Bone Char as a Potential Sorbent for Metal Removal from Urban Runoff: Effect of Temperature on Sorption

Controlling stormwater runoff from impervious surfaces in urban areas presents two main engineering challenges: (1) the handling a large volume of water in a short period of time and (2) the presence of many contaminants. Controlling water quality of infiltrating stormwater is difficult. Bone char has been shown to have a high affinity for copper, zinc, cadmium, arsenic, and lead ions. We investigated the potential of amending bioswale soil with bone char to decrease the dissolved metal transport from parking lot runoff in Detroit, MI. The role of temperature on the sorption rate and capacity of bone char in cold climates must be considered. Various amounts of bone char were added to 40 mL of 500 ppm copper solution (pH ~5.5) in centrifuge tubes and placed on rotators at room temperature. Additional experiments were conducted in tube racks placed at room temperature (25°C), in a refrigerator (5°C), and in a hot water bath (40°C). Copper concentrations were measured with colormetric techniques using a spectrophotometer and were confirmed with ICP-MS analysis. Copper concentrations were measured weekly for 60 days and showed a large effect with temperature. After 60 days, the 5°C, 25°C, 40°C samples had 32%, 88%, and 100% sorption, respectively. The mass loading after 60 days was 64, 176, and 200 mg Cu/g bone char for 5°C, 25°C, 40°C, respectively. These results demonstrate that bone char is a promising bioswale soil amendment to aid sorption of copper and other metals, although temperature effects must be accounted for in design.