Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/5445
標題: 自來水配水管線中水質生物穩定性之研究
A study on the biological stability of drinking water in the distribution system
作者: 朱振華
Chu, Chenghwa
關鍵字: 配水管線
水質生物穩定性
生物可利用有機碳
消毒劑
水質模式
出版社: 環境工程學系
摘要: 隨者科技日趨發達,依目前的淨水處理技術而言,水源經過淨水廠處理後的出流水,大都能夠符合自來水法規標準,然而在民眾的反應上,對於自來水水質滿意度方面,卻不完全理想。造成此現象主要是因為自來水經常在輸送的過程中,受到二次污染所致。由於台灣地處亞熱帶,配水管網的平均水溫本來就高於北美及西歐等地區,提供了配水管線中微生物生長的良好環境。而生物性污染一直被認為是配水管線二次污染最主要的問題,其中更以生物膜累積的問題最為嚴重且難以解決。 本研究的主要研究目的為藉由生物培養技術,探討影響自來水配水管線生物穩定性之因子與有效控制技術。研究中針對配水管網常見的無機營養源 (氮、磷)、有機營養源 (醋酸、草酸、腐植酸) 以及常用的消毒劑 (自由餘氯、二氧化氯、一氯胺) 作為研究對象,以模場配水管線與批次實驗同時並行的方式,來探討不同的營養源與消毒劑對配水管線中的微生物再生長的變化情形。同時配合水質模式,來模擬管線內微生物、營養源及消毒劑之間的消長情形,以做為未來自來水廠控制微生物再生長之主要參考依據。 添加無機營養源的結果顯示,添加濃度低於0.1 mg N/L的銨鹽、硝酸鹽或添加濃度低於0.005 mg P/L的磷酸鹽,對管線中的生物膜生長並沒有明顯的助益。當添加氮源濃度增加至0.5 mg N/L或磷源濃度增加至0.01 mg P/L時,管線生物膜中的異營菌數目有明顯增加的趨勢。比較添加氮源與磷源對管線中生物膜的影響發現,添加磷源對管線中微生物再生長的影響效應明顯大於氮源,而實場批次實驗結果亦顯示台灣中部地區的管線微生物生長有受到磷酸鹽限制的情形。 添加有機營養源的結果顯示,添加醋酸、草酸及腐植酸對管線中的生物可分解性有機物濃度 (AOC)、生物膜及懸浮性微生物均有增加的效應,其效應以醋酸為最大,草酸次之,腐植酸最低。添加不同分子量的腐植酸進入管線時,添加的分子量愈小,其轉化為AOC的比率愈高。由連續流實驗中顯示,水流中AOC的濃度愈高,管線中附著性微生物的生長狀況愈好,而懸浮性微生物會受到附著性微生物的影響,兩者呈現一良好的線性關係。 在中部實場水質生物穩定性的評估上,水質生物穩定性以自來水處理廠出流水為最佳,流經商業區的水樣其次,住商混合區再其次,而流至市郊區的水質生物穩定性較差。 添加消毒劑的結果顯示,在添加相同的當量氯濃度下,對管線中AOC的增加效應以自由餘氯為最高,二氧化氯次之,一氯胺最低。附著性微生物的消毒效率也以自由餘氯最佳,二氧化氯次之,一氯胺最差,懸浮性微生物的消毒效率也呈現相同的趨勢。 水質模式的模擬結果顯示,模式所模擬之營養源與微生物濃度均與實驗值十分吻合。探討模式參數對模擬結果(靈敏度分析)則顯示,隨著微生物對基質的轉換率 (kconv) 愈小、自然死亡速率 (kx) 愈快及附著性細菌對氯殺菌力的阻抗作用 (kr1) 愈小,附著性細菌能夠有效抑制,微生物生長至穩定所需的時間也愈短。 綜合添加營養源的實驗結果,顯示中部地區配水管網的微生物再生長潛能會受到無機及有機營養源的限制,屬於一水質生物穩定性高的區域。而由消毒劑實驗中可知,消毒劑的選用不能單純就其效率來選擇,也需注意因氧化消毒作用而對水質穩定性帶來的衝擊。
Given proper water treatment, finished water meets the standard. However, consumers are still unsatisfied with the quality of drinking water. The main reason is that drinking water deteriorates while being transported through the distribution system to the consumer. Biological pollution has long been the major concern. The growth of microbes and the accumulation of biofilms have been found in the drinking water pipes by many investigators. According to our field observations on the water quality in the distribution system, the biological stability of drinking water is strongly related to nutrients and disinfectant levels. The purposes of this research are to study the effects of different inorganic nutrients (nitrate, ammonium, and phosphate), organic nutrients (acetic acid, oxalic acid, and humic acid), and disinfectants (free chlorine, chlorine dioxide, and monochloramine) on the growth of heterotrophic bacteria in the drinking water distribution system. Effective control strategies to maintain a high biological stability of drinking water in the distribution system are thus proposed to the experimental observations and theoretical results. Results from the effects of adding ammonium or nitrate on the biofilm formation were insignificant for adding levels below 0.1 mg N/L. Analogous results were observed for adding phosphate at levels below 0.005 mg P/L However, as the addition of ammonium level increased to 0.5 mg N/L, significant effects on the biofilm formation could be observed. Similar results were obtained for adding phosphate at levels above 0.01 mg P/L. For addition of same level nutrient, biofilm formation was significantly greater for phosphorous than for nitrogen. The results of batch test indicated that the bacterial growth in the drinking water distribution system of central Taiwan was stimulated by adding phosphate. The results of adding organic nutrients to distributed water showed that the addition of three organic nutrients, acetate, oxalate and humic acid, to treated water has positive effect on the AOC content of drinking water and bacterial regrowth in the water pipe. The effect is enhanced with addition of high-level organic nutrients. The comparisons of AOC results showed the AOC/TOC ratio is the highest with existence of acetic acid, followed by oxalic acid, and then humic acid. The HPCs of free bacteria has a linear relationship with the HPCs of attached bacteria indicating that the increase in HPCs of free bacteria could be attributed to detachment of biofilm caused by fluid shear stress. The blank tests of batch system indicated that the biological stability of distributed drinking water is the highest in treatment plant effluent, the moderate in the commercial area and mixed area, and the lowest in the residential area. The experimental results with addition of different-type disinfectants in the distributed drinking water indicated that most bacterial regrowth was inhibited by free chlorine, followed by chlorine dioxide, and then by monochloramine. The inhibition was enhanced by addition of high-level disinfectants. The theoretical results showed that the water quality model could predict the experimental data very well. The results of sensitivity analysis demonstrated that the growth of attached bacteria could be effectively inhibited under conditions of lower utilized rate of substrates (kconv), higher natural decayed rate (kx) and lower resistive ability to chlorine (kr1), and then took less time to reach steady-state conditions. According to the BRP results, the bacterial regrowth potential were stimulated with adding inorganic and organic nutrients. Therefore, the biological statibility of the distributed water was good in central Taiwan. The strategy for using disinfectant did not only consider the disinfection efficiency, but also needed to evaluate the impact of biological statibility.
URI: http://hdl.handle.net/11455/5445
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