Effect Of Different Vegetative Filter Strips And Soil Infiltration Systems On The Removal Of Nitrogen And Phosphorus

With the process of urbanization in China,urban non-point source pollution caused by surface runoff becomes more serious with the increase of impervious layer.In recent years,non-point source pollution has been the main cause of nitrogen and phosphorus pollution in China,so it can be seen the control of non-point source pollution is an important part of the water quality management of rivers,lakes and other natural waters.As the final barrier for pollutants to flow into the water,the lakeshore zone has important ecological functions,so it is necessary to carry out ecological engineering construction on the lakeshore zone to improve the ability to maintain water quality.Based on this current situation,this research takes the soil in the lakeshore zone of Yezhi Lake in Wuhan,Hubei Province as the research object,and firstly constructs different vegetative filter strips with different herbaceous plants to investigate the effect of vegetative filter strips on the removal of pollutants such as nitrogen,phosphorus and total suspended solids in two processes of surface flow and seepage under three hydraulic loads and three pollution loads,and then selects two plants with better effect on the removal of nitrogen and phosphorus,and constructs different plant-substrate combinations of soil infiltration system to investigate the removal effect of pollutants under different pollutant loads and different hydraulic loads,in order to provide practical ecological engineering measures for non-point source pollution control in urban lakeshore zone and realize effective removal of urban runoff pollutants,the main results obtained are as follows:（1）Compared with the bare ground control filter strips,.the vegetation cover treatment not only increased the runoff reduction rate of the filter strip,but also significantly reduced the surface infiltration flow ratio of the filter strip,allowing more runoff to infiltrate.The runoff reduction rate of filter strips was significantly or highly significantly positively correlated with the removal rates of NH₄⁺-N,TN,TP,TSS,and NO₃^--N during surface flow,and highly significantly correlated with the removal rates of NH₄⁺-N,TP,and TSS during infiltration.The surface seepage flow rate ratio of the filtered zone effluent was highly significantly negatively correlated with the pollutant removal rate in the surface flow process,and was significantly or highly significantly negatively correlated with the NH₄⁺-N,NO₃^--N,and TP removal rate in the seepage process.（2）The hydraulic load affected the reduction of runoff and the removal of pollutants by vegetative filter strips.The runoff reduction rate of all five filter strips decreased significantly with the increase of hydraulic load,and the decrease ranged from 21.04%to46.29%.The hydraulic load intensity was significantly negatively correlated with NH₄⁺-N removal rate during percolation and highly significantly negatively correlated with TP removal rate.The surface seepage flow rate ratio of the filter zone increased significantly with enhanced hydraulic loading,and the surface seepage flow rate ratio showed a highly significant negative correlation with TN,NH₄⁺-N,NO₃^--N,TP,and TSS removal rate in the surface flow process,and a significant or highly significant negative correlation with NH₄⁺-N,NO₃^--N,and TP in the seepage process.（3）Cynodon dactylon and Festuca elata,which are more effective in removing N and P in the vegetatice filter strips experiment,and select four substrates:dolomite,zeolite,sponge iron and charcoal,to construct small soil infiltration systems,and all four substrates have good adsorption capacity for P and NH₄⁺-N.Among all 15 treatments,the treatment with the best NH₄⁺-N removal is the BF（Cynodon dactylon+zeolite）group;the best NO₃^--N removal was the BH（Cynodon dactylon+sponge iron）group,and NO₃^--N removal rate of Cynodon dactylon group was higher than that of Festuca elata group.The highest removal rate of TN was in the GH（Festuca elata+sponge iron）group,followed by the BH group;The two treatments with the highest TP removal rate were GH and BH group,and the TP removal effect of Festuca elata group was better than that of Cynodon dactylon group.The highest removal rate of COD was the treatment of GH.（4）The pollutant removal rate of soil infiltration system is affected by the hydraulic load,and the removal rate of NH₄⁺-N and TP by the system decreases when the intensity of rainfall is enhanced,but the addition of substrate or planting can both improve the pollutant removal effect of soil infiltration system under stronger hydraulic load.The hydraulic loads show a highly significant negative correlation with NH₄⁺-N and TP removal rate,and a significant negative correlation with COD and TN removal rate.The pollutant loads of the influent water also affected the pollutant removal efficiency of the soil infiltration system,and the removal rates of NO₃^--N,TN,TP,and COD by the soil infiltration system increas significantly when the pollutant concentration of the influent water increases.Pollution loads are highly significantly and positively correlated with removal rate of NO₃^--N,TN,TP,and COD.The results of this study show that Cynodon dactylon and Festuca elata vegetative filter strips have better effect on reducing surface runoff,and the soil infiltration system based on sponge iron and zeolite has better removal effect of nitrogen and phosphorus in sewage.Hydraulic load and pollution load significantly affect the pollutant removal efficiency of vegetation filter belt and soil percolation system.Both of them are ecological engineering technologies which can be used to prevent and control non-point source pollution.