Removal of Heavy Metals from Urban Stormwater Runoff Using Bioretention Media Mix

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.

Performance Assessment of a Laboratory Scale Prototype Biofiltration System in Tropical Region

“…The high efficiency in heavy metal removal is attributed to the ion-exchange mechanism with soil media particles, whereas plants play almost no (or very limited) role in heavy metal uptake. This is consistent with several other studies on heavy metals removal in biofiltration systems [20,24,[54][55][56][57][58]. Pedilanthus removed Fe by 76.5%, while the Cyperus removal rate of Fe was 50.6%.…”

Simultaneous Adsorption of Heavy Metals from Roadway Stormwater Runoff Using Different Filter Media in Column Studies

“…In general, subsequent dosings of the columns with synthetic runoff showed that the soil and technical filter media were able to remove the heavy metals, thus significantly reducing the concentrations of Cu, Pb and Zn (Figure 2). The extent of heavy metal removal depends on the initial heavy metal concentration and filter media type or composition [4,24]. The performance of each filter media in reducing the heavy metal levels was assessed based on the influent and effluent concentrations.…”

“…Similar to our findings, Hatt et al [2,5] showed that a wide range of media compositions (i.e., combinations of sand, sandy loam, vermiculite, perlite, compost, mulch, charcoal) achieved more than 90% removal of Cu, Pb and Zn from synthetic stormwater. Results indicated that the natural quartz sand (QS) has lowest sorption capacity compared to soil based and technical filter media which is attributed to its low surface area and few sorption sites [4,6,24]. Table 3 shows the mean and range of heavy metal concentrations measured at the effluent after each column was flushed with 5 g/L NaCl solution.…”

“…Unfortunately, results regarding pollutant removal efficiencies, equilibrium/effluent concentrations and sorption capacities were highly variable among the studies as well as these results may not be comparable to field conditions. These variabilities could be related to many factors including single solute solution versus multi-solute solution, influent concentration, pH, flow rate, flow direction (i.e., upflow vs. downflow mode) and filter bed height [21][22][23][24]. Column sorption experiments were mainly conducted with metal concentrations much higher than the levels in real roadway runoff waters [6,25] and also it is important to consider the simultaneous removal of co-existing metals [23].…”

“…The candidate filter media should be able to bind and adsorb multiple metals of significantly varying concentrations. In this context, the results of both laboratory [13,21,24,26] and field experiments [14,16] have demonstrated that soil-based and mixed media based decentralised stormwater infiltration/filtration are effective and affordable. Metals adsorbed to the filter media might not be permanently immobilized.…”