Abstract

The influence of municipal solid waste composting on the concentration, water solubility, and phase associa-tion of Pb, Cd, Zn and Cu at high concentrations in the starting materials, was studied. The evolution of some chem-ical parameters (total organic carbon, humic and fulvic acid, water-soluble fraction of organic carbon) during compost-ing was examined to establish their influence on heavy metal speciation. Changes of solubility and potential bioavailability of the analyzed heavy metals were investigated using sequen-tial extraction procedure [i.e. water, 0.1 N Ca(NO3)2 and EDTA]. The Cd, Cu and Zn concentrations slightly de-creased during composting due to leaching losses (9.3%, 3.7% and 1.1%, respectively), whereas Pb total concentra-tion did not vary. The progressive decrease in total metal concentration was accompanied by a corresponding decrease in the amounts of water-extractable metals. The water-ex-tractable fractions of Pb and Cu decreased rapidly during composting (losses of 95% and 100%, respectively). The decreases in water-extractable Cd and Zn were lower (losses of 60%). Generally, changes in the water-soluble fractions of metals were reflected by the concentrations of water-soluble organic carbon. The evolution of humic fractions also appeared to be important in determining the solubility of heavy metals. The results obtained showed that during composting the heavy metals in the starting materials have been redis-tributed from more labile and soluble forms to more stabi-lized ones.

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