Assessment of selected bioretention blends for nutrient retention using mesocosm experiments

Area of Science:

• Environmental Engineering
• Water Quality Management
• Stormwater Best Management Practices

Background:

• Urban runoff frequently pollutes waterways with nutrients like nitrogen (N) and phosphorus (P).
• Bioretention systems are engineered to mitigate this pollution using specialized media and vegetation.
• Optimizing bioretention media composition is key to maximizing nutrient removal efficiency.

Purpose of the Study:

• To evaluate three bioretention media blends (TerraSolve, Biofilter, VT Mix) for N and P removal from simulated urban runoff.
• To assess the impact of vegetation and varying hydraulic residence times (HRTs) on nutrient removal performance.
• To determine optimal bioretention media characteristics for nutrient management.

Main Methods:

• Experimental mesocosms were used to test three bioretention media blends with and without vegetation.
• Simulated urban runoff was applied at different hydraulic residence times (HRTs).
• Adsorption isotherm experiments were conducted to understand nutrient binding mechanisms.

Main Results:

• TerraSolve and VT Mix, containing water treatment residuals (WTRs), achieved over 95% total phosphorus (P) removal.
• VT Mix demonstrated the highest total Kjeldahl nitrogen (TKN) removal, with vegetation generally improving TKN removal at longer HRTs.
• Yard-waste compost (YWC) did not lead to significant nutrient export and appeared to enhance N removal, potentially via denitrification.

Conclusions:

• Bioretention media containing water treatment residuals (WTRs) are highly effective for phosphorus removal.
• Yard-waste compost (YWC) can enhance nitrogen removal without causing nutrient export.
• Recommended media composition includes <10% fines, amorphous aluminum for P adsorption, 3-5% stable compost, and adequate plant nutrients; HRT should be optimized based on media characteristics.