飲用水處理流程中三氯乙酸生物降解之研究

Abstract

因含氯消毒劑的消毒效力強、成本低廉及使用技術成熟，加氯消毒長期地廣泛使用於自來水廠之消毒程序，然而飲用水加氯消毒卻衍生出消毒副產物(Disinfection by-products; DBPs)的問題，其中以三鹵甲烷(Trihalomethanes; THMs)為最主要的消毒副產物物種，其次即為含鹵乙酸(Haloacetic acids; HAAs)。含鹵乙酸為毒性有機物質且常被檢測於飲用水及配水系統中，因其對人體具有生理各種毒性及致癌性，美國環保署將五種含鹵乙酸(MCAA、DCAA、TCAA、MBAA、DBAA)之最大容許濃度定為60 µg/L（移動年平均值）。已有許多研究指出含鹵乙酸可被微生物降解，然而對於含鹵乙酸的降解途徑與微生物物種所知並不多。 本研究目的分別包括：瞭解不同起始濃度三氯乙酸被金門自來水廠慢濾砂中微生物與台大生態水池微生物降解之途徑；自經過三氯乙酸馴養的培養液中分離出三氯乙酸降解菌，並進一步進行以純菌降解三氯乙酸之批次實驗；從分子生物的角度分析比較三氯乙酸馴養前與馴養後濾砂表層的微生物菌相並比較金門太湖、榮湖自來水廠慢濾砂中的微生物菌相之差異。 研究結果顯示隨著三氯乙酸濃度下降，伴隨著少量二氯乙酸濃度的增加，因此二氯乙酸可能為三氯乙酸經由部份生物降解而成的中間產物。由三氯乙酸馴養後之培養液中分離出可能具有降解三氯乙酸能力的菌株有Acinetobacter sp. 與 Pseudomonas putida strain NH.50。在微生物菌相分析的結果中，可觀察到經過三氯乙酸馴養後兩株序列和uncultured Bacteroidetes bacterium clone AS56 與 uncultured bacterium clone 9相似的微生物有增加的情形發生，推斷此兩株微生物可能與批次實驗中三氯乙酸的降解有關。另一方面從微生物菌相分析的結果中亦發現兩株序列和uncultured bacterium clone 2 與 Runella slithyformis相似的微生物同時存在於金門太湖、榮湖自來水廠慢濾池之濾砂中。

Due to its stability, effectiveness and low cost, chlorine is a widely used disinfectant in water treatments. However, water chlorination resulted in formation of disinfection by-products (DBPs) and some of DBPs could cause adverse health effects. In general, trihalomethanes (THMs) are the major group of DBPs (by weight) and haloacetic acids (HAAs) are the second. HAAs are toxic organic chemicals which were frequently detected in surface waters and in water distribution systems. Due to the human toxicity and carcinogenicity of HAAs, the United States Environmental Protection Agency has regulated five HAAs (sum of MCAA, DCAA, TCAA, MBAA, and DBAA) at a maximum contaminant level (MCL) of 60 ppb (location running annual average). It has been shown that HAAs are biodegradable. Although a large number of studies have been made on HAAs biodegradation, little information was available on their degradation pathways. There were three main objectives for this study. First of all, to evaluate the biodegradation pathways of TCAA with different initial TCAA concentrations by the microorganisms taken from the filter sand of slow sand filtration unit in Kinmen and the microorganisms from NTU Ecological Pond Water. Secondly, isolate TCAA degraders with TCAA enrichment medium. Thirdly, from molecular biological point of view, analyze the microbial communities before and after TCAA enrichment and compare the microbial communities on sands in the slow sand filtration unit in Tai Lake and Rung Lake drinking water plants in Kinmen. USEPA Method 552.3 was used for HAAs analysis and the microbial community analysis was based on Ribosomal Intergenic Spacer Analysis (RISA) combined with polyacrylamide gel electrophoresis. The results showed that dichloroacetic acid (DCAA) increased in batch experiments during the TCAA degradation, and there was no monochloroacetic acid (MCAA) accumulation; thus it was inferred that DCAA might be an intermediate product in TCAA degradation process. Two pure cultures were isolated from TCAA enrichment medium, Acinetobacter sp. and Pseudomonas putida strain NH.50, which might be able to degrade TCAA. The microbial communities analysis before and after TCAA enrichment showed that there were two bacteria, whose sequences were similar to uncultured Bacteroidetes bacterium clone AS56 and uncultured bacterium clone 9, might be related to TCAA biodegradation. Comparison of the microbial communities of slow sand filtration units between Tai Lake and Rung Lake showed that there were two bacteria, whose sequences were closely related to uncultured bacterium clone 2 and Runella slithyformis, existed simultaneously on the slow sand filtration units in both drinking water plants.