More than 80% of sewage sludge (SS) produced in Iran is landflled with high environmental impact. The chemical properties of SS produced from wastewater plants of cites of Arak, Isfahan, Kermanshah, Rasht, Saveh, Shiraz, Sanandaj, Tehran, Takestan, and Toyserkan were studied to assess the potential benefcial efects of their application to agricultural soil as sustainable SS management. The pH and EC values, total content and water-soluble concentration of nutrients and heavy metals, their water-extractable pools were determined, and their speciation was done through the NICA–Donnan model using the Visual MINTEQ software. Relatively high contents of N, P, and physiologically active cations indicated potential benefcial efects of SS for land application in the agro-ecosystems, whereas the heavy metal content depended on the SS production site, with higher levels found in the SS of the Arak and Saveh wastewater treatment plants. The pH value was the main factor controlling the metal speciation, with Cu and Pb having the highest afnity for the organic matter, and Zn and Mn being mainly present as free ions or inorganic species. Results showed that SS from diferent locations in Iran difered in their main chemical properties and elemental composition and that speciation analysis could be used to predict potential benefcial and harmful efects of SS, particularly upon the modeling of metal– organic complexes by the NICA–Donnan approach. Globally, our results confrmed that while the SS produced in Iran has potential suitable chemical properties for use in agriculture, their heavy metals load should not be ignored.
