楊曉菁─混凝處理自來水中消毒副產物前質之探討
Enhanced Coagulation for Removal of DBP Precursors in Source Waters
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水中天然有機物是屬於非定性、偏酸性，是以芳香族苯環為主體結構的化合物，主要官能基包括氫氧烷基 （ R-OH ）、 C=O 、 COOH 、酚 (Phenol) 等官能基。這些不飽和官能基易在消毒過程中與鹵化 物進行替代反應，形成有害的消毒副產品，對健康有潛在的危害。自來水廠對於水中有機物之傳統處理程序主要透過混凝、沈澱、過濾等流程去除，但在傳統淨水程序中，對於加氯消毒副產物或其有機前質之去除能力有限。

本研究選取六個不同原水特性水廠（澎湖望安、澎湖成功、北縣板新、北市長興、基隆六堵、金門太湖）之原水、沈澱水及實驗室配置腐植酸溶液作為實驗對象，以水廠原水進行強化混凝實驗，由傅立葉紅外線光譜分析 （ FTIR ）、有機物 UV 光譜測定、溶解性有機碳分析探討原水、清水中有機物的特性並探討水廠對有機物處理效率。

水廠原水經混凝處理過後，水中 高分子量之腐植質易於化學混凝中去除，而低分子量之親水性有機質（主要為黃酸）不易於混凝去除。 水廠原水經實驗室進行強化混凝實驗後，與水廠處理過之沈澱水並沒有很明顯的差異。由水廠原水經混凝前後之 FTIR 的光譜分析結果，對照人工配置之腐植酸及黃酸溶液 FTIR 光譜，亦顯示 混凝過程已去除掉較大的分子之有機物 。但水中 腐植質 之去除未必代表三鹵甲烷生成潛能（ THMFP ）之去除；經混凝處理留下之 低分子量親水性有機質亦為主要 THMFP 之來源，水廠若要降低 THM 之生成以降低可能之健康風險，必須要針對去 除低分子量之親水性有機物質之可能方式加以探討。

Natural organic matter (NOM) is present in all of the surface waters. Since the discovery of the disinfection by-products (DBPs), surface water supplies have received much public attention in recent years because carcinogens like trihalomethanes (THMs) can result from the chlorination process. The removal of NOM from drinking water is largely achieved by the chemical coagulation and flocculation using alum. However, due to the presence of the wide variety of NOM, it has been reported that the NOM removal in conventional drinking water treatment processes is quite low, between 10 and 50 percent.

In this study, the effectiveness of enhanced alum coagulation for removal of NOM at various alum dosages and pH values was assessed for six source waters with various concentrations of dissolved organic carbon (DOC) and alkalinity. Between October 2000 and June 2001, raw water samples from Wan-An, Chen-Kong, Ban-Hsin, Charn-Hsin, Liu-Du and King-Men water treatment plants were taken and enhanced coagulation experiments were conducted. Turbidity, DOC, pH, UV254, alkalinity, and THM formation potential (THMFP) in raw water and supernatant were monitored, water quality of settled water from water treatment plants were also analyzed and compared.

For Chen-Kong and Wan-An Water Treatment Plant (high DOC, high alkalinity), laboratory tests showed up to 50% DOC removal at optimum alum dosage after acidifying the raw water to pH = 6. For King-Men Water Treatment Plant (high DOC, low alkalinity), laboratory tests showed that the highest DOC removal was achieved pH = 8 (natural condition). However, alum coagulation showed little DOC removal for source water from Ban-Hsin, Charn-Hsin, and Liu-Du (low DOC, low alkalinity). Higher alkalinity in Chen-Kong and Wan-An account for the necessity to acidify the raw water before enhanced coagulation for optimum NOM removal.

After the enhanced coagulation, humic acids with higher molecular sizes were removed and the fulvic acids with low molecular sizes were left in the water. Although the nonhumic fraction of NOM was considered to exist in clear water without causing water quality problem, higher DBPFP were observed in the supernatant of Wan-An and King-Men waters. This result indicated that a significant percent of DBPs could be formed from the nonhumic fraction of NOM.