American Society of Civil Engineers

Water Treatment Residual as a Bioretention Amendment for Phosphorus. I: Evaluation Studies

by Sean W. O’Neill, (Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Univ. of Maryland, College Park, MD 20742.) and Allen P. Davis, (corresponding author), F.ASCE, (Professor, Dept. of Civil and Environmental Engineering, Univ. of Maryland, College Park, MD 20742. E-mail:

Journal of Environmental Engineering, Vol. 138, No. 3, March 2012, pp. 318-327, (doi:

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Document type: Journal Paper
Special Issue: Advances in Research and Development of Sustainable Environmental Technologies
Abstract: Urban stormwater runoff has been implicated as a major source of excess nutrients to surface waters, contributing to the development of eutrophic conditions. Bioretention, a promising technology for urban stormwater pollution treatment, was investigated to determine whether an aluminum-based water treatment residual (WTR) amended bioretention soil media (BSM) could adsorb sufficient P at low concentrations (120 μ g P L-1), extrapolated for a 20-year facility lifetime. Batch and minicolumn studies were employed to determine both an optimal BSM mixture and media performance. Media tests demonstrated P adsorption proportional to WTR addition. Additional amendments such as quartz sand and hardwood bark mulch produced further significant variations in adsorptive behavior. WTR-amended media showed excellent P removal, meeting the developed benchmark for adsorptive behavior. Predominantly, media met minimal P adsorption requirements when it contained at least 4 to 5% WTR by mass (air dried). The use of an oxalate-extractable aluminum-, iron-, and phosphorus-based metric to predict media P adsorption capacity, the oxalate ratio, is proposed. A media oxalate ratio of 20–40 is expected to meet the P adsorption requirement.

ASCE Subject Headings:
Biological processes
Stormwater management
Nonpoint pollution
Water treatment

Author Keywords:
Storm water
Non point source pollution