自由餘氯存在下之藥物光降解

Enhanced Degradation of Pharmaceuticals during Solar Photolysis of Free Available Chlorine

李佳珮(Chia-Pei Li)

指導教授 ： 林郁真

國立臺灣大學/工學院/環境工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.10045

摘要

在水資源缺乏的時代，新興污染物的存在可能對生態環境構成威脅，亦引起飲用水安全疑慮及成為廢水回收再利用之障礙；然而，新興污染物的宿命與威脅仍有許多待釐清之處。鑑於百年來加氯消毒過程廣泛設立於全世界的淨水場及污水廠，以及自由餘氯(Free available chlorine, FAC; HOCl及OCl-之總稱)自然光解產生各種次級氧化劑的特性，本研究進行常見的微囊藻毒-LR和七種抗氯氧化藥物(ketamine, metoprolol, atenolol, pentoxifylline, clofibric acid, gemfibrozil and ibuprofen)於加氯消毒過程中的自然光降解行為。主要研究目標有二：探討微囊藻毒(LR)於金門水體中的自然光解及自由餘氯光解對於新興污染物降解之影響。
　　間接光解為微囊藻毒-LR主要的自然降解途徑，其降解速率與自然水體中硝酸根及有機物質濃度有關，在金門水體中，微囊藻毒-LR的光解半衰期介於11-21小時之間。許多藥物在自然水體中與微囊藻毒-LR同樣具有較慢的自然光解速率；而且，部分常用藥物在廢水處理過程中不易去除。本研究發現自由餘氯的自然光解現象可以有效地提升藥物及微囊藻毒-LR在水處理過程的降解效率。所有的目標污染物可在2小時內透過自由餘氯光解達到90%的去除效率([FAC]0=0.5 ppm Cl2; pH 7)。水中自由餘氯足夠與藥物進行光解的情況下，藥物的餘氯光解速率可透過偽二階動力方程式加以說明。此光解速率隨著自由餘氯的初始濃度改變，初始濃度越高，速率常數越大( [FAC]0 =0.05(pH=7)，50 ppb ketamine的速率常數為0.0132 M-1 min-1；[FAC]0 =2.00 ppm時(pH=7)，50 ppb ketamine的速率常數為0.4518 M-1 min-1)。溶液pH值對光解亦具影響，藥物的餘氯光解速率於較低的pH值(pH 6，餘氯主要為次氯酸)時較快；反之，高pH值時，藥物的餘氯光解速率較慢(pH 9，餘氯主要為次氯酸根離子)。在餘氯光解產生的各種次級氧化劑中，氫氧自由基和臭氧並非藥物降解的主要影響因子。此外，在自由餘氯光解系統中，若同時存有一種以上的藥物，藥物的降解速率將會受到競爭氧化劑的影響而減緩。
　　Ketamine餘氯光解後的總有機碳(TOC)無明顯改變，此表示餘氯光解僅將ketamine轉化成其他有機物，並無顯著礦化作用。Ketamine餘氯光解副產物和其自然光解副產物完全不同，hydroxyl-ketamine為ketamine餘氯氧化的主要副產物之一(產率2.4%)，與ketamine同樣具抗氯性但可在餘氯光解中降解。此外，ketamine餘氯光解副產物急毒性明顯低於其自然光解副產物；ketamine經三小時餘氯光解後，毒性單位為1-1.4；在30小時自然光解後的毒性單位為6(超純水中)和8(景美溪水中)。

關鍵字

抗氯氧化藥物 ； 自由餘氯 ； 光轉化 ； 加氯消毒 ； 藻毒

並列摘要

The presence of emerging contaminants in aquatic system is a critical issue over the last decade because of the water scarcity resulted in the need of water recycling. Their existence in natural waters poses potential risks to ecosystem and human health. Because chlorination is widely used for disinfection and the photolysis of free available chlorine (FAC; in the form of HOCl and OCl-) generates various secondary oxidants (such as OH• and O3), the degradation of microcystin-LR (MC-LR), a well-known algal toxin, and seven chlorine-resistant pharmaceuticals (ketamine, metoprolol, atenolol, pentoxifylline, clofibric acid, gemfibrozil and ibuprofen) during FAC photolysis was investigated in this work. Objectives of this work were to study the natural photolysis of MC-LR in lake (Kinmen) and to investigate FAC solar photolysis of MC-LR and chlorine-resistant pharmaceuticals in chlorination process.

Indirect photolysis was the major natural attenuation process for MC-LR; the degradation rates depended on the concentrations of photosensitizers (NO3- and DOM) in the water. The photolysis half-lives of MC-LR were in the range of 11-21 hours. Similar to MC-LR, target pharmaceuticals also undergo relatively slower photolysis processes in the natural water systems. During chlorination process, solar photolysis of FAC effectively enhanced the degradation/transformation of MC-LR and chlorine-resistant pharmaceuticals. After three hours of reaction time with [FAC]0=0.5 ppm Cl2 at pH 7, target compounds were completely removed. The rate of chlorine-resistant pharmaceuticals during FAC photolysis was described using a pseudo-second-order equation (except for clofibric acid) when sufficient FAC was present in the system. FAC photolysis rate constants (k) were found to vary with initial concentrations of FAC; for example, the k of 50 ppb ketamine was between 0.0132 and 0.4518 M-1 min-1 when [FAC]0=0.05-2.00 ppm Cl2 at pH 7. Lower pH values (pH 6 (HOCl) compared to pH 9 (OCl-) resulted in higher FAC photolysis rates. During FAC photochemical reactions, OH• and O3 were not the only major secondary oxidants involved in enhanced MC-LR and pharmaceutical degradation. In addition, pharmaceuticals in the mixture competed for the FAC or for secondary oxidants, resulting in slower FAC photolysis rates.

Ketamine was used as a model compound for further mechanism study of FAC photolysis. Ketamine FAC photolysis was found to be a merely transformational process because TOC remained constant over the three-hour reaction period. Hydroxyl-ketamine (HK) was found to be one of the major oxidation byproducts of ketamine with FAC (HK: 2.4% yield). Similar to ketamine, HK was chlorine-resistant but could be degraded during the FAC photolysis. The FAC photolysis byproducts of ketamine differed from those of ketamine from sunlight photolysis alone. The toxicity of ketamine byproducts of this system was found to be much lower than that generated through natural sunlight photolysis.

並列關鍵字

chlorine-resistant ； free available chlorine ； pharmaceutical ； algal toxin ； chlorination ； photodegradation

參考文獻

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