Research On Removal Of Pollutants By SMB Modified Bioretention System

With the fast development of urbanization,the impervious surfaces are becoming larger and larger,which leads to the increase in quantity and dirtier in quality of urban runoff.The bioretention,which is regarded as an effective method in Sponge City construction,can remove the contaminant within runoff effectively This research aims to enhance the pollutant removal efficiency of current bioretention through the modification of a steady saturated anaerobic zone.Moreover,the use of biodegradable container brings up the so-called white pollution issue.SMB,a disposable biodegradable container,can be preliminarily evaluated as a sustained release carbon resource supplement added to bioretention based on its advantages on physics,economic and biodegradation.In this way,higher pollutant removal efficiency is supposed in the modified bioretention,which is also a good sample of purifying polluted water with solid waste.Firstly,the capability of slow-released solid carbon source SMB is well studied in the research,then the effectiveness of pollutant removal of modified bioretention adding SMB under the various precipitation patterns is observed and analyzed,the results demonstrate:(1)In distilled water,COD concentration reaches case-? standard of groundwater in more than 70% time duration while the release of nitrate and ammonia from SMB is slightly,which does little harm to runoff.The nitrate concentration bellows 0.15mg/g of carbon source in whole time while the concentration of ammonia is above case-? standard of groundwater.But ammonia leaches under the existence of simulated runoff.(2)Effective pollutant removal is observed in the simulated runoff with consolidated SMB.COD removal rate is 89.26% while ammonia reaches case-?standard of groundwater,which means a substantial mitigation of ammonia leaching.Nitrate removal rate is 74% and the analysis of its removal curve reveals the participation of SMB as an added carbon source.Conclusion can be drawn from the results that SMB is suitable for bioretention as the carbon sourse.(3)Rainfall intensity and other pollutant concentration show a non-significant impact to COD removal using the enhanced bioretention with SMB.The average COD removal rate ranged from 84%~95%.And excessive leaching of COD is not observed.The system is effective to the removal of COD within the first flush while confronting a significant impact load.The removal of COD in first flush reaches above 90%.(4)In lower C/N ratio,rainfall intensity has a significant impact to the removal of nitrogen and phosphorus compared to C/N ratio.The removal of ammonia and phosphorus in moderate rain reaches above 90% and above 55%,respectively,which is better than 80% and 4% of which in spit rain.And the removal of nitrate in spit rain is 80% which is better than 37% of which in moderate rain.Various rainfall intensity shows a significant influence to the removal of nitrate and phosphorus while the removal of ammonia keeps at least 80%.(5)In the first flush with higher C/N ratio,the impact of rainfall intensity against nitrogen and phosphorus is much less significant.The removal rates of nitrogen,phosphorus and COD in moderate rain are 79%,29%,91%,and in spit rain are 90%,50%,95%,respectively,which demonstrates that the enhanced bioretention with SMB is effective to remove the pollutants in the first flush.(6)In single precipitation event,the enhanced bioretention shows an excellent removal efficiency(>95%)towards nitrate in the first half hour before it declines.The removal rates of ammonia and phosphorus increase as time goes by,the removal rates raise from 59% to 98% and from 82% to 57%,respectively.And the removal of COD remains steady and effective(>90%).