| Urban storm water runoff has become a growing pollution source for many receiving water bodies because of the greater volume from increased impervious surface and increased loading of toxic contaminants from urban areas. After Urban point source pollution had been effective control led,non-point source pollution has become one of leading impairment source for estuaries and lakes in China.Road runoff which contains high concentrations of nutrients could pollute city water body if emissing directly. As typical and effective rainwater harvest facilities in the LID,bioretention has been taking more and more attention by domestic and foreign scholars.However,the effectiveness of bioretention in treating phosphorus and nitrogen were poor and unstable. These disadvantages limit its popularization.Aiming at the status, this paper designed a double media bioretention facilities and experiments were carried out,and removal effect of nitrogen and phosphorus were carried out.At first, this paper introduced the basic structure, the mechanism of removal nitrogen and phosphorus,as well as the factors that affect facilities. At last, the main reason for the poor removal of nitrogen and phosphorus was obtained:based on comprehensive of domestic and foreign status quo and nitrogen、phosphorus removal way,it concluded that the key to remove nitrogen by to remove nitrogen is to meet a demanding anaerobic environment and to afford abundant carbon sources;the key of removal of phosphorus is to select media with low background values and strong adsorption capacityFrom these two aspects, the paper designed a double media bioretention facilities and experiments were carried out. The results indicated that the facility has good removal effect of nitrogen.By dynamic adsorption experiment and packing desorption experiments of the river sand, clay, slag, fly ash, fine quartz sand (1mm), coarse quartz sand (2mm), fly ash, it concluded the slowest of desorption rate is quartz sand. Adding5%into fly ash and clay had better removal effect of phosphorus, and the desorption rate was low.The selection media was applied to new biological stranded facilities. The facilities run four cycles without clogging phenomenon.The results indicated that the facility has good removal effect of nitrogen, especially the NO3--N(removal rate reached more than92%).Column1and column2average removal rate of phosphorus were94.0%and88.5%respectively; nitrogen also had good removal effect:column1and column2average of total nitrogen removal rate were87.5%and84.1%respectively; the average removal rate of NH4+N is95.1%and86.2%respectively;the average removal rate of NO3--N were95.0%and92.4%respectively;the phosphorus removal effect of1column is slightly better than2column. This design can be applied in the engineering because of simple structure and easily implement.For satisfying pollutant treatment effect and reduce the construction cost of infrastructure, the upper media could be300mm, the lower could be200mm. The system has the adsorption of media on ammonia nitrogen removal (reversible), plant absorption and nitrification, and so on. When in Cloth water phase,adsorption is main;microbial nitrification is main in dry period. The quartz sand layer (250mm-550mm) can effectively remove Ammonia nitrogen.The lower hybrid media area (750mm-950mm),has been substantially removed nitrate nitrogen.It indicated that the area had the necessary conditions of microbial denitrification reaction.At last, this paper was discussed how to use biological stranded facilities in the road. |
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