Nature-Based and Engineered Strategies for the Remediation of Nutrients and Emerging Contaminants in Stormwater Runoff

Abstract

Stormwater runoff is a primary pathway for transporting pollutants into aquatic environments, including excess nutrients and pollutants of emerging concern (PECs) such as 6-PPD-quinone (6-PPDq), a toxic transformation product of the tire antioxidant 6-PPD. This study is divided into two parts that explore nature-based and engineered strategies to improve stormwater treatment performance. The first part assessed the phytotoxicity of 6-PPDq through germination bioassays and long-term exposure tests using three species commonly used in green infrastructure: Rudbeckia hirta, Rumex crispus, and Trifolium pratense. Germination assays were conducted at both environmentally relevant (1–100 μg/L) and elevated concentrations (200–3200 μg/L). R. hirta and T. pratense exhibited high germination rates and increased biomass at the highest concentrations, suggesting a hormetic effect and potential for phytoremediation. T. pratense produced up to four times more biomass than R. hirta, making it particularly suitable for stormwater applications. A 21-day soil exposure test with T. pratense confirmed its tolerance to 6-PPDq, with no significant reductions in growth across concentrations from 100 to 1600 μg/L. The second part evaluated the nutrient removal performance of an iron-modified geotextile as a passive treatment layer in infiltration systems. Three sequential column tests were conducted to compare setups with no geotextile, a standard geotextile, and a modified geotextile. The iron-dosed geotextile achieved up to 50% total phosphorus (TP) removal and improved retention across repeated dosing cycles. While total nitrogen (TN) removal remained modest (< 20%), slight improvements were observed over time. Together, these findings highlight the potential of pairing tolerant native vegetation with enhanced filter media to improve the efficiency of stormwater best management practices (BMPs). This integrated approach offers a scalable and minimally invasive strategy for managing nutrient and contaminant loads in urban runoff, particularly where retrofitting is preferred over full system reconstruction.