Research On Simultaneous Removal Of Nitrogen And Phosphorus In Rainwater Runoff By Modified Bioretenion

In order to meet the needs of the construction of Zhenjiang sponge City,This paper combined with the previous research results of bioretention on the basis of studying the quality characteristics of rainwater runoff in Zhenjiang area,The structure and filler of the traditional bioretention was optimized to study the effect of nitrogen and phosphorus removal on simulated rainwater and actual rainwater by the modified bioretention.The bioretention is filled with sand,slag,quartz sand,coal ash,Al-WTR and so on.The structure of bioretention with upper high permeability ratio filler and lower low permeability filler is set up.It ensures the nitrate removal capacity of the bioretention.The main research contents and achievements can be presented as following:The characteristics and related rule of rainwater runoff and water quality on different underlying surfaces are studied.The concentration of COD,SS,NH₃-N and TP in roof runoff and pavement runoff were detected respectively.The results showed that the highest concentrations of COD,SS,NH₃-N and TP in the road runoff were315.9 mg/L,445 mg/L,12.41 mg/L and 0.98 mg/L respectively.The highest concentrations of COD,SS,ammonia nitrogen and total phosphorus in the roof runoff were 113 mg/L,118 mg/L,8.2 mg/L,and 0.52 mg/L.The initial concentration of pollutants in runoff and dry days showed a positive correlation.Compared to the runoff of the road surface,the roof runoff is more significantly affected by the number of dry days before the rain.The dynamic adsorption and adsorption experiments of total phosphorus were carried out to determine suitable fillers and proper proportioning of mixed fillers.It is found that the amount of adsorption of single filler is aluminum Al-WTR>coal ash>quartz sand>slag.The upper composite fillers with sand volume?70%?,slag?10%?and quartz sand?20%?have the best removal effect on total phosphorus,and the removal rate is 57%.The removal effect of nitrogen and phosphorus in simulated rainwater runoff is studied.It is found that the average removal rate of NH₃-N is up to 90%and the removal rate of TP is 80%⁹0%,and the average removal rate of NO₃-N reduction is about 55⁶5%.At the same time,it is found that the removal effect of NO₃-N is strengthened with the depth increase,but with the further increase of depth,the reduction trend of NO₃-N decreases with the depth.Therefore,the suitable depth of the filler layer of the bioretention is 750⁹00 mm,and the maximum depth should not exceed 900 mm.Finally,the actual rainwater runoff is used to test the water purification capacity of the modified bioretention.The upper composite fillers with sand volume?70%?,slag?10%?and quartz sand?20%?;The lower composite fillers with sand?65%?,Al-WTR?30%?,broken newspaper?5%?.The results showed that the improved bioretention has a very stable removal effect on total phosphorus,ammonia nitrogen,and nitrate nitrogen.And the removal efficiency were 84.08%⁹5.05%,76.25%⁹0.44%and 49%⁵8.19%,respectively.