Treatability of Stormwater Toxicants Using Biofiltration Media

Bioretention has been promoted as a stormwater management technique that can reduce the loads of solids, heavy metals, and nutrients to surface waters. Many researchers have reported the treatment effectiveness of bioretention both in terms of percent removal and periodically in terms of effluent concentration. No studies, however, have evaluated the ability of carefully-selected bioretention media to treat pollutants to meet specific permit limits. This project focused on the selection of a bioretention media mixture from pre-selected components – a granular activated carbon (GAC), two zeolites, two sands, and a peat moss – with the goal of treating numerous constituents, including dioxins, mercury, perchlorate, oil and grease, and radioactive components to numeric permit limits. Two series of column tests, one focusing on long-term pollutant removal behavior and the other on the effect of depth/contact time on removal and using stormwater as the base test fluid, showed that a bioretention media containing a specific granular activated carbon (GAC) was able to treat these constituents to the permit limits under a wide range of likely site conditions. Supplemental batch tests, not reported here, also examined treatment capacity, kinetics, and holding ability under interevent aerobic and anaerobic conditions.