以電化學氧化法去除水中含胺基類藥物之研究

Abstract

隨著現代醫學的發展，人工合成藥物被製造且頻繁使用，當不當棄置或經生物體代謝後排出體外，環境中皆可檢測出殘餘藥物，雖然這些微量物質並不會對人體造成立即性的危害，但仍可能會對環境中其它生物造成不良影響，故有關此類新興污染物對公共衛生與環境的影響不容忽視。目前仍缺乏理想的方法能有效處理廢水中所含之所有藥物。先前已有許多針對去除單一藥物的相關研究，但在實際污水及環境中卻是同時存在許多藥物。因此，本研究嘗試利用電化學氧化法，以直接或間接氧化降解兩類環境中常被檢測出的較高濃度藥物—抗生素中的磺胺甲噁唑 (Sulfamethoxazole, SMX) 與非類固醇消炎止痛藥中的乙醯胺酚 (Acetaminophen, ACT) 與雙氯酚酸 (Diclofenac, DIC) 之水樣，進行單一與多重藥物實驗，探討在不同重要操作參數 (電解質添加種類、電流強度、藥物初始濃度、溶液初始酸鹼值) 的反應條件下，電化學去除藥物的效率及其反應動力模式，並研究不同極板種類與反應裝置經各操作參數對電化學反應之影響與其能量消耗情形；接著利用上述所得之最佳反應條件，調整反應裝置後，模擬目標藥物在實廠廢水基質下經電化學氧化反應之效果，並分析目標藥物經電化學反應後的礦化程度及經反應後產生之中間產物，預測其可能的結構及主要降解途徑。 在施加0.5 A的5 mM 硫酸鈉系統中，15 µM的乙醯胺酚 (ACT)、雙氯酚酸 (DIC) 與磺胺甲噁唑 (SMX) 經電化學氧化反應60分鐘後，去除率分別為74.3%、90.0%、81.6% (k = 0.0230、0.0370、0.0270 min–1)，礦化效果分別為48.9%、85.9%、68.2%。在10 mM氯化鈉系統中，施加相同強度進行實驗後，15 µM的乙醯胺酚 (ACT)、雙氯酚酸 (DIC) 與磺胺甲噁唑 (SMX) 經電化學氧化反應降解後，皆可在30分鐘內達完全去除，降解反應動力學呈擬一階反應 (k = 0.117, 0.307, 0.170 min–1)，而反應60分鐘後之礦化效果分別為89.6%、92.6%、99.6%。由結果推論出解離態物質較易受極板表面之靜電力吸引，有較快之質傳速率，可增加其被極板表面或附近產生之氫氧自由基直接氧化去除的機會；而由循環伏安法中的結果顯示，當溶液中的含氯物質經電解產生自由氯後即形成間接氧化反應，進而去除溶液中的目標藥物。三種目標藥物的中間產物經超效能液相層析串聯式質譜儀 (Ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry, UPLC-Q-TOF-MS) 分析鑑定出共17種物質，在單一與多重藥物系統中皆能發現相似的中間產物，可推論出兩種主要降解途徑，其一為藉由極板表面與附近之氫氧自由基進行的直接氧化反應，此反應可形成氧化之中間產物；另一為由溶液中自由氯降解的間接氧化反應，此一產生的中間產物可同時發現氧化副產物與類似加氯消毒之副產物。 然而SMX的錯合物僅在單一藥物系統中產生，多重藥物系統中則發現SMX可能會與ACT或DIC形成錯合化合物，此一結果顯示，不同含胺基類藥物同時存在時可能會與自由氯相互反應形成不同之錯合物。最後，由實廠廢水基質實驗結果可知，溶液中的溶解性有機物可能會降低電化學氧化降解目標藥物之效率。此研究可建立電化學技術降解目標藥物的操作資訊，並提供未來應用之評估參考，藉此防止處理不完全的有機副產物流入環境水體，降低潛在的用水安全與環境生態危害。

Acetaminophen (ACT), diclofenac (DIC), and sulfamethoxazole (SMX) which belong amine-containing emerging contaminants are widely used and often founded in the aquatic environments like surface water, groundwater, hospital wastewater, and domestic wastewater treatment plants (WWTPs) influents and effluents, elevating concerns about their potential impact. These complicated compounds are not effectively removed by conventional processes of WWTPs. Many studies have been focused on the removal of a single pharmaceutical compound. However, numerous pharmaceuticals are simultaneously present in the environment. To contemplate advanced treatment, this study investigates the laboratory-scale electrochemical oxidation degradation of single and multiple amine-containing pharmaceuticals (ACT, DIC, and SMX) with graphite and platinum titanium electrodes were studied. Experimental parameters were varied including the properties of electrolytes (Na2SO4 and NaCl), current intensity (I), initial substance concentration (C0), and initial pH (pHi). These three target compounds and their intermediates in both single- and multiple-pharmaceuticals systems were also identified and tracked by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) during treatment, along with total organic carbon (TOC) to determine the mineralization extent. Moreover, the authentic hospital wastewater spiked samples were also conducted to modify the effects of water matrices during the electro-oxidation process. In contact with 5 mM Na2SO4 under 0.5 A at pHi 7, 74.3%, 90.0%, and 81.6% of 15 µM of ACT, DIC, and SMX were respectively removed after 60 min (k = 0.0230, 0.0370, and 0.0270 min–1), 48.9%, 85.9%, and 68.2% of TOC were respectively removed after reaction. In contrast, the same initial concentration of ACT, DIC, and SMX were eliminated within 30 min (k = 0.117, 0.307, and 0.170 min–1) in 10 mM NaCl under the same operating conditions, 89.6%, 92.6%, and 99.6% of TOC were respectively removed after reaction. Due to electrostatic forces and high mass transformation rates in the direct electro-oxidation process, we observed the dissociated compounds were attracted to the anode. According to the cyclic voltammogram, indirect electro-oxidation occurred when active chlorine species were generated from chloride ions anodically to destroy pollutants. Based on intermediates detected during electro-oxidation treatment by UPLC-Q-TOF-MS, some of the electro-oxidation products in single- and multiple-compound systems were the same. Only oxidized intermediates were found in the direct electro-oxidation system, which both oxidized and chlorinated intermediates were found in the indirect electro-oxidation system. Dimer of SMX and its chlorinated products were found in the single-compound system; however, it would not be found in the multiple-compound system. Moreover, dimers of SMX and ACT or DIC would be found in the multiple-compound system. These findings imply that compared to direct electro-oxidation, indirect electro-oxidation is a much more effective way to remove these substances, but likely leads to a different degradation pathway, and new products may be produced if different amine-containing pharmaceuticals react with free chlorine simultaneously. Finally, results of authentic wastewater matrices experiments suggested that the organic impurities in hospital wastewater may lead to the decrease of amine-containing pharmaceuticals removal. The electrochemical oxidation process holds promise for arresting the release of these amine-containing pharmaceuticals and their intermediates derivatives into the environment.