Characterization Changes of Heavy Metals Contents and Fractions in Sewage Sludge from Sirt Wastewater Treatment Plant, Libya

MONITORING changes of the main chemical properties of
sewage sludge from Sirt Wastewater Treatment Plant, Libya was
investigated. Ten random sewage sludge samples were monthly
collected for a time span of one year. Average year values of TDS, pH,
organic matter and C/N recorded 1428.91 mg kg-1, 6.90, 76.3% and
7.97, respectively. Total N, P and K contents were in the normal range
(5.63, 1.41 and0.019%, respectively). The total concentrations of Fe,
Zn and Mn recorded high levels (2768, 1142 and 169 mg kg-1,
respectively). Low and more fluctuated total concentrations of Cu, Pb
and Ni were recorded (107, 45 and 35 mg kg-1, respectively). In
general, the total concentrations of heavy metals were found to be far
below the US-EPA ceiling limits except Cd and As which had
concentrations at or very close to their ceiling limits. The BCR
sequential extraction scheme was applied to investigate the
fractionation of heavy metals in the sludge. More than 50% of total As,
Pb, Fe, Mn and P were found in the fourth residual stable fraction
while the other heavy metals were mostly released in the first three
more mobile fractions (soluble-exchangeable, reduceable and
oxidizable) of the applied fractionation scheme. Special cautions
should be considered when using this sludge safely in agriculture
concerning the calculation of the loadings of heavy metals and their
mobility in soils.