Conventional bioretention systems face challenges in effectively removing dissolved nutrients, heavy metals, and emerging contaminants from stormwater runoff. This study investigates the application of thermally modified steel slag (700 °C) as a functional bioretention matrix for comprehensive stormwater purification. Three pilot-scale systems were evaluated over 120 days: Control (biochar-zeolite), Unmodified (raw steel slag-biochar-zeolite), and Modified (thermally modified steel slag-biochar-zeolite). The modified system demonstrated superior and stable removal efficiencies for NH4+-N (95.3 ± 1.3%), TN (85.7 ± 1.8%), TP (90.5 ± 1.5%), Cu2+ (96.1 ± 0.7%), Cr6+ (90.5 ± 1.2%), Pb2+ (92.2 ± 1.1%), enrofloxacin (65.6 ± 2.1%), and norfloxacin (62.6 ± 2.4%). Performance remained robust under varying hydraulic conditions, with high removal maintained across rainfall return periods (0.5–2 years) and antecedent dry periods (2–8 days). Mechanistic investigations revealed synergistic effects: (1) Enhanced physical adsorption through increased surface area (2.338 m2/g) and pore volume (0.109 cm3/g); (2) Chemical precipitation via Ca2+/Fe3+ release at alkaline pH (8.2–8.5); (3) Enriched microbial communities with 35% higher Shannon diversity, particularly Hydrogenophaga (12.3%) for autotrophic denitrification using Fe2+ as electron donor. The modified slag matrix creates a “triple-barrier” removal mechanism combining physical, chemical, and biological processes, offering an efficient solution for multi-pollutant stormwater treatment. This study demonstrates that thermally modified steel slag represents a high-performance, cost-effective bioretention matrix for comprehensive stormwater treatment while promoting industrial byproduct utilization and aligning with circular economy principles.
Yu et al. (Sat,) studied this question.