多孔介质模型校验水平潜流人工湿地水力特性的研究

On verifying the hydraulic behaviors of the horizontal subsurface flow constructed wetlands via the porous media model

水平潜流人工湿地对污废水有较好的处理效果,湿地内水力特性对其处理效果有较大影响。理解湿地内部各处的水力特性及优化湿地结构参数是正确构建水平潜流人工湿地水质处理数学模型的前提。运用地下水流多孔介质水力方程建立了水平潜流人工湿地水流特性的数学模型;借助计算流体动力学模拟技术实现了湿地水力模型的数学求解,所得模拟示踪物数值与实测示踪物数值基本吻合,验证了人工湿地中多孔介质模型的正确性。探讨了湿地表面长宽比、水力负荷和水力传导度对湿地水力停留分布密度RTD函数的影响,并计算了人工湿地水力效率。结果表明:长宽比和水力传导度对湿地水力效率影响较大,水力效率随长宽比增大而增大,随水力传导度增大而减小,且水力传导度间接反映颗粒粒径对水力效率的影响;水力负荷对水力效率影响不大,但影响RTD曲线的形状,使湿地水力停留时间改变较大。

The objective of this paper is to propose a hydraulic model for the wetland construction in hoping to identify and determine the hydraulic behavior of the wetlands and optimize its construction parameters via the computational fluid dynamics（ CFD）and build a mathematical model for more successful water treatment in the horizontal subsurface flow constructed wetlands. As is well known,such subsurface flow constructed wetlands enjoy nice sewage and waste water removing efficiency,for its hydraulic function can promote the removal efficiency. It is just for the said purpose that we have established a mathematical model for the flowing behavior of such wetlands by utilizing a group of hydraulic equations of the groundwater flow with the porous media,which is supposed to work on the three pairs of such wetlands with the following aspect ratios： 1： 1,1. 5： 1 and 2： 1. The granular media of each bed in each pair can further be divided into the coarse granitic gravel（ D60= 10 mm） and the small granitic gravel（ D60=3. 5 mm） with the initial water depth of the entire simulation object being set to 0. 5 m and the hydraulic load rate being set to 36 mm/d. In addition,we have also built up a mathematical solution of hydraulic model by using the simulation technology of computational fluid dynamics. The simulated data of the tracer prove to be well in accord with the experimental data,thus verifying the rationality and truthfulness of the porous media model of the wetland construction. Furthermore,we have also made a detailed discussion of the effects of the aspect ratio,the hydraulic load rate and the saturated hydraulic conductivity of the wetlands from the point of view of the hydraulic retention time distribution density（ RTD）and the hydraulic efficiency of the wetlands to be built. The results of our experiments have shown that the aspect ratio and the saturated hydraulic conductivity may have strong influence on the hydraulic efficiency of the wetlands to be built. And the hydraulic efficiency of such wetlands tend to increase with the increase of the aspect ratio. On the other hand,the hydraulic efficiency may decrease with the increase of the saturated hydraulic conductivity,that is to say,the higher aspect ratio,the finer media is needed to be reinforced by increasing the internal dispersion. Although the hydraulic load rates may not have direct influence on the hydraulic efficiency,they may influence the shape of the RTD function and the hydraulic retention time greatly. Thus,it can be concluded that the hydraulic model and hydraulic laws for wetland construction we have proposed are in a position to promote the wetland construction and serve as a guide for wetland layout and management.