Partitioning of Heavy Metals in Some Quebec Municipal Sludges

Abstract

Abstract The process efficiency of metal bioleaching from sewage sludges depends upon various physicochemical characteristics of sludges and the forms in which metals are present in these sludge solids. The aim of this research work was to evaluate the metal speciation in some Quebec sludges with the help of a sequential extraction procedure, in order to better predict the bioleaching process. The distribution of Al, Cu, Fe, Mn and Zn in exchangeable, sorbed, organically bound, carbonate, and residual forms were compared among both undigested and digested sludges. Metal redistribution after aerobic sludge stabilization was also studied. Results indicate that the organic and residual fractions were the principal metal binding phases. Copper was present mostly in the residual fraction while the other metals were mostly organically bound. Statistical tests showed that metal speciation varied significantly from one sludge to another. In terms of metal distribution pattern observed, these sludges could not be regrouped according to the sludge type, their total solids concentration or their total metal concentration. However, the variation in metal distribution among Quebec sludges was similar to the variation range found in the U.K. and U.S. sludges. The metals showed a tendency to redistribute and move towards the organic fraction in stabilized sludges. In conclusion, the present study shows that sewage sludges of different origins do not have similar metal distribution and hence, the speciation of metals must be considered for each sludge on an individual basis in order to predict their fate during the bioleaching process.