碎冰清洗管線對於自來水供水系統中水質與菌群結構之影響

Abstract

自來水清水使用加氯消毒來抑制水中微生物生長，透過大區域且複雜管網的自來水供水系統輸送至用戶端，輸水過程中隨著管齡使用和水力停留時間增加，管中易有生物膜、鬆散沉積物與腐蝕管垢等物質的累積，加速餘氯消耗及促使消毒副產物生成。至目前國內在自來水供水系統中對於碎冰清洗管線與供水環境變化下對水質與微生物相關影響研究甚少。有鑑於此，本研究於一處自來水供水系統進行現地實驗，透過水質參數與次世代定序分析，來了解碎冰清洗管線後對水質與微生物族群相關性影響。結果顯示碎冰清洗可以有效降低水中濁度與重金屬濃度，微生物族群Sphingomonas、Acinetobacter相對豐度降低。水中菌群因受清洗影響，洗後第二週總異營數和水中菌群多樣性上升，導致水中生物不穩定性，而水中餘氯濃度、餘氯衰退並無明顯變化。反而清洗後八個月間總異營數、餘氯濃度、餘氯衰退三者間易受到清水餘氯濃度與季節性溫度影響，當夏季高溫環境和高餘氯效率衰退下，水中總異營數上升，Porphyrobacter與Novosphingobium和總異營數呈顯著正相關。隨著淨水場清水餘氯濃度提升，總異營數能有效降低，但Bacillus、Mycobacterium、Pseudomonas等具消毒耐受性菌屬相對豐度上升，說明餘氯濃度會是驅使微生物族群結構變化的關鍵因子。此外，在供水末端地區有較高總三鹵甲烷與總鹵乙酸濃度，總三鹵甲烷與總鹵乙酸濃度變化與水溫、總溶解性有機碳、餘氯衰退效率皆呈顯著正相關，在季節與空間差異上對消毒副產物生成影響甚大。

Chlorination is often used to inhibit the growth of microorganisms in the drinking water distribution system (DWDS). Treated water is transported to end-users through diverse and complex DWDS. With pipeline age and long retention times, the accumulation of biofilm, loose deposits, and corrosion scale in the pipeline would react with residual chlorine to form disinfection by-products (DBPs). However, few studies discuss microbial populations' impact on water quality in domestic DWDS. Therefore, the objective of this study was to explore the correlations between bulk water microbial population and water quality parameters before and after ice pigging. Water samples were collected, analyzed and the microbial populations were explored through next gene sequencing. Results showed that ice pigging could reduce turbidity and heavy metal concentrations, and the relative abundance of Sphingomonas and Acinetobacter was also decreased in bulk water. Within 13 days after the ice pigging, increased heterotrophic plate count (HPC) and Shannon diversity index were observed in most sampling sites. However, the chlorine residuals and chlorine decay remained unchanged. After 13 days, with elevated water temperature and high chlorine decay, HPCs were increased, as well as the relative abundance of Porphyrobacter and Novosphingobium, which both expressed positive correlations with HPC. With the increased residual chlorine concentration in finished water at 34 days after ice pigging, HPCs had been reduced effectively. Still, the relative abundance of chlorine-resistant bacteria such as Bacillus, Mycobacterium, and Pseudomonas increased, indicating that residual chlorine was a critical contributing factor driving the bacterial community shift. In addition, at the endpoint of DWDS, high trihalomethane (THMs) and haloacetic acids (HAAs) concentrations were observed. THMs and HAAs concentration positively correlated with water temperature, dissolved organic carbon, and residual chlorine decay. These indicated that seasonal and spatial variations impacted DBPs formation.