RESIDUAL EFFECT OF APPLICATION OF SEWAGE-SLUDGE ON HEAVY-METALS SORPTION BY SOIL

Ani environmentally correct disposal of sewage sludge is of crucial im portance for all the industrialized countries. The adsorbing propertie s characterization and persistance of biomass added to soil are of gre at interest for the evaluation of the advantages and the risks followi ng 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 ag o. Results showed that the heavy metal (Zn and Cd) sorption was-higher in the soil treated with sewage sludge, indicating a remarkable persi stance of soil sorptive capacity following the sludge addition. These data reveal that, in order to decrease the heavy metal concentration o f the sewage sludges, specific treatments are needed. In this way a re duction of the sludge polluting load and the water contamination will be obtained increasing, in the meantime, the soil sorption properties to heavy metals.