Abstract

The anchored hydrophyte, Hydrocotyle umbellata L., was employed for the removal of toxic metals from tannery sludge concentrations (w/v) from a tanneries wastewater treatment plant. Different concentrations of wet tannery sludge were prepared and plants of H. umbellata showed a good tolerance for all the prepared concentrations. Plants were retrieved after 30, 60 and 90 days and the sludge concentrations showed reduction in sodium chloride, chlorides and chemical oxygen demand (COD). The accumulation of toxic metals in the plants was significantly increased, with increasing exposure time of plants. A higher amount was accumulated in the roots than in the shoots. The bioconcentration factor of Cr was higher than that of Zn and Cu at the same exposure time, indicating a higher accumulation potential of Cr by H. umbellata. The order of uptake efficiency was Cr > Zn > Na > Cu and the maximum metal uptake was observed after 90 days of exposure of H.  umbellata, being 18,200 mg kg ^-1 for chromium, 15,560 mg kg ^-1 for zinc 7,692 mg kg ^-1 for sodium and 6,660 mg kg ^-1 for copper in the roots.  These plants not only tolerated up to 60% concentration of tannery sludge but also reduced chromium content of sludge to a considerable extent.

Key words: Phytoremediation, rhizofiltration, tannery sludge, heavy metals, hydrophytes.