Comparing urban runoff quality of a felt roof and an asphalt road in Beijing

Water pollution and water shortage are two of the most important environmental problems in Beijing, China. Water quality of rainfall from July to August 2011 and runoff from a felt roof and an asphalt road were analyzed chemically and further investigated because these are potential sources for augmenting city supplies. Results indicate that chemical oxygen demand (COD_Cr), total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen (NH₄⁺-N) concentrations of initial runoff from roofs and roads all exceeded the Class V surface water quality standard developed by the Ministry of Environmental Protection of the People's Republic of China (MEP). COD_Cr concentration from road surfaces was more than 313.55 mg/L at the initial runoff stage, decreasing asymptotically to lower levels with increased rainfall duration. There is strong correlation between COD_Cr, TP, TN concentrations and that of total suspended solids in road runoff. Runoff from roofs, after treatment by grid filter, flocculation and sedimentation, can be used as city municipal and domestic water except during the initial runoff stage. However, runoff from road surfaces cannot be directly reused. For city planning, this conclusion may benefit the promotion of rainwater as a renewable water supply, and avoid flooding and water scarcity.