Understanding the removal of heavy metals from stormwater runoff in permeable pavement system

Understanding the removal of heavy metals (HMs) in permeable pavement systems is of great significance for controlling urban runoff pollution and optimizing structural design. However, few studies have systematically investigated the mechanism of permeable pavement systems in removing HMs from stormwater runoff. In this study, we adopted a hierarchical strategy to understand the efficiency of individual structural layers on HMs removal in a permeable interlocking concrete pavement (PICP) system. Experimental results illuminated that the surface layer exhibited the highest uptakes of HMs, which can remove up to 64 % of Pb²⁺, 50 % of Cu²⁺, 28 % of Cd²⁺ and 13 % of Zn²⁺. Meanwhile, as the rainfall return period increased, the removal rates of HMs in PICP was gradually decreased. In addition, batch experiments were conducted and the adsorption results were in accordance with the rainfall filtration experiments. More importantly, X-ray Photoelectron Spectroscopy (XPS) and leaching results were investigated to understand the HMs removal mechanism, which found that the ion exchange is the main mechanism in the surface layer to remove HMs, whereas the chemical adsorption play a crucial role in the base and sub-base layers. Overall, these findings provided new insights into the transport patterns of HMs in the internal structural layers of the PICP.