Filler Design And Optimization Study For Typical Low Impact Development Facilities

As typical low impact development(LID)technologies,bioretention system and artificial rainwater seepage well system have good regulation effect on storm runoff.However,the control effect of seepage well filler on water quality is limited.Most of the research on LID facilities is about the effect of regulation or scenario simulation.In this study,the effects of artificial rainwater seepage wells on the regulation of storm runoff under different inflow conditions were analyzed through artificial simulation water distribution tests.On this basis,a better mixing scheme of fillers was obtained.The sensitivity analysis was carried out by Morris classification screening method,and the sensitive parameters affecting the regulation effects of water quality and quantity were identified.The HYDRUS-1D model was used to simulate the regulation effects of LID single facilities(bioretention facilities,artificial rainwater seepage wells)on storm rainwater in different scenarios.Based on the simulation results and Design Expert software,multiple regression models between water reduction rates,pollutants load reduction rates and main influent factors were established,and the relationship between them was identified.The key parameters of LID facilities were optimized by combining test data,simulation results,multiple regression model and response surface optimization method.Through monitoring the actual rainfall of artificial rainwater seepage wells in Xianyang Vocational and Technical College,the regulation effect of artificial rainwater seepage wells on actual rainfall was explored.The main conclusions of the study are as follows:(1)The permeability of the main filler was significantly improved by adding the modifier,and the proportion of the modifier has a significant effect on the permeability.The permeability of coarse sand+modifier was better than that of medium coarse sand+modifier.The artificial filler with medium coarse sand as the main filler had certain advantages in the purification of pollutants compared with coarse sand.The artificial filler added with the modifier had a certain increased,the removal effect of pollutants was not significantly improved.90%main filler+5%blast furnace slag+5%zeolite artificial filler has better removal effect on COD,NH3-N and TN.90%mian filler+10%sponge iron artificial filler has better removal effect on NO3-N,TP,Zn.90%main filler+5%sponge iron+5%blast furnace slag artificial filler has better removal effect on Cu,Zn and Cd.Artificial fillers with two or more modifiers had better effect on comprehensive reduction of pollutant load.(2)The results of sensitivity analysis and multiple quadratic regression models show that recurrence period,confluence ratio,type of filler and thickness of filler layer had great influence on water reduction rate.The recurrence period and confluence ratio were negatively correlated with water reduction rate,while the thickness of filler layer and aquifer were positively correlated with water reduction rate.Recurrence period,confluence ratio,influent concentration,type of filler and thickness of filler layer have great influence on the load reduction effect of pollutants.Recurrence period,confluence ratio and influent concentration were negatively correlated with pollutant load reduction rate,while filler layer thickness and aquifer thickness were positively correlated with pollutant load reduction rate.(3)For artificial rainwater seepage,when the thickness of aquifer was about 20 cm and the thickness of artificial filler layer was about 250 cm,the effect of artificial rainwater seepage well with 10#filler on storm runoff control was optimal.However,the effects of the facility on the reduction of pollutant load under different inflow conditions was extremely different.For bioretention facilities,in order to meet the requirements of 25 cm?the thickness of filler layer?120 cm and 85%water reduction rate,the bioretention tank with fly ash+sand or planting soil can treat the incoming water with 2-year recurrence period+10:1?20:1 confluence ratio,5-year recurrence period+10:1?15:1 confluence ratio or 10-year recurrence period+10:1 confluence ratio.The bioretention tank with blast furnace slag can treat the incoming water with 2-year recurrence period+10:1?15:1 confluence ratio,5-year recurrence period+10:1 confluence ratio or 10-year recurrence period+10:1 confluence ratio.(4)The construction time of artificial rainwater seepage well site facility is relatively short,the operation effect is not stable,and the purification effect of pollutants is not ideal.Most of the inflow is roof rainwater,and the water quality is good.Leaching occurs after runoff rainwater enters the seepage well,which results in negative pollutant removal rate.In order to evaluate the operation effect of rainwater seepage wells more obj ectively,it is necessary to conduct further monitoring and research on seepage wells and obtain a large number of data.