The Research On The Pollution Performance Of Bioretention Ponds In The Treatment Of Initial Rainwater And Combined Overflow

In view of the serious pollution of the water environment by the initial rainwater and combined sewer overflows（CSO）,and the problem that the performance of the bioretention to be further improved and its scope of application,this topic has carried out a research on the use of the bioretention to treat the initial rainwater and CSO pollution.For the research on the initial rainwater treatment in the bioretention,the adsorption and desorption characteristics of N and P by the traditional bioretention soil media（BSM）and four kinds of amended BSM including fly ash+coconut bran,zeolite+coconut bran,Water treatment residuals（WTR）+coconut bran,zeolite+WTR,etc.and then the initial rainwater treatment performance of bioretention with different medias was explored through the simulation column test.The results show that the amended BSM can significantly improve the removal performance of TP,NH₄⁺-N,TN,COD,and the removal performance of SS to a certain extent.Among them,the WTR+coconut bran improves the comprehensive performance of the initial rainwater treatment in the BSM bioretention better.Furthermore,this amended BSM was selected as the research object to explore the performance of initial rainwater treatment under different return periods,different rainfall intervals,different influent water quality and different submergence depths.The results show that the return period is related to TP（61.97%-91.69%）,NH₄⁺-N（62.27%-88.26%）,TN（61.20%-84.40%）,COD（77.07%-89.33%）,SS（88.18%-93.12%）and its moisture content are positively correlated;the rainfall interval is negatively correlated with TP（80.29%-91.74%）reduction,positively correlated with TN（75.89%-88.66%）,COD（75.07%-88.40%）reduction,NH₄⁺-N（87.03%-90.47%）and SS（90.75%-91.83%）has no significant effect,and is negatively correlated with its moisture content;the influent concentration is positively correlated with the reduction of TP（76.37%-83.94%）,NO₃^--N（34.55%-46.48%）,TN（53.77-69.65%）,COD（63.49%-73.06%）and SS（69.93%-80.48%）,and the reduction of NH₄⁺-N（62.01%-66.44%）has no obvious correlation with its water content;the submergence depth is negatively correlated with the reduction of TP（84.80%-88.04%）,NH₄⁺-N（81.06%-88.53%）,COD（70.67%-76.93%）,while positively correlated with the reduction of NO₃^--N（39.65%-75.74%）and TN（60.13%-77.92%）.There was no significant correlation with the reduction of SS（90.17%-91.57%）,but a positive correlation with water content.For the research on the treatment of CSO pollution in the bioretention,the N and P adsorption and desorption characteristics of the four types of biofilter medias including gravel,volcanic rock,ceramsite,and zeolite were first explored,and then the effect of biofilter containing different medias on CSO pollution reduction were explored through simulated column tests.The reduction effect of the filter on CSO pollution.The results show that the volcanic rock media among the four types of biofilter medias has the best reduction effect on CSO pollution.On this basis,the volcanic rock media biofilter and the amended medium media bioretention were combined in series to explore the removal effect of combined facilities on CSO pollution under different hydraulic loads and different pollution loads.The results show that the facility has better CSO pollution removal performance when the hydraulic load is low,and the facility has an unstable removal effect on TN and COD when the hydraulic load is large;the facility has better CSO pollution purification performance under different pollution loads.