Research On The Removal Effect Of Oyster Shell Bioretention System On Runoff Pollutants In Qingdao

With the development of urbanization in China,urban impervious pavement has increased,which has aggravated a series of urban environmental problems,such as urban waterlogging caused by rainwater and deterioration of water environment.Biological detention technology has been widely used as a means to treat urban rainwater runoff.The removal efficiency of existing bioretention facilities needs to be improved.In addition,a large amount of shell waste has become an environmental problem in coastal areas.This study combines shells with bioretention facilities to reuse waste resources and control urban runoff pollution.In this experiment,oyster shell and sandy loam soil were used as fillers,and two kinds of bio-retention facilities with mixed fillers and layered fillers were designed.The effects of fillers of bioretention simulation facilities on the nitrogen,phosphorus and COD in urban runoff in Qingdao were studied by using road runoff simulation as inflow,and the removal mechanism of pollutants was discussed.The results were as follows:（1）The removal efficiency of total phosphorus is the best in two kinds of bio-retention devices.The average removal efficiency of non-submerged and submerged devices is 96.12%and 91.02%respectively under the conditions of 0.57-1.83 mg/L influent phosphorus concentration in devices with mixed fillers.There is no significant difference between cultured oyster shell and beach oyster shell in phosphorus removal efficiency,and the submerged area is not conducive to phosphorus removal.Under the condition of 1.62-2.48mg/L influent concentration,the removal rate of total phosphorus is 89.03%-95.14%in devices with layered fillers.The higher oyster shell content,the higher phosphorus removal efficiency,liquid carbon source was better than solid carbon source,waste paper is better than plant litter,and retention time had little effect on phosphorus removal.influence.（2）In the bioretention simulator with mixed fillers,ammonia nitrogen leached during the initial stage of influent,and the removal rate of ammonia nitrogen increased after prolonging the drying period.The removal rate of oyster shell retention device with beach oyster（58.83%）is higher than that with cultured oyster shell（48.77%）.There is no significant effect on ammonia nitrogen removal in the submerged zone or not.In the layered fillers device,the average removal rate of ammonia nitrogen was 30.51%-67.04%.The higher the oyster shell content,the better the removal effect of ammonia nitrogen.（3）In the bioretention simulator with mixed fillers,the removal efficiency of nitrate（NO₃^-）is not good due to the blockage of denitrification,and the phenomenon that the effluent concentration is higher than the influent concentration.Adding the submerged area can improve the removal rate of nitrate nitrogen in the simulator.The removal effect of nitrate nitrogen in the device with layered fillers is better than that with mixed mixed fillers.The higher the content of sandy loam in the lower layer,the higher the treatment effect of nitrate nitrogen.The retention time affects the removal of nitrate nitrogen.The longer the retention time,the better the treatment effect of nitrate nitrogen.（4）In practical engineering applications,layered fillers is chosen as the filling structure of bioretention facilities.The facilitied can effectively remove nitrogen and phosphorus from urban surface runoff,with the upper 300 mm oyster shell and the lower 200 mm sandy loam or the upper 200 mm oyster shell and the lower 300 mm sandy loam and adding waste paper as additional carbon source and ensuring the retention time is more than 8 hours.