Purification effect of integrated subsurface-surface flow constructed wetland on the river water

Based on the environmental conditions of Lake Taihu main inflow rivers and the current situation of water pollution,the ladder-type structured wetland which integrating the advantages of subsurface flow with surface flow wetland systems was designed.The front end of wetland was subsurface flow,back-end was the surface flow,and Zizania caduciflora was planted in test area under the density of 25strains/m2.The purification effect of established wetland for polluted water was investigated,according to the analyzing results,technical parameters for constructing wetland were provided.The results indicated that the integrated constructed wetland had perfect purification efficiency,under the hydraulic retention time of 3.4d,the average removal rate of TN,TP,NH+4-N and permanganate index were 64.3%,63.9%,74.6%and 51.1%respectively during July to December.Compared with those of subsurface flow constructed wetland operated in the same period,the removal rates of TN,TP,NH+4-N and permanganate index were improved by 12.1,10.6,1.8and 5.1percent respectively.In the first 0.25 distance fraction,the pollutant removal rate occupied 74.5%-91.2%of the total.