Composting of urban solid waste in Lomé, Togo: Fate of some heavy metals (Ni, Cu, Zn, Pb and Cd)

Metals may constitute problems in waste management because of their multiple sources and potentially high toxicity of some constituents.  Processes of composting do not always guarantee acceptable quality of the compost in terms of hazardous metals. The aim of this article is to assess the balance of some heavy metals during the composting of different categories of urban waste. The fraction of the super fines, i.e. with a particle size of less than 10 mm, contributes 30 to 56% of the total, average contents of metals in  compost. Sorting of waste into various fractions such as plastics, hazardous materials, glass, miscellaneous combustible material, metals, and super fines lowers the metal contents in finished compost by about 80%. The remaining 20% can be washed during the fermentation of windrows or, still better, can be reduced by chemical complex formation in the compost as shown by the leaching adequate test. Keywords : Heavy metals, composting, leaching test.