Removal of dissolved heavy metals from stormwater by filtration with granular recycled glass and mussel shell with and without microalgae biofilm

Abstract

Stormwater treatment technologies are routinely used to reduce urban stormwater contaminant loads entering surface water and groundwater systems. However, in most cases, their treatment capabilities are limited to particulate contaminants. Research into alternative filtration materials for stormwater treatment is necessary to provide sustainable and environmentally friendly options for the removal of dissolved heavy metals. In addition, periphytic biofilms are known to develop on substrate materials and little is known about their effect on the sorption of dissolved heavy metals. A laboratory study was conducted to assess the effectiveness of recycled glass, mussel shell, and freshwater periphytic biofilm to remove dissolved metals (copper, lead and zinc) from stormwater. Synthetic stormwater containing typical concentrations of heavy metals (Cu, 154 μg/L; Pb, 41 μg/L; Zn, 280 μg/L) was used for all experiments. The stormwater was recirculated through 1-L columns filled with granular recycled glass or mussel shell either colonised with periphytic biofilm (mainly microalgae) or not. The biofilm demonstrated an ability to sorb high concentrations of the dissolved metals. However, its contribution to heavy metal removal was much lower than that of the substrates on their own. In some cases, the biofilm actually reduced the ability of the substrates to remove Cu and Pb presumably by occupying adsorption sites on the filter media. The recirculation of a fixed volume of synthetic stormwater over a 48-hour period resulted in a stable removal efficiency for the three metals with the trend of removal being lead (>97%) ≥ zinc (97%) > copper (89%) for mussel shells and lead (96%) > zinc (86%) > copper (73%) for recycled glass. Both the composition and surface texture of the substrate seem to influence the removal of dissolved heavy metal from aqueous solutions. The use of waste products such as recycled glass and mussel shells for stormwater treatment might contribute to waste minimisation and to increase the value associated with the extended lifecycle of these materials.