Developing nitrogen removal models for stormwater bioretention systems

Area of Science:

• Environmental Engineering
• Water Quality Management
• Stormwater Management

Background:

• Bioretention systems reduce runoff volume and remove nitrogen.
• Internal water storage (IWS) and real-time control (RTC) can enhance bioretention performance.
• Existing models struggle to simulate nitrogen transformations influenced by IWS and environmental factors.

Purpose of the Study:

• Develop and evaluate nitrogen removal models (NRMs) for bioretention systems.
• Compare model performance with varying nitrogen cycling complexity (Single Nitrogen Pool vs. 3 Nitrogen Pool) and kinetics (0-order, 1st-order, Michaelis-Menten).
• Assess model adaptability to systems with IWS and RTC, using soil moisture data.

Main Methods:

• Developed six NRMs by combining SP and 3P models with 0-order, 1st-order, and Michaelis-Menten kinetics.
• Calibrated and validated NRMs using laboratory bioretention system data.
• Integrated NRMs with the Storm Water Management Model (SWMM) for simulation and comparison.

Main Results:

• 0-order kinetics were unsuitable for simulating nitrogen removal in bioretention systems.
• 1st-order kinetics and Michaelis-Menten models showed similar performance.
• The best model (3P-m) improved prediction accuracy for nitrogen event mean concentrations by 20% compared to SWMM.
• 3P-m accurately predicted cumulative nitrogen mass removal rates (±7% error) for systems with IWS/RTC, outperforming SWMM (-23% error).

Conclusions:

• 3P models offer higher accuracy and better biochemical reaction rate predictions than SP models.
• SP models provide improved accuracy with simpler initial condition requirements.
• The developed 3P-m model enhances the simulation of nitrogen removal in bioretention systems, particularly those with IWS and RTC.