Abstract：
Secondary water supply systems (SWSSs) are characterized by long water stagnation and low levels of chlorine residuals, which may pose a high microbial risk to terminal users. In this study, the SWSSs of 12 residential neighborhoods in a metropolitan area of 5 million people in southeastern China were seasonally investigated to assess their microbial risks by determining more than 30 physicochemical and biological parameters. Although the microbiological quality of SWSS water met the requirements of the standards for drinking water quality of China, it did deteriorate in various aspects. The heterotrophic plate counts with R2A media were high (> 100 CFU/mL) in some SWSS tank and tap water samples. Propidium monoazide (PMA)-qPCR revealed a one magnitude higher abundance of viable bacteria in the tank and tap water samples (average 103.63±1.10 and 103.65±1.25 gene copies/mL, respectively) compared with the input water samples, and Enterococcus, Acanthamoeba, and Hartmannella vermiformis were only detected in the tanks. In particular, the high detection frequency of Legionella in 35% tank and 21% tap water samples suggested it is a supplementary microbial safety indicator in SWSSs. The microbial regrowth potential was more obvious in summer, and Illumina sequencing also demonstrated distinct seasonal changes in the relative abundance of bacterial gene sequences at the genus level. Turbidity and residual chlorine were closely connected with total bacterial biomass, and the latter seemed responsible for microbial community structure alteration. The extremely low chlorine residuals associated with a high abundance of total bacteria (as high as 106.48 gene copies/mL) and Legionella (as high as 106.71 gene copies/100 mL) in the closed valve tanks highlighted the high microbial risk increased by mishandling the operation of SWSSs. This study found that SWSSs possessed a higher microbial risk than the drinking water network, which suggested that the frequency and scope of monitoring the microbial risk of SWSSs in megacities should be strengthened for the purpose of waterborne epidemic disease prevention and control.
摘要：
二次供水系统（SWSS）的特点是长时间的水停滞和低水平的氯残留物，这可能对终端用户构成很高的微生物风险。在这项研究中,对中国东南部500万人口的大都市中的12个居民区的SWSS进行了季节性调查，以通过确定30多个物理化学和生物学参数来评估其微生物风险。尽管SWSS水的微生物质量达到了我国饮用水水质标准的要求,它确实在各个方面恶化了。在一些SWSS罐和自来水样品中,具有R2A培养基的异养平板计数高(>100CFU/mL)。单叠氮丙啶（PMA）-qPCR显示，水箱和自来水样品中的活菌丰度较高（平均103.63±1.10和103.65±1.25基因拷贝/mL，分别)与输入水样相比，和肠球菌,棘阿米巴,只有在坦克里发现了HartmannellaVermiformis.特别是,35％的水箱和21％的自来水样品中军团菌的高检测频率表明，它是SWSS中补充的微生物安全指标。微生物再生潜力在夏季更为明显，和Illumina测序也证明了在属水平上细菌基因序列相对丰度的明显季节性变化。浊度和余氯与细菌总生物量密切相关,而后者似乎是微生物群落结构改变的原因。在封闭的阀门罐中，与高丰度的总细菌（高达106.48基因拷贝/mL）和军团菌（高达106.71基因拷贝/100mL）相关的极低的氯残留物强调了通过错误处理增加的高微生物风险SWSS的操作。这项研究发现，SWSSs比饮用水网络具有更高的微生物风险，建议应加强特大城市SWSS微生物风险监测的频率和范围，以预防和控制水传播流行病。
