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Prediction of extractable metals (Cd, Pb, Fe Cu, Mn and Zn)
in sewage
Ololade I. A.
Department of Chemistry and Industrial Chemistry, Adekunle
Ajasin University, P. M. B. 001, Akungba-Akoko, Ondo-State,
Nigeria. E-mail:
olisa200@yahoo.com. Tel: +2348077812009.
Accepted 18 September, 2009 |
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Sewage sludge are residues resulting from the
treatment of wastewater released from various sources
including homes, industries, medical facilities, street run
off and businesses. It consists of nutrients and organic
matter that can provide soil benefits and are widely used as
soil amendments. Over several years, the inability to
determine metal species in sewage hampers efforts
to understand the mobility, bioavailability and fate of
contaminant metals in environmental systems, to
assess health risks posed by them and to develop
methods to remediate metal contaminated sites. In
an attempt to investigate the partitioning of some heavy
metals (Cu, Pb, Fe, Cd, Mn and Zn) in sewage, the four
stages of the Tessier sequential extraction method were
employed. The effect of extractant concentration was also
studied and found to affect extractability across the
various fractions (reducible, oxidizable and residual). High
level of total organic carbon coupled with the neutral pH of
the sewage supports their potential agricultural benefits
for agricultural land application. Across all samples, the
sequence follows the pattern Cu>Fe>Zn>Pb>Mn>Cd. Greater
percentage of all the metals occur in the oxidizable and
residual fractions. The study shows that the
metal ion binding to the biotic surface such as sewage is pH
dependent and
that there is an optimum pH for bioavailability of metals.
The influence of the sludge pH and organic matter was
observed only on copper (r = -0.992 at p < 0.01) and cadmium
(r = -0.970 at p < 0.05) respectively with both displaying
negative correlation.
The concept might be a valuable tool in predicting
quantitatively the metal ion sorption to plants present in a
complex system and to predict the relative change in
availability due to environmental changes.
Key words:
Sewage sludge, heavy metals, sequential extraction,
bioavailability. |
