Sanitary Engineering, Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600GA, Delft, the Netherlands; Institute of Environmental Sciences and Engineering, School of Civil and Environmental Engineering, National University of Science and Technology, H-12 Sector, Islamabad, Pakistan.
Waternet, Korte Ouderkerkerdijk 7, 1096 AC, Amsterdam, the Netherlands.
Environ Res. 2021 Mar;194:110648. doi: 10.1016/j.envres.2020.110648. Epub 2020 Dec 28.
Drinking water distribution systems (DWDSs) have been thoroughly studied, but the concept of thermal energy recovery from DWDSs is very new and has been conceptualized in the past few years. Cold recovery results in a temperature increase of the drinking water. Its effects on drinking water quality and biofilm development are unclear. Hence, we studied both bulk water and biofilm phases for 232 days in two parallel pilot scale distribution systems with two temperature settings after cold recovery, 25 °C and 30 °C, and compared these with a reference pilot system without cold recovery. In all three pilot distributions systems (DSs) our results showed an initial increase in biomass (ATP) in the biofilm phase, along with occurrence of primary colonizers (Betaproteobacteriales) and subsequently a decrease in biomass and an increasing relative abundance of other microbial groups (amoeba resisting groups; Xanthobacteraceae, Legionellales), including those responsible for EPS formation in biofilms (Sphingomonadaceae). The timeline for biofilm microbial development was different for the three pilot DSs: the higher the temperature, the faster the development took place. With respect to the water phase within the three pilot DSs, major microbial contributions came from the feed water (17-100%) and unkown sources (2-80%). Random contributions of biofilm (0-70%) were seen between day 7-77. During this time period six-fold higher ATP concentration (7-11 ng/l) and two-fold higher numbers of high nucleic acid cells (5.20-5.80 × 10 cells/ml) were also observed in the effluent water from all three pilot DSs, compared to the feed water. At the end of the experimental period the microbial composition of effluent water from three pilot DSs revealed no differences, except the presence of a biofilm related microbial group (Sphingomonadaceae), within all three DSs compared to the feed water. In the biofilm phase higher temperatures initiated the growth of primary colonizing bacteria but this did not lead to differences in microbial diversity and composition at the end of the experimental period. Hence, we propose that the microbiological water quality of DWDSs with cold recovery should be monitored more frequently during the first 2-3 months of operation.
饮用水分配系统（DWDS）已经得到了充分的研究，但从 DWDS 中回收热能的概念非常新颖，并且在过去几年中才被提出。冷回收会导致饮用水温度升高。其对饮用水水质和生物膜发展的影响尚不清楚。因此，我们在两个平行的中试规模分配系统中进行了为期 232 天的研究，这两个系统在冷回收后分别设置了 25°C 和 30°C 的两个温度，并将这些结果与未进行冷回收的参考中试系统进行了比较。在所有三个中试分配系统（DS）中，我们的结果都显示出生物膜相中生物量（ATP）的初始增加，同时出现了主要的定植菌（β变形菌目），随后生物量减少，其他微生物群（抗变形虫组；黄杆菌科，军团菌目）的相对丰度增加，包括那些负责生物膜中 EPS 形成的微生物（鞘氨醇单胞菌科）。三个中试 DS 中生物膜微生物的发展时间不同：温度越高，发展速度越快。就三个中试 DS 中的水相而言，主要的微生物来源于原水（17-100%）和未知来源（2-80%）。在第 7-77 天之间，生物膜的随机贡献（0-70%）也可以看到。在此期间，与原水相比，三个中试 DS 的出水 ATP 浓度（7-11ng/l）增加了六倍，高核酸细胞数量（5.20-5.80×10 细胞/ml）增加了一倍。在实验结束时，三个中试 DS 的出水微生物组成没有差异，除了在所有三个 DS 中都存在与生物膜相关的微生物群（鞘氨醇单胞菌科），与原水相比。在生物膜相中，较高的温度会引发主要定植菌的生长，但这并没有导致实验结束时微生物多样性和组成的差异。因此，我们建议在冷回收 DWDS 的运行的头 2-3 个月内应更频繁地监测其微生物水质。
