Trace Metals in Stormwater: Alternative Best Management Practices

Heavy metals, such as copper (Cu) and zinc (Zn), are considered hazardous in natural waters due to their toxicity and non-biodegradability. The focus of this study is to use batch experiments to investigate the heavy metal (Cu and Zn) removal efficiency of perlite and EarthliteTM to improve in-situ filtration systems for stormwater catchment basins. Stormwater samples from two field sites in Portland, OR, chosen to represent a high-use commercial site and high-traffic urban road, were characterized to inform experimental design and compare to values found in literature. The Linear, Freundlich, and Langmuir isotherm models were used to describe equilibrium data and determine partitioning coefficients for single metal batch studies. Both the Freundlich and Langmuir models fit most single metal batch systems, while Cu-Perlite, Zn-Perlite, and Zn-EarthliteTM, were best fit by the Langmuir model, R2 = 0.9594; 0.9538; 0.9811, respectively. Competitive adsorption behaviors for Cu and Zn were evaluated using a synthetic stormwater recipe where relative concentrations of Cu and Zn were maintained to be consistent with representative stormwater samples. Perlite showed a decrease in the sorption capacity of Cu and Zn in the presence of competing ions in solution. EarthliteTM showed no difference in the affinity for copper uptake between competitive and non-competitive batch experiments. EarthliteTM affinity for Zn decreased by two orders of magnitude in the competitive batch system. The results from this study will be applied to estimate filter lifetime for traditional and advanced stormwater filter systems. These results will inform experimental design in dynamic flow-through experiments using various filter media thereby improving filter design and implementation of stormwater best management practices