EVALUATION OF STORMWATER TREATMENT BY VARIOUS REACTIVE MEDIA FOR BIORETENTION CELL DESIGN CONSIDERATIONS

Bioretention cells (BRC) can be effective at filtering particulate pollutants from stormwater runoff, but substantial removal of the dissolved pollutant fraction is challenging. Various reactive treatment media for BRCs were evaluated to address nitrate (NO3-) and dissolved fractions of phosphorus (P), copper (Cu2+), lead (Pb2+), and zinc (Zn2+) removal in BRCs. Fly ash (FA) and iron oxyhydroxide mine drainage residuals (MDR) were blended with sand at 5% (FA5.0) and 7.5% (MDR7.5) by mass. Additionally, APTsorb (APT) and bioAPT (BIO), commercially available granulated and hardened peat products, were evaluated as treatment media, each with a sand layer to augment hydraulic retention time. Pollutant removal performance was evaluated by pumping synthetic stormwater (SS) through packed up-flow columns. 100% sand (SAND) was used as the control media. SS had target concentrations of NO3- at 1.5 milligrams per liter (mg/L) as N, phosphate (PO43-) at 0.5 mg/L as P, Cu2+ at 25 µg/L, Pb2+ at 30 µg/L, and Zn2+ at 100 µg/L. FA5.0 and MDR7.5 both removed over 84% of P. SAND, APT, and BIO had limited TP and TDP removal rates with BIO showing net export. All proposed media had Cu2+ and Zn2+ removal rates of over 75% and 89%, respectively. APT showed the highest Pb2+ removal at over 84%. FA5.0 and MDR7.5 were the most cost-effective options that did not show export of pollutants, therefore they are recommended as amendments to BRC media