Development of Bioretention Media for Phosphorus Control

Excess phosphorus loading from stormwater can lead to eutrophication and the increased probability of harmful algal blooms in sensitive receiving waters. Bioretention systems, which are being increasingly utilized for stormwater treatment and control, have not been developed to address nutrient contamination. In fact, many bioretention systems incorporate substantial amounts of compost or other organic matter, which can lead to an increase in phosphorus concentration in system effluent. A treatment media for phosphorus control is needed. Water treatment residuals (WTRs) are a common waste product from drinking water treatment systems in Washington State. They consist of aluminum- or iron-based flocculants, polymers, and organic particulates. They have shown the propensity to adsorb phosphorus from water and soils. In laboratory and field studies we have evaluated the effectiveness of WTR-based media to remove phosphorus from water. Results indicate that total phosphorus and orthophosphate can be effectively removed from stormwater, reducing concentrations by over 90%. Further, phosphorus removal vs contact time relationships have been developed, which can be used to inform the design criteria for incorporating WTR-based media into bioretention systems