Effects of Temperature and NaCl on Toxic Metal Retention in Bioretention Media

Abstract

Column experiments were performed to compare the removals of Cd, Cu, and Zn from synthetic storm water by bioretention media at 3.6 and 19.4°C and to investigate the potential for metals retained on the bioretention media to be mobilized by a 1,000 mg/L NaCl solution. Bioretention media were effective at capturing Cd and Zn at both temperatures with sorption capacities greater at the lower temperature and increasing with increasing compost volume fraction (CVF). Removal of the primarily particulate-phase Cu was reduced at the lower temperature, suggesting that removal of particulate metals at low temperatures is of greater concern. The NaCl pulse caused accumulated metals in the bioretention media to leach in the order of Cd>Zn≫Cu. The fractions of metal released from the columns in all cases were relatively small (≤3.5%) and decreased with increasing CVF. Overall, the results suggest that bioretention is likely to be effective for metals capture and retention under cold climate conditions, especially when then media contains at least 30% compost by volume.