Bioretention and Treatment Media: A Phosphorus Story

Watch recording


Allen Davis; Charles A. Irish, Sr. Chair in Civil Engineering; Professor, Department of Civil and Environmental Engineering, University of Maryland


Many of the important performance characteristics of media-based stormwater control measures are determined by the media properties. Media filtration and adsorption characteristics will govern both removal performance for most pollutants (particulate matter, phosphorus, heavy metals, many organic pollutants, and nitrogen to some extent) and the resulting pollutant spatial accumulation in the media.  The importance of media properties is exemplified through consideration of phosphorus (P, both particulate and dissolved) in bioretention and related stormwater control measures (SCMs).  Particulate matter and affiliated pollutants are generally very effectively removed in filtration SCMs. Managing dissolved pollutants requires careful consideration of SCM media characteristics.  Foremost, the media must not be a source of pollutants.  P adsorption in soils is typically controlled by the levels of amorphous aluminum and iron present. Use of aluminum-based water treatment residual and aluminum hydroxide (from several sources) as SCM media amendments will increase P removal capacity.

Speaker Bio

Allen P. Davis is Professor and Charles A. Irish Sr. Chair in Civil Engineering in the Department of Civil and Environmental Engineering at the University of Maryland. He earned his BS, MCE and PhD degrees all from the University of Delaware. For over two decades, he has been investigating sources and treatment of pollutants in urban storm water runoff with a
focus on nature-based practices, particularly bioretention. In 2010 he was awarded the A. James Clark School of Engineering Faculty Outstanding Research Award recognizing exceptionally influential research accomplishments related to urban storm water quality, its management, and the concept of Low Impact Development. He is author or co-author of over 125 peer-reviewed journal articles and a text on Stormwater Management for Smart Growth. From 2001 to 2010, he was Director of the Maryland Water Resources Research Center. He is currently Editor-in-Chief of the ASCE Journal of Sustainable Water in the Built Environment and recently completed an assignment as Chair of the National Academies Committee on Improving the EPA Multi-Sector General Permit for Industrial Stormwater Discharges. He is a Licensed Professional Engineer in Maryland, Fellow of the American Society of Civil Engineers, Fellow of the ASCE Environmental and Water Resources Institute, and a Diplomate, Water Resources Engineer.

Allen Davis photo

Speaker Panel

Bryan Pynn - Washington Conservation District
Patrick Martin - City of Richfield
Curt Coudron - Dakota County