环境流体动力学模拟优选人工湿地设计中隔板湿地长度比

采用环境流体动力学模型(environmental fluid dynamics code,EFDC)建立表面流人工湿地水动力-水质耦合模型,研究隔板长度与湿地长度比值(简称隔长比)对表面流人工湿地水力性能及净化效果的影响规律,优选适宜的隔长比。结果表明:1)率定和验证的12组结果中,水动力模型模拟评价结果为中等及以上,即相关系数0.7、纳什系数0.4、相对误差20%,的有7组,水质模型模拟评价结果为中等及以上,即相对误差20%,的有10组。2)表面流人工湿地适宜隔长比随长宽比的增加而增大,当长宽比由1、2、4变为4、8、16时,对应的适宜隔长比分别为0.675、0.850、0.938。3)表面流人工湿地主要水力指标随适宜隔长比的增大而增加,对净化效果指标的提升不明显。4)在适宜隔长比不变的情况下增加湿地的表面积能明显提升水质净化效果(50%)。研究可为表面流人工湿地实际工程设计提供依据。

Appropriate design for obstruction length-to-wetland length ratio in free-water-surface constructed wetlands based on environmental fluid dynamics code

In practical engineering design, obstruction baffles are usually used in free-water-surface constructed wetlands (FWS CWs) to cut the width in half and double the length, thus the aspect ratio (length/width) increased fourfold. The length of the obstruction is often set to difference between boundary length and half the boundary width. In order to explore the design method''s reasonability and get an optimal value, the tests of FWS CWs under different aspect ratios are needed. In this study, we explored the influence of obstruction length-to-wetland length ratio (OL/WL) and aspect ratio on the hydraulic performance of FWS CWs. The environmental fluid dynamics code (EFDC) was used to establish the hydrodynamic model and water quality model of FWS CWs. Based on the tracer data and pollutant data of 12 FWS CWs, the calibration and verification of model parameters were carried out through sensitivity analysis and manual parameter adjustment. 2 kinds of wetlands named model wetlands and actual wetlands were established. 6 different areas and aspect ratios were set for the model wetlands, and the same as the actual wetlands. Each model wetland was provided with an obstruction, while the actual wetlands had no obstruction. The actual wetland corresponded to the model wetland one by one, that was, the aspect ratio of actual wetland was 4 times of the corresponding model wetland. The purpose of the simulation was to find an appropriate OL/WL that increased the aspect ratio of the model wetland to 4 times by comparing the hydraulic and treatment performance of the model wetlands and actual wetlands. The model wetland was simulated with multiple OL/WL to find the ratio that could make the model wetland and the actual wetland had the closest hydraulic and treatment performance. In addition, the hydraulic index, namely effective volume ratio, short circuit indicator, Morril dispersion index and moment index, were used to evaluate the similarity between the hydraulic performance of the 2 kinds wetlands. Similarly, the removal rates of total nitrogen and total phosphorous were used to evaluate the treatment performance''s similarity. The results showed that: 1) The sensitive parameters affecting the hydraulic performance were background horizontal eddy viscosity, dimensionless horizontal momentum diffusion, wall roughness and bottom roughness, and those affecting the treatment performance were maximum nitrification rate, reference temperature for nitrification and constant benthic flux rate of phosphorous. Among the 12 groups, 7 groups were satisfactory or better in hydrodynamic model with correlation coefficient higher than 0.7, Nash-Suttcliffe higher than 0.4, and relative error smaller than 20%; and 10 groups were satisfactory or better in water quality model. The calibrated and verified EFDC model could be used to simulate the hydrodynamic process and purification process of FWS CWs. 2) The 4 hydraulic index had good consistencies. As the increase of OL/WL, effective volume ratio, short circuit indicator and moment index increased and Morril dispersion index decreased. The larger the effective volume ratio, short circuit indicator and moment index would lead to smaller morril dispersion index and better hydraulic performance, which indicated the hydraulic performance increased with the increase of OL/WL. 3) The removal rate of total nitrogen and the phosphorous didn''t change greatly as the OL/WL increased. 4) Changing the area had great impact on the treatment performance. 5) When the aspect ratio ranged from 1, 2, 4 to 4, 8, 16, the appropriate OL/WL was 0.675, 0.850, 0.938, which was different from the values of 0.5, 0.75, 0.875 in the traditional test design or engineering application.