Ferrate-biochar mixed media for enhanced nutrient removal in urban stormwater bioretention systems

Overview

This research proposes a Ferrate-biochar mixed media designed to significantly improve nutrient removal in urban stormwater bioretention systems. The technology targets a critical gap in conventional bioretention infrastructure, where insufficient electron transfer in oxic and anoxic environments limits the conversion and removal of nutrients such as nitrogen from stormwater runoff.

The approach integrates ferrate (Fe VI), a powerful oxidizing agent known to treat heavy metals, suspended particles, organic matter, and microorganisms without producing toxic by-products, with biochar, a carbon-rich material produced from organic feedstock. A baffle configuration is incorporated to enhance electron transfer and improve nutrient conversion efficiency. The goal is to achieve greater than 50% nutrient removal from urban stormwater, addressing water quality challenges faced by municipalities and developers managing stormwater runoff.

Technical specifications

Core technology components:

• Ferrate (Fe VI): A high-valent iron compound capable of simultaneous oxidation, coagulation, flocculation, and disinfection of stormwater contaminants
• Biochar amendment: Carbon-based media, such as bamboo-derived biochar, providing adsorption capacity and supporting biological activity for nitrogen removal
• Multilayer media configuration: A layered design combining ferrate-biochar in distinct zones to optimize treatment across varying oxygen conditions
• Baffle configuration: Structural enhancement to promote electron transfer between oxic and anoxic zones, improving nutrient conversion kinetics

Performance targets:

• Greater than 50% nutrient removal from urban stormwater
• Maintained hydraulic conductivity during peak runoff events
• Potential for heavy metals, organic matter, and microorganism co-removal based on ferrate properties

Anticipated applications:

• Urban stormwater bioretention systems for municipal and commercial developments
• Low C/N wastewater treatment in constructed wetlands
• Green infrastructure projects requiring enhanced nutrient management

Technology readiness level

This technology is currently at an early research stage (TRL 2–3). The hypothesis is supported by existing literature demonstrating that iron-modified biochar and iron-based media can achieve high nutrient removal rates, including up to 95.7% NO3-N removal in prior multilayer media studies. However, the specific combination of ferrate (Fe VI) with biochar in a baffled bioretention configuration has not yet been validated.

The research team plans to conduct laboratory-scale column tests using Ferrate-biochar multilayer media with spiked synthetic stormwater to evaluate nutrient removal efficiency and hydraulic conductivity under peak runoff conditions. Following proof-of-concept validation, the team intends to pursue pilot and field-scale testing in collaboration with an industry partner over a six-month period to evaluate real-world performance. The principal investigator's lab has prior experience assessing ferrate oxidation of contaminants of emerging concern from surface water, providing relevant expertise for this work.