Comparison of black carbon media for removal of dissolved metals in stormwater

Urban stormwater pollution is a persistent threat to surface water quality and aquatic ecosystem health. Stormwater control measures (SCMs) have shown promise in water quality improvements through reduction of particulate matter, pathogens, and other contaminants. However, traditional filtration/infiltration-based SCMs show inconsistent results for the removal of dissolved constituents, including the metals Cu and Zn. The primary focus of this study was to investigate innovative SCM media under realistic conditions by using a novel synthetic stormwater recipe that incorporates natural organic matter (NOM) and co-contaminants (including polychlorinated biphenyls and polycyclic aromatic hydrocarbons). In addition, this study used high flows (20 cm/h) and larger media sizes (0.4-2.4 mm) to increase the real-world relevancy for field application. Emerging and conventional environmental adsorbents were evaluated individually, including two types of pinewood biochar, granular activated carbon (GAC, F400), and regenerated activated carbon (RAC) for the removal of Cu(II) and Zn(II) in continuous columns. Influent and effluent column samples were collected periodically over the course of two months of continuous flow, equivalent to approximately 900 bed volumes. No significant difference was found among the four types of media tested for dissolved Cu(II) and Zn(II) removal, suggesting that the column adsorption is controlled by adsorption and mass transfer rate limitation as this flow rate. Zn(II) exhaustion (C/C_o > 1) occurred after the equivalent of nine years of rainfall. However, by scaling up media mass, it is predicted that exhaustion can be extended to >92 years. Cu(II) exhaustion was observed for biochar, but not for GAC or RAC after 886 bed volumes. This study showed that even in the presence of co-contaminants and NOM, black carbons media like biochar and RAC can provide reduction of dissolved Cu(II) from low input concentrations.