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

Abstract

ONITORING 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.