Mechanisms of enhanced pollutant removal and microbial adaptation in stormwater infiltration systems with construction wastes as key fillers

Urbanization has increased impervious surfaces, leading to greater stormwater runoff and associated pollution. This has driven the search for economical and effective materials to remove these contaminants. This study investigated the decontamination performance and the microbial characteristics of a system using two types of construction wastes B and J. Chemical oxygen demand (COD), total phosphorus (TP), ammonium nitrogen (NH 4 + -N), total nitrogen (TN) and heavy metals (Cu, Mn, Zn) were measured in the effluent according to different resident times. The results showed at a hydraulic retention time of 8 h, the removal of pollutants was effective and stable. Construction waste materials B and J achieved average removal rates of over 81.0% for COD, 90.0% for TP, 80.0% for NH 4 + -N, and 90.0% for TN, indicating a certain feasibility and practicality of the filter media. Nutrient and heavy metals overall removal effect in-creased with increasing the contacting time. Extended hydraulic retention time increased Cu 2+ and Zn 2+ removal to >80%, while Mn transitioned from leaching to removal (up to 70.1%) at 8-h hydraulic retention time via pH-mediated mechanisms. An anaerobic environment inside the column fostered the formation of denitrifying dominant bacteria (i.e. Enterobacter and Azospirillum ). Longer contact time further promoted their growth, which was crucial for removing TN and TP in the system. The system could easily form an anoxic environment at a long retention time. Overall, pollutant removal by the two materials was comparable, with retention time being the key determinant. Construction wastes thus offer an effective and sustainable adsorption solution. • Demonstrates >80% COD, TP, NH₄ + -N, and TN removal by construction waste at an optimal 8-h HRT • Finds >80% Cu 2+ /Zn 2+ removal via synergistic adsorption-precipitation with extended HRT • Links long HRT to anaerobic conditions that boost denitrifying bacteria and nutrient removal • Explains Mn leaching-to-removal shift by HRT-driven pH and material composition • Proposes a mechanism integrating HRT, materials, and microbes for synergistic pollutant removal