氫氧自由基處理水中消毒副產物前質之研究

Abstract

目前台灣地區淨水廠大多以添加氯氣或次氯酸鹽等含氯消毒劑之加氯消毒為主，但許多研究指出原水中的天然有機物會與水中氯反應產生消毒副產物(Disinfection By-Products，DBPs)。外島地區由於原水背景有機物濃度偏高，且受到海水入侵的影響，原水會含有較高濃度的溴離子，因此容易產生含溴的消毒副產物。一般傳統淨水處理流程無法去除水中有機物。由於氫氧自由基具有很強的氧化力，因此本研究利用兩種高級氧化法：Fenton程序(H2O2 / Fe2+)及臭氧氧化法，評估其去除外島地區原水中的有機物質之效能，並探討其減少消毒副產物生成的可能。實驗用水樣為人工配置之黃酸水溶液及採集金門二地區原水，以Fenton程序及臭氧氧化兩種不同方式對水樣進行處理，並觀察水中有機物質的降解情形；在消毒副產物的影響方面，則針對各高級氧化程序不同階段水樣進行消毒副產物生成潛能實驗，以分析水中三鹵甲烷與含鹵乙酸的變化。 實驗結果顯示不論是以Fenton程序或臭氧氧化進行反應，水體pH值的調控是必須注意的。在pH=3時，主要進行Fenton氧化反應，特色為反應快速，1分鐘內即可去除水中有機物40%~50%，消毒副產物的生成也同時有效受到控制；而當pH=4時，Fenton程序則能同時進行氧化與混凝的作用，可去除黃酸水溶液中約70%的有機物，對於金門地區原水中有機物也有60%的去除效果。而隨著水中有機物質的減少，消毒副產物的生成量也隨之降低。當利用臭氧進行氧化反應時，水中pH值會影響反應途徑，使得其對有機物的分解速率受到影響。反應條件在pH=10時進行，可使得臭氧氧化的速率較快，也可在短時間內降低水中消毒副產物的產生。而在利用臭氧進行氧化前，尚需先過濾掉水中大顆粒物質，以避免氧化過程中nonpurgeable dissolved organic carbon, NPDOC測值升高。同時反應時間也不宜過長，以免水中溴離子與臭氧反應，產生對人體健康危害的溴酸鹽。 整體來說，Fenton程序與臭氧氧化反應確實能有效去除消毒副產物的前質，但使用前必須先瞭解水體組成特性，控制適當pH值及反應時間，以增進其在原水處理上之成效。

In Taiwan, chlorination is widely used as a disinfectant in water treatment process. However, many studies have shown that chlorination process results in the formation of Disinfection By-Products (DBPs), and Br-DBPs are formed in raw water containing bromide. In conventional water treatment process, the natural organic matter (NOM) removal is low, about 10% to 40 %. The objective of this study is to use Fenton process and ozonation to remove NOM in raw water and to evaluate their effectiveness to reduce DBPs formation potential. The results indicated that pH is an important factor in advanced oxidation process. In Fenton oxidation process, 40% ~ 50% NPDOC of the fulvic acid and Kinmen raw water is removed at pH=3. The Fenton process contains oxidation and coagulation mechanism at pH=4. For fulvic acid, about 70% of NPDOC is removed; for Kinmen raw water, about 60% NPDOC is removed. The DBPFP was reduced after AOPs due to the reduction of the organic precursor. Compared with Fenton process, the reaction mechian changes with pH in ozonation process. At pH 10, both the oxidation rate and final NPDOC removed ratio are better than that at pH 7. When the particulate organic matter were not removed form water before ozonation, the NPDOC is increased. And if reaction time is longer than 30min, BrO3- will be formed in water. In general, both Fenton process and ozonation can remove organic matter from water, and the effective is based on pH and reaction time. However, the reaction condition is different with different source water, and it is important to evaluate its suitability before AOP is adopted.