| At present,Low Impact Development(LID)in the United States is the most far-reaching rainwater control concept.The bioretention cell is widely applied because of it's beautiful landscape,cutting rainwater effectively,and it's moderate construction expense.The first stage of sponge city construction work in China has been carried out,however,the effect of the completion was not satisfactory,mainly because there was no construction experience and technical measures were applied according to other developed countries mechanically,therefore,it's urgent and necessary to carry out localization work of rainwater control technology measures.According to the climatic condition,soil property and rainfall characteristic in the north region,this paper was investigated to screen several appropriate filters and combine with the local soil,carry out combined fillers test and select the optimal one by measuring permeability coefficient and contaminants removal efficiency.Finally,undertaking bioretention experimental research of planting grass to study control effect on runoff rainwater by bioretention cells.The followings were the research contents and main conclusions:(1)Screening fillers and combined fillers Test:There were six kinds of filters,including perlite,zeolite,ceramsite,volcanic rock,activated charcoal and vermiculite,then perlite,zeolite and volcanic rock were selected as the ingredients of combined filter by determining permeability coefficient and contaminants removal efficiency.Zeolite,volcanic rock,perlite and local campus soil were mixed evenly in different proportions,and obtained fifteen groups of combined filters.Determining permeability coefficient of each group,nine groups of combined filters were selected according to the requirements of foreign codes.Further filtration experiments were carried out to compare contaminants removal efficiency of combined filters.Finally,the eighth combination(40%soil,10%volcanic rock,20%zeolite and 30%perlite)was selected as the combined filter for the bioretention cells.When the recurrence interval was five years,the removal rates of TSS,NH3-N,COD and TP were 92.98%,91.41%,19.05%and 89.21%respectively,and the removal rates of heavy metals Cr,Cu,Zn,Cd,Pd were 35.74%,91.9%,95.66%,98.97%and 98.61%respectively.(2)Bioretention experimental research of planting grass:Planting grass experiment were based on the optimal combined filler in bioretention cells.Bioretention cells were divided into two groups:non-plant group and plant group,which plans iris and poa pratensis.First of all,the effect of bioretention cells on the total amount of runoff rainwater and the reduction rate of flood peak was measured.The results showed that bioretention cells reduced flood peak effectively and had good control of small rainfall.In the early stage of rainfall,plants played an important role in absorbing rainwater,and both facilities would happen overflow when rainfall interval was more than five years.Bioretention cells removed TSS,NH3-N and TP effectively,the removal rate of contaminants was higher than 92%,90%and 80%respectively.However,the removal rate range of COD was 24.05%?46.21%.Whether planting plants had no effect on the treatment effect of TSS.Plants could intercept and absorb COD,NH3-N and TP partially,which had a great influence on the initial 10 minutes effluent quality,while influenced the long-time effluent less.(3)Analysis of influencing factors:The influence of rainfall interval and influent contaminants concentration on effluent quality was analyzed.When the rainfall interval was too long,more than 10 days,the soil and filler would be cracked because of drought,which lowered effluent quality.Once soil and filler structure was stable,the influent concentration had little effect on the effluent concentration of TSS.The effluent concentration and removal rate of COD and NH3-N increased with the increase of the influent concentration.The effluent concentration of TP was advanced with the growth of the influent concentration,while the removal rate decreases slightly. |
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