|
Advances in Environmental Research Volume 6, Number 4, December 2017 , pages 281-299 DOI: https://doi.org/10.12989/aer.2017.6.4.281 |
||
|
Heavy metals leaching behavior and ecological risks in water and wastewater treatment sludges |
||
Raymond A. Wuana, Ishaq S. Eneji and Ezekiel C. Ugwu
|
||
| Abstract | ||
| Single (0.005 M DTPA), sequential (six-step) and kinetic (0.05 M EDTA) extractions were performed to assess Cd, Cr, Cu, Ni, Pb, and Zn mobilization and their potential ecological risks in Abuja (Nigeria) water (WTS) and wastewater (WWTS) treatment sludges. Total metal levels (mg/kg) in WTS and WWTS, respectively were: Cd(3.67 and 5.03), Cr(5.70 and 9.03), Cu(183.59 and 231.53), Ni(1.33 and 3.23), Pb(13.43 and 17.87), Zn(243.45 and 421.29). DTPA furnished metal extraction yields (%) in WTS and WWTS, respectively as: Cd(11 and 6), Cr (15 and 7), Cu(17 and 13), Ni(23 and 3), Pb(11 and 12), and Zn(37 and 33). The metals were associated with the soluble/exchangeable, carbonate, Mn/Fe-oxide, organic matter and residual forms to varying degrees. Kinetic extractions cumulatively leached metal concentrations akin to the mobilizable fractions extracted sequentially and the leaching data fitted well into the Elovich model. Metal mobilities were concordant for the three leaching procedures and varied in the order:WTS>WWTS. Calculated ecological risk indices suggested moderate and considerable metal toxicity in WTS and WWTS, respectively with Cd as the worst culprit. The findings may be useful in predicting heavy metals bioavailability and risks in the sludges to guide their disposal and use in land applications. | ||
| Key Words | ||
| heavy metal; single extraction; sequential extraction; kinetic extraction; ecological risk; industrial sludge | ||
| Address | ||
| Raymond A. Wuana, Ishaq S. Eneji and Ezekiel C. Ugwu: Department of Chemistry and Centre for Agrochemical Technology, Federal University of Agriculture, Makurdi 970001, Nigeria | ||
