Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
Water Res. 2022 Aug 15;222:118890. doi: 10.1016/j.watres.2022.118890. Epub 2022 Jul 29.
Pb in drinking water is one of the main sources of Pb in human bodies. Besides excess lead incidents caused by lead service lines, Pb contamination in non-lead pipe systems (e.g. copper and PVC) is also on the rise. Brass fixtures and lead-solder connections are the primary sources of lead in non-lead systems, which cause intermittent peaks of Pb at the consumer tap. The concentrations of lead in tap water depend on pipeline geometry, sampling methods, and the characteristic of the pipe flow. Using a 3-dimensional computational fluid dynamics model, this study analyzes the Pb concentration variations at taps of copper water supply systems. The turbulent diffusion and shear flow dispersion are fully simulated in the model to provide the most accurate prediction. Water parcels containing lead (clouds) are formed adjacent to lead sources during stagnation and are then dispersed with the flow of water through the pipe when the tap is opened. The geometry of the pipeline has a significant impact on the monitored Pb levels. The complex flow condition in elbow areas leads to a more intense mixing of lead ions. Therefore, the Pb levels at consumer taps in complex plumbing systems in high-rise buildings are higher than in straight pipelines. When the sampling flow rate is large, the peak height of Pb is slightly higher due to higher turbulent intensity. Pb concentrations in sequential samples are predicted with sample volumes of 50, 250, 500, and 1000 mL. Lead levels may be diluted significantly when samples are taken in large volumes (e.g. 500 mL or 1 L), resulting in an underestimation of Pb levels at taps. A sample volume of 250-500 mL is recommended in sequential sampling programs on non-lead service lines in order to identify Pb sources.
饮用水中的铅是人体铅的主要来源之一。除了因铅供水管线而导致的铅超标事件外，非铅管道系统（如铜管和 PVC 管）中的铅污染也呈上升趋势。黄铜装置和铅焊料连接是无铅系统中铅的主要来源，会导致消费者龙头间歇性出现铅峰值。自来水中的铅浓度取决于管道几何形状、采样方法和管道流量特性。本研究使用三维计算流体动力学模型分析了铜管供水系统龙头处的铅浓度变化。该模型充分模拟了紊流扩散和剪切流弥散，以提供最准确的预测。在停滞期间，含铅的水流（云团）会在铅源附近形成，然后在龙头打开时随水流通过管道分散。管道的几何形状对监测到的铅水平有重大影响。弯管区域复杂的流动条件导致铅离子更强烈的混合。因此，高层建筑复杂管道系统中消费者龙头处的铅水平高于直管道。当采样流速较大时，由于紊流强度较高，铅的峰值高度略高。用 50、250、500 和 1000 mL 体积的样品预测连续样品中的 Pb 浓度。当采用大体积（例如 500 或 1 L）取样时，铅浓度可能会显著稀释，导致龙头处的铅水平被低估。建议在非铅供水管线的连续采样计划中使用 250-500 mL 的样品体积，以识别铅源。
