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Bioretention

Engineering Bioretention to Optimize Pollutant Removals

 

This research 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.

 46 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 ug/L, nitrate-N at 2 mg-N/L, ammonium-N at 2 mg-N/L, and total P at 3 mg-P/L.  

 

                                                                                                                        

The 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.

 

 

 

 

 

2001-2003 Field Studies

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.

Two 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.

 

This work was completed by Doctoral student Chi-hsu Hsieh.

 

Clicking on the image should provide a clear figure.

 

Results of this work are being published:

Hsieh, C.-h and Davis, A.P. “Multiple-Event Study of Bioretention for Treatment of Urban Storm Water Runoff,” Water Sci. Technol., 51(3-4), 177-181 (2005).

Hsieh, C.-h and Davis, A.P. “Evaluation and Optimization of Bioretention Media for Treatment of Urban Storm Water Runoff,” J. Environ. Eng., ASCE, 131(11), 1521-1531 (2005).

Hsieh, C.-h., 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

An additional manuscript is in preparation on media and nitrogen removal.

 
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March 23, 2006