Occurrence and bindings strength of metals in composted bio-waste and sewage sludge

A comparative study on Potentially Toxic Elements (PTEs): Ni, Zn, Cd, Cu, Cr and Pb content and their binding strength in selectively collected and composted bio-waste (BWC) and sewage sludge (SS) originating from the historical industrial area was carried out in order to assess their contamination potential, if applied to land. In BWC, Cd contents were found to exceed the EU median values and also mean concentrations in unpolluted soils. Concentrations of PTEs in SS appeared to be several times higher than in BWC, and about 10-fold higher than mean values in soils. Most PTEs originally occurring in BWC and SS were enriched in a reducible fraction of a moderate binding strength, but relatively high metal loads showed affinity to the labile fractions. Contents and mobility of metals in SS and in some cases also in BWC originating from historical industrial areas, suggest precautionary approach to their application to land.