| Summary: | 碩士 === 國立臺灣大學 === 環境衛生研究所 === 97 === 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.
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