Removal of heavy metals from stormwater runoff using granulated drinking water treatment residuals

Stormwater runoff is a significant source of heavy metals, including cadmium (Cd), chromium (Cr), and nickel (Ni), which pose ecological and human health problems. Various filter media have been evaluated for heavy metal removal from stormwater via adsorption, most involving chemical- or energy-intensive processes. Aluminum-based drinking water treatment residuals (WTR), a non-hazardous byproduct of drinking water treatment, are an inexpensive sorbent for heavy metals. However, the low permeability of WTR is a problem and requires mixing with sand and carbon materials to improve flow; but such amendments also reduce its sorption capacity. To overcome this problem, a granulated WTR sorbent was generated using a green technique involving organic materials and a low-energy process. Batch studies showed that WTR granules remove Cd, Cr, and Ni simultaneously. Metal removal was adequately described by pseudo-secondorder kinetic models and Langmuir and Freundlich isotherm models. The overall removal performance was Cr > Cd > Ni. The presence of divalent cations in solution negatively affected metal removal; anions had a strong effect on Cd removal. A triple-layer surface complexation model adequately described metal removal. Results demonstrated the strong potential of the WTR granules to emerge as green filter media for the removal of heavy metals from stormwater runoff.