Phytoextraction of heavy metals from sewage sludge by plants

Cadmium and lead concentrations in polluted soil and their uptake by non-traditional plants (Malva verticillata, Secale cereale var. multicaule and Melilotus alba) were studied in a small-plot trial during the years 2008 and 2009. At the same time, the effect of Bio-algeen preparations on phytoextraction of heavy metals by these plants was investigated. Experimental plots were established on the reclaimed land after closing down mining operations in the town of Zacler (North-East Bohemia) where a layer of sewage sludge from a wastewater treatment plant 0.6-0.8 m thick was subsequently applied. The average concentrations of Pb and Cd in the applied sewage sludge were 180 mg/kg and 6.89 mg/kg, respectively. The experiment had two variants: Variant 1 - sewage sludge without any other substances, and Variant 2 - sewage sludge + Bio-algeen preparations (B. A. S-90 or B. A. Root Concentrate). The highest accumulation of Cd and Pb in the aboveground biomass was found out in rye, viz 14.89 mg/kg DM and 14.89 mg/kg DM, respectively. White sweet clover exhibited the significantly lowest capability to extract both heavy metals (viz 0.22 and 3.20 mg/kg DM of Cd and Pb, respectively). A positive effect of Bio-algeen was evident in all plants. The highest yield of aboveground biomass was recorded on the plot with white sweet clover with added alginate (496 g/m). The fodder mallow seems to be the most suitable crop for the phytoextraction of both metals (0.35 and 5.87 mg/square m of Cd and Pb, respectively).