Physicochemical Characterization of Compost of the Industrial Tannery Sludge

It is very important that tannery wastes in the form of sludge are managed in an environmentally sound manner. This study focused on the heavy metal characterization and the influence of changing the physico-chemical properties of the medium throughout the composting on the concentrations, bioavailability or chemical forms of Cr, Cu, Zn, Pb and Cd in tannery sludge. The physical and chemical properties of the composted sludge during treatment show the stability and maturity of end product. Total metal content in the final compost were much lower than the limit values of composts to be used as good soil fertilizer. Furthermore, it was observed in using a sequential extraction method in sludge compost at different phases of treatment, that a large proportion of the heavy metals were associated to the residual fraction (70– 80%) and more resistant fractions to extraction X–NaOH, X–EDTA, X–HNO3 (12–29%). Less than 2% of metals bound to bioavailable fractions X–(KNO3 + H2O). Bioavailable fractions of all elements tend to decrease. Mobile fractions of metals are poorly predictable from the total content.