Phytoextraction of heavy metal from sewage sludge by plants

In 2008 and 2009, studies made contents of cadmium and lead in the soil and their uptake by non-traditional plants were studied in a small-plot trial. At the same time also 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 Žacléř (North-East Bohemia) where a layer of sewage sludge from a wastewater treatment plant 0.6–0.8 m thick was subsequently applied. The locality is situated in the altitude of 612 m, its average annual temperature is about 6.8 °C and the mean annual precipitations are 857 mm. Analyses revealed higher concentrations of heavy metals in the applied sewage sludge. The average concentrations of lead and cadmium were 180 mg . kg−1 and 6.89 mg . kg−1, 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). To find the most suitable plant species for the phytoextraction of cadmium and lead, the following non-traditional plants were cultivated in both variants: fodder mallow (Malva verticillata L.), rye (Secale cereale L. var. multicaule METZG. ex ALEF.) and white sweet clover (Melilotus alba MEDIC.). The highest accumulation of cadmium and lead in the aboveground biomass was found out in rye, viz 14.89 mg . kg−1 DM and 14.89 mg . kg−1 DM of Cd and Pb, respectively., As compared with other plants under study, white sweet clover exhibited the significantly lowest capability to extract both heavy metals from soil (viz 0.22 and 3.20 mg . kg−1 DM of Cd and Pb, respectively). A positive effect of bio-algeen on phytoextraction of cadmium and lead 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−2). Of plants under study, the fodder mallow seems to be the most suitable crop for the phytoextraction of both metals (0.35 and 5.87 mg . m−2 of Cd and Pb, respectively).