Research On Nitrogen And Phosphorus Removal Characteristics And Microbial Diversity Of Sand-soil-fly Ash Matrix In Rainwater Bioretention

Nowadays,rainwater bioretention technology has become one of the most representative technologies in low-impact development and non-point source pollution control.Regarding the studies of rainwater bioretention,it has been found that using sand-soil-fly ash matrix as fillers has effective control of runoff phosphorus pollution.However,the design of the packing layer structure and the height of the submerged zone in the sand-soil-fly ash matrix rainwater bioretention are not clear;besides,how the structure of microbial population in the rainwater bioretention affects the ability to deal with pollutants is still in dispute.In this sense,this research selected a composite material of sand,soil and fly ash in definite proportions as a filler.A continuous rainfall simulation experiment was carried out with one week as a rainfall cycle.?1?According to the study of adsorption effect of fillers,we found that the adsorption effect of fillers containing fly ash on phosphorus pollutants is better than that of single filler sand and single filler soil,with a higher maximum adsorption?2.738mg/g?.?2?By means of designing the layer structure of the packing layer and increasing the height of submerged zone to varying degrees,the author compared the effects of different external structural conditions on this rainwater bioretention,and analyzed its removal efficiency of nitrogen and phosphorus nutrients in the simulated rainwater.Results reflected that the installing of submerged zone could significantly improve nitrate removal efficiency,the maximum increase is close to 30%,while the removal of ammonia nitrogen and TP sharply decreased with the increase of the submerged area zone.The removal efficiency of ammonia nitrogen declined from 95.15%to 51.81%,whilst that of TP?88.66%?halved to44.50%.Multi-layered structure was better than the mixed structure.The multi-layered structured bioretention system with 40cm high submerged area zone led to the most outstanding results,accounted for 88.26%?NH₃-N?,77.47%?NO₃^-?,75.02%?TN?and81.23%?TP?,respectively.?3?In addition,this research used Miseq high-throughput sequencing to detect the both original filler samples and internal filling samples inside six kinds of rainwater bioretention areas,whose structures and height of submerged zone varied from each other.The characteristics of microbial population structure in the samples were analyzed,and the content of urease and extracellular polymeric substances?EPS?were measured,aiming to analyze the corelation with the removal efficiency of nitrogen and phosphorus nutrients in the rainwater bioretention.Results showed that the Chloroflexi content,Nitrospirae content and EPS concentrations decreased when the height of submerged zone increased.The number of microorganisms of Chloroflexi and Nitrospirae was negatively correlated with the removal efficiency of ammonia nitrogen and nitrate nitrogen,respectively.EPS concentration was positively correlated with TP removal efficiency.However,the urease content increased with the height of the submerged zone,which was positively correlated with the removal efficiency of TN.The results of this study could provide theoretical basis and data support for the design optimization of bioretention systems.