非均质多孔介质对水平潜流人工湿地水力效率的影响

对比以不同粒径(4～9、8～12、11～17mm)非均质多孔介质(玻璃珠)作为基质的水平潜流人工湿地(以有机玻璃板材模拟)的水力效率、水力停留时间等参数,并参照其流态变化进行分析。结果表明:(1)均以上端为进水口、下端为出水口,水流流经不同粒径玻璃珠的水平潜流人工湿地会产生不同的流态。(2)玻璃珠粒径小(4～9mm)的水平潜流人工湿地中,染料在其中运动并最终能够迁移到出水口的有效空间最大,空间利用率最大,则有效体积比最大,染料流经区域面积最大;转角处染料呈圆角流过,死区范围小。(3)当玻璃珠粒径为4～9mm时,水平潜流人工湿地具有最长的平均水力停留时间(0.437 8h)和最小的水流散度(标准方差为0.052 5),使得水平潜流人工湿地的有效体积比最高(0.495 7),水力效率也最高(0.469 6)。随着粒径的增大,平均水力停留时间缩短,水流散度增大,而有效体积比和水力效率均呈减小趋势。(4)合理的水力停留时间分布能够提高有效体积比,而有效体积比越高,即污水在水平潜流人工湿地中运动并最终能够迁移到出水口的有效空间越大,污染物与基质以及附着在基质上的微生物的接触越充分,从而提高污染物的去除率。

Effect of the heterogeneous porous media on the hydraulic efficiency of horizontal subsurface-flow wetlands

Series of simulated horizontal subsurface-flow constructed wetlands using different sized glass beads(4-9,8-12,11-17 mm) as wetland filter media were established to investigate the effect of heterogeneous porous media on the hydraulic efficiency of the wetland.Flow through the filter bed was visualized by injecting dyed fluid into the water-saturated model.The hydraulic parameters such as hydraulic retention time,effective volume fraction and hydraulic efficiency were detected using chloride tracer.The flow patterns were also analyzed.Results showed that the dyed fluid in different experiment apparatus presented different flow pattern.In the simulated constructed wetland filled with small grain size glass beads(4-9 mm),the dyed fluid from top inlet to bottom outlet had the highest effective volume,means the constructed wetland had the highest space utilization ratio,effective volume ratio and dye flow distribution area,the dyed fluid was in arc shape around the corner,and the dead area was the smallest.When the diameter of glass beads ranged 4-9 mm,the mean retention time of wetland and its distribution divergence was 0.437 8 h and 0.052 5,the effective volume ratio and hydraulic efficiency of wetland was 0.495 7 and 0.469 6 respectively.With increasing the diameter of glass beads,the mean retention time was shortened,the distribution divergence of mean retention time was increased and the effective volume ratio and hydraulic efficiency were decreased.Reasonable distribution of hydraulic retention time could increase the effective volume ratio of wetland,namely the wetland had larger effective volume for sewage migration,which was benefit for the sufficient connection of pollutants,substrate and microbes in substrate,so as to improve the removal efficient of pollutants.