The Investigation of Heavy Metal Content and Their Chemical Forms in Tehran Sewage Sludge for Agricultural Application

Among sewage sludge disposal options, land application is more preferred because of economic benefits and decreasing fertilizer cost for farmers. However, if sludge has excess amount of heavy metals and microbial infections, land application may lead to soil and environmental pollution.
In this research, the amount of total, DTPA-extractable and soluble forms of Fe, Zn, Pb, Cd, Co, Cu, Mn and Ni and population of coliform bacteria were determined in the sludge samples of three different sewage sludge treatment plants including Shahrak-e-Gharb, Ekbatan and Shoush and the results were compared to the world pollution limit standards of these metals and the coliform population.
Findings: Results showed that 0.01% of all metals accumulatively in sewage sludge were in soluble form, 1.32% in DTPA-extractable form and 98.67% in other forms, which are unavailable. Shoush sludge had largest amount of sum of eight metals (39.73 gr/kg dry sludge), Ekbatan sludge (28.42 gr/kg dry sludge) and Shahrak-e-Gharb sludge (22.95 gr/kg dry sludge) were the second and third in the rank, respectively.
Discussion and Because of high amounts of Zn and Cu in the sludge samples in compare to the standards, the samples from all the treatment plants did not categorized as the exceptional quality which can be used in agriculture. A comparison between the coliform population and the standards showed that in this regard, sludge samples were in B quality and there would be limitations in their land application.