Resilient constructed wetland system for nitrogen removal from urban stormwater runoff

Overview

Urban stormwater runoff carries nitrogen, phosphate, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and pathogens into waterways, degrading water quality and stressing ecosystems. This research proposes a resilient constructed wetland that integrates carefully proportioned mixed permeable substrates (such as sand, steel slag, biochar, iron filings, zeolite, and calcite) with select native plants including Purple Prairie Clover, Meadowsweet, and Little Bluestem. The system is designed for deployment within urban rights-of-way and drainage corridors, providing passive treatment that requires minimal energy or chemical inputs while addressing multiple contaminant classes simultaneously.

Technical specifications

Core approach:

• Filtration through a layered mixed substrate removes particulate-bound and dissolved contaminants
• Chemical transformation using reactive media such as steel slag, iron filings, and zeolite targets nitrogen species, phosphate, and heavy metals
• Biological uptake and rhizosphere activity from selected native plants enhances removal of nutrients and organic contaminants

Key features:

• Uses commonly available, permeable materials to keep construction costs manageable
• Combines physical filtration with chemical and biological processes for multi-contaminant treatment
• Native plant selection supports ecosystem resilience and seasonal performance
• Passive operation reduces operational complexity and energy demand

Technology readiness level

The concept is at an early-to-mid stage of development. Prior independent studies have demonstrated that permeable mixed substrates effectively remove nutrients, heavy metals, PAHs, and pathogens from urban stormwater, and a small-scale constructed wetland using standard granular soil and a local plant achieved complete removal of total phosphorus (TP) and total Kjeldahl nitrogen (TKN) across multiple seasons during a one-year monitoring period. The next phase of work will rationally select two to three substrate combinations, evaluate filtration performance through small-column tests, confirm plant-substrate compatibility via pot tests, and conduct small-scale constructed wetland testing to validate combined filtration and chemical/biological transformation performance. Field pilot-scale testing will be detailed based on these intermediate validation results.