UV/H2O2程序對含氮有機前質生成消毒副產物特性之研究

Abstract

在多數淨水處理流程中，一般都會選擇添加氯作為消毒劑，以達成去活化水中致病微生物的功能，餘氯則可以持續抑制配水系統中微生物的生長。但是在加氯消毒的過程中，氯與水中有機物質會反應生成各種消毒副產物(disinfectant by-products), 例如三鹵甲烷(Trihalomethanes)和鹵乙酸 （Haloacetic acid）等。這些消毒副產物在過去很多文獻中已被指出可能對人類有致癌性和產生不良健康反應。因此，為了有效控制消毒副產物的生成，必須在水處理流程中採取有效的去除水中有機前質的處理程序。 在水處理系統中，高級氧化處理是一種有效處理水中有機化學物質的方法。其中，UV/H2O2的方法是利用H2O2經紫外燈照射後產生具有高氧化能力的氫氧自由基，此自由基可以不選擇性地與水中的有機物質反應，有效降解有機物，在特定控制條件下甚至達成礦化的階段。因此，當水中的污染物無法有效地被傳統淨水流程去除時，UV/H2O2是一種進階處理方法。已有研究指出UV/H2O2能有效地降低地表水的DOC濃度，同時可在後端加氯消毒時間接性地降低消毒副產物的生成量。 本研究探討以UV/H2O2對特定含氮有機物降解，以及含氮有機物經過高級氧化處理後消毒副產物的生成特性。本研究選取的物質包括N-[3-(Dimethylamino)propyl]methacrylamide (DMAPMA)，(+)-cis-Diltiazem Hydrocloride (Diltiazem) 和 Benzalkonium chloride (BKC)這三種化學物質。 實驗結果顯示這三種化學物質在經過UV/H2O2的處理後，會改變其消毒副產物生成的特性。其中以BKC產生的消毒副產物濃度最高。這三種物質在UV/H2O2處理後皆會產生高濃度的三鹵甲烷、鹵乙酸和三氯硝基甲烷(Trichloronitromethane)。研究也發現消毒副產物的生成量與UV-254吸光度有很高的關聯性，其次是DOC和DON。在進行UV/H2O2的過程中，氫氧自由基的形成效率與水中物質特性有關，對於紫外光具高吸收度的物質會與H2O2造成對紫外光吸收的競爭效應。 本研究的另一部分是要探討以發光二極體 (Light-emitting diode)作為紫外燈光源，對於傳統使用水銀燈效能上的比較。實驗結果顯示，發光二極體在UV/H2O2具有降解高紫外光吸收度的物質的能力，但礦化的效果會比使用一般水銀燈來的差。經過耗能計算公式得出，此實驗中使用的發光二極體裝置並沒有比使用水銀燈節能。

In water treatment processes, chlorination has been widely used as a disinfectant method to oxidize the pollutants or control microorganism growth in water including in distribution systems. Various disinfectant by-products (DBPs) could be formed when chlorine reacts with the organic compounds in the water. Among these, DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs) are proved to have carcinogenicities and can cause adverse health effects on human health. In order to control the DBPs concentration, it is very important for the water treatment plants to include effective water treatment procedures to remove organic precursors in water. The advanced oxidation process (AOP) is a chemical oxidation based method use in the water treatments to remove certain organic chemical materials. In the UV/H2O2 method, it create hydroxyl radicals through the dissociation of H2O2 when it received UV irradiance at the O-O double bonds, which gave it a very high oxidation potential to react with all kinds of organic compounds in non-selectively way. Thus, it shows a great solution to treat polluted water which cannot be treated well with traditional water treatment process. Some studies show effectiveness of UV/H2O2 to reduce dissolved organic compound in the natural water, which resulting in DBPFPs reduction after disinfection, but the complexity of the organic matter in natural water making it hard to clarify the source of DBP precursors. This study intended to assess the effects of UV/H2O2 towards DBP precursors reduction from nitrogen containing chemicals. The chemicals studied include N-[3-(Dimethylamino)propyl]methacrylamide (DMAPMA)，(+)-cis-Diltiazem Hydrocloride (Diltiazem) and Benzalkonium chloride (BKC) . The results showed that UV/H2O2 treatments can alter the DBPs formation trends of the three chemicals tested. These chemicals have high potentials to form DBPs including trihalomethane, haloacetic acids, and trichloronitromethane. The amounts of DBPs formed have strong correlations with values of UV-254 absorbance, followed by DOC and DON. During the UV/H2O2 process, the efficacy of hydroxyl radicals formation rely on the concentration of H2O2 which also act as scavengers to UV light. This study also discussed the efficiency of UV/H2O2 process using LED as alternative UV light source and compare the results with low pressure mercury lamp. Results showed that UV-LED were capable of degrading substances which have high absorbance on 254 nm, but it was ineffective in mineralizing the NPDOC when compared with low pressured mercury lamp. The UV-LED apparatus used in this study are also found to be more energy consuming when the results were compared with low pressure mercury lamp in term of AOP efficiency.