Abstract
Heavy metals from urban stormwater runoff are important sources of surface water pollutants. Sand, zeolite, sandy loam, and quartz-sand were separately mixed with lignin to form four bioretention media mixes for experimental study using synthetic stormwater runoff. The average removal efficiencies of four heavy metals (Cu, Zn, Cd, and Pb) by the four media mixes were all better than 97% at the optimum pH of 6.05 (ranging from 6 to 8) and the seven-day rainfall-event interval. The influence of the influent concentration and the rainfall-event interval on the removal efficiency of heavy metals by the four media mixes was not significant, but the variation of the removal efficiencies at the four-day rainfall-event interval was large. Under acidic conditions, there was a certain heavy metal dissolution in the four reactors, but the effect on the removal efficiency was minor. Heavy metals were present in the media mainly in the form of the residual fraction (>50%). The accumulation of Cu, Zn, and Cd in the surface planting-soil layer (same humus and sandy-loam mixture for all reactors) was significantly larger than the accumulation at deeper depths but not for Pb. Overall, the heavy metal removal efficiencies by the four media mixes were not significantly different, and the choice of the planting-soil layer can become the control factor of heavy metal removal.
Highlights
With rapid urbanization, the extent of impervious urban land has increased
After a preliminary analysis of the permeability the four media mixes, the constant head method was used to measure the permeability coefficient coefficients for the four media mixes, the constant head method was used to measure the for three media mixes, and the variable head permeability coefficient for three media mixes, method was used to measure the permeability coefficient for the sandy-loam media mix at 30 and and the variable head method was used to measure the permeability coefficient for the sandy-loam
The four bioretention media mixes, sand, zeolite, sandy loam, and quartz-sand, that were separately mixed with lignin were investigated experimentally using cylindrical reactors, including separately mixed with lignin were investigated experimentally using cylindrical reactors, including
Summary
The impervious surfaces created by buildings and pavement significantly alter the way water flows through watersheds, conveying additional pollutants with runoff [1]. The accumulation of suspended solids, heavy metals, hydrocarbons, and other pollutants on these surfaces has increased [2,3]. Atmospheric pollutants and pollutants dispersed in catchments are accumulated during no-rainfall dry periods, are flushed by rainfall and runoff, and eventually enter the receiving waterbodies, causing serious pollution of the urban water environment [4,5,6,7,8]. China is in a critical period of urbanization, and stormwater runoff pollution has become the second largest source of non-point pollution, second only to agricultural pollution [9]. The concentrations of heavy metals in stormwater runoff from roads [13,14] and roofs [15] differ when compared with the Chinese
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