Stormwater treatment in constrained urban spaces through a hybrid Sequential Sedimentation Biofiltration System

Urban areas face increasing pressures on water resources, necessitating innovative approaches to climate adaptation and water quality management. Nature-based Solutions (NbS) offer a sustainable pathway, yet their integration with existing infrastructure in urban settings remains occasional. This study presents a novel hybrid system-Sequential Sedimentation Biofiltration System (SSBS)-designed for stormwater treatment within confined urban spaces. The system was adjusted to the existing stormwater infrastructure by integrating a sedimentation tank (SED), three Permeable Reactive Barriers (PRBs), and a biofiltration zone (BIO). The SSBS was evaluated for its efficiency in removing nutrients and sediments, focusing on the performance of PRBs. Our findings showed limited sediment removal in SED and PRBs due to spatial constraints and a high Hydraulic Loading Rate (HLR = 1.31 m/d), achieving an average of 13.6% Total Suspended Solids (TSS) removal. However, PRBs demonstrated effective removal of ammonium (43.4%) and phosphate (59.3%), potentially due to sorption and biofilm activity, with dominant microbial communities including Proteobacteria, Bacteroidetes, and nutrient-transforming taxa such as Nitrospirae. Interestingly, PRBs increased nitrite levels (57.1%) but did not significantly impact nitrate, chloride, or TSS. The BIO zone further enhanced nutrient retention (56% PO₄-P) and served as a sink for TSS (52%). This study underscores the potential for integrating traditional urban infrastructure with NbS in a sequential stormwater treatment system, demonstrating its effectiveness in space-constrained urban environments.