Evaluating bioretention scale effect on stormwater retention and pollutant removal

Area of Science:

• Environmental Engineering
• Water Quality Management
• Stormwater Runoff Treatment

Background:

• Bioretention columns are vital laboratory tools for assessing pollutant removal from stormwater.
• Existing research lacks guidance on optimal bioretention column diameters and scale-up uncertainties.
• Understanding scale effects is critical for reliable laboratory-to-field transfer of bioretention performance data.

Purpose of the Study:

• To investigate the impact of varying bioretention column diameters on stormwater runoff retention and pollutant removal.
• To assess the influence of column size on the variability and reliability of experimental results.
• To determine if laboratory-scale bioretention studies accurately predict field-scale performance, particularly for nitrate.

Main Methods:

• Experimental assessment of three sets of bioretention columns with diameters of 400 mm, 300 mm, and 200 mm.
• Monitoring of runoff retention (R) and removal efficiencies for Total Suspended Solids (TSS), nitrite, phosphate, and nitrate.
• Statistical analysis to compare pollutant removal across different column diameters and identify scale-dependent effects.

Main Results:

• Runoff retention (R) was independent of column diameter but influenced by the time between events; diameter affected R variability.
• High removal rates were observed for TSS (95%), nitrite (98%), and phosphate (96%), with some variability across diameters.
• Nitrate removal varied significantly: 300-mm and 200-mm columns achieved >50% removal, while 400-mm columns released up to 285% more nitrate.

Conclusions:

• Bioretention column diameter significantly influences nitrate removal efficiency, with smaller scales performing better.
• Larger diameter columns (400 mm) can act as nitrate sources, highlighting scale effects in bioretention research.
• Results from small-diameter bioretention columns may not reliably predict field-scale performance, necessitating careful consideration of experimental scale.