Review of dissolved pollutants in urban storm water and their removal and fate in bioretention cells

Storm-water pollutants are widely recognized as a major cause of surface water quality degradation. Most storm-water treatment efforts have focused on capture of particles and particle-associated pollutants, but oftentimes half or more of pollutant loads can be attributed to the dissolved phase. Dissolved pollutants are more mobile, bioavailable, and are captured via different mechanisms than particles. Low-impact development storm-water control measures such as bioretention are being used to infiltrate storm water to reduce storm-water volume as well as to capture storm-water pollutants. Bioretention systems have proven effective at capturing both dissolved and particulate storm-water pollutants. Herein the authors present a state-of-the-art review of dissolved storm-water pollutant sources and typical concentrations, removal mechanisms, and fate in bioretention cells covering three pollutant classes: (1) nutrients (i.e., phosphorus and nitrogen), (2) toxic metals, and (3) organic compounds, including emerging contaminants. Also discussed are recent innovations in bioretention design to enhance dissolved pollutant removal, such as media amendments, saturated zones for promoting denitrification, and vegetation for stimulating biodegradation. Current knowledge gaps and recommendations for future research directions are also discussed.