Stormwater is the major conduit of pollutants from urban areas alongside the Puget Sound. Improving stormwater management to reduce levels of pollutants entering the Sound is one of six key state policy objectives of the Puget Sound Partnership to protect and restore water quality, habitat, and aquatic resources. In the Puget Sound, more than 13,000 pounds of toxic metals are released into the Sound daily.  In addition, many other waters of the State of Washington are polluted with nutrients like nitrogen and phosphorus.

Compost is a popular amendment used in bioretention systems for stormwater treatment because it adsorbs and retains many metals and organic pollutants.  However, over time it can export nutrients as the compost decomposes. In this study, we propose using an alternative iron-enhanced compost to provide a low cost stormwater treatment for removing both toxic metals and nutrients without nutrient bleeding over time.  The study addressed critical questions regarding the capacity and stability of iron-enhanced compost for contaminant removal in bioretention stormwater systems.

The goal of this project was to evaluate the stormwater treatment capabilities of our new iron-compost for the retention/removal of stormwater pollutants by performing the following tasks:

(1) Characterize reactive sites in iron-compost with a suite of chemical and spectroscopic techniques and determine its capacity for lead retention; and

(2) Evaluate the efficiency, stability, and longevity of iron-compost for stormwater treatment in stirred-flow experiments and develop mechanistic-based kinetics models for predicting stormwater quality and fate of sequestered contaminants.

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