College of Water Conservancy and Hydroelectric Power, Hohai University, Nanjing 210098, PR China.
College of Harbour, Coastal and Offshore Engineering, Hohai University, Nanjing 210098, PR China.
Sci Total Environ. 2018 Apr 15;621:1142-1150. doi: 10.1016/j.scitotenv.2017.10.113. Epub 2017 Nov 6.
Vertical flow constructed wetlands are widely used for removing pollutants from wastewater. Substrate clogging is an operational challenge of constructed wetlands, which can result in impeded water flow and finally a significant decline in the ability of the system to treat the wastewater. The entire clogging process in a vertical flow constructed wetland (VFCW) was quantitatively analyzed by measurements of hydraulic conductivity. Tracer tests and model simulations were carried out to investigate internal flow patterns during the clogging and resting processes. This analysis revealed that hydraulic conductivity gradually decreased with operation time. Further, the distribution time of the flow field was different under different degrees of clogging. Non-uniformity in water flow was primarily observed in the first 400min after adding the tracer (NaCl) in the early clogging stage, as opposed to the last 400min in the late clogging stage. Variation in water flow divergence was closely correlated with piston flow; the reaction efficiency was highest in the early stages of clogging. In the later stages, stronger flow mixing was observed. Resting operations can reduce the dispersion of internal flow and improve reaction efficiency. After resting for approximately 15days, tracer concentration fluctuations decreased and internal flow back-mixing was alleviated. A simulation further described the internal flow pattern and elaborated and validated the tracer experiment. The outcomes of this study will assist in understanding how internal flow behavior varies in response to the clogging process and reveal details of the internal clogging mechanism in VFCWs.
垂直流人工湿地被广泛应用于去除废水中的污染物。基质堵塞是人工湿地运行面临的挑战之一，它会阻碍水流，最终导致系统处理废水能力显著下降。通过水力传导率的测量，对垂直流人工湿地（VFCW）中的整个堵塞过程进行了定量分析。通过示踪试验和模型模拟，研究了堵塞和休止过程中的内部流动模式。分析表明，水力传导率随运行时间逐渐降低。此外，在不同堵塞程度下，流场的分布时间也不同。在早期堵塞阶段，加入示踪剂（NaCl）后的前 400min 内，水流场的非均匀性主要表现为，而在后期堵塞阶段的最后 400min 内，水流场的非均匀性主要表现为活塞流。水流发散的变化与活塞流密切相关；堵塞初期的反应效率最高。在后期，观察到更强的水流混合。休止操作可以减少内部流动的分散，提高反应效率。经过大约 15 天的休止后，示踪剂浓度的波动减小，内部流动的返混得到缓解。模拟进一步描述了内部流动模式，阐述并验证了示踪试验。本研究的结果将有助于理解内部流动行为如何响应堵塞过程的变化，并揭示 VFCW 内部堵塞机制的细节。
