COMPREHENSIVE STORMWATER MANAGEMENT: INVESTIGATING POTENTIALLY TOXIC ELEMENT (PTE) FATE AND TRANSPORT, BIORETENTION MEDIA AMENDMENT, BIOCHAR, AND INNOVATIVE DESIGN FOR WATER QUALITY IMPROVEMENT

Stormwater runoff contains a wide range of inorganic pollutants, including potentially toxic elements (PTEs), whose fate and transport are influenced by water quality parameters (e.g., dissolved organic carbon (DOC), salinity, and pH) and storm characteristics (e.g., depth, duration, and intensity). Managing stormwater runoff remains a persistent challenge due to concerns over pollutant loads and ecosystem health. To mitigate these impacts, stormwater management practices (SMPs) are widely implemented. Among SMPs, bioretention systems are constructed with engineered soil media designed to intercept and retain pollutants from infiltrating stormwater. However, due to the variability in stormwater quality, a comprehensive understanding of PTE fate and transport within bioretention systems remains incomplete. Key knowledge gaps remain regarding the governing mechanisms of PTE desorption from bioretention systems under varying DOC concentrations and environmental conditions. The pH buffering capacity of amended engineered media for PTE immobilization has been assessed in other environmental contexts but remains poorly evaluated in stormwater bioretention applications. Sustainable media amendments for enhanced PTE removal and innovative bioretention bed designs also require further evaluation to assess their effectiveness in achieving treatment objectives. To address these knowledge gaps, this study aims to advance stormwater management by focusing on four key objectives: 1. Investigating the influence of DOC on PTE desorption within bioretention media; 2. Evaluating the efficacy of dolomite-amended engineered media for pH neutralization and PTE immobilization; 3. Assessing the capacity of spent coffee ground-derived biochar (SCGB) to sequester PTE from stormwater; and 4. Analyzing the effectiveness of a step-tiered bioretention bed in improving water quality. To examine the effects of DOC on PTE mobility in bioretention media, soil samples were collected from a vegetated bioretention bed and subjected to DOC concentrations of 0, 15, and 50 mg-C/L to assess the desorption of ten PTEs (Mn, Fe, Co, Cu, Zn, As, Cd, Sn, Sb, and Pb). Results indicated that increasing DOC concentrations increased all monitored PTE desorption except Sb. The buffering capacity and immobilization of PTEs by dolomite-amended media were assessed through batch experiments using both laboratory-formulated and field-collected bioretention media, as well as column experiments. Dolomite dissolution (e.g., 0.282 mole fraction) rapidly neutralized pH to the recommended range (pH 5–8) within five minutes and immobilized all PTEs (Mn, Fe, Co, Cu, Zn, Cd, and Pb) except As. To explore a sustainable alternative, SCGB was produced and evaluated for Pb removal. SCGB synthesized at 700°C effectively sequestered Pb from simulated stormwater, reducing solution concentrations below the action level (10 µg/L). Lastly, the effectiveness of a step-tiered bioretention bed was assessed by monitoring key water quality parameters, including conductivity, PTEs (Mn, Fe, Co, Cu, Zn, As, Cd, and Pb), major cations (Na, Mg, K, and Ca), and Cl at different steps. Results indicated that the step-tiered design successfully reduced pollutant concentrations, with decreased concentrations observed as stormwater moved through successive steps. Overall, this research addresses critical gaps in stormwater management, providing novel insights into bioretention system performance and contributing to the development of more effective, sustainable stormwater treatment solutions.