Department of Soil Physics and Land Management, Wageningen University and Research, Wageningen, The Netherlands.
KWR Water Research Institute, Nieuwegein, The Netherlands.
Appl Environ Microbiol. 2023 Aug 30;89(8):e0021923. doi: 10.1128/aem.00219-23. Epub 2023 Jul 17.
For production of clean drinking water, the processes governing bacterial remobilization in the unsaturated zone at transient water flow are critical. Although managed aquifer recharge is an effective way to dispose of pathogens, there are concerns about recontamination after heavy precipitation. To better understand how bacteria that were initially retained in porous media can be released to groundwater due to transient water content, transport experiments and modeling for Escherichia coli and Enterococcus moraviensis were conducted at the soil column scale. After inoculating dune sand columns with a bacteria suspension for 4 h, three rainfall events were performed at 24-h intervals. The effluent from sand columns was collected to analyze bacteria breakthrough curves (BTCs). After the rainfall experiments, the bacteria distribution in the sand column was determined. The collected BTCs and profile retentions were modeled with HYDRUS-1D, using different model concepts, including one-site kinetic attachment/detachment (M1), Langmuirian (M2), Langmuirian and blocking (M3), and two-site attachment/detachment (M4). After inoculation, almost 99% of the bacteria remained in the soil. The M1 and M2 bacteria models had a high agreement between observed and modeled concentrations, and attachment and detachment were two significant mechanisms for regulating bacteria movement in a porous medium with fluctuations in water flow. At the end of the experiment, the majority of bacteria were still found within the depth range of 5 cm to 15 cm. Our experiments show that E. coli is more mobile in sandy soils than E. moraviensis. The results of this study also suggest that the unsaturated zone is an important barrier between microbial contamination at the soil surface and groundwater. Follow-up studies are needed to completely understand the variables that regulate bacteria remobilization in the unsaturated zone of dune sands. At managed artificial recharge sites in the Netherlands, recontamination of infiltrated water with fecal indicator bacteria has been observed. The results of this study suggest that the unsaturated zone is an important barrier between microbial contamination at the soil surface and groundwater. Bacteria that accumulate in the unsaturated zone, on the other hand, can multiply to such an extent that they can be released into the saturated zone when saturation increases due to major rain events or a rise in groundwater level.
为了生产清洁饮用水，瞬变水流条件下控制非饱和带中细菌再移动的过程至关重要。尽管含水层人工补给是处理病原体的有效方法，但人们仍担心在强降水后会发生再污染。为了更好地了解由于瞬变含水量，最初被多孔介质保留的细菌如何因地下水而释放到地下水中，在土壤柱尺度上进行了大肠杆菌和粪肠球菌的运移实验和模拟。在沙丘砂柱中接种细菌悬浮液 4 小时后，每隔 24 小时进行三次降雨事件。收集砂柱的出水以分析细菌突破曲线（BTC）。降雨实验后，确定了砂柱中的细菌分布。使用不同的模型概念，包括单位置动力学附着/脱附（M1）、朗缪尔（M2）、朗缪尔和阻塞（M3）以及双位置附着/脱附（M4），对收集的 BTC 和剖面保留进行了 HYDRUS-1D 模拟。接种后，几乎 99%的细菌仍留在土壤中。M1 和 M2 细菌模型的观测浓度与模型浓度高度一致，附着和脱附是调节水流波动下多孔介质中细菌运动的两个重要机制。实验结束时，大部分细菌仍在 5 cm 至 15 cm 的深度范围内。我们的实验表明，大肠杆菌在砂质土壤中的迁移能力强于粪肠球菌。本研究结果还表明，非饱和带是土壤表面微生物污染与地下水之间的重要屏障。需要进一步的研究来完全了解调节沙丘砂非饱和带中细菌再移动的变量。在荷兰的人工管理补给点，已经观察到渗入水中的粪便指示菌再次受到污染。本研究结果表明，非饱和带是土壤表面微生物污染与地下水之间的重要屏障。另一方面，在非饱和带中积累的细菌可以繁殖到如此程度，以至于当由于大雨事件或地下水位上升导致饱和度增加时，它们可以释放到饱和带中。
