Influence of filter layer positions and hydraulic retention time on removal of nitrogen and phosphorus by porous asphalt pavement.

This study was aimed to investigate the removal processes of nitrogen (TN), NH4 +-N and phosphorus (TP) from surface runoff by performing experiments on the filter layers in porous asphalt pavement (PAP). Experiments were conducted to compare the differences of the filter layer placed at the top, the middle or the bottom of PAP. The effects of retention time on the removal of the pollutants and the adsorption capacity of PAP materials were also investigated. Results indicated that the filter layer placed under the bed course improved the removal rates of pollutants compared to the other two cases on the whole. The concentration of TP in the effluent decreased by 80% after the 48 h retention time. In conclusion, this study demonstrated that the positions of filter layers and the temporary retention time of surface runoff within the bed course of PAP were critical parameters for determining the removal processes of pollutants. Thus, a certain retention time for surface runoff in bed course is of great importance for PAP to serve as an effective low impact development technology for stormwater management.