Abstract：
Secondary disinfection aims to prevent microbial regrowth during distribution by maintaining disinfectant residuals in water systems. However, multi-factorial interactions contribute to free chlorine decay in distribution systems, and even more so in building plumbing. Assembling 1737 samples from nine large institutional buildings, a meta-analysis was conducted to determine whether building managers can actively rely on incoming free chlorine residuals to prevent in-building microbial amplification. Findings showed that free chlorine concentrations in first draws met the 0.2 mg/L common guide level in respectively 26 %, 6 % and 2 % of cold, tepid and hot water samples, whereas flushing for 2-60 min only significantly increased this ratio in cold water (83 %), without reaching background levels found in service lines. Free chlorine was significantly but weakly (R≤ 0.2) correlated to adenosine triphosphate, heterotrophic plate count and total and intact cell counts, thus evidencing that residuals contributed to decreased culturable and viable biomass. Detection of culturable Legionella pneumophila spanning over a 4-log distribution solely occurred when free chlorine levels were below 0.2 mg/L, but no such trend could be distinguished clearly for culturable Pseudomonas aeruginosa. Water temperatures below 20 °C and >60 °C also completely prevented L. pneumophila detection. Overall, the majority of elevated microbial counts were measured in distal sites and in tepid and hot water, where free chlorine is less likely to be present due to stagnation and increased temperature. Therefore, building managers cannot solely rely on this chemical barrier to mitigate bacterial growth in bulk water.
摘要：
二次消毒旨在通过维持水系统中的消毒剂残留物来防止分布过程中的微生物再生长。然而,多因素相互作用有助于分配系统中的游离氯衰变，在建筑管道方面更是如此。从九座大型机构大楼收集1737个样本，进行了一项荟萃分析,以确定建筑管理人员是否可以积极依赖进入的游离氯残留物来防止建筑内微生物扩增.结果表明，第一次抽取的游离氯浓度分别满足0.2mg/L的普通指导水平，分别为26％，6%和2%的冷，温和的热水样本，而冲洗2-60分钟仅在冷水中显着增加了这一比率（83％），没有达到服务线上的背景水平。游离氯与三磷酸腺苷显著相关，但弱相关(R≤0.2)，异养平板计数以及总细胞和完整细胞计数，因此证明残留物导致可培养和可存活生物量减少。当游离氯水平低于0.2mg/L时，仅在4对数分布上检测到可培养的嗜肺军团菌，但是对于可培养的铜绿假单胞菌，这种趋势无法明确区分。低于20°C和>60°C的水温也完全阻止了嗜肺乳杆菌的检测。总的来说,大多数升高的微生物计数是在远端部位、温水和热水中测量的，由于停滞和温度升高，游离氯不太可能存在。因此,建筑管理人员不能仅仅依靠这种化学屏障来减轻散装水中的细菌生长。
