Study On The Improvement Of Bioretention System And Purification Of Heavy Metals

Rainwater as a very important water resource nowadays,plays a crucial role in improving the ecological environment and alleviating regional water resources.Bioretention technology is a typical low-impact development(LID)technology that is most effective in the control of water quality and quantity.It has significant effects in controlling stormwater runoff,recharging groundwater,and improving water quality.The technology is widely used and its technology is effective.It plays a key role in absorbing and purifying rainwater runoff.This study selected Zn,a common heavy metal in urban stormwater runoff,as the main research object.Bioretention fillers(BSM)were used as the basic media to compare the effects of the seven modifiers on the adsorption capacity,desorption ratio,and adsorption energy efficiency of heavy metals.Design parameters of the bio-retention simulation column test,explore and evaluate the preferred high-improved filler;artificial simulation of water distribution test,the main heavy metals(Cu,Zn,Cd)in urban stormwater runoff as the main research object,study the biological retention facilities in different operations Under the operating conditions,the main technical parameters of the bioretention facility are defined;Select typical bioretention facilities(rain gardens,planting stagnant tanks),monitor the operation effects of stormwater runoff on different underlying surfaces,and focus on analyzing the regulation of stormwater runoff by bioretention facilities and the purification effect of heavy metal pollutants.Main conclusions of this study are as follows:(1)Among the seven modifiers and bioretention fillers(BSM),fly ash has the highest adsorption capacity for Zn and the lowest desorption rate,and its adsorption effect is the most stable.Bioretention fillers(BSM),water treatment residual(WTR),medical stone,and green zeolite also have good adsorption effects.The above selected modifiers were added in different ratios(5%,10%,and 15%)to bioretention fillers(BSM)for isotherm adsorption experiments.The results from the Langmuir model and Freundlich model were fitted to previous researcher’s test results.It was found that the bioretention fillers(BSM)with 10%modifier had better adsorption effect.(2)Under the condition that the influent Zn concentration is 0.5mg/L,the concentration of Zn in the effluent of the bioretention simulating column packed with BSM,BSM+10%medical stone,BSM+10%WTR and BSM+10%green zeolite increases with the influent amount of water.Gradually increase,and after the water reaches a return period of 3 years,the effluent shows a steady state with a Zn concentration of 0.4 mg/L,while the simulated column packed with BSM+10%flyash shows a stable long-term adsorption capacity,continuous After 18 days of operation,the simulated column adsorption rate was as high as 72.84%,and the concentration of effluent Zn was less than 0.25 mg/L,meeting the Class Ⅱ water quality standard for surface water environmental quality standards.In the 15 years of water intake,all kinds of mixed packings showed good adsorption effect,especially flyash.(3)The improved filler’s water holding capacity is slightly lower than that of the planting soil,which is 0.84～1.73 times that of BSM,and 3#()BSM+10%WTR(0)),4#(BSM+10%WTR).(150)),6#(BSM(60cm)+WTR(10cm)),8#(BSM(60cm)+flyash(10cm))all have good water regulation effect.The stable infiltration rate of planting soil is relatively The stable infiltration rate of small and improved mixed fillers is 3.25 to 62.78 times that of planted soils,0.24 to 3.30 times that of bioretention fillers(BSM),strong infiltration capacity,and high outflow rate.(4)10#(BSM+5%coconut bran)device has the greatest fluctuation of the removal rate of heavy metals,and the removal performance of heavy metals is poor.The load reduction rate of 3#(BSM+10%WTR(0)),5#(BSM+10%WTR(350)),6#(BSM(60cm)+WTR(10cm))and 8#(BSM(60cm)+flyash(10cm))bioretention facilities is higher than that of the other devices.The load reduction rate of Cu is greater than 75%,and the reduction rate of Zn and Cd load is greater than 85%.(5)Through the on-site monitoring and analysis of the Shangye Road planted depots,the results show that:the bioretention tanks have good effects on total rainfall runoff control and runoff pollutant load reduction,and most of the single-field rainfall runoff reduction rate It can reach more than 90%,and it can achieve 100%reduction for some moderate and light rains.Most of the heavy metal(Cu,Zn,Cd)pollution load reduction rate can be controlled to more than 80%,and the concentration of heavy metals Cu,Zn effluent is basically controlled to meet the Class I standard for Surface Water Environmental Quality Standard,Cd concentration The control meets the Class IV standard of Surface Water Environmental Quality Standard(GB 3838-2002).(6)Through the experimental study on the hydrological process and degradation of pollutants in rainwater runoff on roofs of Tongdejiayuan infiltrating and impervious rainwater gardens,a statistical analysis of 33 rainfall data monitored from 2015 to 2017:infiltration rain garden There have been two overflow events.The rate of water reduction was 45.70%and 36.19%,respectively;the control rate of runoff in rain-fed rain gardens against light rain and moderate rain events(light rainfall of 25mm)was basically above 60%,and the pollution was In terms of annual load reduction rate,and other pollutant load reduction rates of over 70%.