Speciation of heavy metals in municipal sewage sludge from different capacity sewage treatment plants

This article presents the results of heavy metal mobility research on sludge from five municipal sewage treatment plants of different capacities, and methods of sewage sludge stabilisation. Heavy metals were present mainly in the immobile sludge fractions. The capacities of the plants did not demonstrate any explicit influence on the forms of the heavy metals present. It was hypothesised that copper forms in sewage sludge are a feature characteristic of this chemical element. The per cent contributions of zinc, lead, cadmium, nickel and chromium in the BCR fractions did not depend significantly on the method of sludge stabilisation.