Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629, HZ, Delft, the Netherlands.
Evides Industriewater, Schaardijk 150, 3063, NH, Rotterdam, the Netherlands.
Water Res. 2020 Apr 1;172:115505. doi: 10.1016/j.watres.2020.115505. Epub 2020 Jan 17.
Understanding the bacterial dynamics in cooling towers is imperative for the assessment of disinfection efficiency and management of microbial risks linked to aerosol formation. The objective of this study was to evaluate the impact of feed water on the cooling water bacterial microbiome and investigate the survival ability of its members when exposed to continuous chlorine disinfection. Water from an industrial cooling water system (2600 m/h) was collected over a 5-month period at 3 locations along the feed water line and 3 locations in the cooling tower. ATP measurements suggested that the average ATP-per-cell in the cooling tower evolved independently from the average ATP-per-cell in the feed water. Flow cytometry and 16S rRNA gene amplicon sequencing were then combined to quantify the bacterial dynamics in the whole system. A mass balance based equation was established to determine net growth and net decay of the cooling tower bacterial communities in order to evaluate the impact of continuous chlorination (0.35-0.41 mg Cl/L residual chlorine). The results indicated that cooling tower main community members were determined by the input feed water microbiome and the bacterial community structure was further shaped by varying decay rates of the microorganisms. Notably, the order Obscuribacterales showed to be growing in the cooling tower in the presence of residual chlorine up to 0.4 mg Cl/L, with a recurrent net growth of 260 ± 95%, taking into account the impact of the concentration factor. This conclusion was only possible thanks to the systematic analysis described in this paper and generates discussion about the resistance of Obscuribacterales to residual chlorine. The described mass balance approach provides a high level of understanding on bacterial dynamics and should be considered for future characterization studies of cooling towers in which accurate investigation of microbiome changes is essential.
了解冷却塔中的细菌动态对于评估消毒效率和管理与气溶胶形成相关的微生物风险至关重要。本研究的目的是评估进水对冷却水中细菌微生物组的影响，并研究其成员在持续氯消毒暴露下的生存能力。在 5 个月的时间里，从工业冷却水系统（2600 m³/h）的进水线的 3 个位置和冷却塔的 3 个位置收集水。ATP 测量表明，冷却塔中每个细胞的平均 ATP 与进水中每个细胞的平均 ATP 独立演变。然后结合流式细胞术和 16S rRNA 基因扩增子测序来定量整个系统中的细菌动态。建立了一个基于质量平衡的方程来确定冷却塔细菌群落的净生长和净衰减，以评估连续氯化（0.35-0.41 mg Cl/L 余氯）的影响。结果表明，冷却塔主要群落成员由输入的进水微生物组决定，细菌群落结构进一步由微生物的不同衰减率塑造。值得注意的是，在 0.4 mg Cl/L 余氯存在下， obscuribacterales 目菌在冷却塔中表现出生长，考虑到浓度因子的影响，其反复净生长为 260±95%。只有得益于本文中描述的系统分析，才能得出这一结论，并引发关于 obscuribacterales 目菌对余氯的抗性的讨论。所描述的质量平衡方法提供了对细菌动态的高水平理解，应在未来对冷却塔的微生物组变化进行准确调查至关重要的特征研究中加以考虑。
