure)呈線性相關。而有機氮貢獻其氮源之前驅物質在轉化成鹵乙腈或鹵化硝基甲烷則較快速,且呈現二階反應動力式。本研究以數學模式解釋此二類消毒副產物前驅物質的生成動力,並以模式物質酪胺酸(tyrosine)說明。 The toxicity of nitrogenous disinfection byproducts (N-DBP), such as haloacetonitrile (HAN), trihalonitromethane (HNM) and N-nitrosodimethylamine (NDMA), are higher than chlorinated DBPs. Previous studies show that dimethylamine and amino acids are possibly the important precursors of NDMA and HAN. However, given the complexity of natural organic matters, it is very difficult to predict the formation of above DBPs in natural waters. In addition, ozonation-biofiltration, which is gaining its popularity in drinking water treatment, may increase trichloronitromethane (TCNM) formation; the reason for its increase has not been elucidated by experimental data. Therefore, the objective of this study was to explore the formation mechanism of N-DBPs in natural organic matters. The results show that during chloramination, the formation potential of dihaloacetonitrile (DXAN) was linearly correlated with that of trihalomethanes (THM) and dihaloacetic acid (DXAA) combined (in molar basis). This linear correlation was also found in different organic fractions with various hydrophobicity and functional group. The results support that THM, DXAA and DXAN are derived from similar precursors within natural organic matter. 15N-labeled monochloramine was used to explore the nitrogen source of NDMA formed in chloraminated organic fractions. Results indicate that the dimethylamine group of NDMA is mainly originated from dissolved organic nitrogen (DON) within the organic fractions. This study also investigates the formation kinetics of two groups of chlorinated N-DBPs, HAN and HNM, by 15N-isotopic monochloramination of organic fractions. The results show the N-DBP formations from HAN and TCNM precursors of which nitrogen originate from DON are relatively fast, and are second-order reactions. By contrast, the ones that chloramines contribute to their nitrogen sources react with chloramines to form HAN and TCNM in a relatively slow manner; their formation concentrations were linearly correlated with chloramine exposures. This study proposes the possible kinetic equations describing the formation from these two groups of N-DBP precursors. In addition, this study also tests the N-DBP formation from chloraminating tyrosine, and the results support the observation upon chloramination of natural waters. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/60546 |
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顯示於系所單位: | 環境工程學研究所 |
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