Effect of humification and temporal alterations of organogenic waste (sewage sludge) properties on its sorption capacity for metals

A comparative study of the effect of temporal variability of sewage sludge (SS) composition and alteration of its properties, in particular of humification of organic matter (OM), on sorption capacity and binding strength for metals was carried out on two representative samples of freshly generated (Z-09) and 4.5 years old material not exposed to atmospheric conditions (Z-05). In both SS, functional groups of humic substances responsible for metal binding were identified, although Z-05 appeared to be enriched in new OH, COO^- and alcohol groups due to humification. Simultaneously, acidification and OM reduction in older SS was also observed. Batch experiments showed high sorption capacity of SS for metals comparable to NOM and its decreasing trend in older material except for Cu and Ni, which could be explained by the antithetic effect of factors resulting from SS temporal alterations and CaCO₃ variability. Metals originally occurring in SS were predominantly stably bound onto fractions of high binding strength, while in sorption of new metal loads, binding onto labile fractions of a weaker binding strength prevailed.