Residual effect of application of sewage sludge on heavy metals sorption by soil

An environmentally correct disposal of sewage sludge is of crucial importance for all the industrialized countries. The adsorbing properties characterization and persistance of biomass added to soil are of great interest for the evaluation of the advantages and the risks following the use of sewage sludges in agriculture. Aim of this paper was to evaluate the persistance of the effects on soil sorptive capacity of a five-year somministration of sewage sludges finished fifteen years ago. Results showed that the heavy metal (Zn and Cd) sorption was higher in the soil treated with sewage sludge, indicating a remarkable persistance of soil sorptive capacity following the sludge addition. These data reveal that, in order to decrease the heavy metal concentration of the sewage sludges, specific treatments are needed. In this way a reduction of the sludge polluting load and the water contamination will be obtained increasing, in the meantime, the soil sorption properties to heavy metals.