| Our country facts the problem of water ecological security,and the city is faced with the problems of water pollution,water resource depletion and frequent occurrence of flood and drought disasters.As a typical technology of low impact development,biaretention system has good water purification effect and water regulation efficiency.In this study,the removal efficiency of heavy metal(Zn,Cu,Cd)in the bioretention system was analyzed by the influence factors test,intermittent operatipn test,and continuous run off test.Through adsorption experiment,the effects of different dosage of fly ash,different adsorption time and initial concentration of heavy metal ions on the adsorption of heavy metals by fly ash were investigated.Based on the partial least squares regression method,the relationship between the main influencing factors and the Zn removal rate of the bioretention system was established,identify the main influencing factors and their effects.The actual water regulation and the effect of water quality prification were studied by means of the actual rainfall monitoring of the vegetation detention tank and the rain garden.According to the different standards of water reuse,the risk assessment of water reuse in bioretention facilities was carried out.Main conclusions of this study are as follows:(1)The remomal ability of heavy metals in the three groups of bioretention system was Cu>Zn>Cd,the effect of 7#(fly ash + sand)bioreteotion system on Cu removal is best,the average removal rate was 85.57%.Heavy metal removal was affected by rainfall interval The results showed that the removal efficiency of heavy metals in the three test ditches was better than that in the small amount of water.The removal rate of Cu and Zn was higher in the case of uo flooded and area,and the average removal rate of Cd was increased by 40%in the flooded area.(2)Under the 5a recovery peiriod,the effect of water educing effect of 8#bioretention system was gradually decreased with the decrease of temperature.The water volume reduction rate range is 23.25%.Under the 2a recovery period,the rate of water cut decreased slowly and then increased slowly,The water volume reduction rate range is 20.94%.The effluent of heavy metals showed a decreasing trend.(2)The Cu and Zn in7#(fly ash+sand)and 10#(planted soil)bioretention system did not reach the adsorption exhaustion,but the concentration of heavy metals in the effluent was increased under the condition of large amount of water and water.(3)The dosage of fly ash is directly proportional to the removal rate of metal ions and inversely proportional to the adsorption capacity.With the increase of the initial concentration of heavy metal solution,the adsorption capacity of heavy metal ions increased slowly and then increased.The adsorption of heavy metals by fly ash is in accordance with the two order reaction kinetics,and the effect is satisfactory.(4)Antecedent dry time is the impact of bioretention system on the removal of Zn is the most important factor affecting the effect.Other influencing factors is Packing factor>Influent water>Inflow concentration.(5)The single measure of bioretention has a good effect on water volume reduction rate and pollutant removal efficiency.The rate of water volume reduction was more than 90%,and the removal rate of heavy metals was more than 70%;the rate of water volume reduction in the rain garden is above 65%.(6)When the surface water is treated by the bioretention system,the concentration of heavy metals can meet the requirement of surface water quality standard.COD concentration reached high risk level and Cd was moderate risk rating when groundwater recharge.As a city landscape water or industrial water,the risk level is low,meet the reuse water quality standards. |
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