Role of Media: Implication for Application of Urban Storm Water Runoff Bioretention Systems

Bioretention system has been proved to be an effective and low-cost source control technique for decentralized storm water runoff in urbanized areas. However, little information on the feasibility and effectiveness of these systems is available for China, including Shanghai. In this study, five bioretention columns with different sieved (2mm) media mixtures were employed to compare results on storm water runoff infiltration rate and pollutants removal efficiencies. In the columns that packed with media mixtures, the runoff infiltration rate ranged from 0.12 to 1.25×10-5m/s at a fixed 5 cm water head, which significantly improved compared to the control column with native soil only. From start-up to the eighth month, the facilities experienced the lowest and highest temperatures of the operation period in Shanghai and exhibited effective pollutants removals after maturation. For pollutant removal, the result indicated excellent removal for oil/grease (>;98%), total suspended solids (>;95%) and phosphorus (82% to 96%). Heavy metals removal ranged widely (46% to 93%), apparently due to the difference of media mixtures. Both ammonium and nitrate/nitrite were moderate to poorly removed, with removals ranging from 26% to 59% and from-7% to 43%, respectively. Analysis on the fate of nitrogen in bioretention suggests wetting/drying periods ratios was the important factor influencing the removal of nitrogen in bioretention system. Finally, bioretention system design were proposed based on the removal effect of pollutants under conditions of intermittent loadings. These results support the use of bioretention as a stomwater best management practice in Shanghai.