Bioretention nitrogen removal through soil amendments and hydraulic controls

Overview

This research addresses a critical challenge in urban stormwater management: achieving efficient total nitrogen removal in bioretention systems. The approach combines low-cost soil amendments with engineered hydraulic controls to create alternating aerobic and anaerobic zones within a single treatment unit. By forcing all inflow through sequential oxic and saturated, low-oxygen zones enriched with organic carbon, the system promotes complete biological nitrogen conversion from ammonia to nitrogen gas.

The solution targets municipalities, environmental engineering firms, and green infrastructure developers seeking cost-effective, scalable nitrogen removal for stormwater and wastewater applications. The use of inexpensive amendments such as biochar and woodchips keeps material costs low while delivering high adsorptive capacity for ammonia and a steady carbon source for denitrifying bacteria.

Technical specifications

Key features:

• Dual-zone hydraulic design that ensures all stormwater passes through alternating aerobic and anaerobic zones, maximizing contact time for biological treatment
• Soil amendment integration using biochar, woodchips, and other porous media to enhance ammonia adsorption and provide organic carbon for denitrification
• Outlet hydraulic controls that maintain periodic oxic conditions for nitrification while enabling saturated, low-oxygen conditions for denitrification
• Subsurface flow configuration inspired by subsurface constructed wetland design principles, adapted for bioretention scale
• High hydraulic throughput capacity to prevent inlet bypass or surcharging during wet weather events
• Designed detention volume capable of retaining water quality event volumes while displacing previously stored anoxic zone water

The system is designed to detain a volume equal to 30 mm over a tributary drainage area that is ten times the prototype surface area, ensuring practical scalability for real-world drainage basins.

Technology readiness level

This technology is currently at the lab-scale validation stage. The research team will design and monitor total nitrogen fluxes through a prototype bioretention system that combines the filtration capacity of a subsurface flow constructed wetland with the hydraulic capacity needed for urban stormwater events. Future work will involve testing various amendment combinations and hydraulic configurations to optimize removal efficiency before advancing to field-scale pilot demonstrations.