Riga Technical University, Kipsalas str. 6A, LV-1048 Riga, Latvia; Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Riga Technical University, Kipsalas str. 6A, LV-1048 Riga, Latvia.
Water Res. 2018 May 15;135:11-21. doi: 10.1016/j.watres.2018.02.006. Epub 2018 Feb 6.
Changes in bacterial concentration and composition in drinking water during distribution are often attributed to biological (in)stability. Here we assessed temporal biological stability in a full-scale distribution network (DN) supplied with different types of source water: treated and chlorinated surface water and chlorinated groundwater produced at three water treatment plants (WTP). Monitoring was performed weekly during 12 months in two locations in the DN. Flow cytometric total and intact cell concentration (ICC) measurements showed considerable seasonal fluctuations, which were different for two locations. ICC varied between 0.1-3.75 × 10 cells mL and 0.69-4.37 × 10 cells mL at two locations respectively, with ICC increases attributed to temperature-dependent bacterial growth during distribution. Chlorinated water from the different WTP was further analysed with a modified growth potential method, identifying primary and secondary growth limiting compounds. It was observed that bacterial growth in the surface water sample after chlorination was primarily inhibited by phosphorus limitation and secondly by organic carbon limitation, while carbon was limiting in the chlorinated groundwater samples. However, the ratio of available nutrients changed during distribution, and together with disinfection residual decay, this resulted in higher bacterial growth potential detected in the DN than at the WTP. In this study, bacterial growth was found to be higher (i) at higher water temperatures, (ii) in samples with lower chlorine residuals and (iii) in samples with less nutrient (carbon, phosphorus, nitrogen, iron) limitation, while this was significantly different between the samples of different origin. Thus drinking water microbiological quality and biological stability could change during different seasons, and the extent of these changes depends on water temperature, the water source and treatment. Furthermore, differences in primary growth limiting nutrients in different water sources could contribute to biological instability in the network, where mixing occurs.
在分配过程中，饮用水中细菌浓度和组成的变化通常归因于生物（不）稳定性。在这里，我们评估了供应不同类型水源的全规模分配网络（DN）中的时间生物学稳定性：经过处理和氯化的地表水以及在三个水处理厂（WTP）生产的氯化地下水。在 DN 的两个位置每周进行监测 12 个月。流式细胞术总细胞和完整细胞浓度（ICC）测量显示出相当大的季节性波动，这在两个位置有所不同。ICC 在两个位置分别在 0.1-3.75×10cells mL 和 0.69-4.37×10cells mL 之间变化，ICC 的增加归因于分配过程中温度依赖性的细菌生长。用改良的生长潜力法进一步分析来自不同 WTP 的氯化水，确定主要和次要生长限制化合物。观察到，氯化后地表水样本中的细菌生长主要受到磷限制，其次是有机碳限制，而氯化地下水样本中则受到碳限制。然而，在分配过程中，可用营养素的比例发生了变化，再加上消毒残留衰减，这导致在 DN 中检测到的细菌生长潜力高于在 WTP 中。在这项研究中，发现细菌生长更高（i）在较高的水温下，（ii）在氯残留较低的样本中，（iii）在营养物质（碳、磷、氮、铁）限制较少的样本中，而这在不同来源的样本之间存在显著差异。因此，饮用水微生物质量和生物稳定性可能会在不同季节发生变化，这些变化的程度取决于水温和水源和处理方式。此外，不同水源中主要生长限制营养素的差异可能导致混合发生时网络中的生物不稳定性。
