Opportunities and challenges for improving the stormwater treatment performance of permeable pavements

Urban runoff contains numerous pollutants deposited on the paved area during dry weather periods including nutrients, oils, hydrocarbons, dissolved and suspended solids and heavy metals. The ability of permeable pavement systems (PPSs) to treat stormwater runoff up to a certain limit has been established to-date. However, in order to define PPSs as stormwater treatment units (not only infiltration systems) for sustainable management of stormwater quality and quantity, an in-depth understanding of treatment mechanisms of specific pollutants is needed. This chapter discusses the opportunities and challenges for improving stormwater quality by altering the design variables in PPSs. Characterisation of stormwater runoff has shown that it consists of inorganic and organic substances in soluble and insoluble forms in varying combinations. Further, the insoluble component can have particulate material of varying sizes due to physical changes that occur during run off. Due to this degree of variability, treatment of stormwater runoff must consist of a combination of physical methods such as filtration and adsorption, chemical methods such as pH control and precipitation and biological methods such as biodegradation. The PPSs structure can be modified to obtain improved water treatment performance depending on the design rainfall condition and the structural requirements of the proposed site. Investigating the internal mechanisms and fluxes of these treatment processes within PPS is needed for a better understanding of how to remove targeted pollutants from stormwater and to modify the design to optimise treatment processes. Mechanical filtration and adsorption are the main water treatment processes involved in PPSs. Pollutants removed by filtration and sorption may leach back to infiltrate either due to flow conditions or after saturation. These phenomena need to be investigated and addressed in future research. Also, the development of numerical models to simulate the unit operations of PPSs to predict stormwater treatment performance is needed.