Experimental Study On Construction Of Filling Layer Of Stormwater Bioretention Systems

In order to build sponge cities in loess distribution areas according to local conditions,improve the operation effect of rainwater bioretention system,regulate urban road rainwater runoff and pollutants,and promote the application of bioretention technology in Taiyuan City,this paper selects Taiyuan City as the research area,and focuses on its soil The construction of the packing layer of the rainwater bioretention system in Taiyuan City was discussed.The experiment adopted the physical model（1000 mm high,200 mm diameter plexiglass column）,and passed the following three parts of the experiment:the first part set up 5 kinds of bioretention system fillers:T（loess）,TS（60%loess+40%sand）,TSF（42%loess+28%sand+30%fly ash）,TSG（42%loess+28%sand+30%steel slag）,TSC（42%loess+28%sand+30%red mud）;the second part set up 3 kinds of modifiers and soil-sand layered filling systems:TSF^#（42%loess+28%sand+30%fly ash）,TSG^#（42% loess+28%sand+30%steel slag）,TSC^#（42% loess+28%sand+30%red mud）;the third part set the settings TS₀（0 mm）,TS₂₅₀（250 mm）,TS₅₀₀（500 mm）3 submerged heights and TS₅₀₀^*（500 mm）without COD added by stormwater runoff.The effects of different fillers,filler filling methods and submerged heights on stormwater runoff control and pollutant removal were studied,and the main research results were as follows:（1）Adding river sand,steel slag and red mud to the loess filler improved the total runoff control rate of the system,and the total runoff control rate of the TS system was the highest,and it increased with the increase of operating time.Different filler filling methods affect the total control rate of system runoff to different degrees according to the filler.The total runoff control rate of the system decreased significantly with the increase of the submerged height of the system.Among them,TS₀ and TS₂₅₀ systems could meet the total runoff control rate of more than 80%required by Taiyuan City,which is located in Zone.（2）The addition of steel slag was not conducive to the removal of pollutants.The removal rates of NH₄⁺-N,NO₃^--N,TN,and COD in the TSG system were all the lowest,and the average removal rates were 40.21%,31.45%,35.26%,and 52.20%,respectively.The removal rate of NH₄⁺-N and COD by adding river sand was the highest,and the average removal rates were 93.72%and 65.59%,respectively.The removal rate of NO₃^--N and TN was the highest with the addition of red mud,and the average removal rates were 91.35%and87.60%,respectively.（3）Compared with mixed filling,the removal rate of NH₄⁺-N was improved in layered filling,among which the system adding steel slag improved the most,which was 21.03%.Layered filling reduces the removal rate of NO₃^--N and COD.The TN removal rate of system adding steel slag in layered filling was higher than that of mixed filling,and the removal rate of systems adding fly ash and red mud in layered filling were lower than that of mixed filling.（4）The removal rate of NH₄⁺-N,TN and COD did not change significantly with the increase of submerged height,and the removal rate of 250 mm submerged height was the highest.The removal rate of NO₃^--N increased significantly with the increase of submerged height,and the removal rate of 250 mm submerged height was the highest.The effect of adding carbon source to the system on nitrogen removal was as follows:within 12 d of operation,the removal rates of NO₃^--N and TN by TS₅₀₀ system increased with the increase of operating time;TS₅₀₀^*The removal rates of NO₃^--N and TN in the system decreased with the increase of operating time.Taking into account the removal of pollutants by the stormwater bioretention system,the optimal submerged height is recommended to be 250 mm.The lack of carbon source affects the removal rate of nitrogen,especially NO₃^--N.