Influence of Salt on Total and Dissolved Metal Treatment in Bioretention: A Field Study

Abstract Urban areas are affected by anthropogenic activities that cause pollutant load on receiving water bodies. Stormwater bioretention are popular and effective in removing pollutants. The main water quality treatment processes are filtration and adsorption in the top layer (0-10 cm) of the filters. So far, few in-field studies have evaluated effects of cold climate and de-icing salt on bioretention for treating metals. Thus, a comprehensive study of total and dissolved metal removal (Cd, Cr, Cu, Ni, Pb and Zn) in a bioretention system for management of road runoff from the European highway E4 was carried out. Three different filter configurations were examined: a sand filter (SF), a vegetated sand filter (BF) and a vegetated sand filter with chalk additive (BFC). The results show a general trend of significant metal removal in all three filters, BFC, BF and SF, both under impact of high (Cl − > 210 mg/l) and low (Cl − ≤ 98.2 mg/l) chloride concentrations. For total metal concentrations, the results show that removal was most efficient in filter BFC, then BF and least efficient in filter SF. For metals such as Cu, Ni and Pb, this may indicate that better removal could be achieved using vegetated filters with chalk additives that affect pH. For dissolved metals, there is a tendence of Cr, Cu, Ni, Pb and Zn removal in filter BFC when lower chloride impact. With higher chlorides concentrations, there tended to be a release of metals from the filters.