Bioretention to Optimize Pollutant Removals
study began in August 2000 and was completed in March 2004. The investigation
was sponsored by the Cooperative Institute for Coastal and Estuarine
Environmental Technology (CICEET). The
objectives of this study were to test the effectiveness of bioretention for
treatment of urban storm water runoff employing laboratory bioretention
columns and on-site bioretention evaluations. Column and field studies
were employed to
investigate tradeoffs between infiltration rates and pollutant removals in the use of
various media and media mixtures in bioretention.
column studies and 8 on-site bioretention evaluations were
completed. In addition, a series of mechanistic studies for total
phosphorus removal in bioretention facilities was investigated. The target pollutant levels in the experiments were suspended
solids at 150 mg/L, oil/grease at 20 mg/L, lead at 100
nitrate-N at 2 mg-N/L, ammonium-N at 2 mg-N/L, and total P at 3 mg-P/L.
bioretention column studies include 6-hr individual and long-term repetitive tests.
For the individual column tests, different media mixtures,
including natural soils and mixtures of sands and soils, were employed as
uniform or layered media in 19.5-cm diameter columns. The total
media height for all columns was 90 cm. During the testing period,
the synthetic runoff was applied to maintain a 15-cm water head.
Performances of different media, including runoff infiltration rate and
pollutant removal efficiency were evaluated and correlated to the media
properties. Finally, the function of each employed medium was investigated
and applied to bioretention media design recommendations.
Moreover, two repetitive columns were
tested to examine the long-term performance of bioretention, including the
effect of filtered suspended solids on runoff infiltration, phosphorus
transformation in the bioretention media, and the fate of nitrogen during
the testing period.
Totals of 12 and 16 6-hr repetitions for each column, where the interval
between each repetition was 5-9 days, were completed. The advantages of a
surface mulch layer and a bottom fine-sand layer were confirmed.
Nitrification and denitrification processes proceeding during the dormant
period were noted in the second bioretention column.
Synthetic runoff was employed for six on-site
bioretention evaluations. Another two bioretention evaluations were
conducted during a rainfall event to allow the complete field
investigation to include eight different bioretention facilities.
For the first 6 on-site evaluations,
synthetic runoff was pump into a selected area (2.3
m x 2.3 m) in each bioretention cell for 6 hrs. During this period,
effluent was collected from the underdrain pipe every half hour and
transported to the Environmental Engineering Laboratory, University of Maryland for
analysis. Two media samples (10 to 15 cm and 15
to 40 cm depth) for each site were also collected and
characterized. The impacts of these bioretention facilities in runoff
quality improvement were assessed. Additionally, all results from field
studies were compared with laboratory works.
evaluations of bioretention facilities, using a paired bioretention set,
were conducted during a rainfall event (February 3, 2003). This work
characterized incoming runoff and allowed comparison with our synthetic
runoff. Performances of both bioretention cells were evaluated.
work was completed by Doctoral student Chi-hsu Hsieh.
Clicking on the image
should provide a clear figure.
of this work are being published:
C.-h and Davis, A.P. “Multiple-Event Study of Bioretention
for Treatment of Urban Storm Water Runoff,” Water Sci. Technol., 51(3-4),
C.-h and Davis, A.P. “Evaluation and Optimization of Bioretention Media
for Treatment of Urban Storm Water Runoff,” J. Environ. Eng., ASCE,
Davis, A.P. and Needelman, B.A. “Bioretention Column Studies of Phosphorus Removal
from Urban Stormwater Runoff,” Water Environ. Res.,
accepted for publication, February 2006
additional manuscript is in preparation on media and nitrogen removal.
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March 23, 2006