Urban stormwater runoff often contains potentially harmful contaminants, including metals, which can create public health and environmental concerns. Bioretention systems are increasingly being utilized to treat contaminated urban stormwater; however, bioretention media should be carefully selected. In this study, batch experiments were conducted to investigate five low-cost sorbent materials (biochar (BC), iron amended biochar (FeBC), scrap tire (ST), coir coconut (CC) and blast furnace slag (BFS)) potential to treat six common toxic metal contaminants (Pb, Cr, Cd, Cu, Ni and Zn). The effects of pH, ionic strength and dissolved organic carbon (DOC) of solutions on the sorption of metals were also investigated.  CC and BFS had great removal efficiencies for all evaluated metals (&gt;90%), while removal efficiencies of ST and BC were high (&gt;90%) for some of metals (Cr, Pb and Cu). FeBC showed the worst performance removing only Pb and Cr (30-50%). Kinetic experiments showed that metals removal occurred rapidly and reached equilibrium &lt; 5 h and experimental data were well described by a pseudo-second order model. Sorption of metals on the surface of sorbents was strongly dependent on solution pH, as sorption was highest at pH=9 and lowest at pH=3, which is likely due to a combination of H<sup>+</sup> competition and more charged metal species. In addition, sorption was negatively affected by DOC, potentially due to increased metal solubility or site blocking. Ionic strength did not show significant effect on sorption performance. The sorption mechanism of metals on the surface of sorbents was mainly due to electrostatic attraction and precipitation. Vegetated intermittent flow column studies are currently underway to evaluate metals removal in stormwater infiltration relevant systems. Overall, this study demonstrates strengths and limitations of each sorbent, appropriate selection of sorbent as filter media for removing metals from runoff, and on-going testing.

Simultaneous removal of Pb, Cr, Cd, Cu, Ni and Zn from urban stormwater runoff using low-cost agricultural/industrial sorbents

ACS Spring Meeting 2021

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