A Pilot-Scale Bioretention System for Urban Stormwater Treatment Under Tropical Conditions: Influence of Vegetation and Sizing Area

Although bioretention is one of stormwater best management practices (BMPs), its effectiveness in tropical climates remains uncertain. This study examines the hydrology and pollutant removal performance of bioretention systems in Penang, Malaysia. A pilot-scale bioretention was constructed with three plots: no vegetation (P1), single species (P2), and multispecies (P3). Results showed that P3 had the highest water volume reduction (58%), followed by P2 (46%) and P1 (37%). Vegetation significantly improved pollutant removal, especially for total suspended solids (TSS) and total nitrogen (TN), with removal efficiencies up to 95% and 85%, respectively. P3 effectively treated TSS, biological oxygen demand (BOD), and chemical oxygen demand (COD) to class II water quality standards. Findings highlight the importance of plant diversity in bioretention systems for enhanced performance. The study also found a positive correlation between influent concentration and pollutant removal, except for COD and BOD. Even with a smaller sizing ratio, P3 performed well in regulating peak discharge, showing only a 0.3% increase, compared to 22% for P1 and 14% for P2. In tropical climates with intense rainfall, appropriate bioretention sizing is crucial. This study underscores the importance of plant diversity in bioretention systems, enhancing flow reduction and pollutant removal regardless of influent concentration and sizing ratio.