Evaluating Innovative and Sustainable Geomedia for the Removal of Dissolved Cu and Zn in Stormwater Media-Based Treatment

Urban stormwater is a major contributor of pollutants to receiving water bodies. Metals, especially copper (Cu) and zinc (Zn), are ubiquitous in urban runoff and are two of the most critical to aquatic environments. Particulate-bound metals are effectively removed through filtration-based stormwater control measures (SCM) such as bioretention, however dissolved metals have proven to be more difficult to remove and are a concern for bioavailability and toxicity. As the interaction of dissolved metals with the bioretention media is the major mechanism for removal, innovative geomedia amendments and use of these amendments for subsequent polishing treatment is investigated. Continuous, up-flow columns are used to determine the capacity of the media, and modular treatment train mesocosms will test a layered, scaled-up approach using conventional bioretention soil media followed by a polishing layer. The media tested included two pinewood biochars, and two granular activated carbons (GAC, Calgon Filtrasorb®400 and regenerated DSR-C), as well as zeolite, an aluminosilicate mineral. A synthetic stormwater is pumped through columns, consisting of dissolved Cu and Zn at 70 and 200 µg/L and compost leachate, to replicate the complex organic carbon matrix in stormwater. Zn breakthrough occurred after 440 inches of effective rainfall (after accounting for drainage area and adjusting for biochar field-ratio) for all geomedia. Cu did not breakthrough over the 1,870 inches of effective rainfall tested (corresponding to ~47 years assuming 40 in/yr rainfall). Mesocosms will examine effects of intermittent storm flows and configuration of a modular treatment media system in a scaled-up laboratory study. Targeting reduction of metals in SCMs can greatly reduce the risk that metals pose to aquatic ecosystems.