Drinking water distribution systems (DWDSs) are used to supply hygienically safe and biologically stable water for human consumption. The potential of thermal energy recovery from drinking water has been explored recently to provide cooling for buildings. Yet, the effects of increased water temperature induced by this "cold recovery" on the water quality in DWDSs are not known. The objective of this study was to investigate the impact of cold recovery from DWDSs on the microbiological quality of drinking water. For this purpose, three pilot distribution systems were operated in parallel for 38 weeks. System 1 has an operational heat exchanger, mimicking the cold recovery system by maintaining the water temperature at 25 °C; system 2 operated with a non-operational heat exchanger and system 3 run without heat exchanger. The results showed no significant effects on drinking water quality: cell numbers and ATP concentrations remained around 3.5 × 105 cells/ml and 4 ng ATP/l, comparable observed operational taxonomic units (OTUs) (~470-490) and similar Shannon indices (7.7-8.9). In the system with cold recovery, a higher relative abundance of Pseudomonas spp. and Chryseobacterium spp. was observed in the drinking water microbial community, but only when the cold recovery induced temperature difference (ΔT) was higher than 9 °C. In the 38 weeks' old biofilm, higher ATP concentration (475 vs. 89 pg/cm2), lower diversity (observed OTUs: 88 vs. ≥200) and a different bacterial community composition (e.g. higher relative abundance of Novosphingobium spp.) were detected, which did not influence water quality. No impacts were observed for the selected opportunisitic pathogens after introducing cold recovery. It is concluded that cold recovery does not affect bacterial water quality. Further investigation for a longer period is commended to understand the dynamic responses of biofilm to the increased temperature caused by cold recovery.

中文翻译：

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冷回收技术对无氯分配系统中微生物饮用水水质的影响。

饮用水分配系统（DWDS）用于提供卫生安全和生物稳定的水供人类消费。最近已经研究了从饮用水中回收热能的潜力，以为建筑物提供冷却。然而，由这种“冷恢复”引起的水温升高对DWDS中水质的影响尚不清楚。这项研究的目的是研究从DWDS中回收冷水对饮用水微生物质量的影响。为此，三个试点分配系统并行运行了38周。系统1具有可操作的热交换器，通过将水温保持在25°C来模仿冷回收系统；系统2在非运行热交换器下运行，系统3在没有热交换器的情况下运行。结果显示对饮用水水质没有显着影响：细胞数量和ATP浓度保持在3.5×105细胞/ ml和4 ng ATP / l左右，可观察到的可操作分类单位（OTU）（〜470-490）和相似的香农指数（ 7.7-8.9）。在具有冷恢复的系统中，假单胞菌的相对丰度较高。和Chryseobacterium spp。在饮用水微生物群落中观察到了这种现象，但仅当冷恢复引起的温差（ΔT）高于9°C时。在38周大的生物膜中，较高的ATP浓度（475 vs. 89 pg / cm2），较低的多样性（观察到的OTU：88 vs.≥200）和不同的细菌群落组成（例如，新孢子菌属的相对丰度较高）。检测到，但不影响水质。引入冷恢复后，未观察到所选机会病原体的影响。结论是冷恢复不影响细菌水质。为了了解生物膜对冷恢复引起的温度升高的动态响应，建议进行更长时间的研究。