Comparative Study On The Efficiency Of Horizontal Subsurface Flow And Vertical Flow Constructed Wetland In Treating Simulated Initial Rainwater

In view of the large amount of organic pollutants carried in the initial runoff rainwater,which caused serious pollution to rivers and lakes.In this study,gravel,coarse sand and pebble were used as substrates and and four emergent plants:Acorus calamus,Canna indica,Arundo donax and Juncus effusus were mixed to construct two types of constructed wetlands:horizontal subsurface flow and vertical flow constructed wetland.The removal effects of COD_Cr,TN,NH₃-N and TP in simulated initial rainwater under different influent water quality and different hydraulic retention time were investigated.The main results and conclusions of this experiment are as follows:（1）The horizontal subsurface flow constructed wetland had a good purification capacity for simulated initial rainwater.When the hydraulic retention time was 1.0,1.5 and 2.0 d,the COD_Cr,TN,NH₃-N and TP were about 60.8～149.28 mg/L,16.85～35.14 mg/L,11.08～27.54mg/L and 1.08～2.74 mg/L,respectively.The removal rates of the wetland system were 65.47%～84.96%,8.96%～33.82%,5.25%～27.82%and 21.34%～88.07%,respectively.（2）The vertical flow constructed wetland also had a good removal effect on the four pollutants in the simulated initial rainwater.When the hydraulic retention time was 1.0,1.5,2.0d,the removal rates of COD_Cr,TN,NH₃-N and TP were about 60.8～149.28 mg/L,16.85～35.14 mg/L,11.08～27.54 mg/L and 1.08～2.74 mg/L,respectively.The removal rates of the wetland system were 70.03%～88.39%,9.17%～44.45%,3.21%～33.94%and 9.88%～86.41%,respectively.（3）Under the same hydraulic retention time,the influent water quality of different simulated initial rainwater had little effect on the removal of COD_Cr and NH₃-N by horizontal subsurface flow constructed wetland,but had a great influence on the removal of TN and TP.However,the removal of COD_Cr in vertical flow constructed wetland was less affected,and the removal of TN,NH₃-N and TP was more affected.（4）The hydraulic retention time is an important factor affecting the purification effect of horizontal subsurface flow and vertical flow constructed wetlands on simulated initial rainwater.With the extension of hydraulic retention time,the purification effect can be improved.（5）The horizontal subsurface flow and vertical flow constructed wetlands had good removal effect on COD_Cr and TP in simulated initial rainwater,and the removal rate can reach more than 80%.The removal rate of TN and NH₃-N was general.With the extension of the operation time of the constructed wetland,the plant growth was better.The removal rate of TN and NH₃-N increased in the later stage of wetland operation.The removal rate of TN was up to44%,and the removal rate of NH₃-N was up to 34%.（6）The horizontal subsurface flow and vertical flow constructed wetlands have been running for more than one year.The test results showed that Canna indica,Arundo donax grew well and could be used as recommended plant species for the application of constructed wetland technology in Jiangxi.From the above studies,it is found that the removal efficiency of four different pollutants by two different types of constructed wetlands was closely related to the hydraulic retention time,and different influent water quality also affected the removal of pollutants.With the extension of the operation time of constructed wetland,the pollutant removal effect was increased.