Long-term sustainability of escherichia coli removal in conventional bioretention media

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Department of Civil and Environmental Engineering


Bioretention has significant potential for reduction of bacterial levels in urban storm-water discharge. The long-term performance of bacteria removal was evaluated using column studies over an 18-month period, during which synthetic urban storm-water runoff was loaded into conventional bioretention media (CBM) columns once every two weeks. CBM initially achieved a mean of 72% removal efficiency for Escherichia coli O157:H7 strain B6914. The removal efficiency improved over time, achieving 97% or higher efficiency after six months. The trapped B6914 cells died off rapidly between runoff application events. Mechanistic studies indicated that decreased porosity and increased hydrodynamic dispersion observed in mature CBM are favorable for improvement of physical straining of cells and for bacterial adhesion. The temporal change in surface charge on CBM may not be a key factor in the improved bacterial removal. Indigenous protozoa in the CBM grew logistically, and may play an important role in enhancement of bacterial capture and rapid decline in numbers of trapped bacteria via predation. Overall, the long-term bacterial removal process in CBM can be efficient and sustainable.

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© 2011 American Society of Civil Engineers. Publisher’s version of record: https://doi.org/10.1061/(ASCE)EE.1943-7870.0000365

Publication Title

Journal of Environmental Engineering