Research On Modified Bio-retention Removal Effect On The Pollutant Contained In Rainfall Runoff

Recently,with the acceleration of urbanization and industrialization,urban rainfall runoff carrying a huge amount of pollutants flows into the receiving water,causing that the river and lake eutrophication is becoming worse and worse.By the way of doing sample analysis on the pavement and roof rainfall runoff water samples collected by self-made pavement rainfall collecting device and roof rainfall collecting device,it was found that the longer the drying time is,the higher the EMC of the pollutants(NH4+-N?NO3--N?PO43-?COD)remaining in the rainfall runoff is.The average EMC value of the NH4+-N containing in the roof rainfall runoff exceeds that of the V water body of the floor surface;PO43-amount containing in the rainfall runoff outnumbers that of the III water body of the floor surface.The COD concentration of rainfall runoff exceeds the third class national discharge standards.On the initial formation stage of the roof rainfall runoff,the COD concentration reaches 790~1160mg/L;NH4+-N concentration 30~80mg/L;NO3—N concentration 30~80mg/L,exceeding the content of the sanitary sewage;PO43-content reaches 1.4mg/L,exceeding the Level I B standard of sewage discharge.After 50 mins of the rainfall runoff formation,the pollutants content is becoming stabilized,but still higher than that of the V water body of floor surface,among which the COD content is over Level I B standard of sewage discharge.Simultaneously,the pollutants of the roof rainfall runoff will be obviously affected by the rainfall flush but no so obvious effect will be produced on the pavement rainfall runoff even though the pollutant content in the pavement rainfall runoff is comparatively high on the initial formation stage.With the purpose of improving bio-retention pond's structure,the outlet pipe has been upturned for 300 mm,which created a 300 mm height of anaerobic zone in the bio-retention zone.Adding Alum sludge and wood chips into the bio-retention pond to improve its adding compounds.At lab,we make the artificial rainfall to do research on the treatment effect of bio-retention pond on the rainfall runoff.It was found that the adding compounds of the bio-retention pond is the main factor in removing the PO43-contained in the rainfall runoff.Adding sludge will improve its PO43-removal efficiency while the anaerobic area set up in the retention pond will reduce the removal effect.Inlet hydraulic power is one of the factors affecting the PO43-removal efficiency but not the main factor.Different hydraulic powers will brings obviously differently removal effect of the NH4+-N.However,the NH4+-N concentration of the rainfall runoff has no strong relation with the NH4+-N removal efficiency.Adding wooden chips as the outsourced carbon source into the anaerobic area,it was found that NO3--N removal effect is better.Hydraulic power remaining time is the main factor affecting the N removal result.Add-in of wooden chips into retention pond could increase its carbon source,but the emission energy of the carbon source after fermentation treatment is very limited,there is almost no overflow of carbon source.